^^sr^T/e  ^^^^uv/Ci/^>e        O^i^zE    Ai^G/cjc^A^    Jc 


f-toO^ 


UNIVERSITY  OF  CALIFORNIA 

MEDICAL  CENTER  LIBRARY 

SAN  FRANCISCO 


GIFT  OF 
LESTER  J.   SAWYER,  M.D. 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/anatomyofhumanboOOgrayrich 


ANATOMY 


OF 


THE  HUMAN  BODY 


BY 


henry/qbay,  f.r.s. 

FELLOW    OF    THE    KOYAL    COLLEGE    OF    STJHg^NS  ;    LECTURER    ON    ANATOMY    AT   ST.    GEORGE's 
HOSPITAL    MEDICAL    SCHOOL,    LONDON 


TWENTIETH  EDITION 

THOROUGHLY  REVISED  AND  RE-EDITED 
BY 

WARREN  H.  LEWIS,  B.S.,  M.D. 

PROFESSOR    OF   PHYSIOLOGICAL    ANATOMY,    JOHNS    HOPKINS  UNIVERSITY,    BALTIMORE,   MD. 


lUu0tratc^  witb  1247  jengravinGS 


LEA   &   FEBIGER 
PHILADELPHIA  AND   NEW  YORK 


Copyright 
LEA  &  FEBIGER 
1918 


PRINTED  IN  U.  S.  A. 


THE  FIRST  EDITION    OF  THIS   WORK 
WAS    DEDICATED   TO 

SIR  BENJAMIN  COLLINS  BRODIE,  Bart.,  F.R.S.,  D.C.L. 

IN  ADMIRATION   OF 

HIS  GREAT  TALENTS 

AND    IN    REMEMBRANCE    OF 

MANY  ACTS  OF   KINDNESS   SHOWN    TO   THE    ORIGINAL 

AUTHOR  OF    THE   BOOK 

FROM  AN 

EARLY  PERIOD  OF  HIS  PROFESSIONAL  CAREER 


672.7 


PREFACE  TO  THE  TWENTIETH  EDITION. 


Since  the  publication  of  the  first  English  edition  of  this  work  in  1858  and  the 
first  American  edition  in  1859  great  advances  in  the  subject  of  Anatomy  have  been 
made,  especially  in  microscopic  anatomy  and  the  anatomy  of  the  embryo.  This 
knowledge  was  embodied  from  time  to  time  in  the  successive  editions  until  finally 
considerable  portions  of  the  text,  sometimes  sections,  were  devoted  to  these  sub- 
jects. Howe\'er,  the  main  text  has  always  remained  primarily  a  descriptive 
anatomy  of  the  human  body. 

In  the  present  edition  the  special  sections  on  embryology  and  histology  have 
been  distributed  among  the  subjects  under  which  they  naturally  belong.  New 
matter  on  physiological  anatomy,  laws  of  bone  architecture,  the  mechanics  and 
variations  of  muscles  have  been  added,  occupying  much  of  the  space  formerly 
devoted  to  the  sections  on  applied  anatomy. 

The  sections  on  the  ductless  glands  and  the  nervous  system  have  been  largely 
rewritten.  In  the  latter  a  more  rational  presentation  of  the  sympathetic  nervous 
system  has  been  achieved  through  the  use  of  diagrams  and  descriptions  based  on 
physiological  and  pharmacological  work.  The  central  connections  of  the  spinal 
and  cranial  nerves  are  also  emphasized. 

Illustrations  have  been  added  wherever  important  points  could  be  made  more 
clear,  and  throughout  the  work  colored  pictures  have  been  even  more  extensively 
used  than  heretofore.  In  this  respect  special  mention  might  be  made  of  the  central 
nervous  system  and  the  section  on  the  muscles.  In  the  section  on  Syndesmolog}" 
six  illustrations  are  used  from  Quain's  Anatomy  through  the  courtesy  of  the 
publishers,  Messrs.  Longmans,  Green  &  Company,  of  London. 

The  use  of  the  B.  N.  A.  nomenclature  in  English  has  been  retained  practically 
unchanged  in  this  edition  and  important  references  to  the  literature  have  been 
added  at  the  end  of  each  section. 

As  a  practical  work  on  the  subject  for  the  student,  Gray's  Anatomy  has  always 
been  recognized  and  appreciated.  The  plan  originally  formulated,  which  has 
proved  so  successful,  has  been  adhered  to  as  much  as  possible.  It  is  interesting  to 
note  that  although  Henry  Gray  saw  only  the  first  edition,  much  of  the  original 
text  persists  and  many  of  his  illustrations  are  still  in  use.  Bearing  this  in  mind  it 
has  been  the  endeavor  of  the  Editor  to  supply  only  such  changes  as  advances  in 
the  science  made  necessary  in  order  that  this  work  may  reflect  the  latest  accessions 
to  anatomical  knowledge. 

W.  H.  L. 

Baltimore,  1918. 


CONTENTS. 


EMBRYOLOGY. 


The  Animal  Cell. 


Cytoplasm 35 

Nucleus 36 

Reproduction  of  Cells 36 

Prophase 36 

Metaphase •      •  36 

Anaphase     ...  36 

Telophase    ...  .      .  38 

The  Ovum. 


The  Primitive  Segment       .  52 

Separation  of  the  Embryo     .  53 

The   Yolk-sac  ....        54 

Development  of  the  Fetal  Membranes  and  Placenta. 


Yolk  .  39 

Germinal  Vesicle 40  ]  The  Decidua 

Coverings  of  the  Ovum 40    The  Chorion 

Maturation  of  the  Ovum 40    The  Placenta 

Fetal  Portion 
The  Spermatozoon 


The  AUantois 

The  Amnion 

The  Umbilical  Cord  and  Body-stalk  . 
Implantation  or  Imbedding  of  the  Ovum 


Fertilization  of  the  Ovum 

Segmentation  of  the  Fertilized  Ovum. 

The    Primitive    Streak;    Formation    of    the 
Mesoderm 


Maternal  Portion   .... 
Separation  of  the  Placenta 

The  Branchial  Region. 
The  Branchial  or  Visceral  Arches  and  Pharyn- 


54 
56 
57 
58 
59 
60 
62 
62 
63 
64 


_     _  47  I      geal  Pouches 65 

Ectoderm" 47  |  The  Nose  and  Face 67 

Entoderm 49    The  Limbs 71 

Mesoderm 49  ^      ,  ,  ,     r.    7    ^     •.  •  to 

I  Development  of  the  Body  Cavities     .      .  7J 

The  Neural  Groove  and  Tube     .      .       50  ^.„  c. 

I    The  Form  of  the  Embryo  at  Different  Stages 

The  Notochord  ....        52  i  of  its  Growth         ....  74 


OSTEOLOGY. 


Long  Bones 79 

Short  Bones 79 

Flat  Bones 79 

Irregular  Bones 80 

Surfaces  of  Bones 80 

Development  of  the  Skeleton. 

The  Skeleton 80 

The  Vertebral  Column 80 

The  Ribs 82 

The  Sternum 83 

The  Skull 83 

Bone. 

"Structure  and  Physical  Properties       ...  86 

Periosteum           87 

Marrow 87 

Vessels  and  Nerves  of  Bone 88 

Minute  Anatomy 89 

Chemical  Composition         91 

Ossification    ..........  91 

Intramembranous  Ossification      ...  91 

Intercartilaginous  Ossification      ...  93 

The  Vertebral  Column. 
General  Characteristics  of  a  Vertebra. 


The  Cervical  Vertebrae 

The  First  Cervical  Vertebra  . 
The  Second  Cervical  Vertebra 
The  Seventh  Cervical  Vertebra 


97 

99 

100 

101 


The  Thoracic  Vertebra 

The  First  Thoracic  Vertebra 
The  Ninth  Thoracic  Vertebra 
The  Tenth  Thoracic  Vertebra 
The  Eleventh  Thoracic  Vertebra 
The  Twelfth  Thoracic  Vertebra 

The  Lumbar  Vertebrae 

The  Fifth  Lumbar  Vertebra  . 

The  Sacral  and  Coccygeal  Vertebrae 

The  Sacrum 

The  Coccyx 

Ossification  of  the  Vertebral  Column 


The  Vertebral  Column  as  a  Whole. 


Curves 
Surfaces   . 
Vertebral  Canal 


102 
104 
104 
104 
104 
104 
104 
106 
106 
106 
111 
111 


114 
114 
116 


The  Thorax. 

Boundaries 117 

The  Sternuni 119 

Manubrium 120 

Body 120 

Xiphoid  Process 121 

The  Ribs        .      . 123 

Common  Characteristics  of  the  Ribs      .  123 

Peculiar  Ribs 125 

First  Rib 125 

Second  Rib 125 

Tenth  Rib 126 

Eleventh  and  Twelfth  Ribs        .      .  126 

The  Costal  Cartilages 127 

(9) 


10 


CONTENTS 


The  Skull. 
The  Cranial  Bones. 

The  Occipital  Bone 129 

The  Squama 129 

Lateral  Parts 131 

Basilar  Parts 132 

Angles 132 

The  Parietal  Bone 133 

The  Frontal  Bone 135 

Squama 135 

Orbital  or  Horizontal  Part     ....  137 

The  Temporal  Bone 138 

The  Squama 139 

Mastoid  Portion 141 

Petrous  Portion 142 

Tympanic  Part 145 

Styloid  Process 145 

The  Sphenoid  Bone 147 

Body 147 

The  Great  Wings 149 

The  Small  AVings 151 

Pterygoid  Processes 151 

The  Sphenoidal  Conchae   .      .      .      .      .  152 

Ethmoid  bone 153 

Cribriform  plate 153 

Perpendicular  Plate 154 

Labyrinth  or  Lateral  Mass     ....  154 

Sutural  or  Wormian  Bones 156 


The  Facial  Bones. 

The  Nasal  Bones 156 

The  Maxillae  (Upper  Jaw) 157 

The  Maxillary  Sinus  or  Antrum  of  High- 
more 160 

The  Zygomatic  Process 161 

The  Frontal  Process 161 

The  Alveolar  Process 161 

The  Palatine  Process 162 

Changes  Produced  in  the  Maxilla  by  Age  163 

The  Lacrimal  Bone 163 

The  Zygomatic  Bone 164 

The  Palatine  Bone 166 

The  Horizontal  Part 167 

The  Vertical  Part 167 

The  Pyramidal  Process  or  Tuberosity    .  168 

The  Orbital  Process 168 

The  Sphenoidal  Process 169 

The  Inferior  Nasal  Concha 169 

The  Vomer 170 

The  Mandible  (Lower  Jaw)      .      .      .  '    .      .  172 
Changes  Produced  in  the  Mandible  by 

Age  175 

The  Hyoid  Bone       !!!!!!!!  177 


The  Exterior  of  the  Skull. 

Norma  Verticalis 178 

Norma  Basalis 179 

Norma  Lateralis 182 

The  Temporal  Fossa 183 

The  Infratemporal  Fossa        .  .      .184 

The  Pterygopalatine  Fossa    .      .      .      .185 

Norma  Occipitalis 185 

Norma  Frontalis 185 

The  Orbitf 188 


The  Interior  of  the  Skull. 

Inner  Surface  of  the  Skull-cap      .  .      .189 

Under  Surface  of  the  Base  of  the  Skull    .  190 

The  Anterior  Fossa 190 

The  Middle  Fossa        ......  190 

The  Posterior  Fossa 192 

The  Nasal  Cavity 194 

Anterior  Nasal  Aperture 196 

Differences  in  the  Skull  Due  to  Age   .  196 

Sexual  Differences  in  the  Skull      ....  197 

Craniology 197 


Thk  Extremities. 
The  Bones  of  the  Upper  Extremity. 


The 


The 


The 


The 


The 


Clavicle 

Lateral  Third     .... 

Medial  Two-thirds 

The  Sternal  Extremity 

The  Acromial  Extremity  . 

Scapula        .... 

The  Spine 

The  Acromion  .... 

The  Coracoid  Process 

Humerus 

Upper  Extremity    . 

The  Head         ... 
The  Anatomical  Neck 
The  Greater  Tubercle 
The  Lesser  Tubercle 
The  Body  or  Shaft     . 

The  Lower  Extremity 

Ulna 

The  Upper  Extremity 
The  Olecranon 
The  Coronoid  Process 
The  Semilunar  Notch 
The  Radial  Notch      . 

The  Body  or  Shaft       .      . 

The  Lower  Extremity 

Radius 

The  Upper  Extremity 

The  Body  or  Shaft       .      . 

The  Lower  Extremity 


20011 

200 

201 

202 

202 

202 

203 

203 

207 

209 

209 

209 

209 

209 

209 

209 

212 

214 

214 

214 

214 

215 

215 

215 

218 

219 

219 

219 

220 


The  Hand. 

The  Carpus 221 

Common  Characteristics  of  the  Carpal 

Bones       . 221 

Bones  of  the  Proximal  Row   ....  221 

The  Navicular  Bone        ....  221 

The  Lunate  Bone 224 

The  Triangular  Bone       ....  224 

The  Pisiform  Bone 225 

Bones  of  the  Distal  Row         ....  225 

The  Greater  Multangular  Bone  225 

The  Lesser  Multangular  Bone  .      .  225 

The  Capitate  Bone 226 

The  Hamate  Bone 227 

The  Metacarpus       .      . 227 

Common  Characteristics  of  the  Meta- 
carpal Bones 227 

Characteristics  of  the  Individual  Meta- 
carpal Bones 228 

The  First  Metacarpal  Bone       .      .  228 

The  Second  Metacarpal  Bone    .      .  228 

The  Third  Metacarpal  Bone      .      .  228 

The  Fourth  Metacarpal  Bone    .  228 

The  Fifth  Metacarpal  Bone       .      .  228 

The  Phalanges  of  the  Hand 230 

Ossification  of  the  Bones  of  the  Hand     .  230 

The  Bones  of  the  Lower  Extremity. 

The  Hip  Bone 231 

The  Ilium 231 

The  Body        .......  231 

The  Ala 232 

The  Ischium 234 

The  Body 234 

The  Superior  Ramus       ....  235 

The  Inferior  Ramus 235 

The  Pubis 236 

The  Body 236 

The  Superior  Ramus       ....  236 

The  Inferior  Ramus 237 

The  Acetabulum 237 

The  Obturator  Foramen       .      .  237 

The  Pelvis 238 

The  Greater  or  False  Pelvis  ....  238 

The  Lesser  or  True  Pelvis      ....  239 

Axes ...  240 

Position  of  the  Pelvis 241 

Differences  between  Male  and  Female 

Pelves 241 

Abnormalities 242 


CONTENTS 


The  Femur 

The  Upper  Extremity 

The  Head 

The  Neck 

The  Trochanters 

The  Body  or  Shaft 

The  Lower  Extremity 

The  Architecture  of  the  Femur    . 

The  Patella 

The  Tibia 

The  Upper  Extremity 

The  Body  or  Shaft 

The  Lower  Extremity 

The  Fibula 

The  Upper  Extremity  or  Head    . 

The  Body  or  Shaft 

The     Lower     Extremity     or     Lateral 
Malleolus 


The  Foot. 


The  Tarsus    . 

The  Calcaneus 


242 
243 
243 
243 
244 
246 
247 
248 
255 
256 
256 
257 
259 
260 
260 
260 

262 


263 
263 


The  Tarsus—  ^^^^_ 

The  Talus    ....      J^^^^     .  266 

The  Cuboid  Bone  .      .      .  ^^^^.      .  269 

The  Navicular  Bone 270 

The  First  Cuneiform  Bone     ....  270 

The  Second  Cuneiform  Bone        .      .      .  271 
The  Third  Cuneiform  Bone    .      .      .      .271 

The  Metatarsus 272 

Common  Characteristics  of  the   Meta- 
tarsal Bones        .      .      .      .      .      .      .  272 

Characteristics  of  the  Individual  Meta- 
tarsal Bones 272 

The  First  Metatarsal  Bone  .      .      .  272 

The  Second  Metatarsal  Bone     .      .  273 

The  Third  Metatarsal  Bone       .      .  274 

The  Fourth  Metatarsal  Bone     .      .  274 

The  Fifth  Metatarsal  Bone        .      .  274 

The  Phalanges  of  the  Foot 275 

Ossification  of  the  Bones  of  the  Foot        .      ■  275 
Comparison  of  the  Bones  of  the  Hand  and 

Foot 276 

The  Sesamoid  Bones 277 


SYNDESMOLOGY. 


Bone 279 

Hyahne  Cartilage 279 

Articular  Cartilage 280 

Costal  Cartilage      . 281 

White  Fibrocartilage 281 

Ihterarticular  Fibrocartilages        .       .      .  281 

Connecting  Fibrocartilages     ....  282 

Circumferential  Fibrocartilages    .      .      .  282 

Stratiform  Fibrocartilages       ....  282 

Ligaments 282 

The  Articular  Capsules 282 

Mucous  Sheaths 283 

Bursse  Mucosae 283 

Development  of  the  Joints    .      .  283 


Classification  of  Joints 

Synarthrosis 284 

Sutura 284 

Schindylesis 284 

Gomphosis 284 

Synchondrosis 284 

Amphiarthrosis 285 

Diathrosis 285 

Ginglimus 285 

Trochoid 285 

Condyloid    .      .      .  _    .      .      .      .   _  .      .286 

Articulation  by  Reciprocal  Reception    .  286 

Enarthrosis 286 

Arthrodia 286 


The  Kind  of  Movement  Admitted  in  Joints. 

Gliding  Movement 286 

Angular  Movement 286 

Circumduction 286 

Rotation 287 

Ligamentous  Action  of  Muscles    ....  287 

I^V  Articulations  of  the  Thunk. 

I H       Articulations  of  the  Vertebral  Column  287 

I^L  Articulations  of  Vertebral  Bodies  287 

I^H  The    Anterior    Longitudinal    Liga- 

l^t^  ment  .  ..287 

I^^^^K  The    Posterior    Longitudinal    Liga- 

|^^H|  ment 288 

l^^^^r  The  Intervertebral    Fibrocartilages  289 

I^V  Structure 289 

1^^  Articulations  of  Vertebral  Arches  289 

I^^^K  The  Articular  Capsules  ....  290 

I^^^B.  The  Ligamenta  Flava      ....  290 

1^^^^^^^^     The  Supraspinal  Ligament   .  290 


Articulations  of  the  Vertebral  Column — 
Articulations  of  Vertebral  Arches — 

The  Ligamentum  Nuchse      .      .      .  290 
The  Interspinal  Ligaments  .      .      .  291 
The  Intertransverse  Ligaments       .  291 
Articulation  of  the  Atlas  with  the  Epistro- 
pheus or  Axis 292 

The  Articular  Capsules 292 

The  Anterior  Atlantoaxial  Ligament      .  293 

The  Posterior  Atlantoaxial  Ligament     .  293 

The  Transverse  Ligament  of  the  Atlas  .  293 
Articulations  of  the  Vertebral  Column  with 

the  Cranium        .......  295 

Articulation    of    the    Atlas    with    the 

Occipital  Bone 295 

The  Articular  Capsules  ....  295 
The  Anterior  Atlantooccipital  Mem- 
brane        295 

The  Posterior  Atlantooccipital  Mem- 
brane        296 

The  Lateral  Ligaments   ....  296 
Ligaments  Connecting  the  Axis  with  the 

Occipital  Bone 296 

The  Membrana  Tectoria        .      .      .  296 

The  Alar  Ligaments 296 

Articulation  of  the  Mandible 297 

The  Articular  Capsule 297 

The  Temporomandibular  Ligament        .  297 

The  Sphenomandibular  Ligament     .      .  297 

The  Articular  Disk 298 

The  Stylomandibular  Ligament  .      .  298 

Costovertebral  Articulations 299 

Articulations  of  the  Heads  of  the  Ribs  .  299 
The  Articular  Capsule  ....  299 
The  Radiate  Ligament  ....  299 
The  Interarticular  Ligament  .  .  300 
Costotransverse  Articulations  .  .  300 
The  Articular  Capsule  ....  301 
The  Anterior  Costotransverse  Liga- 
ment         301 

The  Posterior  Costotransverse  Liga- 
ment         301 

The  Ligament  of  the  Neck  of  the 

Rib 302 

The  Ligament  of  the  Tubercle  of 

the  Rib 302 

Sternocostal  Articulations 302 

The  Articular  Capsules     .    _ .      .      .      .  302 
The  Radiate  Sternocostal  Ligaments     .  302 
The    Interarticular   Sternocostal    Liga- 
ment    303 

The  Costoxiphoid  Ligaments       .      .      .  304' 

Interchondral  Articulations    ....  304 

Costochondral  Articulations  ....  304 
Articulation  of  the  Manubrium  and  Body  of 

the  Sternum 304 

Mechanism  of  the  Thorax      ....  304 


12 


CONTENTS 


Articulation  of  the  Vertebral  Column  with 

the  Pelvis 306 

The  Iliolumbar  Ligament       ....  306 

Articulations  of  the  Pelvis 306 

Sacroiliac  Articulation 306 

The  Anterior  Sacroiliac  Ligament  .  307 
The  Posterior  Sacroiliac  Ligament.  307 
The    Interosseous   Sacroiliac    Liga- 
ment      . 308 

Ligaments  Connecting  the  Sacrum  and 

Ischium 309 

The  Sacrotuberous  Ligament           .  309 
The  Sacrospinous  Ligament       .      .  309 
Sacrococcygeal  Symphysis      ....  309 
The  Anterior  Sacrococcygeal  Liga- 
ment        •  .      .  309 

The  Posterior  Sacrococcygeal  Liga- 
ment         309 

The  Lateral  Sacrococcygeal   Liga- 
ment         310 

The  Interarticular  Ligaments    .      .  310 

The  Pubic  Symphysis 310 

The  Anterior  Pubic  Ligament     .      .  310 

The  Posterior  Pubic  Ligament  .      .  310 

The  Superior  Pubic  Ligament    .      .  310 

The  Arcuate  Pubic  Ligament    .  310 
The  Interpubic  Fribrocartilaginous 

Lamina 311 

Mechanism  of  the  Pelvis 311 


Articulations  of  the  Upper  Extremity. 

Sternoclavicular  Articulation 313 

The  Articular  Capsule 313 

The  Anterior  Sternoclavicular  Ligament  313 
The    Posterior    Sternoclavicular    Liga- 
ment    313 

The  Interclavicular  Ligament      .      .      .  314 
The  Costoclavicular  Ligament     .      .      .314 

The  Articular  Disk 314 

Acromioclavicular  Articulation      .  .  315 

The  Articular  Capsule 315 

The   Superior   Acromioclavicular   Liga- 
ment    315 

The    Inferior    Acromioclavicular    Liga- 
ment    315 

The  Articular  Disk 315 

The  Coracoclavicular  Ligament  .      .      .  315 
The  Trapezoid  Ligament        .      .      .      .315 

The  Conoid  Ligament 315 

The  Ligaments  of  the  Scapula  .      .  316 

The  Coracoacromial  Ligament    .      .      .  316 

The  Superior  Transverse  Ligament  .      .  317 

The  Inferior  Transverse  Ligament    .      .  317 

Humeral  Articulation  or  Shoulder-joint  .      .  317 

The  Articular  Capsule 317 

The  Coracohumeral  Ligament     .      .      .  318 

Glenohumeral  Ligaments        .      .      .      .  318 

The  Transverse  Humeral  Ligament        .  319 

The  Glenoidal  Labrum 319 

Bursae 319 

Elbow-joint 321 

The  Anterior  Ligament 321 

The  Posterior  Ligament 322 

The  Ulnar  Collateral  Ligament  .      .      .  322 

The  Radial  Collateral  Ligament        .      .  322 

Radioulnar  Articulation 324 

Proximal  Radioulnar  Artifculation    .      .  324 

The  Annular  Ligament   ....  324 

Middle  Radioulnar  Union       ....  325 

The  Oblique  Cord 325 

The  Interosseous  Membrane      .      .  325 

Distal  Radioulnar  Articulation    .      .      .  325 

The  Volar  Radioulnar  Ligament     .  325 

The  Dorsal  Radioulnar  Ligament  .  325 

The  Articular  Disk 325 

Radiocarpal  Articulation  or  Wrist-joint  .      .  327 

The  Volar  Radiocarpal  Ligament      .      .  327 

The  Dorsal  Radiocarpal  Ligament    .      .  328 

The  Ulnar  Collateral  Ligament  .  .  328 

The  Radial  Collateral  Ligament  .  328 

Intercarpal  Articulations 328 

Articulations  of  the  Proximal  Row  of 

Carpal  Bones 328 


Intercarpal  Articulations — 

Articulations  of  the  Proximal   Row  of 

Carpa   Bones — 

The  Dorsal  Ligaments    . 

The  Volar  Ligaments 

The  Interosseous  Ligaments 

Articulations    of    the    Distal    Row    of 

Carpal  Bones 

The  Dorsal  Ligaments    . 
The  Volar  Ligaments 
The  Interosseous  Ligaments 
Articulations    of    the     Two     Rows    of 
Carpal  Bones  with  Each  Other 
The  Volar  Ligaments 
The  Dorsal  Ligaments     . 
The  Collateral  Ligaments     . 
Carpometacarpal  Articulations 

Carpometacarpal    Articulation    of    the 

Thumb 

Articulations  of  the  Other  Four  Meta 
carpal  Bones  with  the  Carpus 
The  Dorsal  Ligaments    . 
The  Volar  Ligaments 
The  Interosseous  Ligaments 
Intermetacarpal  Articulations 

The  Transverse  Metacarpal  Ligament 
Metacarpophalangeal  Articulations    . 

The  Volar  Ligaments 

The  Collateral  Ligaments 
Articulations  of  the  Digits        .... 


328 
328 
328 

329 
329 
329 
329 

329 
329 
329 
329 
330 

330 

331 
331 
331 
331 
331 
331 
332 
332 
332 
333 


Articulations  of  the  Lower  Extremity. 


Coxal  Articulation  or  Hip-joint     . 

The  Articular  Capsule       .... 
The  Iliofemoral  Ligament 
The  Pubocapsular  Ligament 
The  Ischiocapsular  Ligament 
The  Ligamentum  Teres  Femoris 
The  Glenoidal  Labrum      .... 
The  Transverse  Acetabular  Ligament 

The  Knee-joint 

The  Articular  Capsule       .... 
The  Ligamentum  Patellae 
The  Oblique  Popliteal  Ligament 
'The  Tibial  Collateral  Ligament  . 
The  Fibular  Collateral  Ligament 
The  Cruciate  Ligaments  .... 

The  Anterior  Cruciate  Ligament 

The  Posterior  Cruciate  Ligament 
The  Menisci 

The  Medial  Meniscus 

The  Lateral  Meniscus 
The  Transverse  Ligament 
The  Coronarj'  Ligaments 

Bursae 

Articulations  between  the  Tibia  and 
Tibiofibular  Articulation 

The  Articular  Capsule     . 

The  Anterior  Ligament  . 

The  Posterior  Ligament 
Interosseous  Membrane    . 
Tibiofibular  Syndesmosis 

The  Anterior  Ligament  . 

The  Posterior  Ligament 

The  Inferior  Transverse  Ligament 

The  Interosseous  Ligament 
Talocrural  Articulation  or  Ankle-joint  . 
The  Articular  Capsule  .... 
The  Deltoid  Ligament  .... 
The  Anterior  Talofibular  Ligament 
The  Posterior  Talofibular  Ligament 
The  Calcaneofibular  Ligament    . 

Intertarsal  Articulations 

Talocalcaneal  Articulation 

The  Articular  Capsule     . 

The   Anterior   Talocalcaneal   Liga 
ment 

The  Posterior  Talocalcaneal  Liga 
ment 

The    Lateral    Talocalcaneal    Liga 
ment 

The    Medial    Talocalcaneal    Liga 
ment 


333 
334 
335 
335 
335 
336 
336 
336 
339 
340 
340 
340 
341 
341 
342 
342 
342 
342 
343 
343 
343 
343 
345 
347 
348 
348 
348 
348 
348 
348 
348 
348 
349 
349 
349 
350 
350 
351 
351 
351 
352 
352 
352 

352 

352 

352 

353 


CONTENTS 


13 


Intertarsal  Articulations — 

Talocalcaneal  Articulation — 

The   Interosseous   Talocalcaneal 

Ligament 

Talocalcaneonavicular  Articulation  . 
The  Articular  Capsule     . 
The  Dorsal  Talonavicular  Ligamen 
Calcaneocuboid  Articulation 
The  Articular  Capsule     . 
TheDorsalCalcaneocuboidLigament 
The  Bifurcated  Ligament 
The  Long  Plantar  Ligament 
The  Plantar  Calcaneocuboid  Liga 

ment 

The  Ligaments  Connecting  the  Calca 
neus  and  Navicular 
The   Plantar   Calcaneonavicular 

Ligament 

Cuneonavicular  Articulation 
The  Dorsal  Ligaments    . 
The  Plantar  Ligaments  . 
Cuboideonavicular  Articulation  . 
The  Dorsal  Ligament 


353 
353 
354 
354 
354 
354 
354 
354 
354 

354 

355 

355 
356 
356 
356 
356 
357 


Intertarsal  Articulations — 

Cuboideonavicular  Articulation — 

The  Plantar  Ligament    ....  357 
The  Interosseous  Ligament        .      .  357 
Intercuneiform  and  Cuneocuboid  Articu- 
lation        357 

The  Dorsal  Ligaments    ....  357 

The  Plantar  Ligaments  ....  357 

The  Interosseous  Ligaments      .      .  357 

Tarsometatarsal  Articulations       ....  358 

The  Dorsal  Ligaments 358 

The  Plantar  Ligaments 358 

The  Interosseous  Ligaments  ....  358 

Intermetatarsal  Articulations 358 

The  Dorsal  Ligaments 358 

The  Plantar  Ligaments 358 

The  Interosseous  Ligaments  ....  358 

The  Transverse  Metatarsal  Ligament    .  359 

Metatarsophalangeal  Articulations     .      .      .  359 

The  Plantar  Ligaments 359 

The  Collateral  Ligaments       ....  359 

Articulations  of  the  Digits 359 

Arches  of  the  Foot 360 


MYOLOGY. 


Mechanics  of  Muscle. 

The  Direction  of  Muscle  Pull         .      . 
The  Action  of  Muscle  Pull  on  Tendon 
The  Strength  of  Muscles     .... 
The  Work  Accomplished  by  Muscles 
The  Action  of  Muscles  on  Joints 


363 
364 
364 
365 
368 


Development  of  the  Muscles. 

The  Ventro-lateral  Muscles  of  the  Neck  .      .  371 

Muscles  of  the  Shoulder  Girdle  and  Arm       .  371 

The  Muscles  of  the  Leg 372 

The  Muscles  of  the  Head 372 

Striped  or  Voluntary  Muscle 373 

_  ^     Vessels  and  Nerves  of  Striped  Muscle      .      .  376 

■  H  Tendons,  Aponeuroses,  and  Fascia. 

■  H    Tendons 376 

■  H     Aponeuroses 376 

■  ■     Fasciaj 376 

I  ^^^^  The  Fascia  and  Muscles  of  the  Head. 

■  ^^HB  The  Muscles  of  the  Scalp. 

The  Skin  of  the  Scalp 378 

The  Superficial  Fascia 378 

Epicranius 378 

Occipitalis 379 

Frontalis 379 

Galea  Aponeurotica 380 

The  Muscles  of  the  Eyelid. 

Orbicularis  Oculi 380 

Corrugator 381 

The  Muscles  of  the  Nose. 

Procerus  ...  382 

Nasalis 382 

Depressor  Septi .      .  382 

Dilator  Naris  Posterior 382 

Dilator  Naris  Anterior 382 

The  Muscles  of  the  Mouth. 

Quadratus  Labii  SuperioriD 383 

Caninus 383 

Zygomaticus 383 

t: 


Quadratus  Labii  Inferioris 383 

Triangularis 383 

Buccinator 384 

Pterygomandibular  Raph6     ....  384 

Orbicularis  Oris 384 

Risorius 385 

The  Muscles  of  Mastication. 

Parotideomasseteric  Fascia 385 

Masseter 385 

Temporal  Fascia 386 

Temporalis 386 

Pterygoideus  Externus 386 

Pterygoideus  Internus 387 


The  Fascia  and  Muscles  of  the  Antero- 
lateral Region  of  the  Neck. 

The  Superficial  Cervical  Muscle. 

Superficial  Fascia 387 

Platysma 388 

Variations 388 

The  Lateral  Cervical  Muscles. 

The  Fascia  Colli  388 

Sternocleidomastoideus 390 

Variations 390 

Triangles  of  the  Neck 390 

The  Supra-  and  Infrahyoid  Muscles. 

Digastricus 391 

Variations 391 

Stylohyoideus 392 

Variations 392 

The  Stylohyoid  Ligament       ....  392 

Mylohyoideus 393 

Variations 393 

Geniohyoideus 393 

Sternohyoideus 393 

Variations 393 

Sternothyreoideus 393 

Variations 394 

Thyreohyoideus 394 

Omohyoideus 394 

Variations 394 

The  Anterior  Vertebral  Muscles. 

Longus  Colli 394 

Longus  Capitis 395 

Rectus  Capitis  Anterior 395 

Rectus  Capitis  Lateralis 395 


14 


CONTENTS 


The  Lateral   Vertebral  Muscles. 

Scalenus  Anterior 396 

Scalenus  Medius 396 

Scalenus  Posterior 396 

Variations 396 


The  Fasci.e  and  Muscles  of  the  Thunk. 

The  Deep  Muscles  of  the  Back. 

The  Lumbodorsal  Fascia 397 

Splenius  Capitis 397 

Splenius  Cervicis 397 

Variations 397 

Sacrospinalis 397 

Iliocostalis  Lumborum 399 

Iliocostalis  Dorsi 399 

Iliocostalis  Cervicis 399 

Longissimus  Dorsi 399 

Longissimus  Cervicis 399 

Longissimus  Capitis 399 

Spinalis  Dorsi 399 

Spinalis  Cervicis 400 

Spinalis  Capitis 400 

Semispinalis  Dorsi 400 

Semispinalis  Cervicis 400 

Semispinalis  Capitis 400 

Multifidus 400 

Rotatores 400 

Interspinales 400 

Extensor  Coccygis 401 

Intertransversarii 401 


The  Suboccipital  Muscles. 


Rectus  Capitis  Posterior  Major 
Rectus  Capitis  Posterior  Minor 
Obliquus  Capitis  Inferior    . 
Obliquus  Capitis  Superior  . 
The  Suboccipital  Triangle 


401 
401 
402 
402 
402 


The  Muscles  of  the  Thorax. 


Intercostal  Fascia 402 

Intercostales 403 

Intercostales  Externi 403 

Variations 403 

Intercostales  Interni 403 

Subcostales 403 

Transversus  Thoracis 403 

Levatores  Costarum 403 

Serratus  Posterior  Superior 404 

Variations 404 

Serratus  Posterior  Inferior 404 

Variations 404 

Diaphragm          404 

Medial  Lumbocostal  Arch      ....  404 

Lateral  Lumbocostal  Arch      ....  405 

The  Crura 405 

The  Central  Tendon 406 

Openings  in  the  Diaphragm         .      .      .  406 

Variations 406 

Mechanism  of  Respiration 407 

The  Muscles  and  Fascice  of  the  Abdomen. 

The  Antero-lateral  Muscles  of  the  Abdomen  408 

The  Superficial  Fascia 408 

Obliquus  Externus  Abdominis     .            .  409 
Aponeurosis      of       the       Obliquus 

Externus  Abdominis  .  .  410 
Subcutaneous  Inguinal  Ring  .  410 
The  Intercrural  Fibers  .  410 
The  Inguinal  Ligament  .  411 
The  Lacunar  Ligament  .  .  412 
The  Reflected  Inguinal  Liga- 
ment       412 

Ligament  of  Cooper                   .  412 

Variations 412 

Obliquus  Internus  Abdominis  412 

Variations 414 

Cremaster .      .  414 

Transversus  Abdominis                 ...  414 


The  Antero-lateral  Muscles  of  the  Abdomen — 
Transversus  Abdominis — 

Variations 414 

Inguinal  Aponeurotic  Falx   .      .      .  414 

Rectus  Abdominis 415 

Pyramidalis 416 

Variations 417 

The  Linea  Alba 417 

The  Lineae  Semilunares 417 

The  Transversalis  Fascia        ....  418 

The  Abdominal  Inguinal  Ring           .  418 

The  Inguinal  Canal 418 

Extraperitoneal  Connective  Tissue   .  418 

The  Deep  Crural  Arch 419 

The  Posterior  Muscles  of  the  Abdomen  .  419 
The    Fascia    Covering    the    Quadratus 

Lumborum 419 

Quadratus  Lumborum 420 

Variations 420 

The  Muscles  and  Fascice  of  the  Pelvis. 

Pelvic  Fascia 420 

Levator  Ani 422 

Coccygeus 424 

The  Muscles  and  Fascice'  of  the  Perineum. 

Muscles  of  the  Anal  Region 424 

The  Superficial  Fascia 424 

The  Deep  Fascia 425 

Ischiorectal  Fossa 425 

The  Corrugator  Cutis  Ani      ....  425 

Sphincter  Ani  Externus 425 

Sphincter  Ani  Internus                  .      .  426 

The   Muscles  of   the   Urogenital   Region  in 

the  Male 426 

Superficial  Fascia 426 

The    Central    Tendinous    Point    of    the 

Perineum 427 

Transversus  Perinsei  Superficialis      .      .  427 

Variations 427 

Bulbocavernosus 428 

Ischiocavernosus 428 

The  Deep  Fascia 428 

Transversus  Perinsei  Profundus         .      .  429 

Sphincter  Urethrae  Membranacese    .      .  429 

The  Muscles  of  the  Urogenital  Region  in  the 

Female 430 

Transversus  Perinsei  Superficialis      .      .  43o 

Bulbocavernosus 43Q 

Ischiocavernosus 430 

Transversus  Perincei  Profundus               .  431 


The  Fascia  and  Muscles  of  the  Upper 
Extremity. 

The  Muscles  Connecting  the  Upper  Extremity 
to  the  Vertebral  Column. 

Superficial  Fascia 432 

Deep  Fascia .  432 

Trapezius 432 

Variations 432 

Latissimus  Dorsi 432 

Variations 434 

Rhomboideus  Major 434 

Rhomboideus  Minor 434 

Variations 435 

Levator  scapulae 435 

Variations 435 

The  Muscles  Connecting  the  Upper  Extremity  to 
the  Anterior  and  Lateral  Thoracic  Walls. 

Superficial  Fascia 435 

Pectoralis  Major 436 

Variations 437 

Coracoclavicular  Fascia 437 

Pectoralis  Minor 438 

Variations 438 

Subclavius 438 

Variations 438 

Serratus  Anterior 438 

Variations 439- 


CONTENTS 


15 


The  Muscles  and  Fascice  of  the  Shoulder. 

Deep  Fascia 439 

Deltoideus 439 

Variations 440 

Subscapular  Fascia 440 

Subscapularis '    .  440 

Supraspinatous  Fascia 440 

Supraspinatus     . 440 

Infraspinatous  Fascia 441 

Infraspinatus 441 

Teres  Minor 441 

Variations 442 

Teres  Major 442 

The  Muscles  and  Fasciae  of  the  Arm. 

Brachial  Fascia 442 

Coracobrachialis 443 

Variations 443 

Biceps  Brachii    . 443 

Variations 444 

Brachialis 444 

Variations^ 444 

Triceps  Brachii 444 

Variations 445 

The  Muscles  and  Fascia  of  the  Forearm. 

Antibrachial  Fascia 445 

The  Volar  Antibrachial  Muscles    ....  445 

The  Superficial  Group       .      .      .      .      .  446 

Pronator  Teres 446 

Variations 446 

Flexor  Carpi  Radialis      ....  446 

Variations 446 

Palmaris  Longus 446 

Variations 446 

Flexor  Carpi  Ulnaris        ....  447 

Variations 447 

Flexor  Digitorum  Sublimis  .  448 

Variations 448 

The  Deep  Group 448 

Flexor  Digitorum  Profundus            .  448 
Fibrous     Sheaths     of     the     Flexor 

Tendons 448 

Variations 449 

Flexor  Pollicis  Longus     ....  449 

Variations 449 

Pronator  Quadratus 449 

Variations 450 

The  Dorsal  Antibrachial  Muscles.  .451 

The  Superficial  Group 451 

Brachioradialis 451 

Variations 451 

Extensor  Carpi  Radialis  Longus  452 

Extensor  Carpi  Radialis  Brevis       .  452 

Variations       .      .      .      .      .      .  452 

Extensor  Digitorum  Communis       .  452 

Variations 454 

Extensor  Digiti  Quinti  Proprius      .  454 

Variations 454 

Extensor  Carpi  Ulnaris  ....  454 

Variations 454 

Anconseus 454 

The  Deep  Group 454 

Supinator 454 

Abductor  Pollicis  Longus  455 

Variations 455 

Extensor  Pollicis  Brevis        .      .      .  455 

Variations 455 

Extensor  Pollicis  Longus       .      .      .  455 

Extensor  Indicis  Proprius                 .  456 

Variations 456 

The  Muscles  and  Fascia;  of  the  Hand. 

Volar  Carpal  Ligament 456 

Transverse  Carpal  Ligament 456 

The  Mucous  Sheaths  of  the  Tendons  on  the 

Front  of  the  Wrist 457 

Dorsal  Carpal  Ligament 458 

The  Mucous  Sheaths  of  the  Tendons  on  the 

Back  of  the  Wrist      .             459 

Palmar  Aponeurosis 460 


Superficial     Transverse      Ligament     of     the 

Fingers 461 

The  Lateral  Volar  Muscles 461 

Abductor  Pollicis  Brevis 461 

Opponens  Pollicis 461 

Flexor  Pollicis  Brevis 461 

Adductor  Pollicis  (Obliquus)        ...  462 

Adductor  Pollicis  (Transversus)  462 

Variations 462 

The  Medial  Volar  Muscles 462 

Palmaris  Brevis 463 

Abductor  Digiti  Quinti 463 

Flexor  Digiti  Quinti  Brevis    ....  464 

Opponens  Digiti  Quinti 464 

Variations         464 

The  Intermediate  Muscles 464 

Lumbricales 464 

Variations 464 

Interossei 464 

Interossei  Dorsales 464 

Interossei  Volares 465 


The  Muscles  and  Fasci.*;  of  the  Lower 
Extremity. 

The  Muscles  and  Fascice  of  the  Iliac  Region. 

The  Fascia  Covering  the  Psoas  and  Iliacus  466 

Psoas  Major 467 

Psoas  Minor 467 

Iliacus 467 

Variations 467 

The  Muscles  and  Fascice  of  the  Thigh. 

The  Anterior  Femoral  Muscles     ....  467 

Superficial  Fascia 468 

Deep  Fascia 468 

The  Fossa  Ovalis 469 

Sartorius 470 

Variations 470 

Quadriceps  Femoris 470 

Rectus  Femoris 470 

Vastus  Lateralis 470 

Vastus  Medialis 471 

Vastus  Intermedius 471 

Articularis  Genu 471 

The  Medial  Femoral  Muscles        ....  471 

Gracilis 471 

Pectineus 472 

Adductor  Longus 472 

Adductor  Brevis 473 

Adductor  Magnus 473 

Variations 474 

The  Muscles  of  the  Gluteal  Region    .      .      .  474 

Gluteus  Maximus 474 

Bursae 474 

Glutaeus  Medius 474 

Variations 475 

Glutseus  Minimus 475 

Variations 475 

Piriformis 476 

Variations         476 

Tensor  Fasciae  Latae 476 

Obturator  Membrane 477 

Obturator  Internus 477 

Gemelli 477 

Gemellus  Superior 477 

Gemellus  Inferior 477 

Quadratus  Femoris 477 

Obturator  Externus 477 

The  Posterior  Femoral  Muscles     ....  478 

Biceps  Femoris 478 

Variations 479 

Semitendinosus 479 

Semimembranosus        ....  .  479 

Variations        ....  479 

The  Muscles  and  Fascice  of  the  Leg. 

The  Anterior  Crural  Muscles 480 

Deep  Fascia 480 

Tibialis  Anterior 480 

Variations 480 


16 


CONTENTS 


The  Anterior  Crural  Muscles — 

Extensor  Hallucis  Longus       .      .      .      .481' 

Variations 481 

Extensor  Digitorum  Longus  ....  481 

Variations 482 

PeroniEus  Tertius         482 

The  Posterior  Crural  Muscles        ....  482 

The  Superficial  Group 482 

Gastrocnemius      .....  482 

Variations 483 

Soleus 483 

Variations 483 

Tendo  Calcaneus 483 

Plantaris 483 

The  Deep  Group 483 

Deep  Transverse  Fascia        .      .      .  483 

Popliteus 484 

Variations 485 

Flexor  Hallucis  Longus  ....  485 

Variations 485 

Flexor  Digitorum  Longus     .      .      .  485 

Variations 485 

Tibialis  Posterior 485 

The  Lateral  Crural  Muscles 486 

Peronseus  Longus         486 

Peronseus  Brevis 486 

Variations        487 

The  Fascia  Around  the  Ankle. 

Transverse  Crural  Ligament 488 

Cruciate  Crural  Ligament 488 

Laciniate  Ligament ,  489 

Peroneal  Retinacula 489 


The  Mucous  Sheaths  of  the  Tendons  Around 
the  Ankle 

The  Muscles  and  Fasciae  of  the  Foot. 


I 


489 


The  Dorsal  Muscle  of  the  Foot     ....  490 

Extensor  Digitorum  Brevis    ....  490 

Variations 490 

The  Plantar  Muscles  of  the  Foot        .      .      .  490 

Plantar  Aponeurosis 490 

The  First  Layer 491 

Abductor  Hallucis 491 

Variations 491 

Flexor  Digitorum  Brevis       .      .      .491 

Variations 492 

Fibrous  Sheaths  of  the  Flexor 

Tendons 492 

Abductor  Digiti  Quinti   ....  492 

Variations 492 

The  Second  Layer 493 

Quadratus  Plantse 493 

Variations 493 

Lumbricales 493 

Variations 493 

The  Third  Layer 493 

Flexor  Hallucis  Brevis     ....  493 

Variations 493 

Adductor  Hallucis 493 

Variations 494 

Flexor  Digiti  Quinti  Brevis        .      .  494 

The  Fourth  Layer 495 

Interossei 495 

Interossei  Dorsales  ....  495 

Interossei  Plantares       .      .      .  495 


ANGIOLOGY. 


Structure  of  Arteries 498 

Capillaries 499 

Sinusoids 501 

Structure  of  Veins 591 


The  Blood. 

General  Composition  of  the  Blood      .            .  503 

Blood  Corpuscles 503 

Colored  or  Red  Corpuscles   .      .      .  503 

Colorless  Corpuscles  or  Leukocytes  504 


Development  of  the  Vascular  System. 

Further  Development  of  the  Heart     .      .      .  508 

The  Valves  of  the  Heart 514 

Further  Development  of  the  Arteries        .  515 

The  Anterior  Ventral  Aortae         .      .      .  516 

The  Aortic  Arches 516 

The  Dorsal  Aortse 517 

Further  Development  of  the  Veins      .      .      .  518 

The  Visceral  Veins 518 

The  Parietal  Veins 520 

Inferior  Vena  Cava 520 

Venous  Sinuses  of  the  Dura  Mater   .      .  522 


The  Thoracic  Cavity. 

The  Cavity  of  the  Thorax 524 

The  Upper  Opening  of  the  Thorax     .      .      .  524 

The  Lower  Opening  of  the  Thorax     .  524 

The  Pericardium. 

Structure  of  the  Pericardium 525 

The  Heart. 

Size 526 

Component  Parts 526 

Right  Atrium 628 

Sinus  Venarum 628 

Auricula 628 

Right  Ventricle 631 

Left  Atrium 633 

Auricula 533 

Left  Ventricle 635 

Ventricular  Septum 535 

Structure  of  the  Heart        ......  535 

The  Cardiac  Cycle  and  the  Actions  of  the 

Valves 538 

Peculiarities  in  the  Vascular  System  in  the 
Fetus. 

Fetal  Circulation 540 

Changes  in  the  Vascular  System  at  Birth     .  542 


THE  ARTERIES. 


The  Pulmonar 
Relations 

yA 

rtery 

.     543 
.     545 

The 

Aorta. 

The 

Ascending  Aorta. 

Relations 

.     546 

Branches 

.     646 

Branches  of  the  Ascending  Aorta — 

The  Coronary  Arteries 546 

Right  Coronary  Artery  ....  546 

Left  Coronary  Artery      ....  547 

Peculiarities 547 

The  Arch  of  the  Aorta. 

Relations 547 

Peculiarities         548 


CONTENTS 


17 


Branches 548 

Peculiarities 548 

The  Innominate  Artery 548 

Relations 548 

Branches 549 

Thyreoidea  Ima 549 

Collateral  Circxilation 549 


The  Arteries  of  the  Head  and  Neck. 


The  Common  Carotid  Artery. 

Relations 549 

Peculiarities 551 

Collateral  Circulation 551 

The  External  Carotid  Artery 551 

Relations 552 

Branches 552 

Superior  Thyroid  Artery       .      .      .  552 

Relations 552 

Branches 552 

Lingual  Artery 553 

Relations 553 

Branches 553 

External  Maxillary  Artery   .      .  553 

Relations 554 

Branches 554 

Peculiarities 556 

Occipital  Artery 556 

Course  and  Relations    .  556 

Branches 556 

Posterior  Auricular  Artery   .  557 

Branches 557 

Ascending  Pharj-ngeal  Artery    .      .  557 

Branches 558 

Superficial  Temporal  Artery  558 

Relations 558 

Branches 558 

Internal  Maxillary  Artery    .  559 

Branches 560 

The  Triangles  of  the  Neck 562 

Anterior  Triangle 563 

Inferior  Carotid  or   Muscular  Tri- 
angle         563 

Superior   Carotid    or   Carotid   Tri- 
angle         564 

Submaxillary     or     Digastric     Tri- 
angle         564 

Suprahyoid  Triangle        ....  565 

Posterior  Triangle 565 

Occipital  Triangle 565 

Subclavian  Triangle 565 

The  Internal  Carotid  Artery 566 

Course  and  Relations 567 

Cervical  Portion 567 

Petrous  Portion 567 

Cavernous  Portion 567 

Cerebral  Portion 567 

Peculiarities 567 

Branches  _ 568 

Caroticotympanic 568 

Artery  of  the  Pterygoid  Canal  .  568 

Cavernous 568 

Hypophyseal 568 

Semilunar 568 

Anterior  Meningeal 568 

Ophthalmic  artery 568 

Branches 568 

Anterior  Cerebral  Artery      .      .  571 

Branches 571 

Middle  Cerebral  Artery        .      .  572 

Branches 573 

Posterior  Communicating  Artery    .  573 

Anterior  Choroidal  Artery    .  .  574 


The  Arteries  of  the  Brain. 


The  Ganglionic  System 
The  Cortical  Arterial  System 
2 


575 
575 


The  Arteries  of  the  Upper  Extremity. 

The  Subclavian  Artery, 

First  Part  of  the  Right  Subcla\'ian  Artery    .  576 

Relations 576 

First  Part  of  the  Left  Subclavian  Artery       .  577 

Relations 577 

Second  and  Third  Parts  of  the  Subclavian 

Artery 577 

Relations 577 

Relations 577 

Peculiarities 577 

Collateral  Circulation 578 

Branches 578 

Vertebral  Artery 578 

Relations 578 

Branches   ........  579 

Thyrocer\acal  Trunk  .                  .      .      .  581 

Branches 581 

Peculiarities 583 

Internal  Mammarj'  Artery     ....  584 

Relations 584 

Branches 584 

The  Costocervical  Trunk        ....  585 

The  Axilla. 

Boundaries 585 

Contents 686 

The  Axillary  Artery 586 

Relations 586 

Collateral  Circulation 587 

Branches 587 

The  Highest  Thoracic  Artery    .  587 

The  Thoracoacromial  Artery     .  588 

The  Lateral  Thoracic  Artery     .  588 

The  Subscapular  Artery  .  .  .  588 
The  Posterior  Humeral  Circumflex 

Artery 589 

The  Anterior  Humeral  Circumflex 

Artery 589 

Peculiarities 589 

The  Brachial  Artery 589 

Relations 589 

The  Anticubital  Fossa 589 

Peculiarities 690 

Collateral  Circulation 690 

Branches 690 

The  Arteria  Profunda  Brachii  .  591 
The  Nutrient  Artery  .  .  .  .591 
The     Superior     Ulnar     Collateral 

Artery 591 

The   Inferior  Ulnar  Collateral 

Artery 592 

Muscular  Branches 592 

The  Anastomosis  Around  the  Elbow-joint  592 

The  Radial  Artery 592 

Relations 592 

Peculiarities 594 

Branches 594 

Radial  Recurrent  Artery      .      .      .  594 

Muscular 594 

Volar  Carpal 594 

Superficial  Volar 594 

Dorsal  Carpal       .      .      .      .      .  694 

Arteria  Princeps  PoUicis       .      .      .  595 

Arteria  Volaris  Indicis  Radialis       .  595 

Deep  Volar  Arch 595 

Volar  Metacarpal  Arteries    .  696 

Perforating 595 

Recurrent 596 

The  Ulnar  Artery 595 

Relations 595 

Peculiarities 596 

Branches 696 

Anterior  Ulnar  Recurrent  Artery    .  596 

Posterior  Ulnar  Recurrent  Artery  .  596 

Common  Interosseous  Artery    .      .  596 

Muscular 598 

Volar  Carpal 698 

Dorsal  Carpal 698 

Deep  Volar 598 

Superficial  Volar 598 

Relations 598 


18 


CONTENTS 


The  Arteries  of  the  Trunk. 

The  Descending  Aorta. 

The  Thoracic  Aorta 598 

Relations 599 

Peculiarities 599 

Branches 600 

Pericardial 600 

Bronchial 600 

Esophageal 600 

Mediastinal 600 

Intercostal  Arteries 600 

Branches        ...  .  601 

Subcostal  Arteries 601 

Superior  Phrenic 601 

The  Abdominal  Aorta 602 

Relations 603 

Collateral  Circulation 603 

Branches 603 

The  Celiac  Artery 603 

Relations 603 

The  Superior  Mesenteric  Artery      .  606 

Branches 607 

The  Inferior  Mesenteric  Artery       .  609 

Branches 610 

The  Middle  Suprarenal  Arteries      .  610 

The  Renal  Arteries 610 

The  Internal  Spermatic  Arteries     .  611 
The  Ovarian  Arteries      .      .      .      .611 

The  Inferior  Phrenic  Arteries    .      .  612 

The  Lumbar  Arteries      ....  612 

The  Middle  Sacral  Artery    ...  613 


The  Cominon  Iliac  Arteries. 

Peculiarities 614 

Collateral  Circulation 614 

The  Hypogastric  Artery 614 

Relations 614 

Peculiarities 615 

Collateral  Circulation 615 

Branches 615 

Superior  Vesical  Arterj'  .      .      .      .615 

Middle  Vesical  Artery     ....  615 

Inferior  Vesical  Artery    ....  615 

Middle  Hemorrhoidal  Artery     .      .  615 

Uterine  Artery 615 

Vaginal  Artery 616 

Obturator  Artery 616 

Branches 616 

Peculiarities  ......  617 

Internal  Pudendal  Artery-     .      .      .  617 

Relations 618 

Peculiarities 618 

Branches 618 

Inferior  Gluteal  Arterj-   ....  620 

Branches 620 

Lateral  Sacral  Arteries    .      .      .      .621 

Superior  Gluteal  Artery        .      .      .  622 

The  External  Iliac  Artery 622 

Relations 622 

Collateral  Circulation 622 

Branches 622 

Inferior  Epigastric  Artery    .      .      .  623 

Branches 623 

Peculiarities 623 

Deep  Iliac  Circumflex  Artery     .      .  623 


The  Arteries  of  the  Lower  Extremity. 

The  Femoral  Artery. 

The  Femoral  Sheath 6251 

The  Femoral  Triangle 628i 

The  Adductor  Canal 627 

Relations  of  the  Femoral  Artery  ....  627 

Peculiarities  of  the  Femoral  Artery     .       .       .  629 

Collateral  Circulation 629 

Branches 629 

Superficial  Epigastric  Artery  .  629 

Superficial  Iliac  Circumflex  Artery   .      .  629 

Superficial  External  Pudendal  Artery     .  629 

Deep  External  Pudendal  Artery  .  629 

Muscular     . 629 

Profunda  Femoris  Artery        ....  629 

Relations 630 

Peculiarities 630jb!^^ 

Branches    . 63(«l|^| 

Highest  Genicular  Artery        ....  631^fff3B 

The  Popliteal  Fo.ssa 031 

Boundaries 631 

Contents 632 

The  Popliteal  Artery 632 

Relations 632 

Peculiarities       .......  633 

Branches 633 

Superior  Muscular 633 

Sural  Arteries 633 

Cutaneous  Branches  ....  633 
Superior  Genicular  Arteries  .  633 
Middle  Genicular  Artery  .  033 
Inferior  Genicular  Arteries  .  .  633 
The  Anastomosis  Around  the  Knee- 
joint    .       .  634 

The  Anterior  Tibial  Artery 634 

Relations 635 

Peculiarities 635 

Branches 635 

Posterior  Tibial  Recurrent  Artery  .  635 

Fibular  Artery 635 

Anterior  Tibial  Recurrent  Arterj-   .  635 

Muscular  Branches 635 

Anterior  Medial  Malleolar  Artery  .  035 

Anterior  Lateral  Malleolar  Arterv  .  635 

The  Arteria  Dorsalis  Pedis       .      .      .      .  "    .  636 

Relations 636 

Peculiarities 636 

Branches 637 

Lateral  Tarsal  Artery      ....  637 

Medial  Tarsal  Artery      ....  637 

Arcuate  Artery 637 

Deep  Plantar  Arterj-        ....  637 

The  Posterior  Tibial  Artery 637 

Relations 637 

Peculiarities 638 

Branches 638 

Peroneal  Artery 638 

Peculiarities^ 638 

Branches 638 

Nutrient  Artery 638 

Muscular  Branches 639 

Posterior  Medial  Malleolar  Artery  639 

Communicating  Branch  ....  639 

Medial  Calcaneal 639 

Medial  Plantar  Artery     ....  039 

Lateral  Plantar  Arterj     ....  639 

Branches 640 


The  Pulmonary  Veins 
The  Systemic  Veins. 


THE  VEINS. 

.     642 


The  Veins  of  the  Heart. 

Coronary  Sinus 642 

Tributaries 642 

The  Veins  of  the  Head  and  Neck. 

The  Veins  of  the  Exterior  of  the  Head  and 

Face 644 

The  Frontal  Vein 644 


The  Veins  of  the  Exterior  of  the  Head 

and 

Face — 

The  Supraorbital  Vein 645 

The  Angular  Vein 

645 

The  Anterior  Facial  Vein 

645 

Tributaries      .... 

645 

The  Superficial  Temporal  Vein 

645 

Tributaries      .... 

645 

The  Pterygoid  Plexus 

645 

The  Internal  Maxillary  Vein . 

646 

The  Posterior  Facial  Vein 

646 

The  Posterior  Auricular  Vein 

646 

The  Occipital  Vein 

646 

CONTENTS 


19 


The  Veins  of  the  Neck 

The  External  Jugular  Vein 

Tributaries 
The  Posterior  External  Jugular  Vein 
The  Anterior  Jugular  Vein 
The  Internal  Jugular  Vein 

Tributaries 
The  Vertebral  Vein 

Tributaries 
The  Diploic  Veins    . 
The  Veins  of  the  Brain 
The  Cerebral  Veins 
The  External  Veins 

The  Superior  Cerebral  Vein 

The  Middle  Cerebral  Vein    . 

The  Inferior  Cerebral  Vein  . 

The  Internal  Cerebral  Veins 

The  Great  Cerebral  Vein 
The  Cerebellar  Veins  .... 
The  Sinuses  of  the  Dura  Mater.    Ophthalmic 
Veins  and  Emissary  Veins 
The  Superior  Sagittal  Sinus   . 
The  Inferior  Sagittal  Sinus     . 
The  Straight  Sinus       .... 
The  Transverse  Sinuses 
The  Occipital  Sinus     .... 
The  Confluence  of  the  Sinuses 
The  Cavernous  Sinuses 
The  Ophthalmic  Veins 

The  Superior  Ophthalmic  Vein 

The  Inferior  Ophthalmic  Vein 
The  Intercavernous  Sinuses 
The  Superior  Petrosal  Sinus 
The  Inferior  Petrosal  Sinus 
The  Basilar  Plexus 
The  Emissary  Veins 


The 


The 


The 


The  Veins  of  the   Upper  Extremity  and 
Thorax. 


Superficial  Veins  of  the  Upper  Extremity 

Digital  Veins 

The  Cephalic  Vein       .... 

The  Accessory  Cephalic  Vein 
The  Basilic  Vein     .... 
The  Median  Antibrachial  Vein 
Deep  Veins  of  the  Upper  Extremity 
Deep  Veins  of  the  Hand  . 
Deep  Veins  of  the  Forearm 
The  Brachial  Veins 
The  Axillary  Vein 
The  Subclavian  Vein 

Tributaries 
Veins  of  the  Thorax 
The  Innominate  Veins 

The  Right  Innominate  Vein 

The  Left  Innominate  Vein 

Tributaries      .... 

Peculiarities 
The  Internal  Mammary  Veins 
The  Inferior  Thyroid  Veins    . 
The  Highest  Intercostal  Vein 
The  Superior  Vena  Cava 

Relations 

The  Azygos  Vein    .... 

Tributaries      .... 
The  Hemiazygos  Veins 


646 
646 
647 
647 
647 
648 
648 
649 
650 
651 
652 
652 
652 
652 
652 
652 
653 
653 
653 

654 
654 
655 
655 
657 
658 
658 
658 
658 
659 
659 
659 
659 
659 
660 
660 


660 
660 
661 
662 
662 
662 
663 
663 
663 
663 
663 
664 
664 
664 
664 
664 
666 
666 
666 
666 
666 
666 
666 
667 
667 
667 
667 


The  Veins  of  the  Thorax — 
The  Azygos  Vein — 

The  Accessory   Hemiazygos 

Veins 667 

The  Bronchial  Veins 667 

The  Veins  of  the  Vertebral  Column    .      .      .  667 

The  External  Vertebral  Venous  Plexuses  668 

The  Internal  Vertebral  Venous  Plexuses  668 

The  Basivertebral  Veins 668 

The  Intervertebral  Veins         ...  669 

Th«  Veins  of  the  Medulla  Spinalis    .  669 

The  Veins  of  the  Lower  Extremity,  Abdomen, 
and  Pelvis. 

The  Superficial  Veins  of  the  Lower  Extremity  669 

The  Dorsal  Digital  Veins 669 

The  Great  Saphenous  Vein     ....  669 

Tributaries 670 

The  Small  Saphenous  Vein      ....  670 

The  Deep  Veins  of  the  Lower  Extremity       .  671 

The  Plantar  Digital  Veins      ....  671 

The  Posterior  Tibial  Veins     ....  672 

The  Anterior  Tibial  Veins      ....  672 

The  Popliteal  Vein 672 

The  Femoral  Vein 672 

The  Deep  Femoral  Vein  672 

The  Veins  of  the  Abdomen  and  Pelvis  .  672 

The  External  Iliac  Vein 672 

Tributaries 672 

The  Hypogastric  Veins 673 

Tributaries 673 

The  Hemorrhoidal  Plexus       ....  676- 

The  Pudendal  Plexus 676 

The  Vesical  Plexus 676. 

The  Dorsal  Veins  of  the  Penis     .      .      .  676 

The  Uterine  Plexuses 676 

The  Vaginal  Plexuses 677 

The  Common  Iliac  Veins        ....  677 

The  Middle  Sacral  Veins      ...  677 

Peculiarities 677 

The  Inferior  Vena  Cava 677 

Relations 678 

Peculiarities 678 

Applied  Anatomy 678 

Tributaries 678 

Lumbar  Veins 678 

Spermatic  Veins       ....  678 

Ovarian  Veins 679 

Renal  Veins 679 

Suprarenal  Veins      ....  679 

Inferior  Phrenic  Veins  .      .      .  679 

Hepatic  Veins 680 

The  Portal  System  of  Veins. 

The  Portal  Vein 681 

Tributaries 681 

The  Lienal  Vein 681 

Tributaries 681 

The  Superior  Mesenteric  Vein   .      .  682 

Tributaries 682 

The  Coronary  Vein 682 

The  Pyloric  Vein 682 

The  Cystic  Vein 682 

The  Parumbilical  Veins  ....  682 


THE  LYMPHATIC  SYSTEM. 


The  Development  of  the  Lymphatic  Vessels 
Lymphatic  Capillaries 

Distribution 

Lymphatic  Vessels 

Structure  of  Lymphatic  Vessels     .      .      .      . 
The  Lymph  Glands 

Structure  of  Lymph  Glands  .      .      .      . 

Hemolymph  Nodes         

Lymph 


The  Thoracic  Duct. 


The  Cistema  Chyli        .      . 

Tributaries 
The  Right  Lymphatic  Duct 

Tributaries 


683 
684 
684 
687 
687 
688 
688 
690 
690 


691 
691 
691 
692 


The  Lymphatics  of  the  Head,  Face, 
Neck. 

The  Lymph  Glands  of  the  Head   . 
The  Occipital  Glands  . 
The  Posterior  Auricular  Glands 
The  Anterior  Auricular  Glands 
The  Parotid  Glands     .      .      . 
The  Facial  Glands 
The  Deep  Facial  Glands  . 
The  Lingual  Glands 
The  Retropharyngeal  Glands 
The  Lymphatic  Vessels  of  the  Scalp 
The  Lymphatic  Vessels  of  the  Auricul 

and  External  Acoustic  Meatus 
The  Lymphatic  Vessels  of  the  Face 


692 
692 
693 
693 
693 
694 
694 
694 
694 
694 

694 
695 


20 


CONTENTS 


The  Lymph  Glands  of  the  Head— 

The   Lymphatic   Vessels   of   the    Nasal 

Cavities 695 

The  Lymphatic  Vessels  of  the  Mouth  .  695 
The  Lymphatic  Vessels  of  the  Palatine 

Tonsil 695 

The  Lymphatic  Vessels  of  the  Tongue  696 

The  Lymph  Glands  of  the  Neck  ....  697 

The  Submaxillary  Glands       ....  697 

The  Submental  or  Suprahyoid  Glands  .  697 

The  Superficial  Cervical  Glands  .      .    ' .  697 

The  Anterior  Cervical  Glands  .  .  697 
The  Deep  Cervical  Glands  .  .  .  .697 
The  Lymphatic  Vessels  of  the  Skin  and 

Muscles  of  the  Neck 698 


The  Lymphatics  of  the  Upper  Extremity. 

The  Lymph  Glands  of  the  Upper  Extremity  699 

The  Superficial  Lymph  Glands    .      .      .  699 

The  Deep  Lymph  Glands       ....  699 

The  Axillary  Glands        ....  699 

The     Lymphatic     Vessels     of     the     Upper 

Extremity 700 

The  Superficial  Lymphatic  Vessels   .      .  700 

The  Deep  Lymphatic  Vessels        .  .  701 


The  Lymphatics  of  the  Lower  Extremity. 

The  Lymph  Glands  of  the  Lower  Extremity  701 

The  Anterior  Tibial  Gland     ....  701 

The  Popliteal  Glands 701 

The  Inguinal  Glands 702 

The     Lymphatic     Vessels     of     the     Lower 

Extremity 703 

The  Superficial  Lymphatic  Vessels  .  703 

The  Deep  Lymphatic  Vessels      .  703 


The  Lymphatics  of  the  Abdomen  and  Pelvis. 

The  Lymph   Glands  of  the  Abdomen   and 

Pelvis 703 

The  Parietal  Glands 703 

The  External  Iliac  Glands  ...  703 
The  Common  Iliac  Glands  .      .  704 

The  Epigastric  Glands  ....  704 
The  Iliac  Circumflex  Glands  .  .  704 
The  Hypogastric  Glands       .      .      .      704 

The  Sacral  Glands 704 

The  Lumbar  Glands        ....      705 
The  Lymphatic  Vessels  of  the  Abdomen  and 

Pelvis 706 

The  Superficial  Vessels 706 

The  Deep  Vessels 706 

The     Lymphatic     Vessels     of     the 
Perineum  and  External  Genitals       706 

The  Visceral  Glands 706 

706 
706 
706 
709 
709 
709 
709 
710 


The  Gastric  Glands   . 

The  Hepatic  Glands 

The  Pancreaticolienial  Glands 
The  Superior  Mesenteric  Glands 

The  Mesenteric  Glands  . 

The  Ileocolic  Glands 

The  Mesocolic  Glands     . 
The  Inferior  Mesenteric  Glands 
The  Lymphatic  Vessels  of  the  Abdominal 

and  Pelvic  Viscera 710 


The   Lymphatic  Vessels  of   the   Abdomina 
and  Pelvic  Viscera — 
The  Lymphatic  Vessels  of  the  Subdia- 
phragmatic Portions  of  the  Digestive 

Tube 

The  Lymphatic  Vessels  of  the  Stomach  710 
The  Lymphatic  Vessels  of  the  Duodenum  710 
The  Lymphatic  Vessels  of  the  Jejunum         _^^H 

and  Ileum ^^41^1 

The  Lymphatic  Vessels  of  the  Vermiform  !■  ^H 

Process  and  Cecum 710 

The  Lymphatic  Vessels  of  the  Colon  .  711 
The   Lymphatic   Vessels   of   the   Anus,  ^.^^ 

Anal  Canal,  and  Rectum      ....     ''^l^l^H 
The  Lymphatic  Vessels  of  the  Liver  ^^^^1^1 

The    Lymphatic    Vessels    of    the   Gall-         ^B^H 

bladder  '^^flH 

The  Lymphatic  Vessels  of  the  Pancreas     71^H^H 
The  Lymphatic  Vessels  of  the  Spleen  and         ^H^l 

Suprarenal  Glands 7lU^B 

The  Lymphatic  Vessels  of  the  Urinary 

Organs    . 712 

The     Lymphatic     Vessels     of     the 

Kidney 712 

The  Lymphatic  Vessels  of  the  Ureter     712 
The     Lymphatic     Vessels    of    the 

Bladder 712 

The     Lymphatic     Vessels     of    the 

Prostate 713 

The     Lymphatic     Vessels     of     the 

Urethra 713 

The  Lymphatic  Vessels  of  the  Repro- 
ductive Organs 713 

The     Lymphatic    Vessels     of    the 

Testes 713 

The     Lymphatic     Vessels     of    the 

Ductus  Deferens 713 

The  Lymphatic  Vessels  of  the  Ovary     714 
The     Lymphatic     Vessels     of     the 

Uterine  Tube 714 

The     Lymphatic     Vessels     of    the 

Uterus 714 

The     Lymphatic     Vessels     of     the 
Vagina 714 


The  Lymphatics  of  the  Thorax. 


The  Parietal  Lymph  Glands 715 

The  Sternal  Glands 715 

The  Intercostal  Glands 715 

The  Diaphragmatic  Glands    .      .  .715 

The    Superficial  Lymphatic   Vessels   of   the 

Thoracic  Wall 715 

The  Lymphatic  Vessels  of  the  Mamma.  715 

The  Deep  Lymphatic  Vessels  of  the  Thoracic 

Wall 716 

The  Visceral  Lymph  Glands        .      .      .717 

The  Anterior  Mediastinal  Glands     .      .  717 
The  Posterior  Mediastinal  Glands    .      .717 

The  Tracheobronchial  Glands      .      .      .  717 

The    Lymphatic    Vessels    of    the    Thoracic 

Viscera 718 

The  Lymphatic  Vessels  of  the  Heart  .  718 
The  Lymphatic  Vessels  of  the  Lungs  .  718 
The  Lymphatic  Vessels  of  the  Pleura  719 
The  Lymphatic  Vessels  of  the  Thymus  719 
The  Lymphatic  Vessels  of  the  Eso- 
phagus        719 


NEUROLOGY. 


Structure  of  the  Nervous  System. 

Neuroglia 722 

Nerve  Cells 722 

Nerve  Fibers 724 

Wallerian  Degeneration 727 

Non-medullated  Fibers 728 

Structure    of     the    Peripheral    Nerves    and 

Ganglia ,  .v      •      •      •      '  Z^^ 

Origins  and  Terminations  of  Nerves   .      .      .  729 


Ganglia  

Neuron  Theory         

Fasciculi,  Tracts  or  Fiber  Systems 


730 
732 
732 


Development  of  the  Nervous  System. 

The  Medulla  Spinalis 733 

The  Spinal  Nerves 735 

The  Brain 736 


CONTENTS 


21 


The  Brain — 

The  Hind-brain  or  Rhombencephalon    .  738 

The  Mid-brain  or  Mesencephalon      .  741 

The  Fore-brain  or  Prosencephalon  741 

The  Diencephalon 742 

The  Telencephalon 743 

The  Commissures 746 

Fissures  and  Sulci 747 

The  Cranial  Nerves ".  748 


The  Spinal  Cord  or  Medulla  Spinalis. 

Enlargements 751 

Fissures  and  Sulci 752 

The  Anterior  Median  Fissure  752 

The  Posterior  Median  Sulcus  .  752 

The     Internal    Structure    of    the     Medulla 

Spinalis 753 

The  Gray  Substance 753 

Structure  of  the  Gray  Substance  755 

The  White  Substance 758 

Nerve  Fasciculi 759 

Roots  of  the  Spinal  Nerves 764 

The  Anterior  Nerve  Root       ....  764 

The  Posterior  Root 764 


The  Brain  or  Encephalon. 
General  Considerations  and  Divisions 


766 


The  Hind-brain  or  Rhombencephalon. 

The  Medulla  Oblongata 767 

The  Anterior  Median  Fissure             .  767 

The  Posterior  Median  Fissure     .      .      .  767 
Internal     Structure     of     the     Medulla 

Oblongata 775 

The  Cerebrospinal  Fasciculi  775 
Gray    Substance    of    the    Medulla 

Oblongata 779 

Inferior  Peduncle 782 

Formatio  Reticularis       ....  784 

The  Pons 785 

Structure                        785 

The  Cerebellum 788 

Lobes  of  the  Cerebellum 788 

Internal  Structure  of  the  Cerebellum  791 
The  White  Substance      .      .      .      .791 
Projection  Fibres                        .791 

The  Gray  Substance        ....  794 
Microscopic     Appearance     of     the 

Cortex 794 

The  Fourth  Ventricle    ....!!!  797 

Angles 797 

Lateral  Boundaries 797 

Choroid  Plexuses 798 

Openings  in  the  Roof 798 

Rhomboid  Fossa 798 

The  Mid-brain  or  Mesencephalon. 

The  Cerebral  Peduncles 800 

Structure  of  the  Cerebral  Peduncles       .  801 

The  Gray  Substance        ....  802 

The  White  Substance      ....  803 

The  Corpora  Quadrigemina 805 

Structure  of  the  Corpora  Quadrigemina  806 

The  Cerebral  Aqueduct 806 

The  Fore-brain  or  Prosencephalon. 

The  Diencephalon 807 

The  Thalamencephalon 808 

Structure 810 

Connections 810 

The  Metathalamus 811 

The  Epithalamus 812 

The  Hypothalamus 812 

The  Optic  Chiasma 814 

The  Optic  Tracts 814 

The  Third  Ventricle 815 

The  Interpeduncular  Fossa    .      .      .      .816 

The  Telencephalon 817 


The  Cerebral  Hemispheres 817 

The  Longitudinal  Cerebral  Fissure  .  818 
The    Surfaces   of    the    Cerebral    Hemi- 
spheres       818 

The  Lateral  Cerebral  Fissure       .  .  819 

The  Central  Sulcus 819 

The  Parietooccipital  Fissure  ....  820 

The  Calcarine  Fissure 820 

The  Cingulate  Sulcus 820 

The  Collateral  Fissure 820 

The  Sulcus  Circularis 821 

The  Lobes  of  the  Hemispheres    .      .      .  821 

The  Frontal  Lobe 821 

The  Parietal  Lobe 822 

The  Occipital  Lobe 823 

The  Temporal  Lobe 823 

The  Insula 825 

The  Limbic  Lobe 825 

The  Rhinencephalon 826 

The  Olfactory  Lobe   .....  826 
The    Interior    of    the    Cerebral    Hemi- 
spheres    827 

The  Corpus  Callosum      ....  828 

The  Lateral  Ventricles    ....  829 

The  Fornix 838 

The  Interventricular  Foramen  .  840 

The  Anterior  Commissure    .  840 

The  Septum  Pellucidum ....  840 
The  Choroid  Plexus  of  the  Lateral 

Ventricle 840 

Structure    of   the    Cerebral   Hemi- 
spheres   ■.      .  842 

Structure  of  the  Cerebral  Cortex  .  845 

Special  Types  of  Cerebral  Cortex      .      .  847 

Weight  of  Encephalon 848 

Cerebral  Localization 849 

Composition  and  Central  Connections  of  the  Spinal 
Nerves. 

The  Intrinsic  Spinal  Reflex  Paths       .      .  850 
Sensory  Pathways  from  the  Spinal  Cord 

to  the  Brain         851 

Composition  and  Central  Connections  of  the  Cranial 

Nerves. 

The  Hypoglossal  Nerve 855 

The  Accessory  Nerve 855 

The  Vagus  Nerve 855 

The  Glossopharyngeal  Nerve 856 

The  Acoustic  Nerve 857 

The  Vestibular  Nerve 860 

The  Facial  Nerve 861 

The  Abducens  Nerve 861 

The  Trigeminal  Nerve         862 

The  Trochlear  Nerve .  863 

The  Oculomotor  Nerve 863 

The  Optic  Nerve 864 

The  Olfactory  Nerves 866 

Pathways  from  the  Brain  to  the  Spinal  Cord. 

The  Motor  Tract 870 

The  Meninges  of  the  Brain  and  Medulla  Spinalis. 

The  Dura  Mater 872 

The  Cranial  Dura  Mater         ....  872 

Processes 873 

Structure 875 

The  Spinal  Dura  Mater 875 

Structure 876 

The  Arachnoid   . 876 

The  Cranial  Part 876 

The  Spinal  Part 876 

Structure 876 

The  Subarachnoid  Cavity      ....  876 

The  Subarachnoid  Cistemse  ....  876 

The  Arachnoid  Villi 878 

Structure 878 

The  Pia  Mater 878 

The  Cranial  Pia  Mater 879 

The  Spinal  Pia  Mater 879 

The  Ligamentum  Denticulatum        .  880 


22 


CONTENTS 


The  Cerebrospinal  Fluid 

The  Cranial  Nerves. 
The  Olfactory  Nerves 
The  Optic  Nerve. 


The  Optic  Chiasma 
The  Optic  Tract 


The  Oculomotor  Nerve 
The  Trochlear  Nerve     . 
The  Trigeminal  Nerve. 


The  Semilunar  Ganglion     . 
The  Ophthalmic  Nerve 

The  Lacrimal  Nerve    . 

The  Frontal  Nerve 

The  Nasociliary  Nerve 

The  Ciliary  Ganglion  . 
The  Maxillary  Nerve     . 

Branches      .... 

The  Middle  Meningeal  Nerve 
The  Zygomatic  Nerve     . 
The  Sphenopalatine  . 
The  Posterior  Superior  Alveolar 
The  Middle  Superior  Alveolar 
The  Anterior  Superior  Alveolar 
The  Inferior  Palpebral    . 
The  External  Nasal   . 
The  Superior  Labial 
The  Sphenopalatine  Ganglion 
The  Mandibular  Nerve       .... 

Branches      .  .      . 

The  Nervus  Spinosus 
The  Internal  Pterygoid  Nerve 
The  Masseteric  Nerve     . 
The  Deep  Temporal  Nerves 
The  Buccinator  Nerve     . 
The  External  Pterygoid  Nerve 
The  Auriculotemporal  Nerve 
The  Lingual  Nerve    . 
The  Inferior  Alveolar  Nerve 
The  Otic  Ganglion     . 
The  Submaxillary  Ganglion 
Trigeminal  Nerve  Reflexes 


The  Abducent  Nerve 
The  Facial  Nerve. 


880 


881 


883 

884 


885 


886 

887 
887 
887 

888 


890 
890 
891 
891 
891 
891 
891 
891 
893 
894 
894 
894 
894 
895 
895 
895 
895 
895 
896 
897 
898 
899 

899 


The  Greater  Superficial  Petrosal  Nerve  .      .  903 

The  Nerve  to  the  Stapedius 904 

The  Chorda  Tympani  Nerve 904 

The  Posterior  Auricular  Nerve      ....  905 

The  Digastric  Branch 905 

The  Stylohyoid  Branch 905 

The  Temporal  Branches 905 

The  Zygomatic  Branches 905 

The  Buccal  Branches 905 

The  Mandibular  Branch 905 

The  Cervical  Branch 905 

The  Acoustic  Nerve. 

The  Cochlear  Nerve 906 

The  Vestibular  Nerve 906 


The  Ganglion  Nodosum — 

The  Meningeal  Branch      . 

The  Auricular  Branch 

The  Pharyngeal  Branch    . 

The  Superior  Laryngeal  Nerve 

The  Recurrent  Nerve 

The  Superior  Cardiac  Branches 

The  Inferior  Cardiac  Branches 

The  Anterior  Bronchial  Branches 

The  Posterior  Bronchial  Branches 

The  Esophageal  Branches 

The  Gastric  Branches 

The  Celiac  Branches 

The  Hepatic  Branches 


The  Accessory  Nerve, 


The  Cranial  Part 
The  Spinal  Part 


The  Hypoglossal  Nerve. 


The  Glossopharyngeal  Nerve. 

The  Superior  Ganglion        .... 

The  Petrous  Ganglion 

The  Tympanic  Nerve 
The  Carotid  Branches 
The  Pharyngeal  Branches 


908 
908 
909 
909 
909 


The  Muscular  Branches 909 

The  Tonsillar  Branches 909 

The  Lingual  Branches 909 

The  Vagus  Nerve. 

The  Jugular  Ganglion 911 

The  Ganglion  Nodosum 911 


Branches  of  Communication 
Branches  of  Distribution    . 
The  Meningeal  Branches 
The  Descending  Ramus 
The  Thyrohyoid  Branch 
The  Muscular  Branches 


The  Spinal  Nerves. 

Nerve  Roots 

The  Anterior  Root 

The  Posterior  Root 

The  Spinal  Ganglia 

Structure 

Connections  -with  Sympathetic     . 

Structure 

Divisions  of  the  Spinal  Nerves      .... 

The  Posterior  Divisions 

The  Cervical  Nerves  .... 
The  Thoracic  Nerves  .... 
The  Lumbar  Nerves        .... 

The  Sacral  Nerves 

The  Coccygeal  Nerve      .... 

The  Anterior  Divisions 

The  Cervical  Nerves        .... 
The  Cervical  Plexus 

Great  Auricular  Nerve 
Cutaneous  Cervical  Nerve 
Supraclavicular  Nerves     . 
Communicantes  Cervicales 
Phrenic  Nerve  .... 
The  Brachial  Plexus 

Relations 

Dorsal  Scapular  Nerve     . 
Suprascapular  Nerve  . 
Nerve  to  Subclavius    . 
Long  Thoracic  Nerve 
Anterior  Thoracic  Nerves 
Subscapular  Nerves     . 
Thoracodorsal  Nerve  . 
Axillary  Nerve 
Musculocutaneous  Nerve 
Medial  Antibrachial  Cuta- 
neous Nerve 
Medial  Brachial  Cuta- 
neous Nerve 
Median  Nerve  . 
Ulnar  Nerve 
Radial  Nerve    . 
The  Thoracic  Nerves 

First  Thoracic  Nerve 
Upper  Thoracic  Nerves 
Lower  Thoracic  Nerves 
The  Lumbosacral  Plexus 
The  Lumbar  Nerves 

The  Lumbar  Plexus 

Iliohypogastric  Nerve 
Ilioinguinal  Nerve 
Genitofemoral  Nerve 
Lateral  Femoral  Cuta- 
neous Nerve 
Obturator  Nerve 


911 
911 
911 
912 
912 
912 
912 
913 
913 
913 
913 
913 
913 


913 
913 


915 
916 
916 
916 
916 
916 


916 
916 
916 
917 
917 
920 
920 
921 
921 
921 
923 
924 
924 
925 
925 
925 
925 
926 
927 
928 
928 
928 
930 
931 
932 
932 
933 
933 
933 
933 
934 
934 
935 

937 

937 
938 
939 
943 
944 
945 
945 
948 
948 
948 
949 
950 
952 
953 

953 
953 


CONTENTS 


23 


Divisions  of  the  Spinal  Nerves — 
The  Anterior  Divisions — 

The  Lumbosacral  Plexus — 
The  Lumbar  Nerves — 

The  Lumbar  Plexus — 

Accessory     Obturator 

Nerve     ....     955 
Femoral  Nerve     .  955 

Saphenous  Nerve.  956 

The    Sacral    and    Coccygeal 

Nerves 957 

The  Sacral  Ple.xus  957 

Relations        .  957 

Nerve  to  Quadratus 
Femoris     and 
Gemellus  Inferior        957 
Nerve  to  Obturator 
Internus  and   Ge- 
mellus Superior     .       958 
Nerve  to  Piriformis         959 
Superior     Gluteal 

Nerve   ....        959 
Inferior     Gluteal 

Nerve  ....        959  ; 
Posterior       Femoral  j 

Cutaneous  Nerve         959  j 
Sciatic  Nerve      .      .        960 
Tibial  Nerve       .      .       960 
Lateral  Plantar  Nerve     963 
Common      Peroneal 

Nerve     ....     964 
Deep  Peroneal  Nerve    965 
Superficial      Peroneal 
Nerve     ....     966 
The  Pudendal  Plexus  966 

Perforating  Cuta- 

neous Nerve      .      .     967 
Pudendal  Nerve  .     967 

Anococcygeal     Nerve     968 


The  Sympathetic  Nerves. 

The  Cranial  Sympathetics 970 

The  Sacral  Sympathetics 973 

The  Thoracolumbar  Sympathetics      .      .      .  974 

The  Sympathetic  Trunks  976 

Connections  with  the  Spinal  Nerves         .  976 

Development 977 


The  Cephalic  Portion  of  the  Sympathetic 
System. 


The  Internal  Carotid  Plexus 
The  Cavernous  Plexus 


977 
978 


The  Cervical  Portion  of  the  Sympathetic 
System. 


The  Superior  Cervical  Ganglion 
Branches    

The  Middle  Cervical  Ganglion 
Branches    

The  Inferior  Cervical  Ganglion 
Branches    


978 
978 
979 
979 
980 
981 


The   Thoracic  Portion  of  the  Sympathetic 

System. 

The  Greater  Splanchnic  Nerve    ....  981 

The  Lesser  Splanchnic  Nerve       ....  981 

The  Lowest  Splanchnic  Nerve     ....  981 

The  Abdominal  Portion  of  the  Sympathetic 

System  ....  982 

The  Pelvic  Portion  of  the  Sympathetic 

System  ....  984 

The  Great  Plexuses  of  the  Sympathetic  System. 

The  Cardiac  Plexus 984 

The  Celiac  Plexus  985 

,  Phrenic  Plexus 985 

*  Hepatic  Plexus 986 

Lienal  Plexus  986 

Superior  Gastric  Plexus 987 

Suprarenal  Plexus 987 

Renal  Plexus 987 

Spermatic  Plexus  987 

Superior  Mesenteric  Plexus  .      .      .  987 

Abdominal  A^tic  Plexus        ....  987 

Inferior  Mesenteric  Plexus     ....  987 

The  Hypogastric  Plexus 987 

The  Pelvic  Plexuses 987 

The  Middle  Hemorrhoidal  Plexus     .      .  988 

The  Vesical  Plexus 988 

The  Prostatic  Plexus 988 

The  Vaginal  Plexus 989 

The  Uterine  Plexus 989 


THE  ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT. 


The  Peripheral  Organs  of  the  Special 

Senses. 

The  Organs  of  Taste. 

Structure 991 

The  Organ  of  Smell. 

The  External  Nose 992 

Structure 992 

The  Nasal  Cavity 994 

The  Lateral  Wall 994 

The  Medial  Wall 995 

The  Mucous  Membrane  ....  996 
Structure 996 

The  Accessory  Sinuses  of  the  Nose  .  998 

The  Frontal  Sinuses 998 

The  Ethmoidal  Air  Cells      ....       998 

The  Sphenoidal  Sinuses 998 

The  Maxillary  Sinus 999 

The  Organ  of  Sight. 

Development 1001 

The  Tunics  of  the  Eye 1005 

The  Fibrous  Tunic 1005 

The  Sclera 1005 

Structure 1006 

The  Cornea 1006 

Structure 1007 


The  Tunics  of  the  Eye — 

The  Vascular  Tunic 1009 

The  Choroid 1009 

Structure 1010 

The  Ciliary  Body 1010 

Structure 1011 

The  Iris 1012 

Structure 1013 

Membrana  Pupillaris     ....  1014 

The  Retina 1014 

Structure 1015 

The  Refracting  Media 1018 

The  Aqueous  Humor 1018 

The  Vitreous  Bodv 1018 

The  Crystalline  Lens 1019 

Structure 1020 

The  Accessory  Organs  of  the  Eye     .  1021 

The  Ocular  Muscles 1021 

Levator  PalpebrEe  Superioris    .  1021 

The  Recti 1022 

Obliquus  Oculi  Superior      .      .      .  1022 

Obliquus  Oculi  Inferior       .      .      .  1023 

The  Fascia  Bulb 1024 

The  Orbital  Fascia 1025 

The  Eyebrows 1025 

The  Eyelids 1025 

The    Lateral    Palpebral    Commis- 
sure         1025 

The  Eyelashes 1025 

Structure  of  the  Eyelids    .      .  1025 

The  Tarsal  Glands 1026 


24 


CONTENTS 


The  Accessory  Organs  of  the  Eye — 

Structure  of  the  Tarsal  Glands 
The  Conjunctiva 

The  Palpebral  Portion 
The  Bulbar  Portion 
The  Lacrimal  Apparatus 
The  Lacrimal  Gland 

Structure 
The  Lacrimal  Ducts 
The  Lacrimal  Sac 

Structure 
The  Nasolacrimal  Duct 

The  Organ  of  Hearing. 


1026 
1026 
1027 
1027 
1028 
1028 
1028 
1028 
1028 
1029 
1029 


Development 1029 

The  External  Ear 1033 

The  Auricula  or  Pinna 1033 

Structure 1034 

The  External  Acoustic  Meatus        .      .  1036 

Relations 1037 

The  Middle  Ear  or  Tympanic  Cavity    .      .  1037 

The  Tegumental  Wall  or  Roof  .      .      .  1038 

The  Jugular  Wall  or  Floor   ....  1038 

The  Membranous  or  Lateral  Wall         .  1038 

The  Tympanic  Membrane    ....  1039 

Structure 1039 

The  Labyrinthic  or  Medial  Wall     .      .  1040 

The  Mastoid  or  Posterior  Wall        .      .  1042 

The  Carotid  or  Anterior  Wall    .      .      .  1042 

The  Auditory  Tube 1042 

The  Auditory  Ossicles 1044 

The  Malleus X044 

The  Incus 1044 

The  Stapes 1045 

Articulations  of  the  Auditory  Ossicles  1045 

Ligaments  of  the  Ossicles     ....  1045 

The  Muscles  of  the  Tympanic  Cavity  1046 

The  Tensor  Tympani    ....  1046 

The  Stapedius     .      .  , .      .      .      .  1046 

The  Internal  Ear  or  Labyrinth    ....  1047 

The  Osseous  Labyrinth 1047 


The  Internal  Ear  or  Labyrinth — 
The  Osseous  Labyrinth — 

The  Vestibule 

The  Bony  Semicircular  Canals 
The  Cochlea  .  .  . 
The  Membranous  Labyrinth 
The  Utricle  .... 
The  Saccule  .... 
The  Semicircular  Ducts 

Structure 
The  Ductus  Cochlearis 
The  Basilar  Membrane 
The  Spiral  Organ  of  Corti 
Hair  Cells      .... 


1047 
1049 
1050 
1051 
1051 
1052 
1052 
1052 
1054 
1056 
1056 
1057 


Peripheral  Terminations  of  Nerves  of  General 
Sensations. 

Free  Nerve-endings 1059 

Special  End-organs 1059 

End-bulbs  of  Krause 1060 

Tactile  Corpuscles  of  Grandry     ....  1060 

Pacinian  Corpuscles 1060 

Corpuscles  of  Golgi  and  Mazzoni      .      .      .  1061 

Tactile  Corpuscles  of  Wagner  and  Meissner  1061 

Corpuscles  of  Ruffini 1061 

Neurotendinous  Spindles 1061 

Neuromuscular  Spindles 1061 


The  Comon  Integument. 

The  Epidermis,  Cuticle,  or  Scarf  Skin     .      .  1062 
The  Corium,  Cutis  Vera,  Dermis,  or  True 

Skin 1065 

Development 1066 

The  Appendages  of  the  Skin. 

The  Nails 1066 

The  Hairs 1067 

The  Sebaceous  Glands 1069 

The  Sudoriferous  or  Sweat  Glands   .      .      .  1070 


I 


SPLANCHNOLOGY. 


The  Respiratory  Apparatus. 


Development 

1071 

The  Larynx. 

The  Cartilages  of  the  Larynx      ....     1073 

The  Thyroid  Cartilage    . 

1073 

The  Cricoid  Cartilage 

1074 

The  Arytenoid  Cartilage 

1075 

The  Corniculate  Cartilages 

1075 

The  Cuneiform  Cartilages 

1075 

The  Epiglottis      .      .      . 

1075 

Structure 

1076 

The  Ligaments  of  the  Larynx 

1076 

The  Extrinsic  Ligaments 

1076 

The  Intrinsic  Ligaments 

1077 

The  Interior  of  the  Larynx     . 

1078 

The  Ventricular  Folds 

1079 

The  Vocal  Folds  .      .      . 

1079 

The  Ventricle  of  the  Larynx 

1080 

The  Rima  Glottidis   .      . 

1080 

The  Muscles  of  the  Larynx    . 

1081 

Cricothyreoideus 

1081 

Cricoarytsenoideus  Posterior 

1082 

Cricoarytsenoideus  Lateralis 

1082 

Arytsenoideus        .... 

1082 

Thyreoarytsenoideus 

1083 

The  Trachea  and  Bronchi. 

Relations 1084 

The  Right  Bronchus 1085 

The  Left  Bronchus        .......  1085 

Structure 1086 


The  Pleurce. 

Reflections  of  the  Pleura 1088 

Pulmonary  Ligament 1090 

Structure  of  Pleura 1090 

The  Mediastinum. 

Superior  Mediastinum 1090 

Anterior  Mediastinum 1092 

Middle  Mediastinum .  1092 

Posterior  Mediastinum 1093 

The  Lungs. 

The  Apex  of  the  Lungs 1094 

The  Base  of  the  Lungs 1094 

Surfaces  of  the  Lungs 1094 

Borders  of  the  Lungs 1096 

Fissures  and  Lobes  of  the  Lungs       .      .      .  1096 

The  Root  of  the  Lung 1097 

Divisions  of  the  Bronchi 1097 

Structure  of  the  Lungs 1098 

The  Digestive  Apparatus. 

The  Digestive  Tube 1100 

The    Development    of     the    Digestive 

Tube 1101 

The  Mouth 1101 

The  Salivary  Glands      ....  1102 

The  Tongue         1102 

The  Palatine  Tonsils  ....  1103 
The  Further  Development  of  the 

Digestive  Tube 1103 

The  Rectum  and  Anal  Canal   .      .  1 108 


CONTENTS 


25 


The  Mouth. 


The  Abdomen. 


The  Vestibule  of  the  Mouth 1110 

The  Mouth  Cavity  Proper 1110 

Structure 1110 

The  Lips 1111 

The  Labial  Glands 1111 

The  Cheeks 1112 

Structure 1112 

The  Gums 1112 

The  Palate 1112 

The  Hard  Palate 1112 

The  Soft  Palate 1112 

The  Teeth 1112 

General  Characteristics 1114 

The  Permanent  Teeth 1115 

The  Canine  Teeth 1117 

The  Premolar  or  Bicuspid  Teeth  .  1118 

The  Molar  Teeth 1118 

The  Deciduous  Teeth 1118 

Structure  of  the  Teeth 1118 

Development  of  the  Teeth    ....  1121 
Development    of    the    Deciduous 

Teeth 1122 

Development   of    the    Permanent 

Teeth 1124 

Eruption  of  the  Teeth     .      .      .      .  1124 

The  Tongue 1125 

The  Root  of  the  Tongue       ....  1125 

The  Apex  of  the  Tongue       .      .      .  1125 

The  Dorsum  of  the  Tongue        .      .      .  1125 

The  Papilla;  of  the  Tongue  .       .      .      .  1126 

The  Muscles  of  the  Tongue        .      .      .  1128 

Genioglossus 1129 

Hyoglossus 1129 

Chondroglossus 1130 

Styloglossus 1130 

Longitudinalis  Linguae  Superior  1130 

Longitudinalis  Linguae  Inferior  1130 

Transversus  Linguae      .      .      .      .  1130 

Verticalis  Linguae 1131 

Structure  of  the  Tongue              .      .  1131 

Glands  of  the  Tongue 1131 

The  Salivary  Glands 1132 

The  Parotid  Gland 1132 

Structures  within  the  Gland     .      .  1134 

The  Parotid  Duct 1134 

Structure 1134 

The  Submaxillary  Gland       ....  1135 

The  Submaxillary  Duct             .      .  1135 

The  Sublingual  Gland 1136 

Structure  of  the  Salivary  Gland            .  1136 

Accessory  Glands 1137 

The  Fauces. 


The  Glossopalatine  Arch 

1137 

The  Pharyngopalatine  Arch    . 

1137 

The  Palatine  Tonsils    .      .      . 

1137 

Structure 

1139 

The  Palatine  Aponeurosis 

1139 

The  Muscles  of  the  Palate 

1139 

Levator  Veli  Palatini 

1139 

Tensor  Veli  Palatini 

1139 

Musctilus  Uvulae 

1139 

Glossopalatinus 

1139 

Paryngopalatinus 

1139 

The  Pharynx. 

The  Nasal  Part  of  the  Pharynx  ....      1141 

The  Oral  Part  of  the  Pharynx     .      . 

1142 

The  Laryngeal  Part  of  the  Pharynx 

1142 

The  Muscles  of  the  Pharynx 

1142 

Constrictor  Pharyngis  Inferior  . 

1142 

Constrictor  Pharyngis  Medius  . 

1142 

Constrictor  Pharyngis  Superior 

1142 

Stylopharyngeus 

1142 

Salpingopharyngeus  . 

1142 

Structure  of  the  Pharynx 

1143 

The  Esopfiagus. 

Relations 

1145 
1146 

Structure 

Boundaries  of  the  Abdomen  .....  1147 

The  Apertures  in  the  Walls  of  the  Abdomen  1147 

Regions  of  the  Abdomen 1147 

The  Peritoneum 1149 

Vertical  Dispositions  of  the  Main  Peri- 
toneal Cavity 1150 

Vertical    Disposition    of    the    Omental 

Bursa 1152 

Horizontal    Disposition    of    the    Peri- 
toneum         1153 

In  the  Pelvis       .      .      .  .  1153 

In  the  Lower  Abdomen  1154 

In  the  Upper  Abdomen  .      .  1155 

The  Omenta 1156 

The  Mesenteries 1157 

The  Peritoneal  Recesses  or  Fossae  .      .  1158 

The  Duodenal  Fossae     ....  1159 

The  Cecal  Fossae 1160 

The  Intersigmoid  Fossa      .      .      .  1161 

Th^  Stomach. 

Openings  of  the  Stomach 1161 

Curvatures  of  the  Stomach 1162 

Surfaces  of  the  Stomach 1162 

Component  Parts  of  the  Stomach     .      .      .  1163 

Position  of  the  Stomach 1163 

Interior  of  the  Stomach 1164 

Pyloric  Valve *    .      .      .  1164 

Structure  of  the  Stomach 1164 

The  Gastric  Glands 1166 

The  Small  Intestine. 

The  Duodenum 1169 

Relations     .  1169 

The  Jejunum  and  Ileum 1170 

Meckel's  Diverticulum 1172 

Structure 1172 

The  Large  Intestine. 

The  Cecum 1177 

The  Vermiform  Process  or  Appendix  .  1178 

Structure 1179 

The  Colic  Valve 1179 

The  Colon 1180 

The  Ascending  Colon 1180 

The  Transverse  Colon 1180 

The  Descending  Colon 1181 

The  Iliac  Colon 1182 

The  Sigmoid  Colon 1182 

The  Rectum 1183 

Relations  of  the  Rectum       ....  1184 

The  Anal  Canal 1184 

Structure  of  the  Colon 1184 

The  Liver. 

Surfaces  of  the  Liver 1188 

Fossae  of  the  Liver 1191 

Lobes  of  the  Liver 1191 

Ligaments  of  the  Liver 1192 

Fixation  of  the  Liver 1193 

Development  of  the  Liver 1 193 

Structure  of  the  Liver  .      .      .      .  1195 

Excretory  Apparatus  of  the  Liver     .      .      .  1197 

The  Hepatic  Duct 1197 

The  Gall-bladder 1197 

Relations .  1197 

Structure 1198 

The  Common  BUe  Duct       ....  1198 

Structure 1199 

The  Pancreas. 

Relations 1200 

The  Pancreatic  Duct 1202 

Development  of  the  Pancreas      ....  1202 

Structure 1203 


26 


CONTENTS 


The  Urogenital  Apparatus. 


Development  of  the.  Urinary  and  Generative  Organs 

The  Pronephros  and  Wolffian  Duct        .      .  1205 
The    Mesonephros,     Milllerian    Duct,    and 

Genital  Gland 1205 

The  Miillerian  Ducts 1206 

Genital  Glands 1207 

The  Ovary         1207 

The  Testis 1210 

Descent  of  the  Ovaries 1211 

The     Metanephros      and     the     Permanent 

Kidney 1211 

The  Urinary  Bladder         1212 

The  Prostate 1213 

External  Organs  of  Generation  .  1213 

The  Urethra 1215 

The  Urinary  Organs. 

The  Kidneys 1215 

Relations 1215 

Surfaces 1215 

Borders 1218 

Extremities 1219 

Fixation  of  the  Kidney  ....  1220 

General  Structure  of  the  Kidney  .  1220 

The  Ureters 1225 

The  Ureter  Proper 1226 

Structure   .  , 1227 

Variations    ' 1227 

The  Urinary  Bladder 1227 

The  Empty  Bladder 1227 

The  Distended  Bladder 1228 

The  Bladder  in  the  Child      ....  1229 

The  Female  Bladder 1230 

The  Ligaments  of  the  Bladder  .      .      .  1231 

The  Interior  of  the  Bladder        .      .      .  1231 

Structure 1232 

Abnormalities 1233 

The  Male  Urethra 1234 

The  Prostatic  Portion 1234 

The  Membranous  Portion    ....  1235 

The  Cavernous  Portion 1235 

Structure 1235 

Congenital  Defects 1235 

The  Female  Urethra 1236 

Structure 1236 

Th  Male  Genital  Organs. 

The  Testes  and  their  Coverings  ....  1236 

The  Scrotum 1237 

The  Intercrural  Fascia 1238 

The  Cremaster  Muscle 1238 

The  Infundibuliform  Fascia       .      .      .  1239 

The  Tunica  Vaginalis 1239 

The  Inguinal  Canal 1239 

The  Spermatic  Cord 1239 

Structure  of  the  Spermatic  Cord  .  1239 

The  Testes 1240 

The  Epididymis 1242 

Appendages  of  the  Testis  and  Epi- 
didymis      1242 

The  Tunica  Vaginalis  .  1242 

The  Tunica  Albuginea  .  1242 

The  Tunica  Vasculosa  .  1243 

Structure 1243 

Peculiarities 1245 

The  Ductus  Deferens 1245 

The  Ductuli  Aberrantes        ....  1246 

Paradidymis 1246 

Structure 1246 

The  Vesiculse  Seminales 1246 

Structure 1247 

The  Ejaculatory  Ducts     ......  1247 

Structure 1247 

The  Penis 1247 

The  Corpora  Cavernosa  Penis  .      .      .  1248 

The  Corpus  Cavernosum  Urethrse        .  1248 

Structure  of  the  Penis 1250 


The  Prostate     .      .      .     ^^^^^^H"    .  1251 

Structure   .      .      .     ^^^^^^K     •  1253 

The  Bulbourethral  Glands 1253 

Structure 1253 

The  Female  Genital  Organs. 

The  Ovaries 1254 

The  Epoophoron 1255 

The  Paroophoron 1255 

Structure 1255 

Vesicular  Ovarian  Follicles  ....  125& 

Discharge  of  the  OvuVn 1256 

Corpus  Luteum 1256 

The  Uterine  Tube 1257 

Structure 1257 

The  Uterus 1258 

The  Body 1259 

The  Cervix 1259 

The  Interior  of  the  Uterus   ....  1260 

The  Cavity  of  the  Body      .      .      .  1260 

The  Canal  of  the  Cer\ax      .      .      .  1260 

The  Ligaments  of  the  Uterus     .      .      .  1260 

Structure 1262 

The  Vagina 1264 

Relations 1264 

Structure 1264 

The  External  Organs 1264 

The  Mons  Pubis 1265 

The  Labia  Majora 1265 

The  Labia  Minora 1265 

The  Clitoris 1266 

The  Vestibule 1266 

The  Bulb  of  the  Vestibule    ....  1266 

The  Greater  Vestibular  Glands  .  1266 

The  Mammae 1267 

The  Mammary  Papilla  or  Nipple  .  1267 

Development         1267 

Structure 1267 


The  Ductle.ss  Glands. 

The  Thyroid  Gland. 

Development  1270 

Structure 1271 

The  Parathyroid  Glands. 

Development     .  1272 

Structure 1273 

The  Thymus. 

Development 1273 

Structure 1274 

The  Hypophysis  Cerebri. 

Development 1276 

The  Pineal  Body. 

Structure 1277 

The  Chromaphil  and  Cortical  Systems. 

Development 1277 

The  Suprarenal  Glands 1278 

Development         1278 

Relations 1278 

Accessory  Suprarenals 1279 

Structure 1279 

Glomus  Caroticum 1281 

Glomus  Coccygeum 1281 

The  Spleen. 

Development 1282 

Relation 1282 

Structure 1283 


STENTS 


27 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS. 


Surface  Anatomy  of  the  Head  and  Neck. 

The  Bones 1287 

The  Joints  and  Muscles          1288 

THe  Arteries 1290 

Surface  Markings  of  Special  Regions  of  the  Head 
and  Meek. 

The  Cranium 1291 

The  Scalp 1291 

Bony  Landmarks 1291 

The  Brain 1292 

Vessels              1294 

The  Face 1294 

External  Maxillary  Artery   ....  1294 

Trigeminal  Nerve 1295 

Parotid.  Gland 1295 

The  Nose 1296 

The  Mouth 1296 

The  Eye 1299 

The  Ear 1300 

The  Tympanic  Antrum 1301 

The  Neck 1301 

Muscles 1302 

Arteries 1302 

Veins 1303 

Nerves 1303 

Submaxillary  Gland 1303 

Surface  Anatomy  of  the  Back. 

Bones 1303 

Muscles 1304 

Surface  Markings  of  the  Back. 

Bony  Landmarks 1305 

Medulla  Spinalis 1306 

Spinal  Nerves 1307 

Surface  Anatomy  of  the  Thorax. 

Bones 1307 

Muscles 1307 

Mamma \  1308 

Surface  Markings  of  the  Thorax. 

Bony  Landmarks 1308 

Diaphragm [      ]  I309 

Surface  Lines I3O9 

Pleurae          '      "  1309 

Lungs '.'.'.  1310 

Irachea 1311 

Esophagus [      [  1311 

Heart 1311 

Arteries \  1312 

Veins '\  1312 

Surface  Anatomy  of  the  Abdomen. 

|^'° 1313 

?oiies 1313 

Musces 1313 

^?ssels 1313 

Viscera I313 


Surface  Markings  of  the  Abdomen. 

Bony  Landmarks 1315 

Muscles 1315 

Surface  Lines 1315 

Stomach 1317 

Duodenum 1319 

Small  Intestine 1319 

Cecum  and  Vermiform  Process   ....  1319 

Ascending  Colon 1319 

Transverse  Colon 1319 

Descending  Colon 1320 

Iliac  Colon 1320 

Liver 1320 

Pancreas 1320 

Spleen           1320 

Kidneys 1320 

Ureters 1321 

Vessels 1321 

Nerves 1322 

Surface  Anatomy  of  the  Perineum. 

Skin 1322 

Bones 1322 

Muscles  and  Ligaments 1322 

Surface  Markings  of  the  Perineum. 

Rectum  and  Anal  Canal 1322 

Male  Urogenital  Organs    .      .                   .      .  1323 

Female  Urogenital  Organs 1323 

Surface  Anatomy  of  the  Upper  Extremity. 

Skin 1325 

Bones 1326 

Articulations 1327 

Muscles 1327 

Arteries 1331 

Veins 1331 

Nerves 1331 

Surface  Markings  of  the  Upper  Extremity. 

Bony  Landmarks 1331 

Articulations 1331 

Muscles 1332 

Mucous  Sheaths 1334 

Arteries 1334 

Nerves 1335 

Surface  Anatomy  of  the  Lower  Extremity. 

Skin 1336 

Bones 1336 

Articulations 1338 

Muscles 1338 

Arteries 1341 

Veins 1342 

Nerves 1342 

Surface  Markings  of  the  Lower  Extremity. 

Bony  Landmarks 1342 

Articulations 1343 

Muscles 1343 

Mucous  Sheaths 1343 

Arteries 1343 

Veins ]      .  1345 

Nerves 1346 


^^K^  ANATOMICAL  BIBLIOaRAPHY.        ^M 

^^^^^  INDEXES.  ^M 

Anatomical  Bibliography  of  the  Concilium  Bibliographiciim,  ^^^| 

Bibliographic  Service;  Wistar  Institute  of  Anatomy,  1917-         .  ^^^H 

Bibliographie  Anatomique,  1893-        .  fl 

Index  Medicus,  1879-  I 

Index  Catalogue  of  the  Library  of  the  Surgeon-General's  Office,  U.  S.  ArnB 

1880-  \ 

Jahresberichte  iiber  die  Fortschritte  der  Anatoraie  und  Physiologic,  1856-1894. 
Jahresberichte  iiber  die  Fortschritte  der  Anatomic  mid  Entwicklungsgeschichte, 

1895- 

JOURNALS. 

The  Anatomical  Record,  1906- 

The  American  Journal  of  Anatomy,  1901- 

Anatomische  Hefte,  1892- 

Anatomischer  Anzeiger,  1886- 

Archives  d 'Anatomic  Microscopique,  1897- 

Archiv  fiir  Anatomic  und  Physiologic,  1795- 

Archiv  fiir  Entwicklungsmechanik  der  Organismen,  1894- 

Archiv  fiir  Microskopische  Anatomic,  1865- 

Archivo  Italiano  di  Anatomia  e  di  Embriologia,  1902- 

Biological  Bulletin,  1900- 

Brain,  1878- 

Bibliographie  Anatomique,  1893- 

Contributions  to  Embryology,  Carnegie  Institution  of  Washington,  1914-- 

Comptcs  Rendus  de  1' Association  des  Anatomistes,  1899- 

Gegenbaur's  Morphologischcs  Jahrbuch,  1876- 

International  Monatsschrift  fiir  Anatomic  und  Histologic,  1884- 

The  Journal  of  Anatomy  and  Physiology,  1867- 

Journal  of  Comparative  Neurology,  1891- 

. Journal  de  1 'Anatomic  et  de  Physiologic,  etc.,  1864- 

Journal  of  Experimental  Zoology,  1904- 

Journal  of  Morphology,  1887- 

Le  Nevraxe,  1900- 

Morphologischc  Arbciten,  1892-1898. 

Petrus  Camper  Nederlandschc  Bijdragen  tot  de  Anatomic,  1902- 

Proceedings  of  the  Royal  Society,  Scries  B. 

Quarterly  Journal  of  Microscopical  Science,  1853- 

Zcitschrift  fiir  Morphologic  und  Anthropologic,  1899- 

Zeitschrift  fiir  Wissenschaftliche  Mikroskopie,  1884- 


XXV  iii ) 


ANATOMY  OF  THE  HUMAN  BODY 


INTRODUCTION. 


THE  term  human  anatomy  comprises  a  consideration  of  the  various  structures 
which  make  up  the  human  organism.  In  a  restricted  sense  it  deals  merely 
with  the  parts  which  form  the  fully  developed  individual  and  which  can  be  ren- 
dered evident  to  the  naked  eye  by  various  methods  of  dissection.  Regarded  from 
such  a  standpoint  it  may  be  studied  by  two  methods:  (1)  the  various  structures 
may  be  separately  considered— systematic  anatomy;  or  (2)  the  organs  and  tissues 
may  be  studied  in  relation  to  one  another — topographical  or  regional  anatomy. 

It  is,  however,  of  much  advantage  to  add  to  the  facts  ascertained  by  naked- 
eye  dissection  those  obtained  by  the  use  of  the  microscope.  This  introduces 
two  fields  of  investigation,  viz.,  the  study  of  the  minute  structure  of  the  various 
component  parts  of  the  body — histology — and  the  study  of  the  human  organism 
in  its  immature  condition,  i.  e.,  the  various  stages  of  its  intrauterine  develop- 
ment from  the  fertilized  ovum  up  to  the  period  when  it  assumes  an  independent 
existence — embryology.  Owing  to  the  difficulty  of  obtaining  material  illustrating 
all  the  stages  of  this  early  development,  gaps  must  be  filled  up  by  observations 
on  the  development  of  lower  forms — comparative  embryology,  or  by  a  consideration 
of  adult  forms  in  the  line  of  human  ancestry — comparative  anatomy.  The  direct 
application  of  the  facts  of  human  anatomy  to  the  various  pathological  conditions 
which  may  occur  constitutes  the  subject  of  applied  anatomy.  Finally,  the  appre- 
ciation of  structures  on  or  immediately  underlying  the  surface  of  the  body  is 
frequently  made  the  subject  of  special  study — smiace  anatomy. 

Systematic  ANATOMY.^The  various  systems  of  which  the  human  body  is 
composed  are  grouped  under  the  following  headings: 

1.  Osteology — the  bony  system  or  skeleton. 

2.  Syndesmology — the  articulations  or  joints. 

3.  Myology — the  muscles.  With  the  description  of  the  muscles  it  is  convenient 
to  include  that  of  the  fasciae  which  are  so  intimately  connected  with  them. 

4.  Angiology — the  vascular  system,  comprising  the  heart,  bloodvessels,  lymphatic 
vessels,  and  lymph  glands. 

5.  Neurology — the  nervous  system.  The  organs  of  sense  may  be  included  in 
this  system. 

6.  Splanchnology  —  the  visceral  system.  Topographically  the  viscera  form 
two  groups,  viz.,  the  thoracic  viscera  and  the  abdomino-pelvic  viscera.  The 
heart,  a  thoracic  viscus,  is  best  considered  with  the  vascular  system.    The  rest 

3  (33) 


34 


INTRODUCTION 


I 


of  the  viscera  may  be  grouped  according  to  their  functions:  (a)  the  respiratory 
apparatus;  (6)  the  digestive  apparatus;  and  (c)  the  urogenital  apparatus.  Strictly 
speaking,  the  third  subgroup  should  include  only  such  components  of  the 
urogenital  apparatus  as  are  included  within  the  abdomino-pelvic  cavity,  but  it 
is  convenient  to  study  under  this  heading  certain  parts  which  lie  in  relation  to 
the  surface  of  the  body,  e.  g.,  the  testes  and  the  external  organs  of  generation. 

For  descriptive  purposes. the  body  is  supposed  to  be  in  the  erect  posture,  with 
the  arms  hanging  by  the  sides  and  the  palms  of  the  hands  directed  forward.  The 
median  plane  is  a  vertical  antero-posterior  plane,  passing  through  the  center  of  the 
trunk.  This  plane  will  pass  approximately  through  the  sagittal  suture  of  the  skull, 
and  hence  any  plane  parallel  to  it  is  termed  a  sagittal  plane.  A  vertical  plane  at 
right  angles  to  the  median  plane  passes,  roughly  speaking,  through  the  central 
part  of  the  coronal  suture  or  through  a  line  parallel  to  it;  such  a  plane  is  known  as 
a  frontal  plane  or  sometimes  as  a  coronal  plane.  A  plane  at  right  angles  to  both 
the  median  and  frontal  planes  is  termed  a  transverse  plane. 

The  terms  anterior  or  ventral,  and  posterior  or  dorsal,  are  employed  to  indicate 
the  relation  of  parts  to  the  front  or  back  of  the  body  or  limbs,  and  the  terms 
superior  or  cephalic,  and  inferior  or  caudal,  to  indicate  the  relative  levels  of  different 
structures;  structures  nearer  to  or  farther  from  the  median  plane  are  referred  to  as 
medial  or  lateral  respectively. 

The  terms  superficial  and  deep  are  strictly  confined  to  descriptions  of  the 
relative  depth  from  the  surface  of  the  various  structures;  external  and  internal 
are  reserved  almost  entirely  for  describing  the  walls  of  cavities  or  of  hollow 
viscera.  In  the  case  of  the  limbs  the  words  proximal  and  distal  refer  to  the 
relative  distance  from  the  attached  end  of  the  limb. 


EMBRYOLOGY. 


THE  term   Embryology,  in  its  widest  sense,  is  applied  to  the  various  changes 
^^  which  take  place  during  the  growth  of   an  animal  from  the  egg  to  the  adult 

^Hj  condition:  it  is,  however,  usually  restricted  to  the  phenomena  which  occur  before 
^"  birth.  Embryology  may  be  studied  from  two  aspects:  (1)  that  of  ontogeny,  which 
j^  deals  only  with  the  development  of  the  individual;  and  (2)  that  of  phylogeny, 
which  concerns  itself  with  the  evolutionary  history  of  the  animal  kingdom. 

In  vertebrate  animals  the  development  of  a  new  being  can  only  take  place  when 
a  female  germ  cell  or  ovum  has  been  fertilized  by  a  male  germ  cell  or  spermatozoon. 
The  ovum  is  a  nucleated  cell,  and  all  the  complicated  changes  by  which  the  various 
tissues  and  organs  of  the  body  are  formed  from  it,  after  it  has  been  fertilized,  are 
the  result  of  two  general  processes,  viz.,  segmentation  and  differentiation  of  cells. 
Thus,  the  fertilized  ovum  undergoes  repeated  segmentation  into  a  number  of  cells 
which  at  first  closely  resemble  one  another,  but  are,  sooner  or  later,  differentiated 
into  two  groups:  (1)  somatic  cells,  the  function  of  which  is  to  build  up  the  various 
tissues  of  the  body;  and  (2)  germinal  cells,  which  become  imbedded  in  the  sexual 
glands — the  ovaries  in  the  female  and  the  testes  in  the  male — and  are  destined  for 
the  perpetuation  of  the  species. 

Having  regard  to  the  main  purpose  of  this  work,  it  is  impossible,  in  the  space 
available  in  this  section,  to  describe  fully,  or  illustrate  adequately,  all  the  phenom- 
ena which  occur  in  the  different  stages  of  the  development  of  the  human  body. 
Only  the  principal  facts  are  given,  and  the  student  is  referred  for  further  detaUs 
to  one  or  other  of  the  text-books^  on  human  embryology. 

THE   ANIMAL   CELL. 

All  the  tissues  and  organs  of  the  body  originate  from  a  microscopic  structure 
(the  fertilized  ovum),  which  consists  of  a  soft  jelly-like  material  enclosed  in  a 
membrane  and  containing  a  vesicle  or  small  spherical  body  inside  which  are  one 
or  more  denser  spots.  This  may  be  regarded  as  a  complete  cell.  All  the  solid 
tissues  consist  largely  of  cells  essentially  similar  to  it  in  nature  but  differing  in 
external  form. 

In  the  higher  organisms  a  cell  may  be  defined  as  "a  nucleated  mass  of  proto- 
plasm of  microscopic  size."  Its  two  essentials,  therefore,  are:  a  soft  jelly-like 
material,  similar  to  that  found  in  the  ovum,  and  usually  styled  cytoplasm,  and  a 
small  spherical  body  imbedded  in  it,  and  termed  a  nucleus.  Some  of  the  unicellular 
protozoa  contain  no  nuclei  but  granular  particles  which,  like  true  nuclei,  stain  with 
basic  dyes.  The  other  constituents  of  the  ovum,  viz.,  its  limiting  membrane  and 
the  denser  spot  contained  in  the  nucleus,  called  the  nucleolus,  are  not  essential  ta 
the  type  cell,  and  in  fact  many  cells  exist  without  them. 

Csrtoplasm  (protoplas7n)  is  a  material  probably  of  variable  constitution  during 
life,  but  yielding  on  its  disintegration  bodies  chiefly  of  proteid  nature.  Lecithin 
and  cholesterin  are  constantly  found  in  it,  as  well  as  inorganic  salts,  chief  among 

1  Manual  of  Human  Embryology,  Keibel  and  Mall;  Handbuch  der  vergleichenden  und  experimentellen  Entwickel- 
ungslehre  der  Wirbeltiere,  Oskar  Hertwig;  Lehrbuch  der  Entwickelungsgeschichte,  Bonnet;  The  Physiology  of 
Reproduction,  Marshall. 

(36) 


36 


EMBRYOLOGY 


which  are  the  phosphates  and  chlorides  of  potassium,  sodium,  and  calcium.  It  is 
of  a  semifluid,  viscid  consistence,  and  probably  colloidal  in  nature.  The  living 
cjloplasm  appears  to  consist  of  a  homogeneous  and  structureless  ground-substance 
in  which  are  embedded  granules  of  ^'arious  t\'pes.  The  mitochondria  are  the  most 
constant  type  of  granule  and  vary  in  form  from  granules  to  rods  and  threads. 
Their  function  is  unknown.  Some  of  the  granules  are  proteid  in  nature  and  prob- 
ably essential  constituents;  others  are  fat,  glycogen,  or  pigment  granules,  and  are 
regarded  as  adventitious  material  taken  in  from  without,  and  hence  are  styled 
cell-inclusions  or  paraplasm.  When,  however,  cells  have  been  "fixed"  by  reagents 
a  fibrillar  or  granular  appearance  can  often  be  made  out  under  a  high  power  of  the 
microscope.  The  fibrils  are  usually  arranged  in  a  network  or  reticulum,  to  which 
the  term  spongioplasm  is  applied,  the  clear  substance  in  the  meshes  being  termed 
hyaloplasm.  The  size  and  shape  of  the  meshes  of  the  spongioplasm  vary  in  different 
cells  and  in  different  parts  of  the  same  cell.  The  relative  amounts  of  spongioplasm 
and  hyaloplasm  also  vary  in  different  cells,  the  latter  preponderating  in  the  young 
cell  and  the  former  increasing  at  the  expense  of  the  hyaloplasm  as  the  cell  grows. 
Such  appearances  in  fixed  cells  are  no  indication  whatsoever  of  the  existence  of 


Cell  wall 


NvcUar 
membrane 


Vacuole 


Centrosome  consisting  of  cen- 
trosphere  enclosing  ttvo  cen- 
trioles 

Nucleolus 

Net-knot  of  chromatin  form- 
ing a  pseudo-nucleolus 
Chromatin  network 


Cell-inclusions  {paraplasm) 


Fig.  1. — Diagram  of  a  cell.    (Modified  from  Wilson.) 


similar  structures  in  the  living,  although  there  must  have  been  something  in  the 
living  cell  to  give  rise  to  the  fixed  structures.  The  peripheral  layer  of  a  cell  is  in 
all  cases  modified,  either  by  the  formation  of  a  definite  cell  membrane  as  in  the  ovum, 
or  more  frequently  in  the  case  of  animal  cells,  by  a  transformation,  probably 
chemical  in  nature,  which  is  only  recognizable  by  the  fact  that  the  surface  of  the 
cell  behaves  as  a  semipermeable  membrane. 

Nucleus. — The  nucleus  is  a  minute  body,  imbedded  in  the  protoplasm,  and 
usually  of  a  spherical  or  oval  form,  its  size  having  little  relation  to  that  of  the  cell. 
It  is  surrounded  by  a  well-defined  wall,  the  nuclear  membrane;  this  encloses  the 
nuclear  substance  {nuclear  matrix),  which  is  composed  of  a  homogeneous  material 
in  which  is  usually  embedded  one  or  two  nucleoli.  In  fixed  cells  the  nucleus  seems 
to  consist  of  a  clear  substance  or  karyoplasm  and  a  network  or  karyomitome.  The 
former  is  probably  of  the  same  nature  as  the  hyaloplasm  of  the  cell,  but  the  latter, 
which  forms  also  the  wall  of  the  nucleus,  differs  from  the  spongioplasm  of  the  cell 
substance.  It  consists  of  fibers  or  filaments  arranged  in  a  reticular  manner.  These 
filaments  are  composed  of  a  homogeneous  material  known  as  linin,  which  stains 
with  acid  dyes  and  contains  embedded  in  its  substance  particles  which  have  a 
strong  affinity  for  basic  dyes.    These  basophil  granules  have  been  named  chromatin 


THE  ANIMAL  CELL 


37 


or  basichromatin  and  owe  their  staining  properties  to  the  presence  of  nucleic  acid. 
Within  the  nuclear  matrix  are  one  or  more  highly  refracting  bodies,  termed  nucleoli, 
connected  with  the  nuclear  membrane  by  the  nuclear  filaments.  They  are  regarded 
as  being  of  two  kinds.  Some  are  mere  local  condensations  ("net-knots")  of  the 
chromatin;  these  are  irregular  in  shape  and  are  termed  pseudo-nucleoli ;  others  are 
distinct  bodies  differing  from  the  pseudo-nucleoli  both  in  nature  and  chemical 
composition;  they  may  be  termed  true  nucleoli,  and  are  usually  found  in  resting 
cells.    The  true  nucleoli  are  oxis-phil,  i.  e.,  they  stain  with  acid  dyes. 

Most  living  cells  contain,  in  addition  to  their  protoplasm  and  nucleus,  a  small 
particle  which  usually  lies  near  the  nucleus  and  is  termed  the  centrosome.  In  the 
middle  of  the  centrosome  is  a  minute  body  called  the  centriole,  and  surrounding  this 
is  a  clear  spherical  mass  known  as  the  centrosphere.  The  protoplasm  surround- 
ing the  centrosphere  is  frequently'  arranged  in  radiating  fibrillar  rows  of  granules, 
forming  what  is  termed  the  attraction  sphere. 

Reproduction  of  Cells. — Reproduction  of  cells  is  effected  either  by  direct  or  by 
indirect  division.  In  reproduction  by  direct  division  the  nucleus  becomes  constricted 
in  its  center,  assuming  an  hour-glass  shape,  and  then  divides  into  two.  This  is  fol- 
lowed by  a  cleavage  or  division  of  the  whole  protoplasmic  mass  of  the  cell;  and  thus 
two  daughter  cells  are  formed,  each  containing  a  nucleus.  These  daughter  cells  are 
at  first  smaller  than  the  original  mother  cell;  but  they  grow,  and  the  process 
may  be  repeated  in  them,  so  that  multiplication  may  take  place  rapidly.  Indirect 
divsion  or  karyokinesis  (karyomitosis)  has  been  observed  in  all  the  tissues — genera- 
tive cells,  epithelial  tissue,  connective  tissue,  muscular  tissue,  and  nerve  tissue. 
It  is  possible  that  cell  division  may  always  take  place  by  the  indirect  method. 

The  process  of  indirect  cell  division  is  characterized  by  a  series  of  complex 
changes  in  the  nucleus,  leading  to  its  subdivision;  this  is  followed  by  cleavage 
of  the  cell  protoplasm.  Starting  with  the  nucleus  in  the  quiescent  or  resting  stage, 
these  changes  may  be  briefly  grouped  under  the  four  following  phases  (Fig.  2). 

1.  Prophase. — The  nuclear  network  of  chromatin  filaments  assumes  the  form 
of  a  twisted  skein  or  spirem,  while  the  nuclear  membrane  and  nucleolus  disappear. 
The  convoluted  skein  of  chromatin  divides  into  a  definite  number  of  V-shaped 
segments  or  chromosomes.  The  number  of  chromosomes  varies  in  different  animals, 
but  is  constant  for  all  the  cells  in  an  animal  of  any  given  species;  in  man  the  number 
is  given  by  Flemming  and  Duesberg  as  twenty-four.^  Coincidently  with  or  pre- 
ceding these  changes  the  centriole,  which  usually  lies  by  the  side  of  the  nucleus, 
undergoes  subdivision,  and  the  two  resulting  centrioles,  each  surrounded  by  a 
centrosphere,  are  seen  to  be  connected  by  a  spindle  of  delicate  achromatic  fibers 
the  achromatic  spindle.  The  centrioles  move  away  from  each  other — one  toward 
either  extremity  of  the  nucleus — and  the  fibrils  of  the  achromatic  spindle  are  cor- 
respondingly lengthened.  A  line  encircling  the  spindle  midway  between  its  ex- 
tremities or  poles  is  named  the  equator,  and  around  this  the  V-shaped  chromosomes 
arrange  themselves  in  the  form  of  a  star,  thus  constituting  the  mother  star  or 
monaster. 

2.  Metaphase.  —  Each  V-shaped  chromosome  now  undergoes  longitudinal 
cleavage  into  two  equal  parts  or  daughter  chromosomes,  the  cleavage  commencing 
at  the  apex  of  the  V  and  extending  along  its  divergent  limbs. 

3.  Anaphase. — The  daughter  chromosomes,  thus  separated,  travel  in  opposite 
directions  along  the  fibrils  of  the  achromatic  spindle  toward  the  centrioles,  around 
which  they  group  themselves,  and  thus  two  star-like  figures  are  formed,  one  at 
either  pole  of  the  achromatic  spindle.  This  constitutes  the  diaster.  The  daughter 
chromosomes  now  arrange  themselves  into  a  skein  or  spirem,  and  eventually  form 
the  network  of  chromatin  which  is  characteristic  of  the  resting  nucleus. 


Dr.  J.  Duesberg,  Anat.  Anz.,  Band  xxviii.  S.  475. 


38 


EMBRYOLOGY 


4.  Telophase. — The  cell  protoplasm  begins  to  appear  constricted  around  the 
equator  of  the  achromatic  spindle,  where  double  rows  of  granules  are  also  sometimes 
seen.  The  constriction  deepens  and  the  original  cell  gradually  becomes  divided 
into  two  new  cells,  each  with  its  own  nucleus  and  centrosome,  which  assume  the 
ordinary  positions  occupied  by  such  structures  in  the  resting  stage.  The  nuclear 
membrane  and  nucleolus  are  also  differentiated  during  this  phase. 

I      .  -,  II   .  -  """•••-. 


I 


ni 


iim  '. 


Fia.  2.— Diagram  showing  the  changes  which  occur  in  the  centrosomes  and  nucleus  of  a  cell  in  the  process  of  mitotic 
division.     (Schafer.)     /  to  ///,  prophase;  IV,  metaphase;  V  and  VI,  anaphase;  VII  and  VIII,  telophase. 


THE    OVUM. 

The  ova  are  developed  from  the  primitive  germ  cells  which  are  imbedded  in 
the  substance  of  the  ovaries.  Each  primitive  germ  cell  gives  rise,  by  repeated 
divisions,  to  a  number  of  smaller  cells  termed  oogonia,  from  which  the  ova  or 
primary  oocjrtes  are  developed. 

Human  ova  are  extremely  minute,  measuring  about  0.2  mm.  in  diameter,  and 
are  enclosed  within  the  egg  follicles  of  the  ovaries;  as  a  rule  each  follicle  contains 


THE  OVUM 


39 


single  ovum,  but  sometimes  two  or  more  are  present. "^  By  the  enlargement  and 
subsequent  rupture  of  a  follicle  at  the  surface  of  the  ovary,  an  ovum  is  liberated  and 
conveyed  by  the  uterine  tube  to  the  cavity  of  the  uterus.  Unless  it  be  fertilized 
it  undergoes  no  further  development  and  is  discharged  from  the  uterus,  but  if 
fertilization  take  place  it  is  retained  within  the  uterus  and  is  developed  into  a 
new  being. 

In  appearance  and  structure  the  ovum  (Fig.  3)  differs  little  from  an  ordinary 
cell,  but  distinctive  names  have  been  applied  to  its  several  parts;  thus,  the  cell 
substance  is  known  as  the  yolk  or  ooplasm,  the  nucleus  as  the  germinal  vesicle,  and 
the  nucleolus  as  the  germinal  spot.     The  ovum  is  enclosed  within  a  thick,  trans- 


•  3;~Human  ovum  examined  fresh  in  the  liquor  folliculi.  (Waldeyer.)  The  zona  pellucida  is  seen  as  a  thick 
clear  girdle  surrounded  by  the  cells  of  the  corona  radiata.  The  egg  itself  shows  a  central  granular  deutoplasmie  area 
and  a  peripheral  clear  layer,  and  encloses  the  germinal  vesicle,  in  which  is  seen  the  germinal  spot. 

parent  envelope,  the  zona  striata  or  zona  pellucida,  adhering  to  the  outer  surface 
of  which  are  several  layers  of  cells,  derived  from  those  of  the  follicle  and  collectively 
constituting  the  corona  radiata. 

Yolk.— The  yolk  comprises  (1)  the  cytoplasm  of  the  ordinary  animal  cell  with  its 
spongioplasm  and  hyaloplasm;  this  is  frequently  termed  the  formative  yolk;  (2) 
the  nutritive  yolk  or  deutoplasm,  which  consists  of  numerous  rounded  granules  of 
fatty  and  albuminoid  substances  imbedded  in  the  cytoplasm.  In  the  mammalian 
ovum  the  nutritive  yolk  is  extremely  small  in  amount,  and  is  of  service  in  nourish- 


See  description  of  the  ovary  on  a  future  page. 


m  ^^^B       EMBRYOLOGY  .  ^^M 

ing  the  embryo  in  the  early  stages  of  its  development  only,  whereas  in  the  egg 
of  the  bird  there  is  sufficient  to  supply  the  chick  with  nutriment  throughout 
the  whole  period  of  incubation.  The  nutritive  yolk  not  only  varies  in  amount, 
but  in  its  mode  of  distribution  within  the  egg;  thus,  in  some  animals  it  is  almost 
uniformly  distributed  throughout  the  cytoplasm;  in  some  it  is  centrally  placed  and 
is  surrounded  by  the  cytoplasm;  in  others  it  is  accumulated  at  the  lower  pole  of  the 
ovum,  while  the  cytoplasm  occupies  the  upper  pole.  A  centrosome  and  centriole 
are  present  and  lie  in  the  immediate  neighborhood  of  the  nucleus.  ■ 

Germinal  Vesicle. — The  germinal  vesicle  or  nucleus  is  a  large  spherical  body 
which  at  first  occupies  a  nearly  central  position,  but  becomes  eccentric  as  the  growth 
of  the  ovum  proceeds.  Its  structure  is  that  of  an  ordinary  cell-nucleus,  viz.,  it 
consists  of  a  reticulum  or  karyomitome,  the  meshes  of  which  are  filled  with 
karyoplasm,  while  connected  with,  or  imbedded  in,  the  reticulum  are  a  number 
of  chromatin  masses  or  chromosomes,  which  may  present  the  appearance  of  a 
skein  or  may  assume  the  form  of  rods  or  loops.  The  nucleus  is  enclosed  by  a 
delicate  nuclear  membrane,  and  contains  in  its  interior  a  well-defined  nucleolus 
or  germinal  spot. 

Coverings  of  the  Ovum. — The  zona  striata  or  zona  pellucida  (Fig.  3)  is  a  thick 
membrane,  which,  under  the  higher  powers  of  the  microscope,  is  seen  to  be  radially 
striated.  It  persists  for  some  time  after  fertilization  has  occurred,  and  may  serve 
for  protection  during  the  earlier  stages  of  segmentation.  It  is  not  yet  determined 
whether  the  zona  striata  is  a  product  of  the  cytoplasm  of  the  ovum  or  of  the  cells 
of  the  corona  radiata,  or  both. 

The  corona  radiata  (Fig.  3)  consists  or  two  or  three  strata  of  cells;  they  are 
derived  from  the  cells  of  the  follicle,  and  adhere  to  the  outer  surface  of  the  zona 
striata  when  the  ovum  is  set  free  from  the  follicle;  the  cells  are  radially  arranged 
around  the  zona,  those  of  the  innermost  layer  being  columnar  in  shape.  The 
cells  of  the  corona  radiata  soon  disappear;  in  some  animals  they  secrete,  or 
are  replaced  by,  a  layer  of  adhesive  protein,  which  may  assist  in  protecting  and 
nourishing  the  ovum. 

The  phenomena  attending  the  discharge  of  the  ova  from  the  follicles  belong 
more  to  the  ordinary  functions  of  the  ovary  than  to  the  general  subject  of  embry- 
ology, and  are  therefore  described  with  the  anatomy  of  the  ovaries.^ 

Maturation  of  the  Ovum. — Before  an  ovum  can  be  fertilized  it  must  undergo 
a  process  of  maturation  or  ripening.  This  takes  place  previous  to  or  immediately 
after  its  escape  from  the  follicle,  and  consists  essentially  of  an  unequal  subdivision 
of  the  ovum  (Fig.  4)  first  into  two  and  then  into  four  cells.  Three  of  the  four 
cells  are  small,  incapable  of  further  development,  and  are  termed  polar  bodies  or 
polocytes,  while  the  fourth  is  large,  and  constitutes  the  mature  ovum.  The  process 
of  maturation  has  not  been  observed  in  the  human  ovum,  but  has  been  carefully 
studied  in  the  ova  of  some  of  the  lower  animals,  to  which  the  following  description 
applies. 

It  was  pointed  out  on  page  37  that  the  number  of  chromosomes  found  in  the 
nucleus  is  constant  for  all  the  cells  in  an  animal  of  any  given  species,  and  that  in 
man  the  number  is  probably  twenty-four.  This  applies  not  only  to  the  somatic 
cells  but  to  the  primitive  ova  and  their  descendants.  For  the  purpose  of  illustrating 
the  process  of  maturation  a  species  may  be  taken  in  which  the  number  of  nuclear 
chromosomes  is  four  (Fig.  5) .  If  an  ovum  from  such  be  observed  at  the  beginning 
of  the  maturation  process  it  will  be  seen  that  the  number  of  its  chromosomes  is 
apparently  reduced  to  two.  In  reality,  however,  the  number  is  doubled,  since 
each  chromosome  consists  of  four  granules  grouped  to  form  a  tetrad.  During  the 
metaphase  (see  page  37)  each  tetrad  divides  into  two  dyads,  which  are  equally 


'  See  description  of  the  ovary  on  a  future  page. 


THE  OVUM 


41 


distributed  between  the  nuclei  of  the  two  cells  formed  by  the  first  division  of  the 
ovum.  One  of  the  cells  is  almost  as  large  as  the  original  ovum,  and  is  named 
the  secondary  oocyte;  the  other  is  small,  and  is  termed  the  first  polar  body.    The 


f.jm 


Fig.  4. — Formation  of  polar  bodies  in  Asterias  glacialis.  (Slightly  modified  from  Hertwig.)  In  /  the  polar  spindle 
(sp)  has  advanced  to  the  surface  of  the  egg.  In  //  a  small  elevation  (p6')  is  formed  which  receives  half  of  the  spindle. 
In  III  the  elevation  is  constricted  off,  forming  the  first  polar  body  (p6'),  and  a  second  spindle  is  formed.  In  IV  is 
seen  a  second  elevation  which  in  V  has  been  constricted  off  as  the  second  polar  body  (p6').  Out  of  the  remainder  of 
the  spindle  (/.p»  in  VI)  the  female  pronucleus  is  developed. 

secondary  oocyte  now  undergoes  subdivision,  during  which  each  dyad  divides  and 
contributes  a  single  chromosome  to  the  nucleus  of  each  of  the  two  resulting  cells. 


Priviary  oocyte 


Primary  oocyte 
(commencing 
maturation) 


(       f       ]  First  polar 
V  J       body 


Secondary 
oocyte 


Mature  f    *@      \   /^\      /*S\      /*0\ 


V^ 


WV_^ 


I 


Polar  bodies  ' 

FiQ.  5. — Diagram  showing  the  reduction  in  number  of  the  chromosomes  in  the  process  of  maturation  of  the  ovum. 

This  second  division  is  also  unequal,  producing  a  large  cell  which  constitutes  the 
mature  ovum,  and  a  small  cell,  the  second  polar  body.  The  first  polar  body  fre- 
quently divides  while  the  second  is  being  formed,  and  as  a  final  result  four  cells 


42 


EMBRYOLOGY 


are  produced,  viz.,  the  mature  ovum  and  three  polar  bodies,  each  of  which  con- 
tains two  chromosomes,  i.  e.,  one-half  the  number  present  in  the  nuclei  of  the 
somatic  cells  of  members  of  the  same  species.  The  nucleus  of  the  mature  ovum 
is  termed  the  female  pronucleus. 


THE    SPERMATOZOON. 


dl 


The  spermatozoa  or  male  germ  cells  are  developed  in  the  testes  and  are  present 
in  enormous  numbers  in  the  seminal  fluid.  Each  consists  of  a  small  but  greatly 
modified  cell.  The  human  spermatozoon  possesses  a  head,  a  neck,  a  connecting, 
piece  or  body,  and  a  tail  (Fig.  6). 


Head 


Connecting  piece 


•Perforator 


)  Neck 


Tail! 


End-piece  > 


I 


^  Head-cap 


J 


■-•A nterior  centriole 
""Posterior  centriole 


-—'Spiral  thread 

Mitochondria  sheath 


Terminal  disc 
Axial  filament 


I 


Fig.  6. — Human  spermatozoon.      Diagrammatic.      A.  Surface  view.      B.  Profile  view.      In  C  the  head,  neck, 
and  connecting  piece  are  more  highly  magnified. 

The  head  is  oval  or  elliptical,  but  flattened,  so  that  when  viewed  in  profile 
it  is  pear-shaped.  Its  anterior  two-thirds  are  covered  by  a  layer  of  modified  proto- 
plasm, which  is  named  the  head-cap.  This,  in  some  animals,  e.  g.,  the  salamander, 
is  prolonged  into  a  barbed  spear-like  process  or  perforator,  which  probably  facilitates 
the  entrance  of  the  spermatozoon  into  the  ovum.  The  posterior  part  of  the  head 
exhibits  an  affinity  for  certain  reagents,  and  presents  a  transversely  striated  appear- 
ance, being  crossed  by  three  or  four  dark  bands.  In  some  animals  a  central  rod- 
like filament  extends  forward  for  about  two-thirds  of  the  length  of  the  head,  while 
in  others  a  rounded  body  is  seen  near  its  center.    The  head  contains  a  mass  of 


THE  SPERMATOZOON 


43 


chromatin,  and  is  generally  regarded  as  the  nucleus  of  the  cell  surrounded  by  a 
thin  envelope. 

The  neck  is  less  constricted  in  the  human  spermatozoon  than  in  those  of  some 
of  the  lower  animals.  The  anterior  centriole,  represented  by  two  or  three  rounded 
particles,  is  situated  at  the  junction  of  the  head  and  neck,  and  behind  it  is  a  band 
of  homogeneous  substance. 

The  connecting  piece  or  body  is  rod-like,  and  is  limited  behind  by  a  terminal 
disk.  The  posterior  centriole  is  placed  at  the  junction  of  the  body  and  neck  and, 
like  the  anterior,  consists  of  two  or  three  rounded  particles.  From  this  centriole 
an  axial  filament,  surrounded  by  a  sheath,  runs  backward  through  the  body  and 
tail.  In  the  body  the  sheath  of  the  axial  filament  is  encircled  by  a  spiral  thread, 
around  which  is  an  envelope  containing  mitochondria  granules,  and  termed  the 
mitochondria  sheath. 

The  tail  is  of  great  length,  and  consists  of  the  axial  thread  or  filament,  sur- 
rounded by  its  sheath,  which  may  contain  a  spiral  thread  or  may  present  a  striated 
appearance.  The  terminal  portion  or  end-piece  of  the  tail  consists  of  the  axial 
filament  onlv. 


Primary  oocyte 


Primary  spermatocyte 


Secondary  (       \ 
oocyte     K      J 


Mature 


O 


O  Secondary 
spermatocytes 


Oooooo  oo 


Polar  bodies 


Spermatids 


FiQ.  7. — Scheme  showing  analogies  in  the  process  of  maturation  of  the  ovum  and  the  development  of  the  spermatids 

(young  spermatozoa). 


Krause  gives  the  length  of  the  human  spermatozoon  as  between  52 /x  and  62 /x, 
the  head  measuring  4  to  5m,  the  connecting  piece  G^t,  and  the  tail  from  41  ^i  to  52 fx. 

By  virtue  of  their  tails,  which  act  as  propellers,  the  spermatozoa  are  capable  of 
free  movement,  and  if  placed  in  favorable  surroundings,  e.  g.,  in  the  female  pas- 
sages, will  retain  their  vitality  and  power  of  fertilizing  for  several  days.  In  certain 
animals,  e.  g.,  bats,  it  has  been  proved  that  spermatozoa  retained  in  the  female 
passages  for  several  months  are  capable  of  fertilizing. 

The  spermatozoa  are  developed  from  the  primitive  germ  cells  which  have  become 
imbedded  in  the  testes,  and  the  stages  of  their  development  are  very  similar  to  those 
of  the  maturation  of  the  ovum.  The  primary  germ  cells  undergo  division  and 
produce  a  number  of  cells  termed  spermatogonia,  and  from  these  the  primary 
spermatocytes  are  derived.  Each  primary  spermatocyte  divides  into  two  secondary 
spermatocytes,  and  each  secondary  spermatocyte  into  two  spermatids  or  young 
spermatozoa;  from  this  it  will  be  seen  that  a  primary  spermatocyte  gives  rise  to 
four  spermatozoa.  On  comparing  this  process  with  that  of  the  maturation  of  the 
ovum  (Fig.  7)  it  will  be  observed  that  the  primary  spermatocyte  gives  rise  to 
two  cells,  the  secondary  spermatocytes,  and  the  primary  oocyte  to  two  cells,  the 
secondary  oocyte  and  the  first  polar  body.     Again,  the  two  secondary  sperma- 


EMBRYOR 

tocytes  by  their  subdivision  give  origin  to  four  spermatozoa,  and  the  secondary 
oocyte  and  first  polar  body  to  four  cells,  the  mature  ovum  and  three  polar  bodies. 
In  the  development  of  the  spermatozoa,  as  in  the  maturation  of  the  ovum,  there 
is  a  reduction  of  the  nuclear  chromosomes  to  one-half  of  those  present  in  the 
primary  spermatocyte.  But  here  the  similarity  ends,  for  it  must  be  noted  that 
the  four  spermatozoa  are  of  equal  size,  and  each  is  capable  of  fertilizing  a  mature 
ovum,  whereas  the  three  polar  bodies  are  not  only  very  much  smaller  than  the 
mature  ovum  but  are  incapable  of  further  development,  and  may  be  regarded  as 
abortive  ova. 


I 


FERTILIZATION    OF    THE    OVUM. 


Fertilization  consists  in  the  union  of  the  spermatozoon  with  the  mature  ovum 
(Fig.  8).    Nothing  is  known  regarding  the  fertilization  of  the  human  ovum,  but 


II 


1.     Polar  bodies- 
Female  pronucleus 

Male  pronucleus 


Female  pronudetis 
Male  pronucleus 


5. 


Segmentation 
nucleus 


Female  promtcleus 
Male  pronucleus 


~  Fused  pronuclei 


Segmentation 

nucleus 
{commencing 

division) 


Fio.  8. — The  process  of  fertilization  in  the  ovum  of  a  mouse.     (After  Sobotta.) 

the  various  stages  of  the  process  have  been  studied  in  other  mammals,  and  from 
the  knowledge  so  obtained  it  is  believed  that  fertilization  of  the  human  ovum  takes 
place  in  the  lateral  or  ampullary  part  of  the  uterine  tube,  and  the  ovum  is  then 
conveyed  along  the  tube  to  the  cavity  of  the  uterus — a  journey  probably  occupy- 
ing seven  or  eight  days  and  during  which  the  ovum  loses  its  corona  radiata  and  zona 
striata  and  undergoes  segmentation.  Sometimes  the  fertilized  ovum  is  arrested 
in  the  uterine  tube,  and  there  undergoes  development,  giving  rise  to  a  tubal  preg- 
nancy; or  it  may  fall  into  the  abdominal  cavity  and  produce  an  abdominal  preg- 
nancy. Occasionally  the  ovum  is  not  expelled  from  the  follicle  when  the  latter 
ruptures,  but  is  fertilized  within  the  follicle  and  produces  what  is  known  as  an 
ovarian  pregnancy.  Under  normal  conditions  only  one  spermatozoon  enters  the 
yolk  and  takes  part  in  the  process  of  fertilization.    At  the  point  where  the  sperma 


SEGMENTATION  OF  THE  FERTILIZED  OVUM 


45 


tozoon  is  about  to  pierce,  the  yolk  is  drawn  out  into  a  conical  elevation,  termed 
the  cone  of  attraction.  As  soon  as  the  spermatozoon  has  entered  the  yolk,  the  per- 
ipheral portion  of  the  latter  is  transformed  into  a  membrane,  the  vitelline  membrane 
which  prevents  the  passage  of  additional  spermatozoa.  Occasionally  a  second 
spermatozoon  may  enter  the  yolk,  thus  giving  rise  to  a  condition  of  polyspermy: 
when  this  occurs  the  ovum  usually  develops  in  an  abnormal  manner  and  gives  rise 
to  a  monstrosity.  Having  pierced  the  yolk,  the  spermatozoon  loses  its  tail,  while 
its  head  and  connecting  piece  assume  the  form  of  a  nucleus  containing  a  cluster  of 
chromosomes.  This  constitutes  the  male  pronucleus,  and  associated  with  it  there  are 
a  centriole  and  centrosome.  The  male  pronucleus  passes  more  deeply  into  the  yolk, 
and  coincidently  with  this  the  granules  of  the  cytoplasm  surrounding  it  become 
radially  arranged.  The  male  and  female  pronuclei  migrate  toward  each  other,  and. 
meeting  near  the  center  of  the  yolk,  fuse  to  form  a  new  nucleus,  the  segmentation 
nucleus,  which  therefore  contains  both  male  and  female  nuclear  substance;  the 
former  transmits  the  individualities  of  the  male  ancestors,  the  latter  those  of  the 
female  ancestors,  to  the  future  embryo.  By  the  union  of  the  male  and  female 
pronuclei  the  number  of  chromosomes  is  restored  to  that  which  is  present  in  the 
nuclei  of  the  somatic  cells. 


Fig.  9. — First  stages  of  segmentation  of  a  mammalian  ovum.  Semidiagrammatic.  (From  a  drawing  by  Allen 
liomson.)  z.p.  Zona  striata,  p.gl-  Polar  bodies,  a.  Twocell  stage,  h.  Four-cell  stage,  c.  Eight-cell  stage. 
t.  Morula  stage. 


SEGMENTATION   OF   THE   FERTILIZED    OVUM. 

The  early  segmentation  of  the  human  ovum  has  not  yet  been  observed,  but 
judging  from  what  is  known  to  occur  in  other  mammals  it  may  be  regarded  as 
certain  that  the  process  starts  immediately  after  the  ovum  has  been  fertilized, 
i.  e.,  while  the  ovum  is  in  the  uterine  tube.  The  segmentation  nucleus  exhibits 
the  usual  mitotic  changes,  and  these  are  succeeded  by  a  division  of  the  ovum  into 
two  cells  of  nearly  equal  size.^    The  process  is  repeated  again  and  again,  so  that 

>  In  the  mammalian  ova  the  nutritive  yolk  or  deutoplasm  is  small  in  amount  and  uniformly  distributed  through- 
out the  cytoplasm;  such  ova  undergo  complete  division  during  the  process  of  segmentation,  and  are  therefore  termed 
holoblashc.  In  the  ova  of  birds,  reptiles,  and  fishes  where  the  nutritive  volk  forms  by  far  the  larger  portion  of  the 
^K^k'  t  '^'^^^'i^Se  IS  limited  to  the  formative  yolk,  and  is  therefore  only  partial;  such  ova  are  termed  meroblastic.  Again, 
It  has  been  observed,  in  some  of  the  lower  animals,  that  the  pronuclei  do  not  fuse  but  merely  lie  in  apposition.  At 
the  commencement  of  the  segmentation  process  the  chromosomes  of  the  two  pronuclei  group  themselves  around  the 
equator  of  the  nuclear  spindle  and  then  divide ;  .in  equal  number  of  male  and  female  chromosomes  travel  to  the  opposite 
poles  of  the  spindle,  and  thus  the  male  and  female  pronuclei  contribute  equal  shares  of  chromatin  to  the  nuclei  of 
the  two  cells  which  result  from  the  subdivision  of  the  fertilized  ovum 


46 


EMBRYOLOGY 


the  two  cells  are  succeeded  by  four,  eight,  sixteen,  thirty-two,  and  so  on,  with  the 
result  that  a  mass  of  cells  is  found  within  the  zona  striata,  and  to  this  mass  the  term 
morula  is  applied  (Fig.  9).  The  segmentation  of  the  mammalian  ovum  may  not 
take  place  in  the  regular  sequence  of  two,  four,  eight,  etc.,  since  one  of  the  two  first 
formed  cells  may  subdivide  more  rapidly  than  the  other,  giving  rise  to  a  three- 
or  a  five-cell  stage.  The  cells  of  the  morula  are  at  first  closely  aggregated,  but  soon 
they  become  arranged  into  an  outer  or  peripheral  layer,  the  trophoblast,  which 


Inner  cell-mass 

Entoderm 


Blastodermic  vesicle 


Trophoblast 


Fig.   10. — Blastodermic  vesicle  of  Vespertilio  miirinus.     (After  van  Beneden. 

Inner  cell-mass      TrofhMast 


Embryonic  ectoderm        Entoderm 
Fig.   11. — Section  through  embryonic  disk  of  Vespertilio  murinus.     (After  van  Beneden.) 


#1 


Maternal  bloodvessels 


Amniotic  cavity 


Syncytiotrcphoblast 

CyMrcpTioblast 


Embryonic  ectoderm      Entoderm 

Fig.   12. — Section  through  embryonic  area  of  Vespertilio  murinus  to  show  the  formation  of  the  amniotic  cavity. 

(After  van  Beneden,) 

does  not  contribute  to  the  formation  of  the  embryo  proper,  and  an  inner  cell-mass, 
from  which  the  embryo  is  developed.  Fluid  collects  between  the  trophoblast 
and  the  greater  part  of  the  inner  cell-mass,  and  thus  the  morula  is  converted  into 
a  vesicle,  the  blastodermic  vesicle  (Fig.  10).  The  inner  cell-mass  remains  in  con- 
tact, however,  with  the  trophoblast  at  one  pole  of  the  ovum;  this  is  named  the 
embryonic  pole,  since  it  indicates  the  situation  where  the  future  embryo  will  be 
developed.    The  cells  of  thf.  trophoblast  become  differentiated  into  two  strata:  an 


SEGMENTATION  OF  THE  FERTILIZED  OVUM 


47 


I   outer,  termed  the  syncytium  or  s3mcytiotrophoblast,  so  named  because  it  consists  of 
j  a  layer  of  protoplasm  studded  with  nuclei,  but  showing  no  evidence  of  subdivision 
into  cells;  and  an  inner  layer,  the  cytotrophoblast  or  layer  of  Langhans,  in  which 
the  cell  outlines  are  defined.    As  already  stated,  the  cells  of  the  trophoblast  do  not 
contribute  to  the  formation  of  the  embryo  proper;  they  form  the  ectoderm  of  the 
chorion  and  play  an  important  part  in  the  development  of  the  placenta.    On  the 
deep  surface  of  the  inner  cell-mass  a  layer  of  flattened  cells,  the  entoderm,  is  differ- 
entiated and  quickly  assumes  the  form  of  a  small  sac,  the  yolk-sac.    Spaces  appear 
between  the  remaining  cells  of  the  mass  (Fig.  11),  and  by  the  enlargement  and 
coalescence  of  these  spaces  a  cavity,  termed  the  amniotic  cavity  (Fig.  12),  is  gradually 
^^    developed.    The  floor  of  this  cavity  is  formed  by  the  embryonic  disk  composed 
^■1  of  a  layer  of  prismatic  cells,  the  embryonic  ectoderm,  derived  from  the  inner  cell- 
^H  mass  and  lying  in  apposition  with  the  entoderm. 

^■1      The  Primitive  Streak;  Formation  of  the  Mesoderm. — The  embryonic   disk 
^H  becomes  oval  and  then  pear-shaped,  the  wider  end  being  directed  forward.    Near 
!■'  the  narrow,  posterior  end  an  opaque  streak,  the  primitive 
streak  (Figs.  13  and  14),  makes  its  appearance  and  extends 
along  the  middle  of  the  disk  for  about  one-half  of  its 
length;  at  the  anterior  end  of  the  streak  there  is  a  knob- 
like thickening  termed  Hensen's  knot.     A  shallow  groove, 
the  primitive  groove,  appears  on  the  surface  of  the  streak, 
and   the  anterior  end  of  this  groove  communicates  by 
means  of  an  aperture,  the  blastophore,  with  the  yolk-sac. 
The  primitive  streak  is  produced  by  a  thickening  of  the 
axial  part  of  the  ectoderm,  the  cells  of  which  multiply, 
grow  downward,  and   blend  with  those  of  the  subjacent 
entoderm  (Fig.  15).    From  the  sides  of  the  primitive  streak 
a  third  layer  of  cells,  the  mesoderm,  extends  lateralward 
I         between  the  ectoderm  and  entoderm;  the  caudal  end  of 
Hi  the  primitive  streak  forms  the  cloacal  membrane. 
"  ■       The  extension  of  the  mesoderm  takes  place  throughout  the  whole  of  the  embry- 
onic and  extra-embryonic  areas  of  the  ovum,  except  in  certain  regions.    One  of 
these  is  seen  immediately  in  front  of  the  neural  tube.    Here  the  mesoderm  extends 
»        forward  in  the  form  of  two  crescentic  masses,  which  meet  in  the  middle  line  so  as 
Hi  to  enclose  behind  them  an  area  which  is  devoid  of  mesoderm.    Over  this  area  the 
r     ectoderm  and  entoderm  come  into  direct  contact  with  each  other  and  constitute 
a  thin  membrane,  the  buccopharyngeal  membrane,  which  forms  a  septum  between 
the  primitive  mouth  and  pharynx.    In  front  of  the  buccopharyngeal  area,  where 
the  lateral  crescents  of  mesoderm  fuse  in  the  middle  line,  the  pericardium  is 
afterward  developed,  and  this  region  is  therefore  designated  the  pericardial  area.    A 
second  region  where  the  mesoderm  is  absent,  at  least  for  a  time,  is  that  imme- 
diately in  front  of  the  pericardial  area.    This  is  termed  the  proamniotic  area,  and 
is  the  region  where  the  proamnion  is  developed;  in  man,  however,  a  proamnion  is 
apparently  never  formed.     A  third  region  is  at  the  hind  end  of  the  embryo  where 
the  ectoderm  and  entoderm  come  into  apposition  and  form  the  cloacal  membrane. 
The  blastoderm  now  consists  of  three  layers,  named  from  without  inward: 
ectoderm,  mesoderm,  and  entoderm;  each  has  distinctive  characteristics  and  gives 
rise  to  certain  tissues  of  the  body.^ 

Ectoderm. — ^The  ectoderm  consists  of  columnar  cells,  which  are,  however,  somewhat 
flattened  or  cubical  toward  the  margin  of  the  embryonic  disk.  It  forms  the  whole 
of  the  nervous  system,  the  epidermis  of  the  skin,  the  lining  cells  of  the  sebaceous, 


Fig.  13. — Surface  view  of 
embryo  of  a  rabbit.  (After 
KoUiker.)  arg.  Embryonic 
disk.     pr.  Primiti%'e  streak. 


I 


'  The  mode  of  formation  of  the  germ  layers  in  the  human  ovum  has  not  yet  been  observed;  in  the  youngest  known 
human  ovum  (viz.,  that  described  by  Bryce  and  Teacher),  all  three  layers  are  already  present  and  the  mesoderm  is 
split  into  its  two  layers.  The  extra-embryonic  celom  is  of  considerable  size,  and  scattered  mesodermal  strands  are 
seen  stretching  between  the  mesoderm  of  the  yolk-sac  and  that  of  the  chorion. 


Amnion 


Allantois  in  body-stalk 


EMBRYO! 

Yolk-sac 


- — Y  }         Notochord 


Amnion 


-f — -gf •  Neurenteric  canal 

Primitive  streak 


'     Fig.   14. — Surface  view  of  embrj'o  of  Hylobates  concolor.    (After  Selenka.)    The  amnion  has  been  opened  to  expose 

the  embryonic  disk. 


m 


HI 


Fig.  15. — Series  of  transverse  sections  through  the  embryonic  disk  of  Tarsius.  (After  Hubrecht )  Section  /  passes 
through  the  disk,  in  front  of  Hensen's  knot  and  shows  only  the  ectoderm  and  entoderm.  Sections  //,  III,  and  IV  pass 
through  Hensen's  knot,  which  is  seen  in  V  tapering  away  into  the  primitive  streak.  In  III,  IV,  and  V  the  mesoderm 
is  seen  springing  from  the  keel-like  thickening  of  the  ectoderm,  which  in  III  and  IV  is  observed  to  be  continuous  into 
the  entoderm. 


SEGMENTATION  OF  THE  FERTILIZED  OVUM 


49 


sudoriferous-,  and  mammary  glands,  the  hairs  and  nails,  the  epithelium  of  the  nose 
and  adjacent  air  sinuses,  and  that  of  the  cheeks  and  roof  of  the  mouth.  From  it 
also  are  derived  the  enamel  of  the  teeth,  and  the  anterior  lobe  of  the  hypophysis 
cerebri,  the  epithelium  of  the  cornea,  conjunctiva,  and  lacrimal  glands,  and  the 
neuro-epithelium  of  the  sense  organs. 

Entoderm. — The  entoderm  consists  at  first  of  flattened  cells,  which  subsequently 

become  columnar.    It  forms  the  epithelial  lining  of  the  whole  of  the  digestive  tube 

excepting  part  of  the  mouth  and  pharynx  and  the  terminal  part  of  the  rectum 

(which  are  lined  by  involutions  of  the  ectoderm),  the  lining  cells  of  all  the  glands 

I,    which  open  into  the  digestive  tube,  including  those  of  the  liver  and  pancreas, 


HL 


IV.    ^ 


8m 
sp 


Fig.  16. — A  series  of  transverse  sections  through  an  embryo  of  the  dog.  (After  Bonnet.)  Section  I  is  the  most 
anterior.  In  V  the  neural  plate  is  spread  out  nearly  flat.  The  series  shows  the  uprising  of  the  neural  folds  to  form  the 
neural  canal,  a.  Aortse.  c.  Intermediate  cell  mass.  ect.  Ectoderm,  ent.  Entocferm.  h,  h.  Rudiments  of  endothelial 
heart  tubes.  In  ///,  IV,  and  V  the  scattered  cells  represented  between  the  entoderm  and  splanchnic  layer  of  meso- 
derm are  the  vasoformative  cells  which  give  origin  in  front,  according  to  Bonnet,  to  the  heart  tubes,  h;  l.p.  Lateral 
plate  still  undivided  in  7,  II,  and  III;  in  IV  and  V  split  into  somatic  (sm)  and  splanchnic  (sp)  layers  of  mesoderm. 
mea.  Mesoderm,     p.  Pericardium,     so.  Primitive  segment. 

the  epithelium  of  the  auditory  tube  and  tympanic  cavity,  of  the  trachea,  bronchi, 
and  air  cells  of  the  lungs,  of  the  urinary  bladder  and  part  of  the  urethra,  and  that 
which  lines  the  follicles  of  the  thyroid  gland  and  thymus. 

Mesoderm. — ^The  mesoderm  consists  of  loosely  arranged  branched  cells  sur- 
rounded by  a  considerable  amount  of  intercellular  fluid.  From  it  the  remaining 
tissues  of  the  body  are  developed.  The  endothelial  lining  of  the  heart  and  blood- 
vessels and  the  blood  corpuscles  are,  however,  regarded  by  some  as  being  of  ento- 
dermal  origin. 

As  the  mesoderm  develops  between  the  ectoderm  and  entoderm  it  is  separated 
into  lateral  halves  by  the  neural  tube  and  notochord,  presently  to  be  described.  A 
4 


50 


EMBRYOLOGY 


I 


longitudinal  groove  appears  on  the  dorsal  surface  of  either  half  and  divides  it  into 
a  medial  column,  the  paraxial  mesoderm,  lying  on  the  side  of  the  neural  tube,  and 
a  lateral  portion,  the  lateral  mesoderm.  The  mesoderm  in  the  floor  of  the  groove 
connects  the  paraxial  with  the  lateral  mesoderm  and  is  known  as  the  intermediate 
cell-mass;  in  it  the  genito-urinary  organs  are  developed.  The  lateral  mesoderm 
splits  into  two  layers,  an  outer  or  somatic,  which  becomes  applied  to  the  inner  surface 
of  the  ectoderm,  and  with  it  forms  the  somatopleure ;  and  an  inner  or  splanchnic, 
which  adheres  to  the  entoderm,  and  with  it  forms  the  splanchnoplem-e  (Fig.  IG). 
The  space  between  the  two  layers  of  the  lateral   mesoderm  is  termed  the  celom. 

THE  NEURAL  GROOVE  AND  TUBE.  ^1 

In  front  of  the  primitive  streak  two  longitudinal  ridges,  caused  by  a  folding  up 
of  the  ectoderm,  make  their  appearance,  one  on  either  side  of  the  middle  line 
(Fig.  16).    These  are  named  the  neural  folds;  they  commence  some  little  distance 


Ydksac 


Amnion 


Neural  groove 


Neurenteric  canal 

Primitive  streak 
Body-stalk 


f  IG.    17. — Human  embryo — length,  2  mm.     Dorsal  view,  with  the  amnion  laid  open.     X  30.     (After  Graf  Spee.)  ' 


behind  the  anterior  end  of  the  embryonic  disk,  where  they  are  continuous  with 
each  other,  and  from  there  gradually  extend  backward,  one  on  either  side  of  the 
anterior  end  of  the  primitive  streak.  Between  these  folds  is  a  shallow  median 
groove,  the  neural  groove  (Figs.  16, 17) .  The  groove  gradually  deepens  as  the  neural 
folds  become  elevated,  and  ultimately  the  folds  meet  and  coalesce  in  the  middle  line 
and  convert  the  groove  into  a  closed  tube,  the  neural  tube  or  canal  (Fig.  18),  the 
ectodermal  wall  of  which  forrns  the  rudiment  of  the  nervous  system.  After  the 
coalescence  of  the  neural  folds  over  the  anterior  end  of  the  primitive  streak,  the 
blastopore  no  longer  opens  on  the  surface  but  into  the  closed  canal  of  the  neural 
tube,  and  thus  a  transitory  communication,  the  neurenteric  canal,  is  established 
between  the  neural  tube  and  the  primitive  digestive  tube.  The  coalescence  of  the 
neural  folds  occurs  first  in  the  region  of  the  hind-brain,  and  from  there  extends 
forward  and  backward;  toward  the  end  of  the  third  week  the  front  opening  (anterior 
neuropore)  of  the  tube  finally  closes  at  the  anterior  end  of  the  future  brain,  and 
forms  a  recess  which  is  in  contact,  for  a  time,  with  the  overlying  ectoderm;  the 
hinder  part  of  the  neural  groove  presents  for  a  time  a  rhomboidal  shape,  and  to  this 


THE  NEURAL  GROOVE  AND  TUBE 


51 


expanded  portion  the  term  sinus  rhomboidalis  has  been  applied  (Fig.  18).  Before 
the  neural  groove  is  closed  a  ridge  of  ectodermal  cells  appears  along  the  prominent 
margin  of  each  neural  fold ;  this  is  termed  the  neural  crest  or  ganglion  ridge,  and  from 
it  the  spinal  and  cranial  nerve  ganglia  and  the  ganglia  of  the  sympathetic  nervous 
system  are  developed.  By  the  upward  growth  of  the  mesoderm  the  neural  tube 
is  ultimately  separated  from  the  overlying  ectoderm. 


.Head  fold  of  amnion  partly 
covering  the  fore-brain 


Mid-brain  -' 


Hind-brain 


Nerve  ganglion 
Auditory  vesicle 


Vitelline  vein 


Fourteenth  'primitive  -7 
segment 


Paraxial  mesoderm  -%_ 
Neural  fold 


f 


Sinus  rhomboidalis  - 


Htnvains  of  primitive  streak  - 


Heart 


Fig.   18. — Chick  embryo  of  thirty-thi' 

(From  Dm 


ion,  viewed  from  the  dorsal  aspect.     X  30. 
u  Embrj'ologie.") 


The  cephalic  end  of  the  neural  groove  exhibits  several  dilatations,  which,  when 
the  tube  is  closed,  assume  the  form  of  three  vesicles;  these  constitute  the  three 
primary  cerebral  vesicles,  and  correspond  respectively  to  the  future  fore-brain  (pros- 
encephalon), mid-brain  (mesencephalon),  and  hind-brain  (rhombencephalon)  (Fig. 
18).  The  walls  of  the  vesicles  are  developed  into  the  nervous  tissue  and  neuroglia 
of  the  brain,  and  their  cavities  are  modified  to  form  its  ventricles.    The  remainder 


IBRYOLOGY 


I 


of  the  tube  forms  the  medulla  spinalis  or  spinal  cord;  from  its  ectodermal  wall 
the  nervous  and  neuroglial  elements  of  the  medulla  spinalis  are  developed  while 
the  cavity  persists  as  the  central  canal. 


THE  NOTOCHORD.  '■ 

The  notochord  (Fig.  19)  consists  of  a  rod  of  cells  situated  on  the  ventral  aspect 
of  the  neural  tube ;  it  constitutes  the  foundation  of  the  axial  skeleton,  since  around 
it  the  segments  of  the  vertebral  column  are  formed.  Its  appearance  synchronizes 
with  that  of  the  neural  tube.  On  the  ventral  aspect  of  the  neural  groove  an  axial 
thickening  of  the  entoderm  takes  place;  this  thickening  assumes  the  appearance 
of  a  furrow — the  chordal  furrow — the  margins  of  which  come  into  contact,  and  so 
convert  it  into  a  solid  rod  of  cells — the  notochord — which  is  then  separated  from 
the  entoderm.     It  extends  throughout  the  entire  length  of  the  future  vertebral 


Ectoderm  .. 


Neural  canal  Primitive    Wolffian 

segment    duct  Celom 


Somatic  mesoderm 


Entoderm  >'  _ 

Notochord  Aorta      Splanchnic  mesoderm 

Fig.   19. — Transverse  section  of  a  chick  embryo  of  forty-five  hours'  incubation. 


(Balfour.) 


column,  and  reaches  as  far  as  the  anterior  end  of  the  mid-brain,  where  it  ends  in 
a  hook-like  extremity  in  the  region  of  the  future  dorsum  sellse  of  the  sphenoid 
bone.  It  lies  at  first  between  the  neural  tube  and  the  entoderm  of  the  yolk-sac, 
but  soon  becomes  separated  from  them  by  the  mesoderm,  which  grows  medial- 
ward  and  surrounds  it.  From  the  mesoderm 
surrounding  the  neural  tube  and  notochord, 
the  skull  and  vertebral  column,  and  the 
membranes  of  the  brain  and  medulla  spinalis 
are  developed. 

THE   PRIMITIVE    SEGMENTS. 


Toward  the  end  of  the  second  week 
transverse  segmentation  of  the  paraxial 
mesoderm  begins,  and  it  is  converted  into 
a  series  of  well-defined,  more  or  less  cubical 
masses,  the  primitive  segments  (Figs.  18, 
19,  20),  which  occupy  the  entire  length  of 
the  trunk  on  either  side  of  the  middle  line 
from  the  occipital  region  of  the  head.  Each 
segment  contains  a  central  cavity — myocoel 
— which,  however,  is  soon  filled  with  angular 
and  spindle-shaped  cells. 

Thef  primitive  segments  lie  immediately 
under  the  ectoderm  on  the  lateral  aspect  of 
the  neural  tube  and  notochord,  and  are  con- 
nected to  the  lateral  mesoderm  by  the  inter- 
mediate cell-mass.     Those  of  the  trunk  may 


Yolk: 


Cut  edge  of  amnion 
Primitive  segments 


FlQ. 


Neural  folds 


Neurenteric  canal 


20. — Dorsum  of  human  embryo,  2.11  mm.  in 
length.       (.\fter  Eternod.) 


SEPARATION  OF  THE  EMBRYO 


53 


f 


be  arranged  in  the  following  groups,  viz. :  cervical  8,  thoracic  12,  lumbar  5, 
sacral  5,  and  coccygeal  from  5  to  8.  Those  of  the  occipital  region  of  the  head 
are  usually  described  as  being  four  in  number.  In  mammals  primitive  segments 
of  the  head  can  be  recognized  only  in  the  occipital  region,  but  a  study  of  the 
lower  vertebrates  leads  to  the  belief  that  they  are  present  also  in  the  anterior 
part  of  the  head,  and  that  altogether  nine  segments  are  represented  in  the 
cephalic  region. 

SEPARATION    OF    THE   EMBRYO. 

The  embryo  increases  rapidly  in  size,  but  the  circumference  of  the  embryonic 
disk,  or  line  of  meeting  of  the  embryonic  and  amniotic  parts  of  the  ectoderm,  is  of 
relatively  slow  growth  and  gradually  comes  to  form  a  constriction  between  the 
embryo  and  the  greater  part  of  the  yolk-sac.  By  means  of  this  constriction,  which 
corresponds  to  the  future  umbilicus,  a  small  part  of  the  yolk-sac  is  enclosed  within 
the  embryo  and  constitutes  the  primitive  digestive  tube. 


Villi  of  chorion 


Amnion 
Embryonic  disk 


Rudiment  of  heart 


Chorion 

Mesoderm. 

Body-stalk 
Primitive  streak 


Mesoderm 


Bloodvessel 


Fia.  21. — Section  through  the  embryo  which  is  represented  in  Fig.  17.     (After  Graf  Spee.) 


The  embryo  increases  more  rapidly  in  length  than  in  width,  and  its  cephalic  and 
caudal  ends  soon  extend  beyond  the  corresponding  parts  of  the  circumference  of 
the  embryonic  disk  and  are  bent  in  a  ventral  direction  to  form  the  cephalic  and 
caudal  folds  respectively  (Figs.  26  and  27).  The  cephalic  fold  is  first  formed,  and 
as  the  proamniotic  area  (page  47)  lying  immediately  in  front  of  the  pericardial 
area  (page  47)  forms  the  anterior  limit  of  the  circumference  of  the  embryonic 
disk,  the  forward  growth  of  the  head  necessarily  carries  with  it  the  posterior  end 
of  the  pericardial  area,  so  that  this  area  and  the  buccopharyngeal  membrane  are 
folded  back  under  the  head  of  the  embryo  which  now  encloses  a  diverticulum  of  the 
yolk-sac  named  the  fore-gut.  The  caudal  end  of  the  embryo  is  at  first  connected 
to  the  chorion  by  a  band  of  mesoderm  called  the  body-stalk,  but  with  the  formation 
of  the  caudal  fold  the  body-stalk  assumes  a  ventral  position;  a  diverticulum  of  the 
\'olk-sac  extends  into  the  tail  fold  and  is  termed  the  hind-gut.     Between  the  fore-gut 


EMBRYOLOGY 

and  the  hind-gut  there  exists  for  a  time  a  wide  opening  into  the  yolk-sac,  but  the-i 
latter  is  gradually  reduced  to  a  small  pear-shaped  sac  (sometimes  termed  the) 
umbilical  vesicle),  and  the  channel  of  communication  is  at  the  same  time  narrowed ^ 
and  elongated  to  form  a  tube  called  the  vitelline  duct. 

THE   YOLK-SAC. 

The  yolk-sac  (Figs.  22  and  23)  is  situated  on  the  ventral  aspect  of  the  embryo;  i 
it  is  lined  by  entoderm,  outside  of  which  is  a  layer  of  mesoderm.  It  is  filled  with 
fluid,  the  vitelline  fluid,  which  possibly  may  be  utilized  for  the  nourishment  of  the 
embryo  during  the  earlier  stages  of  its  existence.  Blood  is  conveyed  to  the  wall  of 
the  sac  by  the  primitive  aortse,  and  after  circulating  through  a  wide-meshed  capil- 
lary plexus,  is  returned  by  the  vitelline  veins  to  the  tubular  heart  of  the  embryo. 
This  constitutes  the  vitelline  circulation,  and  by  means  of  it  nutritive  material  is 
absorbed  from  the  yolk-sac  and  conveyed  to  the  embryo.  At  the  end  of  the  fourth 
week  the  yolk-sac  presents  the  appearance  of  a  small  pear-shaped  vesicle  (umbilical 
vesicle)  opening  into  the  digestive  tube  by  a  long  narrow  tube,  the  vitelline  duct. 
The  vesicle  can  be  seen  in  the  after-birth  as  a  small,  somewhat  oval-shaped  body 


Amnion 

Heart  Yolk-sac 


Heart 


HTjoid  arch 
Mandibular  arch- 
Maxillary  process 
Eye 


Fore-limb 


Body-stalk 

Fig.  22. — Human  embryo  of  2.6  mm. 


(His.) 


Fig.  23. 


Hind-limb 


-Human  embryo  from  thirty-one  to  thirty-four 
days.      (His.) 


whose  diameter  varies  from  1  mm.  to  5  mm.;  it  is  situated  between  the  amnion 
and  the  chorion  and  may  lie  on  or  at  a  varying  distance  from  the  placenta.  As 
a  rule  the  duct  undergoes  complete  obliteration  during  the  seventh  week,  but 
in  about  three  per  cent,  of  cases  its  proximal  part  persists  as  a  diverticulum 
from  the  small  intestine,  Meckel's  diverticulum,  which  is  situated  about  three  or 
four  feet  above  the  ileocolic  junction,  and  may  be  attached  by  a  fibrous  cord  to 
the  abdominal  wall  at  the  umbilicus.  Sometimes  a  narrowing  of  the  lumen  of  the 
ileum  is  seen  opposite  the  site  of  attachment  of  the  duct. 


DEVELOPMENT   OF   THE   FETAL  MEMBRANES    AND    THE   PLACENTA. 

The  Allantois  (Figs.  25  to  28). — The  allantois  arises  as  a  tubular  diverticulum 
of  the  posterior  part  of  the  yolk-sac;  when  the  hind-gut  is  developed  the  allantois 
is  carried  backward  with  it  and  then  opens  into  the  cloaca  or  terminal  part  of  the 
hind-gut:  it  grows  out  into  the  body-stalk,  a  mass  of  mesoderm  which  lies  below 
and  around  the  tail  end  of  the  embryo.  The  diverticulum  is  lined  by  entoderm 
and  covered  by  mesoderm,  and  in  the  latter  are  carried  the  allantoic  or  umbilical 
vessels. 


)EVELOPMENT  OF  THE  FETAL  MEMBRANES  AXD  THE  PLACENTA     55 


In  reptiles,  birds,  and  many  mammals  the  allantois  becomes  expanded  into  d, 
"vesicle  which  projects  into  the  extra-embryonic  celom.  If  its  further  development 
be  traced  in  the  bird,  it  is  seen  to  project  to  the  right  side  of  the  embryo,  and, 
gradually  expanding,  it  spreads  over  its  dorsal  surface  as  a  flattened  sac  between 
the  amnion  and  the  serosa,  and  extending  in  all  directions,  ultimately  surrounds 
the  yolk.  Its  outer  wall  becomes  applied  to  and  fuses  with  the  serosa,  which  lies 
immediately  inside  the  shell  membrane.    Blood  is  carried  to  the  allantoic  sac  by 


Amniotic  cavity 


FlQ. 


Amniotic  cavity 
Yolk-sac 

Chorion 


2i. — Diagram  showing  earliest  observed  stage 
of  human  ovum. 


FlQ 


Body-stalk 
Allantois 

Yolk-sac 


-  Chorion 


25. — Diagram    illustrating    early    formation 
allantois  and  dififerentiation  of  body-stalk. 


the  two  allantoic  or  umbilical  arteries,  which  are  continuous  with  the  primitive 
aortse,  and  after  circulating  through  the  allantoic  capillaries,  is  returned  to  the 
primitive  heart  by  the  two  umbilical  veins.  In  this  way  the  allantoic  circulation, 
which  is  of  the  utmost  importance  in  connection  with  the  respiration  and  nutrition 
of  the  chick,  is  established.  Oxygen  is  taken  from,  and  carbonic  acid  is  given  up 
to  the  atmosphere  through  the  egg-shell,  while  nutritive  materials  are  at  the  same 
time  absorbed  by  the  blood  from  the  yolk. 


Amniotic  cavity 
Embryo 

Body-stalk 


Placental 
villi 


Placental 
villi 


Allantois 


Yolk-sac 


Chorion 


Body-stalk 

Allantois 
Yolk-sac 

Heart 


Heart 


Fig.  26  — Diagram  showing  later  stage  of  allan- 
toic development  with  commencing  constriction 
of  the  yolk-sac. 


Fore-gut 
Embryo 
Amniotic  cavity 

Fio.  27. — Diagram  showing  the  expansion  of  amnion 
and  delimitation  of  the  umbilicus. 


In  man  and  other  primates  the  nature  of  the  allantois  is  entirely  different  from 
that  just  described.  Here  it  exists  merely  as  a  narrow,  tubular  diverticulum  of  the 
hind-gut,  and  never  assumes  the  form  of  a  vesicle  outside  the  embryo.  With  the 
formation  of  the  amnion  the  embryo  is,  in  most  animals,  entirely  separated  from 
the  chorion,  and  is  only  again  united  to  it  when  the  allantoic  mesoderm  spreads 
over  and  becomes  applied  to  its  inner  surface.  The  human  embryo,  on  the  other 
hand,  as  was  pointed  out  by  His,  is  never  wholly  separated  from  the  chorion,  its 


56 


EMBRYOLOGY 


tail  end  being  from  the  first  connected  with  the  chorion  by  means  of  a  thick  bana 
of  mesoderm,  named  the  body-stalk  (Bauchstiel) ;  into  this  stalk  the  tube  of  th(! 
allantois  extends  (Fig.  21). 

The  Amnion. — The  amnion  is  a  membranous  sac  which  surrounds  and  protects 
the  embryo.  It  is  developed  in  reptiles,  birds,  and  mammals,  which  are  hence 
called  "Amniota;"  but  not  in  amphibia  and  fishes,  which  are  consequently  termed 
"Anamnia." 

In  the  human  embryo  the  earliest  stages  of  the  formation  of  the  amnion  have  not 
been  observed;  in  the  youngest  embryo  which  has  been  studied  the  amnion  was 
already  present  as  a  closed  sac  (Figs.  24  and  32),  and,  as  indicated  on  page  46, 
appears  in  the  inner  cell-mass  as  a  cavity.  This  cavity  is  roofed  in  by  a  single 
stratum  of  flattened,  ectodermal  cells,  the  amniotic  ectoderm,  and  its  floor  consists 
of  the  prismatic  ectoderm  of  the  embryonic  disk — the  continuity  between  the 

roof  and  floor  being  established  at 
the  margin  of  the  embryonic  disk. 
Outside  the  amniotic  ectoderm  is 
a  thin  layer  of  mesoderm,  which 
continuous   with    that   of    the 


Placental  villi 


IS 


Yolk-sac 


Umbilical  cord 

Allantois 
Heart 
Digestive  tvbe 


Embryo 
Amniotic  cavity 

Fio.  28. — Diagram  illustrating  a  later  stage  in  the  development 
of  the  umbilical  cord. 


somatopleure  and  is  connected  by 
the  body-stalk  with  the  meso- 
dermal lining  of  the  chorion. 

When  first  formed  the  amnion 
is  in  contact  with  the  body  of  the 
embryo,  but  about  the  fourth  or 
fifth  week  fluid  {liquor  amnii)  be- 
gins to  accumulate  within  it.  This 
fluid  increases  in  quantity  and 
causes  the  amnion  to  expand  and 
ultimately  to  adhere  to  the  inner 
surface  of  the  chorion,  so  that  the 
extra-embryonic  part  of  the  celom 
is  obliterated.  The  liquor  amnii 
increases  in  quantity  up  to  the 
sixth  or  seventh  month  of  preg- 
nancy, after  which  it  diminishes 
somewhat;  at  the  end  of  preg- 
nancy it  amounts  to  about  1  liter.  It  allows  of  the  free  movements  of  the  fetus 
during  the  later  stages  of  pregnancy,  and  also  protects  it  by  diminishing  the  risk 
of  injury  from  without.  It  contains  less  than  2  per  cent,  of  solids,  consisting  of 
urea  and  other  extractives,  inorganic  salts,  a  small  amount  of  protein,  and  frequently 
a  trace  of  sugar.  That  some  of  the  liquor  amnii  is  swallowed  by  the  fetus  is  proved 
by  the  fact  that  epidermal  debris  and  hairs  have  been  found  among  the  contents  of 
the  fetal  alimentary  canal. 

In  reptiles,  birds,  and  many  mammals  the  amnion  is  developed  in  the  following 
manner:  At  the  point  of  constriction  where  the  primitive  digestive  tube  of  the 
embryo  joins  the  yolk-sac  a  reflection  or  folding  upward  of  the  somatopleure  takes 
place.  This,  the  amniotic  fold  (Fig.  29),  first  makes  its  appearance  at  the  cephalic 
extremity,  and  subsequently  at  the  caudal  end  and  sides  of  the  embryo,  and  grad- 
ually rising  more  and  more,  its  different  parts  meet  and  fuse  over  the  dorsal  aspect 
of  the  embryo,  and  enclose  a  cavity,  the  amniotic  cavity.  After  the  fusion  of  the 
edges  of  the  amniotic  fold,  the  two  layers  of  the  fold  become  completely  separated, 
the  inner  forming  the  amnion,  the  outer  the  false  anmion  or  serosa.  The  space 
between  the  amnion  and  the  serosa  constitutes  the  extra-embryonic  celom,  and 
for  a  time  communicates  with  the  embryonic  celom. 


I 


DEVELOPMENT  OF  THE  FETAL  MEMBRANES  AND  THE  PLACENTA     57 


The  Umbilical  Cord  and  Body-stalk. — ^The  umbilical  cord  (Fig.  28)  attaches 
the  fetus  to  the  placenta;  its  length  at  full  time,  as  a  rule,  is  about  equal  to  the 


Fig.  29. — Diagram  of  a  transverse  section,  showing  the  mode  of  formation  of  the  amnion  in  the  chick.  The  amniotic 
folds  have  nearly  united  in  the  middle  line.  (From  Quain's  Anatomy.)  Ectoderm,  blue;  mesoderm,  red;  entoderm 
and  notochord,  black. 


Umbilical 
cord 

Chorion 


Placenta 


Amnion 


Umbilical 
cord 


Yolk^ac 


Vitelline 
duct 


Fig.  30. — Fetua  of  about  eight  weeks,  enclosed  in  the  amnioa.     Magnified  a  little  over  two  diameters.     (Drawn 
from  stereoscopic  photographs  lent  by  Prof.  A.  Thomson,  Oxford.) 


length  of  the  fetus,  i.  e.,  about  50  cm.,  but  it  may  be  greatly  diminished  or  increased. 
The  rudiment  of  the  umbilical  cord  is  represented  by  the  tissue  which  connects- 
the  rapidly  growing  embryo  with  the  extra-embryonic  area  of  the  ovum.  Included 
in  this  tissue  are  the  body-stalk  and  the  vitelline  duct— the  former  containing  the 
allantoic  diverticulum  and  the  umbilical  vessels,  the  latter  forming  the  communica- 
tion between  the  digestive  tube  and  the  yolk-sac.  The  body-stalk  is  the  posterior 
segment  of  the  embryonic  area,  and  is  attached  to  the  chorion.  It  consists  of  a  plate 
of  mesoderm  covered  by  thickened  ectoderm  on  which  a  trace  of  the  neural  groove 
can  be  seen,  indicating  its  continuity  with  the  embryo.  Running  through  its 
mesoderm  are  the  two  umbilical  arteries  and  the  two  umbilical  veins,  together  with 
the  canal  of  the  allantois — the  last  being  lined  by  entoderm  (Fig.  31).  Its  dorsal] 
surface  is  covered  by  the  amnion,  while  its  ventral  surface  is  bounded  b}^  the  extra- 
embryonic celom,  and  is  in  contact  with  the  vitelline  duct  and  yolk-sac.  With 
the  rapid  elongation  of  the  embryo  and  the  formation  of  the  tail  fold,  the  body 
stalk  comes  to  lie  on  the  ventral  surface  of  the  embryo  (Figs.  27  and  28),  where 


Splanchnic 
mesoderm 
Entoderm, 


Vitelline  veins 


Somatic  iriesodemi 


Amniotic  cavity 
Amniofi 
Neural  groove 


Body-stalk 


Fig.  31. — Model  of  human  embryo  1.3  mm.  long,     (.\fter  Eternod.) 


its  mesoderm  blends  with  that  of  the  yolk-sac  and  the  vitelline  duct.  The  lateral 
leaves  of  somatopleure  then  grow  round  on  each  side,  and,  meeting  on  the  ventral 
aspect  of  the  allantois,  enclose  the  vitelline  duct  and  vessels,  together  with  a  part 
of  the  extra-embryonic  celom;  the  latter  is  ultimately  obliterated.  The  cord  is 
covered  by  a  layer  of  ectoderm  which  is  continuous  with  that  of  the  amnion,  and 
its  various  constitutents  are  enveloped  by  embryonic  gelatinous  tissue,  jelly  of 
Wharton.  The  vitelline  vessels  and  duct,  together  with  the  right  umbilical  vein, 
undergo  atrophy  and  disappear;  and  thus  the  cord,  at  birth,  contains  a  pair  of 
umbilical  arteries  and  one  (the  left)  umbilical  vein. 

Implantation  or  Imbedding  of  the  Ovum. — As  described  (page  44),  fertilization 
of  the  ovum  occurs  in  the  lateral  or  ampullary  end  of  the  uterine  tube  and  is 
immediately  followed  by  segmentation.  On  reaching  the  cavity  of  the  uterus  the 
segmented  ovum  adheres  like  a  parasite  to  the  uterine  mucous  membrane,  destroys 
the  epithelium  over  the  area  of  contact,  and  excavates  for  itself  a  cavity  in  the 
mucous  membrane  in  which  it  becomes  imbedded.     In  the  ovum  described  by 


DEVELOPMENT  OF  THE  FETAL  MEMBRANES  AND  THE  PLACENTA      59 


IBryce  and  Teacher^  the  point  of  entrance  was  visible  as  a  small  gap  closed  by  a 
mass  of  fibrin  and  leucocytes;  in  the  ovum  described  by  Peters^  the  opening  was 
covered  by  a  mushroom-shaped  mass  of  fibrin  and  blood-clot  (Fig.  32),  the  narrow 
stalk  of  which  plugged  the  aperture  in  the  mucous  membrane.  Soon,  however, 
^         all  trace  of  the  opening  is  lost  and  the  ovum  is  then  completely  surrounded  by  the 

It  uterine  mucous  membrane. 
The  structure  actively  concerned  in  the  process  of  excavation  is  the  trophoblast 
•  of  the  ovum,  which  possesses  the  power  of  dissolving  and  absorbing  the  uterine 
tissues.  The  trophoblast  proliferates  rapidly  and  forms  a  network  of  branching 
processes  which  cover  the  entire  ovum  and  invade  and  destroy  the  maternal 
^^  tissues  and  open  into  the  maternal  bloodvessels,  with  the  result  that  the  spaces 
^■(  in  the  trophoblastic  network  are  filled  w  ith  maternal  blood ;  these  spaces  com- 
1^^  municate  freely  with  one  another  and  become  greatly  distended  and  form  the 
intervillous  space. 

TTi.v.  tr.  a.Q.  tr. 


II 


F^o.  32. — Section  through  ovum  imbedded  in  the  uterine  decidua.  Semidiagrammatic.  (After  Peters.)  am. 
Ammotic  cavity,  h.c.  Blood-clot.  h.s.  Body-stalk,  ect.  Embryonic  ectoderm,  ent.  Entoderm,  mes.  Mesoderm. 
m.x.  Maternal  vessels,     tr.  Trophoblast.     u.e.  Uterine  epithelium,     u.g.  Uterine  glands,     j/.s.  Yolk-sac. 

The  Decidua. — Before  the  fertilized  ovum  reaches  the  uterus,  the  mucous 
membrane  of  the  body  of  the  uterus  undergoes  important  changes  and  is  then 
known  as  the  decidua.  The  thickness  and  vascularity  of  the  mucous  membrane 
are  greatly  increased;  its  glands  are  elongated  and  open  on  its  free  surface  by 
funnel-shaped  orifices,  while  their  deeper  portions  are  tortuous  and  dilated  into 
irregular  spaces.  The  interglandular  tissue  is  also  increased  in  quantity,  and 
is  crowded  with  large  round,  oval,  or  polygonal  cells,  termed  decidual  cells.  These 
changes  are  well  advanced  by  the  second  month  of  pregnancy,  when  the  mucous 
membrane  consists  of  the  following  strata  (Fig.  33):  (1)  stratum  compactum,  next 


>  Contribution  to  the  study  of  the  early  development  and  imbedding  of  the  human  ovum,  1908. 
'  Die  Einbettung  des  menschlichen  Eies,  1899. 


60 


EMBRYOLOGY 


MvxMus  membrane 


Muscular  fibers 


Stratum  compactum 


the  free  surface;  in  this  the  uterine  glands  are  only  slightly  expanded,  and  arej 
lined  by  columnar  cells;  (2)  stratum  spongiosum,  in  which  the  gland  tubes  are  greatly 
dilated  and  very  tortuous,  and  are  ultimately  separ-ated  from  one  another  by  only 
a  small  amount  of  interglandular  tissue,  while  their  lining  cells  are  flattened  or' 
cubical;  (3)  a  thin  unaltered  or  boundary  layer,  next  the  uterine  muscular  fibers, 
containing  the  deepest  parts  of  the  uterine  glands,  which  are  not  dilated,  and 

are  lined  with  columnar  epithelium; 
it  is  from  this  epithelium  that  the 
epithelial  lining  of  the  uterus  is  re- 
generated after  pregnancy.  Distinc- 
tive names  are  applied  to  different 
portions  of  the  decidua.  The  part 
which  covers  in  the  ovum  is  named  the 
decidua  capsularis;  the  portion  which 
intervenes  between  the  ovum  and  the 
uterine  wall  is  named  the  decidua 
basalis  or  decidua  placentalis ;  it  is  here 
that  the  placenta  is  subsequently 
developed.  The  part  of  the  decidua 
which  lines  the  remainder  of  the  body 
of  the  uterus  is  known  as  the  decidua 
vera  or  decidua  parietaUs. 

Coincidently  with  the  growth  of 
the  embryo,  the  decidua  capsularis  is 
thinned  and  extended  (Fig.  34)  and 
the  space  between  it  and  the  decidua 
vera  is  gradually  obliterated,  so  that 
by  the  third  month  of  pregnancy  the 
two  are  in  contact.  By  the  fifth 
month  of  pregnancy  the  decidua  cap- 
sularis has  practically  disappeared, 
while  during  the  succeeding  months 
the  decidua  vera  also  undergoes 
atrophy,  owing  to  the  increased  press- 
ure. The  glands  of  the  stratum  com- 
pactum are  obliterated,  and  their 
epithelium  is  lost.  In  the  stratum 
spongiosum  the  glands  are  compressed 
and  appear  as  slit-like  fissures,  while 
their  epithelium  undergoes  degener- 
ation. In  the  unaltered  or  boundary 
layer,  however,  the  glandular  epithe- 
lium retains  a  columnar  or  cubical 
form. 

The  Chorion  (Figs.  23  to  28)  .—The 
chorion  consists  of  two  layers :  an  outer 
formed  by  the  primitive  ectoderm  or 
trophoblast,  and  an  inner  by  the  soma- 
tic mesoderm;  with  this  latter  the  amnion  is  in  contact.  The  trophoblast  is  made 
up  of  an  internal  layer  of  cubical  or  prismatic  cells,  the  c3rtotrophoblast  or  layer 
of  Langhans,  and  an  external  layer  of  richly  nucleated  protoplasm  devoid  of  cell 
boundaries,  the  syncytiotrophoblast.  It  undergoes  rapid  proliferation  and  forms 
numerous  processes,  the  chorionic  villi,  which  invade  and  destroy  the  uterine 
decidua  and  at  the  same  time  absorb  from  it  nutritive  materials  for  the  growth 


Stratum  spongiosum 


Unaltered  or 
boundary  layer 

Muscular  fibers 


Fig.  33. — Diagrammatic  sections  of  the  uterine  mucous 
membrane:  A.  The  non-pregnant  uterus.  B.  The  preg- 
nant uterus,  showing  the  thickened  mucous  membrane 
and  the  altered  condition  of  the  uterine  glands.  (Kundrat 
and  Engelmann.) 


I 


DEVELOPMENT  OP   THE  FETAL  MEMBRANES  AND  THE  PLACENTA     61 


of  the  embryo.  The  chorionic  villi  are  at  first  small  and  non-vascular,  and  consist 
of  trophoblast  only,  but  they  increase  in  size  and  ramify,  while  the  mesoderm, 
carrying  branches  of  the  umbilical  vessels,  grows  into  them,  and  in  this  way  they 
are  vascularized.     Blood  is  carried  to  the  villi  by  the  branches  of  the  umbilical 

Placeyital  villi  imbedded  in  the 

^Decidua  placentalis 

Uterine  tvhe 


Allantois 


Umbilical  cord 
with  its  con- 
tained vessels 


Non-placental  villi  im- 
bedded in  the  decidua 
capsularis 


Cavity  of  uterus 
Yolk-sac 

Cavity  of  amnion 

Decidua  vera 
or  parietalis 


Plug  of  rnucus  in  the 
cervix  uteri 


Fig.  34. — Sectional  plan  of  the  gravid  uterus  in  the  third  and  fourth  month.     (Modified  from  Wagner.) 

arteries,  and  after  circulating  through  the  capillaries  of  the  villi,  is  returned  to 
the  embryo  by  the  umbilical  veins.  Until  about  the  end  of  the  second  month 
of  pregnancy  the  villi  cover  the  entire  chorion,  and  are  almost  uniform  in  size 
(Fig.  25),  but  after  this  they  develop  unequally.    The  greater  part  of  the  chorion 


Trophoblast 


esoderm 


Branches  of  umbilical  i 
Fig.  35. — Transverse  section  of  a  chorionic  villus 


is  in  contact  with  the  decidua  capsularis  (Fig.  34),  and  over  this  portion  the  villi, 

with  their  contained  vessels,  undergo  atrophy,  so  that  by  the  fourth  month  scarcely 

.  a  trace  of  them  is  left,  and  hence  this  part  of  the  chorion  becomes  smooth,  and  is 

named  the  chorion  Iseve;  as  it  takes  no  share  in  the  formation  of  the  placenta,  it 


62 


EMBRYOLOGY 


is  also  named  the  non-placental  part  of  the  chorion.  On  the  other  hand,  the  villi 
on  that  part  of  the  chorion  which  is  in  contact  with  the  decidua  placentalis  increase 
greatly  in  size  and  complexity,  and  hence  this  part  is  named  the  chorion  frondosum 
(Fig.  28). 


Uterine  vessels 


Uterine  glands 


Syncytiolroj)h6blast 
Cytolrophoblast 


Mesoderm  Intervilloiis  space 

Fig.  36. — Primary  chorionic  villi.     Diagrammatic.     (Modified  from  Bryce. 

The  Placenta. — The  placenta  connects  the  fetus  to  the  uterine  wall,  and  is  the 
organ  by  means  of  which  the  nutritive,  respiratory,  and  excretory  functions  of  the 
fetus  are  carried  on.    It  is  composed  of  fetal  and  maternal  portions. 

Fetal  Portion. — The  fetal  portion  of  the  placenta  consists  of  the  villi  of  the 
chorion  frondosum;  these  branch  repeatedly,  and  increase  enormously  in  size. 
These  greatly  ramified  villi  are  suspended  in  the  intervillous  space,  and  are  bathed 


Uterine  glands 


Uterine  vessels 


Syncytiotrophoblast 

Cytolrophoblast 

Core  of  mesoderm 

with  fetal  vessels 


Mesoderm  Intervillous  space 

Fig.  37. — Secondary  chorionic  villi.     Diagrammatic.      (Modified  from  Bryce.) 

in  maternal  blood,  which  is  conveyed  to  the  space  by  the  uterine  arteries  and 
carried  away  by  the  uterine  veins.  A  branch  of  an  umbilical  artery  enters  each 
villus  and  ends  in  a  capillary  plexus  from  which  the  blood  is  drained  by  a  tributary 
of  the  umbilical  vein.  The  vessels  of  the  villus  are  surrounded  by  a  thin  layer  of 
mesoderm  consisting  of  gelatinous  connective  tissue,  which  is  covered  by  two 


DEVELOPMENT  OF  THE  FETAL  MEMBRANES  AND  THE  PLACENTA     63 

strata  of  ectodermal  cells  derived  from  the  trophoblast :  the  deeper  stratum, 
next  the  mesodermic  tissue,  represents  the  cytotrophoblast  or  layer  of  Langhans; 
the  fiuperficial,  in  contact  with  the  maternal  blood,  the  syncytiotrophoblast  (Figs. 
3(3  and  37).  After  the  fifth  month  the  two  strata  of  cells  are  replaced  by  a 
single  layer  of  somewhat  flattened  cells. 

Maternal  Portion. — The  maternal  portion  of  the  placenta  is  formed  by  the 
decidua  placentalis  containing  the  intervillous  space.  As  already  explained,  this 
space  is  produced  by  the  enlargement  and  intercommunication  of  the  spaces  in 
the  trophoblastic  network.  The  changes  involve  the  disappearance  of  the  greater 
portion  of  the  stratum  compactum,  but  the  deeper  part  of  this  layer  persists  and 
is  condensed  to  form  what  is  known  as  the  basal  plate.  Between  this  plate  and 
the  uterine  muscular  fibres  are  the  stratum  spongiosum  and  the  boundary  layer ; 


Wall  of  uterus 


Umbilical  cord 


Cervix  uteri 


Fio.  38. — Fetus  in  utero,  between  fifth  and  sixth  months. 


through  these  and  the  basal  plate  the  uterine  arteries  and  veins  pass  to  and  from 
the  intervillous  space.  The  endothelial  lining  of  the  uterine  vessels  ceases  at  the 
point  where  they  terminate  in  the  intervillous  space  w^hich  is  lined  by  the  syncytio- 
trophoblast. Portions  of  the  stratum  compactum  persist  and  are  condensed  to 
form  a  series  of  septa,  which  extend  from  the  basal  plate  through  the  thickness 
of  the  placenta  and  subdivide  it  into  the  lobules  or  cotyledons  seen  on  the  uterine 
surface  of  the  detached  placenta. 

The  fetal  and  maternal  blood  currents  traverse  the  placenta,  the  former  passing 
through  the  bloodvessels  of  the  placental  villi  and  the  latter  through  the  inter- 

I villous  space  (Fig.  39).  The  two  currents  do  not  intermingle,  being  separated  from 
each  other  by  the  delicate  walls  of  the  villi.    Nevertheless,  the  fetal  blood  is  able 


64 


EMBRYOLOGY 


I 


maternal  blood,  and  give  up  to  the  latter  its  waste  products.  The  blood,  so  purified , 
is  carried  back  to  the  fetus  by  the  umbilical  vein.  It  will  thus  be  seen  that  the 
placenta  not  only  establishes  a  mechanical  connection  between  the  mother  and  the 
fetus,  but  subserves  for  the  latter  the  purposes  of  nutrition,  respiration,  and  ex- 
cretion. In  favor  of  the  view  that  the  placenta  possesses  certain  selective  powers 
may  be  mentioned  the  fact  that  glucose  is  more  plentiful  in  the  maternal  than  in 
the  fetal  blood.  It  is  interesting  to  note  also  that  the  proportion  of  iron,  and  of 
lime  and  potash,  in  the  fetus  is  increased  during  the  last  months  of  pregnancy. 
Further,  there  is  evidence  that  the  maternal  leucocytes  may  migrate  into  the  fetal 
blood,  since  leucocytes  are  much  more  numerous  in  the  blood  of  the  umbilical  vein 
than  in  that  of  the  umbilical  arteries. 

The  placenta  is  usually  attached  near  the  fundus  uteri,  and  more  frequently  on 
the  posterior  than  on  the  anterior  wall  of  the  uterus.  It  may,  however,  occupy 
a  lower  position  and,  in  rare  cases,  its  site  is  close  to  the  orificium  internum  uteri, 
which  it  may  occlude,  thus  giving  rise  to  the  condition  known  as  placenta  previa. 


Stratum  spongiosum 
Limiting  or  boundary  layer 
Maternal  vessels 


Placental  septum 


ViUiLs 


Chorion 
Marginal  sinus 


Fig.  39. — Scheme  of  placental  circulation. 

Separation  of  the  Placenta. — ^After  the  child  is  born,  the  placenta  and  membranes 
are  expelled  from  the  uterus  as  the  after-birth.  The  separation  of  the  placenta  from 
the  uterine  wall  takes  place  through  the  stratum  spongiosum,  and  necessarily 
causes  rupture  of  the  uterine  vessels.  The  orifices  of  the  torn  vessels  are,  however, 
closed  by  the  firm  contraction  of  the  uterine  muscular  fibers,  and  thus  postpartum 
hemorrhage  is  controlled.  The  epithelial  lining  of  the  uterus  is  regenerated  by  the 
proliferation  and  extension  of  the  epithelium  which  lines  the  persistent  portions 
of  the  uterine  glands  in  the  unaltered  layer  of  the  decidua. 

The  expelled  placenta  appears  as  a  discoid  mass  which  weighs  about  450  gm. 
and  has  a  diameter  of  from  15  to  20  cm.  Its  average  thickness  is  about  3  cm., 
but  this  diminishes  rapidly  toward  the  circumference  of  the  disk,  which  is  continu- 
ous with  the  membranes.  Its  uterine  surface  is  divided  by  a  series  of  fissures  into 
lobules  or  cotyledons,  the  fissures  containing  the  remains  of  the  septa  which  extended 
between  the  maternal  and  fetal  portions.  Most  of  these  septa  end  in  irregular 
or  pointed  processes;  others,  especially  those  near  the  edge  of  the  placenta,  pass 


THE  BRANCHIAL  REGION 


65 


through  its  thickness  and  are  attached  to  the  chorion.  In  the  early  months  these 
septa  convey  branches  of  the  uterine  arteries  which  open  into  the  intervillous 
space  on  the  surfaces  of  the  septa.  The  fetal  surface  of  the  placenta  is  smooth, 
being  closely  invested  by  the  amnion.  Seen  through  the  latter,  the  chorion 
presents  a  mottled  appearance,  consisting  of  gray,  purple,  or  yellowish  areas. 
The  umbilical  cord  is  usually  attached  near  the  center  of  the  placenta,  but 
may  be  inserted  anywhere  between  the  center  and  the  margin;  in  some  cases  it 
is  inserted  into  the  membranes,  i.  e.,  the  velamentous  insertion.  From  the  attach- 
ment of  the  cord  the  larger  branches  of  the  umbilical  vessels  radiate  under  the 
amnion,  the  veins  being  deeper  and  larger  than  the  arteries.  The  remains  of 
the  vitelline  duct  and  yolk-sac  may  be  sometimes  observed  beneath  the  amnion, 
close  to  the  cord,  the  former  as  an  attenuated  thread,  the  latter  as  a  minute  sac. 
,  On  section,  the  placenta  presents  a  soft,  spongy  appearance,  caused  by  the 
Ugreatly  branched  villi;  surrounding  them  is  a  varying  amount  of  maternal  blood 
giving  the  dark  red  color  to  the  placenta.  Many  of  the  larger  villi  extend  from 
the  chorionic  to  the  decidual  surface,  while  others  are  attached  to  the  septa  which 
separate  the  cotyledons;  but  the  great  majority  of  the  villi  hang  free  in  the  inter- 
villous space. 


Mid-brain 


Fore-brain 
Stomodeum 
andibtdar  arch 
Heart 


Hind-brain 

Auditory  vesicle 


Visceral 
arches 


Olfactory  pit 
Maxillary  process 
Amnion  (cut)  Mandibular  arch 

Hyoid  arch 

Third  arch 


Body-stalk 

Fio.  40. — Embryo  between  eighteen  and  twenty-one 
days.     (His.) 


Fig.  4t. — Head  end  of  human  embryo,  about  the  end 
of  the  fourth  week.    (From  model  by  Peter.) 


THE  BRANCHIAL  REGION. 

The  Branchial  or  Visceral  Arches  and  Pharyngeal  Pouches. — In  the  lateral  walls 
of  the  anterior  part  of  the  fore-gut  five  pharyngeal  pouches  appear  (Fig.  42) ;  each 
of  the  upper  four  pouches  is  prolonged  into  a  dorsal  and  a  ventral  diverticulum. 
Over  these  pouches  corresponding  indentations  of  the  ectoderm  occur,  forming  what 
are  known  as  the  branchial  or  outer  pharjnageal  grooves.  The  intervening  mesoderm 
is  pressed  aside  and  the  ectoderm  comes  for  a  time  into  contact  with  the  ento- 
dermal  lining  of  the  fore-gut,  and  the  two  layers  unite  along  the  floors  of  the 
grooves  to  form  thin  closing  membranes  between  the  fore-gut  and  the  exterior. 
Later  the  mesoderm  again  penetrates  between  the  entoderm  and  the  ectoderm. 
In  gill-bearing  animals  the  closing  membranes  disappear,  and  the  grooves  become 
5 


66 


EMBRYOLOGY 


I 


Lateral  tongue    Thyroid, 
elevations     diverticvium 


complete  clefts,  the  gill-clefts,  opening  from  the  pharynx  on  to  the  exterior;  p^ 
ration,  however,  does  not  occur  in  birds  or  mammals.  The  grooves  separate  a 
series  of  rounded  bars  or  arches,  the  branchial  or  visceral  arches,  in  which  thickening 
of  the  mesoderm  takes  place  (Figs.  40  and  41).  The  dorsal  ends  of  these  arches 
are  attached  to  the  sides  of  the  head,  while  the  ventral  extremities  ultimately 
meet  in  the  middle  line  of  the  neck.  In  all,  six  arches  make  their  appearance, 
but  of  these  only  the  first  four  are  visible  externally.    The  first  arch  is  named  the 

mandibular,  and  the  second  the  hyoid;  the 
others  have  no  distinctive  names.  In  each 
arch  a  cartilaginous  bar,  consisting  of  right 
and  left  halves,  is  developed,  and  with  each 
of  these  there  is  one  of  the  primitive  aortic 
arches.  Ml 

The  mandibular  arch  lies  between  the  first^^ 
branchial  groove  and  the  stomodeum;  from  it 
are  developed  the  lower  lip,  the  mandible, 
the  muscles  of  mastication,  and  the  anterior 
part  of  the  tongue.  Its  cartilaginous  bar  is 
formed  by  what  are  known  as  Meckel's  carti- 
lages (right  and  left)  (Fig.  43) ;  above  this  the 
incus  is  developed.  The  dorsal  end  of  each 
cartilage  is  connected  with  the  ear-capsule 
and  is  ossified  to  form  the  malleus;  the  ventral  ends  meet  each  other  in  the  region 
of  the  symphysis  menti,  and  are  usually  regarded  as  undergoing  ossification  to  form 
that  portion  of  the  mandible  which  contains  the  incisor  teeth.  The  intervening 
part  of  the  cartilage  disappears;  the  portion  immediately  adjacent  to  the  malleus  is 
replaced  by  fibrous  membrane,  which  constitutes  the  spheno-mandibular  ligament, 


Malleus 


Entrance  to 
larynx 


Fia.  42. — Floor  of  pharynx  of  embryo  shown  in 
Fig.  40. 


Incus 


Tympanic  ring 
'  Mandible 


• —  Meckel's  cartilage 


Hyoid  bone 


Fia.  43. — Head  and  neck  of  a  human  embryo  eighteen  weeks  old,  with  Meckel's  cartilage  and  hyoid  bar  exposed 

(After  Kolliker.) 


while  from  the  connective  tissue  covering  the  remainder  of  the  cartilage  the  greater 
part  of  the  mandible  is  ossified.  From  the  dorsal  ends  of  the  mandibular  arch  a 
triangular  process,  the  maxillary  process,  grows  forward  on  either  side  and  forms 
the  cheek  and  lateral  part  of  the  upper  lip.  The  second  or  hyoid  arch  assists  in 
forming  the  side  and  front  of  the  neck.  From  its  cartilage  are  developed  the  styloid 
process,  stylohyoid  ligament,  and  lesser  cornu  of  the  hyoid  bone.    The  stages  prob- 


1 


THE  BRANCHIAL  REGION 


67 


ably  arises  in  the  upper  part  of  this  arch.  The  cartilage  of  the  third  arch  gives  origin 
to  the  greater  cornu  of  the  hyoid  bone.  The  ventral  ends  of  the  second  and  third 
arches  unite  with  those  of  the  opposite  side,  and  form  a  transverse  band,  from 
which  the  body  of  the  hyoid  bone  and  the  posterior  part  of  the  tongue  are  devel- 
oped. The  ventral  portions  of  the  cartilages  of  the  fourth  and  fifth  arches  unite 
to  form  the  thyroid  cartilage;  from  the  cartilages  of  the  sixth  arch  the  cricoid 
and  arytenoid  cartilages  and  the  cartilages  of  the  trachea  are  developed.  The 
mandibular  and  hyoid  arches  grow  more  rapidly  than  those  behind  them,  with 
the  result  that  the  latter  become,  to  a  certain  extent,  telescoped  within  the 
former,  and  a  deep  depression,  the  sinus  cervicalis,  is  formed  on  either  side  of 
the  neck.  This  sinus  is  bounded  in  front  by  the  hyoid  arch,  and  behind  by  the 
thoracic  wall;  it  is  ultimately  obliterated  by  the  fusion  of  its  walls. 

From  the  first  branchial  groove  the  concha  auriculae  and  external  acoustic 
meatus  are  developed,  while  around  the  groove  there  appear,  on  the  mandibular 
and  hyoid  arches,  a  number  of  swellings  from  which  the  auricula  or  pinna  is  formed. 
The  first  pharyngeal  pouch  is  prolonged  dorsally  to  form  the  auditory  tube  and  the 
tympanic  cavity;  the  closing  membrane  between  the  mandibular  and  hyoid  arches 

Membranous  capsule  over  cerebral  7iemisj)here 


Fronto-nasal  process 


Stomodeum 


Lateral  nasal  process 

Eye 

Globular  process 
Maxillary  process 

Mandibular  arch 
Hyomandibvlar  deft 


Fig.  44. — Under  surface  of  the  head  of  a  human  embryo  about  twenty-nine  days  old.     (After  His.) 

is  invaded  by  mesoderm,  and  forms  the  tympanic  membrane.  No  traces  of  the 
second,  third,  and  fourth  branchial  grooves  persist.  The  inner  part  of  the  second 
pharyngeal  pouch  is  named  the  sinus  tonsillaris;  in  it  the  tonsil  is  developed,  above 
which  a  trace  of  the' sinus  persists  as  the  supratonsillar  fossa.  The  fossa  of  Rosen- 
miiller  or  lateral  recess  of  the  pharynx  is  by  some  regarded  as  a  persistent  part  of 
the  second  pharyngeal  pouch,  but  it  is  probably  developed  as  a  secondary  forma- 
tion. From  the  third  pharyngeal  pouch  the  thymus  arises  as  an  entodermal  diver- 
ticulum on  either  side,  and  from  the  fourth  pouches  small  diverticula  project  and 
become  incorporated  with  the  thymus,  but  in  man  these  diverticula  probably 
never  form  true  thymus  tissue.  The  parathyroids  also  arise  as  diverticula  from 
the  third  and  fourth  pouches.  From  the  fifth  pouches  the  ultimobranchial  bodies 
originate  and  are  enveloped  by  the  lateral  prolongations  of  the  median  thyroid 
rudiment;  they  do  not,  however,  form  true  thyroid  tissue,  nor  are  any  traces 
of  them  found  in  the  human  adult. 

The  Nose  and  Face. — During  the  third  week  two  areas  of  thickened  ectoderm,  the 
olfactory  areas,  appear  immediately  under  the  fore-brain  in  the  anterior  wall  of  the 
stomodeum,  one  on  either  side  of  a  region  termed  the  fronto-nasal  process  (Fig.  44). 
By  the  upgrowth  of  the  surrounding  parts  these  areas  are  converted  into  pits, 


68 


EMBRYOLOGY 


the  olfactory  pits,  which  indent  the  fronto-nasal  process  and  divide  it  into  a 
medial  and  two  lateral  nasal  processes  (Fig.  45).  The  rounded  lateral  angles  ol 
the  medial  process  constitute  the  globular  processes  of  Plis.  The  olfactory  pits  form 


I 


Future  apex  of  nose 

Medial  nasal  frocesa 

Oljactory  -pit 
Lateral  rmsal  process 
Olcbular  ^ocess 
Maxillary  process 
Stomodeura 
Mandibular  arch 


Future  apex  of  nose 

Medial  nasal  process 

Olfactory  pit 

Lateral  nasal  process 

Globular  process 
Maxillary  process 

Rocf  of  pharynx 
Hypophyseal  diverticulum 
Dorsal  wall  of  pharynx 


Fig.  45. — Head  end  of  human  embryo  of  about  thirty 
to  thirty-one  days.    (From  model  by  Peters.) 


Fig.  46. — Same  embryo  as  shown  in  Fig.  45,  with  front 
wall  of  pharynx  removed. 


the  rudiments  of  the  nasal  cavities,  and  from  their  ectodermal  lining  the  epithe- 
lium of  the  nasal  cavities,  with  the  exception  of  that  of  the  inferior  meatuses,  is 
derived.  The  globular  processes  are  prolonged  backward  as  plates,  termed  the  nasal 
laminae :  these  laminse  are  at  first  some  distance  apart,  but,  gradually  approach- 


Lateral  nasal  pro- 
cess 
Olobvlar  processes 


Fig.  47. — Head  of  a  human  embryo  of 
about  eight  weeks,  in  which  the  nose  and 
mouth  are  formed.     (His.) 


Fig.  48. — Diagram  showing  the  regions  of  the  adult  face  and  neck 
related  to  the  fronto-nasal  process  and  the  branchial  arches. 


ing,  they  ultimately  fuse  and  form  the  nasal  septum;  the  processes  themselves 
meet  in  the  middle  line,  and  form  the  premaxillse  and  the  philtrum  or  central 
part  of  the  upper  lip  (Fig.  48).    The  depressed  part  of  the  medial  nasal  process 


THE  BRANCHIAL  REGION 


69 


)etv\'een  the  globular  processes  forms  the  lower  part  of  the  nasal  septum  or 
columella;  while  above  this  is  seen  a  prominent  angle,  which  becomes  the  future 
apex  (Figs.  45,  46),  and  still  higher  a  flat  area,  the  future  bridge,  of  the  nose. 
The  lateral  nasal  processes  form  the  alse  of  the  nose. 

'  Continuous  with  the  dorsal  end  of  the  mandibular  arch,  and  growing  forward 
from  its  cephalic  border,  is  a  triangular  process,  the  maxillary  process,  the  ventral 
extremity  of  which  is  separated  from  the  mandibular  arch  by  a  >  shaped  notch 


Narea 


Primitive 
palate 


Nasal 
cavity 


Bucconasal 
membranes 

Fig.  49. — Primitive  palate  of  a  human  embryo  of  thirty-seven  to  thirty-eight  days.     (From  model  by  Peters.) 
On  the  left  side  the  lateral  waU  of  the  nasal  cavity  has  been  removed. 

(Fig.  44).  The  maxillary  process  forms  the  lateral  wall  and  floor  of  the  orbit, 
and  in  it  are  ossified  the  zygomatic  bone  and  the  greater  part  of  the  maxilla;  it 
meets  with  the  lateral  nasal  process,  from  which,  however,  it  is  separated  for  a 
time  by  a  groove,  the  naso-optic  furrow,  that  extends  from  the  furrow  encircling 
the  eyeball  to  the  olfactory  pit.  The  maxillary  processes  ultimately  fuse  with  the 
ateral  nasal  and  globular  processes,  and  form  the  lateral  parts  of  the  upper  lip 


Gldbvlar  'process 


Mouth  of  olfactory 
pit,  or  naris 


Palatine  process  of 
globular  process 

Palatine  part  of 
maxillary  process 


Maxillary  process 


Pharynx 


Fig.  50. — The  roof  of  the  mouth  of  a  human  embryo,  aged  about  two  and  a  half  months,  showing  the  mode  of 

formation  of  the  palate.     (His.) 


I 


and  the  posterior  boundaries  of  the  nares  (Figs.  47,  48).  From  the  third  to 
the  fifth  month  the  nares  are  filled  by  masses  of  epithelium,  on  the  breaking  down 
and  disappearance  of  which  the  permanent  openings  are  produced.  The  maxillary 
process  also  gives  rise  to  the  lower  portion  of  the  lateral  wall  of  the  nasal  cavity. 
The  roof  of  the  nose  and  the  remaining  parts  of  the  lateral  wall,  viz.,  the  ethmoidal 
labyrinth,  the  inferior  nasal  concha,  the  lateral  cartilage,  and  the  lateral  crus  of 
the  alar  cartilage,  are  developed  in  the  lateral  nasal  process.    By  the  fusion  of  the 


70 


EMBRYOLOGY 


I 


maxillary  and  nasal  processes  in  the  roof  of  the  stomodeum  the  primitive  palate 
(Fig.  49)  is  formed,  and  the  olfactory  pits  extend  backward  above  it.  The  pos- 
terior end  of  each  pit  is  closed  by  an  epithelial  membrane,  the  bucco-nasal  membrane, 
formed  by  the  apposition  of  the  nasal  and  stomodeal  epithelium.  By  the  rupture^! 
of  these  membranes  the  primitive  choanse  or  openings  between  the  olfactory  pits 
and  the  stomodeum  are  established.  The  floor  of  the  nasal  cavity  is  completed 
by  the  development  of  a  pair  of  shelf-like  palatine  processes  which  extend  medial- 
ward  from  the  maxillary  processes  (Figs.  50  and  51);  these  coalesce  with  each 
other  in  the  middle  line,  and  constitute  the  entire  palate,  except  a  small  part  in 
front  which  is  formed  by  the  premaxillary  bones.  Two  apertures  persist  for  a  time 
between  the  palatine  processes  and  the  premaxillse  and  represent  the  permanent 
channels  which  in  the  lower  animals  connect  the  nose  and  mouth.  The  union  of 
the  parts  which  form  the  palate  commences  in  front,  the  premaxillary  and  palatine 
processes  joining  in  the  eighth  week,  while  the  region  of  the  future  hard  palate 


Lateral  part  of_ 
nasal  capsule 


Inferior  concha 


Inferior  meatus 

Vomeronasal         ^^-a^-'S^-v 
cartilage  '    ' 


Palatine  process 


Cartilage  of 
'^!^  nasal  septum 


Vomeronasal 
organ  of  Jacobson 


Inferior  meatus 


Cavity  of  mouth 


Fig.  51. — Frontal  section  of  nasal  cavities  of  a  human  embryo  28  mm.  long.     (Kollmann.) 

is  completed  by  the  ninth,  and  that  of  the  soft  palate  by  the  eleventh  week.  By 
the  completion  of  the  palate  the  permanent  choanse  are  formed  and  are  situated  a 
considerable  distance  behind  the  primitive  choanse.  The  deformity  known  as 
cleft  palate  results  from  a  non-union  of  the  palatine  processes,  and  that  of  hare- 
lip through  a  non-union  of  the  maxillary  and  globular  processes  (see  page  199). 
The  nasal  cavity  becomes  divided  by  a  vertical  septum,  which  extends  downward 
and  backward  from  the  medial  nasal  process  and  nasal  laminae,  and  unites  below 
with  the  palatine  processes.  Into  this  septum  a  plate  of  cartilage  extends  from 
the  under  aspect  of  the  ethmoid  plate  of  the  chodrocranium.  The  anterior  part 
of  this  cartilaginous  plate  persists  as  the  septal  cartilage  of  the  nose  and  the  medial 
crus  of  the  alar  cartilage,  but  the  posterior  and  upper  parts  are  replaced  by  the 
vomer  and  perpendicular  plate  of  the  ethmoid.  On  either  side  of  the  nasal  septum, 
at  its  lower  and  anterior  part,  the  ectoderm  is  invaginated  to  form  a  blind  pouch 
or  diverticulum,  which  extends  backward  and  upward  into  the  nasal  septum  and 
is  supported  by  a  curved  plate  of  cartilage.    These  pouches  form  the  rudiments  of 


THE  BRANCHIAL  REGION 


71 


le  vomero-nasal  organs  of  Jacobson,  which   open  below,  close  to  the  junction 
[of  the  premaxillary  and  maxillary  bones. 

The  Limbs. — The  limbs  begin  to  make  their  appearance  in  the  third  week  as 
[small  elevations  or  buds  at  the  side  of  the  trunk  (Fig.  52).  Prolongations  from 
[the  muscle-  and  cutis-plates  of  several  primitive  segments  extend  into  each  bud, 
and  carry  with  them  the  anterior  divisions  of  the  corresponding  spinal  nerves. 
The  nerves  supplying  the  limbs  indicate  the  number  of  primitive  segments  which 
contribute  to  their  formation — the  upper  limb  being  derived  from  seven,  viz., 
fourth  cervical  to  second  thoracic  inclusive,  and  the  lower  limb  from  ten,  viz., 
twelfth  thoracic  to  fourth  sacral  inclusive.  The  axial  part  of  the  mesoderm  of 
the  limb-bud  becomes  condensed  and  converted  into  its  cartilaginous  skeleton, 
and  by  the  ossification  of  this  the  bones  of  the  limbs  are  formed.  By  the  sixth 
week  the  three  chief  divisions  of  the  limbs  are  marked  off  by  furrows — the  upper 
into  arm,  forearm,  and  hand;  the  lower  into  thigh,  leg,  and  foot  (Fig.  53).  The 
limbs  are  at  first  directed  backward  nearly  parallel  to  the  long  axis  of  the  trunk. 


Heart 


Hyoid  arch 
Mandibvlar  arch 

Maxillary  process 


Auricula 


-  Fore-limb 


—Hind-limb 


Hg.  52. — Human  embryo  from  thirty-one  to  thirty- 
four  days.     (His.) 


Umbilical  cord 

Fig.  53. — Embryo  of  about  six  weeks.     (His. 


and  each  presents  two  surfaces  and  two  borders.  Of  the  surfaces,  one— the  future 
flexor  surface  of  the  limb — is  directed  ventrally;  the  other,  the  extensor  surface, 
dorsally;  one  border,  the  preaxial,  looks  forward  toward  the  cephalic  end  of  the 
embryo,  and  the  other,  the  postaxial,  backward  toward  the  caudal  end.  The  lateral 
epicondyle  of  the  humerus,  the  radius,  and  the  thumb  lie  along  the  preaxial  border 
of  the  upper  limb ;  and  the  medial  epicondyle  of  the  femur,  the  tibia,  and  the  great 
toe  along  the  corresponding  border  of  the  lower  limb.  The  preaxial  part  is  derived 
from  the  anterior  segments,  the  postaxial  from  the  posterior  segments  of  the  limb- 
bud;  and  this  explains,  to  a  large  extent,  the  innervation  of  the  adult  limb,  the 
nerves  of  the  more  anterior  segments  being  distributed  along  the  preaxial  (radial 
or  tibial),  and  those  of  the  more  posterior  along  the  postaxial  (ulnar  or  fibular) 
border  of  the  limb.  The  limbs  next  undergo  a  rotation  or  torsion  through  an  angle 
of  90°  around  their  long  axes  the  rotation  being  effected  almost  entirely  at  the 
limb  girdles.  In  the  upper  limb  the  rotation  is  outward  and  forward;  in  the  lower 
b,  inward  and  backward.    As  a  consequence  of  this  rotation  the  preaxial  (radial) 


Htlim 


72 


EMBRYOLOGY 


border  of  the  fore-limb  is  directed  lateralward,  and  the  preaxial  (tibial)  borde 
of  the  hind-limb  is  directed  medialward;  thus  the  flexor  surface  of  the  fore-limb 
is  turned  forward,  and  that  of  the  hind-limb  backward. 


DEVELOPMENT  OF  THE  BODY  CAVITIES. 


«l 


In  the  human  embryo  described  by  Peters  the  mesoderm  outside  the  embryonic 
disk  is  split  into  two  layers  enclosing  an  extra-embryonic  coelom;  there  is  no  trace 
of  an  intra-embryonic  coelom.  At  a  later  stage  four  cavities  are  formed  within  the 
embryo,  viz.,  one  on  either  side  within  the  mesoderm  of  the  pericardial  area,  and 
one  in  either  lateral  mass  of  the  general  mesoderm.  All  these  are  at  first  independent 
of  each  other  and  of  the  extra-embryonic  celom,  but  later  they  become  continuous. 
The  two  cavities  in  the  general  mesoderm  unite  on  the  ventral  aspect  of  the  gut 
and  form  the  pleuro-peritoneal  cavity,  which  becomes  continuous  with  the  remains 
of  the  extra-embryonic  celom  around  the  umbilicus;  the  two  cavities  in  the  peri- 
cardial area  rapidly  join  to  form  a  single  pericardial  cavity,  and  this  from  two  lateral 
diverticula  extend  caudalward  to  open  into  the  pleuro-peritoneal  cavity  (Fig.  54). 


y'^^K 


Mesentery 


Pleural  cavity  \^ 


lAi/ng. 


Pleuro-  pericardial 
opening 


Pericardium 


Mesoderm 

surrounding 

duct  ofCuvier 


"-^Dorsal  mesocardium 
~^Heart 


Fig.  64. — Figure  obtained  by  combining  several  successive  sections  of  a  human  embryo  of  about  the  fourth  week 
(From  KoUmann.)     The  upper  arrow  is  in  the  pleuroperitoneal  opening,  the  lower  in  the  pleuropericardial. 


Between  the  two  latter  diverticula  is  a  mass  of  mesoderm  containing  the  ducts 
of  Cuvier,  and  this  is  continuous  ventrally  with  the  mesoderm  in  which  the  umbili- 
cal veins  are  passing  to  the  sinus  venosus.  A  septum  of  mesoderm  thus  extends 
across  the  body  of  the  embryo.  It  is  attached  in  front  to  the  body-wall  between 
the  pericardium  and  umbilicus;  behind  to  the  body-wall  at  the  level  of  the  second 
cervical  segment;  laterally  it  is  deficient  where  the  pericardial  and  pleuro-peri- 
toneal cavities  communicate,  while  it  is  perforated  in  the  middle  line  by  the  fore- 
gut.  This  partition  is  termed  the  septum  transversum,  and  is  at  first  a  bulky  plate 
of  tissue.  As  development  proceeds  the  dorsal  end  of  the  septum  is  carried  grad- 
ually caudalward,  and  when  it  reaches  the  fifth  cervical  segment  muscular  tissue 
with  the  phrenic  nerve  grows  into  it.  It  continues  to  recede,  however,  until  it 
reaches  the  position  of  the  adult  diaphragm  on  the  bodies  of  the  upper  lumbar 
vertebrae.  The  liver  buds  grow  into  the  septum  transversum  and  undergo 
development  there. 

The  lung  buds  meantime  have  grown  out  from  the  fore-gut,  and  project  laterally 
into  the  forepart  of  the  pleuro-peritoneal  cavity;  the  developing  stomach  and  liver 
are  imbedded  in  the  septum  transversum;  caudal  to  this  the  intestines  project  into 
the  back  part  of  the  pleuro-peritoneal  cavity  (Fig.  55) .    Owing  to  the  descent  of 


I 


DEVELOPMENT  OF  THE  BODY  CAVITIES 


73 


the  dorsal  end  of  the  septum  transversum  the  lung  buds  come  to  lie  above  the 
septum  and  thus  pleural  and  peritoneal  portions  of  the  pleuro-peritoneal  cavity 
(still,  however,  in  free  communication  with  one  another)  may  be  recognized;  the 
pericardial  cavity  opens  into  the  pleural  part. 


Left  due  of  Cuvier       Hsopluxgus     Right  duct  of  Cuvier 


Omental  bursa 


Stomach 


2Iesoderm 

surrounding  duct 

Pleuro-pericardial 

opening 
Ridge  growing  across 

opening 

Dorsal  mesentery 
Peritoneal  recess 


Fia.  55. — Upper  part  of  celom  of  human  embryo  of  6.8  mm.,  seen  from  behind.     (From  model  by  Piper.) 

The  ultimate  separation  of  the  permanent  cavities  from  one  another  is  effected 
by  the  growth  of  a  ridge  of  tissue  on  either  side  from  the  mesoderm  surrounding 


Bsophagua 


Aorta 

Pleural  cavity 
Lung 

Inferior  vena  cava 


Body  wall 
Pericardium 


Fig.  56. — Diagram  of  transverse  section  through  rabbit  embryo.     (After   Keith.) 


the  duct  of  Cuvier  (Figs.  54,  55).    The  front  part  of  this  ridge  grows  across  and 
obliterates  the  pleuro-pericardial  opening;  the  hinder  part  grows  across  the  pleuro- 

1^    peritoneal  opening. 
■        With  the  continued  growth  of  the  lungs  the  pleural  cavities  are  pushed  forward 
ki 


74 


EMBRYOLOGY 


in  the  body-wall  toward  the  ventral  median  line,  thus  separating  the  pericardium 
from  the  lateral  thoracic  walls  (Fig.  53) .  The  further  development  of  the  peritoneal 
cavity  has  been  described  with  the  development  of  the  digestive  tube  (page  168 
et  seq.). 


Spken 

Colon 
Suprarenal  gland 
Eleventh  rib 
Twelfth  rib 


Sternn-costal part  of 
Diaphragma 
Central  tendon  of  Diaphragma 
Inferioi-  vena  cava 

(Esophagus 

Vertebral  part  of  Diaphragma 
T  Posterior  mediastinal  cavity 
-Aorta 


—  Spino-costal  hiattis 


Left  pleura 


Eight  pleura 


Fig.  57. — The  thoracic  aspect  of  the  diaphragm  of  a  newly  born  child  in  which  the  communication  between  the 
peritoneum  and  pleura  haa  not  been  closed  on  the  left  side;  the  position  of  the  opening  is  marked  on  the  right  side  by 
the  spinocostal  hiatus.     (After  Keith.) 


THE  FORM  OF  THE  EMBRYO  AT  DIFFERENT  STAGES  OF  ITS  GROWTH. 

First  Week. — During  this  period  the  ovum  is  in  the  uterine  tube.  Having  been  fertilized  in 
the  upper  part  of  the  tube,  it  slowly  passes  down,  undergoing  segmentation,  and  reaches  the 
uterus.  Peters^  described  a  specimen,  the  age  of  which  he  reckoned  as  from  three  to  four  days. 
It  was  imbedded  in  the  decidua  on  the  posterior  wall  of  the  uterus  and  enveloped  by  a  decidua 
capsularis,  the  central  part  of  which,  however,  consisted  merely  of  a  layer  of  fibrin.  The  ovum 
was  in  the  form  of  a  sac,  the  outer  wall  of  which  consisted  of  a  layer  of  trophoblast;  inside  this 


Heart 


Amnion 


Fig.  58.- 


Body-stalk 


Chorion 
-Human  embryo  about  fifteen  days  old. 


(His.) 


was  a  thin  layer  of  mesoderm  composed  of  round,  oval,  and  spindle-shaped  cells.  Numerous 
villous  processes — some  consisting  of  trophoblast  only,  others  possessing  a  core  of  mesoderm — 
projected  from  the  surface  of  the  ovum  into  the  surrounding  decidua.  Inside  this  sac  the  rudi- 
ment of  the  embryo  was  found  in  the  form  of  a  patch  of  ectoderm,  covered  by  a  small  but  com- 


'  Die  Einbettung  des  menschlichen  Eies,  1899. 


M 


WRM  OF  THE  EMBRYO  AT  DIFFERENT  STAGES  OF  ITS  GROWTH    75 


pletely  closed  amnion.    It  possessed  a  minute  yolk-sac  and  was  surroimded  by  mesoderm,  which 
was  connected  by  a  band  to  that  lining  the  trophoblast  (Fig.  32).^ 

Second  Week. — By  the  end  of  this  week  the  ovum  has  increased  considerably  in  size,  and  the 
majority  of  its  villi  are  vascularized.  The  embryo  has  assumed  a  definite  form,  and  its  cephaUc 
and  caudal  extremities  are  easily  distinguished.    The  neural  folds  are  partly  united.    The  embryo 


Mid-brain 


Fore-brain 
Stomodeum 
Mandibular  arch 
Heart 


Hind-brain 

Auditory  vesicle 


Amnion  {cut) 


Body-stalk 
Fig.  59. — Human  embryo  between  eighteen  and  twenty-one  days  old.      (His. 

more  completely  separated,  from  the  yolk-sac,  and  the  paraxial  mesoderm  is  being  divided  into 
Jthe  primitive  segments  (Fig.  58). 

Third  Week. — By  the  end  of  the  third  week  the  embryo  is  strongly  curved,  and  the  primitive 
segments  number  about  thirty.     The  primary  divisions  of  the  brain  are  visible,  and  the  optic 


Heart 


Fore-limb 


ki 


Byoid  arch 

Mandibular  arch 
Maxillary  process 

Eye-i 
Olfactory  pit 


Chorion' 

Hind-limb 

Fig.  60. — Human  embryo,  twenty-seven  to  thirty  days  old.     (His.) 

and  auditory  vesicles  are  formed.  Four  branchial  grooves  are  present:  the  stomodeum  is  well- 
marked,  and  the  bucco-pharyngeal  membrane  has  disappeared.  The  rudiments  of  the  hmba 
are  seen  as  short  buds,  and  the  Wolffian  bodies  are  visible  (Fig.  59). 

■  Br>-ce  and  Teacher  {Early  Deielopment  and  Imbedding  of  the  Human  Ovum,  1908)  have  described  an  ovum  which 
they  regard  as  thirteen  to  fourteen  days  old.  In  it  the  two  vesicles,  the  amnion  and  yolk-sac,  were  pre.sent,  but  there 
was  no  trace  of  a  layer  of  embryonic  ectoderm.  They  are  of  opinion  that  the  age  of  Peters'  ovum  has  been  understated, 
and  estimate  it  as  between  thirteen  and  one-half  and  fourteen  and  one-half  days. 


f  was  no  trace  < 

■^>  and  estimate 


76 


EMBRYOLOGY 


Fourth  Week. — The  embryo  is  markedly  curved  on  itself,  and  when  viewed  in  profile  is  almost 
circular  in  outline.  The  cerebral  hemispheres  appear  as  hollow  buds,  and  the  elevations  whica 
form  the  rudiments  of  the  auricula  are  visible.  The  limbs  now  appear  as  oval  flattened  projec- 
tions (Fig.  60). 

Heart 


I 


Hyoid 
Mandibular  arch 
Maxillary  process 
Eye 


limb 


Hind-limb 
Fig.  61. — Human  embryo,  thirty-one  to  thirty-four  days  old.     (His.) 

Fifth  Week. — The  embryo  is  less  curved  and  the  head  is  relatively  of  large  size.  DifTerentiation 
of  the  limbs  into  their  segments  occurs.  The  nose  forms  a  short,  flattened  projection.  The  cloaca! 
tubercle  is  evident  (Fig.  61). 


Auricula 


Fore-limb 


Hind-limb 


Umbilical  cord 


Fio.  62. — Human  embryo  of  about  six  weeks. 
(His.) 


Fio.  63. — Human  embryo  about  eight  and  a  half 
weeks  old.     (His.) 


Sixth  Week. — The  curvature  of  the  embryo  is  further  diminished.  The  branchial  grooves— 
except  the  first — have  disappeared,  and  the  rudiments  of  the  fingers  and  toes  can  be  recognized 
(Fig.  62). 

Seventh  and  Eighth  Weeks. — The  flexure  of  the  head  is  gradually  reduced  and  the  neck  is 
somewhat  lengthened.    The  upper  lip  is  completed  and  the  nose  is  more  prominent.    The  nostrils 


I 


FORM  OF  THE  EMBRYO  AT  DIFFERENT  STAGES  OF  ITS  GROWTH       77 


are  directed  forward  and  the  palate  is  not  completely  developed.  The  eyelids  are  present  in  the 
shape  of  folds  above  and  below  the  eye,  and 'the  different  parts  of  the  auricula  are  distinguish- 
able.   By  the  end  of  the  second  month  the  fetus  measures  from  28  to  30  mm.  in  length  (Fig.  63). 

Third  Month. — The  head  is  extended  and  the  neck  is  lengthened.  The  eyelids  meet  and  fuse, 
remaining  closed  until  the  end  of  the  sixth  month.  The  limbs  are  well-developed  and  nails  appear 
on  the  digits.  The  external  generative  organs  are  so  far  differentiated  that  it  is  possible  to  dis- 
tinguish the  sex.  By  the  end  of  this  month  the  length  of  the  fetus  is  about  7  cm.,  but  if  the  legs 
be  included  it  is  from  9  to  10  cm. 

Fourth  Month. — The  loop  of  gut  which  projected  into  the  umbilical  cord  is  withdrawn  within 
the  fetus.  The  hairs  begin  to  make  their  appearance.  There  is  a  general  increase  in  size  so  that 
by  the  end  of  the  fourth  month  the  fetus  is  from  12  to  13  cm.  in  length,  but  if  the  legs  be  included 
it  is  from  16  to  20  cm. 

Fifth  Month. — It  is  during  this  month  that  the  first  movements  of  the  fetus  are  usually  ob- 
Berved     The  eruption  of  hair  on  the  head  commences,  and  the  vemix  caseosa  begins  to  be  deposited. 

I  By  the  end  of  this  month  the  total  length  of  the  fetus,  including  the  legs,  is  from  25  to  27  cm 
J    Sixth  Month. — The  body  is  covered  by  fine  hairs  (lanugo)  and  the  deposit  of  vernix  caseosa 
Is  considerable.     The  papillae  of  the  skin  are  developed  and  the  free  border  of  the  nail  projects 
from  the  corium  of  the  dermis.      Measured  from  vertex  to  heels,  the  total  length  of  the  fetus 
at  the  end  of  this  month  is  from  30  to  32  cm. 

Seventh  Month. — The  pupillary  membrane  atrophies  and  the  eyehds  are  open.  The  testis 
descends  with  the  vaginal  sac  of  the  peritoneum.  From  vertex  to  heels  the  total  length  at  the 
end  of  the  seventh  month  is  from  35  to  36  cm.    The  weight  is  a  little  over  three  pounds. 

Eighth  Month. — The  skin  assumes  a  pink  color  and  is  now  entirely  coated  with  vemix  caseosa, 
and  the  lanugo  begins  to  disappear.  Subcutaneous  fat  has  been  developed  to  a  considerable 
extent,  and  the  fetus  presents  a  plump  appearance.  The  total  length,  i.  e.,  from  head  to  heels, 
at  the  end  of  the  eighth  month  is  about  40  cm.,  and  the  weight  varies  between  four  and  one-half 
and  five  and  one-half  pounds. 

Ninth  Month. — The  lanugo  has  largely  disappeared  from  the  trunk.  The  umbilicus  is  almost 
in  the  middle  of  the  body  and  the  testes  are  in  the  scrotum.  At  full  time  the  fetus  weighs  from 
aix  and  one-half  to  eight  poimds,  and  measures  from  head  to  heels  about  50  cm. 


Il 


BIBLIOGRAPHY. 


I 


Broman:     Normale  und  abnorme  Entwicklung  des  Menschen,  1911. 

Bryce,  Teacher  and  Kerr:    Contributions  to  the  Study  of  the  Early  Development  and 
Imbedding  of  the  Human  Ovum,  1908. 

Hertwig,  O.:     Handbuch   der  Vergleichenden  und  ExperimenteUen  Entwicklungslehre  der 
Wirbeltiere,  1906. 

His,  W.  :     Anatomie  menschlicher  Embryonen,  1880-1885. 
•  Hochstetter,  F.:     Bil der  der  ausserenKoperformeiniger  menschlicher  Embryonen  aus  den 
beiden  ersten  Monaten  der  Entwicklung,  1907. 

Keibel  and  Elze:     Normentafel  zur  Entwicklimgsgeschichte  des  Menschen,  1908. 

Keibel  and  Mall:     Manual  of  Human  Embryology,  1910-1912. 

KoLLMANN,  J.:     Handatlas  der  Entwicklimgsgeschichte  des  Menschen,  1907. 

tKoLLMANN,  J.:     Lehrbuch  der  Entwicklungsgeschichte  des  Menschen,  1898. 
Mall:     Contribution  to  the  Study  of  the  Pathology  of  the  Human  Embryo,  Jour,  of  Morph., 
908.    See  also  contributions  to  Embryology  of  the  Carnegie  Institution  of  Washington. 
Mall:     Development  of  the  Human  Coelom,  Jour,  of  Morph.,  1897. 

Peters,  H.:    Ueber  die  Einbettung  des  menschlichen  Eies  und  das  frviheste  bisher  bekannte 
menschliche  Placentationsstadium,  1899. 


OSTEOLOGY. 


^ 


rriHE  general  framework  of  the  body  is  built  up  mainh'  of  a  series  of  bones, 
-'-  supplemented,  however,  in  certain  regions  by  pieces  of  cartilage;  the  bony 
part  of  the  framework  constitutes  the  skeleton. 

In  the  skeleton  of  the  adult  there  are  206  distinct  bones,  as  follows: — 


Axial 
Skeleton 


Appendicular 
Skeleton 


Vertebral  column 
Skull    .... 
Hyoid  bone    . 
Ribs  and  sternum 


f  Upper  extremities 
\  Lower  extremities 


Auditory  ossicles 


^ 


Total 


26 

22 

1 

25 

—  74 
64 

62 

—  126 

6 

206 


The  patellse  are  included  in  this  enumeration,  but  the  smaller  sesamoid  bones 
are  not  reckoned. 

Bones  are  divisible  into  four  classes:  Long,  Short,  Flat,  and  Irregular, 
Long  Bones. — The  long  bones  are  found  in  the  limbs,  and  each  consists  of  a  body 
or  shaft  and  two  extremities.  The  body,  or  diaphysis  is  cylindrical,  with  a  central 
cavity  termed  the  medullary  canal;  the  ^all  consists  of  dense,  compact  tissue 
of  considerable  thickness  in  the  middle  part  of  the  body,  but  becoming  thinner 
toward  the  extremities;  within  the  medullary  canal  is  some  cancellous  tissue, 
scanty  in  the  middle  of  the  body  but  greater  in  amount  toward  the  ends.  The 
extremities  are  generally  expanded,  for  the  purposes  of  articulation  and  to  afford 
broad  surfaces  for  muscular  attachment.  They  are  usually  developed  from  sep- 
arate centers  of  ossification  termed  epiphyses,  and  consist  of  cancellous  tissue 
surrounded  by  thin  compact  bone.  The  medullary  canal  and  the  spaces  in  the 
cancellous  tissue  are  filled  with  marrow.  The  long  bones  are  not  straight,  but 
curved,  the  curve  generally  taking  place  in  two  planes,  thus  affording  greater 
strength  to  the  bone.  The  bones  belonging  to  this  class  are:  the  clavicle,  humerus, 
radius,  ulna,  femur,  tibia,  fibula,  metacarpals,  metatarsals,  and  phalanges. 

Short  Bones. — Where  a  part  of  the  skeleton  is  intended  for  strength  and  com- 
pactness combined  with  limited  movement,  it  is  constructed  of  a  number  of  short 
bones,  as  in  the  carpus  and  tarsus.  These  consist  of  cancellous  tissue  covered 
by  a  thin  crust  of  compact  substance.     The  patellae,  together  with  the  other 

.  sesamoid  bones,  are  by  some  regarded  as  short  bones. 

Flat  Bones. — Where  the  principal  requirement  is  either  extensive  protection  or 
the  provision  of  broad  surfaces  for  muscular  attachment,  the  bones  are  expanded 
into  broad,  flat  plates,  as  in  the  skull  and  the  scapula.    These  bones  are  composed 

^  of  two  thin  layers  of  compact  tissue  enclosing  between  them  a  variable  quantity 
of  cancellous  tissue.    In  the  cranial  bones,  the  layers  of  compact  tissue  are  famili- 

\  arly  known  as  the  tables  of  the  skull;  the  outer  one  is  thick  and  tough;  the  inner 
is  thin,  dense,  and  brittle,  and  hence  is  termed  the  vitreous  table.    The  intervening 

(79) 


JTEOLOGY 


I 


I 


cancellous  tissue  is  called  the  diploe,  and  this,  in  certain  regions  of  the  skull, 
becomes  absorbed  so  as  to  leave  spaces  filled  with  air  (air-sinuses)  between 
the  two  tables.  The  flat  bones  are:  the  occipital,  parietal,  frontal,  nasal,  lacrimal, 
vomer,  scapula,  os  coxae  {Jiip  hone),  sternum,  ribs,  and,  according  to  some,  tht- 
patella. 

Irregular  Bones. — The  irregular  bones  are  such  as,  from  their  peculiar  form] 
cannot  be  grouped  under  the  preceding  heads.  They  consist  of  cancellous  tissue 
enclosed  within  a  thin  layer  of  compact  bone.  The  irregular  bones  are:  the 
vertebrae,  sacrum,  coccjrx,  temporal,  sphenoid,  ethmoid,  zygomatic,  maxilla,  mandible, 
palatine,  inferior  nasal  concha,  and  hyoid.  _d^m 

Surfaces  of  Bones. — If  the  surface  of  a  bone  be  examined,  certain  eminence^iJH 
and  depressions  are  seen.  These  eminences  and  depressions  are  of  two  kinds:  ' 
articular  and  non-articular.  Well-marked  examples  of  articular  eminences  are 
found  in  the  heads  of  the  humerus  and  femur;  and  of  articular  depressions  in  the 
glenoid  cavity  of  the  scapula,  and  the  acetabulum  of  the  hip  bone.  Non-articular 
eminences  are  designated  according  to  their  form.  Thus,  a  broad,  rough,  uneven 
elevation  is  called  a  tuberosity,'  protuberance,  or  process,  a  small,  rough  prominence, 
a  tubercle ;  a  sharp,  slender  pointed  eminence,  a  spine ;  a  narrow,  rough  elevation, 
running  some  way  along  the  surface,  a  ridge,  crest,  or  line.  Non-articular  depres- 
sions are  also  of  variable  form,  and  are  described  as  fossae,  pits,  depressions,  grooves, 
furrows,  fissures,  notches,  etc.  These  non-articular  eminences  and  depressions  serve 
to  increase  the  extent  of  surface  for  the  attachment  of  ligaments  and  muscles,  and 
are  usually  well-marked  in  proportion  to  the  muscularity  of  the  subject.  A  short 
perforation  is  called  a  foramen,  a  longer  passage  a  canal. 

DEVELOPMENT  OF  THE  SKELETON. 

The  Skeleton. — The  skeleton  is  of  mesodermal  origin,  and  may  be  divided  into 
(a)  that  of  the  trunk  (axial  skeleton),  comprising  the  vertebral  column,  skull,  ribs, 
and  sternum,  and  (6)  that  of  the  limbs  (appendicular  skeleton). 

The  Vertebral  Column.- — The  notochord  (Fig.  19)  is  a  temporary  structure  and 
forms  a  central  axis,  around  which  the  segments  of  the  vertebral  column  are  devel- 
oped.^ It  is  derived  from  the  entoderm,  and  consists  of  a  rod  of  cells,  which  lies 
on  the  ventral  aspect  of  the  neural  tube  and  reaches  from  the  anterior  end  of  the 
mid-brain  to  the  extremity  of  the  tail.  On  either  side  of  it  is  a  column  of  paraxial 
mesoderm  which  becomes  subdivided  into  a  number  of  more  or  less  cubical  seg- 
ments, the  primitive  segments  (Figs.  19  and  20).  These  are  separated  from  one 
another  by  intersegmental  septa  and  are  arranged  symmetrically  on  either  side  of 
the  neural  tube  and  notochord:  to  every  segment  a  spinal  nerve  is  distributed. 
At  first  each  segment  contains  a  central  cavity,  the  myoccEl,  but  this  is  soon  filled 
■with  a  core  of  angular  and  spindle-shaped  cells.  The  cells  of  the  segment  become 
differentiated  into  three  groups,  which  form  respectively  the  cutis-plate  or  derma- 
tome, the  muscle-plate  or  myotome,  and  the  sclerotome  (Fig.  64).  The  cutis-plate 
is  placed  on  the  lateral  and  dorsal  aspect  of  the  myoccel,  and  from  it  the  true  skin 
of  the  corresponding  segment  is  derived ;  the  muscle-plate  is  situated  on  the  medial 
side  of  the  cutis-plate  and  furnishes  the  muscles  of  the  segment.  The  cells  of  the 
sclerotome  are  largely  derived  from  those  forming  the  core  of  the  myocoel,  and  lie 
next  the  notochord.  Fusion  of  the  individual  sclerotomes  in  an  antero-posterior 
direction  soon  takes  place,  and  thus  a  continuous  strand  of  cells,  the  sclerotogenous 
layer,  is  formed  along  the  ventro-lateral  aspects  of  the  neural  tube.  The  cells  of 
this  layer  proliferate  rapidly,  and  extending  medialward  surround  the  notochord; 
at  the  same  time  they  grow  backward  on  the  lateral  aspects  of  the  neural  tube 
and  eventually  surround  it,  and  thus  the  notochord  and  neural  tube  are  enveloped 

'  In  the  amphioxus  the  notochord  persists  and  forms  the  only  representative  of  a  skeleton  in  that  animal. 


DEVELOPMENT  OF  THE  SKELETON 


81 


i 

I 


by  a  continuous  sheath  of  mesoderm,  which  is  termed  the  membranous  vertebral 
column.  In  this  mesoderm  the  original  segments  are  still  distinguishable,  but  each 
is  now  differentiated  into 
two  portions,  an  anterior, 
consisting  of  loosely  arranged 
cells,  and  a  posterior,  of 
more  condensed  tissue  (Fig. 
65,  A  and  B) .  Between  the 
two  portions  the  rudiment 
of  the  intervertebral  fibro- 
cartilage  is  laid  down  (Fig. 
65,  C).  Cells  from  the  pos- 
terior mass  grow  into  the 
intervals  between  the  myo- 
tomes (Fig.  65,  B  and  C)  of 
the  corresponding  and  suc- 
ceeding segments,  and  extend 
both  dorsally  and  ventrally; 
the  dorsal  extensions  sur- 
round the  neural  tube  and 
represent  the  future  verte- 
bral arch,  while  the  ventral 
extend  into  the  body-wall 
as  the  costal  processes.  The 
hinder  part  of  the  posterior 
mass  joins  the  anterior  mass 
of  the  succeeding  segment 
to  form  the  vertebral  body. 
Each  vertebral  body  is  there- 
fore a  composite  of  two  segments,  being  formed  from  the  posterior  portion  of 
one  segment  and  the  anterior  part  of  that  immediately  behind  it.    The  vertebral 


Fio.  64. — Transverse  section  of  a  human  embryo  of  the  third  week 
to  show  the  dififerentiation  of  the  primitive  segment.  (Kollmann.)  ao. 
Aorta.  m.p.  Muscle-plate,  n.c.  Neural  canal,  sc.  Sclerotome,  s  p. 
cutis-plate. 


Myotome 


Anterior  portion  of  sclerotome 
Notochord 

Posterior  portion  of  sclerotome. 
Intermyolomic  septum 
Costal  process 


'?\ 


Ml  it 


Intervertebral 
fibrocartilage 

Notochord 


Centr 


ISJiii; 


iv;:j 


::*.:: 


m^ 


"tiiiVrr?) 


;;;:: 


/tUli»4i.«»'»«jL      AV.  ••«.... I. i.\ 


/1 1 1  •  I  i  r:  t  r : !!  J  V,  1 '  >?••.".'.*.♦•  i  •  •  u  j  » 
(., . .'. « .V.V,\ .•; \\  I  /•.•:;.v/....;.'.,<3 


B 


FiQ.  65. — Scheme  showing  the  manner  in  which  each  vertebral  centrum  is  developed  from  portions  of  two  adjacent 

segments. 


I 


and  costal  arches  are  derivatives  of  the  posterior  part  of  the  segment  in  front 
of  the  intersegmental  septum  with  which  they  are  associated. 
6 


OSTEOLOGY 


I 


This  stage  is  succeeded  by  that  of  the  cartilaginous  vertebral  column.     In  the 
fourth  week  two  cartilaginous  centers  make  their  appearance,  one  on  either  side  o^^ 
the  notochord;  these  extend  around  the  notochord  and  form  the  body  of  the  cartil-^U 
aginous  vertebra.    A  second  pair  of  cartilaginous  foci  appear  in  the  lateral  parts  of 
the  vertebral  bow,  and  grow  backward  on  either  side  of  the  neural  tube  to  form  ^  ,_ 
the  cartilaginous  vertebral  arch,  and  a  separate  cartilaginous  center  appears  foilMfl 
each  costal  process.    By  the  eighth  week  the  cartilaginous  arch  has  fused  with  the 
body,  and  in  the  fourth  month  the  two  halves  of  the  arch  are  joined  on  the  dorsal 
aspect  of  the  neural  tube.    The  spinous  process  is  developed  from  the  junction  of 
the  two  halves  of  the  vertebral  arch.    The  transverse  process  grows  out  from  the, 
vertebral  arch  behind  the  costal  process. 

In  the  upper  cervical  vertebrae  a  band  of  mesodermal  tissue  connects  the  ends  of 
the  vertebral  arches  across  the  ventral  surfaces  of  the  intervertebral  fibrocartilages. 
This  is  termed  the  hypochordal  bar  or  brace;  in  all  except  the  first  it  is  transitory 
and  disappears  by  fusing  with  the  fibrocartilages.  In  the  atlas,  however,  the  entire 
bow  persists  and  undergoes  chondrification;  it  develops  into  the  anterior  arch  of  the 
bone,  while  the  cartilage  representing  the  body  of  the  atlas  forms  the  dens  or 
odontoid  process  which  fuses  with  the  bod}^  of  the  second  cervical  vertebra. 


Anterior 

longitudiiial 

ligamevt 


Posterior  lo7igiludinal 

ligament 
Cartilaginous  end 

of  vertebral  body 

Nucleus  puljmsus 

Intervertebral  fibro- 
cartilage 

Slight  enlargement 
of  notochord  in 
the  cartilaginous 
vertebral  body 


Fig.  66. — Sagittal  section  through  an  intervertebral  fibrocartilage  and  adjacent  parts  of  two  vertebrae  of  an  advanced 

sheep's  embryo.     (KoUiker.) 

The  portions  of  the  notochord  which  are  surrounded  by  the  bodies  of  the  verte- 
brae atrophy,  and  ultimately  disappear,  while  those  which  lie  in  the  centers  of  the 
intervertebral  fibrocartilages  undergo  enlargement,  and  persist  throughout  life  as 
the  central  nucleus  pulposus  of  the  fibrocartilages  (Fig.  66). 

The  Ribs. — The  ribs  are  formed  from  the  ventral  or  costal  processes  of  the 
primitive  vertebral  bows,  the  processes  extending  between  the  muscle-plates.  In 
the  thoracic  region  of  the  vertebral  column  the  costal  processes  grow  lateralward  to 
form  a  series  of  arches,  the  primitive  costal  arches.  As  already  described,  the 
transverse  process  grows  out  behind  the  vertebral  end  of  each  arch.  It  is  at  first 
connected  to  the  costal  process  by  continuous  mesoderm,  but  this  becomes  differ- 
entiated later  to  form  the  costotransverse  ligament;  between  the  costal  process 
and  the  tip  of  the  transverse  process  the  costotransverse  joint  is  formed  by 
absorption.  The  costal  process  becomes  separated  from  the  vertebral  bow  by  the 
development  of  the  costocentral  joint.  In  the  cervical  vertebroB  (Fig.  67)  the  trans- 
verse process  forms  the  posterior  boundary  of  the  foramen  transversarium,  while 
the  costal  process  corresponding  to  the  head  and  neck  of  the  rib  fuses  with  the 


I 


DEVELOPMENT  OF  THE  SKELETON 


83 


body  of  the  vertebra,  and  forms  the  antero-lateral  boundary  of  the  foramen.  The 
distal  portions  of  the  primitive  costal  arches  remain  undeveloped;  occasionally 
the  arch  of  the  seventh  cervical  vertebra  undergoes  greater  development,  and  by 
the  formation  of  costovertebral  joints  is  separated  off  as  a  rib.  In  the  lumbar 
region  the  distal  portions  of  the  primitive  costal  arches  fail ;  the  proximal  portions 
fuse  with  the  transverse  processes  to  form  the  transverse  processes  of  descriptive 
anatomy.  Occasionally  a  movable  rib  is  developed  in  connection  with  the  first 
lumbar  vertebra.  In  the  sacral  region  costal  processes  are  developed  only  in 
connection  with  the  upper  three,  or  it  may  be  four,  vertebrae;  the  processes  of 
adjacent  segments  fuse  with  one  another  to  form  the  lateral  parts  of  the  sacrum. 
The  coccygeal  vertebrcs  are  devoid  of  costal  processes. 


CERVICAL 


LUMBAR 


THORACIC 


SACRAL 


I 


Fig.  67. — Diagrams  showing  the  portions  of  the  adult  vertebrse  derived  respectively  from  the  bodies,  vertebral 
arches,  and  costal  processes  of  the  embrj'onic  vertebrse.  The  bodies  are  represented  in  yellow,  the  vertebral  arches 
in  red,  and  the  costal  processes  in  blue. 

The  Sternum. — The  ventral  ends  of  the  ribs  become  united  to  one  another  by  a 
longitudinal  bar  termed  the  sternal  plate,  and  opposite  the  first  seven  pairs  of  ribs 
these  sternal  plates  fuse  in  the  middle  line  to  form  the  manubrium  and  body  of  the 
sternum.  The  xiphoid  process  is  formed  by  a  backward  extension  of  the  sternal 
plates. 

The  Skull. — Up  to  a  certain  stage  the  development  of  the  skull  corresponds  with 
that  of  the  vertebral  column;  but  it  is  modified  later  in  association  with  the  expan- 
sion of  the  brain-vesicles,  the  formation  of  the  organs  of  smell,  sight,  and  hearing, 
and  the  development  of  the  mouth  and  pharynx. 


84 


OSTEOLOGY 


I 


Fossa 
hypophyseos 


Mesoderm  of  base 
of  skull 


Parachordal 
cartilage 


The  notochord  extends  as  far  forward  as  the  anterior  end  of  the  mid-brain,  and 
becomes  partly  surrounded  by  mesoderm  (Fig.  68) .  The  posterior  part  of  this  meso- 
dermal investment  corresponds  with  the  basilar  part  of  the  occipital  bone,  and  show  s 
a  subdivision  into  four  segments,  which  are  separated  by  the  roots  of  the  hypo- 
glossal nerve.    The  mesoderm  then  extends  over  the  brain-vesicles,  and  thus  the 

entire  brain  is  enclosed  by  a  mesodermal 
investment,  which  is  termed  the  membran- 
ous cranium.  From  the  inner  layer  of  this 
the  bones  of  the  skull  and  the  membranes 
of  the  brain  are  developed ;  from  the  outer 
laj^er  the  muscles,  bloodvessels,  true  skin, 
and  subcutaneous  tissues  of  the  scalp.  In 
the  shark  and  dog-fish  this  membranous 
cranium  undergoes  complete  chondrifi- 
cation,  and  forms  the  cartilaginous  skull 
or  chondrocranium  of  these  animals.  In 
mammals,  on  the  other  hand,  the  process 
of  chondrification  is  limited  to  the  base 
of  the  skull — ^the  roof  and  sides  being 
covered  in  by  membrane.  Thus  the  bones 
of  the  base  of  the  skull  are  preceded  by 
cartilage,  those  of  the  roof  and  sides 
by  membrane.  The  posterior  part  of  the 
base  of  the  skull  is  developed  around 
the  notochord,  and  exhibits  a  segmented 
condition  analogous  to  that  of  the  vertebral  column,  while  the  anterior  part  arises 
in  front  of  the  notochord  and  shows  no  regular  segmentation.  The  base  of  the  skull 
may  therefore  be  divided  into  (a)  a  chordal  or  vertebral,  and  (b)  a  prechordal  or 
prevertebral  portion. 

SitvMion  of  olfactory  pit     Ethmoid  plate 

and  nasal    Olfactory  organ 


Anterior  arch  of  atlas 

Notochord 

Body  of  axis 

Third  cervical 
vertebra 


Fio.  68. — Sagittal  section  of  ceplialic   end  ot 
chord.    (Keibel.) 


Fossa 
hypophyseos 


Trabecvla 
cranii 

SitvMion  of 

avditory 

vesicle 

Parachordal 

cartilage 

Notochord 


Extension  around 
7       olfactory  organ 
Foramina  for 
olfactory  nerves 

.  Eyeball 

Fossa 
~  hypophyseos 


—  Basilar  plate 
--Auditory  vesicle 

•Notochord 


Fig.  69. — Diagrams  of  the  cartilaginous  cranium.     (Wiedersheim. 

In  the  lower  vertebrates  two  pairs  of  cartilages  are  developed,  viz.,  a  pair  of 
parachordal  cartilages,  one  on  either  side  of  the  notochord;  and  a  pair  of  pre- 
chordal cartilages,  the  trabeculse  cranii,  in  front  of  the  notochord  (Fig.  66).  The 
parachordal  cartilages  (Fig.  69)  unite  to  form  a  basilar  plate,  from  which  the  car- 
tilaginous part  of  the  occipital  bone  and  the  basi-sphenoid  are  developed.  On  the 
lateral  aspects  of  the  parachordal  cartilages  the  auditory  vesicles  are  situated, 


I 


DEVELOPMENT  OF  THE  SKELETON 


85 


and  the  mesoderm  enclosing  them  is  soon  converted  into  cartilage,  forming  the 
cartilaginous  ear-capsules.  These  cartilaginous  ear-capsules,  which  are  of  an  oval 
shape,  fuse  with  the  sides  of  the  basilar  plate,  and  from  them  arise  the  petrous 
and  mastoid  portions  of  the  temporal  bones.  The  trabeculse  cranii  (Fig.  69)  are 
two  curved  bars  of  cartilage  which  embrace  the  hypophysis  cerebri;  their  posterior 
ends  soon  unite  with  the  basilar  plate,  while  their  anterior  ends  join  to  form  the 
ethmoidal  plate,  which  extends  forward  between  the  fore-brain  and  the  olfactory 
pits.    Later  the  trabeculse  meet  and  fuse  below  the  hypophysis,  forming  the  floor 


Crista  gain 


Cribriform  plate 


Meckel's  cartilage 
Malleus 
I71CUS 

Jnt.  acoustic  meat. 
Jugular  foramen 
Tossa  svbarcuata 


janal  for  hypoglossal  nerve 


Small  wing  of  sphenoid 
Optic  foramen 


-Great  wing  of 

sphenoid 

Sella  turcica 

Dorsum  seUce 


Canal  for  facial 
nerve 

Ear  capsule 
Ihictus  endal. 


Foramen  magnum 


FiQ.  70. — Model  of  the  chondrocranium  of  a  human  embryo,  8  cm.  long. 

not  represented. 


(Hertwig.)      The  membrane  bones  are 


of  the  fossa  hypophyseos  and  so  cutting  off  the  anterior  lobe  of  the  hypophysis 
from  the  stomodeum.  The  median  part  of  the  ethmoidal  plate  forms  the  bony 
and  cartilaginous  parts  of  the  nasal  septum.  From  the  lateral  margins  of  the 
trabeculse  cranii  three  processes  grow  out  on  either  side.  The  anterior  forms  the 
ethmoidal  labyrinth  and  the  lateral  and  alar  cartilages  of  the  nose;  the  middle 
gives  rise  to  the  small  wing  of  the  sphenoid,  while  from  the  posterior  the  great 
wing  and  lateral  pterygoid  plate  of  the  sphenoid  are  developed  (Figs.  70,  71). 
The  bones  of  the  vault  are  of  membranous  formation,  and  are  termed  dermal  or 
covering  bones.    They  are  partly  developed  from  the  mesoderm  of  the  membranous 


OSTEOLOGY 


I 


cranium,  and  partly  from  that  which  lies  outside  the  entoderm  of  the  fore- 
gut.  They  comprise  the  upper  part  of  the  occipital  squama  (interparietal),  th(^ 
squamse  and  tympanic  parts  of  the  temporals,  the  parietals,  the  frontal,  the  vomer, 
the  medial  pterygoid  plates,  and  the  bones  of  the  face.  Some  of  them  remain 
distinct  throughout  life,  e.  g.,  parietal  and  frontal,  while  others  join  with  the  bones 
of  the  chondrocranium,  e.  g.,  interparietal,  squamae  of  temporals,  and  medial 
pterygoid  plates. 

Recent  observations  have  shown  that,  in  mammals,  the  basi-cranial  cartilage, 
both  in  the  chordal  and  prechordal  regions  of  the  base  of  the  skull,  is  developed 
as  a  single  plate  which  extends  from  behind  forward.  In  man,  however,  its  posterior 
part  shows  an  indication  of  being  developed  from  two  chondrifying  centers  which 
fuse  rapidly  in  front  and  below.  The  anterior  and  posterior  thirds  of  the  cartilage 
surround  the  notochord,  but  its  middle  third  lies  on  the  dorsal  aspect  of  the  noto- 
chord,  which  in  this  region  is  placed  between  the  cartilage  and  the  wall  of  the 
pharynx. 


Optic  foramen    Small  wing  of  sphenoid 


Great  wing  of  sphenoid 


Nasal 
capsiUe 


Vomer 


Palattne 
bone 


Mandible 


Cricoid  cart. 

Thyroid  cart. 


Styloid  process 
Fen.  cochlew 


Canal  for  hypoglossal 

nerve 


Fio.  71. — The  same  model  as  shown  in  Fig.  70  from  the  left  side.    Certain  of  the  membrane  bones  of  the  right  side 

are  represented  in  yellow.     (Hertwig.) 


BONE 

Structure  and  Physical  Properties. — Bone  is  one  of  the  hardest  structures  of 
the  animal  body;  it  possesses  also  a  certain  degree  of  toughness  and  elasticity. 
Its  color,  in  a  fresh  state,  is  pinkish-white  externally,  and  deep  red  within.  On 
examining  a  section  of  any  bone,  it  is  seen  to  be  composed  of  two  kinds  of  tissue, 
one  of  which  is  dense  in  texture,  like  ivory,  and  is  termed  compact  tissue;  the  other 
consists  of  slender  fibers  and  lamellae,  which  join  to  form  a  reticular  structure; 
this,  from  its  resemblance  to  lattice-work,  is  called  cancellous  tissue.  The  compact 
tissue  is  always  placed  on  the  exterior  of  the  bone,  the  cancellous  in  the  interior. 
The  relative  quantity  of  these  two  kinds  of  tissue  varies  in  different  bones,  and 
in  different  parts  of  the  same  bone,  according  as  strength  or  lightness  is  requisite. 
Close  examination  of  the  compact  tissue  shows  it  to  be  extremely  porous,  so  that 
the  difference  in  structure  between  it  and  the  cancellous  tissue  depends  merely 
upon  the  different  amount  of  solid  matter,  and  the  size  and  number  of  spaces  in 
each;  the  cavities  are  small  in  the  compact  tissue  and  the  solid  matter  between 


I 


BONE 


87 


them  abundant,  while  in  the  cancellous  tissue  the  spaces  are  large  and  the  solid 
matter  is  in  smaller  quantity. 

Bone  during  life  is  permeated  by  vessels,  and  is  enclosed,  except  where  it  is 
coated  with  articular  cartilage,  in  a  fibrous  membrane,  the  periosteum,  by  means 
of  which  many  of  these  vessels  reach  the  hard  tissue.  If  the  periosteum  be  stripped 
from  the  surface  of  the  living  bone,  small  bleeding  points  are  seen  which  mark  the 
entrance  of  the  periosteal  vessels;  and  on  section  during  life  every  part  of  the 
bone  exudes  blood  from  the  minute  vessels  which  ramify  in  it.  The  interior  of 
each  of  the  long  bones  of  the  limbs  presents  a  cylindrical  cavity  filled  with  marrow 
and  lined  by  a  highly  vascular  areolar  structure,  called  the  medullary  membrane. 

The  Strength  of  Bone  Compared  with  other  Materials 


Substance. 


Weight  in 
pounds  per 
cubic  foot. 


Ultimate  strength. 
Pounds  per  square  inch. 


Tension. 


Compression. 


Shear. 


I 


Medium  steel 490  65,000  |      60,000 

Granite 170  1,500  15,000 

Oak,  white 46  12,500^  7,000^ 

Compact  bone  (low) 119  13,200^  18,000i 

Compact  bone  (high) I     i       17,700^  ;       24,000i 


40,000 
2,000 
4,0002 

11,800'' 
7,1601 


Periosteirai. — ^The  periosteum  adheres  to  the  surface  of  each  of  the  bones  in 
nearly  every  part,  but  not  to  cartilaginous  extremities.  When  strong  tendons  or 
ligaments  are  attached  to  a  bone,  the  periosteum  is  incorporated  with  them.  It 
consists  of  two  layers  closely  united  together,  the  outer  one  formed  chiefly  of 
connective  tissue,  containing  occasionally  a  few  fat  cells;  the  inner  one,  of  elastic 
fibers  of  the  finer  kind,  forming  dense  membranous  networks,  which  again  can  be 
separated  into  several  layers.  In  young  bones  the  periosteum  is  thick  and  very 
vascular,  and  is  intimately  connected  at  either  end  of  the  bone  with  the  epiphysial 
cartilage,  but  less  closely  with  the  body  of  the  bone,  from  which  it  is  separated  by 
a  layer  of  soft  tissue,  containing  a  number  of  granular  corpuscles  or  osteoblasts,  by 
which  ossification  proceeds  on  the  exterior  of  the  young  bone.  Later  in  life  the 
periosteum  is  thinner  and  less  vascular,  and  the  osteoblasts  are  converted  into  an 
epithelioid  layer  on  the  deep  surface  of  the  periosteum.  The  periosteum  serves 
as  a  nidus  for  the  ramification  of  the  vessels  previous  to  their  distribution  in  the 
bone;  hence  the  liability  of  bone  to  exfoliation  or  necrosis  when  denuded  of  this 
membrane  by  injury  or  disease.  Fine  nerves  and  lymphatics,  which  generally 
accompany  the  arteries,  may  also  be  demonstrated  in  the  periosteum. 

Marrow. — The  marrow  not  only  fills  up  the  cylindrical  cavities  in  the  bodies  of 
the  long  bones,  but  also  occupies  the  spaces  of  the  cancellous  tissue  and  extends 
into  the  larger  bony  canals  (Haversian  canals)  which  contain  the  bloodvessels. 
It  differs  in  composition  in  different  bones.  In  the  bodies  of  the  long  bones  the 
marrow  is  of  a  yellow  color,  and  contains,  in  100  parts,  96  of  fat,  1  of  areolar  tissue 
and  vessels,  and  3  of  fluid  with  extractive  matter;  it  consists  of  a  basis  of  connective 
tissue  supporting  numerous  bloodvessels  and  cells,  most  of  which  are  fat  cells 
but  some  are  "marrow  cells,"  such  as  occur  in  the  red  marrow  to  be  immediately 
described.  In  the  flat  and  short  bones,  in  the  articular  ends  of  the  long  bones, 
in  the  bodies  of  the  vertebrae,  in  the  cranial  diploe,  and  in  the  sternum  and  ribs 
the  marrow  is  of  a  red  color,  and  contains,  in  100  parts,  75  of  water,  and  25  of  solid 
matter  consisting  of  cell-globulin,  nucleoprotein,  extractives,  salts,  and  only  a 
small  proportion  of  fat.  The  red  marrow  consists  of  a  small  quantity  of  connective 
tissue,  bloodvessels,  and  numerous  cells  (Fig.  72),  some  few  of  which  are  fat  cells, 

1  Indicates  stresses  with  the  grain,  j.  e.,  when  the  load  is  parallel  to  the  long  axis  of  the  material,  or  parallel  to  the 
direction  of  the  fibers  of  the  material. 

2  Indicates  unit-stresses  across  the  grain,  i.  e.,  at  right  angles  to  the  direction  of  the  fibers  of  the  material. 


OSTEOLOGY 

but  the  great  majority  are  roundish  nucleated  cells,  the  true  "marrow  cells' 
of  Kolliker.  These  marrow  cells  proper,  or  myelocjrtes,  resemble  in  appearance' 
lymphoid  corpuscles,  and  like  them  are  ameboid;  they  generally  have  a  hyalin<j 
protoplasm,  though  some  show  granules  either  oxyphil  or  basophil  in  reaction. 
A  number  of  eosinophil  cells  are  also  present.  Among  the  marrow  cells  may  be 
seen  smaller  cells,  which  possess  a  slightly  pinkish  hue;  these  are  the  erythroblasts 
or  normoblasts,  from  which  the  red  corpuscles  of  the  adult  are  derived,  and  which 
may  be  regarded  as  descendants  of  the  nucleated  colored  corpuscles  of  the  embryo. 
Giant  cells  (myeloj^laxes,  osteoclasts),  large,  multinucleated,  protoplasmic  masses, 
are  also  to  be  found  in  both  sorts  of  adult  marrow,  but  more  particularly  in  red 
marrow.  They  were  believed  by  Kolliker  to  be  concerned  in  the  absorption  of 
bone  matrix,  and  hence  the  name  which  he  gave  to  them — osteoclasts.  They 
excavate  in  the  bone  small  shallow  pits  or  cavities,  which  are  named  Howship's 
foveolse,  and  in  these  they  are  found  lying. 


Normoblast  with  dividing  nucleus 


Myelocyte  • 


Erythrocyte  — '^^ 


Myeloplaxe  — '>- — 


Myelocyte ' 


Faf 


[__  Eosinophil 
cell 


11-  Normoblasts 

.L_  Myelocyte 
dividing 

"  Myelocyte 


FiQ.  72. — Human  bone  marrow.     Highly  magnified. 

Vessels  and  Nerves  of  Bone. — The  bloodvessels  of  bone  are  very  numerous.  Those 
of  the  compact  tissue  are  derived  from  a  close  and  dense  network  of  vessels  ramify- 
ing in  the  periosteum.  From  this  membrane  vessels  pass  into  the  minute  orifices 
in  the  compact  tissue,  and  run  through  the  canals  which  traverse  its  substance. 
The  cancellous  tissue  is  supplied  in  a  similar  way,  but  by  less  numerous  and  larger 
vessels,  which,  perforating  the  outer  compact  tissue,  are  distributed  to  the  cavities 
of  the  spongy  portion  of  the  bone.  In  the  long  bones,  numerous  apertures  may 
be  seen  at  the  ends  near  the  articular  surfaces;  some  of  these  give  passage  to  the 
arteries  of  the  larger  set  of  vessels  referred  to;  but  the  most  numerous  and  largest 
apertures  are  for  some  of  the  veins  of  the  cancellous  tissue,  which  emerge  apart 
from  the  arteries.  The  marrow  in  the  body  of  a  long  bone  is  supplied  by  one 
large  artery  (or  sometimes  more),  which  enters  the  bone  at  the  nutrient  foramen 
(situated  in  most  cases  near  the  center  of  the  body),  and  perforates  obliquely  the 
compact  structure.  The  medullary  or  nutrient  artery,  usually  accompanied  by  one 
or  two  veins,  sends  branches  upward  and  downward,  which  ramify  in  the  medul- 
lary membrane,  and  give  twigs  to  the  adjoining  canals.    The  ramifications  of  this 


I 


BONE 


89 


^ 


vessel  anastomose  with  the  arteries  of  the  cancellous  and  compact  tissues.  In  most 
of  the  flat,  and  in  many  of  the  short  spongy  bones,  one  or  more  large  apertures  are 
observed,  which  transmit  to  the  central  parts  of  the  bone  vessels  corresponding  to 
the  nutrient  arteries  and  veins.  The  veins  emerge  from  the  long  bones  in  three 
places  (Kolliker) :  (1)  one  or  two  large  veins  accompany  the  artery;  (2)  numerous 
large  and  small  veins  emerge  at  the  articular  extremities;  (3)  many  small  veins 
pass  out  of  the  compact  substance.  In  the  flat  cranial  bones  the  veins  are  large, 
very  numerous,  and  run  in  tortuous  canals  in  the  diploic  tissue,  the  sides  of  the 
canals  being  formed  by  thin  lamellae  of  bone,  perforated  here  and  there  for  the 
passage  of  branches  from  the  adjacent  cancelli.  The  same  condition  is  also 
found  in  all  cancellous  tissue,  the  veins  being  enclosed  and  supported  by  osseous 
material,  and  having  exceedingly  thin  coats.  When  a  bone  is  divided,  the  vessels 
remain  patulous,  and  do  not  contract  in  the  canals  in  which  they  are  contained. 
L3miphatic  vessels,  in  addition  to  those  found  in  the  periosteum,  have  been  traced 
by  Cruikshank  into  the  substance  of  bone,  and  Klein  describes  them  as  running  in 
the  Haversian  canals.  Nerves  are  distributed  freely  to  the  periosteum,  and  accom- 
pany the  nutrient  arteries  into  the  interior  of  the  bone.  They  are  said  by  Kolliker 
to  be  most  numerous  in  the  articular  extremities  of  the  long  bones,  in  the  vertebrae, 
and  in  the  larger  flat  bones. 


t 


Fig.  73. — Transverse  section  of  compact  tissue  bone.     Magnified.     (Sharpey.) 

Minute  Anatomy. — A  transverse  section  of  dense  bone  may  be  cut  with  a  saw 
and  ground  down  until  it  is  sufficiently  thin. 

If  this  be  examined  with  a  rather  low  power  the  bone  will  be  seen  to-be  mapped 
out  into  a  number  of  circular  districts  each  consisting  of  a  central  hole  surrounded 
by  a  number  of  concentric  rings.  These  districts  are  termed  Haversian  systems; 
the  central  hole  is  an  Haversian  canal,  and  the  rings  are  layers  of  bony  tissue 
arranged  concentrically  around  the  central  canal,  and  termed  lamellae.  More- 
over, on  closer  examination  it  will  be  found  that  between  these  lamellae,  and 
therefore  also  arranged  concentrically  around  the  central  canal,  are  a  number  of 
little  dark  spots,  the  lacimae,  and  that  these  lacunae  are  connected  with  each  other 
a,nd  with  the  central  Haversian  canal  by  a  number  of  fine  dark  lines,  which  radiate 
Uke  the  spokes  of  a  wheel  and  are  called  canaliculi.  Filling  in  the  irregular  intervals 
which  are  left  between  these  circular  systems  are  other  lamellae,  with  their  lacunae 
and  canaliculi  running  in  various  directions,  but  more  or  less  curved  (Fig.  73); 
they  are  termed  interstitial  lamellae.  Again,  other  lamellae,  found  on  the  surface 
f  the  bone,  are  arranged  parallel  to  its  circumference;  they  are  termed  circum- 


90 


OSTEOLOGY 


I 


ferential,  or  by  some  authors  primary  or  fundamental  lamellae,  to  distinguish  them 
from  those  laid  down  around  the  axes  of  the  Haversian  canals,  which  are  then 
termed  secondaiy  or  special  lamellae. 

The  Haversian  canals,  seen  in  a  transverse  section  of  bone  as  round  holes  at  or 
about  the  center  of  each  Haversian  system,  may  be  demonstrated  to  be  true  canah 
if  a  longitudinal  section  be  made  (Fig.  74).  It  will  then  be  seen  that  the  canals 
run  parallel  with  the  longitudinal  axis  of  the  bone  for  a  short  distance  and  then 
branch  and  communicate.  They  vary  considerably  in  size,  some  being  as  much  as 
0.12  mm.  in  diameter;  the  average  size  is,  however,  about  0.05  mm.  Near  the 
medullary  cavity  the  canals  are  larger  than  those  near  the  surface  of  the  bone. 
Each  canal  contains  one  or  two  bloodvessels,  with  a  small  quantity  of  delicate 
connective  tissue  and  some  nerve  filaments.  In  the  larger  ones  there  are  also 
lymphatic  vessels,  and  cells  with  branching  processes  which  communicate,  through 
the  canalculi,  with  the  branched  processes  of  certain  bone  cells  in  the  substance 
of  the  bone.  Those  canals  near  the  surface  of  the  bone  open  upon  it  by  minute 
orifices,  and  those  near  the  medullary  cavity  open  in  the  same  way  into  this  space, 
so  that  the  whole  of  the  bone  is  permeated  by  a  system  of  bloodvessels  running 
through  the  bony  canals  in  the  centers  of  the  Haversian  systems. 

The  lamellae  are  thin  plates  of  bony  tissue 
encircling  the  central  canal,  and  may  be  com- 
pared, for  the  sake  of  illustration,  to  a  number 
of  sheets  of  paper  pasted  one  over  another 
around  a  central  hollow  cylinder.  After 
macerating  a  piece  of  bone  in  dilute  mineral 
acid,  these  lamellae  may  be  stripped  off  in  a 


Fig.  74. — Settion  parallel  to  the  surface 
from  the  body  of  the  femur.  X  100.  o,  Haver- 
sian canals;  b,  lacunffi  seen  from  the  side;  c, 
others  seen  from  the  surface  in  lamellae,  which 
are  cut  horizontally. 


FiQ.  75. — Perforating  fibers,  human  parietal  bone,  decalcified. 
(H.  Muller.)  o,  perforating  fibers  in  situ;  b,  fibres  drawn  out  of 
their  sockets;  c,  sockets. 


longitudinal  direction  as  thin  films.  If  one  of  these  be  examined  with  a  high  power 
of  the  microscope,  it  will  be  found  to  be  composed  of  a  finely  reticular  structure, 
made  up  of  very  slender  transparent  fibers,  decussating  obliquely;  and  coalescing 
at  the  points  of  intersection ;  these  fibers  are  composed  of  fine  fibrils  identical  with 
those  of  white  connective  tissue.  The  intercellular  matrix  between  the  fibers  is 
impregnated  by  calcareous  deposit  which  the  acid  dissolves.  In  many  places  the 
various  lamellae  may  be  seen  to  be  held  together  by  tapering  fibers,  which  run 
obliquely  through  them,  pinning  or  bolting  them  together;  they  were  first  de- 
scribed by  Sharpey,  and  were  named  by  him  perforating  fibers  (Fig.  75). 

The  Lacunae  are  situated  between  the  lamellae,  and  consist  of  a  number  of  oblong 


I 


BONE 


91 


^ 


¥ 


ta 


spaces.  In  an  ordinary  microscopic  section,  viewed  by  transmitted  light,  tliey 
appear  as  fusiform  opaque  spots.  Each  lacuna  is  occupied  during  life  by  a  branched 
cell,  termed  a  bone-cell  or  bone-corpuscle,  the  processes  from  which  extend  into  the 
canaliculi  (Fig.  76). 

The  Canaliculi  are  exceedingly  minute  channels,  crossing  the  lamellae  and  con- 
necting the  lacunae  with  neighboring  lacunae  and  also  with  the  Haversian  canal. 
From  the  Haversian  canal  a  number  of  canaliculi  are  given  off,  which  radiate  from 
it,  and  open  into  the  first  set  of  lacunae  between  the  first  and  second  lamellae. 
From  these  lacunae  a  second  set  of  canaliculi  is  given  off;  these  run  outward  to  the 
next  series  of  lacunae,  and  so  on  until  the  periphery  of  the  Haversian  system  is 
reached;  here  the  canaliculi  given  off  from  the  last  series  of  lacunae  do  not  communi- 
cate with  the  lacunae  of  neighboring  Haversian  systems,  but  after  passing  outward 
for  a  short  distance  form  loops  and  return  to  their  own  lacunae.  Thus  every 
part  of  an  Haversian  system  is  supplied  with  nutrient  fluids  derived  from  the 
vessels  in  the  Haversian  canal  and  distributed 
through  the  canaliculi  and  lacunae. 

The  bone  cells  are  contained  in  the  lacunae, 
which,  however,  they  do  not  completely  fill. 
They  are  flattened  nucleated  branched  cells, 
homologous  with  those  of  connective  tissue;  the 
branches,  especially  in  young  bones,  pass  into 
the  canaliculi  from  the  lacunae. 

In  thin  plates  of  bone  (as  in  the  walls  of 
the  spaces  of  cancellous  tissue)  the  Haversian 
[  canals  are  absent,  and  the  canaliculi  open  into 
the  spaces  of  the  cancellous  tissue  (medullary 
spaces),  which  thus  have  the  same  function  as 
the  Haversian  canals. 

Chemical  Composition. — Bone  consists  of  an 
animal  and  an  earthy  part  intimately  com- 
bined together. 

I  The  animal  part  may  be  obtained  by  immersing  a  bone  for  a  considerable  time 
in  dilute  mineral  acid,  after  which  process  the  bone  comes  out  exactly  the  same 
shape  as  before,  but  perfectly  flexible,  so  that  a  long  bone  (one  of  the  ribs,  for 
example)  can  easily  be  tied  in  a  knot.  If  now  a  transverse  section  is  made 
(Fig.  77)  the  same  general  arrangement  of  the  Haversian  canals,  lamellae,  lacunae, 
and  canaliculi  is  seen. 

The  earthy  part  may  be  separately  obtained  by  calcination,  by  which  the 

animal  matter  is  completely  burnt  out.     The  bone  will  still  retain  its  original 

form,  but  it  will  be  white  and  brittle,  will  have  lost  about  one-third  of  its  original 

I  weight,  and  will  crumble  down  with  the  slightest  force.     The  earthy  matter  is 

I  composed  chiefly  of  calcium  phosphate,  about  58  per  cent,  of  the  weight  of  the 

I  bone,  calcium  carbonate  about  7  per  cent.,  calciimi  fluoride  and  magnesium  phos- 

"  phate  from  1  to  2  per  cent,  each  and  sodium  chloride  less  than  1  per  cent. ;  they  confer 

on  bone  its  hardness  and  rigidity,  while  the  animal  matter  (ossein)  determines  its 

I  tenacity. 
Ossification. — Some  bones  are  preceded  by  membrane,  such  as  those  forming 
the  roof  and  sides  of  the  skull;  others,  such  as  the  bones  of  the  limbs,  are  preceded 
by  rods  of  cartilage.     Hence  two  kinds  of  ossification  are  described:  the  intra- 
membranous  and  the  intracartilaginous. 

(Intramembranous  Ossification. — In  the  case  of  bones  which  are  developed 
in  membrane,  no  cartilaginous  mould  precedes  the  appearance  of  the  bony  tissue. 
The  membrane  which  occupies  the  place  of  the  future  bone  is  of  the  nature  of  con- 
nective tissue,  and  ultimately  forms  the  periosteum;  it  is  composed  of  fibers  and 
granular  cells  in  a  matrix.    The  peripheral  portion  is  more  fibrous,  while,  in  the 


Fig.  76. — Nucleated  bone  cells  and  their 
processes,  contained  in  the  bone  lacunae  and 
their  canaliculi  respectively.  From  a  section 
through  the  vertebra  of  an  adult  mouse. 
(Klein  and  Noble  Smith.) 


92 


OSTEOLOGY 


I 


interior  the  cells  or  osteoblasts  predominate;  the  whole  tissue  is  richly  supplied  with 
bloodvessels.  At  the  outset  of  the  process  of  bone  formation  a  little  network 
of  spicules  is  noticed  radiating  from  the  point  or  center  of  ossification.  These 
rays  consist  at  their  growing  points  of  a  network  of  fine  clear  fibers  and  granular 


Haversian  canal 


Bone  corpuscle 


Bone  corpuscle 
between  inter- 
stitial lamellee 


Fig.  77. — Transverse  section  of  body  of  human  fibula,  decalcified.      X  250. 

corpuscles  with  an  intervening  ground  substance  (Fig.  78).  The  fibers  are  termed 
osteogenetic  fibers,  and  are  made  up  of  fine  fibrils  differing  little  from  those  of  white 
fibrous  tissue.  The  membrane  soon  assumes  a  dark  and  granular  appearance  from 
the  deposition  of  calcareous  granules  in  the  fibers  and  in  the  intervening  matrix, 


Union  of 
adjacent  ~~' 
spicules 


Osteoblasts^^ 


Osteogenetic 
fibers 


Calcified  deposit 

between  the  fibers 


Bony  spicvlea 

FiQ.  78. — Part  of' the  growing  edge  of  the  developing  parietal  bone  of  a  fetal  cat.     (After  J.  Lawrence.) 

and  in  the  calcified  material  some  of  the  granular  corpuscles  or  osteoblasts  are 
enclosed.  By  the  fusion  of  the  calcareous  granules  the  tissue  again  assumes  a 
more  transparent  appearance,  but  the  fibers  are  no  longer  so  distinctly  seen. 
The  involved  osteoblasts  form  the  corpuscles  of  the  future  bone,  the  spaces  in 


I 


BONE 


93 


■ 


which  they  are  enclosed  constituting  the  lacunae.  As  the  osteogenetic  fibers  grow 
out  to  the  periphery  they  continue  to  calcify,  and  give  rise  to  fresh  bone  spicules. 
Thus  a  network  of  bone  is  formed,  the  meshes  of  which  contain  the  bloodvessels 
and  a  delicate  connective  tissue  crowded  with  osteoblasts.  The  bony  trabeculse 
thicken  by  the  addition  of  fresh  layers  of  bone  formed  by  the  osteoblasts  on  their 
surface,  and  the  meshes  are  correspondingly  encroached  upon.  Subsequently, 
successive  layers  of  bony  tissue  are  deposited  under  the  periosteum  and  around 
the  larger  vascular  channels  which  become  the  Haversian  canals,  so  that  the  bone 
increases  much  in  thickness. 

Intercartilaginous  Ossification. — Just  before  ossification  begins  the  mass  is 
entirely  cartilaginous,  and  in  a  long  bone,  which  may  be  taken  as  an  example,  the 
process  commences  in  the  center  and  proceeds  toward  the  extremities,  which  for 
some  time  remain  cartilaginous.  Subsequently  a  similar  process  commences  in 
one  or  more  places  in  those  extremities  and  gradually  extends  through  them. 
The  extremities  do  not,  however,  become  joined  to  the  body  of  the  bone  by  bony 
tissue  until  growth  has  ceased ;  between  the  body  and  either  extremity  a  layer  of 
cartilaginous  tissue  termed  the  epiphysial  cartilage  persists  for  a  definite  period; 

The  first  step  in  the  ossification  of 
the  cartilage  is  that  the  cartilage  cells, 
at  the  point  where  ossification  is  com- 
mencing and  which  is  termed  a  center 
of  ossification,  enlarge  and  arrange 
themselves  in  rows  (Fig.  79).  The 
matrix  in  which  they  are  imbedded 
increases  in  quantity,  so  that  the  cells 
become  further  separated  from  each 
other.  A  deposit  of  calcareous  material 
now  takes  place  in  this  matrix,  between 
the  rows  of  cells,  so  that  they  become 
separated  from  each  other  by  longi- 
tudinal columns  of  calcified  matrix, 
presenting  a  granular  and  opaque  ap- 
pearance. Here  and  there  the  matrix 
between  two  cells  of  the  same  row  also 
becomes  calcified,  and  transverse  bars 
of  calcified  substance  stretch  across 
from  one  calcareous  column  to  another. 
Thus  there  are  longitudinal  groups  of 
the  cartilage  cells  enclosed  in  oblong 
cavities,  the  walls  of  which  are  formed 
of  calcified  matrix  which  cuts  off  all 
nutrition  from  the  cells;  the  cells,  in 
consequence,  atrophy,  leaving  spaces 
called  the  primary  areolae. 

At  the  same  time  that  this  process 
is  going  on  in  the  center  of  the  solid 
bar  of    cartilage,   certain   changes   are 

I  taking  place  on  its  surface.     This  is 

I  covered  by  a  very  vascular  membrane, 

I  the  perichondrium,  entirely  similar  to  the 
embryonic  connective  tissue  already 
described  as  constituting  the  basis  of 
membrane  bone;  on  the  inner  surface  of  this — that  is  to  say,  on  the  surface  in 
contact  with  the  cartilage — are  gathered  the  formative  cells,  the  osteoblasts.  By 
the  agency  of  these  cells  a  thin  layer  of  bony  tissue  is  formed  between  the  peri- 


vnu 


Fig.  79. — Section  of  fetal  bone  of  cat.  tV.  Irruption 
of  the  subperiosteal  tissue,  p.  Fibrous  layer  of  the  pierios- 
teum.  o.  Layer  of  osteoblasts,  im.  Subperiosteal  bony 
deposit.     (From  Quain's  "Anatomy,"  E.  A.  Schafer.) 


OSTEOLOGY 


I 


chondrium  and  the  cartilage,  by  the  intramembranons  mode  of  ossification  just 
described.  There  are  then,  in  this  first  stage  of  ossification,  two  processes  going 
on  simultaneously:  in  the  center  of  the  cartilage  the  formation  of  a  number  of 
oblong  spaces,  formed  of  calcified  matrix  and  containing  the  withered  cartilage 
cells,  and  on  the  surface  of  the  cartilage  the  formation  of  a  layer  of  true  mem- 
brane bone.  The  second  stage  consists  in  the  prolongation  into  the  cartilage  of 
processes  of  the  deeper  or  osteogenetic  layer  of  the  perichondrium,  which  has 
now  become  periosteum  (Fig.  79,  ir).  The  processes  consist  of  bloodvessels  and 
cells — osteoblasts,  or  bone-formers,  and  osteoclasts,  or  bone-destroyers.  The  latter 
are  similar  to  the  giant  cells  (myeloplaxes)  found  in  marrow,  and  they  excavate 
passages  through  the  new-formed  bony  layer  by  absorption,  and  pass  through 
it  into  the  calcified  matrix  (Fig.  80).  Wherever  these  processes  come  in  con- 
tact with  the  calcified  walls  of  the  primary  areolae  they  absorb  them,  and  thus 
cause  a  fusion  of  the  original  cavities  and  the  formation  of  larger  spaces,  which 
are  termed  the  secondary  areolae  or  medullary  spaces.  These  secondary  spaces 
become  filled  with  embryonic  marrow,  consisting  of  osteoblasts  and  vessels,  derived, 

in  the  manner  described  above,  from  the 
osteogenetic  layer  of  the  periosteum  (Fig.  80) . 
Thus  far  there  has  been  traced  the  forma- 
tion of  enlarged  spaces  (secondary  areolae), 
the  perforated  walls  of  which  are  still  formed 
by  calcified  cartilage  matrix,  containing  an 
embryonic  marrow  derived  from  the  processes 
sent  in  from  the  osteogenetic  layer  of  the 
periosteum,  and  consisting  of  bloodvessels  and 
osteoblasts.  The  walls  of  these  secondary 
areolae  are  at  this  time  of  only  inconsiderable 
thickness,  but  they  become  thickened  by  the 
deposition  of  layers  of  true  bone  on  their  sur- 
face. This  process  takes  place  in  the  follow- 
ing manner:  Some  of  the  osteoblasts  of  the 
embryonic  marrow,  after  undergoing  rapid 
division,  arrange  themselves  as  an  epithelioid 
layer  on  the  surface  of  the  wall  of  the  space 
(Fig.  81).  This  layer  of  osteoblasts  forms  a 
bony  stratum,  and  thus  the  wall  of  the  space 
becomes  gradually  covered  with   a  layer  of 


Osteoclasts ^f''"^' 


Fig.  80. — Part  of  a  longitudinal  section  of 
the  developing  femur  of  a  rabbit,  a.  Flattened 
cartilage  cells,  h.  Enlarged  cartilage  cells,  c, 
d.  Newly  formed  bone.  e.  Osteoblasts.  /. 
Giant  cells  or  osteoclasts.  g,  h.  Shrunken 
cartilage  cells.  (From  "Atlas  of  Histology," 
Ivlein  and  Noble  Smith.) 


Osteoblasts 


ug^!,;^^.:3^^W 


Fig.  81. — Osteoblasts  and  osteoclasts  on  trabecula  of  lower  jaw  of 
calf  embryo.     (KoUiker.) 


true  osseous  substance  in  which  some  of  the  bone-forming  cells  are  included  as 
bone  corpuscles.  The  next  stage  in  the  process  consists  in  the  removal  of  these 
primary  bone  spicules  by  the  osteoclasts.  One  of  these  giant  cells  may  be  found 
lying  in  a  Howship's  foveola  at  the  free  end  of  each  spicule.    The  removal  of  the 


I 


BONE  ^^^^^^^K  95 


Pi 


primary  spicules  goes  on  pari  passu  with  the  formation  of  permanent  bone  by 
the  periosteum,  and  in  this  way  the  medullary  cavity  of  the  body  of  the  bone  is 
formed. 

This  series  of  changes  has  been  gradually  proceeding  toward  the  end  of  the  body 
of  the  bone,  so  that  in  the  ossifying  bone  all  the  changes  described  above  may 
be  seen  in  different  parts,  from  the  true  bone  at  the  center  of  the  body  to  the  hyaline 
cartilage  at  the  extremities. 

While  the  ossification  of  the  cartilaginous  body  is  extending  toward  the  articular 
ends,  the  cartilage  immediately  in  advance  of  the  osseous  tissue  continues  to  grow 
until  the  length  of  the  adult  bone  is  reached. 

During  the  period  of  growth  the  articular  end,  or  epiphysis,  remains  for  some 
time  entirely  cartilaginous,  then  a  bony  center  appears,  and  initiates  in  it  the 
process  of  intracartilaginous  ossification;  but  this  process  never  extends  to  any 
great  distance.     The  epiphysis  remains  separated  from  the  body  by  a  narrow 
cartilaginous  layer  for  a  definite  time.    This  layer  ultimately  ossifies,  the  distinc- 
tion between  body  and  epiphysis  is  obliterated,  and  the  bone  assumes  its  completed 
form  and  shape.    The  same  remarks  also  apply  to  such  processes  of  bone  as  are 
separately  ossified,  e.  g.,  the  trochanters  of  the  femur.    The  bones  therefore  con- 
tinue to  grow  until  the  body  has  acquired  its  full  stature.    They  increase  in  length 
by  ossification  continuing  to  extend  behind  the  epiphysial  cartilage,  w^hich  goes 
on  growing  in  advance  of  the  ossifying  process.    They  increase  in  circumference 
by  deposition  of  new  bone,  from  the  deeper  layer  of  the  periosteum,  on  their  exter- 
nal surface,  and  at  the  same  time  an  absorption  takes  place  from  within,  by  which 
I  the  medullary  cavities  are  increased. 
}    The  permanent  bone  formed  by  the  periosteum  when  first  laid  down  is  cancellous 
In  structure.    Later  the  osteoblasts  contained  in  its  spaces  become  arranged  in 
jthe  concentric  layers  characteristic  of  the  Haversian  systems,  and  are  included 
[as  bone  corpuscles. 
The  number  of  ossific  centers  varies  in  different  bones.    In  most  of  the  short 
bones  ossification  commences  at  a  single  point  near  the  center,  and  proceeds  toward 
^_  the  surface.    In  the  long  bones  there  is  a  central  point  of  ossification  for  the  body 
^|[or  diaphysis:  and  one  or  more  for  each  extremity,  the  epiphysis.    That  for  the 
^f  -body  is  the  first  to  appear.    The  times  of  union  of  the  epiphyses  with  the  body 
W    vary  inversely  with  the  dates  at  which  their  ossifications  began  (with  the  exception 
of  the  fibula)  and  regulate  the  direction  of  the  nutrient  arteries  of  the  bones.    Thus, 

I  the  nutrient  arteries  of  the  bones  of  the  arm  and  forearm  are  directed  toward 
rthe  elbow,  since  the  epiphyses  at  this  joint  become  united  to  the  bodies  before 
jthose  at  the  opposite  extremities.  In  the  low^er  limb,  on  the  other  hand,  the 
Inutrient  arteries  are  directed  away  from  the  knee:  that  is,  upward  in  the  femur, 
[downward  in  the  tibia  and  fibula;  and  in  them  it  is  observed  that  the  upper  epiphysis 
of  the  femur,  and  the  lower  epiphyses  of  the  tibia  and  fibula,  unite  first  with  the 
bodies.  Where  there  is  only  one  epiphysis,  the  nutrient  artery  is  directed  toward 
the  other  end  of  the  bone;  as  toward  the  acromial  end  of  the  clavicle,  toward  the 

P  distal  ends  of  the  metacarpal  bone  of  the  thumb  and  the  metatarsal  bone  of  the 
fereat  toe,  and  toward  the  proximal  ends  of  the  other  metacarpal  and  metatarsal 
bones. 

Parsons^  groups  epiphyses  under  three  headings,  viz.:  (1)  pressure  epiphyses, 
appearing  at  the  articular  ends  of  the  bones  and  transmitting  "the  weight  of  the 

r,  body  from  bone  to  bone;"   (2)  traction  epiphyses,  associated  with  the  insertion 
lof  muscles  and  "originally  sesamoid  structures  though  not  necessarily  sesamoid 
bones;"  and  (3)  atavistic  epiphyses,  representing  parts  of  the  skeleton,  which  at 
one  time  formed  separate  bones,  but  which  have  lost  their  function,  "  and  only 
appear  as  separate  ossifications  in  early  life." 
..,...,  ....„.,  P...,™,..  „„..„..... 


96 


OSTEOLOGY 


THE  VERTEBRAL  COLUMN  (COLUMNA  VERTEBRALIS ;  SPINAL 

COLUMN). 

The  vertebral  column  is  a  flexuous  and  flexible  column,  formed  of  a  series  o! 
bones  called  vertebrae. 

The  vertebrae  are  thirty-three  in  number,  and  are  grouped  under  the  names 
cervical,  thoracic,  lumbar,  sacral,  and  coccygeal,  according  to  the  regions  they 
occupy;  there  are  seven  in  the  cervical  region,  twelve  in  the  thoracic,  five  in  the 
lumbar,  five  in  the  sacral,  and  four  in  the  coccygeal. 

This  number  is  sometimes  increased  by  an  additional  vertebra  in  one  region, 
or  it  may  be  diminished  in  one  region,  the  deficiency  often  being  supplied  by  an 
additional  vertebra  in  another.  The  number  of  cervical  vertebrae  is,  however, 
very  rarely  increased  or  diminished. 

The  vertebrae  in  the  upper  three  regions  of  the  column  remain  distinct  through- 
out life,  and  are  known  as  true  or  movable  vertebrae;  those  of  the  sacral  and 
coccygeal  regions,  on  the  other  hand,  are  termed  false  or  fixed  vertebrae,  because 
they  are  united  with  one.  another  in  the  adult  to  form  two  bones — five  forming 
the  upper  bone  or  sacrum,  and  four  the  terminal  bone  or  coccyx. 

With  the  exception  of  the  first  and  second  cervical,  the  true  or  movable  vertebrae 
present  certain  common  characteristics  which  are  best  studied  by  examining  one 
from  the  middle  of  the  thoracic  region. 

GENERAL   CHARACTERISTICS    OF   A    VERTEBRA. 

A  typical  vertebra  consists  of  two  essential  parts — viz.,  an  anterior  segment,  the 
body,  and  a  posterior  part,  the  vertebral  or  neural  arch;  these  enclose  a  foramen, 
the  vertebral  foramen.  The  vertebral  arch  consists  of  a  pair  of  pedicles  and  a  pair 
of  laminae,  and  supports  seven  processes — viz.,  four  articular,  two  transverse,  and 
one  spinous. 


Costal  fovea 

Pedicle  or  roof  of 
vertebral  arch 


Lamina 


Superior  articular  process 


Fig.  82. — A  typical  thoracic  vertebra,  viewed  from  above. 


When  the  vertebrae  are  articulated  with  each  other  the  bodies  form  a  strong 
pillar  for  the  support  of  the  head  and  trunk,  and  the  vertebral  foramina  constitute 
a  canal  for  the  protection  of  the  medulla  spinalis  {spinal  cord),  while  between 
every  pair  of  vertebrae  are  two  apertures,  the  intervertebral  foramina,  one  on 
either  side,  for  the  transmission  of  the  spinal  nerves  and  vessels. 

Body  (corpus  vertebrce). — ^The  body  is  the  largest  part  of  a  vertebra,  and  is 
more  or  less  cylindrical  in  shape.    Its  upper  and  lower  surfaces  are  flattened  and 


THE  CERVICAL  VERTEBRA 


rough,  and  give  attachment  to  the  intervertebral  fibrocartilages,  and  each  presents 
a  rim  around  its  circumference.  In  front,  the  body  is  convex  from  side  to  side 
and  concave  from  above  downward.  Behind,  it  is  flat  from  above  downward 
and  slightly  concave  from  side  to  side.  Its  anterior  surface  presents  a  few  small 
apertures,  for  the  passage  of  nutrient  vessels;  on  the  posterior  surface  is  a  single 
large,  irregular  aperture,  or  occasionally  more  than  one,  for  the  exit  of  the  basi- 
vertebral veins  from  the  body  of  the  vertebra. 

Pedicles  {radices  arci  vertebroe). — The  pedicles  are  two  short,  thick  processes, 
which  project  backward,  one  on  either  side,  from  the  upper  part  of  the  body, 
at  the  junction  of  its  posterior  and  lateral  surfaces.  The  concavities  above  and 
below  the  pedicles  are  named  the  vertebral  notches;  and  when  the  vertebrae  are 
articulated,  the  notches  of  each  contiguous  pair  of  bones  form  the  intervertebral 
foramina,  already  referred  to. 

Laminae. — The  laminae  are  two  broad  plates  directed  backward  and  medialward 
from  the  pedicles.  They  fuse  in  the  middle  line  posteriorly,  and  so  complete  the 
posterior  boundary  of  the  vertebral  foramen.  Their  upper  borders  and  the  lower 
parts  of  their  anterior  surfaces  are  rough  for  the  attachment  of  the  ligamenta 
flava. 

Processes. — Spinous  Process  {processus  spinosus). — The  spinous  process  is 
directed  backward  and  downward  from  the  junction  of  the  laminae,  and  serves 
for  the  attachment  of  muscles  and  ligaments. 

Articular  Processes. — The  articular  processes,  two  superior  and  two  inferior, 
spring  from  the  junctions  of  the  pedicles  and  laminae.  The  superior  project 
upward,  and  their  articular  surfaces  are  directed  more  or  less  backward;  the 
inferior  project  downward,  and  their  surfaces  look  more  or  less  forward.  The 
articular  surfaces  are  coated  with  hyaline  cartilage. 

Transverse  Processes  {processus  transversi). — ^The  transverse  processes,  two  in 
number,  project  one  at  either  side  from  the  point  where  the  lamina  joins  the 
pedicle,  between  the  superior  and  inferior  articular  processes.  They  serve  for 
'the  attachment  of  muscles  and  ligaments. 

Stnictore  of  a  Vertebra  (Fig.  83). — The  body  is  composed  of  cancellous  tissue,  covered  by 

a  thin  coating  of  compact  bone;  the  latter  is  perforated  by  numerous  orifices,  some  of  large  size 
I  for  the  passage  of  vessels;  the  interior  of  the  bone  is  traversed  by  one  or  two  large  canals,  for  the 
[reception  of  veins,  which  converge  toward  a  single  large,  irregular  aperture,  or  several  small 

apertures,  at  the  posterior  part  of  the 

body.     The  thin  bony  lamellae  of  the 

cancellous  tissue  are  more  pronounced 

in  lines  perpendicular  to  the  upper 

and  low^er  surfaces  and  are  developed 

in  response  to  greater  pressure  in  this 

direction    (Fig.   83).     The  arch  and 

processes    projecting    from    it    have 

thick  coverings  of  compact  tissue. 

The  Cervical  Vertebrae  (Verte- 
brae Cervicales). 

The  cervical  vertebrae  (Fig. 
84)  are  the  smallest  of  the  true 
vertebrae,  and   can   be   readily 

distinguished  from  those  of  the  thoracic  or  lumbar  regions  by  the  presence  of  a 
foramen  in  each  transverse  process.  The  first,  second,  and  seventh  present  excep- 
tional features  and  must  be  separately  described ;  the  following  characteristics  are 
k common  to  the  remaining  four. 
The  body  is  small,  and  broader  from  side  to  side  than  from  before  backward 
The  anterior  and  posterior  surfaces  are  flattened  and  of  equal  depth;  the  former 


Fig.  83. — Sagittal  section  of  a  lumbar  vertebra. 


^ 


98 


OSTEOLOGY 


is  placed  on  a  lower  level  than  the  latter,  and  its  inferior  border  is  prolongeo 
downward,  so  as  to  overlap  the  upper  and  forepart  of  the  vertebra  below.  The 
upper  surface  is  concave  transversely,  and  presents  a  projecting  lip  on  either  side ; 
the  lower  surface  is  concave  from  before  backward,  convex  from  side  to  side,  and 
presents  laterally  shallow  concavities  which  receive  the  corresponding  projecting 
lips  of  the  subjacent  vertebra.  The  pedicles  are  directed  lateralward  and  l3ackward, 
and  are  attached  to  the  body  midway  between  its  upper  and  lower  borders,  so  that 
the  superior  vertebral  notch  is  as  deep  as  the  inferior,  but  it  is,  at  the  same  time. 


Anterior  tubercle  of 
transverse  'process 
Foramen 
iransversarium 
Posterior  tvbercle  of—^ 
transverse  process 


Transverse  process 


Superior  articular 
process 

Inferior  articular 
process 


I  Spinmis 
process 

Fig.  84. — A  cervical  vertebra. 


narrower.  The  laminse  are  narrow,  and  thinner  above  than  below;  the  vertebral 
foramen  is  large,  and  of  a  triangular  form.  The  spinous  process  is  short  and  bifid, 
the  two  divisions  being  often  of  unequal  size.  The  superior  and  inferior  articular 
processes  on  either  side  are  fused  to  form  an  articular  pillar,  which  projects  lateral- 
ward  from  the  junction  of  the  pedicle  and  lamina.  The  articular  facets  are  flat 
and  of  an  oval  form:  the  superior  look  backward,  upward,  and  slightly  medial- 
ward:  the  inferior  forward,  downward,  and  slightly  lateralward.  The  transverse 
processes  are  each  pierced  by  the  foramen  transversarium,  which,  in  the  upper  six 


Body 

Anterior  tubercle  of 
transverse  process 


Svlcusfor  nerve 


Superior  articular  surface 
Articular  pillar 


Fig.  85. 


Posterior  tubercle  of 
transverse  process 

■Side  view  of  a  typical  cervical  vertebra. 


Spinous  process 


vertebrae,  gives  passage  to  the  vertebral  artery  and  vein  and  a  plexus  of  sympa- 
thetic nerves.  Each  process  consists  of  an  anterior  and  a  posterior  part.  The 
anterior  portion  is  the  homologue  of  the  rib  in  the  thoracic  region,  and  is  there- 
fore named  the  costal  process  or  costal  element:  it  arises  from  the  side  of  the  body, 
is  directed  lateralward  in  front  of  the  foramen,  and  ends  in  a  tubercle,  the  anterior 
tubercle.  The  posterior  part,  the  true  transverse  process,  springs  from  the 
vertebral  arch  behind  the  foramen,  and  is  directed  forward  and  lateralward;  it 
ends  in  a  flattened  vertical    tubercle,    the  posterior  tubercle.     These   two  parts 


I 


THE  CERVICAL  VERTEBRA 


99 


are  joined,  outside  the  foramen,  by  a  bar  of  bone  which  exhibits  a  deep  sulcus 
on  its  upper  surface  for  the  passage  of  the  corresponding  spinal  nerve. ^ 

First  Cervical  Vertebra. — The  first  cervical  vertebra  (Fig.  86)  is  named  the 
atlas  because  it  supports  the  globe  of  the  head.  Its  chief  peculiarity  is  that  it  has 
no  body,  and  this  is  due  to  the  fact  that  the  body  of  the  atlas  has  fused  with  that 
of  the  next  vertebra.  Its  other  peculiarities  are  that  it  has  no  spinous  process, 
is  ring-like,  and  consists  of  an  anterior  and  a  posterior  arch  and  two  lateral  masses. 
The  anterior  arch  forms  about  one-fifth  of  the  ring:  its  anterior  surface  is  convex, 
and  presents  at  its  center  the  anterior  tubercle  for  the  attachment  of  the  Longus 
colli  muscles;  posteriorly  it  is  concave,  and  marked  by  a  smooth,  oval  or  circular 
facet  (fovea  dentis),  for  articulation  with  the  odontoid  process  (dejis)  of  the  axis. 
The  upper  and  lower  borders  respectively  give  attachment  to  the  anterior  atlanto- 
occipital  membrane  and  the  anterior  atlantoaxial  ligament;  the  former  connects 
it  with  the  occipital  bone  above,  and  the  latter  with  the  axis  below.  The  posterior 
arch  forms  about  two-fifths  of  the  circumference  of  the  ring :  it  ends  behind  in  the 
posterior  tubercle,  which  is  the  rudiment  of  a  spinous  process  and  gives  origin  to 
the  Recti  capitis  posteriores  minores.  The  diminutive  size  of  this  process  pre- 
vents any  interference  with  the  movements  between  the  atlas  and  the  skull. 
The  posterior  part  of  the  arch  presents  above  and  behind  a  rounded  edge  for 


Anterior  tvbercle 


Outline  of  section  of  odontoid 
process 
Outline  cf  section  of  trans- 
verse atlantal  ligament 


Foramen 
transver- 
sarium 


Groove  for  vertebral  artery 
and  first  cervical  nerve 


I 


Posterior  tiibercle 

Fig.  86. — First  cervical  vertebra,  or  atlas. 

the  attachment  of  the  posterior  atlantooccipital  membrane,  while  immediately 
behind  each  superior  articular  process  is  a   groove   (sulcus   arteriw  wrtchralis), 

(sometimes  converted  into  a  foramen  by  a  delicate  bony  spiculum  which  arches 
backward  from  the  posterior  end  of  the  superior  articular  process.  This  groove 
represents  the  superior  vertebral  notch,  and  serves  for  the  transmission  of  the 
vertebral  artery,  which,  after  ascending  through  the  foramen  in  the  transverse 
process,  winds  around  the  lateral  mass  in  a  direction  backward  and  medialward;  it 
also  transmits  the  suboccipital  (first  spinal)  nerve.  On  the  under  surface  of  the 
posterior  arch,  behind  the  articular  facets,  are  two  shallow  grooves,  the  inferior 
vertebral  notches.  The  lower  border  gives  attachment  to  the  posterior  atlanto- 
axial ligament,  which  connects  it  with  the  axis.  The  lateral  masses  are  the  most 
bulky  and  solid  parts  of  the  atlas,  in  order  to  support  the  weight  of  the  head. 

(Each  carries  two  articular  facets,  a  superior  and  an  inferior.  The  superior  facets 
are  of  large  size,  oval,  concave,  and  approach  each  other  in  front,  but  diverge 
behind:  they  are  directed  upward,  medialward,  and  a  little  backward,  each  forming 
a  cup  for  the  corresponding  condyle  of  the  occipital  bone,  and  are  admirably 
adapted  to  the  nodding  movements  of  the  head.     Not  infrequently  they  are 

'  The  costal  element  of  a  cervical  vertebra  not  only  includes  the  portion  which  spriags  from  the  side  of  tlje  body,  but 
^the  anterior  and  posterior  tubercles  and  the  bar  of  bone  which  connects  them  (rig.  67). 


100 


OSTEOLOGY 


partially  subdivided  by  indentations  which  encroach  upon  their  margins.  The 
inferior  articular  facets  are  circular  in  form,  flattened  or  slightly  convex  and  directed 
downward  and  medialward,  articulating  with  the  axis,  and  permitting  the  rotatory 
movements  of  the  head.  Just  below  the  medial  margin  of  each  superior  facet  is 
a  small  tubercle,  for  the  attachment  of  the  transverse  atlantal  ligament  which 
stretches  across  the  ring  of  the  atlas  and  divides  the  vertebral  foramen  into  two 
unequal  parts — the  anterior  or  smaller  receiving  the  odontoid  process  of  the  axis, 
the  posterior  transmitting  the  medulla  spinalis  and  its  membranes.  This  part 
of  the  vertebral  canal  is  of  considerable  size,  much  greater  than  is  required  for  the 
accommodation  of  the  medulla  spinalis,  and  hence  lateral  displacement  of  the 
atlas  may  occur  without  compression  of  this  structure.  The  transverse  processes 
are  large;  they  project  lateralward  and  downward  from  the  lateral  masses,  and 
serve  for  the  attachment  of  muscles  which  assist  in  rotating  the  head.  They 
are  long,  and  their  anterior  and  posterior  tubercles  are  fused  into  one  mass;  the 
foramen  transversarium  is  directed  from  below,  upward  and  backward. 


Dens 


For  alar  ligaments 

For  trans,  ligament  of  atlas 

Superior  artiadar 
surface 


Foramen 

transversarium 


Spinous  process 
Fia.  87. — Second  cervical  vertebra,  or  epistropheus,  from  above. 


Second  Cervical  Vertebra. — ^The  second  cervical  vertebra  (Fig.  87  and  88)  is  named 
the  epistropheus  or  axis  because  it  forms  the  pivot  upon  which  the  first  vertebra, 
carrying  the  head,  rotates.  The  most  distinctive  characteristic  of  this  bone  is 
the  strong  odontoid  process  which  rises  perpendicularly  from  the  upper  surface 
of  the  body.  The  body  is  deeper  in  front  than  behind,  and  prolonged  downward 
anteriorly  so  as  to  overlap  the  upper  and  fore  part  of  the  third  vertebra.  It  pre- 
sents in  front  a  median  longitudinal  ridge,  separating  two  lateral  depressions  for 
the  attachment  of  the  Longus  colli  muscles.  Its  under  surface  is  concave  from 
before  backward  and  covex  from  side  to  side.  The  dens  or  odontoid  process  exhibits 
a  slight  constriction  or  neck,  where  it  joins  the  body.  On  its  anterior  surface 
is  an  oval  or  nearly  circular  facet  for  articulation  with  that  on  the  anterior  arch 
of  the  atlas.  On  the  back  of  the  neck,  and  frequently  extending  on  to  its  lateral 
surfaces,  is  a  shallow  groove  for  the  transverse  atlantal  ligament  which  retains 
the  process  in  position.  The  apex  is  pointed,  and  giAes  attacliment  to  the  apical 
odontoid  ligament;  below  the  apex  the  process  is  somewhat  enlarged,  and  pre- 
sents on  either  side  a  rough  impression  for  the  attachment  of  the  alar  ligament; 
these  ligaments  connect  the  process  to  the  occipital  bone.    The  internal  structure 


I 


THE  CERVICAL  VERTEBRA 


101 


of  the  odontoid  process  is  more  compact  than  that  of  the  body.  The  pedicles 
are  broad  and  strong,  espe;cially  in  front,  where  they  coalesce  with  the  sides  of 
the  body  and  the  root  of  the  odontoid  process.  They  are  covered  above  by  the 
superior  articular  surfaces.      The  laminae  are  thick  and  strong,  and  the  vertebral 


Odontoid  process 


Rough  surface  for  alar  ligament 
Groove  for  transverse  atlantal  ligament 


Spinous  process"^ 


Articular  facet  for 
anterior  arch  of 


Body 


Post,  root 


I 


Transverse  process 
Inferior  articular  process 

Fig.  88. — Second  cervical  vertebra,  epistropheus,  or  axis,  from  the  side. 


foramen  large,  but  smaller  than  that  of  the  atlas.  The  transverse  processes  are 
very  small,  and  each  ends  in  a  single  tubercle;  each  is  perforated  by  the  foramen 
transversarium,  which  is  directed  obliquely  upward  and  lateralward.  The  superior 
articular  surfaces  are  round,  slightly  convex,  directed  upward  and  lateralward, 
and  are   supported   on  the  body, 

pedicles,  and  transverse  processes.  ^'^^^ 

[The  inferior  articular  surfaces  have 
the  same  direction  as  those  of  the 
other  cervical  vertebrae.  The  supe- 
rior vertebral  notches  are  very  shal- 
low, and  lie  behind  the  articular 
k)rocesses;  the  inferior  lie  in  front 
of  the  articular  processes,  as  in  the 
other  cervical  vertebrae.  The  spinous 
process  is  large,  very  strong,  deeply 
channelled  on  its  under  surface, 
and  presents  a  bifid,  tuberculated 
extremity. 

The  Seventh  Cervical  Vertebra 
(Fig.  89). — The  most  distinctive 
characteristic  of  this  vertebra  is 
the  existence  of  a  long  and  promi- 
nent spinous  process,  hence  the 
name  vertebra  prominens.  This  pro- 
cess is  thick,  nearly  horizontal  in 
direction,  not  bifurcated,  but  ter- 
minating in  a  tubercle  to  which  the  lower  end  of  the  ligamentum  nuchse  is 
attached.  The  transverse  processes  are  of  considerable  size,  their  posterior  roots 
are  large  and  prominent,  while  the  anterior  are  small  and  faintly  marked;  the 
upper  surface  of  each  has  usually  a  shallow  sulcus  for  the  eighth  spinal  nerve, 
and  its  extremity  seldom  presents  more  than  a  trace  of  bifurcation.    The  foramen 


Spinous  process 
Fig.  89. — Seventh  cervical  vertebra. 


102 


OSTEOLOGY 


I 


transversarium  may  be  as  large  as  that  in  the  other  cervical  vertebrae,  but  is 
generally  smaller  on  one  or  both  sides;  occasionally  it  is  double,  sometimes  it  is 
absent.  On  the  left  side  it  occasionally  gives  passage  to  the  vertebral  artery; 
more  frequently  the  vertebral  vein  traverses  it  on  both  sides;  but  the  usual 
arrangement  is  for  both  artery  and  vein  to  pass  in  front  of  the  transverse  pro- 
cess, and  not  through  the  foramen.  Sometimes  the  anterior  root  of  the  trans- 
verse process  attains  a  large  size  and  exists  as  a  separate  bone,  which  is  known 
as  a  cervical  rib. 

The  Thoracic  Vertebrae  (Vertebrae  Thoracales). 

The  thoracic  vertebrae  (Fig.  90)  are  intermediate  in  size  between  those  of 
the  cervical  and  lumbar  regions;  they  increase  in  size  from  above  downward,  the 
upper  vertebrae  being  much  smaller  than  those  in  the  lower  part  of  the  region. 
They  are  distinguished  by  the  presence  of  facets  on  the  sides  of  the  bodies  for 
articulation  with  the  heads  of  the  ribs,  and  facets  on  the  transverse  processes  of 
all,  except  the  eleventh  and  twelfth,  for  articulation  with  the  tubercles  of  the  ribs. 


Superior  articular  process 


Demi-facet  for  head  of  rib 


Facet  for  articular  part 
of  tubercle  of  rib 


Demi-facet  for  head  of  rib 
Inferior  articular  process 


Fig.  90. — A  thoracic  vertebra. 


The  bodies  in  the  middle  of  the  thoracic  region  are  heart-shaped,  and  as  broad 
in  the  antero-posterior  as  in  the  transverse  direction.  At  the  ends  of  the  thoracic 
region  they  resemble  respectively  those  of  the  cervical  and  lumbar  vertebrae. 
They  are  slightly  thicker  behind  than  in  front,  flat  above  and  below,  convex  from 
side  to  side  in  front,  deeply  concave  behind,  and  slightly  constricted  laterally 
and  in  front.  They  present,  on  either  side,  two  costal  demi-facets,  one  above, 
near  the  root  of  the  pedicle,  the  other  below,  in  front  of  the  inferior  vertebral 
notch;  these  are  covered  with  cartilage  in  the  fresh  state,  and,  when  the  vertebrae 
are  articulated  with  one  another,  form,  with  the  intervening  intervertebral  fibro- 
cartilages,  oval  surfaces  for  the  reception  of  the  heads  of  the  ribs.  The  pedicles 
are  directed  backward  and  slightly  upward,  and  the  inferior  vertebral  notches 
are  of  large  size,  and  deeper  than  in  any  other  region  of  the  vertebral  column. 
The  laminae  are  broad,  thick,  and  imbricated — that  is  to  say,  they  overlap  those 
of  subjacent  vertebrae  like  tiles  on  a  roof.  The  vertebral  foramen  is  small,  and  of 
a  circular  form.  The  spinous  process  is  long,  triangular  on  coronal  section,  directed 
obliquely  downward,  and  ends  in  a  tuberculated  extremity.     These  processes 


I 


THE  THORACIC  VERTEBRAE 


103 


overlap  from  the  fifth  to  the  eighth,  but  are  less  oblique  in  direction  above  and 
below.  The  superior  articular  processes  are  thin  plates  of  bone  projecting  upward 
from  the  junctions  of  the  pedicles  and  laminse;  their  articular  facets  are  practi- 
cally flat,  and  are  directed  backward  and  a  little  lateralward  and  upward.  The 
inferior  articular  processes  are  fused  to  a  considerable  extent  with    the  laminse. 


An  entire  facet  above; 
a  demi-facet  below 


A  demi-facet  above 


—  One  entire  facet 


One  entire  facet. 
No  facet  on  trans,  proc. 
which  is  rudimentary 


One  entire  facet. 

(No  facet  on  trans- 
I      verse  process, 
-[  Infer.artic.process 
I  convex  and  turned 
\lateralivard3 


Fio.  91. — Peculiar  thoracic  vertebrse. 


I 


and  project  but  slightly  beyond  their  lower  borders;  their  facets  are  directed 
forward  and  a  little  medialward  and  downward.  The  transverse  processes  arise 
from  the  arch  behind  the  superior  articular  processes  and  pedicles;  they  are  thick, 
strong,  and  of  considerable  length,  directed  obliquely  backward  and  lateralward, 
and  each  ends  in  a  clubbed  extremity,  on  the  front  of  which  is  a  small,  concave 
surface,  for  articulation  with  the  tubercle  of  a  rib. 


104 


OSTEOLOGY 


The  first,  ninth,  tenth,  eleventh,  and  twelfth  thoracic  vertebrae  present  certaiai 
pecuHarities,  and  must  be  specially  considered  (Fig.  91). 

The  First  Thoracic  Vertebra  has,  on  either  side  of  the  body,  an  entire  articular 
facet  for  the  head  of  the  first  rib,  and  a  demi-facet  for  the  upper  half  of  the  head 
of  the  second  rib.  The  body  is  like  that  of  a  cervical  vertebra,  being  broad  trans- 
versely; its  upper  surface  is  concave,  and  lipped  on  either  side.  The  superior 
articular  surfaces  are  directed  upward  and  backward;  the  spinous  process  is  thick, 
long,  and  almost  horizontal.  The  transverse  processes  are  long,  and  the  upper 
vertebral  notches  are  deeper  than  those  of  the  other  thoracic  vertebrae. 

The  Ninth  Thoracic  Vertebra  may  have  no  demi-facets  below.  In  some  sub- 
jects however,  it  has  two  demi-facets  on  either  side;  when  this  occurs  the  tenth 
has  only  demi-facets  at  the  upper  part. 

The  Tenth  Thoracic  Vertebra  has  (except  in  the  cases  just  mentioned)  an  entire 
articular  facet  on  either  side,  which  is  placed  partly  on  the  lateral  surface  of  the 
pedicle. 

In  the  Eleventh  Thoracic  Vertebra  the  body  approaches  in  its  form  and  size 
to  that  of  the  lumbar  vertebrae.  The  articular  facets  for  the  heads  of  the  ribs 
are  of  large  size,  and  placed  chiefly  on  the  pedicles,  which  are  thicker  and  stronger 
in  this  and  the  next  vertebra  than  in  any  other  part  of  the  thoracic  region.  The 
spinous  process  is  short,  and  nearly  horizontal  in  direction.  The  transverse  processes 
are  very  short,  tuberculated  at  their  extremities,  and  have  no  articular  facets. 

The  Twelfth  Thoracic  Vertebra  has  the  same  general  characteristics  as  the- 
eleventh,  but  may  be  distinguished  from  it  by  its  inferior  articular  surfaces  being 
convex  and  directed  lateralward,  like  those  of  the  lumbar  vertebrae;  by  the  general 
form  of  the  body,  laminae,  and  spinous  process,  in  which  it  resembles  the  lumbar 
vertebrae;  and  by  each  transverse  process  being  subdivided  into  three  elevations, 
the  superior,  inferior,  and  lateral  tubercles:  the  superior  and  inferior  correspond 
to  the  mammillary  and  accessory  processes  of  the  lumbar  vertebrae.  Traces  of 
similar  elevations  are  found  on  the  transverse  processes  of  the  tenth  and  eleventh 
thoracic  vertebrae. 


Superior  articular  process 


Fig.  92. — A  lumbar  vertebra  seen  from  the  side. 


The  Lumbar  Vertebrae  (Vertebrae  Lumbales). 

The  lumbar  vertebrae  (Figs.  92  and  93)  are  the  largest  segments  of  the  movable 
part  of  the  vertebral  column,  and  can  be  distinguished  by  the  absence  of  a 
foramen  in  the  transverse  process,  and  by  the  absence  of  facets  on  the  sides  of 
the  body. 

The  body  is  large,  wider  from  side  to  side  than  from  before  backward,  and  a 
little  thicker  in  front  than  behind.    It  is  flattened  or  slightly  concave  above  and 


I 


THE  LUMBAR  VERTEBRA 


105 


below,  concave  behind,  and  deeply  constricted  in  front  and  at  the  sides.     The 
pedicles  are  very  strong,  directed  backward  from  the  upper  part  of  the  body; 


Transverse  process 


Inferior  articular 
process 


Superior  articular 
process 


Mamillary  process 
Accessory  process 


FiQ.  93. — A  lumbar  vertebra  from  above  and  behind. 


consequently,  the  inferior  vertebral  notches  are  of  considerable  depth.     The 
laminse  are  broad,  short,  and  strong;  the  vertebral  foramen  is  triangular,  larger 


Fio.  94. — Fifth  lumbar  vertebra,  from  above. 


than  in  the  thoracic,  but  smaller  than  in  the  cervical  region.    The  spinous  process 
is  thick,  broad,  and  somewhat  quadrilateral;  it  projects  backward  and  ends  in 


I 


106  OSTEOLOGY 

a  rough,  uneven  border,  thickest  below  where  it  is  occasionally  notched.  Tht5^ 
superior  and  inferior  articular  processes  are  well-defined,  projecting  respectively 
upward  and  downward  from  the  junctions  of  pedicles  and  laminae.  The  facets 
on  the  superior  processes  are  concave,  and  look  backward  and  medial  ward;  thos(3 
on  the  inferior  are  convex,  and  are  directed  forward  and  lateral  ward.  The  former 
are  wider  apart  than  the  latter,  since  in  the  articulated  column  the  inferior  articular 
processes  are  embraced  by  the  superior  processes  of  the  subjacent  vertebra.  The 
transverse  processes  are  long,  slender,  and  .horizontal  in  the  upper  three  lumbar 
vertebrae;  they  incline  a  little  upward  in  the  lower  two.  In  the  upper  three  verte- 
brae they  arise  from  the  junctions  of  the  pedicles  and  laminae,  but  in  the  lower 
two  they  are  set  farther  forward  and  spring  from  the  pedicles  and  posterior  parts 
of  the  bodies.  They  are  situated  in  front  of  the  articular  processes  instead  of  behind 
them  as  in  the  thoracic  vertebrae,  and  are  homologous  with  the  ribs.  Of  the  three 
tubercles  noticed  in  connection  with  the  transverse  processes  of  the  lower  thoracic 
vertebrae,  the  superior  one  is  connected  in  the  lumbar  region  with  the  back  part 
of  the  superior  articular  process,  and  is  named  the  mammillary  process;  the  inferior 
is  situated  at  the  back  part  of  the  base  of  the  transverse  process,  and  is  called  the 
accessory  process  (Fig.  93). 

The  Fifth  Lumbar  Vertebra  (Fig.  94)  is  characterized  by  its  body  being  much 
deeper  in  front  than  behind,  which  accords  with  the  prominence  of  the  sacro- 
vertebral  articulation;  by  the  smaller  size  of  its  spinous  process;  by  the  wide  interval 
between  the  inferior  articular  processes;  and  by  the  thickness  of  its  transverse 
processes,  which  spring  from  the  body  as  well  as  from  the  pedicles. 

The  Sacral  and  Coccygeal  Vertebrae. 

The  sacral  and  coccygeal  vertebrae  consist  at  an  early  period  of  life  of  nine 
separate  segments  which  are  united  in  the  adult,  so  as  to  form  two  bones,  five 
entering  into  the  formation  of  the  sacrum,  four  into  that  of  the  coccyx.  Some- 
times the  coccyx  consists  of  five  bones;  occasionally  the  number  is  reduced  to 
three. 

The  Sacrum  {os  sacrum). — The  sacrum  is  a  large,  triangular  bone,  situated 
in  the  lower  part  of  the  vertebral  column  and  at  the  upper  and  back  part  of  the 
pelvic  cavity,  where  it  is  inserted  like  a  wedge  between  the  two  hip  bones;  its 
upper  part  or  base  articulates  with  the  last  lumbar  vertebra,  its  apex  with  the 
coccyx.  It  is  curved  upon  itself  and  placed  very  obliquely,  its  base  projecting 
forward  and  forming  the  prominent  sacrovertebral  angle  when  articulated  with 
the  last  lumbar  vertebra;  its  central  part  is  projected  backward,  so  as  to  give 
increased  capacity  to  the  pelvic  cavity. 

Pelvic  Surface  {jades  pelvina). — The  pelvic  surface  (Fig.  95)  is  concave  from 
above  downward,  and  slightly  so  from  side  to  side.  Its  middle  part  is  crossed 
by  four  transverse  ridges,  the  positions  of  which  correspond  with  the  original 
planes  of  separation  between  the  five  segments  of  the  bone.  The  portions  of  bone 
intervening  between  the  ridges  are  the  bodies  of  the  sacral  vertebrae.  The  body 
of  the  first  segment  is  of  large  size,  and  in  form  resembles  that  of  a  lumbar  vertebra; 
the  succeeding  ones  diminish  from  above  downward,  are  flattened  from  before 
backward,  and  curved  so  as  to  accommodate  themselves  to  the  form  of  the  sacrum, 
being  concave  in  front,  convex  behind.  At  the  ends  of  the  ridges  are  seen  the 
anterior  sacral  foramina,  four  in  number  on  either  side,  somewhat  rounded  in  form, 
diminishing  in  size  from  above  downward,  and  directed  lateralward  and  forward; 
they  give  exit  to  the  anterior  divisions  of  the  sacral  nerves  and  entrance  to  the 
lateral  sacral  arteries.  Lateral  to  these  foramina  are  the  lateral  parts  of  the  sacrum, 
each  consisting  of  five  separate  segments  at  an  early  period  of  life;  in  the  adult, 
these  are  blended  wdth  the  bodies  and  with  each  other.    Each  lateral  part  is  tra- 


I 


THE  SACRAL  AND  COCCYGEAL  VERTEBRAE 


107 


versed  by  four  broad,  shallow  grooves,  which  lodge  the  anterior  divisions  of  the 
sacral  nerves,  and  are  separated  by  prominent  ridges  of  bone  which  give  origin 
to  the  Piriformis  muscle. 

If  a  sagittal  section  be  made  through  the  center  of  the  sacrum  (Fig.  99),  the 
bodies  are  seen  to  be  united  at  their  circumferences  by  bone,  wide  intervals  being 
left  centrally,  which,  in  the  fresh  state,  are  filled  by  the  intervertebral  fibro- 
cartilages.  In  some  bones  this  union  is  more  complete  between  the  lower  than 
the  upper  segments. 

Dorsal  Surface  (fades  dorsalis). — The  dorsal  surface  (Fig.  96)  is  convex  and 
narrower  than  the  pelvic.  In  the  middle  line  it  displays  a  crest,  the  middle  sacral 
crest,  surmounted  by  three  or  four  tubercles,  the  rudimentary  spinous  processes 


Promontory 


FiQ.  95. — ^Sacrum,  pelvic  surface. 

rof  the  upper  three  or  four  sacral  vertebrae.  On  either  side  of  the  middle  sacral 
'crest  is  a  shallow  groove,  the  sacral  groove,  which  gives  origin  to  the  Multifidus, 
the  floor  of  the  groove  being  formed  by  the  united  laminae  of  the  corresponding 
vertebrs.  The  laminae  of  the  fifth  sacral  vertebra,  and  sometimes  those  of  the 
fourth,  fail  to  meet  behind,  and  thus  a  hiatus  or  deficiency  occurs  in  the  posterior 
wall  of  the  sacral  canal.  On  the  lateral  aspect  of  the  sacral  groove  is  a  linear 
series  of  tubercles  produced  by  the  fusion  of  the  articular  processes  which  together 
form  the  indistinct  sacral  articular  crests.  The  articular  processes  of  the  first 
sacral  vertebra  are  large  and  oval  in  shape;  their  facets  are  concave  from  side  to 
side,  look  backward  and  medialward,  and  articulate  with  the  facets  on  the  inferior 
processes  of  the  fifth  lumbar  \ertebra.  The  tubercles  which  represent  the  inferior 
articular  processes  of  the  fifth  sacral  vertebra  are  prolonged  downward  as  rounded 


108 


OSTEOLOGY 


I 


processes,  which  are  named  the  sacral  comua,  and  are  connected  to  the  corni:a 
of  the  coccyx.  Lateral  to  the  articular  processes  are  the  four  posterior  sacral 
foramina;  they  are  smaller  in  size  and  less  regular  in  form  than  the  anterior,  and 
transmit  the  posterior  divisions  of  the  sacral  nerves.  On  the  lateral  side  of  the 
posterior  sacral  foramina  is  a  series  of  tubercles,  which  represent  the  transverse 
processes  of  the  sacral  vertebrse,  and  form  the  lateral  crests  of  the  sacrum.  The 
transverse  tubercles  of  the  first  sacral  vertebra  are  large  and  very  distinct;  they, 
together  with  the  transverse  tubercles  of  the  second  vertebra,  give  attachment 
to  the  horizontal  parts  of  the  posterior  sacroiliac  ligaments;  those  of  the  third 
vertebra  give  attachment  to  the  oblique  fasciculi  of  the  posterior  sacroiliac  liga- 
ments; and  those  of  the  fourth  and  fifth  to  the  sacrotuberous  ligaments. 


Saerospinalis 


Latissimus 
dor  si 


Saerospinalis 


er  half  of  fifth 
posterior  sacral  foramen 


Fig.   96. — Sacrum,  dorsal  surface. 


Lateral  Surface. — The  lateral  surface  is  broad  above,  but  narrowed  into  a  thin 
edge  below.  The  upper  half  presents  in  front  an  ear-shaped  surface,  the  auricular 
surface,  covered  with  cartilage  in  the  fresh  state,  for  articulation  with  the  ilium. 
Behind  it  is  a  rough  surface,  the  sacral  tuberosity,  on  which  are  three  deep 
and  uneven  impressions,  for  the  attachment  of  the  posterior  sacroiliac  ligament. 
The  lower  half  is  thin,  and  ends  in  a  projection  called  the  inferior  lateral  angle; 
medial  to  this  angle  is  a  notch,  which  is  converted  into  a  foramen  by  the  trans- 
verse process  of  the  first  piece  of  the  coccyx,  and  transmits  the  anterior  division  of 
the  fifth  sacral  nerve.  The  thin  lower  half  of  the  lateral  surface  gives  attachment 
to  the  sacrotuberous  and  sacrospinous  ligaments,  to  some  fibers  of  the  Glutseus 
maximus  behind,  and  to  the  Coccygeus  in  front. 

Base  {basis  oss.  sacri). — The  base  of  the  sacrum,  which  is  broad  and  expanded, 
is  directed  upward  and  forward.    In  the  middle  is  a  large  oval  articular  surface, 


I 


THE  SACRAL  AND  COCCYGEAL  VERTEBRA 


109 


the  upper  surface  of  the  body  of  the  first  sacral  vertebra,  which  is  connected  with 
the  under  surface  of  the  body  of  the  last  lumbar  vertebra  by  an  intervertebral 


Articular  process 
Medial  sacral  crest 


Cornu  of  sacrum/ 

Cornu  of  coccyx 


Fig.  97. — Lateral  surfaces  of  sacrum  and  coccyx. 


Sacral  canal 

Articular  procesa 


Fig   98.— Base  of  sacrum. 


110 


OSTEOLOGY 


I 


fibrocartilage.  Behind  this  is  the  large  triangular  orifice  of  the  sacral  canal,  whicb 
is  completed  by  the  laminae  and  spinous  process  of  the  first  sacral  vertebra.  The 
superior  articular  processes  project  from  it  on  either  side;  they  are  oval,  concave;, 
directed  backward  and  medialward,  like  the  superior  articular  processes  of  a  lumbar 
vertebra.  They  are  attached  to  the  body  of  the  first  sacral  vertebra  and  to  the 
alae  by  short  thick  pedicles;  on  the  upper  surface  of  each  pedicle  is  a  vertebral 
notch,  which  forms  the  lower  part  of  the  foramen  between  the  last  lumbar  and  first 
sacral  vertebrae.  On  either  side  of  the  body  is  a  large  triangular  surface,  which 
supports  the  Psoas  major  and  the  lumbosacral  trunk,  and  in  the  articulated 
pelvis  is  continuous  with  the  iliac  fossa.    This  is  called  the  ala;  it  is  slightly  concave 


Cornua 


Anterior  Surface 


Posterior  surface 


Fia.  99. — Mediaa  sagittal  section  of  the  sacrum. 


Fig.  100.- 


from  side  to  side,  convex  from  before  backward,  and  gives  attachment  to  a  few 
of  the  fibers  of  the  Iliacus.  The  posterior  fourth  of  the  ala  represents  the  trans- 
verse process,  and  its  anterior  three-fourths  the  costal  process  of  the  first  sacral 
segment. 

Apex  {a'pex  oss.  sacri). — ^The  apex  is  directed  downward,  and  presents  an  oval 
facet  for  articulation  with  the  coccyx. 

Vertebral  Canal  (canalis  sacralis;  sacral  canal). — The  vertebral  canal  (Fig.  99) 
runs  throughout  the  greater  part  of  the  bone;  above,  it  is  triangular  in  form; 
below,  its  posterior  wall  is  incomplete,  from  the  non-development  of  the  laminae 
and  spinous  processes.  It  lodges  the  sacral  nerves,  and  its  walls  are  perforated  by 
the  anterior  and  posterior  sacral  foramina  through  which  these  nerves  pass  out. 


THE  SACRAL  AND  COCCYGEAL  VERTEBRA  111 


^^m-   Structure. — The  sacrum  consists  of  cancellous  tissue  enveloped  by  a  thin  layer  of  compact  bone. 

Articulations. — The  sacrum  articulates  with  four  bones;  the  last  lumbar  vertebra  above,  the 
coccyx  below,  and  the  hip  bone  on  either  side. 

Differences  in  the  Sacrum  of  the  Male  and  Female. — In  the  female  the  sacrum  is  shorter  and 
wider  than  in  the  male;  the  lower  half  forms  a  greater  angle  with  the  upper;  the  upper  half  is 
nearly  straight,  the  lower  half  presenting  the  greatest  amount  of  curvature.  The  bone  is  also 
directed  more  obliquely  backward;  this  increases  the  size  of  the  pelvic  cavity  and  renders  the 
sacrovertebral  angle  more  prominent.  In  the  male  the  curvature  is  more  evenly  distributed 
over  the  whole  length  of  the  bone,  and  is  altogether  greater  than  in  the  female. 

Variations. — The  sacrum,  in  some  cases,  consists  of  six  pieces;  occasionally  the  number  is 
reduced  to  four.  The  bodies  of  the  first  and  second  vertebra  may  fail  to  unite.  Sometimes 
the  uppermost  transverse  tubercles  are  not  joined  to  the  rest  of  the  ala  on  one  or  both  sides, 
or  the  sacral  canal  may  be  open  throughout  a  considerable  part  of  its  length,  in  consequence  of 
the  imperfect  development  of  the  laminse  and  spinous  processes.  The  sacrum,  also,  varies  con- 
siderably with  respect  to  its  degree  of  curvature. 

The  Coccyx  (os  coccygis). — The  coccyx  (Fig.  100)  is  usually  formed  of  four 
rudimentary  vertebrae;  the  number  may  however  be  increased  to  five  or  diminished 
to  three.  In  each  of  the  first  three  segments  may  be  traced  a  rudimentary  body 
and  articular  and  transverse  processes;  the  last  piece  (sometimes  the  third)  is  a 
mere  nodule  of  bone.  All  the  segments  are  destitute  of  pedicles,  laminae,  and 
spinous  processes.  The  first  is  the  largest;  it  resembles  the  lowest  sacral  vertebra, 
and  often  exists  as  a  separate  piece;  the  last  three  diminish  in  size  from  above 
(downward,  and  are  usually  fused  with  one  another. 

Surfaces. — ^The  anterior  surface  is  slightly  concave,  and  marked  with  three  trans- 
verse grooves  which  indicate  the  junctions  of  the  different  segments.  It  gives 
attachment  to  the  anterior  sacrococcygeal  ligament  and  the  Levatores  ani,  and 

H|.$upports  part  of  the  rectum.    The  posterior  surface  is  convex,  marked  by  transverse 

^"  grooves  similar  to  those  on  the  anterior  surface,  and  presents  on  either  side  a  linear 
row  of  tubercles,  the  rudimentary  articular  processes  of  the  coccygeal  vertebrae. 
3f  these,  the  superior  pair  are  large,  and  are  called  the  coccygeal  comua;  they 
project  upward,  and  articulate  with  the  cornua  of  the  sacrum,  and  on  either  side 
complete  the  foramen  for  the  transmission  of  the  posterior  division  of  the  fifth 
sacral  nerve. 

Borders. — ^The  lateral  borders  are  thin,  and  exhibit  a  series  of  small  eminences, 
which  represent  the  transverse  processes  of  the  coccygeal  vertebrae.  Of  these, 
the  first  is  the  largest;  it  is  flattened  from  before  backward,  and  often  ascends 
to  join  the  lower  part  of  the  thin  lateral  edge  of  the  sacrum,  thus  completing  the 
foramen  for  the  transmission  of  the  anterior  division  of  the  fifth  sacral  nerve; 
the  others  diminish  in  size  from  above  downward,  and  are  often  wanting.  The 
borders  of  the  coccyx  are  narrow,  and  give  attachment  on  either  side  to  the  sacro- 
tuberous  and  sacrospinous  ligaments,  to  the  Coccygeus  in  front  of  the  ligaments, 
and  to  the  Glutaeus  maximus  behind  them. 

jM ,   Base. — The  base  presents  an  oval  surface  for  articulation  with  the  sacrum. 

^1 '  Apex. — The  apex  is  rounded,  and  has  attached  to  it  the  tendon  of  the  Sphincter 
ani  externus.    It  may  be  bifid,  and  is  sometimes  deflected  to  one  or  other  side. 

■  Ossification  of  the  Vertebral  Column. — Each  cartilaginous  vertebra  isossified  from  three  primary 
centers  (Fig.  101),  two  for  the  vertebral  arch  and  one  for  the  body.'  Ossification  of  the  vertebral 
arches  begins  in  the  upper  cervical  vertebrae  about  the  seventh  or  eighth  week  of  fetal  hfe,  and  grad- 
ually extends  down  the  column.  The  ossific  granules  first  appear  in  the  situations  where  the  trans- 
verse processes  afterward  project,  and  spread  backward  to  the  spinous  process  forward  into  the 
pedicles,  and  lateralward  into  the  transverse  and  articular  processes.  Ossification  of  thebodies  begins 
about  the  eighth  week  in  the  lower  thoracic  region,  and  subsequently  extends  upward  and  down- 
ward along  the  column.  The  center  for  the  body  does  not  give  rise  to  the  whole  of  the  body  of 
the  adult  vertebra,  the  postero-lateral  portions  of  which  are  ossified  by  extensions  from  the  verte- 
^bral  arch  centers.    The  body  of  the  vertebra  during  the  first  few  years  of  life  shows,  therefore, 

!».*  u  ^^"^bra  is  occasionally  found  in  which  the  body  consists  of  two  lateral  portions — a  condition  which  proves  that 
I  Be  body  IS  sometimes  ossified  from  two  primary  centers,  one  on  either  side  of  the  middle  line. 


112 


OSTEOLOGY 


two  synchondroses,  neurocentral  synchondroses,  tr 
the  three  centers  (Fig.  102).    In  the  thoracic  region, 

Fig.  101. — Ossification  of  a  vertebra 
By  3  primary  centers 

1  for  body  {Sth  week) 


I 


Ifor  each  vertebral  arch  [llh  or  Sth  week) 

Fig.  102. 
By  3  secondary  centers 


Neurocentral 
synchondrosis 


1  for  each 
trans,  process 
16th  year 


aversing  it  along  the  planes  of  junction  of 
the  facets  for  the  heads  of  the  ribs  lie  behhid 
the  neurocentral  synchondroses  and 
are  ossified  from  the  centers  for  tlie 
vertebral  arch.  At  birth  the  vertebra 
consists  of  three  pieces,  the  body  and 
the  halves  of  the  vertebral  arch.  Dur- 
ing the  first  year  the  halves  of  tlie 
arch  unite  behind,  union  taking  place 
first  in  the  lumbar  region  and  them 
extending  upward  through  the  thoracic 
and  cervical  regions.  About  the  third 
year  the  bodies  of  the  upper  cervical 
vertebrae  are  joined  to  the  arches  on 
either  side;  in  the  lower  lumbar  verte- 
brae the  union  is  not  completed  until  the 
sixth  year.     Before  puberty,  no  other 

Additional  centers 
for  costal  elements  * 


At  birth 


1  for  spinous  process  (16fA  year) 

Fig.  103. 
By  2  additional  plates 

1  for  upper  surface' 
of  body 

1  for  under  surface 
of  body 


I6th  year 


Fig.  104.— Atlas. 


By  3  centers 


for  anter.  arch  {end  of  1st  year) 
\  llh  week 


_1  for  each 
lateral  mass 


Fig.  105.— Axis. 


By  7  centers 


2nd  year 


6th  month 
1  for  each  vertebral  arch  (7  th 

or  Sth  week) 
1  for  body  (4th  month) 
1  for  under  surface  of  body 


a 


Fig.  106. — Lumbar  vertebra. 


2  additional  centers  for  mammillary  processes 


Fig.  107 


At  ^  yrs. 


Fig.  108 


Two  epiphysial  plates 
for  each  lateral  surface  * 


At 
25th  year 


Fig.   107-109. — Ossification  of  the  sacrum. 


changes  occur,  excepting  a  gradual  increase  of  these  primary  centers,  the  upper  and  under  sur- 
faces of  the  bodies  and  the  ends  of  the  transverse  and  spinous  processes  being  cartilaginous. 


I 


THE  SACRAL  AND  COCCYGEAL  VERTEBRA 


113 


About  the  sixteenth  year  (Fig.  102),  five  secondary  centers  appear,  one  for  the  tip  of  each  transverse 
process,  one  for  the  extremity  of  the  spinous  process,  one  for  the  upper  and  one  for  the  lower 
surface  of  the  body  (Fig.  103).    These  fuse  with  the  rest  of  the  bone  about  the  age  of  twenty-five. 

Exceptions  to  this  mode  of  development  occur  in  the  first,  second,  and  seventh  cervical  verte- 
bra;, and  in  the  lumbar  vertebrae. 

Atlas.^ — The  atlas  is  usually  ossified  from  three  centers  (Fig.  104).  Of  these,  one  appears  in 
each  lateral  mass  about  the  seventh  week  of  fetal  life,  and  extends  backward;  at  birth,  these 
portions  of  bone  are  separated  from  one  another  behind  by  a  narrow  interval  filled  with  cartilage. 
Between  the  third  and  fourth  years  they  unite  either  directly  or  through  the  medium  of  a  separate 
center  developed  in  the  cartilage.  At  birth,  the  anterior  arch  consists  of  cartilage;  in  this  a 
separate  center  appears  about  the  end  of  the  first  year  after  birth,  and  joins  the  lateral  masses 
from  the  sixth  to  the  eighth  year — the  lines  of  union  extending  across  the  anterior  portions  of 
the  superior  articular  facets.  Occasionally  there  is  no  separate  center,  the  anterior  arch  being 
formed  by  the  forward  extension  and  ultimate  junction  of  the  two  lateral  masses;  sometimes 
this  arch  is  ossified  from  two  centers,  one  on  either  side  of  the  middle  line. 

Epistropheus  or  Axis. — The  axis  is  ossified  from  five  primary  and  two  secondary  centers  (Fig. 
105).  The  body  and  vertebral  arch  are  ossified  in  the  same  manner  as  the  corresponding  parts 
in  the  other  vertebrae,  viz.,  one  center  for  the  body,  and  two  for  the  vertebral  arch.  The  centers 
for  the  arch  appear  about  the  seventh  or  eighth  week  of  fetal  life,  that  for  the  body  about  the 
fc  irth  or  fifth  month.  The  dens  or  odontoid  process  consists  originally  of  a  continuation  upward 
of  the  cartilaginous  mass,  in  which  the  lower  part  of  the  body  is  formed.  About  the  sixth  month 
of  fetal  life,  two  centers  make  their  appearance  in  the  base  of  this  process:  they  are  placed 
laterally,  and  join  before  birth  to  form  a  conical  bilobed  mass  deeply  cleft  above;  the  interval 
between  the  sides  of  the  cleft  and  the  summit  of  the  process  is  formed  by  a  wedge-shaped  piece 
of  cartilage.  The  base  of  the  process  is  separated  from  the  body  by  a  cartilaginous  disk,  which 
gradually  becomes  ossified  at  its  circumference,  but  remains  cartilaginous  in  its  center  until 
advanced  age.  In  this  cartilage,  rudiments  of  the  lower  epiphysial  lamella  of  the  atlas  and 
the  upper  epiphysial  lamella  of  the  axis  may  sometimes  be  found.  The  apex  of  the  odontoid 
process  has  a  separate  center  which  appears  in  the  second  and  joins  about  the  twelfth  year;  this 
is  the  upper  epiphysial  lamella  of  the  atlas.  In  addition  to  these  there  is  a  secondary  center  for 
a  thin  epiphysial  plate  on  the  under  surface  of  the  body  of  the  bone. 

The  Seventh  Cervical  Vertebra. — The  anterior  or  costal  part  of  the  transverse  process  of  this 
vertebra  is  sometimes  ossified  from  a  separate  center  which  appears  about  the  sixth  month  of 
fetal  life,  and  joins  the  body  and  posterior  part  of  the  transverse  process  between  the  fifth  and 
sixth  years.  Occasionally  the  costal  part  persists  as  a  separate  piece,  and,  becoming  lengthened 
lateralward  and  forward,  constitutes  what  is  known  as  a  ceruical  rib.  Separate  ossific  centers 
have  also  been  found  in  the  costal  processes  of  the  fourth,  fifth,  and  sixth  cervical  vertebrae. 

Lumbar  Vertebrae. — The  lumbar  vertebrae  (Fig.  106)  have  each  two  additional  centers,  for 
[the  mammillary  processes.  The  transverse  process  of  the  first  lumbar  is  sometimes  developed  as 
a  separate  piece,  which  may  remain  permanently  ununited  with  the  rest  of  the  bone,  thus  form- 
ing a  lumbar  rib — a  peculiarity,  however, 


Center  for 
neural  a 


Center  for 
neural  arch. 


N 


jOostal 
element. 


body. 


Lateral 
epiphysis. 

Fig.  110. — Base  of  young  sacrum 


Lateral 
epiphysis. 


^ 


rarely  met  with. 

Sacrum  (Figs.  107  to  110).— The  body 
of  each  sacral  vertebra  is  ossified  from  a 
primary  center  and  tivo  epiphysial  plates, 
one  for  its  upper  and  another  for  its  under 
surface,  while  each  vertebral  arch  is  ossi- 
fied from  two  centers. 

The  anterior  portions  of  the  lateral  parts 
have  six  additional  centers,  two  for  each 
of  the  first  three  vertebrae;  these  represent 
the  costal  elements,  and  make  their  ap- 
pearance above  and  lateral  to  the  anterior 
sacral  foramina  (Figs.  107,  108). 

On  each  lateral  surface  two  epiphysial  plates  are  developed  (Figs.  109,  1 10) :  one  for  the  auric- 
ular surface,  and  another  for  the  remaining  part  of  the  thin  lateral  edge  of  the  bone.^ 

Periods  of  Ossification. — About  the  eighth  or  ninth  week  of  fetal  life,  ossification  of  the 
central  part  of  the  body  of  the  first  sacral  vertebra  commences,  and  is  rapidly  foUowed  by  deposit 
of  ossific  matter  in  the  second  and  third ;  ossification  does  not  commence  in  the  bodies  of  the 
lower  two  segments  imtil  between  the  fifth  and  eighth  months  of  fetal  hfe.     Between  the  sixth 

'  The  ends  of  the  spinous  processes  of  the  upper  three  sacral  vertebrae  are  sometimes  developed  from  separate 
epiphyses,  and  Fawcett  (Anatomischer  Anzeiger,  1907,  Band  xxx)  states  that  a  number  of  epiphysial  nodules  may  be 
seen  in  the  sacrum  at  the  age  of  eighteen  years.  These  are  distributed  as  follows:  One  for  each  of  the  mammillary  pro- 
cesses of  the  first  sacral  vertebra ;  twelve — six  on  either  side — in  connection  with  the  costal  elements  (two  each  for  the  first 
and  second  and  one  each  for  the  third  and  fourth)  and  eight  for  the  transverse  processes— four  on  either  side — one  each 
for  the  first,  third,  fourth,  and  fifth.  He  is  further  of  opinion  that  the  lower  part  of  each  lateral  surface  of  the  sacrum 
is  formed  by  the  extension  and  union  of  the  third  and  fourth  "costal"  and  fourth  and  fifth  "transverse"  epiphyses. 


■ 


114  ^^^^^^^        OSTEOLOGY 


and  eighth  months  ossification  of  the  vertebral  arches  takes  place;  and  about  the  same  time  the 
costal  centers  for  the  lateral  parts  make  their  appearance.  The  junctions  of  the  vertebral 
arches  with  the  bodies  take  place  in  the  lower  vertebrae  as  early  as  the  second  year,  but  are  not 
effected  in  the  uppermost  until  the  fifth  or  sixth  year.  About  the  sixteenth  year  the  epiphysial 
plates  for  the  upper  and  under  surfaces  of  the  bodies  are  formed;  and  between  the  eighteenth  and 
twentieth  years,  those  for  the  lateral  surfaces  make  their  appearance.  The  bodies  of  the  sacral 
vertebrae  are,  during  early  life,  separated  from  each  other  by  intervertebral  fibrocartilages,  but 
about  the  eighteenth  year  the  two  lowest  segments  become  united  by  bone,  and  the  process  of 
bony  union  gradually  extends  upward,  with  the  result  that  between  the  twenty-fifth  and  thirtieth 
years  of  life  all  the  segments  are  united.  On  examining  a  sagittal  section  of  the  sacrum,  the  situa- 
tions of  the  intervertebral  fibrocartilages  are  indicated  by  a  series  of  oval  cavities  (Fig.  99). 

Coccyx. — The  coccyx  is  ossified  from  four  centers,  one  for  each  segment.  The  ossific  nuclei 
make  their  appearance  in  the  following  order:  in  the  first  segment  between  the  first  and  fourth 
years;  in  the  second  between  the  fifth  and  tenth  years;  in  the  third  between  the  tenth  and  fifteenth 
years;  in  the  fourth  between  the  fourteenth  and  twentieth  years.  As  age  advances,  the  segments 
unite  with  om  another,  the  union  between  the  first  and  second  segments  being  frequently  delayed 
until  after  the  age  of  twenty-five  or  thirty.  At  a  late  period  of  life,  especially  in  females,  the  coccyx 
often  fuses  with  the  sacrum. 

THE  VERTEBRAL  COLUMN  AS  A  WHOLE. 

The  vertebral  column  is  situated  in  the  median  line,  as  the  posterior  part  of  the 
trunk;  its  average  length  in  the  male  is  about  71  cm.  Of  this  length  the  cervical 
part  measures  12.5  cm.,  the  thoracic  about  28  cm.,  the  lumbar  18  cm.,  and  the 
sacrum  and  coccyx  12.5  cm.     The  female  column  is  about  61  cm.  in  length. 

Curves.- — Viewed  laterally  (Fig.  Ill),  the  vertebral  column  presents  several 
curves,  which  correspond  to  the  different  regions  of  the  column,  and  are  called 
cervical,  thoracic,  lumbar,  and  pelvic.  The  cervical  curve,  convex  forward,  begins 
at  the  apex  of  the  odontoid  process,  and  ends  at  the  middle  of  the  second  thoracic 
vertebra;  it  is  the  least  marked  of  all  the  curves.  The  thoracic  curve,  concave  for- 
ward, begins  at  the  middle  of  the  second  and  ends  at  the  middle  of  the  twelfth 
thoracic  vertebra.  Its  most  prominent  point  behind  corresponds  to  the  spinous 
process  of  the  seventh  thoracic  vertebra.  The  lumbar  curve  is  more  marked  in 
the  female  than  in  the  male;  it  begins  at  the  middle  of  the  last  thoracic  vertebra, 
and  ends  at  the  sacrovertebral  angle.  It  is  convex  anteriorly,  the  convexity  of 
the  lower  three  vertebrse  being  much  greater  than  that  of  the  upper  two.  The 
pelvic  curve  begins  at  the  sacrovertebral  articulation,  and  ends  at  the  point  of  the 
coccyx;  its  concavity  is  directed  downward  and  forward.  The  thoracic  and  pelvic 
curves  are  termed  primary  curves,  because  they  alone  are  present  during  fetal  life. 
The  cervical  and  lumbar  curves  are  compensatory  or  secondary,  and  are  developed 
after  birth,  the  former  when  the  child  is  able  to  hold  up  its  head  (at  three  or  four 
months),  and  to  sit  upright  (at  nine  months),  the  latter  at  twelve  or  eighteen 
months,  when  the  child  begins  to  walk. 

The  vertebral  column  has  also  a  slight  lateral  curvature,  the  convexity  of  which 
is  directed  toward  the  right  side.  This  may  be  produced  by  muscular  action, 
most  persons  using  the  right  arm  in  preference  to  the  left,  especially  in  making 
long-continued  efforts,  when  the  body  is  curved  to  the  right  side.  In  support  of 
this  explanation  it  has  been  found  that  in  one  or  two  individuals  who  were  left- 
handed,  the  convexity  was  to  the  left  side.  By  others  this  curvature  is  regarded  as 
being  produced  by  the  aortic  arch  and  upper  part  of  the  descending  thoracic 
aorta — a  view  which  is  supported  by  the  fact  that  in  cases  where  the  viscera  are 
transposed  and  the  aorta  is  on  the  right  side,  the  convexity  of  the  curve  is 
directed  to  the  left  side. 

Surfaces. — Anterior  Surface. — When  viewed  from  in  front,  the  width  of  the  bodies 
of  the  vertebrse  is  seen  to  increase  from  the  second  cervical  to  the  first  thoracic; 
there  is  then  a  slight  diminution  in  the  next  three  vertebrse;  below  this  there 
is  again  a  gradual  and  progressive  increase  in  width  as  low  as  the  sacrovertebral 
angle.     From  this  point  there  is  a  rapid  diminution,  to  the  apex  of  the  coccyx. 


I 


I 


THE  VERTEBRAL  COLUMN  AS  A  WHOLE 


115 


I 


Posterior  Surface. — The  posterior  surface 
of  the  vertebral  cokimn  presents  in  the 
median  line  the  spinous  processes.  In  the 
cervical  region  (with  the  exception  of  the 
second  and  seventh  vertebrae)  these  are 
short  and  horizontal,  with  bifid  extremities. 
In  the  upper  part  of  the  thoracic  region 
they  are  directed  obliquely  downward;  in 
the  middle  they  are  almost  vertical,  and  in 
the  lower  part  they  are  nearly  horizontal. 
In  the  lumbar  region  they  are  nearly  hori- 
zontal. The  spinous  processes  are  separated 
by  considerable  intervals  in  the  lumbar 
region,  by  narrower  intervals  in  the  neck, 
and  are  closely  approximated  in  the  middle 
of  the  thoracic  region.  Occasionally  one  of 
,  these  processes  deviates  a  little  from  the 
median  line — a  fact  to  be  remembered  in 
practice,  as  irregularities  of  this  sort  are 
attendant  also  on  fractures  or  displacements 
of  the  vertebral  column.  On  either  side  of 
the  spinous  processes  is  the  vertebral  groove 
formed  by  the  laminae  in  the  cervical  and 
lumbar  regions,  where  it  is  shallow,  and  by 
the  laminae  and  transverse  processes  in  the 
thoracic  region,  where  it  is  deep  and  broad ; 
these  grooves  lodge  the  deep  muscles  of  the 
back.  Lateral  to  the  vertebral  grooves  are 
the  articular  processes,  and  still  more  later- 
ally the  transverse  processes.  In  the  tho- 
racic region,  the  transverse  processes  stand 
backward,  on  a  plane  considerably  behind 
that  of  the  same  processes  in  the  cervical 
and  lumbar  regions.  In  the  cervical  region, 
I  the  trans^•erse  processes  are  placed  in  front 
'of  the  articular  processes,  lateral  to  the 
pedicles  and  between  the  intervertebral 
foramina.  In  the  thoracic  region  they  are 
posterior  to  the  pedicles,  intervertebral 
foramina,  and  articular  processes.  In  the 
lumbar  region  they  are  in  front  of  the 
articular  processes,  but  behind  the  inter- 
vertebral foramina. 

Lateral  Surfaces. — ^The  lateral  surfaces  are 
separated  from  the  posterior  surface  by  the 
articular  processes  in  the  cervical  and  lum- 
bar regions,  and  by  the  transverse  processes 
in  the  thoracic   region.    They  present,   in 
I  front,  the  sides  of  the  bodies  of  the  verte- 
I  brae,  marked  in  the  thoracic  region  by  the 
r  facets  for    articulation  with  the  heads  of 
the  ribs.     jNIore  posteriorly  are  the  inter- 
vertebral foramina,   formed  by  the  juxta- 
position of  the  vertebral  notches,  oval  in 


Fia.   111. — Lateral  view  of  the  vertebral  column. 


116 


OSTEOLOGY 


shape,  smallest  in  the  cervical  and  upper  part  of  the  thoracic  regions,  and  gradually] 
increasing  in  size  to  the  last  lumbar.    They  transmit  the  spinal  nerves  and  'ar«3 
situated  between  the  transverse  processes  in  the  cervical  region,  and  in  front  of 
them  in  the  thoracic  and  lumbar  regions. 

Vertebral  Canal. — The  vertebral  canal  follows  the  different  curves  of  the  column; 
it  is  large  and  triangular  in  those  parts  of  the  column  which  enjoy  the  greatest 
freedom  of  movement,  viz.,  the  cervical  and  lumbar  regions;  and  is  small  and 
rounded  in  the  thoracic  region,  where  motion  is  more  limited. 

Abnormalities. — Occasionally  the  coalescence  of  the  laminae  is  not  completed,  and  conse- 
quently a  cleft  is  left  in  the  arches  of  the  vertebrae,  through  which  a  protrusion  of  the  spinal 
membranes  (dura  mater  and  arachnoid),  and  generally  of  the  medulla  spinaUs  itself,  takes  place, 
constituting  the  malformation  known  as  spina  bifida.  This  condition  is  most  common  in  the 
lumbosacral  region,  but  it  may  occur  in  the  thoracic  or  cervical  region,  or  the  arches  throughout 
the  whole  length  of  the  canal  may  remain  incomplete. 


First  thoracic 


Fig.  112. — The  thorax  from  in  front.     (Spalteholz.) 

THE   THORAX. 


The  skeleton  of  the  thorax  or  chest  (Figs.  112,  113,  114)  is  an  osseo-cartilaginous 
cage,  containing  and  protecting  the  principal  organs  of  respiration  and  circulation. 


I 


THE  THORAX 


117 


It  is  conical  in  shape,  being  narrow  above  and  broad  below,  flattened  from  before 
backward,  and  longer  behind  than  in  front.  It  is  somewhat  reniform  on  trans- 
verse section  on  account  of  the  projection  of  the  vertebral  bodies  into  the  cavity. 


First  thoracic 


Fia.  113. — The  thorax  from  behind.     (Spalteholz.) 


Boundaries. — The  posterior  surface  is  formed  by  the  twelve  thoracic  vertebrae 
and  the  posterior  parts  of  the  ribs.  It  is  convex  from  above  downward,  and  pre- 
sents on  either  side  of  the  middle  line  a  deep  groove,  in  consequence  of  the  lateral 
and  backward  direction  which  the  ribs  take  from  their  vertebral  extremities  to 
their  angles.  The  anterior  surface,  formed  by  the  sternum  and  costal  cartilages, 
is  flattened  or  slightly  convex,  and  inclined  from  above  downward  and  forward. 
The  lateral  surfaces  are  convex;  they  are  formed  by  the  ribs,  separated  from 
jcach  other  by  the  intercostal  spaces,  eleven  in  number,  which  are  occupied  by 
fthe  Intercostal  muscles  and  membranes. 

The  upper  opening  of  the  thorax  is  Teniform  in  shape,  being  broader  from  side 
ko  side  than  from  before  backward.  It  is  formed  by  the  first  thoracic  vertebra 
[behind,  the  upper  margin  of  the  sternum  in  front,  and  the  first  rib  on  either  side. 


118 


OSTEOLOGY 


It"  slopes  downward  and  forward,  so  that  the  anterior  part  of  the  opening  is  on  a 
lower  level  than  the  posterior.  Its  antero-posterior  diameter  is  about  5  cm.,  and 
its  transverse  diameter  about  10  em.  The  lower  opening  is  formed  by  the  twelftli 
thoracic  vertebra  behind,  by  the  eleventh  and  twelfth  ribs  at  the  sides,  and  in  front 
by  the  cartilages  of  the  tenth,  ninth,  eighth,  and  seventh  ribs,  which  ascend  on 
either  side  and  form  an  angle,  the  subcostal  angle,  into  the  apex  of  which  the 


First  thoTi 


■Sternum 


Twelfth  thoracic' 


First  lumbar 


Fig.  114. — The  thorax  from  the  right.     (Spalteholz.) 


xiphoid  process  projects.  The  lower  opening  is  wider  transversely  than  from 
before  backward,  and  slopes  obliquely  downward  and  backward,  it  is  closed  by 
the  diaphragm  which  forms  tlie  floor  of  the  thorax. 


The  thorax  of  the  female  differs  from  that  of  the  male  as  follows:  1.  Its  capacity  is  less.  2. 
The  sternum  is  shorter.  3.  The  upper  margin  of  the  sternum  is  on  a  level  with  the  lower  part 
of  the  body  of  the  third  thoracic  vertebra,  whereas  in  the  male  it  is  on  a  level  with  the  lower 
part  of  the  body  of  the  second.  4.  The  upper  ribs  are  more  movable,  and  so  allow  a  greater 
enlargement  of  the  upper  part  of  the  thorax. 


THE  STERNUM 


The  Sternum  (Breast  Bone). 


119 


Tlie  sternum  (F'igs.  115  to  117)  is  an  elongated,  flattened  bone,  forming  the 
middle  portion  of  the  anterior  wall  of  the  thorax.  Its  upper  end  supports  the 
clavicles,  and  its  margins  articulate  with  the  cartilages  of  the  first  seven  pairs 


STEENOCLEIDOMASTOIDEUS 
S0BCLAVIDS     \  '^i<ffulaf 


Fig.   115. — Anterior  surface  of  sternum  and  costa   cartilages. 


of  ribs.  It  consists  of  three  parts,  named  from  above  downward,  the  manubrium, 
the  body  or  gladiolus,  and  the  xiphoid  process ;  in  early  life  the  body  consists  of  four 
segments  or  sternehroB.  In  its  natural  position  the  inclination  of  the  bone  is  oblique 
from  above,  downward  and  forward.     It  is  slightly  convex  in  front  and  concave 


i 


120 


OSTEOLOGY 


I 


behind;  broad  above,  becoming  narrowed  at  the  point  where  the  manubrium  joins 
the  body,  after  which  it  again  widens  a  little  to  below  the  middle  of  the  body, 
and  then  narrows  to  its  lower  extremity.  Its  average  length  in  the  adult  is  about 
17  cm.,  and  is  rather  greater  in  the  male  than  in  the  female. 

Manubrium  {manubrium  sterni). — The  manubrium  is  of  a  somewhat  quad- 
rangular form,  broad  and  thick  above,  narrow  below  at  its  junction  with  the  body. 

Surfaces. — Its  anterior  surface,  convex  from  side  to  side,  concave  from  above 
downward,  is  smooth,  and  affords  attachment  on  either  side  to  the  sternal 
origins  of  the  Pectoralis  major  and  Sternocleidomastoideus.  Sometimes  the 
ridges  limiting  the  attachments  of  these  muscles  are  very  distinct.  Its  posterior 
surface,  concave  and  smooth,  affords  attachment  on  either  side  to  the  Sterno- 
hyoideus  and  Sternothyreoideus. 


For  1st 
^-L  costal 
cartilage 


Sternal 
angle 


Xiphoid  process 


Fig.   116. — Posterior  surface  of  aternum. 


Articular  surface 
for  clavicle 

Depression  for 

lut  costal  cartilage 

Manvhrium 


Demifacets  for  2nd  costal 
cartilage 


Facet  fpY  Zrd  costal  cartilage 
Body 


Facet  for  Atli  costal  cartilage 

Facet  for  5th  costal  cartilage 

-Facet  for  6th  costal  cartilage 
-Facet  for  7th  costal  cartilage 
Xiphoid  process 


Fig.   117. — Lateral  border  of  sternum. 


Borders. — The  superior  border  is  the  thickest  and  presents  at  its  center  the  jugular 
or  presternal  notch ;  on  either  side  of  the  notch  is  an  oval  articular  surface,  directed 
upward,  backward,  and  lateralward,  for  articulation  with  the  sternal  end  of  the 
clavicle.  The  inferior  border,  oval  and  rough,  is  covered  in  a  fresh  state  with  a 
thin  layer  of  cartilage,  for  articulation  with  the  body.  The  lateral  borders  are  each 
marked  above  by  a  depression  for  the  first  costal  cartilage,  and  below  by  a  small 
facet,  which,  with  a  similar  facet  on  the  upper  angle  of  the  body,  forms  a  notch 
for  the  reception  of  the  costal  cartilage  of  the  second  rib.  Between  the  depression 
for  the  first  costal  cartilage  and  the  demi-facet  for  the  second  is  a  narrow,  curved 
edge,  which  slopes  from  above  downward  and  medialward. 

Body  {corpus  sterni;  gladiolus) . — The  body,  considerably  longer,  narrower,  and 
thinner  than  the  manubrium,  attains  its  greatest  breadth  close  to  the  lower  end. 

Surfaces. — Its  anterior  surface  is  nearly  flat,  directed  upward  and  forward, 
and  marked  by  three  transverse  ridges  which  cross  the  bone  opposite  the  third, 


i 


THE  STERNUM  ^^^^^M"  121 


I 


fourth,  and  fifth  articular  depressions.^  It  affords  attachment  on  either  side  to 
the  sternal  origin  of  the  Pectoralis  major.  At  the  junction  of  the  third  and  fourth 
jiieces  of  the  body  is  occasionally  seen  an  orifice,  the  sternal  foramen,  of  varying 
size  and  form.  The  posterior  surface,  slightly  concave,  is  also  marked  by  three 
transverse  lines,  less  distinct,  however,  than  those  in  front;  from  its  lower  part, 
on  either  side,  the  Transversus  thoracis  takes  origin. 

Borders. — The  superior  border  is  oval  and  articulates  with  the  manubrium,  the 
junction  of  the  two  forming  the  sternal  angle  (anguhis  Ludovici").  The  inferior 
border  is  narrow,  and  articulates  with  the  xiphoid  process.  Each  lateral  border 
(Fig.  117),  at  its  superior  angle,  has  a  small  facet,  which  with  a  similar  facet  on 
the  manubrium,  forms  a  cavity  for  the  cartilage  of  the  second  rib;  below  this 
are  four  angular  depressions  which  receive  the  cartilages  of  the  third,  fourth, 
fifth,  and  sixth  ribs,  while  the  inferior  angle  has  a  small  facet,  which,  with  a  cor- 
responding one  on  the  xiphoid  process,  forms  a  notch  for  the  cartilage  of  the  seventh 
rib.  These  articular  depressions  are  separated  by  a  series  of  curved  interarticular 
intervals,  which  diminish  in  length  from  above  downward,  and  correspond  to 
the  intercostal  spaces.  Most  of  the  cartilages  belonging  to  the  true  ribs,  as  will 
be  seen  from  the  foregoing  description,  articulate  with  the  sternum  at  the  lines 
of  junction  of  its  primitive  component  segments.  This  is  well  seen  in  many  of 
the  lower  animals,  where  the  parts  of  the  bone  remain  ununited  longer  than  in 
man. 

Xiphoid  Process  {processus  xiphoideus;  ensiform  or  xiphoid  appendix). — The 
xiphoid  process  is  the  smallest  of  the  three  pieces:  it  is  thin  and  elongated, 
cartilaginous  in  structure  in  youth,  but  more  or  less  ossified  at  its  upper  part  in 
the  adult. 

Surfaces. — Its  anterior  surface  affords  attachment  on  either  side  to  the  anterior 
costoxiphoid  ligament  and  a  small  part  of  the  Rectus  abdominis;  its  posterior  sur- 
face, to  the  posterior  costoxiphoid  ligament  and  to  some  of  the  fibers  of  the  dia- 
phragm and  Transversus  thoracis,  its  lateral  borders,  to  the  aponeuroses  of  the 
abdominal  muscles.  Above,  it  articulates  with  the  lower  end  of  the  body,  and 
on  the  front  of  each  superior  angle  presents  a  facet  for  part  of  the  cartilage  of  the 
seventh  rib;  below,  by  its  pointed  extremity,  it  gives  attachment  to  the  linea 
alba.  The  xiphoid  process  varies  much  in  form;  it  may  be  broad  and  thin,  pointed, 
bifid,  perforated,  curved,  or  deflected  considerably  to  one  or  otner  side. 

Structure. — The  sternum  is  composed  of  highly  vascular  cancellous  tissue,  covered  by  a  thin 
layer  of  compact  bone  which  is  thickest  in  the  manubrium  between  the  articular  facets  for  the 
clavicles. 

Ossification. — The  sternum  originally  consists  of  two  cartilaginous  bars,  situated  one  on  either 
side  of  the  median  plane  and  connected  with  the  cartilages  of  the  upper  nine  ribs  of  its  own  side. 
These  two  bars  fuse  with  each  other  along  the  middle  line  to  form  the  cartilaginous  sternum  which 
is  ossified  from  six  centers:  one  for  the  manubrium,  four  for  the  body,  and  one  for  the  xiphoid 
process  (Fig.  118).  The  ossific  centers  appear  in  the  intervals  between  the  articular  depressions 
for  the  costal  cartilages,  in  the  following  order:  in  the  manubrium  and  first  piece  of  the  body, 
during  the  sixth  month;  in  the  second  and  third  pieces  of  the  body,  during  the  seventh  month  of 
fetal  life;  in  its  fourth  piece,  during  the  first  year  after  birth;  and  in  the  xiphoid  process,  between 
the  fifth  and  eighteenth  years.  The  centers  make  their  appearance  at  the  upper  parts  of  the  seg- 
ments, and  proceed  gradually  downward.^  To  these  may  be  added  the  occasional  existence  of 
two  small  episternal  centers,  which  make  their  appearance  one  on  either  side  of  the  jugular  notch; 
they  are  probably  vestiges  of  the  episternal  bone  of  the  monotremata  and  lizards.  Occasionally 
some  of  the  segments  are  formed  from  more  than  one  center,  the  number  and  position  of  which 
vary  (Fig.  120).    Thus,  the  first  piece  may  have  two,  three,  or  even  six  centers.    When  two  are 

'  Paterson  (The  Human  Sternum,  1904),  who  examined  521  specimens,  points  out  that  these  ridges  are  altogether 
absent  in  26.7  per  cent. ;  that  in  69  per  cent,  a  ridge  exists  opposite  the  third  costal  attachment;  in  39  per  cent,  opposite 
the  fourth;  and  in  4  per  cent,  only,  opposite  the  fifth. 

2  Named  after  the  French  surgeon  Antoine  Louis,  1723-1792.  The  Latin  name  anjulus  Ludovici  is  not  infrequently 
mistranslated  into  English  as  "the  angle  of  Ludwig. " 

'  Out  of  141  sterna  between  the  time  of  birth  and  the  age  of  sixteen  years,  Paterson  (,op.  cit.)  found  the  fourth  or 
lowest  center  for  the  body  present  only  in  thirty-eight  cases — t.  e.,  26.9  per  cent. 


122 


OSTEOLOGY 


Time 

of 

appearance 


Time 

of 
union 


In 

number  of 
centers 


In 

mode  of 


1  for  manubrium   \ 

\6lh  month 
(2) 
3\ 

*\ 

_  5     1st  year  after  birth 


4  for  body 


■  7th  month 


1  for.  xiphoid  \ 

process        f^^^  '^  ^^^^  year 


Fig.   118. — O-ssification  of  the  sternum. 


Rarely  unite,  except  in  old  age 
Between  puberty  and  the  25th  year 

Soon  after  puberty 

Partly  cartilaginous  to  advanced  life 
FiQ.  119 


for  first  piece,  two  or  more  centers 

for  second  piece,  ustudly  one 

for  third  '\ 

,  f  ^>  placed  laterally 
forfouHh)      ^  * 

for  fifth 


Fig.   120. — Peculiaritiea. 


Arrest  of  ossification  of  lateral  ineces. 
producing  : 

Sternal  fissure,  and 


Sternal  foramen 


Fig.  121 


I 


THE  RIBS  Wl^m  123 


^ 


Wh 


present,  they  are  generally  situated  one  above  the  other,  the  upper  being  the  larger;  the  second 
piece  has  seldom  more  than  one;  the  third,  fourth,  and  fifth  pieces  are  often  formed  from  two 
centers  placed  laterally,  the  irregular  union  of  which  explains  the  rare  occurrence  of  the  sternal 
foramen  (Fig.  121),  or  of  the  vertical  fissure  which  occasionally  intersects  this  part  of  the  bone 
constituting  the  malformation  known  as  fissura  sterni;  these  conditions  are  further  explained  by 
the  manner  in  which  the  cartilaginous  sternum  is  formed.  More  rarely  still  the  upper  end  of  the 
sternum  may  be  divided  by  a  fissure.  Union  of  the  various  centers  of  the  body  begins  about 
puberty,  and  proceeds  from  below  upward  (Fig.  119) ;  by  the  age  of  twenty-five  they  are  all  imited. 
The  xiphoid  process  may  become  joined  to  the  body  before  the  age  of  thirty,  but  this  occurs 
more  frequently  after  forty;  on  the  other  hand,  it  sometimes  remains  ununited  in  old  age.  In 
advanced  life  the  manubrium  is  occasionally  joined  to  the  body  by  bone.  When  this  takes  place, 
however,  the  bony  tissue  is  generally  only  superficial,  the  central  portion  of  the  intervening 
cartilage  remaining  unossified. 

Articulations. — The  sternum  articulates  on  either  side  with  the  clavicle  and  upper  seven  costal 
cartilages. 

The  Ribs  (Costae). 

The  ribs  are  elastic  arches  of  bone,  which  form  a  large  part  of  the  thoracic 
skeleton.  They  are  twelve  in  number  oh  either  side;  but  this  number  may  be 
increased  by  the  development  of  a  cervical  or  lumbar  rib,  or  may  be  diminished 
to  eleven.  The  first  seven  are  connected  behind  with  the  vertebral  column,  and  in 
front,  through  the  intervention  of  the  costal  cartilages,  with  the  sternum  (Fig. 
115);  they  are  called  true  or  vertebro-stemal  ribs.^  The  remaining  five  are  false 
ribs ;  of  these,  the  first  three  have  their  cartilages  attached  to  the  cartilage  of  the 
rib  above  (vertebro-chondral) :  the  last  two  are  free  at  their  anterior  extremities 
and  are  termed  floating  or  vertebral  ribs.  The  ribs  vary  in  their  direction,  the 
upper  ones  being  less  oblique  than  the  lower;  the  obliquity  reaches  its  maximum 
at  the  ninth  rib,  and  gradually  decreases  from  that  rib  to  the  twelfth.  The  ribs 
are  situated  one  below  the  other  in  such  a  manner  that  spaces  called  intercostal 
spaces  are  left  between  them.  The  length  of  each  space  corresponds  to  that  of 
[the  adjacent  ribs  and  their  cartilages;  the  breadth  is  greater  in  front  than  behind, 
and  between  the  upper  than  the  lower  ribs.  The  ribs  increase  in  length  from 
the  first  to  the  seventh,  below  which  they  diminish  to  the  twelfth.  In  breadth 
they  decrease  from  above  downward;  in  the  upper  ten  the  greatest  breadth  is  at 
the  sternal  extremity. 

{  Common  Characteristics  of  the  Ribs  (Figs.  122,  123). — A  rib  from  the  middle 
of  the  series  should  be" taken  in  order  to  study  the  common  characteristics  of  these 
bones. 

Each  rib  has  two  extremities,  a  posterior  or  vertebral,  and  an  anterior  or  sternal, 
and  an  intervening  portion — the  body  or  shaft. 

Posterior  Extremity. — The  posterior  or  vertebral  extremity  presents  for  examination 
a  head,  neck,  and  tubercle. 

The  head  is  marked  by  a  kidney-shaped  articular  surface,  divided  by  a  hori- 
zontal crest  into  two  facets  for  articulation  with  the  depression  formed  on  the 
bodies  of  two  adjacent  thoracic  vertebrae;  the  upper  facet  is  the  smallier;  to  the 
crest  is  attached  the  interarticular  ligament.  ^ 

The  neck  is  the  flattened  portion  which  extends  lateralward  from  the  head;  it 
is  about  2.5  cm.  long,  and  is  placed  in  front  of  the  transverse  process  of  the 
lower  of  the  two  vertebrae  with  which  the  head  articulates.  Its  anterior  surface  is 
flat  and  smooth,  its  posterior  rough  for  the  attachment  of  the  ligament  of  the  neck, 
nd  perforated  by  numerous  foramina.  Of  its  two  borders  the  superior  presents  a 
rough  crest  (crista  colli  costoe)  for  the  attachment  of  the  anterior  costotransverse 
ligament;  its  inferior  border  is  rounded.  On  the  posterior  surface  at  the  junction 
of  the  neck  and  body,  and  nearer  the  lower  than  the  upper  border,  is  an  eminence 

_  1  Sometimes  the  eighth  rib  cartilage  articulates  with  the  sternum;  thi-s  coaditioa  occurs  more  frequently  on  the 
right  than  on  the  left  side. 


km 


124 


OSTEOLOGY 


— the  tubercle ;  it  consists  of  an  articular  and  a  non-articular  portion.    The  articuiar 
portion,  the  lower  and  more  medial  of  the  two,  presents  a  small,  oval  surface  lor 


I 


Angle 


•Costal  groove 


S 
Sf 


•Body 


Non-articular  part  of  tubercle 

Articular  part  of  tubercle 


■^ 


Fig.  122.- 


central  rib  of  the  left  side. 
Inferior  aspect. 


articulation  with  the  end  of  the  transverse  pro- 
cess of  the  lower  of  the  two  vertebrae  to  which 
the  head  is  connected.  The  non-articular  por- 
tion is  a  rough  elevation,  and  affords  attach- 
ment to  the  ligament  of  the  tubercle.  The 
tubercle  is  much  more  prominent  in  the  upper 
than  in  the  lower  ribs. 

Body. — The  body  or  shaft  is  thin  and  flat, 
with  two  surfaces,  an  external  and  an  internal ; 
and  two  borders,  a  superior  and  an  inferior. 
The  external  surface  is  convex,  smooth,  and 
marked,  a  little  in  front  of  the  tubercle,  by  a 
prominent  line,  directed  downw^ard  and  lateral- 
ward;  this  gives  attachment  to  a  tendon  of 
the  Iliocostalis,  and  is  called  the  angle.  At 
this  point  the  rib  is  bent  in  tw^o  directions, 
and  at  the  same  time  twisted  on  its  long  axis. 
If  the  rib  be  laid  upon  its  lower  border,  the 
portion  of  the  body  in  front  of  the  angle  rests 
upon  this  border,  while  the  portion  behind  the 
angle  is  bent  medial  ward  and  at  the  same 
time  tilted  upw-ard;  as  the  result  of  the  twist- 
ing, the  external  surface,  behind  the  angle, 
looks  downward,  and  in  front  of  the  angle, 
slightly  upward.  The  distance  between  the 
angle  and  the  tubercle  is  progressively  greater 
from  the  second  to  the  tenth  ribs.  The  por- 
tion between  the  angle  and  the  tubercle  is 
rounded,  rough,  and  irregular,  and  serves  for 
the  attachment  of  the  Longissimus  dorsi.  The 
internal  surface  is  concave,  smooth,  directed  a 
little  upward  behind  the  angle,  a  little  down- 
ward in  front  of  it,  and  is  marked  by  a  ridge 
which  commences  at  the  lower  extremity  of 
the  head;  this  ridge  is  strongly  marked  as  far 
as  the  angle,  and  gradually  becomes  lost  at 
the  junction  of  the  anterior  and  middle  thirds 
of  the  bone.  Between  it  and  the  inferior 
border  is  a  groove,  the  costal  groove,  for  the 
intercostal  vessels  and  nerve.  At  the  back 
part  of  the  bone,  this  groove  belongs  to  the 


I 


THE  RIBS 


125 


inferior  border,  but  just  in  front  of  the  angle,  where  it  is  deepest  and  broadest,  it  is 
on  the  internal  surface.  The  superior  edge  of  the  groove  is  rounded  and  serves 
for  the  attachment  of  an  Intercostalis  internus;  the  inferior  edge  corresponds  to 
the  lower  margin  of  the  rib,  and  gives  attachment  to  an  Intercostalis  externus. 
Within  the  groove  are  seen  the  oriifices  of  numerous  small  foramina  for  nutrient 
vessels  which  traverse  the  shaft  obliquel}'  from  before  backward.  The  superior 
border,  thick  and  rounded,  is  marked  by  an  external  and  an  internal  lip,  more 
distinct  behind  than  in  front,  which  serve  for  the  attachment  of  Intercostales 
externus  and  internus.  The  inferior  border  is  thin,  and  has  attached  to  it  an  Inter- 
costalis externus. 

Anterior  Extremity. — The  anterior  or  sternal  extremity  is  flattened,  and  presents  a 
porous,  oval,  concave  depression,  into  which  the  costal  cartilage  is  received. 

Peculiar  Ribs.— The  first,  second,  tenth,  eleventh,  and  twelfth  ribs  present 
certain  variations  from  the  common  characteristics  described  above,  and  require 
special  consideration. 

'  Demifacet  for  vertebra 

Jnterarticular  crest 

Demifacet  for  vertebra 


A  central  rib  of  the  left  aide,  viewed  from  behind. 


First  Rib. — The  first  rib  (Fig.  124)  is  the  most  curved  and  usually  the  shortest 
)f  all  the  ribs;  it  is  broad  and  flat,  its  surfaces  looking  upward  and  downward, 

■  md  its  borders  inward  and  outward.  The  head  is  small,  rounded,  and  possesses 
-felly  a  single  articular  facet,  for  articulation  with  the  body  of  the  first  thoracic 
'  \^ertebra.  The  neck  is  narrow  and  rounded.  The  tubercle,  thick  and  prominent, 
s  placed  on  the  outer  border.  There  is  no  angle,  but  at  the  tubercle  the  rib  is 
slightly  bent,  with  the  convexity  upward,  so  that  the  head  of  the  bone  is  directed 
downward.  The  upper  surface  of  the  body  is  marked  by  two  shallow  grooves, 
separated  from  each  other  by  a  slight  ridge  prolonged  internally  into  a  tubercle, 
the  scalene  tubercle,  for  the  attachment  of  the  Scalenus  anterior;  the  anterior 
groove  transmits  the  subclavian  vein,  the  posterior  the  subclavian  artery  and 
the  lowest  trunk  of  the  brachial  plexus.^  Behind  the  posterior  groove  is  a  rough 
area  for  the  attachment  of  the  Scalenus  medius.  The  under  surface  is  smooth, 
and  destitute  of  a  costal  groove.  The  outer  border  is  convex,  thick,  and  rounded, 
and  at  its  posterior  part  gives  attachment  to  the  first  digitation  of  the  Serratus 
anterior;  the  inner  border  is  concave,  thin,  and  sharp,  and  marked  about  its  center 
by  the  scalene  tubercle.  The  anterior  extremity  is  larger  and  thicker  than  that 
of  any  of  the  other  ribs. 
Second  Rib. — ^The  second  rib  (Fig.  125)  is  much  longer  than  the  first,  but  has  a 

...... .,„„...„.^, 


'  Anat.  Anzeiger,  1910,  Band  xxxvi. 


126 


OSTEOLOGY 


I 


only  feebly  marked.  The  angle  is  slight,  and  situated  close  to  the  tubercle.  Tlie 
body  is  not  twisted,  so  that  both  ends  touch  any  plane  surface  upon  which  it  may 
be  laid;  but  there  is  a  bend,  with  its  convexity  upward,  similar  to,  though  smaller 
than  that  found  in  the  first  rib.  The  body  is  not  flattened  horizontally  like  that 
of  the  first  rib.  Its  external  surface  is  convex,  and  looks  upward  and  a  little  outward ; 
near  the  middle  of  it  is  a  rough  eminence  for  the  origin  of  the  lower  part  of  the 


FiQ.   124 


Fig.  125 


Angi 


FiQ.   126 
Single  articular  facet  — 


FiQ.  127 
Single  articular  facet 


Fia.  128 
Single  articular  facet 


Figs.    124  to  128. — Peculiar  ribs. 

first  and  the  whole  of  the  second  digitation  of  the  Serratus  anterior;  behind  and 
above  this  is  attached  the  Scalenus  posterior.  The  internal  surface,  smooth,  and 
concave,  is  directed  downward  and  a  little  inward:  on  its  posterior  part  there  is 
a  short  costal  groove. 

Tenth  Rib. — ^The  tenth  rib  (Fig.  126)  has  only  a  single  articular  facet  on  its  head. 

Eleventh  and  Twelfth  Ribs. — The  eleventh  and  twelfth  ribs  (Figs.  127  and  128) 
have  each  a  single  articular  facet  on  the  head,  which  is  of  rather  large  size;  they 


I 


THE  COSTAL  CARTILAGES  ^^^K         127 


have  no  necks  or  tubercles,  and  are  pointed  at  their  anterior  ends.  The  eleventh 
has  a  slight  angle  and  a  shallow  costal  groove.  The  twelfth  has  neither;  it  is  much 
shorter  than  the  eleventh,  and  its  head  is  inclined  slightly  downward.  Sometimes 
the  twelfth  rib  is  even  shorter  than  the  first. 

Structure. — The  ribs  consist  of  liighly  vascular  cancellous  tissue,  enclosed  in  a  thin  layer  of 
compact    bone. 

Ossification. — Each  rib,  with  the  exception  of  the  last  two,  is  ossified  from  four  centers;  a 
primary  center  for  the  body,  and  three  epiphysial  centers,  one  for  the  head  and  one  each  for  the 
articular  and  non-articular  parts  of  the  tubercle.  The  eleventh  and  twelfth  ribs  have  each  only 
two  centers,  those  for  the  tubercles  being  wanting.  Ossification  begins  near  the  angle  toward  the 
end  of  the  second  month  of  fetal  life,  and  is  seen  first  in  the  sixth  and  seventh  ribs.  The  epiphyses 
for  the  head  and  tubercle  make  their  appearance  between  the  sixteenth  and  twentieth  years,  and 
are  united  to  the  body  about  the  twenty-fifth  year.  Fawcett^  states  that  "in  all  probabihty  there 
is  usually  no  epiphysis  on  the  non-articular  part  of  the  tuberosity  below  the  sixth  or  seventh  rib. 

PThe  Costal  Cartilages  (Cartilagines  Costales). 
The  costal  cartilages  (Fig.  115)  are  bars  of  hyaline  cartilage  which  serve  to 
prolong  the  ribs  forward  and  contribute  very  materially  to  the  elasticity  of  the 
walls  of  the  thorax.  The  first  seven  pairs  are  connected  with  the  sternum;  the 
next  three  are  each  articulated  with  the  lower  border  of  the  cartilage  of  the  pre- 
ceding rib;  the  last  two  have  pointed  extremities,  which  end  in  the  wall  of  the 
abdomen.  Like  the  ribs,  the  costal  cartilages  vary  in  their  length,  breadth,  and 
direction.  They  increase  in  length  from  the  first  to  the  seventh,  then  gradually 
decrease  to  the  twelfth.  Their  breadth,  as  well  as  that  of  the  intervals  between 
them,  diminishes  from  the  first  to  the  last.  They  are  broad  at  their  attachments 
to  the  ribs,  and  taper  toward  their  sternal  extremities,  excepting  the  first  two, 
which  are  of  the  same  breadth  throughout,  and  the  sixth,  seventh,  and  eighth, 
v.hich  are  enlarged  where  their  margins  are  in  contact.  They  also  vary  in  direc- 
tion: the  first  descends  a  little,  the  second  is  horizontal,  the  third  ascends  slightly, 
^,'hile  the  others  are  angular,  following  the  course  of  the  ribs  for  a  short  distance, 
find  then  ascending  to  the  sternum  or  preceding  cartilage.  Each  costal  cartilage 
I)resents  two  surfaces,  two  borders,  and  two  extremities. 

Surfaces. — The  anterior  surface  is  convex,  and  looks  forward  and  upward:  that 
of  the  first  gives  attachment  to  the  costoclavicular  ligament  and  the  Subclavius 
muscle;  those  of  the  first  six  or  seven  at  their  sternal  ends,  to  the  Pectoralis  major. 
The  others  are  covered  by,  and  give  partial  attachment  to,  some  of  the  flat  muscles 
of  the  abdomen.  The  posterior  surface  is  concave,  and  directed  backward  and 
downward;  that  of  the  first  gives  attachment  to  the  Sternothyroideus,  those  of 
the  third  to  the  sixth  inclusive  to  the  Transversus  thoracis,  and  the  six  or  seven 
inferior  ones  to  the  Transversus  abdominis  and  the  diaphragm. 

Borders. — Of  the  two  borders  the  superior  is  concave,  the  inferior  convex;  they 
afford  attachment  to  the  Intercostales  interni:  the  upper  border  of  the  sixth  gives 
attachment  also  to  the  Pectoralis  major.  The  inferior  borders  of  the  sixth,  seventh, 
eighth,  and  ninth  cartilages  present  heel-like  projections  at  the  points  of  greatest 
convexity.  These  projections  carry  smooth  oblong  facets  which  articulate  respec- 
tively with  facets  on  slight  projections  from  the  upper  borders  of  the  seventh, 
(eighth,  ninth,  and  tenth  cartilages. 

^  Extremities. — The  lateral  end  of  each  cartilage  is  continuous  with  the  osseous 
tissue  of  the  rib  to  which  it  belongs.  The  medial  end  of  the  first  is  continuous 
with  the  sternum;  the  medial  ends  of  the  six  succeeding  ones  are  rounded  and  are 
received  into  shallow  concavities  on  the  lateral  margins  of  the  sternum.  The 
medial  ends  of  the  eighth,  ninth,  and  tenth  costal  cartilages  are  pointed,  and  are 
connected  each  with  the  cartilage  immediately  above.  Those  of  the  eleventh  and 
twelfth  are  pointed  and  free.  In  old  age  the  costal  cartilages  are  prone  to  undergo 
superficial  ossification. 

1  Journal  of  Anatomy  and  Physiology,  vol.  xlv. 


■ 


128 


OSTEOLOGY 


I 


Cervical  ribs  derived  from  the  seventh  cervical  vei'tebra  (page  83)  are  of  not  infrequent  occur- 
rence, and  are  important  clinically  because  they  may  give  rise  to  obscure  nervous  or  vascular 
symptoms.  The  cervical  rib  may  be  a  mere  epiphysis  articulating  only  with  the  transverse  process 
of  the  vertebra,  but  more  commonly  it  consists  of  a  defined  head,  neck,  and  tubercle,  with  or 
without  a  body.  It  extends  lateralwaixl,  or  forward  and  lateralward,  into  the  posterior  triangle 
of  the  neck,  where  it  may  terminate  in  a  free  end  or  may  join  the  first  thoracic  rib,  the  first  costal 
cartilage,  or  the  sternum. ^  It  varies  much  in  shape,  size,  direction,  and  mobility.  If  it  ret.ch 
far  enough  forward,  part  of  the  brachial  plexus  and  the  subclavian  artery  and  vein  cross  o^er 
it,  and  are  apt  to  suffer  compression  in  so  doing.  Pressure  on  the  artery  may  obstruct  the  circula- 
tion so  much  that  arterial  thrombosis  results,  causing  gangrene  of  the  finger  tips.  Pressure  on 
the  nerves  is  commoner,  and  affects  the  eighth  cervical  and  first  thoracic  nerves,  causing  paralysis 
of  the  muscles  they  supply,  and  neuralgic  pains  and  paresthesia  in  the  area  of  skin  to  which  they 
are  distributed :    no  oculopupillary  changes  are  to  be  found. 

The  thorax  is  frequently  found  to  be  altered  in  shape  in  certain  diseases. 

In  rickets,  the  ends  of  the  ribs,  where  they  join  the  costal  cartilages,  become  enlarged,  giving 
rise  to  the  so-called  "rickety  rosary,"  which  in  mild  cases  is  only  found  on  the  internal  surface 
of  the  thorax.  Lateral  to  these  enlargements  the  softened  ribs  sink  in,  so  as  to  present  a  groove 
passing  downward  and  lateralward  on  either  side  of  the  sternum.  This  bone  is  forced  forward 
by  the  bending  of  the  ribs,  and  the  antero-posterior  diameter  of  the  chest  is  increased.  The  ribs 
affected  are  the  second  to  the  eighth,  the  lower  ones  being  prevented  from  falling  in  by  the  pres- 
ence of  the  liver,  stomach,  and  spleen;  and  when  the  abdomen  is  distended,  as  it  often  is  in  rickets, 
the  lower  ribs  may  be  pushed  outward,  causing  a  transverse  groove  (Harrison's  sulcus)  just 
above  the  costal  arch.  This  deformity  or  forward  projection  of  the  sternum,  often  asymmetrical, 
is  known  as  pigeon  breast,  and  may  be  taken  as  evidence  of  active  or  old  rickets  except  in  cases 
of  primary  spinal  curvature.  In  many  instances  it  is  associated  in  children  with  obstruction  in 
the  upper  air  passages,  due  to  enlarged  tonsils  or  adenoid  growths.  In  some  rickety  children  or 
adults,  and  also  in  others  who  give  no  history  or  further  evidence  of  having  had  rickets,  an  opposite 
condition  obtains.  The  lower  part  of  the  sternum  and  often  the  xiphoid  process  as  well  are  deeply 
depressed  backward,  producing  an  oval  hollow  in  the  lower  sternal  and  upper  epigastric  regions. 
This  is  known  as  funnel  breast  (German,  Trichterbrust) ;  it  never  appears  to  produce  the  least 
disturbance  of  any  of  the  vital  functions.  The  phthisical  chest  is  often  long  and  narrow,  and  with 
great  obliquity  of  the  ribs  and  projection  of  the  scapula?.  In  pulmonary  emphysema  the  chest  is 
enlarged  in  all  its  diameters,  and  presents  on  section  an  almost  circular  outline.  It  has  received 
the  name  of  the  barrel-shaped  chest.  In  severe  cases  of  lateral  curvature  of  the  vertebral  column 
■  the  thorax  becomes  much  distorted.  In  consequence  of  the  rotation  of  the  bodies  of  the  vertebrae 
which  takes  place  in  this  disease,  the  ribs  opposite  the  convexity  of  the  dorsal  curve  become 
extremely  convex  behind,  being  thrown  out  and  bulging,  and  at  the  same  time  flattened  in  front, 
so  that  the  two  ends  of  the  same  rib  are  almost  parallel.  Coincidently  with  this  the  ribs  on  the 
opposite  side,  on  the  concavity  of  the  curve,  are  sunk  and  depressed  behind,  and  bulging  and 
convex  in  front. 

THE  SKULL. 

The  skull  is  supported  on  the  summit  of  the  vertebral  column,  and  is  of  an 
oval  shape,  wider  behind  than  in  front.  It  is  composed  of  a  series  of  flattened 
or  irregular  bones  which,  with  one  exception  (the  mandible),  are  immovably 
jointed  together.  It  is  divisible  into  two  parts:  (1)  the  cranium,  which  lodges 
and  protects  the  brain,  consists  of  eight  bones,  and  (2)  the  skeleton  of  the  face, 
of  fourteen,  as  follows : 


Cranium,  8  bones 


Occipital. 

Two  Parietals. 

Frontal. 

Two  Temporals. 

Sphenoidal. 

Ethmoidal. 

Skull,  22  bones   ]  ^  ^^.^  ^^^^^^ 

Two  Maxillae. 
Two  Lacrimals. 
Two  Zygomatics. 
Two  Palatines. 
Two  Inferior  Nasal  Conchse. 
Vomer. 
1^  Mandible. 

1  W.  Thorburn,  The  Medical  Chronicle,  Manchester,  1907,  4th  series,  xiv.  No.  3 


.  Face,  14  bones 


I 


THE  OCCIPITAL  BONE 


129 


In  the  Basle  nomenclature,  certain  bones  developed  in  association  with  the  nasal 
capsule,  viz.,  the  inferior  nasal  conchse,  the  lacrimals,  the  nasals,  and  the  vomer, 
are  grouped  as  cranial  and  not  as  facial  bones. 

The  hyoid  bone,  situated  at  the  root  of  the  tongue  and  attached  to  the  base 
of  the  skull  by  ligaments,  is  described  in  this  section. 


THE    CRANIAL   BONES    (OSSA    CRANE). 


The  Occipital  Bone  (Os  Occipitale). 


^H  The  occipital  bone  (Figs.  129,  130),  situated  at  the  back  and  lower  part  of  the 
cranium,  is  trapezoid  in  shape  and  curved  on  itself.  It  is  pierced  by  a  large  oval 
aperture,  the  foramen  magnum,  through  w^hich  the  cranial  cavity  communicates 
with  the  vertebral  canal. 


Constrictor  pharyngis 
superior 

Fig.   129. — Occipital  bone.     Outer  surface. 

The  curved,  expanded  plate  behind  the  foramen  magnum  is  named  the  squama; 
the  thick,  somewhat  quadrilateral  piece  in  front  of  the  foramen  is  called  the 
basilar  part,  whilst  on  either  side  of  the  foramen  is  the  lateral  portion. 

The  Squama  {squama  occipitalis). — ^The  squama,  situated  above  and  behind 
the  foramen  magnum,  is  curved  from  above  downward  and  from  side  to  side. 

Surfaces. — The  external  surface  is  convex  and  presents  midway  between  the 
summit  of  the  bone  and  the  foramen  magnum  a  prominence,  the  external  occipital 
protuberance.  Extending  lateralward  from  this  on  either  side  are  two  curved 
ines,  one  a  little  above  the  other.  The  upper,  often  faintly  marked,  is  named 
le  highest  nuchal  line,  and  to  it  the  galea  aponeurotica  is  attached.  The  lower 
9 


130 


OSTEOLOGY 


I 


is  termed  the  superior  nuchal  line.  That  part  of  the  squama  which  Hes  above 
the  highest  nuchal  lines  is  named  the  planum  occipitale,  and  is  covered  by  the 
Occipitalis  muscle;  that  below,  termed  the  planum  nuchale,  is  rough  and  irregular 
for  the  attachment  of  several  muscles.  From  the  external  occipital  protuberance 
a  ridge  or  crest,  the  median nuchalline,  often  faintly  marked,  descends  to  the  fora- 
men magnum,  and  affords  attachment  to  the  ligamentum  nuchae;  running  from 
the  middle  of  this  line  across  either  half  of  the  nuchal  plane  is  the  inferior  nuchal 
line.  Several  muscles  are  attached  to  the  outer  surface  of  the  squama,  thus: 
the  superior  nuchal  line  gives  origin  to  the  Occipitalis  and  Trapezius,  and  insertion 
to  the  Sternocleidomastoideus  and  Splenius  capitis:  into  the  surface  between 


Sufieri'of  Am. 


Fia. 


Inferior  A  ngle 
130. — Occipita  bone. 


Inner  surface. 


the  superior  and  inferior  nuchal  lines  the  Semispinalis  capitis  and  the  Obliquus 
capitis  superior  are  inserted,  while  the  inferior  nuchal  line  and  the  area  below 
it  receive  the  insertions  of  the  Recti  capitis  posteriores  major  and  minor.  The 
posterior  atlantooccipital  membrane  is  attached  around  the  postero-lateral  part 
of  the  foramen  magnum,  just  outside  the  margin  of  the  foramen. 

The  internal  surface  is  deeply  concave  and  divided  into  four  fossae  by  a  cruciate 
eminence.  The  upper  two  fossse  are  triangular  and  lodge  the  occipital  lobes  of 
the  cerebrum;  the  lower  two  are  quadrilateral  and  accommodate  the  hemispheres 
of  the  cerebellum.  At  the  point  of  intersection  of  the  four  divisions  of  the  cruciate 
eminence  is  the  internal  occipital  protuberance.  From  this  protuberance  the  upper 
division  of  the  cruciate  eminence  runs  to  the  superior  angle  of  the  bone,  and  on 


I 


THE  OCCIPITAL  BONE 


131 


^ 


one  side  of  it  (generally  the  right)  is  a  deep  groove,  the  sagittal  sulcus,  which  lodges 
the  hinder  part  of  the  superior  sagittal  sinus;  to  the  margins  of  this  sulcus  the  falx 
cerebri  is  attached.  The  lower  division  of  the  cruciate  eminence  is  prominent, 
and  is  named  the  internal  occipital  crest;  it  bifurcates  near  the  foramen  magnum 
and  gives  attachment  to  the  falx  cerebelli;  in  the  attached  margin  of  this  falx 
is  the  occipital  sinus,  which  is  sometimes  duplicated.  In  the  upper  part  of  the 
internal  occipital  crest,  a  small  depression  is  sometimes  distinguishable;  it  is 
termed  the  vermian  fossa  since  it  is  occupied  by  part  of  the  vermis  of  the  cerebellum. 
Transverse  grooves,  one  on  either  side,  extend  from  the  internal  occipital  protuber- 
ance to  the  lateral  angles  of  the  bone;  those  grooves  accommodate  the  transverse 
sinuses,  and  their  prominent  margins  give  attachment  to  the  tentorium  cerebelli. 
The  groove  on  the  right  side  is  usually  larger  than  that  on  the  left,  and  is 
continuous  with  that  for  the  superior  sagittal  sinus.  Exceptions  to  this  condition 
are,  however,  not  infrequent;  the  left  may  be  larger  than  the  right  or  the  two 
may  be  almost  equal  in  size.  The  angle  of  union  of  the  superior  sagittal  and  trans- 
verse sinuses  is  named  the  confluence  of  the  sinuses  {torcular  Herophili^),  and  its 
position  is  indicated  by  a  depression  situated  on  one  or  other  side  of  the 
protuberance. 

Lateral  Parts  (pars  lateralis). — The  lateral  parts  are  situated  at  the  sides  of 
the  foramen  magnum;  on  their  under  surfaces  are  the  condyles  for  articulation 
with  the  superior  facets  of  the  atlas.    The  condyles  are  oval  or  reniform  in  shape, 
and  their  anterior  extremities,  directed  forward  and  mediahvard,  are  closer  together 
than  their  posterior,  and  encroach  on  the  basilar  portion  of  the  bone;  the  posterior 
extremities  extend  back  to  the  level  of  the  middle  of  the  foramen  magnum.    The 
articular  surfaces  of  the  condyles  are  convex  from  before  backward  and  from 
side  to  side,  and  look  downward  and  lateralward.    To  their  margins  are  attached 
the  capsules  of  the  atlantooccipital  articulations,  and  on  the  medial  side  of  each 
is  a  rough  impression  or  tubercle  for  the  alar  ligament.     At  the  base  of  either 
condyle  the  bone  is  tunnelled  by  a  short  canal,  the  hypoglossal  canal  {anterior 
Icondyloid  foramen) .    This  begins  on  the  cranial  surface  of  the  bone  immediately 
[above  the  foramen  magnum,  and  is  directed  lateralward  and  forward  above  the 
j*condyle.    It  may  be  partially  or  completely  divided  into  two  by  a  spicule  of  bone ; 
it  gives  exit  to  the  hypoglossal  or  twelfth  cerebral  nerve,  and  entrance  to  a  meningeal 
branch  of  the  ascending  pharyngeal  artery.    Behind  either  condyle  is  a  depression, 
Ithe  condyloid  fossa,  which  receives  the  posterior  margin  of  the  superior  facet  of 
the  atlas  when  the  head  is  bent  backward;  the  floor  of  this  fossa  is  sometimes 
perforated  by  the  condyloid  canal,  through  which  an  emissary  vein  passes  from  the 
I  ttransverse  sinus.     Extending  lateralward  from  the  posterior  half  of  the  condyle 
lis  a  quadrilateral  plate  of  bone,  the  jugular  process,  excavated  in  front  by  the  jugvdar 
Ixiotch,  which,  in  the  articulated  skull,  forms  the  posterior  part  of  the  jugular  fora- 
men.   The  jugular  notch  may  be  divided  into  two  by  a  bony  spicule,  the  intra- 
jugular  process,  which  projects  lateralward  above  the  hypoglossal  canal.     The 
■under  surface  of  the  jugular  process  is  rough,  and  gives  attachment  to  the  Rectus 
•capitis  lateralis   muscle   and    the   lateral    atlantooccipital    ligament;    from  this 
surface  an  eminence,  the  paramastoid  process,  sometimes  projects  downward,  and 
may  be  of  sufficient  length  to  reach,  and  articulate  with,  the  transverse  process 
of  the  atlas.    Laterally  the  jugular  process  presents  a  rough  quadrilateral  or  tri- 

( angular  area  which  is  joined  to  the  jugular  surface  of  the  temporal  bone  by  a  plate 
of  cartilage;  after  the  age  of  twenty-five  this  plate  tends  to  ossify. 
The  upper  surface  of  the  lateral  part  presents  an  oval  eminence,  the  jugular 
tubercle,  which  overlies  the  hypoglossal  canal  and  is  sometimes  crossed  by  an 
oblique  groove  for  the  glossopharyngeal,  vagus,  and  accessory  nerves.     On  the 


'  The  columns  of  blood  coming  in  different  directions  were  supposed  to  be  pressed  together  at  this  point  (torcular, 
wine  press). 


132 


OSTEOLOGY 


upper  surface  of  the  jugular  process  is  a  deep  groove  which  curves  medial  ward 
and  forward  and  is  continuous  with  the  jugular  notch.  This  groove  lodges  the 
terminal  part  of  the  transverse  sinus,  and  opening  into  it,  close  to  its  medial 
margin,  is  the  orifice  of  the  condyloid  canal. 

Basilar  Part  (pars  hasilaris)  .■ — The  basilar  part  extends  forward  and  upward 
from  the  foramen  magnum,  and  presents  in  front  an  area  more  or  less  quadrilateral 
in  outline.  In  the  young  skull  this  area  is  rough  and  uneven,  and  is  joined  to  the 
body  of  the  sphenoid  by  a  plate  of  cartilage.  By  the  twenty-fifth  year  this  cartil- 
aginous plate  is  ossified,  and  the  occipital  and  sphenoid  form  a  continuous  bone. 
Surfaces. — On  its  lower  surface,  about  1  cm.  in  front  of  the  foramen  magnum, 
is  the  pharyngeal  tubercle  which  gives  attachment  to  the  fibrous  raphe  of  the  pharynx. 
On  either  side  of  the  middle  line  the  Longus  capitis  and  Rectus  capitis  anterior 
are  inserted,  and  immediately  in  front  of  the  foramen  magnum  the  anterior 
atlantooccipital  membrane  is  attached. 

The  upper  surface  presents  a  broad,  shallow  groove  which  inclines  upward 
and  forward  from  the  foramen  magnum;  it  supports  the  medulla  oblongata,  and 
near  the  margin  of  the  foramen  magnum  gives  attachment  to  the  membrana 
tectoria.  On  the  lateral  margins  of  this  surface  are  faint  grooves  for  the  inferior 
petrosal  sinuses. 

Foramen  Magnum. — The  foramen  magnum  is  a  large  oval  aperture  with  its  long 
diameter  antero-posterior;  it  is  wider  behind  than  in  front  where  it  is  encroached 
upon  by  the  condyles.  It  transmits  the  medulla  oblongata  and  its  membranes, 
the  accessory  nerves,  the  vertebral  arteries,  the  anterior  and  posterior  spinal 
arteries,  and  the  membrana  tectoria  and  alar  ligaments. 

Angles. — The  superior  angle  of  the  occipital  bone  articulates  with  the  occipital 
angles  of  the  parietal  bones  and,  in  the  fetal  skull,  corresponds  in  position  with  the 
posterior  fontanelle.  The  inferior  angle  is  fused  with  the  body  of  the  sphenoid. 
The  lateral  angles  are  situated  at  the  extremities  of  the  grooves  for  the  transverse 

sinuses:  each  is  received  into  the  interval 
between  the  mastoid  angle  of  the  parietal 
and  the  mastoid  part  of  the  temporal. 

Borders.  —  The  superior  borders  extend 
from  the  superior  to  the  lateral  angles: 
they  are  deeply  serrated  for  articulation 
with  the  occipital  borders  of  the  parietals, 
and  form  by  this  union  the  lambdoidal 
suture.  The  inferior  borders  extend  from 
the  lateral  angles  to  the  inferior  angle; 
the  upper  half  of  each  articulates  with 
the  mastoid  portion  of  the  corresponding 
temporal,  the  lower  half  with  the  petrous 
part  of  the  same  bone.  These  two  por- 
tions of  the  inferior  border  are  separated 
from  one  another  by  the  jugular  process, 
the  notch  on  the  anterior  surface  of  which 
forms  the  posterior  part  of  the  jugular 
foramen. 

Fio.   131. — Occipital  bone  at  birth. 

Structure. — The  occipital,  like  the  other  cranial 
bones,    consists  of  two   compact  lamellae,   called 
the  outer  and  inner  tables,  between  which  is  the  cancellous  tissue  or  diploe;  the  bone  is  especially- 
thick  at  the  ridges,  protuberances,  condyles,  and  anterior  part  of  the  basilar  part;  in  the  inferior 
fossse  it  is  thin,  semitransparent,  and  destitute  of  diploe. 

Ossification  (Fig.  131). — The  planum  occipitale  of  the  squama  is  developed  in  membrane, 
and  may  remam  separate  throughout  life  when  it  constitutes  the  interparietal  bone;  the  rest  of 


Planum 
occipitale 


Planum 

nv£hale 

Kerckring^s 
center 

Lateral 
part 


Basilar  part 


THE  PARIETAL  BONE 


133 


the  bone  is  developed  in  cartilage.  The  number  of  nuclei  for  the  planum  occipitale  is  usually- 
given  as  four,  two  appearing  near  the  middle  hne  about  the  second  month,  and  two  some  little 
distance  from  the  middle  line  about  the  third  month  of  fetal  life.  The  planum  nuchale  of  the 
scjuama  is  ossified  from  two  centers,  which  appear  about  the  seventh  week  of  fetal  Ufe  and  soon 
unite  to  form  a  single  piece.  Union  of  the  upper  and  lower  portions  of  the  squama  takes  place 
in  the  third  month  of  fetal  life.  An  occasional  center  (Kerckring)  appears  in  the  posterior  margin 
of  the  foramen  magnum  during  the  fifth  month;  this  forms  a  separate  ossicle  (sometimes  double) 
which  unites  with  the  rest  of  the  squama  before  birth.  Each  of  the  lateral  parts  begins  to 
ossify  from  a  single  center  during  the  eighth  week  of  fetal  Ufe.  The  basilar  portion  is  ossified 
from  two  centers,  one  in  front  of  the  other;  these  appear  about  the  sixth  week  of  fetal  life  and 
rapidly  coalesce.  Mall^  states  that  the  planum  occipitale  is  ossified  from  two  centers  and  the 
basilar  portion  from  one.  About  the  fourth  year  the  squama  and  the  two  lateral  portions  unite, 
and  about  the  sixth  year  the  bone  consists  of  a  single  piece.  Between  the  eighteenth  and  twenty- 
fifth  years  the  occipital  and  sphenoid  become  united,  forming  a  single  bone. 

Articulations. — The  occipital  articulates  with  six  bones :    the  two  parietals,  the  two  temporals, 
the  sphenoid,  and  the  atlas. 


The  Parietal  Bone  (Os  Parietale). 

The  parietal  bones  form,  by  their  union,  the  sides  and  roof  of  the  cranium.  Each 
bone  is  irregularly  quadrilateral  in  form,  and  has  two  surfaces,  four  borders, 
and  four  angles. 

Articulates  with  opposite  parietal  bone 


ticvlates 


rental 


Fig.    132. — Left  parietal  bone. 


With  mastoid  portion  of 
tetniDoral  bone 
Outer  surface. 


Surfaces. — The  external  surface  (Fig.  132)  is  convex,  smooth,  and  marked  near 
le  center  by  an  eminence,  the  parietal  eminence  (tuber  parietale),  which  indicates 
le  point  where  ossification  commenced.    Crossing  the  middle  of  the  bone  in  an 


•  American  Journal  of  Anatomy,  1906,  vol.  v. 


134 


OSTEOLOGY 


arched  direction  are  two  curved  lines,  the  superior  and  inferior  temporal  lines;  the 
former  gives  attachment  to  the  temporal  fascia,  and  the  latter  indicates  the  upper 
limit  of  the  muscular  origin  of  the  Temporalis.  Above  these  lines  the  bone  is 
covered  by  the  galea  aponeurotica;  below  them  it  forms  part  of  the  temporal 
fossa,  and  affords  attachment  to  the  Temporalis  muscle.  At  the  back  part  and 
close  to  the  upper  or  sagittal  border  is  the  parietal  foramen,  which  transmits  a 
vein  to  the  superior  sagittal  sinus,  and  sometimes  a  small  branch  of  the  occipital 
artery;  it  is  not  constantly  present,  and  its  size  varies  considerably. 

The  internal  surface  (Fig.  133)  is  concave;  it  presents  depressions  corresponding 
to  the  cerebral  convolutions,  and  numerous  furrows  for  the  ramifications  of  the 
middle  meningeal  vessel;^  the  latter  run  upward  and  backward  from  the  sphenoidal 
angle,  and  from  the  central  and  posterior  part  of  the  squamous  border.  Along 
the  upper  margin  is  a  shallow  groove,  which,  together  with  that  on  the  opposite 


Ul^^^^^^^'h. 


I 


Occipital 
angle 


Mastoid 
angle 


Frontal 
'   angle 


noidal  anple 


Fig.   133. — Left  parietal  bone.     Inner  surface. 


parietal,  forms  a  channel,  the  sagittal  sulcus,  for  the  superior  sagittal  sinus;  the 
edges  of  the  sulcus  afford  attachment  to  the  falx  cerebri.  Near  the  groove  are 
several  depressions,  best  marked  in  the  skulls  of  old  persons,  for  the  arachnoid 
granulations  {Pacchionian  bodies).  In  the  groove  is  the  internal  opening  of  the 
parietal  foramen  when  that  aperture  exists. 

Borders. — The  sagittal  border,  the  longest  and  thickest,  is  dentated  and  articu- 
lates with  its  fellow  of  the  opposite  side,  forming  the  sagittal  suture.  The  squamous 
border  is  divided  into  three  parts:  of  these,  the  anterior  is  thin  and  pointed,  bevelled 
at  the  expense  of  the  outer  surface,  and  overlapped  by  the  tip  of  the  great  wing 
of  the  sphenoid;  the  middle  portion  is  arched,  bevelled  at  the  expense  of  the  outer 
surface,  and  overlapped  by  the  squama  of  the  temporal ;  the  posterior  part  is  thick 
and  serrated  for  articulation  with  the  mastoid  portion  of  the  temporal.     The 

'  Journal  of  Anatomy  and  Physiology,  1912,  vol   xlvi 


I 


THE  FRONTAL  BONE  ^^^B  135 


IN 


frontal  border  is  deeply  serrated,  and  bevelled  at  the  expense  of  the  outer  surface 
above  and  of  the  inner  below;  it  articulates  with  the  frontal  bone,  forming  one- 
half  of  the  coronal  suture.  The  occipital  border,  deeph'  denticulated,  articulates 
with  the  occipital,  forming  one-half  of  the  lambdoidal  suture. 

Angles. — The  frontal  angle  is  practically  a  right  angle,  and  corresponds  with 
the  point  of  meeting  of  the  sagittal  and  coronal  sutures;  this  point  is  named  the 
bregma;  in  the  fetal  skull  and  for  about  a  year  and  a  half  after  birth  this  region  is 
membranous,  and  is  called  the  anterior  fontanelle.  The  sphenoidal  angle,  thin 
and  acute,  is  received  into  the  interval  between  the  frontal  bone  and  the  great 
wing  of  the  sphenoid.  Its  inner  surface  is  marked  by  a  deep  groove,  sometimes 
a  canal,  for  the  anterior  divisions  of  the  middle  meningeal  artery.  The  occipital 
angle  is  rounded  and  corresponds  with  the  point  of  meeting  of  the  sagittal  and 
lambdoidal  sutures — a  point  which  is  termed  the  lambda;  in  the  fetus  this  part 
of  the  skull  is  membranous,  and  is  called  the  posterior  fontanelle.  The  mastoid 
angle  is  truncated;  it  articulates  with  the  occipital  bone  and  with  the  mastoid 
portion  of  the  temporal,  and  presents  on  its  inner  surface  a  broad,  shallow  groove 
which  lodges  part  of  the  transverse  sinus.  The  point  of  meeting  of  this  angle 
ith  the  occipital  and  the  mastoid  part  of  the  temporal  is  named  the  asterion. 


Ossification. — The  parietal  bone  is  ossified  in  membrane  from  a  single  center,  which  appears 
t  the  parietal  eminence  about  the  eighth  week  of  fetal  life.     Ossification  gradually  extends  in 
n  radial  manner  from  the  center  toward  the  margins  of  the  bone;  the  angles  are  consequently 
he  parts  last  formed,  and  it  is  here  that  the  fontanelles  exist.    Occasionally  the  parietal  bone 
iS  divided  into  two  parts,  upper  and  lower,  by  an  antero-posterior  suture. 

Articulations. — The  parietal  articulates  with  five  bones:  the  opposite  parietal,  the  occipital, 
frontal,  temporal,  and  sphenoid. 

The  Frontal  Bone  (Os  Frontale). 

The  frontal  bone  resembles  a  cockle-shell  in  form,  and  consists  of  two  portions 
-a  vertical  portion,  the  squama,  corresponding  with  the  region  of  the  forehead; 
|fcnd  an  orbital  or  horizontal  portion,  which  enters  into  the  formation  of  the  roofs 
of  the  orbital  and  nasal  cavities. 

Squama  {squama  frontalis). — Surfaces. — The  external  surface  (Fig.  134)  of  this 
portion  is  convex  and  usually  exhibits,  in  the  lower  part  of  the  middle  line,  the 
remains  of  the  frontal  or  metopic  suture ;  in  infancy  this  suture  divides  the  bone  into 
I  two,  a  condition  which  may  persist  tlu-oughout  life.    On  either  side  of  this  suture, 
jiibout  3  cm.  above  the  supraorbital  margin,  is  a  rounded  elevation,  the  frontal  emi- 
I  iience  {tuber  frontale) .    These  eminences  vary  in  size  in  different  individuals,  are 
occasionally  unsymmetrical,.and  are  especially  prominent  in  young  skulls;  the  sur- 
iace  of  the  bone  above  them  is  smooth,  and  covered  by  the  galea  aponeurotica. 
teelow  the  frontal  eminences,  and  separated  from  them  by  a  shallow  groove,  are 
Itwo  arched  elevations,  the  superciliary  arches;  these  are  prominent  medially,  and 
fare  joined  to  one  another  by  a  smooth  elevation  named  the  glabella.    They  are 
larger  in  the  male  than  in  the  female,  and  their  degree  of  prominence  depends 
to  some  extent  on  the  size  of  the  frontal  air  sinuses;^  prominent  ridges  are,  how- 
ever, occasionally  associated  with  small  air  sinuses.     Beneath  each  superciliary 
arch  is  a  curved  and  prominent  margin,  the  supraorbital  margin,  which  forms  the 
upper  boundary  of  the  base  of  the  orbit,  and  separates  the  squama  from  the  orbital 
[portion  of  the  bone.     The  lateral  part  of  this  margin  is  sharp  and  prominent, 
laffording  to  the  eye,  in  that  situation,  considerable  protection  from  injury;  the 
Imedial  part  is  rounded.    At  the  junction  of  its  medial  and  intermediate  thirds  is 

1  Some  confusion  is  occasioned  to  students  commencing  the  study  of  anatomy  by  the  name  "sinus"  having  been 
•  given  to  two  different  kinds  of  space  connected  with  the  skull.  It  may  be  as  well,  therefore,  to  state  here  that  the 
"sinuses"  in  the  interior  of  the  cranium  which  produce  the  grooves  on  the  inner  surfaces  of  the  bones  are  venous 
channels  which  convey  the  blood  from  the  brain,  while  the  "sinuses"  external  to  the  cranial  cavity  (the  frontal, 
sphenoidal,  ethmoidal,  and  maxillary)  are  hollow  spaces  in  the  bones  themselves;  they  communicate  with  the  nasal 
savities  and  contain  air. 


■ 


136 


OSTEOLOGY 


a  notch,  sometimes  converted  into  a  foramen,  the  supraorbital  notch  or  foramen, 
which  transmits  the  supraorbital  vessels  and  nerve.  A  small  aperture  in  the  uppeT 
part  of  the  notch  transmits  a  vein  from  the  diploe  to  join  the  supraorbital  vein. 
The  supraorbital  margin  ends  laterally  in  the  zygomatic  process,  which  is  strong 
and  prominent,  and  articulates  with  the  zygomatic  bone.  Running  upward  and 
backward  from  this  process  is  a  well-marked  line,  the  temporal  line,  which  divid(!S 
into  the  upper  and  lower  temporal  lines,  continuous,  in  the  articulated  skull,  with 
the  corresponding  lines  on  the  parietal  bone.  The  area  below  and  behind  the  tem- 
poral line  forms  the  anterior  part  of  the  temporal  fossa,  and  gives  origin  to  the 
Temporalis  muscle.  Betw^een  the  supraorbital  margins  the  squama  projects  down- 
ward to  a  level  below  that  of  the  zygomatic  processes;  this  portion  is  known  as  the 
nasal  part  and  presents  a  rough,  uneven  interval,  the  nasal  notch,  which  articulates 


I 


Zygomatic 
process 


Frontal    i  spine 
Fig.   134. — Frontal  bone.     Outer  surface. 

on  either  side  of  the  middle  line  with  the  nasal  bone,  and  laterally  with  the  frontal 
process  of  the  maxilla  and  with  the  lacrimal.  The  term  nasion  is  applied  to  the 
middle  of  the  frontonasal  suture.  From  the  center  of  the  notch  the  nasal  process 
projects  downw^ard  and  forward  beneath  the  nasal  bones  and  frontal  processes  of 
the  maxilla^,  and  supports  the  bridge  of  the  nose.  The  nasal  process  ends  below 
in  a  sharp  spine,  and  on  either  side  of  this  is  a  small  grooved  surface  which  enters 
into  the  formation  of  the  roof  of  the  corresponding  nasal  cavity.  The  spine  forms 
part  of  the  septum  of  the  nose,  articulating  in  front  with  the  crest  of  the  nasal 
bones  and  behind  with  the  perpendicular  plate  of  the  ethmoid. 

The  internal  surface  (Fig.  135)  of  the  squama  is  concave  and  presents  in  the 
upper  part  of  the  middle  line  a  vertical  groove,  the  sagittal  sulcus,  the  edges  of 
which  unite  below  to  form  a  ridge,  the  frontal  crest;  the  sulcus  lodges  the  superior 
sagittal  sinus,  w'hile  its  margins  and  the  crest  afford  attachment  to  the  falx  cerebri. 


J 


THE  FRONTAL  BONE 


137 


The  crest  ends  below  in  a  small  notch  which  is  converted  into  a  foramen,  the  fora- 
men cecum,  by  articulation  with  the  ethmoid.  This  foramen  varies  in  size  in 
different  subjects,  and  is  frequently  impervious;  when  open,  it  transmits  a  vein 
from  the  nose  to  the  superior  sagittal  sinus.  On  either  side  of  the  middle  line  the 
bone  presents  depressions  for  the  convolutions  of  the  brain,  and  numerous  small 
furrows  for  the  anterior  branches  of  the  middle  meningeal  vessels.  Several  small, 
irregular  fossae  may  also  be  seen  on  either  side  of  the  sagittal  sulcus,  for  the 
reception  of  the  arachnoid  granulations. 

Orbital  or  Horizontal  Part  {yars  orbitalis). — This  portion  consists  of  two  thin 
triangular  plates,  the  orbital  plates,  which  form  the  vaults  of  the  orbits,  and  are 
separated  from  one  another  by  a  median  gap,  the  ethmoidal  notch. 


Supraorbital 
foramen 


With  maxilla 

With  nasal 


Frontal  sinus 


\vm  nasal,  •     i     \  jj,,^^^  surface  of  nasal  process 

With  ■perpendicular  plate  of  ethmoid       ||         forming  part  of  roof  of  nose 


* 


I 


Fig.   135. — Frontal  bone.     Inner  surface. 


Surfaces. — The  inferior  surface  (Fig.  135)  of  each  orbital  plate  is  smooth  and 
concave,  and  presents,  laterally,  under  cover  of  the  zygomatic  process,  a  shallow 
depression,  the  lacrimal  fossa,  for  the  lacrimal  gland;  near  the  nasal  part  is  a  depres- 
sion, the  fovea  trochlearis,  or  occasionally  a  small  trochlear  spine,  for  the  attach- 
ment of  the  cartilaginous  pulley  of  the  Obliquus  oculi  superior.  The  superior 
surface  is  convex,  and  marked  by  depressions  for  the  convolutions  of  the  frontal 

Llobes  of  the  brain,  and  faint  grooves  for  the  meningeal  branches  of  the  ethmoidal 

rvessels. 

The  ethmoidal  notch  separates  the  two  orbital  plates;  it  is  quadrilateral,  and 
filled,  in  the  articulated  skull,  by  the  cribriform  plate  of  the  ethmoid.  The  margins 
of  the  notch  present  several  half-cells  which,  when  united  with  corresponding 
half-cells  on  the  upper  surface  of  the  ethmoid,  complete  the  ethmoidal  air  cells. 
Two  grooves  cross  these  edges  transversely;  they  are  converted  into  the  anterior 


138 


OSTEOLOGY 


I 


and  posterior  ethmoidal  canals  by  the  ethmoid,  and  open  on  the  medial  wall  of  tlie 
orbit.  The  anterior  canal  transmits  the  nasociliary  nerve  and  anterior  ethmoidal 
vessels,  the  posterior,  the  posterior  ethmoidal  nerve  and  vessels.  In  front  of  tlie 
ethmoidal  notch,  on  either  side  of  the  frontal  spine,  are  the  openings  of  the  frontal 
air  sinuses.  These  are  two  irregular  cavities,  which  extend  backward,  upward, 
and  lateralward  for  a  variable  distance  between  the  two  tables  of  the  skull;  th<;y 
are  separated  from  one  another  by  a  thin  bony  septum,  which  often  deviates  to 
one  or  other  side,  with  the  result  that  the  sinuses  are  rarely  symmetrical.  Absent 
at  birth,  they  are  usually  fairly  well-developed  between  the  seventh  and  eighth 
years,  but  only  reach  their  full  size  after  puberty.  They  vary  in  size  in  different 
persons,  and  are  larger  in  men  than  in  women. ^  They  are  lined  by  mucous  mem- 
brane, and  each  communicates  with  the  corresponding  nasal  cavity  by  means  of  a 
passage  called  the  frontonasal  duct. 

Borders. — The  border  of  the  squama  is  thick,  strongly  serrated,  bevelled  at  the 
expense  of  the  inner  table  above,  where  it  rests  upon  the  parietal  bones,  and  at 
the  expense  of  the  outer  table  on  either  side,  where  it  receives  the  lateral  pressure 
of  those  bones;  this  border  is  continued  below  into  a  triangular,  rough  surface, 
which  articulates  with  the  great  wing  of  the  sphenoid.  The  posterior  borders  of 
the  orbital  plates  are  thin  and  serrated,  and  articulate  with  the  small  wings  of  the 
sphenoid. 

Structure. — The  squama  and  the  zygomatic  processes  are  very  thick,  consisting  of  diploic 
tissue  contained  between  two  compact  laminae;  the  diploic  tissue  is  absent  in  the  regions  occupied 
by  the  frontal  air  sinuses.  The  orbital  portion  is  thin,  translucent,  and  composed  entirely  of 
compact  bone;  hence  the  facility  with  which  instruments  can  penetrate  the  cranium  through 
this  part  of  the  orbit;  when  the  frontal  sinuses  are  exceptionally  large  they  may  extend  backward 
for  a  considerable  distance  into  the  orbital  portion,  which  in  such  cases  also  consists  of  onlj"^  two 
tables. 

Ossification  (Fig.  136).  —  The  frontal  bone  is  ossified  in  membrane  from  two  primary 
centers,  one  for  each  half,  which  appear  toward  the  end  of  the  second  month  of  fetal  life,  one 
above  each  supraorbital  margin.  From  each  of  these  centers  ossification  extends  upward  to  form 
the  corresponding  half  of  the  squama,  and  backward  to  form  the  orbital  plate.     The  spine  is 

ossified  from  a  pair  of  secondary  centers, 
«  on  either  side  of  the  middle  line;    similar 

*  centers  appear  in  the  nasal  part  and  zN'go- 

matic  processes.  At  birth  the  bone  consists 
of  two  pieces,  separated  by  the  frontal 
suture,  which  is  usually  obliterated,  except 
at  its  lower  part,  by  the  eighth  year,  but 
occasionally  persists  throughout  life.  It  is 
generally  maintained  that  the  development 
of  the  frontal  sinuses  begins  at  the  end  of 
the  first  or  beginning  of  the  second  year, 
but  Onodi's  researches  indicate  that  de- 
velopment begins  at  birth.  The  sinuses 
are  of  considerable  size  by  the  seventh  or 
eighth  year,  but  do  not  attain  their  full 
proportions  until  after  puberty. 

Articulations.  —  The  frontal  articulates 
with  twelve  bones:  the  sphenoid,  the  eth- 
moid, the  two  parietals,  the  two  nasals,  the 
two  maxillse,  the  two  lacrimals,  and  the 
two  zygomatics. 


Nasal  part 


Zygomatic  process 


Spine 
Fia.   136. — Frontal  bone  at  birth. 


The  Temporal  Bone  (Os  Temporale). 

The  temporal  bones  are  situated  at  the  sides  and  base  of  the  skull.  Each  consists 
of  five  parts,  viz.,  the  squama,  the  petrous,  mastoid,  and  tympanic  parts,  and  the 
styloid  process. 

•  Aldren  Turner  (The  Accessory  Sinuses  of  the  Nose,  1901)  gives  the  foljowirig  measurements  for  a  sinus  of  average 
size:  height,  \}/i  inches;  breadth,  1  inch;  depth  from  before  backward,  1  inch. 


THE  TEMPORAL  BONE 


139 


The  Squama  (squama  temporalis). — The  squama  forms  the  anterior  and  upper 
part  of  the  bone,  and  is  scale-like,  thin,  and  translucent. 

Surfaces.— Its  outer  surface  (P'ig.  137)  is  smooth  and  convex;  it  affords  attach- 
ment to  the  Temporalis  muscle,  and  forms  part  of  the  temporal  fossa;  on  its  hinder 
part  is  a  vertical  groove  for  the  middle  temporal  artery.  A  curved  line,  the  tem- 
poral line,  or  supramastoid  crest,  runs  backward  and  upward  across  its  posterior 
part;  it  serves  for  the  attachment  of  the  temporal  fascia,  and  limits  the  origin 
of  the  Temporalis  muscle.  The  boundary  between  the  squama  and  the  mastoid 
portion  of  the  bone,  as  indicated  by  traces  of  the  original  suture,  lies  about  1  cm. 
below  this  line.  Projecting  from  the  lower  part  of  the  squama  is  a  long,  arched 
process,  the  zygomatic  process.  This  process  is  at  first  directed  lateralward,  its 
two  surfaces  looking  upward  and  downward;  it  then  appears  as  if  twisted  inward 


Groove  for  middle 
temporal  artery 


Parietal  notch 

Swprameatal 
triangle 

Occipitalis 


Occipital  groove 
Tympanic  part 
Stylohyoideds 

Styloid  process 
Fig.  137. — Left  temporal  bone.     Outer  surface. 

ipon  itself,  and  runs  forward,  its  surfaces  now  looking  medial  ward  and  lateralward. 
?he  superior  border  is  long,  thin,  and  sharp,  and  serves  for  the  attachment  of  the 
_  smporal  fascia;  the  inferior,  short,  thick,  and  arched,  has  attached  to  it  some 
fibers  of  the  Masseter.  The  lateral  surface  is  convex  and  subcutaneous;  the  medial 
is  concave,  and  affords  attachment  to  the  Masseter.  The  anterior  end  is  deeply 
serrated  and  articulates  with  the  zygomatic  bone.    The  posterior  end  is  connected 

I  to  the  squama  by  two  roots,  the  anterior  and  posterior  roots.  The  posterior  root,  a 
prolongation  of  the  upper  border,  is  strongly  marked;  it  runs  backward  above  the 
External  acoustic  meatus,  and  is  continuous  with  the  temporal  line.  The  anterior 
root,  continuous  with  the  lower  border,  is  short  but  broad  and  strong;  it  is  directed 
medialward  and  ends  in  a  rounded  eminence,  the  articular  tubercle  (eminentia 
articidaris).     This  tubercle  forms  the  front  boundary  of  the  mandibular  fossa, 


h 


140 


OSTEOLOGY 


I 


and  in  the  fresh  state  is  covered  with  cartilage.  In  front  of  the  articular  tubenQe 
is  a  small  triangular  area  which  assists  in  forming  the  infratemporal  fossa;  this 
area  is  separated  from  the  outer  surface  of  the  squama  by  a  ridge  which  is  continu- 
ous behind  with  the  anterior  root  of  the  zygomatic  process,  and  in  front,  in  the 
articulated  skull,  with  the  infratemporal  crest  on  the  great  wing  of  the  sphenoid. 
Between  the  posterior  wall  of  the  external  acoustic  meatus  and  the  posterior  root 
of  the  zygomatic  process  is  the  area  called  the  suprameatal  triangle  (Macewen), 
or  mastoid  fossa,  through  which  an  instrument  may  be  pushed  into  the  tympanic 
antrum.  At  the  junction  of  the  anterior  root  with  the  zygomatic  process  is  a  pro- 
jection for  the  attachment  of  the  temporomandibular  ligament;  and  behind  the 
anterior  root'is  an  oval  depression,  forming  part  of  the  mandibular  fossa,  for  the 
reception  of  the  condyle  of  the  mandible.    The  mandibular  fossa  {glenoid  fossa) 


ctctl  ho9ie 


Eminentia 
arcuata 


Mastoid  foramen 

Aquceductus  vestihuli 

Aquceducttis  cochlcce 

Internal  acoustic  yneatua 
Fig.   138. — Left  temporal  bone.     Inner  surface. 

is  bounded,  in  front,  by  the  articular  tubercle;  behind,  by  the  tympanic  part  of 
the  bone,  which  separates  it  from  the  external  acoustic  meatus;  it  is  divided  into 
two  parts  by  a  narrow  slit,  the  petrotympanic  fissure  (Glaserian  fissure).  The 
anterior  part,  formed  by  the  squama,  is  smooth,  covered  in  the  fresh  state  with 
cartilage,  and  articulates  with  the  condyle  of  the  mandible.  Behind  this  part 
of  the  fossa  is  a  small  conical  eminence;  this  is  the  representative  of  a  prominent 
tubercle  which,  in  some  mammals,  descends  behind  the  condyle  of  the  mandible, 
and  prevents  its  backward  displacement.  The  posterior  part  of  the  mandibular 
fossa,  formed  by  the  tympanic  part  of  the  bone,  is  non-articular,  and  sometimes 
lodges  a  portion  of  the  parotid  gland.  The  petrotympanic  fissure  leads  into  the 
middle  ear  or  tympanic  cavity;  it  lodges  the  anterior  process  of  the  malleus,  and 
transmits  the  tympanic  branch  of  the  internal  maxillary  artery.     The  chorda 


i 


THE  TEMPORAL  BONE 


141 


tympani  nerve  passes  through  a  canal  (canal  of  Huguier),  separated  from  the  an- 
terior edge  of  the  petrotympanic  fissure  by  a  thin  scale  of  bone  and  situated  on 
the  lateral  side  of  the  auditory  tube,  in  the  retiring  angle  between  the  squama 
and  the  petrous  portion  of  the  temporal. 

The  internal  surface  of  the  squama  (Fig.  138)  is  concave;  it  presents  depressions 
corresponding  to  the  convolutions  of  the  temporal  lobe  of  the  brain,  and  grooves 
for  the  branches  of  the  middle  meningeal  vessels. 

Borders. — ^The  superior  border  is  thin,  and  bevelled  at  the  expense  of  the  internal 
table,  so  as  to  overlap  the  squamous,  border  of  the  parietal  bone,  forming  with 
it  the  squamosal  suture.  Posteriorly,  the  superior  border  forms  an  angle,  the 
parietal  notch,  with  the  mastoid  portion  of  the  bone.  The  antero-inferior  border 
is  thick,  serrated,  and  bevelled  at  the  expense  of  the  inner  table  above  and  of 
the  outer  below,  for  articulation  with  the  great  wing  of  the  sphenoid. 

Mastoid  Portion  {yars  mastoidea). — The  mastoid  portion  forms  the  posterior 
part  of  the  bone. 


Tympanic  antrum 

Tegmen  tympani 

Prominence,  of  lateral  semicircular  canal 
Prominence  of  facial  canal 
Fenestra  vestibuli 
Bristle  in  semicanal  for  Tensor  tympani 
Septum  canalis  muscviotubarii 

Bristle  m  hiatus  of  facial  canal 


Carotid  canal 
Bony  part  of  auditory  tube 
Promontory 
Bristle  in  pyramid 
Fenestra  cochleae 
Sulcus  tympanicus 
Mastoid  cells    ^''''^^  *^  stylomastoid  foramen 
Fia.  139. — Coronal  section  of  right  temporal  bone. 

Surfaces. — Its  outer  surface  (Fig.  137)  is  rough,  and  gives  attachment  to  the 
Occipitalis  and  Auricularis  posterior.  It  is  perforated  by  numerous  foramina;  one 
of  these,  of  large  size,  situated  near  the  posterior  border,  is  termed  the  mastoid 
foramen;  it  transmits  a  vein  to  the  transverse  sinus  and  a  small  branch  of  the  occipi- 
tal artery  to  the  dura  mater.  The  position  and  size  of  this  foramen  are  very 
■^variable;  it  is  not  always  present;  sometimes  it  is  situated  in  the  occipital  bone, 
pr  in  the  suture  between  the  temporal  and  the  occipital.  The  mastoid  portion  is 
continued  below  into  a  conical  projection,  the  mastoid  process,  the  size  and  form 
of  which  vary  somewhat;  it  is  larger  in  the  male  than  in  the  female.  This  process 
serves  for  the  attachment  of  the  Sternocleidomastoideus,  Splenius  capitis,  and 
Longissimus  capitis.  On  the  medial  side  of  the  process  is  a  deep  groove,  the 
astoid  notch  (digastric  fossa) ,  for  the  attachment  of  the  Digastricus;  medial  to 
is  is  a  shallow  furrow,  the  occipital  groove,  which  lodges  the  occipital  artery. 


OSTEOLOGY 


I 


The  inner  surface  of  the  mastoid  portion  presents  a  deep,  curved  groove,  the 
sigmoid  sulcus,  which  lodges  part  of  the  transverse  sinus;  in  it  may  be  seen  the 
opening  of  the  mastoid  foramen.  The  groove  for  the  transverse  sinus  is  separated 
from  the  innermost  of  the  mastoid  air  cells  by  a  very  thin  lamina  of  bone,  and  even 
this  may  be  partly  deficient. 

Borders. — The  superior  border  of  the  mastoid  portion  is  broad  and  serrated,  for 
articulation  with  the  mastoid  angle  of  the  parietal.  The  posterior  border,  also 
serrated,  articulates  with  the  inferior  border  of  the  occipital  between  the  lateral 
angle  and  jugular  process.  Anteriorly  the  mastoid  portion  is  fused  with  the 
descending  process  of  the  squama  above;  below  it  enters  into  the  formation  of 
the  external  acoustic  meatus  and  the  tympanic  cavity. 

A  section  of  the  mastoid  process  (Fig.  139)  shows  it  to  be  hollowed  out  into  a 
number  of  spaces,  the  mastoid  cells,  which  exhibit  the  greatest  possible  variety 
as  to  their  size  and  number.  At  the  upper  and  front  part  of  the  process  they  are 
large  and  irregular  and  contain  air,  but  toward  the  lower  part  they  diminish  in 
size,  while  those  at  the  apex  of  the  process  are  frequently  quite  small  and  contain 
marrow;  occasionally  they  are  entirely  absent,  and  the  mastoid  is  then  solid 
throughout.  In  addition  to  these  a  large  irregular  cavity  is  situated  at  the  upper 
and  front  part  of  the  bone.  It  is  called  the  tympanic  antrum,  and  must  be  distin- 
guished from  the  mastoid  cells,  though  it  communicates  with  them.  Like  the  mas- 
toid cells  it  is  filled  with  air  and  lined  by  a  prolongation  of  the  mucous  membrane 
of  the  tympanic  cavity,  with  which  it  communicates.  The  tympanic  antrum  is 
bounded  above  by  a  thin  plate  of  bone,  the  tegmen  tympani,  which  separates  it 
from  the  middle  fossa  of  the  base  of  the  skull;  below  by.  the  mastoid  process;  later- 
ally by  the  squama  just  below  the  temporal  line,  and  medially  by  the  lateral  semi- 
circular canal  of  the  internal  ear  which  projects  into  its  cavity.  It  opens  in  front 
into  that  portion  of  the  tympanic  cavity  which  is  known  as  the  attic  or  epitympanic 
recess.  The  tympanic  antrum  I's  a  cavity  of  some  considerable  size  at  the  time  of 
birth;  the  mastoid  air  cells  may  be  regarded  as  diverticula  from  the  antrum, 
and  begin  to  appear  at  or  before  birth;  by  the  fifth  year  they  are  well-marked, 
but  their  development  is  not  completed  until  toward  puberty. 

Petrous  Portion  {pars  petrosa  [pyramis]). — The  petrous  portion  or  pyramid  is 
pyramidal  and  is  wedged  in  at  the  base  of  the  skull  between  the  sphenoid  and 
occipital.  Directed  medialward,  forward,  and  a  little  upward,  it  presents  for 
examination  a  base,  an  apex,  three  surfaces,  and  three  angles,  and  contains,  in 
its  interior,  the  essential  parts  of  the  organ  of  hearing. 

Base. — The  base  is  fused  with  the  internal  surfaces  of  the  squama  and  mastoid 
portion. 

Apex. — ^The  apex,  rough  and  uneven,  is  received  into  the  angular  interval  between 
the  posterior  border  of  the  great  wing  of  the  sphenoid  and  the  basilar  part  of  the 
occipital;  it  presents  the  anterior  or  internal  orifice  of  the  carotid  canal,  and 
forms  the  postero-lateral  boundary  of  the  foramen  lacerum. 

Surfaces. — ^The  anterior  surface  forms  the  posterior  part  of  the  middle  fossa  of 
the  base  of  the  skull,  and  is  continuous  with  the  inner  surface  of  the  squamous 
portion,  to  which  it  is  united  by  the  petrosquamous  suture,  remains  of  which  are 
distinct  even  at  a  late  period  of  life.  It  is  marked  by  depressions  for  the  convolu- 
tions of  the  brain,  and  presents  six  points  for  examination:  (1)  near  the  center, 
an  eminence  (eminentia  arcuata)  which  indicates  the  situation  of  the  superior  semi- 
circular canal;  (2)  in  front  of  and  a  little  lateral  to  this  eminence,  a  depression  indi- 
cating the  position  of  the  tympanic  cavity :  here  the  layer  of  bone  which  separates 
the  tympanic  from  the  cranial  cavity  is  extremely  thin,  and  is  known  as  the 
tegmen  tympani;  (3)  a  shallow  groove,  sometimes  double,  leading  lateralward  and 
backward  to  an  oblique  opening,  the  hiatus  of  the  facial  canal,  for  the  passage  of 
the  greater  superficial  petrosal  nerve  and  the  petrosal  branch  of  the  middle  men- 


I 


THE  TEMPORAL  BONE 


143 


ingeal  artery;  (4)  lateral  to  the  hiatus,  a  smaller  opening,  occasionally  seen,  for 
the  passage  of  the  lesser  superficial  petrosal  nerve;  (5)  near  the  apex  of  the  bone, 
the  termination  of  the  carotid  canal,  the  wall  of  which  in  this  situation  is  deficient 
in  front;  (6)  above  this  canal  the  shallow  trigeminal  impression  for  the  reception 
of  the  semilunar  ganglion. 

The  posterior  surface  (Fig.  138)  forms  the  front  part  of  the  posterior  fossa  of 
the  base  of  the  skull,  and  is  continuous  with  the  inner  surface  of  the  mastoid 
portion.  Near  the  center  is  a  large  orifice,  the  internal  acoustic  meatus,  the  size  of 
which  varies  considerably;  its  margins  are  smooth  and  rounded,  and  it  leads  into 
a  short  canal,  about  1  cm.  in  length,  which  runs  lateralward.  It  transmits  the 
facial  and  acoustic  nerves  and  the  internal  auditory  branch  of  the  basilar  artery. 
The  lateral  end  of  the  canal  is  closed  by  a  vertical  plate,  which  is  divided  by  a 
horizontal  crest,  the  crista  falciformis,  into  two  unequal  portions  (Fig.  140).  Each 
I)ortion  is  further  subdivided  by  a  vertical  ridge  into  an  anterior  and  a  posterior 
])art.  In  the  portion  beneath  the  crista  falciformis  are  three  sets  of  foramina; 
one  group,  just  below  the  posterior  part  of 
the  crest,  situated  in  the  area  cribrosa  media, 
consists  of  several  small  openings  for  the 
nerves  to  the  saccule;  below  and  behind  this 
iirea  is  the  foramen  singulare,  or  opening  for 
the  nerve  to  the  posterior  semicircular  duct; 
in  front  of  and  below  the  first  is  the  tractus 
spiralis  foraminosus,  consisting  of  a  number  of 
small  spirally  arranged  openings,  which  encircle 
the  canalis  centralis  cochleae;  these  openings 
together  with  this  central  canal  transmit  the 
nerves  to  the  cochlea.  The  portion  above 
the  crista  falciformis  presents  behind,  the 
area  cribrosa  superior,  pierced  by  a  series  of 
small  openings,  for  the  passage  of  the  nerves 
to  the  utricle  and  the  superior  and  lateral 
semicircular  ducts,  and,  in  front,  the  area 
facialis,  with  one  large  opening,  the  com- 
mencement of  the  canal  for  the  facial  nerve 
(aquaeductus  Fallopii).  Behind  the  internal 
acoustic  meatus  is  a  small  slit  almost  hidden 
by  a  thin  plate  of  bone,  leading  to  a  canal, 
the  aquaeductus  vestibuli,  which  transmits  the 

ductus  endolymphaticus  together  with  a  small  artery  and  vein.  Above  and 
between  these  two  openings  is  an  irregular  depression  which  lodges  a  process  of 
the  dura  mater  and  transmits  a  small  vein;  in  the  infant  this  depression  is  repre- 
sented by  a  large  fossa,  the  subarcuate  fossa,  which  extends  backward  as  a  blind 
jtunnel  under  the  superior  semicircular  canal. 

'"  The  inferior  surface  (Fig.  141)  is  rough  and  irregular,  and  forms  part  of  the 
exterior  f>i  the  base  of  the  skull.  It  presents  eleven  points  for  examination:  (1) 
near  the  apex  is  a  rough  surface,  quadrilateral  in  form,  which  serves  partly  for  the 
attachment  of  the  Levator  veli  palatini  and  the  cartilaginous  portion  of  the  audi- 
tory tube,  and  partly  for  connection  with  the  basilar  part  of  the  occipital  bone 
through  the  intervention  of  some  dense  fibrous  tissue;  (2)  behind  this  is  the  large 
circular  aperture  of  the  carotid  canal,  which  ascends  at  first  vertically,  and  then, 
making  a  bend,  runs  horizontally  forward  and  medialward;  it  transmits  into  the 
cranium  the  internal  carotid  artery,  and  the  carotid  plexus  of  nerves;  (3)  medial 
to  the  opening  for  the  carotid  canal  and  close  to  its  posterior  border,  in  front  of  the 
jugular  fossa,  is  a  triangular  depression;  at  the  apex  of  this  is  a  small  opening,  the 


Fig.  140. — Diagrammatic  view  of  the  fundus 
of  the  right  internal  acoustic  meatus.  (Testut.) 
1.  Crista  falciformis.  2.  Area  facialis,  with  (2') 
internal  opening  of  the  facial  canal.  3.  Ridge 
separating  the  area  facialis  from  the  area  crib- 
rosa superior.  4.  Area  cribrosa  superior,  with 
(4')  openings  for  nerve  filaments.  5.  Anterior 
inferior  cribriform  area,  with  (5')  the  tractus 
spiralis  foraminosus,  and  (5")  the  canalis  cen- 
tralis of  the  cochlea.  6.  Ridge  separating  the 
tractus  spiralis  foraminosus  from  the  area  crib- 
rosa media.  7.  Area  cribrosa  media,  with  (7') 
orifices  for  nerves  to  saccule.  8.  Foramen 
singulare. 


II 


144 


OSTEOLOGY 


I 


aquaeductus  cochleae,  which  lodges  a  tubular  prolongation  of  the  dura  mater  establish- 
ing a  communication  between  the  perihinphatic  space  and  the  subarachnoid  space, 
and  transmits  a  vein  from  the  cochlea  to  join  the  internal  jugular;  (4)  behind  these 
openings  is  a  deep  depression,  the  jugular  fossa,  of  variable  depth  and  size  in  different 
skulls;  it  lodges  the  bulb  of  the  internal  jugular  vein;  (5)  in  the  bony  ridge  dividing 
the  carotid  canal  from  the  jugular  fossa  is  the  small  inferior  tympanic  canaliculus 
for  the  passage  of  the  tympanic  branch  of  the  glossopharyngeal  nerve;  (6)  in  the 
lateral  part  of  the  jugular  fossa  is  the  mastoid  canaliculus  for  the  entrance  of  the 
auricular  branch  of  the  vagus  nerve;  (7)  behind  the  jugular  fossa  is  a  quadrilateral 
area,  the  jugular  surface,  covered  with  cartilage  in  the  fresh  state,  and  articulating 
with  the  jugular  process  of  the  occipital  bone;  (8)  extending  backward  from  the 
carotid  canal  is  the  vaginal  process,  a  sheath-like  plate  of  bone,  which  divides 

Semicanals  for 

auditory 

tube  a  lid 

Tensor 

tympani 


StylopJiaryngeua 


Lev.  vdi  palatini 

Rough  quadrilaieral  surface 

Openiitg  of  carotid  canal 

Inferior  tympanic  canaliculus 

Aquceductiis  cochlew 

Mastoid  canalicvlus 

Jugular  fossa 

Vaginal  process 

Styloid  process 

Stylomastoid  foramen 

J^igUlar  surface 

Tympanomastoid  fissure 


Fia.  141. — Left  temporal  bone.     Inferior  surface. 

behind  into  two  laminae;  the  lateral  lamina  is  continuous  with  the  tympanic  part 
of  the  bone,  the  medial  with  the  lateral  margin  of  the  jugular  surface;  (9)  between 
these  laminae  is  the  styloid  process,  a  sharp  spine,  about  2.5  cm.  in  length;  (10) 
between  the  styloid  and  mastoid  processes  is  the  stylomastoid  foramen;  it  is  the 
termination  of  the  facial  canal,  and  transmits  the  facial  nerve  and  stylomastoid 
artery;  (11)  situated  between  the  tympanic  portion  and  the  mastoid  process  is  the 
tympanomastoid  fissure,  for  the  exit  of  the  auricular  branch  of  the  vagus  nerve. 
Angles. — ^The  superior  angle,  the  longest,  is  grooved  for  the  superior  petrosal 
sinus,  and  gives  attachment  to  the  tentorium  cerebelli;  at  its  medial  extremity 
is  a  notch,  in  which  the  trigeminal  nerve  lies.  The  posterior  angle  is  intermediate 
in  length  between  the  superior  and  the  anterior.  Its  medial  half  is  marked  by 
a  sulcus,  which  forms,  with  a  corresponding  sulcus  on  the  occipital  bone,  the 
channel  for  the  inferior  petrosal  sinus.  Its  lateral  half  presents  an  excavation 
— the  jugular  fossa — which,  with  the  jugular  notch  on  the  occipital,  forms  the 


THE  TEMPORAL  BONE 


145 


t 


jugular  foramen ;  an  eminence  occasionally  projects  from  the  center  of  the  fossa, 
and  divides  the  foramen  into  two.  The  anterior  angle  is  divided  into  two  parts 
— a  lateral  joined  to  the  squama  by  a  suture  (petrosquamous),  the  remains  of  which 
are  more  or  less  distinct;  a  medial,  free,  which  articulates  with  the  spinous  process 
of  the  sphenoid. 

At  the  angle  of  junction  of  the  petrous  part  and  the  squama  are  two  canals, 
one  above  the  other,  and  separated  by  a  thin  plate  of  bone,  the  septum  canalis 
musculotubarii  {processus  cochleariformis) ;  both  canals  lead  into  the  tympanic 
cavity.  The  upper  one  (semicanalis  m.  tensoris  tympani)  transmits  the  Tensor 
tympani,  the  lower  one  (semicanalis  tubcB  auditivw)  forms  the  bony  part  of  the 
auditory  tube. 

The  tympanic  cavity,  auditory  ossicles,  and  internal  ear,  are  described  with 
the  organ  of  hearing. 

Tympanic  Part  (jmrs  tympanica). — The  tympanic  part  is  a  curved  plate  of  bone 
lying  below  the  squama  and  in  front  of  the  mastoid  process. 

Surfaces. — Its  postero-superior  surface  is  concave,  and  forms  the  anterior  wall, 
the  floor,  and  part  of  the  posterior  wall  of  the  bony  external  acoustic  meatus. 
]Medially,  it  presents  a  narrow  furrow,  the  tympanic  sulcus,  for  the  attachment 
of  the  tympanic  membrane.  Its  antero-inferior  surface  is  quadrilateral  and  slightly 
concave;  it  constitutes  the  posterior  boundary  of  the  mandibular  fossa,  and  is 
in  contact  w^ith  the  retromandibular  part  of  the  parotid  gland. 

Borders. — Its  lateral  border  is  free  and  rough,  and  gives  attachment  to  the  car- 
tilaginous part  of  the  external  acoustic  meatus.  Internally,  the  tympanic  part 
is  fused  with  the  petrous  portion,  and  appears  in  the  retreating  angle  between 
it  and  the  squama,  where  it  lies  below  and  lateral  to  the  orifice  of  the  auditory 
tube.  Posteriorly,  it  blends  with  the  squama  and  mastoid  part,  and  forms  the 
anterior  boundary  of  the  tympanomastoid  fissure.  Its  upper  border  fuses  laterally 
with  the  back  of  the  postglenoid  process,  w^hile  medially  it  bounds  the  petro- 
tympanic fissure.  The  medial  part  of  the  lower  border  is  thin  and  sharp;  its  lateral 
part  splits  to  enclose  the  root  of  the  styloid  process,  and  is  therefore  named  the 
vaginal  process.  The  central  portion  of  the  tympanic  part  is  thin,  and  in  a  consid- 
I  arable  percentage  of  skulls  is  perforated  by  a  hole,  the  foramen  of  Huschke. 

The  external  acoustic  meatus  is  nearly  2  cm.  long  and  is  directed  inward  and 
slightly  forward:  at  the  same  time  it  forms  a  slight  curve,  so  that  the  floor  of  the 
canal  is  convex  upward.  In  sagittal  section  it  presents  an  oval  or  elliptical  shape 
•  with  the  long  axis  directed  downward  and  slightly  backward.  Its  anterior  wall 
land  floor  and  the  lower  part  of  its  posterior  wall  are  formed  by  the  tympanic 
part;  the  roof  and  upper  part  of  the  posterior  wall  by  the  squama.  Its  inner 
end  is  closed,  in  the  recent  state,  by  the  tympanic  membrane;  the  upper  limit 
of  its  outer  orifice  is  formed  by  the  posterior  root  of  the  zygomatic  process,  imme- 
diately below  which  there  is  sometimes  seen  a  small  spine,  the  suprameatal  spine, 
situated  at  the  upper  and  posterior  part  of  the  orifice. 

Styloid  Process  {processus  styloideus) . — The  styloid  process  is  slender,  pointed, 
and  of  varying  length;  it  projects  downward  and  forw^ard,  from  the  under  surface 
■  of  the  temporal  bone.  Its  proximal  part  (tympanohyal)  is  ensheathed  by  the 
'vaginal  process  of  the  tympanic  portion,  while  its  distal  part  (stylohyal)  gives 
attachment  to  the  stylohyoid  and  stylomandibular  ligaments,  and  to  the  Stylo- 
glossus, Stylohyoideus,  and  Stylopharyngeus  muscles.  The  stylohyoid  ligament 
extends  from  the  apex  of  the  process  to  the  lesser  cornu  of  the  hyoid  bone,  and 
in  some  instances  is  partially,  in  others  completely,  ossified. 

Structure. — The  structure  of  the  squama  is  like  that  of  the  other  cranial  bones:  the  mastoid 
portion  is  spongy,  and  the  petrous  portion  dense  and  hard. 

Ossification. — The  temporal  bone  is  ossified  from  eight  centers,  exclusive  of  those  for  the  internal 
ear  and  the  tympanic  ossicles,  viz.,  one  for  the  squama  including  the  zygomatic  process,  one  for 


k 


10 


146 


OSTEOLOGY 


I 


the  tympanic  part,  four  for  the  petrous  and  mastoid  parts,  and  two  for  the  styloid  process.  Just 
before  the  close  of  fetal  Hfe  (Fig.  142)  the  temporal  bone  consists  of  three  principal  parts:  1. 
The  squama  is  ossified  in  membrane  from  a  single  nucleus,  which  appears  near  the  root  of  tlie 
zygomatic  process  about  the  second  month.  2.  The  petromastoid  part  is  developed  from  four 
centers,  which  make  their  appearance  in  the  cartilaginous  ear  capsule  about  the  fifth  or  sixth 
month.  One  (prootic)  appears  in  the  neighborhood  of  the  eminentia  arcuata,  spreads  in  front 
and  above  the  internal  acoustic  meatus  and  extends  to  the  apex  of  the  bone;  it  forms  part  of  the 


Septum  canalis  musculotvbarii 

Fenestra  vestibuli 
Tympanic  antrum. 


Sulcus  tym,panicus 


Bristle  in  facial 
canal 


Lateral  wall  of 
tympanic  antrum 


Fig.   142. 


-The  three  principal  parts  of  the  tempora  bone  at  birth.     1.  Outer  surface  of  petromastoid  part. 
2.   Outer  surface  of  tympanic  ring.     3.   Inner  surface  of  squama. 


cochlea,  vestibule,  superior  semicircular  canal,  and  medial  wall  of  the  tympanic  cavity.  A  second 
(opisthotic)  appears  at  the  promontory  on  the  medial  wall  of  the  tympanic  cavity  and  surrounds 
the  fenestra  cochlea?;  it  forms  the  floor  of  the  tympanic  cavity  and  vestibule,  surrounds  the  carotid 
canal,  invests  the  lateral  and  lower  part  of  the  cochlea,  and  spreads  medially  below  the  internal 
acoustic  meatus.    A  third  (pterotic)  roofs  in  the  tympanic  cavity  and  antrum;  while  the  fourth 


Squ/ima 


Squama 


Petrosquamous 
suiure 


Petrosquamous  suture 
Eminentia  arcuaia 


Tympanic  ring 


Petromastoid  portion 


Fig. 


143. — Temporal  bone  at  birth. 
Outer  aspect. 


Fossa  suharcuata 

Internal  acoustic  meatus 

Fig.   144. — Temporal  bone  at  birth.     Inner 
aspect. 


(epiotic)  appears  near  the  posterior  semicircular  canal  and  extends  to  form  the  mastoid  process 
(Vrolik).  3.  The  tympanic  ring  is  an  incomplete  circle,  in  the  concavity  of  which  is  a  groove, 
the  tympanic  sulcus,  for  the  attachment  of  the  circumference  of  the  tympanic  membrane.  This 
ring  expands  to  form  the  tympanic  part,  and  is  ossified  in  membrane  from  a  single  center  which 
appears  about  the  third  month.  The  styloid  process  is  developed  from  the  proximal  part  of  the 
cartilage  of  the  second  branchial  or  hyoid  arch  by  two  centers:  one  for  the  proximal  part,  the 
iympanohyal,  appears  before  birth;  the  other,  comprising  the  rest  of  the  process,  is  named  the 


J 


THE  SPHENOID  BONE  HHP  147 


I 


I 


stylohyal,  and  does  not  appear  until  after  birth.  The  tympanic  ring  unites  with  the  squama 
shortly  before  birth;  the  petromastoid  part  and  squama  join  during  the  first  year,  and  the  tym- 
panohyal  portion  of  the  styloid  process  about  the  same  time  (Figs.  143,  144).  The  stylohyal 
does  not  unite  with  the  rest  of  the  bone  until  after  puberty,  and  in  some  skulls  never  at  all. 

The  chief  subsequent  changes  in  the  temporal  bone  apart  from  increase  in  size  are:  (1)  The 
tympanic  ring  extends  outward  and  backward  to  form  the  tympanic  part.  This  extension  does 
not,  however,  take  place  at  an  equal  rate  all  around  the  circumference  of  the  ring,  but  occurs  most 
rapidly  on  its  anterior  and  posterior  portions,  and  these  outgrowths  meet  and  blend,  and  thus, 
for  a  time,  there  exists  in  the  floor  of  the  meatus  a  foramen,  the  foramen  of  Huschke;  this  foramen 
is  usually  closed  about  the  fifth  year,  but  may  persist  throughout  life.  (2)  The  mandibular  fossa 
is  at  first  extremely  shallow,  and  looks  lateralward  as  well  as  downward;  it  becomes  deeper  and 
is  ultimately  directed  downward.  Its  change  in  direction  is  accounted  for  as  follows.  The  part 
of  the  squama  which  forms  the  fossa  lies  at  first  below  the  level  of  the  zygomatic  process.  As, 
however,  the  base  of  the  skull  increases  in  width,  this  lower  part  of  the  squama  is  directed  hori- 
zontally inward  to  contribute  to  the  middle  fossa  of  the  skull,  and  its  surfaces  therefore  come 
to  look  upward  and  downward;  the  attached  portion  of  the  zygomatic  process  also  becomes 
everted,  and  projects  like  a  shelf  at  right  angles  to  the  squama.  (3)  The  mastoid  portion  is  at 
first  quite  flat,  and  the  stylomastoid  foramen  and  rudimentary  styloid  process  lie  immediately 
behind  the  tympanic  ring.  With  the  development  of  the  air  cells  the  outer  part  of  the  mastoid 
portion  grows  downward  and  forward  to  form  the  mastoid  process,  and  the  styloid  process  and 
stylomastoid  foramen  now  come  to  lie  on  the  under  surface.  The  descent  of  the  foramen  is 
necessarily  accompanied  by  a  corresponding  lengthening  of  the  facial  canal.  (4)  The  downward 
and  forward  growth  of  the  mastoid  process  also  pushes  forward  the  tympanic  part,  so  that  the 
portion  of  it  which  formed  the  original  floor  of  the  meatus  and  contained  the  foramen  of  Huschke 
is  ultimately  found  in  the  anterior  wall.  (5)  The  fossa  subarcuata  becomes  filled  up  and  almost 
obliterated. 

Articulations. — The  temporal  articulates  with  five  bones :  occipital,  parietal,  sphenoid,  mandible 
and  zygomatic. 

I  The  Sphenoid  Bone  (Os  Sphenoidale). 

The  sphenoid  bone  is  situated  at  the  base  of  the  skull  in  front  of  the  temporals 
and  basilar  part  of  the  occipital.  It  somewhat  resembles  a  bat  with  its  wings 
extended,  and  is  divided  into  a  median  portion  or  body,  two  great  and  two  small 
wings  extending  outward  from  the  sides  of  the  body,  and  two  pterygoid  processes 
which  project  from  it  below\ 

[  Body  {corpus  syhenoidale) . — The  body,  more  or  less  cubical  in  shape,  is  hollowed 
out  in  its  interior  to  form  two  large  cavities,  the  sphenoidal  air  sinuses,  which  are 
separated  from  each  other  by  a  septum. 

Surfaces. — The  superior  surface  of  the  body  (Fig.  145)  presents  in  front  a  promi- 
ent  spine,  the  ethmoidal  spine,  for  articulation  with  the  cribriform  plate  of  the 
ithmoid;  behind  this  is  a  smooth  surface  slightly  raised  in  the  middle  line,  and 
grooved  on  either  side  for  the  olfactory  lobes  of  the  brain.  This  surface  is  bounded 
behind  by  a  ridge,  which  forms  the  anterior  border  of  a  narrow,  transverse  groove, 
the  chiasmatic  groove  {optic  groove),  above  and  behind  which  lies  the  optic  chiasma; 
Ihe  groove  ends  on  either  side  in  the  optic  foramen,  which  transmits  the  optic 
nerve  and  ophthalmic  artery  into  the  orbital  cavity.  Behind  the  chiasmatic 
groove  is  an  elevation,  the  tuberculum  sellae;  and  still  more  posteriorly,  a  deep 
depression,  the  sella  tiu'cica,  the  deepest  part  of  which  lodges  the  hypophysis 
cerebri  and  is  known  as  the  fossa  hypophyseos.  The  anterior  boundary  of  the 
sella  turcica  is  completed  by  two  small  eminences,  one  on  either  side,  called  the 
middle  clinoid  processes,  while  the  posterior  boundary  is  formed  by  a  square- 
shaped  plate  of  bone,  the  dorsum  sellae,  ending  at  its  superior  angles  in  two  tubercles, 
the  posterior  clinoid  processes,  the  size  and  form  of  which  vary  considerably  in 
different  individuals.  The  posterior  clinoid  processes  deepen  the  sella  turcica, 
and  give  attachment  to  the  tentorium  cerebelli.  On  either  side  of  the  dorsum 
sellse  is  a  notch  for  the  passage  of  the  abducent  nerve,  and  below  the  notch  a  sharp 
process,  the  petrosal  process,  which  articulates  with  the  apex  of  the  petrous  portion 
of  the  temporal  bone,  and  forms  the  medial  boundary  of  the  foramen  lacerum. 


148 


OSTEOLOGY 


I 


Behind  the  dorsum  sellse  is  a  shallow  depression,  the  clivus,  which  slopes  obliquely 
backward,  and  is  continuous  with  the  groove  on  the  basilar  portion  of  the  occipii:al 
bone;  it  supports  the  upper  part  of  the  pons. 


Middle  Clinoid  j)rocess 
Posterim-  Clinoid  process 


Ethmoidal 
spine 

Groove  for 
olfactorji 
lobe 


Optic  foramen 
Superior  orbital 
fissure 

Forainen  rotundum 

Foramen  Vesalii 

Foramen  ovale 

Foramen  spinosum 


Spina  angularis 


With 
jialatine 


Fig.  145. — Sphenoid  bone.     Upper  surface. 


The  lateral  surfaces  of  the  body  are  united  with  the  great  w  ings  and  the  medial 
pterygoid  plates.  Above  the  attachment  of  each  great  wing  is  a  broad  groove, 
curved  something  like  the  italic  letter  /;  it  lodges  the  internal  carotid  artery  and 
the  cavernous  sinus,  and  is  named  the  carotid  groove.     Along  the  posterior  part 


Tensor  vel 
palatini 


Medial  pteryijoid  plat, 
Hamiilu. 

Fig.   146. — Sphenoid  bone.     Anterior  and  inferior  surfaces. 

of  the  lateral  margin  of  this  groove,  in  the  angle  between  the  body  and  great  wing, 
is  a  ridge  of  bone,  called  the  lingula. 

The  posterior  surface,  quadrilateral  in  form  (I'ig.  147),  is  joined,  during  infancy 
and  adolescence,  to  the  basilar  part  of  the  occipital  bone  by  a  plate  of  cartilage. 


THE  SPHENOID  BONE 


149 


Between  the  eighteenth  and  twenty-fifth  years  this  becomes  ossified,  ossification 
commencing  above  and  extending  downward. 

The  anterior  surface  of  the  body  (Fig.  146)  presents,  in  the  middle  line,  a  vertical 
crest,  the  sphenoidal  crest,  which  articulates  with  the  perpendicular  plate  of  the 
ethmoid,  and  forms  part  of  the  septum  of  the  nose.  On  either  side  of  the  crest 
is  an  irregular  opening  leading  into  the  corresponding  sphenoidal  air  sinus.  These 
sinuses  are  two  large,  irregular  cavities  hollowed  out  of  the  interior  of  the  body 
of  the  bone,  and  separated  from  one  another  by  a  bony  septum,  which  is  commonly 
bent  to  one  or  the  other  side.  They  vary  considerably  in  form  and  size,^  are 
seldom  symmetrical,  and  are  often  partially  subdivided  by  irregular  bony  laminae. 
Occasionally,  they  extend  into  the  basilar  part  of  the  occipital  nearly  as  far  as  the 
foramen  magnum.  They  begin  to  be  developed  before  birth,  and  are  of  a  consid- 
erable size  by  the  age  of  six.  They  are  partially  closed,  in  front  and  below,  by  two 
thin,  curved  plates  of  bone,  the  sphenoidal  conchse  (see  page  152),  leaving  in  the 
articulated  skull  a  round  opening  at  the  upper  part  of  each  sinus  by  which  it  com- 


ierygoid  canal 
Lateral  pterygoid  lamina 
Medial  -pterygoid  lamina 


Hamulus 


V 


Rostrum 
Fig.  147 — Sphenoid  bone.     Upper  and  posterior  surfaces. 

unicates  with  the  upper  and  back  part  of  the  nasal  cavity  and  occasionally  with 
the  posterior  ethmoidal  air  cells.  The  lateral  margin  of  the  anterior  surface  is 
serrated,  and  articulates  with  the  lamina  papyracea  of  the  ethmoid,  completing 
the  posterior  ethmoidal  cells;  the  lower  margin  articulates  with  the  orbital  process 
of  the  palatine  bone,  and  the  upper  with  the  orbital  plate  of  the  frontal  bone. 

The  inferior  surface  presents,  in  the  middle  line,  a  triangular  spine,  the  sphenoidal 
rostrum,  which  is  continuous  with  the  sphenoidal  crest  on  the  anterior  surface, 
and  is  received  in  a  deep  fissure  between  the  alee  of  the  vomer.  On  either  side  of 
the  rostrum  is  a  projecting  lamina,  the  vaginal  process,  directed  medialward  from 
he  base  of  the  medial  pterygoid  plate,  with  which  it  will  be  described. 

The  Great  Wings  (alee  viagnoe). — The  great  wings,  or  ali-sphenoids,  are  two 
strong  processes  of  bone,  which  arise  from  the  sides  of  the  body,  and  are  curved 
upward,  lateralward,  and  backward;  the  posterior  part  of  each  projects  as  a  tri- 
angular process  which  fits  into  the  angle  between  the  squama  and  the  petrous 

'  Aldren  Turner  (op.  cit.)  gives  the  following  as  their  average  measurements:  vertical  height,  '/s  inch;  antero-posterior 
<Jepth,  '/s  inch;  transverse  breadth,  Ji  inch. 


tak 


150  OSTEOLOGY 


portion  of  the  temporal  and  presents  at  its  apex  a  downwardly  directed  process, 
the  spina  angularis  {sphenoidal  spine). 

Surfaces. — ^The  superior  or  cerebral  surface  of  each  great  wing  (Fig.  145)  forms 
part  of  the  middle  fossa  of  the  skull ;  it  is  deeply  concave,  and  presents  depressions 
for  the  convolutions  of  the  temporal  lobe  of  the  brain.  At  its  anterior  and  medial 
part  is  a  circular  aperture,  the  foramen  rotundum,  for  the  transmission  of  the  maxil- 
lary nerve.  Behind  and  lateral  to  this  is  the  foramen  ovale,  for  the  transmission 
of  the  mandibular  nerve,  the  accessory  meningeal  artery,  and  sometimes  the 
lesser  superficial  petrosal  nerve. ^  Medial  to  the  foramen  ovale,  a  small  aperture, 
the  foramen  Vesalii,  may  occasionally  be  seen  opposite  the  root  of  the  pterygoid 
process;  it  opens  below  near  the  scaphoid  fossa,  and  transmits  a  small  vein  from 
the  cavernous  sinus.  Lastly,  in  the  posterior  angle,  near  to  and  in  front  of  the  spine, 
is  a  short  canal,  sometimes  double,  the  foramen  spinosum,  which  transmits  the 
middle  meningeal  vessels  and  a  recurrent  branch  from  the  mandibular  nerve. 

The  lateral  surface  (Fig.  146)  is  convex,  and  divided  by  a  transverse  ridge,  the 
infratemporal  crest,  into  two  portions.  The  superior  or  temporal  portion,  convex 
from  above  downward,  concave  from  before  backward,  forms  a  part  of  the  tem- 
poral fossa,  and  gives  attachment  to  the  Temporalis;  the  inferior  or  infratemporal, 
smaller  in  size  and  concave,  enters  into  the  formation  of  the  infratemporal  fossa, 
and,  together  with  the  infratemporal  crest,  affords  attachment  to  the  Pterygoideus 
externus.  It  is  pierced  by  the  foramen  ovale  and  foramen  spinosum,  and  at  its 
posterior  part  is  the  spina  angularis,  which  is  frequently  grooved  on  its  medial 
surface  for  the  chorda  tympani  nerve.  To  the  spina  angularis  are  attached  the 
sphenomandibular  ligament  and  the  Tensor  veli  palatini.  Medial  to  the  anterior 
extremity  of  the  infratemporal  crest  is  a  triangular  process  which  serves  to  increase 
the  attachment  of  the  Pterygoideus  externus;  extending  downward  and  medialward 
from  this  process  on  to  the  front  part  of  the  lateral  pterygoid  plate  is  a  ridge  which 
forms  the  anterior  limit  of  the  infratemporal  surface,  and,  in  the  articulated  skull, 
the  posterior  boundary  of  the  pterygomaxillary  fissure. 

The  orbital  surface  of  the  great  wing  (Fig.  146),  smooth,  and  quadrilateral  in 
shape,  is  directed  forward  and  medialward  and  forms  the  posterior  part  of  the 
lateral  wall  of  the  orbit.  Its  upper  serrated  edge  articulates  with  the  orbital  plate 
of  the  frontal.  Its  inferior  rounded  border  forms  the  postero-lateral  boundary  of 
the  inferior  orbital  fissure.  Its  medial  sharp  margin  forms  the  lower  boundary 
of  the  superior  orbital  fissure  and  has  projecting  from  about  its  center  a  little 
tubercle  which  gives  attachment  to  the  inferior  head  of  the  Rectus  lateralis  oculi; 
at  the  upper  part  of  this  margin  is  a  notch  for  the  transmission  of  a  recurrent 
branch  of  the  lacrimal  artery.  Its  lateral  margin  is  serrated  and  articulates  with 
the  zygomatic  bone.  Below  the  medial  end  of  the  superior  orbital  fissure  is  a 
grooved  surface,  which  forms  the  posterior  wall  of  the  pterygopalatine  fossa, 
and  is  pierced  by  the  foramen  rotundum. 

Margin  (Fig.  145). — Commencing  from  behind,  that  portion  of  the  circum- 
ference of  the  great  wing  which  extends  from  the  body  to  the  spine  is  irregular. 
Its  medial  half  forms  the  anterior  boundary  of  the  foramen  lacerum,  and  presents 
the  posterior  aperture  of  the  pterygoid  canal  for  the  passage  of  the  correspond- 
ing nerve  and  artery.  Its  lateral  half  articulates,  by  means  of  a  synchondrosis, 
with  the  petrous  portion  of  the  temporal,  and  between  the  two  bones  on  the 
under  surface  of  the  skull,  is  a  furrow,  the  sulcus  tubae,  for  the  lodgement  of  the 
cartilaginous  part  of  the  auditory  tube.  In  front  of  the  spine  the  circumference 
presents  a  concave,  serrated  edge,  bevelled  at  the  expense  of  the  inner  table  below, 
and  of  the  outer  table  above,  for  articulation  with  the  temporal  squama.  At 
the  tip  of  the  great  wing  is  a  triangular  portion,  bevelled  at  the  expense  of  the 

1  The  lesser  superficial  petrosal  nerve  sometimes  passes  through  a  special  canal  (canaliculus  innominatus  of  Arnold) 
situated  medial  to  the  foramen  spinosum. 


I 


THE  SPHENOID  BONE  151 


internal  surface,  for  articulation  with  the  sphenoidal  angle  of  the  parietal  bone; 
this  region  is  named  the  pterion.  Medial  to  this  is  a  triangular,  serrated  surface, 
for  articulation  with  the  frontal  bone;  this  surface  is  continuous  medially  with 
the  sharp  edge,  w^hich  forms  the  lower  boundary  of  the  superior  orbital  fissure, 
and  laterally  with  the  serrated  margin  for  articulation  with  the  zygomatic  bone. 

The  Small  Wings  {ales  parvcp). — The  small  wings  or  orbito-sphenoids  are  two 
thin  triangular  plates,  which  arise  from  the  upper  and  anterior  parts  of  the  body, 
and,  projecting  lateralward,  end  in  sharp  points  (Fig.  145). 

Surfaces. — The  superior  surface  of  each  is  flat,  and  supports  part  of  the  frontal 
lobe  of  the  brain.  The  inferior  surface  forms  the  back  part  of  the  roof  of  the  orbit, 
and  the  upper  boundary  of  the  superior  orbital  fissure.  This  fissure  is  of  a  triangular 
form,  and  leads  from  the  cavity  of  the  cranium  into  that  of  the  orbit:  it  is  bounded 

P  medially  by  the  body;  above,  by  the  small  wing;  below,  by  the  medial  margin  of 
the  orbital  surface  of  the  great  wing;  and  is  completed  laterally  by  the  frontal 
bone.     It  transmits  the  oculomotor,  trochlear,  and  abducent  nerves,  the  three 
^_  branches  of  the  ophthalmic  division  of  the  trigeminal  nerve,  some  filaments  from 
^■the  cavernous  plexus  of  the  sympathetic,  the  orbital  branch  of  the  middle  menin- 
^^  geal  artery,  a  recurrent  branch  from  the  lacrimal  artery  to  the  dura  mater,  and  the 
ophthalmic  vein. 

Borders. — The  anterior  border  is  serrated  for  articulation  with  the  frontal  bone. 
The  posterior  border,  smooth  and  rounded,  is  received  into  the  lateral  fissure  of 
the  brain;  the  medial  end  of  this  border  forms  the  anterior  clinoid  process,  which 
gives  attachment  to  the  tentorium  cerebelli;  it  is  sometimes  joined  to  the  middle 
clinoid  process  by  a  spicule  of  bone,  and  when  this  occurs  the  termination  of  the 
groove  for  the  internal  carotid  artery  is  converted  into  a  foramen  (carotico-clinoid) . 

rThe  small  wing  is  connected  to  the  body  by  two  roots,  the  upper  thin  and  flat, 
Ithe  lower  thick  and  triangular;  between  the  two  roots  is  the  optic  foramen,  for  the 
transmission  of  the  optic  nerve  and  ophthalmic  artery. 
Pterygoid  Processes  {processus  pterygoidei). — The  pterygoid  processes,  one  on 
either  side,  descend  perpendicularly  from  the  regions  where  the  body  and  great 
wings  unite.    Each  process  consists  of  a  medial  and  a  lateral  plate,  the  upper  parts 
of  which  are  fused  anteriorly ;  a  vertical  sulcus,  the  pterygopalatine  groove,  descends 
on  the  front  of  the  line  of  fusion.    The  plates  are  separated  below  by  an  angular 
L    cleft,  the  pterygoid  fissure,  the  margins  of  which  are  rough  for  articulation  with 
Hlthe  pyramidal  process  of  the  palatine  bone.    The  two  plates  diverge  behind  and 
»    enclose  between  them  a  V-shaped  fossa,  the  pterygoid  fossa,  which  contains  the 
P     Pterygoideus  internus  and  Tensor  veli  palatini.    Above  this  fossa  is  a  small,  oval, 
shallow  depression,  the  scaphoid  fossa,  which  gives  origin  to  the  Tensor  veli  palatini. 
,The  anterior  surface  of  the  pterygoid  process  is  broad  and  triangular  near  its 
iroot,  where  it  forms  the  posterior  wall  of  the  pterygopalatine  fossa  and  presents 
the  anterior  orifice  of  the  pterygoid  canal. 

Lateral  Pterygoid  Plate. — The  lateral  pterygoid  plate  is  broad,  thin,  and  everted; 
its  lateral  surface  forms  part  of  the  medial  wall  of  the  infratemporal  fossa,  and 
gives  attachment  to  the  Pterygoideus  externus;  its  medial  surface  forms  part  of 
the  pterygoid  fossa,  and  gives  attachment  to  the  Pterygoideus  internus. 

Medial  Pterygoid  Plate. — The  medial  pterygoid  plate  is  narrower  and  longer 
than  the  lateral ;  it  curves  lateralward  at  its  lower  extremity  into  a  hook-like  pro- 

fcess,  the  pterygoid  hamulus,  around  which  the  tendon  of  the  Tensor  veli  palatini 
glides.  The  lateral  surface  of  this  plate  forms  part  of  the  pterygoid  fossa,  the 
medial  surface  constitutes  the  lateral  boundary  of  the  choana  or  posterior  aperture 
of  the  corresponding  nasal  cavity.  Superiorly  the  medial  plate  is  prolonged  on  to 
the  under  surface  of  the  body  as  a  thin  lamina,  named  the  vaginal  process,  which 
articulates  in  front  with  the  sphenoidal  process  of  the  palatine  and  behind  this 
with  the  ala  of  the  vomer.    The  angular  prominence  between  the  posterior  margin 


I 


OSTEOLOGY 

of  the  vaginal  process  and  the  medial  border  of  the  scaphoid  fossa  is  named  the 
pterygoid  tubercle,  and  immediately  above  this  is  the  posterior  opening  of  tbe 
pterygoid  canal.  On  the  under  surface  of  the  vaginal  process  is  a  furrow,  which 
is  converted  into  a  canal  by  the  sphenoidal  process  of  the  palatine  bone,  for  the 
transmission  of  the  pharyngeal  branch  of  the  internal  maxillary  artery  and  the 
pharyngeal  nerve  from  the  sphenopalatine  ganglion.  The  pharyngeal  aponeurosis 
is  attached  to  the  entire  length  of  the  posterior  edge  of  the  medial  plate,  and  the 
Constrictor  pharyngis  superior  takes  origin  from  its  lower  third.  Projecting 
backward  from  near  the  middle  of  the  posterior  edge  of  this  plate  is  an  angular 
process,  the  processus  tubarius,  which  supports  the  pharyngeal  end  of  the  auditory 
tube.  The  anterior  margin  of  the  plate  articulates  with  the  posterior  border  of 
the  vertical  part  of  the  palatine  bone. 

The  Sphenoidal  Conchse  (conchce  sphenoidales;  sphenoidal  turbinated  processes). 
— The  sphenoidal  conchse  are  two  thin,  curved  plates,  situated  at  the  anterior 
and  lower  part  of  the  body  of  the  sphenoid.  An  aperture  of  variable  size  exists 
in  the  anterior  wall  of  each,  and  through  this  the  sphenoidal  sinus  opens  into  the 
nasal  cavity.  Each  is  irregular  in  form,  and  tapers  to  a  point  behind,  being  broader 
and  thinner  in  front.  Its  upper  surface  is  concave,  and  looks  toward  the  cavity 
of  the  sinus;  its  under  surface  is  convex,  and  forms  part  of  the  roof  of  the  corre- 
sponding nasal  cavity.  Each  bone  articulates  in  front  with  the  ethmoid,  laterally 
with  the  palatine;  its  pointed  posterior  extremity  is  placed  above  the  vomer, 
and  is  received  between  the  root  of  the  pterygoid  process  laterally  and  the  rostrum 
of  the  sphenoid  medially.  A  small  portion  of  the  sphenoidal  concha  sometimes 
enters  into  the  formation  of  the  medial  wall  of  the  orbit,  between  the  lamina 
papyracea  of  the  ethmoid  in  front,  the  orbital  plate  of  the  palatine  below,  and  the 
frontal  bone  above. 


Ossification. — Until  the  seventh  or  eighth  month  of  fetal  life  the  body  of  the  sphenoid  consists 
of  two  parts,  viz.,  one  in  front  of  the  tuberculum  sella;,  the  presphenoid,  with  which  the  small 
wings  are  continuous;  the  other,  comprising  the  sella  turcica  and  dorsum  sellae,  the  posisphenoid, 

with  which  are  associated  the  great 
wings,  and  pterygoid  processes.  The 
greater  part  of  the  bone  is  ossified  in 
cartilage.  There  are  fourteen  centers 
in  all,  six  for  the  presphenoid  and  eight 
for  the  postsphenoid. 

Presphenoid. — About  the  ninth  week 
of  fetal  hfe  an  ossific  center  appears  for 
each  of  the  small  wings  (orbitosphenoids) 
just  lateral  to  the  optic  foramen;  shortly 
afterward  two  nuclei  appear  in  the  pre- 
sphenoid part  of  the  body.  The  sphe- 
noidal concha;  are  each  developed  from 
a  center  which  makes  its  appearance  about  the  fifth  month  ;i  at  birth  they  consist  of  small 
triangular  laminae,  and  it  is  not  until  the  third  year  that  they  become  hollowed  out  and  cone- 
shaped;  about  the  fourth  year  they  fuse  with  the  labyrinths  of  the  ethmoid,  and  between  the 
ninth  and  twelfth  years  they  unite  with  the  sphenoid. 

Postsphenoid. — The  first  ossific  nuclei  are  those  for  the  great  wings  (ali-sphenoids)-.  One  makes 
its  appearance  in  each  wing  between  the  foramen  rotundum  and  foramen  ovale  about  the  eighth 
week.  The  orbital  plate  and  that  part  of  the  sphenoid  which  is  found  in  the  temporal  fossa,  as 
well  as  the  lateral  pterygoid  plate,  are  ossified  in  membrane  (Fawcett)^  Soon  after,  the  centers 
for  the  postsphenoid  part  of  the  body  appear,  one  on  either  side  of  the  sella  turcica,  and  become 
blended  together  about  the  middle  of  fetal  life.  Each  medial  pterygoid  plate  (with  the  exception 
of  its  hamulus)  is  ossified  in  membrane,  and  its  center  probably  appears  about  the  ninth  or  tenth 
week;  the  hamulus  becomes  chondrified  during  the  third  month,  and  almost  at  once  undergoes 


Fig.  148. — Sphenoid  bone  at  birth.     Posterior  aspect. 


1  According  to  Cleland,  each  sphenoidal  concha  is  ossified  from  four  centers. 

2  Mall,  Am.  Jour.  Anat.,  1906,  states  that  the  pterygoid  center  appears  first  in  an  embryo  fifty-seven  days  old. 
*  Journal  of  Anatomy  and  Physiology,  1910,  vol.  xliv. 


IF 


THE  ETHMOID  BONE 


153 


ossification  (Fawcett).^  The  medial  joins  the  lateral  pterygoid  plate  about  the  sixth  month. 
About  the  fourth  month  a  center  appears  for  each  lingula  and  speedily  joins  the  rest  of  the  bone. 

The  presphenoid  is  united  to  the  postsphenoid  about  the  eighth  month,  and  at  birth  the  bone 
is  in  three  pieces  (Fig.  148) :  a  central,  consisting  of  the  body  and  small  wings,  and  two  lateral, 
each  comprising  a  great  wing  and  pterygoid  process.  In  the  first  year  after  birth  the  great  wings 
and  body  unite,  and  the  small  wings  extend  inward  above  the  anterior  part  of  the  body,  and, 
meeting  with  each  other  in  the  middle  hne,  form  an  elevated  smooth  surface,  termed  the  jugum 
sphenoidale.  By  the  twenty-fifth  year  the  sphenoid  and  occipital  are  completely  fused.  Between 
the  pre-  and  postsphenoid  there  are  occasionally  seen  the  remains  of  a  canal,  the  canalis  cranio- 
pharyngeus,  through  which,  in  early  fetal  Hfe,  the  hypophyseal  diverticulum  of  the  buccal  ecto- 
derm is  transmitted. 

The  sphenoidal  sinuses  are  present  as  minute  cavities  at  the  time  of  birth  (Onodi),  but  do  not 
attain  their  full  size  until  after  puberty. 

Intrinsic  Ligaments  of  the  Sphenoid. — The  more  important  of  these  are :  the  pterygospinous, 
stretching  between  the  spina  angularis  and  the  lateral  pterygoid  plate  (see  cervical  fascia);  the 
iiiterclinoid,  a  fibrous  process  joining  the  anterior  to  the  posterior  clinoid  process;  and  the 
curoticoclinoid ,  connecting  the  anterior  to  the  middle  clinoid  process.  These  ligaments  occa- 
sionally ossify. 

Articulations. — The  sphenoid  articulates  with  twelve  bones:  four  single,  the  vomer,  ethmoid, 
frontal,  and  occipital;  and  four  paired,  the  parietal,  temporal,  zygomatic,  and  palatine.- 

The  Ethmoid  Bone  (Os  Ethmoidale). 

The  ethmoid  bone  is  exceedingly  light  and  spongy,  and  cubical  in  shape;  it 
is  situated  at  the  anterior  part  of  the  base  of  the  cranium,  between  the  two  orbits, 
fit  the  roof  of  the  nose,  and  contributes  to  each  of  these  cavities.  It  consists  of 
four  parts:  a  horizontal  or  cribriform  plate,  forming  part  of  the  base  of  the  cranium; 
a  perpendicular  plate,  constituting  part  of  the  nasal  septum;  and  two  lateral  masses 
or  labyrinths. 

Cribiform  Plate  {lamina  cribrosa;  horizontal  lamina). — The  cribriform  plate 
(Fig.  149)  is  received  into  the  ethmoidal  notch  of  the  frontal  bone  and  roofs  in 
ihe  nasal  cavities.  Projecting  upward  from  the  middle  line  of  this  plate  is  a  thick, 
smooth,  triangular  process,  the  crista  galli,  so  called  from  its  resemblance  to  a 
cock's  comb.  The  long  thin  posterior  border  of  the  crista  galli  serves  for  the 
attachment  of  the  falx  cerebri. 
ts  anterior  border,  short  and 
1  hick,  articulates  with  the  frontal 
bone,  and  presents  two  small  pro- 
.ecting  alae,  which  are  received 
into  corresponding  depressions  in 
:he  frontal  bone  and  complete 
:he  foramen  cecum.  Its  sides  are 
:5mooth,  and  sometimes  bulging 
'rom  the  presence  of  a  small  air 
dnus  in  the  interior.  On  either 
side  of  the  crista  galli,  the  cribri- 
form plate  is  narrow  and  deeply 
grooved;  it  supports  the  olfactory 
bulb  and  is  perforated  by  fora-. 
mina  for  the  passage  of  the  olfac- 
tory nerves.  The  foramina  in  the 
middle  of  the  groove  are  small 
and  transmit  the   nerves  to  the 

roof  of  the  nasal  cavity;  those  at  the  medial  and  lateral  parts  of  the  groove  are 
larger — the  former  transmit  the  nerves  to  the  upper  part  of  the  nasal  septum, 
the  latter  those  to  the  superior  nasal  concha.    At  the  front  part  of  the  cribriform 

1  Anatomischer  Anzeiger,  March,  1905. 
It  also  sometimes  articulates  with  the  tuberosity  of  the  maxilla  (see  page  159). 


Perpendicular  plate 
Ala 


Crista  gain 


Cribriform  plate 

Anterior  ethmoidal 
groove 


Posterior  ethmoidal 
groove 


Fig.  149. — Ethmoid  bone  from  above. 


154 


OSTEOLOGY 


I 


plate,  on  either  side  of  the  crista  galli,  is  a  small  fissure  which  is  occupied  bj  a 
process  of  dura  mater.  Lateral  to  this  fissure  is  a  notch  or  foramen  which  trans- 
mits the  nasociliary  nerve;  from  this  notch  a  groove  extends  backward  to  the 
anterior  ethmoidal  foramen. 


Fig.    150. — Perpendicular  plate  of  ethmoid.     Shown  by  removing  the  right  labyrinth. 

Perpendicular  Plate  (lamina  perpendicularis;  vertical  plate). — The  perpendicular 
plate  (Figs.  150,  151)  is  a  thin,  flattened  lamina,  polygonal  in  form,  which  descends 
from  the  under  surface  of  the  cribriform  plate,  and  assists  in  forming  the  septum 
of  the  nose;  it  is  generally  deflected  a  little  to  one  or  other  side.  The  anterior  border 
articulates  with  the  spine  of  the  frontal  bone  and  the  crest  of  the  nasal  bones. 
The  posterior  border  articulates  by  its  upper  half  with  the  sphenoidal  crest,  by  its 
lower  with  the  vomer.  The  inferior  border  is  thicker  than  the  posterior,  and  serves 
for  the  attachment  of  the  septal  cartilage  of  the  nose.  The  surfaces  of  the  plate 
are  smooth,  except  above,  where  numerous  grooves  and  canals  are  seen;  these 
lead  from  the  medial  foramina  on  the  cribriform  plate  and  lodge  filaments  of  the 
olfactory  nerves. 

The  Labyrinth  or  Lateral  Mass  (labyrinthus  ethmoidalis)  consists  of  a  number 
of  thin-walled  cellular  cavities,  the  ethmoidal  cells,   arranged  in  three  groups, 

anterior,  middle,  and  posterior,  and  inter- 
posed between  two  vertical  plates  of  bone; 
the  lateral  plate  forms  part  of  the  orbit, 
the  medial,  part  of  the  corresponding 
nasal  cavity.  In  the  disarticulated  bone 
many  of  these  cells  are  opened  into,  but 
when  the  bones  are  articulated,  they  are 
closed  in  at  every  part,  except  where 
they  open  into  the  nasal  cavity. 

Surfaces. — The  upper  surface  of  the  laby- 
rinth (Fig.  149)  presents  a  number  of 
half-broken  cells,  the  walls  of  which  are 
completed,  in  the  articulated  skull,  by 
the  edges  of  the  ethmoidal  notch  of  the 
frontal  bone.  Crossing  this  surface  are 
two  grooves,  converted  into  canals  by  articulation  with  the  frontal;  they  are  the 
anterior  and  posterior  ethmoidal  canals,  and  open  on  the  inner  wall  of  the  orbit. 
The  posterior  surface  presents  large  irregular  cellular  cavities,  which  are  closed  in 


Crista  galli 


Labyrinth 

Superior  nasal 

concha 
Superior  meatus 

Uncinate  process 

Middle  nasal  concha 
■  Perpendicular  plate 
Fig.   151. — Ethmoid  bone  from  behind. 


I 


THE  ETHMOID  BONE 


155 


by  articulation  with  the  sphenoidal  concha  and  orbital  process  of  the  palatine. 
The  lateral  surface  (Fig.  152)  is  formed  of  a  thin,  smooth,  oblong  plate,  the  lamina 
papyracea  {os  planum),  which  covers  in  the  middle  and  posterior  ethmoidal  cells 


Ethmoidal 
cells 


Perpendicviar 

plate 


Uncinate  process 


Fig.   152. — Ethmoid  bone  from  the  right  side. 


and  forms  a  large  part  of  the  medial  wall  of  the  orbit;  it  articulates  above  with 
the  orbital  plate  of  the  frontal  bone,  below  with  the  maxilla  and  orbital  process 
of  the  palatine,  in  front  with  the  lacrimal,  and  behind  with  the  sphenoid. 

In  front  of  the  lamina  papyracea  are  some  broken  air  cells  which  are  overlapped 
and  completed  by  the  lacrimal  bone  and  the  frontal  process  of  the  maxilla.    A 


Frontal  simis 


Crista  gain 


Sella  turcica 


Openings  into 
maxillary  sinus 
Medial  pterygoid  plate 
Hamulus 


Lateral  wall  of  nasal  cavity,  showing  ethmoid  bone  in  position. 


I 


ed  lamina,  the  uncinate  process,  projects  downward  and  backward  from  this 
part  of  the  labyrinth;  it  forms  a  small  part  of  the  medial  wall  of  the  maxillary 
sinus,  and  articulates  with  the  ethmoidal  process  of  the  inferior  nasal  concha. 


156 


I 


The  medial  surface  of  the  labyrinth  (Fig.  153)  forms  part  of  the  lateral  ^all 
of  the  corresponding  nasal  cavity.  It  consists  of  a  thin  lamella,  which  descends 
from  the  under  surface  of  the  cribriform  plate,  and  ends  below  in  a  free,  convoluted 
margin,  the  middle  nasal  concha.  It  is  rough,  and  marked  above  by  numerous 
grooves,  directed  nearly  vertically  downward  from  the  cribriform  plate;  they 
lodge  branches  of  the  olfactory  nerves,  which  are  distributed  to  the  mucous  mem- 
brane covering  the  superior  nasal  concha.  The  back  part  of  the  surface  is  sub- 
divided by  a  narrow  oblique  fissure,  the  superior  meatus  of  the  nose,  bounded  above 
by  a  thin,  curved  plate,  the  superior  nasal  concha;  the  posterior  ethmoidal  cells 
open  into  this  meatus.  Below,  and  in  front  of  the  superior  meatus,  is  the  con^'ex 
surface  of  the  middle  nasal  concha;  it  extends  along  the  whole  length  of  the  medial 
surface  of  the  labyrinth,  and  its  lower  margin  is  free  and  thick.  The  lateral  surface 
of  the  middle  concha  is  concave,  and  assists  in  forming  the  middle  meatus  of  the 
nose.  The  middle  ethmoidal  cells  open  into  the  central  part  of  this  meatus,  and  a 
sinuous  passage,  termed  the  infundibulum,  extends  upward  and  forward  through 
the  labyrinth  and  communicates  with  the  anterior  ethmoidal  cells,  and  in  about 
50  per  cent,  of  skulls  is  continued  upward  as  the  frontonasal  duct  into  the  frontal 
sinus. 

Ossification. — The  ethmoid  is  ossified  in  the  cartilage  of  the  nasal  capsule  by  three  centers: 
one  for  the  perpendicular  plate,  and  one  for  each  labyrinth. 

The  labyrinths  are  first  developed,  ossific  granules  making  their  appearance  in  the  region  of 
the  lamina  papyracea  between  the  fourth  and  fifth  months  of  fetal  life,  and  extending  into  the 
conchse.  At  birth,  the  bone  consists  of  the  two  labyrinths,  which  are  small  and  ill-developed. 
During  the  first  year  after  birth,  the  perpendicular  plate  and  crista  galli  begin  to  ossify  from  a 
single  center,  and  are  joined  to  the  labyrinths  about  the  beginning  of  the  second  year.  The 
cribriform  plate  is  ossified  partly  from  the  perpendicular  plate  and  partly  from  the  labyrinths. 
The  development  of  the  ethmoidal  cells  begins  during  fetal  life. 

Articulations. — The  ethmoid  articulates  -with,  fifteen  bones:  four  of  the  cranium — the  frontal, 
the  sphenoid,  and  the  two  sphenoidal  conchae;  and  eleven  of  the  face — the  two  nasals,  two  maxillae, 
two  lacrimals,  two  palatines,  two  inferior  nasal  conchae,  and  the  vomer. 

Sutnral  or  Wormian^  Bones. — In  addition  to  the  usual  centers  of  ossification  of  the  cranium, 
others  may  occur  in  the  course  of  the  sutures,  giving  rise  to  irregular,  isolated  bones,  termed 
suiural  or  Wormian  hones.  They  occur  most  frequently  in  the  course  of  the  lambdoidal  suture, 
but  are  occasionally  seen  at  the  fontanelles,  especially  the  posterior.  One,  the  pterion  ossicle, 
sometimes  exists  between  the  sphenoidal  angle  of  the  parietal  and  the  great  wing  of  the  sphenoid. 
They  have  a  tendency  to  be  more  or  less  symmetrical  on  the  two  sides  of  the  skull,  and  vary 
much  in  size.  Their  number  is  generally  Hmited  to  two  or  three;  but  more  than  a  hundred  have 
been  found  in  the  skull  of  an  adult  hydrocephalic  subject. 


THE  FACIAL  BONES  (OSSA  FACIEI). 

The  Nasal  Bones  (Ossa  Nasalia) . 

The  nasal  bones  are  two  small  oblong  bones,  varying  in  size  and  form  in  different 
individuals;  they  are  placed  side  by  side  at  the  middle  and  upper  part  of  the  face, 
and  form,  by  their  junction,  "the  bridge"  of  the  nose  (Fig.  190).  Each  has  two 
surfaces  and  four  borders. 

Surfaces. — The  outer  surface  (Fig.  155)  is  concavoconvex  from  above  downward, 
convex  from  side  to  side;  it  is  covered  by  the  Procerus  and  Compressor  naris,  and 
perforated  about  its  center  by  a  foramen,  for  the  transmission  of  a  small  vein. 
The  inner  surface  (Fig.  150)  is  concave  from  side  to  side,  and  is  traversed  from  above 
downward,  by  a  groove  for  the  passage  of  a  branch  of  the  nasociliary  nerve. 

Borders. — The  superior  border  is  narrow,  thick,  and  serrated  for  articulation  with 
the  nasal  notch  of  the  frontal  bone.    The  inferior  border  is  thin,  and  gives  attach- 

'  Ole  Worm,  Professor  of  Anatomy  at  Copenhagen,  1624-1639,  was  erroneously  supposed  to  have  given  the  first 
detailed  description  of  these  bones. 


I 


THE  MAXILLA 


157 


nient  to  the  lateral  cartilage  of  the  nose;  near  its  middle  is  a  notch  which  marks 
the  end  of  the  groove  just  referred  to.  The  lateral  border  is  serrated,  bevelled 
at  the  expense  of  the  inner  surface  above,  and  of  the  outer  below,  to  articulate 
Mith  the  frontal  process  of  the  maxilla.    The  medial  border,  thicker  above  than 


Fossa  Jor  lacrimal  sac 


Infraorbital 
foramen 


Fig.  154. — Articulation  of  nasal  and  lacrimal  bones  with  maxilla. 

Delow,  articulates  with  its  fellow  of  the  opposite  side,  and  is  prolonged  behind  into 
a,  vertical  crest,  which  forms  part  of  the  nasal  septum:  this  crest  articulates,  from 
above  downward,  with  the  spine  of  the  frontal,  the  perpendicular  plate  of  the 
ethmoid,  and  the  septal  cartilage  of  the  nose. 


Foramen 
for  vein 


yitt^ 


— Right  nasal  bone.     Outer  surface. 


Crest 


Groove 
for  nerve 


Fig.  156. — Right  nasal  bone.     Inner  surface. 


Ossification. — Each  bone  is  ossified  from  one  center,  which  appears  at  the  beginning  of  the 
third  month  of  fetal  hfe  in  the  membrane  overlying  the  front  part  of  the  cartilaginous  nasal 
capsule. 

Articulations. — The  nasal  articulates  with  foiu-  bones:  two  of  the  cranium,  the  frontal  and 
ethmoid,  and  two  of  the  face,  the  opposite  nasal  and  the  maxilla. 

The  Maxillae  (Upper  Jaw). 

The  maxillae  are  the  largest  bones  of  the  face,  excepting  the  mandible,  and 
form,  by  their  union,  the  whole  of  the  upper  jaw.    Each  assists  in  forming  the 


■ 


158 


OSTEOLOGY 


I 


boundaries  of  three  cavities,  viz.,  the  roof  of  the  mouth,  the  floor  and  lateral 
wall  of  the  nose  and  the  floor  of  the  orbit;  it  also  enters  into  the  formation  of  two 
fossae,  the  infratemporal  and  pterygopalatine,  and  two  fissures,  the  inferior  orbital 
and  pterygomaxillary. 

Each  bone  consists  of  a  body  and  four  processes — zygomatic,  frontal,  alveolar, 
and  palatine. 

The  Body  {corpus  maxilla;). — The  body  is  somewhat  pyramidal  in  shape,  and 
contains  a  large  cavity,  the  maxillary  sinus  (antrum  of  Highmore).  It  has  four 
surfaces — an  anterior,  a  posterior  or  infratemporal,  a  superior  or  orbital,  and.  a 
medial  or  nasal. 

Surfaces. — The  anterior  surface  (Fig,  157)  is  directed  forward  and  lateralward. 
It  presents  at  its  lower  part  a  series  of  eminences  corresponding  to  the  positions 
of  the  roots  of  the  teeth.  Just  above  those  of  the  incisor  teeth  is  a  depression, 
the  incisive  fossa,  which  gives  origin  to  the  Depressor  alaj  nasi;  to  the  alveolar 
border  below  the  fossa  is  attached  a  slip  of  the  Orbicularis  oris;  above  and  a  little 


Med.  jxi 


DlIiATATOE  NARIS  POSTERIOR 


Incisive  fossa 


Alveolar  canals 


Maxillary  tvberosity 


Fia.  157. — Left  maxilla.     Outer  surface. 

lateral  to  it,  the  Nasalis  arises.  Lateral  to  the  incisive  fossa  is  another  depression, 
the  canine  fossa;  it  is  larger  and  deeper  than  the  incisive  fossa,  and  is  separated 
from  it  by  a  vertical  ridge,  the  canine  eminence,  corresponding  to  the  socket  of 
the  canine  tooth;  the  canine  fossa  gives  origin  to  the  Caninus,  Above  the  fossa 
is  the  infraorbital  foramen,  the  end  of  the  infraorbital  canal;  it  transmits  the  infra- 
orbital vessels  and  nerve.  Above  the  foramen  is  the  margin  of  the  orbit,  which 
affords  attachment  to  part  of  the  Quadratus  labii  superioris.  Medially,  the  anterior 
surface  is  limited  by  a  deep  concavity,  the  nasal  notch,  the  margin  of  which  gives 
attachment  to  the  Dilatator  naris  posterior  and  ends  below  in  a  pointed  process, 
which  with  its  fellow  of  the  opposite  side  forms  the  anterior  nasal  spine. 

The  infratemporal  surface  (Fig,  157)  is  convex,*  directed  backward  and  lateral- 
ward,  and  forms  part  of  the  infratemporal  fossa.  It  is  separated  from  the  anterior 
surface  by  the  zygomatic  process  and  by  a  strong  ridge,  extending  upward  from 
the  socket  of  the  first  molar  tooth.  It  is  pierced  about  its  center  by  the  apertures 
of  the  alveolar  canals,  which  transmit  the  posterior  superior  alveolar  vessels  and 
nerves.    At  the  lower  part  of  this  surface  is  a  rounded  eminence,  the  maxillary 


THE  MAXILLA 


159 


tuberosity,  especially  prominent  after  the  growth  of  the  wisdom  tooth;  it  is  rough 
on  its  lateral  side  for  articulation  with  the  pyramidal  process  of  the  palatine  bone 
and  in  some  cases  articulates  with  the  lateral  pterygoid  plate  of  the  sphenoid. 
It  gives  origin  to  a  few  fibers  of  the  Pterygoideus  internus.  Immediately  above 
this  is  a  smooth  surface,  which  forms  the  anterior  boundary  of  the  pterygopalatine 
fossa,  and  presents  a  groove,  for  the  maxillary  nerve;  this  groove  is  directed  lateral- 
ward  and  slightly  upward,  and  is  continuous  with  the  infraorbital  groove  on  the 
orbital  surface. 

The  orbital  surface  (Fig.  157)  is  smooth  and  triangular,  and  forms  the  greater 
part  of  the  floor  of  the  orbit.  It  is  bounded  medially  by  an  irregular  margin  which 
in  front  presents  a  notch,  the  lacrimal  notch;  behind  this  notch  the  margin  articu- 
lates with  the  lacrimal,  the  lamina  papyracea  of  the  ethmoid  and  the  orbital  process 
of  the  palatine.  It  is  bounded  behind  by  a  smooth  rounded  edge  which  forms 
the  anterior  margin  of  the  inferior  orbital  fissure,  and  sometimes  articulates  at 
its  lateral  extremity  with  the  orbital  surface  of  the  great  wing  of  the  sphenoid. 


With  frontal 


Bones  partially  closing  orifice  of  sinus 
marked  in  red 


Ethmoid — 


With  nasal  hone 


inferior  nasal  coiicha— 
Palatine—. 


Ant.  nasal  spine 


Bristle  passed 
through  incisive 
canxd 


Fig.   158. — Left  maxilla.     Nasal  surface. 


It  is  limited  in  front  by  part  of  the  circumference  of  the  orbit,  which  is  continuous 
^aedially  with  the  frontal  process,  and  laterally  with  the  zyogmatic  process.  Near 
the  middle  of  the  posterior  part  of  the  orbital  surface  is  the  infraorbital  groove, 
for  the  passage  of  the  infraorbital  vessels  and  nerve.  The  groove  begins  at  the 
middle  of  the  posterior  border,  where  it  is  continuous  with  that  near  the  upper 
edge  of  the  infratemporal  surface,  and,  passing  forward,  ends  in  a  canal,  which 
subdivides  into  two  branches.  One  of  the  canals,  the  infraorbital  canal,  opens 
just  below  the  margin  of  the  orbit;  the  other,  which  is  smaller,  runs  downward  in 
the  substance  of  the  anterior  wall  of  the  maxillary  sinus,  and  transmits  the  anterior 
superior  alveolar  vessels  and  nerve  to  the  front  teeth  of  the  maxilla.  From  the 
back  part  of  the  infraorbital  canal,  a  second  small  canal  is  sometimes  given  off;  it 
runs  downward  in  the  lateral  wall  of  the  sinus,  and  conveys  the  middle  alveolar 
nerve  to  the  premolar  teeth.  At  the  medial  and  forepart  of  the  orbital  surface, 
just  lateral  to  the  lacrimal  groove,  is  a  depression,  which  gives  origin  to  the  Obliquus 
oculi  inferior. 


i 


160 


OSTEOLOGY 


The  nasal  siirface  (Fig.  158)  presents  a  large,  irregular  opening  leading  into  tbe 
maxillary  sinus.  At  the  upper  border  of  this  aperture  are  some  broken  air  cells, 
which,  in  the  articulated  skull,  are  closed  in  by  the  ethmoid  and  lacrimal  bones. 
Below  the  aperture  is  a  smooth  concavity  which  forms  part  of  the  inferior  meatus 
of  the  nasal  cavity,  and  behind  it  is  a  rough  surface  for  articulation  with  the  per- 
pendicular part  of  the  palatine  bone;  this  surface  is  traversed  by  a  groove,  com- 
mencing near  the  middle  of  the  posterior  border  and  running  obliquely  downward 
and  forward;  the  groove  is  converted  into  a  canal,  the  pterygopalatine  canal,  by  the 
palatine  bone.  In  front  of  the  opening  of  the  sinus  is  a  deep  groove,  the  lacrimal 
groove,  which  is  converted  into  the  nasolacrimal  canal,  by  the  lacrimal  bone  and 
inferior  nasal  concha;  this  canal  opens  into  the  inferior  meatus  of  the  nose  and 
transmits  the  nasolacrimal  duct.  More  anteriorly  is  an  oblique  ridge,  the  conchal 
crest,  for  articulation  with  the  inferior  nasal  concha.  The  shallow  concavity  aboAe 
this  ridge  forms  part  of  the  atrium  of  the  middle  meatus  of  the  nose,  and  that 
below  it,  part  of  the  inferior  meatus. 


Anterior 
ethmoidal  foramen 


Posterior  ethmoidal  foramen 
Orbital  process  of  palatine 
/  Optic  foramen 

Sphenopalatine  foramen 
Sella  turcica 
I  Probe  in  foramen  rot  undum 


Fossa  for 

lacrimal  sac 

Uncinate  process 
of  ethmoid 
Openings  of 
maxillary  sinus 
Inferior  nasal 
concha 


Probe  in  pterygoid  canal 
Probe  in  pterygopalatine  canal 

Palatine  bone 

Lateral  pterygoid  plate 


Pyramidal  process  cf  palatine 


Fig.   159. — Left  maxillary  sinus  opened  from  the  exterior. 


The  Maxillary  Sinus  or  Antrum  of  Highmore  {sinus  maxillaris). — The  maxillary 
sinus  is  a  large  pyramidal  cavity,  within  the  body  of  the  maxilla :  its  apex,  directed 
lateralward,  is  formed  by  the  zygomatic  process;  its  base,  directed  medialward, 
by  the  lateral  wall  of  the  nose.  Its  walls  are  everywhere  exceedingly  thin,  and 
correspond  to  the  nasal  orbital,  anterior,  and  infratemporal  surfaces  of  the  body 
of  the  bone.  Its  nasal  wall,  or  base,  presents,  in  the  disarticulated  bone,  a  large, 
irregular  aperture,  communicating  with  the  nasal  cavity.  In  the  articulated 
skull  this  aperture  is  much  reduced  in  size  by  the  following  bones:  the  uncinate 
process  of  the  ethmoid  above,  the  ethmoidal  process  of  the  inferior  nasal  concha 
below,  the  vertical  part  of  the  palatine  behind,  and  a  small  part  of  the  lacrimal 
above  and  in  front  (Figs.  158,  159) ;  the  sinus  communicates  with  the  middle  meatus 


THE  MAXILLA  161 

of  the  nose,  generally  by  two  small  apertures  left  between  the  above-mentioned 
bones.  In  the  fresh  state,  usually  only  one  small  opening  exists,  near  the  upper 
part  of  the  cavity;  the  other  is  closed  by  mucous  membrane.  On  the  posterior 
wall  are  the  alveolar  canals,  transmitting  the  posterior  superior  alveolar  vessels 
and  nerves  to  the  molar  teeth.  The  floor  is  formed  by  the  alveolar  process  of  the 
maxilla,  and,  if  the  sinus  be  of  an  average  size,  is  on  a  level  with  the  floor  of 
the  nose;  if  the  sinus  be  large  it  reaches  below  this  level. 

Projecting  into  the  floor  of  the  antrum  are  several  conical  processes,  correspond- 
ing to  the  roots  of  the  first  and  second  molar  teeth  ;^  in  some  cases  the  floor  is 
perforated  by  the  fangs  of  the  teeth.  The  infraorbital  canal  usually  projects  into 
the  cavity  as  a  well-marked  ridge  extending  from  the  roof  to  the  anterior  wall; 
additional  ridges  are  sometimes  seen  in  the  posterior  wall  of  the  cavity,  and 
are  caused  by  the  alveolar  canals.  The  size  of  the  cavity  varies  in  different  skulls, 
and  even  on  the  tw^o  sides  of  the  same  skull. ^ 

The  Zygomatic  Process  (processus  zygomaticus;  malar  process). — ^The  zygomatic 
process  is  a  rough  triangular  eminence,  situated  at  the  angle  of  separation  of  the 
anterior,  zygomatic,  and  orbital  surfaces.  In  front  it  forms  part  of  the  anterior 
surface;  behind,  it  is  concave,  and  forms  part  of  the  infratemporal  fossa;  above, 
it  is  rough  and  serrated  for  articulation  with  the  zygomatic  bone;  while  below, 
it  presents  the  prominent  arched  border  which  marks  the  division  between  the 
anterior  and  infratemporal  surfaces. 

The  Frontal  Process  (processus  frontalis;  nasal  process). — The  frontal  process 
is  a  strong  plate,  which  projects  upward,  medialward,  and  backward,  by  the  side 
of  the  nose,  forming  part  of  its  lateral  boundary.  Its  lateral  surface  is  smooth, 
continuous  with  the  anterior  surface  of  the  body,  and  gives  attachment  to  the 
C^uadratus  labii  superioris,  the  Orbicularis  oculi,  and  the  medial  palpebral  ligament. 
Its  medial  surface  forms  part  of  the  lateral  wall  of  the  nasal  cavity;  at  its  upper 
part  is  a  rough,  uneven  area,  which  articulates  with  the  ethmoid,  closing  in  the 
anterior  ethmoidal  cells;  below  this  is  an  oblique  ridge,  the  ethmoidal  crest,  the 
}iosterior  end  of  which  articulates  with  the  middle  nasal  concha,  while  the  anterior 
})art  is  termed  the  agger  nasi;  the  crest  forms  the  upper  limit  of  the  atrium  of  the 
middle  meatus.  The  upper  border  articulates  with  the  frontal  bone  and  the  anterior 
^vith  the  nasal;  the  posterior  border  is  thick,  and  hollowed  into  a  groove,  which  is 
continuous  below  with  the  lacrimal  groove  on  the  nasal  surface  of  the  body:  by 
ihe  articulatioji  of  the  medial  margin  of  the  groove  with  the  anterior  border  of 
ihe  lacrimal  a  corresponding  groove  on  the  lacrimal  is  brought  into  continuity, 
;md  together  they  form  the  lacrimal  fossa  for  the  lodgement  of  the  lacrimal  sac. 
The  lateral  margin  of  the  groove  is  named  the  anterior  lacrimal  crest,  and  is  con- 
linuous  below  with  the  orbital  margin;  at  its  junction  with  the  orbital  surface  is 
a  small  tubercle,  the  lacrimal  tubercle,  which  serves  as  sc  guide  to  the  position  of 
:he  lacrimal  sac. 

The  Alveolar  Process  (processus  alveolaris). — The  alveolar  process  is  the  thickest 
and  most  spongy  part  of  the  bone.  It  is  broader  behind  than  in  front,  and  exca- 
vated into  deep  cavities  for  the  reception  of  the  teeth.  These  cavities  are  eight 
n  number,  and  vary  in  size  and  depth  according  to  the  teeth  they  contain.  That 
:'or  the  canine  tooth  is  the  deepest;  those  for  the  molars  are  the  widest,  and  are 
subdivided  into  minor  cavities  by  septa;  those  for  the  incisors  are  single,  but 
deep  and  narrow.  The  Buccinator  arises  from  the  outer  surface  of  this  process, 
as  far  forward  as  the  first  molar  tooth.  When  the  maxillse  are  articulated  with  each 
other,  their  alveolar  processes  together  form  the  alveolar  arch;  the  center  of  the 
anterior  margin  of  this  arch  is  named  the  alveolar  point. 

'  The  number  of  teeth  whose  roots  are  in  relation  with  the  floor  of  the  antrum  is  variable.  The  sinus  "may  extend 
so  aa  to  be  in  relation  to  all  the  teeth  of  the  true  maxilla,  from  the  canine  to  the  dens  aapienliw. "  _  (Salter.) 

-  Aldren  Turner  (op.  cit.)  gives  the  following  measurements  as  those  of  an  average  sized  sinus:  vertical  height 
opposite  first  molar  tooth,  1}-^  inch;  transverse  breadth,  1  inch;  and  antero-posterior  depth,  \\i  inch. 


i 


11 


162 


OSTEOLOGY 


The  Palatine  Process  (processus  yalatinus;  palatal  process). — The  palatine 
process,  thick  and  strong,  is  horizontal  and  projects  medialward  from  the  nasal 
surface  of  the  bone.  It  forms  a  considerable  part  of  the  floor  of  the  nose  and  the 
roof  of  the  mouth  and  is  much  thicker  in  front  than  behind.  Its  inferior  surface 
(Fig.  160)  is  concave,  rough  and  uneven,  and  forms,  with  the  palatine  process  of 
the  opposite  bone,  the  anterior  three-fourths  of  the  hard  plate.  It  is  perforated 
by  numerous  foramina  for  the  passage  of  the  nutrient  vessels;  is  channelled  at  the 
back  part  of  its  lateral  border  by  a  groove,  sometimes  a  canal,  for  the  transmission 
of  the  descending  palatine  vessels  and  the  anterior  palatine  nerve  from  the  spheno- 
palatine ganglion;  and  presents  little  depressions  for  the  lodgement  of  the  palatine 
glands.  When  the  two  maxillae  are  articulated,  a  funnel-shaped  opening,  the 
incisive  foramen,  is  seen  in  the  middle  line,  immediately  behind  the  incisor  teeth. 
In  this  opening  the  orifices  of  two  lateral  canals  are  visible;  they  are  named  the 


Incisive  cavMs 


Incisive  foramen 


Foramina  of  Scarpa 


Palatine  process  of  maxilla  \        Greater  palatine  foramen 

Horizontal  plate  of  palatine  bone  Lesser  palatine  foramina 

Fig.   160. — The  bony  palate  and  alveolar  arch. 

incisive  canals  or  foramina  of  Stenson;  through  each  of  them  passes  the  terminal 
branch  of  the  descending  palatine  artery  and  the  nasopalatine  nerve.  Occasionally 
two  additional  canals  are  present  in  the  middle  line;  they  are  termed  the  foramina 
of  Scarpa,  and  when  present  transmit  the  nasopalatine  nerves,  the  left  passing 
through  the  anterior,  and  the  right  through  the  posterior  canal.  On  the  under 
surface  of  the  palatine  process,  a  delicate  linear  suture,  well  seen  in  young  skulls, 
may  sometimes  be  noticed  extending  lateralward  and  forward  on  either  side  from 
the  incisive  foramen  to  the  interval  between  the  lateral  incisor  and  the  canine  tooth. 
The  small  part  in  front  of  this  suture  constitutes  the  premaxilla  (os  incisivum), 
which  in  most  vertebrates  forms  an  independent  bone;  it  includes  the  whole  thick- 
ness of  the  alveolus,  the  corresponding  part  of  the  floor  of  the  nose  and  the  anterior 
nasal  spine,  and  contains  the  sockets  of  the  incisor  teeth.  The  upper  surface  of 
the  palatine  process  is  concave  from  side  to  side,  smooth,  and  forms  the  greater 
part  of  the  floor  of  the  nasal  cavity.    It  presents,  close  to  its  medial  margin,  the 


I 


THE  LACRIMAL  BONE 


163 


upper  orifice  of  the  incisive  canal.  The  lateral  border  of  the  process  is  incorporated 
with  the  rest  of  the  bone.  The  medial  border  is  thicker  in  front  than  behind,  and 
is  raised  above  into  a  ridge,  the  nasal  crest,  which,  with  the  corresponding  ridge 
of  the  opposite  bone,  forms  a  groove  for  the  reception  of  the  vomer.  The  front 
part  of  this  ridge  rises  to  a  considerable  height,  and  is  named  the  incisor  crest; 
it  is  prolonged  forw^ard  into  a  sharp  process,  which  forms,  together  wdth  a  similar 
process  of  the  opposite  bone,  the  anterior  nasal  spine.  The  posterior  border  is  ser- 
rated for  articulation  with  the  horizontal  part  of  the  palatine  bone. 

Ossification. — The  maxilla  is  ossified  in  membrane.  Mall^  and  Fawcett^  maintain  that  it  is 
ossified  from  two  centers  only,  one  for  the  maxilla  proper  and  one  for  the  premaxilla.  These 
centers  appear  dm-ing  the  sixth  week  of  fetal  life  and  unite  in  the  beginning  of  the  third  month, 
but  the  suture  between  the  two  portions  persists  on  the  palate  until  nearly  middle  life.  Mall 
states  that  the  frontal  process  is  developed  from  both  centers.  The  maxillary  sinus  appears  as 
a  shallow  groove  on  the  nasal  surface  of  the  bone  about  the  fourth  month  of  fetal  life,  but  does 
not  reach  its  full  size  xmtil  after  the  second  dentition.  The  maxilla  was  formerly  described  as 
ossifying  from  six  centers,  viz.,  one,  the  orbitonasal,  forms  that  portion  of  the  body  of  the  bone 
which  lies  medial  to  the  infraorbital  canal,  including  the  medial  part  of  the  floor  of  the  orbit  and 
the  lateral  wall  of  the  nasal  cavity;  a  second,  the  zygomatic,  gives  origin  to  the  portion  which  lies 
lateral  to  the  infraorbital  canal,  including  the  zygomatic  process;  from  a  third,  the  palatine,  is 
developed  the  palatine  process  posterior  to  the  incisive  canal  together  with  the  adjoining  part 
of  the  nasal  wall;  a  fourth,  the  premaxillary,  forms  the  incisive  bone  which  carries  the  incisor 


:g.  161. — Anterior  surface  of  maxilla  at  birth. 


Fig.   162. — Inferior  surface  of  maxilla  at  birth. 


I 


teeth  and  corresponds  to  the  premaxiUa  of  the  lower  vertebrates;'  a  fifth,  the  nasal,  gives  rise  to 
lhe  frontal  process  and  the  portion  above  the  canine  tooth;  and  a  sixth,  the  infravomerine,  lies 
between  the  palatine  and  premaxillary  centers  and  beneath  the  vomer;  this  center,  together  with 
i,he  corresponding  center  of  the  opposite  bone,  separates  the  incisive  canals  from  each  other. 

Articulations. — The  maxilla  articulates  with  nine  bones:  two  of  the  cranium,  the  frontal  and 
ithmoid,  and  seven  of  the  face,  viz.,  the  nasal,  zygomatic,  lacrimal,  inferior  nasal  concha,  palatine, 
/omer,  and  its  fellow  of  the  opposite  side.  Sometimes  it  articulates  with  the  orbital  surface, 
md  sometimes  with  the  lateral  pterygoid  plate  of  the  sphenoid. 

r  CHANGES   PRODUCED   IN   THE    MAXILLA   BY   AGE. 

At  birth  the  transverse  and  antero-posterior  diameters  of  the  bone  are  each  greater  than  the 
vertical.  The  frontal  process  is  well-marked  and  the  body  of  the  bone  consists  of  little  more  than 
the  alveolar  process,  the  teeth  sockets  reaching  almost  to  the  floor  of  the  orbit.  The  maxillary 
sinus  presents  the  appearance  of  a  furrow  on  the  lateral  wall  of  the  nose.  In  the  adult  the  vertical 
diameter  is  the  greatest,  owing  to  the  development  of  the  alveolar  process  and  the  increase  in 
size  of  the  sinus.  In  old  age  the  bone  reverts  in  some  measure  to  the  infantile  condition;  its 
height  is  diminished,  and  after  the  loss  of  the  teeth  the  alveolar  process  is  absorbed,  and  the 
lower  part  of  the  bone  contracted  and  reduced  in  thickness. 

If  The  lacrimal  bone,  the  smallest  and  most  fragile  bone  of  the  face,  is  situated 
at  the  front  part  of  the  medial  wall  of  the  orbit  (Fig.  164).  It  has  two  surfaces 
and  four  borders. 

1  American  Journal  of  Anatomy,  1906,  vol.  v. 

2  Journal  of  Anatomy  and  Physiology,  1911,  vol.  xlv. 
'  Some  anatomists  believe  that  the  premaxillary  bone  is  ossified  by  two  centers  (see  page  299). 


The  Lacrimal  Bone  (Os  Lacrimale). 


164 


I 


tWM  Fron/til 


With 
Injer.  nasal  concha 
Fig.  163. — Left  lacri- 
mal bone.    Orbital  sur- 
face.   Enlarged. 


Surfaces. — The  lateral  or  orbital  surface  (Fig.  163)  is  divided  by  a  vertical  ridge, 
the  posterior  lacrimal  crest,  into  two  parts.  In  front  of  this  crest  is  a  longitudinal 
groove,  the  lacrimal  sulcus  (sulcus  lacrimalis),  the  inner  margin  of  which  unites 
with  the  frontal  process  of  the  maxilla,  and  the  lacrimal  fossa  is  thus  completed. 
The  upper  part  of  this  fossa  lodges  the  lacrimal  sac,  the  lower  part,  the  naso- 
lacrimal duct.  The  portion  behind  the  crest  is  smooth,  and  forms  part  of  the 
medial  wall  of  the  orbit.  The  crest,  with  a  part  of  the  orbital  surface  imme- 
diately behind  it,  gives  origin  to  the  lacrimal  part  of  the  Orbicularis  oculi  and 
ends  below  in  a  small,  hook-like  projection,  the  lacrimal  hamulus,  which  articu- 
lates with  the  lacrimal  tubercle  of  the  maxilla,  and  completes 
the  upper  orifice  of  the  lacrimal  canal;  it  sometimes  exists  as 
a  separate  piece,  and  is  then  called  the  lesser  lacrimal  bone. 

The  medial  or  nasal  surface  presents  a  longitudinal  furrow, 
corresponding  to  the  crest  on  the  lateral  surface.  The  area  in 
front  of  this  furrow  forms  part  of  the  middle  meatus  of  the 
nose;  that  behind  it  articulates  with  the  ethmoid,  and  completes 
some  of  the  anterior  ethmoidal  cells. 

Borders. — Of  the  four  borders  the  anterior  articulates  with 
the  frontal  process  of  the  maxilla;  the  posterior  with  the  lamina 
papyracea  of  the  ethmoid;  the  superior  with  the  frontal  bone. 
The  inferior  is  divided  by  the  lower  edge  of  the  posterior  lacri- 
mal crest  into  two  parts :  the  posterior  part  articulates  with  the 
orbital  plate  of  the  maxilla;  the  anterior  is  prolonged  downward 
as  the  descending  process,  which  articulates  with  the  lacrimal  process  of  the  inferior 
nasal  concha,  and  assists  in  forming  the  canal  for  the  nasolacrimal  duct. 

Ossification. — The  lacrimal  is  ossified  from  a  single  center,  which  appears  about  the  twelfth 
week  in  the  membrane  covering  the  cartilaginous  nasal  capsule. 

Articulations. — The  lacrimal  articulates  with  four  bones:  two  of  the  cranium,  the  frontal 
and  ethmoid,  and  two  of  the  face,  the  maxilla  and  the  inferior  nasal  concha. 

The  Zygomatic  Bone  (Os  Zygomaticum ;  Malar  Bone). 

The  zygomatic  bone  is  small  and  quadrangular,  and  is  situated  at  the  upper 
and  lateral  part  of  the  face:  it  forms  the  prominence  of  the  cheek,  part  of  the 
lateral  wall  and  floor  of  the  orbit,  and  parts  of  the  temporal  and  infratemporal 
fossae  (Fig.  164).  It  presents  a  malar  and  a  temporal  surface;  four  processes,  the 
frontosphenoidal,  orbital,  maxillary,  and  temporal;  and  four  borders. 

Surfaces. — The  malar  surface  (Fig.  165)  is  convex  and  perforated  near  its  center 
by  a  small  aperture,  the  zygomaticofacial  foramen,  for  the  passage  of  the  zygomatico- 
facial nerve  and  vessels;  below  this  foramen  is  a  slight  elevation,  which  gives 
origin  to  the  Zygomaticus. 

The  temporal  surface  (Fig.  166),  directed  backward  and  medialward,  is  concave, 
presenting  medially  a  rough,  triangular  area,  for  articulation  with  the  maxilla, 
and  laterally  a  smooth,  concave  surface,  the  upper  part  of  which  forms  the  anterior 
boundary  of  the  temporal  fossa,  the  lower  a  part  of  the  infratemporal  fossa.  Near 
the  center  of  this  surface  is  the  zygomaticotemporal  foramen  for  the  transmission 
of  the  zygomaticotemporal  nerve. 

Processes. — The  frontosphenoidal  process  is  thick  and  serrated,  and  articulates 
with  the  zygomatic  process  of  the  frontal  bone.  On  its  orbital  surface,  just  within 
the  orbital  margin  and  about  11  mm.  below  the  zygomaticofrontal  suture  is  a 
tubercle  of  varying  size  and  form,  but  present  in  95  per  cent,  of  skulls  (WhitnalP). 

'  Journal  of  Anatomy  and  Physiology,  vol.  xlv.  The  structures  attached  to  this  tubercle  are:  (1)  the  check 
ligament  of  the  Rectus  lateralis;  (2)  the  lateral  end  of  the  aponeurosis  of  the  Levator  palpebrse  superioris;  (3)  the 
suspensory  ligament  of  the  eye  (Lookwood);  and  (4)  the  lateral  extremities  of  the  superior  and  inferior  tarsi. 


THE  ZYGOMATIC  BONE 


165 


The  orbital  process  is  a  thick,  strong  plate,  projecting  backward  and  medialward 
from  the  orbital  margin.  Its  antero-medial  surface  forms,  by  its  junction  with 
the  orbital  surface  of  the  maxilla  and  with  the  great  wing  of  the  sphenoid,  part 
of  the  floor  and  lateral  wall  of  the  orbit.    On  it  are  seen  the  orifices  of  two  canals, 


Pa  7~{eta1 


Fig.   164 — Left  zygomatic  bone  in  situ. 


the  zygomaticoorbital  foramina;  one  of  these  canals  opens  into  the  temporal  fossa, 
the  other  on  the  malar  surface  of  the  bone;  the  former  transmits  the  zygomatico- 
temporal, the  latter  the  zygomaticofacial  nerve.  Its  postero-lateral  surface,  smooth 
fcsnd  convex,  forms  parts  of  the  temporal  and  infratemporal  fossae.  Its  anterior 
margin,  smooth  and  rounded,  is  part  of  the  circumference  of  the  orbit.    Its  superior 


With  Frontal 


^iristles  passed 
through 
_   zygomatico-        /i 
orbital  foramina  J  a 


Fig.   106. — Left  zygomatic  bone.     Temporal  surface. 


margin,  rough,  and  directed  horizontally,  articulates  with  the  frontal  bone  behind 
xhe  zygomatic  process.  Its  posterior  margin  is  serrated  for  articulation,  with  the 
great  wing  of  the  sphenoid  and  the  orbital  surface  of  the  maxilla.  At  the  angle 
of  junction  of  the  sphenoidal  and  maxillary  portions,  a  short,  concave,  non-articular 


166 


OSTEOLOGY 


I 


part  is  generally  seen;  this  forms  the  anterior  boundary  of  the  inferior  orbital  fissure: 
occasionally,  this  non-articular  part  is  absent,  the  fissure  then  being  completed 
by  the  junction  of  the  maxilla  and  sphenoid,  or  by  the  interposition  of  a  small 
sutural  bone  in  the  angular  interval  between  them.  The  maxillary  process  presents 
a  rough,  triangular  surface  which  articulates  with  the  maxilla.  The  temporal 
process,  long,  narrow,  and  serrated,  articulates  with  the  zygomatic  process  of  the 
temporal. 

Borders. — The  antero-superior  or  orbital  border  is  smooth,  concave,  and  forms 
a  considerable  part  of  the  circumference  of  the  orbit.  The  antero-inferior  or  maxil- 
lary border  is  rough,  and  bevelled  at  the  expense  of  its  inner  table,  to  articulate 
with  the  maxilla;  near  the  orbital  margin  it  gives  origin  to  the  Quadratus  labii 
superioris.  The  postero-superior  or  temporal  border,  curved  like  an  italic  letter  /, 
is  continuous  above  with  the  commencement  of  the  temporal  line,  and  below  with 
the  upper  border  of  the  zygomatic  arch;  the  temporal  fascia  is  attached  to  it. 
The  postero-inferior  or  zygomatic  border  affords  attachment  by  its  rough  edge  to 
the  Masseter. 

Ossification. — The  zygomatic  bone  is  generally  described  as  ossifying  from  three  centers — 
one  for  the  malar  and  two  for  the  orbital  portion;  these  appear  about  the  eighth  week  and  fuse 
about  the  fifth  month  of  fetal  life.  Mall  describes  it  as  being  ossified  from  one  center  which 
appears  just  beneath  and  to  the  lateral  side  of  the  orbit.  After  birth,  the  bone  is  sometimes 
divided  by  a  horizontal  suture  into  an  upper  larger,  and  a  lower  smaller  division.  In  some  quad- 
rumana  the  zygomatic  bone  consists  of  two  parts,  an  orbital  and  a  malar. 

Articulations. — The  zygomatic  articulates  with  four  bones :  the  frontal,  sphenoidal,  temporal, 
and  maxilla. 


Groove  for 
nasolacrimal  duct 


Frontal  process 


Maxillary  sinus 
Orbital  process 


Sphenopalatine 
notch 

Sphenoidal 
process 


Conciial  crest. 


Conchal  crest 


Fio.  167. — Articulation  of  left  palatine  bone  with  maxilla. 

The  Palatine  Bone  (Os  Palatinum;  Palate  Bone). 

The  palatine  bone  is  situated  at  the  back  part  of  the  nasal  cavity  between  the 
maxilla  and  the  pterygoid  process  of  the  sphenoid  (Fig.  167).  It  contributes 
to  the  walls  of  three  cavities:  the  floor  and  lateral  wall  of  the  nasal  cavity,  the 
roof  of  the  mouth,  and  the  floor  of  the  orbit;  it  enters  into  the  formation  of  two 
fossae,  the  pterygopalatine  and  pterygoid  fossae;  and  one  fissure,  the  inferior  orbital 
fissure.  The  palatine  bone  somewhat  resembles  the  letter  L,  and  consists  of  a 
horizontal  and  a  vertical  part  and  three  outstanding  processes — viz.,  the  pyramidal 


THE  PALATINE  BONE 


167 


process,  which  is  directed  backward  and  lateralward  from  the  junction  of  the  two 
parts,  and  the  orbital  and  sphenoidal  processes,  which  surmount  the  vertical 
part,  and  are  separated  by  a  deep  notch,  the  sphenopalatine  notch. 

The  Horizontal  Part  {yars  horizontalis;  horizontal  plate)  (Figs.  168,  169). — The 
horizontal  part  is  quadrilateral,  and  has  two  surfaces  and  four  borders. 

Surfaces. — The  superior  surface,  concave  from  side  to  side,  forms  the  back  part 
of  the  floor  of  the  nasal  cavity.  The  inferior  surface,  slightly  concave  and  rough, 
forms,  with  the  corresponding  surface  of  the  opposite  bone,  the  posterior  fourth 
of  the  hard  palate.  Near  its  posterior  margin  may  be  seen  a  more  or  less  marked 
transverse  ridge  for  the  attachment  of  part  of  the  aponeurosis  of  the  Tensor  veli 
palatini. 


iiCtl  Bl\ 


Maxillary  surface 


Superior  meatus 
Sphenopalatine  foramen 


Sphenopalatine, 
forarrten 

Sphenoidal  process 
Articular  portion 


Posterior 
nasal 
Musevdus  uvulee  spine 


HORIZONTAL  PARI? 

168. — Left  palatine  bone. 
Enlarged. 


Pyramidal 
process 


HORIZONTAL 
PART 


Nasal  aspect. 


Fig.   169.- 


-Left  palatine  bone. 
Enlarged. 


Posterior  aspect. 


Maxillary 
process 


w 

^1  Borders. — The  anterior  border  is  serrated,  and  articulates  with  the  palatine  process 
''  cf  the  maxilla.  The  posterior  border  is  concave,  free,  and  serves  for  the  attachment 
(i  the  soft  palate.  Its  medial  end  is  sharp  and  pointed,  and,  when  united  with 
that  of  the  opposite  bone,  forms  a  projecting  process,  the  posterior  nasal  spine 
lor  the  attachment  of  the  Musculus  uvulae.  The  lateral  border  is  united  with 
the  lower  margin  of  the  perpendicular  part,  and  is  grooved  by  the  lower  end  of 
Ihe  pterygopalatine  canal.  The  medial  border,  the  thickest,  is  serrated  for  articu- 
lation with  its  fellow  of  the  opposite  side;  its  superior  edge  is  raised  into  a  ridge, 
Avhich,  united  with  the  ridge  of  the  opposite  bone,  forms  the  nasal  crest  for  articu- 
lation with  the  posterior  part  of  the  lower  edge  of  the  vomer. 

The  Vertical  Part  {yars  perpendicularis;  perpendicular  plate)  (Figs.  168,  169). — 
The  vertical  part  is  thin,  of  an  oblong  form,  and  presents  two  surfaces  and  four 
^H)>orders. 

H  _  Surfaces. — The  nasal  surface  exhibits  at  its  lower  part  a  broad,  shallow  depres- 
^sion,  which  forms  part  of  the  inferior  meatus  of  the  nose.  Immediately  above  this 
is  a  well-marked  horizontal  ridge,  the  conchal  crest,  for  articulation  with  the 
inferior  nasal  concha;  still  higher  is  a  second  broad,  shallow  depression,  which 
forms  part  of  the  middle  meatus,  and  is  limited  above  by  a  horizontal  crest  less 
prominent  than  the  inferior,  the  ethmoidal  crest,  for  articulation  with  the  middle 
nasal  concha.  Above  the  ethmoidal  crest  is  a  narrow,  horizontal  groove,  which 
forms  part  of  the  superior  meatus. 


i 


168 


OSTEOLOGY 


The  maxillary  surface  is  rough  and  irregular  throughout  the  greater  parTo 
extent,  for  articulation  with  the  nasal  surface  of  the  maxilla;  its  upper  and  back 
part  is  smooth  where  it  enters  into  the  formation  of  the  pterygopalatine  fossa; 
it  is  also  smooth  in  front,  where  it  forms  the  posterior  part  of  the  medial  A^all 
of  the  maxillary  sinus.  On  the  posterior  part  of  this  surface  is  a  deep  vertical 
groove,  converted  into  the  pterygopalatine  canal,  by  articulation  with  the  maxilla; 
this  canal  transmits  the  descending  palatine  vessels,  and  the  anterior  palatine 
nerve. 

Borders. — The  anterior  border  is  thin  and  irregular;  opposite  the  conchal  crest  is  a 
pointed,  projecting  lamina,  the  maxillary  process,  which  is  directed  forward,  and 
closes  in  the  lower  and  back  part  of  the  opening  of  the  maxillary  sinus.  The 
posterior  border  (Fig.  169)  presents  a  deep  groove,  the  edges  of  which  are  serrated 
for  articulation  with  the  medial  pterygoid  plate  of  the  sphenoid.  This  border 
is  continuous  above  with  the  sphenoidal  process;  below  it  expands  into  the 
pyramidal  process.  The  superior  border  supports  the  orbital  process  in  front  and  the 
sphenoidal  process  behind.  These  processes  are  separated  by  the  sphenopalatine 
notch,  which  is  converted  into  the  sphenopalatine  foramen  by  the  under  surface  of 
the  body  of  the  sphenoid.  In  the  articulated  skull  this  foramen  leads  from  the 
pterygopalatine  fossa  into  the  posterior  part  of  the  superior  meatus  of  the  nose, 
and  transmits  the  sphenopalatine  vessels  and  the  superior  nasal  and  nasopalatine 
nerves.  The  inferior  border  is  fused  with  the  lateral  edge  of  the  horizontal  part, 
and  immediately  in  front  of  the  pyramidal  process  is  grooved  by  the  lower  end 
of  the  pterygopalatine  canal. 

The  Pyramidal  Process  or  Tuberosity  (processus  pyrmnidalis) . — The  pyramidal 
process  projects  backward  and  lateralward  from  the  junction  of  the  horizontal 
and  vertical  parts,  and  is  received  into  the  angular  interval  between  the  lower 
extremities  of  the  pterygoid  plates.  On  its  posterior  surface  is  a  smooth,  grooved, 
triangular  area,  limited  on  either  side  by  a  rough  articular  furrow.  The  furrows 
articulate  with  the  pterygoid  plates,  while  the  grooved  intermediate  area  completes 
the  lower  part  of  the  pterygoid  fossa  and  gives  origin  to  a  few  fibers  of  the  Ptery- 
goideus  internus.  The  anterior  part  of  the  lateral  surface  is  rough,  for  articulation 
with  the  tuberosity  of  the  maxilla;  its  posterior  part  consists  of  a  smooth  triangular 
area  which  appears,  in  the  articulated  skull,  beWeen  the  tuberosity  of  the  maxilla 
and  the  lower  part  of  the  lateral  pterygoid  plate,  and  completes  the  lower  part 
of  the  infratemporal  fossa.  On  the  base  of  the  pyramidal  process,  close  to  its 
union  with  the  horizontal  part,  are  the  lesser  palatine  foramina  for  the  transmis- 
sion of  the  posterior  and  middle  palatine  nerves. 

The  Orbital  Process  (processus  orbitalis). — The  orbital  process  is  placed  on  a 
higher  level  than  the  sphenoidal,  and  is  directed  upward  and  lateralward  from 
the  front  of  the  vertical  part,  to  which  it  is  connected  by  a  constricted  neck.  It 
presents  five  surfaces,  which  enclose  an  air  cell.  Of  these  surfaces,  three  are  articu- 
lar and  two  non-articular.  The  articular  surfaces  are:  (1)  the  anterior  or  maxillary, 
directed  forward,  lateralward,  and  downward,  of  an  oblong  form,  and  rough  for 
articulation  with  the  maxilla;  (2)  the  posterior  or  sphenoidal,  directed  backward, 
upward,  and  medialward;  it  presents  the  opening  of  the  air  cell,  w^hich  usually 
communicates  with  the  sphenoidal  sinus;  the  margins  of  the  opening  are  serrated 
for  articulation  with  the  sphenoidal  concha;  (3)  the  medial  or  ethmoidal,  directed 
forward,  articulates  with  the  labyrinth  of  the  ethmoid.  In  some  cases  the  air 
cell  opens  on  this  surface  of  the  bone  and  then  communicates  with  the  posterior 
ethmoidal  cells.  ]More  rarely  it  opens  on  both  surfaces,  and  then  communicates 
with  the  posterior  ethmoidal  cells  and  the  sphenoidal  sinus.  The  non-articular 
surfaces  are:  (1)  the  superior  or  orbital,  directed  upward  and  lateralward;  it  is 
triangular  in  shape,  and  forms  the  back  part  of  the  floor  of  the  orbit;  and  (2)  the 
lateral,  of  an  oblong  form,  directed  toward  the  pterygopalatine  fossa;  it  is  separated 


THE  INFERIOR  NASAL  CONCHA  169 

from  the  orbital  surface  by  a  rounded  border,  which  enters  into  the  formation  of 
the  inferior  orbital  fissure. 

The  Sphenoidal  Process  {processus  sphenoidalis) . — The  sphenoidal  process  is 
a  thin,  compressed  plate,  much  smaller  than  the  orbital,  and  directed  upward 
and  mediahvard.  It  presents  three  surfaces  and  two  borders.  The  superior  surface 
articulates  with  the  root  of  the  pterygoid  process  and  the  under  surface  of  the 
sphenoidal  concha,  its  medial  border  reaching  as  far  as  the  ala  of  the  vomer;  it 
presents  a  groove  which  contributes  to  the  formation  of  the  pharyngeal  canal. 
The  medial  surface  is  concave,  and  forms  part  of  the  lateral  wall  of  the  nasal  cavity. 
The  lateral  surface  is  divided  into  an  articular  and  a  non-articular  portion:  the 
former  is  rough,  for  articulation  with  the  medial  pterygoid  plate;  the  latter  is 
smooth,  and  forms  part  of  the  pterygopalatine  fossa.  The  anterior  border  forms 
the  posterior  boundary  of  the  sphenopalatine  notch.  The  posterior  border,  ser- 
rated at  the  expense  of  the  outer  table,  articulates  with  the  medial  pterygoid 
plate. 

The  orbital  and  sphenoidal  processes  are  separated  from  one  another  by  the 
sphenopalatine  notch.  Sometimes  the  two  processes  are  united  above,  and  form 
between  them  a  complete  foramen  (Fig.  168),  or  the  notch  may  be  crossed  by  one 
or  more  spicules  of  bone,  giving  rise  to  two  or  more  foramina. 

Ossification. — The  palatine  bone  is  ossified  in  membrane  from  a  single  center,  which  makes 
its  appearance  about  the  sixth  or  eighth  week  of  fetal  life  at  the  angle  of  junction  of  the  two  parts 
O"  the  bone.  From  this  point  ossification  spreads  medialward  to  the  horizontal  part,  downward 
into  the  pyramidal  process,  and  upward  into  the  vertical  part.  Some  authorities  describe  the 
bone  as  ossifying  from  four  centers:  one  for  the  pyramidal  process  and  portion  of  the  vertical 
part  behind  the  pterygopalatine  groove;  a  second  for  the  rest  of  the  vertical  and  the  horizontal 
parts;  a  third  for  the  orbital,  and  a  fourth  for  the  sphenoidal  process.  At  the  time  of  birth  the 
height  of  the  vertical  part  is  about  equal  to  the  transverse  width  of  the  horizontal  part,  whereas 
ill  the  adult  the  former  measures  about  twice  as  much  as  the  latter. 

Artictllations. — The  palatine  articulates  with  six  bones:  the  sphenoid,  ethmoid,  maxilla, 
inferior  nasal  concha,  vomer,  and  opposite  palatine. 

"|i 

fthe  Inferior  Nasal  Concha  (Concha  Nasalis  Inferior;  Inferior  Turbinated  Bone). 

The  inferior  nasal  concha  extends  horizontally  along  the  lateral  wall  of  the 
lasal  cavity  (Fig.  170)  and  consists  of  a  lamina  of  spongy  bone,  curled  upon  itself 
ike  a  scroll.    It  has  two  surfaces,  two  borders,  and  two  extremities. 

The  medial  surface  (Fig.  171)  is  convex,  perforated  by  numerous  apertures, 
jid  traversed  by  longitudinal  grooves  for  the  lodgement  of  vessels.  The  lateral 
nrface  is  concave  (Fig.  172),  and  forms  part  of  the  inferior  meatus.  Its  upper 
lorder  is  thin,  irregular,  and  connected  to  various  bones  along  the  lateral  wall 
>f  the  nasal  cavity.  It  may  be  divided  into  three  portions:  of  these,  the  anterior 
urticulates  with  the  conchal  crest  of  the  maxilla;  the  posterior  with  the  conchal 
rest  of  the  palatine;  the  middle  portion  presents  three  well-marked  processes, 
ihich  vary  much  in  their  size  and  form.  Of  these,  the  anterior  or  lacrimal  process 
k  small  and  pointed  and  is  situated  at  the  junction  of  the  anterior  fourth  with 
ihe  posterior  three-fourths  of  the  bone:  it  articulates,  by  its  apex,  with  the  descend- 
ing process  of  the  lacrimal  bone,  and,  by  its  margins,  with  the  groove  on  the  back 
of  the  frontal  process  of  the  maxilla,  and  thus  assists  in  forming  the  canal  for  the 
nasolacrimal  duct.  Behind  this  process  a  broad,  thin  plate,  the  ethmoidal  process, 
ascends  to  join  the  uncinate  process  of  the  ethmoid;  from  its  lower  border  a  thin 
lamina,  the  maxillary  process,  curves  downward  and  lateralward;  it  articulates 
'.vith  the  maxilla  and  forms  a  part  of  the  medial  wall  of  the  maxillary  sinus.  The 
inferior  border  is  free,  thick,  and  cellular  in  structure,  more  especially  in  the  middle 
of  the  bone.  Both  extremities  are  more  or  less  pointed,  the  posterior  being  the 
ore  tapering. 


I 


170 


OSTEOLOGY 


1 


Ossification. — The  inferior  nasal  concha  is  ossified  from  a  single  center,  which  appears' alout 
the  fifth  month  of  fetal  life  in  the  lateral  wall  of  the  cartilaginous  nasal  capsule. 

Articulations. — The  inferior  nasal  concha  articulates  with  four  bones:  the  ethmoid,  maxilla, 
lacrimal,  and  palatine. 


.  Uncinate 

process 
oj  ethmoid 


Openings  into 
maxillary  sinus 
Medial  pterygoid  plate 
Pterygoid  hamulus 


Fig.  170. — Lateral  wall  of  right  naaal  cavity  showing  inferior  concha  in  situ. 
.1- 


Fig.  171. — Right  inferior  nasal  concha. 
Medial  surface. 


Fig.  172. — Right  inferior  nasal  concha. 
Lateral  surface. 


The  Vomer. 

The  vomer  is  situated  in  the  median  plane,  but  its  anterior  portion  is  frequently 
bent  to  one  or  other  side.  It  is  thin,  somewhat  quadrilateral  in  shape,  and  forms 
the  hinder  and  lower  part  of  the  nasal  septum  (Fig.  173) ;  it  has  two  surfaces  and 
four  borders.  The  surfaces  (Fig.  174)  are  marked  by  small  furrows  for  blood- 
vessels, and  on  each  is  the  nasopalatine  groove,  which  runs  obliquely  downward 
and  forward,  and  lodges  the  nasopalatine  nerve  and  vessels.  The  superior  border, 
the  thickest,  presents  a  deep  furrow,  bounded  on  either  side  by  a  horizontal  pro- 
jecting ala  of  bone;  the  furrow  receives  the  rostrum  of  the  sphenoid,  while  the 
margins  of  the  alse  articulate  with  the  vaginal  processes  of  the  medial  pterygoid 
plates  of  the  sphenoid  behind,  and  with  the  sphenoidal  processes  of  the  palatine 
bones  in  front.    The  inferior  border  articulates  with  the  crest  formed  by  the  maxillae 


THE  VOMER 


171 


and  palatine  bones.  The  anterior  border  is  the  longest  and  slopes  downward  and 
forward.  Its  upper  half  is  fused  with  the  perpendicular  plate  of  the  ethmoid; 
its  lower  half  is  grooved  for  the  inferior  margin  of  the  septal  cartilage  of  the  nose. 
The  posterior  border  is  free,  concave,  and  separates  the  choanse.  It  is  thick  and 
bifid  above,  thin  below. 


Rostrum  of  sphenoid 


Crest  of  nasal  hones 
Frontal  spine 


Space  for  triangular 
cartilage  of  septum 


Crest  of  palatines 
Crest  of  maxiUoe 


Fig.  173. — Median  wall  of  left  nasal  cavity  showing  vomer  in  situ. 

Ossification. — At  an  early  period  the  septum  of  the  nose  consists  of  a  plate  of  cartilage,  the 
iQimovomerine  cartilage.  The  postero-superior  part  of  this  cartilage  is  ossified  to  form  the  per-, 
[endicular  plate  of  the  ethmoid;  its  antero-inferior  portion  persists  as  the  septal  cartilage,  while 
the  vomer  is  ossified  in  the  membrane  covering  its  postero-inferior  part.  Two  ossific  centers, 
one  on  either  side  of  the  middle  Une,  appear  about  the  eighth  week  of  fetal  life  in  this  part  of 
llhe  membrane,  and  hence  the  vomer  consists  primarily  of  two  lamellae.    About  the  third  month 


174. — The  vomer. 


Fig    175. — Vomer  of  infant. 


these  unite  below,  and  thus  a  deep  groove  is  formed  in  which  the  cartilage  is  lodged.  As 
:^owth  proceeds,  the  union  of  the  lamellae  extends  upward  and  forward,  and  at  the  same  time  the 
intervening  plate  of  cartilage  undergoes  absorption.  By  the  age  of  puberty  the  lamelte  are  almost 
completely  united  to  form  a  median  plate,  but  evidence  of  the  bilaminar  origin  of  the  bone  is 

Iaeen  in  the  everted  alae  of  its  upper  border  and  the  groove  on  its  anterior  margin. 
I 


172 


OSTEOLOGY 


I 


Articulations. — The  vomer  articulates  with  six  bones:  two  of  the  cranium,  the  sphenoid  and 
ethmoid;  and  four  of  the  face,  the  two  maxillaj  and  the  two  palatine  bones;  it  also  articuUtes 
with  the  septal  cartilage  of  the  nose. 


The  Mandible  (Mandibula ;  Inferior  Maxillary  Bone;  Lower  Jaw). 

The  mandible,  the  largest  and  strongest  bone  of  the  face,  serves  for  the  reception 
of  the  lower  teeth.  It  consists  of  a  curved,  horizontal  portion,  the  body,  and  two 
perpendicular  portions,  the  rami,  which  unite  with  the  ends  of  the  body  nearly 
at  right  angles. 

The  Body  {corpus  mandibuloe) . — The  body  is  curved  somewhat  like  a  horseshoe, 
and  has  two  surfaces  and  two  borders. 

Surfaces. — The  external  surface  (Fig.  176)  is  marked  in  the  median  line  by  a 
faint  ridge,  indicating  the  symphysis  or  line  of  junction  of  the  two  pieces  of  which 
the  bone  is  composed  at  an  early  period  of  life.  This  ridge  divides  below  and 
encloses  a  triangular  eminence,  the  mental  protuberance,  the  base  of  which  is  de- 


Goronoid  process 


Condyle 


TEMPORALIS 


""■■"li'KllUl///'    jif'  V 

^^"      Body  ^^^f" 
^^ntal        m^       "^^y-  ■  ..^^^^^-^^ 
protvherance-W^^^^^^^':^' J 


Qrocme.  for  external 
maxillary  artery 

Fig.   176. — Mandible.     Outer  surface.     Side  view. 


Am.  ale 


pressed  in  the  center  but  raised  on  either  side  to  form  the  mental  tubercle.  On  either 
side  of  the  symphysis,  just  below  the  incisor  teeth,  is  a  depression,  the  incisive 
fossa,  which  gives  origin  to  the  Mentalis  and  a  small  portion  of  the  Orbicularis 
oris.  Below  the  second  premolar  tooth,  on  either  side,  midway  between  the  upper 
and  lower  borders  of  the  body,  is  the  mental  foramen,  for  the  passage  of  the  mental 
vessels  and  nerve.  Running  backward  and  upward  from  each  mental  tubercle 
is  a  faint  ridge,  the  oblique  line,  which  is  continuous  with  the  anterior  border  of  the 
ramus;  it  affords  attachment  to  the  Quadratus  labii  inferioris  and  Triangularis; 
the  Platysma  is  attached  below  it. 

The  internal  surface  (Fig.  177)  is  concave  from  side  to  side.  Near  the  lower 
part  of  the  symphysis  is  a  pair  of  laterally  placed  spines,  termed  the  mental  spines, 
which  give  origin  to  the  Genioglossi.  Immediately  below  these  is  a  second  pair 
of  spines,  or  more  frequently  a  median  ridge  or  impression,  for  the  origin  of  the 
Geniohyoidei.  In  some  cases  the  mental  spines  are  fused  to  form  a  single  eminence, 
in  others  they  are  absent  and  their  position  is  indicated  merely  by  an  irregularity 
of  the  surface.  Above  the  mental  spines  a  median  foramen  and  furrow  are  some- 
times seen;  they  mark  the  line  of  union  of  the  halves  of  the  bone.    Below  the  mental 


THE  MANDIBLE 


173 


spines,  on  either  side  of  the  middle  line,  is  an  oval  depression  for  the  attachment 
of  the  anterior  belly  of  the  Digastricus.  Extending  upward  and  backward  on  either 
side  from  the  lower  part  of  the  symphysis  is  the  mylohyoid  line,  which  gives  origin 
to  the  Mylohyoideus ;  the  posterior  part  of  this  line,  near  the  alveolar  margin, 
gives  attachment  to  a  small  part  of  the  Constrictor  pharyngis  superior,  and  to 
the  pterygomandibular  raphe.  Above  the  anterior  part  of  this  line  is  a  smooth 
triangular  area  against  which  the  sublingual  gland  rests,  and  below  the  hinder 
part,  an  oval  fossa  for  the  submaxillary  gland. 

Borders. — The  superior  or  alveolar  border,  wider  behind  than  in  front,  is  hollowed 
into  cavities,  for  the  reception  of  the  teeth;  these  cavities  are  sixteen  in  number, 
and  vary  in  depth  and  size  according  to  the  teeth  which  they  contain.  To  the 
outer  lip  of  the  superior  border,  on  either  side,  the  Buccinator  is  attached  as 
far  forward  as  the  first  molar  tooth.  The  inferior  border  is  rounded,  longer  than 
the  superior,  and  thicker  in  front  than  behind;  at  the  point  where  it  joins  the 
lower  border  of  the  ramus  a  shallow  groove;  for  the  external  maxillary  artery, 
may  be  present. 


..,|1v  '^'^■"'/'o. 


Oenio- 

glossus 
Genio- 

hyoideus 


Mylohyoid  line 

BODY 
Fig.   177. — Mandible.     Inner  surface.     Side  view. 

\ 


The  Ramus  {ramus  mandibulcp;  perpeiidicular  portion). — The  ramus  is  quadri- 
lateral in  shape,  and  has  two  surfaces,  four  borders,  and  two  processes. 

Surfaces.^ — The  lateral  surface  (Fig.  176)  is  flat  and  marked  by  oblique  ridges 
at  its  lower  part;  it  gives  attachment  throughout  nearly  the  whole  of  its  extent 
tc  the  Masseter.  The  medial  surface  (Fig.  177)  presents  about  its  center  the  oblique 
mandibular  foramen,  for  the  entrance  of  the  inferior  alveolar  vessels  and  nerve. 
The  margin  qf  this  opening  is  irregular;  it  presents  in  front  a  prominent  ridge, 
surmounted  by  a  sharp  spine,  the  lin6:ula  mandibulae,  which  gives  attachment  to 
the  sphenomandibular  ligament ;  at  its  lower  and  back  part  is  a  notch  from  which 
the  mylohyoid  groove  runs  obliquely  downward  and  forward,  and  lodges  the  mylo- 
hyoid vessels  and  nerve.  Behind  this  groove  is  a  rough  surface,  for  the  insertion 
ol  the  Pterygoideus  internus.  The  mandibular  canal  runs  obliquely  downward 
and  forward  in  the  ramus,  and  then  horizontally  forward  in  the  body,  where  it 
is  placed  under  the  alveoli  and  communicates  with  them  by  small  openings.  On 
arriving  at  the  incisor  teeth,  it  turns  back  to  communicate  with  the  mental  foramen, 
giving  off  two  small  canals  which  run  to  the  cavities  containing  the  incisor  teeth. 


■ 


174 


I 


In  the  posterior  two-thirds  of  the  bone  the  canal  is  situated  nearer  the  internal 
surface  of  the  mandible;  and  in  the  anterior  third,  nearer  its  external  surface.  It 
contains  the  inferior  alveolar  vessels  and  nerve,  from  which  branches  are  dis- 
tributed to  the  teeth.  The  lower  border  of  the  ramus  is  thick,  straight,  and  con- 
tinuous W'ith  the  inferior  border  of  the  body  of  the  bone.  At  its  junction  with  the 
posterior  border  is  the  angle  of  the  mandible,  which  may  be  either  inverted  or  everted 
and  is  marked  by  rough,  oblique  ridges  on  each  side,  for  the  attachment  of  the 
Masseter  laterally,  and  the  Pterygoideus  internus  medially;  the  stylomandibular 
ligament  is  attached  to  the  angle  between  these  muscles.  The  anterior  border  is 
thin  above,  thicker  below,  and  continuous  with  the  oblique  line.  The  posterior 
border  is  thick,  smooth,  rounded,  and  covered  by  the  parotid  gland.  The  upper 
border  is  thin,  and  is  surmounted  by  two  processes,  the  coronoid  in  front  and  the 
condyloid  behind,  separated  by  a  deep  concavity,  the  mandibular  notch. 

The  Coronoid  Process  (processus  coronoideus)  is  a  thin,  triangular  eminence, 
which  is  flattened  from  side  to  side  and  varies  in  shape  and  size.  Its  anterior 
border  is  convex  and  is  continuous  below  with  the  anterior  border  of  the  ramus; 
its  posterior  border  is  concave  and  forms  the  anterior  boundary  of  the  mandibular 
notch.  Its  lateral  surface  is  smooth,  and  affords  insertion  to  the  Temporalis  and 
Masseter.  Its  medial  surface  gives  insertion  to  the  Temporalis,  and  presents 
a  ridge  which  begins  near  the  apex  of  the  process  and  runs  downward  and  forward 
to  the  inner  side  of  the  last  molar  tooth.  Between  this  ridge  and  the  anterior 
border  is  a  grooved  triangular  area,  the  upper  part  of  which  gives  attachment 
to  the  Temporalis,  the  lower  part  to  some  fibers  of  the  Buccinator. 

The  Condyloid  Process  (processus  condyloideus)  is  thicker  than  the  coronoid, 
and  consists  of  two  portions :  the  condyle,  and  the  constricted  portion  which  sup- 
ports it,  the  neck.  The  condyle  presents  an  articular  surface  for  articulation  with 
the  articular  disk  of  the  temporomandibular  joint;  it  is  convex  from  before  back- 
ward and  from  side  to  side,  and  extends  farther  on  the  posterior  than  on  the  ante- 
rior surface.  Its  long  axis  is  directed  medialward  and  slightly  backward,  and  if 
prolonged  to  the  middle  line  will  meet  that  of  the  opposite  condyle  near  the  ante- 
rior margin  of  the  foramen  magnum.  At  the  lateral  extremity  of  the  condyle 
is  a  small  tubercle  for  the  attachment  of  the  temporomandibular  ligament.  The 
neck  is  flattened  from  before  backward,  and  strengthened  by  ridges  which  descend 
from  the  forepart  and  sides  of  the  condyle.  Its  posterior  surface  is  convex;  its 
anterior  presents  a  depression  for  the  attachment  of  the  Pterygoideus  externus. 

The  mandibular  notch,  separating  the  two  processes,  is  a  deep  semilunar  depres- 
sion, and  is  crossed  by  the  masseteric  vessels  and  nerve. 

Ossification. — The  mandible  is  ossified  in  the  fibrous  membrane  covering  the  outer  surfaces 
of  Meckel's  cartilages.  These  cartilages  form  the  cartilaginous  bar  of  the  mandibular  arch  (see 
p.  66),  and  are  two  in  number,  a  right  and  a  left.  Their  proximal  or  cranial  ends  are  connected 
with  the  ear  capsules,  and  their  distal  extremities  are  joined  to  one  another  at  the  symphysis 
by  mesodermal  tissue.  They  run  forward  immediately  below  the  condyles  and  then,  bending 
downward,  lie  in  a  groove  near  the  lower  border  of  the  bone;  in  front  of  the  canine  tooth  they 
incUne  upward  to  the  symphysis.  From  the  proximal  end  of  each  cartilage  the  malleus  and 
incus,  two  of  the  bones  of  the  middle  ear,  are  developed;  the  next  succeeding  portion,  as  far  as 
the  lingula,  is  replaced  by  fibrous  tissue,  which  persists  to  form  the  sphenomandibular  ligament. 
Between  the  lingula  and  the  canine  tooth  the  cartilage  disappears,  while  the  portion  of  it  below 
and  behind  the  incisor  teeth  becomes  ossified  and  incorporated  with  this  part  of  the  mandible. 

Ossification  takes  place  in  the  membrane  covering  the  outer  surface  of  the  ventral  end  of 
Meckel's  cartilage  (Figs.  178  to  181),  and  each  half  of  the  bone  is  formed  from  a  single  center 
which  appears,  near  the  mental  foramen,  about  the  sixth  week  of  fetal  life.  By  the  tenth  week 
the  portion  of  Meckel's  cartilage  which  lies  below  and  behind  the  incisor  teeth  is  surrounded  and 
invaded  by  the  membrane  bone.  Somewhat  later,  accessory  nuclei  of  cartilage  make  their  appear- 
ance, viz.,  a  wedge-shaped  nucleus  in  the  condyloid  process  and  extending  downward  through 
the  ramus;  a  small  strip  along  the  anterior  border  of  the  coronoid  process;  and  smaller  nuclei 
in  the  front  part  of  both  alveolar  walls  and  along  the  front  of  the  lower  border  of  the  bone.  These 
accessory  nuclei  possess  no  separate  ossific  centers,  but  are  invaded  by  the  siu-rounding  membrane 


THE  MANDIBLE 


175 


boae  and  undergo  absorption.  The  inner  alveolar  border,  usually  described  as  arising  from  a 
sejjarate  ossific  center  (splenial  center),  is  formed  in  the  human  mandible  by  an  ingrowth  from 
the  main  mass  of  the  bone.  At  birth  the  bone  consists  of  two  parts,  united  by  a  fibrous  symphysis, 
in  which  ossification  takes  place  during  the  first  year. 

The  foregoing  description  of  the  ossification  of  the  mandible  is  based  on  the  researches  of 
Low'  and  Fawcett,-  and  differs  somewhat  from  that  usually  given. 

Articulations. — The  mandible  articulates  with  the  two  temporal  bones. 


Mental  nerve 


Mylohyoid  nerve 

Fio.   178. — Mandible  of  human   embryo  24    mm. 
long.     Outer  aspect.     (From  model  by  Low.) 


Lingual  nerve 
Inf.  alveolar  n. 


Mylohyoid  nerve 
Chorda  tympani 


Stapes 
Facial  nervi 


ReicherVs  cartilage 


Fig.   179. — Mandible  of  human  embryo  24'  mm.  long. 
Inner  aspect.     (From  model  by  Low.) 


Mandibular  nerve 
Meckel's  cartilage 


Mental  nerve 


Anterior  process  of  nuii.i.,^ 

Fig.  180. — Mandible  of  human  embryo  95  mm.  long.     Outer  aspect.     Nuclei  of  cartilage  stippled. 

(From  model  by  Low.) 


AuriciUotem/poral  nerve 


Ant.  process  of  malleus 
Chorda  tympani 


Symphysis 


stylohyoid  nerve 


Fig.  181.- 


-Mandible  of  human  embryo  95  mm.  long.     Inner  aspect. 
(From  model  by  Low.) 


Nuclei  of  cartilage  stippled. 


CHANGES  PRODUCED  IN  THE  MANDIBLE  BY  AGE. 


At  birth  (Fig.  182)  the  body  of  the  bone  is  a  mere  shell,  containing  the  sockets  of  the  two 
incisor,  the  canine,  and  the  two  deciduous  molar  teeth,  imperfectly  partitioned  off  from  one 
another.  The  mandibular  canal  is  of  large  size,  and  runs  near  the  lower  border  of  the  bone;  the 
m<mtal  foramen  opens  beneath  the  socket  of  the  first  deciduous  molar  tooth.  The  angle  is  obtuse 
(175°),  and  the  condyloid  portion  is  nearly  in  Une  with  the  body.  The  coronoid  process  is  of 
comparatively  large  size,  and  projects  above  the  level  of  the  condyle. 

•  Proceedings  of  the  Anatomical  and  -Anthropological  Society  of  the  University  of  Aberdeen,  1905,  and  Journal  of 
Anatomy  and  Physiology,  vol.  xliv. 

•  Journal  of  the  American  Medical  Association,  September  2,  1905. 


OSTEOLOGY 


Fi3.  182.— At  birth. 


Fig.  183. — In  chUdhood. 


Fig.  184.— In  the  adult. 


Fig.  185.— In  old  age. 
Side  view  of  the  mandible  at  different  periods  of  life. 


THE  HYOID  BONE 


177 


After  birth  (Fig.  183)  the  two  segments  of  the  bone  become  joined  at  the  symphysis,  from 
below  upward,  in  the  first  year;  but  a  trace  of  separation  may  be  visible  in  the  beginning  of  the 
second  year,  near  the  alveolar  margin.  The  body  becomes  elongated  in  its  whole  length,  but 
more  especially  behind  the  mental  foramen,  to  provide  space  for  the  three  additional  teeth  devel- 
oped in  this  part.  The  depth  of  the  body  increases  owing  to  increased  growth  of  the  alveolar 
part,  to  afford  room  for  the  roots  of  the  teeth,  and  by  thickening  of  the  subdental  portion  which 
enables  the  jaw  to  withstand  the  powerful  action  of  the  masticatory  muscles;  but  the  alveolar 
portion  is  the  deeper  of  the  two,  and,  consequently,  the  chief  part  of  the  body  hes  above  the 
oblique  line.  The  mandibular  canal,  after  the  second  dentition,  is  situated  just  above  the  level 
of  the  mylohyoid  line;  and  the  mental  foramen  occupies  the  position  usual  to  it  in  the  adult. 
The  angle  becomes  less  obtuse,  owing  to  the  separation  of  the  jaws  by  the  teeth;  about  the  fourth 
year  it  is  140°. 

In  the  adult  (Fig.  184)  the  alveolar  and  subdental  portions  of  the  body  are  usually  of  equal 
depth.  The  mental  foramen  opens  midway  between  the  upper  and  lower  borders  of  the  bone, 
and  the  mandibular  canal  runs  nearly  parallel  with  the  mylohyoid  line.  The  ramus  is  almost 
vertical  in  direction,  the  angle  measuring  from  110°  to  120°. 

In  old  age  (Fig.  185)  the  bone  becomes  greatly  reduced  in  size,  for  with  the  loss  of  the  teeth 
the  alveolar  process  is  absorbed,  and,  consequently,  the  chief  part  of  the  bone  is  below  the  oblique 
line.  The  mandibular  canal,  with  the  mental  foramen  opening  from  it,  is  close  to  the  alveolar 
border.  The  ramus  is  obUque  in  direction,  the  angle  measures  about  140°,  and  the  neck  of  the 
condyle  is  more  or  less  bent  backward. 


The  Hyoid  Bone  (Os  Hyoideum;  Lingual  Bone). 


The  hyoid  bone  is  shaped  hke  a  horseshoe,  and  is  suspended  from  the  tips  of  the 
styloid  processes  of  the  temporal  bones  by  the  stylohyoid  ligaments.  It  consists 
of  five  segments,  viz.,  a  body,  two  greater  comua,  and  two  lesser  comua. 

The  Body  or  Basihyal  (corpus  oss.  hyoidei). — ^The  body  or  central  part  is 
of  a  quadrilateral  form.  Its  anterior  surface  (Fig.  186)  is  convex  and  directed 
forward  and  upward.  It  is  crossed  in  its  upper  half  by  a  well-marked  transverse 
ridge  with  a  slight  downward 
convexity,  and  in  many  cases  i<^;  ^Greater  comu 

a  vertical  median  ridge  divides 
it  into  two  lateral  halves. 
The  portion  of  the  vertical 
ridge  above  the  transverse  line 
is  present  in  a  majority  of 
^pecimens,  but  the  lower  por- 
lion  is  evident  only  in  rare 
cases.  The  anterior  surface 
j;ives  insertion  to  the  Genio- 
liyoideus  in  the  greater  part 
of  its  extent  both  above  and 
below  the  transverse  ridge;  a 
])ortion  of  the  origin  of  the 
llyoglossus  notches  the  lateral 

inargin  of  the  Geniohyoideus  attachment.  Below  the  transverse  ridge  the  Mylo- 
hyoideus,  Sternohyoideus,  and  Omohyoideus  are  inserted.  The  posterior  surface  is 
^mooth,  concave,  directed  backward  and  downward,  and -separated  from  the  epi- 
[,'lottis  by  the  hyothyroid  membrane  and  a  quantity  of  loose  areolar  tissue;  a  bursa 
intervenes  between  it  and  the  hyothyroid  membrane.  The  superior  border  is 
rounded,  and  gives  attachment  to  the  hyothyroid  membrane  and  some  aponeurotic 
libers  of  the  Genioglossus.  The  inferior  border  affords  insertion  medially  to  the 
Sternohyoideus  and  laterally  to  the  Omohyoideus  and  occasionally  a  portion  of  the 
Thyreohyoideus.  It  also  gives  attachment  to  the  Levator  glandulae  thyreoidese, 
^vhen  this  muscle  is  present.  In  early  life  the  lateral  borders  are  connected  to 
the  greater  cornua  by  synchondroses;  after  middle  life  usually  by  bony  union. 
12  ' 


DIGASTRICUS  & 
STYLOHYOIDEUS 

\      THYREOHYOIDECS 

Omohyoideus 


/     mtlohtordeus     sternohyoideus 
Geniohyoideus 

Fig.   186. — Hyoid  bone.     Anterior  surface.     Enlarged. 


178  '^^^^^^^-         OSTEOLOGY 


I 


The  Greater  Cornua  or  Thyrohyals  (cornua  majora) .  — The  greater  cornua 
project  backward  from  the  lateral  borders  of  the  body;  they  are  flattened  from 
above  downward  and  diminish  in  size  from  before  backward;  each  ends  in  a  tubercle 
to  which  is  fixed  the  lateral  hyothyroid  ligament.  The  upper  surface  is  rough 
close  to  its  lateral  border,  for  muscular  attachments:  the  largest  of  these  are  the 
origins  of  the  Hyoglossus  and  Constrictor  pharyngis  medius  which  extend  along 
the  whole  length  of  the  cornu;  the  Digastricus  and  Stylohyoideus  have  small 
insertions  in  front  of  these  near  the  junction  of  the  body  with  the  cornu.  To  the 
medial  border  the  hyothyroid  membrane  is  attached,  while  the  anterior  half  of  the 
lateral  border  gives  insertion  to  the  Thyreohyoideus. 

The  Lesser  Cornua  or  Ceratohyals  {cornua  minora). — The  lesser  cornu  are  two 
small,  conical  eminences,  attached  by  their  bases  to  the  angles  of  junction  between 
the  body  and  greater  cornua.  They  are  connected  to  the  body  of  the  bone  by  fibrous 
tissue,  and  occasionally  to  the  greater  cornua  by  distinct  diarthrodial  joints, 
which  usually  persist  throughout  life,  but  occasionally  become  ankylosed. 

The  lesser  cornua  are  situated  in  the  line  of  the  transverse  ridge  on  the  body 
and  appear  to  be  morphological  continuations  of  it  (Parsons^) .  The  apex  of  each 
cornu  gives  attachment  to  the  stylohyoid  ligament ;2  the  Chondroglossus  rises 
from  the  medial  side  of  the  base. 

Ossification. — The  hyoid  is  ossified  from  six  centers:  two  for  the  body,  and  one  for  each  cornu. 
Ossification  commences  in  the  greater  cornua  toward  the  end  of  fetal  life,  in  the  body  shortly 
afterward,  and  in  the  lesser  cornua  during  the  first  or  second  year  after  birth. 


THE    EXTERIOR    OF    THE    SKULL. 

The  skull  as  a  whole  may  be  viewed  from  different  points,  and  the  views  so 
obtained  are  termed  the  nomise  of  the  skull ;  thus,  it  may  be  examined  from  above 
(norma  verticalis),  from  below  (norma  basalis),  from  the  side  (norma  lateralis), 
from  behind  (norma  occipitalis),  or  from  the  front  (norma  frontalis). 

Norma  Verticalis.— When  viewed  from  above  the  outline  presented  varies 
greatly  in  different  skulls;  in  some  it  is  more  or  less  oval,  in  others  more  nearly 
circular.  The  surface  is  traversed  by  three  sutures,  viz.:  (1)  the  coronal  sutures, 
nearly  transverse  in  direction,  between  the  frontal  and  parietals;  (2)  the  sagittal 
sutures,  medially  placed,  between  the  parietal  bones,  and  deeply  serrated  in  its 
anterior  two-thirds;  and  (3)  the  upper  part  of  the  lambdoidal  suture,  between  the 
parietals  and  the  occipital.  The  point  of  junction  of  the  sagittal  and  coronal  suture 
is  named  the  bregma,  that  of  the  sagittal  and  lambdoid  sutures,  the  lambda;  they 
indicate  respectively  the  positions  of  the  anterior  and  posterior  fontanelles  in  the 
fetal  skull.  On  either  side  of  the  sagittal  suture  are  the  parietal  eminence  and  parietal 
foramen — the  latter,  however,  is  frequently  absent  on  one  or  both  sides.  The 
skull  is  often  somewhat  flattened  in  the  neighborhood  of  the  parietal  foramina, 
and  the  term  obelion  is  applied  to  that  point  of  the  sagittal  suture  which  is  on 
a  level  with  the  foramina.  In  front  is  the  glabella,  and  on  its  lateral  aspects  are 
the  superciliary  arches,  and  above  these  the  frontal  eminences.  Immediately  above 
the  glabella  may  be  seen  the  remains  of  the  frontal  suture;  in  a  small  percentage 
of  skulls  this  suture  persists  and  extends  along  the  middle  line  to  the  bregma. 
Passing  backward  and  upward  from  the  zygomatic  processes  of  the  frontal  bone 
are  the  temporal  lines,  which  mark  the  upper  limits  of  the  temporal  fossae.  The 
zygomatic  arches  may  or  may  not  be  seen  projecting  beyond  the  anterior  portions 
of  these  lines. 

1  See  article  on  "The  Topography  and  Morphology  of  the  Human  Hyoid  Bone,"  by  F.  G.  Parsons,  Journal  of 
Anatomy  and  Physiology,  vol.  xliii. 

2  These  ligaments  in  many  animals  are  distinct  bones,  and  in  man  may  undergo  partial  ossification. 


THE  EXTERIOR  OF  THE  SKULL 


179 


Norma  Basalis  (Fig.  187).- — The  inferior  surface  of  the  base  of  the  skull,  exclu- 
sive of  the  mandible,  is  bounded  in  front  by  the  incisor  teeth  in  the  maxillae;  behind, 


Incisors 


Incisive  canal 


Transmits  left  nasopalatine  nerve 
Transmits  descending  palatine  vesseU 
Transmits  right  nasopalatine  nerve 


Lesser  palatine  foramina 

Posterior  nasal  spine 
Musculus  uvulae 
Pterygoid  hamulus 


Sphenoidal  process  of  palatine 

Pharyngeal  canal 


Tensor  tympani 

Pharyngeal  tubercle 
Situation  of  auditory  tube  and 
liasiiar    '^      Semicanal  foT  TcnsoT  tympani 

\:  '  -part— Tensor  veli  palatini 

S^?i.j^^'^°" inferior  tympanic  canaliculus 

Aquaednctus  cochleae 

Jugular  foramen 
Mastoid  canaliculus 
Tympanomastoid  fissure 


Fig.  187.— I 


one^ 

of  skull.     Inferior  surface. 


180 


OSTEOLOGY 


I 


by  the  superior  nuchal  lines  of  the  occipital;  and  laterally  by  the  alveolar  arch, 
the  lower  border  of  the  zygomatic  bone,  the  zygomatic  arch  and  an  imaginary 
line  extending  from  it  to  the  mastoid  process  and  extremity  of  the  superior  nuchal 
line  of  the  occipital.  It  is  formed  by  the  palatine  processes  of  the  maxillae  and 
palatine  bones,  the  vomer,  the  pterygoid  processes,  the  under  surfaces  of  the 
great  wings,  spinous  processes,  and  part  of  the  body  of  the  sphenoid,  the  under 
surfaces  of  the  squamae  and  mastoid  and  petrous  portions  of  the  temporals,  and 
the  under  surface  of  the  occipital  bone.  The  anterior  part  or  hard  palate  projects 
below  the  level  of  the  rest  of  the  surface,  and  is  bounded  in  front  and  laterally 
by  the  alveolar  arch  containing  the  sixteen  teeth  of  the  maxillae.  Immediately 
behind  the  incisor  teeth  is  the  incisive  foramen.  In  this  foramen  are  two  lateral 
apertures,  the  openings  of  the  incisive  canals  (foramina  of  Stenson)  which  transmit 
the  anterior  branches  of  the  descending  palatine  vessels,  and  the  nasopalatine 
nerves.  Occasionally  two  additional  canals  are  present  in  the  incisive  foramen; 
they  are  termed  the  foramina  of  Scarpa  and  are  situated  in  the  middle  line;  when 
present  they  transmit  the  nasopalatine  nerves.  The  vault  of  the  hard  palate 
is  concave,  uneven,  perforated  by  numerous  foramina,  marked  by  depressions  for 
the  palatine  glands,  and  traversed  by  a  crucial  suture  formed  by  the  junction  of  the 
four  bones  of  which  it  is  composed.  In  the  young  skull  a  suture  may  be  seen  ex- 
tending on  either  side  from  the  incisive  foramen  to  the  interval  between  the  lateral 
incisor  and  canine  teeth,  and  marking  off  the  os  incisivum  or  premaxillary  bone. 
At  either  posterior  angle  of  the  hard  palate  is  the  greater  palatine  foramen,  for  the 
transmission  of  the  descending  palatine  vessels  and  anterior  palatine  nerve;  and 
running  forward  and  medialward  from  it  a  groove,  for  the  same  vessels  and  nerve. 
Behind  the  posterior  palatine  foramen  is  the  pyramidal  process  of  the  palatine  bone, 
perforated  by  one  or  more  lesser  palatine  foramina,  and  marked  by  the  commence- 
ment of  a  transverse  ridge,  for  the  attachment  of  the  tendinous  expansion  of  the 
Tensor  veli  palatini.  Projecting  backward  from  the  center  of  the  posterior  border 
of  the  hard  palate  is  the  posterior  nasal  spine,  for  the  attachment  of  the  Musculus 
uvulae.  Behind  and  above  the  hard  palate  are  the  choanse,  measuring  about 
2.5  cm.  in  their  vertical  and  1.25  cm.  in  their  transverse  diameters.  They  are 
separated  from  one  another  by  the  vomer,  and  each  is  bounded  above  by  the  body 
of  the  sphenoid,  below  by  the  horizontal  part  of  the  palatine  bone,  and  laterally 
by  the  medial  pterygoid  plate  of  the  sphenoid.  At  the  superior  border  of  the 
vomer  may  be  seen  the  expanded  alae  of  this  bone,  receiving  between  them  the  ros- 
trum of  the  sphenoid.  Near  the  lateral  margins  of  the  alae  of  the  vomer,  at  the 
roots  of  the  pterygoid  processes,  are  the  pharyngeal  canals.  The  pterygoid  process 
presents  near  its  base  the  pterygoid  canal,  for  the  transmission  of  a  nerve  and  artery. 
The  medial  pterygoid  plate  is  long  and  narrow;  on  the  lateral  side  of  its  base  is  the 
scaphoid  fossa,  for  the  origin  of  the  Tensor  veli  palatini,  and  at  its  lower  extremity 
the  hamulus,  around  which  the  tendon  of  this  muscle  turns.  The  lateral  pterygoid 
plate  is  broad;  its  lateral  surface  forms  the  medial  boundary  of  the  infratemporal 
fossa,  and  affords  attachment  to  the  Pterygoideus  externus. 

Behind  the  nasal  cavities  is  the  basilar  portion  of  the  occipital  bone,  presenting 
near  its  center  the  pharyngeal  tubercle  for  the  attachment  of  the  fibrous  raphe 
of  the  pharynx,  Avith  depressions  on  either  side  for  the  insertions  of  the  Rectus 
capitis  anterior  and  Longus  capitis.  At  the  base  of  the  lateral  pterygoid  plate 
is  the  foramen  ovale,  for  the  transmission  of  the  mandibular  nerve,  the  accessory 
meningeal  artery,  and  sometimes  the  lesser  superficial  petrosal  nerve;  behind  this  are 
the  foramen  spinosum  which  transmits  the  middle  meningeal  vessels,  and  the  promi- 
nent spina  angularis  {sphenoidal  spine),  which  gives  attachment  to  the  spheno- 
mandibular  ligament  and  the  Tensor  veli  palatini.  Lateral  to  the  spina  angularis 
is  the  mandibular  fossa,  divided  into  two  parts  by  the  petrotympanic  fissure;  the 
anterior  portion,  concave,    smooth,  bounded  in  front  by  the  articular  tubercle, 


THE  EXTERIOR  OF  THE  SKULL  181 


I 


serves  for  the  articulation  of  the  condyle  of  the  mandible;  the  posterior  portion, 
rough  and  bounded  behind  by  the  tympanic  part  of  the  temporal,  is  sometimes 
occupied  by  a  part  of  the  parotid  gland.  Emerging  from  between  the  laminae 
of  the  vaginal  process  of  the  tympanic  part  is  the  styloid  process;  and  at  the  base 
of  this  process  is  the  stylomastoid  foramen,  for  the  exit  of  the  facial  nerve,  and 
entrance  of  the  stylomastoid  artery.  Lateral  to  the  stylomastoid  foramen,  between 
the  tympanic  part  and  the  mastoid  process,  is  the  tympanomastoid  fissure,  for  the 
auricular  branch  of  the  vagus.  Upon  the  medial  side  of  the  mastoid  process  is 
the  mastoid  notch  for  the  posterior  belly  of  the  Digastricus,  and  medial  to  the  notch, 
the  occipital  groove  for  the  occipital  artery.  At  the  base  of  the  medial  pterygoid 
plate  is  a  large  and  somewhat  triangular  aperture,  the  foramen  lacerum,  bounded 
in  front  by  the  great  wing  of  the  sphenoid,  behind  by  the  apex  of  the  petrous 
portion  of  the  temporal  bone,  and  medially  by  the  body  of  the  sphenoid  and  basilar 
portion  of  the  occipital  bone;  it  presents  in  front  the  posterior  orifice  of  the  ptery- 
goid canal;  behind,  the  aperture  of  the  carotid  canal.  The  lower  part  of  this  opening 
IS  filled  up  in  the  fresh  state  by  a  fibrocartilaginous  plate,  across  the  upper  or 
cerebral  surface  of  which* the  internal  carotid  artery  passes.  Lateral  to  this  aperture 
is  a  groove,  the  sulcus  tubse  auditivse,  between  the  petrous  part  of  the  temporal  and 
the  great  wing  of  the  sphenoid.  This  sulcus  is  directed  lateralward  and  backward 
from  the  root  of  the  medial  pterygoid  plate  and  lodges  the  cartilaginous  part  of  the 
auditory  tube;  it  is  continuous  behind  with  the  canal  in  the  temporal  bone  which 
forms  the  bony  part  of  the  same  tube.  At  the  bottom  of  this  sulcus  is  a  narrow 
cleft,  the  petrosphenoidal  fissure,  which  is  occupied,  in  the  fresh  condition,  by  a 
P'late  of  cartilage.  Behind  this  fissure  is  the  under  surface  of  the  petrous  portion 
cf  the  temporal  bone,  presenting,  near  its  apex,  the  quadrilateral  rough  surface, 
part  of  which  affords  attachment  to  the  Levator  veli  palatini ;  lateral  to  this  surface 
is  the  orifice  of  the  carotid  canal,  and  medial  to  it,  the  depression  leading  to  the 
aquseductus  cochleae,  the  former  transmitting  the  internal  carotid  artery  and  the 
( arotid  plexus  of  the  sympathetic,  the  latter  serving  for  the  passage  of  a  vein  from 
the  cochlea.  Behind  the  carotid  canal  is  the  jugular  foramen,  a  large  aperture, 
formed  in  front  by  the  petrous  portion  of  the  temporal,  and  behind  by  the  occipital ; 
it  is  generally  larger  on  the  right  than  on  the  left  side,  and  may  be  subdivided 
into  three  compartments.  The  anterior  compartment  transmits  the  inferior 
])etrosal  sinus;  the  intermediate,  the  glossopharyngeal,  vagus,  and  accessory 
nerves;  the  posterior,  the  transverse  sinus  and  some  meningeal  branches  from  the 
occipital  and  ascending  pharyngeal  arteries.  On  the  ridge  of  bone  dividing  the 
carotid  canal  from  the  jugular  foramen  is  the  inferior  tympanic  canaliculus  for 
the  transmission  of  the  tympanic  branch  of  the  glossopharyngeal  nerve;  and  on  the 
wall  of  the  jugular  foramen,  near  the  root  of  the  styloid  process,  is  the  mastoid 
canaliculus  for  the  passage  of  the  auricular  branch  of  the  vagus  nerve.  Extending 
J'orward  from  the  jugular  foramen  to  the  foramen  lacerum  is  the  petrooccipital  fissure 
occupied,  in  the  fresh  state,  by  a  plate  of  cartilage.  Behind  the  basilar  portion 
ot  the  occipital  bone  is  the  foramen  magnum,  bounded  laterally  by  the  occipital 
condyles,  the  medial  sides  of  which  are  rough  for  the  attachment  of  the  alar 
ligaments.  Lateral  to  each  condyle  is  the  jugular  process  which  gives  attachment 
■zo  the  Rectus  capitis  lateralis  muscle  and  the  lateral  atlantooccipital  ligament. 
The  foramen  magnum  transmits  the  medulla  oblongata  and  its  membranes,  the 
accessory  nerves,  the  vertebral  arteries,  the  anterior  and  posterior  spinal  arteries, 
and  the  ligaments  connecting  the  occipital  bone  with  the  axis.  The  mid-points 
on  the  anterior  and  posterior  margins  of  the  foramen  magnum  are  respectively 
termed  the  basion  and  the  opisthion.  In  front  of  each  condyle  is  the  canal  for  the 
passage  of  the  hypoglossal  nerve  and  a  meningeal  artery.  Behind  each  condyle 
is  the  condyloid  fossa,  perforated  on  one  or  both  sides  by  the  condyloid  canal,  for 
the  transmission  of  a  vein  from  the  transverse  sinus.    Behind  the  foramen  magnum 


182 


OSTEOLOGY 


is  the  median  nuchal  line  ending  above  at  the  external  occipital  protuberance,  while 
on  either  side  are  the  superior  and  inferior  nuchal  lines;  these,  as  well  as  the  surfaces 
of  bone  between  them,  are  rough  for  the  attachment  of  the  muscles  which  are 
enumerated  on  pages  129  and  130. 

Norma  Lateralis  (Fig.  188). — When  viewed  from  the  side  the  skull  is  seen  to 
consist  of  the  cranium  above  and  behind,  and  of  the  face  below  and  in  front.  The 
cranium  is  somewhat  ovoid  in  shape,  but  its  contour  varies  in  different  cases  and 
depends  largely  on  the  length  and  height  of  the  skull  and  on  the  degree  of  promi- 
nence of  the  superciliary  arches  and  frontal  eminences.  Entering  into  its  formation 
are  the  frontal,  the  parietal,  the  occipital,  the  temporal,  and  the  great  wing  of  the 


Fig.  188. — Side  view  of  the  skull. 

sphenoid.  These  bones  are  joined  to  one  another  and  to  the  zygomatic  by  the  follow- 
ing sutures :  the  zygomaticotemporal  between  the  zygomatic  process  of  the  temporal 
and  the  temporal  process  of  the  zygomatic;  the  zygomaticofrontal  uniting  the  zygo- 
matic bone  with  the  zygomatic  process  of  the  frontal ;  the  sutures  surrounding  the 
great  wing  of  the  sphenoid,  viz.,  the  sphenozygomatic  in  front,  the  sphenofrontal 
and  sphenoparietal  above,  and  the  sphenosquamosal  behind.  The  sphenoparietal 
suture  varies  in  length  in  different  skulls,  and  is  absent  in  those  cases  where  the 
frontal  articulates  with  the  temporal  squama.  The  point  corresponding  with  the 
posterior  end  of  the  sphenoparietal  suture  is  named  the  pterion;  it  is  situated  about 
3  cm.  behind,  and  a  little  above  the  level  of  the  zygomatic  process  of  the  frontal 
bone. 


THE  EXTERIOR  OF  THE  SKULL  183 

The  squamosal  suture  arches  backward  from  the  pterion  and  connects  the  tem- 
poral squama  with  the  lower  border  of  the  parietal:  this  suture  is  continuous 
behind  with  the  short,  nearly  horizontal  parietomastoid  suture,  which  unites  the 
mastoid  process  of  the  temporal  with  the  region  of  the  mastoid  angle  of  the  parietal. 
Extending  from  above  downward  and  forward  across  the  cranium  are  the  coronal 
and  lambdoidal  sutures;  the  former  connects  the  parietals  with  the  frontal,  the  latter, 
the  parietals  with  the  occipital.  The  lambdoidal  suture  is  continuous  below  with 
the  occipitomastoid  suture  between  the  occipital  and  the  mastoid  portion  of  the 
temporal.  In  or  near  the  last  suture  is  the  mastoid  foramen,  for  the  transmission 
of  an  emissary  vein.  The  point  of  meeting  of  the  parietomastoid,  occipitomastoid, 
and  lambdoidal  sutures  is  known  as  the  asterion.  Immediately  above  the  orbital 
margin  is  the  superciliary  arch,  and,  at  a  higher  level,  the  frontal  eminence.  Near 
the  center  of  the  parietal  bone  is  the  parietal  eminence.  Posteriorly  is  the  ex- 
ternal occipital  protuberance,  from  which  the  superior  nuchal  line  may  be  followed 
forward  to  the  mastoid  process.  Arching  across  the  side  of  the  cranium  are  the 
temporal  lines,  which  mark  the  upper  limit  of  the  temporal  fossa. 

The  Temporal  Fossa  (fossa  temporalis). — The  temporal  fossa  is  bounded  above 
and  behind  by  the  temporal  lines,  which  extend  from  the  zygomatic  process  of  the 
frontal  bone  upward  and  backward  across  the  frontal  and  parietal  bones,  and  then 
curve  downward  and  forward  to  become  continuous  with  the  supramastoid  crest 
and  the  posterior  root  of  the  zygomatic  arch.  The  point  where  the  upper  temporal 
line  cuts  the  coronal  suture  is  named  the  stephanion.  The  temporal  fossa  is  bounded 
in  front  by  the  frontal  and  zygomatic  bones,  and  opening  on  the  back  of  the  latter 
is  the  zygomaticotemporal  foramen.  Laterally  the  fossa  is  limited  by  the  zygomatic 
arch,  formed  by  the  zygomatic  and  temporal  bones;  below,  it  is  separated  from  the 
infratemporal  fossa  by  the  infratemporal  crest  on  the  great  wing  of  the  sphenoid, 
and  by  a  ridge,  continuous  with  this  crest,  which  is  carried  backward  across  the 
temporal  squama  to  the  anterior  root  of  the  zygomatic  process.  In  front  and 
1  elow,  the  fossa  communicates  with  the  orbital  cavity  through  the  inferior  orbital 
(  r  sphenomaxillary  fissure.  The  floor  of  the  fossa  is  deeply  concave  in  front  and 
( onvex  behind,  and  is  formed  by  the  zygomatic,  frontal,  parietal,  sphenoid,  and 
temporal  bones.  It  is  traversed  by  vascular  furrows;  one,  usually  well-marked,  runs 
upward  above  and  in  front  of  the  external  acoustic  meatus,  and  lodges  the  middle 
temporal  artery.  Two  others,  frequently  indistinct,  may  be  observed  on  the 
J  nterior  part  of  the  floor,  and  are  for  the  anterior  and  posterior  deep  temporal 
jTteries.  The  temporal  fossa  contains  the  Temporalis  muscle  and  its  vessels  and 
nerves,  together  with  the  zygomaticotemporal  nerve. 

The  zygomatic  arch  is  formed  by  the  zygomatic  process  of  the  temporal  and 

1  he  temporal  process  of  the  zygomatic,  the  two  being  united  by  an  oblique  suture ; 

i.he  tendon  of  the  Temporalis  passes  medial  to  the  arch  to  gain  insertion  into  the 

'oronoid  process  of  the  mandible.    The  zygomatic  process  of  the  temporal  arises 

l)y  two  roots,  an  anterior,  directed  inward  in  front  of  the  mandibular  fossa,  where 

^■it  expands  to  form  the  articular  tubercle,  and  a  posterior,  which  runs  backward 

^■above  the  external  acoustic  meatus  and  is  continuous  with  the  supramastoid 

<:rest.     The  upper  border  of  the  arch  gives  attachment  to  the  temppral  fascia; 

■the  lower  border  and  medial  surface  give  origin  to  the  Masseter. 
Below  the  posterior  root  of  the  zygomatic  arch  is  the  elliptical  orifice  of  the 
external  acoustic  meatus,  bounded  in  front,  below,  and  behind  by  the  tympanic 
part  of  the  temporal  bone;  to  its  outer  margin  the  cartilaginous  segment  of  the 
external  acoustic  meatus  is  attached.  The  small  triangular  area  between  the 
posterior  root  of  the  zygomatic  arch  and  the  postero-superior  part  of  the  orifice  is 
termed  the  suprameatal  triangle,  on  the  anterior  border  of  which  a  small  spinous 
process,  the  suprameatal  spine,  is  sometimes  seen.     Between  the  tympanic  part 

I  and  the  articular  tubercle  is  the  mandibular  fossa,  divided  into  two  parts  bv  the 
1 


] 

I 


184 


OSTEOLOGY 


petrotympanic  fissure.  The  anterior  and  larger  part  of  the  fossa  articulates  A^'ith 
the  condyle  of  the  mandible  and  is  limited  behind  by  the  external  acoustic  meatus  r 
the  posterior  part  sometimes  lodges  a  portion  of  the  parotid  gland.  The  styloid 
process  extends  downward  and  forward  for  a  variable  distance  from  the  lower 
part  of  the  tympanic  part,  and  gives  attachment  to  the  Styloglossus,  Stylo hy- 
oideus,  and  Stylopharyngeus,  and  to  the  stylohyoid  and  stylomandibular  ligaments. 
Projecting  downward  behind  the  external  acoustic  meatus  is  the  mastoid  process, 
to  the  outer  surface  of  which  the  Sternocleidomastoideus,  Splenius  capitis,  and 
Longissimus  capitis  are  attached. 

The  Infratemporal  Fossa  (fossa  infratemporalis;  zygomatic  fossa)  (Fig.  189). — 1'he 
infratemporal  fossa  is  an  irregularly  shaped  cavity,  situated  below  and  medial  to  the 
zygomatic  arch.    It  is  bounded,  in  front,  by  the  infratemporal  surface  of  the  maxilla 


m  Parietc 


/     Fronlof 


Sf/uama 

of  lempoTal 


Inferior  orbital  fissure 

Infratemporal  crest 

Pterygomaxillary  fissm  e 


External  acoustic  meatus 
Tympanic  part  of  temporal 
Styloid  process 
Mandibular  cavity 
Zygomatic  process  {cut) 
Lateral  pterygoid  plate 


Pterygoid  hamulus 

Fig.   189. — Left  infratemporal  fossa. 


and  the  ridge  which  descends  from  its  zygomatic  process;  behind,  by  the  articular 
tubercle  of  the  temporal  and  the  spina  angularis  of  the  sphenoid;  above,  by  the  great 
wing  of  the  sphenoid  below  the  infratemporal  crest,  and  by  the  under  surface  of 
the  temporal  squama;  below,  by  the  alveolar  border  of  the  maxilla;  medially,  by 
the  lateral  pterygoid  plate.  It  contains  the  lower  part  of  the  Temporalis,  the 
Pterygoidei  internus  and  externus,  the  internal  maxillary  vessels,  and  the  man- 
dibular and  maxillary  nerves.  The  foramen  ovale  and  foramen  spinosum  open  on 
its  roof,  and  the  alveolar  canals  on  its  anterior  wall.  At  its  upper  and  medial 
part  are  two  fissures,  which  together  form  a  T-shaped  fissure,  the  horizontal  limb 
being  named  the  inferior  orbital,  and  the  vertical  one  the  pterygomaxillary. 

The  inferior  orbital  fissure  (fissura  orbitalis  inferior;  sphenomaxillary  fissnre), 
horizontal  in  direction,  opens  into  the  lateral  and  back  part  of  the  orbit.  It  is 
bounded  above  by  the  lower  border  of  the  orbital  surface  of  the  great  wing  of  the 


THE  EXTERIOR  OF  THE  SKULL  185 

sphenoid;  below,  by  the  lateral  border  of  the  orbital  sirt-face  of  the  maxilla  and  the 
orbital  process  of  the  palatine  bone;  laterally,  by  a  small  part  of  the  zygomatic 
bone  :^  medially,  it  joins  at  right  angles  with  the  pterygomaxillary  fissure.  Through 
the  inferior  orbital  fissure  the  orbit  communicates  with  the  temporal,  infratem- 
poral, and  pterygopalatine  fossae;  the  fissure  transmits  the  maxillary  nerve  and 
its  zygomatic  branch,  the  infraorbital  vessels,  the  ascending  branches  from  the 
sphenopalatine  ganglion,  and  a  vein  which  connects  the  inferior  ophthalmic  vein 
with  the  pterygoid  venous  plexus. 

The  pterygomaxillary  fissure  is  vertical,  and  descends  at  right  angles  from  the 
medial  end  of  the  preceding;  it  is  a  triangular  interval,  formed  by  the  diver- 
gence of  the  maxilla  from  the  pterygoid  process  of  the  sphenoid.  It  connects 
the  infratemporal  with  the  pterygopalatine  fossa,  and  transmits  the  terminal  part 
of  the  internal  maxillary  artery. 

The  Pterygopalatine  Fossa  (fossa  pterygopalatina;  sphenomaxillary  fossa) . — ^The 
pterygopalatine  fossa  is  a  small,  triangular  space  at  the  angle  of  junction  of  the 
inferior  orbital  and  pterygomaxillary  fissures,  and  placed  beneath  the  apex  of 
the  orbit.  It  is  bounded  above  by  the  under  surface  of  the  body  of  the  sphenoid 
and  by  the  orbital  process  of  the  palatine  bone;  in  front,  by  the  infratemporal 
surface  of  the  maxilla;  behind,  by  the  base  of  the  pterygoid  process  and  lower  part 
of  the  anterior  surface  of  the  great  wing  of  the  sphenoid ;  medially,  by  the  vertical 
part  of  the  palatine  bone  with  its  orbital  and  sphenoidal  processes.  This  fossa 
communicates  with  the  orbit  by  the  inferior  orbital  fissure,  with  the  nasal  cavity 
by  the  sphenopalatine  foramen,  and  with  the  infratemporal  fossa  by  the  pterygo- 
maxillary fissure.  Five  foramina  open  into  it.  Of  these,  three  are  on  the  posterior 
V  all,  viz.,  the  foramen  rotimdum,  the  pterygoid  canal,  and  the  pharyngeal  canal, 
in  this  order  downward  and  medialward.  On  the  medial  wall  is  the  sphenopalatine 
foramen,  and  below  is  the  superior  orifice  of  the  pterygopalatine  canal.  The  fossa 
contains  the  maxillary  nerve,  the  sphenopalatine  ganglion,  and  the  terminal  part 
of  the  internal  maxillary  artery. 

Norma  Occipitalis. — When  viewed  from  behind  the  cranium  presents  a  more 
or  less  circular  outline.  In  the  middle  line  is  the  posterior  part  of  the  sagittal 
sature  connecting  the  parietal  bones;  extending  downward  and  lateralward  from 
the  hinder  end  of  the  sagittal  suture  is  the  deeply  serrated  lambdoidal  suture  join- 
i  ig  the  parietals  to  the  occipital  and  continuous  below  with  the  parietomastoid  and 
occipitomastoid  sutures;  it  frequently  contains  one  or  more  sutural  bones.  Near 
the  middle  of  the  occipital  squama  is  the  external  occipital  protuberance  or  inion, 
and  extending  lateralward  from  it  on  either  side  is  the  superior  nuchal  line,  and 
above  this  the  faintly  marked  highest  nuchal  line.  The  part  of  the  squama  above 
the  inion  and  highest  lines  is  named  the  planum  occipitale,  and  is  covered  by  the 
Occipitalis  muscle;  the  part  below  is  termed  the  planum  nuchale,  and  is  divided 
by  the  median  nuchal  line  which  runs  downward  and  forward  from  the  inion  to  the 
faramen  magnum;  this  ridge  gives  attachment  to  the  ligamentum  nuchae.  The 
muscles  attached  to  the  planum  nuchale  are  enumerated  on  p.  130.  Below  and  in 
front  are  the  mastoid  processes,  convex  laterally  and  grooved  medially  b}^  the 
mastoid  notches.  In  or  near  the  occipitomastoid  suture  is  the  mastoid  foramen  for 
the  passage  of  the  mastoid  emissary  vein. 

Norma  Frontalis  (Fig.  190).— When  viewed  from  the  front  the  skull  exhibits  a 
somewhat  oval  outline,  limited  above  by  the  frontal  bone,  belmv  by  the  body  of  the 
raandible,  and  laterally  by  the  zygomatic  bones  and  the  mandibular  rami.  The 
upper  part,  formed  by  the  frontal  squama,  is  smooth  and  convex.  The  lower  part, 
made  up  of  the  bones  of  the  face,  is  irregular;  it  is  excavated  laterally  by  the  orbital 
^cavities,  and  presents  in  the  middle  line  the  anterior  nasal  aperture  leading  to  the 


1  Occasionally  the  maxilla  and  the  sphenoid  articulate  with  each  other  at  the  anterior  extremity  of  this  fissure;  the 
sygomatic  is  then  excluded  from  it. 


■ 


186 


OSTEOLOGY 


nasal  cavities,  and  below  this  the  transverse  slit  between  the  upper  and  loAver 
dental  arcades.  Above,  the  frontal  eminences  stand  out  more  or  less  prominently, 
and  beneath  these  are  the  superciliary  arches,  joined  to  one  another  in  the  middle 
by  the  glabella.  On  and  above  the  glabella  a  trace  of  the  frontal  suture  sometimes 
persists;  beneath  it  is  the  frontonasal  suture,  the  mid-point  of  which  is  termed  the 
nasion.  Behind  and  below  the  frontonasal  suture  the  frontal  articulates  with  the 
frontal  process  of  the  maxilla  and  with  the  lacrimal.  Arching  transversely  below 
the  superciliary  arches  is  the  upper  part  of  the  margin  of  the  orbit,  thin  and  promi- 


Supraorbital  foramen 


Superior  orbital  fissure 

Lamina  papyracea  of  ethmoid 

Lacrimal 

Inferior  orbital  fissure 

Zygomaticofacial  foramen 

Irifraorhital  foramen 
Nasal  cavity 
Inferior  nasal  concha 


Mental  foratMti 


Fig.   190. — The  skull  from  the  front. 


nent  in  its  lateral  two-thirds,  rounded  in  its  medial  third,  and  presenting,  at  the 
junction  of  these  two  portions,  the  supraorbital  notch  or  foramen  for  the  supra- 
orbital nerve  and  vessels.  The  supraorbital  margin  ends  laterally  in  the  zygomatic 
process  which  articulates  w^ith  the  zygomatic  bone,  and  from  it  the  temporal  line 
extends  upward  and  backward.  Below  the  frontonasal  suture  is  the  bridge  of  the 
nose,  convex  from  side  to  side,  concavo-convex  from  above  downward,  and  formed 
by  the  two  nasal  bones  supported  in  the  middle  line  by  the  perpendicular  plate 
of  the  ethmoid,  and  laterally  by  the  frontal  processes  of  the  maxillae  which  are 
prolonged  upward  between  the  nasal  and  lacrimal  bones  and  form  the  lower  and 


THE  EXTERIOR  OF  THE  SKULL 


187 


medial  part  of  the  circumference  of  each  orbit.  Below  the  nasal  bones  and  between 
the  maxillae  is  the  anterior  aperture  of  the  nose,  pyriform  in  shape,  with  the  narrow 
end  directed  upward.  Laterally  this  opening  is  bounded  by  sharp  margins,  to 
\\hich  the  lateral  and  alar  cartilages  of  the  nose  are  attached;  below,  the  margins 
are  thicker  and  curve  medialward  and  forward  to  end  in  the  anterior  nasal  spine. 
On  looking  into  the  nasal  cavity,  the  bony  septum  which  separates  the  nasal 
cavities  presents,  in  front,  a  large  triangular  deficiency;  this,  in  the  fresh  state, 
is  filled  up  by  the  cartilage  of  the  nasal  septum;  on  the  lateral  wall  of  each  nasal 
cavity  the  anterior  part  of  the  inferior  nasal  concha  is  visible.  Below  and  lateral 
to  the  anterior  nasal  aperture  are  the  anterior  surfaces  of  the  maxillae,  each 
perforated,  near  the  lower  margin  of  the  orbit,  by  the  infraorbital  foramen  for  the 


Nasal  bone 


Lacrfmal  sulcus 

Zygomatic  hone 
Maxilla 


Ayit.  ethmoidal  cells 

Nasal  septum 

Probe  in 
infundibulum 
Middle  ethmmdal  cells 

Superior  nasal  concha 
~^ost.  ethmoidal  cells 
Superior  meatus 


Sphenoidal  sinuses 


Infraorbital  groove 


Inferior  orbital 
fissure 


Palatine  hone 


Sphenoidal  hone 
Foramen  rotundum 


Foramen  ovale 
Foramen  spinosum 


Carotid  canal 
Fig.  191. — Horizontal  section  of  nasal  and  orbital  cavities. 


[jJassage  of  the  infraorbital  nerve  and  vessels.  Below  and  medial  to  this  foramen 
is  the  canine  eminence  separating  the  incisive  from  the  canine  fossa.  Beneath 
piiese  fossae  are  the  alveolar  processes  of  the  maxillae  containing  the  upper  teeth, 
rhich  overlap  the  teeth  of  the  mandible  in  front.  The  zygomatic  bone  on  either 
^de  forms  the  prominence  of  the  cheek,  the  lower  and  lateral  portion  of  the  orbital 
lavity,  and  the  anterior  part  of  the  zj'gomatic  arch.  It  articulates  medially  with 
h;he  maxilla,  behind  with  the  zygomatic  process  of  the  temporal,  and  above  with 
me  great  wing  of  the  sphenoid  and  the  zygomatic  process  of  the  frontal;  it  is  per- 
lorated  by  the  zygomaticofacial  foramen  for  the  passage  of  the  zygomaticofacial 
Jierve.  On  the  body  of  the  mandible  is  a  median  ridge,  indicating  the  position 
of  the  symphysis;  this  ridge  divides  below  to  enclose  the  mental  protuberance,  the 
lateral  angles  of  which  constitute  the  mental  tubercles.     Below  the  incisor  teeth 


i 


188 


OSTEOLOGY 


is  the  incisive  fossa,  and  beneath  the  second  premolar  tooth  the  mental  foramen 
which  transmits  the  mental  nerve  and  vessels.  The  oblique  line  runs  upward  from 
the  mental  tubercle  and  is  continuous  behind  with  the  anterior  border  of  the  ramus. 
The  posterior  border  of  the  ramus  runs  downward  and  forward  from  the  condyle 
to  the  angle,  which  is  frequently  more  or  less  everted. 

The  Orbits  (orbitae)  (Fig.  190). — The  orbits  are  two  quadrilateral  pyramidal  cavi- 
ties, situated  at  the  upper  and  anterior  part  of  the  face,  their  bases  being  directed 
forward  and  lateralward,  and  their  apices  backward  and  medialward,  so  that  their 
long  axes,  if  continued  backward,  would  meet  over  the  body  of  the  sphenoid. 
Each  presents  for  examination  a  roof,  a  floor,  a  medial  and  a  lateral  wall,  a  base, 
and  an  apex. 


Anterior 
ethmoidal  foramen 


Posterior  ethmoidal  foramen 
Orbital  process  of  palatine 
Optic  foramen 

Splienopalatine  foramen 

Sella  turcica 
Prdie  in  foramen  rotundum 


Fossa  for 

lacrimal  sac 

Uncinate  process 
of  ethmoid, 
Openings  of 
maxillary  sinus 
Inferior  nasal 
concha 


Probe  in  pterygoid  canal 
-Prdbe  in  pterygopalatine  canal 

Palatine  bone 

Lateral  pterygoid  plate 


Pyramidal  process  of  palatine 


Fig.  192. — Medial  wall  of  left  orbit.     < 

The  roof  is  concave,  directed  downward,  and  slightly  forward,  and  formed  in 
front  by  the  orbital  plate  of  the  frontal;  behind  by  the  small  wing  of  the  sphenoid. 
It  presents  medially  the  trochlear  fovea  for  the  attachment  of  the  cartilaginous 
pulley  of  the  Obliquus  oculi  superior;  laterally,  the  lacrimal  fossa  for  the  lacrimal 
gland;  and  posteriorly,  the  suture  between  the  frontal  bone  and  the  small  wing 
of  the  sphenoid. 

The  floor  is  directed  upward  and  lateralward,  and  is  of  less  extent  than  the 
roof;  it  is  formed  chiefly  by  the  orbital  surface  of  the  maxilla;  in  front  and  laterally, 
by  the  orbital  process  of  the  zygomatic  bone,  and  behind  and  medially,  to  a  small 
extent,  by  the  orbital  process  of  the  palatine.  At  its  medial  angle  is  the  upper 
opening  of  the  nasolacrimal  canal,  immediately  to  the  lateral  side  of  which  is  a 
depression  for  the  origin  of  the  Obliquus  oculi  inferior.  On  its  lateral  part  is  the 
suture  between  the  maxilla  and  zygomatic  bone,  and  at  its  posterior  part  that 
between  the  maxilla  and  the  orbital  process  of  the  palatine.  Running  forward 
near  the  middle  of  the  floor  is  the  infraorbital  groove,  ending  in  front  in  the  infra- 
orbital canal  and  transmitting  the  infraorbital  nerve  and  vessels. 


i 


THE  INTERIOR  OF  THE  SKULL  189 


The  medial  wall  (P'ig.  192)  is  nearly  vertical,  and  is  formed  from  before  back- 
ward by  the  frontal  process  of  the  maxilla,  the  lacrimal,  the  lamina  papyracea 
of  the  ethmoid,  and  a  small  part  of  the  body  of  the  sphenoid  in  front  of  the  optic 
foramen.  Sometimes  the  sphenoidal  concha  forms  a  small  part  of  this  wall  (see 
page  152).  It  exhibits  three  vertical  sutures,  viz.,  the  lacrimomaxillary,  lacrimo- 
ethmoidal,  and  sphenoethmoidal.  In  front  is  seen  the  lacrimal  groove,  which  lodges 
the  lacrimal  sac,  and  behind  the  groove  is  the  posterior  lacrimal  crest,  from  which 
the  lacrimal  part  of  the  Orbicularis  oculi  arises.  At  the  junction  of  the  medial 
wall  and  the  roof  are  the  frontomaxillary,  frontolacrimal,  frontoethmoidal,  and 
sphenofrontal  sutures.  The  point  of  junction  of  the  anterior  border  of  the  lacrimal 
with  the  frontal  is  named  the  dacryon.  In  the  frontoethmoidal  suture  are  the 
anterior  and  posterior  ethmoidal  foramina,  the  former  transmitting  the  nasociliary 
nerve  and  anterior  ethmoidal  vessels,  the  latter  the  posterior  ethmoidal  nerve  and 
vessels. 

The  lateral  wall,  directed  medialward  and  forward,  is  formed  by  the  orbital 
process  of  the  zygomatic  and  the  orbital  surface  of  the  great  wing  of  the  sphenoid; 
these  are  united  by  the  sphenozygomatic  suture  which  terminates  below  at  the 
front  end  of  the  inferior  orbital  fissure.  On  the  orbital  process  of  the  zygomatic 
bone  are  the  orbital  tubercle  (Whitnall)  and  the  orifices  of  one  or  two  canals  which 
transmit  the  branches  of  the  zygomatic  nerve.  Between  the  roof  and  the  lateral 
wall,  near  the  apex  of  the  orbit,  is  the  superior  orbital  fissure.  Through  this  fissure 
the  oculomotor,  the  trochlear,  the  ophthalmic  division  of  the  trigeminal,  and  the 
al)ducent  nerves  enter  the  orbital  cavity,  also  some  filaments  from  the  cavernous 
plexus  of  the  sympathetic  and  the  orbital  branches  of  the  middle  meningeal  artery. 
Passing  backward  through  the  fissure  are  the  ophthalmic  vein  and  the  recurrent 
branch  from  the  lacrimal  artery  to  the  dura  mater.  The  lateral  wall  and  the  floor 
are  separated  posteriorly  by  the  inferior  orbital  fissure  which  transmits  the  maxillary 
nerve  and  its  zygomatic  branch,  the  infraorbital  vessels,  and  the  ascending  branches 
from  the  sphenopalatine  ganglion. 

The  base  of  the  orbit,  quadrilateral  in  shape,  is  formed  above  by  the  supra- 
orbital arch  of  the  frontal  bone,  in  which  is  the  supraorbital  notch  or  foramen  for 
tlie  passage  of  the  supraorbital  vessels  and  nerve;  below  by  the  zygomatic  bone  and 
maxilla,  united  by  the  zygomaticomaxillary  suture;  laterally  by  the  zygomatic 
bDne  and  the  zygomatic  process  of  the  frontal  joined  by  the  zygomaticofrontal 
suture;  medially  by  the  frontal  bone  and  the  frontal  process  of  the  maxilla  united 
by  the  frontomaxillary  suture. 

The  apex,  situated  at  the  back  of  the  orbit,  corresponds  to  the  optic  foramen^ 
a  short,  cylindrical  canal,  which  transmits  the  optic  nerve  and  ophthalmic  artery. 

It  will  thus  be  seen  that  there  are  nine  openings  communicating  with  each 
orbit,  viz.,  the  optic  foramen,  superior  and  inferior  orbital  fissures,  supraorbital 
foramen,  infraorbital  canal,  anterior  and  posterior  ethmoidal  foramina,  zygomatic 
foramen,  and  the  canal  for  the  nasolacrimal  duct. 

THE   INTERIOR   OF   THE    SKULL. 

Inner  Surface  of  the  Skull-cap. — The  inner  surface  of  the  skull-cap  is  concave 
and  presents  depressions  for  the  convolutions  of  the  cerebrum,  together  with 
numerous  furrows  for  the  lodgement  of  branches  of  the  meningeal  vessels.  Along 
tlie  middle  line  is  a  longitudinal  groove,  narrow  in  front,  where  it  commences  at 
the  frontal  crest,  but  broader  behind;  it  lodges  the  superior  sagittal  sinus,  and  its 
margins  afford  attachment  to  the  falx  cerebri.    On  either  side  of  it  are  several 

■  Some  anatomists  describe  the  apex  of  the  orbit  as  corresponding  with  the  medial  end  of  the  superior  orbital  fissure. 
It  seems  better,  however,  to  adopt  the  statement  in  the  text,  since  the  ocular  muscles  take  origin  around  the  optio 
foramen,  and  diverge  from  it  to  the  bulb  of  the  eye. 


■ 


190  OSTEOLOGY 


I 


depressions  for  the  arachnoid  granulations,  and  at  its  back  part,  the  openings  of 
the  parietal  foramina  when  these  are  present.  It  is  crossed,  in  front,  by  the  coronal 
suture,  and  behind  by  the  lambdoidal,  while  the  sagittal  lies  in  the  medial  plane 
between  the  parietal  bones. 

Upper  Surface  of  the  Base  of  the  Skull  (Fig.  19,3). — The  upper  surface  of  the 
base  of  the  skull  or  floor  of  the  cranial  cavity  presents  three  fossae,  called  the  anterior, 
middle,  and  posterior  cranial  fossae. 

Anterior  Fossa  (fossa  cranii  anterior).- — The  floor  of  the  anterior  fossa  is  formed 
by  the  orbital  plates  of  the  frontal,  the  cribriform  plate  of  the  ethmoid,  and  the 
small  wings  and  front  part  of  the  body  of  the  sphenoid ;  it  is  limited  behind  by  the 
posterior  borders  of  the  small  wings  of  the  sphenoid  and  by  the  anterior  margin 
of  the  chiasmatic  groove.  It  is  traversed  by  the  frontoethmoidal,  sphenoethmoidal, 
and  sphenofrontal  sutures.  Its  lateral  portions  roof  in  the  orbital  cavities  and  sup- 
port the  frontal  lobes  of  the  cerebrum;  they  are  convex  and  marked  by  depressions 
for  the  brain  convolutions,  and  grooves  for  branches  of  the  meningeal  vessels. 
The  central  portion  corresponds  with  the  roof  of  the  nasal  cavity,  and  is  markedly 
depressed  on  either  side  of  the  crista  galli.  It  presents,  in  and  near  the  median 
line,  from  before  backward,  the  commencement  of  the  frontal  crest  for  the  attach- 
ment of  the  falx  cerebri;  the  foramen  cecum,  between  the  frontal  bone  and  the  crista 
galli  of  the  ethmoid,  which  usually  transmits  a  small  vein  from  the  nasal  cavity 
to  the  superior  sagittal  sinus;  behind  the  foramen  cecum,  the  crista  galli,  the 
free  margin  of  which  affords  attachment  to  the  falx  cerebri;  on  either  side  of  the 
crista  galli,  the  olfactory  groove  formed  by  the  cribriform  plate,  which  supports 
the  olfactory  bulb  and  presents  foramina  for  the  transmission  of  the  olfactory 
nerves,  and  in  front  a  slit-like  opening  for  the  nasociliary  nerve.  Lateral  to  either 
olfactory  groove  are  the  internal  openings  of  the  anterior  and  posterior  ethmoidal 
foramina;  the  anterior,  situated  about  the  middle  of  the  lateral  margin  of  the  olfac- 
tory groove,  transmits  the  anterior  ethmoidal  vessels  and  the  nasociliary  nerve;  the 
nerve  runs  in  a  groove  along  the  lateral  edge  of  the  cribriform  plate  to  the  slit-like 
opening  above  mentioned;  the  posterior  ethmoidal  foramen  opens  at  the  back  part 
of  this  margin  under  cover  of  the  projecting  lamina  of  the  sphenoid,  and  transmits 
the  posterior  ethmoidal  vessels  and  nerve.  Farther  back  in  the  middle  line  is  the 
ethmoidal  spine,  bounded  behind  by  a  slight  elevation  separating  two  shallow  lon- 
gitudinal grooves  which  support  the  olfactory  lobes.  Behind  this  is  the  anterior 
margin  of  the  chiasmatic  groove,  running  lateralward  on  either  side  to  the  upper 
margin  of  the  optic  foramen. 

The  Middle  Fossa  (fossa  cranii  media). — The  middle  fossa,  deeper  than  the  pre- 
ceding, is  narrow  in  the  middle,  and  wide  at  the  sides  of  the  skull.  It  is  bounded 
in  front  by  the  posterior  margins  of  the  small  wings  of  the  sphenoid,  the  anterior 
clinoid  processes,  and  the  ridge  forming  the  anterior  margin  of  the  chiasmatic 
groove;  behind,  by  the  superior  angles  of  the  petrous  portions  of  the  temporals 
and  the  dorsum  sellse;  laterally  by  the  temporal  squamse,  sphenoidal  angles  of  the 
parietals,  and  great  wings  of  the  sphenoid.  It  is  traversed  by  the  squamosal, 
sphenoparietal,  sphenosquamosal,  and  sphenopetrosal  sutures. 

The  middle  part  of  the  fossa  presents,  in  front,  the  chiasmatic  groove  and  tuber- 
culum  sellse;  the  chiasmatic  groove  ends  on  either  side  at  the  optic  foramen,  which 
transmits  the  optic  nerve  and  ophthalmic  artery  to  the  orbital  cavity.  Behind 
the  optic  foramen  the  anterior  clinoid  process  is  directed  backward  and  medialward 
and  gives  attachment  to  the  tentorium  cerebelli.  Behind  the  tuberculum  sellae 
is  a  deep  depression,  the  sella  turcica,  containing  the  fossa  hypophyseos,  which  lodges 
the  hypophysis,  and  presents  on  its  anterior  wall  the  middle  clinoid  processes. 
The  sella  turcica  is  bounded  posteriori}^  by  a  quadrilateral  plate  of  bone,  the  dorsum 
sellse,  the  upper  angles  of  which  are  surmounted  by  the  posterior  clinoid  processes : 
these  afford  attachment  to  the  tentorium  cerebelli,  and  below  each  is  a  notch  for 


THE  INTERIOR  OF  THE  SKULL 


191 


the  abducent  nerve.    On  either  side  of  the  sella  turcica  is  the  carotid  groove,  which 
is  broad,  shallow,  and  curved  somewhat  like  the  italic  letter  /.    It  begins  behind 


Groove  for  super,  sagittal  sinus 

Grooves  for  anier.  meningeal  vessels 

Foramen  ccecum 

Crista  galli 

Slit  for  nasociliary  nerve 

Groove  for  nasociliary  nerve 

Anterior  ethmoidal  foramen 

Orifices  for  olfactory  nerves 
Posterior  ethmoidal  foramen 

Ethmoidal  spine 


Olfactory  grooves 

Optic  foramen 

Chiasmatic  groove 

Tubercidum  sellae 

Anterior  clinoid  process 

Middle  clinoid  process 

Posterior  clinoid  process 

Groove  for  abdiicent  nerve 

Foramen  lacerum 

Orifice  of  carotid  canal 

ssion  for  semilunar  ganglion 


Let 


tfJJepres 

■ 

I  ^^^K  Internal  acoustic  meatus 

I  ^^H  Slit  for  dura  mater 
I  ^^^R    Groove  for  superior  petrosal  sinus 

I  ^^B  Jugular  foramen 

I  ^^H  Hypoglossal  canal 

I  ^^^B  Aqucedticttis  vestibuli 

I^^H^  Condyloid  foramen, 

B 

I  ^^^^  Mastoid  foramen 

Posterior  meningeal  grooves 


I 


Fig.   193. — Base  of  the  skull.     Upper  surface. 


at  the  foramen  lacerum,  and  ends  on  the  medial  side  of  the  anterior  clinoid  process, 
where  it  is  sonietimes  converted  into  a  foramen  (carotico-clinoid)  by  the  union  of 
the  anterior  with  the  middle  clinoid  process;  posteriorly,  it  is  bounded  laterally 


192 


OSTEOLOGY 


I 


by  the  lingula.  This  groove  lodges  the  cavernous  sinus  and  the  internal  carc>tid 
artery,  the  latter  being  surrounded  by  a  plexus  of  sympathetic  nerves. 

The  lateral  parts  of  the  middle  fossa  are  of  considerable  depth,  and  support 
the  temporal  lobes  of  the  brain.  They  are  marked  by  depressions  for  the  brain 
convolutions  and  traversed  by  furrows  for  the  anterior  and  posterior  branches 
of  the  middle  meningeal  vessels.  These  furrows  begin  near  the  foramen  spinosiim, 
and  the  anterior  runs  forward  and  upward  to  the  sphenoidal  angle  of  the  parietal, 
where  it  is  sometimes  converted  into  a  bony  canal;  the  posterior  runs  lateral  ward 
and  backward  across  the  temporal  squama  and  passes  on  to  the  parietal  near 
the  middle  of  its  lower  border.  The  following  apertures  are  also  to  be  seen.  In 
front  is  the  superior  orbital  fissure,  bounded  above  by  the  small  wing,  below,  by  the 
great  wing,  and  medially,  by  the  body  of  the  sphenoid;  it  is  usually  completed 
laterally  by  the  orbital  plate  of  the  frontal  bone.  It  transmits  to  the  orbital 
cavity  the  oculomotor,  the  trochlear,  the  ophthalmic  division  of  the  trigeminal, 
and  the  abducent  nerves,  some  filaments  from  the  cavernous  plexus  of  the 
sympathetic,  and  the  orbital  branch  of  the  middle  meningeal  artery;  and  from  the 
orbital  cavity  a  recurrent  branch  from  the  lacrimal  artery  to  the  dura  mater,  and 
the  ophthalmic  veins.  Behind  the  medial  end  of  the  superior  orbital  fissure  is 
the  foramen  rotundum,  for  the  passage  of  the  maxillary  nerve.  Behind  and  lateral 
to  the  foramen  rotundum  is  the  foramen  ovale,  which  transmits  the  mandibular 
nerve,  the  accessory  meningeal  artery,  and  the  lesser  superficial  petrosal  nerve.^ 
Medial  to  the  foramen  ovale  is  the  foramen  Vesalii,  which  varies  in  size  in  different 
individuals,  and  is  often  absent;  when  present,  it  opens  below  at  the  lateral  side 
of  the  scaphoid  fossa,  and  transmits  a  small  vein.  Lateral  to  the  foramen  ovale 
is  the  foramen  spinosum,  for  the  passage  of  the  middle  meningeal  vessels,  and  a 
recurrent  branch  from  the  mandibular  nerve.  Medial  to  the  foramen  ovale  is 
the  foramen  lacerum;  in  the  fresh  state  the  lower  part  of  this  aperture  is  filled  up 
by  a  layer  of  fibrocartilage,  while  its  upper  and  inner  parts  transmit  the  internal 
carotid  artery  surrounded  by  a  plexus  of  sympathetic  nerves.  The  nerve  of  the 
pterygoid  canal  and  a  meningeal  branch  from  the  ascending  pharyngeal  artery 
pierce  the  layer  of  fibrocartilage.  On  the  anterior  surface  of  the  petrous  portion 
of  the  temporal  bone  are  seen  the  eminence  caused  by  the  projection  of  the  superior 
semicircular  canal;  in  front  of  and  a  little  lateral  to  this  a  depression  corresponding 
to  the  roof  of  the  tympanic  cavity;  the  groove  leading  to  the  hiatus  of  the  facial 
canal,  for  the  transmission  of  the  greater  superficial  petrosal  nerve  and  the  petrosal 
branch  of  the  middle  meningeal  artery ;  beneath  it,  the  smaller  groove,  for  the  pas- 
sage of  the  lesser  superficial  petrosal  nerve;  and,  near  the  apex  of  the  bone,  the 
depression  for  the  semilunar  ganglion  and  the  orifice  of  the  carotid  canal. 

The  Posterior  Fossa  (fossa  cranii  posterior). — -The  posterior  fossa  is  the  largest 
and  deepest  of  the  three.  It  is  formed  by  the  dorsum  sellse  and  clivus  of  the 
sphenoid,  the  occipital,  the  petrous  and  mastoid  portions  of  the  temporals,  and  the 
mastoid  angles  of  the  parietal  bones;  it  is  crossed  by  the  occipitomastoid  and  the 
parietomastoid  sutures,  and  lodges  the  cerebellum,  pons,  and  medulla  oblongata. 
It  is  separated  from  the  middle  fossa  in  and  near  the  median  line  by  the  dorsum 
sellse  of  the  sphenoid  and  on  either  side  by  the  superior  angle  of  the  petrous  por- 
tion of  the  temporal  bone.  This  angle  gives  attachment  to  the  tentorum  cerebelli, 
is  grooved  for  the  superior  petrosal  sinus,  and  presents  at  its  medial  end  a  notch 
upon  which  the  trigeminal  nerve  rests.  The  fossa  is  limited  behind  by  the  grooves 
for  the  transverse  sinuses.  In  its  center  is  the  foramen  magnum,  on  either  side  of 
which  is  a  rough  tubercle  for  the  attachment  of  the  alar  ligaments;  a  little  above 
this  tubercle  is  the  canal,  which  transmits  the  hypoglossal  nerve  and  a  meningeal 
branch  from  the  ascending  pharyngeal  artery.    In  front  of  the  foramen  magnum 


'  See  footnote,  page  150. 


THE  INTERIOR  OF  THE  SKULL 


193 


the  basilar  portion  of  the  occipital  and  the  posterior  part  of  the  body  of  the  sphenoid 
form  a  grooved  surface  which  supports  the  medulla  oblongata  and  pons;  in  the 
young  skull  these  bones  are  joined  by  a  synchondrosis.  This  grooved  surface  is 
separated  on  either  side  from  the  petrous  portion  of  the  temporal  by  the  petro- 
occipital  fissure,  which  is  occupied  in  the  fresh  state  by  a  plate  of  cartilage;  the 
fissure  is  continuous  behind  with  the  jugular  foramen,  and  its  margins  are  grooved 
for  the  inferior  petrosal  sinus.  The  jugular  foramen  is  situated  between  the  lateral 
part  of  the  occipital  and  the  petrous  part  of  the  temporal.  The  anterior  portion 
of  this  foramen  transmits  the  inferior  petrosal  sinus;  the  posterior  portion,  the 
transverse  sinus  and  some  meningeal  branches  from  the  occipital  and  ascending 
pharyngeal  arteries;  and  the  intermediate  portion,  the  glossopharyngeal,  vagus, 
and  accessory  nerves.  Above  the  jugular  foramen  is  the  internal  acoustic  meatus, 
for  the  facial  and  acoustic  nerves  and  internal  auditory  artery;  behind  and  lateral 


Palatine  bone 
Fig.  194. — Sagittal  section  of  skull. 

this  is  the  slit-like  opening  leading  into  the  aquseductus  vestibuli,  which  lodges 
the  ductus  endolymphaticus;  while  between  these,  and  near  the  superior  angle  of 
the  petrous  portion,  is  a  small  triangular  depression,  the  remains  of  the  fossa  sub- 
arcuata,  which  lodges  a  process  of  the  dura  mater  and  occasionally  transmits  a  small 
ivein.  Behind  the  foramen  magnum  are  the  inferior  occipital  fossae,  which  support 
the  hemispheres  of  the  cerebellum,  separated  from  one  another  by  the  internal 
occipital  crest,  which  serves  for  the  attachment  of  the  falx  cerebelli,  and  lodges 
the  occipital  sinus.  The  posterior  fossae  are  surmounted  by  the  deep  grooves  for 
the  transverse  sinuses.  Each  of  these  channels,  in  its  passage  to  the  jugular  foramen, 
grooves  the  occipital,  the  mastoid  angle  of  the  parietal,  the  mastoid  portion  of  the 
temporal,  and  the  jugular  process  of  the  occipital,  and  ends  at  the  back  part  of 
the  jugular  foramen.  Where  this  sinus  grooves  the  mastoid  portion  of  the  temporal, 
the  orifice  of  the  mastoid  foramen  may  be  seen;  and,  just  previous  to  its  termina- 
I  tion,  the  condyloid  canal  opens  into  it;  neither  opening  is  constant. 
13 


194 


OSTEOLOGY 


The  Nasal  Cavity  {camim.  nasi;  nasal  fossa). — The  nasal  cavities  are  two  irregu 
spaces,  situated  one  on  either  side  of  the  middle  line  of  the  face,  extending  from  the 
base  of  the  cranium  to  the  roof  of  the  mouth,  and  separated  from  each  other  by  a 
thin  vertical  septum.  They  open  on  the  face  through  the  pear-shaped  anterior  nasal 
aperture,  and  their  posterior  openings  or  choanse  communicate,  in  the  fresh 
state,  with  the  nasal  part  of  the  pharynx.  They  are  much  narrower  above  than 
below,  and  in  the  middle  than  at  their  anterior  or  posterior  openings:  their  depth, 
which  is  considerable,  is  greatest  in  the  middle.  They  communicate  with  the 
frontal,  ethmoidal,  sphenoidal,  and  maxillary  sinuses.  Each  cavity  is  bounded 
by  a  roof,  a  floor,  a  medial  and  a  lateral  wall. 

The  roof  (Figs.  195,  196)  is  horizontal  in  its  central  part,  but  slopes  do\An- 
ward  in  front  and  behind;  it  is  formed  in  front  by  the  nasal  bone  and  the  spine 
of  the  frontal;  in  the  middle,  by  the  cribriform  plate  of  the  ethmoid;  and  behind, 


Crest  of  nasal  hones 
Frontal  spine 


Space  for  triangular 
cartilage  of  septum 


Crest  of  palatines 
Crest  of  maxilla 


Fig.  195. — Medial  wall  of  left  nasal  fossa. 


by  the  body  of  the  sphenoid,  the  sphenoidal  concha,  the  ala  of  the  vomer  and  the 
sphenoidal  process  of  the  palatine  bone.  In  the  cribriform  plate  of  the  ethmoid 
are  the  foramina  for  the  olfactory  nerves,  and  on  the  posterior  part  of  the  roof 
is  the  opening  into  the  sphenoidal  sinus. 

The  floor  is  flattened  from  before  backward  and  concave  from  side  to  side. 
It  is  formed  by  the  palatine  process  of  the  maxilla  and  the  horizontal  part  of 
the  palatine  bone;  near  its  anterior  end  is  the  opening  of  the  incisive  canal. 

The  medial  wall  (septum  nasi)  (Fig.  195),  is  frequently  deflected  to  one  or  other 
side,  more  often  to  the  left  than  to  the  right.  It  is  formed,  in  front,  by  the  crest 
of  the  nasal  bones  and  frontal  spine;  in  the  middle,  by  the  perpendicular  plate 
of  the  ethmoid;  behind,  by  the  vomer  and  the  rostrum  of  the  sphenoid;  below, 
by  the  crest  of  the  maxillae  and  palatine  bones.  It  presents,  in  front,  a  large, 
triangular  notch,  which  receives  the  cartilage  of  the  septum;  and  behind,  the 
free  edge  of  the  vomer.     Its  surface  is  marked  by  numerous  furrows  for  vessels 


THE  INTERIOR  OF  THE  SKULL 


195 


and  nerves  and  by  the  grooves  for  the  nasopalatine  nerve,  and  is  traversed  by 
sutures  connecting  the  bones  of  which  it  is  formed. 

The  lateral  wall  (Fig.  196)  is  formed,  in  front,  by  the  frontal  process  of  the 
maxilla  and  by  the  lacrimal  bone;  in  the  middle,  by  the  ethmoid,  maxilla,  and 
inferior  nasal  concha;  behind,  by  the  vertical  plate  of  the  palatine  bone,  and  the 
medial  pterygoid  plate  of  the  sphenoid.  On  this  wall  are  three  irregular  antero- 
posterior passages,  termed  the  superior,  middle,  and  inferior  meatuses  of  the  nose. 
The  superior  meatus,  the  smallest  of  the  three,  occupies  the  middle  third  of  the 
lateral  wall.  It  lies  between  the  superior  and  middle  nasal  conchse;  the  spheno- 
palatine foramen  opens  into  it  behind,  and  the  posterior  ethmoidal  cells  in  front. 
The  sphenoidal  sinus  opens  into  a  recess,  the  sphenoethmoidal  recess,  which  is  placed 
above  and  behind  the  superior  concha.  The  middle  meatus  is  situated  between  the 
middle  and  inferior  conchse,  and  extends  from  the  anterior  to  the  posterior  end  of 


Nasal  bone 
Frontal  spine 


Cribriform  plate  of  ethmoid 
Sphenoid 


Probe  passed  through 
nasolacrimal  canal 

Bristle  passed  through 
infundibulum 


Frontal  prpe.  of  maxilla 

Lacrimal 

Ethmoid 

Uncinate  proc.  of  ethmoid 
Inferior  nasal  concha 
Palatine 

Superior  meatus 
Middle  meatus 
Inferior  meatus 


Anterior  nasal  spine 

Palatine  proc.  of  maxilla 

Ryrizontal  part  of  palatini 

Posterior  nasal  spine 

Incisive  canal- 


Fig.   196. — Roof,  floor,  and  lateral  wall  of  left  nasal  cavity. 


't,he  latter.  The  lateral  wall  of  this  meatus  can  be  satisfactorily  studied  only  after 
t;he  removal  of  the  middle  concha.  On  it  is  a  curved  fissure,  the  hiatus  semilunaris, 
limited  below  by  the  edge  of  the  uncinate  process  of  the  ethmoid  and  above  by 
an  elevation  named  the  bulla  ethmoidaUs;  the  middle  ethmoidal  cells  are  contained 
within  this  bulla  and  open  on  or  near  to  it.  Through  the  hiatus  semilunaris 
i:he  meatus  communicates  with  a  curved  passage  termed  the  infundibulum,  which 
<3ommunicates  in  front  with  the  anterior  ethmoidal  cells  and  in  rather  more  than 
Sfty  per  cent,  of  skulls  is  continued  upward  as  the  frontonasal  duct  into  the  frontal 
air-sinus;  when  this  continuity  fails,  the  frontonasal  duct  opens  directly  into  the 
anterior  part  of  the  meatus.  Below  the  bulla  ethmoidalis  and  hidden  by  the  unci- 
nate process  of  the  ethmoid  is  the  opening  of  the  maxillary  sinus  (ostium  maxillare) ; 
an  accessory  opening  is  frequently  present  above  the  posterior  part  of  the  inferior 
nasal  concha.  The  inferior  meatus,  the  largest  of  the  three,  is  the  space  between 
the  inferior  concha  and  the  floor  of  the  nasal  cavitv.    It  extends  almost  the  entire 


I 


196 


OSTEOLOGY 


length  of  the  lateral  wall  of  the  nose,  is  broader  in  front  than  behind,  and  presents 
anteriorly  the  lower  orifice  of  the  nasolacrimal  canal. 

The  Anterior  Nasal  Aperture  (Fig.  181)  is  a  heart-shaped  or  pyriform  opening, 
whose  long  axis  is  vertical,  and  narrow  end  upward;  in  the  recent  state  it  is  much 
contracted  by  the  lateral  and  alar  cartilages  of  the  nose.  It  is  bounded  above  by 
the  inferior  borders  of  the  nasal  bones;  laterally  by  the  thin,  sharp  margins  which 
separate  the  anterior  from  the  nasal  surfaces  of  the  maxillae;  and  below  by  the  same 
borders,  where  they  curve  medialward  to  join  each  other  at  the  anterior  nasal 
spine. 

The  choanse  are  each  bounded  above  by  the  under  surface  of  the  body  of  the 
sphenoid  and  ala  of  the  vomer;  below,  by  the  posterior  border  of  the  horizontal 
part  of  the  palatine  bone;  laterally,  by  the  medial  pterygoid  plate;  they  are 
separated  from  each  other  by  the  posterior  border  of  the  vomer. 


DIFFERENCES   IN   THE   SKULL   DUE   TO   AGE. 

At  birth  the  skull  is  large  in  proportion  to  the  other  parts  of  the  skeleton,  but  its  facial  portion 
is  small,  and  equals  only  about  one-eighth  of  the  bulk  of  the  cranium  as  compared  with  one-l?aK 
in  the  adult.    The  frontal  and  parietal  eminences  are  prominent,  and  the  greatest  width  of  the 

skull  is  at  the  level  of  the  latter;  on  the  other 
Frontal  fontanel  hand,  the  glabella,  superciliary  arches,  and 

mastoid  processes  are  not  developed.  Ossi- 
fication of  the  skuU  bones  is  not  completed, 
and  many  of  them,  e.  g.,  the  occipital,  temp- 
orals, sphenoid,  frontal,  and  mandible,  consist 
of  more  than  one  piece.  Unossified  mem- 
branous intervals,  termed  Jontanelles,  are  seen 
at  the  angles  of  the  parietal  bones;  these 
fontaneUes  are  six  in  number:  two,  an  ante- 
rior and  a  posterior,  are  situated  in  the  middle 
hne,  and  two,  an  antero-lateral  and  a  postero- 
lateral, on  either  side. 

The  anterior  or  bregmaiic  fontanelle  (Fig. 
197)  is  the  largest,  and  is  placed  at  the  junc- 
tion of  the  sagittal,  coronal,  and  frontal 
sutures;  it  is  lozenge-shaped,  and  measiu-es 
about  4  cm.  in  its  antero-posterior  and  2.5 
cm.  in  its  transverse  diameter.  The  posterior 
fontanelle  is  triangular  in  form  and  is  situated 
at  the  junction  of  the  sagittal  and  lambdoidal 
sutures.  The  lateral  fontaneUes  (Fig,  198)  are 
small,  irregular  in  shape,  and  correspond  re- 
spectively with  the  sphenoidal  and  mastoid 
angles  of  the  parietal  bones.  An  additional 
fontanelle  is  sometimes  seen  in  the  sagittal 
suture  at  the  region  of  the  obehon.  The 
fontaneUes  are  usually  closed  by  the  growth 
and  extension  of  the  bones  which  surround 
them,  but  sometimes  they  are  the  sites  of 
separate  ossific  centers  which  develop  into 
sutural  bones.  The  posterior  and  lateral  fon- 
taneUes are  obliterated  within  a  month  or  two  after  birth,  but  the  anterior  is  not  completely 
closed  until  about  the  middle  of  the  second  year. 

The  smallness  of  the  face  at  birth  is  mainly  accounted  for  by  the  rudimentary  condition  of 
the  maxillae  and  mandible,  the  non-eruption  of  the  teeth,  and  the  small  size  of  the  maxillary  air 
sinuses  and  nasal  cavities.  At  birth  the  nasal  cavities  He  almost  entirely  between  the  orbits,  and 
the  lower  border  of  the  anterior  nasal  aperture  is  only  a  httle  below  the  level  of  the  orbital  floor. 
With  the  eruption  of  the  deciduous  teeth  there  is  an  enlargement  of  the  face  and  jaws,  and  these 
changes  are  still  more  marked  after  the  second  dentition. 

The  skull  grows  rapidly  from  birth  to  the  seventh  year,  by  which  time  the  foramen  magnum 
and  petrous  parts  of  the  temporals  have  reached  their  full  size  and  the  orbital  cavities  are  only 
a  httle  smaller  than  those  of  the  adult.    Growth  is  slow  from  the  seventh  year  until  the  approach 


Occipital  fontanel 


FiQ.  197. — Skull  at  birth,  showing  frontal  and  occipital 
fonticuli. 


CRANIOLOGY 


197 


of  jjuberty,  when  a  second  period  of  activity  occurs :  this  results  in  an  increase  in  all  directions, 
but  it  is  especially  marked  in  the  frontal  and  facial  regions,  where  it  is  associated  with  the  develop- 
ment of  the  air  sinuses. 

Obhteration  of  the  sutures  of  the  vault  of  the  skull  takes  place  as  age  advances.  This  process 
may  commence  between  the  ages  of  thirty  and  forty,  and  is  first  seen  on  the  inner  surface,  and 
some  ten  years  later  on  the  outer  surface  of  the  skull.  The  dates  given  are,  however,  only  approxi- 
mate, as  it  is  impossible  to  state  with  anything  hke  accuracy  the  time  at  which  the  sutures  are 
closed.  Obhteration  usually  occurs  first  in  the  posterior  part  of  the  sagittal  suture,  next  in  the 
coron.  1,  and  then  in  the  lambdoidal. 

In  old  age  the  skull  generally  becomes  thinner  and  Ughter,  but  in  a  small  proportion  of  cases 
it  increases  in  thickness  and  weight,  owing  to  an  hypertrophy  of  the  inner  table.  The  most  strik- 
ing feature  of  the  old  skull  is  the  diminution  in  the  size  of  the  maxillaj  and  mandible  consequent 
on  the  loss  of  the  teeth  and  the  absorption  of  the  alveolar  processes.  This  is  associated  with  a 
marked  reduction  in  the  vertical  measurement  of  the  face  and  with  an  alteration  in  the  angles 
of  the  mandible. 


Frontal  fontanel 


Mastoid  fontanel 

Sphenoidal  fontanel 
Fia.  198. — Skull  at  birth,  showing  sphenoidal  and  mastoid  fonticuli. 


SEXUAL   DIFFERENCES   IN   THE  SKULL. 


^"  Until  the  age  of  puberty  there  is  Httle  difference  between  the  skull  of  the  female  and  that  of 
the  male.  The  skull  of  an  adult  female  is,  as  a  rule,  lighter  and  smaller,  and  its  cranial  capacity 
about  10  per  cent,  less,  than  that  of  the  male.  Its  walls  are  thinner  and  its  muscular  ridges  less 
st:ongly  marked;  the  glabella,  supercihary  arches,  and  mastoid  processes  are  less  prominent, 
aid  the  corresponding  air  sinuses  are  small  or  rudimentary.  The  upper  margin  of  the  orbit  is 
sharp,  the  forehead  vertical,  the  frontal  and  parietal  eminences  prominent,  and  the  vault  some- 
wiat  flattened.  The  contour  of  the  face  is  more  rounded,  the  facial  bones  are  smoother,  and  the 
maxillae  and  mandible  and  their  contained  teeth  smaller.  From  what  has  been  said  it  will  be  seen 
that  more  of  the  infantile  characteristics  are  retained  in  the  skull  of  the  adult  female  than  in  that 
of  the  adult  male.  A  well-marked  male  or  female  skull  can  easily  be  recognized  as  such,  but  in 
some  cases  the  respective  characteristics  are  so  indistinct  that  the  determination  of  the  sex  may 
hv  difficult  or  impossible. 

■  CRANIOLOGY. 

Skulls  vary  in  size  and  shape,  and  the  term  craniology  is  applied  to  the  study  of  these  varia- 
tions. The  capacity  of  the  cranial  cavity  constitutes  a  good  index  of  the  size  of  the  brain  which 
it  contained,  and  is  most  conveniently  arrived  at  by  fiUing  the  cavity  with  shot  and  measuring 
the  contents  in  a  graduated  vessel.  Skulls  may  be  classified  according  to  their  capacities  as 
follows: 

1.  Microcephalic,  with  a  capacity  of  less  than  1350  c.cm. — e.  g.,  those  of  native  Austrahans 
arid  Andaman  Islanders. 

2.  Mesocephalic,  with  a  capacity  of  from  1350  c.cm.  to  1450  c.cm. — e.  g.,  those  of  African 
negroes  and  Chinese. 

3    Megacephalic,  with  a  capacity  of  over  1450  c.cm. — e.  g.,  those  of  Europeans,  Japanese,  and 
ikimos. 


I 


198  OSTEOLOGY 

In  comparing  the  shape  of  one  skull  with  that  of  another  it  is  necessary  to  adopt  some  definite 
position  in  which  the  skulls  should  be  placed  during  the  process  of  examination.  They  should 
be  so  placed  that  a  line  carried  through  the  lower  margin  of  the  orbit  and  upper  margin  oi'  the 
external  acoustic  meatus  is  in  the  horizontal  plane.  The  norma?  of  one  skull  can  then  be  com- 
pared with  those  of  another,  and  the  differences  in  contour  and  surface  form  noted.  Further, 
it  is  necessary  that  the  various  linear  measurements  used  to  determine  the  shape  of  the  tikuU 
should  be  made  between  definite  and  easily  localized  points  on  its  surface.  The  principal  points 
may  be  divided  into  two  groups:    (1)  those  in  the  median  plane,  and  (2)  those  on  either  side  of  it. 

The  Points  in  the  Median  Plane  are  the: 

Mental  Point.    The  most  prominent  point  of  the  chin. 

Alveolar  Point  or  Prosthion.  The  central  point  of  the  anterior  margin  of  the  upper  alveolar 
arch. 

Subnasal  Point.  The  middle  of  the  lower  border  of  the  anterior  nasal  aperture,  at  the  l^ase 
of  the  anterior  nasal  spine. 

Nasion.     The  central  point  of  the  frontonasal  suture. 

Glabella.    The  point  in  the  middle  line  at  the  level  of  the  superciliary  arches. 

Ophryon.  The  point  in  the  middle  line  of  the  forehead  at  the  level  where  the  temporal  lines 
most  nearly  approach  each  other. 

Bregma.    The  meeting  point  of  the  coronal  and  sagittal  sutures. 

Obelion.    A  point  in  the  sagittal  suture  on  a  level  with  the  parietal  foramina. 

Lambda.    The  point  of  junction  of  the  sagittal  and  lambdoidal  sutures. 

Occipital  Point.    The  point  in  the  middle  line  of  the  occipital  bone  farthest  from  the  glabella. 

Inion.    The  external  occipital  protuberance. 

Opisthion.    The  mid-point  of  the  posterior  margin  of  the  foramen  magnum. 

Basion.    The  mid-point  of  the  anterior  margin  of  the  foramen  magnum. 

The  Points  on  Either  Side  of  the  Median  Plane  are  the: 

Gonion.    The  outer  margin  of  the  angle  of  the  mandible. 

Dacryon.  The  point  of  union  of  the  antero-superior  angle  of  the  lacrimal  with  the  frontal 
bone  and  the  frontal  process  of  the  maxilla. 

Stephanion.    The  point  where  the  temporal  line  intersects  the  coronal  suture. 

Pterion.  The  point  where  the  great  wing  of  the  sphenoid  joins  the  sphenoidal  angle  of  the 
parietal. 

Auricular  Point.    The  center  of  the  orifice  of  the  external  acoustic  meatus. 

Asterion.    The  point  of  meeting  of  the  lambdoidal,  mastooccipital,  and  mastoparietal  sutures. 

The  horizontal  circumference  of  the  cranium  is  measured  in  a  plane  passing  through  the  glabella 
(Turner)  or  the  ophryon  (Flower)  in  front,  and  the  occipital  point  behind;  it  averages  about 
50  cm.  in  the  female  and  52.5  cm.  in  the  male. 

The  occipitofrontal  or  longitudinal  arc  is  measm-ed  from  the  nasion  over  the  middle  line  of  the 
vertex  to  the  opisthion:  while  the  basinasal  length  is  the  distance  between  the  basion  and  the 
nasion.  These  two  measurements,  plus  the  antero-posterior  diameter  of  the  foramen  magnum, 
represent  the  vertical  circumference  of  the  cranium. 

The  length  is  measured  from  the  glabella  to  the  occipital  point,  while  the  breadth  or  greatest 

transverse  diameter  is  usually  found  near  the  external  acoustic  meatus.     The  proportion  of 

,  (breadth  X  100)  .  ,    ,  ,   ,.    .    ,  •    ,       ^  ^      ^., 

breadth  to  length  , -r is  termed  the  cephalic  index  or  index  of  breadth. 

The  height  is  usually  measured  from  the  basion  to  the  bregma,  and  the  proportion  of  height 

,    (height  X  100)  .  ,  .    ,       ,    .  ^,  .  ^ 

to  length  ,  — r, constitutes  the  vertical  or  height  index. 

length 

In  studying  the  face  the  principal  points  to  be  noticed  are  the  proportion  of  its  length  and 
breadth,  the  shape  of  the  orbits  and  of  the  anterior  nasal  aperture,  and  the  degree  of  projection 
of  the  jaws. 

The  length  of  the  face  may  be  measured  from  the  ophryon  or  nasion  to  the  chin,  or,  if  the  mandible 
be  wanting,  to  the  alveolar  point;  while  its  width  is  represented  by  the  distance  between  the 
zygomatic  arches.  By  comparing  the  length  with  the  width  of  the  face,  skulls  may  be  divided 
into  two  groups;  dolichofacial  or  leptoprosope  (long  faced)  and  brachy facial  or  chemoprosope  (short 
faced). 

The  orbital  index  signifies  the  proportion  which  the  orbital  height  bears  to  the  orbital  width, 
thus: 

orbital  height  X  100 

orbital  width 
The  nasal  index  expresses  the  proportion  which  the  width  of  the  anterior  nasal  aperture  bears 
to  the  height  of  the  nose,  the  latter  being  measured  from  the  nasion  to  the  lower  margin  of  the 
nasal  aperture,  thus: 

nasal  width  X  100 

nasal  height 


CRANIOLOGY 


199 


The  degree  of  projection  of  the  jaws  is  determined  by  the  gnathic  or  alveolar  index,  which  repre- 
sents the  proportion  between  the  basialveolar  and  basinasal  lengths,  thus: 

basialveolar  length  X  100 
basinasal  length 
The  following  table,  modified  from  that  given  by  Duckworth, i  illustrates  how  these  different 
indices  may  be  utilized  in  the  classification  of  skuUs: 


Index. 

Classification. 

Nomenclature. 

Examples. 

1.  Cephahc 

Below  75 

Between  75  and  80 
Above  80 

Dolichocephalic 

Mesaticephalic 

BrachycephaUc 

Microseme 

Mesoseme 
Megaseme 

Leptorhine 
Mesorhine 
Platyrhine 

Orthognathous 
Mesognathous 
Prognathous 

Kaffirs  and  Native  Australians. 
Europeans  and  Chinese. 
Mongolians  and  Andamans. 

2.  Orbital 

Below  84 

Between  84  and  89 
Above  89 

Tasmanians  and  Native  Austra- 
lians. 
Europeans. 
Chinese  and  Polynesians. 

8.  Nasal 

P 

ft.  Gnathic 

Below  48 

Between  48  and  53 
Above  53 

Below  98 

Between  98  and  103 

Above  103 

Europeans. 

Japanese  and  Chinese. 

Negroes  and  Native  Australians. 

Europeans. 

Chinese  and  Japanese. 

Native  Australians. 

The  chief  function  of  the  skull  is  to  protect  the  brain,  and  therefore  those  portions  of  the  skull 
\7hich  are  most  exposed  to  external  violence  are  thicker  than  those  which  are  shielded  from  injury 
by  overlying  muscles.  Thus,  the  skull-cap  is  thick  and  dense,  whereas  the  temporal  squamae, 
being  protected  by  the  temporales  muscles,  and  the  inferior  occipital  fossa;,  being  shielded  by  the 
muscles  at  the  back  of  the  neck,  are  thin  and  fragile.  Fracture  of  the  skull  is  further  prevented 
by  its  elasticity,  its  rounded  shape,  and  its  construction  of  a  number  of  secondary  elastic  arches, 
each  made  up  of  a  single  bone.  The  manner  in  which  vibrations  are  transmitted  through  the 
bones  of  the  skull  is  also  of  importance  as  regards  its  protective  mechanism,  at  all  events  as  far 
JLS  the  base  is  concerned.  In  the  vault,  the  bones  being  of  a  fairly  equal  thickness  and  density, 
vibrations  are  transmitted  in  a  uniform  manner  in  all  directions,  but  in  the  base,  owing  to  the 
varying  thickness  and  density  of  the  bones,  this  is  not  so;  and  therefore  in  this  situation  there 
are  special  buttresses  which  serve  to  carry  the  vibrations  in  certain  definite  directions.  At  the 
iront  of  the  skull,  on  either  side,  is  the  ridge  which  separates  the  anterior  from  the  middle  fossa 
of  the  base;  and  behind,  the  ridge  or  buttress  which  separates  the  middle  from  the  posterior  fossa; 
and  if  any  violence  is  appHed  to  the  vault,  the  vibrations  would  be  carried  along  these  buttresses 
io  the  sella  turcica,  where  they  meet.  This  part  has  been  termed  the  "center  of  resistance," 
and  here  there  is  a  special  protective  mechanism  to  guard  the  brain.  The  subarachnoid  cavity 
at  the  base  of  the  brain  is  dilated,  and  the  cerebrospinal  fluid  which  fills  it  acts  as  a  water  cushion 
1.0  shield  the  brain  from  injury.  In  hke  manner,  when  violence  is  applied  to  the  base  of  the  skull, 
as  in  falls  upon  the  feet,  the  vibrations  are  carried  backward  through  the  occipital  crest,  and 
i  orward  through  the  basilar  part  of  the  occipital  and  body  of  the  sphenoid  to  the  vault  of  the  skull. 
In  connection  with  the  bones  of  the  face  a  common  malformation  is  cleft  palate.  The  cleft 
usually  starts  posteriorly,  and  its  most  elementary  form  is  a  bifid  uvula;  or  the  cleft  may  extend 
ihrough  the  soft  palate;  or  the  posterior  part  of  the  whole 
i)f  the  hard  palate  may  be  involved,  the  cleft  extending  as 
:'ar  forward  as  the  incisive  foramen.  In  the  severest  forms, 
:he  cleft  extends  through  the  alveolus  and  passes  between 
;he  incisive  or  premaxillary  bone  and  the  rest  of  the  max- 
-11a;  that  is  to  say,  between  the  lateral  incisor  and  canine 
^eeth.  In  some  instances,  the  cleft  runs  between  the  central 
and  lateral  incisor  teeth;  and  this  has  induced  some 
anatomists  to  beheve  that  the  premaxillary  bone  is  devel- 
oped from  two  centers  (Fig.  199)  and  not  from  one,  as  was 
stated  on  p.  163.  The  medial  segment,  bearing  a  central 
incisor,  is  called  an  endognathion;  the  lateral  segment,  bear- 
ing the  lateral  incisor,  is  called  a  mesognathion.  The  cleft 
may  affect  one  or  both  sides;  if  the  latter,  the  central  part  is  frequently  displaced  forward  and  re- 
^ mains  united  to  the  septum  of  the  nose,  the  deficiency  in  the  alveolus  being  complicated  with  a  cleft 

'  Morphology  and  Anthropology,  by  W.  L.  H.  Duckworth.  M.A.,  Cambridge  University  Press. 


Endognathion 
Mesognathion 
Exognathion 


Fig.  199.- 


-The  premaxilla  and  its  sutures. 
(After  Albrecht.) 


200  ^^^^^^^         OSTEOLOGY 


I 


in  the  lip  (hare-lip).  On  examining  a  cleft  palate  in  which  the  alveolus  is  not  implicated,  the  cleft 
will  generally  appear  to  be  in  the  median  line,  but  occasionally  is  unilateral  and  in  some  cases  bilat- 
eral. To  understand  this  it  must  be  borne  in  mind  that  three  processes  are  concerned  in  the  format  ion 
of  the  palate — the  palatine  processes  of  the  two  maxillse,  which  grow  in  horizontally  and  unite 
in  the  middle  line,  and  the  ethmovomerine  process,  which  grows  downward  from  the  base  of 
the  skull  and  frontonasal  process  to  unite  with  the  palatine  processes  in  the  middle  line.  In 
those  cases  where  the  palatine  processes  fail  to  unite  with  each  other  and  with  the  medial  process, 
the  cleft  of  the  palate  is  median;  where  one  palatine  process  unites  with  the  medial  septum,  the 
other  faiUng  to  do  so,  the  cleft  in  the  palate  is  unilateral.  In  some  cases  where  the  palatine  pro- 
cesses fail  to  meet  in  the  middle,  the  ethmovomerine  process  grows  downward  between  them  and 
thus  produces  a  bilateral  cleft.  Occasionally  there  may  be  a  hole  in  the  middle  line  of  the  hard 
palate,  the  anterior  part  of  the  hard  and  the  soft  palate  being  perfect;  this  is  rare,  because,  as 
a  rule,  the  union  of  the  various  processes  progresses  from  before  backward,  and  therefore  the 
posterior  part  of  the  palate  is  more  frequently  defective  than  the  anterior. 

THE   EXTREMITIES. 

The  bones  by  which  the  upper  and  lower  limbs  are  attached  to  the  trunk  con- 
stitute respectively  the  shoulder  and  pelvic  girdles.  The  shoulder  girdle  or  girdle 
of  the  superior  extremity  is  formed  by  the  scapulae  and  clavicles,  and  is  imperfect 
in  front  and  behind.  In  front,  however,  it  is  completed  by  the  upper  end  of  the 
sternum,  with  which  the  medial  ends  of  the  clavicles  articulate.  Behind,  it  is 
widely  imperfect,  the  scapulae  being  connected  to  the  trunk  by  muscles  only. 
The  pelvic  girdle  or  girdle  of  the  inferior  extremity  is  formed  by  the  hip  bones, 
which  articulate  with  each  other  in  front,  at  the  symphysis  pubis.  It  is  imperfect 
behind,  but  the  gap  is  filled  in  by  the  upper  part  of  the  sacrum.  The  pelvic  girdle, 
with  the  sacrum,  is  a  complete  ring,  massive  and  comparatively  rigid,  in  marked 
contrast  to  the  lightness  and  mobility  of  the  shoulder  girdle. 

THE  BONES  OF  THE  UPPER  EXTREMITY  (OSS A  EXTREMITATIS  SUPERIORIS). 

The  Clavicle  (Clavicula;  Collar  Bone). 

The  clavicle  (Figs.  200,  201)  forms  the  anterior  portion  of  the  shoulder  girdle. 
It  is  a  long  bone,  curved  somewhat  like  the  italic  letter/,  and  placed  nearly  horizon- 
tally at  the  upper  and  anterior  part  of  the  thorax,  immediately  above  the  first 
rib.  It  articulates  medially  with  the  manubrium  sterni,  and  laterally  with  the 
acromion  of  the  scapula.^  It  presents  a  double  curvature,  the  convexity  being 
directed  forward  at  the  sternal  end,  and  the  concavity  at  the  scapular  end.  Its 
lateral  third  is  flattened  from  above  downward,  while  its  medial  two-thirds  is  of 
a  rounded  or  prismatic  form. 

Lateral  Third. — The  lateral  third  has  two  surfaces,  an  upper  and  a  lower;  and 
two  borders,  an  anterior  and  a  posterior. 

Surface.^ — The  upper  surface  is  flat,  rough,  and  marked  by  impressions  for  the 
attachments  of  the  Deltoideus  in  front,  and  the  Trapezius  behind;  between  these 
impressions  a  small  portion  of  the  bone  is  subcutaneous.  The  under  surface  is 
flat.  At  its  posterior  border,  near  the  point  where  the  prismatic  joins  with  the 
flattened  portion,  is  a  rough  eminence,  the  coracoid  tuberosity  {conoid  tubercle)', 
this,  in  the  natural  position  of  the  bone,  surmounts  the  coracoid  process  of  the 
scapula,  and  gives  attachment  to  the  conoid  ligament.  From  this  tuberosity  an 
oblique  ridge,  the  oblique  or  trapezoid  ridge,  runs  forward  and  lateralward,  and 
afford  attachment  to  the  trapezoid  ligament. 

'  The  clavicle  acts  especially  as  a  fulcrum  to  enable  the  muscles  to  give  lateral  motion  to  the  arm.  It  is  accordingly 
absent  in  those  animals  whose  fore-limbs  are  used  only  for  progression,  but  is  present  for  the  most  part  in  animals 
whose  anterior  extremities  are  clawed  and  used  for  prehension,  though  in  some  of  them — as,  for  instance,  in  a  large 
number  of  the  carnivora — it  is  merely  a  rudimentary  bone  suspended  among  the  muscles,  and  not  articulating  with 
(either  the  scapula  or  sternum. 


THE 


[VI CLE 


Borders. — The  anterior  border  is  concave,  thin,  and  rough,  and  gives  attachment 
to  the  Deltoideus.  The  posterior  border  is  convex,  rough,  thicker  than  the  anterior, 
and  gives  attachment  to  the  Trapezius. 

Medial  Two-thirds. — The  medial  two-thirds  constitute  the  prismatic  portion 
of  the  bone,  which  is  curved  so  as  to  be  convex  in  front,  concave  behind,  and  is 
marked  by  three  borders,  separating  three  surfaces. 

Borders.^ — The  anterior  border  is  continuous  with  the  anterior  margin  of  the  flat 
portion.  Its  lateral  part  is  smooth,  and  corresponds  to  the  interval  between  the 
attachments  of  the  Pectoralis  major  and  Deltoideus;  its  medial  part  forms  the 
lower  boundary  of  an  elliptical  surface  for  the  attachment  of  the  clavicular  portion 


Sternal  extremity 


Acromial  extremity 


Fig.  200. — Left  clavicle.      Superior  surface. 

of  the  Pectoralis  major,  and  approaches  the  posterior  border  of  the  bone.  The 
superior  border  is  continuous  with  the  posterior  margin  of  the  flat  portion,  and 
separates  the  anterior  from  the  posterior  surface.  Smooth  and  rounded  laterally, 
it  becomes  rough  toward  the  medial  third  for  the  attachment  of  the  Sternocleido- 
raastoideus,  and  ends  at  the  upper  angle  of  the  sternal  extremity.  The  posterior 
or  subclavian  border  separates  the  posterior  from  the  inferior  surface,  and  extends 
from  the  coracoid  tuberosity  to  the  costal  tuberosity;  it  forms  the  posterior  boun- 
dary of  the  groove  for  the  Subclavius,  and  gives  attachment  to  a  layer  of  cervical 
lascia  which  envelops  the  Omohyoideus. 


Articular  capsule 


Inferior  surface. 

Surfaces. — The  anterior  surface  is  included  between  the  superior  and  anterior 
borders.  Its  lateral  part  looks  upward,  and  is  continuous  with  the  superior  sur- 
face of  the  flattened  portion;  it  is  smooth,  convex,  and  nearly  subcutaneous,  being 
covered  only  by  the  Platysma.  Medially  it  is  divided  by  a  narrow  subcutaneous 
area  into  two  parts!  a  lower,  elliptical  in  form,  and  directed  forward,  for  the 
attachment  of  the  Pectoralis  major;  and  an  upper  for  the  attachment  of  the 
Sternocleidomastoideus.  The  posterior  or  cervical  surface  is  smooth,  and  looks 
backward  toward  the  root  of  the  neck.  It  is  limited,  above,  by  the  superior 
border;  below,  by  the  subclavian  border;  medially,  by  the  margin  of  the  sternal 
extremity ;  and  laterally,  by  the  coracoid  tuberosity.    It  is  concave  medio-laterally, 


I 


202  OSTEOLOGY 


■I 


and  is  in  relation,  by  its  lower  part,  with  the  transverse  scapular  vessels.  This 
surface,  at  the  junction  of  the  curves  of  the  bone,  is  also  in  relation  with  the  brachial 
plexus  of  nerves  and  the  subclavian  vessels.  It  gives  attachment,  near  the  sternal 
extremity,  to  part  of  the  Sternohyoideus;  and  presents,  near  the  middle,  an  obliciue 
foramen  directed  lateralward,  which  transmits  the  chief  nutrient  artery  of  the 
bone.  Sometimes  there  are  two  foramina  on  the  posterior  surface,  or  one  on  the 
posterior  and  another  on  the  inferior  surface.  The  inferior  or  subclavian  surface  is 
bounded,  in  front,  by  the  anterior  border;  behind,  by  the  subclavian  border. 
It  is  narrowed  medially,  but  gradually  increases  in  width  laterally,  and  is  contin- 
uous with  the  under  surface  of  the  flat  portion.  On  its  medial  part  is  a  broad 
rough  surface,  the  costal  tuberosity  {rhomboid  impression),  rather  more  than  2  cm. 
in  length,  for  the  attachment  of  the  costoclavicular  ligament.  The  rest  of  this 
surface  is  occupied  by  a  groove,  which  gives  attachment  to  the  Subclavius;  the 
coracoclavicular  fascia,  which  splits  to  enclose  the  muscle,  is  attached  to  the  margins 
of  the  groove.  Not  infrequently  this  groove  is  subdivided  longitudinally  by  a 
line  which  gives  attachment  to  the  intermuscular  septum  of  the  Subclavius. 

The  Sternal  Extremity  {extremitas  sternalis;  internal  extremity). — The  sternal 
extremity  of  the  clavicle  is  triangular  in  form,  directed  medialward,  and  a  little 
downward  and  forward;  it  presents  an  articular  facet,  concave  from  before  back- 
ward, convex  from  above  downward,  which  articulates  with  the  manubrium  sterni 
through  the  intervention  of  an  articular  disk.  The  lower  part  of  the  facet  is  con- 
tinued on  to  the  inferior  surface  of  the  bone  as  a  small  semi-oval  area  for  articula- 
tion with  the  cartilage  of  the  first  rib.  The  circumference  of  the  articular  surface 
is  rough,  for  the  attachment  of  numerous  ligaments;  the  upper  angle  gives  attach- 
ment to  the  articular  disk. 

The  Acromial  Extremity  (extremitas  acromialis;  outer  extremity). — The  acromial 
extremity  presents  a  small,  flattened,  oval  surface  directed  obliquely  downward, 
for  articulation  with  the  acromion  of  the  scapula.  The  circumference  of  the 
articular  facet  is  rough,  especially  above,  for  the  attachment  of  the  acromio- 
clavicular ligaments. 

In  the  female,  the  clavicle  is  generally  shorter,  thinner,  less  curved,  and  smoother  than  in  the 
male.  In  those  persons  who  perform  considerable  manual  labor  it  becomes  thicker  and  more 
curved,  and  its  ridges  for  muscular  attachment  are  prominently  marked. 

Structure. — The  clavicle  consists  of  cancellous  tissue,  enveloped  by  a  compact  layer,  which 
is  much  thicker  in  the  intermediate  part  than  at  the  extremities  of  the  bone. 

Ossification. — The  clavicle  begins  to  ossify  before  any  other  bone  in  the  body;  it  is  ossified 
from  three  centers — viz.,  two  primary  centers,  a  medial  and  a  lateral,  for  the  body,i  which  appear 
during  the  fifth  or  sixth  week  of  fetal  Ufe;  and  a  secondary  center  for  the  sternal  end,  which 
appears  about  the  eighteenth  or  twentieth  year,  and  imites  with  the  rest  of  the  bone  about  the 
twenty-fifth  year. 

The  Scapula  (Shoulder  Blade). 

The  scapula  forms  the  posterior  part  of  the  shoulder  girdle.  It  is  a  flat,  trian- 
gular bone,  with  two  surfaces,  three  borders,  and  three  angles. 

Surfaces. — The  costal  or  ventral  surface  (Fig.  202)  presents  a  broad  concavity, 
the  subscapular  fossa.  The  medial  two-thirds  of  the  fossa  are  marked  by  several 
oblique  ridges,  which  run  lateralward  and  upward.  The  ridges  give  attachment 
to  the  tendinous  insertions,  and  the  surfaces  between  them  to  the  fleshy  fibers, 
of  the  Subscapularis.  The  lateral  third  of  the  fossa  is  smooth  and  covered  by  the 
fibers  of  this  muscle.  The  fossa  is  separated  from  the  vertebral  border  by  smooth 
triangular'  areas  at  the  medial  and  inferior  angles,  and  in  the  interval  between 
these  by  a  narrow  ridge  which  is  often  deficient.  These  triangular  areas  and  the 
intervening  ridge  afford  attachment  to  the  Serratus  anterior.  At  the  upper  part 
of  the  fossa  is  a  transverse  depression,  where  the  bone  appears  to  be  bent  on  itself 

1  Mall,  American  Journal  of  Anatomy,  vol.  v;  Fawcett,  Journal  of  Anatomy  and  Physiology,  vol.  xlvii. 


* 


I 


THE  SCAPULA  flHJHK  ^^^ 

along  a  line  at  right  angles  to  and  passing  through  the  center  of  the  glenoid  cavity, 
forming  a  considerable  angle,  called  the  subscapular  angle;  this  gives  greater 
strength  to  the  body  of  the  bone  by  its  arched  form,  while  the  summit  of  the 
arch  serves  to  support  the  spine  and  acromion. 

The  dorsal  surface  (Fig.  203)  is  arched  from  above  downward,  and  is  subdivided 
into  two  unequal  parts  by  the  spine;  the  portion  above  the  spine  is  called  the 
supraspinatous  fossa,  and  that  below  it  the  infraspinatous  fossa. 

The  supraspinatous  fossa,  the  smaller  of  the  two,  is  concave,  smooth,  and  broader 
at  its  vertebral  than  at  its  humeral  end;  its  medial  two-thirds  give  origin  to  the 
Supraspinatus. 

The  infraspinatous  fossa  is  much  larger  than  the  preceding;  toward  its  vertebral 
margin  a  shallow  concavity  is  seen  at  its  upper  part ;  its  center  presents  a  promi- 
nent convexity,  while  near  the  axillary  border  is  a  deep  groove  which  runs  from 
the  upper  toward  the  lower  part.  The  medial  two-thirds  of  the  fossa  give  origin 
to  the  Infraspinatus;  the  lateral  third  is  covered  by  this  muscle. 

The  dorsal  surface  is  marked  near  the  axillary  border  by  an  elevated  ridge, 
which  runs  from  the  lower  part  of  the  glenoid  cavity,  downward  and  backward 
to  the  vertebral  border,  about  2.5  cm.  above  the  inferior  angle.  The  ridge  serves 
for  the  attachment  of  a  fibrous  septum,  which  separates  the  Infraspinatus  from 
the  Teres  major  and  Teres  minor.  The  surface  between  the  ridge  and  the  axillary 
border  is  narrow  in  the  upper  two-thirds  of  its  extent,  and  is  crossed  near  its 
center  by  a  groove  for  the  passage  of  the  scapular  circumflex  vessels;  it  affords 
attachment  to  the  Teres  minor.  Its  lower  third  presents  a  broader,  somewhat 
triangular  surface,  which  gives  origin  to  the  Teres  major,  and  over  which  the  Latis- 
simus  dorsi  glides;  frequently  the  latter  muscle  takes  origin  by  a  few  fibers  from 
this  part.  The  broad  and  narrow  portions  above  alluded  to  are  separated  by  an 
oblique  line,  which  runs  from  the  axillary  border,  downward  and  backward,  to 
meet  the  elevated  ridge:  to  it  is  attached  a  fibrous  septum  which  separates  the 
Teres  muscles  from  each  other. 

The  Spine  (spina  scapuloB). — The  spine  is  a  prominent  plate  of  bone,  which 
crosses  obliquely  the  medial  four-fifths  of  the  dorsal  surface  of  the  scapula  at  its 
upper  part,  and  separates  the  supra-  from  the  infraspinatous  fossa.  It  begins 
at  the  vertical  border  by  a  smooth,  triangular  area  over  which  the  tendon  of  inser- 
tion of  the  lower  part  of  the  Trapezius  glides,  and,  gradually  becoming  more  ele- 
vated, ends  in  the  acromion,  which  overhangs  the  shoulder-joint.  The  spine  is 
triangular,  and  flattened  from  above  downward,  its  apex  being  directed  toward 
the  vertebral  border.  It  presents  two  surfaces  and  three  borders.  Its  superior 
surface  is  concave;  it  assits  in  forming  the  supraspinatous  fossa,  and  gives  origin 
to  part  of  the  Supraspinatus.  Its  inferior  surface  forms  part  of  the  infraspinatous 
fossa,  gives  origin  to  a  portion  of  the  Infraspinatus,  and  presents  near  its  center 
the  orifice  of  a  nutrient  canal.  Of  the  three  borders,  the  anterior  is  attached  to  the 
dorsal  surface  of  the  bone;  the  posterior,  or  crest  of  the  spine,  is  broad,  and  presents 
two  lips  and  an  intervening  rough  interval.  The  Trapezius  is  attached  to  the  supe- 
rior lip,  and  a  rough  tubercle  is  generally  seen  on  that  portion  of  the  spine  which 
receives  the  tendon  of  insertion  of  the  lower  part  of  this  muscle.  The  Deltoideus 
is  attached  to  the  whole  length  of  the  inferior  lip.  The  interval  between  the  lips 
is  subcutaneous  and  partly  covered  by  the  tendinous  fibers  of  these  muscles.  The 
lateral  border,  or  base,  the  shortest  of  the  three,  is  slightly  concave;  its  edge,  thick 
and  round,  is  continuous  above  with  the  under  surface  of  the  acromion,  below 
with  the  neck  of  the  scapula.  It  forms  the  medial  boundary  of  the  great  scapular 
notch,  which  serves  to  connect  the  supra-  and  infraspinatous  fossae. 

The  Acromion. — The  acromion  forms  the  summit  of  the  shoulder,  and  is  a  large, 
somewhat  triangular  or  oblong  process,  flattened  from  behind  forward,  projecting 
at  first  lateralward,  and  then  curving  forward  and  upward,  so  as  to  overhang  the 


204 


OSTEOLOGY 


glenoid  cavity.  Its  superior  surface,  directed  upward,  backward,  and  lateral war( 
is  convex,  rough,  and  gives  attachment  to  some  fibers  of  the  Deltoideus,  and  in  the 
rest  of  its  extent  is  subcutaneous.  Its  inferior  surface  is  smooth  and  conca\'e. 
Its  lateral  border  is  thick  and  irregular,  and  presents  three  or  four  tubercles  for  the 
tendinous  origins  of  the  Deltoideus.  Its  medial  border,  shorter  than  the  lateral, 
is  concave,  gives  attachment  to  a  portion  of  the  Trapezius,  and  presents  about 
its  center  a  small,  oval  surface  for  articulation  with  the  acromial  end  of  the  clavicle. 


Articular  capsule 


Coracoacromial  _L_li 

ligament 


rticular 
capsule 


Fig.  202. — Left  scapula.     Costal  surface. 


Its  apex,  which  corresponds  to  the  point  of  meeting  of  these  two  borders  in  front, 
is  thin,  and  has  attached  to  it  the  coracoacromial  ligament. 

Borders. — Of  the  three  borders  of  the  scapula,  the  superior  is  the  shortest  and 
thinnest;  it  is  concave,  and  extends  from  the  medial  angle  to  the  base  of  the  cora- 
coid  process.    At  its  lateral  part  is  a  deep,  semicircular  notch,  the  scapular  notch, 


THE  SCAPULA 


205 


formed  partly  by  the  base  of  the  coraeoid  process.  This  notch  is  converted  into 
a  foramen  by  the  superior  transverse  Hgament,  and  serves  for  the"  passage  of  the 
suprascapular  nerve;  sometimes  the  ligament  is  ossified.  The  adjacent  part  of 
the  superior  border  affords  attachment  to  the  Omohyoideus.    The  axillary  border 


Coracohumeral 
ligament 


Coraco-acromial  ligament 


^«Co 


Trapezoid  ligament 


Conoid  ligament 


FiQ.  203. — Left  scapula.     Dorsal  surface. 


I 


is  the  thickest  of  the  three.  It  begins  above  at  the  lower  margin  of  the  glenoid 
:avity,  and  inclines  obliquely  downward  and  backward  to  the  inferior  angle. 
Immediately  below  the  glenoid  cavity  is  a  rough  impression,  the  infraglenoid 
tuberosity,  about  2.5  cm.  in  length,  which  gives  origin  to  the  long  head  of  the  Tri- 
ceps brachii;  in  front  of  this  is  a  longitudinal  groove,  which  extends  as  far  as  the 


206 


OSTEOLOGY 


lower  third  of  this  border,. and  affords  origin  to  part  of  the  Subscapularis.  The 
inferior  third  is  thin  and  sharp,  and  serves  for  the  attachment  of  a  few  fibers  of 
the  Teres  major  behind,  and  of  the  Subscapularis  in  front.  The  vertebral  border 
is  the  longest  of  the  three,  and  extends  from  the  medial  to  the  inferior  angle.  It 
is  arched,  intermediate  in  thickness  between  the  superior  and  the  axillary  borders, 
and  the  portion  of  it  above  the  spine  forms  an  obtuse  angle  with  the  part  below. 
This  border  presents  an  anterior  and  a  posterior  lip,  and  an  intermediate  narrow 
area.  The  anterior  lip  affords  attachment  to  the  Serratus  anterior;  the  posterior 
lip,  to  the  Supraspinatus  above  the  spine,  the   Infraspinatus  below;    the  area 


Fig.  204. — Posterior  view  of  the  thorax  and  shoulder  girdle.     (Morris.) 


between  the  two  lips,  to  the  Levator  scapulae  above  the  triangular  surface  at  the 
commencement  of  the  spine,  to  the  Rhomboideus  minor  on  the  edge  of  that  surface, 
and  to  the  Rhomboideus  major  below  it;  this  last  is  attached  by  means  of  a  fibrous 
arch,  connected  above  to  the  lower  part  of  the  triangular  surface  at  the  base  of 
the  spine,  and  below  to  the  lower  part  of  the  border. 

Angles. — Of  the  three  angles,  the  medial,  formed  by  the  junction  of  the  superior 
and  vertebral  borders,  is  thin,  smooth,  rounded,  inclined  somewhat  lateralward, 
and  gives  attachment  to  a  few  fibers  of  the  Levator  scapulae.  The  inferior  angle, 
thick  and  rough,  is  formed  by  the  union  of  the  vertebral  and  axillary  borders; 
its  dorsal  surface  affords  attachment  to  the  Teres  major  and  frequently  to  a  few 


THE  SCAPULA 


207 


Coracoid 
process 


Acromion 


Infraglenoid  tubercle 


fibers  of  the  Latissimus  dorsi.  The  lateral  angle  is  the  thickest  part  of  the  bone, 
and  is  sometimes  called  the  head  of  the  scapula.  On  it  is  a  shallow  pyriform, 
articular  surface,  the  glenoid  cavity,  which  is  directed  lateralward  and  forward 
and  articulates  with  the  head  of  the  humerus;  it  is  broader  below  than  above 
and  its  vertical  diameter  is  the  longest.  The  surface  is  covered  with  cartilage 
in  the  fresh  state;  and  its  margins,  slightly  raised,  give  attachment  to  a  fibro- 
cartilaginous structure,  the  glenoidal  labrum,  which  deepens  the  cavity.  At  its 
apex  is   a    slight  elevation,  the 

SUpraglenoid    tuberosity,   to    which  Supragleru>id  tubercJe 

the  long  head  of  the  Biceps 
brachii  is  attached.  The  neck 
of  the  scapula  is  the  slightly 
constricted  portion  which  sur- 
rounds the  head;  it  is  more  dis- 
tinct below  and  behind  than 
above  and  in  front. 

The  Coracoid  Process  (processus 
coracoideus) .  —  The  coracoid  pro- 
cess is  a  thick  curved  process  at- 
tached by  a  broad  base  to  the 
u])per  part  of  the  neck  of  the 
scapula;  it  runs  at  first  upward 
and  medialward;  then,  becoming 
smaller,  it  changes  its  direction, 
and  projects  forward  and  lateral- 
ward.  The  ascending  portion, 
flattened  from  before  backward, 
presents  in  front  a  smooth  con- 
cave surface,  across  which  the 
S  ibscapularis  passes.  The  hori- 
zontal portion  is  flattened  from 
al)ove  downward;  its  upper  sur- 
face is  convex  and  irregular,  and 
g  ves  attachment  to  the  Pector- 
ais  minor;  its  under  surface  is 
smooth;  its  medial  and  lateral 
borders  are  rough;  the  former 
g  ves  attachment  to  the  Pectoralis 
n  inor  and  the  latter  to  the  cora- 
coacromial  ligament;  the  apex  is 
embraced  by  the  conjoined  tendon 
o '  origin  of  the  Coracobrachialis 
aid  short  head  of  the  Biceps 
brachii  and  gives  attachment  to 
the  coracoclavicular  fascia.  On 
the  medial  part  of  the  root  of  the 
coracoid  process  is  a  rough  im- 
pression for  the  attachment  of 
the  conoid  ligament;  and  running  from  it  obliquely  forward  and  lateralward, 
on  to  the  upper  surface  of  the  horizontal  portion,  is  an  elevated  ridge  for  the 
ai:tachment  of  the  trapezoid  ligament. 


Fig.  205. 


-Inferior  angle 
-Left  scapula.     Lateral  view. 


I 


Structure.— The  head,  processes,  and  the  thickened  parts  of  the  bone,  contain  cancellous 
ssue;  the  rest  consists  of  a  thin  layer  of  compact  tissue.    The  central  part  of  the  supraspinatous 


208 


OSTEOLOGY 


fossa  and  the  upper  part  of  the  infraspinatous  fossa,  but  especially  the  former,  are  usually  so  thin 
as  to  be  semitransparent;  occasionally  the  bone  is  found  wanting  in  this  situation,  and  the  adjacent 
muscles  are  separated  only  by  fibrous  tissue. 

Ossification  (Fig.  206). — The  scapula  is  ossified  from  seven  or  more  centers:  one  for  the  body, 
two  for  the  coracoid  process,  two  for  the  acromion,  one  for  the  vertebral  border,  and  one  for  the 
inferior  angle. 

Ossification  of  the  body  begins  about  the  second  month  of  fetal  life,  by  the  formation  ol'  an 
irregular  quadrilateral  plate  of  bone,  immediately  behind  the  glenoid  cavity.  This  plate  exte^nds 
so  as  to  form  the  chief  part  of  the  bone,  the  spine  growing  up  from  its  dorsal  surface  about  the 
third  month.  At  birth,  a  large  part  of  the  scapula  is  osseous,  but  the  glenoid  cavity,  the  coraooid 
process,  the  acromion,  the  vertebral  border,  and  the  inferior  angle  are  cartilaginous.  From  the 
fifteenth  to  the  eighteenth  month  after  birth,  ossification  takes  place  in  the  middle  of  the  coraooid 
process,  which  as  a  rule  becomes  joined  with  the  rest  of  the  bone  about  the  fifteenth  year.  Between 
the  fourteenth  and  twentieth  years,  ossification  of  the  remaining  parts  takes  place  in  quick  succes- 
sion, and  usually  in  the  following  order;  first,  in  the  root  of  the  coracoid  process,  in  the  form  of  a 
broad  scale;  secondly,  near  the  base  of  the  acromion;  thirdly,  in  the  inferior  angle  and  contiguous 
part  of  the  vertebral  border;  fourthly,  near  the  extremity  of  the  acromion;  fifthly,  in  the  vertebral 
border.  The  base  of  the  acromion  is  formed  by  an  extension  from  the  spine;  the  two  separate 
nuclei  of  the  acromion  unite,  and  then  join  with  the  extension  from  the  spine.    The  upper  third 


..<^5 


Fia.  206. — Plan  of  ossification  of  the  scapula.     From  seven  centers. 


of  the  glenoid  cavity  is  ossified  from  a  separate  center  (subcoracoid),  which  makes  its  appear- 
ance between  the  tenth  and  eleventh  years  and  joins  between  the  sixteenth  and  the  eighteenth. 
Further,  an  epiphysial  plate  appears  for  the  lower  part  of  the  glenoid  cavity,  while  the  tip  of  the 
coracoid  process  frequently  presents  a  separate  nucleus.  These  various  epiphyses  are  joined 
to  the  bone  by  the  twenty-fifth  year.  Failure  of  bony  union  between  the  acromion  and  spine 
sometimes  occurs,  the  junction  being  effected  by  fibrous  tissue,  or  by  an  imperfect  articulation; 
in  some  cases  of  supposed  fracture  of  the  acromion  with  ligamentous  union,  it  is  probable  that 
the  detached  segment  was  never  united  to  the  rest  of  the  bone. 


THE  HUMERUS  ^^^^^K  209 


The  Humerus  (Arm  Bone). 

The  humerus  (Figs.  207,  208)  is  the  longest  and  largest  bone  of  the  upper 
extremity;  it  is  divisible  into  a  body  and  two  extremities. 

Upper  Extremity. — The  upper  extremity  consists  of  a  large  rounded  head  joined 
to  the  body  by  a  constricted  portion  called  the  neck,  and  two  eminences,  the  greater 
and  lesser  tubercles. 

The  Head  (caput  humeri). — The  head,  nearly  hemispherical  in  form,^  is  directed 
upward,  medialward,  and  a  little  backward,  and  articulates  with  the  glenoid  cavity 
of  the  scapula.  The  circumference  of  its  articular  surface  is  slightly  constricted 
and  is  termed  the  anatomical  neck,  in  contradistinction  to  a  constriction  below  the 
tubercles  called  the  surgical  neck  which  is  frequently  the  seat  of  fracture.  Fracture 
of  the  anatomical  neck  rarely  occurs. 

The  Anatomical  Neck  (collum  anatomicum)  is  obliquely  directed,  forming  an 
obtuse  angle  with  the  body.  It  is  best  marked  in  the  low^er  half  of  its  circum- 
ference; in  the  upper  half  it  is  represented  by  a  narrow  groove  separating  the  head 
from  the  tubercles.  It  affords  attachment  to  the  articular  capsule  of  the  shoulder- 
joint,  and  is  perforated  by  numerous  vascular  foramina. 

The  Greater  Tubercle  (tuberculum  majus;  greater  tuberosity). — The  greater 
tubercle  is  situated  lateral  to  the  head  and  lesser  tubercle.  Its  upper  surface  is 
rounded  and  marked  by  three  flat  impressions :  the  highest  of  these  gives  insertion 
to  the  Supraspinatus;  the  middle  to  the  Infraspinatus;  the  lowest  one,  and  the 
body  of  the  bone  for  about  2.5  cm.  below  it,  to  the  Teres  minor.  The  lateral 
surface  of  the  greater  tubercle  is  convex,  rough,  and  continuous  with  the  lateral 
surface  of  the  body. 

The  Lesser  Tubercle  {tuberculum  minus;  lesser  tuberosity). — The  lesser  tubercle, 
although  smaller,  is  more  prominent  than  the  greater:  it  is  situated  in  front,  and 
hi  directed  medialward  and  forward.  Above  and  in  front  it  presents  an  impression 
for  the  insertion  of  the  tendon  of  the  Subscapularis. 

The  tubercles  are  separated  from  each  other  by  a  deep  groove,  the  intertubercular 
groove  (bicipital  groove),  which  lodges  the  long  tendon  of  the  Biceps  brachii  and 
transmits  a  branch  of  the  anterior  humeral  circumflex  artery  to  the  shoulder-joint. 
It  runs  obliquely  downward,  and  ends  near  the  junction  of  the  upper  with  the 
middle  third  of  the  bone.  In  the  fresh  state  its  upper  part  is  covered  with  a 
thin  layer  of  cartilage,  lined  by  a  prolongation  of  the  synovial  membrane  of  the 
shoulder-joint;  its  lower  portion  gives  insertion  to  the  tendon  of  the  Latissimus 
(lorsi.  It  is  deep  and  narrow  above,  and  becomes  shallow  and  a  little  broader 
J  is  it  descends.  Its  lips  are  called,  respectively,  the  crests  of  the  greater  and  lesser 
tubercles  (bicipital  ridges),  and  form  the  upper  parts  of  the  anterior  and  medial 
borders  of  the  body  of  the  bone. 

The  Body  or  Shaft  (corpus  humeri). — The  body  is  almost  cylindrical  in  the  upper 
lialf  of  its  extent,  prismatic  and  flattened  below,  and  has  three  borders  and  three 
surfaces. 

Borders. — The  anterior  border  runs  from  the  front  of  the  greater  tubercle  above 
t;o  the  coronoid  fossa  below,  separating  the  antero-medial  from  the  antero-lateral 
surface.  Its  upper  partis  a  prominent  ridge,  the  crest  of  the  greater  tubercle; 
it  serves  for  the  insertion  of  the  tendon  of  the  Pectoralis  major.  About  its  center 
it  forms  the  anterior  boundary  of  the  deltoid  tuberosity;  below,  it  is  smooth  and 
rounded,  affording  attachment  to  the  Brachialis. 

The  lateral  border  runs  from  the  back  part  of  the  greater   tubercle  to  the 

'  Though  the  head  is  nearly  hemispherical  in  form,  its  margin,  as  Humphry  has  shown,  is  by  no  means  a  true  circle. 
Its  greatest  diameter  is,  from  the  top  of  the  intertubercular  groove  in  a  direction  downward,  medialward,  and  back- 
ward. Hence  it  follows  that  the  greatest  elevation  of  the  arm  can  be  obtained  by  rolling  the  articular  surface  in  this 
direction — that  is  to  say,  obliquely  upward,  lateralward,  and  forward. 

14 


■ 


210 


OSTEOLOGY 
Articular  capavle 


Surqi4HjU  Neek- 


Brachioradialis 


Common  origin  of" 
Flexor  carpi  radialis 
Palmaris  longua  "'^ 

Flexor  digitorum  svblimis 
Flexor  carpi  vlnaria 


Capit- 
ulum 


-v^ 


Extensor  carpi  radialis 
1  longtis 

,  Articular  capsule 

■  Common  origin  of 

Extensor  carpi  rad.  brev. 
,,    digitorum  convmunia 
,,     digiti  quinti  prop. 
, ,    carpi  idnaris 

Supinator 


Fig.   207. — Left  humerus.     Anterior  view. 


THE  HUMERUS 


1 

I 


I 


lateral  epicondyle,  and  separates  the  antero- 
lateral from  the  posterior  surface.  Its  upper 
half  is  rounded  and  indistinctly  marked,  serv- 
ing for  the  attachment  of  the  lower  part  of  the 
insertion  of  the  Teres  minor,  and  below  this 
giving  origin  to  the  lateral  head  of  the  Triceps 
brachii;  its  center  is  traversed  by  a  broad  but 
shallow  oblique  depression,  the  radial  sulcus 
(musculospiral  groove).  Its  lower  part  forms  a 
prominent,  rough  margin,  a  little  curved  from 
behind  forward,  the  lateral  supracondylar  ridge, 
which  presents  an  anterior  lip  for  the  origin 
of  the  Brachioradialis  above,  and  Extensor 
carpi  radialis  longus  below,  a  posterior  lip  for 
the  Triceps  brachii,  and  an  intermediate  ridge 
for  the  attachment  of  the  lateral  intermuscu- 
lar septum. 

The  medial  border  extends  from  the  lesser 
tubercle  to  the  medial  epicondyle.  Its  upper 
third  consists  of  a  prominent  ridge,  the  crest  of 
the  lesser  tubercle,  which  gives  insertion  to  the 
t(3ndon  of  the  Teres  major.  About  its  center 
is  a  slight  impression  for  the  insertion  of  the 
C!oracobrachialis,  and  just  below  this  is  the 
entrance  of  the  nutrient  canal,  directed  down- 
ward; sometimes  there  is  a  second  nutrient 
canal  at  the  commencement  of  the  radial  sulcus. 
T'he  inferior  third  of  this  border  is  raised  into 
a  slight  ridge,  the  medial  supracondylar  ridge, 
v/hich  becomes  very  prominent  below;  it  pre- 
sents an  anterior  lip  for  the  origins  of  the 
IJrachialis  and  Pronator  teres,  a  posterior  lip 
for  the  medial  head  of  the  Triceps  brachii, 
{.nd  an  intermediate  ridge  for  the  attachment 
of  the  medial  intermuscular  septum. 

Surfaces. — The  antero-lateral  surface  is  di- 
rected lateralward  above,  where  it  is  smooth, 
rounded,  and  covered  by  the  Deltoideus;  for- 
^vard  and  lateralward  below,  where  it  is  slightly 
concave  from  above  downward,  and  gives  origin 
1.0  part  of  the  Brachialis.  About  the  middle 
)f  this  surface  is  a  rough,  triangular  elevation, 
[the  deltoid  tuberosity  for  the  insertion  of  the 
Deltoideus;  below  this  is  the  radial  sulcus, 
directed  obliquely  from  behind,  forward,  and 
downward,  and  transmitting  the  radial  nerve 
and  profunda  artery. 

The  antero-medial  surface,  less  extensive  than 
the  antero-lateral,  is  directed  medialward  above, 
i'orward  and  medialward  below;  its  upper  part 
is  narrow,  and  forms  the  floor  of  the  intertuber- 
cular  groove  which  gives  insertion  to  the  tendon 
of  the  Latissimus  dorsi;  its  middle  part  is 
.slightly  rough  for  the  attachment  of  some  of 


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Articular 
capsule 


Articular 
capsule 


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Fig.  208. — Left  humerus.     Posterior  view. 


212 


OSTEOLOGY 


the  fibers  of  the  tendon  of  insertion  of  the  Coracobrachialis;  its  loweT  part  is 
smooth,  concave  from  above  downward,  and  gives  origin  to  the  BrachiaHs.^ 

The  posterior  surface  appears  somewhat  twisted,  so  that  its  upper  part  is 
directed  a  Httle  medialward,  its  lower  part  backward  and  a  Httle  laterahvard. 
Nearly  the  whole  of  this  surface  is  covered  by  the  lateral  and  medial  heads  of 
the  Triceps  brachii,  the  former  arising  above,  the  latter  below  the  radial 
sulcus. 

The  Lower  Extremity. — The  lower  extremity  is  flattened  from  before  backward, 
and  curved  slightly  forward;  it  ends  below  in  a  broad,  articular  surface,  which  is 
divided  into  two  parts  by  a  slight  ridge.  Projecting  on  either  side  are  the  latt^ral 
and  medial  epicondyles.  The  articular  sm-face  extends  a  little  lower  than  the 
epicondyles,  and  is  curved  slightly  forward;  its  medial  extremity  occupies  a  lower 
level  than  the  lateral.  The  lateral  portion  of  this  surface  consists  of  a  smooth, 
rounded  eminence,  named  the  capitulum  of  the  humerus;  it  articulates  with  the  cup- 
shaped  depression  on  the  head  of  the  radius,  and  is  limited  to  the  front  and  lower 
part  of  the  bone.  On  the  medial  side  of  this  eminence  is  a  shallow  groove,  in  which 
is  received  the  medial  margin  of  the  head  of  the  radius.  Above  the  front  part 
of  the  capitulum  is  a  slight  depression,  the  radial  fossa,  which  receives  the  anterior 
border  of  the  head  of  the  radius,  when  the  forearm  is  flexed.  The  medial  portion 
of  the  articular  surface  is  named  the  trochlea,  and  presents  a  deep  depression  be- 
tween two  well-marked  borders;  it  is  convex  from  before  backward,  concave  from 
side  to  side,  and  occupies  the  anterior,  lower,  and  posterior  parts  of  the  extremity. 
The  lateral  border  separates  it  from  the  groove  which  articulates  with  the  margin 
of  the  head  of  the  radius.  The  medial  border  is  thicker,  of  greater  length,  and 
consequently  more  prominent,  than  the  lateral.  The  grooved  portion  of  the  artic- 
ular surface  fits  accurately  within  the  semilunar  notch  of  the  ulna;  it  is  broader  and 
deeper  on  the  posterior  than  on  the  anterior  aspect  of  the  bone,  and  is  inclined 
obliquely  downward  and  forward  toward  the  medial  side.  Above  the  front  part 
of  the  trochlea  is  a  small  depression,  the  coronoid  fossa,  which  receives  the  coronoid 
process  of  the  ulna  during  flexion  of  the  forearm.  Above  the  back  part  of  the  troch- 
lea is  a  deep  triangular  depression,  the  olecranon  fossa,  in  which  the  summit  of  the 
olecranon  is  received  in  extension  of  the  forearm.  These  fossae  are  separated  from 
one  another  by  a  thin,  transparent  lamina  of  bone,  which  is  sometimes  perforated 
by  a  supratrochlear  foramen;  they  are  lined  in  the  fresh  state  by  the  synovial 
membrane  of  the  elbow-joint,  and  their  margins  afford  attachment  to  the  anterior 
and  posterior  ligaments  of  this  articulation.  The  lateral  epicondyle  is  a  small, 
tuberculated  eminence,  curved  a  little  forward,  and  giving  attachment  to  the  radial 
collateral  ligament  of  the  elbow-joint,  and  to  a  tendon  common  to  the  origin  of 
the  Supinator  and  some  of  the  Extensor  muscles.  The  medial  epicondyle,  larger 
and  more  prominent  than  the  lateral,  is  directed  a  little  backward;  it  gives  attach- 
ment to  the  ulnar  collateral  ligament  of  the  elbow-joint,  to  the  Pronator  teres, 
and  to  a  common  tendon  of  origin  of  some  of  the  Flexor  muscles  of  the  forearm ; 
the  ulnar  nerve  runs  in  a  groove  on  the  back  of  this  epicondyle.  The  epicondyles 
are  continuous  above  with  the  supracondylar  ridges. 

Structure. — The  extremities  consist  of  cancellous  tissue,  covered  with  a  thin,  compact  layer 
(Fig.  209) ;  the  body  is  composed  of  a  cylinder  of  compact  tissue,  thicker  at  the  center  than  toward 
the  extremities,  and  contains  a  large  medullary  canal  which  extends  along  its  whole  length. 


1  A  small,  hook-shaped  process  of  bone,  the  supracondylar  process,  varying  from  2  to  20  mm.  in  length,  is  not  infre- 
quently found  projectmg  from  the  antero-medial  surface  of  the  body  of  the  humerus  5  cm.  above  the  medial  epicondjle. 
It  is  curved  downward  and  forward,  and  its  pointed  end  is  connected  to  the  medial  border,  just  above  the  medial 
epicondyle,  by  a  fibrous  band,  which  gives  origin  to  a  portion  of  the  Pronator  teres;  through  the  arch  completed  by 
this  fibrous  band  the  median  nerve  and  brachial  artery  pass,  when  these  structures  deviate  from  their  usual  course. 
Sometimes  the  nerve  alone  is  transmitted  through  it,  or  the  nerve  may  be  accompanied  by  the  ulnar  artery,  in  cases 
of  high  division  of  the  brachial.  A  well-marked  groove  is  usually  found  behind  the  process,  in  which  the  nerve  and 
artery  are  lodged.  This  arch  is  the  homologue  of  the  supracondyloid  foramen  found  in  many  animals,  and  probably 
serves  in  them  to  protect  the  nerve  and  artery  from  compression  during  the  contraction  of  the  muscles  in  this  region. 


THE  HUMERUS 


213 


Ossification  (Figs.  210,  211). — The  htimerus  is  ossi- 
fied from  eight  centers,  one  for  each  of  the  following 
parts:  the  body,  the  head,  the  greater  tubercle,  the 
les.ser  tubercle,  the  capitulum,  the  trochlea,  and  one 
for  each  epicondyle.  The  center  for  the  body  appears 
near  the  middle  of  the  bone  in  the  eighth  week  of  fetal 
life,  and  soon  extends  toward  the  extremities.  At  birth 
the  humerus  is  ossified  in  nearly  its  whole  length,  only 
the  extremities  remaining  cartilaginous.  During  the 
first  year,  sometimes  before  birth,  ossification  commences 
in  the  head  of  the  bone,  and  during  the  third  year  the 
center  for  the  greater  tubercle,  and  during  the  fifth  that 
for  the  lesser  tubercle,  make  their  appearance.  By  the 
sixth  year  the  centers  for  the  head  and  tubercles  have 
joined,  so  as  to  form  a  single  large  epiphysis,  which  fuses 
with  the  body  about  the  twentieth  year.  The  lower  end 
of  the  humerus  is  ossified  as  follows.  At  the  end  of 
the  second  year  ossification  begins  in  the  capitulum, 
and  extends  medialward,  to  form  the  chief  part  of  the 
articular  end  of  the  bone;  the  center  for  the  medial  part 
of  the  trochlea  appears  about  the  age  of  twelve.  Ossifi- 
cation begins  in  the  medial  epicondyle  about  the  fifth 
year,  and  in  the  lateral  about  the  thirteenth  or  four- 
teenth year.  About  the  sixteenth  or  seventeenth  year, 
the  lateral  epicondyle  and  both  portions  of  the  articu- 
lating surface,  having  already  joined,  unite  with  the 
body,  and  at  the  eighteenth  year  the  medial  epicon- 
dyle becomes  joined  to  it. 


Epiphysial  line 


Fia.  209. — Longitudinal  section  of  head  of 
left  humerus. 


Epiphyses  of  head  and' 
t  ubercles  blend  at  fifth 
year,  and  unite  with 
body  at  twentieth 
year 


Unites  with  body\  -S 
I  i   at  eighteenth  year  J  ^ 


Bleni  of,  i^t 


Fia.  210. — Plan  of  ossification  of  the  humerus. 


Fig.  211. — Epiphysial  lines  of  humerus  in  a  young 
adult.  Anterior  aspect.  The  lines  of  attachment  of 
the  articular  capsules  are  in  blue. 


JSTEOLOGY 


Olecranons. 


The  Ulna  (Elbow  Bone).i 

The  ulna  (Figs.  212,  213)  is  a  long  bone,  prismatic  in  form,  placed  at  the  maiial 
side  of  the  forearm,  parallel  with  the  radius.  It  is  divisible  into  a  body  and 
two  extremities.  Its  upper  extremity,  of  great  thickness  and  strength,  forms 
a  large  part  of  the  elbow-joint;  the  bone  diminishes  in  size  from  above  downward, 

its  lower  extremity  being  very  small,  and  excluded 
from  the  wrist-joint  by  the  interposition  of  an 
articular  disk. 

The  Upper  Extremity  {proximal  extremity)  (Fig. 
212). — The  upper  extremity  presents  two  curved 
processes,  the  olecranon  and  the  coronoid  process; 
and  two  concave,  articular  cavities,  the  semilunar 
and  radial  notches. 

The  Olecranon  {olecranon  process). — The  olecra- 
non is  a  large,  thick,  curved  eminence,  situated 
at  the  upper  and  back  part  of  the  ulna.  It  is  bent 
forward  at  the  summit  so  as  to  present  a  promi- 
nent lip  which  is  received  into  the  olecranon  fossa 
of  the  humerus  in  extension  of  the  forearm.  Its 
base  is  contracted  where  it  joins  the  body  and  the 
narrowest  part  of  the  upper  end  of  the  ulna.  Its 
posterior  surface,  directed  backward,  is  triangular, 
smooth,  subcutaneous,  and  covered  by  a  bursa. 
Its  superior  surface  is  of  quadrilateral  form,  marked 
behind  by  a  rough  impression  for  the  insertion  of 
the  Triceps  brachii;  and  in  front,  near  the  margin, 
by  a  slight  transverse  groove  for  the  attachment 
of  part  of  the  posterior  ligament  of  the  elbow-joint. 
Its  anterior  surface  is  smooth,  concave,  and  forms 
the  upper  part  of  the  semilunar  notch.  Its  borders 
present  continuations  of  the  groove  on  the  margin 
of  the  superior  surface;  they  serve  for  the  attach- 
ment of  ligaments,  viz.,  the  back  part  of  the  ulnar 
collateral  ligament  medially,  and  the  posterior 
ligament  laterally.  From  the  medial  border  a  part 
of  the  Flexor  carpi  ulnaris  arises;  while  to  the 
lateral  border  the  Anconseus  is  attached. 

The  Coronoid  Process  {processus  coronoideus) . — 
The  coronoid  process  is  a  triangular  eminence 
projecting  forward  from  the  upper  and  front  part 
of  the  ulna.  Its  base  is  continuous  with  the  body 
of  the  bone,  and  of  considerable  strength.  Its 
apex  is  pointed,  slightly  curved  upward,  and  in 
flexion  of  the  forearm  is  received  into  the  coronoid 
fossa  of  the  humerus.  Its  upper  surface  is  smooth,  concave,  and  forms  the  lower 
part  of  the  semilunar  notch.  Its  antero-inferior  surface  is  concave,  and  marked  by 
a  rough  impression  for  the  insertion  of  the  Brachialis.  At  the  junction  of  this 
surface  w  ith  the  front  of  the  body  is  a  rough  eminence,  the  tuberosity  of  the  ulna, 
which  gives  insertion  to  a  part  of  the  Brachialis;  to  the  lateral  border  of  this 
tuberosity  the  oblique  cord  is  attached.  Its  lateral  surface  presents  a  narrow, 
oblong,  articular  depression,  the  radial  notch.    Its  medial  surface,  by  its  prominent, 

1  In  the  anatomical  position,  the  forearm  ia  placed  in  extension  and  supination  with  the  palm  looking  forward 
and  the  thumb  on  the  outer  side. 


Fig.  212. — Upper  extremity  of  left  ulna. 
Lateral  aspect. 


THE  ULNA 


215 


free  margin,  serves  for  the  attachment  of  part  of  the  ulnar  collateral  ligament. 
At  the  front  part  of  this  surface  is  a  small  rounded  eminence  for  the  origin 
of  one  head  of  the  Flexor  digitorum  sublimis;  behind  the  eminence  is  a  depression 
for  part  of  the  origin  of  the  Flexor  digitorum  profundus;  descending  from  the 
eminence  is  a  ridge  which  gives  origin  to  one  head  of  the  Pronator  teres.  Fre- 
quently, the  Flexor  pollicis  longus  arises  from  the  lower  part  of  the  coronoid 
process  by  a  rounded  bundle  of  muscular  fibers. 

The  Semilunar  Notch  {incisura  semilunaris;  greater  sigmoid  cavity). — ^The  semi- 
lunar notch  is  a  large  depression,  formed  by  the  olecranon  and  the  coronoid  process, 
and  serving  for  articulation  with  the  trochlea  of  the  humerus.  About  the  middle 
of  either  side  of  this  notch  is  an  indentation,  which  contracts  it  somewhat,  and 
indicates  the  junction  of  the  olecranon  and  the  coronoid  process.  The  notch  is 
concave  from  above  downward,  and  divided  into  a  medial  and  a  lateral  portion  by 
a  smooth  ridge  running  from  the  summit  of  the  olecranon  to  the  tip  of  the  coronoid 
process.  The  medial  portion  is  the  larger,  and  is  slightly  concave  transversely; 
the  lateral  is  convex  above,  slightly  concave  below. 

The  Radial  Notch  (incisura  radialis;  lesser  sigmoid  cavity). — The  radial  notch 
is  a  narrow,  oblong,  articular  depression  on  the  lateral  side  of  the  coronoid  process ; 
it  receives  the  circumferential  articular  surface  of  the  head  of  the  radius.  It  is 
concave  from  before  backw^ard,  and  its  prominent  extremities  serve  for  the  attach- 
ment of  the  annular  ligament. 

The  Body  or  Shaft  (corpus  ulnce). — The  body  at  its  upper  part  is  prismatic 
in  form,  and  curved  so  as  to  be  convex  behind  and  lateral  ward;  its  central  part 
is  straight;  its  lower  part  is  rounded,  smooth,  and  bent  a  little  lateralward.  It 
tapers  gradually  from  above  downward,  and  has  three  borders  and  three  surfaces. 

Borders. — The  volar  border  (margo  volaris;  anterior  border)  begins  above  at  the 
jDrominent  medial  angle  of  the  coronoid  process,  and  ends  below  in  front  of  the 
styloid  process.  Its  upper  part,  well-defined,  and  its  middle  portion,  smooth  and 
i-ounded,  give  origin  to  the  Flexor  digitorum  profundus;  its  lower  fourth  serves 
'or  the  origin  of  the  Pronator  quadratus.  This  border  separates  the  volar  from 
the  medial  surface. 

The  dorsal  border  (margo  dorsalis;  posterior  border)  begins  above  at  the  apex  of 
I  the  triangular  subcutaneous  surface  at  the  back  part  of  the  olecranon,  and  ends 
below  at  the  back  of  the  styloid  process;  it  is  well-marked  in  the  upper  three- 
fourths,  and  gives  attachment  to  an  aponeurosis  which  affords  a  common  origin  to 
the  Flexor  carpi  ulnaris,  the  Extensor  carpi  ulnaris,  and  the  Flexor  digitorum  pro- 
I  fundus;  its  lower  fourth  is  smooth  and  rounded.  This  border  separates  the  medial 
I  from  the  dorsal  surface. 

The  interosseous  crest  (crista  interossea;  external  or  interosseous  border)  begins 
above  by  the  union  of  two  lines,  which  converge  from  the  extremities  of  the  radial 
notch  and  enclose  between, them  a  triangular  space  for  the  origin  of  part  of  the 
Supinator;  it  ends  below  at  the  head  of  the  ulna.  Its  upper  part  is  sharp,  its  lower 
fourth  smooth  and  rounded.  This  crest  gives  attachment  to  the  interosseous  mem- 
brane, and  separates  the  volar  from  the  dorsal  surface. 

Surf  aces. -^-The  volar  surface  (fades  volaris;  anterior  surface),  much  broader 
I  above  than  below,  is  concave  in  its  upper  three-fourths,  and  gives  origin  to  the 
Flexor  digitorum  profundus;  its  lower  fourth,  also  concave,  is  covered  by  the 
Pronator  quadratus.  The  lower  fourth  is  separated  from  the  remaining  portion 
by  a  ridge,  directed  obliquely  downward  and  medialward,  which  marks  the  extent 
of  origin  of  the  Pronator  quadratus.  At  the  junction  of  the  upper  with  the 
I  middle  third  of  the  bone  is  the  nutrient  canal,  directed  obliquely  upward. 

The  dorsal  surface  (fades  dorsalis;  posterior  surface)  directed  backward  and 
lateralward,  is  broad  and  concave  above;  convex  and  somewhat  narrower  in  the 
I  middle;  narrow,  smooth,  and  rounded  below.    On  its  upper  part  is  an  oblique 


216 


OSTEOLOGY 


Articular  capsule 


Flexor  digilorum 
sublimis 


Prcmator 
teres 


Occasional  origin 
of  Flexor  pollicis  longus 


Articular 
capsule 


Styloid  process 


Radial  origin  of 
Flexor  digitorum 
sublimis 


Brachioradialis 

Groove  for  Abductor 
pollicis  longus  and 
Extensor  pollicis  brevis 


Styloid  process 
Fig.  213. — Bones  of  left  forearm.     Anterior  aspect. 


THE  ULNA 


217 


C Abductor  pollicis 
ForJ  longus 

(Extensor  pollicis 
brevis 


RADIUS 


Articular  capsule 


Flexor  digitorum  sublimit 


Articular  capsule 


For  Ext.  carpi  radialis  longus 
For  Extensor  carpi  radialis  brevia 

For  Extensor  pollicis  longus 

Fia.  214. — Bones  of  left  forearm 


Fen"  Extensor  carpi  vlnaris 
For  Extensor  digiti  quinti  projyrius 


For^ 


Extensor  indicis  proprius 
Extensor  digitorum  communis 

Posterior  aspect. 


218 


OSTEOLOGY 


ridge,  which  runs  from  the  dorsal  end  of  the  radial  notch,  downward  to  the  dorsal 
border;  the  triangular  surface  above  this  ridge  receives  the  insertion  of  the 
Anconseus,  while  the  upper  part  of  the  ridge  affords  attachment  to  the  Supinator. 
Below  this  the  surface  is  subdivided  by  a  longitudinal  ridge,  sometimes  called  the 
perpendicular  line,  into  two  parts:  the  medial  part  is  smooth,  and  covered  by  the 
Extensor  carpi  ulnaris;  the  lateral  portion,  wider  and  rougher,  gives  origin  from 
above  downward  to  the  Supinator,  the  Abductor  pollicis  longus,  the  Extensor  pollicis 
longus,  and  the  Extensor  indicis  proprius. 

The  medial  surface  {fades  medialis;  internal  surface)  is  broad  and  concave 
above,  narrow  and  convex  below.  Its  upper  three-fourths  give  origin  to  the 
Flexor  digitorum  profundus;  its  lower  fourth  is  subcutaneous. 


Olecranon 

Appears  at ,^^^^__  Joins  body  at 

tenth  year      ^^^^     sixteenth  year 


Appears  at  t 
fourth  year 


Joins  body  at 
twentieth  year 


Inferior  extremity 


Fio.  215. — Plan  of  ossification  of  the  ulna. 
From  three'centers. 


FiQ.  216. — Epiphysial  lines  of  ulna  in  a  young  ridult. 
Lateral  aspect.  The  lines  of  attachment  of  the  articular 
capsules  are  in  blue. 


The  Lower  Extremity  {distal  extremity). — The  lower  extremity  of  the  ulna  is 
small,  and  presents  two  eminences;  the  lateral  and  larger  is  a  rounded,  articular 
eminence,  termed  the  head  of  the  ulna;  the  medial,  narrower  and  more  projecting, 
is  a  non-articular  eminence,  the  styloid  process.  The  head  presents  an  articular 
surface,  part  of  which,  of  an  oval  or  semilunar  form,  is  directed  downward,  and 
articulates  with  the  upper  surface  of  the  triangular  articular  disk  which  separates  it 
from  the  wrist-joint;  the  remaining  portion,  directed  lateralward,  is  narrow,  convex, 
and  received  into  the  ulnar  notch  of  the  radius.  The  styloid  process  projects  from 
the  medial  and  back  part  of  the  bone;  it  descends  a  little  lower  than  the  head, 
and  its  rounded  end  affords  attachment  to  the  ulnar  collateral  ligament  of  the 
wrist-joint.  The  head  is  separated  from  the  styloid  process  by  a  depression  for 
the  attachment  of  the  apex  of  the  triangular  articular  disk,  and  behind,  by  a  shallow 
groove  for  the  tendon  of  the  Extensor  carpi  ulnaris. 


THE  RADIUS  WKKKKK         ^^^ 

Structure. — The  long,  narrow  medullary  cavity  is  enclosed  in  a  strong  wall  of  compact  tissue 
which  is  thickest  along  the  interosseous  border  and  dorsal  surface.  At  the  extremities  the  compact 
layer  thins.  The  compact  layer  is  continued  onto  the  back  of  the  olecranon  as  a  plate  of  close 
spongy  bone  with  lamellae  parallel.  From  the  inner  surface  of  this  plate  and  the  compact  layer 
below  it  trabeculae  arch  forward  toward  the  olecranon  and  coronoid  and  cross  other  trabeculse, 
passing  backward  over  the  medullary  cavity  from  the  upper  part  of  the  shaft  below  the  coronoid. 
Below  the  coronoid  process  there  is  a  small  area  of  compact  bone  from  which  trabecule  curve 
ui)ward  to  end  obliquely  to  the  surface  of  the  semilunar  notch  which  is  coated  with  a  thin  layer  of 
compact  bone.     The  trabecular  at  the  lower  end  have  a  more  longitudinal  direction. 

Ossification  (Figs.  215, 216). — The  ulna  is  ossified  from  three  centers:  one  each  for  the  body,  the 
inferior  extremity,  and  the  top  of  the  olecranon.  Ossification  begins  near  the  middle  of  the  body, 
about  the  eighth  week  of  fetal  life,  and  soon  extends  through  the  greater  part  of  the  bone.  At  birth 
the  ends  are  cartilaginous.  About  the  fourth  year,  a  center  appears  in  the  middle  of  the  head, 
and  soon  extends  into  the  styloid  process.  About  the  tenth  year,  a  center  appears  in  the  olecranon 
near  its  extremity,  the  chief  part  of  this  process  being  formed  by  an  upward  extension  of  the  body. 
The  upper  epiphysis  joins  the  body  about  the  sixteenth,  the  lower  about  the  twentieth  year. 

Articulations. — The  ulna  articulates  with  the  humerus  and  radius. 

The  Radius. 

The  radius  (Figs.  213,  214)  is  situated  on  the  lateral  side  of  the  ulna,  which 
exceeds  it  in  length  and  size.  Its  upper  end  is  small,  and  forms  only  a  small  part 
of  the  elbow-joint;  but  its  low^er  end  is  large,  and  forms  the  chief  part  of  the  wrist- 
joint.  It  is  a  long  bone,  prismatic  in  form  and  slightly  curved  longitudinally.  It 
has  a  body  and  two  extremities. 

The  Upper  Extremity  {yroximal  extremity). — The  upper  extremity  presents  a 
head,  neck,  and  tuberosity.  The  head  is  of  a  cylindrical  form,  and  on  its  upper 
surface  is  a  shallow  cup  or  fovea  for  articulation  with  the  capitulum  of  the  humerus. 
The  circumference  of  the  head  is  smooth;  it  is  broad  medially  where  it  articulates 
\Aith  the  radial  notch  of  the  ulna,  narrow  in  the  rest  of  its  extent,  which  is  embraced 
by  the  annular  ligament.  The  head  is  supported  on  a  round,  smooth,  and  con- 
stricted portion  called  the  neck,  on  the  back  of  which  is  a  slight  ridge  for  the  inser- 
tion of  part  of  the  Supinator.  Beneath  the  neck,  on  the  medial  side,  is  an  eminence, 
the  radial  tuberosity;  its  surface  is  divided  into  a  posterior,  rough  portion,  for  the 
i  isertion  of  the  tendon  of  the  Biceps  brachii,  and  an  anterior,  smooth  portion,  on 
v/hich  a  bursa  is  interposed  between  the  tendon  and  the  bone. 

The  Body  or  Shaft  {corpus  radii). — The  body  is  prismoid  in  form,  narrower 
above  than  below,  and  slightly  curved,  so  as  to  be  convex  lateralward.  It  presents 
three  borders  and  three  surfaces. 

Borders. — The  volar  border  {mar go  volaris;  anterior  border)  extends  from  the  lower 
part  of  the  tuberosity  above  to  the  anterior  part  of  the  base  of  the  styloid  process 
below,  and  separates  the  volar  from  the  lateral  surface.  Its  upper  third  is  promi- 
iient,  and  from  its  oblique  direction  has  received  the  name  of  the  oblique  line  of  the 
radius ;  it  gives  origin  to  the  Flexor  digitorum  sublimis  and  Flexor  pollicis  longus ;  the 
surface  above  the  line  gives  insertion  to  part  of  the  Supinator.  The  middle  third  of 
the  volar  border  is  indistinct  and  rounded.  The  lower  fourth  is  prominent,  and  gives 
insertion  to  the  Pronator  quadratus,  and  attachment  to  the  dorsal  carpal  ligament; 
it  ends  in  a  small  tubercle,  into  which  the  tendon  of  the  Brachioradialis  is  inserted. 

The  dorsal  border  {margo  dorsalis;  posterior  border)  begins  above  at  the  back  of 
the  neck,  and  ends  below  at  the  posterior  part  of  the  base  of  the  styloid  process; 
it  separates  the  posterior  from  the  lateral  surface.  It  is  indistinct  above  and  below, 
but  well-marked  in  the  middle  third  of  the  bone. 

The  interosseous  crest  {crista  interossea;  internal  or  interosseous  border)  begins 
above,  at  the  back  part  of  the  tuberosity,  and  its  upper  part  is  rounded  and  indis- 
tinct; it  becomes  sharp  and  prominent  as  it  descends,  and  at  its  lower  part  divides 
into  two  ridges  which  are  continued  to  the  anterior  and  posterior  margins  of  the 
ulnar  notch.    To  the  posterior  of  the  two  ridges  the  lower  part  of  the  interosseous 


OSTEOLOGY 

membrane  is  attached,  while  the  triangular  surface  between  the  ridges  gives  inser- 
tion to  part  of  the  Pronator  quadratus.  This  crest  separates  the  volar  from  the 
dorsal  surface,  and  gives  attachment  to  the  interosseous  membrane. 

Surface. — The  volar  surface  (fades  volaris;  anterior  surface)  is  concave  in  its 
upper  three-fourths,  and  gives  origin  to  the  Flexor  pollicis  longus;  it  is  broad  and  flat 
in  its  lower  fourth,  and  affords  insertion  to  the  Pronator  quadratus.  A  prominent 
ridge  limits  the  insertion  of  the  Pronator  quadratus  below,  and  between  this  and 
the  inferior  border  is  a  triangular  rough  surface  for  the  attachment  of  the  volar 
radiocarpal  ligament.  At  the  junction  of  the  upper  and  middle  thirds  of  the 
volar  surface  is  the  nutrient  foramen,  which  is  directed  obliquely  upward. 

The  dorsal  surface  (fades  dorsalis;  posterior  surface)  is  convex,  and  smooth  in 
the  upper  third  of  its  extent,  and  covered  by  the  Supinator.  Its  middle  third  is 
broad,  slightly  concave,  and  gives  origin  to  the  Abductor  pollicis  longus  above, 
and  the  Extensor  pollicis  brevis  below.  Its  lower  third  is  broad,  convex,  and 
covered  by  the  tendons  of  the  muscles  which  subsequently  run  in  the  grooves  on 
the  lower  end  of  the  bone. 

The  lateral  surface  (fades  lateralis;  external  surface)  is  convex  throughout  its 
entire  extent.  Its  upper  third  gives  insertion  to  the  Supinator.  About  its  center  is 
a  rough  ridge,  for  the  insertion  of  the  Pronator  teres.  Its  lower  part  is  narrow,  and 
covered  by  the  tendons  of  the  Abductor  pollicis  longus  and  Extensor  pollicis  brevis. 

The  Lower  Extremity. — The  lower  extremity  is  large,  of  quadrilateral  form, 
and  provided  with  two  articular  surfaces — one  below,  for  the  carpus,  and  another 
at  the  medial  side,  for  the  ulna.  The  carpal  articular  surface  is  triangular,  concave, 
smooth,  and  divided  by  a  slight  antero-posterior  ridge  into  two  parts.  Of  these, 
the  lateral,  triangular,  articulates  with  the  navicular  bone;  the  medial,  quadri- 
lateral, with  the  lunate  bone.  The  articular  surface  for  the  ulna  is  called  the  ulnar 
notch  (sigmoid  cavity)  of  the  radius;  it  is  narrow,  concave,  smooth,  and  articulates 
with  the  head  of  the  ulna.  These  two  articular  surfaces  are  separated  by  a  promi- 
nent ridge,  to  which  the  base  of  the  triangular  articular  disk  is  attached ;  this  disk 
separates  the  wrist-joint  from  the  distal  radioulnar  articulation.  This  end  of  the 
bone  has  three  non-articular  surfaces — volar,  dorsal,  and  lateral.  The  volar  surface, 
rough  and  irregular,  affords  attachment  to  the  volar  radiocarpal  ligament.  The 
dorsal  surface  is  convex,  affords  attachment  to  the  dorsal  radiocarpal  ligament, 
and  is  marked  by  three  grooves.  Enumerated  from  the  lateral  side,  the  first 
groove  is  broad,  but  shallow,  and  subdivided  into  two  by  a  slight  ridge;  the  lateral 
of  these  two  transmits  the  tendon  of  the  Extensor  carpi  radialis  longus,  the  medial 
the  tendon  of  the  Extensor  carpi  radialis  brevis.  The  second  is  deep  but  narrow, 
and  bounded  laterally  by  a  sharply  defined  ridge ;  it  is  directed  obliquely  from  above 
downward  and  lateralward,  and  transmits  the  tendon  of  the  Extensor  pollicis 
longus.  The  third  is  broad,  for  the  passage  of  the  tendons  of  the  Extensor  indicis 
proprius  and  Extensor  digitorum  communis.  The  lateral  surface  is  prolonged 
obliquely  downward  into  a  strong,  conical  projection,  the  styloid  process,  which 
gives  attachment  by  its  base  to  the  tendon  of  the  Brachioradialis,  and  by  its  apex 
to  the  radial  collateral  ligament  of  the  wrist-joint.  The  lateral  surface  of  this 
process  is  marked  by  a  flat  groove,  for  the  tendons  of  the  Abductor  pollicis  longus 
and  Extensor  pollicis  brevis. 

Structure. — The  long  narrow  medullary  cavity  is  enclosed  in  a  strong  wall  of  compact  tissue 
which  is  thickest  along  the  interosseous  border  and  thinnest  at  the  extremities  except  over  the 
cup-shaped  articular  surface  (fovea)  of  the  head  where  it  is  thickened.  The  trabecular  of  the 
spongy  tissue  are  somewhat  arched  at  the  upper  end  and  pass  upward  from  the  compact  layer  of 
the  shaft  to  the  fovea  capituli;  they  are  crossed  by  others  parallel  to  the  surface  of  the  fovea. 
The  arrangement  at  the  lower  end  is  somewhat  similar. 

Ossification  (Figs.  217,  218). — The  radius  is  ossified  from  three  centers:  one  for  the  body, 
and  one  for  either  extremity.  That  for  the  body  makes  its  appearance  near  the  center  of  the  bone, 
during  the  eighth  week  of  fetal  hfe.    About  the  end  of  the  second  year,  ossification  commences 


THE  CARPUS 

in  the  lower  end;  and  at  the  fifth  year,  in  the  upper  end.  The  upper  epiphysis  fuses  with  the 
body  at  the  age  of  seventeen  or  eighteen  years,  the  lower  about  the  age  of  twenty.  An  additional 
center  sometimes  found  in  the  radial  tuberosity,  appears  about  the  fourteenth  or  fifteenth  year. 


Herid 


Appears  at 
fifth  year 


Unites  with  body 
about  pvherty 


Unites  with  body 
about  ttoentieth 
year 


Lower  extremity 


Fig.  217.- 


-Plan  of  ossification  of  the  radius. 
From  three  centers. 


Fig.  218. — Epiphysial  lines  of  radius  in  a  young 
adult.  Anterior  aspect.  The  line  of  attachment  of  the 
articular  capsule  of  the  wrist-joint  is  in  blue. 


THE  HAND. 


I 

^H    The  skeleton  of  the  hand  (Figs.  219,  220)  is  subdivided  into  three  segments:  the 
^■carpus  or  wrist  bones;  the  metacarpus  or  bones  of  the  palm;  and  the  phalanges  or 
^■bones  of  the  digits. 
^M  The  Carpus  (Ossa  Carpi). 

^H    The  carpal  bones,  eight  in  number,  are  arranged  in  two  rows.    Those  of  the 
^■|)roximal  row,  from  the  radial  to  the  ulnar  side,  are  named  the  navicular,  lunate, 
^^triangular,  and  pisiform ;  those  of  the  distal  row,  in  the  same  order,  are  named  the 
greater  multangular,  lesser  multangular,  capitate,  and  hamate. 

Common  Characteristics  of  the  Carpal  Bones. — Each  bone  (excepting  the  pisi- 
form) presents  six  surfaces.  Of  these  the  volar  or  anterior  and  the  dorsal  or  posterior 
surfaces  are  rough,  for  ligamentous  attachment;  the  dorsal  surfaces  being  the 
broader,  except  in  the  navicular  and  lunate.  The  s^ijjerior  or  proximal,  and  inferior 
or  distal  surfaces  are  articular,  the  superior  generally  convex,  the  inferior  concave; 
the  medial  and  lateral  surfaces  are  also  articular  where  they  are  in  contact  with 
contiguous  bones,  otherwise  they  are  rough  and  tuberculated.  The  structure  in 
all  is  similar,  viz.,  cancellous  tissue  enclosed  in  a  layer  of  compact  bone. 

Bones  of  the  Proximal  Row  {upper  row). — The  Navicular  Bone  (os  naviculare  manus; 
scaphoid  bone)  (Fig.  221), — The  navicular  bone  is  the  largest  bone  of  the  proximal 
row,  and  has  received  its  name  from  its  fancied  resemblance  to  a  boat.  It  is  situated 
at  the  radial  side  of  the  carpus,  its  long  axis  being  from  above  downward,  lateralward, 
and  forward.    The  superior  surface  is  convex,  smooth,  of  triangular  shape,  and  artic- 


222 


OSTEOLOGY 


ulates  with  the  lower  end  of  the  radius.  The  inferior  surface,  directed  downwaiv 
lateralward,  and  backward,  is  also  smooth,  convex,  and  triangular,  and  is  divided 
by  a  slight  ridge  into  two  parts,  the  lateral  articulating  with  the  greater  multangu- 
lar, the  medial  with  the  lesser  multangillar.  On  the  dorsal  surface  is  a  narrow, 
rough  groove,  which  runs  the  entire  length  of  the  bone,  and  serves  for  the  attach- 
ment of  ligaments.  The  volar  surface  is  concave  above,  and  elevated  at  its  lower 
and  lateral  part  into  a  rounded  projection,  the  tubercle,  which  is  directed  forward 


Carpus 

Flexor  carpi  ulnakis 
Flexor  digiti  quinti  bkevis 

OpPONENS  I>IQITI  QUINTl 


Metacarpus 


Groove  for  tendon  of 
Flexor  carpi  radialis 

Opponens  pollicis 
Flexor  polucis  brkvis 


//Abductor  pollicis 


Flexor  brevis'\ 

AND  I 

Abductor      J    "' 

digiti  QniNTI.    / 


Sesamoid 

bones 


Abductor 
pollicis 
brevis 


Flexor  digitorum  sublimis 


Flexor  digitorum  profundus 


FiQ.  219. — Bones  of  the  left  hand.     Volar  surface. 


I 


THE  CARPUS 


223 


and  gives  attachment  to  the  transverse  carpal  ligament  and  sometimes  origin  to 
a  few  fibers  of  the  Abductor  pollicis  brevis.  The  lateral  surface  is  rough  and  narrow, 
and  gives  attachment  to  the  radial  collateral  ligament  of  the  wrist.  The  medial 
surface  presents  two  articular  facets;  of  these,  the  superior  or  smaller  is  flattened 
of  semilunar  form,  and  articulates  with  the  lunate  bone;  the  inferior  or  larger  is 
concave,  forming  with  the  lunate  a  concavity  for  the  head  of  the  capitate  bone. 


CARPI  RADIALIS 
LONG0S 

BXT.  CARPI  RADIALIS 
BREVIS 


sr-fjiffw 


Fig.  220. — Boaes  of  the  left  hand.     Dorsal  surface. 


224 


OSTEOLOGY 


Articulations. — The  navicular  articulates  with  five  bones:  the  radius  proximally,  greater  and 
lesser  multangulars  distally,  and  capitate  and  lunate  medially. 

The  Lunate  Bone  (os  lunatum;  semilunar  bone)  (Fig.  222). — The  lunate  bone  may 
be  distinguished  by  its  deep  concavity  and  crescentic  outHne.  It  is  situated  in 
the  center  of  the  proximal  row  of  the  carpus,  between  the  navicular  and  triangul  ar. 
The  superior  surface,  convex  and  smooth,  articulates  with  the  radius.  The  inferior 
surface  is  deeply  concave,  and  of  greater  extent  from  before  backward  than  trans- 


For  radius 


For  lunate 


Tubercle 

\ 


For  greater 
multangular 


For  capitate 


For  lesser  multangular 
Fig.  221. — The  left  navicular  bone. 


versely:  it  articulates  with  the  head  of  the  capitate,  and,  by  a  long,  narrow  facet 
(separated  by  a  ridge  from  the  general  surface),  with  the  hamate.  The  dorsal 
and  volar  surfaces  are  rough,  for  the  attachment  of  ligaments,  the  former  being 
the  broader,  and  of  a  somewhat  rounded  form.     The  lateral  surface  presents  a 


For  triangular 


For  radius 


For  navicular 
For  Iiamate      For  capitate 

Fig.  222.— The  left  lunate  bone. 

narrow,  flattened,  semilunar  facet  for  articulation  with  the  navicular.  The  medial 
surface  is  marked  by  a  smooth,  quadrilateral  facet,  for  articulation  with  the 
triangular. 

Articulations. — The  lunate  articulates  with  five  bones:     the  radius  proximally,  capitate  and 
hamate  distally,  navicular  laterally,  and  triangular  medially. 


For  pisiform 


For  lunate 


For  triangular 


For  hamate 
Fig.  223.— The  left  triangular  bone. 


Fig.  224. — The  left  pisiform  bone. 


The  Triangular  Bone  (os  triquetum;  cuneiform  hone)  (Fig.  223). — The  triangular 
bone  may  be  distinguished  by  its  pyramidal  shape,  and  by  an  oval  isolated  facet 
for  articulation  with  the  pisiform  bone.  It  is  situated  at  the  upper  and  ulnar  side 
of  the  carpus.  The  superior  surface  presents  a  medial,  rough,  non-articular  portion, 
and  a  lateral  convex  articular  portion  which  articulates  with  the  triangular  articular 
disk  of  the  wrist.  The  inferior  surface,  directed  lateralward,  is  concave,  sinuously 
curved,  and  smooth  for  articulation  with  the  hamate.  The  dorsal  surface  is  rough 
for  the  attachment  of  ligaments.    The  volar  surface  presents,  on  its  medial  part, 


THE  CARPUS 


225 


an  oval  facet,  for  articulation  with  the  pisiform;  its  lateral  part  is  rough  for  liga- 
mentous attacliment.  The  lateral  surface,  the  base  of  the  pyramid,  is  marked  by  a 
fiat,  quadrilateral  facet,  for  articulation  with  the  lunate.  The  medial  surface, 
the  summit  of  the  pyramid,  is  pointed  and  roughened,  for  the  attachment  of  the 
» ulnar  collateral  ligament  of  the  wrist. 

Ar^'culations. — The  triangular  articulates  with  three  bones:  the  lunate  laterally,  the  pisiform 
in  front,  the  hamate  distaUy;  and  with  the  triangular  articular  disk  which  separates  it  from  the 
lower  end  of  the  ulna. 

The  Pisiform  Bone  (os  pisiforme)  (Fig.  224). — The  pisiform  bone  may  be  known 
by  its  small  size,  and  by  its  presenting  a  single  articular  facet.  It  is  situated  on  a 
plane  anterior  to  the  other  carpal  bones  and  is  spheroidal  in  form.  Its  dorsal 
surface  presents  a  smooth,  oval  facet,  for  articulation  with  the  triangular :  this  facet 
approaches  the  superior,  but  not  the  inferior  border  of  the  bone.  The  volar  surface 
is  rounded  and  rough,  and  gives  attachment  to  the  transverse  carpal  ligament, 
and  to  the  Flexor  carpi  ulnaris  and  Abductor  digiti  quinti.  The  lateral  and  medial 
surfaces  are  also  rough,  the  former  being  concave,  the  latter  usually  convex. 

Articulation. — The  pisiform  articulates  with  one  bone,  the  triangular. 

Bones  of  the  Distal  Row  {lower  row). — The  Greater  Multangular  Bone  (os  mul- 
tangulum  majus;  trapezium)  (Fig.  225). — The  greater  multangular  bone  may  be 
distinguished  by  a  deep  groove  on  its  volar  surface.  It  is  situated  at  the  radial 
side  of  the  carpus,  between  the  navicular  and  the  first  metacarpal  bone.  The 
superior  surface  is  directed  upward  and  medialward;  medially  it  is  smooth,  and 
articulates  with  the  navicular ;  laterally  it  is  rough  and  continuous  with  the  lateral 
surface.  The  inferior  surface  is  oval,  concave  from  side  to  side,  convex  from  before 
backward,  so  as  to  form  a  saddle-shaped  surface  for  articulation  with  the  base 


For  lesser 
vivitangtdar 


Groove 


For  navicular 


For  2nd 
metacarpal 


Ridge 


For  \st  metacarpal 

Fig.  225. — The  left  greater  multangular  bone 


For  lesser 
mvltanguMT 


For  2)id  metacarpal 


)f  the  first  metacarpal  bone.  The  dorsal  surface  is  rough.  The  volar  surface  is 
barrow  and  rough.  At  its  upper  part  is  a  deep  groove,  running  from  above  obliquely 
pownward  and  medialward;  it  transmits  the  tendon  of  the  Flexor  carpi  radialis, 
^nd  is  bounded  laterally  by  an  oblique  ridge.  This  surface  gives  origin  to  the 
Opponens  pollicis  and  to  the  Abductor  and  Flexor  pollicis  brevis;  it  also  affords 
attachment  to  the  transverse  carpal  ligament.  The  lateral  surface  is  broad  and 
rough,  for  the  attachment  of  ligaments.  The  medial  surface  presents  two  facets; 
the  upper,  large  and  concave,  articulates  with  the  lesser  multangular;  the  lower, 
small  and  oval,  with  the  base  of  the  second  metacarpal. 

;    Articulations. — The  greater  multangular  articulates  with  four  bones :    the  navicular  proximally, 
[  the  first  metacarpal  distally,  and  the  lesser  multangular  and  second  metacarpal  medially. 

The  Lesser  Multangular  Bone  (os  multangulum  minus;  trapezoid  hone)  (Fig.  226). 
-The  lesser  multangular  is  the  smallest  bone  in  the  distal  row.    It  may  be  known 
llby  its  wedge-shaped  form,  the  broad  end   of  the  wedge  constituting  the  dorsal, 
l^he  narrow  end  the  volar  surface;  and  by  its  having  four  articular  facets  touching 
ich  other,  and  separated  by  sharp  edges.     The  superior  surface,  quadrilateral, 
15 


226 


OSTEOLOGY 


For  navicular 


Volar 
surface 


For  greater 
multangular 


smooth,  and  slightly  concave,  articulates  with  the  navicular.  The  inferioT'surFace 
articulates  with  the  proximal  end  of  the  second  metacarpal  bone;  it  is  convex  from 
side  to  side,  concave  from  before  backward  and  subdivided  by  an  elevated  ridge  into 

two  unequal  facets.  The  dorsal  and  volar 
surfaces  are  rough  for  the  attachment  of 
ligaments,  the  former  being  the  larger 
of  the  two.  The  lateral  surface,  con\'ex 
and  smooth,  articulates  with  the  greater 
multangular.  The  medial  surface  is  con- 
cave and  smooth  in  front,  for  artic- 
ulation with  the  capitate;  rough  behind, 
for  the  attachment  of  an  interosseous 
ligament. 


For 

capitate 


Dorsal 

surface 

Fig.  226. — The  left  lesser  multangular  bone. 


For  2nd 

vielacarpal 


Articulations. — The  lesser  multangular  articulates  with /our  bones:  the  navicular  proximally, 
second  metacarpal  distally,  greater  multangular  laterally,  and  capitate  medially. 

The  Capitate  Bone  {os  capitatum;  os  magnum)  (Fig.  227). — The  capitate  bone 
is  the  largest  of  the  carpal  bones,  and  occupies  the  center  of  the  wrist.  It  presents, 
above,  a  rounded  portion  or  head,  which  is  received  into  the  concavity  formed  by 


For  lunate 


For 

navicular 


For  lesser 
multangular 


For 
hamate 


For  3rd 

For  2nd     metacarpal 
metacarpal 


For  4ih  metacarpal 
Fig.   227.— The  left  capitate  bone. 


Volar  surface 


the  navicular  and  lunate;  a  constricted  portion  or  neck;  and  below  this,  the  body. 
The  superior  surface  is  round,  smooth,  and  articulates  with  the  lunate.  The  inferior 
surface  is  divided  by  two  ridges  into  three  facets,  for  articulation  with  the  second, 
third,  and  fourth  metacarpal  bones,  that  for  the  third  being  the  largest.  The 
dorsal  surface  is  broad  and  rough.  The  volar  surface  is  narrow,  rounded,  and  rough, 
for  the  attachment  of  ligaments  and  a  part  of  the  Adductor  pollicis  obliquus. 


For  lunate 


For  triangular 


For  capitate 
For  Ath  metacarpal 


For  5th  metacarpal 


Hamulus 

Fig.   228.— The  left  hamate  bone. 


For  5th  metacarpal 


The  lateral  surface  articulates  with  the  lesser  multangular  by  a  small  facet  at 
its  anterior  inferior  angle,  behind  which  is  a  rough  depression  for  the  attach- 
ment of  an  interosseous  ligament.  Above  this  is  a  deep,  rough  groove,  forming 
part  of  the  neck,  and  serving  for  the  attachment  of  ligaments;  it  is  bounded  supe- 
riorly by  a  smooth,  convex  surface,  for  articulation  with  the  navicular.    The  medial 


I 


THE  METACARPUS 


I 


surface  articulates  with  the  hamate  by  a  smooth,  concave,  oblong  facet,  which 
occupies  its  posterior  and  superior  parts;  it  is  rough  in  front,  for  the  attachment 
of  an  interosseous  ligament. 

Articulations. — The  capitate  articulates  with  seven  bones :  the  navicular  and  lunate  proximally, 
the  second,  third,  and  fourth  metacarpals  distally,  the  lesser  multangular  on  the  radial  side,  and 
the  hamate  on  the  ulnar  side. 

The  Hamate  Bone  {os  hamaium;  unciform  bone)  (Fig.  228). — The  hamate  bone 
may  be  readily  distinguished  by  its  wedge-shaped  form,  and  the  hook-like  process 
which  projects  from  its  volar  surface.  It  is  situated  at  the  medial  and  lower  angle 
of  the  carpus,  with  its  base  downward,  resting  on  the  fourth  and  fifth  metacarpal 
bones,  and  its  apex  directed  upward  and  lateralward.  The  superior  surface,  the 
ai)ex  of  the  wedge,  is  narrow,  convex,  smooth,  and  articulates  with  the  lunate. 
The  inferior  surface  articulates  with  the  fourth  and  fifth  metacarpal  bones,  by 
concave  facets  which  are  separated  by  a  ridge.  The  dorsal  surface  is  triangular 
and  rough  for  ligamentous  attachment.  The  volar  surface  presents,  at  its  lower 
and  ulnar  side,  a  curved,  hook-like  process,  the  hamulus,  directed  forward  and 
lateralward.  This  process  gives  attachment,  by  its  apex,  to  the  transverse  carpal 
ligament  and  the  Flexor  carpi  ulnaris;  by  its  medial  surface  to  the  Flexor  brevis 
and  Opponens  digiti  quinti;  its  lateral  side  is  grooved  for  the  passage  of  the  Flexor 
tendons  into  the  palm  of  the  hand.  It  is  one  of  the  four  eminences  on  the  front 
of  the  carpus  to  which  the  transverse  carpal  ligament  of  the  wrist  is  attached; 
tlie  others  being  the  pisiform  medially,  the  oblique  ridge  of  the  greater  multangular 
and  the  tubercle  of  the  navicular  laterally.  The  medial  surface  articulates  with 
tlie  triangular  bone  by  an  oblong  facet,  cut  obliquely  from  above,  downward 
and  medial  ward.  The  lateral  surface  articulates  with  the  capitate  by  its  upper 
and  posterior  part,  the  remaining  portion  being  rough,  for  the  attachment  of 
ligaments. 

Articulations. — The  hamate  articulates  with  five  bones:     the  lunate  proximally,  the  fourth 
fth  metacarpals  distally,  the  triangular  medially,  the  capitate  laterally. 


^f 


The  Metacarpus. 


I 


The  metacarpus  consists  of  five  cylindrical  bones  which  are  numbered  from  the 
iteral  side  {ossa  metacarpalia  I-V) ;  each  consists  of  a  body  and  two  extremities. 

Common  Characteristics  of  the  Metacarpal  Bones.— The  Body  (corpus;  shaft). — 
?he  body  is  prismoid  in  form,  and  curved,  so  as  to  be  convex  in  the  longitudinal 
lirection  behind,  concave  in  front.  It  presents  three  surfaces:  medial,  lateral, 
iid  dorsal.  The  medial  and  lateral  surfaces  are  concave,  for  the  attachment  of 
he  Interossei,  and  separated  from  one  another  by  a  prominent  anterior  ridge. 

^[Tie  dorsal  surface  presents  in  its  distal  two-thirds  a  smooth,  triangular,  flattened 
jea  which  is  covered  in  the  fresh  state,  by  the  tendons  of  the  Extensor  muscles. 
This  surface  is  bounded  by  two  lines,  which  commence  in  small  tubercles  situated 
>n  either  side  of  the  digital  extremity,  and,  passing  upward,  converge  and  meet 
bme  distance  above  the  center  of  the  bone  and  form  a  ridge  which  runs  along  the 
test  of  the  dorsal  surface  to  the  carpal  extremity.  This  ridge  separates  two 
'oping  surfaces  for  the  attachment  of  the  Interossei  dorsales.  To  the  tubercles 
»n  the  digital  extremities  are  attached  the  collateral  ligaments  of  the  metacarpo- 
phalangeal joints. 

The  Base  or  Carpal  Extremity  (basis)  is  of  a  cuboidal  form,  and  broader  behind 
lian  in  front:  it  articulates  with  the  carpus,  and  with  the  adjoining  metacarpal 
>ones;  its  dorsal  and  volar  surfaces  are  rough,  for  the  attachment  of  ligaments. 
[  The  Head  or  Digital  Extremity  (capitulum)  presents  an  oblong  surface  markedly 

'convex  from  before  backward,  less  so  transversely,  and  flattened  from  side  to  side; 

it  articulates  with  the  proximal  phalanx.    It  is  broader,  and  extends  farther  up- 


228 


For  greater 
multangular 


For  greater 
multangular 


FiQ.  229. — The  first  metacarpal. 
(Left.) 


ward,  on  the  volar  than  on  the  dorsal  aspect,  and  is  longer  in  the  antero-post(;rior 
than  in  the  transverse  diameter.  On  either  side  of  the  head  is  a  tubercle  for  the 
attachment  of  the  collateral  ligament  of  the  metacarpophalangeal  joint.  The 
dorsal  surface,  broad  and  flat,  supports  the  Extensor  tendons;  the  volar  smface 
is  grooved  in  the  middle  line  for  the  passage  of  the  Flexor  tendons,  and  mai-ked 
on  either  side  by  an  articular  eminence  continuous  with  the  terminal  articular 
surface. 

Characteristics  of  the  Individual  Metacarpal  Bones. — The  First  Metacarpal 
Bone  {os  vietacarpale  I;  metacarpal  bone  of  the  thumb)  (Fig.  229)  is  shorter  and 

stouter  than  the  others,  diverges  to  a  greater  degree 
from  the  carpus,  and  its  volar  surface  is  directed 
toward  the  palm.  The  body  is  flattened  and  broad 
on  its  dorsal  surface,  and  does  not  present  the  ridge 
which  is  found  on  the  other  metacarpal  bones;  its 
volar  surface  is  concave  from  above  downward.  On 
its  radial  border  is  inserted  the  Opponens  pollicis; 
its  ulnar  border  gives  origin  to  the  lateral  head  of 
the  first  Interosseus  dorsalis.  The  base  presents  a 
concavo-convex  surface,  for  articulation  with  the 
greater  multangular;  it  has  no  facets  on  its  sides,  but 
on  its  radial  side  is  a  tubercle  for  the  insertion  of  the 
Abductor  pollicis  longus.  The  head  is  less  convex 
than  those  of  the  other  metacarpal  bones,  and  is 
broader  from  side  to  side  than  from  before  backward. 
On  its  volar  surface  are  two  articular  eminences,  of 
which  the  lateral  is  the  larger,  for  the  two  sesamoid 
bones  in  the  tendons  of  the  Flexor  pollicis  brevis. 
The  Second  Metacarpal  Bone  (os  metacarpale  II;  metacarpal  bone  of  the  index 
finger)  (Fig.  230)  is  the  longest,  and  its  base  the  largest,  of  the  four  remaining 
bones.  Its  base  is  prolonged  upward  and  medialward,  forming  a  prominent  ridge. 
It  presents  four  articular  facets:  three  on  the  upper  surface  and  one  on  the  ulnar 
side.  Of  the  facets  on  the  upper  surface  the  intermediate  is  the  largest  and  is 
concave  from  side  to  side,  convex  from  before  backward  for  articulation  with  the 
lesser  multangular;  the  lateral  is  small,  flat  and  oval  for  articulation  with  the  greater 
multangular;  the  medial,  on  the  summit  of  the  ridge,  is  long  and  narrow  for  articu- 
lation with  the  capitate.  The  facet  on  the  ulnar  side  articulates  with  the  third 
metacarpal.  The  Extensor  carpi  radialis  longus  is  inserted  on  the  dorsal  surface 
and  the  Flexor  carpi  radialis  on  the  volar  surface  of  the  base. 

The  Third  Metacarpal  Bone  {os  metacarpale  III;  metacarpal  bone  of  the  middle 
finger)  (Fig.  231)  is  a  little  smaller  than  the  second.  The  dorsal  aspect  of  its 
base  presents  on  its  radial  side  a  pyramidal  eminence,  the  styloid  process,  which 
extends  upward  behind  the  capitate;  immediately  distal  to  this  is  a  rough  surface 
for  the  attachment  of  the  Extensor  carpi  radialis  brevis.  The  carpal  articular 
facet  is  concave  behind,  flat  in  front,  and  articulates  with  the  capitate.  On  the 
radial  side  is  a  smooth,  concave  facet  for  articulation  with  the  second  metacarpal, 
and  on  the  ulnar  side  two  small  oval  facets  for  the  fourth  metacarpal. 

The  Fourth  Metacarpal  Bone  {os  metacarpale  IV;  metacarpal  bone  of  the  ring 
finger)  (Fig.  232)  is  shorter  and  smaller  than  the  third.  The  base  is  small  and 
quadrilateral;  its  superior  surface  presents  two  facets,  a  large  one  medially  for 
articulation  with  the  hamate,  and  a  small  one  laterally  for  the  capitate.  On  the 
radial  side  are  two  oval  facets,  for  articulation  with  the  third  metacarpal ;  and  on 
the  ulnar  side  a  single  concave  facet,  for  the  fifth  metacarpal. 

The  Fifth  Metacarpal  Bone  {os  metacarpale  V;  metacarpal  bone  of  the  little  finger) 
(Fig.  233)  presents  on  its  base  one  facet  on  its  superior  surface,  which  is  concavo- 


THE  METACARPUS 


229 


convex  and  articulates  with  the  hamate,  and  one  on  its  radial  side,  which  articulates 
with  the  fourth  metacarpal.  On  its  ulnar  side  is  a  prominent  tubercle  for  the  inser- 
tion of  the  tendon  of  the  Extensor  carpi  ulnaris.    The  dorsal  surface  of  the  body 


For  greater         For  '6rd 
Fo  '•  lesser    multangxdar    metacarpal      For      For  lesser 
mt  Uangular  capitate     mult- 

angular 

Fio.  230. — The  second  metacarpal.     (Left.) 


Styloid  Far  2nd 
process     meta- 
carpal 

Fig.  231. — The  third  metacarpal.     (Left.) 


For 
capitate 


For  ^th 
metacarpal 


is  divided  by  an  oblique  ridge,  which  extends  from  near  the  ulnar  side  of  the  base 
to  the  radial  side  of  the  head.  The  lateral  part  of  this  surface  serves  for  the  attach- 
mjnt  of  the  fourth  Interosseus  dorsalis;  the  medial  part  is  smooth,  triangular,  and 
covered  by  the  Extensor  tendons  of  the  little  finger. 

•f 


For 
capitate 


For  3rd 


For 


For  5th 

metO' 
carpal 


metacarpal    hamate 
Fig.  232.— The  fourth  metacarpal.     (Left.) 


For  4:th 
metacarpal 


For  hamate 


Fig.  233. — The  fifth  metacarpal.     (Left.) 


Articulations. — Besides  their  phalangeal  articulations,  the  metacarpal  bones  articulate  as 
follows:  the  first  with  the  greater  multangular;  the  second  with  the  greater  multangular,  lesser 
multangular,  capitate  and  third  metacarpal;  the  third  with  the  capitate  and  second  and  fourth 
metacarpals;  the  fourth  with  the  capitate,  hamate,  and  third  and  fifth  metacarpals;  and  the 
fifth  with  the  hamate  and  fourth  metacarpal. 


230 


OSTEOLOGY 


The  Phalanges  of  the  Hand  (Phalanges  Digitonim  Manus). 

The  phalanges  are  fourteen  in  number,  three  for  each  finger,  and  two  for  the 
thumb.  Each  consists  of  a  body  and  two  extremities.  The  body  tapers  from  above 
downward,  is  convex  posteriorly,  concave  in  front  from  above  downward,  flat 
from  side  to  side;  its  sides  are  marked  by  rough  ridges  which  give  attachment 
to  the  fibrous  sheaths  of  the  Flexor  tendons.  The  proximal  extremities  of  the  bones 
of  the  first  row  present  oval,  concave  articular  surfaces,  broader  from  side  to  side 
than  from  before  backward.  The  proximal  extremity  of  each  of  the  bones  of  the 
second  and  third  rows  presents  a  double  concavity  separated  by  a  median  ridge. 
The  distal  extremities  are  smaller  than  the  proximal,  and  each  ends  in  two  condyles 
separated  by  a  shallow  groove;  the  articular  surface  extends  farther  on  the  volar 
than  on  the  dorsal  surface,  a  condition  best  marked  in  the  bones  of  the  first  row. 

The  ungual  phalanges  are  convex  on  their  dorsal  and  flat  on  their  volar  surfaces; 
they  are  recognized  by  their  small  size,  and  by  a  roughened,  elevated  surface  of 
a  horseshoe  form  on  the  volar  surface  of  the  distal  extremity  of  each  which  serves 
to  support  the  sensitive  pulp  of  the  finger. 


One  center  for  each  hone  : 
All  cartilaginous  at  birth 


METACARPALS  OF  FINGERS 

Tloo  centers  for  each  bone  . 
One  for  body 
One  for  head 


PHALANOZIS 

Two  centers  for  each  bone 
One  for  body 
One  for  proximal 
extremity 


ajifieari  /^-S*r  y  t- 
\    unite  18  ZO'^yZ. 


FiG.   234. — Plan  of  ossification  of  the  hand. 

Articulations. — In  the  four  fingers  the  phalanges  of  the  first  row  articulate  with  those  of  the 
second  row  and  with  the  metacarpals;  the  phalanges  of  the  second  row  with  those  of  the  first 
and  third  rows,  and  the  ungual  phalanges  with  those  of  the  second  row.  In  the  thumb,  which 
has  only  two  phalanges,  the  first  phalanx  articulates  by  its  proximal  extremity  with  the  meta- 
carpal bone  and  by  its  distal  with  the  ungual  phalanx. 

Ossification  of  the  Bones  of  the  Hand. — The  carpal  bones  are  each  ossified  from  a  single  center, 
and  ossification  proceeds  in  the  following  order  (Fig.  234) :    in  the  capitate  and  hamate,  during 


1 


THE  HIP  BONE  231 


the  first  year,  the  former  preceding  the  latter;  in  the  triangular,  during  the  third  year;  in  the 
lunate  and  greater  multangular,  during  the  fifth  year,  the  former  preceding  the  latter;  in  the 
navicular,  during  the  sixth  year;  in  the  lesser  multangular,  during  the  eighth  year;  and  in 
the  pisiform,  about  the  twelfth  year 

Occasionally  an  additional  bone,  the  os  centrale,  is  found  on  the  back  of  the  carpus,  lying 
between  the  navicular,  lesser  multangular,  and  capitate.  During  the  second  month  of  fetal  life 
it  is  represented  by  a  small  cartilaginous  nodule,  which  usually  fuses  with  the  cartilaginous  navic- 
ular. Sometimes  the  styloid  process  of  the  third  metacarpal  is  detached  and  forms  an  additional 
ossicle. 

The  metacarpal  bones  are  each  ossified  from  two  centers:  one  for  the  body  and  one  for  the 
distal  extremity  of  each  of  the  second,  third,  fourth,  and  fifth  bones;  one  for  the  body  and  one 
for  the  base  of  the  first  metacarpal  bone.^  The  first  metacarpal  bone  is  therefore  ossified  in  the 
same  manner  as  the  phalanges,  and  this  has  led  some  anatomists  to  regard  the  thumb  as  being 
made  up  of  three  phalanges,  and  not  of  a  metacarpal  bone  and  two  phalanges.  Ossification  com- 
mences in  the  middle  of  the  body  about  the  eighth  or  ninth  week  of  fetal  life,  the  centers  for  the 
second  and  third  metacarpals  being  the  first,  and  that  for  the  first  metacarpal,  the  last,  to  appear; 
about  the  third  year  the  distal  extremities  of  the  metacarpals  of  the  fingers,  and  the  base  of  the 
metacarpal  of  the  thumb,  begin  to  ossify;  they  unite  with  the  bodies  about  the  twentieth  year. 

The  phalanges  are  each  ossified  from  two  centers:  one  for  the  body,  and  one  for  the  proximal 
extremity.  Ossification  begins  in  the  body,  about  the  eighth  week  of  fetal  life.  Ossification  of 
the  proximal  extremity  commences  in  the  bones  of  the  first  row  between  the  third  and  fourth 
y(!ars,  and  a  year  later  in  those  of  the  second  and  third  rows.  The  two  centers  become  united 
in  each  row  between  the  eighteenth  and  twentieth  years. 

In  the  ungual  phalanges  the  centers  for  the  bodies  appear  at  the  distal  extremities  of  the 
phalanges,  instead  of  at  the  middle  of  the  bodies,  as  in  the  other  phalanges.  Moreover,  of  all 
the  bones  of  the  hand,  the  ungual  phalanges  are  the  first  to  ossify. 

THE  BONES  OF  THE  LOWER  EXTREMITY  (OSSA  EXTREMITATIS  INFERIORIS). 

The  Hip  Bone  (Os  Coxae;  Innominate  Bone). 

The  hip  bone  is  a  large,  flattened,  irregularly  shaped  bone,  constricted  in  the 
center  and  expanded  above  and  below.  It  meets  its  fellow  on  the  opposite  side 
ill  the  middle  line  in  front,  and  together  they  form  the  sides  and  anterior  wall  of 
tie  pelvic  cavity.  It  consists  of  three  parts,  the  ilium,  ischium,  and  pubis,  which 
are  distinct  from  each  other  in  the  young  subject,  but  are  fused  in  the  adult; 
t  tie  union  of  the  three  parts  takes  place  in  and  around  a  large  cup-shaped  articular 
cavity,  the  acetabulum,  which  is  situated  near  the  middle  of  the  outer  surface  of  the 
lone.  The  ilium,  so-called  because  it  supports  the  flank, is  the  superior  broad  and 
expanded  portion  which  extends  upward  from  the  acetabulum.  The  ischium  is  the 
lowest  and  strongest  portion  of  the  bone;  it  proceeds  downward  from  the  acetab- 
ilum,  expands  into  a  large  tuberosity,  and  then,  curving  forward,  forms,  with 
the  pubis,  a  large  aperture,  the  obturator  foramen.  The  pubis  extends  medialward 
and  downward  from  the  acetabulum  and  articulates  in  the  middle  line  with  the 
I  one  of  the  opposite  side:  it  forms  the  front  of  the  pelvis  and  supports  the  external 
crgans  of  generation.  ' 

The  niiim  {os  ilii). — ^The  ilium  is  divisible  into  two  parts,  the  body  and  the 
ala;  the  separation  is  indicated  on  the  internal  surface  by  a  curved  line,  the  arcuate 
Ime,  and  on  the  external  surface  by  the  margin  of  the  acetabuluni. 

The  Body  {corpus  oss.  ilii). — The  body  enters  into  the  formation  of  the  acetab- 
jlum,  of  which  it  forms  rather  less  than  two-fifths.  Its  external  surface  is  partly 
articular,  partly  non-articular;  the  articular  segment  forms  part  of  the  lunate 
surface  of  the  acetabulum,  the  non-articular  portion  contributes  to  the  acetabular 
fossa.  The  internal  surface  of  the  body  is  part  of  the  wall  of  the  lesser  pelvis  and 
gives  origin  to  some  fibers  of  the  Obturator  internus.  Below,  it  is  continuous  with 
the  pelvic  surfaces  of  the  ischium  and  pubis,  only  a  faint  line  indicating  the  place 
of  union. 


an 

■ 


Allen  Thomson  demonstrated  the  fact  that  the  first  metacarpal  bone  is  often  developed  from  three  centers:    that  is 
say,  there  is  a  separate  nucleus  for  the  distal  end,  forming  a  distinct  epiphysis  visible  at  the  age  of  seven  or  eight 
®*,'^,      .  .°  stated  that  there  are  traces  of  a  proximal  epiphysis  in  the  second  metacarpal  bone,  Journal  of  Anatomy 
and  Physiology,  1869. 


232 


OSTEOLOGY 


The  Ala  {ala  oss.  ilii). — The  ala  is  the  large  expanded  portion  which  bounds 
the  greater  pelvis  laterally.  It  presents  for  examination  two  surfaces — an  extei-nal 
and  an  internal — a  crest,  and  two  borders — an  anterior  and  a  posterior.  The 
external  surf  ace  (Fig.  235),  known  as  the  dorsum  ilii,  is  directed  backward  and  lateral- 
ward  behind,  and  downward  and  lateralward  in  front.  It  is  smooth,  convex  in  front, 


Posterior 

superio 

spine 


Posterior 
inferior 
spine 


Oemellus  superior 
JSpine  of  ischium 

Qemdlus  inferior 


Ant.  superior 
spine 


-Anterior  inferior  spine 

Articular  capsule 
Ligamentum  teres 


_    o/\       Rectus 
Fuhia]^^  abdominis 


Pyramidalis 

Adductor 
longus 


Fig.  235. — Right  hip  bone.     External  surface. 

deeply  concave  behind;  bounded  above  by  the  crest,  below  by  the  upper  border 
of  the  acetabulum,  in  front  and  behind  by  the  anterior  and  posterior  borders. 
This  surface  is  crossed  in  an  arched  direction  by  three  lines — the  posterior,  anterior,, 
and  inferior  gluteal  lines.  The  posterior  gluteal  line  {superior  curved  line),  the  short- 
est of  the  three,  begins  at  the  crest,  about  5  cm.  in  front  of  its  posterior  extremity; 
it  is  at  first  distinctly  marked,  but  as  it  passes  downward  to  the  upper  part  of  the 


THE  HIP  BONE 


233 


greater  sciatic  notch,  where  it  ends,  it  becomes  less  distinct,  and  is  often  altogether 
lost.  Behind  this  line  is  a  narrow  semilunar  surface,  the  upper  part  of  which 
is  rough  and  gives  origin  to  a  portion  of  the  Glutseus  maximus ;  the  lower  part  is 
smooth  and  has  no  muscular  fibers  attached  to  it.  The  anterior  gluteal  line  {middle 
curved  line),  the  longest  of  the  three,  begins  at  the  crest,  about  4  cm.  behind  its 
anterior  extremity,  and,  taking  a  curved  direction  downward  and  backward,  ends 


Levator  dm 


Constrictor  urethroe 

Cms  penis 
Via.  236. — Right  hip  bone.     Internal  surface. 


Transversus  perincei  superfic 
Ischiocavemosus 


at  the  upper  part  of  the  greater  sciatic  notch.  The  space  between  the  anterior 
and  posterior  gluteal  lines  and  the  crest  is  concave,  and  gives  origin  to  the  Glutseus 
medius.  Near  the  middle  of  this  line  a  nutrient  foramen  is  often  seen.  The 
inferior  gluteal  line  {inferior  curved  line),  the  least  distinct  of  the  three,  begins  in 
front  at  the  notch  on  the  anterior  border,  and,  curving  backward  and  downward, 
ends  near  the  middle  of  the  greater  sciatic  notch.    The  surface  of  bone  included 


234  OSTEOLOGY 


^IHR" 


between  the  anterior  and  inferior  gluteal  lines  is  concave  from  above  downward, 
convex  from  before  backward,  and  gives  origin  to  the  Glutseus  minimus.  Betwtien 
the  inferior  gluteal  line  and  the  upper  part  of  the  acetabulum  is  a  rough,  shallow 
groove,  from  which  the  reflected  tendon  of  the  Rectus  femoris  arises. 

The  internal  surface  (Fig.  236)  of  the  ala  is  bounded  above  by  the  crest,  below, 
by  the  arcuate  line;  in  front  and  behind,  by  the  anterior  and  posterior  borders. 
It  presents  a  large,  smooth,  concave  surface,  called  the  iliac  fossa,  which  gives 
origin  to  the  Iliacus  and  is  perforated  at  its  inner  part  by  a  nutrient  canal;  and 
below  this  a  smooth,  rounded  border,  the  arcuate  line,  which  runs  downward,  for- 
ward, and  medialward.  Behind  the  iliac  fossa  is  a  rough  surface,  divided  into  two 
portions,  an  anterior  and  a  posterior.  The  anterior  surface  {auricular  surface), 
so  called  from  its  resemblance  in  shape  to  the  ear,  is  coated  with  cartilage  in  the 
fresh  state,  and  articulates  with  a  similar  surface  on  the  side  of  the  sacrum. 
The  posterior  portion,  known  as  the  iliac  tuberosity,  is  elevated  and  rough,  for 
the  attachment  of  the  posterior  sacroiliac  ligaments  and  for  the  origins  of  the 
Sacrospinalis  and  Multifidus.  Below^  and  in  front  of  the  auricular  surface  is  the 
preauricular  sulcus,  more  commonly  present  and  better  marked  in  the  female 
than  in  the  male;  to  it  is  attached  the  pelvic  portion  of  the  anterior  sacroiliac 
ligament. 

The  crest  of  the  ilium  is  convex  in  its  general  outline  but  is  sinuously  curved, 
being  concave  inward  in  front,  concave  outward  behind.  It  is  thinner  at  the  center 
than  at  the  extremities,  and  ends  in  the  anterior  and  posterior  superior  iliac  spines. 
The  surface  of  the  crest  is  broad,  and  divided  into  external  and  internal  lips, 
and  an  intermediate  line.  About  5  cm.  behind  the  anterior  superior  iliac  spine 
there  is  a  prominent  tubercle  on  the  outer  lip.  To  the  external  lip  are  attached 
the  Tensor  fasciae  latse,  Obliquus  externus  abdominis,  and  Latissimus  dorsi,  and 
along  its  whole  length  the  fascia  lata;  to  the  intermediate  line  the  Obliquus  internus 
abdominis;  to  the  internal  lip,  the  fascia  iliaca,  the  Transversus  abdominis, 
Quadratus  lumborum,  Sacrospinalis,  and  Iliacus. 

The  anterior  border  of  the  ala  is  concave.  It  presents  two  projections,  separated 
by  a  notch.  Of  these,  the  uppermost,  situated  at  the  junction  of  the  crest  and 
anterior  border,  is  called  the  anterior  superior  iliac  spine;  its  outer  border  gives 
attachment  to  the  fascia  lata,  and  the  Tensor  fasciae  latse,  its  inner  border,  to  the 
Iliacus;  while  its  extremity  affords  attachment  to  the  inguinal  ligament  and  gives 
origin  to  the  Sartorius.  Beneath  this  eminence  is  a  notch  from  which  the  Sartorius 
takes  origin  and  across  which  the  lateral  femoral  cutaneous  nerve  passes.  Below 
the  notch  is  the  anterior  inferior  iliac  spine,  which  ends  in  the  upper  lip  of  the 
acetabulum;  it  gives  attachment  to  the  straight  tendon  of  the  Rectus  femoris  and 
to  the  iliofemoral  ligament  of  the  hip-joint.  Medial  to  the  anterior  inferior  spine 
is  a  broad,  shallow  groove,  over  which  the  Iliacus  and  Psoas  major  pass.  This 
groove  is  bounded  medially  by  an  eminence,  the  iliopectineal  eminence,  which 
marks  the  point  of  union  of  the  ilium  and  pubis. 

The  posterior  border  of  the  ala,  shorter  than  the  anterior,  also  presents  two 
projections  separated  by  a  notch,  the  posterior  superior  iliac  spine  and  the  posterior 
inferior  iliac  spine.  The  former  serves  for  the  attachment  of  the  oblique  portion 
of  the  posterior  sacroiliac  ligaments  and  the  Multifidus;  the  latter  corresponds 
with  the  posterior  extremity  of  the  auricular  surface.  Below  the  posterior  inferior 
spine  is  a  deep  notch,  the  greater  sciatic  notch. 

The  Ischium  {os  ischii). — The  ischium  forms  the  lower  and  back  part  of  the 
hip  bone.    It  is  divisible  into  three  portions — a  body  and  two  rami. 

The  Body  {corpus  oss.  ischii). — The  body  enters  into  and  constitutes  a  little 
more  than  two-fifths  of  the  acetabulum.  Its  external  surface  forms  part  of  the 
lunate  surface  of  the  acetabulum  and  a  portion  of  the  acetabular  fossa.  Its  internal 
surface  is  part  of  the  wall  of  the  lesser  pelvis;  it  gives  origin  to  some  fibers  of  the 


THE  HIP  BONE 


235 


Obturator  mternus.  Its  anterior  border  projects  as  the  posterior  obturator  tubercle; 
from  its  posterior  border  there  extends  backward  a  thin  and  pointed  triangular 
eminence,  the  ischial  spine,  more  or  less  elongated  in  different  subjects.  The 
external  surface  of  the  spine  gives  attachment  to  the  Gemellus  superior,  its  internal 
surface  to  the  Coccygeus,  Levator  ani,  and  the  pelvic  fascia;  while  to  the  pointed 
extremity  the  sacrospinous  ligament  is  attached.  Above  the  spine  is  a  large  notch, 
the  greater  sciatic  notch,  converted  into  a  foramen  by  the  sacrospinous  ligament; 
it  transmits  the  Piriformis,  the  superior  and  inferior  gluteal  vessels  and  nerves, 
the  sciatic  and  posterior  femoral  cutaneous  nerves,  the  internal  pudendal  vessels, 
and  nerve,  and  the  nerves  to  the  Obturator  internus  and  Quadratus  femoris.  Of 
these,  the  superior  gluteal  vessels  and  nerve  pass  out  above  the  Piriformis,  the 
other  structures  below  it.  Below  the  spine  is  a  smaller  notch,  the  lesser  sciatic 
notch;  it  is  smooth,  coated  in  the  recent  state  with  cartilage,  the  surface  of  which 
presents  two  or  three  ridges  corresponding  to  the  subdivisions  of  the  tendon  of 
the  Obturator  internus,  which  winds  over  it.  It  is  converted  into  a  foramen  by 
the  sacrotuberous  and  sacrospinous  ligaments,  and  transmits  the  tendon  of  the 
Obturator  internus,  the  nerve  which  supplies  that  muscle,  and  the  internal 
pudendal  vessels  and  rterve. 

The  Superior  Ramus  {ramus  superior  oss.  ischii;  descending  ramus). — The 
superior  ramus  projects  downward  and  backward  from  the  body  and  presents 
for  examination  three  surfaces:  external,  internal,  and  posterior.  The  external 
surface  is  quadrilateral  in  shape.  It  is  bounded  above  by  a  groove  which  lodges 
the  tendon  of  the  Obturator  externus;  below,  it  is  continuous  with  the  inferior 
ramus;  in  front  it  is  limited  by  the  posterior  margin  of  the  obturator  foramen; 
behind,  a  prominent  margin  separates  it  from  the  posterior  surface.  In  front  of 
this  margin  the  surface  gives  origin  to  the  Quadratus  femoris,  and  anterior  to  this 
to  some  of  the  fibers  of  origin  of  the  Obturator  externus;  the  lower  part  of  the  sur- 
iace  gives  origin  to  part  of  the  Adductor  magnus.  The  internal  surface  forms  part 
of  the  bony  wall  of  the  lesser  pelvis.  In  front  it  is  limited  by  the  posterior  margin 
of  the  obturator  foramen.  Below,  it  is  bounded  by  a  sharp  ridge  which  gives 
attachment  to  a  falciform  prolongation  of  the  sacrotuberous  ligament,  and,  more 
anteriorly,  gives  origin  to  the  Transversus  perinsei  and  Ischiocavernosus.  Poste- 
liorly  the  ramus  forms  a  large  swelling,  the  tuberosity  of  the  ischium,  which  is  divided 
into  two  portions:  a  lower,  rough,  somewhat  triangular  part,  and  an  upper,  smooth, 
juadrilateral  portion.  The  lower  portion  is  subdivided  by  a  prominent  longitudinal 
:*idge,  passing  from  base  to  apex,  into  two  parts;  the  outer  gives  attachment  to 
"he  Adductor  magnus,  the  inner  to  the  sacrotuberous  ligament.  The  upper  portion 
s  subdivided  into  two  areas  by  an  oblique  ridge,  which  runs  downward  and  out- 
ward; from  the  upper  and  outer  area  the  Semimembranosus  arises;  from  the  lower 
and  inner,  the  long  head  of  the  Biceps  femoris  and  the  Semitendinosus. 

The  Inferior  Ramus  {ramus  inferior  oss.  ischii;  ascending  ramus). — The  inferior 
ramus  is  the  thin,  flattened  part  of  the  ischium,  which  ascends  from  the  superior 
ramus,  and  joins  the  inferior  ramus  of  the  pubis — the  junction  being  indicated  in 
the  adult  by  a  raised  line.  The  outer  surface  is  uneven  for  the  origin  of  the  Obturator 
externus  and  some  of  the  fibers  of  the  Adductor  magnus;  its  inner  surface  forms 
part  of  the  anterior  wall  of  the  pelvis.  Its  medial  border  is  thick,  rough,  slightly 
everted,  forms  part  of  the  outlet  of  the  pelvis,  and  presents  two  ridges  and  an 
intervening  space.  The  ridges  are  continuous  with  similar  ones  on  the  inferior 
tamus  of  the  pubis :  to  the  outer  is  attached  the  deep  layer  of  the  superficial  peri- 
heal  fascia  {fascia  of  Colles),  and  to  the  inner  the  inferior  fascia  of  the  urogenital 
diaphragm.  If  these  two  ridges  be  traced  downward,  they  will  be  found  to  join 
i«^^ith  each  other  just  behind  the  point  of  origin  of  the  Transversus  periniei;  here 

She  two  layers  of  fascia  are  continuous  behind  the  posterior  border  of  the  muscle. 
^o  the  intervening  space,  just  in  front  of  the  point  of  junction  of  the  ridges,  the 


236  ^^^^^^^       OSTEOLOGY 


Transversus  perinan  is  attached,  and  in  front  of  this  a  portion  of  the  cms  penis 
vel  clitoridis  and  the  Ischiocavernosus.  Its  lateral  border  is  thin  and  sharp,  and 
forms  part  of  the  medial  margin  of  the  obturator  foramen. 

The  Pubis  {os  imbis) . — The  pubis,  the  anterior  part  of  the  hip  bone,  is  divisible 
into  a  body,  a  superior  and  an  inferior  ramus. 

The  Body  {corpus  oss.  pubis). — The  body  forms  one-fifth  of  the  acetabulum, 
contributing  by  its  external  surface  both  to  the  lunate  surface  and  the  acetabular 
fossa.  Its  internal  surface  enters  into  the  formation  of  the  wall  of  the  lesser  peh'is 
and  gives  origin  to  a  portion  of  the  Obturator  internus. 

The  Superior  Ramus  {ramus  superior  oss.  pubis;  ascending  ramus) . — The  superior 
ramus  extends  from  the  body  to  the  median  plane  where  it  articulates  with  its 
fellow  of  the  opposite  side.  It  is  conveniently  described  in  two  portions,  viz.,  a 
medial  flattened  part  and  a  narrow  lateral  prismoid  portion. 

The  Medial  Portion  of  the  superior  ramus,  formerly  described  as  the  body  of 
the  pubis,  is  somewhat  quadrilateral  iil  shape,  and  presents  for  examination  two 
surfaces  and  three  borders.  The  anterior  surface  is  rough,  directed  downward  and 
outward,  and  serves  for  the  origin  of  various  muscles.  The  Adductor  longus  arises 
from  the  upper  and  medial  angle,  immediately  below  the  crest;  lower  down,  the 
Obturator  externus,  the  Adductor  brevis,  and  the  upper  part  of  the  Gracilis  take 
origin.  The  posterior  surface,  convex  from  above  downward,  concave  from  side 
to  side,  is  smooth,  and  forms  part  of  the  anterior  wall  of  the  pelvis.  It  gives  origin 
to  the  Levator  ani  and  Obturator  internus,  and  attachment  to  the  puboprostatic 
ligaments  and  to  a  few  muscular  fibers  prolonged  from  the  bladder.  The  upper 
border  presents  a  prominent  tubercle,  the  pubic  tubercle  {pubic  spine),  which  pro- 
jects forward;  the  inferior  crus  of  the  subcutaneous  inguinal  ring  {external  abdominal 
ring),  and  the  inguinal  ligament  {Pouparfs  ligament)  are  attached  to  it.  Passing 
upward  and  lateralward  from  the  pubic  tubercle  is  a  well-defined  ridge,  forming 
a  part  of  the  pectineal  line  which  marks  the  brim  of  the  lesser  pelvis:  to  it  are 
attached  a  portion  of  the  inguinal  falx  {conjoined  tendon  of  Obliquus  internus 
and  Transversus),  the  lacunar  ligament  {Gimbernafs  ligament),  and  the  reflected 
inguinal  ligament  {triangular  fascia).  Medial  to  the  pubic  tubercle  is  the  crest, 
which  extends  from  this  process  to  the  medial  end  of  the  bone.  It  affords  attach- 
ment to  the  inguinal  falx,  and  to  the  Rectus  abdominis  and  Pyramidalis.  The 
point  of  junction  of  the  crest  with  the  medial  border  of  the  bone  is  called  the  angle ; 
to  it,  as  well  as  to  the  symphysis,  the  superior  crus  of  the  subcutaneous  inguinal 
ring  is  attached.  The  medial  border  is  articular;  it  is  oval,  and  is  marked  by  eight 
or  nine  transverse  ridges,  or  a  series  of  nipple-like  processes  arranged  in  rows, 
separated  by  grooves;  they  serve  for  the  attachment  of  a  thin  layer  of  cartilage, 
which  intervenes  between  it  and  the  interpubic  fibrocartilaginous  lamina.  The 
lateral  border  presents  a  sharp  margin,  the  obturator  crest,  which  forms  part  of  the 
circumference  of  the  obturator  foramen  and  affords  attachment  to  the  obturator 
membrane. 

The  Lateral  Portion  of  the  ascending  ramus  has  three  surfaces :  superior,  inferior, 
and  posterior.  The  superior  surface  presents  a  continuation  of  the  pectineal  line, 
already  mentioned  as  commencing  at  the  pubic  tubercle.  In  front  of  this  line,  the 
surface  of  bone  is  triangular  in  form,  wider  laterally  than  medially,  and  is  covered 
by  the  Pectineus.  The  surface  is  bounded,  laterally,  by  a  rough  eminence,  the 
iliopectineal  eminence,  which  serves  to  indicate  the  point  of  junction  of  the  ilium 
and  pubis,  and  below  by  a  prominent  ridge  which  extends  from  the  acetabular 
notch  to  the  pubic  tubercle.  The  inferior  surface  forms  the  upper  boundary  of 
the  obturator  foramen,  and  presents,  laterally,  a  broad  and  deep,  oblique  groove, 
for  the  passage  of  the  obturator  vessels  and  nerve;  and  medially,  a  sharp  margin, 
the  obturator  crest,  forming  part  of  the  circumference  of  the  obturator  foramen, 
and  giving  attachment  to  the  obturator  membrane.    The  posterior  surface  consti- 


THE  HIP  BONE 


lutes  part  of  the  anterior  boundary  of  the  lesser  pelvis.  It  is  smooth,  convex  from 
above  downward,  and  affords  origin  to  some  fibers  of  the  Obturator  internus. 

The  Inferior  Ramus  {ramus  inferior  oss.  pubis;  descending  ramus). — The  inferior 
ramus  is  thin  and  flattened.  It  passes  lateralward  and  downward  from  the  medial 
end  of  the  superior  ramus;  it  becomes  narrower  as  it  descends  and  joins  with  the 
inferior  ramus  of  the  ischium  below  the  obturator  foramen.  Its  anterior  surface 
is  rough,  for  the  origin  of  muscles — the  Gracilis  along  its  medial  border,  a  portion 
of  the  Obturator  externus  where  it  enters  into  the  formation  of  the  obturator 
foramen,  and  between  these  two,  the  Adductores  brevis  and  magnus,  the  former 
being  the  more  medial.  The  posterior  surface  is  smooth,  and  gives  origin  to  the 
Obturator  internus,  and,  close  to  the  medial  margin,  to  the  Constrictor  urethra?. 
The  medial  border  is  thick,  rough,  and  everted,  especially  in  females.  It  presents 
two  ridges,  separated  by  an  intervening  space.  The  ridges  extend  downward,  and 
are  continuous  with  similar  ridges  on  the  inferior  ramus  of  the  ischium;  to  the 
external  is  attached  the  fascia  of  Colles,  and  to  the  internal  the  inferior  fascia  of 
the  urogenital  diaphragm.  The  lateral  border  is  thin  and  sharp,  forms  part  of  the 
circumference  of  the  obturator  foramen,  and  gives  attachment  to  the  obturator 
membrane. 

The  Acetabulum  (cotyloid  cavity) . — The  acetabulum  is  a  deep,  cup-shaped,  hemi- 
spherical depression,  directed  downward,  lateralward,  and  forward.  It  is  formed 
medially  by  the  pubis,  above  by  the  ilium,  laterally  and  below  by  the  ischium; 
a  little  less  than  two-fifths  is  contributed  by  the  ilium,  a  little  more  than  two- 
lifths  by  the  ischium,  and  the  remaining  fifth  by  the  pubis.  It  is  bounded  by  a 
])rominent  uneven  rim,  which  is  thick  and  strong  above,  and  serves  for  the  attach- 
ment of  the  glenoidal  labrum  (cotyloid  ligament),  which  contracts  its  orifice,  and 
deepens  the  surface  for  articulation.  It  presents  below  a  deep  notch,  the  acetabular 
notch,  which  is  continuous  with  a  circular  non-articular  depression,  the  acetabular 
riossa,  at  the  bottom  of  the  cavity:  this  depression  is  perforated  by  numerous 
[apertures,  and  lodges  a  mass  of  fat.  The  notch  is  converted  into  a  foramen  by 
l^e  transverse  ligament;  through  the  foramen  nutrient  vessels  and  nerves  enter 
[the  joint;  the  margins  of  the  notch  serve  for  the  attachment  of  the  ligamentum 
teres.  The  rest  of  the  acetabulum  is  formed  by  a  curved  articular  surface,  the 
lunate  surface,  for  articulation  with  the  head  of  the  femur. 

The  Obturator  Foramen  (foramen  ohturatum;  thyroid  foramen). — The  obturator 
foramen  is  a  large  aperture,  situated  between  the  ischium  and  pubis.  In  the  male 
it  is  large  and  of  an  oval  form,  its  longest  diameter  slanting  obliquely  from  before 
backward;  in  the  female  it  is  smaller,  and  more  triangular.  It  is  bounded  by  a 
thin,  uneven  margin,  to  which  a  strong  membrane  is  attached,  and  presents, 
I  superiorly,  a  deep  groove,  the  obturator  groove,  which  runs  from  the  pelvis  obliquely 
medialward  and  downward.  This  groove  is  converted  into  a  canal  by  a  ligamentous 
band,  a  specialized  part  of  the  obturator  membrane,  attached  to  two  tubercles: 
one,  the  posterior  obturator  tubercle,  on  the  medial  border  of  the  ischium,  just  in 
front  of  the  acetabular  notch;  the  other,  the  anterior  obturator  tubercle,  on  the 
obturator  crest  of  the  superior  ramus  of  the  pubis.  Through  the  canal  the 
1  obturator  vessels  and  nerve  pass  out  of  the  pelvis. 

Structure. — The  thicker  parts  of  the  bone  consist  of  cancellous  tissue,  enclosed  between  two 
[layers  of  compact  tissue;  the  thinner  parts,  as  at  the  bottom  of  the  acetabulum  and  center  of 
[the  ihac  fossa,  are  usually  semitransparent,  and  composed  entirely  of  compact  tissue. 

Ossification  (Fig.  237). — The  hip  bone  is  ossified  from  eight  .centers:  three  primary — one  each 
for  the  ihum,  ischium,  and  pubis;  and  ^ye  secondary — one  each  for  the  crest  of  the  ilium,  the 
anterior  inferior  spine  (said  to  occur  more  frequently  in  the  male  than  in  the  female),  the  tuberosity 
lof  the  ischium,  the  pubic  symphysis  (more  frequent  in  the  female  than  in  the  male),  and  one  or 
Imore  for  the  Y-shaped  piece  at  the  bottom  of  the  acetabulum.  The  centers  appear  in  the  foUow- 
ling  order:  in  the  lower  part  of  the  ihum,  immediately  above  the  greater  sciatic  notch,  about 
I  the  eighth  or  ninth  week  of  fetal  life;  in  the  superior  ramus  of  the  ischium,  about  the  third  month; 


238 


OSTEOLOGY 


k 


in  the  superior  ramus  of  the  pubis,  between  the  fourth  and  fifth  months.  At  birth,  the  three 
primary  centers  are  quite  separate,  the  crest,  the  bottom  of  the  acetabulum,  the  ischial  tuberosity, 
and  the  inferior  rami  of  the  ischium  and  pubis  being  still  cartilaginous.  By  the  seventh  or  eighth 
year,  the  inferior  rami  of  the  pubis  and  ischium  are  almost  completely  united  by  bone.  About 
the  thirteenth  or  fourteenth  year,  the  three  primary  centers  have  extended  their  growth  into  the 
bottom  of  the  acetabulum,'  and  are  there  separated  from  each  other  by  a  Y-shaped  portion  of 
cartilage,  which  now  presents  traces  of  ossification,  often  by  two  or  more  centers.  One  of  these, 
the  OS  acetabuli,  appears  about  the  age  of  twelve,  between  the  ilium  and  pubis,  and  fuses  with  them 
about  the  age  of  eighteen;  it  forms  the  pubic  part  of  the  acetabulum.  The  iUum  and  ischium 
then  become  joined,  and  lastly  the  pubis  and  ischium,  through  the  intervention  of  this  Y-shaped 
portion.  At  about  the  age  of  puberty,  ossification  takes  place  in  each  of  the  remaining  porti(ms, 
and  they  join  with  the  rest  of  the  bone  between  the  twentieth  and  twenty-fifth  years.  Separate 
centers  are  frequently  found  for  the  pubic  tubercle  and  the  ischial  spine,  and  for  the  crest  and 
angle  of  the  pubis. 

Articulations. — The  hip  bone  articulates  with  its  fellow  of  the  opposite  side,  and  with  the 
sacrum  and  femur. 

By  eight  centers  \  ^^''^^  primary  {Ilium.  lacUum.  and  Pvhia) 
.  "     "  I  Five  secondary 


(J.      ^^^''^^i* 


i'.Tui'*' 


Fig.  237. — Plan  of  ossification  of  the  hip  bone.    The  three  primary  centers  unite  through  a  Y-shaped  piece  about 
puberty.     Epiphyses  appear  about  puberty,  and  unite  about  twenty-fifth  year. 

The  Pelvis. 

The  pelvis,  so  called  from  its  resemblance  to  a  basin,  is  a  bony  ring,  interposed 
between  the  movable  vertebrae  of  the  vertebral  column  which  it  supports,  and  the 
lower  limbs  upon  which  it  rests;  it  is  stronger  and  more  massively  constructed 
than  the  wall  of  the  cranial  or  thoracic  cavities,  and  is  composed  of  four  bones: 
the  two  hip  bones  laterally  and  in  front  and  the  sacrum  and  cocc3rx  behind. 

The  pelvis  is  divided  by  an  oblique  plane  passing  through  the  prominence  of 
the  sacrum,  the  arcuate  and  pectineal  lines,  and  the  upper  margin  of  the  symphysis 
pubis,  into  the  greater  and  the  lesser  pelvis.  The  circumference  of  this  plane  is 
termed  the  linea  terminaUs  or  pelvic  brim. 

The  Greater  or  False  Pelvis  (pelvis  major). — The  greater  pelvis  is  the  expanded 
portion  of  the  cavity  situated  above  and  in  front  of  the  pelvic  brim.  It  is  bounded 
on  either  side  by  the  ilium;  in  front  it  is  incomplete,  presenting  a  wide  interval 
between  the  anterior  borders  of  the  ilia,  which  is  filled  up  in  the  fresh  state  by 


THE  PELVIS 


239 


the  parietes  of  the  abdomen;  behind  is  a  deep  notch  on  either  side  between  the  ilium 
and  the  base  of  the  sacrum."  It  supports  the  intestines,  and  transmits  part  of  their 
weight  to  the  anterior  wall  of  the  abdomen. 

The  Lesser  or  True  Pelvis  {pelvis  minor). — The  lesser  pelvis  is  that  part  of  the 
pelvic  cavity  which  is  situated  below  and  behind  the  pelvic  brim.  Its  bony  walls 
are  more  complete  than  those  of  the  greater  pehis.  For  convenience  of  descrip- 
tion, it  is  divided  into  an  inlet  bounded  by  the  superior  circumference,  and  outlet 
bounded  by  the  inferior  circumference,  and  a  cavity. 

The  Superior  Circumference. — The  superior  circumference  forms  the  brim  of  the 
pelvis,  the  included  space  being  called  the  superior  aperture  or  inlet  (apertura  pelvis 
[yninoris]  superior)  (Fig.  238).  It  is  formed  laterally  by  the  pectineal  and  arcuate 
lines,  in  front  by  the  crests  of  the  pubes,  and  behind  by  the  anterior  margin  of  the 
base  of  the  sacrum  and  sacrovertebral  angle.  The  superior  aperture  is  somewhat 
heart-shaped,  obtusely  pointed  in  front,  diverging  on  either  side,  and  encroached 
upon  behind  by  the  projection  forward  of  the  promontory  of  the  sacrum.  It  has 
three  principal  diameters:  antero-posterior,  transverse,  and  oblique.  The  antero- 
posterior or  conjugate  diameter  extends  from  the  sacrovertebral  angle  to  the  sym- 


fi 

I 


I 


Fig.  238. — Diameters  of  superior  aperture  of  lesser  pelvis  (female). 

physis  pubis;  its  average  measurement  is  about  110  mm.  in  the  female.  The 
t'ansverse  diameter  extends  across  the  greatest  width  of  the  superior  aperture, 
from  the  middle  of  the  brim  on  one  side  to  the  same  point  on  the  opposite;  its  aver- 
age measurement  is  about  135  mm.  in  the  female.  The  oblique  diameter  extends 
from  the  iliopectineal  eminence  of  one  side  to  the  sacroiliac  articulation  of  the 

pposite  side;  its  average  measurement  is  about  125  mm.  in  the  female. 
The  cavity  of  the  lesser  pelvis  is  bounded  in  front  and  below  by  the  pubic  sym- 

'hysis  and  the  superior  rami  of  the  pubes;  above  and  behind,  by  the  pelvic  surfaces 
of  the  sacrum  and  coccyx,  which,  cijrving  forward  above  and  below,  contract 
the  superior  and  inferior  apertures  of  the  cavity;  laterally,  by  a  broad,  smooth, 
quadrangular  area  of  bone,  corresponding  to  the  inner  surfaces  of  the  body  and 
superior  ramus  of  the  ischium  and  that  part  of  the  ilium  which  is  below  the  arcuate 
line.  From  this  description  it  will  be  seen  that  the  cavity  of  the  lesser  pelvis 
hi  a  short,  curved  canal,  considerably  deeper  on  its  posterior  than  on  its  anterior 
v/all.  It  contains,  in  the  fresh  subject,  the  pelvic  colon,  rectum,  bladder,  and  some 
of  the  organs  of  generation.  The  rectum  is  placed  at  the  back  of  the  pelvis,  in 
the  curve  of  the  sacrum  and  coccyx;  the  bladder  is  in  front,  behind  the  pubic  sym- 
physis. In  the  female  the  uterus  and  vagina  occupy  the  interval  between  these  viscera. 


240 


OSTEOLOGY 


The  Lower  Circumference. — The  lower  circumference  of  the  pelvis  is  very  irregu  ar; 
the  space  enclosed  by  it  is  named  the  inferior  aperture  or  outlet  {apertura  pelvis 
[minoris]  inferior)  (Fig.  239),  and  is  bounded  behind  by  the  point  of  the  coccyx, 
and  laterally  by  the  ischial  tuberosities.  These  eminences  are  separated  by  three 
notches:  one  in  front,  the  pubic  arch,  formed  by  the  convergence  of  the  inferior 


Fia.  239. — Diameters  of  inferior  aperture  of  lesser  pelvis  (female). 

rami  of  the  ischium  and  pubis  on  either  side.  The  other  notches,  one  on  either 
side,  are  formed  by  the  sacrum  and  coccyx  behind,  the  ischium  in  front,  and 
the  ilium  above;  they  are  called  the  sciatic  notches;  in  the  natural  state  they  are 
converted  into  foramina  by  the  sacrotuberous  and  sacrospinous  ligaments.  When 
the  ligaments  are  in  situ,  the  inferior  aperture  of  the  pelvis  is  lozenge-shaped, 

bounded,  in  front,  by  the  pubic  arcuate  ligament 
and  the  inferior  rami  of  the  pubes  and  ischia;  later- 
ally, by  the  ischial  tuberosities;  and  behind,  by  the 
sacrotuberous  ligaments  and  the  tip  of  the  coccyx. 

The  diameters  of  the  outlet  of  the  pelvis  are  two, 
antero-posterior  and  transverse.  The  antero-posterior 
diameter  extends  from  the  tip  of  the  coccyx  to  the 
lower  part  of  the  pubic  symphysis;  its  measurement 
is  from  90  to  115  mm.  in  the  female.  It  varies  with 
the  length  of  the  coccyx,  and  is  capable  of  increase 
or  diminution,  on  account  of  the  mobility  of  that 
bone.  The  transverse  diameter,  measured  between 
the  posterior  parts  of  the  ischial  tuberosities,  is  about 
115  mm.  in  the  female.* 

Axes  (Fig.  240). — A  Hne  at  right  angles  to  the  plane 
of  the  superior  aperture  at  its  center  would,  if  prolonged, 
pass  through  the  umbilicus  above  and  the  middle 
of  the  coccyx  below ;  the  axis  of  the  superior  aperture 
is  therefore  directed  downward  and  backward.  The 
axis  of  the  inferior  aperture,  produced  upward,  would 
touch  the  base  of  the  sacrum,  and  is  also  directed 
downward,  and  slightly  backward.  The  axis  of  the  cavity — i.  e.,  an  axis  at  right 
angles  to  a  series  of  planes  between  those  of  the  superior  and  inferior  apertures 

'  The  measurements  of  the  pelvis  given  above  are  fairly  accurate,  but  different  figures  are  given  by  various  authors 
no  doubt  due  mainly  to  differences  in  the  physique  and  stature  of  the  population  from  whom  the  measurements  have 
been  taken. 


Fia.  240. 


-Median  sagittal  section  of 
pelvis. 


— is  curved  like  the  cavity  itself:  this  curve  corresponds  to  the  concavity  of  the 
sacrum  and  coccyx,  the  extremities  being  indicated  by  the  central  points  of  the 
superior  and  inferior  apertures.  A  knowledge  of  the  direction  of  these  axes 
serves  to  explain  the  course  of  the  fetus  in  its  passage  through  the  pelvis  during 
parturition. 

Position  of  the  Pelvis  (Fig.  240). — In  the  erect  posture,  the  pelvis  is  placed 
obliquely  with  regard  to  the  trunk :  the  plane  of  the  superior  aperture  forms  an 
angle  of  from  50°  to  60°,  and  that  of  the  inferior  aperture  one  of  about  15°  with 
the  horizontal  plane.  The  pelvic  surface  of  the  symphysis  pubis  looks  upward 
and  backward,  the  concavity  of  the  sacrum  and  coccyx  downward  and  forward. 
The  position  of  the  pelvis  in  the  erect  posture  may  be  indicated  by  holding  it  so 
that  the  anterior  superior  iliac  spines  and  the  front  of  the  top  of  the  symphysis 
pubis  are  in  the  same  vertical  plane. 


Fig.   241. — Male  pelvis. 


Differences  between  the  Male  and  Female  Pelves. — The  female  pelvis  (Fig. 
1'42)  is  distinguished  from  that  of  the  male  (Fig.  241)  by  its  bones  being  more 
<lelicate  and  its  depth  less.  The  whole  pelvis  is  less  massive,  and  its  muscular 
impressions  are  slightly  marked.  The  ilia  are  less  sloped,  and  the  anterior  iliac 
opines  more  widely  separated;  hence  the  greater  lateral  prominence  of  the  hips. 
The  preauricular  sulcus  is  more  commonly  present  and  better  marked.  The  supe- 
rior aperture  of  the  lesser  pelvis  is  larger  in  the  female  than  in  the  male;  it  is  more 
nearly  circular,  and  its  obliquity  is  greater.  The  cavity  is  shallower  and  wider; 
the  sacrum  is  shorter  wider,  and  its  upper  part  is  less  curved;  the  obturator 
1  bramina  are  triangular  in  shape  and  smaller  in  size  than  in  the  male.  The  inferior 
aperture  is  larger  and  the  coccyx  more  movable.  The  sciatic  notches  are  wider 
and  shallower,  and  the  spines  of  the  ischia  project  less  inward.  The  acetabula 
are  smaller  and  look  more  distinctly  forward  (Derry^).  The  ischial  tuberosities 
and  the  acetabula  are  wider  apart,  and  the  former  are  more  everted.  The  pubic 
^symphysis  is  less  deep,  and  the  pubic  arch  is  wider  and  more  rounded  than  in  the 
male,  where  it  is  an  angle  rather  than  an  arch. 


16 


'  Journal  of  Anatomy  and  Physiology,  vol.  xliii. 


242 


OSTEOLOGY 


The  size  of  the  pelvis  varies  not  only  in  the  two  sexes,  but  also  in  diffen 
members  of  the  same  sex,  and  does  not  appear  to  be  influenced  in  any  way  by  the 
height  of  the  individual.  Women  of  short  stature,  as  a  rule,  have  broad  pelves. 
Occasionally  the  pelvis  is  equally  contracted  in  all  its  dimensions,  so  much  so 
that  all  its  diameters  measure  12.5  mm.  less  than  the  average,  and  this  even  in 
well-formed  women  of  average  height.  The  principal  divergences,  however,  are 
found  at  the  superior  aperture,  and  affect  the  relation  of  the  antero-posterior 
to  the  transverse  diameter.  Thus  the  superior  aperture  may  be  elliptical  either 
in  a  transverse  or  an  antero-posterior  direction,  the  transverse  diameter  in  the 
former,  and  the  antero-posterior  in  the  latter,  greatly  exceeding  the  other  diameters; 
in  other  instances  it  is  almost  circular. 


Fig.  242. — Female  pelvis. 

In  the  fetus,  and  for  several  years  after  birth,  the  pelvis  is  smaller  in  proportion 
than  in  the  adult,  and  the  projection  of  the  sacrovertebral  angle  less  marked. 
The  characteristic  differences  between  the  male  and  female  pelvis  are  distinctly 
indicated  as  early  as  the  fourth  month  of  fetal  life. 

Abnormalities. — There  is  arrest  of  development  in  the  bones  of  the  pelvis  in  cases  of  extro- 
version of  the  bladder;  the  anterior  part  of  the  pelvic  girdle  is  deficient,  the  superior  rami  of 
the  pubes  are  imperfectly  developed,  and  the  symphysis  is  absent.  "The  pubic  bones  are  sepa- 
rated to  the  extent  of  from  two  to  four  inches,  the  superior  rami  shortened  and  directed  forward, 
and  the  obturator  foramen  diminished  in  size,  narrowed,  and  turned  outward.  The  iliac  bones 
are  straightened  out  more  than  normal.  The  sacrum  is  very  peculiar.  The  lateral  curve,  instead 
of  being  concave,  is  flattened  out  or  even  convex,  with  the  iliosacral  facets  turned  more  outward 
than  normal,  while  the  vertical  curve  is  straightened."^ 


The  Femur  (Thigh  Bone). 

The  femur  (Figs.  244,  245),  the  longest  and  strongest  bone  in  the  skeleton,  is 
almost  perfectly  cylindrical  in  the  greater  part  of  its  extent.  In  the  erect  posture 
it  is  not  vertical,  being  separated  above  from  its  fellow  by  a  considerable  interval, 
which  corresponds  to  the  breadth  of  the  pelvis,  but  inclining  gradually  downward 
and  medialward,  so  as  to  approach  its  fellow  toward  its  lower  part,  for  the  purpose 
of  bringing  the  knee-joint  near  the  line  of  gravity  of  the  body.  The  degree  of  this 
inclination  varies  in  different  persons,  and  is  greater  in  the  female  than  in  the  male, 

'  Wood,  Heath's  Dictionary  of  Practical  Surgery,  i,  426. 


THE  FEMUR 


243 


on  account  of  the  greater  breadth  of  the  pelvis.  The  femur,  like  other  long  bones, 
is  divisible  into  a  body  and  two  extremities. 

The  Upper  Extremity  {yroximal  extremity,  Fig.  243). — The  upper  extremity 
presents  for  examination  a  head,  a  neck,  a  greater  and  a  lesser  trochanter. 

The  Head  {caput  femoris) .■ — The  head  which  is  globular  and  forms  rather  more 
than  a  hemisphere,  is  directed  upward,  medialward,  and  a  little  forward,  the  greater 
part  of  its  convexity  being  above  and  in  front.  Its  surface  is  smooth,  coated  with 
cartilage  in  the  fresh  state,  except  over  an  ovoid  depression,  the  fovea  capitis 
femoris,  which  is  situated  a  little  below  and  behind  the  center  of  the  head,  and  gives 
attachment  to  the  ligamentum  teres. 

The  Neck  (collum  femoris) . — The  neck  is  a  flattened  pyramidal  process  of  bone, 
connecting  the  head  with  the  body,  and  forming  with  the  latter  a  wide  angle  open- 
ing medialward.  The  angle  is  widest  in  infancy,  and  becomes  lessened  during 
growth,  so  that  at  puberty  it  forms  a  gentle  curve  from  the  axis  of  the  body  of  the 
bone.  In  the  adult,  the  neck  forms  an  angle  of  about  125°  with  the  body,  but  this 
varies  in  inverse  proportion  to  the  development  of  the  pelvis  and  the  stature.    In 


Fovea  capitis, 
for  lig.  teres 


Obturator  internus  and  Gemelli 

Pirifor/mis 

Insertion  of  Obturator 
externum 


Oreater  trocJmnter 


Lesser  trochanter 


Fig.  243. — Upper  e.\tremity  of  right  femur  viewed  from  behind  and  above. 


the  female,  in  consequence  of  the  increased  width  of  the  pelvis,  the  neck  of  the 
femur  forms  more  nearly  a  right  angle  with  the  body  than  it  does  in  the  male. 
^^he  angle  decreases  during  the  period  of  growth,  but  after  full  growth  has  been 
attained  it  does  not  usually  undergo  any  change,  even  in  old  age;  it  varies  con- 
siderably in  different  persons  of  the  same  age.  It  is  smaller  in  short  than  in  long 
bones,  and  when  the  pelvis  is  wide.  In  addition  to  projecting  upward  and  medial- 
V7ard  from  the  body  of  the  femur,  the  neck  also  projects  somewhat  forward ;  the 
amount  of  this  forward  projection  is  extremely  variable,  but  on  an  average  is  from 
12°  to  14°. 

The  neck  is  flattened  from  before  backward,  contracted  in  the  middle,  and 
broader  laterally  than  medially.  The  vertical  diameter  of  the  lateral  half  is  in- 
creased by  the  obliquity  of  the  lower  edge,  which  slopes  downward  to  join  the 
body  at  the  level  of  the  lesser  trochanter,  so  that  it  measures  one-third  more 
than  the  antero-posterior  diameter.  The  medial  half  is  smaller  and  of  a  more 
circular  shape.  The  anterior  sm-f ace  of  the  neck  is  perforated  by  numerous  vascular 
foramina.  Along  the  upper  part  of  the  line  of  junction  of  the  anterior  surface 
with   the    head    is    a  shallow   groove,   best  marked    in    elderly    subjects;    this 


I 


244 


OSTEOLOGY 


Obturator  internus 
and  Oemelli 
Piriformis 


Tubercle 


Articular  capsule 


Articvlar  capsule 


Adductor 
tvbercle 

Medial 
Cpicondyle 


Fio.  244. — Right  femur.     Anterior  surface. 


groove  lodges  the  orbicular  fibers 
of  the  capsule  of  the  hip-joint. 
The  posterior  surface  is  smooth,  and 
is  broader  and  more  concave  than 
the  anterior:  the  posterior  part  of 
the  capsule  of  the  hip-joint  is 
attached  to  it  about  1  cm.  above 
the  intertrochanteric  crest.  The 
superior  border  is  short  and  thick, 
and  ends  laterally  at  the  greater 
trochanter;  its  surface  is  perforated 
by  large  foramina.  The  inferior 
border,  long  and  narrow,  curves  a 
little  backward,  to  end  at  the  lesser 
trochanter. 

The  Trochanters.^ — The  trochan- 
ters are  prominent  processes  which 
afford  leverage  to  the  muscles  that 
rotate  the  thigh  on  its  axis.  They 
are  two  in  number,  the  greater  and 
the  lesser. 

The  Greater  Trochanter  {trochanter 
major;  great  trochanter)  is  a  large, 
irregular,  quadrilateral  eminence, 
situated  at  the  junction  of  the  neck 
with  the  upper  part  of  the  body.  It 
is  directed  a  little  lateralward  and 
backward,  and,  in  the  adult,  is  about 
1  cm.  lower  than  the  head.  It  has 
two  surfaces  and  four  borders.  The 
lateral  surface,  quadrilateral  in  form, 
is  broad,  rough,  convex,  and  marked 
by  a  diagonal  impression,  which 
extends  from  the  postero-superior 
to  the  antero-inferior  angle,  and 
serves  for  the  insertion  of  the  ten- 
don of  the  Glutaeus  medius.  Above 
the  impression  is  a  triangular  sur- 
face, sometimes  rough  for  part  of 
the  tendon  of  the  same  muscle, 
sometimes  smooth  for  the  inter- 
position of  a  bursa  between  the 
tendon  and  the  bone.  Below  and 
behind  the  diagonal  impression  is 
a  smooth,  triangular  surface,  over 
which  the  tendon  of  the  Glutseus 
maximus  plays,  a  bursa  being  inter- 
posed. The  medial  surface,  of  much 
less  extent  than  the  lateral,  pre- 
sents at  its  base  a  deep  depression, 
the  trochanteric  fossa  (digital  fossa), 
for  the  insertion  of  the  tendon  of 
the  Obturator  externus,  and  above 
and  in  front  of  this  an  impression 
for    the   insertion  of   the  Obtura- 


tor  internus  and  Gemelli.  The 
superior  border  is  free;  it  is  thick 
and  irregular,  and  marked  near 
the  center  by  an  impression  for 
the  insertion  of  the  Piriformis. 
The  inferior  border  corresponds 
to  the  line  of  junction  of  the 
base  of  the  trochanter  with  the 
lateral  surface  of  the  body;  it  is 
marked  by  a  rough,  prominent, 
slightly  curved  ridge,  which  gives 
origin  to  the  upper  part  of  the 
Vastus  lateralis.  The  anterior 
border  is  prominent  and  some- 
what irregular;  it  affords  inser- 
tion at  its  lateral  part  to  the 
Glutseus  minimus.  The  posterior 
border  is  very  prominent  and 
apipears  as  a  free,  rounded  edge, 
which  bounds  the  back  part  of 
the  trochanteric  fossa. 

The  Lesser  Trochanter  (tro- 
chanter minor;  small  trochanter) 
is  a  conical  eminence,  which 
varies  in  size  in  different  sub- 
jects; it  projects  from  the  lower 
and  back  part  of  the  base  of  the 
nuck.  From  its  apex  three  well- 
narked  borders  extend;  two  of 
these  are  above — a  medial  con- 
tinuous with  the  lower  border 
o'  the  neck,  a  lateral  with  the 
intertrochanteric  crest;  the  in- 
ferior border  is  continuous  with 
tlie  middle  division  of  the  linea 
aipera.    The  summit  of  the  tro- 

Piianter  is  rough,  and  gives  in- 
ortion    to   the   tendon  of  the 
Psoas  major. 

A  prominence,  of  variable  size, 
occurs  at  the  junction  of  the 
upper  part  of  the  neck  with  the 
greater  trochanter,  and  is  called 
tie  tubercle  of  the  femur;  it  is 
tie  point  of  meeting  of  five 
nmscles:  the  Gluta^us  minimus 
laterally,  the  Vastus  lateralis 
below,  and  the  tendon  of  the 
Obturator  internus  and  two 
Cremelli  above.  Running  ob- 
liquely downward  and  medial- 
ward  from  the  tubercle  is  the 
intertrochanteric  line  (spiral  line 
of  the  femur) ;  it  winds  around 
the  medial  side  of  the  body  of 
he  bone,  below  the  lesser  tro- 


THE  FEMUR 


Articular 
capsule 


Latenil 
epicondyle 

Groove  for 
tendon  of 
Popliteus 


I 


FiQ.  245 


Articular 
capsule 
Right  femur. 


Posterior  surface. 


i 


246  ^^^^^^  OSTEOLOGY 


chanter,  and  ends  about  5  cm.  below  this  eminence  in  the  linea  aspera.  Its  upper 
half  is  rough,  and  affords  attachment  to  the  iliofemoral  ligament  of  the  hip-joint; 
its  lower  half  is  less  prominent,  and  gives  origin  to  the  upper  part  of  the  Vastus 
medialis.  Running  obliquely  downward  and  medialward  from  the  summit  of  the 
greater  trochanter  on  the  posterior  surface  of  the  neck  is  a  prominent  ridge,  the 
intertrochanteric  crest.  Its  upper  half  forms  the  posterior  border  of  the  greater  tro- 
chanter, and  its  lower  half  runs  downward  and  medialward  to  the  lesser  trochanter. 
A  slight  ridge  is  sometimes  seen  commencing  about  the  middle  of  the  intertrochan- 
teric crest,  and  reaching  vertically  downward  for  about  5  cm.  along  the  back  part 
of  the  body:  it  is  called  the  linea  quadrata,  and  gives  attachment  to  the  Quad- 
ratus  femoris  and  a  few  fibers  of  the  Adductor  magnus.  Generally  there  is  merely 
a  slight  thickening  about  the  middle  of  the  intertrochanteric  crest,  marking  the 
attachment  of  the  upper  part  of  the  Quadratus  femoris. 

The  Body  or  Shaft  (corpus  femoris). — The  body,  almost  cylindrical  in  form,  is 
a  little  broader  above  than  in  the  center,  broadest  and  somewhat  flattened  from 
before  backward  below.  It  is  slightly  arched,  so  as  to  be  convex  in  front,  and  con- 
cave behind,  where  it  is  strengthened  by  a  prominent  longitudinal  ridge,  the  linea 
aspera.  It  presents  for  examination  three  borders,  separating  three  surfaces.  Of 
the  borders,  one,  the  linea  aspera,  is  posterior,  one  is  medial,  and  the  other,  lateral. 

The  linea  aspera  (Fig.  245)  is  a  prominent  longitudinal  ridge  or  crest,  on  the 
middle  third  of  the  bone,  presenting  a  medial  and  a  lateral  lip,  and  a  narrow 
rough,  intermediate  line.  Above,  the  linea  aspera  is  prolonged  by  three  ridges. 
The  lateral  ridge  is  very  rough,  and  runs  almost  vertically  upward  to  the  base  of 
the  greater  trochanter.  It  is  termed  the  gluteal  tuberosity,  and  gives  attachment 
to  part  of  the  Glutseus  maximus :  its  upper  part  is  often  elongated  into  a  roughened 
crest,  on  which  a  more  or  less  well-marked,  rounded  tubercle,  the  third  trochanter, 
is  occasionally  developed.  The  intermediate  ridge  or  pectineal  line  is  continued 
to  the  base  of  the  lesser  trochanter  and  gives  attachment  to  the  Pectineus;  the 
medial  ridge  is  lost  in  the  intertrochanteric  line;  between  these  two  a  portion  of  the 
Iliacus  is  inserted.  Below,  the  linea  aspera  is  prolonged  into  two  ridges,  enclosing 
between  them  a  triangular  area,  the  popliteal  surface,  upon  which  the  popliteal 
artery  rests.  Of  these  two  ridges,  the  lateral  is  the  more  prominent,  and  descends 
to  the  summit  of  the  lateral  condyle.  The  medial  is  less  marked,  especially  at  its 
upper  part,  where  it  is  crossed  by  the  femoral  artery.  It  ends  below  at  the  summit 
of  the  medial  condyle,  in  a  small  tubercle,  the  adductor  tubercle,  which  affords 
insertion  to  the  tendon  of  the  Adductor  magnus. 

From  the  medial  lip  of  the  linea  aspera  and  its  prolongations  above  and  below, 
the  Vastus  medialis  arises;  and  from  the  lateral  lip  and  its  upward  prolongation, 
the  Vastus  lateralis  takes  origin.  The  Adductor  magnus  is  inserted  into  the  linea 
aspera,  and  to  its  lateral  prolongation  above,  and  its  medial  prolongation  below. 
Between  the  Vastus  lateralis  and  the  Adductor  magnus  two  muscles  are  attached 
— viz.,  the  Glutseus  maximus  inserted  above,  and  the  short  head  of  the  Biceps 
femoris  arising  below.  Betweeen  the  Adductor  magnus  and  the  Vastus  medialis 
four  muscles  are  inserted:  the  Iliacus  and  Pectineus  above;  the  Adductor  brevis 
and  Adductor  longus  below.  The  linea  aspera  is  perforated  a  Uttle  below  its  center 
by  the  nutrient  canal,  which  is  directed  obliquely  upward. 

The  other  two  borders  of  the  femur  are  only  slightly  marked:  the  lateral  border 
extends  from  the  antero-inferior  angle  of  the  greater  trochanter  to  the  anterior 
extremity  of  the  lateral  condyle ;  the  medial  border  from  the  intertrochanteric  line, 
at  a  point  opposite  the  lesser  trochanter,  to  the  anterior  extremity  of  the  medial 
condyle. 

The  anterior  surface  includes  that  portion  of  the  shaft  which  is  situated  between 
the  lateral  and  medial  borders.  It  is  smooth,  convex,  broader  above  and  below 
than  in  the  center.  From  the  upper  three-fourths  of  this  surface  the  Vastus  inter- 
medius  arises;  the  lower  fourth  is  separated  from  the  muscle  by  the  intervention 


■THE  FEMUR 


247" 


of  the  synovial  membrane  of  the  knee-joint  and  a  bursa;  from  the  upper  part  of  it 
the  Articularis  genu  takes  origin.  The  lateral  surface  includes  the  portion  between 
the  lateral  border  and  the  linea  aspera;  it  is  continuous  above  with  the  correspond- 
ing surface  of  the  greater  trochanter,  below  with  that  of  the  lateral  condyle :  from 
its  upper  three-fourths  the  ^''astus  intermedins  takes  origin.  The  medial  surface 
includes  the  portion  between  the  medial  border  and  the  linea  aspera ;  it  is  continu- 
ous above  with  the  lower  border  of  the  neck,  below  with  the  medial  side  of  the 
medial  condyle:  it  is  covered  by  the  Vastus  medialis. 

The  Lower  Extremity  (distal  extremity) ,  (Fig.  246) . — The  lower  extremity,  larger 
than  the  upper,  is  somewhat  cuboid  in  form,  but  its  transverse  diameter  is  greater 
than  its  antero-posterior;  it  consists  of  two  oblong  eminences  known  as  the  condyles. 
In  front,  the  condyles  are  but  slightly  prominent,  and  are  separated  from  one  another 
by  a  smooth  shallow  articular  depression  called  the  patellar  surface;  behind,  they 
project  considerably,  and  the  interval  between  them  forms  a  deep  notch,  the 
intercondyloid  fossa.  The  lateral  condyle  is  the  more  prominent  and  is  the  broader 
both  in  its  antero-posterior  and  transverse  diameters,  the  medial  condyle  is  the 
longer  and,  when  the  femur  is  held  with  its  body  perpendicular,  projects  to  a  lower 


Laieral  groove 
Lateral  epicondyle 


Medial  groove 


Medial  epicondyle 
Semilunar  area 


Fio.  246. — Lower  extremity  of  right  femur  viewed  from  below. 

level.  When,  however,  the  femur  is  in  its  natural  oblique  position  the  lower  sur- 
faces of  the  two  condyles  lie  practically  in  the  same  horizontal  plane.  The  condyles 
ire  not  quite  parallel  with  one  another;  the  long  axis  of  the  lateral  is  almost 
directly  antero-posterior,  but  that  of  the  medial  runs  backward  and  medialward. 

P Their  opposed  surfaces  are  small,  rough,  and  concave,  and  form  the  walls  of  the 
intercondyloid  fossa.  This  fossa  is  limited  above  by  a  ridge,  the  intercondyloid 
line,  and  below  by  the  central  part  of  the  posterior  margin  of  the  patellar  surface. 
The  posterior  cruciate  ligament  of  the  knee-joint  is  attached  to  the  lower  and  front 
^^  part  of  the  medial  wall  of  the  fossa  and  the  anterior  cruciate  ligament  to  an  impres- 
^m  sion  on  the  upper  and  back  part  of  its  lateral  wall.  Each  condyle  is  surmounted 
by  an  elevation,  the  epicondyle.  The  medial  epicondyle  is  a  large  convex  eminence 
to  which  the  tibial  collateral  ligament  of  the  knee-joint  is  attached.  At  its  upper 
part  is  the  adductor  tubercle,  already  referred  to,  and  behind  it  is  a  rough  impres- 
sion which  gives  origin  to  the  medial  head  of  the  Gastrocnemius.  The  lateral 
epicondyle,  smaller  and  less  prominent  than  the  medial,  gives  attachment  to  the 
fibular  collateral  ligament  of  the  knee-joint.  Directly  below  it  is  a  small  depression 
from  which  a  smooth  well-marked  groove  curves  obliquely  upward  and  backward 
to  the  posterior  extremity  of  the  condyle.  This  groove  is  separated  from  the 
articular  surface  of  the  condyle  by  a  prominent  lip  across  which  a  second,  shallower 
groove  runs  vertically  downward  from  the  depression.  In  the  fresh  state  these 
grooves  are  covered  with  cartilage.  The  Popliteus  arises  from  the  depression; 
its  tendon  lies  in  the  oblique  groove  when  the  knee  is  flexed  and  in  the  vertical 


I 


248  ^        OSTEOLOGY 


h 


groove  when  the  knee  is  extended.  Above  and  behind  the  lateral  epieondyle  is 
an  area  for  the  origin  of  the  lateral  head  of  the  Gastrocnemius,  above  and  to  the 
medial  side  of  which  the  Plantaris  arises. 

The  articular  surface  of  the  lower  end  of  the  femur  occupies  the  anterior,  inferior, 
and  posterior  surfaces  of  the  condyles.  Its  front  part  is  named  the  patellar  surface 
and  articulates  with  the  patella;  it  presents  a  median  groove  which  extends  down- 
ward to  the  intercondyloid  fossa  and  two  convexities,  the  lateral  of  which  is  broader, 
more  prominent,  and  extends  farther  upward  than  the  medial.  The  lower  and 
posterior  parts  of  the  articular  surface  constitute  the  tibial  surfaces  for  articulation 
with  the  corresponding  condyles  of  the  tibia  and  menisci.  These  surfaces  are 
separated  from  one  another  by  the  intercondyloid  fossa  and  from  the  patellar 
surface  by  faint  grooves  which  extend  obliquely  across  the  condyles.  The  lateral 
groove  is  the  better  marked ;  it  runs  lateralward  and  forward  from  the  front  part 
of  the  intercondyloid  fossa,  and  expands  to  form  a  triangular  depression.  When 
the  knee-joint  is  fully  extended,  the  triangular  depression  rests  upon  the  anterior 
portion  of  the  lateral  meniscus,  and  the  medial  part  of  the  groove  comes  into  con- 
tact with  the  medial  margin  of  the  lateral  articular  surface  of  the  tibia  in  front 
of  the  lateral  tubercle  of  the  tibial  intercondyloid  eminence.  The  medial  groove 
is  less  distinct  than  the  lateral.  It  does  not  reach  as  far  as  the  intercondyloid 
fossa  and  therefore  exists  only  on  the  medial  part  of  the  condyle;  it  receives  the 
anterior  edge  of  the  medial  meniscus  when  the  knee-joint  is  extended.  Where  the 
groove  ceases  laterally  the  patellar  surface  is  seen  to  be  continued  backward  as 
a  semilunar  area  close  to  the  anterior  part  of  the  intercondyloid  fossa;  this  semi- 
lunar area  articulates  with  the  medial  vertical  facet  of  the  patella  in  forced  flexion 
of  the  knee-joint.  The  tibial  surfaces  of  the  condyles  are  convex  from  side  to  side 
and  from  before  backward.  Each  presents  a  double  curve,  its  posterior  segment 
being  an  arc  of  a  circle,  its  anterior,  part  of  a  cycloid.^ 

The  Architecture  of  the  Femur. — Koch'^  by  mathematical  analysis  has  "shown  that  in  every 
part  of  the  femur  there  is  a  remarkable  adaptation  of  the  inner  structure  of  the  bone  to  the  machan- 
ical  requirements  due  to  the  load  on  the  femur-head.  The  various  parts  of  the  femur  taken 
together  form  a  single  mechanical  structure  wonderfully  well-adapted  for  the  efficient,  economical 
transmission  of  the  loads  from  the  acetabulum  to  the  tibia;  a  structure  in  which  every  element 
contributes  its  modicum  of  strength  in  the  manner  required  by  theoretical  mechanics  for  maximum 
efficiency."  "The  internal  structure  is  everywhere  so  formed  as  to  provide  in  an  efficient  manner 
for  all  the  internal  stresses  which  occur  due  to  the  load  on  the  femur-head.  Throughout  the  femur, 
with  the  load  on  the  femur-head,  the  bony  material  is  arranged  in  the  paths  of  the  maximum 
internal  stresses,  which  are  thereby  resisted  with  the  greatest  efficiency,  and  hence  with  maximum 
economy  of  material."  "The  conclusion  is  inevitable  that  the  inner  structure  and  outer  form  of 
the  femur  are  governed  by  the  conditions  of  maximum  stress  to  which  the  bone  is  subjected 
normally  by  the  preponderant  load  on  the  femur- head;  that  is,  by  the  body  weight  transmitted 
to  the  femur-head  through  the  acetabulum."  "The  femur  obeys  the  mechanical  laws  that  govern 
other  elastic  bodies  under  stress ;  the  relation  between  the  computed  internal  stresses  due  to  the 
load  on  the  femur-head,  and  the  internal  structure  of  the  different  portions  of  the  femur  is  in  very 
close  agreement  with  the  theoretical  relations  that  should  exist  between  stress  and  structure  for 
maximum  economy  and  efficiency;  and,  therefore,  it  is  believed  that  the  following  laws  of  bone 
structure  have  been  demonstrated  for  the  femur: 

"1.  The  inner  structure  and  external  form  of  human  bone  are  closely  adapted  to  the  mechanical 
conditions  existing  at  every  point  in  the  bone. 

"2.  The  inner  architecture  of  normal  bone  is  determined  by  definite  and  exact  requirements  of 
mathematical  and  mechanical  laws  to  produce  a  maximum  of  strength  with  a  minimum  of 
material." 

The  Inner  Architecture  of  the  Upper  Femur. — "The  spongy  bone  of  the  upper  femur  (to  the 
lower  limit  of  the  lesser  trochanter)  is  composed  of  two  distinct  systems  of  trabeculae  arranged  in 
curved  paths:  one,  which  has  its  origin  in  the  medial  (inner)  side  of  the  shaft  and  curving  upward 

'  A  cycloid  is  a  curve  traced  by  a  point  in  the  circumference  of  a  wheel  when  the  wheel  is  rolled  along  in  a  straight 
line. 

»  The  Laws  of  Bone  .\rchitecture.  Am.  Jour,  of  Anat.,  21,  1917.  The  following  paragraphs  are  taken  almost  ver- 
batum  from  Koch's  article  in  which  we  have  the  first  correct  mathematical  analysis  of  the  femur  in  support  of  the 
theory  of  the  functional  form  of  bone  proposed  by  Wolff  and  also  by  Rous. 


THE  FEMUR 


249 


in  a  fan-like  radiation  to  the  opposite  side  of  the  bone;  the  other,  having  origin  in  the  lateral 
(outer)  portion  of  the  shaft  and  arching  upward  and  medially  to  end  in  the  upper  surface  of  the 
greater  trochanter,  neck  and  head.    These  two  systems  intersect  each  other  at  right  angles. 

"A.  Medial  (Compressive)  System  of  Traheculce. — As  the  compact  bone  of  the  medial  (inner) 
part  of  the  shaft  nears  the  head  of  the  femur  it  gradually  becomes  thinner  and  finally  reaches  the 
articular  surface  of  the  head  as  a  very  thin  layer.    From  a  point  at  about  the  lower  level  of  the 


Fig.  247. — Frontal  longitudinal  midsection  of  upper  femur. 


lesser  trochanter,  2|  to  3  inches  from  the  lower  limit  of  the  articular  surface  of  the  head,  the 
Irabecula;  branch  off  from  the  shaft  in  smooth  curves,  spreading  radially  to  cross  to  the  opposite 
.-ide  in  two  well-defined  groups:  a  lower,  or  secondary  group,  and  an  upper,  or  principal  group. 

"a.  The  Secondary  Compressive  Group. — This  group  of  trabecular  leaves  the  inner  border  of  the 
shaft  beginning  at  about  the  level  of  the  lesser  trochanter,  and  for  a  distance  of  almost  2  inches 
along  the  curving  shaft,  with  which  the  separate  trabecular  make  an  angle  of  about  15  degrees. 


■ 


OSTEOLOGY 


II 


They  curve  outwardly  and  upwardly  to  cross  in  radiating  smooth  curves  to  the  opposite  side. 
The  lower  filaments  end  in  the  region  of  the  greater  trochanter:  the  adjacent  filaments  above 
these  pursue  a  more  nearly  vertical  course  and  end  in  the  upper  portion  of  the  neck  of  the  femur. 
The  trabeculae  of  this  group  are  thin  and  with  wide  spaces  between  them.  As  they  traverse 
the  space  between  the  medial  and  lateral  surfaces  of  the  bone  they  cross  at  right  angles  the  system 
of  curved  trabeculae  which  arise  from  the  lateral  (outer)  portion  of  the  shaft.  (Figs.  247  and  249.) 
"b.  The  Principal  Compressive  Group. — This  group  of  trabeculae  (l^igs.  247  and  249)  springs 
from  the  medial  portion  of  the  shaft  just  above  the  group  above-described,  and  spreads  upward 
and  in  slightly  radial  smooth  curved  lines  to  reach  the  upper  portion  of  the  articular  surface  of 
the  head  of  the  femur.  These  trabeculse  are  placed  very  closely  together  and  are  the  thickest  ones 
seen  in  the  upper  femur.  They  are  a  prolongation  of  the  shaft  from  which  they  spring  in  straight 


LOAD 


n 


Fig.  248. — Diagram  of  the  lines  of  stress  in  the  upper  femur,  based  upon  the  mathematical  analysis  of  the  right 
femur.  These  result  from  the  combination  of  the  different  kinds  of  stres.ses  at  each  point  in  the  femur.  (After 
Koch.) 

lines  which  gradually  curve  to  meet  at  right-angles  the  articular  surface.  There  is  no  change  as 
they  cross  the  epiphyseal  line.  They  also  intersect  at  right-angles  the  system  of  lines  which  rise 
from  the  lateral  side  of  the  femur. 

"This  system  of  principal  and  secondary  compressive  trabeculae  corresponds  in  position  and  in 
curvature  with  the  lines  of  maximum  compressive  stress,  which  were  traced  out  in  the  mathematical 
analysis  of  this  portion  of  the  femur.     (Figs.  247  and  250.) 

"B.  Lateral  (Tensile)  System  of  Traheculce. — As  the  compact  bone  of  the  outer  portion  of  the 
shaft  approaches  the  greater  trochanter  it  gradually  decreases  in  thickness.  Beginning  at  a  point 
about  1  inch  below  the  level  of  the  lower  border  of  the  greater  trochanter,  numerous  thin  trabeculae 
are  given  off  from  the  outer  portion  of  the  shaft.     These  trabeculae  lie  in  three  distinct  groups. 

"c.  The  Greater  Trochanter  Group. — These  trabeculae  rise  from  the  outer  part  of  the  shaft  just 
below  the  greater  trochanter  and  rise  in  thin,  curving  lines  to  cross  the  region  of  the  greater 
trochanter  and  end  in  its  upper  surface.    Some  of  these  filaments  are  poorly  defined.    This  group 


THE  FEMUR 


251 


I 


Fig.  249. — Frontal  longitudinal  midsection  of  left 
;mur.  Taken  from  the  same  subject  as  the  one  that 
■as  analyzed  and  shown  in  Figs.  248  and  250.  4  of 
atural  size.     (After  Koch.) 


Fig.  250.  —  Diagram  of  the  computed  lines  of 
maximum  stress  in  the  normal  femur.  The  section 
numbers  2,  4,  6,  8,  etc.,  show  the  positions  of  the 
transverse  sections  analyzed.  The  amounts  of  the 
maximum  tensile  and  compressive  stress  at  the 
various  sections  are  given  for  a  load  of  100  pounds  on 
the  femur-head.  For  the  standing  position  ("at  at- 
tention") these  stresses  are  multiplied  by  0.6,  for 
walking  by  1.6  and  for  running  by  3.2.     (After  Koch.) 


OSTEOLOGY 


The  trabecule  of  this 


intersects  the  trabeculse  of  group  (o)  which  rise  from  the  opposite  side, 
group  evidently  carry  small  stresses,  as  is  shown  by  their  slenderness. 

"d.  The  Principal  Tensile  Group. — This  group  springs  from  the  outer  part  of  the  shaft  imme- 
diately below  group  c,  and  curves  convexly  upward  and  inward  in  nearly  parallel  lines  across  1  he 
neck  of  the  femur  and  ends  in  the  inferior  portion  of  the  head.  These  trabeculse  are  somewhat 
thinner  and  more  widely  spaced  than  those  of  the  principal  compressive  group  (6).  All  the  trabec- 
ular of  this  group  cross  those  of  groups  (a)  and  (6)  at  right  angles.  This  group  is  the  most  impor- 
tant of  the  lateral  system  (tensile)  and,  as  will  be  shown  later,  the  greatest  tensile  stresses  of  the 
upper  femur  are  carried  by  the  trabecular  of  this  group. 

"e.  The  Secondary  Tensile  Group. — This  group  consists  of  the  trabeculse  which  spring  from  the 
outer  side  of  the  shaft  and  lie  below  those  of  the  preceding  group.  They  curve  upward  and  medially 
across  the  axis  of  the  femur  and  end  more  or  less  irregularly  after  crossing  the  midline,  but  a 
number  of  these  filaments  end  in  the  medial  portion  of  the  shaft  and  neck.  They  cross  at  right 
angles  the  trabeculse  of  group  (a). 


FiQ.  251.- 


0  =  C0MPRESS10N 
•  =  TENSION 
C=COMP.  &  TENSION 
NEUTRAL  AXIS 


-Intensity  of  the  maximum  tensile  and  compressive  stresses  in  the  upper  femur.    Computed  for  the  loatl  of 
100  pounds  on  the  right  femur.     Corresponds  to  the  upper  part  of  Fig.  250.     (After  Koch.) 


"In  general,  the  trabeculse  of  the  tensile  system  are  lighter  in  structure  than  those  of  the  com- 
pressive system  in  corresponding  positions.  The  significance  of  the  difference  in  thickness  of  these 
two  systems  is  that  the  thickness  of  the  trabeculse  varies  with  the  intensity  of  the  stresses  at  any 
given  point.  Comparison  of  Fig.  247  with  Fig.  251  will  show  that  the  trabeculse  of  the  com- 
pressive system  carry  heavier  stresses  than  those  of  the  tensile  system  in  corresponding  positions. 
For  example,  the  maximum  tensile  stress  at  section  8  (Fig.  251)  in  the  outermost  fiber  is  771 
pounds  per  square  inch,  and  at  the  corresponding  point  on  the  compressive  side  the  compressive 
stress  is  954  pounds  per  square  inch.  Similar  comparisons  may  be  made  at  other  points,  which 
confirm  the  conclusion  that  the  thickness  and  closeness  of  spacing  of  the  trabeculse  varies  in 
proportion  to  the  intensity  of  the  stresses  carried  by  them. 

"It  will  be  seen  that  the  trabeculse  lie  exactly  in  the  paths  of  the  maximum  tensile  and  com- 
pressive stresses  (compare  Figs.  247,  248  and  251),  and  hence  these  trabeculse  carry  these  stresses 
in  the  most  economical  manner.  This  is  in  accordance  with  the  well-recognized  principle  of 
mechanics  that  the  most  direct  manner  of  transmitting  stress  is  in  the  direction  in  which  the  stress 
acts. 


THE  FEMUR 


253 


"Fig.  249  shows  a  longitudinal  frontal  section  through  the  left  femur,  which  is  the  mate  of  the 
right  femur  on  which  the  mathematical  analysis  was  made.  In  this  midsection  the  system  of 
tensile  trabeculse,  which  rises  from  the  lateral  (outer)  part  of  the  shaft  and  crosses  over  the  central 
area  to  end  in  the  medial  portion  of  the  shaft,  neck  and  head,  is  clearly  shown.  This  figure  also 
shows  the  compressive  system  of  trabeculse  which  rises  on  the  medial  portion  of  the  shaft  and 
crosses  the  central  area  to  end  in  the  head,  neck  and  greater  trochanter.  By  comparing  the  posi- 
lion  of  these  two  systems  of  trabecula?  shown  in  Fig.  249  with  the  lines  of  maximum  and  minimum 
stresses  sho^Ti  in  Figs.  248  and  2.50  it  is  seen  that  the  tensile  system  of  trabeculse  corresponds 
exactly  with  the  position  of  the  lines  of  maximum  and  minimum  tensile  stresses  which  were 
<letermined  by  mathematical  analysis.  In  a  similar  manner,  the  compressive  system  of  trabecular 
in  Fig.  249  corresponds  exactly  with  the  lines  of  maximum  and  minimum  compressive  stresses 
("omputed  by  mathematical  analysis. 

"The  amount  of  vertical  shear  varies  almost  uniformly  from  a  maximum  of  90  pounds  (90  per 
cent,  of  the  load  on  the  femur-head)  midway  between  sections  4  and  6,  to  a  minimum  of  — 5.7 
])ounds  at  section  18"  (Fig.  251).  There  is  a  gradual  diminution  of  the  spongy  bone  from  section 
()  to  section  18  parallel  with  the  diminished  intensities  of  the  vertical  shear. 

1.  The  trabeculse  of  the  upper  femur,  as  shown  in  frontal  sections,  are  arranged  in  two  general 
systems,  compressive  and  tensile,  which  correspond  in  position  with  the  lines  of  maximum  and 
minimum  stresses  in  the  femur  determined  by  the  mathematical  analysis  of  the  femur  as  a  mechan- 
ical structure. 

2.  The  thickness  and  spacing  of  the  trabeculse  vary  with  the  intensity  of  the  maximum  stresses 
at  various  points  in  the  upper  femur,  being  thickest  and  most  closely  spaced  in  the  regions  where 
the  greatest  stresses  occur. 

3.  The  amount  of  bony  material  in  the  spongy  bone  of  the  upper  femur  varies  in  proportion  to 
lhe  intensity  of  the  shearing  force  at  the  various  sections. 

4.  The  arrangement  of  the  trabeculse  in  the  positions  of  maximum  stresses  is  such  that  the 
greatest  strength  is  secured  with  a  minimum  of  material. 

Significance  of  the  Inner  Architecture  of  the  Shaft. — 1 .  Economy  for  resisting  shear.  The  shearing 
stresses  are  at  a  minimum  in  the  shaft.  "It  is  clear  that  a  minimum  amount  of  material  will  be 
lequired  to  resist  the  shearing  stresses."  As  horizontal  and  vertical  shearing  stresses  are  most 
efficiently  resisted  by  material  placed  near  the  neutral  plane,  in  this  region  a  minimum  amount 
i)f  material  will  be  needed  near  the  neutral  axis.  In  the  shaft  there  is  very  little  if  any  material 
in  the  central  space,  practically  the  only  material  near  the  neutral  plane  being  in  the  compact 
()one,  but  l>ing  at  a  distance  from  the  neutral  axis.    This  conforms  to  the  requirement  of  mechanics 

I  ■or  economy,  as  a  minimum  of  material  is  provided  for  resisting  shearing  stresses  where  these 

I  .stresses  are  a  minimum. 

2.  Economy  for  resisting  bending  moment.  "The  bending  moment  increases  from  a  minimum 
[.it  section  4  to  a  maximum  between  sections  16  and  18,  then  gradually  decreases  almost  uniformly 

X)  0  near  section  75."  "To  resist  bending  moment  stresses  most  effectively  the  material  should 
06  as  far  from  the  neutral  axis  as  possible."  It  is  evident  that  the  hollow  shaft  of  the  femur  is 
in  efficient  sti-ucture  for  resisting  bending  moment  stresses,  all  of  the  material  in  the  shaft  being 
•elatively  at  a  considerable  distance  from  the  neutral  axis.  It  is  evident  that  the  hollow  shaft 
jrovides  efficiently  for  resisting  bending  moment  not  only  due  to  the  load  on  the  femur-head,  but 
Tom  any  other  loads  tending  to  produce  bending  in  other  planes. 

3.  Economy  for  resisting  axial  stress. 

The  inner  architecture  of  the  shaft  is  adapted  to  resist  in  the  most  efficient  manner  the  com- 
oined  action  of  the  minimal  shearing  forces  and  the  axial  and  maximum  bending  stre.sses. 

The  structure  of  the  shaft  is  such  as  to  secure  great  strength  with  a  relatively  small  amount  of 
Jiaterial. 

The  Distal  Portion  of  the  Femur.— In  frontal  section  (Fig.  249)  in  the  distal  6  inches  of  the 
"emur  "there  are  to  be  seen  two  main  systems  of  trabeculse,  a  longitudinal  and  a  transverse 
[;jystem.  The  trabeculse  of  the  former  rise  from  the  inner  wall  of  the  shaft  and  continue  in  per- 
"ectly  straight  lines  parallel  to  the  axis  of  the  shaft  and  proceed  to  the  epiphyseal  line,  whence 
phey  continue  in  more  or  less  curved  lines  to  meet  the  articular  surface  of  the  knee-joint  at  right 
kiingles  at  every  point.  Near  the  center  there  are  a  few  thin,  delicate,  longitudinal  trabecula; 
rjehich  spring  from  the  longitudinal  trabeculse  just  described,  to  which  they  are  joined  by  fine 
jiiransverse  filaments  that  lie  in  planes  parallel  to  the  sagittal  plane. 

"The  trabeculse  of  the  transverse  sj'stem  are  somewhat  lighter  in  structure  than  those  of  the 
longitudinal  system,  and  consist  of  numerous  trabeculse  at  right  angles  to  the  lattef. 

"As  the  distal  end  of  the  femur  is  approached  the  shaft  gradually  becomes  thinner  until  the 

[iirticular  surface  is  reached,  where  there  remains  only  a  thin  shell  of  compact  bone.    With  the 

radual  thinning  of  the  compact  bone  of  the  shaft,  there  is  a  simultaneous  increase  in  the  amount 

[of  the  spongy  bone,  and  a  gradual  flaring  of  the  femur  which  gives  this  portion  of  the  bone  a 

radually  increasing  gross  area  of  cross-section. 

"There  is  a  marked  thickening  of  the  shell  of  bone  in  the  region  of  the  intercondyloid  fossa 
[where  the  anterior  and  posterior  crucial  ligaments  are  attached.     This  thickened  area  is  about 


254 


OSTEOLOGY 


Appears  at 
4:th  year  ; 
joins  body 

about  ISth  yr. 


Appears  at 
end  of  1st  yr.  ; 

joins  body 
about  ISth  yr. 

Appears  ISth-lith 
year  ;  joins  body 
about  18th  year 


Joins  body  at 
20th  year 


Appears  at 

9th  month  of 

fetal  life 

Lower  extremity 

Fig.  252. — Plan  of  ossification  of  the  femur. 
five  centers. 


From 


0.4  inch  iri  diameter  and  consists  of  compac 
bone  from  which  a  number  of  thick  trabeci  Uae'' 
pass  at  right  angles  to  the  main  longitudinal 
system.  The  inner  structure  of  the  bone  is  here 
evidently  adapted  to  the  efficient  distribution  of 
the  stresses  arising  from  this  ligamentary  at- 
tachment. 

"Near  the  distal  end  of  the  femur  the  longi- 
tudinal trabecular  gradually  assume  curved 
paths  and  end  perpendicularly  to  the  articular 
surface  at  every  point.  Such  a  structure  is  in 
accordance  with  the  principles  of  mechanics, 
as  stresses  can  be  communicated  througli  a 
frictionless  joint  only  in  a  direction  perpendic- 
ular to  the  joint  surface  at  every  point. 

"With  practically  no  increase  in  the  amount 
of  bony  material  used,  there  is  a  greatly  increased 
stability  produced  by  the  expansion  of  the  lower 
femur  from  a  hollow  shaft  of  compact  bone  to  a 
structure  of  much  larger  cross-section  almost 
entirely  composed  of  spongy  bone. 

"Significance  of  the  Inner  Architecture  of  the 
Distal  Part  of  the  Femur. — The  function  of  the 
lower  end  of  the  femur  is  to  transmit  through  a 
hinged  joint  the  loads  carried  by  the  femur.  For 
stability  the  width  of  the  bearing  on  which  the 
hinge  action  occurs  should  be  relatively  large. 
For  economy  of  material  the  expansion  of  the  end 
bearing  should  be  as  lightly  constructed  as  is 
consistent  with  proper  strength.  In  accordance 
with  the  principles  of  mechanics , 


Fig.  253. — Epiphysial  lines  of  femur  in  a  young 
adult.  Anterior  aspect.  The  lines  of  attachment  of 
the  articular  capsules  are  in  blue. 


Fig.  254. — Epiphysial  lines  of  femur  in  a  young  adult. 
Posterior  aspect.  The  lines  of  attachment  of  the  articular 
capsules  are  in  blue. 


THE  PATELLA 


255 


The  Patella  (Ejiee  Cap). 


the  most  efficient  manner  in  which  stresses  are  transmitted  is  by  the  arrangement  of  the  resist- 
ing material  in  lines  parallel  to  the  direction  in  which  the  stresses  occur  and  in  the  paths  taken 
b}'  the  stresses.  Theoretically  the  most  efficient  manner  to  attain  these  objects  would  be  to  pro- 
long the  innermost  filaments  of  the  bone  as  straight  lines  parallel  to  the  longitudinal  axis  of 
the  bone,  and  gradually  to  flare  the  outer  shell  of  compact  bone  outward,  and  continuing  to  give 
ofr  filaments  of  bone  parallel  to  the  longitudinal  axis  as  the  distal  end  of  the  femur  is  approached. 
Tliese  filaments  should  be  well-braced  transversely  and  each  should  carry  its  proportionate 
part  of  the  total  load,  parallel  to  the  longitudinal  axis,  transmitting  it  eventually  to  the 
articular  surface,  and  in  a  direction  perpendicular  to  that  surface." 

Referring  to  Fig.  249,  it  is  seen  that  the  large  expansion  of  the  bone  is  produced  by  the  gradual 
transition  of  the  hollow  shaft  of  compact  bone  to  cancellated  bone,  resulting  in  the  production 
of  a  much  larger  volume.  The  trabecular  are  given  off  from  the  shaft  in  lines  parallel  to  the 
longitudinal  axis,  and  are  braced  transversely  by  two  series  of  trabeculae  at  right  angles  to 
each  other,  in  the  same  manner  as  required  theoretically  for  economy. 

Although  the  action  of  the  muscles  exerts  an  appreciable  effect  on  the  stresses  in  the  femur, 
it  is  relatively  small  and  very  complex  to  analyze  and  has  not  been  considered  in  the  above  analj'sis. 

Ossification  (Figs.  252,  253,  254). — The  femur  is  ossified  from  jive  centers:  one  for  the  body, 
one  for  the  head,  one  for  each  trochanter,  and  one  for  the  lower  extremity.  Of  all  the  long  bones, 
except  the  clavicle,  it  is  the  first  to  show  traces  of  ossification;  this  commences  in  the  middle  of 
the  body,  at  about  the  seventh  week  of  fetal  life,  and  rapidly  extends  upw^frd  and  downward. 
The  centers  in  the  epiphyses  appear  in  the  following  order :  in  the  lower  end  of  the  bone,  at  the 
ninth  month  of  fetal  life  (from  this  center  the  condyles  and  epicondyles  are  formed) ;  in  the  head, 
at  the  end  of  the  first  year  after  birth;  in  the  greater  trochanter,  during  the  fourth  year;  and 
in  the  lesser  trochanter,  between  the  thirteenth  and  fourteenth  years.  The  order  in  which  the 
epiphyses  are  joined  to  the  body  is  the  reverse  of  that  of  their  appearance;  they  are  not  united 
uritil  after  puberty,  the  lesser  trochanter  being  first  joined,  then  the  greater,  then  the  head,  and, 
lastly,  the  inferior  extremity,  which  is  not  united  until  the  twentieth  year. 

The  patella  (Figs.  255,  25G)  is  a  flat,  triangular  bone,  situated  on  the  front  of 
tj  e  knee-joint.  It  is  usually  regarded  as  a  sesamoid  bone,  developed  in  the 
tendon  of  the  Quadriceps  femoris, 
and  resembles  these  bones  (1)  in 
b<ing  developed  in  a  tendon;  (2)  in 
iti  center  of  ossification  presenting 
a  knotty  or  tuberculated  outline; 
(3)  in  being  composed  mainly  of 
d<!nse  cancellous  tissue.  It  serves 
tc  protect  the  front  of  the  joint, 
and  increases  the  leverage  of  the 
Quadriceps  femoris  by  making  it 
a(t  at  a  greater  angle.  It  has  an 
anterior  and  a  posterior  surface 
three  borders,  and  an  apex. 

Surfaces. — ^The  anterior  surface  is  convex,  perforated  by  small  apertures  for  the 
p;,ssage  of  nutrient  vessels,  and  marked  by  numerous  rough,  longitudinal  striae. 
T  lis  surface  is  covered,  in  the  recent  state,  by  an  expansion  from  the  tendon  of 
the  Quadriceps  femoris,  which  is  continuous  below  with  the  superficial  fibers  of 
the  ligamentum  patelLne.  '  It  is  separated  from  the  integument  by  a  bursa.  The 
posterior  surface  presents  above  a  smooth,  oval,  articular  area,  divided  into  two 
facets  by  a  vertical  ridge;  the  ridge  corresponds  to  the  groove  on  the  patellar 
surface  of  the  femur,  and  the  facets  to  the  medial  and  lateral  parts  of  the  same 
surface;  the  lateral  facet  is  the  broader  and  deeper.  Below  the  articular  surface 
is  a  rough,  convex,  non-articular  area,  the  lower  half  of  which  gives  attachment 
to  the  ligamentum  patellae;  the  upper  half  is  separated  from  the  head  of  the  tibia 
by  adipose  tissue. 

Borders. — The  base  or  superior  border  is  thick,  and  sloped  from  behind,  down- 
ward, and  forward :  it  gives  attachment  to  that  portion  of  the  Quadriceps  femoris 


Fia.  255.— Right  patella. 
Anterior  surface. 


Fig.  256.— Right  patella. 
Posterior  surface. 


256 


I 


which  is  derived  from  the  Rectus  femoris  and  Vastus  intermedius.  The  medial  and 
lateral  borders  are  thinner  and  converge  below:  they  give  attachment  to  tliose 
portions  of  the  Quadriceps  femoris  which  are  derived  from  the  Vasti  laterahs  and 
mediahs. 

Apex. — The  apex  is  pointed,  and  gives  attachment  to  the  hgaraentum  patellae. 

Structure. — The  patella  consists  of  a  nearly  uniform  dense  cancellous  tissue,  covered  by  a 
thin  compact  lamina.  The  cancelli  immediately  beneath  the  anterior  surface  are  arranged 
parallel  with  it.  In  the  rest  of  the  bone  they  radiate  from  the  articular  surface  toward  the  other 
parts  of  the  bone. 

Ossification. — The  patella  is  ossified  from  a  single  center,  which  usually  makes  its  appearance 
in  the  second  or  third  year,  but  may  be  delayed  until  the  sixth  year.  More  rarely,  the  bone  is 
developed  by  two  centers,  placed  side  by  side.    Ossification  is  completed  about  the  age  of  puberty. 

Articulation. — The  patella  articulates  with  the  femur. 


Tuberosity 


feral 

di/Ze 


Inter  condyloid  eminence. 

Fig.  257. — Upper  surface  of  right  tibia. 


The  Tibia  (Shin  Bone). 

The  tibia   (Figs.   258,   259)   is  situated   at    the  medial   side  of  the  leg,  and, 
excepting  the  femur,  is  the  longest  bone  of  the  skeleton.    It  is  prismoid  in  form, 

expanded  above,  where  it  enters  into  the 
knee-joint,  contracted  in  the  lower  third, 
and  again  enlarged  but  to  a  lesser  extent 
below.  In  the  male,  its  direction  is  vertical, 
and  parallel  with  the  bone  of  the  opposite 
side;  but  in  the  female  it  has  a  slightly 
oblique  direction  downward  and  lateralward, 
to  compensate  for  the  greater  obliquity  of 
the  femur.  It  has  a  body  and  two  extremities. 
The  Upper  Extremity  {proximal  extremity). 
— The  upper  extremity  is  large,  and  expanded 
into  two  eminences,  the  medial  and  lateral 
condyles.  The  superior  articular  surface  pre- 
sents two  smooth  articular  facets  (Fig.  257). 
The  medial  facet,  oval  in  shape,  is  slightly 
concave  from  side  to  side,  and  from  before 
backward.  The  lateral,  nearly  circular,  is 
concave  from  side  to  side,  but  slightly  convex  from  before  backward,  especially 
at  its  posterior  part,  where  it  is  prolonged  on  to  the  posterior  surface  for  a 
short  distance.  The  central  portions  of  these  facets  articulate  with  the  con- 
dyles of  the  femur,  while  their  peripheral  portions  support  the  menisci  of  the 
knee-joint,  which  here  intervene  between  the  two  bones.  Between  the  artic- 
ular facets,  but  nearer  the  posterior  .than  the  anterior  aspect  of  the  bone,  is  the 
intercondyloid  eminence  {spine  of  tibia),  surmounted  on  either  side  by  a  prominent 
tubercle,  on  to  the  sides  of  which  the  articular  facets  are  prolonged;  in  front  of 
and  behind  the  intercondyloid  eminence  are  rough  depressions  for  the  attachment 
of  the  anterior  and  posterior  cruciate  ligaments  and  the  menisci.  The  anterior 
surfaces  of  the  condyles  are  continuous  with  one  another,  forming  a  large  somewhat 
flattened  area;  this  area  is  triangular,  broad  above,  and  perforated  by  large  vascular 
foramina;  narrow  below  where  it  ends  in  a  large  oblong  elevation,  the  tuberosity  of 
the  tibia,  which  gives  attachment  to  the  ligamentum  patellae;  a  bursa  intervenes 
between  the  deep  surface  of  the  ligament  and  the  part  of  the  bone  immediately 
above  the  tuberosity.  Posteriorly,  the  condyles  are  separated  from  each  other  by 
a  shallow  depression,  the  posterior  intercondyloid  fossa,  which  gives  attachment  to 
part  of  the  posterior  cruciate  ligament  of  the  knee-joint.  The  medial  condyle 
presents  posteriorly  a  deep  transverse  groove,  for  the  insertion  of  the  tendon  of 


THE  TIBIA 


25i 


I 


the  Semimembranosus.  Its  medial 
s^urface  is  convex,  rough,  and  promi- 
nent; it  gives  attachment  to  the 
tibial  collateral  ligament.  The  lat- 
eral condyle  presents  posteriorly  a 
flat  articular  facet,  nearly  circular 
in  form,  directed  downward,  back- 
ward, and  lateral  ward,  for  articu- 
lation with  the  head  of  the  fibula. 
Its  lateral  surface  is  convex,  rough, 
and  prominent  in  front:  on  it  is 
an  eminence,  situated  on  a  level 
with  the  upper  border  of  the  tuber- 
osity and  at  the  junction  of  its 
anterior  and  lateral  surfaces,  for 
the  attachment  of  the  iliotibial 
band.  Just  below  this  a  part  of 
the  Extensor  digitorum  longus 
takes  origin  and  a  slip  from  the 
tendon  of  the  Biceps  femoris  is 
inserted. 

The  Body  or  Shaft  {coryiLS  tibiw). 
— The  body  has  three  borders  and 
three  surfaces. 

Borders. — The  anterior  crest  or 
border,  the  most  prominent  of  the 
three,  commences  above  at  the 
tuberosity,  and  ends  below  at  the 
anterior  margin  of  the  medial 
jnalleolus.  It  is  sinuous  and 
j)rominent  in  the  upper  two-thirds 
of  its  extent,  but  smooth  and 
]«unded  below;  it  gives  attach- 
]tient  to  the  deep  fascia  of  the  leg. 

The  medial  border  is  smooth  and 
K)unded  above  and  below,  but 
more  prominent  in  the  center;  it 
begins  at  the  back  part  of  the 
medial  condyle,  and  ends  at  the 
posterior  border  of  the  medial 
malleolus;  its  upper  part  gives 
attachment  to  the  tibial  collat- 
eral ligament  of  the  knee-joint 
to  the  extent  of  about  5  cm., 
and  insertion  to  some  fibers  of 
the  Popliteus;  from  its  middle 
|hird  some  fibers  of  the  Soleus 
and  Flexor  digitorum  longus  take 
origin. 

The  interosseous  crest  or  lateral 

fider  is  thin  and  prominent,  espe- 
lially  its  central  part,  and  gives  at- 

chment  to  the  interosseous  mem- 
rane;  it  commences  above  in  front 
f  the  fibular  articular  facet,  and 
17 


Articular  capsule 


Styloid  process ' 

Fibular 
collateral' 
ligament 


'  condyle 


■^eat' 


JcVo* 


'Mis     "I"!'. 


/ 


v; 


8    "^ 


Articular 
capsule 


ttredi,.  jt. 


H-\ 


'.t~-t^5 


Lateral  malleolus 
Fig.  258. — Bones  of  the  right  leg. 


Medial  malleolus 


Anterior  surface. 


258 


OSTEOLOGY 


femur 


Articidar 
capsule 


Articular 
capsule 

Styloid 
process 


bifurcates  below,  to  form  the  boundaries  of  a  triangular  rough  surface,  for  the 
attachment  of  the  interosseous  ligament  connecting  the  tibia  and  fibula. 

Surfaces. — The  medial  surface 
is  smooth,  convex,  and  broader 
above  than  below;  its  up})er 
third,  directed  forward  and 
medial  ward,  is  covered  by  the 
aponeurosis  derived  from  the 
tendon  of  the  Sartorius,  and  by 
the  tendons  of  the  Gracilis  and 
Semitendinosus,  all  of  which 
are  inserted  nearly  as  far  for- 
ward as  the  anterior  crest;  in 
the  rest  of  its  extent  it  is  sub- 
cutaneous. 

The  lateral  surface  is  narrower 
than  the  medial ;  its  upper  tw  o- 
thirds  present  a  shallow  groove 
for  the  origin  of  the  Tibialis 
anterior;  its  lower  third  is 
smooth,  convex,  curves  grad- 
ually forward  to  the  anterior 
aspect  of  the  bone,  and  is 
covered  by  the  tendons  of  the 
Tibialis  anterior,  Extensor  hal- 
lucis  longus,  and  Extensor  digi- 
torum  longus,  arranged  in  this 
order  from  the  medial  side. 

The  posterior  surface  (Fig.  259) 
presents,  at  its  upper  part,  a 
prominent  ridge,  the  popliteal 
line,  which  extends  obliquely 
downward  from  the  back  part  of 
the  articular  facet  for  the  fibula 
to  the  medial  border,  at  the 
junction  of  its  upper  and  middle 
thirds;  it  marks  the  lower  limit 
of  the  insertion  of  the  Popliteus, 
serves  for  the  attachment  of  the 
fascia  covering  this  muscle,  and 
gives  origin  to  part  of  the 
Soleus,  Flexor  digitorum  longus, 
and  Tibialis  posterior.  The 
triangular  area,  above  this  line, 
gives  insertion  to  the  Popliteus. 
The  middle  third  of  the  poste- 
rior surface  is  divided  by  a  ver- 
tical ridge  into  two  parts;  the 
ridge  begins  at  the  popliteal  line 
and  is  well-marked  above,  but 
indistinct  below;  the  medial  and 
broader  portion  gives  origin  to 
the  Flexor  digitorum  longus, 
.  ,.    ,  ,         ,  the  lateral  and  narrower  to  part 

Articular  capsule  T'-u*    r  +     •  T'U 

259.— Bones  of  the  right  leg.     Posterior  surface.  01   the     ilbiallS    pOStCriOr.       1116 


I 


THE  TIBIA 


remaining  part  of  the  posterior  surface  is  smooth  and  covered  by  the  Tibialis 
posterior.  Flexor  digitorum  longus,  and  Flexor  hallucis  longus.  Immediately  below 
the  popliteal  line  is  the  nutrient  foramen,  which  is  large  and  directed  obliquely 
downward. 

The  Lower  Extremity  (distal  extremity). — The  lower  extremity,  much  smaller 
than  the  upper,  presents  five  surfaces;  it  is  prolonged  downward  on  its  medial 
side  as  a  strong  process,  the  medial  malleolus. 

Surfaces. — The  inferior  articular  surface  is  quadrilateral,  and  smooth  for  articu- 
lation with  the  talus.  It  is  concave  from  before  backward,  broader  in  front  than 
behind,  and  traversed  from  before  backward  by  a  slight  elevation,  separating 
two  depressions.    It  is  continuous  with  that  on  the  medial  malleolus. 


Upper  extremity 


Appears  before  or 
shortly  after  birth 


Joins  body 
abovi  20lh  year 


Joins  body  about 
I8th  year 


Lower  extremity 


'Fig.  260. 


-Plan  of  ossification  of  the  tibia, 
centers. 


From  three 


Fig.  261. — Epiphysial  lines  of  tibia  and  fibula 
in  a  young  adult.     Anterior  aspect. 


The  anterior  surface  of  the  lower  extremity  is  smooth  and  rounded  above,  and 
covered  by  the  tendons  of  the  Extensor  muscles;  its  lower  margin  presents  a  rough 
transverse  depression  for  the  attachment  of  the  articular  capsule  of  the  ankle- 
joint. 

The  posterior  surface  is  traversed  by  a  shallow  groove  directed  obliquely  down- 
ward and  medialward,  continuous  with  a  similar  groove  on  the  posterior  surface 
I  of  the  talus  and  serving  for  the  passage  of  the  tendon  of  the  Flexor  hallucis  longus. 

The  lateral  surface  presents  a  triangular  rough  depression  for  the  attachment 
[of  the  inferior  interosseous  ligament  connecting  it  with  the  fibula;  the  lower  part 
of  this  depression  is  smooth,  covered  with  cartilage  in  the  fresh  state,  and  articu- 
lates with  the  fibula.  The  surface  is  bounded  by  two  prominent  borders,  con- 
pnuous  above  with  the  interosseous  crest;  they  afford  attachment  to  the  anterior 
[and  posterior  ligaments  of  the  lateral  malleolus. 

The  medial  surface  is  prolonged  downward  to  form  a  strong  pyramidal  process, 

[flattened  from  without  inward — the  medial  malleolus.  The  medial  surface  of  this 

[process  is  convex  and  subcutaneous;  its  lateral  or  articular  surface  is  smooth  and 

lightly  concave,  and  articulates  with  the  talus;  its  anterior  border  is  rough,  for 


260  OSTEOLOGY 

the  attachment  of  the  anterior  fibers  of  the  deltoid  ligament  of  the  ankle-joint; 
its  posterior  border  presents  a  broad  groove,  the  malleolar  sulcus,  directed  obliquely 
downward  and  medial  ward,  and  occasionally  double;  this  sulcus  lodges  the  tendons 
of  the  Tibialis  posterior  and  Flexor  digitorum  longus.  The  summit  of  the  medial 
malleolus  is  marked  by  a  rough  depression  behind,  for  the  attachment  of  the 
deltoid  ligament. 

Structure. — The  structure  of  the  tibia  is  like  that  of  the  other  long  bones.  The  compact  wall 
of  the  body  is  thickest  at  the  junction  of  the  middle  and  lower  thirds  of  the  bone. 

Ossification. — The  tibia  is  ossified  from  three  centers  (Figs.  260,  261):  one  for  the  body  and 
one  for  either  extremity.  Ossification  begins  in  the  center  of  the  body,  about  the  seventh  week 
of  fetal  life,  and  gradually  extends  toward  the  extremities.  The  center  for  the  upper  epiphysis 
appears  before  or  shortly  after  birth;  it  is  flattened  in  form,  and  has  a  thin  tongue-shaped  process 
in  front,  which  forms  the  tuberosity  (Fig.  2t30) ;  that  for  the  lower  epiphysis  appears  in  the  second 
year.  The  lower  epiphysis  joins  the  body  at  about  the  eighteenth,  and  the  upper  one  joins  about 
the  twentieth  year.  Two  additional  centers  occasionally  exist,  one  for  the  tongue-shaped  process 
of  the  upper  epiphysis,  which  forms  the  tuberosity,  and  one  for  the  medial  malleolus. 

The  Fibula  (Calf  Bone). 

The  fibula  (Figs.  258,  259)  is  placed  on  the  lateral  side  of  the  tibia,  with  which 
it  is  connected  above  and  below.  It  is  the  smaller  of  the  two  bones,  and,  in 
proportion  to  its  length,  the  most  slender  of  all  the  long  bones.  Its  upper 
extremity  is  small,  placed  toward  the  back  of  the  head  of  the  tibia,  below  the  level 
of  the  knee-joint,  and  excluded  from  the  formation  of  this  joint.  Its  lower  extremity 
inclines  a  little  forward,  so  as  to  be  on  a  plane  anterior  to  that  of  the  upper  end; 
it  projects  below  the  tibia,  and  forms  the  lateral  part  of  the  ankle-joint.  The 
bone  has  a  body  and  two  extremities. 

The  Upper  Extremity  or  Head  (capitulum  fibulw;  proximal  extremity). — The 
upper  extremity  is  of  an  irregular  quadrate  form,  presenting  above  a  flattened 
articular  surface,  directed  upward,  forward,  and  medialward,  for  articulation  with 
a  corresponding  surface  on  the  lateral  condyle  of  the  tibia.  On  the  lateral  side 
is  a  thick  and  rough  prominence  continued  behind  into  a  pointed  eminence,  the 
apex  {styloid  process),  which  projects  upward  from  the  posterior  part  of  the  head. 
The  prominence,  at  its  upper  and  lateral  part,  gives  attachment  to  the  tendon  of 
the  Biceps  femoris  and  to  the  fibular  collateral  ligament  of  the  knee-joint,  the  liga- 
ment dividing  the  tendon  into  two  parts.  The  remaining  part  of  the  circumference 
of  the  head  is  rough,  for  the  attachment  of  muscles  and  ligaments.  It  presents  in 
front  a  tubercle  for  the  origin  of  the  upper  and  anterior  fibers  of  the  Perona^us 
longus,  and  a  surface  for  the  attachment  of  the  anterior  ligament  of  the  head; 
and  behind,  another  tubercle,  for  the  attachment  of  the  posterior  ligament  of  the 
head  and  the  origin  of  the  upper  fibers  of  the  Soleus. 

The  Body  or  Shaft  {corpus  fibidce). — The  body  presents  four  borders — the 
antero-lateral,  the  antero-medial,  the  postero-lateral,  and  the  postero-medial ;  and 
four  surfaces — anterior,  posterior,  medial,  and  lateral. 

Borders. — The  antero-lateral  border  begins  above  in  front  of  the  head,  runs  ver- 
tically downward  to  a  little  below  the  middle  of  the  bone,  and  then  curving  some- 
what lateralward,  bifurcates  so  as  to  embrace  a  triangular  subcutaneous  surface 
immediately  above  the  lateral  malleolus.  This  border  gives  attachment  to  an 
intermuscular  septum,  which  separates  the  Extensor  muscles  on  the  anterior 
surface  of  the  leg  from  the  Peronaei  longus  and  brevis  on  the  lateral  surface. 

The  antero-medial  border,  or  interosseous  crest,  is  situated  close  to  the  medial 
side  of  the  preceding,  and  runs  nearly  parallel  with  it  in  the  upper  third  of  its 
extent,  but  diverges  from  it  in  the  lower  two-thirds.  It  begins  above  just  beneath 
the  head  of  the  bone  (sometimes  it  is  quite  indistinct  for  about  2.5  cm.  below  the 
head),  and  ends  at  the  apex  of  a  rough  triangular  surface  immediately  above  the 


THE  FIBULA 


261 


articular  facet  of  the  lateral  malleolus.  It  serves  for  the  attachment  of  the  inter- 
osseous membrane,  which  separates  the  Extensor  muscles  in  front  from  the  Flexor 
muscles  behind. 

The  postero-lateral  border  is  prominent;  it  begins  above  at  the  apex,  and  ends 
below  in  the  posterior  border  of  the  lateral  malleolus.  It  is  directed  lateralward 
above,  backward  in  the  middle  of  its  course,  backward,  and  a  little  medialward 
below,  and  gives  attachment  to  an  aponeurosis  which  separates  the  Peronsei  on 
the  lateral  surface  from  the  Flexor  muscles  on  the  posterior  surface. 

The  postero-medial  border,  sometimes  called  the  oblique  line,  begins  above  at  the 
medial  side  of  the  head,  and  ends  by  becoming  continuous  with  the  interosseous 
crest  at  the  lower  fourth  of  the  bone.  It  is  well-marked  and  prominent  at  the  upper 
and  middle  parts  of  the  bone.  It  gives  attachment  to  an  aponeurosis  which  sep- 
arates the  Tibialis  posterior  from  the  Soleus  and  Flexor  hallucis  longus. 


Upper  extremity 


Interossecms 
crest 


Appears  about _ 
4.th  year 


Unites  about 
25th  year 


For  posterior 
talofbular  ligt. 


Appears  at 
2nd  year 


Unites  about 
20th  year 


Lower  extremity 


Fia.  262. — Lower  extremity  of  right  fibula. 
Medial  aspect. 


Fig.    263. — Plan  of  ossification   of  tlie 
fibula.     From  three  centers. 


Surfaces. — The  anterior  surface  is  the  interval  between  the  antero-lateral  and 
antero-medial  borders.  It  is  extremely  narrow  and  flat  in  the  upper  third  of  its 
extent;  broader  and  grooved  longitudinally  in  its  lower  third;  it  serves  for  the 
origin  of  three  muscles:  the  Extensor  digitorum  longus,  Extensor  hallucis  longus, 
and  Peronseus  tertius. 

The  posterior  surface  is  the  space  included  between  the  postero-lateral  and  the 
postero-medial  borders;  it  is  continuous  below  with  the  triangular  area  above 
the  articular  surface  of  the  lata-al  malleolus;  it  is  directed  backward  above,  back- 
ward and  medialward  at  its  middle,  directly  medialward  below.  Its  upper  third 
is  rough,  for  the  origin  of  the  Soleus;  its  lower  part  presents  a  triangular  surface, 
connected  to  the  tibia  by  a  strong  interosseous  ligament;  the  intervening  part  of 
the  surface  is  covered  by  the  fibers  of  origin  of  the  Flexor  hallucis  longus.  Near 
the  middle  of  this  surface  is  the  nutrient  foramen,  which  is  directed  downward. 

The  medial  surface  is  the  interval  included  between  the  antero-medial  and  the 
postero-medial  borders.     It  is  grooved  for  the  origin  of  the  Tibialis  posterior. 


OSTEOLOGY 


The  lateral  surface  is  the  space  between  the  antero-lateral  and  postero-lateral 
borders.  It  is  broad,  and  often  deeply  grooved;  it  is  directed  lateralward  in  the 
upper  two-thirds  of  its  course,  backward  in  the  lower  third,  where  it  is  continuous 
with  the  posterior  border  of  the  lateral  malleolus.  This  surface  gives  origin  to 
the  Peronsei  longus  and  brevis. 

The  Lower  Extremity  or  Lateral  Malleolus  (malleolus  lateralis;  distal  extremity; 
external  malleolus). — The  lower  extremity  is  of  a  pyramidal  form,  and  somewhat 
flattened  from  side  to  side;  it  descends  to  a  lower  level  than  the  medial  malleolus. 
The  lateral  surface  is  convex,  subcutaneous,  and  continuous  with  the  triangular, 
subcutaneous  surface  on  the  lateral  side  of  the  body.  The  medial  surface  (Fig. 
262)  presents  in  front  a  smooth  triangular  surface,  convex  from  above  downward, 
which  articulates  with  a  corresponding  surface  on  the  lateral  side  of  the  talus. 
Behind  and  beneath  the  articular  surface  is  a  rough  depression,  w^hich  gives  attach- 
ment to  the  posterior  talofibular  ligament.  The  anterior  border  is  thick  and  rough, 
and  marked  below  by  a  depression  for  the  attachment  of  the  anterior  talofibular 
ligament.  The  posterior  border  is  broad  and  presents  the  shallow  malleolar  sulcus, 
for  the  passage  of  the  tendons  of  the  Peronsei  longus  and  brevis.  The  summit 
is  rounded,  and  give  attachment  to  the  calcaneofibular  ligament. 

Ossification. — The  fibula  is  ossified  from  three  centers  (Fig.  263) :  one  for  the  body,  and  one 
for  either  end.  Ossification  begins  in  the  body  about  the  eighth  week  of  fetal  Ufe,  and  extends 
toward  the  extremities.  At  birth  the  ends  are  cartilaginous.  Ossification  commences  in  the 
lower  end  in  the  second  year,  and  in  the  upper  about  the  fourth  year.  The  lower  epiphysis, 
the  first  to  ossify,  unites  with  the  body  about  the  twentieth  year;  the  upper  epiphysis  joins 
about  the  twenty-fifth  year. 

Groove  for  PeroncBUs  longus 


Trochlear  process 

Middle  articular  surface 
Anterior  artic.  surface 
Post,  artic.  surface 


Trochlear  process 

For  cuboid  bone 
For  attachment 

of  plantar  calcaneo- 
cuboid ligament 

Sustentaculum 
tali 


Sustentaculum.  Sulcus  for  Flexor 

'*"  haUu^is  longus 


Sulcus  calcanei 


Tuberosity 
Fio.  264.— Left  calcaneus,  superior  surface. 


Medial  process 

Tuberosity 

Lateral  process 
Fig.  265. — Left  calcaneus,  inferior  surface. 


THE    FOOT. 

The  skeleton  of  the  foot  (Figs.  268  and  269)  consists  of  three  parts:  the  tarsus, 
metatarsus,  and  phalanges. 


THE  TARSUS 


The  Tarsus  (Ossa  Tarsi). 


263 


The  tarsal  bones  are  seven  in  number,  viz.,  the  calcaneus,  talus,  cuboid,  navicular, 
and  the  first,  second,  and  third  cuneiforms. 

The  Calcaneus  (os  calcis)  (Figs.  264  to  267).— The  calcaneus  is  the  largest  of  the 
tarsal  bones.  It  is  situated  at  the  lower  and  back  part  of  the  foot,  serving  to 
transmit  the  weight  of  the  body  to  the  ground,  and  forming  a  strong  lever  for 
the  muscles  of  the  calf.  It  is  irregularly  cuboidal  in  form,  having  its  long  axis 
directed  forward  and  lateralward;  it  presents  for  examination  six  surfaces. 


Sulcus  calcanei 
Middle  articular  surface  for  talus 


Posterior  articular  surface  for  talus 


Trochlear  process 
Groove  for  Peronaeus  longua 


Lateral  process' 


Tuberosity 


Fig.  266. — Left  calcaneus,  lateral  surface. 


Middle  articular  surface  for  talus 
Sustentaculum  tali 
Posterior  articular  surface  for  talus 


Tuberosity 


Anterior  articxdar  surface 
for  talus 


Sulcus  for  Flexor 
hallucis  longus 
Medial  process 


Fig.  267. — Left  calcaneus,  medial  surface. 


For  cuboid  bone 


Surfaces. — The  superior  surface  extends  behind  on  to  that  part  of  the  bone  which 
projects  backward  to  form  the  heel.  This  varies  in  length  in  different  individuals, 
is  convex  from  side  to  side,  concave  from  before  backward,  and  supports  a  mass  of 
fat  placed  in  front  of  the  tendo  calcaneus.  In  front  of  this  area  is  a  large  usually 
somewhat  oval-shaped  facet,  the  posterior  articular  surface,  which  looks  upward 
and  forward;  it  is  convex  from  behind  forward,  and  articulates  with  the  posterior 
calcaneal  facet  on  the  under  surface  of  the  talus.  It  is  bounded  anteriorly  by  a 
deep  depression  which  is  continued  backward  and  medialward  in  the  form  of  a 
groove,  the  calcaneal  sulcus.  In  the  articulated  foot  this  sulcus  lies  below  a  similar 
one  on  the  under  surface  of  the  talus,  and  the  two  form  a  canal  (sinus  tarsi)  for  the 


264 


OSTEOLOGY 


Groove  for  tendon  of 
Peron^u8   long  us 


Groove  for  tendon  of 

.   PEEON^rs     BREVIS 


Peron^us  teetitb 

PERONiETJS     BEEVIS 


Groove  for  tendon  of 
Flexor  hallucis  longps 


TarsiLS 


Metatarsus 


-Ext.  niGiTORCM  brevis 


Phalanges 


Ext.  HALLrcis  longus 


Fia.  268. — Bones  of  the  right  foot.     Dorsal  surface. 


TARSUS 


265 


Abductor  halluois 
Medial  head  or 


Flexor  hallucis  urkvis 


Tvbercle  of 
navicular 


Tibialis  anterior 


Tvx)  sesamoid 
bones 


Lateral  head  of  quadratus 

PLANTS 


Flexor  brevis 
AND  Abductor 

DIGITI  QUINTI 


Flexor  digitorum 

BREVIS 


Flexor  digitorum 

LONQUS 


FiQ.  269. — Bones  of  the  right  foot.     Plantar  surface. 


OSTEOLOGY 


lodgement  of  the  interosseous  talocalcaneal  ligament.  In  front  and  to  the  medial 
side  of  this  groove  is  an  elongated  facet,  concave  from  behind  forward,  and  with  its 
long  axis  directed  forward  and  lateralward.  This  facet  is  frequently  divided  into 
two  by  a  notch :  of  the  two,  the  posterior,  and  larger  is  termed  the  middle  articular 
surface;  it  is  supported  on  a  projecting  process  of  bone,  the  sustentaculum  tali, 
and  articulates  with  the  middle  calcaneal  facet  on  the  under  surface  of  the  talus; 
the  anterior  articular  surface  is  placed  on  the  anterior  part  of'  the  body,  and  articu- 
lates with  the  anterior  calcaneal  facet  on  the  talus.  The  upper  surface,  anterior 
and  lateral  to  the  facets,  is  rough  for  the  attachment  of  ligaments  and  for  the  origin 
of  the  Extensor  digitorum  brevis. 

The  inferior  or  plantar  surface  is  uneven,  wider  behind  than  in  front,  and  convex 
from  side  to  side;  it  is  bounded  posteriorly  by  a  transverse  elevation,  the  calcaneal 
tuberosity,  which  is  depressed  in  the  middle  and  prolonged  at  either  end  into  a 
process;  the  lateral  process,  small,  prominent,  and  rounded,  gives  origin  to  part 
of  the  Abductor  digiti  quinti;  the  medial  process,  broader  and  larger,  gives  attach- 
ment, by  its  prominent  medial  margin,  to  the  Abductor  hallucis,  and  in  front 
to  the  Flexor  digitorum  brevis  and  the  plantar  aponeurosis ;  the  depression  between 
the  processes  gives  origin  to  the  Abductor  digiti  quinti.  The  rough  surface  in 
front  of  the  processes  gives  attachment  to  the  long  plantar  ligament,  and  to  the 
lateral  head  of  the  Quadratus  plantse;  while  to  a  prominent  tubercle  nearer  the 
anterior  part  of  this  surface,  as  well  as  to  a  transverse  groove  in  front  of  the  tubercle, 
is  attached  the  plantar  calcaneocuboid  ligament. 

The  lateral  surface  is  broad  behind  and  narrow  in  front,  flat  and  almost  sub- 
cutaneous; near  its  center  is  a  tubercle,  for  the  attachment  of  the  calcaneofibular 
ligament.  At  its  upper  and  anterior  part,  this  surface  gives  attachment  to  the 
lateral  talocalcaneal  ligament;  and  in  front  of  the  tubercle  it  presents  a  narrow 
surface  marked  by  two  oblique  grooves.  The  grooves  are  separated  by  an  elevated 
ridge,  or  tubercle,  the  trochlear  process  {peroneal  tubercle),  which  varies  much  in 
size  in  different  bones.  The  superior  groove  transmits  the  tendon  of  the  Perona^us 
brevis;  the  inferior  groove,  that  of  the  Perona^us  longus. 

The  medial  surface  is  deeply  concave;  it  is  directed  obliquely  downward  and 
forward,  and  serves  for  the  transmission  of  the  plantar  vessels  and  nerves  into  the 
sole  of  the  foot;  it  affords  origin  to  part  of  the  Quadratus  plantee.  At  its  upper 
and  forepart  is  a  horizontal  eminence,  the  sustentaculum  tali,  which  gives  attach- 
ment to  a  slip  of  the  tendon  of  the  Tibialis  posterior.  This  eminence  is  concave 
above,  and  articulates  with  the  middle  calcaneal  articular  surface  of  the  talus; 
below,  it  is  grooved  for  the  tendon  of  the  Flexor  hallucis  longus ;  its  anterior  margin 
gives  attachment  to  the  plantar  calcaneonavicular  ligament,  and  its  medial, 
to  a  part  of  the  deltoid  ligament  of  the  ankle-joint. 

The  anterior  or  cuboid  articular  surface  is  of  a  somewhat  triangular  form.  It  is 
concave  from  above  downward  and  lateralward,  and  convex  in  a  direction  at  right 
angles  to  this.  Its  medial  border  gives  attachment  to  the  plantar  calcaneonavicular 
ligament. 

The  posterior  surface  is  prominent,  convex,  wider  below  than  above,  and  divisible 
into  three  areas.  The  lowest  of  these  is  rough,  and  covered  by  the  fatty  and  fibrous 
tissue  of  the  heel;  the  middle,  also  rough,  gives  insertion  to  the  tendo  calcaneus 
and  Plantaris;  while  the  highest  is  smooth,  and  is  covered  by  a  bursa  which  inter- 
venes between  it  and  the  tendo  calcaneus. 

Articulations. — The  calcaneus  articulates  with  two  bones:    the  talus  and  xjuboid. 

The  Talus  {astragalus;  ankle  hone)  (Figs.  270  to  273). — The  talus  is  the  second 
largest  of  the  tarsal  bones.  It  occupies  the  middle  and  upper  part  of  the  tarsus, 
supporting  the  tibia  above,  resting  upon  the  calcaneus  below,  articulating  on 
either  side  with  the  malleoli,  and  in  front  with  the  navicular.  It  consists  of  a 
body,  a  neck,  and  a  head 


THE  TARSUS 


267 


The  Body  (corpus  tali). — ^The  superior  surface  of  the  body  presents,  behind,  a 
smooth  trochlear  surface,  the  trochlea,  for  articulation  with  the  tibia.  The  trochlea 
is  broader  in  front  than  behind,  convex  from  before  backward,  slightly  concave 
from  side  to  side:  in  front  it  is  continuous  with  the  upper  surface  of  the  neck  of 
the  bone. 

For  medial  malleolus 
Head 
Neck 


For  lateral  m,aUeolus 
For  inferior  transverse  ligarnent 


Medial  tubercle 
Sulcus  for  Flexor  Iiailucis  longus 


Trochlea  for  tibia 
Lateral  tubercle 

Fig.  270. — Left  talus,  from  above. 


For  plantar  calcaneonavicular  ligament 
For  navicular  bone 

Anterior  calcaneal  articular  surface 


Sulcus  tali 


^Posterior  calcaneal  articular 
surface 


Lateral  tubercle 
Sulcus  for  Flexor  hallucis  longus 
Middle  calcaneal  articular  surface 
Fig.  271. — Left  talus,  from  below. 


The  inferior  surface  presents  two  articular  areas,  the  posterior  and  middle  cal- 
janeal  surfaces,  separated  from  one  another  by  a  deep  groove,  the  sulcus  tali. 
The  groove  runs  obliquely  forward  and  lateralward,  becoming  gradually  broader 
ind  deeper  in  front:  in  the  articulated  foot  it  lies  above  a  similar  groove  upon 
he  upper  surface  of  the  calcaneus,  and  forms,  with  it,  a  canal  (sinus  tarsi)  filled 


268 


OSTEOLOGY 


up  in  the  fresh  state  by  the  interosseous  talocalcaneal  ligament.  The  posterior 
calcaneal  articular  surface  is  large  and  of  an  oval  or  oblong  form.  It  articulates 
with  the  corresponding  facet  on  the  upper  surface  of  the  calcaneus/  and  is  deei)ly 
concave  in  the  direction  of  its  long  axis  which  runs  forward  and  lateralward  at 
an  angle  of  about  45°  with  the  median  plane  of  the  body.  The  middle  calcaneal 
articular  surface  is  small,  oval  in  form  and  slightly  convex;  it  articulates  with  the 
upper  surface  of  the  sustentaculum  tali  of  the  calcaneus. 

The  medial  surface  presents  at  its  upper  part  a  pear-shaped  articular  facet  for 
the  medial  malleolus,  continuous  above  with  the  trochlea;  below  the  articular 
surface  is  a  rough  depression  for  the  attachment  of  the  deep  portion  of  the  deltoid 
ligament  of  the  ankle-joint. 


Trochlea  for  tibia 


For  medial  malleolus 


hieck 


Sulcus  for  Flex.  haUucis  longus 


For  navicular  hone 

'  For  plantar  calcaneonavicular  ligament 
Fig.  272. — Left  talus,  medial  surface. 


Trochlea  for  tibia 


For  lateral  malleolus 


Sulcus  tali 


Posterior  calcaneal  articular 
surface 


Anterior  calcaneal  articular  surface 
For  navicular  hone 

Fig.  273. — Left  talus,  lateral  surface. 

The  lateral  surface  carries  a  large  triangular  facet,  concave  from  above  downward, 
for  articulation  with  the  lateral  malleolus;  its  anterior  half  is  continuous  above  with 
the  trochlea;  and  in  front  of  it  is  a  rough  depression  for  the  attachment  of  the  ante- 
rior talofibular  ligament.  Between  the  posterior  half  of  the  lateral  border  of  the 
trochlea  and  the  posterior  part  of  the  base  of  the  fibular  articular  surface  is  a  tri- 
angular facet  (Fawcett^)  which  comes  into  contact  with  the  transverse  inferior 
tibiofibular  ligament  during  flexion  of  the  ankle-joint;  below  the  base  of  this  facet 
is  a  groove  which  affords  attachment  to  the  posterior  talofibular  ligament. 

The  posterior  surface  is  narrow,  and  traversed  by  a  groove  running  obliquely 

'  Sewell  (Journal  of  Anatomy  and  Physiology,  vol.  xxxviii)  pointed  out  that  in  about  10  per  cent,  of  bones  a  small 
triangular  facet,  continuous  with  the  posterior  calcaneal  facet,  is  present  at  the  junction  of  the  lateral  surface  of  the 
body  with  the  posterior  wall  of  the  .sulcus  tali. 

-  Edinburgh  Medical  Journal,  1895. 


i 


THE  TARSUS 


269 


downward  and  medialward,  and  transmitting  the  tendon  of  the  Flexor  hallucis 
longus.  Lateral  to  the  groove  is  a  prominent  tubercle,  the  posterior  process,  to 
which  the  posterior  talofibular  ligament  is  attached;  this  process  is  sometimes 
separated  from  the  rest  of  the  talus,  and  is  then  known  as  the  os  trigonum.  Medial 
to  the  groove  is  a  second  smaller  tubercle. 

The  Neck  {collum  tali). — The  neck  is  directed  forward  and  medialward,  and. 
comprises  the  constricted  portion  of  the  bone  between  the  body  and  the  oval  head. 
Its  upper  and  medial  surfaces  are  rough,  for  the  attachment  of  ligaments;  its  lateral 
surface  is  concave  and  is  continuous  below  with  the  deep  groove  for  the  inter- 
osseous talocalcaneal  ligament. 

The  Head  (caput  tali). — The  head  looks  forward  and  medialward;  its  anterior 
articular  or  navicular  surface  is  large,  oval,  and  convex.  Its  inferior  surface  has  two 
facets,  which  are  best  seen  in  the  fresh  condition.  The  medial,  situated  in  front 
of  the  middle  calcaneal  facet,  is  convex,  triangular,  or  semi-oval  in  shape,  and 
rests  on  the  plantar  calcaneonavicular  ligament;  the  lateral,  named  the  anterior 
calcaneal  articular  surface,  is  somewhat  flattened,  and  articulates  with  the  facet  on 
the  upper  surface  of  the  anterior  part  of  the  calcaneus. 

Articulations. — The  talus  articulates  with,  four  bones:    tibia,  fibula,  calcaneus,  and  navicular. 

The  Cuboid  Bone  (os  cuboideum)  (Figs.  274,  275) . — The  cuboid  bone  is  placed  on 
the  lateral  side  of  the  foot,  in  front  of  the  calcaneus,  and  behind  the  fourth  and  fifth 
metatarsal  bones.    It  is  of  a  pyramidal  shape,  its  base  being  directed  medialward. 


For  3rd  cuneiform        For  4th  metatarsal 


For  Uh 
metatarsal 


Peronceal       Tuberosity  For  calcaneus 
evlcus 


Fig.  274. — The  left  cuboid.     Antero-medial  view. 


Fig.  275. — The  left  cuboid.     Postero-lateral  view. 


Surfaces. — The  dorsal  surface,  directed  upward  and  lateralward,  is  rough,  for  the 
ittachment  of  ligaments.  The  plantar  surface  presents  in  front  a  deep  groove, 
Jie  peroneal  sulcus,  which  runs  obliquely  forward  and  medialward;  it  lodges  the 
;<indon  of  the  Peronseus  longus,  and  is  bounded  behind  by  a  prominent  ridge, 
fO  which  the  long  plantar  ligament  is  attached.  The  ridge  ends  laterally  in  an 
^ininence,  the  tuberosity,  the  surface  of  which  presents  an  oval  facet;  on  this  facet 
tUdes  the  sesamoid  bone  or  cartilage  frequently  found  in  the  tendon  of  the  Pero- 

?us  longus.  The  surface  of  bone  behind  the  groove  is  rough,  for  the  attachment 
\l  the  plantar  calcaneocuboid  ligament,  a  few  fibers  of  the  Flexor  hallucis  brevis, 
md  a  fasciculus  from  the  tendon  of  the  Tibialis  posterior.  The  lateral  surface 
p>resents  a  deep  notch  form.ed  by  the  commencement  of  the  peroneal  sulcus.  The 
posterior  surface  is  smooth,  triangular,  and  concavo-convex,  for  articulation  with 
the  anterior  surface  of  the  calcaneus;  its  infero-medial  angle  projects  backward 
as  a  process  which  underlies  and  supports  the  anterior  end  of  the  calcaneus.  The 
anterior  surface,  of  smaller  size,  but  also  irregularly  triangular,  is  divided  by  a 
vertical  ridge  into  two  facets:  the  medial,  quadrilateral  in  form,  articulates  with 
the  fourth  metatarsal;  the  lateral,  larger  and  more  triangular,  articulates  with  the 
fifth.  The  medial  surface  is  broad,  irregularly  quadrilateral,  and  presents  at 
its  middle  and  upper  part  a  smooth  oval  facet,  for  articulation  with  the  third 


I 


270 


OSTEOLOGY 


cuneiform;  and  behind  this  (occasionally)  a  smaller  facet,  for  articulation  with 
the  navicular;  it  is  rough  in  the  rest  of  its  extent,  for  the  attachment  of  strong 
interosseous  ligaments. 

Articulations. — The  cuboid  articulates  with /our  bones:  the  calcaneus,  third  cuneiform,  jind 
fourth  and  fifth  metatarsals;  occasionally  with  a  fifth,  the  navicular. 

The  Navicular  Bone  {os  naviculare  pedis;  scaphoid  bone)  (Figs.  276,  277). — The 
navicular  bone  is  situated  at  the  medial  side  of  the  tarsus,  between  the  talus 
behind  and  the  cuneiform  bones  in  front. 


For  1st  cuneijorm 


For  2iid  cuneiforvi 


For  3rd 

cuneiform 


Fig.  276.— The  left  naviciilar. 


Occasional 
facet  for 
cvboid 
Antero-lateral  view. 


For  talus        Tuberosity 
Fig.  277. — Theleft  navicular.     Postero-niedialview. 


Surfaces. — The  anterior  surface  is  convex  from  side  to  side,  and  subdivided  by  two 
ridges  into  three  facets,  for  articulation  with  the  three  cuneiform  bones.  The 
posterior  surface  is  oval,  concave,  broader  laterally  than  medially,  and  articulates 
with  the  rounded  head  of  the  talus.  The  dorsal  surface  is  convex  from  side  to  side, 
and  rough  for  the  attachment  of  ligaments.  The  plantar  surface  is  irregular,  and 
also  rough  for  the  attachment  of  ligaments.    The  medial  surface  presents  a  rounded 

tuberosity,  the  lower  part  of  which 
Fcr  2nd  For  gives  attachment  to  part  of  the 

For  1st  metatarsal  metatarsal       2nd  cuneiform       tendon  of  the  Tibialis  posterior. 

The  lateral  surface  is  rough  and 
irregular  for  the  attachment  of 
ligaments,  and  occasionally  pre- 
sents a  small  facet  for  articula- 
tion with  the  cuboid  bone. 

Articulations. — Thenavicular  articu- 
lates with  four  bones:  the  talus  and 
the  three  cuneiforms;  occasionally  with 
a  fifth,  the  cuboid. 


For  tendon  of 
Tibialis  anterior 


For  navicular 


Fig.  278. — The  left  first  cunei- 
form.    Antero-medial  view. 


The  First  Cuneiform  Bone  {os 

cvneiform  privium;  internal ciinei- 
''form.''-roSrifii\?;fi  vTw'-    fomi)  (Figs.  278,  _279).-The  first 

cuneiform  bone  is  the  largest  of 
the  three  cuneiforms.  It  is  situated  at  the  medial  side  of  the  foot,  between  the 
navicular  behind  and  the  base  of  the  first  metatarsal  in  front. 

Surf aces.^ — ^Tlie  medial  surface  is  subcutaneous,  broad,  and  quadrilateral ;  at  its 
anterior  plantar  angle  is  a  smooth  oval  impression,  into  which  part  of  the  tendon 
of  the  Tibialis  anterior  is  inserted;  in  the  rest  of  its  extent  it  is  rough  for  the 
attachment  of  ligaments.  The  lateral  surface  is  concave,  presenting,  along  its 
superior  and  posterior  borders  a  narrow  F-shaped  surface,  the  vertical  limb  and 
posterior  part  of  the  horizontal  limb  of  which  articulate  with  the  second  cuneiform, 
while  the  anterior  part  of  the  horizontal  limb  articulates  with  the  second  metatarsal 


THE  TARSUS 


271 


bone :  the  rest  of  this  surface  is  rough  for  the  attachment  of  ligaments  and  part 
of  the  tendon  of  the  Peronaeus  longus.  The  anterior  surface,  kidney-shaped  and 
much  larger  than  the  posterior,  articulates  with  the  first  metatarsal  bone.  The 
posterior  surface  is  triangular,  concave,  and  articulates  with  the  most  medial  and 
largest  of  the  three  facets  on  the  anterior  surface  of  the  navicular.  The  plantar 
surface  is  rough,  and  forms  the  base  of  the  wedge;  at  its  back  part  is  a  tuberosity 
for  the  insertion  of  part  of  the  tendon  of  the  Tibialis  posterior.  It  also  gives 
insertion  in  front  to  part  of  the  tendon  of  the  Tibialis  anterior.  The  dorsal  surface 
is  the  narrow  end  of  the  wedge,  and  is  directed  upward  and  lateralward;  it  is 
rough  for  the  attachment  of  ligaments. 

Articulations. — The  first  cuneiform  articulates  with  four  bones:  the  navicular,  second  cunei- 
form, and  first  and  second  metatarsals. 

The  Second  Cuneiform  Bone  (os  cuneiforme  secundum;  middle  cuneiform)  (Figs. 
280,  281).— The  second  cuneiform  bone,  the  smallest  of  the  three,  is  of  very  reg- 
ular wedge-like  form,  the  thin  end  being  directed  downward.  It  is  situated  between 
the  other  two  cuneiforms,  and  articulates  with  the  navicular  behind,  and  the 
second  metatarsal  in  front. 

-  Surfaces. — The  anterior  surface,  triangular  in  form,  and  narrower  than  the  pos- 
terior, articulates  with  the  base  of  the  second  metatarsal  bone.  The  posterior  sur- 
face, also  triangular,  articulates  with  the  intermediate  facet  on  the  anterior  surface 
of  the  navicular.  The  medial  surface  carries  an  L-shaped  articular  facet,  running 
along  the  superior  and  posterior  borders,  for  articulation  w^ith  the  first  cuneiform, 
and  is  rough  in  the  rest  of  its  extent  for  the  attachment  of  ligaments.    The  lateral 


For  1st  cuneiform 


For  navicular 


For  2nd  metatarsal  For  3rd  cuneiform 


Fig.  280.— The  left  second 
ctineiform.  An  t  ero-media  1 
vi  'w. 


Fig.  281.— The  left 
second  cuneiform.  Pos- 
tero-lateral  view. 


surface  presents  posteriorly  a  smooth 
facet  for  articulation  with  the  third 
cuneiform  bone.  The  dorsal  surface 
forms  the  base  of  the  wedge;  it  is 
quadrilateral  and  rough  for  the  at- 
tachment of  ligaments.  The  plantar 
surface,  sharp  and  tuberculated,  is 
also  rough  for  the  attachment  of 
ligaments,  and  for  the  insertion  of  a 
slip  from  the  tendon  of  the  Tibialis 
posterior. 

Articulations. — The  second  cuneiform  articulates  with  four  bones:  the  navicular,  first  and 
tl  ird  cuneiforms,  and  second  metatarsal. 

The  Third  Cuneiform  Bone  {os  cuneiforme  iertium;  external  cuneiform)  (Figs.  282, 
2S3). — The  third  cuneiform  bone,  intermediate  in  size  between  the  two  preceding, 
is  wedge-shaped,  the  base  being  uppermost.  It  occupies  the  center  of  the  front  row 
ol  the  tarsal  bones,  between  the  second  cuneiform  medially,  the  cuboid  laterally, 
the  navicular  behind,  and  the  third  metatarsal  in  front. 

Surfaces. — The  anterior  surface,  triangular  in  form,  articulates  with  the  third 
metatarsal  bone.  The  posterior  surface  articulates  with  the  lateral  facet  on  the 
anterior  surface  of  the  navicular,  and  is  rough  below  for  the  attachment  of  liga- 
mentous fibers.  The  medial  surface  presents  an  anterior  and  a  posterior  articular 
facet,  separated  by  a  rough  depression:  the  anterior,  sometimes  divided,  articulates 
with  the  lateral  side  of  the  base  of  the  second  metatarsal  bone;  the  posterior  skirts 
tl  e  posterior  border,  and  articulates  with  the  second  cuneiform;  the  rough  depres- 
sion gives  attachment  to  an  interosseous  ligament.  The  lateral  surface  also  pre- 
sents two  articular  facets,  separated  by  a  rough  non-articular  area;  the  anterior 
facet,  situated  at  the  superior  angle  of  the  bone,  is  small  and  semi-oval  in  shape, 
and  articulates  with  the  medial  side  of  the  base  of  the  fourth  metatarsal  bone; 


272 


OSTEOLOGY 


the  posterior  and  larger  one  is  triangular  or  oval,  and  articulates  with  the  cuboid; 
the  rough,  non-articular  area  serves  for  the  attachment  of  an  interosseous  ligament. 
The  three  facets  for  articulation  with  the  three  metatarsal  bones  are  continuous 
with  one  another;  those  for  articulation  with  the  second  cuneiform  and  navicular 
are  also  continuous,  but  that  for  articulation  with  the  cuboid  is  usually  separate. 
The  dorsal  surface  is  of  an  oblong  form,  its  postero-lateral  angle  being  prolonged 
backward.  The  plantar  surface  is  a  rounded  margin,  and  serves  for  the  attachment 
of  part  of  the  tendon  of  the  Tibialis  posterior,  part  of  the  Flexor  hallucis  brevis, 
and  ligaments. 


Articulations. — ^The  third  cuneiform  articulates  with  six  bones: 
form,  cuboid,  and  second,  third,  and  fourth  metatarsals. 


the  navicular,  second  cunei- 


For  navicular    For  2nd  cuneiform 


For  cuboid 


Fig.  282. — The  left  third  cuneiform, 
view. 


For  2nd 

metatarsal 


Postero-medial 


Fig. 


Forird 
metatarsal 

283. — The  third  left  cuneiform, 
lateral  view. 


Antero- 


The  Metatarsus. 

The  metatarsus  consists  of  five  bones  which  are  numbered  from  the  medial 
side  {ossa  metatarsalia  I.-V.);  each  presents  for  examination  a  body  and  two 
extremities. 

Common  Characteristics  of  the  Metatarsal  Bones. — The  body  is  prismoid  in 
form,  tapers  gradually  from  the  tarsal  to  the  phalangeal  extremity,  and  is  curved 
longitudinally,  so  as  to  be  concave  below,  slightly  convex  above.  The  base  or 
posterior  extremity  is  wedge-shaped,  articulating  proximally  with  the  tarsal  bones, 
and  by  its  sides  with  the  contiguous  metatarsal  bones:  its  dorsal  and  plantar 
surfaces  are  rough  for  the  attachment  of  ligaments.  The  head  or  anterior  extremity 
presents  a  convex  articular  surface,  oblong  from  above  downward,  and  extend- 
ing farther  backward  below  than  above.  Its  sides  are  flattened,  and  on  each  is  a 
depression,  surmounted  by  a  tubercle,  for  ligamentous  attachment.  Its  plantar 
surface  is  grooved  antero-posteriorly  for  the  passage  of  the  Flexor  tendons,  and 
marked  on  either  side  by  an  articular  eminence  continuous  with  the  terminal 
articular  surface. 

Characteristics  of  the  Individual  Metatarsal  Bones.  —  The  First  Metatarsal 
Bone  (os  metatarsale  I;  metatarsal  bone  of  the  great  toe)  (Fig.  284). — The  first 
metatarsal  bone  is  remarkable  for  its  great  thickness,  and  is  the  shortest  of 
the  metatarsal  bones.  The  body  is  strong,  and  of  well-marked  prismoid  form. 
The  base  presents,  as  a  rule,  no  articular  facets  on  its  sides,  but  occasionally 
on  the  lateral  side  there  is  an  oval  facet,  by  which  it  articulates  with  the  second 
metatarsal.  Its  proximal  articular  surface  is  of  large  size  and  kidney-shaped;  its 
circumference  is  grooved,  for  the  tarsometatarsal  ligaments,  and  medially  gives 
insertion  to  part  of  the  tendon  of  the  Tibialis  anterior;  its  plantar  angle  presents 
a  rough  oval  prominence  for  the  insertion  of  the  tendon  of  the  Peronseus  longus. 
The  head  is  large;  on  its  plantar  surface  are  two  grooved  facets,  on  which  glide 
sesamoid  bones;  the  facets  are  separated  by  a  smooth  elevation. 


THE  METATARSUS 


273 


The  Second  Metatarsal  Bone  {os  metatarsale  II)  (Fig.  285). — The  second  meta- 
tarsal bone  is  the  longest  of  the  metatarsal  bones,  being  prolonged  backward 


For  sesamoid  bones 


For  1st  For  PeroruBfua 

CU7ieiform  Umgus 

Fig.  284.— The  first  metatarsal.     (Left.) 


Fm  1st 

cuneiform      For  2nd  For  'Srd 

cuneiform  cuneiform 

Fig.  285. — The  second  metatarsal.     (Left.) 


For  2nd 

metatarsal  I    For  2nd 

For       meta- 
3rd        tarsal 
cuneiform 


For  Ath 
metatarsal 


Fig.  286.— The  third  metatarsal.     (Left.) 


For  Srd 
metatarsal 


For  cuboid 

For  3rd  cuneiform  For  5th  metatarsal 

Fig.  287. — The  fourth  metatarsal.     (Left.) 


into  the  recess  formed  by  the  three  cuneiform  bones.  Its  base  is  broad  above, 
narrow  and  rough  below.  It  presents  four  articular  surfaces:  one  behind,  of  a 
triangular  form,  for  articulation  with  the  second  cuneiform;  one  at  the  upper  part 

IS 


274 


OSTEOLOGY 


I 


of  its  medial  surface,  for  articulation  with  the  first  cuneiform;  and  two  on  its  lat(;ral 
surface,  an  upper  and  lower,  separated  by  a  rough  non-articular  interval.  Each 
of  these  lateral  articular  surfaces  is  divided  into  two  by  a  vertical  ridge;  the  two 
anterior  facets  articulate  with  the  third  metatarsal;  the  two  posterior  (sometiraes 
continuous)  with  the  third  cuneiform.  A  fifth  facet  is  occasionally  present  for 
articulation  with  the  first  metatarsal;  it  is  oval  in  shape,  and  is  situated  on  the 
medial  side  of  the  body  near  the  base. 

The  Third  Metatarsal  Bone  {os  metatarsale  III)  (Fig.  286). — The  third  meta- 
tarsal bone  articulates  proximally,  by  means  of  a  triangular  smooth  surface, 
with  the  third  cuneiform;  medially,  by  two  facets,  with  the  second  metatarsal; 
and  laterally,  by  a  single  facet,  with  the  fourth  metatarsal.  This  last  facet  is 
situated  at  the  dorsal  angle  of  the  base. 


iir 


P. 

For  Uk 
metatarsal        For  cuboid        Tuberosity 

Fia.  288.— The  fifth  metatarsal.     (Left.) 

The  Fourth  Metatarsal  Bone  {os  metatarsale  IV)  (Fig.  2<S7). — The  fourth  meta- 
tarsal bone  is  smaller  in  size  than  the  preceding;  its  base  presents  an  oblique 
quadrilateral  surface  for  articulation  with  the  cuboid ;  a  smooth  facet  on  the  medial 
side,  divided  by  a  ridge  into  an  anterior  portion  for  articulation  witli  the  third 
metatarsal,  and  a  posterior  portion  for  articulation  with  the  third  cuneiform;  on 
the  lateral  side  a  single  facet,  for  articulation  with  the  fifth  metatarsal. 

The  Fifth  Metatarsal  Bone  {os  metatarsale  V)  (Fig.  288). — The  fifth  metatarsal 
bone  is  recognized  by  a  rough  eminence,  the  tuberosity,  on  the  lateral  side  of  its 
base.  The  base  articulates  behind,  by  a  triangular  surface  cut  obliquely  in  a  trans- 
verse direction,  with  the  cuboid;  and  medially,  wuth  the  fourth  metatarsal.  On 
the  medial  part  of  its  dorsal  surface  is  inserted  the  tendon  of  the  Peron?eus  tertius 
and  on  the  dorsal  surface  of  the  tuberosity  that  of  the  Peronseus  brevis.  A  strong 
band  of  the  plantar  aponeurosis  connects  the  projecting  part  of  the  tuberosity 
with  the  lateral  process  of  the  tuberosity  of  the  calcaneus.  The  plantar  surface 
of  the  base  is  grooved  for  the  tendon  of  the  Abductor  digiti  quinti,  and  gives  origin 
to  the  Flexor  digiti  quinti  brevis. 

Articulations. — The  base  of  each  metatarsal  bone  articulates  with  one  or  more  of  the  tarsal 
bones,  and  the  head  with  one  of  the  first  row  of  phalanges.  The  first  metatarsal  articulates  with 
the  first  cuneiform,  the  second  with  all  three  cuneiforms,  the  third  with  the  third  cuneiform,  the 
fourth  with  the  third  cuneiform  and  the  cuboid,  and  the  fifth  with  the  cuboid. 


THE  PHALANGESOF  THE  FOOT 


The  Phalanges  of  the  Foot  (Phalanges  Digitorum  Pedis). 


275 


The  phalanges  of  the  foot  correspond,  in  number  and  general  arrangement, 
with  those  of  the  hand;  there  are  two  in  the  great  toe,  and  three  in  each  of  the 
other  toes.  They  differ  from  them,  however,  in  their  size,  the  bodies  being  much 
reduced  in  length,  and,  especially  in  the  first  row,  laterally  compressed. 

First  Row. — The  body  of  each  is  compressed  from  side  to  side,  convex  above, 
concave  below.  The  base  is  concave;  and  the  head  presents  a  trochlear  surface 
for  articulation  with  the  second  phalanx. 

Second  Row. — The  phalanges  of  the  second  row  are  remarkably  small  and  short, 
but  rather  broader  than  those  of  the  first  row. 

The  ungual  phalanges,  in  form,  resemble  those  of  the  fingers;  but  they  are  smaller 
and  are  flattened  from  above  downward ;  each  presents  a  broad  base  for  articula- 
tion with  the  corresponding  bone  of  the  second  row,  and  an  expanded  distal 
extremity  for  the  support  of  the  nail  and  end  of  the  toe. 


One  center  for  each  bone, 
except  calcaneus 


OUTER  FOtJE  METATARSALS. 

Tv)o  centers  for  each  hone  . 
One  for  body 
One  for  Jiead 


PHALANQES. 

Two  centers  for  each  bone  : 
One  for  body 
One  for  metatarsal 
extremity 


Appears  10th  year; 
unites  after  puberty 


Appears  Srd  year 
}  Unite  18th-20th  year 

~  Apjxars  1th  week 


Unite  18-20  j/r.  ^ 
Apps.  Srd  yr. 

App.  ith  yr^ 
Unite  17-18  yr. 

App.  2-4  mo.  _ 


App.  6-7th  yr. 
Unite  17-18  yr.  J 

App.  2-4  mo. 

App.  6th  yr. 
Unite  17-18  yr.  | 

App,  7th  wk, 

FiQ.  289. — Plan  of  ossification  of  the  foot. 


iculations. — In  the  second,  third,  fourth,  and  fifth  toes  the  phalanges  of  the  first  row  articu- 
late behind  with  the  metatarsal  bones,  and  in  front  with  the  second  phalanges,  which  in  their 
turn  articulate  with  the  first  and  third:    the  ungual  phalanges  articulate  with  the  second. 

Ossification  of  the  Bones  of  the  Foot  (Fig.  289). — The  tarsal  bones  are  each  ossified  from  a 
single  center,  excepting  the  calcaneus,  which  has  an  epiphysis  for  its  posterior  extremity.  The 
centers  make  their  appearance  in  the  following  order:    calcaneus  at  the  sixth  month  of  fetal  life; 


276 


OSTEOLOGY 


talus,  about  the  seventh  month;  cuboid,  at  the  ninth  nronth;  third  cuneiform,  during  the  first 
year;  first  cuneiform,  in  the  third  year;  second  cuneiform  and  navicular,  in  the  fourth  year. 
The  epiphysis  for  the  posterior  extremity  of  the  calcaneus  appears  at  the  tenth  year,  and  unites 
with  the  rest  of  the  bone  soon  after  puberty.  The  posterior  process  of  the  talus  is  sometimt^a 
ossified  from  a  separate  center,  and  may  remain  distinct  from  the  main  mass  of  the  bone,  when 
it  is  named  the  os  trigonum. 

The  metatarsal  bones  are  each  ossified  from  two  centers:  one  for  the  body,  and  one  for  the 
head,  of  the  second,  third,  fourth,  and  fifth  metatarsals;  one  for  the  body,  and  one  for  the  base, 
of  the  first  metatarsal.^  Ossification  commences  in  the  center  of  the  body  about  the  ninth  week, 
and  extends  toward  either  extremity.  The  center  for  the  base  of  the  first  metatarsal  appeai-s 
about  the  third  year;  the  centers  for  the  heads  of  the  other  bones  between  the  fifth  and  eighth 
years;  they  join  the  bodies  between  the  eighteenth  and  twentieth  years. 

The  phalanges  are  each  ossified  from  two  centers:  one  for  the  body,  and  one  for  the  base. 
The  center  for  the  body  appears  about  the  tenth  week,  that  for  the  base  between  the  fourth  and 
tenth  years;  it  joins  the  body  about  the  eighteenth  year. 

Comparison  of  the  Bones  of  the  Hand  and  Foot. 

The  hand  and  foot  are  constructed  on  somewhat  similar  principles,  each  con- 
sisting of  a  proximal  part,  the  carpus  or  the  tarsus,  a  middle  portion,  the  meta- 
carpus, or  the  metatarsus,  and  a  terminal  portion,  the  phalanges.  The  proximal 
part  consists  of  a  series  of  more  or  less  cubical  bones  which  allow  a  slight  amount 
of  gliding  on  one  another  and  are  chiefly  concerned  in  distributing  forces  transmitted 
to  or  from  the  bones  of  the  arm  or  leg.  The  middle  part  is  made  up  of  slightly 
movable  long  bones  which  assist  the  carpus  or  tarsus  in  distributing  forces  and 
also  give  greater  breadth  for  the  reception  of  such  forces.  The  separation  of  the 
individual  bones  from  one  another  allows  of  the  attachments  of  the  Interossei  and 
protects  the  dorsi-palmar  and  dorsi-plantar  vascular  anastomoses.  The  terminal 
portion  is  the  most  movable,  and  its  separate  elements  enjoy  a  varied  range  of 
movements,  the  chief  of  which  are  flexion  and  extension. 


Fig.  290. — Skeleton  of  foot.     Medial  aspect. 

The  function  of  the  hand  and  foot  are,  however,  very  different,  and  the  general 
similarity  between  them  is  greatly  modified  to  meet  these  requirements.  Thus  the 
foot  forms  a  firm  basis  of  support  for  the  body  in  the  erect  posture,  and  is  there- 
fore more  solidly  built  up  and  its  component  parts  are  less  movable  on  each  other 
than  those  of  the  hand.  In  the  case  of  the  phalanges  the  difference  is  readily 
noticeable;  those  of  the  foot  are  smaller  and  their  movements  are  more  limited 
than  those  of  the  hand.  Very  much  more  marked  is  the  difference  between  the 
metacarpal  bone  of  the  thumb  and  the  metatarsal  bone  of  the  great  toe.  The  meta- 
carpal bone  of  the  thumb  is  constructed  to  permit  of  great  mobility,  is  directed  at 
an  acute  angle  from  that  of  the  index  finger,  and  is  capable  of  a  considerable  range 

'  As  was  noted  in  the  first  metacarpal  (see  footnote,  page  231),  so  in  the  first  metatarsal,  there  is  often  a  second 
epiphysis  for  its  head. 


THESM 


277 


of  movements  at  its  articulation  with  the  carpus.  The  metatarsal  bone  of  the 
great  toe  assists  in  supporting  the  weigh  fc  of  the  body,  is  constructed  with  great 
sohdity,  lies  parallel  with  the  other  metatarsals,  and  has  a  very  limited  degree  of 
mobility.  The  carpus  is  small  in  proportion  to  the  rest  of  the  hand,  is  placed 
in  line  with  the  forearm,  and  forms  a  transverse  arch,  the  concavity  of  which 
constitutes  a  bed  for  the  Flexor  tendons  and  the  palmar  vessels  and  nerves.  The 
tarsus  forms  a  considerable  part  of  the  foot,  and  is  placed  at  right  angles  to  the 
leg,  a  position  w^hich  is  almost  peculiar  to  man,  and  has  relation  to  his  erect  pos- 
ture. In  order  to  allow  of  their  supporting  the  weight  of  the  body  with  the  least 
expenditure  of  material  the  tarsus  and  a  part  of  the  metatarsus  are  constructed 
in  a  series  of  arches  (Figs.  290,  291),  the  disposition  of  which  will  be  considered 
after  the  articulations  of  the  foot  have  been  described. 


Fig.  291. — Skeleton  of  foot.     Lateral  aspect. 

The  Sesamoid  Bones  (Ossa  Sesamoidea). 

Sesamoid  bones  are  small  more  or  less  rounded  masses  embedded  in  certain 
tendons  and  usually  related  to  joint  surfaces.  Their  functions  probably  are  to 
modify  pressure,  to  diminish  friction,  and  occasionally  to  alter  the  direction  of  a 
muscle  pull.  That  they  are  not  developed  to  meet  certain  physical  requirements 
in  the  adult  is  evidenced  by  the  fact  that  they  are  present  as  cartilaginous  nodules 
in  the  fetus,  and  in  greater  numbers  than  in  the  adult.  They  must  be  regarded, 
according  to  Thilenius,  as  integral  parts  of  the  skeleton  phylogenetically  inherited.* 
Physical  necessities  probably  come  into  play  in  selecting  and  in  regulating  the 
degree  of  development  of  the  original  cartilaginous  nodules.  Nevertheless,  irreg- 
ular nodules  of  bone  may  appear  as  the  result  of  intermittent  pressure  in  certain 
regions,  e.  g.,  the  "rider's  bone,"  which  is  occasionally  developed  in  the  Adductor 
muscles  of  the  thigh. 

Sesamoid  bones  are  invested  by  the  fibrous  tissue  of  the  tendons,  except  on  the 
surfaces  in  contact  with  the  parts  over  which  they  glide,  where  they  present 
smooth  articular  facets. 

In  the  upper  extremity  the  sesamoid  bones  of  the  joints  are  found  only  on  the 
palmar  surface  of  the  hand.  Two,  of  which  the  medial  is  the  the  larger,  are  constant 
at  the  metacarpophalangeal  joint  of  the  thumb;  one  is  frequently  present  in  the 
corresponding  joint  of  the  little  finger,  and  one  (or  two)  in  the  same  joint  of  the 
index  finger.  Sesamoid  bones  are  also  found  occasionally  at  the  metacarpopha- 
langeal joints  of  the  middle  and  ring  fingers,  at  the  interphalangeal  joint  of  the 
thumb  and  at  the  distal  interphalangeal  joint  of  the  index  finger. 

In  the  lower  extremity  the  largest  sesamoid  bone  of  the  joints  is  the  patella, 
developed  in  the  tendon  of  the  Quadriceps  femoris.  On  the  plantar  aspect  of  the 
foot,  two,  of  which  the  medial  is  the  larger,  are  always  present  at  the  metatar- 

»  Morpholog.  Arbeiten,  1906,  v,  309. 


18 


OSTEOLOGY 


sophalangeal  joint  of  the  great  toe;  one  sometimes  at  the  metatarsophalangeal 
joints  of  the  second  and  fifth  toes,  one  occasionally  at  the  corresponding  joint  of 
the  third  and  fourth  toes,  and  one  at  the  interphalangeal  joint  of  the  great  toe. 

Sesamoid  bones  apart  from  joints  are  seldom  found  in  the  tendons  of  the  upp(;r 
limb;  one  is  sometimes  seen  in  the  tendon  of  the  Biceps  brachii  opposite  the  radial 
tuberosity.  They  are,  however,  present  in  several  of  the  tendons  of  the  lower 
limb,  viz.,  one  in  the  tendon  of  the  Peronseus  longus,  where  it  glides  on  the  cuboid; 
one,  appearing  late  in  life,  in  the  tendon  of  the  Tibialis  anterior,  opposite  the  smooth 
facet  of  the  first  cuneiform  bone;  one  in  the  tendon  of  the  Tibialis  posterior,  oppo- 
site the  medial  side  of  the  head  of  the  talus;  one  in  the  lateral  head  of  the  Gastroo 
nemius,  behind  the  lateral  condyle  of  the  femur;  and  one  in  the  tendon  of  the  Psoas 
major,  where  it  glides  over  the  pubis.  Sesamoid  bones  are  found  occasionally 
in  the  tendon  of  the  Glutseus  maximus,  as  it  passes  over  the  greater  trochanter, 
and  in  the  tendons  which  wind  around  the  medial  and  lateral  malleoli. 


SYNDESMOLOGY. 


THE  bones  of  the  skeleton  are  joined  to  one  another  at  different  parts  of  their 
surfaces,  and  such  connections  are  termed  Joints  or  Articulations,  Where 
the  joints  are  immovable,  as  in  the  articulations  between  practically  all  the  bones 
of  the  skull,  the  adjacent  margins  of  the  bones  are  almost  in  contact,  being  separated 
merely  by  a  thin  layer  of  fibrous  membrane,  named  the  sutural  ligament.  In  certain 
regions  at  the  base  of  the  skull  this  fibrous  membrane  is  replaced  by  a  layer  of  car- 
tilage. Where  slight  movement  combined  with  great  strength  is  required,  the  osseous 
surfaces  are  united  by  tough  and  elastic  fibrocartilages,  as  in  the  joints  between  the 
vertebral  bodies,  and  in  the  interpubic  articulation.  In  the  freely  movable  joints 
the  surfaces  are  completely  separated;  the  bones  forming  the  articulation  are  ex- 
panded for  greater  convenience  of  mutual  connection,  covered  by  cartilage  and 
enveloped  by  capsules  of  fibrous  tissue.  The  cells  lining  the  interior  of  the  fibrous 
capsule  form  an  imperfect  membrane— the  sjmovial  membrane — which  secretes 
a  lubricating  fluid.  The  joints  are  strengthened  by  strong  fibrous  bands  called 
ligaments,  which  extend  between  the  bones  forming  the  joint. 

Bone. — Bone  constitutes  the  fundamental  element  of  all  the  joints.  In  the 
long  bones,  the  extremities  are  the  parts  which  form  the  articulations;  they  are 
generally  somewhat  enlarged;  and  consist  of  spongy  cancellous  tissue  with  a  thin 
coating  of  compact  substance.  In  the  flat  bones,  the  articulations  usually  take 
place  at  the  edges;  and  in  the  short  bones  at  various  parts  of  their  surfaces.  The 
layer  of  compact  bone  which  forms  the  joint  surface,  and  to  which  the  articular 
cartilage  is  attached,  is  called  the  articular  lamella.  It  differs  from  ordinary 
bone  tissue  in  that  it  contains  no  Haversian  canals,  and  its  lacunae  are  larger 
and  have  no  canaliculi.  The  vessels  of  the  cancellous  tissue,  as  they  approach 
the  articular  lamella,  turn  back  in  loops,  and  do  not  perforate  it;  this  layer  is  con- 
sequently denser  and  firmer  than  ordinary  bone,  and  is  evidently  designed  to  form 
an  unyielding  support  for  the  articular  cartilage. 

Cartilage. — Cartilage  is  a  non-vascular  structure  which  is  found  in  various 
parts  of  the  body — in  adult  life  chiefly  in  the  joints,  in  the  parietes  of  the  thorax, 
and  in  various  tubes,  such  as  the  trachea  and  bronchi,  nose,  and  ears,  which  require 
to  be  kept  permanently  open.  In  the  fetus,  at  an  early  period,  the  greater  part 
of  the  skeleton  is  cartilaginous;  as  this  cartilage  is  afterward  replaced  by  bone, 
it  is  called  temporary,  in  contradistinction  to  that  which  remains  unossified  during 
the  whole  of  life,  and  is  called  permanent. 

Cartilage  is  divided,  according  to  its  minute  structure,  into  hyaline  cartjlage, 
white  fibrocartilage,  and  yellow  or  elastic  fibrocartilage. 

Hyaline  Cartilage. — Hyaline  cartilage  consists  of  a  gristly  mass  of  a  firm  consist- 
ence, but  of  considerable  elasticity  and  pearly  bluish  color.  Except  where  it  coats 
the  articular  ends  of  bones,  it  is  covered  externally  by  a  fibrous  membrane,  the 
perichondrium,  from  the  vessels  of  which  it  imbibes  its  nutritive  fluids,  being  itself 
destitute  of  bloodvessels.  It  contains  no  nerves.  Its  intimate  structure  is  very 
simple.  If  a  thin  slice  be  examined  under  the  microscope,  it  will  be  found  to  consist 
of  cells  of  a  rounded  or  bluntly  angular  form,  lying  in  groups  of  two  or  more  in 
a  granular  or  almost  homogeneous  matrix  (Fig.  292).  The  cells,  when  arranged 
in  groups  of  two  or  more,  have  generally  straight  outlines  where  they  are  in  contact 

(279) 


280 


SYNDESMOLOGY 


with  each  other,  and  in  the  rest  of  their  circumference  are  rounded.  They  con- 
sist of  clear  translucent  protoplasm  in  which  fine  interlacing  filaments  and  minute 
granules  are  sometimes  present;  imbedded  in  this  are  one  or  two  round  nuchi, 
having  the  usual  intranuclear  network.  The  cells  are  contained  in  cavities  in 
the  matrix,  called  cartilage  lacunae ;  around  these  the  matrix  is  arranged  in  co)i- 
centric  lines,  as  if  it  had  been  formed  in  successive  portions  around  the  cartilage 
cells.     This  constitutes  the  so-called  capsule  of  the  space.    Each  lacuna  is  generally 

occupied  by  a  single  cell,  but  dur- 
ing the  division  of  the  cells  it  may 
contain  two,  four,  or  eight  cells. 

The  matrix  is  transparent  and 
apparently  without  structure,  or 
else  presents  a  dimly  granular  ap- 
pearance, like  ground  glass.  Some 
observers  have  shown  that  the 
matrix  of  hyaline  cartilage,  and 
especially  of  the  articular  variety, 
after  prolonged  maceration,  can 
be  broken  up  into  fine  fibrils. 
These  fibrils  are  probably  of  the  same  nature,  chemically,  as  the  w^hite  fibers 
of  connective  tissue.  It  is  believed  by  some  histologists  that  the  matrix  is  per- 
meated by  a  number  of  fine  channels,  which  connect  the  lacunae  with  each  other, 
and  that  these  canals  communicate  with  the  lymphatics  of  the  perichondrium, 
and  thus  the  structure  is  permeated  by  a  current  of  nutrient  fluid. 

Articular  cartilage,  costal  cartilage,  and  temporary  cartilage  are  all  of  the  hyaline 
variety.  They  present  difi^erences  in  the  size,  shape,  and  arrangement  of  their 
cells. 


Fig.  292. — Human  cartilage  cells  from  the  cricoid  cartilage. 
X  350 


"J^g|  Superficial  fiattened  cells 


Vertical  rows  of  cells 


%3t'. v!^"'*'!-' "."•'•"•?h^^^  f  Colcifi^ 


matrix 


Bone 


Fig.  293. — Vertical  section  of  articular  cartUage. 


Fig.  294. — Costal  cartilage  from  a  man,  aged 
seventy-six  years,  showing  the  development  of 
fibrous  structure  in  the  matrix.  In  several  por- 
tions of  the  specimen  two  or  three  generations  of 
cells  are  seen  enclosed  in  a  parent  cell  wall. 
Highly  magnified. 


In  Articular  Cartilage  (Fig.  293),  which  shows  no  tendency  to  ossification,  the 
matrix  is  finely  granular;  the  cells  and  nuclei  are  small,  and  are  disposed  parallel 
to  the  surface  in  the  superficial  part,  while  nearer  to  the  bone  they  are  arranged  in 
vertical  rows.  Articular  cartilages  have  a  tendency  to  split  in  a  vertical  direction; 
in  disease  this  tendency  becomes  very  manifest.  The  free  surface  of  articular 
cartilage,  where  it  is  exposed  to  friction,  is  not  covered  by  perichondrium,  although 
a  layer  of  connective  tissue  continuous  with  that  of  the  synovial  membrane  can  be 


A 


I 


CARTILAGE 


281 


traced  in  the  adult  over  a  small  part  of  its  circumference,  and  here  the  cartilage 
cells  are  more  or  less  branched  and  pass  insensibly  into  the  branched  connective 
tissue  corpuscles  of  the  synovial  membrane.  Articular  cartilage  forms  a  thin 
incrustation  upon  the  joint  surfaces  of  the  bones,  and  its  elasticity  enables  it  to 
break  the  force  of  concussions,  while  its  smoothness  affords  ease  and  freedom  of 
movement.  It  varies  in  thickness  according  to  the  shape  of  the  articular  surface 
on  which  it  lies;  where  this  is  convex  the  cartilage  is  thickest  at  the  center,  the 
reverse  being  the  case  on  concave  articular  surfaces.  It  appears  to  derive  its 
nutriment  partly  from  the  vessels  of  the  neighboring  synovial  membrane  and 
partly  from  those  of  the  bone  upon  which  it  is  implanted.  Toynbee  has  shown 
that  the  minute  vessels  of  the  cancellous  tissue  as  they  approach  the  articular 
lamella  dilate  and  form  arches,  and  then  return  into  the  substance  of  the  bone. 

In  Costal  Cartilage  the  cells  and  nuclei  are  large,  and  the  matrix  has  a  tendency 
to  fibrous  striation,  especially  in  old  age  (Fig.  294).  In  the  thickest  parts  of  the 
costal  cartilages  a  few  large  vascular  channels  may  be  detected.  This  appears, 
at  first  sight,  to  be  an  exception  to  the  statement  that  cartilage  is  a  non-vascular 
tissue,  but  is  not  so  really,  for  the  vessels  give  no  branches  to  the  cartilage  sub- 
stance itself,  and  the  channels  may  rather  be  looked  upon  as  involutions  of  the 
])erichondrium.  The  xiphoid  process  and  the  cartilages  of  the  nose,  larynx,  and 
trachea  (except  the  epiglottis  and  corniculate  cartilages  of  the  larynx,  which  are 
(jomposed  of  elastic  fibrocartilage)  resemble  the  costal  cartilages  in  microscopic 
(characteristics.  The  arytenoid  cartilage  of  the  larynx  shows  a  transition  from 
jiyaline  cartilage  at  its  base  to  elastic  cartilage  at  the  apex. 

The  hyaline  cartilages,  especially  in  adult  and  advanced  life,  are  prone  to  calcify 
— that  is  to  say,  to  have  their  matrix  permeated  by  calcium  salts  without  any 
appearance  of  true  bone.  The  process  of  calcification  occurs  frequently,  in  such 
cartilages  as  those  of  the  trachea  and  in  the  costal  cartilages,  where  it  may  be 
succeeded  by  conversion  into  true  bone. 

White  Fibrocartilage. — ^White  fibrocartilage  consists  of  a  mixture  of  white  fibrous 
tissue  and  cartilaginous  tissue  in  various  proportions;  to  the  former  of  these  con' 
stituents  it  owes  its  flexibility  and 
toughness,  and  to  the  latter  its 
elasticity.  When  examined  under 
the  microscope  it  is  found  to  be 
made  up  of  fibrous  connective 
tissue  arranged  in  bundles,  with 
cartilage  cells  between  the  bundles; 
the  cells  to  a  certain  extent  re- 
semble tendon  cells,  but  may  be 
distinguished  from  them  by  being 
surrounded  by  a  concentrically 
striated  area  of  cartilage  matrix 
and  by  being  less  flattened  (Fig. 
295).  The  white  fibrocartilages  ad- 
mit of  arrangement  into  four 
groups — ^interarticular,  connecting, 
circumferential,  and  stratiform. 

1.  The  Interarticular  Fibrocartilages  {menisci)  are  flattened  fibrocartilaginous 
plates,  of  a  round,  oval,  triangular,  or  sickle-like  form,  interposed  between  the 
articular  cartilages  of  certain  joints.  They  are  free  on  both  surfaces,  usually 
thinner  toward  the  center  than  at  the  circumference,  and  held  in  position  by  the 
attachment  of  their  margins  and  extremities  to  the  surrounding  ligaments.  The 
synovial  membranes  of  the  joints  are  prolonged  over  them.  They  are  found 
in  the  temporomandibular,  sternoclavicular,  acromioclavicular,  wrist,  and  knee 


Fig.  295. — White  fibrocartilage  from  an  intervertebral 
fibrocartilage. 


I 


282  SYNDESMOLOGY 

joints — i.  e.,  in  those  joints  which  are  most  exposed  to  violent  concussion  and  I 
subject  to  frequent  movement.  Their  uses  are  to  obHterate  the  intervals  between 
opposed  surfaces  in  their  various  motions;  to  increase  the  depths  of  the  articular 
surfaces  and  give  ease  to  the  gliding  movements;  to  moderate  the  effects  of  great 
pressure  and  deaden  the  intensity  of  the  shocks  to  which  the  parts  may  be  sub- 
jected. Humphry  has  pointed  out  that  these  interarticular  fibrocartilages  serve 
an  important  purpose  in  increasing  the  varieties  of  movement  in  a  joint.  Thus 
in  the  knee  joint  there  are  two  kinds  of  motion,  viz.,  angular  movement  and  rota- 
tion, although  it  is  a  hinge  joint,  in  which,  as  a  rule,  only  one  variety  of  motion 
is  permitted ;  the  former  movement  takes  place  between  the  condyles  of  the  femur 
and  the  interarticular  cartilages,  the  latter  between  the  cartilages  and  the  head 
of  the  tibia.  So,  also,  in  the  temporomandibular  joint,  the  movements  of  opening 
and  shutting  the  mouth  take  place  between  the  fibrocartilage  and  the  mandible, 
the  grinding  movement  between  the  mandibular  fossa  and  the  fibrocartilage,  the 
latter  moving  with  the  mandible. 

2.  The  Connecting  Fibrocartilages  are  interposed  between  the  bony  surfaces  of 
those  joints  which  admit  of  only  slight  mobility,  as  between  the  bodies  of  the 
vertebrae.  They  form  disks  which  are  closely  adherent  to  the  opposed  surfaces. 
Each  disk  is  composed  of  concentric  rings  of  fibrous  tissue,  'with  cartilaginous 
laminae  interposed,  the  former  tissue  predominating  toward  the  circumference, 
the  latter  toward  the  center. 

3.  The  Circumferential  Fibrocartilages  consist  of  rims  of  fibrocartilage,  which 
surround  the  margins  of  some  of  the  articular  cavities,  e.  g.,  the  glenoidal  labrum 
of  the  hip,  and  of  the  shoulder;  they  serve  to  deepen  the  articular  cavities  and  to 
protect  their  edges. 

4.  The  Stratiform  Fibrocartilages  are  those  which  form  a  thin  coating  to  osseous 
grooves  through  which  the  tendons  of  certain  muscles  glide.  Small  masses  of  fibro- 
cartilage are  also  developed  in  the  tendons  of  some  muscles,  where  they  glide 
over  bones,  as  in  the  tendons  of  the  Peronseus  longus  and  Tibialis  posterior. 

The  distinguishing  feature  of  cartilage  chemically  is  that  it  yields  on  boiling  a 
substance  called  chondrin,  very  similar  to  gelatin,  but  differing  from  it  in  several 
of  its  reactions.  It  is  now  believed  that  chondrin  is  not  a  simple  body,  but  a 
mixture  of  gelatin  with  mucinoid  substances,  chief  among  which,  perhaps,  is  a 
compound  termed  chondro-mucoid. 

Ligaments.— Ligaments  are  composed  mainly  of  bundles  of  white  fibrous  tissue 
placed  parallel  with,  or  closely  interlaced  with  one  another,  and  present  a  white, 
shining,  silvery  appearance.  They  are  pliant  and  flexible,  so  as  to  allow  perfect 
freedom  of  movement,  but  strong,  tough,  and  inextensible,  so  as  not  to  yield 
readily  to  applied  force.  Some  ligaments  consist  entirely  of  yellow  elastic  tissue, 
as  the  ligamenta  flava  which  connect  together  the  laminse  of  adjacent  vertebrae, 
and  the  ligamentum  nuchse  in  the  lower  animals.  In  these  cases  the  elasticity  of 
the  ligament  is  intended  to  act  as  a  substitute  for  muscular  power. 

The  Articular  Capsules. — The  articular  capsules  form  complete  envelopes  for  the 
freely  movable  joints.  Each  capsule  consists  of  two  strata — an  external  {stratum 
fihrosum)  composed  of  white  fibrous  tissue,  and  an  internal  {stratmn  synoviale) 
which  is  a  secreting  layer,  and  is  usually  described  separately  as  the  synovial 
membrane. 

The  fibrous  capsule  is  attached  to  the  whole  circumference  of  the  articular  end 
of  each  bone  entering  into  the  joint,  and  thus  entirely  surrounds  the  articulation. 

The  S3movial  membrane  invests  the  inner  surface  of  the  fibrous  capsule,  and  is 
reflected  over  any  tendons  passing  through  the  joint  cavity,  as  the  tendon  of  the 
Popliteus  in  the  knee,  and  the  tendon  of  the  Biceps  brachii  in  the  shoulder.  It  is 
composed  of  a  thin,  delicate,  connective  tissue,  with  branched  connective-tissue 
-corpuscles.    Its  secretion  is  thick,  viscid,  and  glairy,  like  the  white  of  an  egg,  and 


I 


DEVELOPMENT  OF  THE  JOIl 


I 


is  hence  termed  synovia.  In  the  fetus  this  membrane  is  said,  by  Toynbee,  to  be 
(3ontinued  over  the  surfaces  of  the  cartilages ;  but  in  the  adult  such  a  continuation 
is  wanting,  excepting  at  the  circumference  of  the  cartilage,  upon  which  it  encroaches 
for  a  short  distance  and  to  which  it  is  firmly  attached.  In  some  of  the  joints  the 
synovial  membrane  is  thrown  into  folds  which  pass  across  the  cavity;  they  are 
especially  distinct  in  the  knee.  In  other  joints  there  are  flattened  folds,  subdivided 
at  their  margins  into  fringe-like  processes  which  contain  convoluted  vessels. 
These  folds  generally  project  from  the  synovial  membrane  near  the  margin  of  the 
cartilage,  and  lie  flat  upon  its  surface.  They  consist  of  connective  tissue,  covered 
with  endothelium,  and  contain  fat  cells  in  variable  quantities,  and,  more  rarely, 
isolated  cartilage  cells ;  the  larger  folds  often  contain  considerable  quantities  of  fat. 

Closely  associated  with  synovial  membrane,  and  therefore  conveniently  described 
in  this  section,  are  the  mucous  sheaths  of  tendons  and  the  mucous  bursae. 

Mucous  sheaths  {vaginoe  viucoscf)  serve  to  facilitate  the  gliding  of  tendons  in 
fibroosseous  canals.  Each  sheath  is  arranged  in  the  form  of  an  elongated  closed 
sac,  one  layer  of  which  adheres  to  the  wall  of  the  canal,  and  the  other  is  reflected 
upon  the  surface  of  the  enclosed  tendon.  These  sheaths  are  chiefly  found  surround- 
ing the  tendons  of  the  Flexor  and  Extensor  muscles  of  the  fingers  and  toes  as  they 
pass  through  fibroosseous  canals  in  or  near  the  hand  and  foot. 

Suisse  mucosae  are  interposed  between  surfaces  which  glide  upon  each  other. 
They  consist  of  closed  sacs  containing  a  minute  quantity  of  clear  viscid  fluid,  and 
may  be  grouped,  according  to  their  situations,  under  the  headings  subcutaneous, 
submuscular,  subfacial,  and  subtendinous. 

I  DEVELOPMENT   OF   THE   JOINTS. 

The  mesoderm  from  which  the  different  parts  of  the  skeleton  are  formed  shows 
at  first  no  differentiation  into  masses  corresponding  with  the  individual  bones. 
Thus  continuous  cores  of  mesoderm  form  the  axes  of  the  limb-buds  and  a  continu- 
ous column  of  mesoderm  the  future  vertebral  column.  The  first  indications  of  the 
Ibones  and  joints  are  circumscribed  condensations  of  the  mesoderm;  these  condensed 
parts  become  chondrified  and  finally  ossified  to  form  the  bones  of  the  skeleton. 
The  inter\Tning  non-condensed  portions  consist  at  first  of  undifferentiated  meso- 
derm, which  may  develop  in  one  of  three  directions.  It  may  be  converted  into 
fibrous  tissue  as  in  the  case  of  the  skull  bones,  a  synarthrodia!  joint  being  the 
result,  or  it  may  become  partly  cartilaginous,  in  which  case  an  amphiarthrodial 
joint  is  formed.  Again,  it  may  become  looser  in  texture  and  a  cavity  ultimately 
appear  in  its  midst;  the  cells  lining  the  sides  of  this  cavity  form  a  synovial  mem- 
brane and  thus  a  diarthrodial  joint  is  developed. 

The  tissue  surrounding  the  original  mesodermal  core  forms  fibrous  sheaths  for 
the  developing  bones,  i.  e.,  periosteum  and  perichondrium,  which  are  continued 
between  the  ends  of  the  bones  over  the  synovial  membrane  as  the  capsules  of  the 
joints.  These  capsules  are  not  of  uniform  thickness,  so  that  in  them  may  be 
recognized  especially  strengthened  bands  which  are  described  as  ligaments.  This, 
however,  is  not  the  only  method  of  formation  of  ligaments.  In  some  cases  by 
modification  of,  or  derivations  from,  the  tendons  surrounding  the  joint,  additional 
ligamentous  bands  are  provided  to  further  strengthen  the  articulations. 

In  several  of  the  movable  joints  the  mesoderm  which  originally  existed  between 
the  ends  of  the  bones  does  not  become  completely  absorbed — a  portion  of  it 
persists  and  forms  an  articular  disk.  These  disks  may  be  intimately  associated  in 
their  development  with  the  muscles  surrounding  the  joint,  e.  g.,  the  menisci  of  the 
knee-joint,  or  with  cartilaginous  elements,  representatives  of  skeletal  structures, 
which  are  vestigial  in  human  anatomy,  e.  g.,  the  articular  disk  of  the  sterno- 
clavicular joint. 


^ 


284 


SYNDESMOLOGY 


CLASSIFICATION   OF  JOINTS. 

The  articulations  are  divided  into  three  classes:  synarthroses  or  immovablej 
amphiarthroses  or  slightly  movable,  and  diarthroses  or  freely  movable,  joints. 

Synarthroses  {immovable  articulations). — Synarthroses  include  all  those  articu- 
lations in  which  the  surfaces  of  the  bones  are  in  almost  direct  contact,  fastened 
together  by  intervening  connective  tissue  or  hyaline  cartilage,  and  in  which  there 
is  no  appreciable  motion,  as  in  the  joints  between  the  bones  of  the  skull,  excepting 
those  of  the  mandible.  There  are  four  varieties  of  synarthrosis :  sutura,  schindylesis, 
gomphosis,  and  sjmchondrosis. 

Sutura.— Sutura  is  that  form  of  articulation  where  the  contiguous  margins  of  the 
bones  are  united  by  a  thin  layer  of  fibrous  tissue;  it  is  met  with  only  in  the  skull 
(Fig.  296).  When  the  margins  of  the  bones  are  connected  by  a  series  of  processes, 
and  indentations  interlocked  together,  the  articulation  is  termed  a  true  suture 
(sutura  vera) ;  and  of  this  there  are  three  varieties :  sutura  dentata,  serrata,  and 
limbosa.  The  margins  of  the  bones  are  not  in  direct  contact,  being  separated  by  a 
thin  layer  of  fibrous  tissue,  continuous  externally  with  the  pericranium,  internally 
with  the  dura  mater.  The  sutura  dentata  is  so  called  from  the  tooth-like  form  of 
the  projecting  processes,  as  in  the  suture  between  the  parietal  bones.     In  the 


Periosteum 


Sutural  ligament 


Cartilage 


FiQ.  296. — Section  across  the  sagittal  suture. 


Perichondrium 

Periosteum 

Fig.  297. — Section  through  occipitosphenoid  synchon- 
drosis of  an  infant. 


sutura  serrata  the  edges  of  the  bones  are  serrated  like  the  teeth  of  a  fine  saw,  as 
between  the  two  portions  of  the  frontal  bone.  In  the  sutura  limbosa,  there  is  besides 
the  interlocking,  a  certain  degree  of  bevelling  of  the  articular  surfaces,  so  that  the 
bones  overlap  one  another,  as  in  the  suture  between  the  parietal  and  frontal  bones. 
When  the  articulation  is  formed  by  roughened  surfaces  placed  in  apposition  with 
one  another,  it  is  termed  a  false  suture  (sutura  notha),  of  which  there  are  two  kinds: 
the  sutura  squamosa,  formed  by  the  overlapping  of  contiguous  bones  by  broad 
bevelled  margins,  as  in  the  squamosal  suture  between  the  temporal  and  parietal, 
and  the  sutura  harmonia,  where  there  is  simple  apposition  of  contiguous  rough 
surfaces,  as  in  the  articulation  between  the  maxillae,  or  between  the  horizontal 
parts  of  the  palatine  bones. 

Schindylesis. — Schindylesis  is  that  form  of  articulation  in  which  a  thin  plate 
of  bone  is  received  into  a  cleft  or  fissure  formed  by  the  separation  of  two  laminae  in 
another  bone,  as  in  the  articulation  of  the  rostrum  of  the  sphenoid  and  perpendicular 
plate  of  the  ethmoid  with  the  vomer,  or  in  the  reception  of  the  latter  in  the  fissure 
between  the  maxillae  and  between  the  palatine  bones. 

Gomphosis. — Gomphosis  is  articulation  by  the  insertion  of  a  conical  process  into 
a  socket;  this  is  not  illustrated  by  any  articulation  between  bones,  properly  so 
called,  but  is  seen  in  the  articulations  of  the  roots  of  the  teeth  with  the  alveoli 
of  the  mandible  and  maxillae. 

Synchondrosis. — ^Where  the  connecting  medium  is  cartilage  the  joint  is  termed 
a  synchondrosis  (Fig.  297).  This  is  a  temporary  form  of  joint,  for  the  cartilage 
is  converted  into  bone  before  adult  life.  Such  joints  are  found  between  the 
epiphyses  and  bodies  of  long  bones,  between  the  occipital  and  the  sphenoid  at, 
and  for  some  years  after,  birth,  and  between  the  petrous  portion  of  the  temporal 
and  the  jugular  process  of  the  occipital. 


CLASSIFICATION  OF  JOINTS 


285 


Amphiarthroses  {slightly  movable  articulations)  .^In  these  articulations  the 
contiguous  bony  surfaces  are  either  connected  by  broad  flattened  disks  of  fibro- 
cartilage,  of  a  more  or  less  complex  struc- 
ture, as  in  the  articulations  between  the 
bodies  of  the  vertebrae;  or  are  united  by  an 
interosseous  ligament,  as  in  the  inferior 
tibiofibular  articulation.  The  first  form  is 
termed  a  symphysis  (Fig.  298),  the  second 
a  sjmdesmosis. 

Diarthroses  (freely  movable  articulations). 
— This  class  includes  the  greater  number 

of  the  joints  in  the  body.  In  a  diarthrodial  joint  the  contiguous  bony  surfaces 
are  covered  with  articular  cartilage,  and  connected  by  ligaments  lined  by  synovial 
membrane  (Fig.  299).  The  joint  may  be  divided,  completely  or  incompletely, 
by  an  articular  disk  or  meniscus,  the  periphery  of  which  is  continuous  with 
the  fibrous  capside  while  its  free  surfaces  are  covered  by  synovial  membrane 
(Fig.  300). 


Ligament 

Disc  of 
fibrocartilage 
Articular  cartilage. 


Fig.  298. — Diagrammatic  section  of  a  symphysis. 


Articular  cartilage 

Synovial  1 

stratum  \  Articular 
Fibrous  I  capsule 
stratum  J 


Synovial  stratum 
Articular  cartilage 
Articular  disk 


Fibrous  stratum 


Fig.  299. — Diagrammatic  section  of  a  diarthrodial  joint. 


Fig.  300. — Diagrammatic  section  of  a  diarthrodial 
joint,  with  an  articular  disk. 


P 
I 

II 


The  varieties  of  joints  in  this  class  have  been  determined  by  the  kind  of  motion 
permitted  in  each.  There  are  two  varieties  in  which  the  movement  is  uniaxial,  that 
is  to  say,  all  movements  take  place  around  one  axis.  In  one  form,  the  gingl3rmus, 
,  this  axis  is,  practically  speaking,  transverse;  in  the  other,  the  trochoid  or  pivot- 
fejoint,  it  is  longitudinal.  There  are  two  varieties  where  the  movement  is  biaxial, 
or  around  two  horizontal  axes  at  right  angles  to  each  other,  or  at  any  intervening 
axis  between  the  two.    These  are  the  condyloid  and  the  saddle-joint.      There  is 

(one  form  where  the  movement  is  polyaxial,  the  enarthrosis  or  ball-and-socket  joint; 
and  finally  there  are  the  arthrodia  or  gliding  joints. 
Ginglymus  or  Hinge-joint.- — In  this  form  the  articular  surfaces  are  moulded 
to  each  other  in  such  a  manner  as  to  permit  motion  only  in  one  plane,  forward 
and  backward,  the  extent  of  motion  at  the  same  time  being  considerable.  The 
direction  which  the  distal  bone  takes  in  this  motion  is  seldom  in  the  same  plane 
as  that  of  the  axis  of  the  proximal  bone;  there  is  usually  a  certain  amount  of  devia- 
tion from  the  straight  line  during  flexion.  The  articular  surfaces  are  connected 
together  by  strong  collateral  ligaments,  which  form  their  chief  bond  of  union. 
The  best  examples  of  ginglymus  are  the  interphalangeal  joints  and  the  joint  between 
the  humerus  and  ulna;  the  knee-  and  ankle-joints  are  less  typical,  as  they  allow 
a  slight  degree  of  rotation  or  of  side-to-side  movement  in  certain  positions  of  the 
limb. 

Trochoid  or  Pivot-joint  (articulatio  trochoidea;  rotary  joint) . — Where  the  movement 
is  limited  to  rotation,  the  joint  is  formed  by  a  pivot-like  process  turning  within 


L. 


286  ^m^^V  SYNDESMOLOGY 

a  ring,  or  a  ring  on  a  pivot,  the  ring  being  formed  partly  of  bone,  partly  of  ligament. 
In  the  proximal  radioulnar  articulation,  the  ring  is  formed  by  the  radial  notch 
of  the  ulna  and  the  annular  ligament;  here,  the  head  of  the  radius  rotates  within 
the  ring.  In  the  articulation  of  the  odontoid  process  of  the  axis  with  the  atlas 
the  ring  is  formed  in  front  by  the  anterior  arch,  and  behind  by  the  transverse 
ligament  of  the  atlas;  here,  the  ring  rotates  around  the  odontoid  process. 

Condyloid  Articulation  (articidatio  ellipsoidea) .■ — In  this  form  of  joint,  an  ovoid 
articular  surface,  or  condyle,  is  received  into  an  elliptical  cavity  in  such  a  manner 
as  to  permit  of  flexion,  extension,  adduction,  abduction,  and  circumduction,  but 
no  axial  rotation.    The  wrist-joint  is  an  example  of  this  form  of  articulation. 

Articulation  by  Reciprocal  Reception  {articulatio  sellaris;  saddle-joint). — In  this 
variety  the  opposing  surfaces  are  reciprocally  concavo-convex.  The  movements 
are  the  same  as  in  the  preceding  form;  that  is  to  say,  flexion,  extension,  adduction, 
abduction,  and  circumduction  are  allowed ;  but  no  axial  rotation.  The  best  example 
of  this  form  is  the  carpometacarpal  joint  of  the  thumb. 

Enarthrosis  {ball-and-socket  joints) . — Enarthrosis  is  a  joint  in  which  the  distal 
bone  is  capable  of  motion  around  an  indefinite  number  of  axes,  which  have  one 
common  center.  It  is  formed  by  the  reception  of  a  globular  head  into  a  cup-like 
cavity,  hence  the  name  "ball-and-socket."  Examples  of  this  form  of  articulation 
are  found  in  the  hip  and  shoulder. 

Arthrodia  (gliding  joints)  is  a  joint  which  admits  of  only  gliding  movement;  it 
is  formed  by  the  apposition  of  plane  surfaces,  or  one  slightly  concave,  the  other 
slightly  convex,  the  amount  of  motion  between  them  being  limited  by  the  ligaments 
or  osseous  processes  surrounding  the  articulation.  It  is  the  form  present  in  the 
joints  between  the  articular  processes  of  the  vertebrae,  the  carpal  joints,  except 
that  of  the  capitate  with  the  navicular  and  lunate,  and  the  tarsal  joints  with  the 
exception  of  that  between  the  talus  and  the  navicular. 


THE  KINDS  OF  MOVEMENT  ADMITTED  IN  JOINTS. 

The  movements  admissible  in  joints  may  be  divided  into  four  kinds:  gliding 
and  angular  movements,  circumduction,  and  rotation.  These  movements  are  often, 
however,  more  or  less  combined  in  the  various  joints,  so  as  to  produce  an  infinite 
variety,  and  it  is  seldom  that  only  one  kind  of  motion  is  found  in  any  particular 
joint. 

Gliding  Movement. — Gliding  movement  is  the  simplest  kind  of  motion  that  can 
take  place  in  a  joint,  one  surface  gliding  or  moving  over  another  without  any 
angular  or  rotatory  movement.  It  is  common  to  all  movable  joints ;  but  in  some, 
as  in  most  of  the  articulations  of  the  carpus  and  tarsus,  it  is  the  only  motion  per- 
mitted. This  movement  is  not  confined  to  plane  surfaces,  but  may  exist  between 
any  two  contiguous  surfaces,  of  whatever  form. 

Angular  Movement.^ — Angular  movement  occurs  only  between  the  long  bones, 
and  by  it  the  angle  between  the  two  bones  is  increased  or  diminished.  It  may 
take  place:  (1)  forward  and  backward,  constituting  flexion  and  extension;  or  (2) 
toward  and  from  the  median  plane  of  the  body,  or,  in  the  case  of  the  fingers  or 
toes,  from  the  middle  line  of  the  hand  or  foot,  constituting  adduction  and  abduction. 
The  strictly  ginglymoid  or  hinge-joints  admit  of  flexion  and  extension  only.  Abduc- 
tion and  adduction,  combined  with  flexion  and  extension,  are  met  with  in  the  more 
movable  joints;  as  in  the  hip,  the  shoulder,  the  wrist,  and  the  carpometacarpal 
joint  of  the  thumb. 

Circumduction.^ — Circumduction  is  that  form  of  motion  which  takes  place  between 
the  head  of  a  bone  and  its  articular  cavity,  when  the  bone  is  made  to  circumscribe 
a  conical  space;  the  base  of  the  cone  is  described  by  the  distal  end  of  the  bone, 


ARTICULATIONS  OF  THE  VERTEBRAL  COLUMN 


287 


II 


the  apex  is  in  the  articular  cavity;  this  kind  of  motion  is  best  seen  in  the  shoulder- 
and  hip-joints. 

Rotation. — Rotation  is  a  form  of  movement  in  which  a  bone  moves  around  a 
central  axis  without  undergoing  any  displacement  from  this  axis;  the  axis  of  rota- 
tion may  lie  in  a  separate  bone,  as  in  the  case  of  the 'pivot  formed  by  the  odontoid 
process  of  the  axis  vertebrae  around  which  the  atlas  turns;  or  a  bone  may  rotate 
around  its  own  longitudinal  axis,  as  in  the  rotation  of  the  humerus  at  the  shoulder- 
joint;  or  the  axis  of  rotation  may  not  be  quite  parallel  to  the  long  axis  of  the 
bone,  as  in  the  movement  of  the  radius  on  the  ulna  during  pronation  and  supina- 
tion of  the  hand,  where  it  is  represented  by  a  line  connecting  the  center  of  the 
head  of  the  radius  above  with  the  center  of  the  head  of  the  ulna  below. 

Ligamentous  Action  of  Muscles. — The  movements  of  the  different  joints  of  a  limb  are  combined 
by  means  of  the  long  muscles  passing  over  more  than  one  joint.  These,  when  relaxed  and  stretched 
to  their  greatest  extent,  act  as  elastic  ligaments  in  restraining  certain  movements  of  one  joint, 
except  when  combined  with  corresponding  movements  of  the  other — the  latter  movements  being 
usually  in  the  opposite  direction.  Thus  the  shortness  of  the  hamstring  muscles  prevents  com- 
plete flexion  of  the  hip,  unless  the  knee-joint  is  also  flexed  so  as  to  bring  their  attachments  nearer 
together.  The  uses  of  this  arrangement  are  threefold:  (1)  It  coordinates  the  kinds  of  move- 
ments which  are  the  most  habitual  and  necessary,  and  enables  them  to  be  performed  with  the 
least  expenditmre  of  power.  (2)  It  enables  the  short  muscles  which  pass  over  only  one  joint  to 
act  upon  more  than  one.  (3)  It  provides  the  joints  with  ligaments  which,  while  they  are  of  very 
great  power  in  resisting  movements  to  an  extent  incompatible  with  the  mechanism  of  the  joint, 
at  the  same  time  spontaneously^  yield  when  necessary. 

The  articulations  may  be  grouped  into  those  of  the  trunk,  and  those  of  the  upper 
and  lower  extremities. 


ARTICULATIONS   OF   THE   TRUNK. 

These  may  be  divided  into  the  following  groups,  viz.: 


I.  Of  the  Vertebral  Column.  VI. 

II.  Of  the  Atlas  with  the  Axis. 
III.  Of  the  Vertebral  Column  with      VII. 
the  Cranium.  VIII. 

Of  the  Mandible. 
Of  the  Ribs  with  the  Vertebrae. 


iIV. 
V. 


IX. 


Of  the  Cartilages  of  the  Ribs  with  the 
Sternum,  and  with  Each  Other. 

Of  the  Sternum. 

Of  the  Vertebral  Column  with  the 
Pelvis. 

Of  the  Pelvis. 


I.    Articulations  of  the  Vertebral  Column. 


arthrodial  joints  between  the  vertebral  bodies,  and  (2) 
joints  between  the  vertebral  arches. 

1.  Articulations  of  Vertebral  Bodies  {intercentral  ligaments). — The  articulations 
between  the  bodies  of  the  vertebrae  are  amphiarthrodial  joints,  and  the  individual 
vertebrae  move  only  slightly  on  each  other.  When,  however,  this  slight  degree 
of  movement  between  the  pairs  of  bones  takes  place  in  all  the  joints  of  the  vertebral 
column,  the  total  range  of  movement  is  very  considerable.  The  ligaments  of  these 
articulations  are  the  following: 


a  series  of  amphi- 
a  series  of  diathrodial 


ir 


The  Anterior  Longitudinal.  The  Posterior  Longitudinal. 

The  Intervertebral  Fibrocartilages. 


The  Anterior  Longitudinal  Ligament  {ligavientum  longitudinale  anterius;  anterior 
common  ligament)  (Figs.  301,  312). — The  anterior  longitudinal  ligament  is  a  broad 
and  strong  band  of  fibers,  which  extends  along  the  anterior  surfaces  of  the  bodies 
of  the  vertebrae,  from  the  axis  to  the  sacrum.    It  is  broader  below  than  above, 


288 


SYNDESMOLOGY 


thicker  in  the  thoracic  than  in  the  cervical  and  lumbar  regions,  and  somewhaT 
thicker  opposite  the  bodies  of  the  vertebrae  than  opposite  the  intervertebral  fibro- 
cartilages.  It  is  attached,  above,  to  the  body  of  the  axis,  where  it  is  continuous 
with  the  anterior  atlantoaxial  ligament,  and  extends  down  as  far  as  the  upper 
part  of  the  front  of  the  sacrum.  It  consists  of  dense  longitudinal  fibers,  which 
are  intimately  adherent  to  the  intervertebral  fibrocartilages  and  the  prominent: 
margins  of  the  vertebrae,  but  not  to  the  middle  parts  of  the  bodies.  In  the  latter 
situation  the  ligament  is  thick  and  serves  to  fill  up  the  concavities  on  the  anterior 
surfaces,  and  to  make  the  front  of  the  vertebral  column  more  even.  It  is  composed 
of  several  layers  of  fibers,  which  vary  in  length,  but  are  closely  interlaced  with 
each  other.  The  most  superficial  fibers  are  the  longest  and  extend  between  four 
or  five  vertebrae.  A  second,  subjacent  set  extends  between  two  or  three  vertebrae; 
while  a  third  set,  the  shortest  and  deepest,  reaches  from  one  vertebra  to  the  next. 
At  the  sides  of  the  bodies  the  ligament  consists  of' a  few  short  fibers  which  pass 
from  one  vertebra  to  the  next,  separated  from  the  concavities  of  the  vertebral 
bodies  by  oval  apertures  for  the  passage  of  vessels. 


Fig.  301. — ^Median  sagittal  section  of  two  lumbar  vertebrse  and  their  ligaments. 


The  Posterior  Longitudinal  Ligament  {ligamentum  longitudinale  posteritis;  posterior 
common  ligament)  (Figs.  301,  302).— The  posterior  longitudinal  ligament  is  situated 
within  the.  vertebral  canal,  and  extends  along  the  posterior  surfaces  of  the  bodies 
of  the  vertebrae,  from  the  body  of  the  axis,  where  it  is  continuous  with  the  membrana 
tectoria,  to  the  sacrum.  It  is  broader  above  than  below,  and  thicker  in  the  thoracic 
than  in  the  cervical  and  lumbar  regions.  In  the  situation  of  the  intervertebral 
fibrocartilages  and  contiguous  margins  of  the  vertebrae,  where  the  ligament  is  more 
intimately  adherent,  it  is  broad,  and  in  the  thoracic  and  lumbar  regions  presents 
a  series  of  dentations  with  intervening  concave  margins ;  but  it  is  narrow  and  thick 
over  the  centers  of  the  bodies,  from  which  it  is  separated  by  the  basivertebral 
veins.  This  ligament  is  composed  of  smooth,  shining,  longitudinal  fibers,  denser 
and  more  compact  than  those  of  the  anterior  ligament,  and  consists  of  superficial 
layers  occupying  the  interval  between  three  or  four  vertebrae,  and  deeper  layers 
which  extend  between  adjacent  vertebrae. 


I 


ARTICULATIONS  OF  THE  VERTEBRAL  COLUMN 


289 


I 

H[  The  Intervertebral  Fibrocartilages  (fibrocartilagines  mtervertehrales ;  intervertebral 
^\dis1cs)  (Figs.  301,  313). — The  intervertebral  fibrocartilages  are  interposed  between 
^  the  adjacent  surfaces  of  the  bodies  of  the  vertebrae,  from  the  axis  to  the  sacrum, 

and  form  the  chief  bonds  of  connection  between  the  vertebrae.  They  vary  in  shape, 

size,  and  thickness,  in  different  parts  of  the  vertebral  column.    In  shape  and  size 

they  correspond  with  the  surfaces  of  the  bodies  between  which  they  are  placed. 
Hi  except  in  the  cervical  region,  where  they  are  slightly  smaller  from  side  to  side  than 
™-  the  corresponding  bodies.     In  thickness  they  vary  not  only  in  the  different -regions 

of  the  column,  but  in  different  parts  of  the  same  fibrocartilage;  they  are  thicker 

in  front  than  behind  in  the  cervical  and  lumbar 

regions,  and  thus  contribute  to  the  anterior  con- 
vexities of  these  parts  of  the  column;  while  they 

are  of  nearly  uniform  thickness  in  the  thoracic 

region,  the  anterior  concavity  of  this  part  of 

the  column  being  almost  entirely  owing  to  the 

shape  of  the  vertebral  bodies.  The  interverte- 
bral fibrocartilages  constitute  about  one-fourth 

of  the  length  of  the  vertebral  column,  exclusive 

of  the  first  two  vertebrae;  but  this  amount  is 

not  equally  distributed  between  the  various 

bones,  the  cervical  and  lumbar  portions  having, 

in  proportion  to  their  length,  a  much  greater 

amount  than  the  thoracic  region,  with  the  result 

that  these  parts  possess  greater  pliancy  and 

freedom    of    movement.     The    intervertebral 

H  fibrocartilages  are  adherent,  by  their  surfaces, 
to  thin  layers  of  hyaline  cartilage  which  cover 
the  upper  and  under  surfaces  of  the  bodies  of 
the  vertebrae;  in  the  lower  cervical  vertebrae, 
however,  small  joints  lined  by  synovial  membrane  are  occasionally  present  between 
the  upper  surfaces  of  the  bodies  and  the  margins  of  the  fibrocartilages  on  either 
side.  By  their  circumferences  the  intervertebral  fibrocartilages  are  closely  con- 
nected in  front  to  the  anterior,  and  behind  to  the  posterior,  longitudinal  liga- 
ments. In  the  thoracic  region  they  are  joined  laterally,  by  means  of  the  inter- 
articular  ligaments,  to  the  heads  of  those  ribs  which  articulate  with  two  vertebrae. 


Pedicle  {cut) 


Intervertebral 
fibrocartilage 


Fig.  302.- 


-Poaterior  longitudinal  ligament,  in 
the  thoracic  region. 


II 


Structure  of  the  Intervertebral  Fibrocartilages. — Each  is  composed,  at  its  circumference,  of 
laminse  of  fibrous  tissue  and  fibrocartilage,  forming  the  annulus  fibrosus;  and,  at  its  center,  of 
a  soft,  pulpy,  highly  elastic  substance,  of  a  yellowish  color,  which  projects  considerably  above 
the  surrounding  level  when  the  disk  is  divided  horizontally.  This  pulpy  substance  {nucleus 
pulposus),  especially  well-developed  in  the  lumbar  region,  is  the  remains  of  the  notochord.  The 
laminae  are  arranged  concentrically;  the  outermost  consist  of  ordinary  fibrous  tissue,  the  others 
of  white  fibrocartilage.  The  laminae  are  not  quite  vertical  in  their  direction,  those  near  the  cir- 
cumference being  curved  outward  and  closely  approximated;  while  those  nearest  the  center 
curve  in  the  opposite  direction,  and  are  somewhat  more  widely  separated.  The  fibers  of  which 
each  lamina  is  composed  are  directed,  for  the  most  part,  obhquely  from  above  downward,  the 
fibers  of  adjacent  laminae  passing  in  opposite  directions  and  varying  in  every  layer;  so  that  the 
fibers  of  one  layer  are  directed  across  those  of  another,  like  the  limbs  of  the  letter  X.  This  laminar 
arrangement  belongs  to  about  the  outer  half  of  each  fibrocartilage.  The  pulpy  substance  presents 
no  such  arrangement,  and  consists  of  a  fine  fibrous  matrix,  containing  angular  cells  united  to 
form  a  reticular  structure. 

The  intervertebral  fibrocartilages  are  important  shock  absorbers.  Under  pressure  the  highly 
elastic  nucleus  pulposus  becomes  flatter  and  broader  and  pushes  the  more  resistant  fibrous  laminae 
outward  in  all  directions. 

2.  Articulations  of  Vertebral  Arches. — The  joints  between  the  articular  pro- 
cesses of  the  vertebrae  belong  to  the  arthrodial  variety  and  are  enveloped  by 

19 


II 


SYNDESMOLOGY 


I 


capsules  lined  by  synovial  membranes;  while  the  laminse,  spinous  and  transvers(? 
processes  are  connected  by  the  following  ligaments: 


The  Ligamentum  Nuchse. 
The  Interspinal. 
The  Intertransverse. 


The  Ligamenta  Flava. 
The  Supraspinal. 

il 

The  Articular  Capsules  (capsules  articulares;  capsular  ligaments)  (Fig.  301). — 
The  articular  capsules  are  thin  and  loose,  and  are  attached  to  the  margins  of  the 
articular  processes  of  adjacent  vertebrae.  They  are  longer  and  looser  in  the  cervical 
than  in  the  thoracic  and  lumbar  regions. 

The  Ligamenta  Flava  (ligamenta  subfiava,  Fig.  303). — The  ligamenta  flava  connect 
the  laminae  of  adjacent  vertebrae,  from  the  axis  to  the  first  segment  of  the  sacrum. 
They  are  best  seen  from  the  interior  of  the  vertebral  canal ;  when  looked  at  from  the 
outer  surface  they  appear  short,  being  overlapped  by  the  laminae.  Each  ligament 
consists  of  two  lateral  portions  w^hich  commence  one  on  either  side  of  the  roots 
of  the  articular  processes,  and  extend  backw^ard  to  the  point  where  the  laminae 
meet  to  form  the  spinous  process ;  the  posterior  margins  of  the  tw^o  portions  are  in 
contact  and  to  a  certain  extent  united,  slight  intervals  being  left  for  the  passage 
of  small  vessels.   Each  consists  of  yellow  elastic  tissue,  the  fibers  of  which,  almost 

perpendicular  in  direction,  are  at- 
tached to  the  anterior  surface  of 
the  lamina  above,  some  distance 
from  its  inferior  margin,  and  to  the 
posterior  surface  and  upper  margin 
of  the  lamina  below.  In  the  cervical 
region  the  ligaments  are  thin,  but 
broad  and  long;  they  are  thicker  in 
the  thoracic  region,  and  thickest  in 
the  lumbar  region.  Their  marked 
elasticity  serves  to  preserve  the  up- 
right posture,  and  to  assist  the 
vertebral  column  in  resuming  it 
after  flexion. 

The  Supraspinal  Ligament  (liga- 
mentum supraspinale;  supraspinous 
ligament)  (Fig.  301). — The  supra- 
spinal ligament  is  a  strong  fibrous 
cord,  which  connects  together  the 
apices  of  the  spinous  processes  from 
the  seventh  cervical  vertebra  to  the  sacrum ;  at  the  points  of  attachment  to  the 
tips  of  the  spinous  processes  fibrocartilage  is  developed  in  the  ligament.  It  is 
thicker  and  broader  in  the  lumbar  than  in  the  thoracic  region,  and  intimately 
blended,  in  both  situations,  with  the  neighboring  fascia.  The  most  superficial 
fibers  of  this  ligament  extend  over  three  or  four  vertebrae;  those  more  deeply 
seated  pass  between  two  or  three  vertebrae;  while  the  deepest  connect  the  spinous 
processes  of  neighboring  vertebrae.  Between  the  spinous  processes  it  is  continuous 
with  the  interspinal  ligaments.  It  is  continued  upward  to  the  external  occipital 
protuberance  and  median  nuchal  line,  as  the  ligamentum  nuchae. 

The  Ligamentum  Nuchas. — The  ligamentum  nuchae  is  a  fibrous  membrane,  which, 
in  the  neck,  represents  the  supraspinal  ligaments  of  the  lower  vertebrae.  It  extends 
from  the  external  occipital  protuberance  and  median  nuchal  line  to  the  spinous 
process  of  the  seventh  cervical  vertebra.  From  its  anterior  border  a  fibrous  lamina 
is  given  off,  which  is  attached  to  the  posterior  tubercle  of  the  atlas,  and  to  the 
spinous  processes  of  the  cervical  vertebrae,  and  forms  a  septum  between  the  muscles 


Pedicle  {cut) 


Lamina 


Fig.  303. — Vertebral  arches  of  three  thoracic  vertebrae 
viewed  from  the  front. 


ARTICULATIONS  OF  THE  VERTEBRAL  COLUMN  291 

on  either  side  of  the  neck.  In  man  it  is  merely  the  rudiment  of  an  important  elastic 
ligament,  which,  in  some  of  the  lower  animals,  serves  to  sustain  the  weight  of  the 
head. 

The  Interspinal  Ligaments  (ligamenta  inter spinalia;  interspinous  ligaments) 
(Fig.  301). — The  interspinal  ligaments  thin  and  membranous,  connect  adjoining 
spinous  processes  and  extend  from  the  root  to  the  apex  of  each  process.  They 
meet  the  ligamenta  flava  in  front  and  the  supraspinal  ligament  behind.  They 
are  narrow  and  elongated  in  the  thoracic  region;  broader,  thicker,  and  quadrilateral 
in  form  in  the  lumbar  region;  and  only  slightly  developed  in  the  neck. 

The  Intertransverse  Ligaments  (ligamenta  intertransversaria) . — The  intertransverse 
ligaments  are  interposed  between  the  transverse  processes.  In  the  cervical  region 
they  consist  of  a  few  irregular,  scattered  fibers;  in  the  thoracic  region  they  are 
rounded  cords  intimately  connected  with  the  deep  muscles  of  the  back;  in  the 
lumbar  region  they  are  thin  and  membranous. 

Movements. — The  movements  permitted  in  the  vertebral  column  are:  flexion,  extension, 
lateral  movement,  circumduction,  and  rotation. 

In  flexion,  or  movement  forward,  the  anterior  longitudinal  ligament  is  relaxed,  and  the  inter- 
vertebral fibrocartilages  are  compressed  in  front;  while  the  posterior  longitudinal  ligament,  the 
ligamenta  flava,  and  the  inter-  and  supraspinal  ligaments  are  stretched,  as  well  as  the  posterior 
fibers  of  the  intervertebral  fibrocartUages.  The  interspaces  between  the  laminae  are  widened, 
and  the  inferior  articular  processes  gUde  upward,  upon  the  superior  articular  processes  of  the 
subjacent  vertebrae.  Flexion  is  the  most  extensive  of  aU  the  movements  of  the  vertebral  column, 
and  is  freest  in  the  lumbar  region. 

In  extension,  or  movement  backward,  an  exactly  opposite  disposition  of  the  parts  takes  place. 
This  movement  is  limited  by  the  anterior  longitudinal  hgament,  and  by  the  approximation  of 
the  spinous  processes.    It  is  freest  in  the  cervical  region. 

In  lateral  movement,  the  sides  of  the  intervertebral  fibrocartilages  are  compressed,  the  extent 
of  motion  being  limited  by  the  resistance  offered  by  the  surrounding  hgaments.  This  movement 
may  take  place  in  any  part  of  the  column,  but  is  freest  in  the  cervical  and  lumbar  regions. 

Circumduction  is  very  Umited,  and  is  merely  a  succession  of  the  preceding  movements. 

Rotation  is  produced  by  the  twisting  of  the  intervertebral  fibrocartilages;  this,  although  only 
slight  between  any  two  vertebrae,  allows  of  a  considerable  extent  of  movement  when  it  takes  place 
in  the  whole  length  of  the  column,  the  front  of  the  upper  part  of  the  column  being  turned  to  one 
or  other  side.  This  movement  occurs  to  a  sUght  extent  in  the  cervical  region,  is  freer  in  the  upper 
part  of  the  thoracic  region,  and  absent  in  the  lumbar  region. 

The  extent  and  variety  of  the  movements  are  influenced  by  the  shape  and  direction  of  the 
articular  surfaces.  In  the  cervical  region  the  upward  incUnation  of  the  superior  articular  surfaces 
allows  of  free  flexion  and  extension.  Extension  can  be  carried  farther  than  flexion;  at  the  upper 
end  of  the  region  it  is  checked  by  the  locking  of  the  posterior  edges  of  the  superior  atlantal  facets 
in  the  condyloid  fossae  of  the  occipital  bone;  at  the  lower  end  it  is  limited  by  a  mechanism  whereby 
the  inferior  articular  processes  of  the  seventh  cervical  vertebra  slip  into  grooves  behind  and 
below  the  superior  articular  processes  of  the  first  thoracic.  Flexion  is  arrested  just  beyond  the 
point  where  the  cervical  convexity  is  straightened;  the  movement  is  checked  by  the  apposition 
of  the  projecting  lower  hps  of  the  bodies  of  the  vertebrae  with  the  shelving  surfaces  on  the  bodies 
of  the  subjacent  vertebrae.  Lateral  flexion  and  rotation  are  free  in  the  cervical  region;  they  are, 
however,  always  combined.  The  upward  and  medial  inclinations  of  the  superior  articular  surfaces 
impart  a  rotatory  movement  during  lateral  flexion,  while  pure  rotation  is  prevented  by  the  slight 
medial  slope  of  these  surfaces. 

In  the  thoracic  region,  notably  in  its  upper  part,  all  the  movements  are  limited  in  order  to 
reduce  interference  with  respiration  to  a  minimum.  The  almost  complete  absence  of  an  upward 
inclination  of  the  superior  articular  surfaces  prohibits  any  marked  flexion,  while  extension  is 
checked  by  the  contact  of  the  inferior  articular  margins  with  the  laminae,  and  the  contact  of  the 
spinous  processes  with  one  another.  The  mechanism  between  the  seventh  cervical  and  the  first 
thoracic  vertebrae,  which  Umits  extension  of  the  cervical  region,  will  also  ser\'e  to  limit  flexion  of 
the  thoracic  region  when  the  neck  is  extended.  Rotation  is  free  in  the  thoracic  region:  the 
superior  articular  processes  are  segments  of  a  cyUnder  whose  axis  is  in  the  mid-ventral  line  of  the 
vertebral  bodies.  The  direction  of  the  articular  facets  would  allow  of  free  lateral  flexion,  but 
this  movement  is  considerably  limited  in  the  upper  part  of  the  region  by  the  resistance  of  the 
ribs  and  sternum. 

In  the  lumbar  region  flexion  and  extension  are  free.  Flexion  can  be  carried  farther  than  exten- 
sion, and  is  possible  to  just  beyond  the  straightening  of  the  lumbar  curve;  it  is,  therefore,  greatest 
at  the  lowest  part  where  the  curve  is  sharpest.    The  inferior  articular  facets  are  not  in  close  appo- 


292 


SYNDESMOLOGY 


sition  with  the  superior  facets  of  the  subjacent  vertebrae,  and  on  this  account  a  considerable 
amount  of  lateral  flexion  is  permitted.  For  the  same  reason  a  slight  amount  of  rotation  can  be 
carried  out,  but  this  is  so  soon  checked  by  the  interlocking  of  the  articular  surfaces  that  it  is 
negligible. 

The  principal  muscles  which  produce  flexion  are  the  Sternocleidomastoideus,  Longus  capitis, 
and  Longus  colh;  the  Scaleni;  the  abdominal  muscles  and  the  Psoas  major.  Extension  is  produced 
by  the  intrinsic  muscles  of  the  back,  assisted  in  the  neck  by  the  Splenius,  Semispinales  dorsi  and 
cervicis,  and  the  Multifidus.  Lateral  motion  is  produced  by  the  intrinsic  muscles  of  the  back 
by  the  Splenius,  the  Scaleni,  the  Quadratus  lumborum,  and  the  Psoas  major,  the  muscles  of  one 
side  only  acting;  and  rotation  by  the  action  of  the  following  muscles  of  one  side  only,  viz.,  the 
Sternocleidomastoideus,  the  Longus  capitis,  the  Scaleni,  the  Multifidus,  the  SemispinaUs  capitis, 
and  the  abdominal  muscles. 


n.    Articulation  of  the  Atlas  with  the  Epistropheus  or  Axis  (Articulatio 

Atlantoepistrophica) . 


*l 


The  articulation  of  the  atlas  with  the  axis  is  of  a  complicated  nature,  com- 
prising no  fewer  than  four  distinct  joints.  There  is  a  pivot  articulation  between 
the  odontoid  process  of  the  axis  and  the  ring  formed  by  the  anterior  arch  and 
the  tranverse  ligament  of  the  atlas  (see  Fig.  306);  here  there  are  two  joints:  one 
between  the  posterior  surface  of  the  anterior  arch  of  the  atlas  and  the  front  of 
the  odontoid  process;  the  other  between  the  anterior  surface  of  the  ligament  and 
the  back  of  the  process.  Between  the  articular  processes  of  the  two  bones  there 
is  on  either  side  an  arthrodial  or  gliding  joint.  The  ligaments  connecting  these 
bones  are: 


Two  Articular  Capsules. 
The  Anterior  Atlantoaxial. 


The  Posterior  Atlantoaxial. 
The  Transverse. 


Atlanto- 

occipital      f  Articular  capsule 

— ■ '.  and 

[^synovial  membrane 


C  Articular  capgule 
<  and 

ysynovial  membrane 


Fig.  304. — Anterior  atlantooccipital  membrane  and  atlantoaxial  ligament. 


q 


The  Articular  Capsules  (capsulce  articulares;  capsular  ligaments). — The  articular 
capsules  are  thin  and  loose,  and  connect  the  margins  of  the  lateral  masses  of  the 
atlas  with  those  of  the  posterior  articular  surfaces  of  the  axis.  Each  is  strength- 
ened at  its  posterior  and  medial  part  by  an  accessory  ligament,  which  is  attached 


[RTICULATION  OF  THE  ATLAS  WITH  THE  EPISTROPHEUS  OR  AXIS 


)elow  to  the  body  of  the  axis  near  the  base  of  the  odontoid  process,  and  above 
to  the  lateral  mass  of  the  atlas  near  the  transverse  ligament. 

The  Anterior  Atlantoaxial  Ligament  (Fig.  304). — This  ligament  is  a  strong  mem- 
brane, fixed,  above,  to  the  lower  border  of  the  anterior  arch  of  the  atlas;  below, 
to  the  front  of  the  body  of  the  axis.    It  is  strengthened  in  the  middle  line  by  a 


Arch  for  passage  of 
vertebral  artery 
and  first  cervical 
nerve 


Fig.  305. — Posterior  atlantooccipital  membrane  and  atlantoaxial  ligament. 

rounded  cord,  which  connects  the  tubercle  on  the  anterior  arch  of  the  atlas  to  the 
body  of  the  axis,  and  is  a  continuation  upward  of  the  anterior  longitudinal  liga- 
ment.   The  ligament  is  in  relation,  in  front,  with  the  Longi  capitis. 


Fig.  306. — Articulation  between  odontoid  process  and  atlas. 

The  Posterior  Atlantoaxial  Ligament  (Fig.  305). — This  ligament  is  a  broad,  thin 
"membrane  attached,  above,  to  the  lower  border  of  the  posterior  arch  of  the  atlas; 
beloui,  to  the  upper  edges  of  the  laminae  of  the  axis.  It  supplies  the  place  of 
the  ligamenta  flava,  and  is  in  relation,  behind,  with  the  Obliqui  capitis  inferiores. 

The  Transverse  Ligament  of  the  Atlas  (ligamentum  transversum  atlantis)  (Figs. 
306,  307,  308) . — The  transverse  ligament  of  the  atlas  is  a  thick,  strong  band,  which 


294 


SYNDESMOLOGY 


Apical  odontoid 
ligament 


Atlanta.  (  Articular  capsule 
and 


■{.. 


^ifr\    '^'^P'^^'^^synovial  membrane 


.^■,     .     f  Artyyular  caps^de 
Atlanta-)  ^„^j  ^ 

axial    y  synovial  membrane 


Fia.  307. — Membrana  tectoria,  transverae,  and  alar  ligament3. 


Superficial  layer  of  menibrana  tectoria 


Anterior  atlanto- 
occipital  membrane 

Membrana  tectoria 

Cms  swperius  of 

transverse  ligament 

Apical  odont.  lig. 

Ant.  arch  of  atlas 

Odontoid  process, 
of  axis 
Articular  cavity 

Transverse  ligament 

Anterior  atlanto- 
axial ligament 


Jntervertebral 
Jibrocartilage 


Anterior  longitudinal 
ligament 


Posterior  atlanto- 
ipiial  membrane 

Posterior  arch 
of  atlas 

itboccipital  nerve 


Posterior  longitudinal  ligament 
Fia.  308  —Median  sagittal  section  through  the  occipital  bone  and  first  three  cervical  vertebra.      (Spaltehola.) 


I  ARTICULATIONS  OF  THE  VERTEBRAL  COLUMN  WITH  THE  CRANIUM  295 
arches  across  the  ring  of  the  atlas,  and  retains  the  odontoid  process  in  contact  with 
the  anterior  arch.  It  is  concave  in  front,  convex  behind,  broader  and  thicker  in 
the  middle  than  at  the  ends,  and  firmly  attached  on  either  side  to  a  small  tubercle 
on  the  medial  surface  of  the  lateral  mass  of  the  atlas.  As  it  crosses  the  odontoid 
process,  a  small  fasciculus  (crus  superius)  is  prolonged  upward,  and  another  (cms 

II  inferius)  downward,  from  the  superficial  or  posterior  fibers  of  the  ligament.    The 
I  former  is  attached  to  the  basilar  part  of  the  occipital  bone,  in  close  relation  with 
I  the  membrana  tectoria;  the  latter  is  fixed  to  the  posterior  surface  of  the  body 
jof  the  axis;  hence,  the  whole  ligament  is  named  the  cruciate  ligament  of  the  atlas. 
I  The  transverse  ligament  divides  the  ring  of  the  atlas  into  two  unequal  parts: 
j  of  these,  the  posterior  and  larger  serves  for  the  transmission  of  the  medulla  spinalis 
land  its  membranes  and  the  accessory  nerves;  the  anterior  and  smaller  contains 
\  the  odontoid  process.    The  neck  of  the  odontoid  process  is  constricted  where  it  is 
embraced  posteriorly  by  the  transverse  ligament,  so  that  this  ligament  suffices 
^   to  retain  the  odontoid  process  in  position  after  all  the  other  ligaments  have  been 
Hi  divided. 

^■1  S3movial  Membranes. — There  is  a  synovial  membrane  for  each  of  the  four  joints;  the  joint 
^■f  cavity  between  the  odontoid  process  and  the  transverse  hgament  is  often  continuous  with  those 
of  the  atlantooccipital  articulations. 

Movements. — The  opposed  articular  surfaces  of  the  atlas  and  axis  are  not  reciprocally  curved; 
both  surfaces  are  convex  in  their  long  axes.  When,  therefore,  the  upper  facet  glides  forward 
on  the  lower  it  also  descends;  the  fibers  of  the  articular  capsule  are  relaxed  in  a  vertical  direc- 
tion, and  will  then  permit  of  movement  in  an  antero-posterior  direction.  By  this  means  a 
shorter  capsule  suffices  and  the  strength  of  the  joint  is  materially  increased.^ 

This  joint  allows  the  rotation  of  the  atlas  (and,  with  u,  the  skull)  upon  the  axis,  the  extent 
of  rotation  being  hmited  by  the  alar  hgaments. 

The  principal  muscles  by  which  these  movements  are  produced  are  the  Sternocleidomastoideus 
and  Semispinalis  capitis  of  one  side,  acting  with  the  Longus  capitis,  Splenius,  Longissimus  capitis, 
Rectus  capitis  posterior  major,  and  Obliqui  capitis  superior  and  inferior  of  the  other  side. 


n 


in.    Articulations  of  the  Vertebral  Column  with  the  Cranium. 


II 


The  ligaments  connecting  the  vertebral  column  with  the  cranium  may  be 
divided  into  two  sets:  those  uniting  the  atlas  with  the  occipital  bone,  and  those 
connecting  the  axis  with  the  occipital  bone. 

Articulation  of  the  Atlas  with  the  Occipital  Bone  (articulatio  atlantodccipitalis). 
■ — The  articulation  between  the  atlas  and  the  occipital  bone  consists  of  a  pair  of 
condyloid  joints.    The  ligaments  connecting  the  bones  are: 

Two  Articular  Capsules.  The  Posterior  Atlantooccipital 

The  Anterior  Atlantooccipital  membrane. 

membrane.  Two  Lateral  Atlantooccipital. 

The  Articular  Capsules  {capsulcB  articulares;  capsular  ligaments). — The  articular 
capsules  surround  the  condyles  of  the  occipital  bone,  and  connect  them  with  the 
articular  processes  of  the  atlas :  they  are  thin  and  loose. 

The  Anterior  Atlantooccipital  Membrane  (membrana  atlantodccipitalis  anterior; 
anterior  atlantooccipital  ligament)  (Fig.  304). — The  anterior  atlantooccipital  mem- 
brane is  broad  and  composed  of  densely  woven  fibers,  which  pass  between  the 
anterior  margin  of  the  foramen  magnum  above,  and  the  upper  border  of  the 
anterior  arch  of  the  atlas  below;  laterally,  it  is  continuous  with  the  articular 
capsules;  in  front,  it  is  strengthened  in  the  middle  line  by  a  strong,  rounded 

'  Comer  ("The  Physiology  of  the  Atlanto-axial  Joints,"  Journal  of  Anatomj'  and  Physiology,  vol.  xli)  states  that 
the  movements  which  take  place  at  these  articulations  are  of  a  complex  nature.  The  first  part  of  the  movement  is 
.an  eccentric  or  asymmetrical  one;  the  atlanto-axial  joint  of  the  side  to  which  the  head  is  moved  is  fixed,  or  practically 
fixed,  by  the  muscles  of  the  neck,  and  forms  the  center  of  the  movement,  while  the  opposite  atlantal  facet  is  carried 
downward  and  forward  on  the  corresponding  axial  facet.  The  second  part  of  the  movement  is  centric  and  symmetrical, 
the  odontoid  process  forming  the  axis  of  the  movement 


296  J^^^^^.  SYNDESMOLOGY 


ll 


cord,  which  connects  the  basilar  part  of  the  occipital  bone  to  the  tubercle  on  tli€ 
anterior  arch  of  the  atlas.  This  membrane  is  in  relation  in  front  with  the  Recti 
capitis  anteriores,  behind  with  the  alar  ligaments. 

The  Posterior  Atlantobccipital  Membrane  (membrana  atlantooccipitalis  posterior; 
posterior  atlantooccipital  ligament)  (Fig.  305) . — The  posterior  atlantooccipital  mem- 
brane, broad  but  thin,  is  connected  above,  to  the  posterior  margin  of  the  foramen 
magnum;  below,  to  the  upper  border  of  the  posterior  arch  of  the  atlas.    On  either  ^_ 
side  this  membrane  is  defective  below,  over  the  groove  for  the  vertebral  artery,  ^M 
and  forms  with  this  groove  an  opening  for  the  entrance  of  the  artery  and  the 
exit  of  the  suboccipital  nerve.    The  free  border  of  the  membrane,  arching  over 
the  artery  and  nerve,  is  sometimes  ossified.     The  membrane  is  in  relation,  behind, 
with  the  Recti  capitis  posteriores  minores  and  Obliqui  capitis  superiores ;  in  fronts  ^h 
with  the  dura  mater  of  the  vertebral  canal,  to  which  it  is  intimately  adherent.         ^M 

The  Lateral  Ligaments. — The  lateral  ligaments  are  thickened  portions  of  the 
articular  capsules,  reinforced  by  bundles  of  fibrous  tissue,  and  are  directed  obliquely 
upward  and  medialward;  they  are  attached  above  to  the  jugular  processes  of  the 
occipital  bone,  and  below,  to  the  bases  of  the  transverse  processes  of  the  atlas. 

Synovial  Membranes. — There  are  two  synovial  membranes:  one  lining  each  of  the  articular 
capsules.  The  joints  frequently  communicate  with  that  between  the  posterior  siuface  of  the 
odontoid  process  and  the  transverse  ligament  of  the  atlas. 

Movements. — The  movements  permitted  in  this  joint  are  (a)  flexion  and  extension,  which 
give  rise  to  the  ordinary  forward  and  backward  nodding  of  the  head,  and  (6)  slight  lateral  motion 
to  one  or  other  side.  Flexion  is  produced  mainly  by  the  action  of  the  Longi  capitis  and  Recti 
capitis  anteriores;  extension  by  the  Recti  capitis  posteriores  major  and  minor,  the  Obliquus  su- 
perior, the  SemispinaUs  capitis,  Splenius  capitis,  Sternocleidomastoideus,  and  upper  fibers  of  the 
Trapezius.  The  Recti  laterales  are  concerned  in  the  lateral  movement,  assisted  by  the  Trapezius, 
Splenius  capitis,  Semispinalis  capitis,  and  the  Sternocleidomastoideus  of  the  same  side,  all  acting 
together. 

Ligaments  Connecting  the  Axis  with  the  Occipital  Bone. — 

The  Membrana  Tectoria.  Two  Alar.  The  Apical  Odontoid. 

The  Membrana  Tectoria  (occipitoaxial  ligament)  (Figs.  307,  308). — The  mem- 
brana tectoria  is  situated  within  the  vertebral  canal.  It  is  a  broad,  strong  bands 
which  covers  the  odontoid  process  and  its  ligaments,  and  appears  to  be  a  prolon- 
gation upward  of  the  posterior  longitudinal  ligament  of  the  vertebral  column.  It 
is  fixed,  below,  to  the  posterior  surface  of  the  body  of  the  axis,  and,  expanding  as 
it  ascends,  is  attached  to  the  basilar  groove  of  the  occipital  bone,  in  front  of  the 
foramen  magnum,  where  it  blends  with  the  cranial  dura  mater.  Its  anterior  sur- 
face is  in  relation  with  the  transverse  ligament  of  the  atlas,  and  its  posterior 
surface  with  the  dura  mater. 

The  Alar  Ligaments  (ligamenta  alaria;  odontoid  ligaments)  (Fig.  307). — The  alar 
ligaments  are  strong,  rounded  cords,  which  arise  one  on  either  side  of  the  upper 
part  of  the  odontoid  process,  and,  passing  obliquely  upward  and  lateralward,  are 
inserted  into  the  rough  depressions  on  the  medial  sides  of  the  condyles  of  the  occipi- 
tal bone.  In  the  triangular  interval  between  these  ligaments  is  another  fibrous 
cord,  the  apical  odontoid  ligament  (Fig.  308),  which  extends  from  the  tip  of  the  odon- 
toid process  to  the  anterior  margin  of  the  foramen  magnum,  being  intimately 
blended  with  the  deep  portion  of  the  anterior  atlantooccipital  membrane  and 
superior  crus  of  the  transverse  ligament  of  the  atlas.  It  is  regarded  as  a  rudimentary 
intervertebral  fibrocartilage,  and  in  it  traces  of  the  notochord  may  persist.  The 
alar  ligaments  limit  rotation  of  the  cranium  and  therefore  receive  the  name  of 
check  ligaments. 

In  addition  to  the  ligaments  which  unite  the  atlas  and  axis  to  the  skull, 
the  ligamentum  nuchse  (page  290)  must  be  regarded  as  one  of  the  ligaments 
connecting  the  vertebral  column  with  the  cranium. 


ARTICULATION  OF  THE  MANDIBLE 


297 


rv.     Articulation  of  the  Mandible  (Articulatio  Mandibularis ;  Temporo- 
mandibular Articulation). 

This  is  a  ginglymo-arthrodial  joint;  the  parts  entering  into  its  formation  on 
either  side  are:  the  anterior  part  of  the  mandibular  fossa  of  the  temporal  bone 
and  the  articular  tubercle  above;  and  the  condyle  of  the  mandible  below.  The 
ligaments  of  the  joint  are  the  following: 

The  Articular  Capsule.  The  Sphenomandibular. 

The  Temporomandibular.  The  Articular  Disk. 

The  Stylomandibular. 

The  Articular  Capsule  (capsula  articularis;  capsular  ligament). — The  articular 
capsule  is  a  thin,  loose  envelope,  attached  above  to  the  circumference  of  the 
mandibular  fossa  and  the  articular  tubercle  immediately  in  front;  below,  to  the 
neck  of  the  condyle  of  the  mandible. 


Fig.  309. — Articulation  of  the  mandible.     Lateral  aspect. 


I 


le  Temporomandibular  Ligament  (ligamentum  temporomandibulare;  external 
lateral  ligament)  (Fig.  309).— The  temporomandibular  ligament  consists  of  two 
short,  narrow  fasciculi,  one  in  front  of  the  other,  attached,  above,  to  the  lateral 
surface  of  the  zygomatic  arch  and  to  the  tubercle  on  its  lower  border;  below, 
to  the  lateral  surface  and  posterior  border  of  the  neck  of  the  mandible.  It  is  broader 
above  than  below,  and  its  fibers  are  directed  obliquely  downward  and  backward. 
It  is  covered  by  the  parotid  gland,  and  by  the  integument. 

The  Sphenomandibular  Ligament  (ligamentum  sphenomandibulare;  internal  lateral 
ligament)  (Fig.  310). — The  sphenomandibular  ligament  is  a  flat,  thin  band  which  is 
attached  above  to  the  spina  angularis  of  the  sphenoid  bone,  and,  becoming  broader 
as  it  descends,  is  fixed  to  the  lingula  of  the  mandibular  foramen.  Its  lateral  surface 
is  in  relation,  above,  with  the  Pterygoideus  externus;  lower  down,  it  is  separated 
from  the  neck  of  the  condyle  by  the  internal  maxillary  vessels;  still  lower,  the 
inferior  alveolar  vessels  and  nerve  and  a  lobule  of  the  parotid  gland  lie  between 
it  and  the  ramus  of  the  mandible.  Its  medial  surface  is  in  relation  with  the  Ptery- 
goideus internus. 


298 


SYNDESMOLOGY 


The  Articular  Disk  (discus  articularis;  interarticular  fihrocartilage ;  articular  menS 
cus)  (Fig.  311).— The  articular  disk  is  a  thin,  oval  plate,  placed  between  the 
condyle  of  the  mandible  and  the  mandibular  fossa.  Its  upper  surface  is  concavo-j 
convex  from  before  backward,  to  accommodate  itself  to  the  form  of  the  man- 
dibular fossa  and  the  articular  tubercle.  Its  under  surface,  in  contact  with  the 
condyle,  is  concave.  Its  circumference  is  connected  to  the  articular  capsule;  and  in 
front  to  the  tendon  of  the  Pterygoideus  externus.  It  is  thicker  at  its  periphery, 
especially  behind,  than  at  its  center.  The  fibers  of  which  it  is  composed  have  a 
concentric  arrangement,  more  apparent  at  the  circumference  than  at  the  center. 
It  divides  the  joint  into  two  cavities,  each  of  which  is  furnished  with  a  synovial 
membrane. 


Fig.  310. — ^Articulation  of  the  mandible.     Medial  aspect. 


Fig. 


311. — Sagittal  section  of  the  articulation  of  the 
mandible. 


The  Synovial  Membranes. — The  synovial  membranes,  two  in  number,  are  placed  one  above, 
and  the  other  below,  the  articular  disk.  The  upper  one,  the  larger  and  looser  of  the  two,  ia 
continued  from  the  margin  of  the  cartilage  covering  the  mandibular  fossa  and  articular  tubercle 
on  to  the  upper  surface  of  the  disk.  The  lower  one  passes  from  the  under  surface  of  the  disk 
to  the  neck  of  the  condyle,  being  prolonged  a  little  farther  downward  behind  than  in  front.  The 
articular  disk  is  sometimes  perforated  in  its  center,  and  the  two  cavities  then  communicate  with 
each  other. 

The  Stylomandibular  Ligament  {ligamentum  stylomandihulare) ;  stylomaxillary 
ligament  (Fig.  310). — The  stylomandibular  ligament  is  a  specialized  band  of  the 
cervical  fascia,  which  extends  from  near  the  apex  of  the  styloid  process  of  the 
temporal  bone  to  the  angle  and  posterior  border  of  the  ramus  of  the  mandible, 
between  the  Masseter  and  Pterygoideus  internus.  This  ligament  separates  the 
parotid  from  the  submaxillary  gland,  and  from  its  deep  surface  some  fibers  of  the 
Styloglossus  take  origin.  Although  classed  among  the  ligaments  of  the  temporo- 
mandibular joint,  it  can  only  be  considered  as  accessory  to  it. 

The  nerves  of  the  temporomandibular  joint  are  derived  from  the  auriculotemporal  and  masse- 
teric branches  of  the  mandibular  nerve,  the  arteries  from  the  superficial  temporal  branch  of  the 
external  carotid. 

Movements. — The  movements  permitted  in  this  articulation  are  extensive.  Thus,  the  mandible 
may  be  depressed  or  elevated,  or  carried  forward  or  backward;  a  slight  amount  of  side-to-side 
movement  is  also  permitted.  It  must  be  borne  in  mind  that  there  are  two  distinct  joints  in  this 
articulation — one  between  the  condyle  and  the  articular  disk,  and  another  between  the  disk  and 
the  mandibular  fossa.    When  the  mouth  is  but  sUghtly  opened,  as  during  ordinary  conversation, 


COSTOVERTEBRAL  ARTICULATIONS  299 

the  movement  is  confined  to  the  lower  of  the  two  joints.  On  the  other  hand,  when  the  mouth 
is  opened  more  widely,  both  joints  are  concerned  in  the  movement;  in  the  lower  joint  the  move- 
ment is  of  a  hinge-Uke  character,  the  condyle  moving  around  a  transverse  axis  on  the  disk,  while 
in  the  upper  joint  the  movement  is  of  a  ghding  character,  the  disk,  together  with  the  condyle, 
gUding  forward  on  to  the  articular  tubercle,  around  an  axis  which  passes  through  the  mandibular 
foramina.  These  two  movements  take  place  simultaneously,  the  condyle  and  disk  move  for- 
ward on  the  eminence,  and  at  the  same  time  the  condyle  revolves  on  the  disk.  In  shutting  the 
mouth  the  reverse  action  takes  place;  the  disk  glides  back,  carrying  the  condyle  with  it,  and  this 
at  the  same  time  moves  back  to  its  former  position.  When  the  mandible  is  carried  horizontally 
forward,  as  in  protruding  the  lower  incisor  teeth  in  front  of  the  upper,  the  movement  takes  place 
principally  in  the  upper  joint,  the  disk  and  the  condyle  gUding  forward  on  the  mandibular  fossa 
and  articular  tubercle.  The  grinding  or  chewing  movement  is  produced  by  one  condyle,  with 
its  disk,  gUding  alternately  forward  and  backward,  while  the  other  condyle  moves  simultaneously 
in  the  opposite  direction;  at  the  same  time  the  condyle  undergoes  a  vertical  rotation  on  the  disk. 
One  condyle  advances  and  rotates,  the  other  condyle  recedes  and  rotates,  in  alternate  succession. 
The  mandible  is  depressed  by  its  own  weight,  assisted  by  the  Platysma,  the  Digastricus,  the 
Mylohyoideus,  and  the  Geniohyoideus.  It  is  elevated  by  the  Masseter,  Pterygoideus  internus, 
and  the  anterior  part  of  the  Temporalis.  It  is  drawn  forward  by  the  simultaneous  action  of  the 
Pterygoidei  internus  and  externus,  the  superficial  fibers  of  the  Masseter  and  the  anterior  fibers 
of  the  Temporalis;  and  backward  by  the  deep  fibers  of  the  Masseter  and  the  posterior  fibers  of  the 
Temporalis.  The  grinding  movement  is  caused  by  the  alternate  action  of  the  Pterygoidei  of 
either  side. 


IT 


V.    Costovertebral  Articulations  (Articulationes  Costovertebrales). 

The  articulations  of  the  ribs  with  the  vertebral  column  may  be  divided  into  two 
sets,  one  connecting  the  heads  of  the  ribs  with  the  bodies  of  the  vertebrae,  another 
uniting  the  necks  and  tubercles  of  the  ribs  with  the  transverse  processes. 

1 ,  Articulations  of  the  Heads  of  the  Ribs  (articulationes  capitulorum;  costocentral 
articulations)  (Fig.  312). — These  constitute  a  series  of  gliding  or  arthrodial  joints, 
and  are  formed  by  the  articulation  of  the  heads  of  the  typical  ribs  with  the  facets 
on  the  contiguous  margins  of  the  bodies  of  the  thoracic  vertebrae  and  with  the 
intervertebral  fibrocartilages  between  them;  the  first,  tenth,  eleventh,  and  twelfth 

I  ribs  each  articulate  with  a  single  vertebra.    The  ligaments  of  the  joints  are: 
I    The  Articular  Capsule.  The  Radiate.  The  Interarticular. 

'  The  Articular  Capsule  (capsula  articularis;  capsular  ligament). — The  articular 
capsule  surrounds  the  joint,  being  composed  of  short,  strong  fibers,  connecting 
the  head  of  the  rib  with  the  circumference  of  the  articular  cavity  formed  by  the 
intervertebral  fibrocartilage  and  the  adjacent  vertebrae.  It  is  most  distinct  at 
the  upper  and  lower  parts  of  the  articulation ;  some  of  its  upper  fibers  pass  through 
the  intervertebral  foramen  to  the  back  of  the  intervertebral  fibrocartilage,  while 
its  posterior  fibers  are  continuous  with  the  ligament  of  the  neck  of  the  rib. 

The  Radiate  Ligament  (ligamentum  capituli  costce  radiatum;  anterior  costoverte- 
bral or  stellate  ligament). — The  radiate  ligament  connects  the  anterior  part  of  the 
head  of  each  rib  with  the  side  of  the  bodies  of  two  vertebrae,  and  the  interverte- 
bral fibrocartilage  between  them.  It  consists  of  three  flat  fasciculi,  which  are 
attached  to  the  anterior  part  of  the  head  of  the  rib,  just  beyond  the  articular  sur- 
face. The  superior  fasciculus  ascends  and  is  connected  with  the  body  of  the  verte- 
bra above ;  the  inferior  one  descends  to  the  body  of  the  vertebra  below ;  the  middle 
one,  the  smallest  and  least  distinct,  is  horizontal  and  is  attached  to  the  interver- 
tebral fibrocartilage.  The  radiate  ligament  is  in  relation,  in  front,  with  the  thoracic 
ganglia  of  the  sympathetic  trunk,  the  pleura,  and,  on  the  right  side,  with  the  azygos 
vein;  behind,  with  the  interarticular  ligament  and  synovial  membranes. 

In  the  case  of  the  first  rib,  this  ligament  is  not  divided  into  three  fasciculi,  but 
its  fibers  are  attached  to  the  body  of  the  last  cervical  vertebra,  as  well  as  to  that 
of  the  first  thoracic.  In  the  articulations  of  the  heads  of  the  tenth,  eleventh,  and 
twelfth  ribs,  each  of  which  articulates  with  a  single  vertebra,  the  triradiate  arrange- 


300 


SYNDESMOLOGY 


ment  does  not  exist;  but  the  fibers  of  the  ligament  in  each  case  are   connecteic 
the  vertebra  above,  as  well  as  to  that  with  which  the  rib  articulates. 

The  Interarticular  Ligament  {ligavientum  capituli  costcc  interarticulare) . — The  in- 
terarticular  ligament  is  situated  in  the  interior  of  the  joint.  It  consists  of  a  short 
band  of  fibers,  flattened  from  above  downward,  attached  by  one  extremity  to  the 
crest  separating  the  two  articular  facets  on  the  head  of  the  rib,  and  by  the  other 
to  the  intervertebral  fibrocartilage;  it  divides  the  joint  into  two  cavities.  In  the 
joints  of  the  first,  tenth,  eleventh,  and  twelfth  ribs,  the  interarticular  ligament  does 
not  exist;  consequently,  there  is  but  one  cavity  in  each  of  these  articulations. 
This  ligament  is  the  homologue  of  the  ligamentum  conjugale  present  in  some 
mammals,  and  uniting  the  heads  of  opposite  ribs,  across  the  back  of  the  inter- 
vertebral fibrocartilage. 


Anterior 

costotransverse 

ligaments 


Jnterarticidar  ligament  Intervertebral  fibrocartilage 

Fig.  312. — Costovertebral  articulations.     Anterior  view. 


«ll 


Synovial  Membranes. — There  are  two  synovial  membranes  in  each  of  the  articulations  where 
an  interarticular  ligament  exists,  one  above  and  one  below  this  structure;  but  only  one  in  those 
joints  where  there  are  single  cavities. 

2.  Costotransverse  Articulations  (articulationes  costotransversaricB)  (Fig.  313). — 
The  articular  portion  of  the  tubercle  of  the  rib  forms  with  the  articular  surface 
on  the  adjacent  transverse  process  an  arthrodial  joint. 

In  the  eleventh  and  twelfth  ribs  this  articulation  is  wanting. 
The  ligaments  of  the  joint  are : 

The  Articular  Capsule.  The  Posterior  Costotransverse. 

The  Anterior  Costotransverse.  The  Ligament  of  the  Neck  of  the  Rib. 

The  Ligament  of  the  Tubercle  of  the  Rib. 


COSTOVERTEBRAL  ARTICULATIONS 


301 


The  Articular  Capsule  (capsula  articularis;  capsular  ligament). — ^The  articular  cap- 
sule is  a  thin  membrane  attached  to  the  circumferences  of  the  articular  surfaces, 
.and  lined  by  a  synovial  membrane. 


/Synovial  cavity 


Anterior  costotransverse 
ligament  divided, 

Ligament  of  the  neck 

Ligament  of  the 
tubercle 


Fig.  313. — Costotransverse  articulation.     Seen  from  above. 

The  Anterior  Costotransverse  Ligament  (liga- 
mentum  costotransversarium  anterius;  anterior 
superior  ligament). — The  anterior  costotrans- 
verse ligament  is  attached  below  to  the  sharp 
crest  on  the  upper  border  of  the  neck  of  the 
rib,  and  passes  obliquely  upward  and  lateral- 
ward  to  the  lower  border  of  the  transverse 
process  immediately  above.  It  is  in  relation, 
in  front,  with  the  intercostal  vessels  and 
nerves;  its  medial  border  is  thickened  and 
free,  and  bounds  an  aperture  which  transmits 
the  posterior  branches  of  the  intercostal  vessels 
and  nerves;  its  lateral  border  is  continuous 
with  a  thin  aponeurosis,  which  covers  the 
Intercostalis  externus. 

The  first  rib  has  no  anterior  costotransverse 
ligament.  A  band  of  fibers,  the  lumbocostal 
ligament,  in  series  with  the  anterior  costotrans- 
verse ligaments,  connects  the  neck  of  the 
twelfth  rib  to  the  base  of  the  transverse  pro- 
cess of  the  first  lumbar  vertebra;  it  is  merely 
a  thickened  portion  of  the  posterior  layer  of 
the  lumbodorsal  fascia. 

The  Posterior  Costotransverse  Ligament  {liga- 
mentum  costotransversarium  posterius).  —  The 
posterior  costotransverse  ligament  is  a  feeble 
band  which  is  attached  below  to  the  neck  of 
the  rib  and  passes  upward  and  medialward  to  the  base  of  the  transverse  process 
and  lateral  border  of  the  inferior  articular  process  of  the  vertebra  above. 


Fig.  314. — Section  of  the  costotransverse 
joints  from  the  third  to  the  ninth  inclusive. 
Contrast  the  concave  facets  on  the  upper  with 
the  flattened  facets  on  the  lower  transverse 
processes. 


302  SYNDESMOLOGY 

The  Ligament  of  the  Neck  of  the  Rib  (ligamentum  colli  costce;  middle  costotransverse 
or  interosseous  ligament). — The  ligament  of  the  neck  of  the  rib  consists  of  shoii 
but  strong  fibers,  connecting  the  rough  surface  on  the  back  of  the  neck  of  the  ril: 
with  the  anterior  surface  of  the  adjacent  transverse  process.  A  rudimentary 
ligament  may  be  present  in  the  case  of  the  eleventh  and  twelfth  ribs. 

The  Ligament  of  the  Tubercle  of  the  Rib  (ligamentum  tuherculi  costce;  posterior 
costotransverse  ligament). — The  ligament  of  the  tubercle  of  the  rib  is  a  short  but 
thick  and  strong  fasciculus,  which  passes  obliquely  from  the  apex  of  the  transverse 
process  to  the  rough  non-articular  portion  of  the  tubercle  of  the  rib.  The  ligaments 
attached  to  the  upper  ribs  ascend  from  the  transverse  processes;  they  are  shorter 
and  more  oblique  than  those  attached  to  the  inferior  ribs,  which  descend  slightly. 

Movements. — The  heads  of  the  ribs  are  so  closely  connected  to  the  bodies  of  the  vertebrse 
by  the  radiate  and  interarticular  ligaments  that  only  slight  ghding  movements  of  the  articular 
surfaces  on  one  another  can  take  place.  Similarly,  the  strong  ligaments  binding  the  necks  and 
tubercles  of  the  ribs  to  the  transverse  processes  limit  the  movements  of  the  costotransverse 
joints  to  slight  gliding,  the  nature  of  which  is  determined  by  the  shape  and  direction  of  the  articular 
surfaces  (Fig.  314).  In  the  upper  six  ribs  the  articular  surfaces  on  the  tubercles  are  oval  in  shape 
and  convex  from  above  downward;  they  fit  into  corresponding  concavities  on  the  anterior  sur- 
faces of  the  transverse  processes,  so  that  upward  and  downward  movements  of  the  tubercles  are 
associated  with  rotation  of  the  rib  neck  on  its  long  axis.  In  the  seventh,  eighth,  ninth,  and  tenth 
ribs  the  articular  surfaces  on  the  tubercles  are  flat,  and  are  directed  obliquely  downward,  medial- 
ward,  and  backward.  The  surfaces  with  which  they  articulate  are  placed  on  the  upper  margins 
of  the  transverse  processes;  when,  therefore,  the  tubercles  are  drawn  up  they  are  at  the  same 
time  carried  backward  and  medialward.  The  two  joints,  costocentral  and  costotransverse,  move 
simultaneously  and  in  the  same  directions,  the  total  effect  being  that  the  neck  of  the  rib  moves 
as  if  on  a  single  joint,  of  which  the  costocentral  and  costotransverse  articulations  form  the  ends. 
In  the  upper  six  ribs  the  neck  of  the  rib  moves  but  shghtly  upward  and  downward;  its  chief 
movement  is  one  of  rotation  around  its  own  long  axis,  rotation  backward  being  associated  with 
depression,  rotation  forward  with  elevation.  In  the  seventh,  eighth,  ninth,  and  tenth  ribs  the 
neck  of  the  rib  moves  upward,  backward,  and  medialward,  or  downward,  forward,  and  lateral- 
ward;  very  slight  rotation  accompanies  these  movements. 

VI.     Sternocostal  Articulations  (Articulationes  Sternocostales ;  Costostemal 

Articulations)  (Fig.  .315). 

The  articulations  of  the  cartilages  of  the  true  ribs  with  the  sternum  are 
arthrodial  joints,  with  the  exception  of  the  first,  in  which  the  cartilage  is  directly 
united  with  the  sternum,  and  which  is,  therefore,  a  synarthrodial  articulation. 
The  ligaments  connecting  them  are  : 

The  Articular  Capsules.  The  Interarticular  Sternocostal. 

The  Radiate  Sternocostal.  The  Costoxiphoid. 

The  Articular  Capsules  (capsulce  articulares;  capsular  ligaments). — The  articular 
capsules  surround  the  joints  between  the  cartilages  of  the  true  ribs  and  the 
sternum.  They  are  very  thin,  intimately  blended  with  the  radiate  sternocostal 
ligaments,  and  strengthened  at  the  upper  and  lower  parts  of  the  articulations  by  a 
few  fibers,  which  connect  the  cartilages  to  the  side  of  the  sternum. 

The  Radiate  Sternocostal  Ligaments  (ligamenta  sternocostalia  radiata;  chondro- 
sternal  or  sternocostal  ligaments) . — These  ligaments  consist  of  broad  and  thin  mem- 
branous bands  that  radiate  from  the  front  and  back  of  the  sternal  ends  of  the 
cartilages  of  the  true  ribs  to  the  anterior  and  posterior  surfaces  of  the  sternum. 
They  are  composed  of  fasciculi  which  pass  in  different  directions.  The  superior 
fasciculi  ascend  obliquely,  the  inferior  fasciculi  descend  obliquely,  and  the  middle 
fasciculi  run  horizontally.  The  superficial  fibers  are  the  longest;  they  intermingle 
with  the  fibers  of  the  ligaments  above  and  below  them,  with  those  of  the  opposite 
side,  and  in  front  with  the  tendinous  fibers  of  origin  of  the  Pectoralis  major,  form- 


STERNOCOSTAL  ARTICULATIONS 


303 


ing  a  thick  fibrous  membrane  (membrana  sterni)  which  envelopes  the  sternum. 
This  is  more  distinct  at  the  lower  than  at  the  upper  part  of  the  bone. 

The  Interarticular  Sternocostal  Ligament  (ligamentum  sternocostale  inter  articular  e; 
interarticular  chondrosternal  ligament). — This  ligament  is  found  constantly  only 
between  the  second  costal  cartilages  and  the  sternum.    The  cartilage  of  the  second 

The  synovial  cavities  are  exposed  by 
a  coronal  section  of  the  sternum  and  cartilages 

Cartilage  continturus  with 
sternum 


Interarticular  ligament  and 
two  synovial  membranes 


Single  synovial 
membrane 


Fig.  315. — Sternocostal  and  interchondral  articulations.     Anterior  view. 


'n6  is  connected  with  the  sternum  by  means  of  an  interarticular  ligament,  attached 
by  one  end  to  the  cartilage  of  the  rib,  and  by  the  other  to  the  fibrocartilage  which 
unites  the  manubrium  and  body  of  the  sternum.  This  articulation  is  provided 
with  two  synovial  membranes.  Occasionally  the  cartilage  of  the  third  rib  is  con- 
nected with  the  first  and  second  pieces  of  the  body  of  the  sternum  by  an  interartic- 
ular ligament.    Still  more  rarely,  similar  ligaments  are  found  in  the  other  four 


304  SYNDESMOLOGY 


I 


joints  of  the  series.    In  the  lower  two  the  ligament  sometimes  completely  obliterates 
the  cavity,  so  as  to  convert  the  articulation  into  an  amphiarthrosis. 

The  Costoxiphoid  Ligaments  (ligamenta  costoxiphoidea;  chondroxiphoid  ligaments). 
— These  ligaments  connect  the  anterior  and  posterior  surfaces  of  the  seventh 
costal  cartilage,  and  sometimes  those  of  the  sixth,  to  the  front  and  back  of  the 
xiphoid  process.  They  vary  in  length  and  breadth  in  different  subjects;  those  on 
the  back  of  the  joint  are  less  distinct  than  those  in  front. 

Synovial  Membranes. — There  is  no  synovial  membrane  between  the  first  costal  cartilage  ana 
the  sternum,  as  this  cartilage  is  directly  continuous  with  the  manubrium.  There  are  two  in  the 
articulation  of  the  second  costal  cartilage  and  generally  one  in  each  of  the  other  joints;  but  those 
of  the  sixth  and  seventh  sternocostal  joints  are  sometimes  absent;  where  an  interarticular  liga- 
ment is  present,  there  are  two  synovial  cavities.  After  middle  life  the  articular  surfaces  lose  their 
poUsh,  become  roughened,  and  the  synovial  membranes  apparently  disappear.  In  old  age,  the 
cartilages  of  most  of  the  ribs  become  continuous  with  the  sternum,  and  the  joint  cavities  are 
consequently  obUterated. 

Movements. — Slight  gliding  movements  are  permitted  in  the  sternocostal  articulations. 

Interchondral  Articulations  {articulationes  interchondrales;  articulations  of  the 
cartilages  of  the  ribs  with  each  other)  (Fig.  315). — The  contiguous  borders  of  the  sixth, 
seventh,  and  eighth,  and  sometimes  those  of  the  ninth  and  tenth,  costal  cartilages 
articulate  with  each  other  by  small,  smooth,  oblong  facets.  Each  articulation 
is  enclosed  in  a  thin  articular  capsule,  lined  by  sjmovial  membrane  and  strengthened 
laterally  and  medially  by  ligamentous  fibers  (interchondral  ligaments)  which  pass 
from  one  cartilage  to  the  other.  Sometimes  the  fifth  costal  cartilages,  more  rarely 
the  ninth  and  tenth,  articulate  by  their  lower  borders  with  the  adjoining  cartilages 
by  small  oval  facets;  more  frequently  the  connection  is  by  a  few  ligamentous  fibers. 

Costochondral  Articulations. — The  lateral  end  of  each  costal  cartilage  is  received 
into  a  depression  in  the  sternal  end  of  the  rib,  and  the  two  are  held  together  by  the 
periosteum. 

Vn.    Articulation  of  the  Manubrium  and  Body  of  the  Sternum. 

The  manubrium  is  united  to  the  body  of  the  sternum  either  by  an  amphiarthrodial 
joint — a  piece  of  fibrocartilage  connecting  the  segments — or  by  a  diarthrodial 
joint,  in  which  the  articular  surface  of  each  bone  is  clothed  with  a  lamina  of  car- 
tilage. In  the  latter  case,  the  cartilage  covering  the  body  is  continued  without 
interruption  on  to  the  cartilages  of  the  facets  for  the  second  ribs.  Rivington 
found  the  diarthrodial  form  of  joint  in  about  one-third  of  the  specimens  examined 
by  him,  Maisonneuve  more  frequently.  It  appears  to  be  rare  in  childhood,  and 
13  formed,  in  Rivington's  opinion,  from  the  amphiarthrodial  form,  by  absorption. 
The  diarthrodial  joint  seems  to  have  no  tendency  to  ossify,  while  the  amphiar- 
throdial is  more  liable  to  do  so,  and  has  been  found  ossified  as  early  as  thirty-four 
years  of  age.  The  two  segments  are  further  connected  by  anterior  and  posterior 
interstemal  ligaments  consisting  of  longitudinal  fibers. 

Mechanism  of  the  Thorax. — Each  rib  possesses  its  own  range  and  variety  of  movements,  but 
the  movements  of  all  are  combined  in  the  respiratory  excursions  of  the  thorax.  Each  rib  may 
be  regarded  as  a  lever  the  fulcrum  of  which  is  situated  immediately  outside  the  costotransverse 
articulation,  so  that  when  the  body  of  the  rib  is  elevated  the  neck  is  depressed  and  vice  versa; 
from  the  disproportion  in  length  of  the  arms  of  the  lever  a  shght  movement  at  the  vertebral  end 
of  the  rib  is  greatly  magnified  at  the  anterior  extremity. 

The  anterior  ends  of  the  ribs  He  on  a  lower  plane  than  the  posterior;  when  therefore  the  body 
of  the  rib  is  elevated  the  anterior  extremity  is  thrust  also  forward.  Again,  the  middle  of  the  body 
of  the  rib  hes  in  a  plane  below  that  passing  through  the  two  extremities,  so  that  when  the  body 
is  elevated  relatively  to  its  ends  it  is  at  the  same  time  carried  outward  from  the  median  plane 
of  the  thorax.  Further,  each  rib  forms  the  segment  of  a  curve  which  is  greater  than  that  of  the 
rib  immediately  above,  and  therefore  the  elevation  of  a  rib  increases  the  transverse  diameter 
of  the  thorax  in  the  plane  to  which  it  is  raised.  The  modifications  of  the  rib  movements  at  their 
vertebral  ends  have  already  been  described  (page  302).     Further  modifications  result  from  the 


R 


r 

If        ARTICULATION  OF  THE  MANUBRIUM  AND  BODY  OF  STERNUM     305 

II  attachments  of  their  anterior  extremities,  and  it  is  convenient  therefore  to  consider  separately 
II  the  movements  of  the  ribs  of  the  three  groups — vertebrosternal,  vertebrochondral,  and  vertebral. 
11  Vertebroslerrial  Ribs  (Figs.  316, 
3 17). — The  first  rib  differs  from  the 
others  of  this  group  in  that  its  at- 
tachment to  the  sternum  is  a  rigid 
one ;  this  is  counterbalanced  to  some 
extent  by  the  fact  that  its  head 
possesses  no  interarticular  hgament, 
and  is  therefore  more  movable.  The 
first  pair  of  ribs  with  the  manu- 
brium sterni  move  as  a  single  piece, 
the  anterior  portion  being  elevated 
by  rotatory  movements  at  the 
vertebral  extremities.  In  normal 
quiet  respiration  the  movement  of 
this  arc  is  practically  nil;  when  it 
does  occur  the  anterior  part  is 
raised  and  carried  forward,  increas- 
ing the  antero-posterior  and  trans- 
verse diameters  of  this  region  of  the 
chest.  The  movement  of  the  second 
rib  is  also  slight  in  normal  respira- 
tion, as  its  anterior  extremity  is 
fixed  to  the  manubrium,  and  pre- 
vented therefore  from  moving  up- 
ward. The  sternocostal  articulation, 
however,  allows  the  middle  of  the 
body  of  the  rib  to  be  drawn  up,  and 

in  this  way  the  transverse  thoracic  diameter  is  increased.  Elevation  of  the  third,  fourth,  fifth) 
and  sixth  ribs  raises  and  thrusts  forward  their  anterior  extremities,  the  greater  part  of  the  move- 
ment being  effected  by  the  rotation  of  the  rib  neck  backward.  The  thrust  of  the  anterior 
extremities  carries  forward  and  upward  the  body  of  the  sternum,   which  moves  on  the  joint 


Fig.  316. — Lateral  view  of  first  and  seventh  ribs  in  position,  show- 
ing the  movements  of  the  sternum  and  ribs  in  A,  ordinary  expiration; 
li,  quiet  inspiration;  C,  deep  inspiration. 


Fig.  317 . — Diagram  showing  the  axes  of  movement 
{A  B  and  C  D)  oi  a  vertebrosternal  rib.  The  inter- 
rupted lines  indicate  the  position  of  the  rib  in 
inspiration. 


Fig.  318. — Diagram  showing  the  axis  of  movement 
{A  B)  of  a  vertebrochondral  rib.  The  interrupted  lines 
indicate  the  position  of  the  rib  in  inspiration. 


between  it  and  the  manubrium,  and  thus  the  antero-posterior  thoracic  diameter  is  increased. 
This  movement  is,  however,  soon  arrested,  and  the  elevating  force  is  then  expended  in  raising 
the  middle  part  of  the  body  of  the  rib   and    everting  its  lower  border;  at   the  same  time  the 
20 


306  ^W^^fHF       SYNDESMOLOGY 

costochondral  angle  is  opened  out.  By  these  latter  movements  a  considerable  increase  in  the 
transverse  diameter  of  the  thorax  is  effected. 

Verlebrochondral  Ribs  (Fig.  318). — The  seventh  rib  is  included  with  this  group,  as  it  conforms 
more  closely  to  their  type.  While  the  movements  of  these  ribs  assist  in  enlarging  the  thorax 
for  respiratory  purposes,  they  are  also  concerned  in  increasing  the  upper  abdominal  space  for 
viscera  displaced  by  the  action  of  the  diaphragm.  The  costal  cartilages  articulate  with  one 
another,  so  that  each  pushes  up  that  above  it,  the  final  thrust  being  directed  to  pushing  forward 
and  upward  the  lower  end  of  the  body  of  the  sternum.  The  amount  of  elevation  of  the  anterior 
extremities  is  limited  on  account  of  the  very  shght  rotation  of  the  rib  neck.  Elevation  of  the 
shaft  is  accompanied  by  an  outward  and  backward  movement;  the  outward  movement  everts 
the  anterior  end  of  the  rib  and  opens  up  the  subcostal  angle,  while  the  backward  movement 
pulls  back  the  anterior  extremity  and  counteracts  the  forward  thrust  due  to  its  elevation;  this 
latter  is  most  noticeable  in  the  lower  ribs,  which  are  the  shortest.  The  total  result  is  a  consider- 
able increase  in  the  transverse  and  a  diminution  in  the  median  antero-posterior  diameter  of  the 
upper  part  of  the  abdomen;  at  the  same  time,  however,  the  lateral  antero-posterior  diameters  of 
the  abdomen  are  increased. 

Vertebral  Ribs. — Since  these  ribs  have  free  anterior  extremities  and  only  costocentral  articula- 
tions with  no  interarticular  ligaments,  they  are  capable  of  slight  movements  in  all  directions. 
When  the  other  ribs  are  elevated  these  are  depressed  and  fixed  to  form  points  of  action  for  the 
diaphragm. 

Vm.    Articulation  of  the  Vertebral  Column  with  the  Pelvis. 

The  ligaments  connecting  the  fifth  lumbar  vertebra  with  the  sacrum  are  similar 
to  those  which  join  the  movable  segments  of  the  vertebral  column  with  each  other 
— viz.:  1.  The  continuation  downward  of  the  anterior  and  posterior  longitudinal 
ligaments.  2.  The  intervertebral  fibrocartilage,  connecting  the  body  of  the  fifth 
lumbar  to  that  of  the  first  sacral  vertebra  and  forming  an  amphiarthrodial  joint. 
3.  Ligamenta  flava,  uniting  the  laminae  of  the  fifth  lumbar  vertebra  with  those 
of  the  first  sacral.  4.  Capsules  connecting  the  articular  processes  and  forming 
a  double  arthrodia.    5.  Inter-  and  supraspinal  ligaments. 

On  either  side  an  additional  ligament,  the  iliolumbar,  connects  the  pelvis  with 
the  vertebral  column. 

The  Iliolumbar  Ligament  (ligamentum  iliolumhale)  (Fig.  319). — The  iliolumbar 
ligament  is  attached  above  to  the  lower  and  front  part  of  the  transverse  process 
of  the  fifth  lumbar  vertebra.  It  radiates  as  it  passes  lateralward  and  is  attached 
by  two  main  bands  to  the  pelvis.  The  lower  bands  run  to  the  base  of  the  sacrum, 
blending  with  the  anterior  sacroiliac  ligament;  the  upper  is  attached  to  the  crest 
of  the  ilium  immediately  in  front  of  the  sacroiliac  articulation,  and  is  continuous 
above  with  the  lumbodorsal  fascia.  Iw  front,  it  is  in  relation  with  the  Psoas  major; 
behind,  with  the  muscles  occupying  the  vertebral  groove ;  above,  with  the  Quadratus 
lumborum. 

IX.    Articulations  of  the  Pelvis. 

The  ligaments  connecting  the  bones  of  the  pelvis  with  each  other  may  be  divided 
into  four  groups:  1.  Those  connecting  the  sacrum  and  ilium.  2.  Those  passing 
between  the  sacrum  and  ischium.  3.  Those  uniting  the  sacrum  and  coccyx.  4. 
Those  between  the  two  pubic  bones. 

1.  Sacroiliac  Articulation  (articulatio  sacroiliaca) . — The  sacroiliac  articulation 
is  an  amphiarthrodial  joint,  formed  between  the  auricular  surfaces  of  the  sacrum 
and  the  ilium.  The  articular  surface  of  each  bone  is  covered  with  a  thin  plate 
of  cartilage,  thicker  on  the  sacrum  than  on, the  ilium.  These  cartilaginous  plates 
are  in  close  contact  with  each  other,  and  to  a  certain  extent  are  united  together 
by  irregular  patches  of  softer  fibrocartilage,  and  at  their  upper  and  posterior  part 
by  fine  interosseous  fibers.  In  a  considerable  part  of  their  extent,  especially  in 
advanced  life,  they  are  separated  by  a  space  containing  a  synovia-like  fluid,  and 
hence  the  joint  presents  the  characteristics  of  a  diarthrosis.  The  ligaments  of  the 
joint  are: 

The  Anterior  Sacroiliac.  The  Posterior  Sacroiliac. 

The  Interosseous. 


m 


ARTICULATION  OF  THE  PELVIS 


307 


The  Anterior  Sacroiliac  Ligament  (ligamentum  sacroiliacum  anterius)  (Fig.  319). — 
The  anterior  sacroiliac  ligament  consists  of  numerous  thin  bands,  which  connect 
the  anterior  surface  of  the  lateral  part  of  the  sacrum  to  the  margin  of  the  auricular 
surface  of  the  ilium  and  to  the  preauricular  sulcus. 


Anterior  sacroiliac  lig. 

Iliolumbar  ligament   Lumbosacral  ligament 

/        Anterior  longitudinal  lig. 


r  pubic  fibrocart. 


Anterior  view.     (Quain.) 


The  Posterior  Sacroiliac  Ligament  {ligamentum  sacroiliacum  posterius)  (Fig.  320). 
■ — The  posterior  sacroiliac  ligament  is  situated  in  a  deep  depression  between  the 
sacrum  and  ilium  behind;  it  is  strong  and  forms  the  chief  bond  of  union  between 
the  bones.     It  consists  of  numerous  fasciculi,  which  pass  between  the  bones  in 


308 


SYNDESMOLOGY 


various  directions.  The  upper  part  (short  posterior  sacroiliac  ligament)  is  nearl.^' 
horizontal  in  direction,  and  passes  from  the  first  and  second  transverse  tubercles 
on  the  back  of  the  sacrum  to  the  tuberosity  of  the  ilium.  The  lower  part  (long 
posterior  sacroiliac  ligament)  is  oblique  in  direction;  it  is  attached  by  one  extremitj' 


Iliolumbar  ligament 
Supraspinal  ligament  I 

Short  post,  sacroiliac  lig 
I 
I 


Superficial  post,  sacrococ- 
cygeal ligament 


"'Long  post,  sacroiliac  lig 


Sacrospinous  ligament 


Sacrotuherous  ligament 
Fio.  320. — Articulations  of  pelvis.     Posterior  view.      (Quaiii.) 


II 


to  the  third  transverse  tubercle  of  the  back  of  the  sacrum,  and  by  the  other  to  the 
posterior  superior  spine  of  the  ilium. 

The  Interosseous  Sacroiliac  Ligament  (ligamentum  sacroiliacum  interosseum) . — 
This  ligament  lies  deep  to  the  posterior  ligament,  and  consists  of  a  series  of  short, 
strong  fibers  connecting  the  tuberosities  of  the  sacrum  and  ilium. 


h 


ARTICULATIONS  OF  THE  PELVIS  309 

2.  Ligaments  Connecting  the  Sacrum  and  Ischium  (Fig.  320). 
The  Sacrotuberous.  The  Sacrospinous. 

The  Sacrotuberous  Ligament  (Jigamentum  sacrotuherosum;  great  or  posterior 
sacroscmtic  ligament). — The  sacrotuberous  ligament  is  situated  at  the  lower  and 
back  part  of  the  pelvis.  It  is  flat,  and  triangular  in  form;  narrower  in  the  middle 
than  at  the  ends;  attached  by  its  broad  base  to  the  posterior  inferior  spine  of  the 
ilium,  to  the  fourth  and  fifth  transverse  tubercles  of  the  sacrum,  and  to  the  lower 
part  of  the  lateral  margin  of  that  bone  and  the  coccyx.  Passing  obliquely  downward, 
forward,  and  lateralward,  it  becomes  narrow  and  thick,  but  at  its  insertion  into 
the  inner  margin  of  the  tuberosity  of  the  ischium,  it  increases  in  breadth,  and  is 
prolonged  forward  along  the  inner  margin  of  the  ramus,  as  the  falciform  process, 
the  free  concave  edge  of  which  gives  attachment  to  the  obturator  fascia;  one  of  its 
surfaces  is  turned  toward  the  perineum,  the  other  toward  the  Obturator  internus. 
The  lower  border  of  the  ligament  is  directly  continuous  with  the  tendon  of  origin 
of  the  long  head  of  the  Biceps  femoris,  and  by  many  is  believed  to  be  the  proximal 
end  of  this  tendon,  cut  off  by  the  projection  of  the  tuberosity  of  the  ischium. 

Relations. — The  posterior  surface  of  this  Ugament  gives  origin,  by  its  whole  extent,  to  the 
GlutiEUS  maximus.  Its  anterior  surface  is  in  part  united  to  the  sacrospinous  Hgament.  Its  upper 
border  forms,  above,  the  posterior  boundary  of  the  greater  sciatic  foramen,  and,  below,  the  pos- 
terior boundary  of  the  lesser  sciatic  foramen.  Its  lower  border  forms  part  of  the  boundary  of  the 
perineum.  It  is  pierced  by  the  coccygeal  nerve  and  the  coccygeal  branch  of  the  inferior  gluteal 
artery. 

The  Sacrospinous  Ligament  (ligamentum  sacrospinosum;  small  or  anterior  sacro- 
sciatic  ligament). — The  sacrospinous  ligament  is  thin,  and  triangular  in  form; 
it  is  attached  by  its  apex  to  the  spine  of  the  ischium,  and  medially,  by  its  broad 
base,  to  the  lateral  margins  of  the  sacrum  and  coccyx,  in  front  of  the  sacrotuberous 
ligament  with  which  its  fibers  are  intermingled. 

Relations. — It  is  in  relation,  anteriorly,  with  the  Coccygeus  muscle,  to  which  it  is  closely  con- 
nected; posteriorly,  it  is  covered  by  the  sacrotuberous  ligament,  and  crossed  by  the  internal 
pudendal  vessels  and  nerve.  Its  upper  border  forms  the  lower  boundary  of  the  greater  sciatic 
foramen;  its  lower  border,  part  of  the  margin  of  the  lesser  sciatic  foramen. 

These  two  Ugaments  convert  the  sciatic  notches  into  foramina.  The  greater  sciatic  foramen 
is  bounded,  ia.  front  and  above,  by  the  posterior  border  of  the  hip  bone;  behind,  by  the  sacrotuberous 
ligament;  and  below,  by  the  sacrospinous  Ugament.  It  is  partially  filled  up,  in  the  recent  state, 
by  the  Piriformis  which  leaves  the  pelvis  through  it.  Above  this  muscle,  the  superior  gluteal 
vessels  and  nerve  emerge  from  the  pelvis;  and  below  it,  the  inferior  gluteal  vessels  and  nerve, 
the  internal  pudendal  vessels  and  nerve,  the  sciatic  and  posterior  femoral  cutaneous  nerves,  and 
the  nerves  to  the  Obturator  internus  and  Quadratus  femoris  make  their  exit  from  the  pelvis. 
The  lesser  sciatic  foramen  is  bounded,  in  front,  by  the  tuberosity  of  the  ischium;  above,  by  the 
spine  of  the  ischium  and  sacrospinous  ligament;  behind,  by  the  sacrotuberous  hgament.  It  trans- 
mits the  tendon  of  the  Obturator  internus,  its  nerve,  and  the  internal  pudendal  vessels  and  nerve. 

3.  Sacrococcygeal  Symphysis  {symphysis  sacrococcygea;  articulation  of  the  sacrum 
and  coccyx)  .—This  articulation  is  an  amphiarthrodial  joint,  formed  between  the 
oval  surface  at  the  apex  of  the  sacrum,  and  the  base  of  the  coccyx.  It  is  homol- 
ogous with  the  joints  between  the  bodies  of  the  vertebrae,  and  is  connected  by 
similar  ligaments.    They  are: 

The  Anterior  Sacrococcygeal.  The  Lateral  Sacrococcygeal. 

The  Posterior  Sacrococcygeal.  The  Interposed  Fibrocartilage. 

The  Interarticular. 


The  Anterior  Sacrococcygeal  Ligament  {ligamentum  sacrococcygeiim  anterius). — 
This  consists  of  a  few  irregular  fibers,  which  descend  from  the  anterior  surface 
of  the  sacrum  to  the  front  of  the  coccyx,  blending  with  the  periosteum. 

The  Posterior  Sacrococcygeal  Ligament  {ligamentum  sacrococcygeum  posterius). — 
This  is  a  flat  band,  which  arises  from  the  margin  of  the  lower  orifice  of  the. sacral 


310  SYNDESMOLOGY 

canal,  and  descends  to  be  inserted  into  the  posterior  surface  of  the  coccyx.  This 
ligament  completes  the  lower  and  back  part  of  the  sacral  canal,  and  is  divisible 
into  a  short  deep  portion  and  a  longer  superficial  part.  It  is  in  relation,  behind, 
with  the  Glutseus  maximus. 

The  Lateral  Sacrococcygeal  Ligament  (ligamentum  sacrococcygeum  laterale;  inter- 
transverse ligament).- — The  lateral  sacrococcygeal  ligament  exists  on  either  side  }| 
and  connects  the  transverse  process  of  the  coccyx  to  the  lower  lateral  angle  of  the  || 
sacrum;  it  completes  the  foramen  for  the  fifth  sacral  nerve.  jl 

A  disk  of  fibrocartilage  is  interposed  between  the  contiguous  surfaces  of  the  || 
sacrum  and  coccyx;  it  differs  from  those  betw^een  the  bodies  of  the  vertebrae  in 
that  it  is  thinner,  and  its  central  part  is  firmer  in  texture.  It  is  somewhat  thicker 
in  front  and  behind  than  at  the  sides.  Occasionally  the  coccyx  is  freely  movable 
on  the  sacrum,  most  notably  during  pregnancy ;  in  such  cases  a  synovial  membrane 
is  present. 

The  Literarticular  Ligaments  are  thin  bands,  which  unite  the  cornua  of  the  two 
bones. 

The  different  segments  of  the  coccyx  are  connected  together  by  the  extension 
downward  of  the  anterior  and  posterior  sacrococcygeal  ligaments,  thin  annular 
disks  of  fibrocartilage  being  interposed  between  the  segments.  In  the  adult  male, 
all  the  pieces  become  ossified  together  at  a  comparatively  early  period ;  but  in  the 
female,  this  does  not  commonly  occur  until  a  later  period  of  life.  At  more  advanced 
age  the  joint  between  the  sacrum  and  coccyx  is  obliterated. 

Movements.— The  movements  which  take  place  between  the  sacrum  and  coccyx,  and  between 
the  different  pieces  of  the  latter  bone,  are  forward  and  backward;  they  are  very  limited.  Their 
extent  increases  during  pregnancy. 

4.  The  Pubic  Symphysis  {symphysis  ossium  pubis;  articulation  of  the  pubic 
bones)  (Fig.  321). — The  articulation  between  the  pubic  bones  is  an  amphiarthro- 
dial  joint,  formed  between  the  two  oval  articular  surfaces  of  the  bones.  The 
ligaments  of  this  articulation  are: 

The  Anterior  Pubic.  The  Superior  Pubic. 

The  Posterior  Pubic.  The  Arcuate  Pubic. 

The  Interpubic  Fibrocartilaginous  Lamina. 

The  Anterior  Pubic  Ligament  (Fig.  319). — The  anterior  pubic  ligament  consists 
of  several  superimposed  layers,  which  pass  across  the  front  of  the  articulation. 
The  superficial  fibers  pass  obliquely  from  one  bone  to  the  other,  decussating  and 
forming  an  interlacement  with  the  fibers  of  the  aponeuroses  of  the  Obliqui  externi 
and  the  medial  tendons  of  origin  of  the  Recti  abdominis.  The  deep  fibers  pass 
transversely  across  the  symphysis,  and  are  blended  with  the  fibrocartilaginous 
lamina. 

The  Posterior  Pubic  Ligament. — The  posterior  pubic  ligament  consists  of  a  few 
thin,  scattered  fibers,  which  unite  the  two  pubic  bones  posteriorly. 

The  Superior  Pubic  Ligament  (ligamentum  pubicum  sujjerius)  .—The  superior 
pubic  ligament  connects  together  the  two  pubic  bones  superiorly,  extending  later- 
ally as  far  as  the  pubic  tubercles. 

The  Arcuate  Pubic  Ligament  (ligamentum  arcuatum  pubis;  inferior  pubic  or 
subpubic  ligament). — The  arcuate  pubic  ligament  is  a  thick,  triangular  arch  of 
ligamentous  fibers,  connecting  together  the  two  pubic  bones  below,  and  forming 
the  upper  boundary  of  the  pubic  arch.  Above,  it  is  blended  with  the  interpubic 
fibrocartilaginous  lamina;  laterally,  it  is  attached  to  the  inferior  rami  of  the 
pubic  bones;  below,  it  is  free,  and  is  separated  from  the  fascia  of  the  urogenital 
diaphragm  by  an  opening  through  which  the  deep  dorsal  vein  of  the  penis  passes 
into  the  pelvis. 


ARTICULATIONS  OF  THE  PELVIS 


311 


The  Interpubic  Fibrocartilaginous  Lamina  {lamina  fibrocartilaginea  interpubica; 
interpubic  disk). — The  interpubic  fibrocartilaginous  lamina  connects  the  opposed 
surfaces  of  the  pubic  bones.  Each  of  these  surfaces  is  covered  by  a  thin  layer  of 
hyaline  cartilage  firmly  joined  to  the  bone  by  a  series  of  nipple-like  processes  which 
accurately  fit  into  corresponding  depressions  on  the  osseous  surfaces.  These 
opposed  cartilaginous  surfaces  are  connected  together  by  an  intermediate  lamina 
of  fibrocartilage  which  varies  in  thickness  in  different  subjects.  It  often  contains 
a  cavity  in  its  interior,  probably  formed  by  the  softening  and  absorption  of  the 
fibrocartilage,  since  it  rarely  appears  before  the  tenth  year  of  life  and  is  not  lined 
by  synovial  membrane.  This  cavity  is  larger  in  the  female  than  in  the  male,  but 
it  is  very  doubtful  whether  it  enlarges,  as  was  formerly  supposed,  during  pregnancy. 
It  is  most  frequently  limited  to  the  upper  and  back  part  of  the  joint;  it  occasion- 
ally reaches  to  the  front,  and  may  extend  the  entire  length  of  the  cartilage.  It  may 
be  easily  demonstrated  when  present  by  making  a  coronal  section  of  the  symphysis 
pubis  near  its  posterior  surface  (Fig.  321). 


Ani.  sup.  iliac  spine--~J^ 


Obturator  canal 
Lacunar  ligament 
Pvbic  tubercle 


Inierjyubic 

fibro- 

cariilaginous 

lamina 


Transverse  acetabular 
ligament 


Fio.  321. — Sjmiphysia  pubis  exposed  by  a  coronal  section. 

Mechanism  of  the  Pelvis. — The  pelvic  girdle  supports  and  protects  the  contained  viscera  and 
affords  surfaces  for  the  attachments  of  the  trunk  and  lower  limb  muscles.  Its  most  important 
mechanical  function,  however,  is  to  transmit  the  weight  of  the  trunk  and  upper  limbs  to  the 
lower  extremities. 

It  may  be  divided  into  two  arches  by  a  vertical  plane  passing  through  the  acetabular  cavities; 
the  posterior  of  these  arches  is  the  one  chiefly  concerned  in  the  function  of  transmitting  the 
weight.  Its  essential  parts  are  the  upper  three  sacral  vertebrae  and  two  strong  pillars  of  bone 
running  from  the  sacroihac  articulations  to  the  acetabular  cavities.  For  the  reception  and  diffu- 
sion of  the  weight  each  acetabular  cavity  is  strengthened  by  two  additional  bars  running  toward 
the  pubis  and  ischium.  In  order  to  lessen  concussion  in  rapid  changes  of  distribution  of  the 
weight,  joints  (sacroiliac  articulations)  are  interposed  between  the  sacrum  and  the  iliac  bones; 
an  accessory  joint  (pubic  symphysis)  exists  in  the  middle  of  the  anterior  arch.  The  sacrum  forms 
the  summit  of  the  posterior  arch;  the  weight  transmitted  falls  on  it  at  the  lumbosacral  articula- 
tion and,  theoretically,  has  a  component  in  each  of  two  directions.  One  component  of  the  force 
is  expended  in  driving  the  sacrum  downward  and  backward  between  the  iUac  bones,  while  the 
other  thrusts  the  upper  end  of  the  sacrum  downward  and  forward  toward  the  pelvic  cavity. 


312 


SYNDESMOLOGY 


The  movements  of  the  sacrum  are  regulated  by  its  form.    Viewed  as  a  whole,  it  presents  the 
shape  of  a  wedge  with  its  base  upward  and  forward.    The  first  component  of  the  force  ia  there- 


.'V«.'»; 


Fig.  322. — Coronal  section  of  anterior  sacral  segment. 

fore  acting  against  the  resistance  of  the  wedge,  and  its  tendency  to  separate  the  iliac  bones  is 
resisted  by  the  sacroiliac  and  iliolumbar  ligaments  and  by  the  ligaments  of  the  pubic  symphysis. 


Fia.  323.— Coronal  section  of  middle  sacra   segment. 

If  a  series  of  coronal  sections  of  the  sacroiliac  joints  be  made,  it  will  be  found  possible  to  divide 
the  articular  portion  of  the  sacrum  into  three  segments:  anterior,  middle,  and  posterior.  In 
the  anterior  segment  (Fig.  322),  which  involves  the  first  sacral  vertebra,  the  articular  surfaces 

show  slight  sinuosities  and  are  almost  parallel 
to  one  another;  the  distance  between  their 
dorsal  margins  is,  however,  slightly  greater 
than  that  between  their  ventral  margins. 
This  segment  therefore  presents  a  slight 
wedge  shape  with  the  truncated  apex  down- 
ward. The  middle  segment  (Fig.  323)  is  a 
narrow  band  across  the  centers  of  the  articu- 
lations. Its  dorsal  width  is  distinctly 
greater  than  its  ventral,  so  that  the  segment 
is  more  definitely  wedge-shaped,  the  trun- 
cated apex  being  again  directed  downward. 
Each  articular  surface  presents  in  the  center 
a  marked  concavity  from  above  downward, 
and  into  this  a  corresponding  convexity  of  the  iliac  articular  surface  fits,  forming  an  interlocking 
mechanism.  In  the  posterior  segment  (Fig.  324)  the  ventral  width  is  greater  than  the  dorsal, 
so  that  the  wedge  form  is  the  reverse  of  those  of  the  other  segments — i.  e.,  the  truncated  apex 
is  directed  upward.     The  articular  surfaces  are  only  slightly  concave. 

Dislocation  downward  and  forward  of  the  sacrum  by  the  second  component  of  the  force  applied 
to  it  is  prevented  therefore  by  the  middle  segment,  which  interposes  the  resistance  of  its  wedge 


I 


Fig.  324. — Coronal  section  of  posterior  sacral  segment. 


STERNOCLAVICULAR  ARTICULATION  313 

shape  and  that  of  the  interlocking  mechanism  on  its  surfaces;  a  rotatory  movement,  however, 
is  produced  by  which  the  anterior  segment  is  tilted  downward  and  the  posterior  upward;  the  axis 
of  this  rotation  passes  through  the  dorsal  part  of  the  middle  segment.  The  movement  of  the 
anterior  segment  is  slightly  limited  by  its  wedge  form,  but  chiefly  by  the  posterior  and  inter- 
osseous sacroihac  ligaments;  that  of  the  posterior  segment  is  checked  to  a  sUght  extent  by  its 
wedge  form,  but  the  chief  hmiting  factors  are  the  sacrotuberous  and  sacrospinous  ligaments. 
In  all  these  movements  the  effect  of  the  sacroiUac  and  iUolumbar  ligaments  and  the  ligaments 
of  the  symphysis  pubis  in  resisting  the  separation  of  the  iUac  bones  must  be  recognized. 

During  pregnancy  the  pelvic  joints  and  hgaments  are  relaxed,  and  capable  therefore  of  more 
extensive  movements.  When  the  fetus  is  being  expelled  the  force  is  applied  to  the  front  of  the 
sacrum.  Upward  dislocation  is  again  prevented  by  the  interlocking  mechanism  of  the  middle 
segment.  As  the  fetal  head  passes  the  anterior  segment  the  latter  is  carried  upward,  enlarging 
the  antero-posterior  diameter  of  the  pelvic  inlet;  when  the  head  reaches  the  posterior  segment 
this  also  is  pressed  upward  against  the  resistance  of  its  wedge,  the  movement  only  being  possible 
by  the  laxity  of  the  joints  and  the  stretching  of  the  sacrotuberous  and  sacrospinous  ligaments. 

ARTICULATIONS   OF   THE  UPPER  EXTREMITY. 

The  articulations  of  the  Upper  Extremity  may  be  arranged  as  follows: 

I.  Sternoclavicular.  VI.  Wrist. 

II.  Acromioclavicular.  VII.  Intercarpal. 

III.  Shoulder.  VIII.  Carpometacarpal. 

IV.  Elbow.  IX.  Intermetacarpal. 
V.  Radioulnar.  X.  Metacarpophalangeal. 

XI.  Articulations  of  the  Digits. 

I.    Sternoclavicular  Articulation  (Articulatio  Stemoclavicularis)  (Fig.  325). 

The  sternoclavicular  articulation  is  a  double  arthrodial  joint.  The  parts  entering 
into  its  formation  are  the  sternal  end  of  the  clavicle,  the  upper  and  lateral  part 
of  the  manubrium  sterni,  and  the  cartilage  of  the  first  rib.  The  articular  surface 
of  the  clavicle  is  much  larger  than  that  of  the  sternum,  and  is  invested  with  a  layer 
of  cartilage,^  which  is  considerably  thicker  than  that  on  the  latter  bone.  The 
igaments  of  this  joint  are: 

The  Articular  Capsule.  The  Interclavicular. 

The  Anterior  Sternoclavicular.  The  Costoclavicular. 

The  Posterior  Sternoclavicular.  The  Articular  Disk. 

The  Articular  Capsule  {capsula  articularis;  capsular  ligament). — The  articular 
capsule  surrounds  the  articulation  and  varies  in  thickness  and  strength.  In  front 
and  behind  it  is  of  considerable  thickness,  and  forms  the  anterior  and  posterior 
sternoclavicular  ligaments;  but  above,  and  especially  below,  it  is  thin  and  par- 
takes more  of  the  character  of  areolar  than  of  true  fibrous  tissue. 

The  Anterior  Sternoclavicular  Ligament  {ligamentum  sternoclaviculare  anterior). — 
The  anterior  sternoclavicular  ligament  is  a  broad  band  of  fibers,  covering  the 
anterior  surface  of  the  articulation;  it  is  attached  above  to  the  upper  and  front  part 
of  the  sternal  end  of  the  clavicle,  and,  passing  obliquely  downward  and  medialward, 
is  attached  below  to  the  front  of  the  upper  part  of  the  manubrium  sterni.  This 
ligament  is  covered  by  the  sternal  portion  of  the  Sternocleidomastoideus  and  the 
integument;  behind,  it  is  in  relation  with  the  capsule,  the  articular  disk,  and  the 
two  synovial  membranes. 

The  Posterior  Sternoclavicular  Ligament  {ligamentum  sternoclaviculare  posterius). — 
The  posterior  sternoclavicular  ligament  is  a  similar  band  of  fibers,  covering  the 
posterior  surface  of  the  articulation;   it  is  attached  above  to  the  upper  and  back 

>  According  to  Bruch,  the  sternal  end  of  the  clavicle  is  covered  by  a  tissue  which  is  fibrous  rather  than  cartilaginous 
in  structure. 


314 


SYNDESMOLOGY 


part  of  the  sternal  end  of  the  clavicle,  and,  passing  obliquely  downward  and 
medialward,  is  fixed  below  to  the  back  of  the  upper  part  of  the  manubrium  sterni. 
It  is  in  relation,  in  front,  with  the  articular  disk  and  synovial  membranes;  behind,  ^- 
with  the  Sternohyoideus  and  Sternothyreoideus.  H 

The  Interclavicular  Ligament  (ligamentum  inierclaviculare) . — This  ligament  is  a  ™ 
flattened  band,  which  varies  considerably  in  form  and  size  in  diflferent  individuals, 
it  passes  in  a  curved  direction  from  the  upper  part  of  the  sternal  end  of  one  clavicle 
to  that  of  the  other,  and  is  also  attached  to  the  upper  margin  of  the  sternum.  It 
is  in  relation,  in  frojit,  with,  the  integument  and  Sternocleidomastoidei ;  behind, 
with  the  Sternothyreoidei.  H 

The  Costoclavicular  Ligament  (ligamentum  costoclavicular e;  rhomboid  ligament). — ^| 
This  ligament  is  short,  flat,  strong,  and  rhomboid  in  form.  Attached  below  to 
the  upper  and  medial  part  of  the  cartilage  of  the  first  rib,  it  ascends  obliquely 
backward  and  lateralw  ard,  and  is  fixed  above  to  the  costal  tuberosity  on  the  under 
surface  of  the  clavicle.  It  is  in  relation,  in  front,  with  the  tendon  of  origin  of  the 
Subclavius;  behind,  with  the  subclavian  vein. 


m\ 


Fig.  325. — Sternoclavicular  articulation.     An  terior  view. 


The  Articular  Disk  (discus  articularis) . — The  articular  disk  is  flat  and  nearly 
circular,  interposed  between  the  articulating  surfaces  of  the  sternum  and  clavicle. 
It  is  attached,  above,  to  the  upper  and  posterior  border  of  the  articular  surface  of 
the  clavicle;  below,  to  the  cartilage  of  the  first  rib,  near  its  junction  with  the  sternum; 
and  by  its  circumference  to  the  interclavicular  and  anterior  and  posterior  sterno- 
clavicular ligaments.  It  is  thicker  at  the  circumference,  especially  its  upper  and 
back  part,  than  at  its  center.  It  divides  the  joint  into  two  cavities,  each  of  which 
is  furnished  with  a  synovial  membrane. 

Synovial  Membranes. — Of  the  two  synovial  membranes  found  in  this  articulation,  the  lateral 
is  reflected  from  the  sternal  end  of  the  clavicle,  over  the  adjacent  sui-face  of  the  articular  disk, 
and  around  the  margin  of  the  facet  on  the  cartilage  of  the  first  rib ;  the  medial  is  attached  to  the 
margin  of  the  articular  surface  of  the  sternum  and  clothes  the  adjacent  surface  of  the  articular 
disk;  the  latter  is  the  larger  of  the  two. 

Movements. — This  articulation  admits  of  a  limited  amount  of  motion  in  nearly  every  direc- 
tion— upward,  downward,  backward,  forward,  as  well  as  circumduction.  When  these  move- 
ments take  place  in  the  joint,  the  clavicle  in  its  motion  carries  the  scapula  with  it,  this  bone 
gliding  on  the  outer  surface  of  the  chest.  This  joint  therefore  forms  the  center  from  which  all 
movements  of  the  supporting  arch  of  the  shoulder  originate,  and  is  the  only  point  of  articulation 
of  the  shoulder  girdle  with  the  trunk.  The  movements  attendant  on  elevation  and  depression  of 
the  shoulder  take  place  between  the  clavicle  and  the  articular  disk,  the  bone  rotating  upon  the 
ligament  on  an  axis  drawn  from  before  backward  through  its  own  articular  facet;  when  the  shoulder 
is  moved  forward  and  backward,  the  clavicle,  with  the  articular  disk  rolls  to  and  fro  on  the 


A  C  ROM  IOC  LA  VIC  ULAR  ARTIC  ULA  TION 


315 


articular  surface  of  the  sternum,  revolving,  with  a  sliding  movement,  around  an  axis  drawn  nearly 
vertically  through  the  sternum;  in  the  circumduction  of  the  shoulder,  which  is  compounded  of 
these  two  movements,  the  clavicle  revolves  upon  the  articular  disk  and  the  latter,  with  the  clavicle, 
rolls  upon  the  sternum.^  Elevation  of  the  shoulder  is  limited  principally  by  the  costoclavicular 
hgament;  depression,  by  the  interclavicular  ligament  and  articular  disk.  The  muscles  which 
raise  the  shoulder  are  the  upper  fibers  of  the  Trapezius,  the  Levator  scapulae,  and  the  clavicular 
head  of  the  Sternocleidomastoideus,  assisted  to  a  certain  extent  by  the  Rhomboidei,  which  pull 
the  vertebral  border  of  the  scapula  backward  and  upward  and  so  raise  the  shoulder.  The  depres- 
sion of  the  shoulder  is  principally  effected  by  gravity  assisted  by  the  Subclavius,  Pectoralis  minor 
and  lower  fibers  of  the  Trapezius.  The  shoulder  is  drawn  backward  by  the  Rhomboidei  and  the 
middle  and  lower  fibers  of  the  Trapezius,  and  forward  by  the  Serratus  anterior  and  Pectoralis 


n.    Acromioclavicular  Articulation  (Articulatio  Acromioclavicularis ;  Scapulo- 
clavicular Articulation)  (Fig.  326). 

The  acromioclavicular  articulation  is  an  arthrodial  joint  between  the  acromial 
end  of  the  clavicle  and  the  medial  margin  of  the  acromion  of  the  scapula.  Its 
ligaments  are: 

The  Articular  Capsule.  The  Articular  Disk. 

The  Superior  Acromioclavicular.       rr-i     /^  i     •     i       /Trapezoid  and 

^  Ihe  Coracociavicular  i       >^_     -j 


The  Inferior  Acromioclavicular. 


I       Conoid. 


The  Articular  Capsule  {capsula  articularis;  capsular  ligament). — The  articular 
capsule  completely  surrounds  the  articular  margins,  and  is  strengthened  above 
and  below  by  the  superior  and  inferior  acromioclavicular  ligaments. 

The  Superior  Acromioclavicular  Ligament  (ligamentum  acromioclamculare) . — 
This  ligament  is  a  quadrilateral  band,  covering  the  superior  part  of  the  articula- 
tion, and  extending  between  the  upper  part  of  the  acromial  end  of  the  clavicle 
and  the  adjoining  part  of  the  upper  surface  of  the  acromion.  It  is  composed 
of  parallel  fibers,  which  interlace  with  the  aponeuroses  of  the  Trapezius  and 
Deltoideus;  below,  it  is  in  contact  with  the  articular  disk  when  this  is  present. 

The  Inferior  Acromioclavicular  Ligament. — This  ligament  is  somewhat  thinner 
than  the  preceding;  it  covers  the  under  part  of  the  articulation,  and  is  attached  to 
the  adjoining  surfaces  of  the  two  bones.  It  is  in  relation,  above,  in  rare  cases  with 
the  articular  disk ;  below,  with  the  tendon  of  the  Supraspinatus. 

The  Articular  Disk  (discus  articularis). — The  articular  disk  is  frequently  absent 
in  this  articulation.  When  present,  it  generally  only  partially  separates  the  artic- 
ular surfaces,  and  occupies  the  upper  part  of  the  articulation.  More  rarely,  it 
completely  divides  the  joint  into  two  cavities. 

The  Synovial  Membrane. — There  is  usually  only  one  synovial  membrane  in  this  articulation, 
but  when  a  complete  articular  disk  is  present,  there  are  two. 

The  Coracoclavicular  Ligament  (ligamentum  coracoclaviculare)  (Fig.  326). — This 
ligament  serves  to  connect  the  clavicle  with  the  coracoid  process  of  the  scapula. 
It  does  not  properly  belong  to  this  articulation,  but  is  usually  described  with  it, 
since  it  forms  a  most  efficient  means  of  retaining  the  clavicle  in  contact  with  the 
acromion.    It  consists  of  two  fasciculi,  called  the  trapezoid  and  conoid  ligaments. 

The  Trapezoid  Ligament  (ligamentum  trapezoidewn) ,  the  anterior  and  lateral  fas- 
ciculus, is  broad,  thin,  and  quadrilateral:  it  is  placed  obliquely  between  the  cora- 
coid process  and  the  clavicle.  It  is  attached,  below,  to  the  upper  surface  of  the 
coracoid  process;  above,  to  the  oblique  ridge  on  the  under  surface  of  the  clavicle. 
Its  anterior  border  is  free;  its  posterior  border  is  joined  with  the  conoid  ligament, 
the  two  forming,  by  their  junction,  an  angle  projecting  backward. 

The  Conoid  Ligament  (ligamentum  conoideum),  the  posterior  and  medial  fasciculus, 
is  a  dense  band  of  fibers,  conical  in  form,  with  its  base  directed  upward.    It  is 

1  Humphry,  On  the  Human  Skeleton,  page  402. 


316 


SYNDESMOLOGY 


attached  by  its  apex  to  a  rough  impression  at  the  base  of  the  coracoid  process, 
medial  to  the  trapezoid  ligament;  above,  by  its  expanded  base,  to  the  coracoid 
tuberosity  on  the  under  surface  of  the  clavicle,  and  to  a  line  proceeding  medial- 
ward  from  it  for  1.25  cm.  These  ligaments  are  in  relation,  in  front,  with  the 
Subclavius  and  Deltoideus ;  behind,  with  the  Trapezius. 


Fig.  326. — The  left  shoulder  and  acromioclavicular  joints,  and  the  proper  ligaments  of  the  scapula. 

Movements. — The  movements  of  this  articulation  are  of  two  kinds:  (1)  a  gliding  motion  of 
the  articular  end  of  the  clavicle  on  the  acromion;  (2)  rotation  of  the  scapula  forward  and  back- 
ward upon  the  clavicle.  The  extent  of  this  rotation  is  limited  by  the  two  portions  of  the  coraco- 
clavicular  Ugament,  the  trapezoid  limiting  rotation  forward,  and  the  conoid  backward. 

The  acromioclavicular  joint  has  important  functions  in  the  movements  of  the  upper  extremity. 
It  has  been  well  pointed  out  by  Humphry,  that  if  there  had  been  no  joint  between  the  clavicle 
and  scapula,  the  circular  movement  of  the  scapula  on  the  ribs  (as  in  throwing  the  shoulders  back- 
ward or  forward)  would  have  been  attended  with  a  greater  alteration  in  the  direction  of  the 
shoulder  than  is  consistent  with  the  free  use  of  the  arm  in  such  positions,  and  it  would  have  been 
impossible  to  give  a  blow  straight  forward  with  the  fuU  force  of  the  arm;  that  is  to  say,  with  the 
combined  force  of  the  scapula,  arm,  and  forearm.  "This  joint,"  as  he  happily  says,  "is  so  adjusted 
as  to  enable  either  bone  to  turn  in  a  hinge-Uke  manner  upon  a  vertical  axis  drawn  through  the 
other,  and  it  permits  the  surfaces  of  the  scapula,  hke  the  baskets  in  a  roundabout  swing,  to  look 
the  same  way  in  every  position,  or  nearly  so."  Again,  when  the  whole  arch  formed  by  the  clavicle 
and  scapula  rises  and  falls  (in  elevation  or  depression  of  the  shoulder),  the  joint  between  these 
two  bones  enables  the  scapula  still  to  maintain  its  lower  part  in  contact  with  the  ribs. 


THE  LIGAMENTS   OF  THE   SCAPULA. 

The  ligaments  of  the  scapula  (Fig.  326)  are : 

Coracoacromial,  Superior  and  Inferior  Transverse. 

The  Coracoacromial  Ligament  {ligamentum  coracoacromiale) . — This  ligament  is  a 
strong  triangular  band,  extending  between  the  coracoid  process  and  the  acromion. 


HUMERAL  ARTICULATION  OR  SHOULDER-JOINT 


317 


It  is  attached,  by  its  apex,  to  the  summit  of  the  acromion  just  in  front  of  the 
articular  surface  for  the  clavicle;  and  by  its  broad  base  to  the  whole  length  of  the 
lateral  border  of  the  coracoid  process.  This  ligament,  together  with  the  coracoid 
process  and  the  acromion,  forms  a  vault  for  the  protection  of  the  head  of  the 
humerus.  It  is  in  relation,  above,  with  the  clavicle  and  under  surface  of  the  Del- 
toideus;  beloiv,  with  the  tendon  of  the  Supraspinatus,  a  bursa  being  interposed. 
Its  lateral  border  is  continuous  with  a  dense  lamina  that  passes  beneath  the  Del- 
toideus  upon  the  tendons  of  the  Supraspinatus  and  Infraspinatus.  The  ligament 
is  sometimes  described  as  consisting  of  two  marginal  bands  and  a  thinner  inter- 
vening portion,  the  two  bands  being  attached  respectively  to  the  apex  and  the 
base  of  the  coracoid  process,  and  joining  together  at  the  acromion.  When  the 
Pectoralis  minor  is  inserted,  as  occasionally  is  the  case,  into  the  capsule  of  the 
shoulder-joint  instead  of  into  the  coracoid  process,  it  passes  between  these  two 
bands,  and  the  intervening  portion  of  the  ligament  is  then  deficient. 

The  Superior  Transverse  Ligament  (ligamentum  transversum  scapulcB  swperius; 
transverse  or  suprascapular  ligavient). — This  ligament  converts  the  scapular  notch 
into  a  foramen.  It  is  a  thin  and  flat  fasciculus,  narrower  at  the  middle  than  at  the 
extremities,  attached  by  one  end  to  the  base  of  the  coracoid  process,  and  by  the 
other  to  the  medial  end  of  the  scapular  notch.  The  suprascapular  nerve  runs 
through  the  foramen;  the  transverse  scapular  vessels  cross  over  the  ligament. 
The  ligament  is  sometimes  ossified. 

The  Inferior  Transverse  Ligament  {ligamentum  transversum  scapula'  inferius; 
spinoglenoid  ligament).— This  ligament  is  a  weak  membranous  band,  situated 
behind  the  neck  of  the  scapula  and  stretching  from  the  lateral  border  of  the  spine 
to  the  margin  of  the  glenoid  cavity.  It  forms  an  arch  under  which  the  transverse 
scapular  vessels  and  suprascapular  nerve  enter  the  infraspinatous  fossa. 


in.    Humeral  Articulation  or  Shoulder- joint  (Articulatio  Humeri)  (Fig.  326). 

The  shoulder-joint  is  an  enarthrodial  or  ball-and-socket  joint.  The  bones 
entering  into  its  formation  are  the  hemispherical  head  of  the  humerus  and  the 
shallow  glenoid  cavity  of  the  scapula,  an  arrangement  which  permits  of  very 
considerable  movement,  while  the  joint  itself  is  protected  against  displacement 
by  the  tendons  which  surround  it.  The  ligaments  do  not  maintain  the  joint  sur- 
faces in  apposition,  because  when  the}'  alone  remain  the  humerus  can  be  separated 
to  a  considerable  extent  from  the  glenoid  cavit}';  their  use,  therefore,  is  to  limit 
the  amount  of  movement.  The  joint  is  protected  above  by  an  arch,  formed  by 
the  coracoid  process,  the  acromion,  and  the  coracoacromial  ligament.  The  artic- 
ular cartilage  on  the  head  of  the  humerus  is  thicker  at  the  center  than  at  the  cir- 
cumference, the  reverse  being  the  case  with  the  articular  cartilage  of  the  glenoid 
cavity.    The  ligaments  of  the  shoulder  are: 


'I       ^ 


The  Articular  Capsule. 
The  Coracohumeral. 


The  Glenohumeral. 

The  Transverse  Humeral. 


The  Glenoidal  Labrum.^ 


The  Articular  Capsule  (capsula  articularis;  capsular  ligament)  (Fig.  327). — The 
articular  capsule  completely  encircles  the  joint,  being  attached,  above,  to  the 
circumference  of  the  glenoid  cavity  beyond  the  glenoidal  labrum;  below,  to  the 
anatomical  neck  of  the  humerus,  approaching  nearer  to  the  articular  cartilage 
above  than  in  the  rest  of  its  extent.  It  is  thicker  above  and  below  than  elsewhere, 
and  is  so  remarkably  loose  and  lax,  that  it  has  no  action  in  keeping  the  bones  in 
contact,  but  allows  them  to  be  separated  from  each  other  more  than  2.5  cm.,  an 


'  The  long  tendon  of  origin  of  the  bicejjs  Ijrachii  also  acts  as  one  of  the  ligaments  of  this  joint.    See  the  observations 
on  page  287,  on  the  function  of  the  muscles  passing  over  more  than  one  joint. 


318 


SYNDESMOLOGY 


evident  provision  for  that  extreme  freedom  of  movement  which  is  pecuHar  to  this 
articulation.  It  is  strengthened,  above,  by  the  Supraspinatus;  below,  by  the  long 
head  of  the  Triceps  brachii ;  behind,  by  the  tendons  of  the  Infraspinatus  and  Teres 
minor;  and  in  front,  by  the  tendon  of  the  Subscapularis.  There  are  usually  three 
openings  in  the  capsule.  One  anteriorly,  below  the  coracoid  process,  establishes 
a  communication  between  the  joint  and  a  bursa  beneath  the  tendon  of  the  Sub- 
scapularis. The  second,  which  is  not  constant,  is  at  the  posterior  part,  where  an 
opening  sometimes  exists  between  the  joint  and  a  bursal  sac  under  the  tendon 
of  the  Infraspinatus.  The  third  is  between  the  tubercles  of  the  humerus,  for  the 
passage  of  the  long  tendon  of  the  Biceps  brachii. 

The  Coracohmneral  Ligament  {ligamentum  coracohwnerale) . — This  ligament  is 
a  broad  band  which  strengthens  the  upper  part  of  the  capsule.  It  arises  from 
the  lateral  border  of  the  coracoid  process,  and  passes  obliquely  downward  and 
lateralward  to  the  front  of  the  greater  tubercle  of  the  humerus,  blending  with  the 


Superior  transverse  Ligament 


m 


Transverse 
humeral 
ligament 

Prolongation  of 
synovial  mem- 
brane on  tendon 
of  Biceps  brachii 


m 

i 


Bursa 

under 

Svbscapularia 


Fia.  327. — Capsule  of  shoulder-joint  (distended).     Anterior  aspect. 

tendon  of  the  Supraspinatus.  This  ligament  is  intimately  united  to  the  capsule 
by  its  hinder  and  lower  border;  but  its  anterior  and  upper  border  presents  a  free 
edge,  which  overlaps  the  capsule. 

Glenohumeral  Ligaments. — In  addition  to  the  coracohumeral  ligament,  three 
supplemental  bands,  which  are  named  the  glenohumeral  ligaments,  strengthen 
the  capsule.  These  may  be  best  seen  by  opening  the  capsule  at  the  back  of  the 
joint  and  removing  the  head  of  the  humerus.  One  on  the  medial  side  of  the  joint 
passes  from  the  medial  edge  of  the  glenoid  cavity  to  the  lower  part  of  the  lesser 
tubercle  of  the  humerus.  A  second  at  the  lower  part  of  the  joint  extends  from 
the  under  edge  of  the  glenoid  cavity  to  the  under  part  of  the  anatomical  neck  of 
the  humerus.  A  third  at  the  upper  part  of  the  joint  is  fixed  above  to  the  apex 
of  the  glenoid  cavity  close  to  the  root  of  the  coracoid  process,  and  passing  down- 
ward along  the  medial  edge  of  the  tendon  of  the  Biceps  brachii,  is  attached  below 
to  a  small  depression  above  the  lesser  tubercle  of  the  humerus.    In  addition  to 


HUMERAL  ARTICULATION  OR  SHOULDER-JOINT 


319 


CONOID    LIGAMENT 


TRAPEZOID 
LIGAMENT 


RACOIO 
PROCESS 


these,  the  capsule  is  strengthened  in  front  by  two  bands  derived  from  the  tendons 
of  the  PectoraHs  major  and  Teres  major  respectively. 

The  Transverse  Humeral  Ligament  (Fig.  327)  is  a  broad  band  passing  from  the 
lesser  to  the  greater  tubercle  of  the  humerus,  and  always  limited  to  that  portion 
of  the  bone  which  lies  above  the  epiphysial  line.  It  converts  the  intertubercular 
groove  into  a  canal,  and  is  the  homologue  of  the  strong  process  of  bone  which 
connects  the  summits  of  the  two  tubercles  in  the  musk  ox. 

The  Glenoidal  Labrum  {labrimn  glenoidale;  glenoid  ligament)  is  a  fibrocartilaginous 
rim  attached  around  the  margin  of  the  glenoid  cavity.  It  is  triangular  on  section, 
the  base  being  fixed  to  the  circumference  of  the  cavity,  while  the  free  edge  is  thin 
and  sharp.  It  is  continuous  above  with  the  tendon  of  the  long  head  of  the  Biceps 
brachii,  w^hich  gives  off  two  fasciculi  to  blend  with  the  fibrous  tissue  of  the  labrum. 
It  deepens  the  articular  cavity,  and  protects  the  edges  of  the  bone. 

Synovial  Membrane. — The  synovial  membrane  is  reflected  from  the  margin  of  the  glenoid 
cavity  over  the  labrum;  it  is  then  reflected  over  the  inner  surface  of  the  capsule,  and  covers 
the  lower  part  and  sides  of  the  anatomical  neck  of  the 
humerus  as  far  as  the  articular  cartilage  on  the  head  of 
the  bone.  The  tendon  of  the  long  head  of  the  Biceps 
brachii  passes  through  the  capsule  and  is  enclosed  in  a 
tubular  sheath  of  synovial  membrane,  which  is  reflected 
upon  it  from  the  summit  of  the  glenoid  cavity  and  is 
continued  around  the  tendon  into  the  intertubercular 
groove  as  far  as  the  surgical  neck  of  the  humerus  (Fig. 
327).  The  tendon  thus  traverses  the  articulation,  but  it 
is  not  contained  within  the  synovial  cavity. 

Bursse.  —  The  bursse  in  the  neighborhood  of  the 
shoulder-joint  are  the  following:  (1)  A  constant  bursa 
is  situated  between  the  tendon  of  the  Subscapularis 
muscle  and  the  capsule;  it  communicates  with  the 
synovial  cavity  thi'ough  an  opening  in  the  front  of  the 
capsule;  (2)  a  bursa  which  occasionally  communicates 
with  the  joint  is  sometimes  found  between  the  tendon 
of  the  Infraspinatus  and  the  capsule;  (3)  a  large  bursa 
exists  between  the  under  surface  of  the  Deltoideus  and 
the  capsule,  but  does  not  communicate  with  the  joint; 
this  bursa  is  prolonged  under  the  acromion  and  coraco- 

acromial  ligament,  and  intervenes  between  these  structures  and  the  capsule;  (4)  a  large  bursa 
is  situated  on  the  summit  of  the  acromion;  (5)  a  bursa  is  frequently  found  between  the  cora- 
coid  process  and  the  capsule;  (6)  a  bursa  exists  beneath  the  Coracobrachialis;  (7)  one  lies 
between  the  Teres  major  and  the  long  head  of  the  Triceps  brachii;  (8)  one  is  placed  in  front  of, 
and  another  behind,  the  tendon  of  the  Latissimus  dorsi. 

The  muscles  in  relation  with  the  joint  are,  above,  the  Supraspinatus;  below,  the  long  head  of 
the  Triceps  brachii;  in  front,  the  Subscapularis;  behind,  the  Infraspinatus  and  Teres  minor;  within, 
the  tendon  of  the  long  head  of  the  Biceps  brachii.  The  Deltoideus  covers  the  articulation  in 
front,  behind,  and  laterally. 

The  arteries  supplying  the  joint  are  articular  branches  of  the  anterior  and  posterior  humeral 
circumflex,  and  transverse  scapular. 

The  nerves  are  derived  from  the  axillary  and  suprascapular. 

Movements. — The  shoulder-joint  is  capable  of  every  variety  of  movement,  flexion,  extension, 
abduction,  adduction,  circumduction,  and  rotation.  The  humerus  is  flexed  (drawn  forward) 
by  the  PectoraUs  major,  anterior  fibers  of  the  Deltoideus,  Coracobrachialis,  and  when  the  fore- 
arm is  flexed,  by  the  Biceps  brachii;  extended  (drawn  backward)  by  the  Latissimus  dorsi,  Teres 
major,  posterior  fibers  of  the  Deltoideus,  and,  when  the  forearm  is  extended,  by  the  Triceps 
brachii;  it  is  abducted  by  the  Deltoideus  and  Supraspinatus;  it  is  adduded  by  the  Subscapularis, 
PectoraUs  major,  Latissimus  dorsi,  and  Teres  major,  and  by  the  weight  of  the  limb;  it  is  rotated 
outward  by  the  Infraspinatus  and  Teres  minor;  and  it  is  rotated  inward  by  the  Subscapularis, 
Latissimus  dorsi,  Teres  major,  Pectoralis  major,  and  the  anterior  fibers  of  the  Deltoideus. 

The  most  striking  peculiarities  in  this  joint  are:  (1)  The  large  size  of  the  head  of  the  humerus 
in  comparison  with  the  depth  of  the  glenoid  cavity,  even  when  this  latter  is  supplemented  by  the 
glenoidal  labrum.  (2)  The  looseness  of  the  capsule  of  the  joint.  (3)  The  intimate  connection  of 
the  capsule  with  the  muscles  attached  to  the  head  of  the  humerus.  (4)  The  peculiar  relation  of 
the  tendon  of  the  long  head  of  the  Biceps  brachii  to  the  joint. 


Fig.  328. — Glenoid  fossa  of  right  side. 


320 


SYNDESMOLOGY 


It  is  in  consequence  of  the  relative  sizes  of  the  two  articular  surfaces,  and  the  looseness  Oi 
the  articular  capsule,  that  the  joint  enjoys  such  free  movement  in  all  directions.  When  thes& 
movements  of  the  arm  are  arrested  in  the  shoulder- joint  by  the  contact  of  the  bony  surfaces, 
and  by  the  tension  of  the  fibers  of  the  capsule,  together  with  that  of  the  muscles  acting  as  accessory 
ligaments,  the  arm  can  be  carried  considerably  farther  by  the  movements  of  the  scapula,  involv- 
ing, of  course,  motion  at  the  acromio-  and  sternoclavicular  joints.  These  joints  are  therefore 
to  be  regarded  as  accessory  structures  to  the  shoulder-joint  (see  pages  314  and  316).  The  extent 
of  the  scapular  movements  is  very  considerable,  especially  in  extreme  elevation  of  the  arm,  u 
movement  best  accomphshed  when  the  arm  is  thrown  somewhat  forward  and  outward,  because; 
the  margin  of  the  head  of  the  humerus  is  by  no  means  a  true  circle;  its  greatest  diameter  is  from 
the  intertubercular  groove,  downward,  medialward,  and  backward,  and  the  greatest  elevation 
of  the  arm  can  be  obtained  by  rolling  its  articular  surface  in  the  direction  of  this  measurement. 
The  great  width  of  the  central  portion  of  the  humeral  head  also  allows  of  very  free  horizontal 
movement  when  the  arm  is  raised  to  a  right  angle,  in  which  movement  the  arch  formed  by  the 
acromion,  the  coracoid  process  and  the  coracoacromial  ligament,  constitutes  a  sort  of  supple- 
mental articular  cavity  for  the  head  of  the  bone. 

The  looseness  of  the  capsule  is  so  great  that  the  arm  will  fall  about  2.5  cm.  from  the  scapula 
when  the  muscles  are  dissected  from  the  capsule,  and  an  opening  made  in  it  to  counteract  the 
atmospheric  pressure.  The  movements  of  the  joint,  therefore,  are  not  regulated  by  the  capsule 
so  much  as  by  the  surrounding  muscles  and  by  the  pressure  of  the  atmosphere,  an  arrangement 
which  "renders  the  movements  of  the  joint  much  more  easy  than  they  would  otherwise  have 
been,  and  permits  a  swinging,  pendulum-hke  vibration  of  the  limb  when  the  muscles  are  at  rest" 
(Humphry).  The  fact,  also,  that  in  all  ordinary  positions  of  the  joint  the  capsule  is  not  put  on 
the  stretch,  enables  the  arm  to  move  freely  in  all  directions.  Extreme  movements  are  checked 
by  the  tension  of  appropriate  portions  of  the  capsule,  as  well  as  by  the  interlocking  of  the  bones. 
Thus  it  is  said  that  "abduction  is  checked  by  the  contact  of  the  great  tuberosity  with  the  upper 
edge  of  the  glenoid  cavity;  adduction  by  the  tension  of  the  coracohumeral  ligament"  (Beaunis 
et  Bouchard).  Cleland'  maintains  that  the  limitations  of  movement  at  the  shoulder-joint  are 
due  to  the  structure  of  the  joint  itself,  the  glenoidal  labrum  fitting,  in  different  positions  of  the 
elevated  arm,  into  the  anatomical  neck  of  the  humerus. 

The  scapula  is  capable  of  being  moved  upward  and  downward,  forward  and  backward,  or,  by 
a  combination  of  these  movements,  circumducted  on  the  wall  of  the  chest.  The  muscles  which 
raise  the  scapula  are  the  upper  fibers  of  the  Trapezius,  the  Levator  scapula",  and  the  Rhomboidei; 
those  which  depress  it  are  the  lower  fibers  of  the  Trapezius,  the  Pectoralis  minor,  and,  through 
the  clavicle,  the  Subclavius.  The  scapula  is  drawn  backward  by  the  Rhomboidei  and  the  middle 
and  lower  fibers  of  the  Trapezius,  and  forward  by  the  Serratus  anterior  and  Pectoralis  minor, 
assisted,  when  the  arm  is  fixed,  by  the  Pectoralis  major.  The  mobility  of  the  scapula  is  very 
considerable,  and  greatly  assists  the  movements  of  the  arm  at  the  shoulder-joint.  Thus,  in 
raising  the  arm  from  the  side,  the  Deltoideus  and  Supraspinatus  can  only  lift  it  to  a  right  angle 
with  the  trunk,  the  fvuther  elevation  of  the  limb  being  effected  by  the  Trapezius  and  Serratus 
anterior  moving  the  scapula  on  the  wall  of  the  chest.  This  mobility  is  of  special  importance  in 
ankylosis  of  the  shoulder- joint,  the  movements  of  this  bone  compensating  to  a  veiy  great  extent 
for  the  immobility  of  the  joint. 

Cathcart^  has  pointed  out  that  in  abducting  the  arm  and  raising  it  above  the  head,  the  scapula 
rotates  throughout  the  whole  movement  with  the  exception  of  a  short  space  at  the  beginning 
and  at  the  end;  that  the  humerus  moves  on  the  scapula  not  only  while  passing  from  the  hanging 
to  the  horizontal  position,  but  also  in  travelling  upward  as  it  approaches  the  vertical  above; 
that  the  clavicle  moves  not  only  during  the  second  half  of  the  movement  but  in  the  first  as  well, 
though  to  a  less  extent — i.  e.,  the  scapula  and  clavicle  are  concerned  in  the  first  stage  as  well 
as  in  the  second;  and  that  the  humerus  is  partly  involved  in  the  second  as  well  as  chiefly  in  the 
first. 

The  intimate  union  of  the  tendons  of  the  Supraspinatus,  Infraspinatus,  Teres  minor  and 
Subscapularis  with  the  capsule,  converts  these  muscles  into  elastic  and  spontaneously  acting 
ligaments  of  the  joint. 

The  pecuhar  relations  of  the  tendon  of  the  long  head  of  the  Biceps  brachii  to  the  shoulder- 
joint  appear  to  subserve  various  purposes.  In  the  first  place,  by  its  connection  with  both  the 
shoulder  and  elbow  the  muscle  harmonizes  the  action  of  the  two  joints,  and  acts  as  an  elastic 
ligament  in  all  positions,  in  the  manner  previously  discussed  (see  page  287).  It  strengthens  the 
upper  part  of  the  articular  cavity,  and  prevents  the  head  of  the  humerus  from  being  pressed  up 
against  the  acromion,  when  the  Deltoideus  contracts;  it  thus  fixes  the  head  of  the  humerus  as 
the  center  of  motion  in  the  glenoid  cavity.  By  its  passage  along  the  intertubercular  groove  it 
assists  in  steadying  the  head  of  the  humerus  in  the  various  movements  of  the  arm.  When  the 
arm  is  raised  from  the  side  it  assists  the  Supraspinatus  and  Infraspinatus  in  rotating  the  head 
of  the  humerus  in  the  glenoid  cavity.  It  also  holds  the  head  of  the  bone  firmly  in  contact  with 
the  glenoid  cavity,  and  prevents  its  slipping  over  its  lower  edge,  or  being  displaced  by  the  action 
of  the  Latissimus  dorsi  and  Pectoralis  major,  as  in  climbing  and  many  other  movements. 


'  Journal  of  Anatomy  and  Physiology,  1867,  i,  85. 


»Ibid..  18S4,  vol.  xviii. 


ELBOW-JOINT 


321 


IV.     Elbow-joint  (Articulatio  Cubiti)  (Figs.  329,  330). 

The  elbow-joint  is  a  ginglymus  or  hinge-joint.  The  trochlea  of  the  humerus  is 
received  into  the  semilunar  notch  of  the  ulna,  and  the  capitulum  of  the  humerus 
articulates  with  the  fovea  on  the  head  of  the  radius.  The  articular  surfaces  are 
connected  together  by  a  capsule,  which  is  thickened  medially  and  laterally,  and, 
to  a  less  extent,  in  front  and  behind.  These  thickened  portions  are  usually  described 
as  distinct  ligaments  under  the  following  names: 

The  Anterior.  The  Ulnar  Collateral. 

The  Posterior.  The  Radial  Collateral. 


Fig. 


329. — Left  elbow-Joint,  showing  anterior  and 
ulnar  collateral  ligaments. 


FiQ.  330. — Left  elbow-joint,  showing  posterior  and 
radial  collateral  ligaments. 


The  Anterior  Ligament  (Fig.  329). — The  anterior  ligament  is  a  broad  and  thin 
fibrous  layer  covering  the  anterior  surface  of  the  joint.  It  is  attached  to  the  front 
of  the  medial  epicondyle  and  to  the  front  of  the  humerus  immediately  above  the 
coronoid  and  radial  fossse;  helow,  to  the  anterior  surface  of  the  coronoid  process 
of  the  ulna  and  to  the  annular  ligament  (page  324),  being  continuous  on  either 
side  with  the  collateral  ligaments.  Its  superficial  fibers  pass  obliquely  from  the 
medial  epicondyle  of  the  humerus  to  the  annular  ligament.  The  middle  fibers, 
vertical  in  direction,  pass  from  the  upper  part  of  the  coronoid  depression  and 
become  partly  blended  with  the  preceding,  but  are  inserted  mainly  into  the  anterior 
surface  of  the  coronoid  process.  The  deep  or  transverse  set  intersects  these  at 
right  angles.  This  ligament  is  in  relation,  in  front,  with  the  Brachialis,  except 
at  its  most  lateral  part. 
21 


322  ^^^^Br        SYNDESMOLOGY 


The  Posterior  Ligament  (Fig.  330). — This  posterior  ligament  is  thin  ana  mem 
branous,  and  consists  of  transverse  and  oblique  fibers.  Above,  it  is  attached  to 
the  humerus  immediately  behind  the  capitulum  and  close  to  the  medial  margin 
of  the  trochlea,  to  the  margins  of  the  olecranon  fossa,  and  to  the  back  of  the  lateral 
epicondyle  some  little  distance  from  the  trochlea.  Below,  it  is  fixed  to  the  upper 
and  lateral  margins  of  the  olecranon,  to  the  posterior  part  of  the  annular  ligament, 
and  to  the  ulna  behind  the  radial  notch.  The  transverse  fibers  form  a  strong  band 
which  bridges  across  the  olecranon  fossa;  under  cover  of  this  band  a  pouch  of 
synovial  membrane  and  a  pad  of  fat  project  into  the  upper  part  of  the  fossa  when 
the  joint  is  extended.  In  the  fat  are  a  few  scattered  fibrous  bundles,  which  pass 
from  the  deep  surface  of  the  transverse  band  to  the  upper  part  of  the  fossa.  This 
ligament  is  in  relation,  behind,  with  the  tendon  of  the  Triceps  brachii  and  the 
Anconeus. 

The  Ulnar  Collateral  Ligament  (ligamentum  collaterale  ulnare;  internal  lateral 
ligament)  (Fig.  329) . — This  ligament  is  a  thick  triangular  band  consisting  of  two 
portions,  an  anterior  and  posterior  united  by  a  thinner  intermediate  portion.  The 
anterior  portion,  directed  obliquely  forward,  is  attached,  a6o«e,  by  its  apex,  to  the 
front  part  of  the  medial  epicondyle  of  the  humerus;  and,  below,  by  its  broad  base 
to  the  medial  margin  of  the  coronoid  process.  The  posterior  portion,  also  of  trian- 
gular form,  is  attached,  above,  by  its  apex,  to  the  lower  and  back  part  of  the  medial 
epicondyle;  below,  to  the  medial  margin  of  the  olecranon.  Between  these  two 
bands  a  few  intermediate  fibers  descend  from  the  medial  epicondyle  to  blend  with 
a  transverse  band  which  bridges  across  the  notch  between  the  olecranon  and  the 
coronoid  process.  This  ligament  is  in  relation  with  the  Triceps  brachii  and  Flexor 
carpi  ulnaris  and  the  ulnar  nerve,  and  gives  origin  to  part  of  the  Flexor  digitorum 
sublimis. 

The  Radial  Collateral  Ligament  {ligamentum  collaterale  radiate;  external  lateral 
ligament)  (Fig.  330). — ^This  ligament  is  a  short  and  narrow  fibrous  band,  less  dis- 
tinct than  the  ulnar  collateral,  attached,  above,  to  a  depression  below  the  lateral 
epicondyle  of  the  humerus;  below,  to  the  annular  ligament,  some  of  its  most  pos- 
terior fibers  passing  over  that  ligament,  to  be  inserted  into  the  lateral  margin  of 
the  ulna.    It  is  intimately  blended  with  the  tendon  of  origin  of  the  Supinator. 

Synovial  Membrane  (Figs.  331,  332). — The  synovial  membrane  is  very  extensive.  It  extends 
from  the  margin  of  the  articular  siu"face  of  the  humerus,  and  lines  the  coronoid,  radial  and  olec- 
ranon fossae  on  that  bone;  it  is  reflected  over  the  deep  surface  of  the  capsule  and  forms  a  pouch 
between  the  radial  notch,  the  deep  surface  of  the  annular  ligament,  and  the  circumference  of  the 
head  of  the  radius.  Projecting  between  the  radius  and  ulna  into  the  cavity  is  a  crescentic  fold  of 
synovial  membrane,  suggesting  the  division  of  the  joint  into  two;  one  the  humeroradial,  the 
other  the  humeroulnar. 

Between  the  capsule  and  the  synovial  membrane  are  three  masses  of  fat:  the  largest,  over 
the  olecranon  fossa,  is  pressed  into  the  fossa  by  the  Triceps  brachii  during  the  flexion ;  the  second, 
over  the  coronoid  fossa,  and  the  third,  over  the  radial  fossa,  are  pressed  by  the  Brachialis  into 
their  respective  fossae  during  extension. 

The  muscles  in  relation  with  the  joint  are,  in  front,  the  Brachiahs;  behind,  the  Triceps  brachii 
and  Anconajus;  laterally,  the  Supinator,  and  the  common  tendon  of  origin  of  the  Extensor  muscles; 
medially,  the  common  tendon  of  origin  of  the  Flexor  muscles,  and  the  Flexor  carpi  ulnaris. 

The  arteries  supplying  the  joint  are  derived  from  the  anastomosis  between  the  profunda  and 
the  superior  and  inferior  ulnar  collateral  branches  of  the  brachial,  with  the  anterior,  posterior, 
and  interosseous  recurrent  branches  of  the  ulnar,  and  the  recurrent  branch  of  the  radial.  These 
vessels  form  a  complete  anastomotic  network  around  the  joint. 

The  nerves  of  the  joint  are  a  twig  from  the  ulnar,  as  it  passes  between  the  medial  condyle  and 
the  olecranon;  a  filament  from  the  musculocutaneous,  and  two  from  the  median. 

Movements. — The  elbow-joint  comprises  three  different  portions — viz.,  the  joint  between 
the  ulna  and  hmnerus,  that  between  the  head  of  the  radius  and  the  himierus,  and  the  proximal 
radioulnar  articulation,  described  below.  AU  these  articular  surfaces  are  enveloped  by  a  common 
synovial  membrane,  and  the  movements  of  the  whole  joint  should  be  studied  together.  The  com- 
bination of  the  movements  of  flexion  and  extension  of  the  forearm  with  those  of  pronation  and 
supination  of  the  hand,  which  is  ensured  by  the  two  being  performed  at  the  same  joint,  is  essential 
to  the  acciu-acy  of  the  various  minute  movements  of  the  hand. 


I 


ELBOW-JOINT 


323 


The  portion  of  the  joint  between  the  ukia  and  humerus  is  a  simple  hinge-joint,  and  allows  of 
movements  of  flexion  and  extension  only.  Owing  to  the  obUquity  of  the  trochlea  of  the  humerus, 
this  movement  does  not  take  place  in  the  antero-posterior  plane  of  the  body  of  the  humerus. 
When  the  forearm  is  extended  and  supinated,  the  axes  of  the  arm  and  forearm  are  not  in  the  same 
line;  the  arm  forms  an  obtuse  angle  with  the  forearm,  the  hand  and  forearm  being  directed  lateral- 
ward.  During  flexion,  however,  the  forearm  and  the  hand  tend  to  approach  the  middle  line  of 
the  body,  and  thus  enable  the  hand  to  be  easily  carried  to  the  face.  The  accurate  adaptation 
of  the  trochlea  of  the  humerus,  with  its  prominences  and  depressions,  to  the  semilunar  notch  of 
the  ulna,  prevents  any  lateral  movement.  Flexion  is  produced  by  the  action  of  the  Biceps  brachii 
and  Brachialis,  assisted  by  the  BrachioradiaUs  and  the  muscles  arising  from  the  medial  condyle 
of  the  humerus;  extension,  by  the  Triceps  brachii  and  Ancona?us,  assisted  by  the  Extensors  of 
the  wrist,  the  Extensor  digitorum  commimis,  and  the  Extensor  digiti  quinti  proprius. 


Fio.  331. — Capsule  of  elbow-joint  (distended). 
Anterior  aspect. 


Fig.  332. — Capsule  of  elbow-joint  (distended). 
Posterior  aspect. 


The  joint  between  the  head  of  the  radius  and  the  capitulum  of  the  humerus  is  an  arthrodial 
joint.  The  bony  surfaces  would  of  themselves  constitute  an  enarthrosis  and  allow  of  movement 
in  all  directions,  were  it  not  for  the  annular  ligament,  by  which  the  head  of  the  radius  is  boimd 
to  thr  radial  notch  of  the  ulna,  and  which  prevents  any  separation  of  the  two  bones  laterally. 
It  is  to  the  same  ligament  that  the  head  of  the  radius  owes  its  security  from  dislocation,  which 
would  otherwise  tend  to  occur,  from  the  shallowness  of  the  cup-Uke  surface  on  the  head  of  the 
radius.  In  fact,  but  for  this  ligament,  the  tendon  of  the  Biceps  brachii  would  be  hable  to  pull 
the  head  of  the  radius  out  of  the  joint.  The  head  of  the  radius  is  not  in  complete  contact  with 
the  capitulum  of  the  humerus  in  all  positions  of  the  joint.  The  capitulima  occupies  only  the 
anterior  and  inferior  surfaces  of  the  lower  end  of  the  humerus,  so  that  in  complete  extension  a 
part  of  the  radial  head  can  be  plainly  felt  projecting  at  the  back  of  the  articulation.  In  full 
flexion  the  movement  of  the  radial  head  is  hampered  by  the  compression  of  the  surrounding  soft 
parts,  so  that  the  freest  rotatory  movement  of  the  radius  on  the  humerus  (pronation  and  supina- 
tion) takes  place  in  semiflexion,  in  which  position  the  two  articular  surfaces  are  in  most  intimate 


524 


SYNDESMOLOGY 


contact.  Flexion  and  extension  of  the  elbow-joint  are  limited  by  the  tension  of  the  structures 
on  the  front  and  back  of  the  joint;  the  limitation  of  flexion  is  also  aided  by  the  soft  structures  of 
the  arm  and  forearm  coming  into  contact. 

In  any  position  of  flexion  or  extension,  the  radius,  carrying  the  hand  with  it,  can  be  rotated  in 
the  proximal  radioulnar  joint.  The  hand  is  directly  articulated  to  the  lower  surface  of  the  radius 
only,  and  the  ulnar  notch  on  the  lower  end  of  the  radius  travels  around  the  lower  end  of  the  ulna. 
The  latter  bone  is  excluded  from  the  wrist-joint  by  the  articular  disk.  Thus,  rotation  of  the  head 
of  the  radius  around  an  axis  passing  through  the  center  of  the  radial  head  of  the  humerus  imparts 
circular  movement  to  the  hand  through  a  very  considerable  arc. 


V.    Radioulnar  Articulations  (Articulatio  Radioulnaris). 


The  articulation  of  the  radius  with  the  ulna  is  effected  by  ligaments  which  co 
nect  together  the  extremities  as  well  as  the  bodies  of  these  bones.  The  ligaments 
may,  consequently,  be  subdivided  into  three  sets:  1,  those  of  the  proximal  radio- 
ulnar articulation;  2,  the  middle  radioulnar  ligaments;  3,  those  of  the  distal  radio- 
ulnar articulation. 

Proximal  Radioulnar  Articulation  (articulatio  radioulnaris  proximalis;  superior 
radioulnar  joint).— This  articulation  is  a  trochoid  or  pivot-joint  between  the 
circumference  of  the  head  of  the  radius  and  the  ring  formed  by  the  radial  notch 
of  the  ulna  and  the  annular  ligament. 

Head  of  radius    Quadrate  Semilunar 

(cut)  ligament  notch 


Annular  ligament 

Radial 


Olecranon  (ciii) 


Fig.  333. — Annular  ligament  of  radius,  from  above.    The  head  of  the  radius  has  been  sawn  off  and  the  bone 

dislodged  from  the  ligament. 


The  Annular  Ligament  {ligamentum  annulare  radii;  orbicular  ligament)  (Fig.  333). 
— This  ligament  is  a  strong  band  of  fibers,  which  encircles  the  head  of  the  radius, 
and  retains  it  in  contact  with  the  radial  notch  of  the  ulna.  It  forms  about  four- 
fifths  of  the  osseo-fibrous  ring,  and  is  attached  to  the  anterior  and  posterior  margins 
of  the  radial  notch ;  a  few  of  its  lower  fibers  are  continued  around  below  the  cavity 
and  form  at  this  level  a  complete  fibrous  ring.  Its  upper  border  blends  with  the 
anterior  and  posterior  ligaments  of  the  elbow,  while  from  its  lower  border  a  thin 
loose  membrane  passes  to  be  attached  to  the  neck  of  the  radius;  a  thickened  band 
which  extends  from  the  inferior  border  of  the  annular  ligament  below  the  radial 
notch  to  the  neck  of  the  radius  is  known  as  the  quadrate  ligament.  The  superficial 
surface  of  the  annular  ligament  is  strengthened  by  the  radial  collateral  ligament 
of  the  elbow,  and  affords  origin  to  part  of  the  Supinator.  Its  deep  surface  is  smooth, 
and  lined  by  synovial  membrane,  which  is  continuous  with  that  of  the  elbow-joint. 


I 
I 


II 


RADIOULNAR  ARTICULATIONS  325 

Movements. — The  movements  allowed  in  this  articulation  are  limited  to  rotatory  movements 
of  the  head  of  the  radius  within  the  ring  formed  by  the  annular  ligament  and  the  radial  notch 
of  the  ulna;  rotation  forward  being  called  pronation;  rotation  backward,  supination.  Supination 
is  performed  by  the  Biceps  brachii  and  Supinator,  assisted  to  a  slight  extent  by  the  Extensor 
muscles  of  the  thumb.    Pronation  is  performed  by  the  Pronator  teres  and  Pronator  quadratus. 

Middle  Radioulnar  Union. — The  shafts  of  the  radius  and  ulna  are  connected 
by  the  Oblique  Cord  and  the  Interosseous  Membrane. 

The  Oblique  Cord  {chorda  ohliqua;  oblique  ligament)  (Fig.  329). — The  oblique 
cord  is  a  small,  flattened  band,  extending  downward  and  lateral  ward,  from  the 
lateral  side  of  the  tubercle  of  the  ulna  at  the  base  of  the  coronoid  process  to  the 
radius  a  little  below  the  radial  tuberosity.  Its  fibers  run  in  the  opposite  direction 
to  those  of  the  interosseous  membrane.    It  is  sometimes  wanting. 

The  Interosseous  Membrane  {membrana  interossea  antebrachii) . — The  interosseous 
membrane  is  a  broad  and  thin  plane  of  fibrous  tissue  descending  obliquely  down- 
ward and  medialward,  from  the  interosseous  crest  of  the  radius  to  that  of  the  ulna; 
the  lower  part  of  the  membrane  is  attached  to  the  posterior  of  the  two  lines  into 
which  the  interosseous  crest  of  the  radius  divides.  It  is  deficient  above,  commencing 
about  2.5  cm.  beneath  the  tuberosity  of  the  radius;  is  broader  in  the  middle  than 
at  either  end ;  and  presents  an  oval  aperture  a  little  above  its  lower  margin  for  the 
passage  of  the  volar  interosseous  vessels  to  the  back  of  the  forearm.  This  mem- 
brane serves  to  connect  the  bones,  and  to  increase  the  extent  of  surface  for  the 
attachment  of  the  deep  muscles.  Between  its  upper  border  and  the  oblique  cord 
is  a  gap,  through  which  the  dorsal  interosseous  vessels  pass.  Two  or  three  fibrous 
bands  are  occasionally  found  on  the  dorsal  surface  of  this  membrane;  they  descend 
obliquely  from  the  ulna  toward  the  radius,  and  have  consequently  a  direction 
contrary  to  that  of  the  other  fibers.  The  membrane  is  in  relation,  in  front,  by 
its  upper  three-fourths,  with  the  Flexor  pollicis  longus  on  the  radial  side,  and  with 
the  Flexor  digitorum  profundus  on  the  ulnar,  lying  in  the  interval  between  which 
are  the  volar  interosseous  vessels  an(J  nerve;  by  its  lower  fourth  with  the  Pronator 
quadratus;  behind,  with  the  Supinator,  Abductor  pollicis  longus.  Extensor  pollicis 
brevis.  Extensor  pollicis  longus,  Extensor  indicis  proprius;  and,  near  the  wrist, 
•  with  the  volar  interosseous  artery  and  dorsal  interosseous  nerve. 

Distal  Radioulnar  Articulation  (articidatio  radioulnaris  distalis;  inferior  radio- 
ulnar joint). — This  is  a  pivot-joint  formed  between  the  head  of  the  ulna  and  the 
uhiar  notch  on  the  lower  end  of  the  radius.  The  articular  surfaces  are  connected 
together  by  the  follo'^ving  ligaments: 

The  Volar  Radioulnar.  The  Dorsal  Radioulnar. 

The  Articular  Disk. 

The  Volar  Radioulnar  Ligament  {anterior  radioulnar  ligament)  (Fig.  334). — This 
ligament  is  a  narrow  band  of  fibers  extending  from  the  anterior  margin  of  the  ulnar 
notch  of  the  radius  to  the  front  of  the  head  of  the  ulna. 

The  Dorsal  Radioulnar  Ligament  {posterior  radioulnar  ligament)  (Fig.  335). — 
This  ligament  extends  between  corresponding  surfaces  on  the  dorsal  aspect  of  the 
articulation. 

The  Articular  Disk  {discus  articularis;  triangular  fibrocartilage)  (Fig.  336). — The 
articular  disk  is  triangular  in  shape,  and  is  placed  transversely  beneath  the  head 
of  the  ulna,  binding  the  lower  ends  of  the  ulna  and  radius  firmly  together.  Its 
periphery  is  thicker  than  its  center,  which  is  occasionally  perforated.  It  is  attached 
by  its  apex  to  a  depression  between  the  styloid  process  and  the  head  of  the  ulna; 
and  by  its  base,  which  is  thin,  to  the  prominent  edge  of  the  radius,  which  separates 
the  ulnar  notch  from  the  carpal  articular  surface.  Its  margins  are  united  to  the 
ligaments  of  the  wrist-joint.  Its  upper  surface,  smooth  and  concave,  articulates 
with  the  head  of  the  ulna,  forming  an  arthrodial  joint;  its  under  surface,  also  con- 


I- 


326 


SYNDESMOLOGY 


cave  and  smooth,  forms  part  of  the  wrist-joint  and  articulates  with  the  trianguh 
bone  and  medial  part  of  the  lunate.    Both  surfaces  are  clothed  by  synovial  mem-^ 
brane;  the  upper,  by  that  of  the  distal  radioulnar  articulation,  the  under,  by  that 
of  the  wrist. 


Distal  radio-vXnar 
articulation 

Wrist-joint 


IrUercarpal  artictdaiions 


Pisohamate  ligament 
Pisometacarpal  ligament 

Carpometacar'pal 
articulaiions 


Fig.  334. — Ligaments  of  wrist.     Anterior  view 

Synovial  Membrane  (Fig.  336). — The  synovial  membrane  of  this  articulation  is  extremely 
loose,  and  extends  upward  as  a  recess  {recessus  sacciformis)  between  the  radius  and  the  ulna. 


Distal  radio-vlnar, 
articulation 

Wrist-joint 


Inlercarpal  articvlations 


Carpometacarpcd 
articidationa 


Fig.  335. — Ligaments  of  wrist.     Posterior  view. 


Movements. — The  movements  in  the  distal  radioulnar  articulation  consist  of  rotation  of  the 
lower  end  of  the  radius  around  an  axis  which  passes  through  the  center  of  the  head  of  the  ulna. 
When  the  radius  rotates  forward,  'pronation  of  the  forearm  and  hand  is  the  result;  and  when  back- 
ward, supination.    It  will  thus  be  seen  that  in  pronation  and  supination  the  radius  describes  the 


RADIOCARPAL  ARTICULATION 


WRIST-JOINT 


segment  of  a  cone,  the  axis  of  which  extends  from  the  center  of  the  head  of  the  radius  to  the 
middle  of  the  head  of  the  ulna.  In  this  movement  the  head  of  the  ulna  is  not  stationary,  but 
describes  a  curve  in  a  direction  opposite  to  that  taken  by  the  head  of  the  radius.  This,  however, 
is  not  to  be  regarded  as  a  rotation  of  the  ulna — the  curve  which  the  head  of  this  bone  describes 
is  due  to  a  combined  antero-posterior  and  rotatory  movement,  the  former  taking  place  almost 
entirely  at  the  elbow-joint,  the  latter  at  the  shoulder-joint. 


Wrist-joint 


Madial  collateral 
ligament 


Distal  radioulnar 
articulation 

Articular  disc 

Ulnar  collateral  ligament 


—  Pisiform 


Fig.  336. — Vertical  section  through  the  articulations  at  the  wrist,  showing  the  synovial  cavities. 


VI. 


Radiocarpal  Articulation  or  Wrist-joint  (Articulatio  Radiocarpea) 

(Figs.  334,  335). 


The 


wrist-joint  is  a  condyloid  articulation.  The  parts  forming  it  are  the  lower 
end  of  the  radius  and  under  surface  of  the  articular  disk  above;  and  the  navicular, 
lunate,  and  triangular  bones  below.  The  articular  surface  of  the  radius  and  the 
under  surface  of  the  articular  disk  form  together  a  transversely  elliptical  concave 
surface,  the  receiving  cavity.  The  superior  articular  surfaces  of  the  navicular, 
lunate,  and  triangular  form  a  smooth  convex  surface,  the  condyle,  which  is  received 
into  the  concavity.  The  joint  is  surrounded  by  a  capsule,  strengthened  by  the 
following  ligaments: 


The  Volar  Radiocarpal. 
The  Dorsal  Radiocarpal. 


The  Ulnar  Collateral. 
The  Radial  Collateral. 


The  Volar  Radiocarpal  Ligament  (ligamentum  radiocarpeum  volare;  anterior  liga- 
ment) (Fig.  334). — This  ligament  is  a  broad  membranous  band,  attached  above 
to  the  anterior  margin  of  the  lower  end  of  the  radius,  to  its  styloid  process,  and  to 
the  front  of  the  lower  end  of  the  ulna;  its  fibers  pass  downward  and  medialward 
to  be  inserted  into  the  volar  surfaces  of  the  navicular,  lunate,  and  triangular 
bones,  some  being  continued  to  the  capitate.  In  addition  to  this  broad  mem- 
brane, there  is  a  rounded  fasciculus,  superficial  to  the  rest,  which  reaches  from  the 
base  of  the  styloid  process  of  the  ulna  to  the  lunate  and  triangular  bones.  The 
ligament  is  perforated  by  apertures  for  the  passage  of  vessels,  and  is  in  relation, 
in  front,  with  the  tendons  of  the  Flexor  digitorum  profundus  and  Flexor  pollicis 


328  SYNDESMOLOGY 

longus;  behind,  it  is  closely  adherent  to  the  anterior  border  of  the  articular  disk 
of  the  distal  radioulnar  articulation.  _■ 

The  Dorsal  Radiocarpal  Ligament  iligamentum  radiocarpeiim  dorsale;  'posteriorWm 
ligament)  (Fig.  335). — The  dorsal  radiocarpal  ligament  less  thick  and  strong  than 
the  volar,  is  attached,  above,  to  the  posterior  border  of  the  lower  end  of  the  radius; 
its  fibers  are  directed  obliquely  downward  and  medialward,  and  are  fixed,  6eZo2/;,M| 
to  the  dorsal  surfaces  of  the  navicular,  lunate,  and  triangular,  being  continuous 
with  those  of  the  dorsal  intercarpal  ligaments.  It  is  in  relation,  behind,  with  the 
Extensor  tendons  of  the  fingers;  m  front,  it  is  blended  with  the  articular  disk. 

The  Ulnar  Collateral  Ligament  (ligamentum  collaterale  carpi  ulnar e;  internal 
lateral  ligament)  (Fig.  334). — The  ulnar  collateral  ligament  is  a  rounded  cord, 
attached  above  to  the  end  of  the  styloid  process  of  the  ulna,  and  dividing  below 
into  two  fasciculi,  one  of  which  is  attached  to  the  medial  side  of  the  triangular 
bone,  the  other  to  the  pisiform  and  transverse  carpal  ligament. 

The  Radial  Collateral  Ligament  {ligamentum  collaterale  carpi  radiale;  external 
lateral  ligament)  (Fig.  335). — The  radial  collateral  ligament  extends  from  the  tip 
of  the  styloid  process  of  the  radius  to  the  radial  side  of  the  navicular,  some  of  its 
fibers  being  prolonged  to  the  greater  multangular  bone  and  the  transverse  carpal 
ligament.  It  is  in  relation  with  the  radial  artery,  which  separates  the  ligament 
from  the  tendons  of  the  Abductor  pollicis  longus  and  Extensor  pollicis  brevis. 

Sjoiovial  Membrane  (Fig.  33G). — The  synovial  membrane  lines  the  deep  surfaces  of  the  hga- 
ments  above  described,  extending  from  the  margin  of  the  lower  end  of  the  radius  and  articular 
disk  above  to  the  margins  of  the  articular  surfaces  of  the  carpal  bones  below.  It  is  loose  and 
lax,  and  presents  numerous  folds,  especially  behind. 

The  wrist-joint  is  covered  in  front  by  the  Flexor,  and  behind  by  the  Extensor  tendons. 

The  arteries  supplying  the  joint  are  the  volar  and  dorsal  carpal  branches  of  the  radial  and 
ulnar,  the  volar  and  dorsal  metacarpals,  and  some  ascending  branches  from  the  deep  volar  arch. 

The  nerves  are  derived  from  the  ulnar  and  dorsal  interosseous. 

Movements. — The  movements  permitted  in  this  joint  are  flexion,  extension,  abduction,  adduc- 
tion, and  circumduction.  They  will  be  studied  with  those  of  the  carpus,  with  which  they  are 
combined. 

Vn.    Intercarpal  Articulations  (Articulationes  Intercarpeae ;  Articulations 

of  the  Carpus). 

These  articulations  may  be  subdivided  into  three  sets: 

1.  The  Articulations  of  the  Proximal  Row  of  Carpal  Bones. 

2.  The  Articulations  of  the  Distal  Row  of  Carpal  Bones. 

3.  The  Articulations  of  the  Two  Rows  with  each  Other. 

Articulations  of  the  Proximal  Row  of  Carpal  Bones. — These  are  arthrodial 
joints.  The  navicular,  lunate,  and  triangular  are  connected  by  dorsal,  volar,  and 
interosseous  ligaments. 

The  Dorsal  Ligaments  (ligamenta  intercarpea  dorsalia). — The  dorsal  ligaments, 
two  in  number,  are  placed  transversely  behind  the  bones  of  the  first  row;  they 
connect  the  navicular  and  lunate,  and  the  lunate  and  triangular. 

The  Volar  ligaments  {ligamenta  intercarpea  volaria;  palmar  ligaments). — The  volar 
ligaments,  also  two,  connect  the  navicular  and  lunate,  and  the  lunate  and  trian- 
gular; they  are  less  strong  than  the  dorsal,  and  placed  very  deeply  behind  the 
Flexor  tendons  and  the  volar  radiocarpal  ligament. 

The  Interosseous  Ligaments  {ligamenta  intercarpea  interossea)  (Fig.  336). — The 
interosseous  ligaments  are  two  narrow  bundles,  one  connecting  the  lunate  with 
the  navicular,  the  other  joining  it  to  the  triangular.  They  are  on  a  level  with  the 
superior  surfaces  of  these  bones,  and  their  upper  surfaces  are  smooth,  and  form 
part  of  the  convex  articular  surface  of  the  wrist-joint. 


INTERCARPAL  ARTICULATIONS  32? 

The  ligaments  connecting  the  pisiform  bone  are  the  articular  capsule  and  the 
two  volar  ligaments. 

The  articular  capsule  is  a  thin  membrane  which  connects  the  pisiform  to  the 
triangular;  it  is  lined  by  synovial  membrane. 

The  two  volar  ligaments  are  strong  fibrous  bands;  one,  the  pisohamate  ligament,- 
IB  connects  the  pisiform  to  the  hamate,  the  other,  the  pisometacarpal  ligament,  joins 
the  pisiform  to  the  base  of  the  fifth  metacarpal  bone  (Fig.  334).  These  ligaments 
are,  in  reality,  prolongations  of  the  tendon  of  the  Flexor  carpi  ulnaris. 

IH  Articulations  of  the  Distal  Row  of  Carpal  Bones. — These  also  are  arthrodial 
^■joints;  the  bones  are  connected  by  dorsal,  volar,  and  interosseous  ligaments. 

The  Dorsal  Ligaments  {ligamenta  intercarpea  dorsalia). — The  dorsal  ligaments, 
three  in  number,  extend  transversely  from  one  bone  to  another  on  the  dorsal 
surface,  connecting  the  greater  with  the  lesser  multangular,  the  lesser  multangular 
with  the  capitate,  and  the  capitate  with  the  hamate. 

The  Volar  Ligaments  {ligamenta  intercarpea  volaria;  palmar  ligaments). — The 
volar  ligaments,  also  three,  have  a  similar  arrangement  on  the  volar  surface. 

The  Interosseous  Ligaments  (ligamenta  intercarpea  interossea). — The  three  inter- 
osseous ligaments  are  much  thicker  than  those  of  the  first  row;  one  is  placed  be- 
tween the  capitate  and  the  hamate,  a  second  between  the  capitate  and  the  lesser 
multangular,  and  a  third  between  the  greater  and  lesser  multangulars.  The  first 
is  much  the  strongest,  and  the  third  is  sometimes  wanting. 

Articulations  of  the  Two  Rows  of  Carpal  Bones  with  Each  Other. — The  joint 
between  the  navicular,  lunate,  and  triangular  on  the  one  hand,  and  the  second 
row  of  carpal  bones  on  the  other,  is  named  the  midcarpal  joint,  and  is  made  up  of 
three  distinct  portions:  in  the  center  the  head  of  the  capitate  and  the  superior 
surface  of  the  hamate  articulate  with  the  deep  cup-shaped  cavity  formed  by  the 
navicular  and  lunate,  and  constitute  a  sort  of  ball-and-socket  joint.  On  the 
radial  side  the  greater  and  lesser  multangulars  articulate  with  the  navicular,  and 
on  the  ulnar  side  the  hamate  articulates  with  the  triangular,  forming  gliding  joints. 

The  ligaments  are:  volar,  dorsal,  ulnar  and  radial  collateral. 

The  Volar  Ligaments  {ligamenta  intercarpea  volaria;  anterior  or  palmar  ligaments). 
— The  volar  ligaments  consist  of  short  fibers,  which  pass,  for  the  most  part,  from 
the  volar  surfaces  of  the  bones  of  the  first  row  to  the  front  of  the  capitate. 

The  Dorsal  Ligaments  {ligamenta  intercarpea  dorsalia;  posterior  ligaments). — 
The  dorsal  ligaments  consist  of  short,  irregular  bundles  passing  between  the  dorsal 
surfaces  of  the  bones  of  the  first  and  second  rows. 

The  Collateral  Ligaments  (lateral  ligaments)  .—The  collateral  ligaments  are  very 
short;  one  is  placed  on  the  radial,  the  other  on  the  ulnar  side  of  the  carpus;  the 
former,  the  stronger  and  more  distinct,  connects  the  navicular  and  greater  mul- 
tangular, the  latter  the  triangular  and  hamate;  they  are  continuous  with  the 
collateral  ligaments  of  the  wrist-joint.  In  addition  to  these  ligaments,  a  slender 
interosseous  band  sometimes  connects  the  capitate  and  the  navicular. 

Synovial  Membrane. — The  synovial  membrane  of  the  carpus  is  very  extensive  (Fig.  336), 
and  bounds  a  synovial  cavity  of  very  irregular  shape.  The  upper  portion  of  the  cavity  inter- 
venes between  the  under  surfaces  of  the  navicular,  lunate,  and  triangular  bones  and  the  upper 
surfaces  of  the  bones  of  the  second  row.  It  sends  two  prolongations  upward — between  the  navic- 
ular and  lunate,  and  the  lunate  and  triangular — and  three  prolongations  downward  between 
the  four  bones  of  the  second  row.  The  prolongation  between  the  greater  and  lesser  multangulars, 
or  that  between  the  lesser  multangular  and  capitate,  is,  owing  to  the  absence  of  the  interosseous 
ligament,  often  continuous  with  the  cavity  of  the  carpometacarpal  joints,  sometimes  of  the 
second,  third,  fourth,  and  fifth  metacarpal  bones,  sometimes  of  the  second  and  third  only.  In 
the  latter  condition  the  joint  between  the  hamate  and  the  fourth  and  fifth  metacarpal  bones 
has  a  separate  synovial  membrane.  The  synovial  cavities  of  these  joints  are  prolonged  for  a 
short  distance  between  the  bases  of  the  metacarpal  bones.  There  is  a  separate  synovial  mem- 
brane between  the  pisiform  and  triangular. 


330  -^^^  SYNDESMOLOGY 

Movements. — The  articulation  of  the  hand  and  wrist  considered  as  a  whole  involves  four 
articular  surfaces:  (a)  the  inferior  surfaces  of  the  radius  and  articular  disk;  (6)  the  superior 
surfaces  of  the  navicular,  lunate,  and  triangular,  the  pisiform  having  no  essential  part  in  the 
movement  of  the  hand;  (c)  the  S-shaped  surface  formed  by  the  inferior  surfaces  of  the  navicular, 
lunate,  and  triangular;  (d)  the  reciprocal  surface  formed  by  the  upper  surfaces  of  the  bones  of 
the  second  row.  These  four  surfaces  form  two  joints:  (1)  a  proximal,  the  wrist-joint  proper; 
and  (2)  a  distal,  the  mid-carpal  joint. 

1.  The  wrist-joint  proper  is  a  true  condyloid  articulation,  and  therefore  all  movements  but 
rotation  are  permitted.  Flexion  and  extension  are  the  most  free,  and  of  these  a  greater  amount 
of  extension  than  of  flexion  is  permitted,  since  the  articulating  surfaces  extend  farther  on  the  dorsal 
than  on  the  volar  surfaces  of  the  carpal  bones.  In  this  movement  the  carpal  bones  rotate  on  a 
transverse  axis  drawn  between  the  tips  of  the  styloid  processes  of  the  radius  and  ulna.  A  certain 
amount  of  adduction  (or  ulnar  flexion)  and  abduction  (or  radial  flexion)  is  also  permitted.  The 
former  is  considerably  greater  in  extent  than  the  latter  on  account  of  the  shortness  of  the  styloid 
process  of  the  ulna,  abduction  being  soon  Hmited  by  the  contact  of  the  styloid  process  of  the 
radius  with  the  greater  multangular.  In  this  movement  the  carpus  revolves  upon  an  antero- 
posterior axis  drawn  through  the  center  of  the  wrist.^  Finally,  circumduction  is  permitted  by 
the  combined  and  consecutive  movements  of  adduction,  extension,  abduction,  and  flexion.  No 
rotation  is  possible,  but  the  effect  of  rotation  is  obtained  by  the  pronation  and  supination  of  the 
radius  on  the  ulna.  The  movement  oi  flexion  is  performed  by  the  Flexor  carpi  radiaUs,  the  Flexor 
carpi  ulnaris,  and  the  Palmaris  longus;  extension  by  the  Extensores  carpi  radiales  longus  and 
brevis  and  the  Extensor  carpi  ulnaris;  adduction  (ulnar  flexion)  by  the  Flexor  carpi  ulnaris  and 
the  Extensor  carpi  ulnaris;  and  abduction  (radial  flexion)  by  the  Abductor  poUicis  longus,  the 
Extensors  of  the  thumb,  and  the  Extensores  carpi  radiales  longus  and  brevis  and  the  Flexor  carpi 
radiaUs.  When  the  fingers  are  extended,  flexion  of  the  wrist  is  performed  by  the  Flexores  carpi 
radialis  and  ulnaris  and  extension  is  aided  by  the  Extensor  digitorum  communis.  When  the 
fingers  are  flexed,  flexion  of  the  wrist  is  aided  by  the  Flexores  digitorum  sublimis  and  profundus, 
and  extension  is  performed  by  the  Extencores  carpi  radiales  and  ulnaris. 

2.  The  chief  movements  permitted  in  the  mid-carpal  joint  are  flexion  and  extension  and  a 
slight  amount  of  rotation.  In  flexion  and  extension,  which  are  the  movements  most  freely  enjoyed, 
the  greater  and  lesser  multangulars  oh  the  radial  side  and  the  hamate  on  the  ulnar  side  glide 
forward  and  backward  on  the  navicular  and  triangular  respectively,  while  the  head  of  the  capitate 
and  the  superior  surface  of  the  hamate  rotate  in  the  cup-shaped  cavity  of  the  navicular  and 
lunate.  Flexion  at  this  joint  is  freer  than  extension.  A  very  trifling  amount  of  rotation  is  also 
permitted,  the  head  of  the  capitate  rotating  around  a  vertical  axis  drawn  through  its  own  center, 
while  at  the  same  time  a  sUght  ghding  movement  takes  place  in  the  lateral  and  medial  portions 
of  the  joint. 

Vm.    Carpometacarpal  Articulations  (Articulationes  Carpometacarpese). 

Carpometacarpal  Articulation  of  the  Thumb  {articulatio  carpometacarpea  pollicis). 
— This  is  a  joint  of  reciprocal  reception  between  the  first  metacarpal  and  the 
greater  multangular;  it  enjoys  great  freedom  of  movement  on  account  of  the 
configuration  of  its  articular  surfaces,  which  are  saddle-shaped.  The  joint  is  sur- 
roimded  by  a  capsule,  which  is  thick  but  loose,  and  passes  from  the  circumference 
of  the  base  of  the  metacarpal  bone  to  the  rough  edge  bounding  the  articular  surface 
of  the  greater  multangular;  it  is  thickest  laterally  and  dorsally,  and  is  lined  by 
synovial  membrane. 

Movements. — In  this  articulation  the  movements  permitted  are  flexion  and  extension  in  the 
plane  of  the  palm  of  the  hand,  abduction  and  adduction  in  a  plane  at  right  angles  to  the  palm, 
circumduction,  and  opposition.  It  is  by  the  movement  of  opposition  that  the  tip  of  the  thumb 
is  brought  into  contact  with  the  volar  surfaces  of  the  slightly  flexed  fingers.  This  movement  is 
effected  through  the  medium  of  a  small  sloping  facet  on  the  anterior  Up  of  the  saddle-shaped 
articular  surface  of  the  greater  multangular.  The  Flexor  muscles  pull  the  corresponding  part 
of  the  articular  surface  of  the  metacarpal  bone  on  to  this  facet,  and  the  movement  of  opposition 
is  then  carried  out  by  the  Adductors. 

Flexion  of  this  joint  is  produced  by  the  Flexores  poUicis  longus  and  brevis,  assisted  by  the 
Opponens  pollicis  and  the  Adductor  pollicis.  Extension  is  effected  mainly  by  the  abductor 
pollicis  longus,  assisted  by  the  Extensores  polhcis  longus  and  brevis.  Adduction  is  carried  out 
by  the  Adductor;  abduction  mainly  by  the  Abductores  polhcis  longus  and  brevis,  assisted  by  the 
Extensors. 

>  H.  M.  Johnaton  (Journal  of  Anatomy  and  Physiology,  vol.  xli)  maintains  that  n  ulnar  and  radial  flexion  only 
slight  lateral  movement  occurs  at  the  radiocarpal  joint,  and  that  in  cornglete  flexion  and  extension  of  the  hand  there 
is  a  small  degree  of  ulnar  flexion  at  the  radiocarpal  joint. 


^V  ISSTEtCMETAfJAKlrAL  AlCTlLuLATlUNS  661 

Articulations  of  the  Other  Four  Metacarpal  Bones  with  the  Carpus  {articulationes 
carpometacarpecp). — The  joints  between  the  carpus  and  the  second,  third,  fourth, 
and  fifth  metacarpal  bones  are  arthrodial.  The  bones  are  united  by  dorsal,  volar, 
and  interosseous  ligaments. 

The  Dorsal  Ligaments  {ligamenta  carpometacarpea  dorsalia) . — The  dorsal  ligaments, 
the  strongest  and  most  distinct,  connect  the  carpal  and  metacarpal  bones  on  their 
dorsal  surfaces.  The  second  metacarpal  bone  receives  two  fasciculi,  one  from  the 
greater,  the  other  from  the  lesser  multangular;  the  third  metacarpal  receives  two, 
one  each  from  the  lesser  multangular  and  capitate;  the  fourth  two,  one  each  from 
the  capitate  and  hamate;  the  fifth  receives  a  single  fasciculus  from  the  hamate, 
and  this  is  continuous  with  a  similar  ligament  on  the  volar  surface,  forming  an 
incomplete  capsule. 

The  Volar  Ligaments  (ligamenta  carpometacarpea  volaria;  palmar  ligaments). — 
The  volar  ligaments  have  a  somewhat  similar  arrangement,  with  the  exception 
of  those  of  the  third  metacarpal,  which  are  three  in  number :  a  lateral  one  from  the 
greater  multangular,  situated  superficial  to  the  sheath  of  the  tendon  of  the  Flexor 
carpi  radialis;  and  intermediate  one  from  the  capitate;  and  a  medial  one  from 
the  hamate. 

The  Interosseous  Ligaments. — The  interosseous  ligaments  consist  of  short,  thick 
fibers,  and  are  limited  to  one  part  of  the  carpometacarpal  articulation;  they  con- 
nect the  contiguous  inferior  angles  of  the  capitate  and  hamate  with  the  adjacent 
surfaces  of  the  third  and  fourth  metacarpal  bones. 

Synovial  Membrane. — The  synovial  membrane  is  a  continuation  of  that  of  the  intercarpal 
joints.  Occasionally,  the  joint  between  the  hamate  and  the  fourth  and  fifth  metacarpal  bones 
has  a  separate  synovial  membrane. 

The  synovial  membranes  of  the  wrist  and  carpus  (Fig.  336)  are  thus  seen  to  be  five  in  number. 
The  first  passes  from  the  lower  end  of  the  ulnar  to  the  ulnar  notch  of  the  radius,  and  fines  the  upper 
surface  of  the  articular  disk.  The  second  passes  from  the  articular  disk  and  the  lower  end  of  the 
radius  above,  to  the  bones  of  the  first  row  below.  The  third,  the  most  extensive,  passes  between 
the  contiguous  margins  of  the  two  rows  of  carpal  bones,  and  sometimes,  in  the  event  of  one  of 
the  interosseous  ligaments  being  absent,  between  the  bones  of  the  second  row  to  the  carpal  extremi- 
ties of  the  second,  third,  fourth,  and  fifth  metacarpal  bones.  The  fourth  extends  from  the  margin 
of  the  greater  multangular  to  the  metacarpal  bone  of  the  thvunb.  The  fifth  runs  between  the 
adjacent  margins  of  the  triangular  and  pisiform  bones.  Occasionally  the  fourth  and  fifth  carpo- 
metacarpal joints  have  a  separate  synovial  membrane. 

Movements. — The  movements  permitted  in  the  carpometacarpal  articulations  of  the  fingers 
are  limited  to  slight  gliding  of  the  articular  surfaces  upon  each  other,  the  extent  of  which  varies 
in  the  different  joints.  The  metacarpal  bone  of  the  little  finger  is  most  movable,  then  that  of 
the  ring  finger;  the  metacarpal  bones  of  the  index  and  middle  fingers  are  almost  immovable. 

DC.  Intermetacarpal  Articulations  (Articulationes  Intermetacarpese;  Articulations 
of  the  Metacarpal  Bones  with  Each  Other). 

The  bases  of  the  second,  third,  fourth  and  fifth  metacarpal  bones  articulate 
with  one  another  by  small  surfaces  covered  with  cartilage,  and  are  connected 
together  by  dorsal,  volar,  and  interosseous  ligaments. 

The  dorsal  (ligamenta  basium  oss.  metacarp.  dorsalia)  and  volar  ligaments  (liga- 
menta hasium  oss.  metacarp.  volaria;  palmar  ligaments)  pass  transversely  from 
one  bone  to  another  on  the  dorsal  and  volar  surfaces.  The  interosseous  ligaments 
(ligamenta  hasium  oss.  metacarp.  interossea)  connect  their  contiguous  surfaces, 
just  distal  to  their  collateral  articular  facets. 

The  synovial  membrane   for  these  joints  is  continuous  with  that  of  the  carpometacarpal 

articulations. 

The  Transverse  Metacarpal  Ligament  (ligamentum  capitulorum  [oss.  metacarpalium] 
transversum)  (Fig.  337). — This  ligament  is  a  narrow  fibrous  band,  which  runs  across 
the  volar  surfaces  of  the  heads  of  the  second,  third,  fourth  and  fifth  meta- 
carpal bones,  connecting  them  together.    It  is  blended  with  the  volar  (glenoid) 


332 


SYNDESMOLOGY 


ligaments  of  the  metacarpophalangeal  articulations.  Its  volar  surface  is  concave 
where  the  Flexor  tendons  pass  over  it;  behind  it  the  tendons  of  the  Interossei  pass 
to  their  insertions. 

X.    Metacarpophalangeal  Articulations  (Articulationes  Metacarpophalangese ; 
Metacarpophalangeal  Joints)  (Figs.  337,  338). 

These  articulations  are  of  the  condyloid  kind,  formed  by  the  reception  of  the 
rounded  heads  of  the  metacarpal  bones  into  shallow  cavities  on  the  proximal  ends 
of  the  first  phalanges,  with  the  exception  of  that  of  the  thumb,  which  presents 
more  of  the  characters  of  a  ginglymoid  joint.  Each  joint  has  a  volar  and  two 
collateral  ligaments. 


Metacarpal  bone 


Transverse 

metacarpal 

ligament 

Groove  for 
Flexor  tendons 


let  phalange 


Volar  ligament 


Volar  ligament 


Metacarpal  __\ 
bone 


3rd  phalanx 


I 


Collateral 
ligament 


Collateral 
ligament 


2nd  phalanx 


Collateral 
ligament 


Fig.  337. — Metacarpophalangeal  articulation  and 
articulations  of  digit.     Volar  aspect. 


Fig.   338. — Metacarpophalangeal   articulation   and 
articulations  of  digit.     Ulnar  aspect. 


The  Volar  Ligaments  (glenoid  ligaments  of  Cruveilhier;  palmar  or  vaginal  ligaments) . 
— The  volar  ligaments  are  thick,  dense,  fibrocartilaginous  structures,  placed  upon 
the  volar  surfaces  of  the  joints  in  the  intervals  between  the  collateral  ligaments,  to 
which  they  are  connected ;  they  are  loosely  united  to  the  metacarpal  bones,  but  are 
very  firmly  attached  to  the  bases  of  the  first  phalanges.  Their  volar  surfaces  are 
intimately  blended  with  the  transverse  metacarpal  ligament,  and  present  grooves 
for  the  passage  of  the  Flexor  tendons,  the  sheaths  surrounding  which  are  connected 
to  the  sides  of  the  grooves.  Their  deep  surfaces  form  parts  of  the  articular  facets 
for  the  heads  of  the  metacarpal  bones,  and  are  lined  by  synovial  membranes. 

The  Collateral  Ligaments  {ligamenta  collateralia;  lateral  ligaments). — The  col- 
lateral ligaments  are  strong,  rounded  cords,  placed  on  the  sides  of  the  joints; 


I 
I 


COXAL  ARTICULATION  OR  HIP- JOINT 


333 


each  is  attached  by  one  extremity  to  the  posterior  tubercle  and  adjacent  depres- 
sion on  the  side  of  the  head  of  the  metacarpal  bone,  and  by  the  other  to  the 
contiguous  extremity  of  the  phalanx. 

The  dorsal  surfaces  of  these  joints  are  covered  by  the  expansions  of  the  Extensor 
tendons,  together  with  some  loose  areolar  tissue  which  connects  the  deep  surfaces 
of  the  tendons  to  the  bones. 

Movements. — The  movements  which  occur  in  these  joints  are  flexion,  extension,  adduction, 
abduction,  and  circumduction;  the  movements  of  abduction  and  adduction  are  very  Umited, 
and  cannot  be  performed  when  the  fingers  are  flexed. 


XI.    Articulations  of  the  Digits  f  Articulationes  Digitorum  Manus ;  Interphalangeal 

Joints)  (Figs.  337,  338). 

The  interphalangeal  articulations  are  hinge-joints;  each  has  a  volar  and  tw^o 
collateral  ligaments.  The  arrangement  of  these  ligaments  is  similar  to  those  in 
the  metacarpophalangeal  articulations.  The  Extensor  tendons  supply  the  place 
of  posterior  ligaments. 

Movements. — The  only  movements  permitted  in  the  interphalangeal  joints  are  flexion  and 
extension;  these  movements  are  more  extensive  between  the  first  and  second  phalanges  than 
between  the  second  and  third.  The  amount  of  flexion  is  very  considerable,  but  extension  is 
limited  by  the  volar  and  collateral  ligaments. 

Muscles  Acting  on  the  Joints  of  the  Digits. — Flexion  of  the  metacarpophalangeal  joints  of  the 
fingers  is  eff'ected  by  the  Flexores  digitorum  subUmis  and  profundus,  Lumbricales,  and  Interossei, 
assisted  in  the  case  of  the  little  finger  by  the  Flexor  digiti  quinti  brevis.  Extension  is  produced 
by  the  Extensor  digitorvun  communis.  Extensor  indicis  proprius,  and  Extensor  digiti  quinti  pro- 
prius. 

Flexion  of  the  interphalangeal  joints  of  the  fingers  is  accomplished  by  the  Flexor  digitorum 
profundus  acting  on  the  proximal  and  distal  joints  and  by  the  Flexor  digitorum  sublimis  acting 
oil  the  proximal  joints.  Extension  is  effected  mainly  by  the  Lumbricales  and  Interossei,  the 
long  Extensors  having  little  or  no  action  upon  these  joints. 

Flexion  of  the  metacarpophalangeal  joint  of  the  thumb  is  effected  by  the  Flexores  pollicis 
longus  and  brevis;  extension  by  the  Extensores  pollicis  longus  and  brevis.  Flexion  of  the  inter- 
phalangeal joint  is  accomplished  by  the  Flexor  poUicis  longus,  and  extension  by  the  Extensor 
pollicis  longus. 

ARTICULATIONS   OF   THE  LOWER  EXTREMITY. 

The  articulations  of  the  Lower  Extremity  comprise  the  following: 

V.  Intertarsal. 
VI.  Tarsometatarsal. 
VII.  Intermetatarsal. 
VIII.  Metatarsophalangeal. 
IX.  Articulations  of  the  Digits. 

I.     Coxal  Articulation  or  Hip-joint  (Articulatio  Coxae). 

his  articulation  is  an  enarthrodial  or  ball-and-socket  joint,  formed  by  the 
reception  of  the  head  of  the  femur  into  the  cup-shaped  cavity  of  the  acetabulum. 
The  articular  cartilage  on  the  head  of  the  femur,  thicker  at  the  center  than  at  the 
circumference,  covers  the  entire  surface  with  the  exception  of  the  fovea  capitis 
femoris,  to  which  the  ligamentum  teres  is  attached ;  that  on  the  acetabulum  forms 
an  incomplete  marginal  ring,  the  lunate  surface.  Within  the  lunate  surface  there 
is  a  circular  depression  devoid  of  cartilage,  occupied  in  the  fresh  state  by  a  mass 
of  fat,  covered  by  synovial  membrane.    The  ligaments  of  the  joint  are: 


I. 

Hip. 

II. 

Knee. 

III. 

Tibiofibular, 

IV. 

Ankle. 

The  Articular  Capsule. 
The  Iliofemoral. 
The  Ischiocapsular. 


The  Pubocapsular. 

The  Ligamentum  Teres  Femoris. 

The  Glenoidal  Labrum. 


The  Transverse  Acetabular 


334 


SYNDESMOLOGY 


The  Articular  Capsule  {capsula  articularis;  capsular  ligament)  (Figs.  339,  340). — 
The  articular  capsule  is  strong  and  dense.  Above,  it  is  attached  to  the  margin 
of  the  acetabulum  5  to  6  mm.  beyond  the  glenoidal  labrum  behind;  but  in  front, 
it  is  attached  to  the  outer  margin  of  the  labrum,  and,  opposite  to  the  notch  where 
the  margin  of  the  cavity  is  deficient,  it  is  connected  to  the  transverse  ligament, 
and  by  a  few  fibers  to  the  edge  of  the  obturator  foramen.  It  surrounds  the  neck 
of  the  femur,  and  is  attached,  in  front,  to  the  intertrochanteric  line;  above,  to  the 
base  of  the  neck;  behind,  to  the  neck,  about  1.25  cm.  above  the  intertrochanteric 
crest;  below,  to  the  lower  part  of  the  neck,  close  to  the  lesser  trochanter.  From 
its  femoral  attachment  some  of  the  fibers  are  reflected  upward  along  the  neck 
as  longitudinal  bands,  termed  retinacula.  The  capsule  is  much  thicker  at  the  upper 
and  forepart  of  the  joint,  where  the  greatest  amount  of  resistance  is  required; 


Ani.  inf.  iliuc  3pine 


I 


I 


JrUertrocharUeric 
line 


Fig.  339. — Right  hip-joint  from  the  front.     (Spalteholz.) 


behind  and  below,  it  is  thin  and  loose.  It  consists  of  two  sets  of  fibers,  circular 
and  longitudinal.  The  circular  fibers,  zona  orbicularis,  are  most  abundant  at  the 
lower  and  back  part  of  the  capsule  (Fig.  342),  and  form  a  sling  or  collar  arourd  the 
neck  of  the  femur.  Anteriorly  they  blend  with  the  deep  surface  of  the  iliofemoral 
ligament,  and  gain  an  attachment  to  the  anterior  inferior  iliac  spine.  The  longi- 
tudinal fibers  are  greatest  in  amount  at  the  upper  and  front  part  of  the  capsule, 
where  they  are  reinforced  by  distinct  bands,  or  accessory  ligaments,  of  which  the 
most  important  is  the  iliofemoral  ligament.  The  other  accessory  bands  are  known 
as  the  pubocapsular  and  the  ischiocapsular  ligaments.  The  external  surface  of  the 
capsule  is  rough,  covered  by  numerous  muscles,  and  separated  in  front  from  the 
Psoas  major  and  Iliacus  by  a  bursa,  which  not  infrequently  communicates  by  a 
circular  aperture  with  the  cavity  of  the  joint. 


COXAL  ARTICULATION  OR  HIP-JOINT 


The  Iliofemoral  Ligament  (ligamentum  iliofemorale;  Y-ligameni;  ligament  of 
Bigeloic)  (Fig.  339). — The  iliofemoral  ligament  is  a  band  of  great  strength  which 
lies  in  front  of  the  joint;  it  is  intimately  connected  with  the  capsule,  and  serves 
to  strengthen  it  in  this  situation.  It  is  attached,  above,  to  the  lower  part  of  the 
anterior  inferior  iliac  spine;  below,  it  divides  into  two  bands,  one  of  which  passes 
downward  and  is  fixed  to  the  lower  part  of  the  intertrochanteric  line;  the  other 
is  directed  downward  and  lateralward  and  is  attached  to  the  upper  part  of  the 
same  line.  Between  the  two  bands  is  a  thinner  part  of  the  capsule.  In  some 
cases  there  is  no  division,  and  the  ligament  spreads  out  into  a  flat  triangular  band 
which  is  attached  to  the  whole  length  of  the  intertrochanteric  line.  This  ligament 
is  frequently  called  the  Y-shaped  ligament  of  Bigelow;  and  its  upper  band  is  some- 
times named  the  iliotrochanteric  ligament. 


Horizontal  fibers 

Ischiofemoral  ligament 


w 


(Quain.) 

The  Pubocapsular  Ligament  (ligamentum  pubocapsulare;  pubofemoral  ligament). — 
This  ligament  is  attached,  above,  to  the  obturator  crest  and  the  superior  ramus 
of  the  pubis;  below,  it  blends  with  the  capsule  and  with  the  deep  surface  of  the 
vertical  band  of  the  iliofemoral  ligament. 

The  Ischiocapsular  Ligament  (ligamentum  ischiocapsulare;  ischiocapsular  band; 
ligament  of  Berlin).- — The  ischiocapsular  ligament  consists  of  a  triangular  band  of 
strong  fibers,  which  spring  from  the  ischium  below  and  behind  the  acetabulum, 
and  blend  with  the  circular  fibers  of  the  capsule  (Fig.  340). 


336 


SYNDESMOLOGY 


The  Ligamentum  Teres  Femoris  (Fig.  341), — The  ligamentum  teres  femoris  is  a 
triangular,  somewhat  flattened  band  implanted  by  its  apex  into  the  antero-superior 
part  of  the  fovea  capitis  femoris ;  its  base  is  attached  by  two  bands,  one  into  either 
side  of  the  acetabular  notch,  and  between  these  bony  attachments  it  blends  with  the 
transverse  ligament.  It  is  ensheathed  by  the  synovial  membrane,  and  varies  greatly 
in  strength  in  different  subjects;  occasionally  only  the  synovial  fold  exists,  and  in 
rare  cases  even  this  is  absent.  The  ligament  is  made  tense  when  the  thigh  is 
semiflexed  and  the  limb  then  adducted  or  rotated  outward;  it  is,  on  the  other 
hand,  relaxed  when  the  limb  is  abducted.  It  has,  however,  but  little  influence  as  a 
ligament. 


Spine  of 
ischium 


Ant,  inf. 
iliac  spine 

Fovea  capitis 


Iliofemoral  ligament 


II 


Lesser  trochanter 


Fig.  341. — Left  hip-joint,  opened  by  removing  the  floor  of  the  acetabulum  from  within  the  pelvis. 


The  Glenoidal  Labnim  (labrum  glenoidale;  cotyloid  ligament). — The  glenoidal 
labrum  is  a  fibrocartilaginous  rim  attached  to  the  margin  of  the  acetabulum,  the 
cavity  of  which  it  deepens;  at  the  same  time  it  protects  the  edge  of  the  bone,  and 
fills  up  the  inequalities  of  its  surface.  It  bridges  over  the  notch  as  the  transverse 
ligament,  and  thus  forms  a  complete  circle,  which  closely  surrounds  the  head  of  the 
femur  and  assists  in  holding  it  in  its  place.  It  is  triangular  on  section,  its  base  being 
attached  to  the  margin  of  the  acetabulum,  while  its  opposite  edge  is  free  and 
sharp.  Its  two  surfaces  are  invested  by  synovial  membrane,  the  external  one 
being  in  contact  with  the  capsule,  the  internal  one  being  inclined  inward  so  as 
to  narrow  the  acetabulum,  and  embrace  the  cartilaginous  surface  of  the  head  of 
the  femur.  It  is  much  thicker  above  and  behind  than  below  and  in  front,  and 
consists  of  compact  fibers. 

The  Transverse  Acetabular  Ligament  {ligamentum  transversum  acetabuli;  transverse 
ligament)  .—This  ligament  is  in  reality  a  portion  of  the  glenoidal  labrum,  though 
differing  from  it  in  having  no  cartilage  cells  among  its  fibers.    It  consists  of  strong, 


COXAL  ARTICULATION  OR  HIP-JOINT 


337 


Fia.  342. — Hip-joint,  front  view.     The  capsular  ligament  has  been  largely  removed. 


Spine  of 
ischium 


Capsvie 

Greater  trochanter 


FiQ.  343. — Capsule  of  hip-joint  (distended).     Posterior  aspect. 


22 


338 


SYNDESMOLOGY 


flattened  fibers,  which  cross  the  acetabular  notch,  and  convert  it  into  a  foramen 
through  which  the  nutrient  vessels  enter  the  joint. 

Synovial  Membrane  (Fig.  343). — The  synovial  membrane  is  very  extensive.  Commencing 
at  the  margin  of  the  cartilaginous  surface  of  the  head  of  the  femur,  it  covers  the  portion  of  the 
neck  which  is  contained  within  the  joint;  from  the  neck  it  is  reflected  on  the  internal  surface  of 
the  capsule,  covers  both  surfaces  of  the  glenoidal  labrum  and  the  mass  of  fat  contained  in  the 
depression  at  the  bottom  of  the  acetabulum,  and  ensheathes  the  ligamentum  teres  as  far  as  the 
head  of  the  femur.  The  joint  cavity  sometimes  communicates  through  a  hole  in  the  capsule 
between  the  vertical  band  of  the  iliofemoral  hgament  and  the  pubocapsular  ligament  with  a  bursa 
situated  on  the  deep  surfaces  of  the  Psoas  major  and  Iliacus. 

The  muscles  in  relation  with  the  joint  are,  in  front,  the  Psoas  major  and  Iliacus,  separated 
from  the  capsule  by  a  bursa;  above,  the  reflected  head  of  the  Rectus  femoris  and  Glutajus  minimus, 
the  latter  being  closely  adherent  to  the  capsule;  medially,  the  Obturator  extemus  and  Pectineus; 
behind,  the  Piriformis,  Gemellus  superior,  Obturator  intemus,  Gemellus  inferior,  Obturator 
extemus,  and  Quadratus  femoris  (Fig.  344). 

Femoral  artery 
Femoral  nerve         |         Femoral  vein 


Iliofemoral  ligament 
Rectus  femoris 


Ligamentum,  teres 
Obturator  nerve 


Piriformis  \  Sciatic  nerve 

Obturator  intermu 

Fig.  344. — Structures  surrounding  right  hii>-joint. 

The  arteries  supplying  the  joint  are  derived  from  the  obturator,  medial  femoral  circumflex, 
and  superior  and  inferior  gluteals. 

The  nerves  are  articular  branches  from  the  sacral  plexus,  sciatic,  obturator,  accessory  obturator, 
and  a  filament  from  the  branch  of  the  femoral  supplying  the  Rectus  femoris. 

Movements. — The  movements  of  the  hip  are  very  extensive,  and  consist  of  flexion,  extension, 
adduction,  abduction,  circvunduction,  and  rotation. 

The  length  of  the  neck  of  the  femvur  and  its  inclinations  to  the  body  of  the  bone  have  the^ 
effect  of  converting  the  angular  movements  of  flexion,  extension,  adduction,  and  abduction  par- 
tially into  rotatory  movements  in  the  joint.  Thus  when  the  thigh  is  flexed  or  extended,  the 
head  of  the  femur,  on  account  of  the  medial  incUnation  of  the  neck,  rotates  within  the  acetabulum 
with  only  a  slight  amount  of  gliding  to  and  fro.  The  forward  slope  of  the  neck  similarly  affects 
the  movements  of  adduction  and  abduction.  Conversely  rotation  of  the  thigh  which  is  permitted 
by  the  upward  inclination  of  the  neck,  is  not  a  simple  rotation  of  the  head  of  the  femur  in  the 
acetabulum,  but  is  accompanied  by  a  certain  amount  of  gliding. 


THE  KNEE-JOINT 


339 


The  hip-joint  presents  a  very  striking  contrast  to  the  shoulder-joint  in  the  much  more  com- 
plete mechanical  arrangements  for  its  security  and  for  the  limitation  of  its  movements.  In  the 
shoulder,  as  has  been  seen,  the  head  of  the  humerus  is  not  adapted  at  all  in  size  to  the  glenoid 
cavity,  and  is  hardly  restrained  in  any  of  its  ordinary  movements  by  the  capsule.  In  the  hip- 
joint,  on  the  contrary,  the  head  of  the  femur  is  closely  fitted  to  the  acetabulimi  for  an  area  extend- 
ing over  nearly  half  a  sphere,  and  at  the  margin  of  the  bony  cup  it  is  still  more  closely  embraced 
by  the  glenoidal  labrum,  so  that  the  head  of  the  femur  is  held  in  its  place  by  that  ligament  even 
when  the  fibers  of  the  capsule  have  been  quite  divided.  The  iliofemoral  ligament  is  the  strongest 
of  all  the  ligaments  in  the  body,  and  is  put  oi)  the  stretch  by  any  attempt  to  extend  the  femur 
beyond  a  straight  line  with  the  trunk.  That  is  to  say,  this  ligament  is  the  chief  agent  in  main- 
taining the  erect  position  without  muscular  fatigue;  for  a  vertical  Une  passing  through  the  center 
of  gravity  of  the  trunk  falls  behind  the  centers  of  rotation  in  the  hip-joints,  and  therefore  the 
pelvis  tends  to  fall  backward,  but  is  prevented  by  the  tension  of  the  iUofemoral  ligaments.  The 
security  of  the  joint  may  be  provided  for  also  by  the  two  bones  being  directly  united  through  the 
ligamentum  teres ;  but  it  is  doubtful  whether  this  ligament  has  much  influence  upon  the  mechanism 
of  the  joint.  When  the  knee  is  flexed,  flexion  of  the  hip-joint  is  arrested  by  the  soft  parts  of  the 
thigh  and  abdomen  being  brought  into  contact,  and  when  the  knee  is  extended,  by  the  action  of 
the  hamstring  muscles;  extension  is  checked  by  the  tension  of  the  iliofemoral  ligament;  adduc- 
tion by  the  thighs  coming  into  contact;  adduction  with  flexion  by  the  lateral  band  of  the  ilio- 
femoral ligament  and  the  lateral  part  of  the  capsule;  abduction  by  the  medial  band  of  the 
iliofemoral  ligament  and  the  pubocapsular  ligament ;  rotation  outward  by  the  lateral  band  of  the 
iliofemoral  ligament;  and  rotation  inward  by  the  ischiocapsular  hgament  and  the  hinder  part  of 
the  capsule.  The  muscles  which  ^ex  the  femur  on  the  pelvis  are  the  Psoas  major,  Iliacus,  Rectus 
femoris,  Sartorius,  Pectineus,  Adductores  longus  and  brevis,  and  the  anterior  fibers  of  the  Glutaei 
medius  and  minimus.  Extension  is  mainly  performed  by  the  Glutseus  maximus,  assisted  by  the 
hamstring  muscles  and  the  ischial  head  of  the  Adductor  magnus.  The  thigh  is  adducted  by  the 
Adductores  magnus,  longus,  and  brevis,  the  Pectineus,  the  Gracilis,  and  lower  part  of  the  Glutseus 
maximus,  and  abducted  by  the  Glutaei  medius  and  minimus,  and  the  upper  part  of  the  Glutseus 
maximus.  The  muscles  which  rotate  the  thigh  inward  are  the  Glutseus  minimus  and  the  anterior 
fibers  of  the  Glutajus  medius,  the  Tensor  fascise  latae  and  the  lUacus  and  Psoas  major;  while 
those  which  rotate  it  outward  are  the  posterior  fibers  of  the  Glutseus  medius,  the  Piriformis, 
Obturatores  extemus  and  intem\is,  Gemelli  superior  and  inferior,  Quadratus  femoris,  Glutseus 
maximus,  the  Adductores  longus,  brevis,  and  magnus,  the  Pectineus,  and  the  Sartorius. 


n.    The  Knee-joint  (Articulatio  Genu). 


The  knee-joint  was  formerly  described  as  a  ginglymus  or  hinge-joint,  but  is 
really  of  a  much  more  complicated  character.  It  must  be  regarded  as  consisting 
of  three  articulations  in  one:  two  condyloid  joints,  one  between  each  condyle 
of  the  femur  and  the  corresponding  meniscus  and  condyle  of  the  tibia;  and  a  third 
between  the  patella  and  the  femur,  partly  arthrodial,  but  not  completely  so, 
since  the  articular  surfaces  are  not  mutually  adapted  to  each  other,  so  that  the 
movement  is  not  a  simple  gliding  one.  This  view  of  the  construction  of  the  knee- 
joint  receives  confirmation  from  the  study  of  the  articulation  in  some  of  the  lower 
mammals,  where,  corresponding  to  these  three  subdivisions,  three  synovial  cavities 
are  sometimes  found,  either  entirely  distinct  or  only  connected  together  by  small 
communications.  This  view  is  further  rendered  probable  by  the  existence  in  the 
middle  of  the  joint  of  the  two  cruciate  ligaments,  which  must  be  regarded  as 
the  collateral  ligaments  of  the  medial  and  lateral  joints.  The  existence  of  the 
patellar  fold  of  synovial  membrane  would  further  indicate  a  tendency  to  separa- 
tion of  the  synovial  cavity  into  two  minor  sacs,  one  corresponding  to  the  lateral 
and  the  other  to  the  medial  joint. 

The  bones  are  connected  together  by  the  following  ligaments: 


The  Articular  Capsule. 
The  Ligamentum  Patellae. 
The  Oblique  Popliteal. 
The  Tibial  Collateral. 
The  Fibular  Collateral. 


The  Anterior  Cruciate. 

The  Posterior  Cruciate. 

The  Medial  and  Lateral  Menisci. 

The  Transverse. 

The  Coronary. 


340 


SYNDESMOLOGY 


■^ 


The  Articular  Capsule  {capsula  articularis;  capsular  ligamenf)  (Fig.  345).— The 
articular  capsule  consists  of  a  thin,  but  strong,  fibrous  membrane  which  is  strength- 
ened in  almost  its  entire  extent  by  bands  inseparably  connected  with  it.  Above 
and  in  front,  beneath  the  tendon  of  the  Quadriceps  femoris,  it  is  represented  only 
by  the  synovial  membrane.  Its  chief  strengthening  bands  are  derived  from  the 
fascia  lata  and  from  the  tendons  surrounding  the  joint.  In  front,  expansions 
from  the  Vasti  and  from  the  fascia  lata  and  its  iliotibial  band  fill  in  the  intervals 
between  the  anterior  and  collateral  ligaments,  constituting  the  medial  and  lateral 
patellar  retinacula.  Behind  the  capsule  consists  of  vertical  fibers  which  arise 
from  the  condyles  and  from  the  sides  of  the  intercondyloid  fossa  of  the  femur; 

the  posterior  part  of  the  capsule  is  therefore 
situated  on  the  sides  of  and  in  front  of  the 
cruciate  ligaments,  which  are  thus  excluded  from 
the  joint  cavity.  Behind  the  cruciate  ligaments 
is  the  oblique  popliteal  ligament  which  is  aug- 
mented by  fibers  derived  from  the  tendon  of  the 
Semimembranosus.  Laterally,  a  prolongation 
from  the  iliotibial  band  fills  in  the  interval  be- 
tween the  oblique  popliteal  and  the  fibular  collat- 
eral ligaments,  and  partly  covers  the  latter. 
Medially,  expansions  from  the  Sartorius  and 
Semimembranosus  pass  upward  to  the  tibial 
collateral  ligament  and  strengthen  the  capsule. 
The  Ligamentimi  Patellae  {anterior  ligament) 
(Fig.  345) . — The  ligamentum  patellfe  is  the  cen- 
tral portion  of  the  common  tendon  of  the  Quad- 
riceps femoris,  which  is  continued  from  the 
patella  to  the  tuberosity  of  the  tibia.  It  is  a 
strong,  flat,  ligamentous  band,  about  8  cm.  in 
length,  attached,  above,  to  the  apex  and  adjoin- 
ing margins  of  the  patella  and  the  rough  depres- 
sion on  its  posterior  surface;  helaio,  to  the 
tuberosity  of  the  tibia;  its  superficial  fibers  are 
continuous  over  the  front  of  the  patella  with 
those  of  the  tendon  of  the  Quadriceps  femoris. 
The  medial  and  lateral  portions  of  the  tendon 
of  the  Quadriceps  pass  down  on  either  side  of 
the  patella,  to  be  inserted  into  the  upper  extremity 
of  the  tibia  on  either  side  of  the  tuberosity;  these 
portions  merge  into  the  capsule,  as  stated  above, 
forming  the  medial  and  lateral  patellar  retinacula.  The  posterior  surface  of  the 
ligamentum  patellae  is  separated  from  the  synovial  membrane  of  the  joint  by  a 
large  infrapatellar  pad  of  fat,  and  from  the  tibia  by  a  bursa. 

The  Oblique  PopUteal  Ligament  (ligamentum  popliteum  ohliquum;  posterior  liga- 
ment) (Fig.  346). — This  ligament  is  a  broad,  flat,  fibrous  band,  formed  of  fasciculi 
separated  from  one  another  by  apertures  for  the  passage  of  vessels  and  nerves. 
It  is  attached  above  to  the  upper  margin  of  the  intercondyloid  fossa  and  posterior 
surface  of  the  femur  close  to  the  articular  margins  of  the  condyles,  and  below  to 
the  posterior  margin  of  the  head  of  the  tibia.  Superficial  to  the  main  part  of  the 
ligament  is  a  strong  fasciculus,  derived  from  the  tendon  of  the  Semimembranosus 
and  passing  from  the  back  part  of  the  medial  condyle  of  the  tibia  obliquely  upward 
and  iateralward  to  the  back  part  of  the  lateral  condyle  of  the  femur.  The  oblique 
popliteal  ligament  forms  part  of  the  floor  of  the  popliteal  fossa,  and  the  popliteal 
artery  rests  upon  it. 


Fig.  345. — Right  knee-joint, 
view. 


Anterior 


THE  KNEE-JOINT 


341 


The  Tibial  Collateral  Ligament  (ligamentum  collaterale  tibiale;  internal  lateral  liga- 
ment) (Fig.  345).— The  tibial  collateral  is  a  broad,  flat,  membranous  band,  situated 
nearer  to  the  back  than  to  the  front  of  the  joint.  It  is  attached,  above,  to  the  medial 
condyle  of  the  femur  immediately  below  the  adductor  tubercle;  below,  to  the  medial 
condyle  and  medial  surface  of  the  body  of  the  tibia.  The  fibers  of  the  posterior 
part  of  the  ligament  are  short  and  incline  backward  as  they  descend;  they  are 
inserted  into  the  tibia  above  the  groove  for  the  Semimembranosus.  The  anterior 
part  of  the  ligament  is  a  flattened  band,  about  10  cm.  long,  which  inclines  forward 
as  it  descends.  It  is  inserted  into  the  medial  surface  of  the  body  of  the  tibia  about 
2.5  cm.  below  the  level  of  the  condyle.  It  is  crossed,  at  its  lower  part,  by  the 
tendons  of  the  Sartorius,  Gracilis,  and  Semitendinosus,  a  bursa  being  interposed. 
Its  deep  surface  covers  the  inferior  medial  genicular  vessels  and  nerve  and  the 
anterior  portion  of  the  tendon  of  the  Semimembranosus,  with  which  it  is  connected 
■■  by  a  few  fibers;  it  is  intimately  adherent  to  the  medial  meniscus. 

I 


Posterior  view. 


Fig.  347. — Right  knee-joint,  from  the  front, 
showing  interior  ligaments. 


The  Fibular  Collateral  Ligament  (ligamentum  collaterale  fibular e;  external  lateral  or 
long  external  lateral  ligament)  (Fig.  348).— The  fibular  collateral  is  a  strong,  rounded, 
fibrous  cord,  attached,  above,  to  the  back  part  of  the  lateral  condyle  of  the  femur, 
immediately  above  the  groove  for  the  tendon  of  the  Popliteus;  below,  to  the  lateral 
side  of  the  head  of  the  fibula,  in  front  of  the  styloid  process.  The  greater  part  of 
its  lateral  surface  is  covered  by  the  tendon  of  the  Biceps  femoris;  the  tendon, 
however,  divides  at  its  insertion  into  two  parts,  which  are  separated  by  the  liga- 
ment. Deep  to  the  ligament  are  the  tendon  of  the  Popliteus,  and  the  inferior 
lateral  genicular  vessels  and  nerve.    The  ligament  has  no  attachment  to  the  lateral 


meniscus. 


342 


SYNDESMOLOGY 


An  inconstant  bundle  of  fibers,  the  short  fibular  collateral  ligament,  is  placed  behind  and 
parallel  with  the  preceding,  attached,  above,  to  the  lower  and  back  part  of  the  lateral  condyle 
of  the  femur;  below,  to  the  summit  of  the  styloid  process  of  the  fibula.  Passing  deep  to  it  are 
the  tendon  of  the  Popliteus,  and  the  inferior  lateral  genicular  vessels  and  nerve. 

The  Cruciate  Ligaments  {ligamenia  cruciata  genu;  crucial  ligaments). — The  cru- 
ciate ligaments  are  of  considerable  strength,  situated  in  the  middle  of  the  joint, 
nearer  to  its  posterior  than  to  its  anterior  surface.  They  are  called  cruciate  because 
they  cross  each  other  somewhat  like  the  lines  of  the  letter  X;  and  have  received 
the  names  anterior  and  posterior,  from  the  position  of  their  attachments  to  the 
tibia. 

The  Anterior  Cruciate  Ligament  {ligamentum  cruciatum  anterius;  external  crucial 
ligament)  (Fig.  347)  is  attached  to  the  depression  in  front  of  the  intercondyloid 
eminence  of  the  tibia,  being  blended  with  the  anterior  extremity  of  the  lateral 
meniscus;  it  passes  upward,  backward,  and  lateralward,  and  is  fixed  into  the  medial 
and  back  part  of  the  lateral  condyle  of  the  femur. 


H 


Ant.  cruciateligament 
Tendon  of  Poplitetis 

Lateral  meniscus 

Fibular  collateral 
ligament 


Fia.  348. — ^Left  knee-joint  from  behind,  showing  interior  ligaments. 

The  Posterior  Cruciate  Ligament  {ligamentum  cruciatum  posterius;  internal  crucial 
ligament)  (Fig.  348)  is  stronger,  but  shorter  and  less  oblique  in  its  direction,  than 
the  anterior.  It  is  attached  to  the  posterior  intercondyloid  fossa  of  the  tibia,  and 
to  the  posterior  extremity  of  the  lateral  meniscus;  and  passes  upward,  forward, 
and  medialward,  to  be  fixed  into  the  lateral  and  front  part  of  the  medial  condyle 
of  the  femur. 

The  Menisci  {semilunar  fihrocartilages)  (Fig.  349). — The  menisci  are  two  crescentic 
lamellae,  which  serve  to  deepen  the  surfaces  of  the  head  of  the  tibia  for  articulation 
with  the  condyles  of  the  femur.  The  peripheral  border  of  each  meniscus  is  thick, 
convex,  and  attached  to  the  inside  of  the  capsule  of  the  joint ;  the  opposite  border 


THE  KNEE-JOINT 


343 


is  thin,  concave,  and  free.  The  upper  surfaces  of  the  menisci  are  concave,  and 
in  contact  with  the  condyles  of  the  femur;  their  lower  surfaces  are  flat,  and  rest 
upon  the  head  of  the  tibia;  both  surfaces  are  smooth,  and  invested  by  synovial 
membrane.  Each  meniscus  covers  approximately  the  peripheral  two-thirds  of 
the  corresponding  articular  surface  of  the  tibia. 

The  medial  meniscus  {meniscus  medialis;  internal  semilunar  fibrocartilage)  is 
nearly  semicircular  in  form,  a  little  elongated  from  before  backward,  and  broader 
behind  than  in  front;  its  anterior  end,  thin  and  pointed,  is  attached  to  the  anterior 
intercondyloid  fossa  of  the  tibia,  in  front  of  the  anterior  cruciate  ligament;  its 
posterior  end  is  fixed  to  the  posterior  intercondyloid  fossa  of  the  tibia,  between 
the  attachments  of  the  lateral  meniscus  and  the  posterior  cruciate  ligament. 


Anterior  cruciate  ligament 


Transverse  ligament 


Ligament  of  Wrisberg 
Posterior  cruciate  ligament 

Fig.  349. — Head  of  right  tibia  seen  from  above,  showing  menisci  and  attachments  of  ligaments. 


The  lateral  meniscus  {meniscus  lateralis;  external  semilunar  fibrocartilage)  is  nearly 
circular  and  covers  a  larger  portion  of  the  articular  surface  than  the  medial  one. 
It  is  grooved  laterally  for  the  tendon  of  the  Popliteus,  which  separates  it  from  the 
fibular  collateral  ligament.  Its  anterior  end  is  attached  in  front  of  the  intercon- 
dyloid eminence  of  the  tibia,  lateral  to,  and  behind,  the  anterior  cruciate  ligament, 
with  which  it  blends;  the  posterior  end  is  attached  behind  the  intercondyloid 
eminence  of  the  tibia  and  in  front  of  the  posterior  end  of  the  medial  meniscus. 
The  anterior  attachment  of  the  lateral  meniscus  is  twisted  on  itself  so  that  its 
free  margin  looks  backward  and  upward,  its  anterior  end  resting  on  a  sloping 
shelf  of  bone  on  the  front  of  the  lateral  process  of  the  intercondyloid  eminence. 
Close  to  its  posterior  attachment  it  sends  off  a  strong  fasciculus,  the  ligament  of 
Wrisberg  (Figs.  348,  349),  which  passes  upward  and  medialward,  to  be  inserted 
into  the  medial  condyle  of  the  femur,  immediately  behind  the  attachment  of  the 
posterior  cruciate  ligament.  Occasionally  a  small  fasciculus  passes  forward  to 
be  inserted  into  the  lateral  part  of  the  anterior  cruciate  ligament.  The  lateral 
meniscus  gives  off  from  its  anterior  convex  margin  a  fasciculus  which  forms  the 
transverse  ligament. 

The  Transverse  Ligament  {ligamentum  transversum  genu). — The  transverse  liga- 
ment connects  the  anterior  convex  margin  of  the  lateral  meniscus  to  the  anterior 
end  of  the  medial  meniscus ;  its  thickness  varies  considerably  in  different  subjects, 
and  it  is  sometimes  absent. 

The  coronary  ligaments  are  merely  portions  of  the  capsule,  which  connect  the 
periphery  of  each  meniscus  with  the  margin  of  the  head  of  the  tibia. 


344 


SYNDESMOLOGY 


Synovial  Membrane. — The  synovial  membrane  of  the  knee-joint  is  the  largest  and  most  exten- 
sive in  the  body.  Commencing  at  the  upper  border  of  the  patella,  it  forms  a  large  cul-de-sac 
beneath  the  Quadriceps  femoris  (Figs.  3.50,  3.51)  on  the  lower  part  of  the  front  of  the  femur, 
and  frequently  communicates  with  a  bursa  interposed  between  the  tendon  and  the  front  of  the 
femur.  The  pouch  of  synovial  membrane  between  the  Quadriceps  and  front  of  the  femur  is 
supported,  during  the  movements  of  the  knee,  by  a  small  muscle,  the  Articularis  genu,  which 
is  inserted  into  it.  On  either  side  of  the  patella,  the  synovial  membrane  extends  beneath  the 
aponeuroses  of  the  Vasti,  and  more  especially  beneath  that  of  the  Vastus  medialis.  Below  the 
patella  it  is  separated  from  the  ligamentum  patella;  by  a  considerable  quantity  of  fat,  known  as 


Oblique  poplitea 
ligament 


Medial  meniscus 


^ —  Adipose  tissue 


-1 — .  Bursa  under  Quadriceps 
femoris 


Medial  meniscus 
Ligamentum  patellce 


I     _  Bursa  between  tibia  arid 
ligamentum  patellae 


Fia.  350. — -Sagittal  section  of  right  knee-joint. 


the  infrapatellar  pad.  From  the  medial  and  lateral  borders  of  the  articular  surface  of  the  patella, 
reduplications  of  the  synovial  membrane  project  into  the  interior  of  the  joint.  These  form  two 
fringe-like  folds  termed  the  alar  folds ;  below,  these  folds  converge  and  are  continued  as  a  single 
band,  the  patellar  fold  {ligamentum  mucosum),  to  the  front  of  the  intercondyloid  fossa  of  the  femur. 
On  either  side  of  the  joint,  the  synovial  membrane  passes  downward  from  the  femur,  lining  the 
capsule  to  its  point  of  attachment  to  the  menisci;  it  may  then  be  traced  over  the  upper  surfaces 
of  these  to  their  free  borders,  and  thence  along  their  under  sm-faces  to  the  tibia  (Figs.  351,  352). 
At  the  back  part  of  the  lateral  meniscus  it  forms  a  cul-de-sac  between  the  groove  on  its  surface 
and  the  tendon  of  the  Popliteus;  it  is  reflected  across  the  front  of  the  cruciate  ligaments,  which 
are  therefore  situated  outside  the  synovial  cavitj'. 


THE  KNEE-JOINT 

Bursse. — The  burs£E  near  the  knee-joint  are  the  following:  In  front  there  are  four  bursae:  a 
large  one  is  interposed  between  the  patella  and  the  skin,  a  small  one  between  the  upper  part  of 
the  tibia  and  the  ligamentum  patella;,  a  third  between  the  lower  part  of  the  tuberosity  of  the 
tibia  and  the  skin,  and  a  fourth  between  the  anterior  surface  of  the  lower  part  of  the  femur  and 
the  deep  surface  of  the  Quadriceps  femoris,  usually  communicating  with  the  knee-joint.  Laterally 
there  are  four  bursse:  (1)  one  (which  sometimes  communicates  with  the  joint)  between  the 
lateral  head  of  the  Gastrocnemius  and  the  capsule;  (2)  one  between  the  fibular  collateral  ligament 
and  the  tendon  of  the  Biceps;  (3)  one  between  the  fibular  collateral  ligament  and  the  tendon  of 
the  PopUteus  (this  is  sometimes  only  an  expansion  from  the  next  bursa);  (4)  one  between  the 
tendon  of  the  Pophteus  and  the  lateral  condyle  of  the  femiu",  usually  an  extension  from  the 
synovial  membrane  of  the  joint.  ]Medially,  there  are  five  bursa?:  (1)  one  between  the  medial 
head  of  the  Gastrocnemius  and  the  capsule;  this  sends  a  prolongation  between  the  tendon  of  the 


Quadriceps 
femoris 


Fibular  collateral 

ligament 

Tendon  of  PopUteus 

Lateral  meniscus 


Ligamentum 
patella 


Fia.  351. — Capsule  of  right  knee-joint  (distended).     Lateral  aspect. 


medial  head  of  the  Gastrocnemius  and  the  tendon  of  the  Semimembranosus  and  often  communi- 
cates with  the  joint;  (2)  one  superficial  to  the  tibial  collateral  ligament,  between  it  and  the  tendons 
of  the  Sartorius,  Gracilis,  and  Semitendinosus;  (3)  one  deep  to  the  tibial  collateral  ligament, 
between  it  and  the  tendon  of  the  Semimembranosus  (this  is  sometimes  only  an  expansion 
from  the  next  bursa) ;  (4)  one  between  the  tendon  of  the  Semimembranosus  and  the  head  of 
the  tibia;  (5)  occasionally  there  is  a  bursa  between  the  tendons  of  the  Semimembranosus  and 
Semitendinosus. 

Structures  Around  the  Joint. — In  front,  and  at  the  sides,  is  the  Quadriceps  femoris;  laterally 
the  tendons  of  the  Biceps  femoris  and  Popliteus  and  the  common  peroneal  nerve;  medially, 
the  Sartorius,  Gracilis,  Semitendinosus,  and  Semimembranosus;  behind,  the  popliteal  vessels 
and  the  tibial  nerve,  Popliteus,  Plantaris,  and  medial  and  lateral  heads  of  the  Gastrocnemius, 
some  lymph  glands,  and  fat. 

The  arteries  supplying  the  joint  are  the  highest  genicular  (anastomotica  magna),  a  branch 


SYNDESMOLOGY 

of  the  femoral,  the  genicular  branches  of  the  ]:)opUteal,  the  recurrent  branches  of  the  anterior 
tibial,  and  the  descending  branch  from  the  lateral  femoral  circumflex  of  the  profunda  femoris. 

The  nerves  are  derived  from  the  obturator,  femoral,  tibial,  and  common  peroneal. 

Movements. — The  movements  which  take  place  at  the  knee-joint  are  flexion  and  extension, 
and,  in  certain  positions  of  the  joint,  internal  and  external  rotation.  The  movements  of  flexion 
and  extension  at  this  joint  differ  from  those  in  a  typical  hinge-joint,  such  as  the  elbow,  in  that 
(a)  the  axis  around  which  motion  takes  place  is  not  a  fixed  one,  but  shifts  forward  during  extension 
and  backward  during  flexion;  (6)  the  commencement  of  flexion  and  the  end  of  extension  are 
accompanied  by  rotatory  movements  associated  with  the  fixation  of  the  limb  in  a  position  of 
great  stabiUty.  The  movement  from  full  flexion  to  full  extension  may  therefore  be  described 
in  three  phases: 

1.  In  the  fully  flexed  condition  the  posterior  parts  of  the  femoral  condyles  rest  on  the  corre- 
sponding portions  of  the  meniscotibial  surfaces,  and  in  this  position  a  slight  amount  of  simple ' 
rolling  movement  is  allowed. 


Posterior  cruciate 
ligament 

Medial  menisciis — ^ 


Tibial  collateral 
ligament 


rUerior  cruciate 
ligament 

Lateral  meniscus 

Fibular  collateral 
ligament 


Fia.  352. — Capsule  of  right  knee-joint  (distended).     Posterior  aspect. 


2.  During  the  passage  of  the  limb  from  the  flexed  to  the  extended  position  a  gUding  movement 
is  superposed  on  the  rolling,  so  that  the  axis,  which  at  the  commencement  is  represented  by  a 
line  through  the  inner  and  outer  condyles  of  the  femur,  gradually  shifts  forward.  In  this  part 
of  the  movement,  the  posterior  two-thirds  of  the  tibial  articular  surfaces  of  the  two  femoral 
condyles  are  involved,  and  as  these  have  similar  curvatures  and  are  parallel  to  one  another,  they 
move  forward  equally. 

3.  The  lateral  condyle  of  the  femur  is  brought  almost  to  rest  by  the  tightening  of  the  anterior 
cruciate  ligament;  it  moves,  however,  shghtly  forward  and  medialward,  pushing  before  it  the 
anterior  part  of  the  lateral  meniscus.  The  tibial  surface  on  the  medial  condyle  is  prolonged 
farther  forward  than  that  on  the  lateral,  and  this  prolongation  is  directed  lateralward.  When, 
therefore,  the  movement  forward  of  the  condyles  is  checked  by  the  anterior  cruciate  ligament, 
continued  muscular  action  causes  the  medial  condyle,  dragging  with  it  the  meniscus,  to  travel 
backward  and  medialward,  thus  producing  an  internal  rotation  of  the  thigh  on  the  leg.  When 
the  position  of  full  extension  is  reached  the  lateral  part  of  the  groove  on  the  lateral  condyle  is 
pressed  against  the  anterior  part  of  the  corresponding  meniscus,  while  the  medial  part  of  the 


ARTICULATIONS  BETWEEN  THE  TIBIA  AND  FIBULA 


347 


groove  rests  on  the  articular  margin  in  front  of  the  lateral  process  of  the  tibial  intercondyloid 
eminence.  Into  the  groove  on  the  medial  condyle  is  fitted  the  anterior  part  of  the  medial  meniscus, 
while  the  anterior  cruciate  ligament  and  the  articular  margin  in  front  of  the  medial  process  of 
the  tibial  intercondyloid  eminence  are  received  into  the  forepart  of  the  intercondyloid  fossa  of 
the  femur.  This  third  phase  by  which  all  these  parts  are  brought  into  accurate  apposition  is 
known  as  the  "screwing  home,"  or  locking  movement  of  the  joint. 

The  complete  movement  of  flexion  is  the  converse  of  that  described  above,  and  is  therefore 
preceded  by  an  external  rotation  of  the  femur  which  unlocks  the  extended  joint. 

The  axes  around  which  the  movements  of  flexion  and  extension  take  place  are  not  precisely 
at  right  angles  to  either  bone;  in  flexion,  the  femur  and  tibia  are  in  the  same  plane,  but  in  exten- 
sion the  one  bone  forms  an  angle,  opening  lateralward  with  the  other. 

In  addition  to  the  rotatory  movements  associated  with  the  completion  of  extension  and  the 
initiation  of  flexion,  rotation  inward  or  outward  can  be  effected  when  the  joint  is  partially  flexed; 
these  movements  take  place  mainly  between  the  tibia  and  the  menisci,  and  are  freest  when  the 
leg  is  bent  at  right  angles  with  the  thigh. 

Movements  of  Patella. — The  articular  surface  of  the  patella  is  indistinctly  divided  into  seven 
facets — upper,  middle,  and  lower  horizontal  pairs,  and  a  medial  perpendicular  facet  (Fig.  353). 
When  the  knee  is  forcibly  flexed,  the  medial  perpendicular 
facet  is  in  contact  with  the  semilunar  surface  on  the  lateral 
part  of  the  mediaL condyle;  this  semilunar  surface  is  a  pro- 
longation backward  of  the  medial  part  of  the  patellar  surface. 
As  the  leg  is  carried  from  the  flexed  to  the  extended  position, 
first  the  highest  pair,  then  the  middle  pair,  and  lastly  the 
lowest  pair  of  horizontal  facets  is  successively  brought  into 
contact  with  the  patellar  surface  of  the  femur.  In  the  ex- 
tended position,  when  the  Quadriceps  femoris  is  relaxed,  the 
patella  lies  loosely  on  the  front  of  the  lower  end  of  the  femur. 

During  flexion,  the  ligamentum  patella?  is  put  upon 
the  stretch,  and  in  extreme  flexion  the  posterior  cruciate 
ligament,  the  obhque  popliteal,  and  collateral  hgaments, 
and,  to  a  sUght  extent,  the  anterior  cruciate  ligament, 
are  relaxed.  Flexion  is  checked  during  life  by  the  contact 
of  the  leg  with  the  thigh.  'When  the  knee-joint  is  fuUy 
extended  the  oblique  popliteal  and  collateral  ligaments, 
the  anterior  cruciate  ligament,  and  the  posterior  cruciate 
in  the  act  of  extending  the  knee,  the  ligamentum  patellae 
femoris,  but  in  full  extension  with  the  heel  supported  it  is  relaxed.  Rotation  inward  is  checked 
by  the  anterior  cruciate  ligament;  rotation  outward  tends  to  uncross  and  relax  the  cruciate  liga- 
ments, but  is  checked  by  the  tibial  collateral  ligament.  The  main  function  of  the  cruciate  liga- 
ment is  to  act  as  a  direct  bond  between  the  tibia  and  femur  and  to  prevent  the  former  bone  from 
being  carried  too  far  backward  or  forward.  They  also  assist  the  collateral  ligaments  in  resisting 
any  bending  of  the  joint  to  either  side.  The  menisci  are  intended,  as  it  seems,  to  adapt  the  surfaces 
of  the  tibia  to  the  shape  of  the  femoral  condyles  to  a  certain  extent,  so  as  to  fill  up  the  intervals 
which  would  otherwise  be  left  in  the  varying  positions  of  the  joint,  and  to  obviate  the  jars  which 
would  be  so  frequently  transmitted  up  the  limb  in  jumping  or  by  falls  on  the  feet;  also  to  permit 
of  the  two  varieties  of  motion,  flexion  and  extension,  and  rotation,  as  explained  above.  The 
patella  is  a  great  defence  to  the  front  of  the  knee-joint,  and  distributes  upon  a  large  and  tolerably 
even  surface,  during  kneeling,  the  pressure  which  would  otherwise  fall  upon  the  prominent  ridges 
of  the  condyles;  it  also  affords  leverage  to  the  Quadriceps  femoris. 

When  standing  erect  in  the  attitude  of  "attention,"  the  weight  of  the  body  falls  in  front  of 
a  line  carried  across  the  centers  of  the  knee-joints,  and  therefore  tends  to  produce  overextension 
of  the  articulations;  this,  however,  is  prevented  by  the  tension  of  the  anterior  cruciate,  oblique 
pophteal,  and  collateral  Hgaments. 

Extension  of  the  leg  on  the  thigh  is  performed  by  the  Quadriceps  femoris;  flexion  by  the  Biceps 
femoris,  Semitendinosus,  and  Semimembranosus,  assisted  by  the  Gracilis,  Sartorius,  Gastroc- 
nemius, Popliteus,  and  Plantaris.  Rotation  outward  is  effected  by  the  Biceps  femoris,  and  rota- 
tion inward  by  the  Popliteus,  Semitendinosus,  and,  to  a  sUght  extent,  the  Semimembranosus,  the 
Sartorius,  and  the  Gracihs.  The  PopUteus  comes  into  action  especially  at  the  commencement 
of  the  movement  of  flexion  of  the  knee;  by  its  contraction  the  leg  is  rotated  inward,  or,  if  the 
tibia  be  fixed,  the  thigh  is  rotated  outward,  and  the  knee-joint  is  unlocked. 


Fio.  353. — Posterior  surface  of  the 
right  patella,  showing  diagrammatically 
the  areas  of  contact  with  the  femur  in 
different  positions  of  the  knee. 


ligament,    are   rendered    tense; 
is  tightened  by  the  Quadriceps 


m.    Articulations  between  the  Tibia  and  Fibula. 


I 

\^m       .  The  articulations  between  the  tibia  and  fibula  are  effected  by  ligaments  which 
^^K    connect  the  extremities  and  bodies  of  the  bones.    The  ligaments  may  consequently 


348 

be  subdivided  into  three  sets:  (1)  those  of  the  Tibiofibular  articulation;  (2)  the 
interosseous  membrane;  (3)  those  of  the  Tibiofibular  syndesmosis. 

Tibiofibular  Articulation  {articulatio  iibiofibularis;  superior  tibiofibular  articula- 
tion).— This  articulation  is  an  arthrodial  joint  between  the  lateral  condyle  of  the 
tibia  and  the  head  of  the  fibula.  The  contiguous  surfaces  of  the  bones  present 
flat,  oval  facets  covered  with  cartilage  and  connected  together  by  an  articular 
capsule  and  by  anterior  and  posterior  ligaments. 

The  Articular  Capsule  {caysula  articularis;  capsular  ligament). — The  articular 
capsule  surrounds  the  articulation,  being  attached  around  the  margins  of  the 
articular  facets  on  the  tibia  and  fibula;  it  is  much  thicker  in  front  than 
behind. 

The  Anterior  Ligament  {anterior  superior  ligament). — The  anterior  ligament  of 
the  head  of  the  fibula  (Fig.  347)  consists  of  two  or  three  broad  and  flat  bands, 
which  pass  obliquely  upward  from  the  front  of  the  head  of  the  fibula  to  the  front 
of  the  lateral  condyle  of  the  tibia. 

The  Posterior  Ligament  (posterior  superior  ligament). — The  posterior  ligament  of 
the  head  of  the  fibula  (Fig.  348)  is  a  single  thick  and  broad  band,  which  passes 
obliquely  upward  from  the  back  of  the  head  of  the  fibula  to  the  back  of  the  lateral 
condyle  of  the  tibia.    It  is  covered  by  the  tendon  of  the  Popliteus. 

Sjoiovial  Membrane. — A  synovial  membrane  lines  the  capsule;  it  is  continuous  with  that  of 
the  knee-joint  in  occasional  cases  when  the  two  joints  communicate. 

Interosseous  Membrane  (membrana  interossea  cruris;  middle  tibiofibular  liga- 
ment).— An  interosseous  membrane  extends  between  the  interosseous  crests  of  the 
tibia  and  fibula,  and  separates  the  muscles  on  the  front  from  those  on  the  back 
of  the  leg.  It  consists  of  a  thin,  aponeurotic  lamina  composed  of  oblique  fibers, 
which  for  the  most  part  run  downward  and  lateralward ;  some  f cav  fibers,  however, 
pass  in  the  opposite  direction.  It  is  broader  above  than  below.  Its  upper  margin 
does  not  quite  reach  the  tibiofibular  joint,  but  presents  a  free  concave  border, 
above  which  is  a  large,  oval  aperture  for  the  passage  of  the  anterior  tibial  vessels 
to  the  front  of  the  leg.  In  its  lower  part  is  an  opening  for  the  passage  of  the  anterior 
peroneal  vessels.  It  is  continuous  below  with  the  interosseous  ligament  of  the  tibio- 
fibular syndesmosis,  and  presents  numerous  perforations  for  the  passage  of  small 
vessels.  It  is  in  relation,  in  front,  with  the  Tibialis  anterior,  Extensor  digitorum 
longus.  Extensor  hallucis  proprius,  Peronseus  tertius,  and  the  anterior  tibial 
vessels  and  deep  peroneal  nerve;  behind,  with  the  Tibialis  posterior  and  Flexor 
hallucis  longus. 

Tibiofibular  Syndesmosis  {syndesmosis  tibiofibularis;  inferior  tibiofibular  articu- 
lation).— This  syndesmosis  is  formed  by  the  rough,  convex  surface  of  the  medial 
side  of  the  lower  end  of  the  fibula,  and  a  rough  concave  surface  on  the  lateral  side 
of  the  tibia.  Below,  to  the  extent  of  about  4  mm.  these  surfaces  are  smooth,  and 
covered  with  cartilage,  which  is  continuous  with  that  of  the  ankle-joint.  The 
ligaments  are:  anterior,  posterior,  inferior  transverse,  and  interosseous. 

The  Anterior  Ligament  {ligamentum  malleoli  lateralis  anterius;  anterior  inferior 
ligamejit)  .—The  anterior  ligament  of  the  lateral  malleolus  (Fig.  355)  is  a  flat, 
triangular  band  of  fibers,  broader  below  than  above,  which  extends  obliquely 
downward  and  lateralward  between  the  adjacent  margins  of  the  tibia  and  fibula, 
on  the  front  aspect  of  the  syndesmosis.  It  is  in  relation,  in  front,  with  the  Peronseus 
tertius,  the  aponeurosis  of  the  leg,  and  the  integument;  behind,  with  the  interosseous 
ligament;  and  lies  in  contact  with  the  cartilage  covering  the  talus. 

The  Posterior  Ligament  (ligamentum  malleoli  lateralis  posterius;  posterior  inferior 
ligament). — The  posterior  ligament  of  the  lateral  malleolus  (Fig.  355),  smaller 
than  the  preceding,  is  disposed  in  a  similar  manner  on  the  posterior  surface  of 
the  syndesmosis. 


TALOCRURAL  ARTICULATION  OR  ANKLE-JOINT 


349 


I 


The  Inferior  Transverse  Ligament. — The  inferior  transverse  ligament  lies  in  front 
of  the  posterior  ligament,  and  is  a  strong,  thick  band,  of  yellowish  fibers  which 
passes  transversely  across  the  back  of  the  joint,  from  the  lateral  malleolus  to  the 
posterior  border  of  the  articular  surface  of  the  tibia,  almost  as  far  as  its  malleolar 
process.  This  ligament  projects  below  the  margin  of  the  bones,  and  forms  part 
of  the  articulating  surface  for  the  talus. 

The  Interosseous  Ligament. — The  interosseous  ligament  consists  of  numerous 
short,  strong,  fibrous  bands,  which  pass  between  the  contiguous  rough  surfaces  of 
the  tibia  and  fibula,  and  constitute  the  chief  bond  of  union  between  the  bones. 
It  is  continuous,  above,  with  the  interosseous  membrane  (Fig.  356). 

Synovial  Membrane. — The  synovial  membrane  associated  with  the  small  arthrodial  part  of 
this  joint  is  continuous  with  that  of  the  ankle-joint. 

IV.  Talocrural  Articulation  or  Ankle-joint  (Articulatio  Talocruralis ;  Tibiotarsal 

Articulation). 

The  ankle-joint  is  a  ginglymus,  or  hinge-joint.  The  structures  entering  into  its 
formation  are  the  lower  end  of  the  tibia  and  its  malleolus,  the  malleolus  of  the 


^^  Post,  talotibial  ligament 


,  Medial  talocalcaneal  lig. 
Post,  talocalcaneal  lig. 


tr  capsule   Medial  cuneonavic.  lig.  \ 
Calcaneocuboid  ligament  ' 

Plantar  calcaneonaoic. 
liaament 


Long  plantar  ligament 
Fig.  354. — Ligaments  of  the  medial  aspect  of  the  foot.     (Quain.) 


fibula,  and  the  transverse  ligament,  which  together  form  a  mortise  for  the  recep- 
tion of  the  upper  convex  surface  of  the  talus  and  its  medial  and  lateral  facets. 
The  bones  are  connected  by  the  following  ligaments: 


The  Articular  Capsule. 
The  Deltoid. 


The  Anterior  Talofibular. 
The  Posterior  Talofibular. 


The  Calcaneofibular. 


350 


SYNDESMOLOGY 


The  Articular  Capsule  (capsula  articularis;  capsular  ligament). — The  articular  ca^ 
sule  surrounds  the  joints,  and  is  attached,  above,  to  the  borders  of  the  articular 
surfaces  of  the  tibia  and  malleoli ;  and  below,  to  the  talus  around  its  upper  articular 
surface.  The  anterior  part  of  the  capsule  (anterior  ligament)  is  a  broad,  thin, 
membranous  layer,  attached,  above,  to  the  anterior  margin  of  the  lower  end  of 
the  tibia;  below,  to  the  talus,  in  front  of  its  superior  articular  surface.  It  is  in 
relation,  in  front,  with  the  Extensor  tendons  of  the  toes,  the  tendons  of  the  Tibialis 
anterior  and  Peronseus  tertius,  and  the  anterior  tibial  vessels  and  deep  peroneal 
nerve.  The  posterior  part  of  the  capsule  (posterior  ligament)  is  very  thin,  and 
consists  principally  of  transverse  fibers.  It  is  attached,  above,  to  the  margin  of  the 
articular  surface  of  the  tibia,  blending  with  the  transverse  ligament;  below,  to  the 
talus  behind  its  superior  articular  facet.  Laterally,  it  is  somewhat  thickened,  and 
is  attached  to  the  hollow  on  the  medial  surface  of  the  lateral  malleolus. 


i 


Post.  lot.  malleol.  Eg 


Dorsal  talonavic.  lia. 

\  Calcaneonavic,  parl\r,-, 
I  Calcaneocuboid  part]^^^'^'"^^^'^  ^'O- 
I  Dorsal  cuboideonavic.  tig. 

Dorsal  navicular  cuneif.  lig, 
\  Dorsal  cuneocuboid  lig. 
.1     \Dorsal  intercuneif,  Uq, 


/y  Dorsal  tarsometat.  lig 


Post,  talofibular  lig 


Dorsal 
\calcaneocub 
lig. 
Long  plantar  lig.        \ 
]Interos.  talocalcan.  lig 
I     Ant.  talofibular  lig, 
Caicaneofibular  lig. 


Dorsal  intermet.  lig. 
Dorsal  tarsomet.  lig. 


Fig.  355. — The  ligaments  of  the  foot  from  the  lateral  aspect.     (Cjuain.) 


I 


The  Deltoid  Ligament  (ligamentum  deltoideum;  internal  lateral  ligament) 
(Fig.  331). — The  deltoid  ligament  is  a  strong,  flat,  triangular  band,  attached, 
above,  to  the  apex  and  anterior  and  posterior  borders  of  the  medial  malleolus. 
It  consists  of  two  sets  of  fibers,  superficial  and  deep.  Of  the  superficial  fibers  the 
most  anterior  (tibionavicular)  pass  forward  to  be  inserted  into  the  tuberosity  of 
the  navicular  bone,  and  immediately  behind  this  they  blend  with  the  medial  margin 
of  the  plantar  calcaneonavicular  ligament;  the  middle  (calcaneotibial)  descend 
almost  perpendicularly  to  be  inserted  into  the  w^hole  length  of  the  sustentaculum 
tali  of  the  calcaneus;  the  posterior  fibers  (posterior  talotibial)  pass  backward  and 
lateralward  to  be  attached  to  the  inner  side  of  the  talus,  and  to  the  prominent 


TALOCRURAL  ARTICULATION  OR  ANKLE-JOINT 


351 


11^^ 


ercle  on  its  posterior  surface,  medial  to  the  groove  for  the  tendon  of  the  Flexor 
hallucis  longus.  The  deep  fibers  {anterior  talotibial)  are  attached,  above,  to  the 
tip  of  the  medial  malleolus,  and,  below,  to  the  medial  surface  of  the  talus.  The 
deltoid  ligament  is  covered  by  the  tendons  of  the  Tibialis  posterior  and  Flexor 
digitorum  longus. 

The  anterior  and  posterior  talofibular  and  the  calcaneofibular  ligaments  were 
formerly  described  as  the  three  fasciculi  of  the  external  lateral  ligament  of  the 
ankle-joint. 

The  Anterior  Talofibular  Ligament  {lig amentum  talofibulare  anterius)  (Fig.  355). 

The  anterior  talofibular  ligament,  the  shortest  of  the  three,  passes  from  the 
anterior  margin  of  the  fibular  malleolus,  forward  and  medially,  to  the  talus,  in 
front  of  its  lateral  articular  facet. 

The  Posterior  Talofibular  Ligament  (ligamentum  talofibulare  posterius)  (Fig.  355). 

The  posterior  talofibular  ligament,  the  strongest  and  most  deeply  seated,  runs 
almost  horizontally  from  the  depression  at  the  medial  and  back  part  of  the  fibular 
malleolus  to  a  prominent  tubercle  on  the  posterior  surface  of  the  talus  immediately 
lateral  to  the  groove  for  the  tendon  of  the  Flexor  hallucis  longus. 

The  Calcaneofibular  Ligament  {ligamentum  calcaneqfibulare)  (Fig.  355). — The 
calcaneofibular  ligament,  the  longest  of  the  three,  is  a  narrow,  rounded  cord,  run- 
ning from  the  apex  of  the  fibular  malleolus  downward  and  slightly  backward  to  a 
tubercle  on  the  lateral  surface  of  the  calcaneus.  It  is  covered  by  the  tendons  of 
the  Peronsei  longus  and  brevis. 


Anterior  talofibular  ligament 


Posterior  ialofihular  ligament 
Calcaneofibtdar  ligament 
Lateral  kUocalcaneal  ligament 


II 


Anterior 

talocalcaneal 

ligament 


Fig.  356. — Capsule  of  left  talocrura   articulation  (distended).     Lateral  aspect. 


Synovial  Membrane  (Fig.  356). — The  synovial  membrane  invests  the  deep  surfaces  of  the 
ligaments,  and  sends  a  small  process  upward  between  the  lower  ends  of  the  tibia  and  fibula. 

Relations. — The  tendons,  vessels,  and  nerves  in  connection  with  the  joint  are,  in  front,  from  the 
medial  side,  the  Tibialis  anterior,  Extensor  hallucis  proprius,  anterior  tibial  vessels,  deep  peroneal 
nerve.  Extensor  digitorum  longus,  and  Perona^us  tertius;  behind,  from  the  medial  side,  the  Tibialis 
posterior,  Flexor  digitonma  longus,  posterior  tibial  vessels,  tibial  nerve,  Flexor  hallucis  longus; 
and,  in  the  groove  behind  the  fibular  malleolus,  the  tendons  of  the  Peromei  longus  and  brevis. 

The  arteries  supplying  the  joint  are  derived  from  the  malleolar  branches  of  the  anterior  tibial 
and  the  peroneal. 

The  nerves  are  derived  from  the  deep  peroneal  and  tibial. 

Movements. — When  the  body  is  in  the  erect  position,  the  foot  is  at  right  angles  to  the  leg. 
The  movements  of  the  joint  are  those  of  dorsiflexion  and  extension;  dorsiflexion  consists  in  the 


352  -^^^^™r        SYNDESMOLOGY 

approximation  of  the  dorsum  of  the  foot  to  the  front  of  the  leg,  while  in  extension  the  heel  'is 
drawn  up  and  the  toes  pointed  downward.  The  range  of  movement  varies  in  different  individuals 
from  about  50°  to  90°.  The  transverse  axis  about  which  movement  takes  place  is  slightly  oblique. 
The  malleoli  tightly  embrace  the  talus  in  all  positions  of  the  joint,  so  that  any  slight  degree  of 
side-to-side  movement  which  may  exist  is  simply  due  to  stretching  of  the  ligaments  of  the  talo- 
fibular syndesmosis,  and  slight  bending  of  the  body  of  the  fibula.  The  superior  articular  surface 
of  the  talus  is  broader  in  front  than  behind.  In  doisiflexion,  herefore,  greater  space  is  required 
between  the  two  malleoU.  This  is  obtained  by  a  slight  outward  rotatory  movement  of  the  lower 
end  of  the  fibula  and  a  stretching  of  the  ligaments  of  the  syndesmosis;  this  lateral  movement  is 
faciUtated  by  a  slight  gliding  at  the  tibiofibular  articulation,  and  possibly  also  by  the  bending  of 
the  body  of  the  fibula.  Of  the  Ugaments,  the  deltoid  is  of  very  great  power — so  much  so,  that 
it  usually  resists  a  force  which  fractures  the  process  of  bone  to  which  it  is  attached.  Its  middle 
portion,  together  with  the  calcaneofibular  Ugament,  binds  the  bones  of  the  leg  firmly  to  the 
foot,  and  resists  displacement  in  every  direction.  Its  anterior  and  posterior  fibers  limit  extension 
and  flexion  of  the  foot  respectively,  and  the  anterior  fibers  also  limit  abduction.  The  posterior 
talofibular  ligament  assists  the  calcaneofibular  in  resisting  the  displacement  of  the  foot  back- 
ward, and  deepens  the  cavity  for  the  reception  of  the  talus.  The  anterior  talofibular  is  a 
security  against  the  displacement  of  the  foot  forward,  and  hmits  extension  of  the  joint. 

The  movements  of  inversion  and  eversion  of  the  foot,  together  with  the  minute  changes  in 
form  by  which  it  is  appUed  to  the  ground  or  takes  hold  of  an  object  in  cUmbing,  etc.,  are  mainly 
effected  in  the  tarsal  joints;  the  joint  which  enjoys  the  greatest  amount  of  motion  being  that  be- 
tween the  talus  and  calcaneus  behind  and  the  navicular  and  cuboid  in  front.  This  is  often  called 
the  transverse  tarsal  joint,  and  it  can,  with  the  subordinate  joints  of  the  tarsus,  replace  the  ankle- 
joint  in  a  great  measure  when  the  latter  has  become  ankylosed. 

Extension  of  the  foot  upon  the  tibia  and  fibula  is  produced  by  the  Gastrocnemius,  Soleus, 
Plantaris,  Tibiahs  posterior,  Peronai  longus  and  brevis.  Flexor  digitorum  longus,  and  Flexor 
hallucis  longus;  dorsiflexion,  Ijy  the  TibiaUs  anterior,  Peronseus  tertius,  Extensor  digitorum  longus, 
and  Extensor  hallucis  proprius.^ 

V.    Intertarsal  Articulatdons  (Articulationes  Intertarseae ;  Articulations 

of  the  Tarsus). 

Talocalcaneal  Articulation  (articulatio  talocalcanea;  articulation  of  the  calcaneus 
and  astragalus;  calcaneo-astragaloid  articulation). — The  articulations  between  the 
calcaneus  and  talus  are  two  in  number — anterior  and  posterior.  Of  these,  the 
anterior  forms  part  of  the  talocalcaneonavicular  joint,  and  will  be  described  with 
that  articulation.  The  posterior  or  talocalcaneal  articulation  is  formed  betw^een 
the  posterior  calcaneal  facet  on  the  inferior  surface  of  the  talus,  and  the  posterior 
facet  on  the  superior  surface  of  the  calcaneus.  It  is  an  arthrodial  joint,  and  the 
two  bones  are  connected  by  an  articular  capsule  and  by  anterior,  posterior,  lateral , 
medial,  and  interosseous  talocalcaneal  ligaments. 

The  Articular  Capsule  (capsula  articularis) . — The  articular  capsule  envelops 
the  joint,  and  consists  for  the  most  part  of  short  fibers,  which  are  split  up  into 
distinct  slips;  betw^een  these  there  is  only  a  weak  fibrous  investment. 

The  Anterior  Talocalcaneal  Ligament  {ligamentum  talocalcaneum  anterius;  anterior 
calcaneo-astragaloid  ligament)  (Figs.  356,  359). — The  anterior  talocalcaneal  liga- 
ment extends  from  the  front  and  lateral  surface  of  the  neck  of  the  talus  to 
the  superior  surface  of  the  calcaneus.  It  forms  the  posterior  boundary  of  the 
talocalcaneonavicular  joint,  and  is  sometimes  described  as  the  anterior  interosseous 
ligament. 

The  Posterior  Talocalcaneal  Ligament  {ligamentum  talocalcaneum  posteriiis; 
posterior  calcaneo-astragaloid  ligament)  (Fig.  354). — The  posterior  talocalcaneal 
ligament  connects  the  lateral  tubercle  of  the  talus  with  the  upper  and  medial  part 
of  the  calcaneus;  it  is  a  short  band,  and  its  fibers  radiate  from  their  narrow  attach- 
ment to  the  talus. 

The  Lateral  Talocalcaneal  Ligament  (ligamentum  talocalcaneum  laterale;  external 
calcaneo-astragaloid  ligament)  (Figs.  356,  359).— The  lateral  talocalcaneal  ligament 

1  The  student  must  bear  in  mind  that  the  Extensor  digitorum  longus  and  Extensor  hallucis  proprius  are  extenaora 
of  the  toes,  but  flexors  of  the  ankle:  and  that  the  Flexor  digitorum  longus  and  Flexor  hallucis  longus  are  flexors  of  the 
toes,  but  extensors  of  the  ankle 


INTERTARSAL  ARTICULATIONS 


353 


IS  a  short,  strong  fasciculus,  passing  from  the  lateral  surface  of  the  talus,  imme- 
diately beneath  its  fibular  facet  to  the  lateral  surface  of  the  calcaneus.  It  is  placed 
in  front  of,  but  on  a  deeper  plane  than,  the  calcaneofibular  ligament,  with  the  fibers 
of  which  it  is  parallel. 

The  Medial  Talocalcaneal  Ligament  (ligamentum  talocalcaneum  mediale;  internal 
calcaneo-astragaloid  ligament). — The  medial  talocalcaneal  ligament  connects  the 
medial  tubercle  of  the  back  of  the  talus  with  the  back  of  the  sustentaculum  tali. 
Its  fibers  blend  with  those  of  the  plantar  calcaneonavicular  ligament  (Fig.  354) . 


Interosseous  ligament  of  tibia 
fibular  syndesmosis 


Medial  malleolus - 

Deltoid  ligament  • 

Tibialis  posterior' 


l^lexor  digitorum  longus 

Flexor  fiallucis  longus 

Med.  plantar  nerve  and  vessels 

Quadratus  plantCB 

Abductor  hallucis 

Lat.  plantar  nerve  and  vessels 
Flexor  digitorum  brevis 


Lateral  malleolus 

Calcaneofibular  ligament 
,terosseou6 
ligament 

Peroncetcs  brevis 


PeroncBus  longus 
Abductor  digiti  quinti 


Fig.  357. — Coronal  section  through  right  talocrural  and  talocalcaneal  joints. 

The  Interosseous  Talocalcaneal  Ligament  (ligamentum  talocalcaneum  interosseum) 
(Figs.  357,  359). — The  interosseous  talocalcaneal  ligament  forms  the  chief  bond 
of  union  between  the  bones.  It  is,  in  fact,  a  portion  of  the  united  capsules  of  the 
talocalcaneonavicular  and  the  talocalcaneal  joints,  and  consists  of  two  partially 
united  layers  of  fibers,  one  belonging  to  the  former  and  the  other  to  the  latter  joint. 
It  is  attached,  above,  to  the  groove  between  the  articular  facets  of  the  under  surface 
of  the  talus;  below,  to  a  corresponding  depression  on  the  upper  surface  of  the  cal- 
caneus.' It  is  very  thick  and  strong,  being  at  least  2.5  cm.  in  breadth  from  side 
to  side,  and  serves  to  bind  the  calcaneus  and  talus  firmly  together. 

Synovial  Membrane  (Fig.  360). — The  synovial  membrane  lines  the  capsule  of  the  joint,  and 
is  distinct  from  the  other  synovial  membranes  of  the  tarsus. 

Movements. — The  movements  permitted  between  the  talus  and  calcaneus  are  limited  to  glid- 
ing of  the  one  bone  on  the  other  backward  and  forward  and  from  side  to  side. 

Talocalcaneonavicular    Articulation    {articulatio   talocalcaneonacicularis) . — This 

articulation  is  an  arthrodial  joint:  the  rounded  head  of  the  talus  being  received 

into  the  concavity  formed  by  the  posterior  surface  of  the  navicular,  the  anterior 

articular  surface  of  the  calcaneus,  and  the  upper  surface  of  the  plantar  calcaneo- 

23 


354  SYNDESMOLOGY 

navicular  ligament.    There  are  two  ligaments  in  this  joint:  the  articular  capsule] 
and  the  dorsal  talonavicular. 

The  Articular  Capsule  (capsula  articularis) . — The  articular  capsule  is  imperfectly 
developed  except  posteriorly,  where  it  is  considerably  thickened  and  forms,  with 
a  part  of  the  capsule  of  the  talocalcaneal  joint,  the  strong  interosseous  ligament 
which  fills  in  the  canal  formed  by  the  opposing  grooves  on  the  calcaneus  and  talus, 
as  above  mentioned. 

The  Dorsal  Talonavicular  Ligament  {ligamentum  talonaviculare  dorsale;  superior 
astragalonavicular  ligament)  (Fig.  354).— This  ligament  is  a  broad,  thin  band,  which 
connects  the  neck  of  the  talus  to  the  dorsal  surface  of  the  navicular  bone;  it  is 
covered  by  the  Extensor  tendons.  The  plantar  calcaneonavicular  supplies  the 
place  of  a  plantar  ligament  for  this  joint. 

Synovial  Membrane. — The  synovial  membrane  lines  all  parts  of  the  capsule  of  the  joint 
Movements. — This  articulation  permits  of  a  considerable  range  of  ghding  movements,  and  some 

rotation;  its  feeble  construction  allows  occasionally  of  dislocation  of  the  other  bones  of  the  tarsus 

from  the  talus. 

Calcaneocuboid  Articulation  (articulatio  calcaneocuhoidea;  articulation  of  the 
calcaneus  with  the  cuboid). — The  ligaments  connecting  the  calcaneus  with  the 
cuboid  are  five  in  number,  viz.,  the  articular  capsule,  the  dorsal  calcaneocuboid, 
part  of  the  bifurcated,  the  long  plantar,  and  the  plantar  calcaneocuboid. 

The  Articular  Capsule  {capsula  articularis). — The  articular  capsule  is  an  imper- 
fectly developed  investment,  containing  certain  strengthened  bands,  which  form 
the  other  ligaments  of  the  joint. 

The  Dorsal  Calcaneocuboid  Ligament  {ligamentum  calcaneocuhoideum  dorsale;  supe- 
rior calcaneocuboid  ligament)  (Fig.  355). — The  dorsal  calcaneocuboid  ligament  is 
a  thin  but  broad  fasciculus,  which  passes  between  the  contiguous  surfaces  of  the 
calcaneus  and  cuboid,  on  the  dorsal  surface  of  the  joint. 

The  Bifurcated  Ligament  {ligamentum  bifurcatum;  internal  calcaneocuboid;  inter- 
osseous ligament)  (Fig.  355,  359). — The  bifurcated  ligament  is  a  strong  band, 
attached  behind  to  the  deep  hollow  on  the  upper  surface  of  the  calcaneus  and  divid- 
ing in  froi^t  in  a  Y-shaped  manner  into  a  calcaneocuboid  and  a  calcaneonavicular 
part.  The  calcaneocuboid  part  is  fixed  to  the  medial  side  of  the  cuboid  and  forms 
one  of  the  principal  bonds  between  the  first  and  second  rows  of  the  tarsal  bones. 
The  calcaneonavicular  part  is  attached  to  the  lateral  side  of  the  navicular. 

The  Long  Plantar  Ligament  {ligamentum  plantare  longum;  long  calcaneocuboid 
ligament;  superiicial  long  plantar  ligament)  (Fig.  358) . — The  long  plantar  ligament 
is  the  longest  of  all  the  ligaments  of  the  tarsus :  it  is  attached  behind  to  the  plantar 
surface  of  the  calcaneus  in  front  of  the  tuberosity,  and  in  front  to  the  tuberosity 
on  the  plantar  surface  of  the  cuboid  bone,  the  more  superficial  fibers  being  con- 
tinued forward  to  the  bases  of  the  second,  third,  and  fourth  metatarsal  bones. 
This  ligament  converts  the  groove  on  the  plantar  surface  of  the  cuboid  into  a 
canal  for  the  tendon  of  the  Peronseus  longus. 

The  Plantar  Calcaneocuboid  Ligament  {ligamentum  calcaneocuboideum  plantare; 
short  calcaneocuboid  ligament;  short  plantar  ligament)  (Fig.  358). — The  'plantar 
calcaneocuboid  ligament  lies  nearer  to  the  bones  than  the  preceding,  from  which 
it  is  separated  by  a  little  areolar  tissue.  It  is  a  short  but  wide  band  of  great  strength, 
and  extends  from  the  tubercle  and  the  depression  in  front  of  it,  on  the  forepart 
of  the  plantar  surface  of  the  calcaneus,  to  the  plantar  surface  of  the  cuboid  behind 
the  peroneal  groove. 

Synovial  Membrane. — The  synovial  membrane  lines  the  inner  surface  of  the  capsule  and  is 
distinct  from  that  of  the  other  tarsal  articulations  (Fig.  360). 

Movements. — The  movements  permitted  between  the  calcaneus  and  cuboid  are  limited  to 
slight  ghding. movements  of  the  bones  upon  each  other. 

The  transverse  tarsal  joint  is  formed  by  the  articulation  of  the  calcaneus  with  the  cuboid,  and 


INTERTARSAL  ARTICULATIONS 


355 


the  articulation  of  the  talus  with  the  navicular.  The  movement  which  takes  place  in  this  joint 
is  more  extensive  than  that  in  the  other  tarsal  joints,  and  consists  of  a  sort  of  rotation  by  means 
of  which  the  foot  may  be  sUghtly  flexed  or  extended,  the  sole  being  at  the  same  time  carried 
medially  (inverted)  or  laterally  (everted). 

The  Ligaments  Connecting  the  Calcaneus  and  Navicular. — Though  the  calcaneus 
and  navicular  do  not  directly  articulate,  they  are  connected  by  two  ligaments: 
the  calcaneonavicular  part  of  the  bifurcated,  and  the  plantar  calcaneonavicular. 

The  calcaneonavicular  part  of  the  bifurcated  ligament  is  described  on  page  354. 


Plantar  intermetatar .  lig. 


irdar  calcaneocub.  lig.  —— 


Tendon  peronanis  longus 
muscle 

Long  plantar  ligament 


Tendon  peronceus 
^  longus  muscle 


--•^ Plantar  tarsometatar.  lig. 


Tendon  tibialis  anticua 
nvuscle 


'Plantar  cuneonavic.  lig, 

'^"Plantar  cuboideonavic, 
ligament 

^i_  Plantar  calcaneonavic. 
ligament 


Tendon  tibialis  posticus 
muscle 


Fig.  358.- 


-Ligaments  of  the  sole  of  the  foot,  with  the  tendons  of  the  Peronseus  longus.  Tibialis  posterior  and  Tibialis 
anterior  muscles.     (Quain.) 


The  Plantar  Calcaneonavicular  Ligament  (ligamentum  ealcaneonaviculare  plantare; 
inferior  or  internal  calcaneonavicular  ligament;  calcaneonavicular  ligament)  (Figs. 
354,  358) . — The  plantar  calcaneonavicular  ligament  is  a  broad  and  thick  band  of 
fibers,  which  connects  the  anterior  margin  of  the  sustentaculum  tali  of  the  calca- 
IB  neus  to  the  plantar  surface  of  the  navicular.  This  ligament  not  only  serves  to 
H    connect  the  calcaneus  and  navicular,  but  supports  the  head  of  the  talus,  forming 


356 


SYNDESMOLOGY 


part  of  the  articular  cavity  in  which  it  is  received.  The  dorsal  surface  of  the 
ligament  presents  a  fibrocartilaginous  facet,  lined  by  the  synovial  membrane, 
and  upon  this  a  portion  of  the  head  of  the  talus  rests.  Its  plantar  surface  is 
supported  by  the  tendon  of  the  Tibialis  posterior;  its  medial  border  is  blended  with 
the  forepart  of  the  deltoid  ligament  of  the  ankle-joint. 


Tibialis 
'posterior 


Interosseous 

talocalcaneal 

ligament 


Lateral 
talocalcaneal 

ligament 

Anterior 
talocalcaneal 

ligament 


Fio.  359. — Talocalcaneal  and  talocalcaneonavicular  articulations  exposed  from  above  by  removing  the  talus. 

The  plantar  calcaneonavicular  ligament,  by  supporting  the  head  of  the  talus,  is  principally 
concerned  in  maintaining  the  arch  of  the  foot.  When  it  yields,  the  head  of  the  talus  is  pressed 
downward,  medialward,  and  forward  by  the  weight  of  the  body,  and  the  foot  becomes  flattened, 
expanded,  and  turned  lateralward,  and  exhibits  the  condition  known  as  flal-foot.  This  ligament 
contains  a  considerable  amount  of  elastic  fibers,  so  as  to  give  elasticity  to  the  arch  and  spring 
to  the  foot;  hence  it  is  sometimes  called  the  "spring"  ligament.  It  is  supported,  on  its  plantar 
surface,  by  the  tendon  of  the  Tibialis  posterior,  which  spreads  out  at  its  insertion  into  a  number 
of  fasciculi,  to  be  attached  to  most  of  the  tarsal  and  metatarsal  bones.  This  prevents  undue 
stretching  of  the  ligament,  and  is  a  protection  against  the  occurrence  of  flat-foot;  hence  muscular 
weakness  is,  in  most  cases,  the  primary  cause  of  the  deformity. 

Cuneonavicular  Articulation  (articulatio  cuneonavicularis;  articulation  of  the 
navicular  with  the  cuneiform  bones). — The  navicular  is  connected  to  the  three 
cuneiform  bones  by  dorsal  and  plantar  ligaments. 

The  Dorsal  Ligaments  (ligamenta  navicularicuneiformia  dorsalia). — The  dorsal 
ligaments  are  three  small  bundles,  one  attached  to  each  of  the  cuneiform  bones. 
The  bundle  connecting  the  navicular  with  the  first  cuneiform  is  continuous  around 
the  medial  side  of  the  articulation  with  the  plantar  ligament  which  unites  these 
two  bones  (Figs.  354,  355) . 

The  Plantar  Ligaments  {ligamenta  navicularicuneiformia  plantaria) . — The  plantar 
ligaments  have  a  similar  arrangement  to  the  dorsal,  and  are  strengthened  by  slips 
from  the  tendon  of  the  Tibialis  posterior  (Fig.  358). 

Sjmovial  Membrane. — The  sjTiovial  membrane  of  these  joints  is  part  of  the  great  tarsal  synovial 
membrane  (Fig.  360). 

Movements. — Mere  gliding  movements  are  permitted  between  the  navicular  and  cuneiform 
bones. 

Cuboideonavicular  Articulation. — The  navicular  bone  is  connected  with  the 
cuboid  by  dorsal,  plantar,  and  interosseous  ligaments. 


INTERTARSAL  ARTICULATIONS 


357 


II 


The  Dorsal  Ligament  {ligamentum  cuboideonaviculare  dorsale) . — The  dorsal  ligament 
extends  obliquely  forward  and  lateralward  from  the  navicular  to  the  cuboid  bone 
(Fig.  355). 

The  Plantar  Ligament  (ligavientum  cuboideonaviculare  plantare). — The  plantar 
ligament  passes  nearly  transversely  between  these  two  bones  (Fig.  358), 

The  Interosseous  Ligament. — The  interosseous  ligament  consists  of  strong  trans- 
verse fibers,  and  connects  the  rough  non-articular  portions  of  the  adjacent  surfaces 
of  the  two  bones  Fig.  360). 

Ssmovial  Membrane. — The  synovial  membrane  of  this  joint  is  part  of  the  great  tarsal  synovial 
membrane  (Fig.  360). 

Movements. — The  movements  permitted  between  the  navicular  and  cuboid  bones  are  limited 
to  a  slight  gliding  upon  each  other. 


Deltoid 
ligament 


Ankle-joint 


Talofibular 
ligament 


Interosseous 
talocalcaneal 
ligament 


Metatarsals 

Fig,  360. — Oblique  section  of  left  intertarsal  and  tarsometatarsal  articulations,  showing  the  synovial  cavities. 


Intercuneiform  and  Cuneocuboid  Articulations. — The  three  cuneiform  bones  and 
the  cuboid  are  connected  together  by  dorsal,  plantar,  and  interosseous  ligaments. 

The  Dorsal  Ligaments  (ligamenta  intercuneiformia  dorsalia). — The  dorsal  liga- 
ments consist  of  three  transverse  bands :  one  connects  the  first  with  the  second 
cuneiform,  another  the  second  with  the  third  cuneiform,  and  another  the  third 
cuneiform  with  the  cuboid. 

The  Plantar  Ligaments  (ligamenta  intercuneiformia  plantaria). — The  plantar  liga- 
ments have  a  similar  arrangement  to  the  dorsal,  and  are  strengthened  by  slips 
from  the  tendon  of  the  Tibialis  posterior. 

The  Interosseous  Ligaments  (ligamenta  intercuneiformia  interossea). — The  inter- 
osseous ligaments  consist  of  strong  transverse  fibers  which  pass  between  the  rough 
non-articular  portions  of  the  adjacent  surfaces  of  the  bones  (Fig.  360) . 


358  SYNDESMOLOGY 

Synovial  Membrane. — The  synovial  membrane  of  these  joints  is  part  of  the  great  tarsal  synovial 
membrane  (Fig.  360). 

Movements. — The  movements  permitted  between  these  bones  are  limited  to  a  slight  gUding 
upon  each  other. 


VI.    Tarsometatarsal  Articulations  (Articulationes  Tarsometatarseae). 

These  are  arthrodial  joints.  The  bones  entering  into  their  formation  are  the 
first,  second,  and  third  cuneiforms,  and  the  cuboid,  which  articulate  with  the  bases 
of  the  metatarsal  bones.  The  first  metatarsal  bone  articulates  with  the  first  cunei- 
form; the  second  is  deeply  wedged  in  between  the  first  and  third  cuneiforms 
articulating  by  its  base  with  the  second  cuneiform;  the  third  articulates  with  the 
third  cuneiform;  the  fourth,  with  the  cuboid  and  third  cuneiform;  and  the  fifth, 
with  the  cuboid.  The  bones  are  connected  by  dorsal,  plantar,  and  interosseous 
ligaments. 

The  Dorsal  Ligaments  {ligamenta  tarsometatarsea  dorsalia) . — The  dorsal  ligaments 
are  strong,  flat  bands.  The  first  metatarsal  is  joined  to  the  first  cuneiform  by  a 
broad,  thin  band;  the  second  has  three,  one  from  each  cuneiform  bone;  the  third 
has  one  from  the  third  cuneiform;  the  fourth  has  one  from  the  third  cuneiform 
and  one  from  the  cuboid;  and  the  fifth,  one  from  the  cuboid  (Figs.  354,  355). 

The  Plantar  Ligaments  (ligamenta  tarsometatarsea  plantaria)  .—The  plantar  liga- 
ments consist  of  longitudinal  and  oblique  bands,  disposed  with  less  regularity 
than  the  dorsal  ligaments.  Those  for  the  first  and  second  metatarsals  are  the 
strongest;  the  second  and  third  metatarsals  are  joined  by  oblique  bands  to  the 
first  cuneiform;  the  fourth  and  fifth  metatarsals  are  connected  by  a  few  fibers 
to  the  cuboid  (Fig.  358). 

The  Interosseous  Ligaments  (ligamenta  cuneometatarsea  interossia). — The  inter- 
osseous ligaments  are  three  in  number.  The  first  is  the  strongest,  and  passes  from 
the  lateral  surface  of  the  first  cuneiform  to  the  adjacent  angle  of  the  second  meta- 
tarsal. The  second  connects  the  third  cuneiform  with  the  adjacent  angle  of  the 
second  metatarsal.  The  third  connects  the  lateral  angle  of  the  third  cuneiform 
with  the  adjacent  side  of  the  base  of  the  third  metatarsal. 

Synovial  Membrane  (Fig.  360). — The  synovial  membrane  between  the  first  cuneiform  and 
the  first  metatarsal  forms  a  distinct  sac.  The  synovial  membrane  between  the  second  and  third 
cuneiforms  behind,  and  the  second  and  third  metatarsal  bones  in  front,  is  part  of  the  great  tarsal 
synovial  membrane.  Two  prolongations  are  sent  forward  from  it,  one  between  the  adjacent  sides 
of  the  second  and  third,  and  another  between  those  of  the  third  and  fourth  metatarsal  bones. 
The  synovial  membrane  between  the  cuboid  and  the  fourth  and  fifth  metatarsal  bones  forms  a 
distinct  sac.    From  it  a  prolongation  is  sent  forward  between  the  fourth  and  fifth  metatarsal  bones. 

Movements. — The  movements  permitted  between  the  tarsal  and  metatarsal  bones  are  limited 
to  slight  ghding  of  the  bones  upon  each  other. 

Nerve  Supply. — The  intertarsal  and  tarsometatarsal  joints  are  supphed  by  the  deep  peroneal 
nerve. 

VII.     Intermetatarsal  Articulations  (Articulationes  Intermetatarsese). 

The  base  of  the  first  metatarsal  is  not  connected  with  that  of  the  second  by  any 
ligaments;  in  this  respect  the  great  toe  resembles  the  thumb. 

The  bases  of  the  other  four  metatarsals  are  connected  by  the  dorsal,  plantar, 
and  interosseous  ligaments. 

The  Dorsal  Ligaments  (ligamenta  hasium  [oss.  metatars.]  dorsalia)  pass  transversely 
between  the  dorsal  surfaces  of  the  bases  of  the  adjacent  metatarsal  bones. 

The  Plantar  Ligaments  (ligamenta  hasium  [oss.  metatars]  'plantaria) . — The  plantar 
ligaments  have  a  similar  arrangement  to  the  dorsal. 

The  Interosseous  Ligaments  (ligamenta  hasium  [oss.  metatars.]  interossea). — The 
interosseous  ligaments  consist  of  strong  transverse  fibers  which  connect  the  rough 
non-articular  portions  of  the  adjacent  surfaces. 


II 


ARTICULATIONS  OF  THE  DIGITS  359 

Synovial  Membranes  (Fig.  360). — The  synovial  membranes  between  the  second  and  third, 
and  the  third  and  fourth  metatarsal  bones  are  part  of  the  great  tarsal  synovial  membrane;  that 
between  the  fourth  and  fifth  is  a  prolongation  of  the  synovial  membrane  of  the  cuboideometatarsal 
joint. 

Movements. — The  movement  permitted  between  the  tarsal  ends  of  the  metatarsal  bones 
is  Hmited  to  a  shght  gUding  of  the  articular  surfaces  upon  one  another. 

The  heads  of  all  the  metatarsal  bones  are  connected  together  by  the  transverse 
metatarsal  ligament. 

The  Transverse  Metatarsal  Ligament. — The  transverse  metatarsal  ligament  is  a 
narrow  band  which  runs  across  and  connects  together  the  heads  of  all  the  meta- 
tarsal bones;  it  is  blended  anteriorly  with  the  plantar  (glenoid)  ligaments  of  the 
metatarsophalangeal  articulations.  Its  plantar  surface  is  concave  where  the 
Flexor  tendons  run  below  it;  above  it  the  tendons  of  the  Interossei  pass  to  their 
insertions.  It  differs  from  the  transverse  metacarpal  ligament  in  that  it  connects 
the  metatarsal  to  the  others. 

The  Synovial  Membranes  in  the  Tarsal  and  Tarsometatarsal  Joints  (Fig.  360). — The  synovial 
membranes  found  in  the  articulations  of  the  tarsus  and  metatarsus  are  six  in  number:  one  for 
the  talocalcaneal  articulation;  a  second  for  the  talocalcaneonavicular  articulation;  a  third  for 
the  calcaneocuboid  articulation;  and  a  fourth  for  the  cuneonavicular,  intercuneiform,  and  cimeo- 
cuboid  articulations,  the  articulations  of  the  second  and  third  cuneiforms  with  the  bases  of  the 
second  and  third  metatarsal  bones,  and  the  adjacent  surfaces  of  the  bases  of  the  second,  third, 
and  fourth  metatarsal  bones;  a  fifth  for  the  first  cuneiform  with  the  metatarsal  bone  of  the  great 
toe;  and  a  sixth  for  the  articulation  of  the  cuboid  with  the  fourth  and  fifth  metatarsal  bones. 
A  small  synovial  cavity  is  sometimes  foimd  between  the  contiguous  surfaces  of  the  navicular 
and  cuboid  bones. 

VIII.  Metatarsophalangeal  Articulations  (Articulationes  Metatarsophalangese). 

The  metatarsophalangeal  articulations  are  of  the  condyloid  kind,  formed  by 
the  reception  of  the  rounded  heads  of  the  metatarsal  bones  in  shallow  cavities 
on  the  ends  of  the  first  phalanges. 

The  ligaments  are  the  plantar  and  two  collateral. 

The  Plantar  Ligaments  {ligamenta  accessoria  plantaria;  glenoid  ligaments  of  Cru- 
veilhier). — The  plantar  ligaments  are  thick,  dense,  fibrous  structures.  They  are 
placed  on  the  plantar  surfaces  of  the  joints  in  the  intervals  between  the  collateral 
ligaments,  to  which  they  are  connected ;  they  are  loosely  united  to  the  metatarsal 
bones,  but  very  firmly  to  the  bases  of  the  first  phalanges.  Their  plantar  surfaces 
are  intimately  blended  with  the  transverse  metatarsal  ligament,  and  grooved  for 
the  passage  of  the  Flexor  tendons,  the  sheaths  surrounding  which  are  connected 
to  the  sides  of  the  grooves.  Their  deep  surfaces  form  part  of  the  articular  facets 
for  the  heads  of  the  metatarsal  bones,  and  are  lined  by  synovial  membrane. 

The  Collateral  Ligaments  {ligamenta  collateralia;  lateral  ligaments)  .—The  collat- 
eral ligaments  are  strong,  rounded  cords,  placed  one  on  either  side  of  each  joint, 
and  attached,  by  one  end,  to  the  posterior  tubercle  on  the  side  of  the  head  of  the 
metatarsal  bone,  and,  by  the  other,  to  the  contiguous  extremity  of  the  phalanx. 

The  place  of  dorsal  ligaments  is  supplied  by  the  Extensor  tendons  on  the  dorsal 
surfaces  of  the  joints. 

Movements. — The  movements  permitted  in  the  metatarsophalangeal  articulations  are  flexion, 
extension,  abduction,  and  adduction. 

IX.  Articulations  of  the  Digits  (Articulationes  Digitorum  Pedis;  Articulations  of 

the  Phalanges). 

The  interphalangeal  articulations  are  ginglymoid  joints,  and  each  has  a  plantar 
and  two  collateral  ligaments. 

The  arrangement  of  these  ligaments  is  similar  to  that  in  the  metatarsophalangeal 
articulations:  the  Extensor  tendons  supply  the  places  of  dorsal  ligaments. 


360  ^^^^^^m.        SYNDESMOLOGY 

Movements. — The  only  movements  permitted  in  the  joints  of  the  digits  are  flexion  and  exten- 
sion; these  movements  are  more  extensive  between  the  first  and  second  phalanges  than  between 
the  second  and  third.  The  amomit  of  flexion  is  very  considerable,  but  extension  is  hmited  by  the 
plantar  and  collateral  ligaments. 

Arches  of  the  Foot. 

In  order  to  allow  it  to  support  the  weight  of  the  body  in  the  erect  posture  with 
the  least  expenditure  of  material,  the  foot  is  constructed  of  a  series  of  arches 
formed  by  the  tarsal  and  metatarsal  bones,  and  strengthened  by  the  ligaments 
and  tendons  of  the  foot. 

The  main  arches  are  the  antero-posterior  arches,  which  may,  for  descriptive 
purposes,  be  regarded  as  divisible  into  two  types — a  medial  and  a  lateral.  The 
medial  arch  (see  Fig.  290,  page  276)  is  made  up  by  the  calcaneus,  the  talus,  the 
navicular,  the  three  cuneiforms,  and  the  first,  second,  and  third  metatarsals.  Its 
summit  is  at  the  superior  articular  surface  of  the  talus,  and  its  two  extremities  or 
piers,  on  which  it  rests  in  standing,  are  the  tuberosity  on  the  plantar  surface  of 
the  calcaneus  posteriorly  and  the  heads  of  the  first,  second,  and  third  metatarsal 
bones  anteriorly.  The  chief  characteristic  of  this  arch  is  its  elasticity,  due  to  its 
height  and  to  the  number  of  small  joints  between  its  component  parts.  Its  weakest 
part,  i.  e.,  the  part  most  liable  to  yield  from  overpressure,  is  the  joint  between 
the  talus  and  navicular,  but  this  portion  is  braced  by  the  plantar  calcaneonavicular 
ligament,  which  is  elastic  and  is  thus  able  to  quickly  restore  the  arch  to  its  pristine 
condition  when  the  disturbing  force  is  removed.  The  ligament  is  strengthened 
medially  by  blending  with  the  deltoid  ligament  of  the  ankle-joint,  and  is  supported 
inferiorly  by  the  tendon  of  the  Tibialis  posterior,  which  is  spread  out  in  a  fan- 
shaped  insertion  and  prevents  undue  tension  of  the  ligament  or  such  an  amount 
of  stretching  as  would  permanently  elongate  it.  The  arch  is  further  supported  by 
the  plantar  aponeurosis,  by  the  small  muscles  in  the  sole  of  the  foot,  by  the  tendons 
of  the  Tibialis  anterior  and  posterior  and  Peronseus  longus,  and  by  the  ligaments 
of  all  the  articulations  involved.  The  lateral  arch  (see  Fig.  291,  page  277)  is  com- 
posed of  the  calcaneus,  the  cuboid,  and  the  fourth  and  fifth  metatarsals.  Its 
summit  is  at  the  talocalcaneal  articulation,  and  its  chief  joint  is  the  calcaneocuboid^ 
which  possesses  a  special  mechanism  for  locking,  and  allows  only  a  limited  move- 
ment. The  most  marked  features  of  this  arch  are  its  solidity  and  its  slight  eleva- 
tion; two  strong  ligaments,  the  long  plantar  and  the  plantar  calcaneocuboid, 
together  with  the  Extensor  tendons  and  the  short  muscles  of  the  little  toe,  preserve 
its  integrity. 

While  these  medial  and  lateral  arches  may  be  readily  demonstrated  as  the 
component  antero-posterior  arches  of  the  foot,  yet  the  fundamental  longitudinal 
arch  is  contributed  to  by  both,  and  consists  of  the  calcaneus,  cuboid,  third  cunei- 
form, and  third  metatarsal:  all  the  other  bones  of  the  foot  may  be  removed  without 
destroying  this  arch. 

In  addition  to  the  longitudinal  arches  the  foot  presents  a  series  of  transverse 
arches.  At  the  posterior  part  of  the  metatarsus  and  the  anterior  part  of  the  tarsus 
the  arches  are  complete,  but  in  the  middle  of  the  tarsus  they  present  more  the 
characters  of  half-domes  the  concavities  of  which  are  directed  downward  and 
medialward,  so  that  when  the  medial  borders  of  the  feet  are  placed  in  apposition 
a  complete  tarsal  dome  is  formed.  The  transverse  arches  are  strengthened  by  the 
interosseous,  plantar,  and  dorsal  ligaments,  by  the  short  muscles  of  the  first  and 
fifth  toes  (especially  the  transverse  head  of  the  Adductor  hallucis),  and  by  the 
Peronseus  longus,  whose  tendon  stretches  across  between  the  piers  of  the  arches. 

BIBLIOGRAPHY. 

R.  Fick:  Handbuch  der  Anatomie  und  Mechanik  der  Gelenke  (Bardeleben 's  Handbuch  der 
Anatomie). 


I 
II 


myology; 


THE  Muscles  are  connected  with  the  bones,  cartilages,  ligaments,  and  skin, 
either  directly,  or  through  the  intervention  of  fibrous  structures  called  tendons 
or  aponeuroses.  Where  a  muscle  is  attached  to  bone  or  cartilage,  the  fibers  end 
in  blunt  extremities  upon  the  periosteum  or  perichondrium,  and  do  not  come  into 
direct  relation  with  the  osseous  or  cartilaginous  tissue.  Where  muscles  are  con- 
nected with  its  skin,  they  lie  as  a  flattened  layer  beneath  it,  and  are  connected 
with  its  areolar  tissue  by  larger  or  smaller  bundles  of  fibers,  as  in  the  muscles  of 
the  face. 

The  muscles  vary  extremely  in  their  form.  In  the  limbs,  they  are  of  considerable 
length,  especially  the  more  superficial  ones;  they  surround  the  bones,  and  constitute 
an  important  protection  to  the  various  joints.  In  the  trunk,  they  are  broad, 
flattened,  and  expanded,  and  assist  in  forming  the  walls  of  the  trunk  cavities. 
Hence  the  reason  of  the  terms,  long,  broad,  short,  etc.,  used  in  the  description  of  a 
muscle. 

There  is  considerable  variation  in  the  arrangement  of  the  fibers  of  certain  muscles 
with  reference  to  the  tendons  to  which  they  are  attached.  In  some  muscles  the 
fibers  are  parallel  and  run  directly  from  their  origin  to  their  insertion;  these  are 
quadrilateral  muscles,  such  as  the  Thyreohyoideus.  A  modification  of  these  is 
found  in  the  fusiform  muscles,  in  which  the  fibers  are  not  quite  parallel,  but  slightly 
curved,  so  that  the  muscle  tapers  at  either  end;  in  their  actions,  however,  they 
resemble  the  quadrilateral  muscles.  Secondly,  in  other  muscles  the  fibers  are 
convergent;  arising  by  a  broad  origin,  they  converge  to  a  narrow  or  pointed  inser- 
tion. This  arrangement  of  fibers  is  found  in  the  triangular  muscles — e.  g.,  the 
Temporalis.  In  some  muscles,  which  otherwise  would  belong  to  the  quadrilateral 
or  triangular  type,  the  origin  and  insertion  are  not  in  the  same  plane,  but  the  plane 
of  the  line  of  origin  intersects  that  of  the  line  of  insertion;  such  is  the  case  in  the 
Pectineus.  Thirdly,  in  some  muscles  (e.  g.,  the  Peronei)  the  fibers  are  oblique  and 
converge,  like  the  plumes  of  a  quill  pen,  to  one  side  of  a  tendon  which  runs  the  entire 
length  of  the  muscle;  such  muscles  are  termed  unipennate.  A  modification  of  this 
condition  is  found  where  oblique  fibers  converge  to  both  sides  of  a  central  tendon; 
these  are  called  bipennate,  and  an  example  is  afforded  in  the  Rectus  femoris. 
Finally,  there  are  muscles  in  which  the  fibers  are  arranged  in  curved  bundles  m 
one  or  more  planes,  as  in  the  Sphincters.  The  arrangement  of  the  fibers  is  of  con- 
siderable importance  in  respect  to  the  relative  strength  and  range  of  movement 
of  the  muscle.  Those  muscles  where  the  fibers  are  long  and  few  in  number  have 
great  range,  but  diminished  strength;  where,  on  the  other  hand,  the  fibers  are 
short  and  more  numerous,  there  is  great  power,  but  lessened  range. 

The  names  applied  to  the  various  muscles  have  been  derived:  (1)  from  their 
situation,  as  the  Tibialis,  Radialis,  Ulnaris,  Peronaeus;  (2)  from  their  direction,  as 
the  Rectus  abdominis,  Obliqui  capitis,  Transversus  abdominis;  (3)  from  their  uses, 
as  Flexors,  Extensors,  Abductors,  etc.;  (4)  from  their  shape,  as  the  Deltoideus, 

1  The  muscles  and  fasciae  are  described  conjointly,  in  order  that  the  student  may  consider  the  arrangement  of  the 
latter  in  his  dissection  of  the  former.  It  is  rare  for  the  student  of  anatomy  in  this  country  to  have  the  opportunity 
of  dissecting  the  fascise  separately;  and  it  is  for  this  reason,  as  well  as  from  the  close  connection  that  exists  between 
the  muscles  and  their  investing  sheaths,  that  they  are  considered  together.  Some  general  observations  are  first  made 
on  the  anatomy  of  the  muscles  and  fascis,  the  special  descriptions  being  given  in  connection  with  the  different  regions. 

(361) 


362  ^^^^^^^-        MYOLOGY 

Rhomboideus;  (5)  from  the  number  of  their  divisions,  as  the  Biceps  and  Triceps; 
(6)  from  their  points  of  attachment,  as  the  Sternocleidomastoideus,  Sternohyoideus,   ._ 
Sternothyreoideus.  ll 

In  the  description  of  a  muscle,  the  term  origin  is  meant  to  imply  its  more  fixed 
or  central  attachment;  and  the  term  insertion  the  movable  point  on  which  the  force 
of  the  muscle  is  applied;  but  the  origin  is  absolutely  jBxed  in  only  a  small  number  MM 
of  muscles,  such  as  those  of  the  face  which  are  attached  by  one  extremity  to  immov-  ■■ 
able  bones,  and  by  the  other  to  the  movable  integument;  in  the  greater  number, 
the  muscle  can  be  made  to  act  from  either  extremity.  MM 

In  the  dissection  of  the  muscles,  attention  should  be  directed  to  the  exact  origin,  H 
insertion,  and  actions  of  each,  and  to  its  more  important  relations  with  surrounding 
parts.  While  accurate  knowledge  of  the  points  of  attachment  of  the  muscles  is 
of  great  importance  in  the  determination  of  their  actions,  it  is  not  to  be  regarded 
as  conclusive.  The  action  of  the  muscle  deduced  from  its  attachments,  or  even 
by  pulling  on  it  in  the  dead  subject,  is  not  necessarily  its  action  in  the  living.  By 
pulling,  for  example,  on  the  Brachioradialis  in  the  cadaver  the  hand  may  be  slightly 
supinated  when  in  the  prone  position  and  slightly  pronated  when  in  the  supine 
position,  but  there  is  no  evidence  that  these  actions  are  performed  by  the  muscle 
during  life.  It  is  impossible  for  an  individual  to  throw  into  action  any  one  muscle; 
in  other  words,  movements,  not  muscles,  are  represented  in  the  central  nervous 
system.  To  carry  out  a  movement  a  definite  combination  of  muscles  is  called  into 
play,  and  the  individual  has  no  power  either  to  leave  out  a  muscle  from  this  com- 
bination or  to  add  one  to  it.  One  (or  more)  muscle  of  the  combination  is  the  chief 
moving  force;  when  this  muscle  passes  over  more  than  one  joint  other  muscles 
(synergic  muscles)  come  into  play  to  inhibit  the  movements  not  required;  a  third 
set  of  muscles  (fixation  muscles)  fix  the  limb — i.  e.,  in  the  case  of  the  limb-movements 
— and  also  prevent  disturbances  of  the  equilibrium  of  the  body  generally.  As  an 
example,  the  movement  of  the  closing  of  the  fist  may  be  considered:  (1)  the  prime 
movers  are  the  Flexores  digitorum.  Flexor  pollicis  longus,  and  the  small  muscles 
of  the  thumb;  (2)  the  synergic  muscles  are  the  Extensores  carpi,  which  prevent 
flexion  of  the  wrist;  while  (3)  the  fixation  muscles  are  the  Biceps  and  Triceps 
brachii,  which  steady  the  elbow  and  shoulder.  A  further  point  which  must  be 
borne  in  mind  in  considering  the  actions  of  muscles  is  that  in  certain  positions 
a  movement  can  be  effected  by  gravity,  and  in  such  a  case  the  muscles  acting  are 
the  antagonists  of  those  which  might  be  supposed  to  be  in  action.  Thus  in  flexing 
the  trunk  when  no  resistance  is  interposed  the  Sacrospinales  contract  to  regulate 
the  action  of  gravity,  and  the  Recti  abdominis  are  relaxed.^ 

By  a  consideration  of  the  action  of  the  muscles,  the  surgeon  is  able  to  explain 
the  causes  of  displacement  in  various  forms  of  fracture,  and  the  causes  which  pro- 
duce distortion  in  various  deformities,  and,  consequently,  to  adopt  appropriate 
treatment  in  each  case.  The  relations,  also,  of  some  of  the  muscles,  especially 
those  in  immediate  apposition  with  the  larger  bloodvessels,  and  the  surface  mark- 
ings they  produce,  should  be  remembered,  as  they  form  useful  guides  in  the 
application  of  ligatures  to  those  vessels. 

MECHANICS   OF  MUSCLE.^ 

In  studying  the  mechanical  action  of  muscles  the  individual  muscle  cannot 
always  be  treated  as  a  single  unit,  since  different  parts  of  the  same  muscle  may 
have  entirely  different  actions,  as  with  the  Pectoralis  major,  the  Deltoid,  and  the 
Trapezius  where  the  nerve  impulses  control  and  stimulate  different  portions  of  the 

'  Consult  in  this  connection  the  Croonian  Lectures  (1903)  on  "Muscular  Movements  and  Their  Representation  in 
the  Central  Nervous  System,"  by  Charles  E.  Beevor,  M.D. 
2  R.  Fick.     Bd.  ii,  in  Bardeleben's  Handbuch  der  Anatomie  des  Menschen. 


MECHANICS  OF  MUSCLE 


363 


muscle  in  succession  or  at  different  times.  Most  muscles  are,  however,  in  a  mechanical 
sense  units.  But  in  either  case  the  muscle  fibers  constitute  the  elementary  motor 
elements. 


Fio.  361 


The  Direction  of  the  Muscle  Pull. — In  those  muscles  where  the  fibers  always  run 
in  a  straight  line  from  origin  to  insertion  in  all  positions  of  the  joint,  a  straight  line 
joining  the  middle  of  the  surface  of  origin  with  the  middle  of  the  insertion  surface 


Fig.  362 


w^ill  give  the  direction  of  the  pull  (Fig.  361).  If,  however,  the  muscle  or  its  tendon 
is  bent  out  of  a  straight  line  by  a  bony  process  or  ligament  so  that  it  runs  ove::  a 
pulley-like  arrangement,  the  direction  of  the  muscle  pull  is  naturally  bent  out  of 


Fig.  363 


line.  The  direction  of  the  pull  in  such  cases  is  from  the  middle  point  of  insertion 
to  the  middle  point  of  the  pulley  where  the  muscle  or  tendon  is  bent.  Muscles  or 
tendons  of  muscles  which  pass  over  more  than  one  joint  and  pass  through  more  than 


364 


MYOLOGY 


one  pulley  may  be  resolved,  so  far  as  the  direction  of  the  pull  is  concerned,  into  two 
or  more  units  or  single-joint  muscles  (Fig.  362).  The  tendons  of  the  Flexor  pro- 
fundus digitorum,  for  example,  pass  through  several  pulleys  formed  by  fibrous 
sheaths.  The  direction  of  the  pull  is  different  for  each  joint  and  varies  for  each 
joint  according  to  the  position  of  the  bones.  The  direction  is  determined  in  each 
case,  however,  by  a  straight  line  between  the  centers  of  the  pulleys  on  either  side  of 
the  joint  (Fig.  363).  The  direction  of  the  pull  in  any  of  the  segments  would  not 
be  altered  by  any  change  in  the  position  or  origin  of  the  muscle  belly  above  the 
proximal  pulley. 

The  Action  of  the  Muscle  Pull  on  the  Tendon. — 'WTiere  the  muscle  fibers  are  parallel 
or  nearly  parallel  to  the  direction  of  the  tendon  the  entire  strength  of  the  muscle 
contraction  acts  in  the  direction  of  the  tendon. 

In  pinnate  muscles,  however,  only  a  portion  of  the  strength  of  contraction  is  effi- 
cient in  the  direction  of  the  tendon,  since  a  portion  of  the  pull  would  tend  to  draw 
the  tendon  to  one  side,  this  is  mostly  annulled  by  pressure  of  surrounding  parts. 
In  bipinnate  muscles  this  lateral  pull  is  counterbalanced.    If,  for  example,  the  muscle 

fibers  are  inserted  into  the  tendon  at  an  angle  of  60 
degrees  (Fig.  364),  it  is  easy  to  determine  by  the 
parallelogram  of  forces  that  the  strength  of  the  pull 
along  the  direction  of  the  tendon  is  equal  to  one-half 
the  muscle  pull. 

T   =  tendon,  m  =  strength  and  direction  of  muscle 
pull. 

t  =   component   acting   in   the    direction    of   the 
tendon. 
</>  =  angle  of  insertion  of  muscle  fibers  into  tendon. 
t 


^ 


y^ 


cos  (^  = 
0.5  =  ^ 


m 


cos 


z  60° 


0.50000 


t  = 


If 


72'* 
41° 
90° 
0° 


_  1 
—  1 

30' 
20' 


m 


cos  =  1" 
cos  =  f 
cos  =  0 
=  1 


Fia.  364 


cos  = 

The  more  acute  the  angle  ^,  that  is  the  smaller 

the  angle,  the  greater  the  component  acting  in  the 

direction  of  the  tendon  pull.    At  41°  20'  three-fourths 

of  the  pull  would  be  exerted  in  the  direction  of  the 

tendon  and  at  0°  the  entire  strength.     On  the  other 

hand,  the  greater  the  angle  the  smaller  the  tendon  component;  at  72°  30'  one-third 

the  muscle  strength  would  act  in  the  direction  of  the  tendon  and  at  90°  the  tendon 

component  would  be  nil. 

The  Strength  of  Muscles. — The  strength  of  a  muscle  depends  upon  the  number  of 
fibers  in  what  is  known  as  the  physiological  cross-section,  that  is,  a  section  which 
passes  through  practically  all  of  the  fibers.  In  a  muscle  with  parallel  or  nearly 
parallel  fibers  which  have  the  same  direction  as  the  tendon  this  corresponds  to  the 
anatomical  cross-section,  but  in  unipinnate  and  bipinnate  muscles  the  physiological 
cross-section  may  be  nearly  at  right  angles  to  the  anatomical  cross-section  as  shown 
in  Fig.  365.  Since  Huber  has  shown  that  muscle  fibers  in  a  single  fasciculus  of  a 
given  muscle  vary  greatly  in  length,  in  some  fasciculi  from  9  mm.  to  30.4  mm.,  it 
is  unlikely  that  the  physiological  cross-section  will  pass  through  all  the  fibers. 
Estimates  have  been  made  of  the  strength  of  muscles  and  it  is  probable  that  coarse- 
fibered  muscles  are  somewhat  stronger  per  square  centimeter  of  physiological 


MECHANICS  OF  MUSCLE 


365 


cross-section  than  are  the  fine-fibered  muscles.  Fick  estimates  the  average  strength 
as  about  10  kg.  per  square  cm.  This  is  known  as  the  absolute  muscle  strength. 
The  total  strength  of  a  muscle  would  be  equal  to  the  number  of  square  centimeters 
in  its  physiological  cross-section  X  10  kg. 


-PCS 


PCS 


A  B  c 

Fig.  365 — A,  fusiform;  B,  unipinnate;  C,  bipinnate;  P.C.S.,  physiological  cross-section. 


The  Work  Accomplished  by  Muscles. — For  practical  uses  this  should  be  expressed 
in  kilogr ammeters.     In  order  to  reckon  the  amount  of  work  which  a  muscle  can 
perform  under  the  most  favorable  conditions  it  is  necessary  to  know  (1)  its  physio- 
logical cross-section  (2)  the  maximum  shortening,  and  (3)  the  position  of  the  joint 
■  when  the  latter  is  obtained. 
Work  =  lifted  weight  X  height  through  which  the  weight  is  lifted;  or 
Work  =  tension  X  distance;  tension  =  physiological   cross-section  X  absolute 
^  muscle  strength. 

^b  If  a  muscle  has  a  physiological  cross-section  of  5  sq.  cm,  its  tension  strength  = 
^■5  X  10  or  50  kg.  If  it  shortens  5  cm.  the  work  =  50  X  .05  =  2.5  kilogrammeters. 
^P  If  one  determines  then  the  physiological  cross-section  and  multiplies  the  absolute 
muscle  strength,  10  kg,  by  this,  the  amount  of  tension  is  easily  obtained.  Then 
one  must  determine  only  the  amount  of  shortening  of  the  muscle  for  any  particular 
position  of  the  joint  in  order  to  determine  the  amount  of  work  the  muscle  can  do, 
since  work  =  tension  X  distance. 

The  tension  of  a  muscle  is,  howevsr,  not  constant  during  the  course  of  contraction 
but  is  continually  decreasing  during  contraction.    It  is  at  a  maximum  at  the  begin- 

■  ning  and  gradually  decreases. 
This  can  be  illustrated  by  the  work  diagram  Fig.  366. 
AMD  (ordinate)  =  tension. 
A  V  X  (abscissa)  =  shortening. 

A  D  =  tension  of  muscle  in  extended  or  antagonistic  position. 
A  V   =  amount  of  actual  shortening. 
A  M  =  tension  in  midposition  =  absolute  muscle  strength. 
D  V  =  shows  how  the  tension  sinks  from  maximum  (in  the  extended  position  of 

the  muscle)  where  it  is  about  double  that  in  the  midposition  {M)  to 

nothing  on  complete  contraction. 


366 


MYOLOGY 


A  A  D  V  =  work  diagram,  in  reality  the  hypothenose  is  not  straight  but  has  a 
concave  curve.    The  A  has  the  same  area  as  the  rectangle  A  M  M'  V. 

A  M  =  the  average  tension. 

Work  =  A  M  X  A  V  kilogrammeters  if  the  size  of  the  ordinate  as  expressed  in 
kilograms  and  the  abscissa  in  meters. 


^  SHORTENING 


Although  the  muscle  works  with  a  changing  tension,  yet  the  accomplishment  is 
the  same  as  if  it  were  contracting  with  the  tension  of  the  midposition. 

In  reality  the  amount  of  work  is  somewhat  greater  since  even  in  extreme  con- 
traction the  muscle  still  retains  a  certain  amount  of  tension  so  that  the  maximum 
amount  of  work  is  more  nearly  like  A  D  X.  We  know  that  a  muscle  may  have 
an  extreme  actual  shortening  of  about  80  per  cent,  of  its  length  when  the  tendon 
of  insertion  is  cut. 

The  trapezoid  A  D  S  V  represents  more  nearly  the  amount  cf  wox'k,  but  since 
there  are  only  approximate  values  and  AD  S  Vis  not  much  larger  than  AM  M'  F, 
we  may  use  the  latter. 

Only  the  tension  and  amount  of  shortening  are  needed  to  determine  the  amount 
of  work  of  the  muscle.  Neither  the  lever  arm  nor  the  fiber  angle  in  pinnate  muscles 
need  be  considered." 

The  diagram  Fig.  367  shows  that  the  lever  arm  is  of  no  importance  for  deter- 
mining the  amount  of  work  the  muscle  performs. 

J B  and  J B^  =  two  bones  jointed  at  J.  CD  and  E F  =  the  direction  of  the  pull 
of  two  muscles  of  equal  cross-section,  each  having  a  muscle  tension  of  1000  gms. 

The  centers  of  the  attachments  are  such  that  perpendiculars  /  c  and  J  e  to 
C  D  and  E  F  are  equal  to  40  and  23  mm.  respectively,  J  c  =  40  mm.  and  J  e  = 
23  mm.  The  static  moments  are  equal  to  1000  X  40  and  1000  X  23,  therefore  the 
first  muscle  can  hold  a  much  larger  load  (L)  on  the  bone  J  B^  at  H^  (100  mm.  from 
J)  than  the  second  muscle  whose  load  can  be  designated  as  L^. 

Equilibrium  exists  for  the  first  muscle  if 

i  X  100  =  1000  X  40  or  L  =  ^^^qq  ^^  =  400  gms. 

For  the  second  muscle  D  X 100  =  1000  X  23. 

1000  X  23 
D  =    ^ =  230  gms. 

If  we  suppose  J  JS  to  be  fixed  and  J  B^  to  move  in  the  plane  of  the  paper  about 
J  and  the  muscle  C  D  to  shorten  5  mm.  C  d  =  C  D  —  5  mm.  and  with  the  tension 
of  1000  gms.,  J  B^  will  take  the  position  J  B^  and  the  load  (L)  will  be  lifted  from 
H'  to  H\ 


MECHANICS  OF  MUSCLE 


367 


H 


the  second  muscle  likewise  shortens  5  mm.  then  E  f  =  E  F  —  5  mm.,  and 
with  the  tension  of  1000  gms.  the  bone  J  B^  will  take  the  position  J  B^  and  the 
weight  or  load  (D)  will  be  lifted  from  H^  to  H^.  The  question  now  is  to  prove 
that  the  work  done  is  the  same  in  both  cases,  namely,  5  X  1000  grammillimeters. 
If  so,  400  X  H'W-  =  230  X  H'  H^  =  5000  grammillimeters. 

Since  the  two  radii  Cd  and  C  d'  are  very  long  as  compared  with  the  arc  d  d'  we 
may  consider  this  short  arc  as  a  line  J_  to  C  Z)  at  d',  likewise  the  arc  //'  may  be 
considered  as  a  straight  line  \_to  E  F.  In  the  same  manner  we  can  consider  the 
short  arcs  F  f,  D  d,  H'  H'-  and  H'  H'  ±  to  the  line  J  B\  The  sides  D  d'  and  Ff 
of  the  A  D  d  d'  and  F  ff  are  each  5  mm. 

The  lever  arm  D  J  =  60  mm.  and  J  F  =  30  mm. 


Fig.  367 


The  A  D  d  d'  k  similar  to  the  A  D  c  J 


hence  D  d 
also  H'  m 


5      ::    60  :  40 

Dd  ::  100  :  60 
300 


Dd     = 


40 


::  100  :  60       H' H'-  = 


300 
40 

300 
24 


The  AFff  is  similar  to  F  e  J 

Ff     =i-'^ 

^    J  OQ 


30  :  23 


[  hence  F  f     :  5 

also    H'H'  :Ff  ::  100  :  30 

150 
mm-.—  ::  100:  30       H' H'  = 

.    400  X  f  =  230  X  1-|0  .  5000 

Thus  we  see  that  the  work  of  the  two  muscles  depends  on  the  size  of  the  contrac- 
tion and  on  the  tension  and  not  on  the  lever  arm  in  very  small  contractions  or  in 


23 

1500 
69 


368 


MYOLOGY 


the  summation  of  such  contractions  and  therefore  for  large  contractions.  In  the 
first  muscle  a  large  load  is  moved  through  a  short  distance  and  in  the  second  muscle 
a  lighter  load  is  moved  through  a  greater  distance. 

The  amount  of  work  accomplished  by  pinnate  muscles  is  not  dependent  upon 
the  angle  of  insertion  of  the  muscle  fibers  into  the  tendon,  as  will  be  seen  b\'  the 
following  diagram  Fig.  368. 

T'  T  =  direction  of  the  tendon  pull. 
w  a  =  direction  of  muscle  fiber  before  con- 
traction. 
m'  =  direction  of  muscle  fiber  after  contrac- 
tion. 
V  =  amount  of  contraction. 
m  =  tension  of  the  muscle. 
(^  =  angle  of  insertion  of  muscle  fiber. 
t  =  tendon  component  =  m  X  cos  (/>  = 
the  weight  carried  by  the  tendon 
to  balance  the  muscle  tension. 
d  =  distance  tendon  is  drawn  up. 

(1)  TO  X  V  =  work  done  by  the  muscle  fiber. 

(2)  t  X  d  =  work  done   by  the  movement  of 
the  tendon. 

If  we  consider  the  distance  v  as  being  very 
short  then  the  line  b  c  can  be  dealt  with  as 
though  it  were  perpendicular  to  a  c. 

then  V  =  d  X  cos  ^  or  d 


I 


since  t  =  m  X  cos  </>  or  m  = 


cos  (p 
t 


m  X  v  = 


t 


cos  (f) 

X  d  X  COS  (f)  =  t  X  d 


T' 

o 


Fig.  368 


COS  </> 

If  this  is  true  for  very  minute  contractions  it 
is  likewise  true  for  a  series  of  such  contraction 
and  hence  for  larger  contractions. 

If  we  assume  that  <^  =  60°,  m  =  10  kg.  and  v 
=  5  mm.,  the  work  done  by  the  contracting 
muscle  fiber  =  m  v  or  lOX  5  kilogrammilli- 
meters. 


cos  z  60°  =  I;  hence  t  =  ^  m;  and  d  =  j  ==  2  v;  ^  m  =  5  kg.;  and  2  v  =  10  mm. 

hence  t  d  =  50  kilogrammillimeters  or  the  work  done  by  the  movement  of  the 
tendon  in  lifting  the  load  of  5  kg.  a  distance  of  10  mm.,  and  is  exactly  the  same  as 
that  done  by  the  muscle  fiber.  The  load  on  the  tendon  is  but  one-half  the  tension 
of  the  muscle,  but  the  distance  through  which  the  load  is  lifted  is  twice  that  of  the 
amount  of  shortening  of  the  muscle. 

If    (^  =  41°  20'        then  cos    (^  =  f 
hence  t  =  f  w         and  d  =  ^  v  and  t  d  =  m  v 

In  pinnate  muscles,  then,  we  have  the  rather  unexpected  condition  in  which 
the  same  amount  of  movement  of  the  tendon  can  be  accomplished  with  less  contrac- 
tion of  the  muscle  than  in  muscles  where  the  fibers  have  the  same  direction  as  the 
tendon. 

The  Action  of  Muscles  on  Joints. — If  we  consider  now  the  action  of  a  single  muscle 
extending  over  a  single  joint  in  which  one  bone  is  fixed  and  the  other  movable,  we 


MECHANICS  OF  MUSCLE 


369 


will  find  that  muscle  pull  can  be  resolved  into  two  components,  a  turning  com- 
ponent and  a  friction  or  pressure  component  as  shown  in  Fig.  369. 


D  F  =  the  fixed  bone  from  which  the  muscle  takes  its  origin. 

D  K  =  the  movable  bone. 

01    =  a  line  from  the  middle  of  origin  to  the  middle  of  insertion. 

/  M  =  size  and  direction  of  the  muscle  pull. 

If  the  parallelogram  is  constructed  with  /  t  and  M  h  \_to  D  K,  \hen  1 1  =  the 
turning  component  and  7  6  =  the  component  which  acts  against  the  joint. 

The  size  of  the  two  components  depends  upon  the  insertion  angle  4>.  The  smaller 
this  angle  the  smaller  the  turning  component,  and  ^he  nearer  this  angle  4>  is  to 
90°  the  larger  the  turning  component. 

/  i  =  I  il/  X  sin  (^ 

lb  =  I  M  X  cos  <}> 

li  <}>  =  90^*        cos  </)  =  0,  sine  0  =  1 
hence  I  b  =  0         and  1 1  =  I  m 

If  <^  =  0°  cos  0  =  1,  sine  0  =  0 

hence  I  b  =  I  and  7  /  =  0 

With  movements  of  the  bone  D  K  the  angle  of  insertion  is  continually  changing, 
and  hence  the  two  components  are  changing  in  value. 


Fig.  370 


If,  for  example,  the  distance  from  origin  0  to  the  joint  D  is  greater  than  from 

D  to  I,  as  in  the  Brachialis  or  Biceps  muscles,  the  turning  component  increases  until 

the  insertion  angle  0  =  90°,  which  is  the  optimum  angle  for  muscle  action,  while 

the  pressure  component  gradually  decreases.     If  the  movement  continues  beyond 

24 


370 


MYOLOGY 


this  point  the  turning  component  grcadually  decreases  and  the  pressure  compoui 
changes  into  a  component  which  tends  to  draw  the  two  bones  apart  and  which 
gradually  increases  as  shown  in  Fig.  370. 

^Yhen  the  bone  D  K  is  in  such  a  position  that  the  insertion  angle  ^  =  41°  20' 
the  pressure  component  =  f  /  w  and  the  turning  component  1 1  m,  at  60°  the  two 
components  are  equal,  at  90°  the  pressure  component  =  0  and  the  turning  com- 
ponent =  I  M  and  at  131°  21'  the  pressure  component  has  been  converted  into  a 
pulling  component  =  j  I  M  and  the  turning  component  =  f  /  M. 


I 


If,  for  example,  the  distance  from  the  origin  0  to  the  joint  D  is  less  than  the  dis- 
tance from  the  insertion  /  to  the  joint  D,  as  in  the  Brachioradialis  muscle,  the 
insertion  angle  increases  with  the  flexion  but  ne^•e^  reaches  90°.  The  turning 
component  gradually  increases  to  a  certain  point  and  then  slowly  decreases  as  shown 
in  Fig.  371,  w^hile  the  pressure  component  gradually  decreases  and  then  slowly 
increases.  It  always  remains  large  and  its  action  is  always  in  the  direction  of  the 
joint. 

Levers. — ^The  majority  of  the  muscles  of  the  body  act  on  bones  as  the  power  on 
levers.  Levers  of  the  III  class  are  the  most  common,  as  the  action  of  the  Biceps, 
and  the  Brachialis  muscles  on  the  forearm  bones.  Levers  of  the  I  Class  are  found 
in  movements  of  the  head  where  the  occipito-atlantal  joint  acts  as  the  fulcrum  and 
the  muscles  on  the  back  of  the  neck  as  the  power.    Another  common  example  is 


w 

n 


s 


2i 


w 


s 


w 


\F 


U 


lU 


Fig.  372 


the  foot  when  one  raises  the  body  by  contracting  the  Gastrocnemius  and  Soleus. 
Here  the  ankle-joint  acts  as  the  fulcrum  and  the  pressure  of  the  toes  on  the  ground 
as  the  weight.  This  is  frequently,  though  WTongly,  considered  a  lever  of  the  II  Class. 
If  one  were  to  stand  on  one's  head  with  the  legs  up  and  with  a  weight  on  the  plantar 
surface  of  the  toes,  it  is  easy  to  see  that  we  would  have  a  lever  of  the  I  Class  if  the 
weight  were  raised  by  contraction  of  the  Gastrocnemius  muscle.  The  confusion 
has  arisen  by  not  considering  the  fact  that  the  fulcrmn  and  the  power  in  all  three 
classes  of  levers  must  have  a  common  basis  of  action,  as  sho\Mi  in  Fig.  372. 


DEVELOPMENT  OF  THE  MUSCLES  371 

If  the  fulcrum  rests  on  the  earth  the  power  must  either  directly  or  indirectly 
push  from  the  earth  or  be  attached  to  the  earth  either  by  gravity  or  otherwise  if  it 
pulls  toward  the  earth.  If  the  power  were  attached  to  the  weight  no  lever  action 
could  be  obtained. 

There  are  no  levers  of  the  II  Class  represented  in  the  body. 


DEVELOPMENT  OF  THE  MUSCLES. 

Both  the  cross-striated  and  smooth  muscles,  with  the  exception  of  a  few  that  are 
of  ectodermal  origin,  arise  from  the  mesoderm.  The  intrinsic  muscles  of  the  trunk 
are  derived  from  the  myotomes  while  the  muscles  of  the  head  and  limbs  differentiate 
directly  from  the  mesoderm. 

The  Myotomic  Muscles. — The  intrinsic  muscles  of  the  trunk  which  are  derived 
directly  from  the  myotomes  are  conveniently  treated  in  two  groups,  the  deep 
muscles  of  the  back  and  the  thoraco-abdominal  muscles. 

The  deep  muscles  of  the  back  extend  from  the  sacral  to  the  occipital  region  and 
vary  much  in  length  and  size.  They  act  chiefly  on  the  vertebral  column.  The 
shorter  muscles,  such  as  the  Interspinales,  Intertransversarii,  the  deeper  layers  of 
the  Multifidus,  the  Rotatores,  Levatores  costarum,  Obliquus  capitis  inferior, 
Obliquus  capitis  superior  and  Rectus  capitis  posterior  minor  which  extend  between 
adjoining  vertebrae,  retain  the  primitive  segmentation  of  the  myotomes.  Other 
muscles,  such  as  the  Splenius  capitis,  Splenius  cervicis,  Sacrospinalis,  Semispinalis, 
Multifidus,  Iliocostalis,  Longissimus,  Spinales,  Semispinales,  and  Rectus  capitis 
posterior  major,  which  extend  over  several  vertebrae,  are  formed  by  the  fusion  of 
successive  myotomes  and  the  splitting  into  longitudinal  columns. 

The  fascia  lumbo-dorsalis  develops  between  the  true  myotomic  muscles  and  the 
more  superficial  ones  which  migrate  over  the  back  such  as  the  Trapezius,  Rhom- 
boideus,  and  Latissimus. 

The  anterior  vertebral  muscles,  the  Longus  colli,  Longus  capitis,  Rectus  capitis 
anterior  and  Rectus  capitis  lateralis  are  derived  from  the  ventral  part  of  the  cervical 
myotomes  as  are  probably  also  the  Scaleni. 

The  thoraco-abdominal  muscles  arise  through  the  ventral  extension  of  the 
thoracic  myotomes  into  the  body  wall.  This  process  takes  place  coincident  with  the 
ventral  extension  of  the  ribs.  In  the  thoracic  region  the  primitive  myotomic 
segments  still  persist  as  the  intercostal  muscles,  but  over  the  abdomen  these  ventral 
myotomic  processes  fuse  into  a  sheet  which  splits  in  various  ways  to  form  the 
Rectus,  the  Obliquus  externus  and  internus,  and  the  Transversalis.  Such  muscles 
as  the  Pectoralis  major  and  minor  and  the  Serratus  anterior  do  not  belong  to  the 
above  group. 

The  Ventrolateral  Muscles  of  the  Neck. — The  intrinsic  muscles  of  the  tongue,  the 
Infrahyoid  muscles  and  the  diaphragm  are  derived  from  a  more  or  less  continuous 
premuscle  mass  which  extends  on  each  side  from  the  tongue  into  the  lateral  region 
of  the  upper  half  of  the  neck  and  into  it  early  extend  the  hypoglossal  and  branches 
of  the  upper  cervical  nerves.  The  two  halves  which  form  the  Infrahyoid  muscles 
and  the  diaphragm  are  at  first  widely  separated  from  each  other  by  the  heart. 
As  the  latter  descends  into  the  thorax  the  diaphragmatic  portion  of  each  lateral 
mass  is  carried  with  its  nerve  down  into  the  thorax  and  the  laterally  placed  Infra- 
hyoid muscles  move  toward  the  midventral  line  of  the  neck. 

Muscles  of  the  Shoulder  Girdle  and  Arm. — The  Trapezius  and  Sternocleidomas- 
toideus  arise  from  a  common  premuscle  mass  in  the  occipital  region  just  caudal  to 
the  last  branchial  arch;  as  the  mass  increases  in  size  it  spreads  downward  to  the 
shoulder  girdle  to  which  it  later  becomes  attached.  It  also  spreads  backward  and 
downward  to  the  spinous  processes,  gaining  attachment  at  a  still  later  period. 


372  "^^^^^^m  MYOLOGY 

^  The  Levator  scapulse,  Serratus  anterior  and  the  Rhomboids  arise  from  premusclel 
tissue  in  the  lower  cervical  region  and  undergo  extensive  migration.  } 

The  Latissimus  dorsi  and  Teres  major  are  associated  in  their  origin  from  the] 
premuscle  sheath  of  the  arm  as  are  also  the  two  Pectoral  muscles  when  the  arm 
bud  lies  in  the  lower  cervical  region. 

The  intrinsic  muscles  of  the  arm  develop  in  situ  from  the  mesoderm  of  the  arm 
bud  and  probably  do  not  receive  cells  or  buds  from  the  myotomes.  The  nerves 
enter  the  arm  bud  when  it  still  lies  in  the  cervical  region  and  as  the  arm  shifts 
caudally  over  the  thorax  the  lower  cervical  nerves  which  unite  to  form  the  brachial 
plexus,  acquire  a  caudal  direction. 

The  Muscles  of  the  Leg. — The  muscles  of  the  leg  like  those  of  the  arm  develop 
in  situ  from  the  mesoderma  of  the  leg  bud,  the  myotomes  apparently  taking  no  _. 
part  in  their  formation.  ■I 

The  Muscles  of  the  Head. — The  muscles  of  the  orbit  arise  from  the  mesoderm  over 
the  dorsal  and  caudal  sides  of  the  optic  stalk. 

The  muscles  of  mastication  arise  from  the  mesoderm  of  the  mandibular  arch. 
The  mandibular  division  of  the  trigeminal  nerve  enters  this  premuscle  mass  before 
it  splits  into  the  Temporal,  Masseter  and  Pterygoideus. 

The  facial  muscles  (muscles  of  expression)  arise  from  the  mesoderm  of  the  hyoid 
arch.  The  facial  nerve  enters  this  mass  before  it  begins  to  split,  and  as  the  muscle 
mass  spreads  out  over  the  face  and  head  and  neck  it  splits  more  or  less  incompletely 
into  the  various  muscles. 

The  early  differentiation  of  the  muscular  system  apparently  goes  on  independ- 
ently of  the  nervous  system  and  only  later  does  it  appear  that  muscles  are  dependent 
on  the  functional  stimuli  of  the  nerves  for  their  continued  existence  and  growth. 
Although  the  nervous  system  does  not  influence  muscle  differentiation,  the  nerves, 
owing  to  their  early  attachments  to  the  muscle  rudiments,  are  in  a  general  way 
indicators  of  the  position  of  origin  of  many  of  the  muscles  and  likewise  in  many 
instances  the  nerves  indicate  the  paths  along  which  the  developing  muscles  have 
migrated  during  development.  The  muscle  of  the  diaphragm,  for  example,  has  its 
origin  in  the  region  of  the  fourth  and  fifth  cervical  segments.  The  phrenic  nerve  enters 
the  muscle  mass  while  the  latter  is  in  this  region  and  is  drawn  out  as  the  diaphragm 
migrates  through  the  thorax.  The  Trapezius  and  Sternocleidomastoideus  arise 
in  the  lateral  occipital  region  as  a  common  muscle  mass,  into  which  at  a  very  early 
period  the  nervus  accessorius  extends  and  as  the  muscle  mass  migrates  and  extends 
caudally  the  nerve  is  carried  with  it.  The  Pectoralis  major  and  minor  arise  in  the 
cervical  region,  receive  their  nerves  while  in  this  position  and  as  the  muscle  mass 
migrates  and  extends  caudally  over  the  thorax  the  nerves  are  carried  along.  The 
Latissimus  dorsi  and  Serratus  anterior  are  excellent  examples  of  migrating  muscles 
whose  nerve  supply  indicates  their  origin  in  the  cervical  region.  The  Rectus 
abdominis  and  the  other  abdominal  muscles  migrate  or  shift  from  a  lateral  to  a 
ventrolateral  or  abdominal  position,  carrying  with  them  the  nerves. 

The  facial  nerve,  which  early  enters  the  common  facial  muscle  mass  of  the  second 
branchial  or  hyoid  arch,  is  dragged  about  with  the  muscle  as  it  spreads  over  the  head 
and  face  and  neck,  and  as  the  muscle  splits  into  the  various  muscles  of  expression, 
the  nerve.is  correspondingly  split.  The  mandibular  division  of  the  trigeminal  nerve 
enters  at  an  early  time  the  muscle  mass  in  the  mandibular  arch  and  as  this  mass 
splits  and  migrates  apart  to  form  the  muscles  of  mastication  the  nerve  splits  into 
its  various  branches. 

The  nerve  supply  then  serves  as  a  key  to  the  common  origin  of  certain  groups  of 
muscles.  The  muscles  supplied  by  the  oculomotor  nerve  arise  from  a  single  mass 
in  the  eye  region;  the  lingual  muscles  arise  from  a  common  mass  supplied  by  the 
hypoglossal  nerve. 


DEVELOPMENT  OF  THE  MUSCLES 


373 


I 


Striped  or  Voluntary  Muscle. — Striped  or  voluntary  muscle  is  composed  of  bundles 
of  fibers  each  enclosed  in  a  delicate  web  called  the  perimysium  in  contradistinction 
to  the  sheath  of  areolar  tissue  which  invests  the  entire  muscle,  the  epimysium. 
The  bundles  are  termed  fasciculi;  they  are  prismatic  in  shape,  of  different  sizes 
in  different  muscles,  and  are  for  the  most  part  placed  parallel  to  one  another, 
though  they  have  a  tendency  to  converge  toward  their  tendinous  attachments. 
Each  fasciculus  is  made  up  of  a  strand  of  fibers,  which  also  run  parallel  with  each 
other,  and  are  separated  from  one  another  by  a  delicate  connective  tissue  derived 
from  the  perimysium  and  termed  endomysium.  This  does  not  form  the  sheath 
of  the  fibers,  but  serves  to  support  the  bloodvessels  and  nerves  ramifying  between 
them. 

A  muscular  fiber  may  be  said  to  consist  of  a  soft  contractile  substance,  enclosed 
in  a  tubular  sheath  named  by  Bowman  the  sarcolemma.  The  fibers  are  cylindrical 
or  prismatic  in  shape  (Fig.  373),  and  are  of  no  great  length,  not  exceeding,  as  a  rule, 
40  mm.  Huber'  has  recently  found  that  the  muscle  fibers  in  the  adductor  muscle 
of  the  thigh  of  the  rabbit  vary  greatly  in  length  even  in  the  same  fasciculus.  In  a 
fasciculus  40  mm.  in  length  the  fibers  varied  from  30.4  mm.  to  9  mm.  in  length. 
Their  breadth  varies  in  man  from  0.01  to  0.1  mm.    As  a  rule,  the  fibers  do  not 


IG.  373. — Transverse  section  of  human  striped  muscle  fibers. 
X  255. 


Fig.  374.- 


-Striped  muscle  fibers  from  tongue  of 
cat.      X  250. 


I 


divide  or  anastomose;  but  occasionally,  especially  in  the  tongue  and  facial  mus- 
cles, they  may  be  seen  to  divide  into  several  branches.  In  the  substance  of  the 
muscle,  the  fibers  end  by  tapering  extremities  which  are  joined  to  the  ends  of 
other  fibers  by  the  sarcolemma.  At  the  tendinous  end  of  the  muscle  the  sarco- 
lemma appears  to  blend  with  a  small  bundle  of  fibers,  into  which  the  tendon 
becomes  subdivided,  while  the  muscular  substance  ends  abruptly  and  can  be 
readily  made  to  retract  from  the  point  of  junction.  The  areolar  tissue  between 
the  fibers  appears  to  be  prolonged  more  or  less  into  the  tendon,  so  as  to  form  a  kind 
of  sheath  around  the  tendon  bundles  for  a  longer  or  shorter  distance.  When 
muscular  fibers  are  attached  to  skin  or  mucous  membranes,  their  fibers  become 
continuous  with  those  of  the  areolar  tissue. 

The  sarcolemma,  or  tubular  sheath  of  the  fiber,  is  a  transparent,  elastic,  and 
apparently  homogeneous  membrane  of  considerable  toughness,  so  that  it  some- 
times remains  entire  when  the  included  substance  is  ruptured.  On  the  internal 
surface  of  the  sarcolemma  in  mammalia,  and  also  in  the  substance  of  the  fiber 
in  frogs,  elongated  nuclei  are  seen,  and  in  connection  with  these  is  a  little  granular 
protoplasm. 

Upon  examination  of  a  voluntary  muscular  fiber  by  transmitted  light,  it  is 


'Anat.   Rec,   1916,   11. 


374 


MYOLOGY 


found  to  be  marked  by  alternate  light  and  dark  bands  or  striae,  which  pass  trans- 
versely across  the  fiber  (Fig.  374).  When  examined  by  polarized  light  the 
dark  bands  are  found  to  be  doubly  refracting  (anisotropic),  while  the  clear 
stripes  are  singly  refracting  (isotropic).  The  dark  and  light  bands  are  of  nearly 
equal  breadth,  and  alternate  with  great  regularity;  they  vary  in  breadth  from  about 

1  to  2/i.  If  the  surface  be  carefully 
focussed,  rows  of  granules  will  be  de- 
tected at  the  points  of  junction  of  the 
dark  and  light  bands,  and  very  fine 
longitudinal  lines  may  be  seen  rim- 
ning  through  the  dark  bands  and 
joining  these  granules  together.  By 
treating  the  specimen  with  certain 
reagents  (e.  g.,  chloride  of  gold)  fine 
lines  may  be  seen  running  transversely 
between  the  granules  and  uniting  them 
together.  This  appearance  is  believed 
to  be  due  to  a  reticulum  or  network 
of  interstitial  substance  lying  between 
the  contractile  portions  of  the  muscle. 
The  longitudinal  striation  gives  the 
fiber  the  appearance  of  being  made 
up  of  a  bundle  of  fibrils  which  have 
been  termed  sarcostyles  or  muscle 
columns,  and  if  the  fiber  be  hardened 
in  alcohol,  it  can  be  broken  up  longitu- 
dinally and  the  sarcostyles  separated 
from  each  other  (Fig.  375.)  The  retic- 
ulum, with  its  longitudinal  and  trans- 
verse meshes,  is  called  sarcoplasm. 
In  a  transverse  section,  the  muscular  fiber  is  seen  to  be  divided  into  a  number 
of  areas,  called  the  areas  of  Cohnheim,  more  or  less  polyhedral  in  shape  and  con- 
sisting of  the  transversely  divided  sarcostyles,  surrounded  by  transparent  sarco- 
plasm (Fig.  373). 


Fig.  375. — A.  Portion  of  a  medium-sized  human  muscular 
fiber.  Magnified  nearly  800  diameters.  B.  Separated  bundles 
of  fibrils,  equally  magnified,  a,  a.  Larger,  and  b,  b,  smaller 
collections,  c.  Still  smaller,  d,  d.  The  smallest  which  could 
be  detached. 


S.E. 


H 


S.E. 


Fig.  376. — Diagram  of  a  .sarcomere.    (After  Sehafer.)      A.  In  moderately  extended  condition.      B.  In  a  contracted 
condition.    k,k.  Membranes  of  Krause.    H.  Line  or  plane  of  Hensen.     S.E.  Poriferous  sarcous  element. 

Upon  closer  examination,  and  by  somewhat  altering  the  focus,  the  appearances 
become  more  complicated,  and  are  susceptible  of  various  interpretations.  The 
transverse  striation,  which  in  Fig.  374  appears  as  a  mere  alternation  of  dark  and 
light  bands,  is  resolved  into  the  appearance  seen  in  Fig.  375,  which  shows  a  series 
of  broad  dark  bands,  separated  by  light  bands,  each  of  which  is  divided  into  two 


DEVELOPMENT  OF  THE  MUSCLES  375 

by  a  dark  dotted  line.  This  line  is  termed  Dobie's  line  or  Krause's  membrane 
(Fig.  376,  k),  because  it  was  believed  by  Krause  to  be  an  actual  membrane,  con- 
tinuous with  the  sarcoiemma,  and  dividing  the  light  band  into  two  compartments. 
In  addition  to  the  membrane  of  Krause,  fine  clear  lines  may  be  made  out,  with  a 
sufficiently  high  power,  crossing  the  center  of  the  dark  band;  these  are  known  as 
the  lines  of  Hensen  (Fig.  376,  H). 

Schafer  has  worked  out  the  minute  anatomy  of  muscular  fiber,  particularly  in 
the  wing  muscles  of  insects,  which  are  peculiarly  adapted  for  this  purpose  on 
account  of  the  large  amount  of  interstitial  sarcoplasm  which  separates  the  sarco- 
styles.    In  the  following  description  that  given  by  Schafer  will  be  closely  followed. 

A  sarcostyle  may  be  said  to  be  made  up  of  successive  portions,  each  of  which 
is  termed  a  sarcomere.  The  sarcomere  is  situated  between  two  membranes  of  Krause 
and  consists  of  (1)  a  central  dark  part,  which  forms  a  portion  of  the  dark  band 
of  the  whole  fiber,  and  is  named  a  sarcous  element.  This  sarcous  element  really 
consists  of  two  parts,  superimposed  one  on  the  top  of  the  other,  and  when  the  fiber 
is  stretched  these  two  parts  become  separated  from  each  other  at  the  line  of  Hensen 
(Fig.  376,  A).  (2)  On  either  side  of  this  central  dark  portion  is  a  clear  layer,  most 
visible  when  the  fiber  is  extended;  this  is  situated  between  the  dark  center  and  the 
membrane  of  Krause,  and  w^hen  the  sarcomeres  are  joined  together  to  form  the 
sarcostyle,  constitutes  the  light  band  of  the  striated  muscular  fiber. 

When  the  sarcostyle  is  extended,  the  clear  intervals  are  well-marked  and  plainly 
to  be  seen;  when,  on  the  other  hand,  the  sarcostyle  is  contracted,  that  is  to  say, 
when  the  muscle  is  in  a  state  of  contraction,  these  clear  portions  are  very  small 
or  they  may  have  disappeared  altogether  (Fig.  376,  B).  When  the  sarcostyle  is 
stretched  to  its  full  extent,  not  only  is  the  clear  portion  well-marked,  but  the  dark 
portion — the  sarcous  element — is  separated  into  its  two  constituents  along  the 
line  of  Hensen.  The  sarcous  element  does  not  lie  free  in  the  sarcomere,  for  when 
the  sarcostyle  is  stretched,  so  as  to  render  the  clear  portion  visible,  very  fine 
lines,  which  are  probably  septa,  may  be  seen  running  through  it  from  the  sarcous 
element  to  the  membrane  of  Krause. 

Schafer  explains  these  phenomena  in  the  following  way:  He  considers  that  each 
sarcous  element  is  made  up  of  a  number  of  longitudinal  channels,  which  open 
into  the  clear  part  toward  the  membrane  of  Krause  but  are  closed  at  the  line  of 
Hensen.  When  the  muscular  fiber  is  contracted  the  clear  part  of  the  muscular 
substance  is  driven  into  these  channels  or  tubes,  and  is  therefore  hidden  from 
sight,  but  at  the  same  time  it  swells  up  the  sarcous  element  and  widens  and  shortens 
the  sarcomere.  When,  on  the  other  hand,  the  fiber  is  extended,  this  clear  sub- 
stance is  driven  out  of  the  tubes  and  collects  between  the  sarcous  element  and 
the  membrane  of  Krause,  and  gives  the  appearance  of  the  light  part  between 
these  two  structures;  by  this  means  it  elongates  and  narrows  the  sarcomere. 

If  this  view  be  true,  it  is  a  matter  of  great  interest,  and,  as  Schafer  has  shown, 
harmonizes  the  contraction  of  muscle  with  the  ameboid  action  of  protoplasm. 
In  an  ameboid  cell,  there  is  a  framework  of  spongioplasm,  which  stains  with 
hematoxylin  and  similar  reagents,  enclosing  in  its  meshes  a  clear  substance,  hyalo- 
plasm, which  will  not  stain  with  these  reagents.  Under  stimulation  the  hyaloplasm 
passes  into  the  pores  of  the  spongioplasm;  without  stimulation  it  tends  to  pass 
out  as  in  the  formation  of  pseudopodia.  In  muscle  there  is  the  same  thing,  viz., 
a  framework  of  spongioplasm  staining  with  hematoxylin — the  substance  of  the 
sarcous  element — and  this  encloses  a  clear  hyaloplasm,  the  clear  substance  of 
the  sarcomere,  which  resists  staining  with  this  reagent.  During  contraction  of  the 
muscle — i.  e.,  stimulation — this  clear  substance  passes  into  the  pores  of  the  spongio- 
plasm; while  during  extension  of  the  muscle — i.  e.,  when  there  is  no  stimulation — 
it  tends  to  pass  out  of  the  spongioplasm. 

In  this  way  the  contraction  is  brought  about:  under  stimulation  the  proto- 


376  MYOLOGY 

plasmic  material  (the  clear  substance  of  the  sarcomere)  recedes  into  the  sarcous 
element,  causing  the  sarcomere  to  widen  out  and  shorten.  The  contraction  of  the 
muscle  is  merely  the  sum  total  of  this  widening  out  and  shortening  of  these  bodies. 

Vessels  and  Nerves  of  Striped  Muscle. — The  capillaries  of  striped  muscle  are  ■! 
very  abundant,  and  form  a  sort  of  rectangular  network,  the  branches  of  which  run 
longitudinally  in  the  endomysium  between  the  muscular  fibers,  and  are  joined  at 
short  intervals  by  transverse  anastomosing  branches.  In  the  red  muscles  of  the 
rabbit  dilatations  occur  on  the  transverse  branches  of  the  capillary  network.  The 
larger  vascular  channels,  arteries  and  veins,  are  found  only  in  the  perimysium, 
between  the  muscular  fasciculi.  Nerves  are  profusely  distributed  to  striped  muscle. 
Their  mode  of  termination  is  described  on  page  730.  The  existence  of  lymphatic 
vessels  in  striped  muscle  has  not  been  ascertained,  though  they  have  been  found  in 
tendons  and  in  the  sheaths  of  the  muscles. 

Ossification  of  muscular  tissue  as  a  result  of  repeated  strain  or  injury  is  not  infrequent.  It 
is  oftenest  found  about  the  tendon  of  the  Adductor  longus  and  Vastus  mediahs  in  horsemen, 
or  in  the  Pectoralis  major  and  Deltoideus  of  soldiers.  It  may  take  the  form  of  exostoses  firmly 
fixed  to  the  bone — e.  g.,  "rider's  bone"  on  the  femur — or  of  layers  or  spicules  of  bone  lying  in 
the  muscles  or  their  fasciae  and  tendons.  Busse  states  that  these  bony  deposits  are  preceded 
by  a  hemorrhagic  myositis  due  to  injury,  the  effused  blood  organizing  and  being  finally  converted 
into  bone.  In  the  rarer  disease,  progressive  myositis  ossificans,  there  is  an  unexplained  tendency 
for  practically  any  of  the  voluntary  muscles  to  become  converted  into  solid  and  brittle  bony 
masses  which  are  completely  rigid. 

TENDONS,  APONEUROSES,  AND  FASClffl. 

Tendons  are  white,  glistening,  fibrous  cords,  varying  in  length  and  thickness, 
sometimes  round,  sometimes  flattened,  and  devoid  of  elasticity.  They  consist 
almost  entirely  of  white  fibrous  tissue,  the  fibrils  of  which  have  an  undulating 
course  parallel  with  each  other  and  are  firmly  united  together.  When  boiled  in 
water  tendon  is  almost  completely  converted  into  gelatin,  the  white  fibers  being 
composed  of  the  albuminoid  collagen,  which  is  often  regarded  as  the  anhydride  of 
gelatin.  They  are  very  sparingly  supplied  with  bloodvessels,  the  smaller  tendons 
presenting  in  their  interior  no  trace  of  them.  Nerves  supplying  tendons  have  special 
modifications  of  their  terminal  fibers,  named  organs  of  Golgi. 

Aponeuroses  are  flattened  or  ribbon-shaped  tendons,  of  a  pearly  white  color, 
iridescent,  glistening,  and  similar  in  structure  to  the  tendons.  They  are  only 
sparingly  supplied  with  bloodvessels. 

The  tendons  and  aponeuroses  are  connected,  on  the  one  hand,  with  the  muscles, 
and,  on  the  other  hand,  with  the  movable  structures,  as  the  bones,  cartilages  liga- 
ments, and  fibrous  membranes  (for  instance,  the  sclera) .  Where  the  muscular  fibers 
are  in  a  direct  line  with  those  of  the  tendon  or  aponeurosis,  the  two  are  directly 
continuous.  But  where  the  muscular  fibers  join  the  tendon  or  aponeurosis  at  an 
oblique  angle,  they  end,  according  to  Kolliker,  in  rounded  extremities  which  are 
received  into  corresponding  depressions  on  the  surface  of  the  latter,  the  connective 
tissue  between  the  muscular  fibers  being  continuous  with  that  of  the  tendon.  The 
latter  mode  of  attachment  occurs  in  all  the  penniform  and  bipenniform  muscles, 
and  in  those  muscles  the  tendons  of  which  commence  in  a  membranous  form, 
as  the  Gastrocnemius  and  Soleus. 

The  fasciae  are  fibroareolar  or  aponeurotic  laminae,  of  variable  thickness  and 
strength,  found  in  all  regions  of  the  body,  investing  the  softer  and  more  delicate 
organs.  During  the  process  of  development  many  of  the  cells  of  the  mesoderm 
are  differentiated  into  bones,  muscles,  vessels,  etc. ;  the  cells  of  the  mesoderm  which 
are  not  so  utilized  form  an  investment  for  these  structures  and  are  differentiated 
into  the  true  skin  and  the  fasciae  of  the  body.  They  have  been  subdivided,  from 
the  situations  in  which  they  occur,  into  superficial  and  deep. 


TENDONS,  APONEUROSES,  AND  FASCIA 


377 


The  superficial  fascia  is  found  immediately  beneath  the  integument  over  almost  the 
entire  surface  of  the  body.  It  connects  the  skin  with  the  deep  fascia,  and  consists 
of  fibroareolar  tissue,  containing  in  its  meshes  pellicles  of  fat  in  varying  quantity. 
Fibro-areolar  tissue  is  composed  of  white  fibers  and  yellow  elastic  fibers  intercrossing 
in  all  directions,  and  united  together  by  a  homogeneous  cement  or  ground  substance, 
the  matrix. 

The  cells  of  areolar  tissue  are  of  four  principal  kinds:  (1)  Flattened  lamellar 
cells,  which  may  be  either  branched  or  unbranched.  The  branched  lamellar  cells 
are  composed  of  clear  cytoplasm,  and  contain  oval  nuclei;  the  processes  of  these 
cells  may  unite  so  as  to  form  an  open  network,  as  in  the  cornea.  The  unbranched 
cells  are  joined  edge  to  edge  like  the  cells  of  an  epithelium;  the  "  tendon  cells,"  pres- 
ently.to  be  described,  are  examples  of  this  variety.  (2)  Clasmatocytes,  large  irregular 
cells  characterized  by  the  presence  of  granules  or  vacuoles  in  their  protoplasm, 


Plasma  cell 


^  White 

'Z^"' fibres 


Elastic 
fibres 


Fibrillated 
cell 


Lamellar  cell 
Fig.  377. — Subcutaneous  tissue  from  a  young  rabbit.     Highly  magnified. 


(Schafer.) 


and  containing  oval  nuclei.  (3)  Granule  cells  (Mastzellen),  which  are  ovoid  or 
spheroidal  in  shape.  They  are  formed  of  a  soft  protoplasm,  containing  granules 
which  are  basophil  in  character.  (4)  Plasma  cells  of  Waldeyer,  usually  spheroidal 
and  distinguished  by  containing  a  vacuolated  protoplasm.  The  vacuoles  are  filled 
with  fluid,  and  the  protoplasm  between  the  spaces  is  clear,  with  occasionally  a  few 
scattered  basophil  granules. 

In  addition  to  these  four  typical  forms  of  connective-tissue  corpuscles,  areolar 
tissue  may  be  seen  to  possess  wandering  cells,  i.  e.,  leucocytes  which  have  emigrated 
from  the  neighboring  vessels;  in  some  instances,  as  in  the  choroid  coat  of  the  eye 
cells  filled  with  granules  of  pigment  (pigment  cells)  are  found. 

The  cells  lie  in  spaces  in  the  ground  substance  between  the  bundles  of  fibers, 
and  these  spaces  may  be  brought  into  view  by  treating  the  tissue  with  nitrate  of 
silver  and  exposing  it  to  the  light.  This  will  color  the  ground  substance  and  leave 
the  cell-spaces  unstained. 


378  ^^^^^^^       MYOLOGY 

Fat  is  entirely  absent  in  the  subcutaneous  tissue  of  the  eyelids,  of  the  penis 
and  scrotum,  and  of  the  labia  minora.  It  varies  in  thickness  in  different  parts  of 
the  body;  in  the  groin  it  is  so  thick  that  it  may  be  subdivided  into  several  laminae. 
Beneath  the  fatty  layer  there  is  generally  another  layer  of  superficial  fascia,  com- 
paratively devoid  of  adipose  tissue,  in  which  the  trunks  of  the  subcutaneous  vessels 
and  nerves  are  found,  as  the  superficial  epigastric  vessels  in  the  abdominal  region, 
the  superficial  veins  in  the  forearm,  the  saphenous  veins  in  the  leg  and  thigh,  and  the 
superficial  lymph  glands.  Certain  cutaneous  muscles  also  are  situated  in  the  super- 
ficial fascia,  as  the  Platysma  in  the  neck,  and  the  Orbicularis  oculi  around  the  eyelids. 
This  fascia  is  most  distinct  at  the  lower  part  of  the  abdomen,  perineum,  and  extremi- 
ties; it  is  very  thin  in  those  regions  where  muscular  fibers  are  inserted  into  the 
integument,  as  on  the  side  of  the  neck,  the  face,  and  around  the  margin  of  the  anus. 
It  is  very  dense  in  the  scalp,  in  the  palms  of  the  hands,  and  soles  of  the  feet,  forming  a 
fibro-fatty  layer,  which  binds  the  integument  firmly  to  the  underlying  structures. 

The  superficial  fascia  connects  the  skin  to  the  subjacent  parts,  facilitates  the 
movement  of  the  skin,  serves  as  a  soft  nidus  for  the  passage  of  vessels  and  nerves 
to  the  integument,  and  retains  the  warmth  of  the  body,  since  the  fat  contained  in 
its  areolae  is  a  bad  conductor  of  heat. 

The  deep  fascia  is  a  dense,  inelastic,  fibrous  membrane,  forming  sheaths  for  the 
muscles,  and  in  some  cases  affording  them  broad  surfaces  for  attachment.  It 
consists  of  shining  tendinous  fibers,  placed  parallel  with  one  another,  and  connected 
together  by  other  fibers  disposed  in  a  rectilinear  manner.  It  forms  a  strong  invest- 
ment which  not  only  binds  down  collectively  the  muscles  in  each  region,  but  gives  a 
separate  sheath  to  each,  as  well  as  to  the  vessels  and  nerves.  The  fasciae  are  thick 
in  unprotected  situations,  as  on  the  lateral  side  of  a  limb,  and  thinner  on  the  medial 
side.  The  deep  fasciae  assist  the  muscles  in  their  actions,  by  the  degree  of  tension 
and  pressure  they  make  upon  their  surfaces;  the  degree  of  tension  and  pressure 
is  regulated  by  the  associated  muscles,  as,  for  instance,  by  the  Tensor  fasciae  latae 
and  Glutaeus  maximus  in  the  thigh,  by  the  Biceps  in  the  upper  and  lower  extremi- 
ties, and  Palmaris  longus  in  the  hand.  In  the  limbs,  the  fasciae  not  only  invest 
the  entire  limb,  but  give  off  septa  which  separate  the  various  muscles,  and  are 
attached  to  the  periosteum :  these  prolongations  of  fasciae  are  usually  spoken  of  as 
intermuscular  septa. 

The  Fasciae  and  Muscles  may  be  arranged,  according  to  the  general  division 
of  the  body,  into  those  of  the  head  and  neck;  of  the  trunk;  of  the  upper  extremity; 
^nd  of  the  lower  extremity. 


THE  FASCLffi  AND  MUSCLES   OF  THE   HEAD. 

I.  THE   MUSCLE   OF   THE   SCALP. 

Epicranius. 

The  Skin  of  the  Scalp. — This  is  thicker  than  in  any  other  part  of  the  body.  It  is  intimately 
adherent  to  the  superficial  fascia,  which  attaches  it  firmly  to  the  underlying  aponeurosis  and 
muscle.  Movements  of  the  muscle  move  the  skin.  The  hair  follicles  are  very  closely  set  together, 
and  extend  throughout  the  whole  thickness  of  the  skin.  It  also  contains  a  number  of  sebaceous 
glands. 

The  superficial  fascia  in  the  cranial  region  is  a  firm,  dense,  fibro-fatty  layer, 
intimately  adherent  to  the  integument,  and  to  the  Epicranius  and  its  tendinous 
aponeurosis;  it  is  continuous,  behind,  with  the  superficial  fascia  at  the  back  of  the 
neck;  and,  laterally,  is  continued  over  the  temporal  fascia.  It  contains  between 
its  layers  the  superficial  vessels  and  nerves  and  much  granular  fat. 

•The  Epicranius  (Occipitofrontalis)  (Fig.  378)  is  a  broad,  musculofibrous  layer, 


THE  MUSCLE  OF  THE  SCALP 


379 


which  covers  the  whole  of  one  side  of  the  vertex  of  the  skull,  from  the  occipital 
bone  to  the  eyebrow.  It  consists  of  two  parts,  the  Occipitalis  and  the  Frontalis, 
connected  by  an  intervening  tendinous  aponeurosis,  the  galea  aponeurotica. 

The  Occipitalis,  thin  and  quadrilateral  in  form,  arises  by  tendinous  fibers  from 
the  lateral  two-thirds  of  the  superior  nuchal  line  of  the  occipital  bone,  and  from 
the  mastoid  part  of  the  temporal.    It  ends  in  the  galea  aponeurotica. 


Corrugaior 


Dilatator  narig  ant. 

Dilatator  narispost 

I^'asalis 

Depressor  septi 


Mentalis- 


Fia.  378. — Muscles  of  the  head,  face,  and  neck. 


The  Frontalis  is  thin,  of  a  quadrilateral  form,  and  intimately  adherent  to  the 
superficial  fascia.  It  is  broader  than  the  Occipitalis  and  its  fibers  are  longer  and 
paler  in  color.  It  has  no  bony  attachments.  Its  medial  fibers  are  continuous  with 
those  of  the  Procerus;  its  immediate  fibers  blend  with  the  Corrugator  and  Orbicu- 
laris oculi;  and  its  lateral  fibers  are  also  blended  with  the  latter  muscle  over 
the  zj^gomatic  process  of  the  frontal  bone.  From  these  attachments  the  fibers 
are  directed  upward,  and  join  the  galea  aponeurotica  below  the  coronal  suture. 


380  -^^^^^^»^        MYOLOGY 

The  medial  margins  of  the  Frontales  are  joined  together  for  some  distance  above 
the  root  of  the  nose;  but  between  the  Occipitales  there  is  a  considerable,  though  __ 
variable,  interval,  occupied  by  the  galea  aponeurotica.  ■I 

The  galea  aponeurotica  {epicranial  aponeurosis)  covers  the  upper  part  of  the 
cranium;  behind,  it  is  attached,  in  the  interval  between  its  union  with  the  Occipi- 
tales, to  the  external  occipital  protuberance  and  highest  nuchal  lines  of  the  occipital 
bone;  in  front,  it  forms  a  short  and  narrow  prolongation  between  its  union  with 
the  Frontales.  On  either  side  it  gives  origin  to  the  Auriculares  anterior  and  supe- 
rior; in  this  situation  it  loses  its  aponeurotic  character,  and  is  continued  over  the 
temporal  fascia  to  the  zygomatic  arch  as  a  layer  of  laminated  areolar  tissue.  It 
is  closely  connected  to  the  integument  by  the  firm,  dense,  fibro-fatty  layer  which 
forms  the  superficial  fascia  of  the  scalp :  it  is  attached  to  the  pericranium  by  loose 
cellular  tissue,  which  allows  the  aponeurosis,  carrying  with  it  the  integument  to 
move  through  a  considerable  distance. 

Vaiiations. — Both  Frontalis  and  Occipitalis  vary  considerably  in  size  and  in  extent  of  attach- 
ment; either  may  be  absent;  fusion  of  Frontalis  to  skin  has  been  noted. 

Nerves. — The  Frontahs  is  suppUed  by  the  temporal  branches  of  the  facial  nerve,  and  the 
OccipitaUs  by  the  posterior  auricular  branch  of  the  same  nerve. 

Actions. — The  Frontales  raise  the  eyebrows  and  the  skin  over  the  root  of  the  nose,  and  at  the 
same  time  draw  the  scalp  forward,  throwing  the  integument  of  the  forehead  into  transverse 
wrinkles.  The  Occipitales  draw  the  scalp  backward.  By  bringing  alternately  into  action  the 
Frontales  and  Occipitales  the  entire  scalp  may  be  moved  forward  and  backward.  In  the  ordinary 
action  of  the  muscles,  the  eyebrows  are  elevated,  and  at  the  same  time  the  aponeurosis  is  fixed 
by  the  Occipitales,  thus  giving  to  the  face  the  expression  of  surprise;  if  the  action  be  exaggerated, 
the  eyebrows  are  still  further  raised,  and  the  skin  of  the  forehead  thrown  into  transverse  wrinkles, 
as  in  the  expression  of  fright  or  horror. 

A  thin  muscular  slip,  the  Transversus  nuchas,  is  present  in  a  considerable  pro- 
portion (25  per  cent.)  of  cases;  it  arises  from  the  external  occipital  protuberance 
or  from  the  superior  nuchal  line,  either  superficial  or  deep  to  the  Trapezius;  it 
is  frequently  inserted  with  the  Auricularis  posterior,  but  may  join  the  posterior 
edge  of  the  Sternocleidomastoideus. 

n.     THE  MUSCLES  OF  THE  EYELmS. 
The  muscles  of  the  eyelids  are : 

Levator  palpebrse  superioris.        Orbicularis  oculi.  Corrugator. 

The  Levator  palpebrse  superioris  is  described  with  the  Anatomy  of  the  Eye. 

The  Orbicularis  oculi  (Orbicularis  palpebrarum)  (Fig.  379)  arises  from  the  nasal 
part  of  the  frontal  bone,  from  the  frontal  process  of  the  maxilla  in  front  of  the 
lacrimal  groove,  and  from  the  anterior  surface  and  borders  of  a  short  fibrous  band, 
the  medial  palpebral  ligament.  From  this  origin,  the  fibers  are  directed  lateral- 
ward,  forming  a  broad  and  thin  layer,  which  occupies  the  eyelids  or  palpebrse, 
surrounds  the  circumference  of  the  orbit,  and  spreads  over  the  temple,  and  down- 
ward on  the  cheek.  The  palpebral  portion  of  the  muscle  is  thin  and  pale;  it  arises 
from  the  bifurcation  of  the  medial  palpebral  ligament,  forms  a  series  of  concentric 
curves,  and  is  inserted  into  the  lateral  palpebral  raphe.  The  orbital  portion  is  thicker 
and  of  a  reddish  color;  its  fibers  form  a  complete  ellipse  without  interruption  at 
the  lateral  palpebral  commissure;  the  upper  fibers  of  this  portion  blend  with  the 
Frontalis  and  Corrugator.  The  lacrimal  part  ( Tensor  tarsi)  is  a  small,  thin  muscle, 
about  6  mm.  in  breadth  and  12  mm.  in  length,  situated  behind  the  medial  palpebral 
ligament  and  lacrimal  sac  (Fig.  379).  It  arises  from  the  posterior  crest  and  adjacent 
part  of  the  orbital  surface  of  the  lacrimal  bone,  and  passing  behind  the  lacrimal 
sac,  divides  into  two  slips,  upper  and  lower,  which  are  inserted  into  the  superior 
and  inferior  tarsi  medial  to  the  puncta  lacrimalia;  occasionally  it  is  very  indistinct. 


THE  MUSCLES  OF  THE  EYELIDS 


381 


The  medial  palpebral  ligament  {tendo  oculi),  about  4  mm.  in  length  and  2  mm. 
in  breadth,  is  attached  to  the  frontal  process  of  the  maxilla  in  front  of  the  lacrimal 
groove.  Crossing  the  lacrimal  sac,  it  divides  into  two  parts,  upper  and  lower, 
each  attached  to  the  medial  end  of  the  corresponding  tarsus.  As  the  ligament 
crosses  the  lacrimal  sac,  a  strong  aponeurotic  lamina  is  given  off  from  its  posterior 
surface;  this  expands  over  the  sac,  and  is  attached  to  the  posterior  lacrimal  crest. 

The  lateral  palpebral  raphe  is  a  much  weaker  structure  than  the  medial  palpebral 
ligament.  It  is  attached  to  the  margin  of  the  frontosphenoidal  process  of  the 
zygomatic  bone,  and  passes  medialward  to  the  lateral  commissure  of  the  eyelids, 
where  it  divides  into  two  slips,  which  are  attached  to  the  margins  of  the  respective 
tarsi. 


Probe  in  frontal  sinus 


Probe  in  ant.  eth- 
moidal cells 

Crista  galli 


Lacrimal  part  of 
Orbicularis  ocidi 

Probe  in  lacrimal  sac 

—  (  Probes  from,  frontal 
\sinus  and  ant.  eth- 
moidal, cells 

Middle  meatus 


Septum  of  nose 


Probe  in  nasolacrimal 
duct 


Infraorbital  nerve  and  artery 


Fig.  379. — Left  orbicularis  oculi,  seen  from  behind. 


The  Corrugator^  (Corrugator  swperdlii)  is  a  small,  narrow,  pyramidal  muscle, 
placed  at  the  medial  end  of  the  eyebrow,  beneath  the  Frontalis  and  Orbicularis 
oculi.  It  arises  from  the  medial  end  of  the  superciliary  arch;  and  its  fibers  pass 
upward  and  lateralward,  between  the  palpebral  and  orbital  portions  of  the  Orbicu- 
laris oculi,  and  are  inserted  into  the  deep  surface  of  the  skin,  above  the  middle  of 
the  orbital  arch. 

Nerves. — The  Orbicularis  oculi  and  Corrugator  are  supplied  by  the  facial  nerve. 

Actions. — The  Orbicularis  oculi  is  the  sphincter  muscle  of  the  eyelids.  The  palpebral  portion 
acts  involuntarily,  closing  the  lids  gently,  as  in  sleep  or  in  blinking;  the  orbital  portion  is  subject 
to  the  will.  When  the  entire  muscle  is  brought  into  action,  the  skin  of  the  forehead,  temple, 
and  cheek  is  drawn  toward  the  medial  angle  of  the  orbit,  and  the  eyeUds  are  firmly  closed,  as  in 
photophobia.  The  skin  thus  drawn  upon  is  thrown  into  folds,  especially  radiating  from  the 
lateral  angle  of  the  eyelids;  these  folds  become  permanent  in  old  age,  and  form  the  so-called 
"crows'  feet."  The  Levator  palpebrae  superioris  is  the  direct  antagonist  of  this  muscle;  it  raises 
the  upper  eyehd  and  exposes  the  front  of  the  bulb  of  the  eye.  Each  time  the  eyelids  are  closed 
through  the  action  of  the  Orbicularis,  the  medial  palpebral  ligament  is  tightened,  the  wall  of 
the  lacrimal  sac  is  thus  drawn  lateralward  and  forward,  so  that  a  vacuiun  is  made  in  it  and  the 

1  The  corrugator  is  not  recognized  as  a  separate  muscle  in  the  Basle  Nomenclature. 


382  ^^^^^^^^        MYOLOGY 

tears  are  sucked  along  the  lacrimal  canals  into  it.  The  lacrimal  part  of  the  Orbicularis  oculi 
draws  the  eyelids  and  the  ends  of  the  lacrimal  canals  medialward  and  compresses  them  against 
the  surface  of  the  globe  of  the  eye,  thus  placing  them  in  the  most  favorable  situation  for  receiving 
the  tears;  it  also  compresses  the  lacrimal  sac.  The  Corrugator  draws  the  eyebrow  downward 
and  medialwai'd,  producing  the  vertical  wrinkles  of  the  forehead.  It  is  the  "frowning"  muscle, 
and  may  be  regarded  as  the  principal  muscle  in  the  expression  of  suffering. 

m.     THE  MUSCLES  OF  THE  NOSE  (Fig.   378). 
The  muscles  of  the  nose  comprise: 

Procerus.  Depressor  septi. 

NasaHs.  Dilatator  naris  posterior. 

Dilatator  naris  anterior. 

The  Procerus  (Pyramidalis  nasi)  is  a  small  pyramidal  slip  arising  by  tendinous 
fibers  from  the  fascia  covering  the  lower  part  of  the  nasal  bone  and  upper  part 
of  the  lateral  nasal  cartilage;  it  is  inserted  into  the  skin  over  the  lower  part  of 
the  forehead  between  the  two  eyebrows,  its  fibers  decussating  with  those  of  the 
Frontalis. 

The  Nasalis  {Compressor  naris)  consists  of  two  parts,  transverse  and  alar.  The 
transverse  part  arises  from  the  maxilla,  above  and  lateral  to  the  incisive  fossa; 
its  fibers  proceed  upward  and  medialward,  expanding  into  a  thin  aponeurosis 
which  is  continuous  on  the  bridge  of  the  nose  with  that  of  the  muscle  of  the  oppo- 
site side,  and  with  the  aponeurosis  of  the  Procerus.  The  alar  part  is  attached  by 
one  end  to  the  greater  alar  cartilage,  and  by  the  other  to  the  integument  at  the 
point  of  the  nose. 

The  Depressor  septi  (Depressor  alee  nasi)  arises  from  the  incisive  fossa  of  the 
maxilla;  its  fibers  ascend  to  be  inserted  into  the  septum  and  back  part  of  the  ala 
of  the  nose.  It  lies  between  the  mucous  membrane  and  muscular  structure  of 
the  lip. 

The  Dilatator  naris  posterior  is  placed  partly  beneath  the  Quadratus  labii 
superioris.  It  arises  from  the  margin  of  the  nasal  notch  of  the  maxilla,  and  from 
the  lesser  alar  cartilages,  and  is  inserted  into  the  skin  near  the  margin  of  the 
nostril. 

The  Dilatator  naris  anterior  is  a  delicate  fasciculus,  passing  from  the  greater 
alar  cartilage  to  the  integument  near  the  margin  of  the  nostril;  it  is  situated  in 
front  of  the  preceding. 

Variations. — These  muscles  vary  in  size  and  strength  or  may  be  absent. 

Nerves. — All  the  muscles  of  this  group  are  supplied  by  the  facial  nerve. 

Actions. — The  Procerus  draws  down  the  medial  angle  of  the  eyebrows  and  produces  transverse 
wrinkles  over  the  bridge  of  the  nose.  The  two  Dilatatores  enlarge  the  apertm-e  of  the  nares. 
Their  action  in  ordinary  breathing  is  to  resist  the  tendency  of  the  nostrils  to  close  from  atmos- 
pheric pressure,  but  in  difficult  breathing,  as  well  as  in  some  emotions,  such  as  anger,  they  con- 
tract strongly.  The  Depressor  septi  is  a  direct  antagonist  of  the  other  muscles  of  the  nose,  drawing 
the  ala  of  the  nose  downward,  and  thereby  constricting  the  aperture  of  the  nares.  The  Nasalis 
depresses  the  cartilaginous  part  of  the  nose  and  draws  the  ala  toward  the  septum. 

IV.     THE  MUSCLES  OF  THE  MOUTH. 

The  muscles  of  the  mouth  are : 

Quadratus  labii  superioris.  Quadratus  labii  inferioris. 

Caninus.  Triangularis. 

Zygomaticus.  Buccinator. 

Mentalis.  Orbicularis  oris. 

Risorius. 


THE  MUSCLES  OF  THE  MOUTH  383 

The  Quadratus  labii  superioris  is  a  broad  sheet,  the  origin  of  which  extends 
from  the  side  of  the  nose  lo  the  zygomatic  bone.  Its  medial  fibers  form  the  angular 
head,  which  arises  by  a  pointed  extremity  from  the  upper  part  of  the  frontal  process 
of  the  maxilla  and  passing  obliquely  downward  and  lateralward  divides  into  two 
slips.  One  of  these  is  inserted  into  the  greater  alar  cartilage  and  skin  of  the  nose; 
the  other  is  prolonged  into  the  lateral  part  of  the  upper  lip,  blending  with  the 
infraorbital  head  and  with  the  Orbicularis  oris.  The  intermediate  portion  or 
infraorbital  head  arises  from  the  lower  margin  of  the  orbit  immediately  above  the 
infraorbital  foramen,  some  of  its  fibers  being  attached  to  the  maxilla,  others  to  the 
zygomatic  bone.  Its  fibers  converge,  to  be  inserted  into  the  muscular  substance 
of  the  upper  lip  between  the  angular  head  and  the  Caninus.  The  lateral  fibers, 
forming  the  zygomatic  head,  arise  from  the  malar  surface  of  the  zygomatic  bone 
immediately  behind  the  zygomaticomaxillary  suture  and  pass  downward  and 
medialward  to  the  upper  lip. 

The  Caninus  {Levator  anguli  oris)  arises  from  the  canine  fossa,  immediately 
below  the  infraorbital  foramen;  its  fibers  are  inserted  into  the  angle  of  the  mouth, 
intermingling  with  those  of  the  Zygomaticus,  Triangularis,  and  Orbicularis  oris. 

The  Zygomaticus  {Zygomaticus  major)  arises  from  the  zygomatic  bone,  in  front 
of  the  zygomaticotemporal  suture,  and  descending  obliquely  with  a  medial  inclina- 
tion, is  inserted  into  the  angle  of  the  mouth,  where  it  blends  with  the  fibers  of  the 
Caninus,  Orbicularis  oris,  and  Triangularis. 

Nerves. — This  group  of  nmscles  is  supplied  by  the  facial  nerve. 

Actions. — The  Quadratus  labii  superioris  is  the  proper  elevator  of  the  upper  lip,  carrying  it 
at  the  same  time  a  little  forward.  Its  angular  head  acts  as  a  dilator  of  the  naris;  the  infraorbital 
and  zygomatic  heads  assist  in  forming  the  nasolabial  furrow,  which  passes  from  the  side  of  the 
nose  to  the  upper  Mp  and  give^  to  the  face  an  expression  of  sadness.  When  the  whole  muscle 
is  in  action  it  gives  to  the  countenance  an  expression  of  contempt  and  disdain.  The  Quad- 
ratus labii  superioris  raises  the  angle  of  the  mouth  and  assists  the  Caninus  in  producing  the 
nasolabial  furrow.  The  Zygomaticus  draws  the  angle  of  the  mouth  backward  and  upward,  as 
in  laughing. 

The  Mentalis  {Levator  menti)  is  a  small  conical  fasciculus,  situated  at  the  side 
of  the  frenulum  of  the  lower  lip.  It  arises  from  the  incisive  fossa  of  the  mandible, 
and  descends  to  be  inserted  into  the  integument  of  the  chin. 

The  Quadratus  labii  inferioris  {Depressor  labii  inferioris;  Quadratus  menti)  is 
a  small  quadrilateral  muscle.  It  arises  from  the  oblique  line  of  the  mandible, 
between  the  symphysis  and  the  mental  foramen,  and  passes  upward  and  medial- 
ward,  to  be  inserted  into  the  integument  of  the  lower  lip,  its  fibers  blending  with 
the  Orbicularis  oris,  and  with  those  of  its  fellow  of  the  opposite  side.  At  its  origin 
it  is  continuous  with  the  fibers  of  the  Platysma.  Much  yellow  fat  is  intermingled 
with  the  fibers  of  this  muscle. 

The  Triangularis  {Depressor  anguli  oris)  arises  from  the  oblique  line  of  the 
mandible,  whence  its  fibers  converge,  to  be  inserted,  by  a  narrow  fasciculus,  into 
the  angle  of  the  mouth.  At  its  origin  it  is  continuous  with  the  Platysma,  and  at 
its  insertion  with  the  Orbicularis  oris  and  Risorius;  some  of  its  fibers  are  directly 
continuous  with  those  of  the  Caninus,  and  others  are  occasionally  found  crossing 
from  the  muscle  of  one  side  to  that  of  the  other;  these  latter  fibers  constitute 
the  Transversus  menti. 

Nerves. — This  group  of  muscles  is  suppHed  by  the  facial  nerve. 

Actions. — The  Mentahs  raises  and  protrudes  the  lower  Up,  and  at  the  same  time  wrinkles  the 
skin  of  the  chin,  expressing  doubt  or  disdain.  The  Quadratus  labii  inferioris  draws  the  lower 
Up  directly  downward  and  a  little  lateralward,  as  in  the  expression  of  irony.  The  Triangularis 
depresses  the  angle  of  the  mouth,  being  the  antagonist  of  the  Caninus  and  Zygomaticus;  acting 
^vath  the  Caninus,  it  will  draw  the  angle  of  the  mouth  medialward.  The  Platysma  which  retracts 
and  depresses  the  angle  of  the  mouth  belongs  with  this  group. 


384 


MYOLOGY 


The  Buccinator  (Fig,  380)  is  a  thin  quadrilateral  muscle,  occupying  the  interval 
between  the  maxilla  and  the  mandible  at  the  side  of  the  face.  It  arises  from  the 
outer  surfaces  of  the  alveolar  processes  of  the  maxilla  and  mandible,  corresponding 

to  the  three  molar  teeth ;  and  behind,  from 
the  anterior  border  of  the  pterygomandib- 
ular raphe  which  separates  it  from  the 
Constrictor  pharyngis  superior.  The  fibers 
converge  toward  the  angle  of  the  mouth, 
where  the  central  fibers  intersect  each 
other,  those  from  below  being  continuous 
with  the  upper  segment  of  the  Orbicu- 
laris oris,  and  those  from  above  with  the 
lower  segment;  the  upper  and  lower  fibers 
are  continued  forward  into  the  corre- 
sponding lip  without  decussation. 


Fig.  380. — Muscles  of  the  pharynx  and  cheek. 


TRIANGULARJS 

Fig.  381. — Scheme  showing  arrangement  of  fibers  of 
Orbicularis  oris. 


Relations. — The  Buccinator  is  covered  by  the  buccopharyngeal  fascia,  and  is  in  relation  by 
its  superficial  surface,  behind,  with  a  large  mass  of  fat,  which  separates  it  from  the  ramus  of  the 
mandible,  the  Masseter,  and  a  small  portion  of  the  Temporalis;  this  fat  has  been  named  the 
suctorial  pad,  because  it  is  supposed  to  assist  in  the  act  of  sucking.  The  parotid  duct  pierces  the 
Buccinator  opposite  the  second  molar  tooth  of  the  maxUla.  The  deep  surface  is  in  relation  with 
the  buccal  glands  and  mucous  membrane  of  the  mouth. 

The  pterygomandibular  raphe  (pterygomandibular  ligament)  is  a  tendinous  band 
of  the  buccopharyngeal  fascia,  attached  by  one  extremity  to  the  hamulus  of  the 
medial  pterygoid  plate,  and  by  the  other  to  the  posterior  end  of  the  mylohyoid 
line  of  the  mandible.  Its  medial  surface  is  covered  by  the  mucous  membrane  of 
the  mouth.  Its  lateral  surface  is  separated  from  the  ramus  of  the  mandible  by  a 
quantity  of  adipose  tissue.  Its  posterior  border  gives  attachment  to  the  Constrictor 
pharyngis  superior;  its  anterior  border,  to  part  of  the  Buccinator  (Fig.  380). 

The  Orbicularis  oris  (Fig.  381)  is  not  a  simple  sphincter  muscle  like  the  Orbic- 
ularis oculi;  it  consists  of  numerous  strata  of  muscular  fibers  surrounding  the 
orifice  of  the  mouth  but  having  different  direction.  It  consists  partly  of  fibers 
derived  from  the  other  facial  muscles  which  are  inserted  into  the  lips,  and  partly 
of  fibers  proper  to  the  lips.  Of  the  former,  a  considerable  number  are  derived  from 
the  Buccinator  and  form  the  deeper  stratum  of  the  Orbicularis.  Some  of  the 
Buccinator  fibers — namely,  those  near  the  middle  of  the  muscle — decussate  at 
the  angle  of  the  mouth,  those  arising  from  the  maxilla  passing  to  the  lower  lip, 
and  those  from  the  mandible  to  the  upper  lip.  The  uppermost  and  lowermost 
fibers  of  the  Buccinator  pass  across  the  lips  from  side  to  side  without  decussation. 
Superficial  to  this  stratum  is  a  second,  formed  on  either  side  by  the  Caninus  and 


THE  MUSCLES  OF  MASTICATION  385 

Triangularis,  which  cross  each  other  at  the  angle  of  the  mouth;  those  from  the 
Caninus  passing  to  the  lower  lip,  and  those  from  the  Triangularis  to  the  upper  lip, 
along  which  they  run,  to  be  inserted  into  the  skin  near  the  median  line.  In  addi- 
tion to  these  there  are  fibers  from  the  Quadratus  labii  superioris,  the  Zygomaticus, 
and  the  Quadratus  labii  inferioris;  these  intermingle  with  the  transverse  fibers 
above  described,  and  have  principally  an  oblique  direction.  The  proper  fibers 
of  the  lips  are  oblique,  and  pass  from  the  under  surface  of  the  skin  to  the  mucous 
membrane,  through  the  thickness  of  the  lip.  Finally  there  are  fibers  by  which  the 
muscle  is  connected  with  the  maxillae  and  the  septum  of  the  nose  above  and  with 
the  mandible  below.  In  the  upper  lip  these  consist  of  two  bands,  lateral  and  medial, 
on  either  side  of  the  middle  line;  the  lateral  band  (m.  incisivus  labii  superioris) 
arises  from  the  alveolar  border  of  the  maxilla,  opposite  the  lateral  incisor  tooth, 
and  arching  lateralward  is  continuous  with  the  other  muscles  at  the  angle  of  the 
mouth;  the  medial  band  {m.  nasolabialis)  connects  the  upper  lip  to  the  back  of  the 
septum  of  the  nose.  The  interval  between  the  two  medial  bands  corresponds 
with  the  depression,  called  the  philtrum,  seen  on  the  lip  beneath  the  septum  of  the 
nose.  The  additional  fibers  for  the  lower  lip  constitute  a  slip  (m.  incisimis  labii 
inferioris)  on  either  side  of  the  middle  line;  this  arises  from  the  mandible,  lateral 
to  the  Mentalis,  and  intermingles  with  the  other  muscles  at  the  angle  of  the 
mouth. 

The  Risorius  arises  in  the  fascia  over  the  Masseter  and,  passing  horizontally 
forward,  superficial  to  the  Platysma,  is  inserted  into  the  skin  at  the  angle  of  the 
mouth  (Fig.  378).  It  is  a  narrow  bundle  of  fibers,  broadest  at  its  origin,  but  varies 
much  in  its  size  and  form. 

Variations. — The  zygomatic  head  of  the  Quadratus  labii  superioris  and  Risorius  are  frequently 
absent  and  more  rarely  the  Zygomaticus.  The  Zygomaticus  and  Risorius  may  be  doubled  or  the 
latter  greatly  enlarged  or  blended  with  the  Platysma. 

Nerves. — The  muscles  in  this  group  are  all  supphed  by  the  facial  nerve. 

Actions. — The  Orbicularis  oiis  in  its  ordinary  action  effects  the  direct  closure  of  the  lips;  by 
its  deep  fibers,  assisted  by  the  oblique  ones,  it  closely  applies  the  Ups  to  the  alveolar  arch.  The 
superficial  part,  consisting  principally  of  the  decussating  fibers,  brings  the  lips  together  and  also 
protrudes  them  forward.  The  Buccinators  compress  the  cheeks,  so  that,  during  the  process  of 
mastication,  the  food  is  kept  under  the  immediate  pressure  of  the  teeth.  When  the  cheeks  have 
been  previously  distended  with  air,  the  Buccinator  muscles  expel  it  from  between  the  lips,  as  in 
blowing  a  trumpet;  hence  the  name  {buccina,  a  trumpet).  The  Risorius  retracts  the  angle  of 
the  mouth,  and  produces  an  unpleasant  grinning  expression. 

For  more  extensive  consideration  of  the  facial  muscles,  see  Charles  Darwin, 
Expression  of  the  Emotions  in  Man  and  Animals. 

IV.     THE  MUSCLES  OF  MASTICATION. 

The  chief  muscles  of  mastication  are: 

Masseter.  Pterygoideus  externus. 

Temporalis.  Pterygoideus  internus. 

Parotideomasseteric  Fascia  {masseteric  fascia) . — Covering  the  Masseter,  and  firmly 
connected  with  it,  is  a  strong  layer  of  fascia  derived  from  the  deep  cervical  fascia. 
Above,  this  fascia  is  attached  to  the  lower  border  of  the  zygomatic  arch,  and  behind, 
it  invests  the  parotid  gland. 

The  Masseter  (Fig.  378)  is  a  thick,  somewhat  quadrilateral  muscle,  consisting 
of  two  portions,  superficial  and  deep.  The  superficial  portion,  the  larger,  arises 
by  a  thick,  tendinous  aponeurosis  from  the  zygomatic  process  of  the  maxilla,  and 
from  the  anterior  two-thirds  of  the  lower  border  of  the  zygomatic  arch:  its  fibers 
pass  downward  and  backward,  to  be  inserted  into  the  angle  and  lower  half  of  the 
lateral  surface  of  the  ramus  of  the  mandible.  The  deep  portion  is  much  smaller, 
25 


386 


MYOLOGY 


and  more  muscular  in  texture;  it  arises  from  the  posterior  third  of  the  lower  bordei 
and  from  the  whole  of  the  medial  surface  of  the  zygomatic  arch;  its  fibers  pass] 
downward  and  forward,  to  be  inserted  into  the  upper  half  of  the  ramus  and  the! 
lateral  surface  of  the  coronoid  process  of  the  mandible.  The  deep  portion  of  the! 
muscle  is  partly  concealed,  in  front,  by  the  superficial  portion;  behind,  it  is  covere4l 
by  the  parotid  gland.  The  fibers  of  the  two  portions  are  continuous  at  thei|j 
insertion. 

Temporal  Fascia. — ^The  temporal  fascia  covers  the  Temporalis  muscle.  It  is  a 
strong,  fibrous  investment,  covered,  laterally,  by  the  Auricularis  anterior  and  supe- 
rior, by  the  galea  aponeurotica,  and  by  part  of  the  Orbicularis  oculi.  The  super- 
ficial temporal  vessels  and  the  auriculotemporal  nerve  cross  it  from  below  upward. 
Above,  it  is  a  single  layer,  attached  to  the  entire  extent  of  the  superior  temporal 
line;  but  below,  where  it  is  fixed  to  the  zygomatic  arch,  it  consists  of  two  layers,  one 
of  which  is  inserted  into  the  lateral,  and  the  other  into  the  medial  border  of  the 
arch.  A  small  quantity  of  fat,  the  orbital  branch  of  the  superficial  temporal  artery, 
and  a  filament  from  the  zygomatic  branch  of  the  maxillary  nerve,  are  contained 
between  these  two  layers.  It  affords  attachment  by  its  deep  surface  to  the  super- 
ficial fibers  of  the  Temporalis. 


II 


Fig.  382. — The  Temporalis;  the  zygomatic  arch  and  Masseter  have  been  removed. 


The  Temporalis  (Temporal  muscle)  (Fig.  382)  is  a  broad,  radiating  muscle, 
situated  at  the  side  of  the  head.  It  arises  from  the  whole  of  the  temporal  fossa 
(except  that  portion  of  it  which  is  formed  by  the  zygomatic  bone)  and  from  the 
deep  surface  of  the  temporal  fascia.  Its  fibers  converge  as  they  descend,  and  end 
in  a  tendon,  which  passes  deep  to  the  zygomatic  arch  and  is  inserted  into  the  medial 
surface,  apex,  and  anterior  border  of  the  coronoid  process,  and  the  anterior  border 
of  the  ramus  of  the  mandible  nearly  as  far  forward  as  the  last  molar  tooth. 

The  Pterygoideus  extemus  {External  pterygoid  muscle)  (Fig.  383)  is  a  short,  thick 
muscle,  somewhat  conical  in  form,  which  extends  almost  horizontally  between  the 
infratemporal  fossa  and  the  condyle  of  the  mandible.  It  arises  by  tw^o  heads; 
an  upper  from  the  lower  part  of  the  lateral  surface  of  the  great  wing  of  the  sphenoid 
and  from  the  infratemporal  crest;  a  lower  from  the  lateral  surface  of  the  lateral 
pterygoid  plate.     Its  fibers  pass  horizontally  backward  and  lateralward,  to  be 


THE  SUPERFICIAL  CERVICAL  MUSCLE 


387 


inserted  Into  a  depression  in  front  of  the  neck  of  the  condyle  of  the  mandible,  and 
into  the  front  margin  of  the  articular  disk  of  the  temporomandibular  articulation. 
The  Pterygoideus  intemus  {Internal  pterygoid  muscle)  (Fig.  383)  is  a  thick,  quad- 
rilateral muscle.  It  arises  from  the  medial  surface  of  the  lateral  pterygoid  plate 
and  the  grooved  surface  of  the  pyramidal  process  of  the  palatine  bone;  it  has  a 
second  slip  of  origin  from  the  lateral  surfaces  of  the  pyramidal  process  of  the  pala- 
tine and  tuberosity  of  the  maxilla.  Its  fibers  pass  downward,  lateralward,  and 
backward,  and  are  inserted,  by  a  strong  tendinous  lamina,  into  the  lower  and  back 
part  of  the  medial  surface  of  the  ramus  and  angle  of  the  mandible,  as  high  as  the 
mandibular  foramen. 


Fig.  383. — The  Pterygoidei;  the  zygomatic  arch  and  a  portion  of  the  ramus  of  the  mandible  have  been  removed. 

Nerves. — The  muscles  of  mastication  are  supplied  by  the  mandibular  nerve. 

Actions. — The  TemporaUs,  Masseter,  and  Pterygoideus  intemus  raise  the  mandible  against 
the  maxilliE  with  great  force.  The  Pterygoideus  externus  assists  in  opening  the  mouth,  but  its 
main  action  is  to  draw  forward  the  condyle  and  articular  disk  so  that  the  mandible  is  protruded 
and  the  inferior  incisors  projected  in  front  of  the  upper;  in  this  action  it  is  assisted  by  the  Ptery- 
goideus intemus.  The  mandible  is  retracted  by  the  posterior  fibers  of  the  Temporalis.  If  the 
Pterygoidei  intemus  and  externus  of  one  side  act,  the  corresponding  side  of  the  mandible  is 
drawn  forward  while  the  opposite  condyle  remains  comparatively  fixed,  and  side-to-side  move- 
ments, such  as  occur  during  the  trituration  of  food,  take  place. 

THE  FASCIA  AND  MUSCLES  OF  THE  ANTERO-LATERAL  REGION 

OF  THE  NECK. 

The  antero-lateral  muscles  of  the  neck  may  be  arranged  into  the  following 
groups : 

I.  Superficial  Cervical.  III.  Supra-  and  Infrahyoid. 

II.  Lateral  Cervical.  IV.  Anterior  Vertebral. 

V.  Lateral  Vertebral. 


I.     THE  SUPERFICIAL  CERVICAL  MUSCLE. 

Platysma. 

The  Superficial  Fascia  of  the  neck  is  a  thin  lamina  investing  the  Platysma, 
and  is  hardly  demonstrable  as  a  separate  membrane. 


388  '^^^^^^^^        MYOLOGY 


I 


The  Platysma  (Fig.  378)  is  a  broad  sheet  arising  from  the  fascia  covering  the 
upper  parts  of  the  Pectoralis  major  and  Deltoideus;  its  fibers  cross  the  clavicle, 
and  proceed  obliquely  upward  and  medialward  along  the  side  of  the  neck.  The 
anterior  fibers  interlace,  below  and  behind  the  symphysis  menti,  with  the  fibers 
of  the  muscle  of  the  opposite  side;  the  posterior  fibers  cross  the  mandible,  some 
being  inserted  into  the  bone  below  the  oblique  line,  others  into  the  skin  and  sub- 
cutaneous tissue  of  the  lower  part  of  the  face,  many  of  these  fibers  blending  with 
the  muscles  about  the  angle  and  lower  part  of  the  mouth.  Sometimes  fibers  can 
be  traced  to  the  Zygomaticus,  or  to  the  margin  of  the  Orbicularis  oculi.  Beneath 
the  Platysma,  the  external  jugular  vein  descends  from  the  angle  of  the  mandible 
to  the  clavicle.  || 

Variations  occur  in  the  extension  over  the  face  and  over  the  clavicle  and  shoulder;  it  may 
be  absent  or  interdigitate  with  the  muscle  of  the  opposite  side  in  front  of  the  neck;  attachment 
to  clavicle,  mastoid  process  or  occipital  bone  occurs.  A  more  or  less  independent  fasciculus,  the 
Occipitalis  minor,  may  extend  from  the  fascia  over  the  Trapezius  to  fascia  over  the  insertion  of 
the  Sternocleidomastoideus. 

Nerve. — The  Platysma  is  supplied  by  the  cervical  branch  of  the  facial  nerve. 

Actions. — When  the  entire  Platysma  is  in  action  it  produces  a  slight  wrinkling  of  the  surface 
of  the  skin  of  the  neck  in  an  oblique  direction.  Its  anterior  portion,  the  thickest  part  of  the 
muscle,  depresses  the  lower  jaw;  it  also  serves  to  draw  down  the  lower  lip  and  angle  of  the  mouth 
in  the  expression  of  melancholy. 

n.     THE  LATERAL  CERVICAL  MUSCLES. 
The  lateral  muscles  are : 

Trapezius  and  Sternocleidomastoideus. 

The  Trapezius  is  described  on  page  432. 

The  Fascia  Colli  {deep  cervical  fascia)  (Fig.  384). — The  fascia  colli  lies  under  cover 
of  the  Platysma,  and  invests  the  neck;  it  also  forms  sheaths  for  the  carotid  vessels, 
and  for  the  structures  situated  in  front  of  the  vertebral  column.  j 

The  investing  portion  of  the  fascia  is  attached  behind  to  the  ligamentum  nuchse  ^ 
and  to  the  spinous  process  of  the  seventh  cervical  vertebra.  It  forms  a  thin  in- 
vestment to  the  Trapezius,  and  at  the  anterior  border  of  this  muscle  is  continued 
forward  as  a  rather  loose  areolar  layer,  covering  the  posterior  triangle  of  the  neck, 
to  the  posterior  border  of  the  Sternocleidomastoideus,  where  it  begins  to  assume 
the  appearance  of  a  fascial  membrane.  Along  the  hinder  edge  of  the  Sterno- 
cleidomastoideus it  divides  to  enclose  the  muscle,  and  at  the  anterior  margin  again 
forms  a  single  lamella,  which  covers  the  anterior  triangle  of  the  neck,  and  reaches 
forward  to  the  middle  line,  where  it  is  continuous  with  the  corresponding  part  from 
the  opposite  side  of  the  neck.  In  the  middle  line  of  the  neck  it  is  attached  to  the 
symphysis  menti  and  the  body  of  the  hyoid  bone. 

Above,  the  fascia  is  attached  to  the  superior  nuchal  line  of  the  occipital,  to  the 
mastoid  process  of  the  temporal,  and  to  the  whole  length  of  the  inferior  border 
of  the  body  of  the  mandible.  Opposite  the  angle  of  the  mandible  the  fascia  is  very 
strong,  and  binds  the  anterior  edge  of  the  Sternocleidomastoideus  firmly  to  that 
bone.  Between  the  mandible  and  the  mastoid  process  it  ensheathes  the  parotid 
gland — the  layer  which  covers  the  gland  extends  upward  under  the  name  of  the 
parotideomasseteric  fascia  and  is  fixed  to  the  zygomatic  arch.  From  the  part  which 
passes  under  the  parotid  gland  a  strong  band  extends  upward  to  the  styloid  process, 
forming  the  stylomandibular  ligament.  Two  other  bands  may  be  defined:  the 
sphenomandibular  (page  297)  and  the  pterygospinous  ligaments.  The  pterygospinous 
ligament  stretches  from  the  upper  part  of  the  posterior  border  of  the  lateral  ptery- 
goid plate  to  the  spinous  process  of  the  sphenoid.  It  occasionally  ossifies,  and  in 
such  cases,  between  its  upper  border  and  the  base  of  the  skull,  a  foramen  is  formed 
which  transmits  the  branches  of  the  mandibular  nerve  to  the  muscles  of  mastication. 


THE  LATERAL  CERVICAL  MUSCLES 


389 


Below,  the  fascia  is  attached  to  the  acromion,  the  clavicle,  and  the  manubrium 
sterni.  Some  little  distance  above  the  last  it  splits  into  two  layers,  superficial 
and  deep.  The  former  is  attached  to  the  anterior  border  of  the  manubrium,  the 
latter  to  its  posterior  border  and  to  the  interclavicular  ligament.  Between  these 
two  layers  is  a  slit-like  interval,  the  suprasternal  space  {space  of  Burns) ;  it  contains 
a  small  quantity  of  areolar  tissue,  the  lower  portions  of  the  anterior  jugular  veins 
and  their  transverse  connecting  branch,  the  sternal  heads  of  the  Sternocleido- 
mastoidei,  and  sometimes  a  lymph  gland. 


Omohyoideus 


Thyroid  gland 


Common  carotid  artery 
Int.  jugvlar  vein 
\ 


Stemocle  idomastoideus 


Vagus  nerve^~~^/j* 


Ext.  jugv2ar  vein  • 
Scalenus  anierior- 
Scalenus  medius' 

Sjienius  colli' 
Levator  8capuUE~ 


Trapezius' 


"      Ant.  Jugular  vein 
\""  Stemohyoideus 
Stemothyreoideua 

" ' '  Trachea 


^^^p £sophagus 


J        6th  cenncai  vertebra 
~  Vertebral  vessels 


■  Semispinalis  colli 


Fio.  384. — Section  of  the  neck  at  about  the  level  of  the  sixth  cervical  vertebra. 

fascia  coli. 


Semispinalis  capitis 
Splenitis  capitis 


Showing  the  arrangement  of  the 


The  fascia  which  lines  the  deep  surface  of  the  Sternocleidomastoideus  gives  off 
the  following  processes:  (1)  A  process  envelops  the  tendon  at  the  Omohj'oideus, 
and  binds  it  down  to  the  sternum  and  first  costal  cartilage.  (2)  A  strong  sheath, 
the  carotid  sheath,  encloses  the  carotid  artery,  internal  jugular  vein,  and  vagus 
nerve.  (3)  The  prevertebral  fascia  extends  medialward  behind  the  carotid  vessels, 
where  it  assists  in  forming  their  sheath,  and  passes  in  front  of  the  prevertebral 
muscles.  It  forms  the  posterior  limit  of  a  fibrous  compartment,  which  contains 
the  larynx  and  trachea,  the  thyroid  gland,  and  the  pharym:  and  esophagus.    The 


390  ^       MYOLOGY 

prevertebral  fascia  is  fixed  above  to  the  base  of  the  skull,  and  below  is  continued 
into  the  thorax  in  front  of  the  Longus  colli  muscles.  Parallel  to  the  carotid  sheath 
and  along  its  medial  aspect  the  prevertebral  fascia  gives  off  a  thin  lamina,  the 
buccopharyngeal  fascia,  which  closely  invests  the  Constrictor  muscles  of  the  pharynx, 
and  is  continued  forward  from  the  Constrictor  pharyngis  superior  on  to  the  Buc- 
cinator. It  is  attached  to  the  prevertebral  layer  by  loose  connective  tissue  only, 
and  thus  an  easily  distended  space,  the  retropharyngeal  space,  is  found  between 
them.  This  space  is  limited  above  by  the  base  of  the  skull,  while  below  it  extends 
behind  the  esophagus  into  the  posterior  mediastinaf  cavity  of  the  thorax.  The  pre- 
vertebral fascia  is  prolonged  downward  and  lateralward  behind  the  carotid  vessels 
and  in  front  of  the  Scaleni,  and  forms  a  sheath  for  the  brachial  nerves  and  sub- 
clavian vessels  in  the  posterior  triangle  of  the  neck ;  it  is  continued  under  the  clavicle 
as  the  axillary  sheath  and  is  attached  to  the  deep  surface  of  the  coracoclavicular 
fascia.  Immediately  above  and  behind  the  clavicle  an  areolar  space  exists  between 
the  investing  layer  and  the  sheath  of  the  subclavian  vessels,  and  in  this  space  are 
found  the  lower  part  of  the  external  jugular  vein,  the  descending  clavicular  nerves, 
the  transverse  scapular  and  transverse  cervical  vessels,  and  the  inferior  belly  of  the 
Omohyoideus  muscle.  This  space  is  limited  below  by  the  fusion  of  the  coraco- 
clavicular fascia  with  the  anterior  wall  of  the  axillary  sheath.  (4)  The  pretrachial 
fascia  extends  medially  in  front  of  the  carotid  vessels,  and  assists  in  forming  the 
carotid  sheath.  It  is  continued  behind  the  depressor  muscles  of  the  hyoid  bone, 
and,  after  enveloping  the  thyroid  gland,  is  prolonged  in  front  of  the  trachea  to 
meet  the  corresponding  layer  of  the  opposite  side.  Above,  it  is  fixed  to  the  hyoid 
bone,  while  below  it  is  carried  downward  in  front  of  the  trachea  and  large  vessels 
at  the  root  of  the  neck,  and  ultimately  blends  with  the  fibrous  pericardium.  This 
layer  is  fused  on  either  side  with  the  prevertebral  fascia,  and  with  it  completes  the 
compartment  containing  the  larynx  and  trachea,  the  thyroid  gland,  and  the  pharynx 
and  esophagus.^ 

The  Stemocleidomastoideus  (Sternomastoid  muscle)  (Fig.  385)  passes  obliquely 
across  the  side  of  the  neck.  It  is  thick  and  narrow  at  its  central  part,  but  broader 
and  thinner  at  either  end.  It  arises  from  the  sternum  and  clavicle  by  two  heads. 
The  medial  or  sternal  head  is  a  rounded  fasciculus,  tendinous  in  front,  fleshy  behind, 
which  arises  from  the  upper  part  of  the  anterior  surface  of  the  manubrium  sterni, 
and  is  directed  upward,  lateralward,  and  backward.  The  lateral  or  clavicular  head, 
composed  of  fleshy  and  aponeurotic  fibers,  arises  from  the  superior  border  and 
anterior  surface  of  the  medial  third  of  the  clavicle;  it  is  directed  almost  vertically 
upward.  The  two  heads  are  separated  from  one  another  at  their  origins  by  a 
triangular  interval,  but  gradually  blend,  below  the  middle  of  the  neck,  into  a  thick, 
rounded  muscle  which  is  inserted,  by  a  strong  tendon,  into  the  lateral  surface  of 
the  mastoid  process,  from  its  apex  to  its  superior  border,  and  by  a  thin  aponeurosis 
into  the  lateral  half  of  the  superior  nuchal  line  of  the  occipital  bone. 

Variations. — The  Stemocleidomastoideus  varies  much  in  the  extent  of  its  origin  from  the  clavicle: 
in  some  cases  the  clavicular  head  may  be  as  narrow  as  the  sternal;  in  others  it  may  be  as  much 
as  7.5  cm.  in  breadth.  When  the  clavicular  origin  is  broad,  it  is  occasionally  subdivided  into 
several  slips,  separated  by  narrow  intervals.  More  rarely,  the  adjoining  margins  of  the  Stemo- 
cleidomastoideus and  Trapezius  have  been  found  in  contact.  The  Supraclavicularis  muscle  arises 
from  the  manubrium  behind  the  Stemocleidomastoideus  and  passes  behind  the  Stemocleido- 
mastoideus to  the  upper  surface  of  the  clavicle. 

Triangles  of  the  Neck. — This  muscle  divides  the  quadrilateral  area  of  the  side  of  the  neck 
into  two  triangles,  an  anterior  and  a  posterior.  The  boundaries  of  the  anterior  triangle  are,  in 
front,  the  median  line  of  the  neck;  above,  the  lower  border  of  the  body  of  the  mandible,  and  an 
imaginary  line  drawn  from  the  angle  of  the  mandible  to  the  Stemocleidomastoideus;  behind, 
the  anterior  border  of  the  Stemocleidomastoideus.     The  apex  of  the  triangle  is  at  the  upper 

1  F.  G.  Parsons  (Journal  of  Anatomy  and  Physiology,  vol._xliv)_  regards  the  carotid  sheath  and  the  fascial  planes 
in  the  neck  as  structures  which  are  artificially  produced  by  dissection. 


THE  SUPRA-  AND  INFRAHYOID  MUSCLES 


391 


border  of  the  sternum.  The  boundaries  of  the  posterior  triangle  are,  in  front,  the  posterior  borcler 
of  the  Sternocleidomastoideus;  below,  the  middle  third  of  the  clavicle;  behind,  the  anterior  margin 
of  the  Trapezius.  The  apex  corresponds  with  the  meeting  of  the  Sternocleidomastoideus  and 
Trapezius  on  the  occipital  bone.  The  anatomy  of  these  triangles  will  be  more  fully  described 
with  that  of  the  vessels  of  the  neck  (p.  562). 

Nerves. — The  Sternocleidomastoideus  is  suppMed  by  the  accessory  nerve  and  branches  from 
the  anterior  divisions  of  the  second  and  third  cervical  nerves. 

Actions. — When  only  one  Sternocleidomastoideus  acts,  it  draws  the  head  toward  the  shoulder 
of  the  same  side,  assisted  by  the  Splenius  and  the  Obliquus  capitis  inferior  of  the  opposite  side. 
At  the  same  time  it  rotates  the  head  so  as  to  carry  the  face  toward  the  opposite  side.  Acting 
together  from  their  sternoclavicular  attachments  the  muscles  will  flex  the  cervical  part  of  the 
vertebral  column.  If  the  head  be  fixed,  the  two  muscles  assist  in  elevating  the  thorax  in  forced 
inspiration. 


Via.  6i>o. — Muscles  of  tne  neck,     l^ateral  view. 


m.     THE  SUPRA-  AND  INFRAHYOID  MUSCLES  (Figs.  385,  386). 


The  suprahyoid  muscles  are : 

Digastricus. 
Stylohyoideus. 


Mylohyoideus. 
Geniohvoideus. 


The  Digastricus  (Digastric  muscle)  consists  of  two  fleshy  belHes  united  by  an 
intermediate  rounded  tendon.  It  lies  below  the  body  of  the  mandible,  and  extends, 
in  a  curved  form,  from  the  mastoid  process  to  the  symphysis  menti.  The  posterior 
belly,  longer  than  the  anterior,  arises  from  the  mastoid  notch  of  the  temporal 
bone  and  passes  downward  and  forward.  The  anterior  belly  arises  from  a  depression 
on  the  inner  side  of  the  lower  border  of  the  mandible,  close  to  the  symphysis,  and 
passes  downward  and  backward.  The  two  bellies  end  in  an  intermediate  tendon 
which  perforates  the  Stylohyoideus  muscle,  and  is  held  in  connection  with  the  side 
of  the  body  and  the  greater  cornu  of  the  hyoid  bone  hy  a  fibrous  loop,  which  is 


392 


MYOLOGY 


sometimes  lined  by  a  mucous  sheath.  A  broad  aponeurotic  layer  is  given  off 
from  the  tendon  of  the  Digastricus  on  either  side,  to  be  attached  to  the  body 
and  greater  cornu  of  the  hyoid  bone;  this  is  termed  the  suprahyoid  aponeurosis. 

Variations  are  numerous.  The  posterior  belly  may  arise  partly  or  entirely  from  the  styloid 
process,  or  be  connected  by  a  slip  to  the  middle  or  inferior  constrictor;  the  anterior  belly  may 
be  double  or  extra  slips  from  this  belly  may  pass  to  the  jaw  or  Mylohyoideus  or  decussate  with 
a  simUar  slip  on  opposite  side;  anterior  belly  may  be  absent  and  posterior  belly  inserted  into  the 
middle  of  the  jaw  or  hyoid  bone.  The  tendon  may  pass  in  front,  more  rarely  behind  the  Stylo- 
hoideus.     The  Mentohyoideus  muscle  passes  from  the  body  of  hyoid  bone  to  chin . 

The  Digastricus  divides  the  anterior  triangle  of  the  neck  into  three  smaller  triangle  (1)  the 
submaxillary  triangle,  bounded  above  by  the  lower  border  of  the  body  of  the  mandible,  and 
a  line  drawn  from  its  angle  to  the  Stemocleidomastoideus,  below  by  the  posterior  belly  of  the 
Digastricus  and  the  Stylohyoideus,  in  front  by  the  anterior  belly  of  the  Digastricus;  (2)  the 
carotid  triangle,  bounded  above  by  the  posterior  belly  of  the  Digastricus  and  Stylohyoideus, 
behind  by  the  Stemocleidomastoideus,  below  by  the  Omohyoideus;  (3)  the  suprahyoid  or  sub- 
mental triangle,  bounded  laterally  by  the  anterior  belly  of  the  Digastricus,  medially  by  the 
middle  line  of  the  neck  from  the  hyoid  bone  to  the  symphysis  menti,  and  inferiorly  by  the  body 
of  the  hyoid  bone. 


Fig.  386. — Muscles  of  the  neck.     Anterior  view.  '^, 

1 

The  Stylohyoideus  (Stylohyoid  muscle)  is  a  slender  muscle,  lying  in  front  of,  and 
above,  the  posterior  belly  of  the  Digastricus.  It  arises  from  the  back  and  lateral 
surface  of  the  styloid  process,  near  the  base;  and,  passing  downward  and  forward, 
is  inserted  into  the  body  of  the  hyoid  bone,  at  its  junction  with  the  greater  cornu, 
and  just  above  the  Omohyoideus.  It  is  perforated,  near  its  insertion,  by  the  tendon 
of  the  Digastricus. 

Variations. — It  may  be  absent  or  doubled,  lie  beneath  the  carotid  artery,  or  be  inserted  into 
the  Omohyoideus,  Thyreohyoideus,  or  Mylohyoideus. 

The  Stylohyoid  Ligament  (ligamentuvi  stylohyoideus). — In  connection  with  the 
Stylohyoideus   muscle   a   ligamentous   band,    the   stylohyoid   ligament,    may   be 


THE  SUPRA-  AND  INFRAHYOID  MUSCLES  393 

described.  It  is  a  fibrous  cord,  which  is  attached  to  the  tip  of  the  styloid  process 
of  the  temporal  and  the  lesser  cornii  of  the  hyoid  bone.  It  frequently  contains  a 
little  cartilage  in  its  center,  is  often  partially  ossified,  and  in  many  animals  forms 
a  distinct  bone,  the  epihyal. 

The  Mylohyoideus  (Mylohyoid  muscle),  flat  and  triangular,  is  situated  imme- 
diately above  the  anterior  belly  of  the  Digastricus,  and  forms,  with  its  fellow  of  the 
opposite  side,  a  muscular  floor  for  the  cavity  of  the  mouth.  It  arises  from  the  whole 
length  of  the  mylohyoid  line  of  the  mandible,  extending  from  the  symphysis  in 
front  to  the  last  molar  tooth  behind.  The  posterior  fibers  pass  medialward  and 
slightly  downward,  to  be  inserted  into  the  body  of  the  hyoid  bone.  The  middle  and 
anterior  fibers  are  inserted  into  a  median  fibrous  raphe  extending  from  the  sym- 
physis menti  to  the  hyoid  bone,  where  they  join  at  an  angle  with  the  fibers  of  the 
opposite  muscle.  This  median  raphe  is  sometimes  wanting;  the  fibers  of  the  two 
muscles  are  then  continuous. 

Variations. — It  may  be  united  to  or  replaced  by  the  anterior  belly  of  the  Digastricus;  accessory 
slips  to  other  hyoid  muscles  are  frequent. 

The  Geniohyoideus  {Geniohyoid  muscle)  is  a  narrow  muscle,  situated  above  the 
medial  border  of  the  Mylohyoideus.  It  arises  from  the  inferior  mental  spine  on 
the  back  of  the  symphysis  menti,  and  runs  backward  and  slightly  downward,  to 
be  inserted  into  the  anterior  surface  of  the  body  of  the  hyoid  bone;  it  lies  in  con- 
tact with  its  fellow  of  the  opposite  side. 

Variations. — It  may  be  blended  with  the  one  on  opposite  side  or  double;  slips  to  greater 
cornu  of  hyoid  bone  and  Genioglossus  occur. 

Nerves. — The  Mylohyoideus  and  anterior  belly  of  the  Digastricus  are  supplied  by  the  mylo- 
hyoid branch  of  the  inferior  alveolar;  the  Stylohyoideus  and  posterior  belly  of  the  Digastricus, 
by  the  facial;  the  Geniohyoideus,  by  the  hypoglossal. 

Actions. — These  muscles  perform  two  very  important  actions.  During  the  act  of  deglutition 
they  raise  the  hyoid  bone,  and  with  it  the  base  of  the  tongue;  when  the  hyoid  bone  is  fixed  by  its 
depressors  and  those  of  the  larynx,  they  depress  the  mandible.  During  the  first  act  of  degluti- 
tion, when  the  mass  of  food  is  being  driven  from  the  mouth  into  the  pharynx,  the  hyoid  bone 
and  with  it  the  tongue,  is  carried  upward  and  forward  by  the  anterior  bellies  of  the  Digastrici, 
the  Mylohyoidei,  and  Geniohyoidei.  In  the  second  act,  when  the  mass  is  passing  through  the 
pharynx,  the  direct  elevation  of  the  hyoid  bone  takes  place  by  the  combined  action  of  aU  the 
muscles;  and  after  the  food  has  passed,  the  hyoid  bone  is  carried  upward  and  backward  by  the 
posterior  bellies  of  the  Digastrici  and  the  Stylohyoidei,  which  assist  in  preventing  the  return 
of  the  food  into  the  mouth. 

The  infrahyoid  muscles  are : 

Sternohyoideus.  Thyreohyoideus. 

Sternothyreoideus.  Omohyoideus. 

The  Sternohyoideus  {Sternohyoid  muscle)  is  a  thin,  narrow  muscle,  which  arises 
from  the  posterior  surface  of  the  medial  end  of  the  clavicle,  the  posterior  sterno- 
clavicular ligament,  and  the  upper  and  posterior  part  of  the  manubrium  sterni. 
Passing  upward  and  medialward,  it  is  inserted,  by  short,  tendinous  fibers,  into  the 
lower  border  of  the  body  of  the  hyoid  bone.  Below,  this  muscle  is  separated 
from  its  fellow  by  a  considerable  interval;  but  the  two  muscles  come  into  contact 
with  one  another  in  the  middle  of  their  course,  and  from  this  upward,  lie  side  by 
side.  It  sometimes  presents,  immediately  above  its  origin,  a  transverse  tendinous 
inscription. 

Variations. — Doubling;  accessory  slips  (Cleidohyoideus) ;  absence. 

The  Sternothyreoideus  {Sternothyroid  muscle)  is  shorter  and  wider  than  the 
preceding  muscle,  beneath  which  it  is  situated.  It  arises  from  the  posterior  surface 
of  the  manubrium  sterni,  below  the  origin  of  the  Sternohyoideus,  and  from  the  edge 
of  the  cartilage  of  the  first  rib,  and  sometimes  that  of  the  second  rib,  it  is  inserted 


MYOLOGY 

into  the  oblique  line  on  the  lamina  of  the  thyroid  cartilage.  This  muscle  is  in 
close  contact  with  its  fellow  at  the  lower  part  of  the  neck,  but  diverges  somewhat 
as  it  ascends;  it  is  occasionally  traversed  by  a  transverse  or  oblique  tendinous 
inscription. 

Variations.— Doubling;  absence;  accessory  slips  to  Thyreohyoideus,  Inferior  constrictor,  or 
carotid  sheath. 

The  Thyreohyoideus  (Thyrohyoid  muscle)  is  a  small,  quadrilateral  muscle 
appearing  like  an  upward  continuation  of  the  Sternothyreoideus.  It  arises  from 
the  oblique  line  on  the  lamina  of  the  thyroid  cartilage,  and  is  inserted  into  the 
lower  border  of  the  greater  cornu  of  the  hyoid  bone. 

The  Omohyoideus  (Omohyoid  muscle)  consists  of  two  fleshy  bellies  united  by 
a  central  tendon.  It  arises  from  the  upper  border  of  the  scapula,  and  occasionally 
from  the  superior  transverse  ligament  which  crosses  the  scapular  notch,  its  extent 
of  attachment  to  the  scapula  varying  from  a  few  millimetres  to  2.5  cm.  From 
this  origin,  the  inferior  belly  forms  a  flat,  narrow  fasciculus,  which  inclines  forward 
and  slightly  upward  across  the  lower  part  of  the  neck,  being  bound  down  to  the 
clavicle  by  a  fibrous  expansion;  it  then  passes  behind  the  Sternocleidomastoideus, 
becomes  tendinous  and  changes  its  direction,  forming  an  obtuse  angle.  It  ends 
in  the  superior  belly,  which  passes  almost  vertically  upward,  close  to  the  lateral 
border  of  the  Sternohyoideus,  to  be  inserted  into  the  lower  border  of  the  body 
of  the  hyoid  bone,  lateral  to  the  insertion  of  the  Sternohyoideus.  The  central 
tendon  of  this  muscle  varies  much  in  length  and  form,  and  is  held  in  position  by 
a  process  of  the  deep  cervical  fascia,  which  sheaths  it,  and  is  prolonged  down  to 
be  attached  to  the  clavicle  and  first  rib;  it  is  by  this  means  that  the  angular  form 
of  the  muscle  is  maintained. 

Variations. — Doubling;  absence;  origin  from  clavicle;  absence  or  doubling  of  either  belly. 

The  inferior  belly  of  the  Omohyoideus  divides  the  posterior  triangle  of  the  neck  into  an  upper 
or  occipital  triangle  and  a  lower  or  subclavian  triangle,  while  its  superior  belly  divides  the  anterior 
triangle  into  an  upper  or  carotid  triangle  and  a  lower  or  muscular  triangle. 

Nerves. — The  Infrahyoid  muscles  are  supplied  by  branches  from  the  first  three  cervical  nerves. 
From  the  first  two  nerves  the  branch  joins  the  hypoglossal  trunk,  runs  with  it  some  distance, 
and  sends  off  a  branch  to  the  Thyreohyoideus;  it  then  leaves  the  hypoglossal  to  form  the  descendens 
hypoglossi  and  unites  with  the  communicantes  cervicalis  from  the  second  and  third  cervical  nerves 
to  form  the  ansa  hypoglossi  from  which  nerves  pass  to  the  other  Infrahyoid  muscles. 

Actions. — These  muscles  depress  the  larynx  and  hyoid  bone,  after  they  have  been  drawn  up 
with  the  pharynx  in  the  act  of  deglutition.  The  Omohyoidei  not  only  depress  the  hyoid  bone, 
but  carry  it  backward  and  to  one  or  the  other  side.  They  are  concerned  especially  in  prolonged 
inspiratory  efforts;  for  by  rendering  the  lower  part  of  the  cervical  fascia  tense  they  lessen  the 
inward  suction  of  the  soft  parts,  which  would  otherwise  compress  the  great  vessels  and  the 
apices  of  the  lungs.  The  Thyreohyoideus  may  act  as  an  elevator  of  the  thyroid  cartilage,  when 
the  hyoid  bone  ascends,  drawing  the  thyroid  cartilage  up  behind  the  hyoid  bone.  The  Sterno- 
thyreoideus acts  as  a  depressor  of  the  thyroid  cartilage. 

IV.     THE  ANTERIOR  VERTEBRAL  MUSCLES  (Fig.  387). 

The  anterior  vertebral  muscles  are : 

Longus  colli.  Rectus  capitis  anterior. 

Longus  capitis.  Rectus  capitis  lateralis. 

The  Longus  colli  is  situated  on  the  anterior  surface  of  the  vertebral  column, 
between  the  atlas  and  the  third  thoracic  vertebra.  It  is  broad  in  the  middle, 
narrow  and  pointed  at  either  end,  and  consists  of  three  portions,  a  superior  oblique, 
an  inferior  oblique,  and  a  vertical.  The  superior  oblique  portion  arises  from  the 
anterior  tubercles  of  the  transverse  processes  of  the  third,  fourth,  and  fifth  cervical 
vertebrae;  and,  ascending  obliquely  with  a  medial  inclination,  is  inserted  by  a  narrow 


i 


THE  ANTERIOR  VERTEBRAL  MUSCLES 


395 


tendon  into  the  tubercle  on  the  anterior  arch  of  the  atlas.  The  inferior  oblique 
portion,  the  smallest  part  of  the  muscle,  arises  from  the  front  of  the  bodies  of  the 
first  two  or  three  thoracic  vertebrae;  and,  ascending  obliquely  in  a  lateral  direction, 
is  inserted  into  the  anterior  tubercles  of  the  transverse  processes  of  the  fifth  and 
sixth  cervical  vertebrae.  The  vertical  portion  arises,  below,  from  the  front  of  the 
bodies  of  the  upper  three  thoracic  and  lower  three  cervical  vertebrae,  and  is  in- 
serted into  the  front  of  the  bodies  of  the  second,  third,  and  fourth  cervical  vertebrge. 
The  Longus  capitis  (Rectus  capitis  anticus  major),  broad  and  thick  above, 
narrow  below,  arises  by  four  tendinous  slips,  from  the  anterior  tubercles  of  the 
transverse  processes  of  the  third,  fourth,  fifth,  and  sixth  cervical  vertebrae,  and 
ascends,  converging  toward  its  fellow  of  the  opposite  side,  to  be  inserted  into  the 
inferior  surface  of  the  basilar  part  of  the  occipital  bone. 


Fig.  387. — The  anterior  vertebral  muscles. 

The  Rectus  capitis  anterior  {Rectus  capitis  anticus  minor)  is  a  short,  flat  muscle, 
situated  immediately  behind  the  upper  part  of  the  Longus  capitis.  It  arises  from 
the  anterior  surface  of  the  lateral  mass  of  the  atlas,  and  from  the  root  of  its 
transverse  process,  and  passing  obliquely  upward  and  medialward,  is  inserted  into 
the  inferior  surface  of  the  basilar  part  of  the  occipital  bone  immediately  in  front 
of  the  foramen  magnum. 

The  Rectus  capitis  lateralis,  a  short,  flat  muscle,  arises  from  the  upper  surface 
of  the  transverse  process  of  the  atlas,  and  is  inserted  into  the  under  surface  of  the 
jugular  process  of  the  occipital  bone. 

Nerves. — The  Rectus  capitis  anterior  and  the  Rectus  capitis  lateralis  are  supplied  from  the 
loop  between  the  first  and  second  cervical  nerves;  the  Longus  capitis,  by  branches  from  the 


396  ^^       MYOLOGY 

first,  second,  and  third  cervical;  the  Longus  colli,  by  branches  from  the  second  to  the  seventh 
cervical  nerves. 

Actions. — The  Longus  capitis  and  Rectus  capitis  anterior  are  the  direct  antagonists  of  the 
muscles  at  the  back  of  the  neck,  serving  to  restore  the  head  to  its  natural  position  after  it  has 
been  drawn  backward.  These  muscles  also  flex  the  head,  and  from  their  obhquity,  rotate  it, 
BO  as  to  turn  the  face  to  one  or  the  other  side.  The  Rectus  lateralis,  acting  on  one  side,  bends 
the  head  laterally.  The  Longus  colli  flexes  and  slightly  rotates  the  cervical  portion  of  the  vertebral 
column. 

V.     THE  LATERAL  VERTEBRAL  MUSCLES  (Fig.  387). 

The  lateral  vertebral  muscles  are : 

Scalenus  anterior.  Scalenus  medius. 

Scalenus  posterior. 

The  Scalenus  anterior  {Scalenus  anticus)  lies  deeply  at  the  side  of  the  nee 
behind  the  Sternocleidomastoideus.  It  arises  from  the  anterior  tubercles  of  the 
transverse  processes  of  the  third,  fourth,  fifth,  and  sixth  cervical  vertebrae,  and 
descending,  almost  vertically,  is  inserted  by  a  narrow,  flat  tendon  into  the  scalene 
tubercle  on  the  inner  border  of  the  first  rib,  and  into  the  ridge  on  the  upper  surface 
of  the  rib  in  front  of  the  subclavian  groove. 

The  Scalenus  medius,  the  largest  and  longest  of  the  three  Scaleni,  arises 
from  the  posterior  tubercles  of  the  transverse  processes  of  the  lower  six  cervical 
vertebrae,  and  descending  along  the  side  of  the  vertebral  column,  is  iriserted  by  a 
broad  attachment  into  the  upper  surface  of  the  first  rib,  between  the  tubercle 
and  the  subclavian  groove. 

The  Scalenus  posterior  (Scalenus  posticus),  the  smallest  and  most  deeply  seated 
of  the  three  Scaleni,  arises,  by  two  or  three  separate  tendons,  from  the  posterior 
tubercles  of  the  transverse  processes  of  the  lower  two  or  three  cervical  vertebrae, 
and  is  inserted  by  a  thin  tendon  into  the  outer  surface  of  the  second  rib,  behind 
the  attachment  of  the  Serratus  anterior.  It  is  occasionally  blended  with  the 
Scalenus  medius. 

Variations. — The  Scaleni  muscles  vary  considerably  in  their  attachments  and  in  the  arrange- 
ment of  their  fibers.  A  slip  from  the  Scalenus  anticus  may  pass  behind  the  subclavian  artery. 
The  Scalenus  posticus  may  be  absent  or  extend  to  the  third  rib.  The  Scalenus  pleuralis  muscle 
extends  from  the  transverse  process  of  the  seventh  cervical  vertebra  to  the  fascia  supporting  the 
dome  of  the  pleura  and  inner  border  of  first  rib. 

Nerves. — The  Scaleni  are  supplied  by  branches  from  the  second  to  the  seventh  cervical  nerves. 

Actions. — When  the  Scaleni  act  from  above,  they  elevate  the  first  and  second  ribs,  and  are, 
therefore,  inspiratory  muscles.  Acting  from  below,  they  bend  the  vertebral  column  to  one  or 
other  side;  if  the  muscles  of  both  sides  act,  the  vertebral  column  is  slightly  flexed. 

THE  FASCLffi  AND  MUSCLES  OF  THE  TRUNK. 

The  muscles  of  the  trunk  may  be  arranged  in  six  groups: 

I.  Deep  Muscles  of  the  Back.  IV.  Muscles  of  the  Abdomen. 

II.  Suboccipital  Muscles.  V.  Muscles  of  the  Pelvis. 

III.  Muscles  of  the  Thorax.  VI.  Muscles  of  the  Perineum. 

L     THE  DEEP  MUSCLES  OF  THE  BACK  (Fig.  388). 

The  deep  or  intrinsic  muscles  of  the  back  consist  of  a  complex  group  of  muscles 
extending  from  the  pelvis  to  the  skull.    They  are: 

Splenius  capitis.  Multifidus. 

Splenius  cervicis.  Rotatores. 

Sacrospinalis.  Interspinales. 

Semispinalis.  Intertransversarii . 


THE  DEEP  MUSCLES  OF  THE  BACK 


397 


The  Lumbodorsal  Fascia  (fascia  lumbodorsalis;  lumbar  aponeurosis  and  vertebral 
fascia). — The  lumbodorsal  fascia  is  a  deep  investing  membrane  which  covers  the 
deep  muscles  of  the  back  of  the  trunk.  Above,  it  passes  in  front  of  the  Serratus 
posterior  superior  and  is  continuous  with  a  similar  investing  layer  on  the  back  of 
the  neck — the  nuchal  fascia. 

In  the  thoracic  region  the  lumbodorsal  fascia  is  a  thin  fibrous  lamina  which 
serves  to  bind  down  the  Extensor  muscles  of  the  vertebral  column  and  to  separate 
them  from  the  muscles  connecting  the  vertebral  column  to  the  upper  extremity. 
It  contains  both  longitudinal  and  transverse  fibers,  and  is  attached,  medially,  to 
the  spinous  processes  of  the  thoracic  vertebrae ;  laterally  to  the  angles  of  the  ribs. 

In  the  lumbar  region  the  fascia  (lumbar  aponeurosis)  is  in  two  layers,  anterior 
and  posterior  (Figs.  388,  409).  The  posterior  layer  is  attached  to  the  spinous 
processes  of  the  lumbar  and  sacral  vertebrae  and  to  the  supraspinal  ligament ;  the 
anterior  layer  is  attached,  medially,  to  the  tips  of  the  transverse  processes  of  the 
lumbar  vertebrae  and  to  the  intertransverse  ligaments,  below,  to  the  iliolumbar 
ligament,  and  above,  to  the  lumbocostal  ligament.  The  two  layers  unite  at  the 
lateral  margin  of  the  Sacrospinalis,  to  form  the  tendon  of  origin  of  the  Transversus 
abdominis.  The  aponeurosis  of  origin  of  the  Serratus  posterior  inferior  and  the 
Latissimus  dorsi  are  intimately  blended  with  the  lumbodorsal  fascia. 


^Obliquus  externus 
Mbliquus  intemus 
Transversus 


Fascia  on 
Qtuid.  Lumb. 

lAimbod(yrsal\^'^^^^  ^V^ 

[    Posterior  layer  , 
Fia.  388. — Diagram  of  a  transverse  section  of  the  posterior  abdominal  wall,  to  show  the  disposition  of  the 

lumbodorsal  fascia. 

The  Splenius  capitis  (Fig.  409)  arises  from  the  lower  half  of  the  ligamentum 
nuchae,  from  the  spinous  process  of  the  seventh  cervical  vertebra,  and  from  the 
spinous  processes  of  the  upper  three  or  four  thoracic  vertebrae.  The  fibers  of 
the  muscle  are  directed  upward  and  lateralward  and  are  inserted,  under  cover  of 
the  Sternocleidomastoideus,  into  the  mastoid  process  of  the  temporal  bone,  and 
into  the  rough  surface  on  the  occipital  bone  just  below  the  lateral  third  of  the 
superior  nuchal  line. 

The  Splenius  cervicis  (Splenius  colli)  (Fig.  409)  arises  by  a  narrow  tendinous 
band  from  the  spinous  processes  of  the  third  to  the  sixth  thoracic  vertebrae;  it  is 
inserted,  by  tendinous  fasciculi,  into  the  posterior  tubercles  of  the  transverse 
processes  of  the  upper  two  or  three  cervical  vertebrae. 

Variations. — The  origin  is  frequently  moved  up  or  down  one  or  two  vertebrae.  Accessory  slips 
are  occasionally  found. 

Nerves. — The  Splenii  are  supplied  by  the  lateral  branches  of  the  posterior  divisions  of  the 
middle  and  lower  cervical  nerves. 

Actions. — The  Splenii  of  the  two  sides,  acting  together,  draw  the  head  directly  backward, 
assisting  the  Trapezius  and  Semispinahs  capitis;  acting  separately,  they  draw  the  head  to  one 
side,  and  shghtly  rotate  it,  turning  the  face  to  the  same  side.  They  also  assist  in  supporting  the 
head  in  the  erect  position. 

The  Sacrospinalis  (Erector  spines)  (Fig.  389),  and  its  prolongations  in  the 
thoracic  and  cervical  regions,  lie  in  the  groove  on  the  side  of  the  vertebral  column. 


398 


MYOLOGY 


They  are  covered  in  the  lumbar  and  thoracic  regions  by  the  lumbodorsal  fascia,| 
and  in  the  cervical  region  by  the  nuchal  fascia.    This  large  muscular  and  tendinous 

Occipital  bom 


Multibus 


First  thoracic  vertebra 


First  lumbar  vertebra 


First  sacral  vertebra 


Fig.  389. — Deep  musclea  of  tlie  back. 


THE  DEEP  MUSCLES  OF  THE  BACK  399 

mass  varies  in  size  and  structure  at  different  parts  of  the  vertebral  column.  In 
the  sacral  region  it  is  narrow  and  pointed,  and  at  its  origin  chiefly  tendinous  in 
structure.  In  the  lumbar  region  it  is  larger,  and  forms  a  thick  fleshy  mass  which, 
on  being  followed  upward,  is  subdivided  into  three  columns;  these  gradually 
diminish  in  size  as  they  ascend  to  be  inserted  into  the  vertebrae  and  ribs. 

The  Sacrospinalis  arises  from  the  anterior  surface  of  a  broad  and  thick  tendon, 
which  is  attached  to  the  medial  crest  of  the  sacrum,  to  the  spinous  processes  of 
the  lumbar  and  the  eleventh  and  twelfth  thoracic  vertebrae,  and  the  supraspinal 
ligament,  to  the  back  part  of  the  inner  lip  of  the  iliac  crests  and  to  the  lateral 
crests  of  the  sacrum,  where  it  blends  with  the  sacrotuberous  and  posterior  sacro- 
iliac ligaments.  Some  of  its  fibers  are  continuous  with  the  fibers  of  origin  of  the 
Glutseus  maximus.  The  muscular  fibers  form  a  large  fleshy  mass  which  splits, 
in  the  upper  lumbar  region  into  three  columns,  viz.,  a  lateral,  the  Iliocostalis,  an 
intermediate,  the  Longissimus,  and  a  medial,  the  Spinalis.  Each  of  these  consists 
from  below  upward,  of  three  parts,  as  follows: 

Lateral  Column.  Intermediate  Column.  Medial  Column. 
Iliocostalis.                          Longissimus.  Spinalis, 

(a)  I.  lumborum.  (a)  L.  dorsi.  (a)  S.  dorsi. 

(6)  I.  dorsi.  (6)  L.  cervicis.  (b)  S.  cervicis. 

(c)  I.  cervicis.  (c)  L.  capitis.  (c)  S.  capitis. 

The  Iliocostalis  lumborum  (Iliocostalis  muscle;  Sacrolumbalis  muscle)  is  inserted, 
by  six  or  seven  flattened  tendons,  into  the  inferior  borders  of  the  angles  of  the  lower 
six  or  seven  ribs. 

The  Iliocostalis  dorsi  (Musculus  accessorius)  arises  by  flattened  tendons  from 
the  upper  borders  of  the  angles  of  the  lower  six  ribs  medial  to  the  tendons  of 
insertion  of  the  Iliocostalis  lumborum;  these  become  muscular,  and  are  inserted 
into  the  upper  borders  of  the  angles  of  the  upper  six  ribs  and  into  the  back  of  the 
transverse  process  of  the  seventh  cervical  vertebra. 

The  Iliocostalis  cervicis  {Cermcalis  ascendens)  arises  from  the  angles  of  the  third, 
fourth,  fifth,  and  sixth  ribs,  and  is  inserted  into  the  posterior  tubercles  of  the  trans- 
verse processes  of  the  fourth,  fifth,  and  sixth  cervical  vertebrae. 

The  Longissimus  dorsi  is  the  intermediate  and  largest  of  the  continuations  of 
the  Sacrospinalis.  In  the  lumbar  region,  where  it  is  as  yet  blended  with  the  Ilio- 
costalis lumborum,  some  of  its  fibers  are  attached  to  the  whole  length  of  the  pos- 
terior surfaces  of  the  transverse  processes  and  the  accessory  processes  of  the  lumbar 
vertebrae,  and  to  the  anterior  layer  of  the  lumbodorsal  fascia.  In  the  thoracic 
region  it  is  inserted,  by  rounded  tendons,'  into  the  tips  of  the  transverse  processes 
of  all  the  thoracic  vertebrae,  and  by  fleshy  processes  into  the  lower  nine  or  ten  ribs 
between  their  tubercles  and  angles. 

The  Longissimus  cervicis  {Transversalis  cervicis),  situated  medial  to  the  Longis- 
simus dorsi,  arises  by  long  thin  tendons  from  the  summits  of  the  transverse  pro- 
cesses of  the  upper  four  or  five  thoracic  vertebrae,  and  is  inserted  by  similar  tendons 
into  the  posterior  tubercles  of  the  transverse  processes  of  the  cervical  vertebrae 
from  the  second  to  the  sixth  inclusive. 

The  Longissimus  capitis  ( Trachelomastoid  muscle)  lies  medial  to  the  Longissimus 
cervicis,  between  it  and  the  Semispinalis  capitis.  It  arises  by  tendons  from  the 
transverse  processes  of  the  upper  four  or  five  thoracic  vertebrae,  and  the  artic- 
ular processes  of  the  lower  three  or  four  cervical  vertebrae,  and  is  inserted  into  the 
posterior  margin  of  the  mastoid  process,  beneath  the  Splenius  capitis  and  Sterno- 
cleidomastoideus.  It  is  almost  always  crossed  by  a  tendinous  intersection  near 
its  insertion. 

The  Spinalis  dorsi,  the  medial  continuation  of  the  Sacrospinalis,  is  scarcely 
separable  as  a  distinct  muscle.    It  is  situated  at  the  medial  side  of  the  Longissimus 


MYOLOGY 

dorsi,  and  is  intimately  blended  with  it ;  it  arises  by  three  or  four  tendons  from  the 
spinous  processes  of  the  first  two  lumbar  and  the  last  two  thoracic  vertebrae :  these, 
uniting,  form  a  small  muscle  which  is  inserted  by  separate  tendons  into  the  spinous 
processes  of  the  upper  thoracic  vertebrse,  the  number  varying  from  four  to  eight. 
It  is  intimately  united  with  the  Semispinalis  dorsi,  situated  beneath  it. 

The  Spinalis  cervicis  {Spinalis  colli)  is  an  inconstant  muscle,  which  arises  from 
the  lower  part  of  the  ligamentum  nuchae,  the  spinous  process  of  the  seventh  cer- 
vical, and  sometimes  from  the  spinous  processes  of  the  first  and  second  thoracic 
vertebrse,  and  is  inserted  into  the  spinous  process  of  the  axis,  and  occasionally  into 
the  spinous  processes  of  the  two  vertebrse  below  it. 

The  Spinalis  capitis  {Biventer  cervicis)  is  usually  inseparably  connected  with  the 
Semispinalis  capitis  (see  below). 

The  Semispinalis  dorsi  consists  of  thin,  narrow,  fleshy  fasciculi,  interposed 
between  tendons  of  considerable  length.  It  arises  by  a  series  of  small  tendons 
from  the  transverse  processes  of  the  sixth  to  the  tenth  thoracic  vertebrse,  and  is 
inserted,  by  tendons,  into  the  spinous  processes  of  the  upper  four  thoracic  and  lower 
two  cervical  vertebrse. 

The  Semispinalis  cervicis  (Semispinalis  colli),  thicker  than  the  preceding, 
arises  by  a  series  of  tendinous  and  fleshy  fibers  from  the  transverse  processes  of 
the  upper  five  or  six  thoracic  vertebrae,  and  is  inserted  into  the  cervical  spinous 
processes,  from  the  axis  to  the  fifth  inclusive.  The  fasciculus  connected  with  the 
axis  is  the  largest,  and  is  chiefly  muscular  in  structure. 

The  Semispinalis  capitis  (Complexus)  is  situated  at  the  upper  and  back  part 
of  the  neck^  beneath  the  Splenius,  and  medial  to  the  Longissimus  cervicis  and 
capitis.  It  arises  by  a  series  of  tendons  from  the  tips  of  the  transverse  processes 
of  the  upper  six  or  seven  thoracic  and  the  seventh  cervical  vertebrse,  and  from  the 
articular  processes  of  the  three  cervical  above  this.  The  tendons,  uniting,  form 
a  broad  muscle,  which  passes  upward,  and  is  inserted  between  the  superior  and 
inferior  nuchal  lines  of  the  occipital  bone.  The  medial  part,  usually  more  or  less 
distinct  from  the  remainder  of  the  muscle,  is  frequently  termed  the  Spinalis  capitis; 
it  is  also  named  the  Biventer  cervicis  since  it  is  traversed  by  an  imperfect  tendinous 
inscription. 

The  Multiiidus  (Multifidvs  spince)  consists  of  a  number  of  fleshy  and  tendinous 
fasciculi,  which  fill  up  the  groove  on  either  side  of  the  spinous  processes  of  the  ver- 
tebrse, from  the  sacrum  to  the  axis.  In  the  sacral  region,  these  fasciculi  arise  from 
the  back  of  the  sacrum,  as  low  as  the  fourth  sacral  foramen,  from  the  aponeu- 
rosis of  origin  of  the  Sacrospinalis,  from  the  medial  surface  of  the  posterior  superior 
iliac  spine,  and  from  the  posterior  sacroiliac  ligaments;  in  the  lumbar  region, 
from  all  the  mamillary  processes;  in  the  thoracic  region,  from  all  the  transverse 
processes;  and  in  the  cervical  region,  from  the  articular  processes  of  the  lower 
four  vertebrse.  Each  fasciculus,  passing  obliquely  upward  and  medialward,  is 
inserted  into  the  whole  length  of  the  spinous  process  of  one  of  the  vertebrse  above. 
These  fasciculi  vary  in  length:  the  most  superficial,  the  longest,  pass  from  one 
vertebra  to  the  third  or  fourth  above;  those  next  in  order  run  from  one  vertebra 
to  the  second  or  third  above;  while  the  deepest  connect  two  contiguous  vertebrse. 

The  Rotatores  (Rotatores  spince)  lie  beneath  the  Multifidus  and  are  found  only 
in  the  thoracic  region;  they  are  eleven  in  number  on  either  side.  Each  muscle  is 
small  and  somewhat  quadrilateral  in  form;  it  arises  from  the  upper  and  back  part  of 
the  transverse  process,  and  is  inserted  into  the  lower  border  and  lateral  surface  of 
the  lamina  of  the  vertebra  above,  the  fibers  extending  as  far  as  the  root  of  the  spinous 
process.  ,  The  first  is  found  between  the  first  and  second  thoracic  vertebrse;  the 
last,  between  the  eleventh  and  twelfth.  Sometimes  the  number  of  these  muscles 
is  diminished  by  the  absence  of  one  or  more  from  the  upper  or  lower  end. 

The  Interspinales  are  short   muscular  fasciculi,  placed  in  pairs  between  the 


THE  SUBOCCIPITAL  MUSCLES  401 

spinous  processes  of  tlie  contiguous  vertebrae,  one  on  either  side  of  the  interspinal 
ligament.  In  the  cervical  region  they  are  most  distinct,  and  consist  of  six  pairs, 
the  first  being  situated  between  the  axis  and  third  vertebra,  and  the  last  between 
the  seventh  cervical  and  the  first  thoracic.  They  are  small  narrow  bundles, 
attached,  above  and  below,  to  the  apices  of  the  spinous  processes.  In  the  thoracic 
region,  they  are  found  between  thq  first  and  second  vertebrae,  and  sometimes  be- 
tween the  second  and  third,  and  between  the  eleventh  and  twelfth.  In  the  lumbar 
region  there  are  four  pairs  in  the  intervals  between  the  five  lumbar  vertebrae. 
There  is  also  occasionally  one  between  the  last  thoracic  and  first  lumbar,  and  one 
between  the  fifth  lumbar  and  the  sacrum. 

The  Extensor  coccygis  is  a  slender  muscular  fasciculus,  which  is  not  always  present;  it  extends 
over  the  lower  part  of  the  posterior  surface  of  the  sacrum  and  coccyx.  It  arises  by  tendinous 
fibers  from  the  last  segment  of  the  sacrum,  or  first  piece  of  the  coccyx,  and  passes  downward  to 
be  inserted  into  the  lower  part  of  the  coccyx.  It  is  a  rudiment  of  the  Extensor  muscle  of  the 
caudal  vertebrae  of  the  lower  animals. 

The  Intertransversarii  (Intertransversales)  are  small  muscles  placed  between 
the  transverse  processes  of  the  vertebrae.  In  the  cervical  region  they  are  best 
developed,  consisting  of  rounded  muscular  and  tendinous  fasciculi,  and  are  placed 
in  pairs,  passing  between  the  anterior  and  the  posterior  tubercles  respectively  of 
the  transverse  processes  of  two  contiguous  vertebrae,  and  separated  from  one 
another  by  an  anterior  primary  division  of  the  cervical  nerve,  which  lies  in  the 
groove  between  them.  The  muscles  connecting  the  anterior  tubercles  are  termed 
the  Intertransversarii  anteriores;  those  between  the  posterior  tubercles,  the  Inter- 
transversarii posteriores;  both  sets  are  supplied  by  the  anterior  divisions  of  the 
spinal  nerves  (LickleyO-  There  are  seven  pairs  of  these  muscles,  the  first  pair 
being  between  the  atlas  and  axis,  and  the  last  pair  between  the  seventh  cervical 
and  first  thoracic  vertebrae.  In  the  thoracic  region  they  are  present  between  the 
transverse  processes  of  the  lower  three  thoracic  vertebrae,  and  between  the  trans- 
verse processes  of  the  last  thoracic  and  the  first  lumbar.  In  the  lumbar  region 
they  are  arranged  in  pairs,  on  either  side  of  the  vertebral  column,  one  set  occupy- 
ing the  entire  interspace  between  the  transverse  processes  of  the  lumbar  vertebrae, 
the  Intertransversarii  laterales;  the  other  set,  Intertransversarii  mediales,  passing 
from  the  accessory  process  of  one  vertebra  to  the  mammillary  of  the  vertebra  below. 
The  Intertransversarii  laterales  are  supplied  by  the  anterior  divisions,  and  the 
Intertransversarii  mediales  by  the  posterior  divisions  of  the  spinal  nerves  (Lichley, 
op.  cit). 

n.     THE  SUBOCCIPITAL  MUSCLES  (Fig.  389). 

The  suboccipital  group  comprises: 

Rectus  capitis  posterior  major.  Obliquus  capitis  inferior. 

Rectus  capitis  posterior  minor.  Obliquus  capitis  superior. 

The  Rectus  capitis  posterior  major  (Rectus  capitis  posticus  major)  arises  by  a 
pointed  tendon  from  the  spinous  process  of  the  axis,  and,  becoming  broader  as 
it  ascends,  is  inserted  into  the  lateral  part  of  the  inferior  nuchal  line  of  the  occipital 
bone  and  the  surface  of  the  bone  immediately  below  the  line.  As  the  muscles  of 
the  two  sides  pass  upward  and  lateralward,  they  leave  between  them  a  triangular 
space,  in  which  the  Recti  capitis  posteriores  minores  are  seen. 

The  Rectus  capitis  posterior  minor  (Rectus  capitis  posticus  minor)  arises  by  a 
narrow  pointed  tendon  from  the  tubercle  on  the  posterior  arch  of  the  atlas,  and, 
widening  as  it  ascends,  is  inserted  into  the  medial  part  of  the  inferior  nuchal  line 
of  the  occipital  bone  and  the  surface  between  it  and  the  foramen  magnum. 

'■  Journal  of  Anatomy  and  Physiology,  1904,  vol.  xxxix. 

26 


402  '^^^^^^^        MYOLOGY 

The  Obliquus  capitis  inferior  (Obliquus  inferior),  the  larger  of  the  two  Oblique 
muscles,  arises  from  the  apex  of  the  spinous  process  of  the  axis,  and  passes  lateral- 
ward  and  slightly  upward,  to  be  inserted  into  the  lower  and  back  part  of  the 
transverse  process  of  the  atlas. 

The  Obliquus  capitis   superior   {Ohliqnus  superior),  narrow  below,  wide  an 
expanded  above,  arises  by  tendinous  fibers  from  the  upper  surface  of  the  transversa 
process  of  the  atlas,  joining  with  the  insertion  of  the  preceding.    It  passes  upward 
and  medialward,  and  is  inserted  into  the  occipital  bone,  between  the  superior  and 
inferior  nuchal  lines,  lateral  to  the  Semispinalis  capitis 


I 

I 


^1 


The  Suboccipital  Triangle. — Between  the  Obliqui  and  the  Rectus  capitis  posterior  major  is 
the  suboccipital  triangle.  It  is  bounded,  above  and  medially,  by  the  Rectus  capitis  posterior 
major;  above  and  laterally,  by  the  Obliquus  capitis  superior;  below  and  laterally,  by  the  Obliquus 
capitis  inferior.  It  is  covered  by  a  layer  of  dense  fibro-fatty  tissue,  situated  beneath  the  Semi- 
spinalis capitis.  The  floor  is  formed  by  the  posterior  occipito-atlantal  membrane,  and  the  posterior 
arch  of  the  atlas.  In  the  deep  groove  on  the  upper  surface  of  the  posterior  arch  of  the  atlas  are 
the  vertebral  artery  and  the  first  cervical  or  suboccipital  nerve. 

Nerves. — The  deep  muscles  of  the  back  and  the  suboccipital  muscles  are  supplied  by  the 
posterior  primary  divisions  of  the  spinal  nerves. 

Actions. — The  Sacrospinalis  and  its  upward  continuations  and  the  Spinales  serve  to  main- 
tain the  vertebral  column  in  the  erect  posture;  they  also  serve  to  bend  the  trunk  backward  when 
it  is  required  to  counterbalance  the  influence  of  any  weight  at  the  front  of  the  body — as,  for 
instance,  when  a  heavy  weight  is  suspended  from  the  neck,  or  when  there  is  any  great  abdominal 
distension,  as  in  pregnancy  or  dropsy;  the  peculiar  gait  under  such  circumstances  depends  upon 
the  vertebral  column  being  drawn  backward,  by  the  counterbalancing  action  of  the  Sacrospinales. 
The  muscles  which  form  the  continuation  of  the  Sacrospinales  on  to  the  head  and  neck  steady 
those  parts  and  fix  them  in  the  upright  position.  If  the  IHocostalis  lumborum  and  Longissimus 
dorsi  of  one  side  act,  they  serve  to  draw  down  the  chest  and  vertebral  column  to  the  correspond- 
ing side.  The  Iliocostales  cervicis,  taking  their  fixed  points  from  the  cervical  vertebriE,  elevate 
those  ribs  to  which  they  are  attached;  taking  their  fixed  points  from  the  ribs,  both  muscles  help 
to  extend  the  neck;  while  one  muscle  bends  the  neck  to  its  own  side.  When  both  Longissimi 
cervicis  act  from  below,  they  bend  the  neck  backward.  When  both  Longissimi  capitis  act  from 
below,  they  bend  the  head  backward;  while,  if  only  one  muscle  acts,  the  face  is  turned  to  the 
side  on  which  the  muscle  is  acting,  and  then  the  head  is  bent  to  the  shoulder.  The  two  Recti 
draw  the  head  backward.  The  Rectus  capitis  posterior  major,  owing  to  its  obliquity,  rotates 
the  skull,  with  the  atlas,  arovmd  the  odontoid  process,  turning  the  face  to  the  same  side.  The 
Multifidus  acts  successively  upon  the  different  parts  of  the  column;  thus,  the  sacrum  furnishes 
a  fixed  point  from  which  the  fasciculi  of  this  muscle  acts  upon  the  lumbar  region;  which  in  tui'n 
becomes  the  fixed  point  for  the  fascicuU  moving  the  thoracic  region,  and  so  on  throughout  the 
entire  length  of  the  column.  The  Multifidus  also  serves  to  rotate  the  column,  so  that  the  front 
of  the  trimk  is  turned  to  the  side  opposite  to  that  from  which  the  muscle  acts,  this  muscle  being 
assisted  in  its  action  by  the  Obliquus  extemus  abdominis.  The  Obliquus  capitis  superior  draws 
the  head  backward  and  to  its  own  side.  The  Obliquus  inferior  rotates  the  atlas,  and  with  it  the 
skull,  around  the  odontoid  process,  turning  the  face  to  the  same  side.  When  the  Semispinals  of 
the  two  sides  act  together,  they  help  to  extend  the  vertebral  column;  when  the  muscles  of  only 
one  side  act,  they  rotate  the  thoracic  and  cervical  parts  of  the  column,  turning  the  body  to  the 
opposite  side.  The  Semispinales  capitis  draw  the  head  directly  backward;  if  one  muscle  acts, 
it  draws  the  head  to  one  side,  and  rotates  it  so  that  the  face  is  turned  to  the  opposite  side.  The 
Interspinales  by  approximating  the  spinous  processes  help  to  extend  the  column.  The  Inter- 
transversarii  approximate  the  transverse  processes,  and  help  to  bend  the  column  to  one  side. 
The  Rotatores  assist  the  Multifidus  to  rotate  the  vertebral  column,  so  that  the  front  of  the  trunk 
is  turned  to  the  side  opposite  to  that  from  which  the  miiscles  act. 

III.    THE   MUSCLES    OF   THE    THORAX. 

The  muscles  belonging  to  this  group  are  the 

Intercostales  externi.  Levatores  costarum. 

Intercostales  interni.  Serratus  posterior  superior, 

Subcostales.  Serratus  posterior  inferior. 

Transversus  thoracis.  Diaphragm. 

Intercostal  Fasciae. — In  each  intercostal  space  thin  but  firm  layers  of  fascia 
cover  the  outer  surface  of  the  Intercostalis  externus  and  the  inner  surface  of  the 


THE  MUSCLES  OF  THE  THORAX  403 

Intercostalis  internus;  and  a  third,  more  delicate  layer,  is  interposed  between  the 
two  planes  of  muscular  fibers.  They  are  best  marked  in  those  situations  where 
the  muscular  fibers  are  deficient,  as  between  the  Intercostales  externi  and  sternum 
in  front,  and  between  the  Intercostales  interni  and  vertebral  column  behind. 

The  Intercostales  (Intercostal  muscles)  (Fig.  411)  are  two  thin  planes  of  muscular 
and  tendinous  fibers  occupying  each  of  the  intercostal  spaces.  They  are  named 
external  and  internal  from  their  surface  relations — the  external  being  superficial 
to  the  internal. 

The  Intercostales  extern!  {External  intercostals)  are  eleven  in  number  on  either 
side.  They  extend  from  the  tubercles  of  the  ribs  behind,  to  the  cartilages  of  the 
ribs  in  front,  where  they  end  in  thin  membranes,  the  anterior  intercostal  membranes, 
which  are  continued  forward  to  the  sternum.  Each  arises  from  the  lower  border 
of  a  rib,  and  is  inserted  into  the  upper  border  of  the  rib  below.  In  the  two  lower 
spaces  they  extend  to  the  ends  of  the  cartilages,  and  in  the  upper  two  or  three 
spaces  they  do  not  quite  reach  the  ends  of  the  ribs.  They  are  thicker  than  the 
Intercostales  interni,  and  their  fibers  are  directed  obliquely  downward  and  lateral- 
ward  on  the  back  of  the  thorax,  and  downward,  forward,  and  medialward  on  the  front. 

Variations. — Continuation  with  the  ObHquus  externus  or  Serratus  anterior:  A  Supracostalis 
muscle,  from  the  anterior  end  of  the  first  rib  down  to  the  second,  third  or  fourth  ribs  occasionally 
occurs. 

The  Intercostales  interni  (Internal  intercostals)  are  also  eleven  in  number  on 
either  side.  They  commence  anteriorly  at  the  sternum,  in  the  interspaces  between 
the  cartilages  of  the  true  ribs,  and  at  the  anterior  extremities  of  th6  cartilages  of 
the  false  ribs,  and  extend  backward  as  far  as  the  angles  of  the  ribs,  whence  they 
are  continued  to  the  vertebral  column  by  thin  aponeuroses,  the  posterior  intercostal 
membranes.  Each  arises  from  the  ridge  on  the  inner  surface  of  a  rib,  as  well  as 
from  the  corresponding  costal  cartilage,  and  is  inserted  into  the  upper  border 
of  the  rib  below.  Their  fibers  are  also  directed  obliquely,  but  pass  in  a  direction 
opposite  to  those  of  the  Intercostales  externi. 

The  Subcostales  (Infracostales)  consist  of  muscular  and  aponeurotic  fasciculi, 
which  are  usually  well-developed  only  in  the  lower  part  of  the  thorax;  each  arises 
from  the  inner  surface  of  one  rib  near  its  angle,  and  is  inserted  into  the  inner 
surface  of  the  second  or  third  rib  below.  Their  fibers  run  in  the  same  direction 
as  those  of  the  Intercostales  interni. 

The  Transversus  thoracis  (Triangidaris  sterni)  is  a  thin  plane  of  muscular  and 
tendinous  fibers,  situated  upon  the  inner  surface  of  the  front  wall  of  the  chest 
(Fig.  390).  It  arises  on  either  side  from  the  lower  third  of  the  posterior  surface 
of  the  body  of  the  sternum,  from  the  posterior  surface  of  the  xiphoid  process, 
and  from  the  sternal  ends  of  the  costal  cartilages  of  the  lower  three  or  four  true 
ribs.  Its  fibers  diverge  upward  and  lateralward,  to  be  inserted  by  slips  into  the 
lower  borders  and  inner  surfaces  of  the  costal  cartilages  of  the  second,  third,  fourth, 
fifth,  and  sixth  ribs.  The  lowest  fibers  of  this  muscle  are  horizontal  in  their  direc- 
tion, and  are  continuous  with  those  of  the  Transversus  abdominis;  the  intermediate 
fibers  are  oblique,  while  the  highest  are  almost  vertical.  This  muscle  varies  in  its 
attachments,  not  only  in  different  subjects,  but  on  opposite  sides  of  the  same 
subject. 

The  Levatores  costamm  (Fig.  389),  twelve  in  number  on  either  side,  are  small 
tendinous  and  fleshy  bundles,  which  arise  from  the  ends  of  the  transverse  pro- 
cesses of  the  seventh  cervical  and  upper  eleven  thoracic  vertebrae;  they  pass 
obliquely  downward  and  lateralward,  like  the  fibers  of  the  Intercostales  externi, 
and  each  is  inserted  into  the  outer  surface  of  the  rib  immediately  below  the 
vertebra  from  which  it  takes  origin,  between  the  tubercle  and  the  angle  (Levatores 
costamm  breves).   Each  of  the  four  lower  muscles  divides  into  two  fasciculi,  one 


MYOLOGY 

The  Obliquus  capitis  inferior  (Obliquus  inferior),  the  larger  of  the  two  Oblique 
muscles,  arises  from  the  apex  of  the  spinous  process  of  the  axis,  and  passes  lateral- 
ward  and  slightly  upward,  to  be  inserted  into  the  lower  and  back  part  of  the 
transverse  process  of  the  atlas. 

The  Obliquus  capitis  superior  {Obliquus  superior),  narrow  below,  wide  and 
expanded  above,  arises  by  tendinous  fibers  from  the  upper  surface  of  the  transverse 
process  of  the  atlas,  joining  with  the  insertion  of  the  preceding.  It  passes  upward 
and  medialward,  and  is  inserted  into  the  occipital  bone,  between  the  superior  and 
inferior  nuchal  lines,  lateral  to  the  Semispinalis  capitis 

The  Suboccipital  Triangle. — Between  the  Obliqui  and  the  Rectus  capitis  posterior  major  is 
the  suboccipital  triangle.  It  is  bounded,  above  and  medially,  by  the  Rectus  capitis  posterior 
major;  above  and  laterally,  by  the  Obliquus  capitis  superior;  below  and  laterally,  by  the  ObMquus 
capitis  inferior.  It  is  covered  by  a  layer  of  dense  fibro-fatty  tissue,  situated  beneath  the  Semi- 
spinahs  capitis.  The  floor  is  formed  by  the  posterior  occipito-atlantal  membrane,  and  the  posterior 
arch  of  the  atlas.  In  the  deep  groove  on  the  upper  surface  of  the  posterior  arch  of  the  atlas  are 
the  vertebral  artery  and  the  first  cervical  or  suboccipital  nerve. 

Nerves. — The  deep  muscles  of  the  back  and  the  suboccipital  muscles  are  supplied  by  the 
posterior  primary  divisions  of  the  spinal  nerves. 

Actions. — The  Sacrospinalis  and  its  upward  continuations  and  the  Spinales  serve  to  main- 
tain the  vertebral  column  in  the  erect  posture;  they  also  serve  to  bend  the  trunk  backward  when 
it  is  required  to  counterbalance  the  influence  of  any  weight  at  the  front  of  the  body — as,  for 
instance,  when  a  heavy  weight  is  suspended  from  the  neck,  or  when  there  is  any  great  abdominal 
distension,  as  in  pregnancy  or  dropsy;  the  peculiar  gait  under  such  circumstances  depends  upon 
the  vertebral  column  being  drawn  backward,  by  the  counterbalancing  action  of  the  Sacrospinales. 
The  muscles  which  form  the  continuation  of  the  Sacrospinales  on  to  the  head  and  neck  steady 
those  parts  and  fix  them  in  the  upright  position.  If  the  Iliocostalis  lumborum  and  Longissimus 
dorsi  of  one  side  act,  they  serve  to  draw  down  the  chest  and  vertebral  column  to  the  correspond- 
ing side.  The  Ihocostales  cervicis,  taking  their  fixed  points  from  the  cervical  vertebra?,  elevate 
those  ribs  to  which  they  are  attached;  taking  their  fixed  points  from  the  ribs,  both  muscles  help 
to  extend  the  neck;  while  one  muscle  bends  the  neck  to  its  own  side.  When  both  Longissimi 
cervicis  act  from  below,  they  bend  the  neck  backward.  When  both  Longissimi  capitis  act  from 
below,  they  bend  the  head  backward;  while,  if  only  one  muscle  acts,  the  face  is  turned  to  the 
side  on  which  the  muscle  is  acting,  and  then  the  head  is  bent  to  the  shoulder.  The  two  Recti 
draw  the  head  backward.  The  Rectus  capitis  posterior  major,  owing  to  its  obliquity,  rotates 
the  skull,  with  the  atlas,  around  the  odontoid  process,  turning  the  face  to  the  same  side.  The 
Multifidus  acts  successively  upon  the  different  parts  of  the  column;  thus,  the  sacrum  furnishes 
a  fixed  point  from  which  the  fasciculi  of  this  muscle  acts  upon  the  lumbar  region ;  which  in  tm-n 
becomes  the  fixed  point  for  the  fasciculi  moving  the  thoracic  region,  and  so  on  throughout  the 
entire  length  of  the  column.  The  Multifidus  also  serves  to  rotate  the  column,  so  that  the  front 
of  the  trunk  is  turned  to  the  side  opposite  to  that  from  which  the  muscle  acts,  this  muscle  being 
assisted  in  its  action  by  the  Obliquus  extemus  abdominis.  The  Obliquus  capitis  superior  draws 
the  head  backward  and  to  its  own  side.  The  Obhquus  inferior  rotates  the  atlas,  and  with  it  the 
skull,  aroimd  the  odontoid  process,  turning  the  face  to  the  same  side.  When  the  Semispinales  of 
the  two  sides  act  together,  they  help  to  extend  the  vertebral  column;  when  the  muscles  of  only 
one  side  act,  they  rotate  the  thoracic  and  cervical  parts  of  the  column,  turning  the  body  to  the 
opposite  side.  The  Semispinales  capitis  draw  the  head  directly  backward;  if  one  muscle  acts, 
it  draws  the  head  to  one  side,  and  rotates  it  so  that  the  face  is  turned  to  the  opposite  side.  The 
Interspinals  by  approximating  the  spinous  processes  help  to  extend  the  column.  The  Inter- 
transversarii  approximate  the  transverse  processes,  and  help  to  bend  the  column  to  one  side. 
The  Rotatores  assist  the  Multifidus  to  rotate  the  vertebral  column,  so  that  the  front  of  the  trxmk 
is  turned  to  the  side  opposite  to  that  from  which  the  muscles  act. 

ra.    THE   MUSCLES    OF   THE   THORAX. 

The  muscles  belonging  to  this  group  are  the 

Intercostales  externi.  Levatores  costarum. 

Intercostales  interni.  Serratus  posterior  superior. 

Subcostales.  Serratus  posterior  inferior. 

Transversus  thoracis.  Diaphragm. 

Intercostal  Fasciae. — In  each  intercostal  space  thin  but  firm  layers  of  fascia 
cover  the  outer  surface  of  the  Intercostalis  externus  and  the  inner  surface  of  the 


THE  MUSCLES  OF  THE  THORAX  403 

Intercostalis  internus;  and  a  third,  more  delicate  layer,  is  interposed  between  the 
two  planes  of  muscular  fibers.  They  are  best  marked  in  those  situations  where 
the  muscular  fibers  are  deficient,  as  between  the  Intercostales  externi  and  sternum 
in  front,  and  between  the  Intercostales  interni  and  vertebral  column  behind. 

The  Intercostales  (Intercostal  muscles)  (Fig.  411)  are  two  thin  planes  of  muscular 
and  tendinous  fibers  occupying  each  of  the  intercostal  spaces.  They  are  named 
external  and  internal  from  their  surface  relations — the  external  being  superficial 
to  the  internal. 

The  Intercostales  externi  (External  intercostals)  are  eleven  in  number  on  either 
side.  They  extend  from  the  tubercles  of  the  ribs  behind,  to  the  cartilages  of  the 
ribs  in  front,  where  they  end  in  thin  membranes,  the  anterior  intercostal  membranes, 
which  are  continued  forward  to  the  sternum.  Each  arises  from  the  lower  border 
of  a  rib,  and  is  inserted  into  the  upper  border  of  the  rib  below.  In  the  two  lower 
spaces  they  extend  to  the  ends  of  the  cartilages,  and  in  the  upper  two  or  three 
spaces  they  do  not  quite  reach  the  ends  of  the  ribs.  They  are  thicker  than  the 
Intercostales  interni,  and  their  fibers  are  directed  obliquely  downward  and  lateral- 
ward  on  the  back  of  the  thorax,  and  downward,  forward,  and  medialward  on  the  front. 

Variations. — Continuation  with  the  Obhquus  externus  or  Serratus  anterior:  A  Supracostalis 
muscle,  from  the  anterior  end  of  the  first  rib  down  to  the  second,  third  or  fourth  ribs  occasionally 
occurs. 

The  Intercostales  interni  (Internal  intercostals)  are  also  eleven  in  number  on 
either  side.  They  commence  anteriorly  at  the  sternum,  in  the  interspaces  between 
the  cartilages  of  the  true  ribs,  and  at  the  anterior  extremities  of  th6  cartilages  of 
the  false  ribs,  and  extend  backward  as  far  as  the  angles  of  the  ribs,  whence  they 
are  continued  to  the  vertebral  column  by  thin  aponeuroses,  the  posterior  intercostal 
membranes.  Each  arises  from  the  ridge  on  the  inner  surface  of  a  rib,  as  well  as 
from  the  corresponding  costal  cartilage,  and  is  inserted  into  the  upper  border 
of  the  rib  below.  Their  fibers  are  also  directed  obliquely,  but  pass  in  a  direction 
opposite  to  those  of  the  Intercostales  externi. 

The  Subcostales  (Infracostales)  consist  of  muscular  and  aponeurotic  fasciculi, 
which  are  usually  well-developed  only  in  the  lower  part  of  the  thorax;  each  arises 
from  the  inner  surface  of  one  rib  near  its  angle,  and  is  inserted  into  the  inner 
surface  of  the  second  or  third  rib  below.  Their  fibers  run  in  the  same  direction 
as  those  of  the  Intercostales  interni. 

The  Transversus  thoracis  ( Triangularis  sterni)  is  a  thin  plane  of  muscular  and 
tendinous  fibers,  situated  upon  the  inner  surface  of  the  front  wall  of  the  chest 
(Fig.  390).  It  arises  on  either  side  from  the  lower  third  of  the  posterior  surface 
of  the  body  of  the  sternum,  from  the  posterior  surface  of  the  xiphoid  process, 
and  from  the  sternal  ends  of  the  costal  cartilages  of  the  lower  three  or  four  true 
ribs.  Its  fibers  diverge  upward  and  lateralward,  to  be  inserted  by  slips  into  the 
lower  borders  and  inner  surfaces  of  the  costal  cartilages  of  the  second,  third,  fourth, 
fifth,  and  sixth  ribs.  The  lowest  fibers  of  this  muscle  are  horizontal  in  their  direc- 
tion, and  are  continuous  with  those  of  the  Transversus  abdominis;  the  intermediate 
fibers  are  oblique,  while  the  highest  are  almost  vertical.  This  muscle  varies  in  its 
attachments,  not  only  in  different  subjects,  but  on  opposite  sides  of  the  same 
subject. 

The  Levatores  costarum  (Fig.  389),  twelve  in  number  on  either  side,  are  small 
tendinous  and  fleshy  bundles,  which  arise  from  the  ends  of  the  transverse  pro- 
cesses of  the  seventh  cervical  and  upper  eleven  thoracic  vertebrae;  they  pass 
obliquely  downward  and  lateralward,  like  the  fibers  of  the  Intercostales  externi, 
and  each  is  inserted  into  the  outer  surface  of  the  rib  immediately  below  the 
vertebra  from  which  it  takes  origin,  between  the  tubercle  and  the  angle  (Levatores 
costarum  breves) .  Each  of  the  four  lower  muscles  divides  into  two  fasciculi,  one 


404 


MYOLOGY 


of  which  is  inserted  as  above  described;  the  other  passes  down  to  the  seconc 
rib  below  its  origin  (Levatores  costaramlongi). 

The  Serratus  posterior  superior  {Serratus  'posticus  superior)  is  a  thin,  quadri-j 
lateral  muscle,  situated  at  the  upper  and  back  part  of  the  thorax.    It  arises  bj 
a  thin  and  broad  aponeurosis  from  the  lower  part  of  the  ligamentum  nuchae,' 
from  the  spinous  processes  of  the  seventh  cervical  and  upper  two  or  three  thoracic 

vertebrae  and  from  the  supraspinal  liga- 
ment. Inclining  downward  and  lateral-^^— 
ward  it  becomes  muscular,  and  is  in-^| 
serted,  by  four  fleshy  digitations,  into 
the  upper  borders  of  the  second,  third, 
fourth,  and  fifth  ribs,  a  little  beyond 
their  angles. 

Variations. — Increase  or  decrease  in  size  and 
number  of  slips  or  entire  absence. 

The  Serratus  posterior  inferior  {Ser- 
ratus posticus  inferior)  (Fig.  409)  is  sit- 
uated at  the  junction  of  the  thoracic 
and  lumbar  regions:  it  is  of  an  irreg- 
ularly quadrilateral  form,  broader  than 
the  preceding,  and  separated  from  it  by 
a  wide  interval.  It  arises  by  a  thin 
aponeurosis  from  the  spinous  processes 
of  the  lower  two  thoracic  and  upper  two 
or  three  lumbar  vertebrae,  and  from 
the  supraspinal  ligament.  Passing 
obliquely  upward  and  lateral  ward,  it 
becomes  fleshy,  and  divides  into  four 
flat  digitations,  w^hich  are  inserted  into 
the  inferior  borders  of  the  lower  four 
ribs,  a  little  beyond  their  angles.  The 
thin  aponeurosis  of  origin  is  intimately 
blended  with  the  lumbodorsal  fascia, 
and  aponeurosis  of  the  Latissimus  dorsi. 


Sternal 
origin  of 
Diaphragm 


Fig.  390. — Posterior  surface  of  sternum  and  costal 
cartilages,  showing  Transversus  thoracis. 


Variations. — Increase  or  decrease  in  size  and  number  of  slips  or  entire  absence. 
Nerves. — The  muscles  of  this  group  are  supplied  by  the  intercostal  nerves. 

The  Diaphragm  (Fig.  391)  is  a  dome-shaped  musculofibrous  septum  which 
separates  the  thoracic  from  the  abdominal  cavity,  its  convex  upper  surface  forming 
the  floor  of  the  former,  and  its  concave  under  surface  the  roof  of  the  latter.  Its 
peripheral  part  consists  of  muscular  fibers  which  take  origin  from  the  circumference 
of  the  thoracic  outlet  and  converge  to  be  inserted  into  a  central  tendon. 

The  muscular  fibers  may  be  grouped  according  to  their  origins  into  three  parts 
— sternal,  costal,  and  lumbar.  The  sternal  part  arises  by  two  fleshy  slips  from 
the  back  of  the  xiphoid  process ;  the  costal  part  from  the  inner  surfaces  of  the  car- 
tilages and  adjacent  portions  of  the  lower  six  ribs  on  either  side,  interdigitating 
with  the  Transversus  abdominis;  and  the  lumbar  part  from  aponeurotic  arches, 
named  the  lumbocostal  arches,  and  from  the  lumbar  vertebrae  by  two  pillars  or 
crura.    There  are  two  lumbocostal  arches,  a  medial  and  a  lateral,  on  either  side. 

The  Medial  Lumbocostal  Arch  (arcus  lumbocostalis  medialis  [Halleri];  internal 
arcuate  ligament)  is  a  tendinous  arch  in  the  fascia  covering  the  upper  part  of  the 
Psoas  major;  medially,  it  is  continuous  with  the  lateral  tendinous  margin  of  the 
corresponding  crus,  and  is  attached  to  the  side  of  the  body  of  the  first  or  second 


THE  MUSCLES  OF  THE  THORAX 


405 


lumbar  vertebra;  laterally,  it  is  fixed  to  the  front  of  the  transverse  process  of  the 
first  and,  sometimes  also,  to  that  of  the  second  lumbar  vertebra. 

The  Lateral  Lumbocostal  Arch  (arcus  lumbocostalis  lateralis  [Halleri];  external 
arcuate  ligament)  arches  across  the  upper  part  of  the  Quadratus  lumborum,  and 
is  attached,  medially,  to  the  front  of  the  transverse  process  of  the  first  lumbar 
vertebra,  and,  laterally,  to  the  tip  and  lower  margin  of  the  twelfth  rib. 

The  Crura. — At  their  origins  the  crura  are  tendinous  in  structure,  and  blend 
with  the  anterior  longitudinal  ligament  of  the  vertebral  column.  The  right  cms, 
larger  and  longer  than  the  left,  arises  from  the  anterior  surfaces  of  the  bodies  and 
intervertebral  fibrocartilages  of  the  upper  three  lumbar  vertebrae,  while  the  left 
cms  arises  from  the  corresponding  parts  of  the  upper  two  only.  The  medial  ten- 
dinous margins  of  the  crura  pass  forward  and  medialward,  and  meet  in  the  middle 
line  to  form  an  arch  across  the  front  of  the  aorta;  this  arch  is  often  poorly  defined. 


Xiphoid  process 


Opening  for  Lesser  Splanchnic  Nerve 


FiQ.  391. — The  diaphragm.     Under  surface. 


From  this  series  of  origins  the  fibers  of  the  diaphragm  converge  to  be  inserted 
into  the  central  tendon.  The  fibers  arising  from  the  xiphoid  process  are  very  short, 
and  occasionally  aponeurotic;  those  from  the  medial  and  lateral  lumbocostal 
arches,  and  more  especially  those  from  the  ribs  and  their  cartilages,  are  longer, 
and  describe  marked  curves  as  they  ascend  and  converge  to  their  insertion.  The 
fibers  of  the  crura  diverge  as  they  ascend,  the  most  lateral  being  directed  upward 
and  lateralward  to  the  central  tendon.  The  medial  fibers  of  the  right  crus  ascend 
on  the  left  side  of  the  esophageal  hiatus,  and  occasionally  a  fasciculus  of  the  left 
crus  crosses  the  aorta  and  runs  obliquely  through  the  fibers  of  the  right  crus  toward 
the  vena  caval  foramen  (Low^). 

'  Journal  of  Anatomy  and  Physiology,  vol.  xlii. 


406 

The  Central  Tendon. — The  central  tendon  of  the  diaphragm  is  a  thin  but  strong 
aponeurosis  situated  near  the  center  of  the  vault  formed  by  the  muscle,  but  some- 
what closer  to  the  front  than  to  the  back  of  the  thorax,  so  that  the  posterior  muscu- 
lar fibers  are  the  longer.  It  is  situated  immediately  below  the  pericardium,  with 
which  it  is  partially  blended.  It  is  shaped  somewhat  like  a  trefoil  leaf,  consisting 
of  three  divisions  or  leaflets  separated  from  one  another  by  slight  indentations.] 
The  right  leaflet  is  the  largest,  the  middle,  directed  toward  the  xiphoid  process," 
the  next  in  size,  and  the  left  the  smallest.  In  structure  the  tendon  is  composed 
of  several  planes  of  fibers,  which  intersect  one  another  at  various  angles  and  unite 
into  straight  or  curved  bundles — an  arrangement  which  gives  it  additional  strength. 

Openings  in  the  Diaphragm. — The  diaphragm  is  pierced  by  a  series  of  apertures 
to  permit  of  the  passage  of  structures  between  the  thorax  and  abdomen.  Three 
large  openings— the  aortic,  the  esophageal,  and  the  vena  caval— and  a  series  of 
smaller  ones  are  described. 

The  aortic  hiatus  is  the  lowest  and  most  posterior  of  the  large  apertures;  it  lies 
at  the  level  of  the  twelfth  thoracic  vertebra.  Strictly  speaking,  it  is  not  an  aperture 
in  the  diaphragm  but  an  osseoaponeurotic  opening  between  it  and  tbe  vertebral 
column,  and  therefore  behind  the  diaphragm ;  occasionally  some  tendinous  fibers 
prolonged  across  the  bodies  of  the  vertebrae  from  the  medial  parts  of  the  lower  ends 
of  the  crura  pass  behind  the  aorta,  and  thus  convert  the  hiatus  into  a  fibrous  ring. 
The  hiatus  is  situated  slightly  to  the  left  of  the  middle  line,  and  is  bounded  in  front 
by  the  crura,  and  behind  by  the  body  of  the  first  lumbar  vertebra.  Through  it 
pass  the  aorta,  the  azygos  vein,  and  the  thoracic  duct;  occasionally  the  azygos 
vein  is  transmitted  through  the  right  crus. 

The  esophageal  hiatus  is  situated  in  the  muscular  part  of  the  diaphragm  at 
the  level  of  the  tenth  thoracic  vertebra,  and  is  elliptical  in  shape.  It  is  placed 
above,  in  front,  and  a  little  to  the  left  of  the  aortic  hiatus,  and  transmits  the 
esophagus,  the  vagus  nerves,  and  some  small  esophageal  arteries. 

The  vena  caval  foramen  is  the  highest  of  the  three,  and  is  situated  about  the  level 
of  the  fibrocartilage  between  the  eighth  and  ninth  thoracic  vertebrae.  It  is  quad- 
rilateral in  form,  and  is  placed  at  the  junction  of  the  right  and  middle  leaflets 
of  the  central  tendon,  so  that  its  margins  are  tendinous.  It  transmits  the  inferior 
vena  cava,  the  wall  of  which  is  adherent  to  the  margins  of  the  opening,  and  some 
branches  of  the  right  phrenic  nerve. 

Of  the  lesser  apertures,  two  in  the  right  crus  transmit  the  greater  and  lesser 
right  splanchnic  nerves;  three  in  the  left  crus  give  passage  to  the  greater  and  lesser 
left  splanchnic  nerves  and  the  hemiazygos  vein.  The  gangliated  trunks  of  the 
sympathetic  usually  enter  the  abdominal  cavity  behind  the  diaphragm,  under 
the  medial  lumbocostal  arches. 

On  either  side  two  small  intervals  exist  at  which  the  muscular  fibers  of  the 
diaphragm  are  deficient  and  are  replaced  by  areolar  tissue.  One  between  the 
sternal  and  costal  parts  transmits  the  superior  epigastric  branch  of  the  internal 
mammary  artery  and  some  lymphatics  from  the  abdominal  wall  and  convex 
surface  of  the  liver.  The  other,  between  the  fibers  springing  from  the  medial  and 
lateral  lumbocostal  arches,  is  less  constant;  when  this  interval  exists,  the  upper 
and  back  part  of  the  kidney  is  separated  from  the  pleura  by  areolar  tissue  only. 

Variations. — The  sternal  portion  of  the  muscle  is  sometimes  wanting' and  more  rarely  defects 
occur  in  the  lateral  part  of  the  central  tendon  or  adjoining  muscle  fibers. 

Nerves. — The  diaphragm  is  supplied  by  the  phrenic  and  lower  intercostal  nerves. 

Actions. — The  diaphragm  is  the  principal  muscle  of  inspiration,  and  presents  the  form  of 
a  dome  concave  toward  the  abdomen.  The  central  part  of  the  dome  is  tendinous,  and  the  peri- 
cardium is  attached  to  its  upper  surface;  the  circumference  is  muscular.  During  inspiration  the 
lowest  ribs  are  fixed,  and  from  these  and  the  crura  the  muscular  fibers  contract  and  draw  down- 
ward and  forward  the  central  tendon  with  the  attached  pericardium.  In  this  movement  the 
curvature  of  the  diaphragm  is  scarcely  altered,  the  dome  moving  downward  nearly  parallel 


THE  MUSCLES  OF  THE  THORAX  407 

to  its  original  position  and  pushing  before  it  the  abdominal  viscera.  The  descent  of  the  abdominal 
viscera  is  permitted  by  the  elasticity  of  the  abdominal  wall,  but  the  hmit  of  this  is  soon  reached. 
The  central  tendon  applied  to  the  abdominal  viscera  then  becomes  a  fixed  point  for  the  action 
of  the  diaphragm,  the  effect  of  which  is  to  elevate  the  lower  ribs  and  through  them  to  push 
forward  the  body  of  the  sternum  and  the  upper  ribs.  The  right  cupola  of  the  diaphragm, 
lying  on  the  liver,  has  a  greater  resistance  to  overcome  than  the  left,  which  lies  over  the  stomach, 
but  to  compensate  for  this  the  right  crus  and  the  fibers  of  the  right  side  generally  are  stronger 
than  those  of  the  left. 

In  all  expulsive  acts  the  diaphragm  is  called  into  action  to  give  additional  power  to  each 
expulsive  effort.  Thus,  before  sneezing,  coughing,  laughing,  crying,  or  vomiting,  and  previous 
to  the  expulsion  of  urine  or  feces,  or  of  the  fetus  from  the  uterus,  a  deep  inspiration  takes  place. 
The  height  of  the  diaphragm  is  constantly  varying  during  respiration;  it  also  varies  with  the 
degree  of  distension  of  the  stomach  and  intestines  and  with  the  size  of  the  hver.  After  a  forced 
expiration  the  right  cupola  is  on  a  level  in  front  with  the  fourth  costal  cartilage,  at  the  side  with 
the  fifth,  sixth,  and  seventh  ribs,  and  behind  with  the  eighth  rib;  the  left  cupola  is  a  little  lower 
than  the  right.  Halls  Dally ^  states  that  the  absolute  range  of  movement  between  deep  inspira- 
tion and  deep  expiration  averages  in  the  male  and  female  30  mm.  on  the  right  side  and  28  mm. 
on  the  left;  in  quiet  respiration  the  average  movement  is  12.5  mm.  on  the  right  side  and  12  mm. 
on  the  left. 

Skiagraphy  shows  that  the  height  of  the  diaphragm  in  the  thorax  varies  considerably  with 
the  position  of  the  body.  It  stands  highest  when  the  body  is  horizontal  and  the  patient  on  his 
back,  and  in  this  position  it  performs  the  largest  respiratory  excursions  with  normal  breathing. 
When  the  body  is  erect  the  dome  of  the  diaphragm  falls,  and  its  respiratory  movements  become 
smaller.  The  dome  falls  still  lower  when  the  sitting  posture  is  assumed,  and  in  this  position  its 
respiratory  excursions  are  smallest.  These  facts  may,  perhaps,  explain  why  it  is  that  patients 
suffering  from  severe  dyspnoea  are  most  comfortable  and  least  short  of  breath  when  they  sit  up. 
When  the  body  is  horizontal  and  the  patient  on  his  side,  the  two  halves  of  the  diaphragm  do 
not  behave  alike.  The  uppermost  half  sinks  to  a  level  lower  even  than  when  the  patient  sits, 
and  moves  little  with  respiration;  the  lower  half  rises  higher  in  the  thorax  than  it  does  when  the 
patient  is  supine,  and  its  respiratory  excursions  are  much  increased.  In  unilateral  disease  of  the 
plem'a  or  lungs  analogous  interference  with  the  position  or  movement  of  the  diaphragm  can 
generally  be  observed  skiagraphically. 

It  appears  that  the  position  of  the  diaphragm  in  the  thorax  depends  upon  three  main  factors, 
viz.:  (1)  the  elastic  retraction  of  the  lung  tissue,  tending  to  pull  it  upward;  (2)  the  pressure 
exerted  on  its  under  surface  by  the  viscera;  this  naturally  tends  to  be  a  negative  pressure,  or  down- 
ward suction,  when  the  patient  sits  or  stands,  and  positive,  or  an  upward  pressure,  when  he  lies; 
(3)  the  intra-abdominal  tension  due  to  the  abdominal  muscles.  These  are  in  a  state  of  contrac- 
tion in  the  standing  position  and  not  in  the  sitting;  hence  the  diaphragm,  when  the  patient 
stands,  is  pushed  up  higher  than  when  he  sits. 

The  Intercostales  interni  and  externi  have  probably  no  action  in  moving  the  ribs.  They  con- 
tract simultaneously  and  form  strong  elastic  supports  which  prevent  the  intercostal  spaces  being 
pushed  out  or  drawn  in  during  respiration.  The  anterior  portions  of  the  Intercostales  interni 
probably  have  an  additional  function  in  keeping  the  sternocostal  and  interchondral  joint  sur- 
faces in  apposition,  the  posterior  parts  of  the  Intercostales  externi  performing  a  similar  function 
for  the  costovertebral  articulations.  The  Levatores  costarum  being  inserted  near  the  fulcra  of 
the  ribs  can  have  little  action  on  the  ribs;  they  act  as  rotators  and  lateral  flexors  of  the  vertebral 
column.  The  Transversus  thoracis  draws  down  the  costal  cartilages,  and  is  therefore  a  muscle 
of  expiration. 

The  Serrati  are  respiratory  muscles.  The  Serratus  posterior  superior  elevates  the  ribs  and 
is  therefore  an  inspiratory  muscle.  The  Serratus  posterior  inferior  draws  the  lower  ribs  down- 
ward and  backward,  and  thus  elongates  the  thorax;  it  also  fixes  the  lower  ribs,  thus  assisting 
the  inspiratory  action  of  the  diaphragm  and  resisting  the  tendency  it  has  to  draw  the  lower 
ribs  upward  and  forward.    It  must  therefore  be  regarded  as  a  muscle  of  inspiration. 

Mechanism  of  Respiration. — The  respiratory  movements  must  be  examined  dm-ing  (a)  quiet 
respiration,  and  {h)  deep  respiration. 

Quiet  Respiration. — The  first  and  second  pairs  of  ribs  are  fixed  by  the  resistance  of  the  cervical 

structures;  the  last  pair,  and  through  it  the  eleventh,  by  the  Quadratus  lumborum.    The  other 

ribs  are  elevated,  so  that  the  first  two  intercostal  spaces  are  diminished  while  the  others  are 

increased  in  v/idth.    It  has  already  been  shown  (p.  304)  that  elevation  of  the  third,  fourth,  fifth, 

and  sixth  ribs  leads  to  an  increase  in  the  antero-posterior  and  transverse  diameters  of  the  thorax; 

the  vertical  diameter  is  increased  by  the*  descent  of  the  diaphragmatic  dome  so  that  the  lungs 

__      are  expanded  in  all  directions  except  backward  and  upward.     Elevation  of  the  eighth,  ninth, 

!■     and  tenth  ribs  is  accompanied  by  a  lateral  and  backward  movement,  leading  to  an  increase  in 

II     the  transverse  diameter  of  the  upper  part  of  the  abdomen;  the  elasticity  of  the  anterior  abdominal 


W 

II 

II 


'  Journal  of  Anatomy  and  Physiology,  1908,  vol.  xliii. 


MYOLOGY 

ones  being  attached  close  to  the  cartilages  of  the  corresponding  ribs,  the  lowest 
to  the  apex  of  the  cartilage  of  the  last  rib,  the  intermediate  ones  to  the  ribs  at 
some  distance  from  their  cartilages.  The  five  superior  serrations  increase  in  size 
from  above  downward,  and  are  received  between  corresponding  processes  of  the 
Serratus  anterior;  the  three  lower  ones  diminish  in  size  from  above  downward 
and  receive  between  them  corresponding  processes  from  the  Latissimus  dorsi. 
From  these  attachments  the  fleshy  fibers  proceed  in  various  directions.  Those 
from  the  lowest  ribs  pass  nearly^  vertically  downward,  and  are  inserted  into  the 
anterior  half  of  the  outer  lip  of  the  iliac  crest;  the  middle  and  upper  fibers,  directed 
downward  and  forward,  end  in  an  aponeurosis,  opposite  a  line  drawn  from  the 
prominence  of  the  ninth  costal  cartilage  to  the  anterior  superior  iliac  spine. 

The  aponeurosis  of  the  Obliquus  extemus  abdominis  is  a  thin  but  strong  mem- 
branous structure,  the  fibers  of  which  are  directed  downward  and  medialward. 
It  is  joined  with  that  of  the  opposite  muscle  along  the  middle  line,  and  covers 
the  whole  of  the  front  of  the  abdomen;  above,  it  is  covered  by  and  gives  origin 
to  the  lower  fibers  of  the  Pectoralis  major;  belotv,  its  fibers  are  closely  aggregated 
together,  and  extend  obliquely  across  from  the  anterior  superior  iliac  spine  to 
the  pubic  tubercle  and  the  pectineal  line.  In  the  middle  line,  it  interlaces  with 
the  aponeurosis  of  the  opposite  muscle,  forming  the  linea  alba,  which  extends  from 
the  xiphoid  process  to  the  symphysis  pubis. 

That  portion  of  the  aponeurosis  which  extends  between  the  anterior  superior 
iliac  spine  and  the  pubic  tubercle  is  a  thick  band,  folded  inward,  and  continuous 
below  with  the  fascia  lata;  it  is  called  the  inguinal  ligament.  The  portion  which 
is  reflected  from  the  inguinal  ligament  at  the  pubic  tubercle  is  attached  to  the 
pectineal  line  and  is  called  the  lacunar  ligament.  From  the  point  of  attachment 
of  the  latter  to  the  pectineal  line,  a  few  fibers  pass  upward  and  medialward,  behind 
the  medial  crus  of  the  subcutaneous  inguinal  ring,  to  the  linea  alba;  they  diverge 
as  they  ascend,  and  form  a  thin  triangular  fibrous  band  which  is  called  the  reflected 
inguinal  ligament. 

In  the  aponeurosis  of  the  Obliquus  extemus,  immediately  above  the  crest  of 
the  pubis,  is  a  triangular  opening,  the  subcutaneous  inguinal  ring,  formed  by  a 
separation  of  the  fibers  of  the  aponeurosis  in  this  situation. 

The  following  structures  require  further  description,  viz.,  the  subcutaneous 
inguinal  ring,  the  intercrural  fibers  and  fascia,  and  the  inguinal,  lacunar,  and  reflected 
inguinal  ligaments. 

The  Subcutaneous  Inguinal  Ring  (annulus  inguinalis  suhcutaneus;  external 
abdominal  ring)  (Fig.  393). — The  subcutaneous  inguinal  ring  is  an  interval  in  the 
aponeurosis  of  the  Obliquus  externus,  just  above  and  lateral  to  the  crest  of  the 
pubis.  The  aperture  is  oblique  in  direction,  somew^hat  triangular  in  form,  and 
corresponds  with  the  course  of  the  fibers  of  the  aponeurosis.  It  usually  measures 
from  base  to  apex  about  2.5  cm.,  and  transversely  about  1.25  cm.  It  is  bounded 
below  by  the  crest  of  the  pubis;  on  either  side  by  the  margins  of  the  opening  in  the 
aponeurosis,  which  are  called  the  crura  of  the  ring ;  and  above,  by  a  series  of  curved 
Intercrural  fibers.  The  inferior  crus  {external  'pillar)  is  the  stronger  and  is  formed  by 
that  portion  of  the  inguinal  ligament  which  is  inserted  into  the  pubic  tubercle; 
it  is  curved  so  as  to  form  a  kind  of  groove,  upon  which,  in  the  male,  the  spermatic 
cord  rests.  The  superior  crus  {internal  'pillar)  is  a  broad,  thin,  flat  band,  attached  to 
the  front  of  the  symphysis  pubis  and  interlacing  with  its  fellow  of  the  opposite  side. 

The  subcutaneous  inguinal  ring  gives  passage  to  the  spermatic  cord  and  ilio- 
inguinal nerve  in  the  male,  and  to  the  round  ligament  of  the  uterus  and  the 
ilioinguinal  nerve  in  the  female;  it  is  much  larger  in  men  than  in  women,  on 
account  of  the  large  size  of  the  spermatic  cord. 

The  Intercrural  Fibers  {fibra;  intercr urates;  intercolumnar  fibers) . — The  intercrural 
fibers  are  a  series  of  curved  tendinous  fibers,  which  arch  across  the  lower  part  of 


THE  ANTERO-LATERAL  MUSCLES  OF  THE  ABDOMEN 


411 


the  aponeurosis  of  the  ObHquus  externus,  describing  curves  with  the  convexities 
downward.  They  have  received  their  name  from  stretching  across  between  the 
two  crura  of  the  subcutaneous  inguinal  ring,  and  they  are  much  thicker  and  stronger 
at  the  inferior  crus,  where  they  are  connected  to  the  inguinal  ligament,  than  supe- 
riorly, where  they  are  inserted  into  the  linea  alba.  The  intercrural  fibers  increase 
the  strength  of  the  lower  part  of  the  aponeurosis,  and  prevent  the  divergence  of 
the  crura  from  one  another;  they  are  more  strongly  developed  in  the  male  than  in 
the  female. 

As  they  pass  across  the  subcutaneous  inguinal  ring,  they  are  connected  together 
I  by  delicate  fibrous  tissue,  forming  a  fascia,  called  the  intercrural  fascia.    This  inter- 


Superficial  iliac 
circumflex  vein 


Subcutaneous  inguinal 
ring 


Fig.  393. — The  subcutaneous  inguinal  ring. 


jrural  fascia  is  continued  down  as  a  tubular  prolongation  around  the  spermatic 
cord  and  testis,  and  encloses  them  in  a  sheath;  hence  it  is  also  called  the  external 
spermatic  fascia.  The  subcutaneous  inguinal  ring  is  seen  as  a  distinct  aperture 
only  after  the  intercrural  fascia  has  been  removed. 

The  Inguinal  Ligament  (ligamentuvi  inguinale  [Pouparti]  ;  Poupart's  ligament) 
(Fig.  394) . — The  inguinal  ligament  is  the  lower  border  of  the  aponeurosis  of  the 
Obliquus  externus,  and  extends  from  the  anterior  superior  iliac  spine  to  the  pubic 
tubercle.  From  this  latter  point  it  is  reflected  backward  and  lateralward  to  be 
attached  to  the  pectineal  line  for  about  1.25  cm.,  forming  the  lacunar  ligament. 
Its  general  direction  is  convex  downward  toward  the  thigh,  where  it  is  continuous 
with  the  fascia  lata.    Its  lateral  half  is  rounded,  and  oblique  in  direction;   its 


412 


MYOLOGY 


medial  half  gradually  widens  at  its  attachment  to  the  pubis,  is  more  horizontal 
in  direction,  and  lies  beneath  the  spermatic  cord. 

The  Lacunar  Ligament  {ligamentum  lacunare  [Gimbernati]  ;  Gimhernafs  ligament) 
(Fig.  394) . — The  lacunar  ligament  is  that  part  of  the  aponeurosis  of  the  Obliquus 
externus  which  is  reflected  backward  and  lateralward,  and  is  attached  to  the  pecti- 
neal line.  It  is  about  1.25  cm.  long,  larger  in  the  male  than  in  the  female,  almost 
horizontal  in  direction  in  the  erect  posture,  and  of  a  triangular  form  with  the  base 
directed  lateralward.  Its  base  is  concave,  thin,  and  sharp,  and  forms  the  medial 
boundary  of  the  femoral  ring.  Its  apex  corresponds  to  the  pubic  tubercle.  Its 
posterior  margin  is  attached  to  the  pectineal  line,  and  is  continuous  with  the 
pectineal  fascia.  Its  anterior  margin  is  attached  to  the  inguinal  ligament, 
surfaces  are  directed  upward  and  downward. 


Ant.  sup.  iliac  spine. 


Symphysis 
pubis 


Its 

I 


Transverse  acetabular 
ligainent 


Fig.  394. — The  inguinal  and  lacunar  ligaments. 


The  Reflected  Inguinal  Ligament  {ligamentum  inguinale  reflexum  [  Collesi] ;  trian- 
gular fascia) . — The  reflected  inguinal  ligament  is  a  layer  of  tendinous  fibers  of  a 
triangular  shape,  formed  by  an  expansion  from  the  lacunar  ligament  and  the  inferior 
cms  of  the  subcutaneous  inguinal  ring.  It  passes  medialward  behind  the  spermatic 
cord,  and  expands  into  a  somewhat  fan-shaped  band,  lying  behind  the  superior 
crus  of  the  subcutaneous  inguinal  ring,  and  in  front  of  the  inguinal  aponeurotic 
falx,  and  interlaces  with  the  ligament  of  the  other  side  of  the  linea  alba  (Fig.  396). 

Ligament  of  Cooper. — This  is  a  strong  fibrous  band,  which  was  first  described  by  Sir  Astley 
Cooper.  It  extends  lateralward  from  the  base  of  the  lacunar  ligament  (Fig.  394)  along  the 
pectineal  hne,  to  which  it  is  attached.  It  is  strengthened  by  the  pectineal  fascia,  and  by  a 
lateral  expansion  from  the  lower  attachment  of  the  hnea  alba  {adminiculum  linece  alhce). 

Variations. — The  Obliquus  externus  may  show  decrease  or  doubling  of  its  attachments  to  the 
ribs;  addition  slips  from  lumbar  aponeurosis;  doubling  between  lower  ribs  and  ilium  or  inguinal 
ligament.    Rarely  tendinous  inscriptions  occur. 

The  Obliquus  intemus  abdominis  {Internal  or  ascending  oblique  muscle)  (Fig. 
395),  thinner  and  smaller  than  the  Obliquus  externus,  beneath  which  it  lies,  is  of 


THE  ANTERO-LATERAL  MUSCLES  OF  THE  ABDOMEN 


413 


an  irregularly  quadrilateral  form,  and  situated  at  the  lateral  and  anterior  parts 
of  the  abdomen.  It  arises,  by  fleshy  fibers,  from  the  lateral  half  of  the  grooved 
upper  surface  of  the  inguinal  ligament,  from  the  anterior  two-thirds  of  the  middle 
lip  of  the  iliac  crest,  and  from  the  posterior  lamella  of  the  lumbodorsal  fascia. 
From  this  origin  the  fibers  diverge;  those  from  the  inguinal  ligament,  few  in  number 
and  paler  in  color  than  the  rest,  arch  downward  and  medialward  across  the  sper- 
matic cord  in  the  male  and  the  round  ligament  of  the  uterus  in  the  female,  and, 
becoming  tendinous,  are  inserted,  conjointly  with  those  of  the  Transversus,  into 
the  crest  of  the  pubis  and  medial  part  of  the  pectineal  line  behind  the  lacunar 
ligament,  forming  what  is  known  as  the  inguinal  aponeurotic  falx.    Those  from  the 


Inguinal  apo- 
neurotic falz 

Cremaster 


Fia.  395. — The  Obliquua  internua  abdominis. 


[anterior  third  of  the  iliac  origin  are  horizontal  in  their  direction,  and,  becoming 
tendinous  along  the  lower  fourth  of  the  linea  semilunaris,  pass  in  front  of  the  Rectus 
abdominis  to  be  inserted  into  the  linea  alba.  Those  arising  from  the  middle  third 
of  the  iliac  origin  run  obliquely  upward  and  medialward,  and  end  in  an  aponeurosis; 
this  divides  at  the  lateral  border  of  the  Rectus  into  two  lamellse,  which  are  con- 
tinued forward,  one  in  front  of  and  the  other  behind  this  muscle,  to  the  linea  alba: 
the  posterior  lamella  has  an  attachment  to  the  cartilages  of  the  seventh,  eighth, 
and  ninth  ribs.  The  most  posterior  fibers  pass  almost  vertically  upward,  to  be 
inserted  into  the  inferior  borders  of  the  cartilages  of  the  three  lower  ribs,  being 
continuous  with  the  Intercostales  interni. 


414 


MYOLOGY 


Variations.— Occasionally,  tendinous  inscriptions  occur  from  the  tips  of  the  tenth  or  eleventh 
cartilages  or  even  from  the  ninth;  an  additional  slip  to  the  ninth  cartilage  is  sometimes  found;' 
separation  between  iliac  and  inguinal  parts  may  occur. 

The  Cremaster  (Fig.  396)  is  a  thin  muscular  layer,  composed  of  a  number  of 
fasciculi  which  arise  from  the  middle  of  the  inguinal  ligament  where  its  fibers- 

are  continuous  with  those  of  the 
Obliquus  internus  and  also  occasion- 
ally with  the  Transversus.  It  passes 
along  the  lateral  side  of  the  spermatic 
cord,  descends  with  it  through  the  sub- 
cutaneous inguinal  ring  upon  the  front 
and  sides  of  the  cord,  and  forms  a  series 
of  loops  which  differ  in  thickness  and 
length  in  different  subjects.  At  the 
upper  part  of  the  cord  the  loops  are 
short,  but  they  become  in  succession 
longer  and  longer,  the  longest  reaching 
down  as  low  as  the  testis,  where  a  few 
are  inserted  into  the  tunica  vaginalis. 
These  loops  are  united  together  by 
areolar  tissue,  and  form  a  thin  cover- 
ing over  the  cord  and  testis,  the  cremas- 
teric fascia.  The  fibers  ascend  along 
the  medial  side  of  the  cord,  and  are 
inserted  by  a  small  pointed  tendon 
into  the  tubercle  and  crest  of  the 
pubis  and  into  the  front  of  the  sheath 
of  the  Rectus  abdominis. 

The  Transversus  abdominis  (Trans- 
versalis  vmscle)  (Fig.  397),  so  called 
from  the  direction  of  its  fibers,  is  the 
most  internal  of  the  flat  muscles  of 
the  abdomen,  being  placed  imme- 
diately beneath  the  Obliquus  internus.  It  arises,  by  fleshy  fibers,  from  the 
lateral  third  of  the  inguinal  ligament,  from  the  anterior  three-fourths  of  the,  inner 
lip  of  the  iliac  crest,  from  the  inner  surfaces  of  the  cartilages  of  the  lower  six 
ribs,  interdigitating  with  the  diaphragm,  and  from  the  lumbodorsal  fascia. 
The  muscle  ends  in  front  in  a  broad  aponeurosis,  the  lower  fibers  of  w^hich 
curve  downward  and  medial  ward,  and  are  inserted,  together  with  those  of  the 
Obliquus  internus,  into  the  crest  of  the  pubis  and  pectineal  line,  forming  the  ingui- 
nal aponeurotic  falx.  Throughout  the  rest  of  its  extent  the  aponeurosis  passes 
horizontally  to  the  middle  line,  and  is  inserted  into  the  linea  alba;  its  upper 
three-fourths  lie  behind  the  Rectus  and  blend  with  the  posterior  lamella  of  the 
aponeurosis  of  the  Obliquus  internus;  its  lower  fourth  is  in  front  of  the  Rectus. 

Variations. — It  may  be  more  or  less  fused  with  the  Obliquus  internus  or  absent.  The 
spermatic  cord  may  pierce  its  lower  border.  Slender  muscle  slips  from  the  ileopectineal  line  to 
transversalis  fascia,  the  aponeurosis  of  the  Transversus  abdominis,  or  the  outer  end  of  the  linea 
semicircularis  and  other  slender  slips  are  occasionally  found. 

The  inguinal  aponeurotic  falx  {falx  aponeurotica  inguinalis;  conjoined  tendon  of 
Internal  oblique  and  Transversalis  muscle)  of  the  Obliquus  internus  and  Trans- 
versus is  mainly  formed  by  the  lower  part  of  the  tendon  of  the  Transversus,  and 
is  inserted  into  the  crest  of  the  pubis  and  pectineal  line  immediately  behind 
the  subcutaneous  inguinal  ring,  serving  to  protect  what  would  otherwise  be  a 


Fig.  396.— The  Cremaster. 


THE  ANTERO-LATERAL  MUSCLES  OF  THE  ABDOMEN 


415 


weak  point  in  the  abdominal  wall.  Lateral  to  the  falx  is  a  ligamentous  band  con- 
nected with  the  lower  margin  of  the  Transversus  and  extending  down  in  front  of  the 
inferior  epigastric  artery  to  the  superior  ramus  of  the  pubis ;  it  is  termed  the  inter- 
foveolar  ligament  of  Hesselbach  (Fig.  398)  and  sometimes  contains  a  few  muscular 
fibers. 


397. — The  Transversus  abdominis,  Rectus  abdominis,  and  Pyramidalis. 


The  Rectus  abdominis  (Fig.  397)  is  a  long  flat  muscle,  which  extends  along 
the  whole  length  of  the  front  of  the  abdomen,  and  is  separated  from  its  fellow 
of  the  opposite  side  by  the  linea  alba.  It  is  much  broader,  but  thinner,  above  than 
below,  and  arises  by  tw^o  tendons;  the  lateral  or  larger  is  attached  to  the  crest 
of  the  pubis,  the  medial  interlaces  with  its  fellow  of  the  opposite  side,  and  is  con- 
nected with  the  ligaments  covering  the  front  of  the  symphysis  pubis.  The  muscle 
is  inserted  by  three  portions  of  unequal  size  into  the  cartilages  of  the  fifth,  sixth, 
and  seventh  ribs.    The  upper  portion,  attached  principally  to  the  cartilage  of  the 


416 


MYOLOGY 


fifth  rib,  usually  has  some  fibers  of  insertion  into  the  anterior  extremity  of  the  rib 
itself.  Some  fibers  are  occasionally  connected  with  the  costoxiphoid  ligaments, 
and  the  side  of  the  xiphoid  process.  ^_l 

The  Rectus  is  crossed  by  fibrous  bands,  three  in  number,  which  are  named  the  fl 
tendinous  inscriptions;  one  is  usually  situated  opposite  the  umbilicus,  one  at  the 
extremity  of  the  xiphoid  process,  and  the  third  about  midway  between  the  xiphoid 
process  and  the  umbilicus.  These  inscriptions  pass  transversely  or  obliquely 
across  the  muscle  in  a  zigzag  course;  they  rarely  extend  completely  through  its 
substance  and  may  pass  only  halfway  across  it;  they  are  intimately  adherent  in 
front  to  the  sheath  of  the  muscle.  Sometimes  one  or  tM^o  additional  inscriptions, 
generally  incomplete,  are  present  below  the  umbilicus. 


Linea 
semicircularis 


Transmrsus 


Beetus 
abdominis 


Inferior  epigastric 
artery  arid  vein 


Obliquus 
intemus 


Inguinal  aponeurotic  falx       Interjoveolar  ligament 

Fig.  398. — The  interfoveolar  ligament,  seen  from  in  front.     (Modified  from  Braune.) 


The  Rectus  is  enclosed  in  a  sheath  (Fig.  399)  formed  by  the  aponeuroses  of  the 
Obliqui  and  Transversus,  which  are  arranged  in  the  following  manner.  At  the  lateral 
margin  of  the  Rectus,  the  aponeurosis  of  the  Obliquus  intemus  divides  into  two 
lamellae,  one  of  which  passes  in  front  of  the  Rectus,  blending  with  the  aponeurosis 
of  the  Obliquus  externus,  the  other,  behind  it,  blending  with  the  aponeurosis  of 
the  Transversus,  and  these,  joining  again  at  the  medial  border  of  the  Rectus, 
are  inserted  into  the  linea  alba.  This  arrangement  of  the  aponeurosis  exists  from 
the  costal  margin  to  midway  between  the  umbilicus  and  symphysis  pubis,  where 
the  posterior  wall  of  the  sheath  ends  in  a  thin  curved  margin,  the  linea  semicircu- 
laris, the  concavity  of  which  is  directed  downward :  below  this  level  the  aponeuroses 
of  all  three  muscles  pass  in  front  of  the  Rectus.  The  Rectus,  in  the  situation  where 
its  sheath  is  deficient  below,  is  separated  from  the  peritoneum  by  the  transversalis 
fascia  (Fig.  400).  Since  the  tendons  of  the  Obliquus  intemus  and  Transversus 
only  reach  as  high  as  the  costal  margin,  it  follows  that  above  this  level  the  sheath 
of  the  Rectus  is  deficient  behind,  the  muscle  resting  directly  on  the  cartilages  of 
the  ribs,  and  being  covered  merely  by  the  tendon  of  the  Obliquus  externus. 

The  Pyramidalis  (Fig.  397)  is  a  small  triangular  muscle,  placed  at  the  lower 
part  of  the  abdomen,  in  front  of  the  Rectus,  and  contained  in  the  sheath  of  that 


THE  ANTERO-LATERAL  MUSCLES  OF  THE  ABDOMEN 


417 


muscle.  It  arises  by  tendinous  fibers  from  the  front  of  the  pubis  and  the  anterior 
pubic  ligament;  the  fleshy  portion  of  the  muscle  passes  upward,  diminishing 
in  size  as  it  ascends,  and  ends  by  a  pointed  extremity  which  is  inserted  into  the 
linea  alba,  midway  between  the  umbilicus  and  pubis.  This  muscle  may  be  wanting 
on  one  or  both  sides;  the  lower  end  of  the  Rectus  then  becomes  proportionately 
increased  in  size.  Occasionally  it  is  double  on  one  side,  and  the  muscles  of  the  two 
sides  are  sometimes  of  unequal  size.    It  may  extend  higher  than  the  level  stated. 


Linea  alba 


Ohliquus  intemug  > 

TransverstiS 
Fig.  399. — Diagram  of  sheath  of  Rectus. 


Besides  the  Rectus  and  Pyramidalis,  the  sheath  of  the  Rectus  contains  the  superior  and  inferior 
epigastric  arteries,  and  the  lower  intercostal  nerves. 

Variations. — The  Rectus  may  insert  as  high  as  the  fourth  ot  third  rib  or  may  fail  to  reach  the 
fifth.    Fibers  may  spring  from  the  lower  part  of  the  linea  alba. 

Nerves. — The  abdominal  muscles  are  supphed  by  the  lower  intercostal  nerves.  The  Obliquus 
internus  and  Transversus  also  receive  filaments  from  the  anterior  branch  of  the  iliohypogastric 
and  sometimes  from  the  iUoinguinal.  The  Cremaster  is  suppUed  by  the  external  spermatic  branch 
of  the  genitofemoral  and  the  PyramidaUs  usually  by  the  twelfth  thoracic. 

The  Linea  Alba. — The  linea  alba  is  a  tendinous  raphe  in  the  middle  line  of  the  abdomen, 
stretching  between  the  xiphoid  process  and  the  symphysis  pubis.  It  is  placed  between  the  medial 
borders  of  the  Recti,  and  is  formed  by  the  blending  of  the  aponeuroses  of  the  Obliqui  and  Trans- 
versa It  is  narrow  below,  corresponding  to  the  hnear  interval  existing  between  the  Recti;  but 
broader  above,  where  these  muscles  diverge  from  one  another.  At  its  lower  end  the  Unea  alba 
has  a  double  attachment — its  superficial  fibers  passing  in  front  of  the  medial  heads  of  the  Recti 
to  the  symphysis  pubis,  while  its  deeper  fibers  form  a  triangular  lamella,  attached  behind  the 
Recti  to  the  posterior  lip  of  the  crest  of  the  pubis,  and  named  the  adminiculum  lines  albse. 
It  presents  apertures  for  the  passage  of  vessels  and  nerves;  the  umbihcus,  which  in  the  fetus 
exists  as  an  aperture  and  transmits  the  umbiHcal  vessels,  is  closed  in  .the  adult. 


Obliquug  extemua . 
Obliquus  internus  - 

Transversusy 
Fig.  400. — Diagram  of  a  transverse  section  through  the  anterior  abdomina   wall,  below  the  linea  semicircularis 

The  Linese  Semilunares. — The  hneae  semilimares  are  two  curved  tendinous  fines  placed  one 
on  either  side  of  the  hnea  alba.  Each  corresponds  with  the  lateral  border  of  the  Rectus,  extends 
from  the  cartilage  of  the  ninth  rib  to  the  pubic  tubercle,  and  is  formed  by  the  aponeurosis  of  the 
Obliquus  internus  at  its  line  of  division  to  enclose  the  Rectus,  reinforced  in  front  by  that  of  the 
Obhquus  extemus,  and  behind  by  that  of  the  Transversus. 

Actions. — When  the  pelvis  and  thorax  are  fixed,  the  abdominal  muscles  compress  the  abdominal 
viscera  by  constricting  the  cavity  of  the  abdomen,  in  which  action  they  are  materially  assisted 
by  the  descent  of  the  diaphragm.  By  these  means  assistance  is  given  in  expelling  the  feces 
from  the  rectmn,  the  urine  from  the  bladder,  the  fetus  from  the  uterus,  and  the  contents  of  the 
stomach  in  vomiting. 

If  the  pelvis  and  vertebral  column  be  fixed,  these  muscles  compress  the  lower  part  of  the  thorax, 
materially  assisting  expiration.    If  the  pelvis  alone  be  fixed,  the  thorax  is  bent  directly  forward, 
when  the  muscles  of  both  sides  act;  when  the  muscles  of  only  one  side  contract,  the  trunk  is  bent 
toward  that  side  and  rotated  toward  the  opposite  side. 
27 


418  MYOLOGY 

If  the  thorax  be  fixed,  the  muscles,  acting  together,  draw  the  pelvis  upward,  as  in  climbing; 
or,  acting  singly,  they  draw  the  pelvis  upward,  and  bend  the  vertebral  column  to  one  side  or  the 
other.  The  Recti,  acting  from  below,  depress  the  thorax,  and  consequently  flex  the  vertebral 
column ;  when  acting  from  above,  they  flex  the  pelvis  upon  the  vertebral  column.  The  Pyramidales 
are  tensors  of  the  linea  alba. 

The  Transversalis  Fascia. — The  transversalis  fascia  is  a  thin  aponeurotic  membrane 
which  lies  between  the  inner  surface  of  the  Transversus  and  the  extraperitoneal 
fat.  It  forms  part  of  the  general  layer  of  fascia  lining  the  abdominal  parietes,  and 
is  directly  continuous  with  the  iliac  and  pelvic  fasciae.  In  the  inguinal  region, 
the  transversalis  fascia  is  thick  and  dense  in  structure  and  is  joined  by  fibers  from 
the  aponeurosis  of  the  Transversus,  but  it  becomes  thin  as  it  ascends  to  the  dia- 
phragm, and  blends  with  the  fascia  covering  the  under  surface  of  this  muscle. 
Behind,  it  is  lost  in  the  fat  which  covers  the  posterior  surfaces  of  the  kidneys. 
Below,  it  has  the  following  attachments:  posteriorly,  to  the  whole  length  of  the  iliac 
crest,  between  the  attachments  of  the  Transversus  and  Iliacus;  between  the  ante- 
rior superior  iliac  spine  and  the  femoral  vessels  it  is  connected  to  the  posterior 
margin  of  the  inguinal  ligament,  and  is  there  continuous  with  the  iliac  fascia. 
Medial  to  the  femoral  vessels  it  is  thin  and  attached  to  the  pubis  and  pectineal 
line,  behind  the  inguinal  aponeurotic  falx,  with  which  it  is  united;  it  descends  in 
front  of  the  femoral  vessels  to^rm  the  anterior  wall  of  the  femoral  sheath.  Beneath 
the  inguinal  ligament  it  is  strengthened  by  a  band  of  fibrous  tissue,  which  is  only 
loosely  connected  to  the  ligament,  and  is  specialized  as  the  deep  crural  arch.  The 
spermatic  cord  in  the  male  and  the  round  ligament  of  the  uterus  in  the  female 
pass  through  the  transversalis  fascia  at  a  spot  called  the  abdominal  inguinal  ring. 
This  opening  is  not  visible  externally,  since  the  transversalis  fascia  is  prolonged  on 
these  structures  as  the  infundibuliform  fascia. 

The  Abdominal  Inguinal  Ring  (annulus  inguinalis  abdominis;  internal  or  deep 
abdominal  ring). — The  abdominal  inguinal  ring  is  situated  in  the  transversalis 
fascia,  midway  between  the  anterior  superior  iliac  spine  and  the  symphysis  pubis, 
and  about  1.25  cm.  above  the  inguinal  ligament  (Fig.  401).  It  is  of  an  oval  form, 
the  long  axis  of  the  oval  being  vertical;  it  varies  in  size  in  different  subjects,  and 
is  much  larger  in  the  male  than  in  the  female.  It  is  bounded,  above  and  laterally, 
by  the  arched  lower  margin  of  the  Transversus ;  below  and  medially,  by  the  inferior 
epigastric  vessels.  It  transmits  the  spermatic  cord  in  the  male  and  the  round 
ligament  of  the  uterus  in  the  female.  From  its  circumference  a  thin  funnel-shaped 
membrane,  the  infundibuliform  fascia,  is  continued  around  the  cord  and  testis, 
enclosing  them  in  a  distinct  covering. 

The  Inguinal  Canal  (canalis  inguinalis;  spermatic  canal). — The  inguinal  canal 
contains  the  spermatic  cord  and  the  ilioinguinal  nerve  in  the  male,  and  the  round 
ligament  of  the  uterus  and  the  ilioinguinal  nerve  in  the  female.  It  is  an  oblique 
canal  about  4  cm.  long,  slanting  downward  and  medialward,  and  placed  parallel 
with  and  a  little  above  the  inguinal  ligament;  it  extends  from  the  abdominal 
inguinal  ring  to  the  subcutaneous  inguinal  ring.  It  is  bounded,  m  front,  by  the 
integument  and  superficial  fascia,  by  the  aponeurosis  of  the  Obliquus  externus 
throughout  its  whole  length,  and  by  the  Obliquus  internus  in  its  lateral  third; 
behind,  by  the  reflected  inguinal  ligament,  the  inguinal  aponeurotic  falx,  the  trans- 
versalis fascia,  the  extraperitoneal  connective  tissue  and  the  peritoneum;  above, 
by  the  arched  fibers  of  Obliquus  internus  and  Transversus  abdominis;  below,  by 
the  union  of  the  transversalis  fascia  with  the  inguinal  ligament,  and  at  its  medial 
end  by  the  lacunar  ligament. 

Extraperitoneal  Connective  Tissue.— Between  the  inner  surface  of  the  general 
layer  of  the  fascia  which  lines  the  interior  of  the  abdominal  and  pelvic  cavities, 
and  the  peritoneum,  there  is  a  considerable  amount  of  connective  tissue,  termed 
the  extraperitoneal  or  subperitoneal  connective  tissue. 


THE  POSTERIOR  MUSCLES  OF  THE  ABDOMEN 


419 


I 


The  parietal  portion  lines  the  cavity  in  varying  quantities  in  different  situations. 
It  is  especially  abundant  on  the  posterior  wall  of  the  abdomen,  and  particularly 
around  the  kidneys,  where  it  contains  much  fat.  On  the  anterior  wall  of  the  abdo- 
men, except  in  the  pubic  region,  and  on  the  lateral  wall  above  the  iliac  crest, 
it  is  scanty,  and  here  the  transversalis  fascia  is  more  closely  connected  with  the 
peritoneum.  There  is  a  considerable  amount  of  extraperitoneal  connective  tissue 
in  the  pelvis. 

The  visceral  portion  follows  the  course  of  the  branches  of  the  abdominal  aorta 
between  the  layers  of  the  mesenteries  and  other  folds  of  peritoneum  which  connect 
the  various  viscera  to  the  abdominal  wall.  The  two  portions  are  directly  con- 
tinuous with  each  other. 


bdominal  inguinal 

ring 

Inf.  epigastric  artery  -4 — 


Fia.  401. — The  abdominal  inguinal  ring. 

The  Deep  Crural  Arch. — Curving  over  the  external  iliac  vessels,  at  the  spot  where 
they  become  femoral,  on  the  abdominal  side  of  the  inguinal  ligaments  and  loosely 
connected  with  it,  is  a  thickened  band  of  fibers  called  the  deep  crural  arch.  It 
is  apparently  a  thickening  of  the  transversalis  fascia  joined  laterally  to  the  center 
of  the  lower  margin  of  the  inguinal  ligament,  and  arching  across  the  front  of 
the  femoral  sheath  to  be  inserted  by  a  broad  attachment  into  the  pubic  tubercle 
and  pectineal  line,  behind  the  inguinal  aponeurotic  falx.  In  some  subjects  this 
structure  is  not  very  prominently  marked,  and  not  infrequently  it  is  altogether 
wanting. 

2.  The  Posterior  Muscles  of  the  Abdomen. 


Psoas  major. 
Psoas  minor. 


Iliacus. 

Quadratus  lumborum. 


The  Psoas  major,  the  Psoas  minor,  and  the  Iliacus,  with  the  fasciae  covering 
them,  will  be  described  with  the  muscles  of  the  lower  extremity  (see  page  466). 

The  Fascia  Covering  the  Quadratus  Lumborum. — This  is  a  thin  layer  attached, 
medially,  to  the  bases  of  the  transverse  processes  of  the  lumbar  vertebrae;  below, 


420  MYOLOGY 

to  the  iliolumbar  ligament;  above,  to  the  apex  and  lower  border  of  the  last  rib. 
The  upper  margin  of  this  fascia,  which  extends  from  the  transverse  process  of  the 
first  lumbar  vertebra  to  the  apex  and  lower  border  of  the  last  rib,  constitutes  the 
lateral  lumbocostal  arch  (page  405).  Laterally,  it  blends  with  the  lumbodorsal 
fascia,  the  anterior  layer  of  which  intervenes  between  the  Quadratus  lumborum 
and  the  Sacrospinalis. 

The  Quadratus  lumborum  (Fig.  389,  page  398)  is  irregularly  quadrilateral  in 
shape,  and  broader  below  than  above.  It  arises  by  aponeurotic  fibers  from  the 
iliolumbar  ligament  and  the  adjacent  portion  of  the  iliac  crest  for  about  5  cm., 
and  is  inserted  into  the  lower  border  of  the  last  rib  for  about  half  its  length,  and 
by  four  small  tendons  into  the  apices  of  the  transverse  processes  of  the  upper  four 
lumbar  vertebrae.  Occasionally  a  second  portion  of  this  muscle  is  found  in  front 
of  the  preceding.  It  arises  from  the  upper  borders  of  the  transverse  processes  of 
the  lower  three  or  four  lumbar  vertebrae,  and  is  inserted  into  the  lower  margin  of 
the  last  rib.  In  front  of  the  Quadratus  lumborum  are  the  colon,  the  kidney,  the 
Psoas  major  and  minor,  and  the  diaphragm;  between  the  fascia  and  the  muscle 
are  the  twelfth  thoracic,  ilioinguinal,  and  iliohypogastric  nerves. 

Variations. — The  number  of  attachments  to  the  vertebrae  and  the  extent  of  its  attachment  to 
the  last  rib  vary. 

Nerve  Supply. — The  twelfth  thoracic  and  first  and  second  lumbar  nerves  supply  this  muscle. 

Actions. — The  Quadratus  lumborvun  draws  down  the  last  rib,  and  acts  as  a  muscle  of  inspira- 
tion by  helping  to  fix  the  origin  of  the  diaphragm.  If  the  thorax  and  vertebral  column  are 
fixed,  it  may  act  upon  the  pelvis,  raising  it  toward  its  own  side  when  only  one  muscle  is  put  in 
action;  and  when  both  muscles  act  together,  either  from  below  or  above,  they  flex  the  trunk. 


V.     THE  MUSCLES  AND  FASCIA  OF  THE  PELVIS. 

Obturator  internus.  Levator  ani. 

Piriformis.  Coccygeus. 

The  muscles  within  the  pelvis  may  be  divided  into  two  groups :  (1)  the  Obturator 
internus  and  the  Piriformis,  which  are  muscles  of  the  lower  extremity,  and  will  be 
described  with  these  (pages  476  and  477) ;  (2)  the  Levator  ani  and  the  Coccygeus, 
which  together  form  the  pelvic  diaphragm  and  are  associated  with  the  pelvic  viscera. 
The  classification  of  the  two  groups  under  a  common  heading  is  convenient  in 
connection  with  the  fasciae  investing  the  muscles.  These  fasciae  are  closely  related 
to  one  another  and  to  the  deep  fascia  of  the  perineum,  and  in  addition  have  special 
connections  with  the  fibrous  coverings  of  the  pelvic  viscera ;  it  is  customary  there- 
fore to  describe  them  together  under  the  term  pelvic  fascia. 

Pelvic  Fascia. — The  fascia  of  the  pelvis  may  be  resolved  into:  (a)  the  fascial 
sheaths  of  the  Obturator  internus.  Piriformis,  and  pelvic  diaphragm;  (b)  the 
fascia  associated  with  the  pelvic  viscera. 

The  fascia  of  the  Obturator  internus  covers  the  pelvic  surface  of,  and  is  attached 
around  the  margin  of  the  origin  of,  the  muscle.  Above,  it  is  loosely  connected  to 
the  back  part  of  the  arcuate  line,  and  here  it  is  continuous  with  the  iliac  fascia. 
In  front  of  this,  as  it  follows  the  line  of  origin  of  the  Obturator  internus,  it  gradually 
separates  from  the  iliac  fascia  and  the  continuity  between  the  two  is  retained  only 
through  the  periosteum.  It  arches  beneath  the  obturator  vessels  and  nerve,  com- 
pleting the  obturator  canal,  and  at  the  front  of  the  pelvis  is  attached  to  the  back 
of  the  superior  ramus  of  the  pubis.  Below,  the  obturator  fascia  is  attached  to  the 
falciform  process  of  the  sacrotuberous  ligament  and  to  the  pubic  arch,  where  it 
becomes  continuous  with  the  superior  fascia  of  the  urogenital  diaphragm.  Behind, 
it  is  prolonged  into  the  gluteal  region. 

The  internal  pudendal  vessels  and  pudendal  nerve  cross  the  pelvic  surface  of 


I 


THE  MUSCLES  AND  FASCIA  OF  THE  PELVIS 


421 


the  Obturator  internus  and  are  enclosed  in  a  special  canal — Alcock's  canal — 
formed  by  the  obturator  fascia. 

The  fascia  of  the  Piriformis  is  very  thin  and  is  attached  to  the  front  of  the  sacrum 
and  the  sides  of  the  greater  sciatic  foramen;  it  is  prolonged  on  the  muscle  into 
the  gluteal  region.  At  its  sacral  attachment  around  the  margins  of  the  anterior 
sacral  foramina  it  comes  into  intimate  association  with  and  ensheathes  the 
nerves  emerging  from  these  foramina.  Hence  the  sacral  nerves  are  frequently 
described  as  lying  behind  the  fascia.  The  internal  iliac  vessels  and  their  branches, 
on  the  other  hand,  lie  in  the  subperitoneal  tissue  in  front  of  the  fascia,  and  the 
branches  to  the  gluteal  region  emerge  in  special  sheaths  of  this  tissue,  above  and 
below  the  Piriformis  muscle. 


,_.    ,  (Srtperior 

Diaphragmatic  I     layer 
part  of  pelvic  J 

fascia  Inferior 

\   layer 

Tendinous  arch 


Fascia  endopelvina 
Vesicida  seminalie 

Ductus  deferens 
Rectovegical  layer 

Fig.  402. — Coronal  section  of  pelvis,  showing  arrangement  of  fasciae.     Viewed  from  behind.    (Diagrammatic.) 


The  diaphragmatic  part  of  the  pelvic  fascia  (Fig.  402)  covers  both  surfaces  of  the 
Levatores  ani.  The  inferior  layer  is  known  as  the  anal  fascia;  it  is  attached  above 
to  the  obturator  fascia  along  the  line  of  origin  of  the  Levator  ani,  while  below  it 
is  continuous  with  the  superior  fascia  of  the  urogenital  diaphragm,  and  with  the 
fascia  on  the  Sphincter  ani  internus.  The  layer  covering  the  upper  surface  of  the 
pelvic  diaphragm  follows,  above,  the  line  of  origin  of  the  Levator  ani  and  is  there- 
fore somewhat  variable.  In  front  it  is  attached  to  the  back  of  the  symphysis 
pubis  about  2  cm.  above  its  lower  border.  It  can  then  be  traced  laterally  across 
the  back  of  the  superior  ramus  of  the  pubis  for  a  distance  of  about  L25  cm.,  when 
it  reaches  the  obturator  fascia.  It  is  attached  to  this  fascia  along  a  line  which 
pursues  a  somewhat  irregular  course  to  the  spine  of  the  ischium.  The  irregularity 
of  this  line  is  due  to  the  fact  that  the  origin  of  the  Levator  ani,  which  in  lower 
forms  is  from  the  pelvic  brim,  is  in  man  lower  down,  on  the  obturator  fascia. 
Tendinous  fibers  of  origin  of  the  muscle  are  therefore  often  found  extending  up 
toward,  and  in  some  cases  reaching,  the  pelvic  brim,  and  on  these  the  fascia  is 
carried. 

It  will  be  evident  that  the  fascia  covering  that  part  of  the  Obturator  internus 
which  lies  above  the  origin  of  the  Levator  ani  is  a  composite  fascia  and  includes 
the  following:  (a)  the  obturator  fascia;  (b)  the  fascia  of  the  Levator  ani;  (c) 
degenerated  fibers  of  origin  of  the  Levator  ani. 


422 


MYOLOGY 


The  lower  margin  of  the  fascia  covering  the  upper  surface  of  the  pelvic  diaphragm 
is  attached  along  the  line  of  insertion  of  the  Levator  ani.  ^i 

At  the  level  of  a  line  extending  from  the  lower  part  of  the  symphysis  pubis"' 
to  the  spine  of  the  ischium  is  a  thickened  whitish  band  in  this  upper  layer  of  the 
diaphragmatic  part  of  the  pelvic  fascia.    It  is  termed  the  tendinous  arch  or  white 
line  of  the  pelvic  fascia,  and  marks  the  line  of  attachment  of  the  special  fascia 
(pars  endopelvina  fascice  pelvis)  which  is  associated  with  the  pelvic  viscera. 


Peritoneum 


Vesical  layer 


Fascia  0/  {^^^^ 
urogenital  ->  j^l.,.^ 
diaphragm  y    ^^^^ 


Vesicula 
"seminalis 

Rectovesical  layer 

!  _  Capsule  of 

prostate 


Rectal  layer 

Transverstis  perincei  superficialis 
Collet  fascia 
Urogenital  diaphragm 
Fig.  403. — Median  sagittal  section  of  pelvis,  showing  arrangement  of  fascise. 

The  endopelvic  part  of  the  pelvic  fascia  is  continued  over  the  various  pelvic 
viscera  (Fig.  403)  to  form  for  them  fibrous  coverings  which  will  be  described  later 
(see  section  on  Splanchnology).  It  is  attached  to  the  diaphragmatic  part  of  the 
pelvic  fascia  along  the  tendinous  arch,  and  has  been  subdivided  in  accordance 
with  the  viscera  to  which  it  is  related.  Thus  its  anterior  part,  known  as  the  vesical 
layer,  forms  the  anterior  and  lateral  ligaments  of  the  bladder.  Its  middle  part 
crosses  the  floor  of  the  pelvis  between  the  rectum  and  vesiculse  seminales  as  the 
rectovesical  layer;  in  the  female  this  is  perforated  by  the  vagina.  Its  posterior 
portion  passes  to  the  side  of  the  rectum;  it  forms  a  loose  sheath  for  the  rectum, 
but  is  firmly  attached  around  the  anal  canal ;  this  portion  is  known  as  the  rectal 
layer. 

The  Levator  ani  (Fig.  404)  is  a  broad,  thin  muscle,  situated  on  the  side  of  the 
pelvis.    It  is  attached  to  the  inner  surface  of  the  side  of  the  lesser  pelvis,  and  unites 


THE  MUSCLES  AND  FASCIA  OF  THE  PELVIS 


423 


with  its  fellow  of  the  opposite  side  to  form  the  greater  part  of  the  floor  of  the  pelvic 
cavity.  It  supports  the  viscera  in  this  cavity,  and  surrounds  the  various  structures 
which  pass  through  it.  It  arises,  in  front,  from  the  posterior  surface  of  the  superior 
ramus  of  the  pubis  lateral  to  the  symphysis;  behind,  from  the  inner  surface  of  the 
spine  of  the  ischium;  and  between  these  two  points,  from  the  obturator  fascia. 
Posteriorly,  this  fascial  origin  corresponds,  more  or  less  closely,  with  the  tendinous 
arch  of  the  pelvic  fascia,  but  in  front,  the  muscle  arises  from  the  fascia  at  a  vary- 
ing distance  above  the  arch,  in  some  cases  reaching  nearly  as  high  as  the  canal 


Superior  glutccal  vessels 


Obturator  nerve 
and  vessels 


Left  lobe  of  prostate  (cut) 


Anococcygeal  raphe 


Fia.  404. — Left  Levator  ani  from  within. 

for  the  obturator  vessels  and  nerve.  The  fibers  pass  downward  and  backward 
to  the  middle  line  of  the  floor  of  the  pelvis;  the  most  posterior  are  inserted  into  the 
side  of  the  last  two  segments  of  the  coccyx;  those  placed  more  anteriorly  unite 
with  the  muscle  of  the  opposite  side,  in  a  median  fibrous  raphe  (anococcygeal 
raphe),  which  extends  between  the  coccyx  and  the  margin  of  the  anus.  The  middle 
fibers  are  inserted  into  the  side  of  the  rectum,  blending  with  the  fibers  of  the 
Sphincter  muscles;  lastly,  the  anterior  fibers  descend  upon  the  side  of  the  prostate 
to  unite  beneath  it  with  the  muscle  of  the  opposite  side,  joining  with  the  fibers  of 
the  Sphincter  ani  externus  and  Transversus  perinsei,  at  the  central  tendinous  point 
of  the  perineum. 


424  MYOLOGY 

The  anterior  portion  is  occasionally  separated  from  the  rest  of  the  muscle  by 
connective  tissue.  From  this  circumstance,  as  well  as  from  its  peculiar  relation 
with  the  prostate,  which  it  supports  as  in  a  sling,  it  has  been  described  as  a  distinct 
muscle,  under  the  name  of  Levator  prostatse.  In  the  female  the  anterior  fibers  of 
the  Levator  ani  descend  upon  the  side  of  the  vagina. 

The  Levator  ani  may  be  divided  into  iliococcygeal  and  pubococcygeal  parts. 

The  Iliococcygeus  arises  from  the  ischial  spine  and  from  the  posterior  part  of  the  tendinous 
arch  of  the  pelvic  fascia,  and  is  attached  to  the  coccyx  and  anococcygeal  raph6;  it  is  usually  thin, 
and  may  fail  entirely,  or  be  largely  replaced  by  fibrous  tissue.  An  accessory  slip  at  its  posterior 
part  is  sometimes  named  the  Iliosacralis.  The  Pubococcygeus  arises  from  the  back  of  the  pubis 
and  from  the  anterior  part  of  the  obturator  fascia,  and  "is  dii-ected  backward  almost  horizontally 
along  the  side  of  the  anal  canal  toward  the  coccyx  and  sacrum,  to  which  it  finds  attachment. 
Between  the  termination  of  the  vertebral  column  and  the  anus,  the  two  Pubococcygei  muscles 
come  together  and  form  a  thick,  fibromuscular  layer  lying  on  the  raphe  formed  by  the  Ihococcygei" 
(Peter  Thompson).  The  greater  part  of  this  muscle  is  inserted  into  the  coccyx  and  into  the  last 
one  or  two  pieces  of  the  sacrum.  This  insertion  into  the  vertebral  column  is,  however,  not 
admitted  by  all  observers.  The  fibers  which  form  a  sling  for  the  rectum  are  named  the  Pubo- 
rectalis  or  Sphincter  recti.  They  arise  from  the  lower  part  of  the  symphysis  pubis,  and  from  the 
superior  fascia  of  the  urogenital  diaphragm.  They  meet  with  the  corresponding  fibers  of  the 
opposite  side  around  the  lower  part  of  the  rectum,  and  form  for  it  a  strong  sUng. 

Nerve  Supply. — The  Levator  ani  is  suppUed  by  a  branch  from  the  fourth  sacral  nerve  and 
by  a  branch  which  is  sometimes  derived  from  the  perineal,  sometimes  from  the  inferior  hemor- 
rhoidal division  of  the  pudendal  nerve. 

The  Coccygeus  (Fig.  404)  is  situated  behind  the  preceding.  It  is  a  triangular 
plane  of  muscular  and  tendinous  fibers,  arising  by  its  apex  from  the  spine  of  the 
ischium  and  sacrospinous  ligament,  and  inserted  by  its  base  into  the  margin  of  the 
coccyx  and  into  the  side  of  the  lowest  piece  of  the  sacrum.  It  assists  the  Levator 
ani  and  Piriformis  in  closing  in  the  back  part  of  the  outlet  of  the  pelvis. 

Nerve  Supply. — The  Coccygeus  is  supplied  by  a  branch  from  the  fourth  and  fifth  sacral  nerves. 

Actions. — The  Levatores  ani  constrict  the  lower  end  of  the  rectum  and  vagina.  They  elevate 
and  invert  the  lower  end  of  the  rectum  after  it  has  been  protruded  and  everted  during  the  expul- 
sion of  the  feces.  They  are  also  muscles  of  forced  expiration.  The  Coccygei  pull  forward  and 
support  the  coccyx,  after  it  has  been  pressed  backward  during  defecation  or  parturition.  The 
Levatores  ani  and  Coccygei  together  form  a  muscular  diaphragm  which  supports  the  pelvic 
viscera. 

VI.    THE   MUSCLES    AND    FASCMJ    OF   THE   PERINEUM. 

The  perineum  corresponds  to  the  outlet  of  the  pelvis.  Its  deep  boundaries 
are — in  front,  the  pubic  arch  and  the  arcuate  ligament  of  the  pubis;  behind,  the  tip 
of  the  coccyx;  and  on  either  side  the  inferior  rami  of  the  pubis  and  ischium,  and  the 
sacrotuberous  ligament.  The  space  is  somewhat  lozenge-shaped  and  is  limited 
on  the  surface  of  the  body  by  the  scrotum  in  front,  by  the  buttocks  behind,  and 
laterally  by  the  medial  side  of  the  thigh.  A  line  drawn  transversely  across  in 
front  of  the  ischial  tuberosities  divides  the  space  into  two  portions.  The  pos- 
terior contains  the  termination  of  the  anal  canal  and  is  known  as  the  anal  region; 
the  anterior,  which  contains  the  external  urogenital  organs,  is  termed  the  urogenital 
region. 

The  muscles  of  the  perineum  may  therefore  be  divided  into  two  groups: 

1.  Those  of  the  anal  region. 

2.  Those  of  the  urogenital  region:  a,  In  the  male;  b.  In  the  female. 

L  The  Muscles  of  the  Anal  Region. 

Corrugator  cutis  ani.  Sphincter  ani  externus.        Sphincter  ani  internus. 

The  Superficial  Fascia. — The  superficial  fascia  is  very  thick,  areolar  in  texture, 
and  contains  much  fat  in  its  meshes.    On  either  side  a  pad  of  fatty  tissue  extends 


THE  MUSCLES  OF  THE  ANAL  REGION 


425 


i 


deeply  between  the  Levator  ani  and  Obturator  internus  into  a  space  known  as  the 
ischiorectal  fossa. 

The  Deep  Fascia. — The  deep  fascia  forms  the  lining  of  the  ischiorectal  fossa; 
it  comprises  the  anal  fascia,  and  the  portion  of  obturator  fascia  below  the  origin 
of  Levator  ani. 

Ischiorectal  Fossa  {fossa  ischioredalis)  (Fig.  405). — The  fossa  is  somewhat  pris- 
matic in  shape,  with  its  base  directed  to  the  surface  of  the  perineum,  and  its  apex 
at  the  line  of  meeting  of  the  obturator  and  anal  fasciae.  It  is  bounded  medially 
by  the  Sphincter  ani  externus  and  the  anal  fascia ;  laterally,  by  the  tuberosity  of 
the  ischium  and  the  obturator  fascia;  anteriorly,  by  the  fascia  of  Colles  covering 
the  Transversus  perinsei  superficialis,  and  by  the  inferior  fascia  of  the  urogenital 
diaphragm;  posteriorly,  by  the  Glutseus  maximus  and  the  sacrotuberous  ligament. 
Crossing  the  space  transversely  are  the  inferior  hemorrhoidal  vessels  and  nerves; 


Fig.  405. — The  perineum.     The  integument  and  superficial  layer  of  superficial  fascia  reflected. 


at  the  back  part  are  the  perineal  and  perforating  cutaneous  branches  of  the 
pudendal  plexus;  while  from  the  forepart  the  posterior  scrotal  (or  labial)  vessels 
and  nerves  emerge.  The  internal  pudendal  vessels  and  pudendal  nerve  lie  in 
Alcock's  canal  on  the  lateral  wall.  The  fossa  is  filled  with  fatty  tissue  across 
which  numerous  fibrous  bands  extend  from  side  to  side. 

The  Comigator  Cutis  Ani.— Around  the  anus  is  a  thin  stratum  of  involuntary 
muscular  fiber,  which  radiates  from  the  orifice.  Medially  the  fibers  fade  off  into 
the  submucous  tissue,  while  laterally  they  blend  with  the  true  skin.  By  its  contrac- 
tion it  raises  the  skin  into  ridges  around  the  margin  of  the  anus. 

The  Sphincter  ani  externus  {External  sphincter  ani)  (Fig  405)  is  a  flat  plane 
of  muscular  fibers,  elliptical  in  shape  and  intimately  adherent  to  the  integument 
surrounding  the  margin  of  the  anus.  It  measures  about  8  to  10  cm.  in  length,  from 
its  anterior  to  its  posterior  extremity,  and  is  about  2.5  cm.  broad  opposite  the 
anus.    It  consists  of  two  strata,  superficial  and  deep.    The  superficial,  constituting 


426  MYOLOGY 

the  main  portion  of  the  muscle,  arises  from  a  narrow  tendinous  band,  the  anococcy- 
geal raphe,  which  stretches  from  the  tip  of  the  coccyx  to  the  posterior  margin  offll 
the  anus;  it  forms  two  flattened  planes  of  muscular  tissue,  which  encircle  the  anus™' 
and  meet  in  front  to  be  inserted  into  the  central  tendinous  point  of  the  perineum, 
joining  with  the  Transversus  perinsei  superficialis,  the  Levator  ani,  and  the  Bul- 
bocavernosus.  The  deeper  portion  forms  a  complete  sphincter  to  the  anal  canal. 
Its  fibers  surround  the  canal,  closely  applied  to  the  Sphincter  ani  internus,  and  in 
front  blend  with  the  other  muscles  at  the  central  point  of  the  perineum.  In  a 
considerable  proportion  of  cases  the  fibers  decussate  in  front  of  the  anus,  and  are 
continuous  with  the  Transversi  perinaei  superficiales.  Posteriorly,  they  are  not 
attached  to  the  coccyx,  but  are  continuous  with  those  of  the  opposite  side  behind 
the  anal  canal.  The  upper  edge  of  the  muscle  is  ill-defined,  since  fibers  are  given 
off  from  it  to  join  the  Levator  ani. 

Nerve  Supply. — A  branch  from  the  fourth  sacral  and  twigs  from  the  inferior  hemorrhoidal 
branch  of  the  pudendal  supply  the  muscle. 

Actions. — The  action  of  this  muscle  is  pecuUar.  (1)  It  is,  like  other  muscles,  always  in  a  state 
of  tonic  contraction,  and  having  no  antagonistic  muscle  it  keeps  the  anal  canal  and  orifice  closed. 

(2)  It  can  be  put  into  a  condition  of  greater  contraction  under  the  influence  of  the  will,  so  as 
more  firmly  to  occlude  the  anal  aperture,  in  expiratory  efforts  unconnected  with  defecation. 

(3)  Taking  its  fixed  point  at  the  coccyx,  it  helps  to  fix  the  central  point  of  the  perineum,  so  that 
the  Bulbocavernosus  may  act  from  this  fixed  point. 

The  Sphincter  ani  internus  (Internal  sphincter  ani)  is  a  muscular  ring  which 
surrounds  about  2.5  cm.  of  the  anal  canal;  its  inferior  border  is  in  contact  with, 
but  quite  separate  from,  the  Sphincter  ani  externus.  It  is  about  5  mm.  thick,  and 
is  formed  by  an  aggregation  of  the  involuntary  circular  fibers  of  the  intestine. 
Its  lower  border  is  about  6  mm.  from  the  orifice  of  the  anus. 

Actions. — Its  action  is  entirely  involuntary.  It  helps  the  Sphincter  ani  externus  to  occlude 
the  anal  aperture  and  aids  in  the  expulsion  of  the  feces. 

2.  A.  The  Muscles  of  the  Urogenital  Region  in  the  Male  (Fig.  406). 

Transversus  perinaei  superficialis.  Ischiocavernosus. 

Bulbocavernosus.  Transversus  perinsei  profundus. 

Sphincter  urethrse  membranacese. 

Superficial  Fascia. — The  superficial  fascia  of  this  region  consists  of  two  layers, 
superficial  and  deep. 

The  superficial  layer  is  thick,  loose,  areolar  in  texture,  and  contains  in  its  meshes 
much  adipose  tissue,  the  amount  of  which  varies  in  different  subjects.  In  front, 
it  is  continuous  with  the  dartos  tunic  of  the  scrotum;  behind,  with  the  subcuta- 
neous areolar  tissue  surrounding  the  anus;  and,  on  either  side,  with  the  same  fascia 
on  the  inner  sides  of  the  thighs.  In  the  middle  line,  it  is  adherent  to  the  skin  on 
the  raphe  and  to  the  deep  layer  of  the  superficial  fascia. 

The  deep  layer  of  superficial  fascia  {fascia  of  Colles)  (Fig.  405)  is  thin,  aponeurotic 
in  structure,  and  of  considerable  strength,  serving  to  bind  down  the  muscles  of 
the  root  of  the  penis.  It  is  continuous,  in  front,  with  the  dartos  tunic,  the  deep 
fascia  of  the  penis,  the  fascia  of  the  spermatic  cord,  and  Scarpa's  fascia  upon  the 
anterior  wall  of  the  abdomen;  on  either  side  it  is  firmly  attached  to  the  margins 
of  the  rami  of  the  pubis  and  ischium,  lateral  to  the  crus  penis  and  as  far  back  as 
the  tuberosity  of  the  ischium;  posteriorly,  it  curves  around  the  Transversi  perinsei 
superficiales  to  join  the  lower  margin  of  the  inferior  fascia  of  the  urogenital  dia- 
phragm. In  the  middle  line,  it  is  connected  with  the  superficial  fascia  and  with  the 
median  septum  of  the  Bulbocavernosus.  This  fascia  not  only  covers  the  muscles 
in  this  region,  but  at  its  back  part  sends  upward  a  vertical  septum  from  its  deep 
surface,  which  separates  the  posterior  portion  of  the  subjacent  space  into  two. 


THE  MUSCLES  OF  THE  UROGENITAL  REGION  IN  THE  MALE      427 

The  Central  Tendinous  Point  of  the  Perineum. — This  is  a  fibrous  point  in  the  middle 
line  of  the  perineum,  between  the  urethra  and  anus,  and  about  1.25  cm.  in  front 
of  the  latter.  At  this  point  six  muscles  converge  and  are  attached:  viz.,  the 
Sphincter  ani  externus,  the  Bulbocavernosus,  the  two  Transversi  perinsei  super- 
ficiales,  and  the  anterior  fibers  of  the  Levatores  ani. 


Fio.  406. — Muscles  of  male  perineum. 

The  Transversus  perinsei  superficialis  ( Transversus  yerinaei;  Suyerficial  transverse 
perineal  muscle)  is  a  narrow  muscular  slip,  which  passes  more  or  less  transversely 
across  the  perineal  space  in  front  of  the  anus.  It  arises  by  tendinous  fibers  from 
the  inner  and  forepart  of  the  tuberosity  of  the  ischium,  and,  running  medialward, 
is  inserted  into  the  central  tendinous  point  of  the  perineum,  joining  in  this  situa- 
tion with  the  muscle  of  the  opposite  side,  with  the  Sphincter  ani  externus  behind, 
and  with  the  Bulbocavernosus  in  front.  In  some  cases,  the  fibers  of  the  deeper 
layer  of  the  Sphincter  ani  externus  decussate  in  front  of  the  anus  and  are  con- 
tinued into  this  muscle.  Occasionally  it  gives  off  fibers,  which  join  with  the 
Bulbocavernosus  of  the  same  side. 


^H       Variations  are  numerous. 


It  may  be  absent  or  double,  or  insert  into  Bulbocavernosus  or 


I 


428  MYOLOGY 

Actions. — The  simultaneous  contraction  of  the  two  muscles  serves  to  fix  the  central  tendinous 
point  of  the  perineum. 

The  Bulbocavemosus  (Ejaculator  urince;  Accelerator  urince)  is  placed  in  the 
middle  line  of  the  perineum,  in  front  of  the  anus.  It  consists  of  two  symmetrical 
parts,  united  along  the  median  line  by  a  tendinous  raphe.  It  arises  from  the  cen- 
tral tendinous  point  of  the  perineum  and  from  the  median  raphe  in  front.  Its 
fibers  diverge  like  the  barbs  of  a  quill-pen;  the  most  posterior  form  a  thin  layer, 
which  is  lost  on  the  inferior  fascia  of  the  urogenital  diaphragm;  the  middle  fibers 
encircle  the  bulb  and  adjacent  parts,  of  the  corpus  cavernosum  urethrae,  and  join 
with  the  fibers  of  the  opposite  side,  on  the  upper  part  of  the  corpus  cavernosum 
urethrae,  in  a  strong  aponeurosis;  the  anterior  fibers,  spread  out  over  the  side  ^| 
of  the  corpus  cavernosum  penis,  to  be  inserted  partly  into  that  body,  anterior  to  HI 
the  Ischiocavernosus,  occasionally  extending  to  the  pubis,  and  partly  ending  in  a 
tendinous  expansion  which  covers  the  dorsal  vessels  of  the  penis.  The  latter 
fibers  are  best  seen  by  dividing  the  muscle  longitudinally,  and  reflecting  it  from 
the  surface  of  the  corpus  cavernosum  urethrse. 

Actions. — This  muscle  serves  to  empty  the  canal  of  the  urethra,  after  the  bladder  has  expelled 
its  contents;  during  the  greater  part  of  the  act  of  micturition  its  fibers  are  relaxed,  and  it  only 
comes  into  action  at  the  end  of  the  process.  The  middle  fibers  are  supposed  by  Krause  to  assist 
in  the  erection  of  the  corpus  cavernosum  urethra?,  by  compressing  the  erectile  tissue  of  the  bulb. 
The  anterior  fibers,  according  to  Tyrrel,  also  contribute  to  the  erection  of  the  penis  by  compressing 
the  deep  dorsal  vein  of  the  penis  as  they  are  inserted  into,  and  continuous  with,  the  fascia  of  the 
penis. 

The  Ischiocavernosus  {Erector  penis)  covers  the  crus  penis.  It  is  an  elongated 
muscle,  broader  in  the  middle  than  at  either  end,  and  situated  on  the  lateral  bound- 
ary of  the  perineum.  It  arises  by  tendinous  and  fleshy  fibers  from  the  inner  sur- 
face of  the  tuberosity  of  the  ischium,  behind  the  crus  penis;  and  from  the  rami  of 
the  pubis  and  ischium  on  either  side  of  the  crus.  From  these  points  fleshy  fibers 
succeed,  and  end  in  an  aponeurosis  which  is  inserted  into  the  sides  and  under 
surface  of  the  crus  penis. 

Action. — The  Ischiocavernosus  compresses  the  crus  penis,  and  retards  the  return  of  the  blood 
through  the  veins,  and  thus  serves  to  maintain  the  organ  erect. 

Between  the  muscles  just  examined  a  triangular  space  exists,  bounded  medially  by  the  Bulbo- 
cavemosus, laterally  by  the  Ischiocavernosus,  and  behind  by  the  Transversus  perinai  super- 
ficialis;  the  floor  is  formed  by  the  inferior  fascia  of  the  urogenital  diaphragm.  Running  from 
behind  forward  in  the  space  are  the  posterior  scrotal  vessels  and  nerves,  and  the  perineal  branch 
of  the  posterior  femoral  cutaneous  nerve;  the  transverse  perineal  artery  courses  along  its  posterior 
boundary  on  the  Transversus  perinaei  superficialis. 

The  Deep  Fascia. — The  deep  fascia  of  the  urogenital  region  forms  an  investment 
for  the  Transversus  perinsei  profundus  and  the  Sphincter  urethrse  membranacese, 
but  within  it  lie  also  the  deep  vessels  and  nerves  of  this  part,  the  whole  forming  a 
transverse  septum  which  is  known  as  the  urogenital  diaphragm.  From  its  shape 
it  is  usually  termed  the  triangular  ligament,  and  is  stretched  almost  horizontally 
across  the  pubic  arch,  so  as  to  close  in  the  front  part  of  the  outlet  of  the  pelvis. 
It  consists  of  two  dense  membranous  laminae  (Fig.  407),  which  are  united  along 
their  posterior  borders,  but  are  separated  in  front  by  intervening  structures.  The 
superficial  of  these  two  layers,  the  inferior  fascia  of  the  urogenital  diaphragm,  is  tri- 
angular in  shape,  and  about  4  cm.  in  depth.  Its  apex  is  directed  forward,  and  is 
separated  from  the  arcuate  pubic  ligament  by  an  oval  opening  for  the  transmission 
of  the  deep  dorsal  vein  of  the  penis.  Its  lateral  margins  are  attached  on  either  side 
to  the  inferior  rami  of  the  pubis  and  ischium,  above  the  crus  penis.  Its  base  is 
directed  toward  the  rectum,  and  connected  to  the  central  tendinous  point  of  the 
perineum.  It  is  continuous  w  ith  the  deep  layer  of  the  superficial  fascia  behind  the 
Transversus  perinaei  superficialis,  and  with  the  inferior  layer  of  the  diaphragmatic 


THE  MUSCLES  OF  THE  UROGENITAL  REGION  IN  THE  MALE      429 


I 


part  of  the  pelvic  fascia.  It  is  perforated,  about  2.5  cm.  below  the  symphysis 
pubis,  by  the  urethra,  the  aperture  for  which  is  circular  and  about  6  mm.  in  diameter 
by  the  arteries  to  the  bulb  and  the  ducts  of  the  bulbourethral  glands  close  to  the 
urethral  orifice;  by  the  deep  arteries  of  the  penis,  one  on  either  side  close  to  the 
pubic  arch  and  about  halfway  along  the  attached  margin  of  the  fascia;  by  the  dorsal 
arteries  and  nerves  of  the  penis  near  the  apex  of  the  fascia.  Its  base  is  also  perfor- 
ated by  the  perineal  vessels  and  nerves,  while  between  its  apex  and  the  arcuate 
pubic  ligament  the  deep  dorsal  vein  of  the  penis  passes  upward  into  the  pelvis. 

If  the  inferior  fascia  of  the  urogenital  diaphragm  be  detached  on  either  side, 
the  following  structures  will  be  seen  between  it  and  the  superior  fascia:  the  deep 
dorsal  vein  of  the  penis;  the  membranous  portion  of  the  urethra;  the  Transversus 
perinsei  profundus  and  Sphincter  urethrse  membranacese  muscles;  the  bulbo- 
urethral glands  and  their  ducts;  the  pudendal  vessels  and  dorsal  nerves  of  the  penis; 
the  arteries  and  nerves  of  the  urethral  bulb,  and  a  plexus  of  veins. 


urogenitaU  j^y^.^ 
diaphragm  [    ^^^^^ 


Ischiocavernostis 


Bulbocavemosus 
IFio.   407. — Coronal  section  of  anterior  part  of  pelvis,  through  the  pubic  arch.     Seen  from  in  front.     (Diagrammatic.) 


I 


The  superior  fascia  of  the  urogenital  diaphragm  is  continuous  with  the  obturator 
fascia  and  stretches  across  the  pubic  arch.  If  the  obturator  fascia  be  traced  medially 
after  leaving  the  Obturator  internus  muscle,  it  will  be  found  attached  by  some  of 
its  deeper  or  anterior  fibers  to  the  inner  margin  of  the  pubic  arch,  while  its  super- 
ficial or  posterior  fibers  pass  over  this  attachment  to  become  continuous  with  the 
superior  fascia  of  the  urogenital  diaphragm.  Behind,  this  layer  of  the  fascia  is 
continuous  with  the  inferior  fascia  and  with  the  fascia  of  Colles ;  in  front  it  is  con- 
tinuous with  the  fascial  sheath  of  the  prostate,  and  is  fused  with  the  inferior  fascia 
to  form  the  transverse  ligament  of  the  pelvis. 

The  Transversus  perinsei  profundus  arises  from  the  inferior  rami  of  the  ischium 
and  runs  to  the  median  line,  where  it  interlaces  in  a  tendinous  raphe  with  its  fellow 
of  the  opposite  side.  It  lies  in  the  same  plane  as  the  Sphincter  urethrse  membran- 
acese;  formerly  the  two  muscles  were  described  together  as  the  Constrictor  urethrse. 

The  Sphincter  urethrae  membranacese  surrounds  the  whole  length  of  the  mem- 
branous portion  of  the  urethra,  and  is  enclosed  in  the  fasciae  of  the  urogenital  dia- 
phragm.  Its  external  fibers  arise  from  the  junction  of  the  inferior  rami  of  the  pubis 


430  mHKm  MYOLOGY 

;'T, ,.'-;    X- 

and  ischium  to  the  extent  of  1.25  to  2  em.,  and  from  the  neighboring  fasciae. 
They  arch  across  the  front  of  the  urethra  and  bulbourethral  glands,  pass  around 
the  urethra,  and  behind  it  unite  with  the  muscle  of  the  opposite  side,  by  means 
of  a  tendinous  raphe.  Its  innermost  fibers  form  a  continuous  circular  investment 
for  the  membranous  urethra.  ^1 

Nerve  Supply. — The  perineal  branch  of  the  pudendal  nerve  supplies  this  group  of  muscles. 

Actions. — The  muscles  of  both  sides  act  together  as  a  sphincter,  compressing  the  membranous 
portion  of  the  urethra.  During  the  transmission  of  fluids  they,  hke  the  Bulbocavernosus,  are, 
relaxed,  and  only  come  into  action  at  the  end  of  the  process  to  eject  the  last  drops  of  the  fluid. 

^     2.  B.   The  Muscles  of  the  Urogenital  Region  in  the  Female  (Fig.  408). 

Transversus  perinsei  superficialis.  Ischiocavernosus. 

Bulbocavernosus.  Transversus  perinjsi  profundus. 

Sphincter  urethrse  membranacese. 

The  Transversus  perinaei  superficialis  {Transversus  perinosi;  Superficial  trans- 
verse perineal  muscle)  in  the  female  is  a  narrow  muscular  slip,  which  arises  by  a 
small  tendon  from  the  inner  and  forepart  of  the  tuberosity  of  the  ischium,  and 
is  inserted  into  the  central  tendinous  point  of  the  perineum,  joining  in  this  situa- 
tion with  the  muscle  of  the  opposite  side,  the  Sphincter  ani  externus  behind,  and 
the  Bulbocavernosus  in  front. 

Action. — The  simultaneous  contraction  of  the  two  muscles  serves  to  fix  the  central  tendinous 
point  of  the  perineum. 

The  Bulbocavernosus  (Sphincter  vaginoe)  surrounds  the  orifice  of  the  vagina. 
It  covers  the  lateral  parts  of  the  vestibular  bulbs,  and  is  attached  posteriorly 
to  the  central  tendinous  point  of  the  perineum,  where  it  blends  with  the  Sphincter 
ani  externus.  Its  fibers  pass  forward  on  either  side  of  the  vagina  to  be  inserted 
into  the  corpora  cavernosa  clitoridis,  a  fasciculus  crossing  over  the  body  of  the 
organ  so  as  to  compress  the  deep  dorsal  vein. 

Actions. — The  Bulbocavernosus  diminishes  the  orifice  of  the  vagina.  The  anterior  fibers 
contribute  to  the  erection  of  the  clitoris,  as  they  are  inserted  into  and  are  continuous  with  the 
fascia  of  the  clitoris,  compressing  the  deep  dorsal  vein  during  the  contraction  of  the  muscle. 

The  Ischiocavernosus  {Erector  clitoridis)  is  smaller  than  the  corresponding 
muscle  in  the  male.  It  covers  the  unattached  surface  of  the  crus  clitoridis.  It  is 
an  elongated  muscle,  broader  at  the  middle  than  at  either  end,  and  situated  on 
the  side  of  the  lateral  boundary  of  the  perineum.  It  arises  by  tendinous  and  fleshy 
fibers  from  the  inner  surface  of  the  tuberosity  of  the  ischium,  behind  the  crus 
clitoridis;  from  the  surface  of  the  crus;  and  from  the  adjacent  portion  of  the  ramus 
of  the  ischium.  From  these  points  fleshy  fibers  succeed,  and  end  in  an  aponeurosis, 
which  is  inserted  into  the  sides  and  under  surface  of  the  crus  clitoridis. 

Actions. — The  Ischiocavernosus  compresses  the  crus  clitoridis  and  retards  the  return  of  blood 
through  the  veins,  and  thus  serves  to  maintain  the  organ  erect. 

The  fascia  of  the  urogenital  diaphragm  in  the  female  is  not  so  strong  as  in  the 
male.  It  is  attached  to  the  pubic  arch,  its  apex  being  connected  with  the  arcuate 
pubic  ligament.  It  is  divided  in  the  middle  line  by  the  aperture  of  the  vagina, 
with  the  external  coat  of  which  it  becomes  blended,  and  in  front  of  this  is  perfor- 
ated by  the  urethra.  Its  posterior  border  is  continuous,  as  in  the  male,  with  the 
deep  layer  of  the  superficial  fascia  around  the  Transversus  perinsei  superficialis. 

Like  the  corresponding  fascia  in  the  male,  it  consists  of  two  layers,  between 
which  are  to  be  found  the  following  structures :  the  deep  dorsal  vein  of  the  clitoris, 
a  portion  of  the  urethra  and  the  Constrictor  urethra  muscle,  the  larger  vestibular 


THE  MUSCLES  AND  FASCIA  OF  THE  UPPER  EXTREMITY 


431 


glands  and  their  ducts;  the  internal  pudendal  vessels  and  the  dorsal  nerves  of  the 
clitoris;  the  arteries  and  nerves  of  the  bulbi  vestibuli,  and  a  plexus  of  veins. 

The  Transversus  perinsei  profundus  arises  from  the  inferior  rami  of  the  ischium 
and  runs  across  to  the  side  of  the  vagina.  The  Sphincter  urethrse  membranacese 
'.Constrictor  urethras),  like  the  corresponding  muscle  on  the  male,  consists  of  external 


Clitoris 


Sphincter  ani  extemus 
Fig.  408. — Muscles  of  the  female  perineum.     (Modified  from  a  drawing  by  Peter  Thompson.) 


and  internal  fibers.  The  external  fibers  arise  on  either  side  from  the  margin  of  the 
inferior  ramus  of  the  pubis.  They  are  directed  across  the  pubic  arch  in  front  of 
the  urethra,  and  pass  around  it  to  blend  with  the  muscular  fibers  of  the  opposite 
side,  between  the  urethra  and  vagina.  The  innermost  fibers  encircle  the  lower  end 
of  the  urethra. 


Nerve  Supply. — The  muscles  of  this  group  are  supplied  by  the  perineal  branch  of  the  pudendal. 


I 


THE   MUSCLES   AND  FASCLffi   OF  THE   UPPER  EXTREMITY. 


The  muscles  of  the  upper  extremity  are  divisible  into  groups,  corresponding 
with  the  different  regions  of  the  limb. 

I.  Muscles  Connecting  the  Upper  Extremity  to  the  Vertebral  Column. 
II.  Muscles  Connecting  the  Upper  Extremity  to  the  Anterior  and  Lateral 
Thoracic  Walls. 

III.  Muscles  of  the  Shoulder.  V.  Muscles  of  the  Forearm. 

IV.  Muscles  of  the  Arm.  VI.  Muscles  of  the  Hand. 


432  MYOLOGY 

I.     THE  MUSCLES  CONNECTING  THE  UPPER  EXTREMITY  TO  THE 
VERTEBRAL  COLUMN. 

The  muscles  of  this  group  are : 

Trapezius.  Rhomboideus  major. 

Latissimus  dorsi.  Rhomboideus  minor. 

Levator  scapulae. 

Superficial  Fascia. — The  superficial  fascia  of  the  back  forms  a  layer  of  con- 
siderable  thickness  and  strength,  and  contains  a  quantity  of  granular  fat.  It  is 
continuous  with  the  general  superficial  fascia.  fli 

Deep  Fascia, — The  deep  fascia  is  a  dense  fibrous  layer,  attached  above  to  the 
superior  nuchal  line  of  the  occipital  bone;  in  the  middle  line  it  is  attached  to  the 
ligamentum  nuchse  and  supraspinal  ligament,  and  to  the  spinous  processes  of  all 
the  vertebrae  below  the  seventh  cervical ;  laterally,  in  the  neck  it  is  continuous  with 
the  deep  cervical  fascia;  over  the  shoulder  it  is  attached  to  the  spine  of  the  scapula 
and  to  the  acromion,  and  is  continued  downward  over  the  Deltoideus  to  the  arm ; 
on  the  thorax  it  is  continuous  with  the  deep  fascia  of  the  axilla  and  chest,  and  on 
the  abdomen  with  that  covering  the  abdominal  muscles;  below,  it  is  attached  to 
the  crest  of  the  ilium. 

The  Trapezius  (Fig.  409)  is  a  flat,  triangular  muscle,  covering  the  upper  and 
back  part  of  the  neck  and  shoulders.  It  arises  from  the  external  occipital  protu- 
berance and  the  medial  third  of  the  superior  nuchal  line  of  the  occipital  bone,  from 
the  ligamentum  nuchse,  the  spinous  process  of  the  seventh  cervical,  and  the  spinous 
processes  of  all  the  thoracic  vertebrae,  and  from  the  corresponding  portion  of  the 
supraspinal  ligament.  From  this  origin,  the  superior  fibers  proceed  downward 
and  lateralward,  the  inferior  upward  and  lateralward,  and  the  middle  horizontally; 
the  superior  fibers  are  inserted  into  the  posterior  border  of  the  lateral  third  of  the 
clavicle;  the  middle  fibers  into  the  medial  margin  of  the  acromion,  and  into  the  supe- 
rior lip  of  the  posterior  border  of  the  spine  of  the  scapula;  the  inferior  fibers  con- 
verge near  the  scapula,  and  end  in  an  aponeurosis,  which  glides  over  the  smooth 
triangular  surface  on  the  medial  end  of  the  spine,  to  be  inserted  into  a  tubercle 
at  the  apex  of  this  smooth  triangular  surface.  At  its  occipital  origin,  the  Trapezius 
is  connected  to  the  bone  by  a  thin  fibrous  lamina,  firmly  adherent  to  the  skin. 
At  the  middle  it  is  connected  to  the  spinous  processes  by  a  broad  semi-elliptical 
aponeurosis,  which  reaches  from  the  sixth  cervical  to  the  third  thoracic  vertebrae, 
and  forms,  with  that  of  the  opposite  muscle,  a  tendinous  ellipse.  The  rest  of  the 
muscle  arises  by  numerous  short  tendinous  fibers.  The  two  Trapezius  muscles 
together  resemble  a  trapezium,  or  diamond-shaped  quadrangle:  two  angles  corre- 
sponding to  the  shoulders;  a  third  to  the  occipital  protuberance;  and  the  fourth 
to  the  spinous  process  of  the  twelfth  thoracic  vertebra. 

Variations. — The  attachments  to  the  dorsal  vertebrae  are  often  reduced  and  the  lower  ones  are 
often  wanting;  the  occipital  attachment  is  often  wanting;  separation  between  cervical  and  dorsal 
portions  is  frequent.    Extensive  deficiencies  and  complete  absence  occur. 

The  clavicular  insertion  of  this  muscle  varies  in  extent;  it  sometimes  reaches 
as  far  as  the  middle  of  the  clavicle,  and  occasionally  may  blend  with  the  posterior 
edge  of  the  Sternocleidomastoideus,  or  overlap  it. 

The  Latissimus  dorsi  (Fig.  409)  is  a  triangular,  flat  muscle,  which  covers  the 
lumbar  region  and  the  lower  half  of  the  thoracic  region,  and  is  gradually  con- 
tracted into  a  narrow  fasciculus  at  its  insertion  into  the  humerus.  It  arises  by 
tendinous  fibers  from  the  spinous  processes  of  the  lower  six  thoracic  vertebrae 
and  from  the  posterior  layer  of  the  lumbodorsal  fascia  (see  page  397),  by  which 
it  is  attached  to  the  spines  of  the  lumbar  and  sacral  vertebrae,  to  the  supraspinal 
ligament,  and  to  the  posterior  part  of  the  crest  of  the  ilium.    It  also  arises  by 


I 


I 


MUSCLES  OF  THE  UPPER  EXTREMITY 


433 


Fia    409. — Muscles  connecting  the  upper  extremity  to  the  vertebral  column. 


28 


434  VHaBHaV        MYOLOGY 

muscular  fibers  from  the  external  lip  of  the  crest  of  the  ilium  lateral  to  the  margin  j 
of  the  Sacrospinalis,  and  from  the  three  or  four  lower  ribs  by  fleshy  digitations^ ' 
which  are  interposed  between  similar  processes  of  the  Obliquus  abdominis  externus  j 
(Fig.  392,  page  409).    From  this  extensive  origin  the  fibers  pass  in  different  direc-  [ 
tions,  the  upper  ones  horizontally,  the  middle  obliquely  upward,  and  the  lower 
vertically  upward,  so  as  to  converge  and  form  a  thick  fasciculus,  which  crosses  the 
inferior  angle  of  the  scapula,  and  usually  receives  a  few  fibers  from  it.    The  muscle 
curves  around  the  lower  border  of  the  Teres  major,  and  is  twisted  upon  itself,  so 
that  the  superior  fibers  become  at  first  posterior  and  then  inferior,  and  the  vertical 
fibers  at  first  anterior  and  then  superior.    It  ends  in  a  quadrilateral  tendon,  about 
7  cm,  long,  which  passes  in  front  of  the  tendon  of  the  Teres  major,  and  is  inserted 
into  the  bottom  of  the  intertubercular  groove  of  the  humerus;  its  insertion  extends 
higher  on  the  humerus  than  that  of  the  tendon  of  the  Pectoralis  major.    The  lower 
border  of  its  tendon  is  united  with  that  of  the  Teres  major,  the  surfaces  of  the  two  | 
being  separated  near  their  insertions  by  a  bursa;  another  bursa  is  sometimes  inter- 
posed between  the  muscle  and  the  inferior  angle  of  the  scapula.    The  tendon  of 
the  muscle  gives  off  an  expansion  to  the  deep  fascia  of  the  arm. 

Variations. — The  number  of  dorsal  vertebrae  to  which  it  is  attached  vary  from  four  to  seven  or 
eight;  the  number  of  costal  attachments  varies;  muscle  fibers  may  or  may  not  reach  the  crest  of 
the  ilium.  \ 

A  muscular  slip,  the  axillary  arch,  varying  from  7  to  10  cm.  in  length,  and  from  5  to  15  mm. 
in  breadth,  occasionally  springs  from  the  upper  edge  of  the  Latissimus  dorsi  about  the  middle 
of  the  posterior  fold  of  the  axilla,  and  crosses  the  axilla  in  front  of  the  axillary  vessels  and  nerves, 
to  join  the  under  surface  of  the  tendon  of  the  Pectoralis  major,  the  Coracobrachialis,  or  the  fascia 
over  the  Biceps  brachii.  This  axillary  arch  crosses  the  axillary  artery,  just  above  the  spot  usually 
selected  for  the  apphcation  of  a  hgature,  and  may  mislead  the  surgeon  during  the  operation.  It 
is  present  in  about  7  per  cent,  of  subjects  and  may  be  easily  recognized  by  the  transverse  direction 
of  its  fibers. 

A  fibrous  slip  usually  passes  from  the  lower  border  of  the  tendon  of  the  Latissimus  dorsi,  near 
its  insertion,  to  the  long  head  of  the  Triceps  brachii.  This  is  occasionally  muscular,  and  is  the 
representative  of  the  Dorsoepitrochlearis  brachii  of  apes. 

The  lateral  margin  of  the  Latissimus  dorsi  is  separated  below  from  the  Obliquus 
externus  abdominis  by  a  small  triangular  interval,  the  lumbar  triangle  of  Petit, 
the  base  of  which  is  formed  by  the  iliac  crest,  and  its  floor  by  the  Obliquus  internum 
abdominis.  Another  triangle  is  situated  behind  the  scapula.  It  is  bounded  above 
by  the  Trapezius,  below  by  the  Latissimus  dorsi,  and  laterally  by  the  vertebral 
border  of  the  scapula;  the  floor  is  partly  formed  by  the  Rhomboideus  major. 
If  the  scapula  be  drawn  forward  by  folding  the  arms  across  the  chest,  and  the 
trunk  bent  forward,  parts  of  the  sixth  and  seventh  ribs  and  the  interspace  between 
them  become  subcutaneous  and  available  for  auscultation.  The  space  is  there- 
fore known  as  the  triangle  of  auscultation. 

Nerves. — The  Trapezius  is  supplied  by  the  accessory  nerve,  and  by  branches  from  the  third 
and  fourth  cervical  nerves;  the  Latissimus  dorsi  by  the  sixth,  seventh,  and  eighth  cervical  nerves 
through  the  thoracodorsal  (long  subscapular)  nerve. 

The  Rhomboideus  major  (Fig.  409)  arises  by  tendinous  fibers  from  the  spinous 
processes  of  the  second,  third,  fourth,  and  fifth  thoracic  vertebrae  and  the  supra- 
spinal ligament,  and  is  inserted  into  a  narrow  tendinous  arch,  attached  above  to 
the  lower  part  of  the  triangular  surface  at  the  root  of  the  spine  of  the  scapula; 
below  ^o  the  inferior  angle,  the  arch  being  connected  to  the  vertebral  border  by  a 
thin  membrane.  When  the  arch  extends,  as  it  occasionally  does,  only  a  short 
distance,  the  muscular  fibers  are  inserted  directly  into  the  scapula. 

The  Rhomboideus  minor  (Fig.  409)  arises  from  the  lower  part  of  the  ligamentum 
nuchse  and  from  the  spinous  processes  of  the  seventh  cervical  and  first  thoracic 
vertebrae.  It  is  inserted  into  the  base  of  the  triangular  smooth  surface  at  the  root 
of  the  spine  of  the  scapula,  and  is  usually  separated  from  the  Rhomboideus  major 


■■^^P  MUSCLES  OF  THE  UPPER  EXTREMITY  435 

by  a  slight  interval,  but  the  adjacent  margins  of  the  two  muscles  are  occasionally 
united. 

Variations. — The  vertebral  and  scapular  attachments  of  the  two  muscles  vary  in  extent.  A 
small  slip  from  the  scapula  to  the  occipital  bone  close  to  the  minor  occasionally  occurs,  the  Rhom- 
boideus  occipitalis  muscle. 

The  Levator  scapulae*  (Levator  anguli  scapulce)  (Fig.  409)  is  situated  at  the 
back  and  side  of  the  neck.  It  arises  by  tendinous  slips  from  the  transverse  pro- 
cesses of  the  atlas  and  axis  and  from  the  posterior  tubercles  of  the  transverse 
processes  of  the  third  and  fourth  cervical  vertebrae.  It  is  inserted  into  the  verte- 
bral border  of  the  scapula,  between  the  medial  angle  and  the  triangular  smooth 
surface  at  the  root  of  the  spine. 

Variations.— The  number  of  vertebral  attachments  varies;  a  slip  may  extend  to  the  occipital  or 
mastoid,  to  the  Trapezius,  Scalene  or  Serratus  anterior,  or  to  the  first  or  second  rib.  The  muscle 
may  be  subdivided  into  several  distinct  parts  from  origin  to  insertion.  Levator  claviculce  from  the 
transverse  processes  of  one  or  two  upper  cervical  vertebrae  to  the  outer  end  of  the  clavicle  corre- 
sponds to  a  muscle  of  lower  animals.    More  or  less  union  with  the  Serratus  anterior. 

Nerves. — The  Rhomboidei  are  supplied  by  the  dorsal  scapular  nerve  from  the  fifth  cervical; 
the  Levator  scapula?  by  the  third  and  fourth  cervical  nerves,  and  frequently  by  a  branch  from 
the  dorsal  scapular. 

Actions. — The  movements  effected  by  the  preceding  muscles  are  numerous,  as  may  be  con- 
ceived from  their  extensive  attachments.  When  the  whole  Trapezius  is  in  action  it  retracts  the 
scapula  and  braces  back  the  shoulder;  if  the  head  be  fixed,  the  upper  part  of  the  muscle  will  elevate 
the  point  of  the  shoulder,  as  in  supporting  weights;  when  the  lower  fibers  contract  they  assist 
in  depressing  the  scapula.  The  middle  and  lower  fibers  of  the  muscle  rotate  the  scapula,  causing 
elevation  of  the  acromion.  If  the  shoulders  be  fixed,  the  Trapezii,  acting  together,  will  draw 
the  head  directly  backward;  or  if  only  one  act,  the  head  is  drawn  to  the  corresponding  side. 

When  the  Latissimus  dorsi  acts  upon  the  humerus,  it  depresses  and  draws  it  backward,  and 
at  the  same  time  rotates  it  inward.  It  is  the  muscle  which  is  principally  employed  in  giving  a 
downward  blow,  as  in  felling  a  tree  or  jn  sabre  practice.  If  the  arm  be  fixed,  the  muscle  may 
act  in  various  ways  upon  the  trunk;  thus,  it  may  raise  the  lower  ribs  and  assist  in  forcible  inspira- 
tion; or,  if  both  arms  be  fixed,  the  two  muscles  may  assist  the  abdominal  muscles  and  Pectorales 
in  suspending  and  drawing  the  trunk  forward,  as  in  cUmbing. 

If  the  head  be  fixed,  the  Levator  scapula;  raises  the  medial  angle  of  the  scapula;  if  the  shoulder 
be  fixed,  the  muscle  inclines  the  neck  to  the  corresponding  side  and  rotates  it  in  the  same  direc- 
tion. The  Rhomboidei  carry  the  inferior  angle  backward  and  upward,  thus  producing  a  shght 
rotation  of  the  scapula  upon  the  side  of  the  chest,  the  Rhomboideus  major  acting  especially  on 
the  inferior  angle  of  the  scapula,  through  the  tendinous  arch  by  which  it  is  inserted.  The  Rhom- 
boidei, acting  together  with  the  middle  and  inferior  fibers  of  the  Trapezius,  will  retract  the 
scapula.  4) 

n.     THE   MUSCLES   CONNECTING   THE   UPPER   EXTREMITY   TO    THE 
ANTERIOR    AND   LATERAL   THORACIC   WALLS. 

The  muscles  of  the  anterior  and  lateral  thoracic  regions  are: 

Pectoralis  major.  Subclavius. 

Pectoralis  minor.  Serratus  anterior. 

Superficial  Fascia.— The  superficial  fascia  of  the  anterior  thoracic  region  is  con- 
tinuous with  that  of  the  neck  and  upper  extremity  above,  and  of  the  abdomen 
below.  It  encloses  the  mamma  and  gives  off  numerous  septa  which  pass  into  the 
gland,  supporting  its  various  lobes.  From  the  fascia  over  the  front  of  the  mamma, 
fibrous  processes  pass  forward  to  the  integument  and  papilla;  these  were  called 
by  Sir  A.  Cooper  the  ligamenta  suspensoria. 

Pectoral  Fascia. — The  pectoral  fascia  is  a  thin  lamina,  covering  the  surface  of 
the  Pectoralis  major,  and  sending  numerous  prolongations  between  its  fasciculi: 
it  is  attached,  in  the  middle  line,  to  the  front  of  the  sternum;  above,  to  the  clavicle; 
laterally  and  below  it  is  continuous  with  the  fascia  of  the  shoulder,  axilla,  and 
thorax.    It  is  very  thin  over  the  upper  part  of  the  Pectoralis  major,  but  thicker 


436 


MYOLOGY 


in  the  interval  between  it  and  the  Latissimus  dorsi,  where  it  closes  in  the  axillarjf 
space  and  forms  the  axillary  fascia ;  it  divides  at  the  lateral  margin  of  the  Latis- 
simus dorsi  into  two  layers,  one  of  which  passes  in  front  of,  and  the  other  behind 
it;  these  proceed  as  far  as  the  spinous  processes  of  the  thoracic  vertebrae,  to  which 
they  are  attached.  As  the  fascia  leaves  the  lower  edge  of  the  Pectoralis  major  to  cross 
the  floor  of  the  axilla  it  sends  a  layer  upward  under  cover  of  the  muscle;  this  lamina 
splits  to  envelop  the  Pectoralis  minor,  at  the  upper  edge  of  which  it  is  continuous 
with  the  coracoclavicular  fascia.  The  hollow  of  the  armpit,  seen  when  the  arm 
is  abducted,  is  produced  mainly  by  the  traction  of  this  fascia  on  the  axillary  floor, 
and  hence  the  lamina  is  sometimes  named  the  suspensory  ligament  of  the  axilla. 
At  the  lower  part  of  the  thoracic  region  the  deep  fascia  is  well-developed,  and  is 
continuous  with  the  fibrous  sheaths  of  the  Recti  abdominis. 


n 


Fia.  410. — Superficial  muscles  of  the  chest  and  front  of  the  arm.  m 

The  Pectoralis  major  (Fig.  410)  is  a  thick,  fan-shaped  muscle,  situated  at  the 
upper  and  forepart  of  the  chest.  It  arises  from  the  anterior  surface  of  the  sternal 
half  of  the  clavicle;  from  half  the  breadth  of  the  anterior  surface  of  the  sternum, 
as  low  down  as  the  attachment  of  the  cartilage  of  the  sixth  or  seventh  rib ;  from  the 


I 


MUSCLES  OF  THE  UPPER  EXTREMITY  437 

cartilages  of  all  the  true  ribs,  with  the  exception,  frequently,  of  the  jBrst  or  seventh, 
or  both,  and  from  the  aponeurosis  of  the  Obliquus  externus  abdominis.  From  this 
extensive  origin  the  fibers  converge  toward  their  insertion;  those  arising  from  the 
clavicle  pass  obliquely  downward  and  lateralward,  and  are  usually  separated  from 
the  rest  by  a  slight  interval;  those  from  the  lower  part  of  the  sternum,  and  the 
cartilages  of  the  lower  true  ribs,  run  upward  and  lateralward;  while  the  middle 
fibers  pass  horizontally.  They  all  end  in  a  flat  tendon,  about  5  cm.  broad,  w^hich 
is  inserted  into  the  crest  of  the  greater  tubercle  of  the  humerus.  This  tendon  con- 
l^psists  of  two  laminae,  placed  one  in  front  of  the  other,  and  usually  blended  together 
^^^below.  The  anterior  lamina,  the  thicker,  receives  the  clavicular  and  the  uppermost 
sternal  fibers;  they  are  inserted  in  the  same  order  as  that  in  which  they  arise: 
that  is  to  say,  the  most  lateral  of  the  clavicular  fibers  are  inserted  at  the  upper 
part  of  the  anterior  lamina;  the  uppermost  sternal  fibers  pass  down  to  the  lower 
part  of  the  lamina  which  extends  as  low  as  the  tendon  of  the  Deltoideus  and  joins 
with  it.  The  posterior  lamina  of  the  tendon  receives  the  attachment  of  the  greater 
part  of  the  sternal  portion  and  the  deep  fibers,  i.  e.,  those  from  the  costal  cartilages. 
These  deep  fibers,  and  particularly  those  from  the  lower  costal  cartilages,  ascend 

I^_  the  higher,  turning  backward  successively  behind  the  superficial  and  upper  ones, 
^Bso  that  the  tendon  appears  to  be  twisted.  The  posterior  lamina  reaches  higher 
on  the  humerus  than  the  anterior  one,  and  from  it  an  expansion  is  given  off  which 
covers  the  intertubercular  groove  and  blends  with  the  capsule  of  the  shoulder- 
joint.  From  the  deepest  fibers  of  this  lamina  at  its  insertion  an  expansion  is  given 
off  which  lines  the  intertubercular  groove,  while  from  the  lower  border  of  the  tendon 
a  third  expansion  passes  downward  to  the  fascia  of  the  arm. 

I^B     Variations. — The  more  frequent  variations  are  greater  or  less  extent  of  attachment  to  the  ribs 
I  ^m  and  sternum,  varying  size  of  the  abdominal  part  or  its  absence,  greater  or  less  extent  of  separation 

of  sternocostal  and  clavicular  parts,  fusion  of  clavicular  part  with  deltoid,  decussation  in  front  of 

the  sternum.     Deficiency  or  absence  of  the  sternocostal  part  is  not  uncommon.     Absence  of  the 

clavicular  part  is  less  frequent.    Rarely  the  whole  muscle  is  wanting. 

Costocoracaideus  is  a  muscular  band  occasionally  found  arising  from  the  ribs  or  aponeurosis  of  the 

External  oblique  between  the  Pectoralis  major  and  Latissimus  dorsi  and  inserted  into  the  coracoid 

process. 

Chondro-epitrochlearis  is  a  muscular  slip  occasionally  found  arising  from  the  costal  cartilages  or 

from  the  aponeurosis  of  the  External  oblique  below  the  Pectoralis  major  or  from  the  Pectoralis 

major  itself.    The  insertion  is  variable  on  the  inner  side  of  the  arm  to  fascia,  intermuscular  septum 

or  internal  condyle. 

ISternalis,  in  front  of  the  sternal  end  of  the  Pectoralis  major  parallel  to  the  margin  of  the  sterniun. 
It  is  supplied  by  the  anterior  thoracic  nerves  and  is  probably  a  misplaced  part  of  the  pectoralis. 
Coracoclavicular  Fascia  {fascia  cora^oclavicularis;  costocoracoid  membrane;  clavi- 
pedoral  fascia). — The  coracoclavicular  fascia  is  a  strong  fascia  situated  under 
cover  of  the  clavicular  portion  of  the  Pectoralis  major.    It  occupies  the  interval 
between  the  Pectoralis  minor  and  Subclavius,  and  protects  the  axillary  vessels 
^H  and  nerves.    Traced  upward,  it  splits  to  enclose  the  Subclavius,  and  its  two  layers 
^fare  attached  to  the  clavicle,  one  in  front  of  and  the  other  behind  the  muscle;  the 
latter  layer  fuses  with  the  deep  cervical  fascia  and  with  the  sheath  of  the  axillary 
,  vessels.     Medially,  it'  blends  with  the  fascia  covering  the  first  two  intercostal 
spaces,  and  is  attached  also  to  the  first  rib  medial  to  the  origin  of  the  Subclavius. 
"^Laterally,  it  is  very  thick  and  dense,  and  is  attached  to  the  coracoid  process. 
The  portion  extending  from  the  first  rib  to  the  coracoid  process  is  often  whiter  and 
denser  than  the  rest,  and  is  sometimes  called  the  costocoracoid  ligament.    Below 
this  it  is  thin,  and  at  the  upper  border  of  the  Pectoralis  minor  it  splits  into  two 
layers  to  invest  the  muscle;  from  the  lower  border  of  the  Pectoralis  minOr  it  is 
continued  downward  to  join  the  axillary  fascia,  and  lateralward  to  join  the  fascia 
over  the  short  head  of  the  Biceps  brachii.    The  coracoclavicular  fascia  is  pierced 
by  the  cephalic  vein,  thoracoacromial  artery  and  vein,  and  external  anterior 
thoracic  nerve. 


438 


MYOLOGY 


The  Pectoralis  minor  (Fig.  411)  is  a  thin,  triangular  muscle,  situated  at  the 
upper  part  of  the  thorax,  beneath  the  Pectoralis  major.  It  arises  from  the  upper 
margins  and  outer  surfaces  of  the  third,  fourth,  and  fifth  ribs,  near  their  cartilage 
and  from  the  aponeuroses  covering  the  Intercostalis;  the  fibers  pass  upward  and 
lateralward  and  converge  to  form  a  flat  tendon,  which  is  inserted  into  the  medial 
border  and  upper  surface  of  the  coracoid  process  of  the  scapula. 

Variations. — Origin  from  second,  third  and  fourth  or  fifth  ribs.  The  tendon  of  insertion  may 
extend  over  the  coracoid  process  to  the  greater  tubercle.  May  be  split  into  several  parts.  Absence 
rare. 

Pectoralis  minimus,  first  rib-cartilage  to  coracoid  process.     Rare. 


Badius 
Fig.  411. — Deep  musclea  of  the  chest  and  front  of  the  arm,  with  the  boundariea  of  the  axilla. 

The  Subclavius  (Fig.  411)  is  a  small  triangular  muscle,  placed  between  the 
clavicle  and  the  first  rib.  It  arises  by  a  short,  thick  tendon  from  the  first  rib  and 
its  cartilage  at  their  junction,  in  front  of  the  costoclavicular  ligament;  the  fleshy 
fibers  proceed  obliquely  upward  and  lateralward,  to  be  inserted  into  the  groove 
on  the  under  surface  of  the  clavicle  between  the  costoclavicular  and  conoid 
ligaments. 

Variations. — Insertion  into  coracoid  process  instead  of  clavicle  or  into  both  clavicle  and  coracoid 
process.  Sternoscapular  fasciculus  to  the  upper  border  of  scapula.  Sternoclavicularis  from  manu- 
brium to  clavicle  between  Pectoralis  major  and  coracoclavicular  fascia. 

The  Serratus  anterior  {Serratus  magnus)  (Fig.  411)  is  a  thin  muscular  sheet, 
situated   between  the   ribs   and   the  scapula  at   the  upper  and  lateral  part  of 


1^ 


■s 


THE  MUSCLES  AND  FASCIA  OF  THE  SHOULDER  439 

tne  chest.  It  arises  by  fleshy  digitations  from  the  outer  surfaces  and  superior 
borders  of  the  upper  eight  or  nine  ribs,  and  from  the  aponeuroses  covering  the 
intervening  Intercostales.  Each  digitation  (except  the  first)  arises  from  the 
corresponding  rib ;  the  first  sprjngs  from  the  first  and  second  ribs ;  and  from  the  fascia 
covering  the  first  intercostal  space.  From  this  extensive  attachment  the  fibers 
pass  backward,  closely  applied  to  the  chest-wall,  and  reach  the  vertebral  border 
pf  the  scapula,  and  are  inserted  into  its  ventral  surface  in  the  following  manner, 
he  first  digitation  is  inserted  into  a  triangular  area  on  the  ventral  surface  of  the 
tnedial  angle.  The  next  two  digitations  spread  out  to  form  a  thin,  triangular 
sheet,  the  base  of  which  is  directed  backward  and  is  inserted  into  nearly  the  whole 
length  of  the  ventral  surface  of  the  vertebral  border.  The  low^er  five  or  six  digita- 
tions converge  to  form  a  fan-shaped  mass,  the  apex  of  which  is  inserted,  by  muscular 
and  tendinous  fibers,  into  a  triangular  impression  on  the  ventral  surface  of  the 
inferior  angle.  The  lower  four  slips  interdigitate  at  their  origins  with  the  upper 
five  slips  of  the  Obliquus  externus  abdominis. 


Variations. — ^Attachment  to  tenth  rib.  Absence  of  attachments  to  first  rib,  to  one  or  more  of 
he  lower  ribs.  Division  into  three  parts;  absence  or  defect  of  middle  part.  Union  with  Levator 
scapulae,  External  intercostals  or  External  oblique. 

Nerves. — The  Pectoralis  major  is  suppUed  by  the  medial  and  lateral  anterior  thoracic  nerves; 
through  these  nerves  the  muscle  receives  filaments  from  all  the  spinal  nerves  entering  into  the 
formation  of  the  brachial  plexus;  the  Pectoralis  minor  receives  its  fibers  from  the  eighth  cervical 
and  first  thoracic  nerves  through  the  medial  anterior  thoracic  nerve.  The  Subclavius  is  suplied 
by  a  filament  from  the  fifth  and  sixth  cervical  nerves;  the  Serratus  anterior  is  supplied  by  the 
long  thoracic,  which  is  derived  from  the  fifth,  sixth,  and  seventh  cervical  nerves. 

Actions. — If  the  arm  has  been  raised  by  the  Deltoideus,  the  Pectorahs  major  will,  conjointly 
with  the  Latissimus  dorsi  and  Teres  major,  depress  it  to  the  side  of  the  chest.  If  acting  alone, 
it  adducts  and  draws  forward  the  arm,  bringing  it  across  the  front  of  the  chest,  and  at  the  same 
time  rotates  it  inward.  The  Pectoralis  minor  depresses  the  point  of  the  shoulder,  drawing  the 
scapula  downward  and  medialward  toward  the  thorax,  and  throwing  the  inferior  angle  back- 
ward. The  Subclavius  depresses  the  shoulder,  carrying  it  downward  and  forward.  When  the 
arms  are  fixed,  all  three  of  these  muscles  act  upon  the  ribs;  drawing  them  upward  and  expand- 
ing the  chest,  and  thus  becoming  very  important  agents  in  forced  inspiration.  The  Serratus 
anterior,  as  a  whole,  carries  the  scapula  forward,  and  at  the  same  time  raises  the  vertebral  border 
of  the  bone.  It  is  therefore  concerned  in  the  action  of  pushing.  Its  lower  and  stronger  fibers 
move  forward  the  lower  angle  and  assist  the  Trapezius  in  rotating  the  bone  at  the  sternoclavicular 
joint,  and  thus  assist  this  muscle  in  raising  the  acromion  and  supporting  weights  upon  the  shoulder. 
It  is  also  an  assistant  to  the  Deltoideus  in  raising  the  arm,  inasmuch  as  during  the  action  of  this 
latter  muscle  it  fixes  the  scapula  and  so  steadies  the  glenoid  cavity  on  which  the  head  of  the 
humerus  rotates.  After  the  Deltoideus  has  raised  the  arm  to  a  right  angle  with  the  trunk,  the 
Serratus  anterior  and  the  Trapezius,  by  rotating  the  scapula,  raise  the  arm  into  an  almost  vertical 
position.  It  is  possible  that  when  the  shoulders  are  fixed  the  lower  fibers  of  the  Serratus  anterior 
may  assist  in  raising  and  everting  the  ribs;  but  it  is  not  the  important  inspiratory  muscle  it  was 
formerly  beheved  to  be 


in.     THE   MUSCLES    AND    FASCMl   OF   THE   SHOULDER. 


I  In  this  group  are  included: 

Deltoideus.  Infraspinatus. 

Subscapularis.  Teres  minor. 

Supraspinatus.  Teres  major. 

Deep  Fascia. — The  deep  fascia  covering  the  Deltoideus  invests  the  muscle,  and 
sends  numerous  septa  between  its  fasciculi.  In  front  it  is  continuous  with  the  fascia 
covering  the  Pectoralis  major;  behind,  where  it  is  thick  and  strong,  with  that 
covering  the  Infraspinatus;  above,  it  is  attached  to  the  clavicle,  the  acromion, 
and  the  spine  of  the  scapula;  below,  it  is  continuous  with  the  deep  fascia  of  the 
arm. 

The  Deltoideus  {Deltoid  muscle)  (Fig.  410)  is  a  large,  thick,  triangular  muscle,  which 
covers  the  shoulder- joint  in  front,  behind,  and  laterally.    It  arises  from  the  anterior 

/ 


440  MYOLOGY 


I 


border  and  upper  surface  of  the  lateral  third  of  the  clavicle;  from  the  lateral  margm 
and  upper  surface  of  the  acromion,  and  from  the  lower  lip  of  the  posterior  border 
of  the  spine  of  the  scapula,  as  far  back  as  the  triangular  surface  at  its  medial  end.iH 
From  this  extensive  origin  the  fibers  converge  toward  their  insertion,  the  middle-™ 
passing  vertically,  the  anterior  obliquely  backward  and  lateralward,  the  posterior 
obliquely  forward  and  lateralward;  they  unite  in  a  thick  tendon,  which  is  inserted 
into  the  deltoid  prominence  on  the  middle  of  the  lateral  side  of  the  body  of  the 
humerus.  At  its  insertion  the  muscle  gives  off  an  expansion  to  the  deep  fascia  of 
the  arm.  This  muscle  is  remarkably  coarse  in  texture,  and  the  arrangement  of 
its  fibers  is  somewhat  peculiar;  the  central  portion  of  the  muscle — that  is  to  say, 
the  part  arising  from  the  acromion — consists  of  oblique  fibers;  these  arise  in  a 
bipenniform  manner  from  the  sides  of  the  tendinous  intersections,  generally  four 
in  number,  which  are  attached  above  to  the  acromion  and  pass  downward  parallel 
to  one  another  in  the  substance  of  the  muscle.  The  oblique  fibers  thus  formed  are 
inserted  into  similar  tendinous  intersections,  generally  three  in  number,  which 
pass  upward  from  the  insertion  of  the  muscle  and  alternate  with  the  descending 
septa.  The  portions  of  the  muscle  arising  from  the  clavicle  and  spine  of  the  scapula 
are  not  arranged  in  this  manner,  but  are  inserted  into  the  margins  of  the  inferior 
tendon. 

Variations. — Large  variations  uncommon.  More  or  less  splitting  common.  Continuation  into 
the  Trapezius;  fusion  with  the  Pectoralis  major;  additional  slips  from  the  vertebral  border  of  the 
scapula,  infraspinous  fascia  and  axillary  border  of  scapula  not  uncommon.  Insertion  varies  in 
extent  or  rarely  is  prolonged  to  origin  of  Brachioradialis. 

Nerves. — The  Deltoideus  is  suppUed  by  the  fifth  and  sixth  cervical  through  the  axillary  nerve. 

Actions. — The  Deltoideus  raises  the  arm  from  the  side,  so  as  to  bring  it  at  right  angles  with 
the  trunk.  Its  anterior  fibers,  assisted  by  the  Pectoralis  major,  draw  the  arm  forward;  and  its 
posterior  fibers,  aided  by  the  Teres  major  and  Latissimus  dorsi,  draw  it  backward. 

Subscapular  Fascia  (fascia  subscapularis) . — The  subscapular  fascia  is  a  thin 
membrane  attached  to  the  entire  circumference  of  the  subscapular  fossa,  and 
affording  attachment  by  its  deep  surface  to  some  of  the  fibers  of  the  Sub- 
scapularis. 

The  Subscapularis  (Fig.  411)  is  a  large  triangular  muscle  which  fills  the  sub- 
scapular fossa,  and  arises  from  its  medial  two-thirds  and  from  the  lower  two- 
thirds  of  the  groove  on  the  axillary  border  of  the  bone.  Some  fibers  arise  from 
tendinous  laminae  which  intersect  the  muscle  and  are  attached  to  ridges  on  the 
bone;  others  from  an  aponeurosis,  which  separates  the  muscle  from  the  Teres 
major  and  the  long  head  of  the  Triceps  brachii.  The  fibers  pass  lateralward, 
and,  gradually  converging,  end  in  a  tendon  which  is  inserted  into  the  lesser  tubercle 
of  the  humerus  and  the  front  of  the  capsule  of  the  shoulder-joint.  The  tendon 
of  the  muscle  is  separated  from  the  neck  of  the  scapula  by  a  large  bursa,  which 
communicates  with  the  cavity  of  the  shoulder-joint  through  an  aperture  in  the 
capsule. 

Nerves. — The  Subscapularis  is  supplied  by  the  fifth  and  sixth  cervical  nerves  through  the 
upper  and  lower  subscapular  nerves. 

Actions. — The  Subscapularis  rotates  the  head  of  the  humerus  inward;  when  the  arm  is  raised, 
it  draws  the  humerus  forward  and  downward.  It  is  a  powerful  defence  to  the  front  of  the  shoulder- 
joint,  preventing  displacement  of  the  head  of  the  humerus. 

Supraspinatous  Fascia  (fascia  supraspinata) . — ^The  supraspinatous  fascia  com- 
pletes the  osseofibrous  case  in  which  the  Supraspinatus  muscle  is  contained;  it 
affords  attachment,  by  its  deep  surface,  to  some  of  the  fibers  of  the  muscle.  It  is 
thick  medially,  but  thinner  laterally  under  the  coracoacromial  ligament. 

The  Supraspinatus  (Fig.  412)  occupies  the  whole  of  the  supraspinatous  fossa, 
arising  from  its  medial  two-thirds,  and  from  the  strong  supraspinatous  fascia. 
The  muscular  fibers  converge  to  a  tendon,  which  crosses  the  upper  part  of  the 


I 


THE  MUSCLES  AND  FASCIA  OF  THE  SHOULDER 


441 


fder-joint,  and  is  inserted  into  the  highest  of  the  three  impressions  on  the 
greater  tubercle  of  the  humerus;  the  tendon  is  intimately  adherent  to  the  capsule 
of  the  shoulder-joint. 

Infraspinatous  Fascia  (fascia  infraspinata). — The  infraspinatous  fascia  is  a  dense 
fibrous  membrane,  covering  the  Infraspinatous  muscle  and  fixed  to  the  circumfer- 
ence of  the  infraspinatous  fossa;  it  affords  attachment,  by  its  deep  surface,  to  some 
fibers  of  that  muscle.  It  is  intimately  attached  to  the  deltoid  fascia  along  the  over- 
lapping border  of  the  Deltoideus. 


Fig.  412. — Muscles  on  the  dorsum  of  the  scapula,  and  the  Triceps  brachii. 

The  Infraspinatus  (Fig.  412)  is  a  thick  triangular  muscle,  which  occupies  the 
chief  part  of  the  infraspinatous  fossa;  it  arises  by  fleshy  fibers  from  its  medial  two- 
thirds,  and  by  tendinous  fibers  from  the  ridges  on  its  surface;  it  also  arises  from 
the  infraspinatous  fascia  which  covers  it,  and  separates  it  from  the  Teretes  major 
and  minor.  The  fibers  converge  to  a  tendon,  which  glides  over  the  lateral  border 
of  the  spine  of  the  scapula,  and,  passing  across  the  posterior  part  of  the  capsule  of 
the  shoulder-joint,  is  inserted  into  the  middle  impression  on  the  greater  tubercle 
of  the  humerus.  The  tendon  of  this  muscle  is  sometimes  separated  from  the 
capsule  of  the  shoulder-joint  by  a  bursa,  which  may  communicate  with  the  joint 
cavity. 

The  Teres  minor  (Fig,  412)  is  a  narrow,  elongated  muscle,  which  arises  from 
the  dorsal  surface  of  the  axillary  border  of  the  scapula  for  the  upper  two-thirds  of 
its  extent,  and  from  two  aponeurotic  laminae,  one  of  which  separates  it  from  the 
Infraspinatus,  the  other  from  the  Teres  major.  Its  fibers  run  obliquely  upward 
and  lateralward;  the  upper  ones  end  in  a  tendon  which  is  inserted  into  the  lowest 
of  the  three  impressions  on  the  greater  tubercle  of  the  humerus;  the  lowest  fibers 
are  inserted  directly  into  the  humerus  immediately  below  this  impression.    The 


442  MYOLOGY 

tendon  of  this  muscle  passes  across,  and  is  united  with,  the  posterior  part  of 
capsule  of  the  shoulder-joint. 

Variations. — It  is  sometimes  inseparable  from  the  Infraspinatus. 

The  Teres  major  (Fig.  412)  is  a  thick  but  somewhat  flattened  muscle,  which 
arises  from  the  oval  area  on  the  dorsal  surface  of  the  inferior  angle  of  the  scapula, 
and  from  the  fibrous  septa  interposed  between  the  muscle  and  the  Teres  minor 
and  Infraspinatus;  the  fibers  are  directed  upward  and  lateralward,  and  end  in  a 
flat  tendon,  about  5  cm.  long,  which  is  inserted  into  the  crest  of  the  lesser  tubercle 
of  the  humerus.  The  tendon,  at  its  insertion,  lies  behind  that  of  the  Latissimus 
dorsi,  from  which  it  is  separated  by  a  bursa,  the  two  tendons  being,  however, 
united  along  their  lower  borders  for  a  short  distance. 

Nerves. — The  Supraspinatus  and  Infraspinatus  are  suppUed  by  the  fifth  and  sixth  cervical 
nerves  through  the  suprascapular  nerve;  the  Teres  minor,  by  the  fifth  cervical,  through  the 
axillary;  and  the  Teres  major,  by  the  fifth  and  sixth  cervical,  through  the  lowest  subscapular. 

Actions. — The  Supraspinatus  assists  the  Deltoideus  in  raising  the  arm  from  the  side  of  the 
trunk  and  fixes  the  head  of  the  humerus  in  the  glenoid  cavity.  The  Infraspinatus  and  Teres 
minor  rotate  the  head  of  the  humerus  outward;  they  also  assist  in  carrying  the  arm  backward. 
One  of  the  most  important  uses  of  these  three  muscles  is  to  protect  the  shoulder-joint,  the  Supra- 
spinatus supporting  it  above,  and  the  Infraspinatus  and  Teres  minor  behind.  The  Teres  major 
assists  the  Latissimus  dorsi  in  drawing  the  previously  raised  humerus  downward  and  backward, 
and  in  rotating  it  inward;  when  the  arm  is  fixed  it  may  assist  the  Pectorales  and  th^  Latissimus 
dorsi  in  drawing  the  trunk  forward. 


IV.    THE   MUSCLES    AND   FASCLffl   OF   THE    ARM. 

The  muscles  of  the  arm  are: 

Coracobrachialis.  Brachialis. 

Biceps  brachii.  Triceps  brachii. 

Brachial  Fascia  (fascia  brachii;  deep  fascia  of  the  arm) . — The  brachial  fascia  is 
continuous  with  that  covering  the  Deltoideus  and  the  Pectoralis  major,  by  means 
of  which  it  is  attached,  above,  to  the  clavicle,  acromion,  and  spine  of  the  scapula; 
it  forms  a  thin,  loose,  membranous  sheath  for  the  muscles  of  the  arm,  and  sends 
septa  between  them ;  it  is  composed  of  fibers  disposed  in  a  circular  or  spiral  direc- 
tion, and  connected  together  by  vertical  and  oblique  fibers.  It  differs  in  thickness 
at  different  parts,  being  thin  over  the  Biceps  brachii,  but  thicker  where  it  covers 
the  Triceps  brachii,  and  over  the  epicondyles  of  the  humerus:  it  is  strengthened 
by  fibrous  aponeuroses,  derived  from  the  Pectoralis  major  and  Latissimus  dorsi 
medially,  and  from  the  Deltoideus  laterally.  On  either  side  it  gives  off  a  strong 
intermuscular  septum,  which  is  attached  to  the  corresponding  supracondylar 
ridge  and  epicondyle  of  the  humerus.  The  lateral  intermuscular  septmn  extends 
from  the  lower  part  of  the  crest  of  the  greater  tubercle,  along  the  lateral  supra- 
condylar ridge,  to  the  lateral  epicondyle;  it  is  blended  with  the  tendon  of  the  Del- 
toideus, gives  attachment  to  the  Triceps  brachii  behind,  to  the  Brachialis,  Brachio- 
radialis,  and  Extensor  carpi  radialis  longus  in  front,  and  is  perforated  by  the  radial 
nerve  and  profunda  branch  of  the  brachial  artery.  The  medial  intermuscular 
septum,  thicker  than  the  preceding,  extends  from  the  lower  part  of  the  crest  of 
the  lesser  tubercle  of  the  humerus  below  the  Teres  major,  along  the  medial  supra- 
condylar ridge  to  the  medial  epicondyle;  it  is  blended  with  the  tendon  of  the 
Coracobrachialis,  and  affords  attachment  to  the  Triceps  brachii  behind  and  the 
Brachialis  in  front.  It  is  perforated  by  the  ulnar  nerve,  the  superior  ulnar 
collateral  artery,  and  the  posterior  branch  of  the  inferior  ulnar  collateral  artery. 
At  the  elbow,  the  deep  fascia  is  attached  to  the  epicondyles  of  the  humerus  and 
the  olecranon  of  the  ulna,  and  is  continuous  with  the  deep  fascia  of  the  forearm. 


THE  MUSCLES  AND  FASCIA  OF  THE  ARM 


443 


Tust  below  the  middle  of  the  arm,  on  its  medial  side,  is  an  oval  opening  in  the  deep 
fascia,  which  transmits  the  basilic  vein  and  some  lymphatic  vessels. 

The  Coracobrachialis  (Fig.  411),  the  smallest  of  the  three  muscles  in  this  region, 
is  situated  at  the  upper  and  medial  part  of  the  arm.  It  arises  from  the  apex  of 
the  coracoid  process,  in  common  with  the  short  head  of  the  Biceps  brachii,  and  from 
the  intermuscular  septum  between  the  two  muscles ;  it  is  inserted  by  means  of  a  flat 
tendon  into  an  impression  at  the  middle  of  the  medial  surface  and  border  of  the 
body  of  the  humerus  between  the  origins  of  the  Triceps  brachii  and  Brachialis. 
lit  is  perforated  by  the  musculocutaneous  nerve. 


Biceps  brachii  M 


Cephalic  vein-. 


Brachialis 'M. 


Radial  nerve- 
Dorsal  antihrachial, 
cutaneous  nerve 

Radial  collateral  arteri/ 

Lateral  intermuscular 
septum  of  humerus 


Lateral  antibrachial 
cutaneous  nerve 

Brachial  artery  and  veins 

Median  nerve 

^Medial  antibrachial 
V   cutaneous  nerve 
l^  ^'-Basilic  vein 
.    >,..  Ulnar  nerve 


Superior  ulnar 
collateral  artery 


Medial  intermuscular 
septum  of  humerus 


-Humerus 


''Triceps  brachii  M. 


Fig.  413. — Cross-section  through  the  middle  of  upper  arm.      (Eycleshymer  and  Schoemaker.O 

Variations. — A  bony  head  may  reach  the  medial  epicondyle;  a  short  head  more  rarely  foimd 
ly  insert  into  the  lesser  tubercle. 

The  Biceps  brachii  {Biceps;  Biceps  flexor  cuhiti)  (Fig.  411)  is  a  long  fusiform 
muscle,  placed  on  the  front  of  the  arm,  and  arising  by  two  heads,  from  which 
circumstance  it  has  received  its  name.  The  short  head  arises  by  a  thick  flattened 
tendon  from  the  apex  of  the  coracoid  process,  in  common  with  the  Coracobrachialis. 
The  long  head  arises  from  the  supraglenoid  tuberosity  at  the  upper  margin  of  the 
glenoid  cavity,  and  is  continuous  with  the  glenoidal  labrum.  This  tendon,  enclosed 
,in  a  special  sheath  of  the  synovial  membrane  of  the  shoulder-joint,  arches  over 
the  head  of  the  humerus;  it  emerges  from  the  capsule  through  an  opening  close 
to  the  humeral  attachment  of  the  ligament,  and  descends  in  the  intertubercular 
groove;  it  is  retained  in  the  groove  by  the  transverse  humeral  ligament  and  by  a 
fibrous  prolongation  from  the  tendon  of  the  Pectoralis  major.  Each  tendon  is 
succeeded  by  an  elongated  muscular  belly,  and  the  two  bellies,  although  closely 
applied  to  each  other,  can  readily  be  separated  until  within  about  7.5  cm.  of  the 
elbow-joint.  Here  they  end  in  a  flattened  tendon,  which  is  inserted  into  the  rough 
posterior  portion  of  the  tuberosity  of  the  radius,  a  bursa  being  interposed  between 
the  tendon  and  the  front  part  of  the  tuberosity.  As  the  tendon  of  the  muscle 
approaches  the  radius  it  is  twisted  upon  itself,  so  that  its  anterior  surface  becomes 


1  A  Cross-section  Anatomy,  New  York,   1911. 


444  ^^MAMJa^^       MYOLOGY 


lateral  and  is  applied  to  the  tuberosity  of  the  radius  at  its  insertion.    Opposrte 
the  bend  of  the  elbow  the  tendon  gives  off,  from  its  medial  side,  a  broad  aponeu- 
rosis, the  lacertus  fibrosus  (bicipital  fascia)  which  passes  obliquely  downward  and 
medial  ward  across  the  brachial  artery,  and  is  continuous  with  the  deep  fascia  j^ 
covering  the  origins  of  the  Flexor  muscles  of  the  forearm  (Fig.  410).  H 

Variations. — A  third  head  (10  per  cent.)  to  the  Biceps  brachii  is  occasionally  found,  arising  at 
the  upper  and  medial  part  of  the  Brachialis,  with  the  fibers  of  which  it  is  continuous,  and  inserted 
into  the  lacertus  fibrosus  and  medial  side  of  the  tendon  of  the  muscle.  In  most  cases  this  additional 
slip  lies  behind  the  brachial  artery  in  its  coarse  down  the  arm.  In  some  instances  the  third  head 
consists  of  two  slips,  which  pass  down,  one  in  front  of  and  the  other  behind  the  artery,  concealing 
the  vessel  in  the  lower  half  of  the  arm.  More  rarely  a  fourth  head  occurs  arising  from  the  outer 
side  of  the  humerus,  from  the  intertubercular  groove,  or  from  the  greater  tubercle.  Other  heads 
are  occasionally  found.  Slips  sometimes  pass  from  the  inner  border  of  the  muscle  over  the  brachial 
artery  to  the  medial  intermuscular  septum,  or  the  medial  epicondyle;  more  rarely  to  the  Pronator 
teres  or  Brachialis.    The  long  head  may  be  absent  or  arise  from  the  intertubercular  groove. 

The  Brachialis  (Brachialis  anticus)  (Fig.  411)  covers  the  front- of  the  elbow-joint 
and  the  lower  half  of  the  humerus.  It  arises  from  the  lower  half  of  the  front 
of  the  humerus,  commencing  above  at  the  insertion  of  the  Deltoideus,  which  it 
embraces  by  two  angular  processes.  Its  origin  extends  below  to  within  2.5  cm. 
of  the  margin  of  the  articular  surface.  It  also  arises  from  the  intermuscular  septa, 
but  more  extensively  from  the  medial. than  the  lateral;  it  is  separated  from  the 
lateral  below  by  the  Brachioradialis  and  Extensor  carpi  radialis  longus.  Its  fibers 
converge  to  a  thick  tendon,  which  is  inserted  into  the  tuberosity  of  the  ulna  and 
the  rough  depression  on  the  anterior  surface  of  the  coronoid  process. 

Variations. — Occasionally  doubled;  additional  slips  to  the  Supinator,  Pronator  teres,  Biceps, 
lacertus  fibrosus,  or  radius  are  more  rarely  found. 

Nerves. — The  Coracobrachialis,  Biceps  brachii  and  Brachialis  are  supplied  by  the  musculo- 
cutaneous nerve;  the  Brachiahs  usually  receives  an  additional  filament  from  the  radial.  The 
Coracobrachialis  receives  its  supply  primarily  from  the  seventh  cervical,  the  Biceps  brachii  and 
Brachialis  from  the  fifth  and  sixth  cervical  nerves. 

Actions. — The  CoracobrachiaUs  draws  the  humerus  forward  and  medialward,  and  at  the 
same  time  assists  in  retaining  the  head  of  the  bone  in  contact  with  the  glenoid  cavity.  The 
Biceps  brachii  is  a  flexor  of  the  elbow  and,  to  a  less  extent,  of  the  shoulder;  it  is  also  a  powerful 
supinator,  and  serves  to  render  tense  the  deep  fascia  of  the  forearm  by  means  of  the  lacertus 
fibrosus  given  off  from  its  tendon.  The  Brachialis  is  a  flexor  of  the  forearm,  and  forms  an  impor- 
tant defence  to  the  elbow-joint.  When  the  forearm  is  fixed,  the  Biceps  brachii  and  Brachialis 
flex  the  arm  upon  the  forearm,  as  in  efforts  of  climbing. 

The  Triceps  brachii  {Triceps;  Triceps  extensor  cubiti)  (Fig.  412)  is  situated  on 
the  back  of  the  arm,  extending  the  entire  length  of  the  dorsal  surface  of  the  humerus. 
It  is  of  large  size,  and  arises  by  three  heads  (long,  lateral,  and  medial),  hence  its 
name. 

The  long  head  arises  by  a  flattened  tendon  from  the  infraglenoid  tuberosity 
of  the  scapula,  being  blended  at  its  upper  part  with  the  capsule  of  the  shoulder- 
joint;  the  muscular  fibers  pass  downward  between  the  two  other  heads  of  the 
muscle,  and  join  with  them  in  the  tendon  of  insertion. 

The  lateral  head  arises  from  the  posterior  surface  of  the  body  of  the  humerus, 
between  the  insertion  of  the  Teres  minor  and  the  upper  part  of  the  groove  for  the 
radial  nerve,  and  from  the  lateral  border  of  the  humerus  and  the  lateral  intermus- 
cular septum;  the  fibers  from  this  origin  converge  toward  the  tendon  of  insertion. 

The  medial  head  arises  from  the  posterior  surface  of  the  body  of  the  humerus, 
below  the  groove  for  the  radial  nerve;  it  is  narrow  and  pointed  above,  and  extends 
from  the  insertion  of  the  Teres  major  to  within  2.5  cm.  of  the  trochlea:  it  also 
arises  from  the  medial  border  of  the  humerus  and  from  the  back  of  the  whole 
length  of  the  medial  intermuscular  septum.  Some  of  the  fibers  are  directed 
downward  to  the  olecranon,  while  others  converge  to  the  tendon  of  insertion. 

The  tendon  of  the  Triceps  brachii  begins  about  the  middle  of  the  muscle:  it  con- 


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sists  of  two  aponeurotic  laminae,  one  of  which  is  subcutaneous  and  covers  the  back 
of  the  lower  half  of  the  muscle;  the  other  is  more  deeply  seated  in  the  substance 
of  the  muscle.  After  receiving  the  attachment  of  the  muscular  fibers,  the  two 
lamellae  join  together  above  the  elbow,  and  are  inserted,  for  the  most  part,  into 
the  posterior  portion  of  the  upper  surface  of  the  olecranon;  a  band  of  fibers  is, 
however,  continued  downward,  on  the  lateral  side,  over  the  Anconseus,  to  blend 
with  the  deep  fascia  of  the  forearm. 

The  long  head  of  the  Triceps  brachii  descends  between  the  Teres  minor  and  Teres  major, 
dividing  the  triangular  space  between  these  two  muscles  and  the  humerus  into  two  smaller  spaces, 
one  triangular,  the  other  quadrangular  (Fig.  412).  The  triangular  space  contains  the  scapular 
circumflex  vessels;  it  is  bounded  by  the  Teres  minor  above,  the  Teres  major  below,  and  the 
scapular  head  of  the  Triceps  laterally.  The  quadrangular  space  transmits  the  posterior  humeral 
circumflex  vessels  and  the  axillary  nerve;  it  is  bounded  by  the  Teres  minor  and  capsule  of  the 
ehoulder-joint  above,  the  Teres  major  below,  the  long  head  of  the  Triceps  brachii  medially,  and 
the  humerus  laterally. 

Variations. — A  fourth  head  from  the  inner  part  of  the  humerus;  a  slip  between  Triceps  and 
Latissimus  dorsi  corresponding  to  the  Dorso-epitrochlearis. 

The  Subanconaeus  is  the  name  given  to  a  few  fibers  which  spring  from  the  deep  surface  of 
the  lower  part  of  the  Triceps  brachii,  and  are  inserted  into  the  posterior  Ugament  and  synovial 
membrane  of  the  elbow-joint. 

Nerves. — The  Triceps  brachii  is  supplied  by  the  seventh  and  eighth  cervical  nerves  through 
the  radial  nerve. 

Actions. — The  Triceps  brachii  is  the  great  extensor  muscle  of  the  forearm,  and  is  the  direct 
antagonist  of  the  Biceps  brachii  and  Brachialis.  When  the  arm  is  extended,  the  long  head  of 
the  muscle  may  assist  the  Teres  major  and  Latissimus  dorsi  in  drawing  the  humerus  backward 
and  in  adducting  it  to  the  thorax.  The  long  head  supports  the  under  part  of  the  shoulder-joint. 
The  Subanconseus  draws  up  the  synovial  membrane  of  the  elbow-joint  during  extension  of  the 
forearm. 

V.    THE   MUSCLES    AND    FASCMl   OF   THE    FOREARM. 

Antibrachial  Fascia  (fascia  antibrachii;  deep  fascia  of  the  forearm). — The  anti- 
brachial  fascia  continuous  above  with  the  brachial  fascia,  is  a  dense,  membranous 
investment,  which  forms  a  general  sheath  for  the  muscles  in  this  region;  it  is  at- 
tached, behind,  to  the  olecranon  and  dorsal  border  of  the  ulna,  and  gives  off  from  its 
deep  surface  numerous  intermuscular  septa,  which  enclose  each  muscle  separately. 
Over  the  Flexor  tendons  as  they  approach  the  wrist  it  is  especially  thickened,  and 
forms  the  volar  carpal  ligament.  This  is  continuous  with  the  transverse  carpal  liga- 
ment, and  forms  a  sheath  for  the  tendon  of  the  Palmaris  longus  which  passes  over 
the  transverse  carpal  ligament  to  be  inserted  into  the  palmar  aponeurosis.  Behind, 
near  the  wrist-joint,  it  is  thickened  by  the  addition  of  many  transverse  fibers,  and 
■forms  the  dorsal  carpal  ligament.  It  is  much  thicker  on  the  dorsal  than  on  the  volar 
surface,  and  at  the  lower  than  at  the  upper  part  of  the  forearm,  and  is  strengthened 
above  by  tendinous  fibers  derived  from  the  Biceps  brachii  in  front,  and  from  the 
Triceps  brachii  behind.  It  gives  origin  to  muscular  fibers,  especially  at  the  upper 
part  of  the  medial  and  lateral  sides  of  the  forearm,  and  forms  the  boundaries  of 
a  series  of  cone-shaped  cavities,  in  which  the  muscles  are  contained.  Besides  the 
vertical  septa  separating  the  individual  muscles,  transverse  septa  are  given  off 
both  on  the  volar  and  dorsal  surfaces  of  the  forearm,  separating  the  deep  from  the 
superficial  layers  of  muscles.  Apertures  exist  in  the  fascia  for  the  passage  of 
vessels  and  nerves;  one  of  these  apertures  of  large  size,  situated  at  the  front  of  the 
elbow,  serves  for  the  passage  of  a  communicating  branch  between  the  superficial 
and  deep  veins. 

The  antibrachial  or  forearm  muscles  may  be  divided  into  a  volar  and  a  dorsal 
group. 

1.  The  Volar  Antibrachial  Muscles. 

These  muscles  are  divided  for  convenience  of  description  into  two  groups, 
superficial  and  deep. 


The  Superficial  Group  (Fig.  414). 

Pronator  teres.  Palmaris  longus. 

Flexor  carpi  radialis.  Flexor  carpi  ulnaris. 

Flexor  digitorum  sublimis. 

The  muscles  of  this  group  take  origin  from  the  medial  epicondyle  of  the  humerus 
by  a  common  tendon;  they  receive  additional  fibers  from  the  deep  fascia  of  the  fore- 
arm near  the  elbow,  and  from  the  septa  which  pass  from  this  fascia  between  the 
individual  muscles. 

The  Pronator  teres  has  two  heads  of  origin — humeral  and  ulnar.  The  humeral 
head,  the  larger  and  more  superficial,  arises  immediately  above  the  medial  epi- 
condyle, and  from  the  tendon  common  to  the  origin  of  the  other  muscles;  also 
from  the  intermuscular  septum  between  it  and  the  Flexor  carpi  radialis  and  from 
the  antibrachial  fascia.  The  ulnar  head  is  a  thin  fasciculus,  which  arises  from  the 
medial  side  of  the  coronoid  process  of  the  ulna,  and  joins  the  preceding  at  an  acute 
angle.  The  median  nerve  enters  the  forearm  between  the  two  heads  of  the  muscle, 
and  is  separated  from  the  ulnar  artery  by  the  ulnar  head.  The  muscle  passes  ob- 
liquely across  the  forearm,  and  ends  in  a  flat  tendon,  which  is  inserted  into  a  rough 
impression  at  the  middle  of  the  lateral  surface  of  the  body  of  the  radius.  The 
lateral  border  of  the  muscle  forms  the  medial  boundary  of  a  triangular  hollow 
situated  in  front  of  the  elbow-joint  and  containing  the  brachial  artery,  median 
nerve,  and  tendon  of  the  Biceps  brachii. 

Variations. — Absence  of  ulnar  head;  additional  slips  from  the  medial  intermuscular  septum, 
from  the  Biceps  and  from  the  Brachialis  anticus  occasionally  occur. 

The  Flexor  carpi  radialis  lies  on  the  medial  side  of  the  preceding  muscle.  It 
arises  from  the  medial  epicondyle  by  the  common  tendon;  from  the  fascia  of  the 
forearm;  and  from  the  intermuscular  septa  between  it  and  the  Pronator  teres 
laterally,  the  Palmaris  longus  medially,  and  the  Flexor  digitorum  sublimis  beneath. 
Slender  and  aponeurotic  in  structure  at  its  commencement,  it  increases  in  size, 
and  ends  in  a  tendon  which  forms  rather  more  than  the  lower  half  of  its  length. 
This  tendon  passes  through  a  canal  in  the  lateral  part  of  the  transverse  carpal 
ligament  and  runs  through  a  groove  on  the  greater  multangular  bone;  the  groove 
is  converted  into  a  canal  by  fibrous  tissue,  and  lined  by  a  mucous  sheath.  The  ten- 
don is  inserted  into  the  base  of  the  second  metacarpal  bone,  and  sends  a  slip  to 
the  base  of  the  third  metacarpal  bone.  The  radial  artery,  in  the  lower  part  of  the 
forearm,  lies  between  the  tendon  of  this  muscle  and  the  Brachioradialis. 

Variations. — Slips  from  the  tendon  of 'the  Biceps,  the  lacertus  fibrosus,  the  coronoid,  and  the 
radius  have  been  found.  Its  insertion  often  varies  and  may  be  mostly  into  the  annular  ligament, 
the  trapezium,  or  the  fourth  metacarpal  as  well  as  the  second  or  third.  The  muscle  may  be 
absent. 

The  Palmaris  longus  is  a  slender,  fusiform  muscle,  lying  on  the  medial  side 
of  the  preceding.  It  arises  from  the  medial  epicondyle  of  the  humerus  by  the 
common  tendon,  from  the  intermuscular  septa  between  it  and  the  adjacent 
muscles,  and  from  the  antibrachial  fascia.  It  ends  in  a  slender,  flattened  tendon, 
which  passes  over  the  upper  part  of  the  transverse  carpal  ligament,  and  is  inserted 
into  the  central  part  of  the  transverse  carpal  ligament  and  lower  part  of  the 
palmar  aponeurosis,  frequently  sending  a  tendinous  slip  to  the  short  muscles  of 
the  thumb. 

Variations. — One  of  the  most  variable  muscles  in  the  body.  This  muscle  is  often  absent  about 
(10  per  cent.),  and  is  subject  to  many  variations;  it  may  be  tendinous  above  and  muscular  below; 
or  it  may  be  muscular  in  the  center  with  a  tendon  above  and  below;  or  it  may  present  two  muscular 
bimdles  with  a  central  tendon;  or  finally  it  may  consist  solely  of  a  tendinous  band.  The  muscle 
may  be  double.     Slips  of  origin  from  the  coronoid  process  or  from  the  radius  have  been  seen. 


i 


THE  VOLAR  ANTIBRACHIAL' MUSCLES 


447 


Partial  or  complete  insertion  into  the  fascia 
of  the  forearm,  into  the  tendon  of  the  Flexor 
carpi  ulnaris  and  pisiform  bone,  into  the 
navicular,  and  into  the  muscles  of  the  little 
finger  have  been  observed. 

The  Flexor  carpi  ulnaris  lies  along 
the  uhiar  side  of  the  forearm.  It 
arises  by  two  heads,  humeral  and 
ulnar,  connected  by  a  tendinous  arch, 
beneath  which  the  ulnar  nerve  and 
posterior  ulnar  recurrent  artery  pass. 
The  humeral    head   arises  from    the 


Fig.  414.— Front  of  the  left  forearm.     Superficial 

muscles. 


FiQ.  415. — Front  of  the  left  forearm.     Deep 
muscles. 


MYOLOGY 

medial  epicondyle  of  the  humerus  by  the  common  tendon;  the  uhiar  head 
arises  from  the  medial  margin  of  the  olecranon  and  from  the  upper  two-thirds 
of  the  dorsal  border  of  the  ulna  by  an  aponeurosis,  common  to  it  and  the  Extensor 
carpi  ulnaris  and  Flexor  digitorum  profundus ;  and  from  the  intermuscular  septum 
between  it  and  the  Flexor  digitorum  sublimis.  The  fibers  end  in  a  tendon,  which 
occupies  the  anterior  part  of  the  lower  half  of  the  muscle  and  is  inserted  into  the  MM 
pisiform  bone,  and  is  prolonged  from  this  to  the  hamate  and  fifth  metacarpal"" 
bones  by  the  pisohamate  and  pisometacarpal  ligaments;  it  is  also  attached  by  a 
few  fibers  to  the  transverse  carpal  ligament.  The  ulnar  vessels  and  nerve  lie  on 
the  lateral  side  of  the  tendon  of  this  muscle,  in  the  lower  two-thirds  of  the  forearm- 


Variations. — Slips  of  origin  from  the  coronoid.  The  Epitrochleo-anconceus,  a  small  muscle  oftea 
present  runs  from  the  back  of  the  inner  condyle  to  the  olecranon,  over  the  ulnar  nerve. 

The  Flexor  digitorum  sublimis  is  placed  beneath  the  previous  muscle;  it  is 
the  largest  of  the  muscles  of  the  superficial  group,  and  arises  by  three  heads — 
humeral,  ulnar,  and  radial.  The  humeral  head  arises  from  the  medial  epicondyle 
of  the  humerus  by  the  common  tendon,  from  the  ulnar  collateral  ligament  of  the 
elbow-joint,  and  from  the  intermuscular  septa  between  it  and  the  preceding 
muscles.  The  ulnar  head  arises  from  the  medial  side  of  the  coronoid  process, 
above  the  ulnar  origin  of  the  Pronator  teres  (see  Fig.  213,  page  216).  The  radial 
head  arises  from  the  oblique  line  of  the  radius,  extending  from  the  radial  tuberosity 
to  the  insertion  of  the  Pronator  teres.  The  muscle  speedily  separates  into  two 
planes  of  muscular  fibers,  superficial  and  deep:  the  superficial  plane  divides  into 
two  parts  which  end  in  tendons  for  the  middle  and  ring  fingers;  the  deep  plane 
gives  off  a  muscular  slip  to  join  the  portion  of  the  superficial  plane  which  is  asso- 
ciated with  the  tendon  of  the  ring  finger,  and  then  divides  into  two  parts,  which 
end  in  tendons  for  the  index  and  little  fingers.  As  the  four  tendons  thus  formed 
pass  beneath  the  transverse  carpal  ligament  into  the  palm  of  the  hand,  they  are 
arranged  in  pairs,  the  superficial  pair  going  to  the  middle  and  ring  fingers,  the  deep 
pair  to  the  index  and  little  fingers.  The  tendons  diverge  from  one  another  in  the 
palm  and  form  dorsal  relations  to  the  superficial  volar  arch  and  digital  branches 
of  the  median  and  ulnar  nerves.  Opposite  the  bases  of  the  first  phalanges  each 
tendon  divides  into  two  slips  to  allow  of  the  passage  of  the  corresponding  tendon 
of  the  Flexor  digitorum  profundus ;  the  two  slips  then  reunite  and  form  a  grooved 
channel  for  the  reception  of  the  accompanying  tendon  of  the  Flexor  digitorum 
profundus.  Finally  the  tendon  divides  and  is  inserted  into  the  sides  of  the  second 
phalanx  about  its  middle. 

Variations. — Absence  of  radial  head,  of  little  finger  portion;  accessory  slips  from  ulnar  tuberosity 
to  the  index  and  middle  finger  portions;  from  the  inner  head  to  the  Flexor  profundus;  from  the 
ulnar  or  annvilar  ligament  to  the  little  finger. 

The  Deep  Group  (Fig.  415). 

Flexor  digitorum  profundus.  Flexor  pollicis  longus. 

Pronator  quadratus. 

The  Flexor  digitorum  profundus  is  situated  on  the  ulnar  side  of  the  forearm, 
immediately  beneath  the  superficial  Flexors.  It  arises  from  the  upper  three- 
fourths  of  the  volar  and  medial  surfaces  of  the  body  of  the  ulna,  embracing  the 
insertion  of  the  Brachialis  above,  and  extending  below  to  within  a  short  distance 
of  the  Pronator  quadratus.  It  also  arises  from  a  depression  on  the  medial  side  of 
the  coronoid  process ;  by  an  aponeurosis  from  the  upper  three-fourths  of  the  dorsal 
border  of  the  ulna,  in  common  with  the  Flexor  and  Extensor  carpi  ulnaris;  and 
from  the  ulnar  half  of  the  interosseous  membrane.  The  muscle  ends  in  four  tendons 
which  run  under  the  transverse  carpal  ligament  dorsal  to  the  tendons  of  the  Flexor 


I 


THE  VOLAR  ANTI BRACHIAL  MUSCLES  449 

digitorum  sublimis.  Opposite  the  first  phalanges  the  tendons  pass  through  the 
openings  in  the  tendons  of  the  Flexor  digitorum  sublimis,  and  are  finally  inserted 
into  the  bases  of  the  last  phalanges.    The  portion  of  the  muscle  for  the  index  finger 

His  usually  distinct  throughout,  but  the  tendons  for  the  middle,  ring,  and  little 
fingers  are  connected  together  by  areolar  tissue  and  tendinous  slips,  as  far  as  the 
palm  of  the  hand. 
Fibrous  Sheaths  of  the  Flexor  Tendons. — After  leaving  the  palm,  the  tendons 
of  the  Flexores  digitorum  sublimis  and  profundus  lie  in  osseo-aponeurotic  canals 
(Fig.  427),  formed  behind  by  the  phalanges  and  in  front  by  strong  fibrous  bands, 
which  arch  across  the  tendons,  and  are  attached  on  either  side  to  the  margins  of 
the  phalanges.  Opposite  the  middle  of  the  proximal  and  second  phalanges  the 
bands  (digital  vaginal  ligaments)  are  very  strong,  and  the  fibers  are  transverse; 
but  opposite  the  joints  they  are  much  thinner,  and  consist  of  annular  and  cruciate 
ligamentous  fibers.    Each  canal  contains  a  mucous  sheath,  which  is  reflected  on 

I^«  the  contained  tendons. 
H  Within  each  canal  the  tendons  of  the  Flexores  digitorum  sublimis  and  profundus 
are  connected  to  each  other,  and  to  the  phalanges,  by  slender,  tendinous  bands, 
called  vincula  tendina  (Fig.  416).  There  are  two  sets  of  these;  (a)  the  vincula 
brevia,  which  are  two  in  number  in  each  finger,  and  consist  of  triangular  bands 
of  fibers,  one  connecting  the  tendon  of  the  Flexor  digitorum  sublimis  to  the  front 
of  the  first  interphalangeal  joint  and  head  of  the  first  phalanx,  and  the  other  the 
tendon  of  the  Flexor  digitorum  profundus  to  the  front  of  the  second  interphalan- 
geal joint  and  head  of  the  second  phalanx;  (6)  the  vincula  longa,  which  connect 
the  under  surfaces  of  the  tendons  of  the  Flexor  digitorum  profundus  to  thos j  of  the 
•  subjacent  Flexor  sublimis  after  the  tendons  of  the  former  have  passed  through 
the  latter. 

^^B  Variations. — The  index  finger  portion  may  arise  partly  from  the  upper  part  of  the  radius.  Slips 
from  the  inner  head  of  the  Flexor  sublimis,  medial  epicondyle,  or  the  coronoid  are  found.  Connec- 
tion with  the  Flexor  pollicis  longus. 

I^P  Four  small  muscles,  the  Lumbricales,  are  connected  with  the  tendons  of  the 
Flexor  profundus  in  the  palm.    They  will  be  described  with  the  muscles  of  the 

■hand  (page  464). 
The  Flexor  pollicis  longus  is  situated  on  the  radial  side  of  the  forearm,  lying 
in  the  same  plane  as  the  preceding.  It  arises  from  the  grooved  volar  surface  of 
the  body  of  the  radius,  extending  from  immediately  below  the  tuberosity  and 
oblique  line  to  within  a  short  distance  of  the  Pronator  quadratus.  It  arises  also 
from  the  adjacent  part  of  the  interosseous  membrane,  and  generally  by  a  fleshy 
slip  from  the  medial  border  of  the  coronoid  process,  or  from  the  medial  epicondyle 
of  the  humerus.  The  fibers  end  in  a  flattened  tendon,  which  passes  beneath  the 
transverse  carpal  ligament,  is  then  lodged  between  the  lateral  head  of  the  Flexor 
pollicis  brevis  and  the  oblique  part  of  the  Adductor  pollicis,  and,  entering  an  osseo- 
aponeurotic  canal  similar  to  those  for  the  Flexor  tendons  of  the  fingers,  is  inserted 
into  the  base  of  the  distal  phalanx  of  the  thumb.  The  volar  interosseous  nerve 
and  vessels  pass  downward  on  the  front  of  the  interosseous  membrane  between 
the  Flexor  pollicis  longus  and  Flexor  digitorum  profundus. 

Variations.— Slips  may  connect  with  Flexor  sublimis,  or  Profimdus,  or  Pronator  teres.  An  addi- 
[■tional  tendon  to  the  index  finger  is  sometimes  found. 

The  Pronator  quadratus  is  a  small,  flat,  quadrilateral  muscle,  extending  across 
[the  front  of  the  lower  parts  of  the  radius  and  ulna.    It  arises  from  the  pronator 
ridge  on  the  lower  part  of  the  volar  surface  of  the  body  of  the  ulna;  from  the  medial 
part  of  the  volar  surface  of  the  lower  fourth  of  the  ulna;  and  from  a  strong  apon- 
eurosis which  covers  the  medial  third  of  the  muscle.    The  fibers  pass  lateral  ward 
29 


450 


MYOLOGY 


and  slightly  downward,  to  be  inserted  into  the  lower  fourth  of  the  lateral  borS5 
and  the  volar  surface  of  the  body  of  the  radius.  The  deeper  fibers  of  the  muscle 
are  inserted  into  the  triangular  area  above  the  ulnar  notch  of  the  radius — aa 
attachment  comparable  with  the  origin  of  the  Supinator  from  the  triangular  area 
below  the  radial  notch  of  the  ulna. 


Tendon  of  Ext. 
carpi  rod.  longus 


Tendon  of  Ext. 
digitorum  communis 


Tendon  of  Extensor  indicis 
proprius 


First  Lumbricalis 


Vincula  hrevia 


Tendon  of  Ahdv^tor 

poinds  longus 
Cheater  multangular  bone 


Radial  artery 


Tendon  of  Ext.  pollicis  hrevis 


-Tendon  of  Ext.  pollicis  longus 


'lexor  digitorum  suhlimis 
Flexor  digitorum  profundus 


FiQ.  416. — Tendons  of  forefinger  and  vincula  tendina 


Variations. — Rarely  absent;  split  into  two  or  three  layers;  increased  attachment  upward  or 
downward. 

Nerves. — All  the  muscles  of  the  superficial  layer  are  supplied  by  the  median  nerve,  excepting 
the  Flexor  carpi  ulnaris,  which  is  supplied  by  the  ulnar.  The  Pronator  teres,  the  Flexor  carpi 
radialis,  and  the  Palmaris  longus  derive  their  supply  primarily  from  the  sixth  cervical  nerve; 
the  Flexor  digitorum  subUmis  from  the  seventh  and  eighth  cervical  and  first  thoracic  nerves, 
and  the  Flexor  carpi  ulnaris  from  the  eighth  cervical  and  first  thoracic.  Of  the  deep  layer,  the 
Flexor  digitorum  profundus  is  supplied  by  the  eighth  cervical  and  first  thoracic  through  the 
ulnar,  and  the  volar  interosseous  branch  of  the  median.  The  Flexor  pollicis  longus  and  Pronator 
quadratus  are  supplied  by  the  eighth  cervical  and  first  thoracic  through  the  volar  interosseous 
branch  of  the  median. 

Actions. — These  muscles  act  upon  the  forearm,  the  wrist,  and  hand.  The  Pronator  teres 
rotates  the  radius  upon  the  ulna,  rendering  the  hand  prone;  when  the  radius  is  fixed,  it  assists 
in  flexing  the  forearm.  The  Flexor  carpi  radialis  is  a  flexor  and  abductor  of  the  wrist;  it  also 
assists  in  pronating  the  hand,  and  in  bending  the  elbow.  The  Flexor  carpi  ulnaris  is  a  flexor  and 
adductor  of  the  wrist;  it  also  assists  in  bending  the  elbow.  The  Palmaris  longus  is  a  flexor  of  the 
wrist-joint;  it  also  assists  in  flexing  the  elbow.  The  Flexor  digitorum  subMmis  flexes  first  the 
middle  and  then  the  proximal  phalanges;  it  also  assists  in  flexing  the  wrist  and  elbow.  The 
Flexor  digitorum  profundus  is  one  of  the  flexors  of  the  phalanges.  After  the  Flexor  sublimis 
has  bent  the  second  phalanx,  the  Flexor  profundus  flexes  the  terminal  one;  but  it  cannot  do  so 
until  after  the  contraction  of  the  superficial  muscle.     It  also  assists  in  flexing  the  wrist.    The 


THE  DORSAL  ANTIBRACHIAL  MUSCLES 


451 


Flexor  pollicis  longus  is  a  flexor  of  the  phalanges  of  the  thumb;  when  the  thumb  is  fixed,  it  assists 
in  flexing  the  wrist.  The  Pronator  quadratus  rotates  the  radius  upon  the  ulna,  rendering  the 
hand  prone. 


Flexor  carpi  radialis  M 

Antibrachial  interos- 
seous membrane 


Lateral  antibrachial 
cutaneous  nerve 

Radial  artery 
and  nerve 


Median  nerve 

Palmaris  longus  M. 

Medial  antibrachial 
cutaneous  nerve 
[volar  branch] 

Flexor  digitorum 
sublimis  M. 


Cephalic  vein~~, 
Brachioradialis  Af ... 


Flexor  pollicis 
longus  M.' 


Radius - 


Tendo  m.  pronatoris,^ 
teretis 


Hxtensores  carpi  radiales, 
longus  and  brevis  Mm 

Extensor  digitorum.- 
■   communis  M. 


,,  Ulnar  artery  and  nerve 


Flexor  digitorum 
profundus  M. 


-Flexor  carpi  ulnaris 


"Basilic  vein 


''  Ulna 


Abductor  pollicis  / 

longus  M.  i 

Volar  interosseous  artery 

and  volar  antibrachial 

interosseous  nerve 


Extensor  carpi 
ulnaris  M. 

j  Extensor  pollicis 

S  longus  M. 

Extensor  digiti  quinti 
proprius  M.  and  dor- 
sal interosseous  artery 


Fig.  417. — Cross-section  through  the  middle  of  the  forearm.     (Eycleshymer  and  Schoemaker.) 


2.  The  Dorsal  Antibrachial  Muscles. 


These  muscles  are  divided  for  convenience  of  description  into  two  groups, 
superficial  and  deep. 

The  Superficial  Group  (Fig.  418). 

Brachioradialis.  Extensor  digitorum  communis. 

Extensor  carpi  radialis  longus.  Extensor  digiti  quinti  proprius. 

Extensor  carpi  radialis  brevis.  Extensor  carpi  ulnaris. 

Anconseus. 

The  Brachioradialis  {Supinator  longus)  is  the  most  superficial  muscle  on  the 
radial  side  of  the  forearm.  It  arises  from  the  upper  two-thirds  of  the  lateral 
supracondylar  ridge  of  the  humerus,  and  from  the  lateral  intermuscular  septum, 
being  limited  above  by  the  groove  for  the  radial  nerve.  Interposed  between  it 
and  the  Brachialis  are  the  radial  nerve  and  the  anastomosis  between  the  anterior 
branch  of  the  profunda  artery  and  the  radial  recurrent.  The  fibers  end  above 
the  middle  of  the  forearm  in  a  flat  tendon,  which  is  inserted  into  the  lateral  side 
of  the  base  of  the  styloid  process  of  the  radius.  The  tendon  is  crossed  near  its 
insertion  by  the  tendons  of  the  Abductor  pollicis  longus  and  Extensor  pollicis 
brevis;  on  its  ulnar  side  is  the  radial  artery. 

Variations. — Fusion  with  the  Brachialis;  tendon  of  insertion  may  be  divided  into  two  or  three 
slips;  insertion  partial  or  complete  into  the  middle  of  the  radius,  fasciculi  to  the  tendon  of  the 
Biceps,  the  tuberosity  or  oblique  line  of  the  radius;  slips  to  the  Extensor  carpi  radialis  longus  or 
Abductor  pollicis  longus;  absence;  rarely  doubled. 


452  ^^^^^^^        MYOLOGY 

The  Extensor  carpi  radialis  longus  {Exiemor  carpi  radialis  longior)  is  placed  partly 
beneath  the  Brachioradialis.  It  arises  from  the  lower  third  of  the  lateral  supracon- 
dylar ridge  of  the  humerus,  from  the  lateral  intermuscular  septum,  and  by  a  few 
fibers  from  the  common  tendon  of  origin  of  the  Extensor  muscles  of  the  forearm. 
The  fibers  end  at  the  upper  third  of  the  forearm  in  a  flat  tendon,  which  runs  along 
the  lateral  border  of  the  radius,  beneath  the  Abductor  pollicis  longus  and  Extensor 
pollicis  brevis ;  it  then  passes  beneath  the  dorsal  carpal  ligament,  where  it  lies  in  a 
groove  on  the  back  of  the  radius  common  to  it  and  the  Extensor  carpi  radialis  brevis, 
immediately  behind  the  styloid  process.  It  is  inserted  into  the  dorsal  surface  of 
the  base  of  the  second  metacarpal  bone,  on  its  radial  side. 

The  Extensor  carpi  radialis  brevis  {Extensor  carpi  radialis  brevior)  is  shorter  and 
thicker  than  the  preceding  muscle,  beneath  which  it  is  placed.  It  arises  from  the 
lateral  epicondyle  of  the  humerus,  by  a  tendon  common  to  it  and  the  three  following 
muscles;  from  the  radial  collateral  ligament  of  the  elbows-joint;  from  a  strong 
aponeurosis  which  covers  its  surface;  and  from  the  intermuscular  septa  between  it 
and  the  adjacent  muscles.  The  fibers  end  about  the  middle  of  the  forearm  in  a 
flat  tendon,  which  is  closely  connected  with  that  of  the  preceding  muscle,  and 
accompanies  it  to  the  wrist;  it  passes  beneath  the  Abductor  pollicis  longus  and 
Extensor  pollicis  brevis,  then  beneath  the  dorsal  carpal  ligament,  and  is  inserted 
into  the  dorsal  surface  of  the  base  of  the  third  metacarpal  bone  on  its  radial  side. 
Under  the  dorsal  carpal  ligament  the  tendon  lies  on  the  back  of  the  radius  in 
a  shallow  groove,  to  the  ulnar  side  of  that  which  lodges  the  tendon  of  the  Extensor 
carpi  radialis,  longus,  and  separated  from  it  by  a  faint  ridge. 

The  tendons  of  the  two  preceding  muscles  pass  through  the  same  compartment 
of  the  dorsal  carpal  ligament  in  a  single  mucous  sheath. 

Variations. — Either  muscle  may  split  into  two  or  three  tendons  of  insertion  to  the  second  and 
third  or  even  the  fourth  metacarpal.  The  two  muscles  may  unite  into  a  single  belly  with  two 
tendons.  Cross  slips  between  the  two  muscles  may  occur.  The  Extensor  carpi  radialis  inter- 
medius  rarely  arises  as  a  distinct  muscle  from  the  humerus,  but  is  not  uncommon  as  an  accessory 
slip  from  one  or  both  muscles  to  the  second  or  third  or  both  metacarpals.  The  Extenscrr  carpi 
radialis  accessorius  is  occasionally  found  arising  from  the  humerus  with  or  below  the  Extensor  carpi 
radialis  longus  and  inserted  into  the  first  metacarpal^  the  Abductor  pollicis  brevis,  the  First  dorsal 
interosseous,  or  elsewhere. 

The  Extensor  digitorum  communis  arises  from  the  lateral  epicondyle  of  the 
humerus,  by  the  common  tendon;  from  the  intermuscular  septa  between  it  and  the 
adjacent  muscles,  and  from  the  antibrachial  fascia.  It  divides  below  into  four 
tendons,  which  pass,  together  with  that  of  the  Extensor  indicis  proprius,  through 
a  separate  compartment  of  the  dorsal  carpal  ligament,  within  a  mucous  sheath. 
The  tendons  then  diverge  on  the  back  of  the  hand,  and  are  inserted  into  the  second 
and  third  phalanges  of  the  fingers  in  the  following  manner.  Opposite  the  meta- 
carpophalangeal articulation  each  tendon  is  bound  by  fasciculi  to  the  collateral 
ligaments  and  serves  as  the  dorsal  ligament  of  this  joint;  after  having  crossed  the 
joint,  it  spreads  out  into  a  broad  aponeurosis,  which  covers  the  dorsal  surface  of 
the  first  phalanx  and  is  reinforced,  in  this  situation,  by  the  tendons  of  the  Inter- 
ossei  and  Lumbricalis.  Opposite  the  first  interphalangeal  joint  this  aponeurosis 
divides  into  three  slips;  an  intermediate  and  two  collateral:  the  former  is  inserted 
into  the  base  of  the  second  phalanx;  and  the  two  collateral,  which  are  continued 
onward  along  the  sides  of  the  second  phalanx,  unite  by  their  contiguous  margins, 
and  are  inserted  into  the  dorsal  surface  of  the  last  phalanx.  As  the  tendons  cross 
the  interphalangeal  joints,  they  furnish  them  with  dorsal  ligaments.  The  tendon 
to  the  index  finger  is  accompanied  by  the  Extensor  indicis  proprius,  which  lies 
on  its  ulnar  side.  On  the  back  of  the  hand,  the  tendons  to  the  middle,  ring,  and 
little  fingers  are  connected  by  two  obliquely  placed  bands,  one  from  the  third 
tendon  passing  downward  and  lateralward  to  the  second  tendon,  and  the  other 


THE  DORSAL  ANTIBRACHIAL  MUSCLES 


453 


Fig.  419. — Posterior  surface  of  the  forearm.     Deep 
muscles. 


454  ^BBBRSi^r        MYOLOGY 

passing  from  the  same  tendon  downward  and  medialward  to  the  fourth.     Occa- 
sionally the  first  tendon  is  connected  to  the  second  by  a  thin  transverse  band. 

Variations. — An  increase  or  decrease  in  the  number  of  tendons  is  common;  an  additional  slip- 
to  the  thumb  is  sometimes  present. 

The  Extensor  digit!  quinti  proprius  {Extensor  minimi  digiti)  is  a  slender  musck; 
placed  on  the  medial  side  of  the  Extensor  digitorum  communis,  with  which  it  is 
generally  connected.  It  arises  from  the  common  Extensor  tendon  by  a  thin 
tendinous  slip,  from  the  intermuscular  septa  between  it  and  the  adjacent  muscles. 
Its  tendon  runs  through  a  compartment  of  the  dorsal  carpal  ligament  behind  the 
distal  radio-ulnar  joint,  then  divides  into  two  as  it  crosses  the  hand,  and  finally 
joins  the  expansion  of  the  Extensor  digitorum  communis  tendon  on  the  dorsum 
of  the  first  phalanx  of  the  little  finger. 

Variations. — An  additional  fibrous  slip  from  the  lateral  epicondyle;  the  tendon  of  insertion  may 
not  divide  or  may  send  a  slip  to  the  ring  finger.  Absence  of  muscle  rare;  fusion  of  the  beUy  with 
the  Extensor  digitorum  commimis  not  uncommon. 

The  Extensor  carpi  ulnaris  lies  on  the  ulnar  side  of  the  forearm.  It  arises 
from  the  lateral  epicondyle  of  the  humerus,  by  the  common  tendon;  by  an  aponeu- 
rosis from  the  dorsal  border  of  the  ulna  in  common  with  the  Flexor  carpi  ulnaris 
and  the  Flexor  digitorum  profundus;  and  from  the  deep  fascia  of  the  forearm. 
It  ends  in  a  tendon,  which  runs  in  a  groove  between  the  head  and  the  styloid 
process  of  the  ulna,  passing  through  a  separate  compartment  of  the  dorsal  carpal 
ligament,  and  is  inserted  into  the  prominent  tubercle  on  the  ulnar  side  of  the  base 
of  the  fifth  metacarpal  bone. 

Variations. — Doubling;  reduction  to  tendinous  band;  insertion  partially  into  fourth  metacarpal. 
In  many  cases  (52  per  cent.)  a  slip  is  continued  from  the  insertion  of  the  tendon  anteriorly 
over  the  Opponens  digiti  quinti,  to  the  fascia  covering  that  muscle,  the  metacarpal  bone,  the 
capsule  of  the  metacarpophalangeal  articulation,  or  the  first  phalanx  of  the  little  finger.  This  slip 
may  be  replaced  by  a  muscular  fasciculus  arising  from  or  near  the  pisiform. 

The  Anconseus  is  a  small  triangular  muscle  which  is  placed  on  the  back  of  the 
elbow-joint,  and  appears  to  be  a  continuation  of  the  Triceps  brachii.  It  arises 
by  a  separate  tendon  from  the  back  part  of  the  lateral  epicondyle  of  the  humerus; 
its  fibers  diverge  and  are  inserted  into  the  side  of  the  olecranon,  and  upper  fourth 
of  the  dorsal  surface  of  the  body  of  the  ulna. 


The  Deep  Group  (Fig.  419). 

Supinator.  Extensor  pollicis  brevis. 

Abductor  pollicis  longus.  Extensor  pollicis  longus. 

Extensor  indicis  proprius. 

The  Supinator  (Supinator  brevis)  (Fig.  420)  is  a  broad  muscle,  curved  around 
the  upper  third  of  the  radius.  It  consists  of  two  planes  of  fibers,  between  which 
the  deep  branch  of  the  radial  nerve  lies.  The  two  planes  arise  in  common^ — the 
superficial  one  by  tendinous  and  the  deeper  by  muscular  fibers — from  the  lateral 
epicondyle  of  the  humerus;  from  the  radial  collateral  ligament  of  the  elbow-joint, 
and  the  annular  ligament;  from  the  ridge  on  the  ulna,  which  runs  obliquely  down- 
ward from  the  dorsal  end  of  the  radial  notch ;  from  the  triangular  depression  below 
the  notch;  and  from  a  tendinous  expansion  which  covers  the  surface  of  the  muscle. 
The  superficial  fibers  surround  the  upper  part  of  the  radius,  and  are  inserted  into 
the  lateral  edge  of  the  radial  tuberosity  and  the  oblique  line  of  the  radius,  as  low 
down  as  the  insertion  of  the  Pronator  teres.    The  upper  fibers  of  the  deeper  plane 


I 


THE  DORSAL  ANTIBRACHIAL  MUSCLES 


455 


the  neck  of  the  radius  above  the  tuber- 
its  medial  surface;  the  greater  part  of 
the  dorsal  and  lateral  surfaces  of  the 
oblique  line  and  the  head  of  the  bone. 


Lateral  epicondyle 

Radial  collateral  I  ig. 
Annular  ligament 

Deep  branch  of  radial 
nerve 


Interosseous  recurrent 
art. 


Deep  "branch  of  radial 

nerve 
Dorsal  interosseous 

art. 


form  a  sling-like  fasciculus,  which  encircles 
osity  and  is  attached  to  the  back  part  of 
this  portion  of  the  muscle  is  inserted  into 
body  of  the  radius,  midway  between  the 

The  Abductor  pollicis  longus  {Ex- 
tensor OSS.  metacarpi  pollicis)  lies  im- 
mediately below  the  Supinator  and 
is  sometimes  united  with  it.  It 
arises  from  the  lateral  part  of  the 
dorsal  surface  of  the  body  of  the  ulna 
below  the  insertion  of  the  Anco- 
nseus,  from  the  interosseous  mem- 
brane, and  from  the  middle  third  of 
the  dorsal  surface  of  the  body  of  the 
radius.  Passing  obliquely  downward 
and  lateralward,  it  ends  in  a  tendon, 
which  runs  through  a  groove  on  the 
lateral  side  of  the  lower  end  of  the 
radius,  accompanied  by  the  tendon 
of  the  Extensor  pollicis  brevis,  and 
is  inserted  into  the  radial  side  of  the 
base  of-  the  first  metacarpal  bone. 
It  occasionally  gives  off  two  slips 
near  its  insertion :  one  to  the  greater 
multangular  bone  and  the  other  to 
blend  with  the  origin  of  the  Abduc- 
tor pollicis  brevis. 

Variations.  —  More  or  less  doubling  of 
muscle  and  tendon  with  insertion  of  the 
extra  tendon  into  the  first  metacarpal,  the 
greater  multangular,  or  into  the  Abductor 
pollicis  brevis  or  Opponens  pollicis. 

The  Extensor  pollicis  brevis  {Ex- 
tensor primi  internodii  pollicis)  lies 
on  the  medial  side  of,  and  is  closely 
connected  with,  the  Abductor  pollicis 
longus.  It  arises  from  the  dorsal  surface  of  the  body  of  the  radius  below  that 
muscle,  and  from  the  interosseous  membrane.  Its  direction  is  similar  to  that  of 
the  Abductor  pollicis  longus,  its  tendon  passing  through  the  same  groove  on  the 
lateral  side  of  the  lower  end  of  the  radius,  to  be  inserted  into  the  base  of  the  first 
phalanx  of  the  thumb. 

Variations. — Absence;  fusion  of  tendon  with  that  of  the  Extensor  pollicis  longus. 

The  Extensor  pollicis  longus  {Extensor  secundi  internodii  pollicis)  is  much  larger 
than  the  preceding  muscle,  the  origin  of  which  it  partly  covers.  It  arises  from 
the  lateral  part  of  the  middle  third  of  the  dorsal  surface  of  the  body  of  the  ulna 
below  the  origin  of  the  Abductor  pollicis  longus,  and  from  the  interosseous  mem- 
brane. It  ends  in  a  tendon,  which  passes  through  a  separate  compartment  in  the 
dorsal  carpal  ligament,  lying  in  a  narrow,  oblique  groove  on  the  back  of  the  lower 
end  of  the  radius.  It  then  crosses  obliquely  the  tendons  of  the  Extensores  carpi 
radialis  longus  and  brevis,  and  is  separated  from  the  Extensor  brevis  pollicis  by  a 
triangular  interval,  in  which  the  radial  artery  is  found;  and  is  finally  inserted  into 
the  base  of  the  last  phalanx  of  the  thumb.     The  radial  artery  is  crossed  by  the 


Fig.  420.— The  Supinator. 


456  Tdi^Mn^^        MYOLOGY 

tendons  of  the  Abductor  pollicis  longus  and  of  the  Extensores  pollicis  lon^^nl 
brevis. 

The  Extensor  indicis  proprius  (Extensor  indicis)  is  a  narrow,  elongated  muscle, 
placed  medial  to,  and  parallel  with,  the  preceding.  It  arises,  from  the  dorsal  sur- 
face of  the  body  of  the  ulna  below  the  origin  of  the  Extensor  pollicis  longus,  and 
from  the  interosseous  membrane.  Its  tendon  passes  under  the  dorsal  carpal 
ligament  in  the  same  compartment  as  that  which  transmits  the  tendons  of  the 
Extensor  digitorum  communis,  and  opposite  the  head  of  the  second  metacarpal 
bone,  joins  the  ulnar  side  of  the  tendon  of  the  Extensor  digitorum  communis 
which  belongs  to  the  index  finger. 

Variations. — Doubling;  the  ulnar  part  may  pass  beneath  the  dorsal  carpal  ligament  with  the 
Extensor  digitorum  communis;  a  slip  from  the  tendon  may  pass  to  the  index  finger. 

Nerves. — The  Brachioradialis  is  supphed  by  the  fifth  and  sixth,  the  Extensores  carpi  radialis 
longus  and  brevis  by  the  sixth  and  seventh,  and  the  Anconajus  by  the  seventh  and  eighth  cervical 
nerves,  through  the  radial  nerve;  'the  remaining  muscles  are  innervated  through  the  deep  radial 
nerve,  the  Supinator  being  supplied  by  the  sixth,  and  all  the  other  muscles  by  the  seventh  cervical. 

Actions. — The  muscles  of  the  lateral  and  dorsal  aspects  of  the  forearm,  which  comprise  all 
the  Extensor  muscles  and  the  Supinator,  act  upon  the  forearm,  wrist,  and  hand;  they  are  the 
direct  antagonists  of  the  Pronator  and  Flexor  muscles.  The  Anconeus  assists  the  Triceps  in 
extending  the  forearm.  The  Brachioradialis  is  a  flexor  of  the  elbow-joint,  but  only  acts  as  such 
when  the  movement  of  flfexion  has  been  initiated  by  the  Biceps  brachii  and  Brachialis.  The 
action  of  the  Supinator  is 'suggested  by  its  name;  it  assists  the  Biceps  in  bringing  the  hand  into 
the  supine  position.  The  Extensor  carpi  radialis  longus  extends  the  wrist  and  abducts  the  hand. 
It  may  also  assist  in  bending  the  elbow-joint;  at  all  events  it  serves  to  fix  or  steady  this' articula- 
tion. The  Extensor  carpi/radialis  brevis  extends  the  wrist,  and  may  also  act  slightly  as  an  abductor 
of  the  hand.  The  Extensor  carpi  ulnaris  extends  the  wrist,  but  when  acting  alone  inclines  the 
hand  toward  the  ulnar  side;  by  its  continued  action  it  extends  the  elbow-joint.  The  Extensor 
digitorum  communis  extends  the  phalanges,  then  the  wrist,  and  finally  the  elbow.  It  acts  prin- 
cipally on  the  proximal  phalanges,  the  middle  and  terminal  phalanges  being  extended  mainly 
by  the  Interossei  and  Lumbricales.  It  tends  to  separate  the  fingers  as  it  extends  them.  The 
Extensor  digiti  quinti  proprius  extends  the  little  finger,  and  by  its  continued  action  assists  in 
extending  the  wrist.  It  is  owing  to  this  muscle  that  the  little  finger  can  be  extended  or  pointed 
while  the  others  are  flexed.  The  chief  action  of  the  Abductor  pollicis  longus  is  to  carry  the  thumb 
laterally  from  the  palm  of  the  hand.  By  its  continued  action  it  helps  to  extend  and  abduct  the 
wrist.  The  Extensor  poUicis  brevis  extends  the  proximal  phalanx,  and  the  Extensor  pollicis 
longus  the  terminal  phalanx  of  the  thumb;  by  their  continued  action  they  help  to  extend  and 
abduct  the  wrist.  The  Extensor  indicis  proprius  extends  the  index  finger,  and  by  its  continued 
action  assists  in  extending  the  wrist. 

VI.     THE   MUSCLES    AND   FASCM)   OF   THE   HAND. 

The  muscles  of  the  hand  are  subdivided  into  three  groups:  (1)  those  of  the 
thumb,  which  occupy  the  radial  side  and  produce  the  thenar  eminence ;  (2)  those 
of  the  little  finger,  which  occupy  the  ulnar  side  and  give  rise  to  the  hypothenar 
eminence ;  (3)  those  in  the  middle  of  the  palm  and  between  the  metacarpal  bones. 

Volar  Carpal  Ligament  (ligamentum  carpi  volare). — The  volar  carpal  ligament 
is  the  thickened  band  of  antibrachial  fascia  which  extends  from  the  radius  to  the 
ulna  over  the  Flexor  tendons  as  they  enter  the  wrist. 

Transverse  Carpal  Ligament  (ligamentum  carpi  transversum;  anterior  annular 
ligament)  (Figs.  421,  422). — The  transverse  carpal  ligament  is  a  strong,  fibrous 
band,  which  arches  over  the  carpus,  converting  the  deep  groove  on  the  front  of 
the  carpal  bones  into  a  tunnel,  through  which  the  Flexor  tendons  of  the  digits 
and  the  median  nerve  pass.  It  is  attached,  medially,  to  the  pisiform  and  the 
hamulus  of  the  hamate  bone;  laterally,  to  the  tuberosity  of  the  navicular,  and  to 
the  medial  part  of  the  volar  surface  and  the  ridge  of  the  greater  multangular.  It 
is  continuous,  above,  with  the  volar  carpal  ligament;  and  below,  with  the  palmar 
aponeurosis.  It  is  crossed  by  the  ulnar  vessels  and  nerve,  and  the  cutaneous 
branches  of  the  median  and  ulnar  nerves.    At  its  lateral  end  is  the  tendon  of  the 


I 


THE  MUSCLES  AND  FASCIA  OF  THE  HAND 


457 


lexor  carpi  radialis,  which  Hes  in  the  groove  on  the  greater  multangular  between 
the  attachments  of  the  ligament  to  the  bone.  On  its  volar  surface  the  tendons  of 
the  Palmaris  longus  and  Flexor  carpi  ulnaris  are  partly  inserted;  below,  it  gives 
origin  to  the  short  muscles  of  the  thumb  and  little  finger 

Median  nerve      _,  , , .    . 

Palmaris  longus      |         Flexor  dig.  svbhmts 

__  .  \        I  A  XJlTiar  artery 


raimans  Longus 
Flex.  poll.  long.    \ 
Flex.  carp.  rod.        \,-\- 
JRadial  artery  ~      ^^^"Z^^P^  r' 

Abd.  poll.  long. 
Ext  poll  brev. 

Ext.  carp.  rad.  long. 


Ulnar  nerve 

Flex.  carp,  vln. 


Flex.  dig.  profundus. 


Ext.  carp.  rad.  brev.  ."      ,    ~\ " V       \  Ext.  carp.  vln. 

Ext.  poll.  long.         \       \  \       Distal  radio-ulnar  artic. 

Ext,  indicis.  prop.      \  Ext.  dig.  quinfi  prop. 

Ext.  dig.  commun. 
Fia.  421. — Transverse  section  across  distal  ends  of  radius  and  ulna. 

The  Mucous  Sheaths  of  the  Tendons  on  the  Front  of  the  Wrist. — Two  sheaths  envelop 
the  tendons  as  they  pass  beneath  the  transverse  carpal  ligament,  one  for  the 
Flexores  digitorum  sublimis  and  profundus,  the  other  for  the  Flexor  pollicis 
longus  (Fig.  423).  They  extend  into  the  forearm  for  about  2.5  cm.  above  the 
transverse  carpal  ligament,  and  occasionally  communicate  with  each  other  under 

Median  nerve    Transverse  carpal  ligament 
Flex.  poll.  long.    \    \  Palmaris  longus 
Flex,  carpi  rad.     \    \    \  Flex.  dig.  sublimis 

2Iusdes  of  thumb       \      \    \    \  \  //         Ulnar  art.  and  nerve 

_  \__— -^    \    \   -\— \         //         £_^  Muscles  of  little  finger 

Abd.poU.  long. 

Ext.  poll.  brev. 


Flex,  dig,  profundus 


Bxt.  carp.  rad.  long, 

Badial  artery 

Ext.  carp.  rad.  brev. 

Ext,  poll,  long. 


Ext.  carp.  uln. 
Ext.  dig.  quinti  prop. 


Ext.  dig.  communis 
Ext.  indicis  prop. 
Fig.  422. — Transverse  section  across  the  wrist  and  digits. 


the  ligament.  The  sheath  which  surrounds  the  Flexores  digitorum  extends  down- 
ward about  half-way  along  the  metacarpal  bones,  where  it  ends  in  blind  diverticula 
around  the  tendons  to  the  index,  middle,  and  ring  fingers.  It  is  prolonged  on 
the  tendons  to  the  little  finger  and  usually  communicates  with  the  mucous 


458 


MYOLOGY 


■ 


sheath  of  these  tendons.  The  sheath  of  the  tendon  of  the  Flexor  polHcis  longus 
is  continued  along  the  thumb  as  far  as  the  insertion  of  the  tendon.  The  mucous 
sheaths  enveloping  the  terminal  parts  of  the  tendons  of  the  Flexores  digitorum 
have  been  described  on  page  449. 


Sheaths  of  terminal 
parts  of  Flexores 
digitorum 


Muscles  of  thenar 
eminence 


Sheath  of  Flexor 
poinds  longus 

SJieath  of  Flexor  carpi 
radialis 


Muscles  of  hypo- 
thenar  emirteiux 


Common  sheath  of 
Flexores  digitorum 
sublimis  and 
profundus 


Flexor  carpi  idnaris 


FiQ.  423. — The  mucous  sheaths  of  the  tendons  on  the  front  of  the  wrist  and  digits. 

Dorsal  Carpal  Ligament  (ligamentum  carpi  dorsale;  posterior  annular  ligament) 
(Figs.  421,  422). — The  dorsal  carpal  ligament  is  a  strong,  fibrous  band,  extending 
obliquely  downward  and  medialward  across  the  back  of  the  wrist,  and  consisting 
of  part  of  the  deep  fascia  of  the  back  of  the  forearm,  strengthened  by  the  addition 
of  some  transverse  fibers.    It  is  attached,  medially,  to  the  styloid  process  of  the  ulna 


THE  MUSCLES  AND  FASCIA  OF  THE  HAND 


459 


and  to  the  triangular  and  pisiform  bones;  laterally,  to  the  lateral  margin  of  the 
radius;  and,  in  its  passage  across  the  wrist,  to  the  ridges  on  the  dorsal  surface  of 
the  radius. 


^^.) 


T. 


CXTCS 


jlTOP 


Abd.  poll.  long. 


Ext.  carp.  rod.  long. 
Ext.  carp.  rad.  hrev. 


Fia.  424. — The  mucous  sheaths  of  the  tendons  on  the  back  of  the  wrist. 


The  Mucous  Sheaths  of  the  Tendons  on  the  Back  of  the  Wrist. — Between  the  dorsal 
carpal  ligament  and  the  bones  six  compartments  are  formed  for  the  passage  of 
tendons,  each  compartment  having  a  separate  mucous  sheath.  One  is  found  in 
each  of  the  following  positions  (Fig.  424) :  (1)  on  the  lateral  side  of  the  styloid  pro- 
cess, for  the  tendons  of  the  Abductor  pollicis  longus  and  Extensor  pollicis  brevis; 
(2)  behind  the  styloid  process,  for  the  tendons  of  the  Extensores  carpi  radialis 


460 


MYOLOGY 


longus  and  brevis;  (3)  about  the  middle  of  the  dorsal  surface  of  the  radius,  for  the 
tendon  of  the  Extensor  pollicis  longus;  (4)  to  the  medial  side  of  the  latter,  for  the 
tendons  of  the  Extensor  digitorum  communis  and  Extensor  indicis  proprius;  (5) 
opposite  the  interval  between  the  radius  and  ulna,  for  the  Extensor  digiti  quinti 
proprius;  (6)  between  the  head  and  styloid  process  of  the  ulna,  for  the  tendon  of 
the  Extensor  carpi  ulnaris.  The  sheaths  lining  these  compartments  extend  from 
above  the  dorsal  carpal  ligament;  those  for  the  tendons  of  Abductor  pollicis  longus, 
Extensor  brevis  pollicis,  Extensores  carpi  radialis,  and  Extensor  carpi  ulnaris 
stop  immediately  proximal  to  the  bases  of  the  metacarpal  bones,  while  the  sheaths 
for  Extensor  communis  digitorum.  Extensor  indicis  proprius,  and  Extensor  digiti 
quinti  proprius  are  prolonged  to  the  junction  of  the  proximal  and  intermediate 
thirds  of  the  metacarpus. 


Proper  digital  artery  and  nerve 


I 


Ulnar  artery  and  nerve 


Fig.    iJ'j       1  In  ij.il.ii.u  aponeurosis. 


Palmar  Aponeurosis  {aponeurosis  palmaris;  palmar  fascia)  (Fig.  425).  —  The 
palmar  aponeurosis  invests  the  muscles  of  the  palm,  and  consists  of  central,  lateral, 
and  medial  portions. 

The  central  portion  occupies  the  middle  of  the  palm,  is  triangular  in  shape,  and 
of  great  strength  and  thickness.  Its  apex  is  continuous  with  the  lower  margin 
of  the  transverse  carpal  ligament,  and  receives  the  expanded  tendon  of  the  Pal 


THE  LATERAL  VOLAR  MUSCLES  461 

maris  longus.  Its  base  divides  below  into  four  slips,  one  for  each  finger.  Each 
slip  gives  off  superficial  fibers  to  the  skin  of  the  palm  and  fihger,  those  to  the  palm 
joining  the  skin  at  the  furrow  corresponding  to  the  metacarpophalangeal  articula- 
tions, and  those  to  the  fingers  passing  into  the  skin  at  the  transverse  fold  at  the 
bases  of  the  fingers.  The  deeper  part  of  each  slip  subdivides  into  two  processes, 
which  are  inserted  into  the  fibrous  sheaths  of  the  Flexor  tendons.  From  the  sides 
of  these  processes  offsets  are  attached  to  the  transverse  metacarpal  ligament. 
By  this  arrangement  short  channels  are  formed  on  the  front  of  the  heads  of  the 
metacarpal  bones;  through  these  the  Flexor  tendons  pass.  The  intervals  between 
the  four  slips  transmit  the  digital  vessels  and  nerves,  and  the  tendons  of  the  Lum- 
bricales.  At  the  points  of  division  into  the  slips  mentioned,  numerous  strong, 
transverse  fasciculi  bind  the  separate  processes  together.  The  central  part  of  the 
palmar  aponeurosis  is  intimately  bound  to  the  integument  by  dense  fibroareolar 
tissue  forming  the  superficial  palmar  fascia,  and  gives  origin  by  its  medial  margin 
to  the  Palmaris  brevis.  It  covers  the  superficial  volar  arch,  the  tendons  of  the 
Flexor  muscles,  and  the  branches  of  the  median  and  ulnar  nerves;  and  on  either 
side  it  gives  off  a  septum,  which  is  continuous  with  the  interosseous  aponeurosis, 
and  separates  the  intermediate  from  the  collateral  groups  of  muscles. 

The  lateral  and  medial  portions  of  the  palmar  aponeurosis  are  thin,  fibrous  layers, 
which  cover,  on  the  radial  side,  the  muscles  of  the  ball  of  the  thumb,  and,  on  the 
ulnar  side,  the  muscles  of  the  little  finder;  they  are  continuous  with  the  central 
portion  and  with  the  fascia  on  the  dorsum  of  the  hand. 

The  Superficial  Transverse  Ligament  of  the  Fingers  is  a  thin  band  of  transverse 
fasciculi  (Fig.  425) ;  it  stretches  across  the  roots  of  the  four  fingers,  and  is  closely 
attached  to  the  skin  of  the  clefts,  and  medially  to  the  fifth  metacarpal  bone, 
forming  a  sort  of  rudimentary  web.  Beneath  it  the  digital  vessels  and  nerves 
pass  to  their  destinations. 

1.  The  Lateral  Volar  Muscles  (Figs.  426,  427). 

Abductor  pollicis  brevis.  Flexor  pollicis  brevis. 

Opponens  pollicis.  Adductor  pollicis  (obliquus). 

Adductor  pollicis  (transversus). 

The  Abductor  pollicis  brevis  (Abductor  pollicis)  is  a  thin,  flat  muscle,  placed 
immediately  beneath  the  integument.  It  arises  from  the  transverse  carpal  liga- 
ment, the  tuberosity  of  the  navicular,  and  the  ridge  of  the  greater  multangular, 
frequently  by  two  distinct  slips.  Running  lateralward  and  downward,  it  is 
inserted  by  a  thin,  flat  tendon  into  the  radial  side  of  the  base  of  the  first  phalanx 
of  the  thumb  and  the  capsule  of  the  metacarpophalangeal  articulation. 

The  Opponens  pollicis  is  a  small,  triangular  muscle,  placed  beneath  the  pre- 
ceding. It  arises  from  the  ridge  on  the  greater  multangular  and  froih  the  trans- 
verse carpal  ligament,  passes  downward  and  lateralward,  and  is  inserted  into  the 
whole  length  of  the  metacarpal  bone  of  the  thumb  on  its  radial  side. 

The  Flexor  pollicis  brevis  consists  of  two  portions,  lateral  and  medial.  The 
lateral  and  more  superficial  portion  arises  from  the  lower  border  of  the  transverse 
carpal  ligament  and  the  lower  part  of  the  ridge  on  the  greater  multangular  bone; 
it  passes  along  the  radial  side  of  the  tendon  of  the  Flexor  pollicis  longus,  and, 
becoming  tendinous,  is  inserted  into  the  radial  side  of  the  base  of  the  first  phalanx 
of  the  thumb;  in  its  tendon  of  insertion  there  is  a  sesamoid  bone.  The  medial 
and  deeper  portion  of  the  muscle  is  very  small,  and  arises  from  the  ulnar  side  of  the 
first  metacarpal  bone  between  the  Adductor  pollicis  (obliquus)  and  the  lateral 
head  of  the  first  Interosseous  dorsalis,  and  is  inserted  into  the  ulnar  side  of  the  base 
of  the  first  phalanx  with  the  Adductor  pollicis  (obliquus).  The  medial  part  of 
the  Flexor  brevis  pollicis  is  sometimes  described  as  the  first  Interosseous  volaris. 


462 


MYOLOGY 


The  Adductor  pollicis  (obliquus)  {Adductor  ohliquus  j^ollicis)  arises  by  several 
slips  from  the  capitate  bone,  the  bases  of  the  second  and  third  metacarpals,  the 
intercarpal  ligaments,  and  the  sheath  of  the  tendon  of  the  Flexor  carpi  radialis. 
From  this  origin  the  greater  number  of  fibers  pass  obliquely  downward  and  con- 
verge to  a  tendon,  which,  uniting  with  the  tendons  of  the  medial  portion  of  the 
Flexor  pollicis  brevis  and  the  transverse  part  of  the  Adductor,  is  inserted  into 
the  ulnar  side  of  the  base  of  the  first  phalanx  of  the  thumb,  a  sesamoid  bone 
being  present  in  the  tendon.  A  considerable  fasciculus,  however,  passes  more 
obliquely  beneath  the  tendon  of  the  Flexor  pollicis  longus  to  join  the  lateral  portion 
of  the  Flexor  brevis  and  the  Abductor  pollicis  brevis. 


I 


Piaometacarpal  lig. 


Fia.  426. — The  muscles  of  the  thumb. 

The  Adductor  pollicis  (transversus)  (Adductor  transversus  pollicis)  (Fig.  426) 
is  the  most  deeply  seated  of  this  group  of  muscles.  It  is  of  a  triangular  form 
arising  by  a  broad  base  from  the  lower  two-thirds  of  the  volar  surface  of  the 
third  metacarpal  bone;  the  fibers  converge,  to  be  inserted  with  the  medial  part  of 
the  Flexor  pollicis  brevis  and  the  Adductor  pollicis  (obliquus)  into  the  ulnar  side 
of  the  base  of  the  first  phalanx  of  the  thumb. 

Variations. — The  Abductor  pollicis  brevis  is  often  divided  into  an  outer  and  an  inner  part; 
accessory  slips  from  the  tendon  of  the  Abductor  pollicis  longus  or  Palmaris  longus,  more  rarely 
from  the  Extensor  carpi  radialis  longus,  from  the  styloid  process  or  Opponens  pollicis  or  from  the 
skin  over  the  thenar  eminence.  The  deep  head  of  the  Flexor  poUicis  brevis  may  be  absent  or 
enlarged.  The  two  adductors  vary  in  their  relative  extent  and  in  the  closeness  of  their  connection. 
The  Adductor  obliquus  may  receive  a  slip  from  the  transverse  metacarpal  ligament. 

Nerves. — The  Abductor  brevis,  Opponens,  and  lateral  head  of  the  Flexor  pollicis  brevis  are 
supplied  by  the  sixth  and  seventh  cervical  nerves  through  the  median  nerve;  the  medial  head 
of  the  Flexor  brevis,  and  the  Adductor,  by  the  eighth  cervical  through  the  ulnar  nerve. 

Actions. — The  Abductor  pollicis  brevis  draws  the  thumb  forward  in  a  plane  at  right  angles 
to  that  of  the  palm  of  the  hand.  The  Adductor  pollicis  is  the  opponent  of  this  muscle,  and  approxi- 
mates the  thumb  to  the  palm.  The  Opponens  polUcis  flexes  the  metacarpal  bone,  i.  e.,  draws 
it  medialward  over  the  palm;  the  Flexor  pollicis  brevis  flexes  and  adducts  the  proximal  phalanx. 

2.  The  Medial  Volar  Muscles  (Figs.  426,  427). 

Palmaris  brevis.  Flexor  digiti  quinti  brevisi 

Abductor  digiti  quinti.  Opponens  digiti  quinti. 


THE  MEDIAL  VOLAR  MUSCLES 


463 


The  Palmaris  brevis  is  a  thin,  quadrilateral  muscle,  placed  beneath  the  integu- 
ment of  the  ulnar  side  of  the  hand.    It  arises  by  tendinous  fasciculi  from  the 
transverse  carpal  ligament  and  palmar  aponeurosis;  the  fleshy  fibers  are  inserted 
skin  on  the  ulnar  border  of  the  palm  of  the  hand. 


1^ 


427. — The  muscles  of  the  left  hand.     Palmar  surface. 

The  Abductor  digiti  quinti  (Abductor  minimi  digiti)  is  situated  on  the  ulnar 
border  of  the  palm  of  the  hand.  It  arises  from  the  pisiform  bone  and  from  the 
iendon  of  the  Flexor  carpi  ulnaris,  and  ends  in  a  flat  tendon,  which  divides  into  two 
slips ;  one  is  inserted  into  the  ulnar  side  of  the  base  of  the  first  phalanx  of  the  little 
finger;  the  other  into  the  ulnar  border  of  the  aponeurosis  of  the  Extensor  digiti 
quinti  proprius. 


K— 


464 


MYOLOGY 


I 


The  Flexor  digit!  quinti  brevis  {Flexor  brevis  minimi  digiti)  lies  on  the  sane 
plane  as  the  preceding  muscle,  on  its  radial  side.  It  arises  from  the  convex  surface 
of  the  hamulus  of  the  hamate  bone,  and  the  volar  surface  of  the  transverse  carpal 
ligament,  and  is  inserted  into  the  ulnar  side  of  the  base  of  the  first  phalanx  of  tlie 
little  finger.  It  is  separated  from  the  Abductor,  at  its  origin,  by  the  deep  branches 
of  the  ulnar  artery  and  nerve.  This  muscle  is  sometimes  wanting;  the  Abductor 
is  then,  usually,  of  large  size. 

The  Opponens  digiti  quinti  {Opponens  minimi  digiti)  (Fig.  426)  is  of  a  tri- 
angular form,  and  placed  immediately  beneath  the  preceding  muscles.  It  arises 
from  the  convexity  of  the  hamulus  of  the  hamate  bone,  and  contiguous  portion 
of  the  transverse  carpal  ligament ;  it  is  inserted  into  the  whole  length  of  the  meta- 
carpal bone  of  the  little  finger,  along  its  ulnar  margin. 

Variations. — The  Palmaris  brevis  varies  greatly  in  size.  The  Abductor  digiti  quinti  may  be 
divided  into  two  or  three  slips  or  united  with  the  Flexor  digiti  quinti  brevis.  Accessory  head  from 
the  tendon  of  the  Flexor  carpi  ulnaris,  the  transverse  carpal  ligament,  the  fascia  of  the  forearm 
or  the  tendon  of  the  Palmaris  longus.  A  portion  of  the  muscle  may  insert  into  the  metacarpal, 
or  separate  slips  the  Pisimetacarpus,  Pisiuncinatus  or  the  Pisianmdaris  muscle  may  exist. 

Nerves. — All  the  muscles  of  this  group  are  supplied  by  the  eighth  cervical  nerve  through  the 
ulnar  nerve.  v 

Actions. — The  Abductor  and  Flexor  digiti  quinti  brevis  abduct  the  little  finger  from  the  ring 
finger  and  assist  in  flexing  the  proximal  phalanx.  The  Opponens  digiti  quinti  draws  forward 
the  fifth  metacarpal  bone,  so  as  to  deepen  the  hollow  of  the  palm.  The  Palmaris  brevis  corrugates 
the  skin  on  the  ulnar  side  of  the  palm. 


3.  The  Intermediate  Muscles. 


Lumbricales. 


Interossei. 


The  Lumbricales  (Fig.  427)  are  four  small  fleshy  fasciculi,  associated  with  the 
tendons  of  the  Flexor  digitorum  profundus.  The  first  and  second  arise  from  the 
radial  sides  and  volar  surfaces  of  the  tendons  of  the  index  and  middle  fingers 
respectively;  the  third,  from  the  contiguous  sides  of  the  tendons  of  the  middle  and 
ring  fingers;  and  the  fourth,  from  the  contiguous  sides  of  the  tendons  of  the  ring 
and  little  fingers.  Each  passes  to  the  radial  side  of  the  corresponding  finger,  and 
opposite  the  metacarpophalangeal  articulation  is  inserted  into  the  tendinous 
expansion  of  the  Extensor  digitorum  communis  covering  the  dorsal  aspect  of  the 
finger. 

Variations. — The  Lumbricales  vary  in  niunber  from  two  to  five  or  six  and  there  is  considerable 
variation  in  insertions. 

The  Interossei  (Figs.  428,  429)  are  so  named  from  occupying  the  intervals 
between  the  metacarpal  bones,  and  are  divided  into  two  sets,  a  dorsal  and  a  volar. 

The  Interossei  dorsales  {Dorsal  interossei)  are  four  in  number,  and  occupy  the 
intervals  between  the  metacarpal  bones.  They  are  bipenniform  muscles,  each  arising 
by  two  heads  from  the  adjacent  sides  of  the  metacarpal  bones,  but  more  exten- 
sively from  the  metacarpal  bone  of  the  finger  into  which  the  muscle  is  inserted. 
They  are  inserted  into  the  bases  of  the  first  phalanges  and  into  the  aponeuroses 
of  the  tendons  of  the  Extensor  digitorum  communis.  Between  the  double  origin 
of  each  of  these  muscles  is  a  narrow  triangular  interval ;  through  the  first  of  these 
the  radial  artery  passes ;  through  each  of  the  other  three  a  perforating  branch  from 
the  deep  volar  arch  is  transmitted. 

The  first  or  Abductor  indicis  is  larger  than  the  others.  It  is  flat,  triangular  in 
form,  and  arises  by  two  heads,  separated  by  a  fibrous  arch  for  the  passage  of  the 
radial  artery  from  the  dorsum  to  the  palm  of  the  hand.  The  lateral  head  arises 
from  the  proximal  half  of  the  ulnar  border  of  the  first  metacarpal  bone;  the  medial 
head,  from  almost  the  entire  length  of  the  radial  border  of  the  second  metacarpal 
bone;  the  tendon  is  inserted  into  the  radial  side  of  the  index  finger.    The  second 


THE  MUSCLES  AND  FASCIA  OF  THE  LOWER  EXTREMITY 


465 


and  third  are  inserted  into  the  middle  finger,  the  former  into  its  radial,  the  latter 
into  its  ulnar  side.    The  fourth  is  inserted  into  the  ulnar  side  of  the  ring  finger. 

The  Interossei  volares  {Palmar  interossei),  three  in  number,  are  smaller  than  the 
Interossei  dorsales,  and  placed  upon  the  volar  surfaces  of  the  metacarpal  bones, 
rather  than  between  them.  Each  arises  from  the  entire  length  of  the  metacarpal 
bone  of  one  finger,  and  is  inserted  into  the  side  of  the  base  of  the  first  phalanx  and 
aponeurotic  expansion  of  the  Extensor  communis  tendon  to  the  same  finger. 

The  first  arises  from  the  ulnar  side  of  the  second  metacarpal  bone,  and  is  inserted 
into  the  same  side  of  the  first  phalanx  of  the  index  finger.  The  second  arises  from 
the  radial  side  of  the  fourth  metacarpal  bone,  and  is  inserted  into  the  same  side 
of  the  ring  finger.  The  third,  arises  from  the  radial  side  of  the  fifth  metacarpal 
bone,  and  is  inserted  into  the  same  side  of  the  little  finger.  From  this  account 
it  may  be  seen  that  each  finger  is  provided  with  two  Interossei,  with  the  exception 
of  the  little  finger,  in  which  the  Abductor  takes  the  place  of  one  of  the  pair. 

As  already  mentioned  (p.  461),  the  medial  head  of  the  Flexor  pollicis  brevis  is 
sometimes  described  as  the  Interosseus  volaris  primus. 


Fig.  428. — The  Interossei  dorsales  of  left  hand. 


Fig.  429. — The  Interossei  volares  of  left  hand. 


Nerves. — The  two  lateral  Lumbricales  are  supplied  by  the  sixth  and  seventh  cervical  nerves, 
through  the  third  and  fourth  digital  branches  of  the  median  nerve;  the  two  medial  Lumbricales 
and  all  the  Interossei  are  supphed  by  the  eighth  cervical  nerve,  through  the  deep  palmar  branch 
of  the  ulnar  nerve.    The  third  Lumbricahs  frequently  receives  a  twig  from  the  median. 

Actions. — The  Interossei  volares  adduct  the  fingers  to  an  imaginary  line  drawn  longitudinally 
through  the  center  of  the  middle  finger;  and  the  Interossei  dorsales  abduct  the  fingers  from  that 
line.  In  addition  to  this  the  Interossei,  in  conjunction  with  the  Lumbricales,  flex  the  first 
phalanges  at  the  metacarpophalangeal  joints,  and  extend  the  second  and  third  phalanges  in 
consequence  of  their  insertions  into  the  expansions  of  the  Extensor  tendons.  The  Extensor 
digitorum  communis  is  believed  to  act  almost  entirely  on  the  first  phalanges. 


THE  MUSCLES  AND  FASCLffi  OF  THE  LOWER  EXTREMITY. 

The  muscles  of  the  lower  extremity  are  subdivided  into  groups  corresponding 
with  the  different  regions  of  the  limb. 


I.  Muscles  of  the  Iliac  Region. 
II.  Muscles  of  the  Thigh. 


III.  Muscles  of  the  Leg. 

IV.  Muscles  of  the  Foot. 


466 


3.^] 


h^i 


ri 


'  ''^\ 


Fig.  430  — Muscles  of  the  iliac  and  anterior 
femoral  regions. 


MYOLOGY 

I.     THE  MUSCLES  AND  FASCLffi  OF  THE 
ILIAC  REGION  (Fig.  430). 

Psoas  major.  Psoas  minor.  Iliacus 

The  Fascia  Covering  the  Psoas  and  Iliacus  is 
thin  above,  and  becomes  gradually  thicker 
below  as  it  approaches  the  inguinal  ligament. 

The  portion  covering  the  Psoas  is  thickened 
above  to  form  the  medial  lumbocostal  arch, 
which  stretches  from  the  transverse  process  of 
the  first  lumbar  vertebra  to  the  body  of  the 
second.  Medially,  it  is  attached  by  a  series  of 
arched  processes  to  the  intervertebral  fibro- 
cartilages,  and  prominent  margins  of  the  bodies 
of  the  vertebrae,  and  to  the  upper  part  of  the 
sacrum;  the  intervals  left,  opposite  the  con- 
stricted p>ortions  of  the  bodies,  transmit  the 
lumbar  arteries  and  veins  and  filaments  of  the 
sympathetic  trunk.  Laterally,  above  the  crest 
of  the  ilium,  it  is  continuous  with  the  fascia 
covering  the  front  of  the  Quadratus  lumborum 
(see  page  419),  while  below  the  crest  of  the 
ilium  it  is  continuous  with  the  fascia  covering 
the  Iliacus. 

The  portions  investing  the  Iliacus  {fascia  iliaca; 
iliac  fascia)  is  connected,  laterally  to  the  whole 
length  of  the  inner  lip  of  the  iliac  crest;  and 
medially,  to  the  linea  terminalis  of  the  lesser 
pelvis,  where  it  is  continuous  with  the  peri- 
osteum. At  the  iliopectineal  eminence  it  re- 
ceives the  tendon  of  insertion  of  the  Psoas 
minor,  when  that  muscle  exists.  Lateral  to  the 
femoral  vessels  it  is  intimately  connected  to 
the  posterior  margin  of  the  inguinal  ligament, 
and  is  continuous  with  the  transversalis  fascia. 
Immediately  lateral  to  the  femoral  vessels  the 
iliac  fascia  is  prolonged  backward  and  medial- 
ward  from  the  inguinal  ligament  as  a  band, 
the  iliopectineal  fascia,  which  is  attached  to 
the  iliopectineal  eminence.  This  fascia  divides 
the  space  between  the  inguinal  ligament  and 
the  hip  bone  into  two  lacunae  or  compart- 
ments, the  medial  of  which  transmits  the 
femoral  vessels,  the  lateral  the  Psoas  major 
and  Iliacus  and  the  femoral  nerve.  Medial 
to  the  vessels  the  iliac  fascia  is  attached  to 
the  pectineal  line  behind  the  inguinal  apo- 
neurotic falx,  where  it  is  again  continuous  with 
the  transversalis  fascia.  On  the  thigh  the 
fasciae  of  the  Iliacus  and  Psoas  form  a  single 
sheet  termed  the  iliopectineal  fascia.  Where 
the  external  iliac  vessels  pass  into  the  thigh,  the 
fascia  descends  behind  them,  forming  the  pos- 
terior wall  of  the  femoral  sheath.  The  portion 
of  the  iliopectineal  fascia  which  passes  behind 


■ 


THE  ANTERIOR  FEMORAL  MUSCLES 


467 


the  femoral  vessels  is  also  attached  to  the  pectineal  line  beyond  the  limits  of  the 
attachment  of  the  inguinal  aponeurotic  falx;  at  this  part  it  is  continuous  with 
the  pectineal  fascia.  The  external  iliac  vessels  lie  in  front  of  the  iliac  fascia,  but 
all  the  branches  of  the  lumbar  plexus  are  behind  it;  it  is  separated  from  the  peri- 
toneum by  a  quantity  of  loose  areolar  tissue. 

The  Psoas  major  {Psoas  magnns)  (Fig.  430)  is  a  long  fusiform  muscle  placed  on 
the  side  of  the  lumbar  region  of  the  vertebral  column  and  brim  of  the  lesser  pelvis. 
It  arises  (1)  from  the  anterior  surfaces  of  the  bases  and  lower  borders  of  the  transverse 
processes  of  all  the  lumbar  vertebrae;  (2)  from  the  sides  of  the  bodies  and  the  corre- 
sponding intervertebral  fibrocartilages  of  the  last  thoracic  and  all  the  lumbar  verte- 
brae by  five  slips,  each  of  which  is  attached  to  the  adjacent  upper  and  lower  margins 
of  two  vertebrae,  and  to  the  intervertebral  fibrocartilage;  (3)  from  a  series  of 
tendinous  arches  which  extend  across  the  constricted  parts  of  the  bodies  of  the 
lumbar  vertebrae  between  the  previous  slips;  the  lumbar  arteries  and  veins,  and 
filaments  from  the  sympathetic  trunk  pass  beneath  these  tendinous  arches.  The 
muscle  proceeds  downward  across  the  brim  of  the  lesser  pelvis,  and  diminishing 
gradually  in  size,  passes  beneath  the  inguinal  ligament  and  in  front  of  the  capsule 
of  the  hip-joint  and  ends  in  a  tendon;  the  tendon  receives  nearly  the  whole  of 
the  fibers  of  the  Iliacus  and  is  inserted  into  the  lesser  trochanter  of  the  femur. 
A  large  bursa  w^hich  may  communicate  with  the  cavity  of  the  hip-joint,  separates 
the  tendon  from  the  pubis  and  the  capsule  of  the  joint. 

The  Psoas  minor  (Psoas  parvus)  is  a  long  slender  muscle,  placed  in  front  of  the 
Psoas  major.  It  arises  from  the  sides  of  the  bodies  of  the  twelfth  thoracic  and  first 
lumbar  vertebrae  and  from  the  fibrocartilage  between  them.  It  ends  in  a  long 
flat  tendon  which  is  inserted  into  the  pectineal  line  and  iliopectineal  eminence, 
and,  by  its  lateral  border,  into  the  iliac  fascia.    This  muscle  is  often  absent. 

The  Iliacus  is  a  flat,  triangular  muscle,  which  fills  the  iliac  fossa.  It  arises  from 
the  upper  two-thirds  of  this  fossa,  and  from  the  inner  lip  of  the  iliac  crest;  behind, 
from  the  anterior  sacroiliac  and  the  iliolumbar  ligaments,  and  base  of  the  sacrum; 
in  front,  it  reaches  as  far  as  the  anterior  superior  and  anterior  inferior  iliac  spines, 
and  the  notch  between  them.  The  fibers  converge  to  be  inserted  into  the  lateral 
side  of  the  tendon  of  the  Psoas  major,  some  of  them  being  prolonged  on  to  the  body 
of  the  femur  for  about  2.5  cm.  below  and  in  front  of  the  lesser  trochanter.^ 

Variations. — The  Iliacus  minor  or  Iliocapsidaris,  a  small  detached  part  of  the  Iliacus  is  frequently 
present.  It  arises  from  the  anterior  inferior  spine  of  the  ilium  and  is  inserted  into  the  lower  part 
of  the  intertrochanteric  line  of  the  femur  or  into  the  iliofemoral  ligament. 

Nerves. — The  Psoas  major  is  supphed  by  branches  of  the  second  and  third  lumbar  nerve; 
the  Psoas  minor  by  a  branch  of  the  first  lumbar  nerve;  and  the  lUacus  by  branches  of  the  second 
and  third  lumbar  nerves  through  the  femoral  nerve. 

Actions. — The  Psoas  major,  acting  from  above,  flexes  the  thigh  upon  the  pelvis,  being  assisted 
by  the  Iliacus;  acting  from  below,  with  the  femur  fixed,  it  bends  the  lumbar  portion  of  the  verte- 
bral column  forward  and  to  its  own  side,  and  then,  in  conjunction  with  the  Iliacus,  tilts  the  pelvis 
forward.  When  the  muscles  of  both  sides  are  acting  from  below,  they  serve  to  maintain  the 
erect  posture  by  supporting  the  vertebral  column  and  pelvis  upon  the  femora,  or  in  continued 
action  bend  the  trunk  and  pelvis  forward,  as  in  raising  the  trunk  from  the  recimibent  posture. 

The  Psoas  minor  is  a  tensor  of  the  ihac  fascia. 


n.     THE  MUSCLES  AND  FASCIA  OF  THE  THIGH. 


1.  The  Anterior  Femoral  Muscles  (Fig.  430) 

'  Rectus  femoris. 
o    ,     .  Quadriceps 

S^^tonus.  femoris 


Articularis  genu. 


Vastus  lateralis. 
Vastus  medialis. 
Vastus  intermedins. 


1  The  Psoas  major  and  iliacus  are  sometimes  regarded  as  a  single  muscle  named  the  Ilioptoai. 


468  MYOLOGY 

Superficial  Fascia. — The  superficial  fascia  forms  a  continuous  layer  over  the  whole 
of  the  thigh;  it  consists  of  areolar  tissue  containing  in  its  meshes  much  fat,  and  may 
be  separated  into  two  or  more  layers,  between  which  are  found  the  superficial 
vessels  and  nerves.  It  varies  in  thickness  in  different  parts  of  the  limb ;  in  the  groin 
it  is  thick,  and  the  two  layers  are  separated  from  one  another  by  the  superficial 
inguinal  lymph  glands,  the  great  saphenous  vein,  and  several  smaller  vessels. 
The  superficial  layer  is  continuous  above  with  the  superficial  fascia  of  the  abdomen. 
The  deep  layer  of  the  superficial  fascia  is  a  very  thin,  fibrous  stratum,  best  marked 
on  the  medial  side  of  the  great  saphenous  vein  and  below  the  inguinal  ligament. 
It  is  placed  beneath  the  subcutaneous  vessels  and  nerves  and  upon  the  surface  of  the 
fascia  lata.  It  is  intimately  adherent  to  the  fascia  lata  a  little  below  the  inguinal 
ligament.  It  covers  the  fossa  ovalis  (saphenous  opening),  being  closely  united  to 
its  circumference,  and  is  connected  to  the  sheath  of  the  femoral  vessels.  The 
portion  of  fascia  covering  this  fossa  is  perforated  by  the  great  saphenous  vein  and 
by  numerous  blood  and  lymphatic  vessels,  hence  it  has  been  termed  the  fascia 
cribrosa,  the  openings  for  these  vessels  having  been  likened  to  the  holes  in  a  sieve. 
A  large  subcutaneous  bursa  is  found  in  the  superficial  fascia  over  the  patella. 

Deep  Fascia. — ^The  deep  fascia  of  the  thigh  is  named,  from  its  great  extent, 
the  fascia  lata ;  it  constitutes  an  investment  for  the  whole  of  this  region  of  the  limb, 
but  varies  in  thickness  in  different  parts.  Thus,  it  is  thicker  in  the  upper  and  lateral 
part  of  the  thigh,  where  it  receives  a  fibrous  expansion  from  the  Glutseus  maximus, 
and  where  the  Tensor  fasciae  latse  is  inserted  between  its  layers;  it  is  very  thin 
behind  and  at  the  upper  and  medial  part,  where  it  covers  the  Adductor  muscles, 
and  again  becomes  stronger  around  the  knee,  receiving  fibrous  expansions  from  the 
tendon  of  the  Biceps  femoris  laterally,  from  the  Sartorius  medially,  and  from  the 
Quadriceps  femoris  in  front.  The  fascia  lata  is  attached,  above  and  behind,  to  the 
back  of  the  sacrum  and  coccyx;  laterally,  to  the  iliac  crest;  in  front,  to  the  inguinal 
ligament,  and  to  the  superior  ramus  of  the  pubis;  and  medially,  to  the  inferior 
ramus  of  the  pubis,  to  the  inferior  ramus  and  tuberosity  of  the  ischium,  and  to 
the  low^er  border  of  the  sacrotuberous  ligament.  From  its  attachment  to  the  iliac 
crest  it  passes  down  over  the  Glutseus  medius  to  the  upper  border  of  the  Glutseus 
maximus,  where  it  splits  into  two  layers,  one  passing  superficial  to  and  the  other 
beneath  this  muscle;  at  the  lower  border  of  the  muscle  the  two  layers  reunite. 
Laterally,  the  fascia  lata  receives  the  greater  part  of  the  tendon  of  insertion  of 
the  Glutseus  maximus,  and  becomes  proportionately  thickened.  The  portion  of 
the  fascia  lata  attached  to  the  front  part  of  the  iliac  crest,  and  corresponding  to 
the  origin  of  the  Tensor  fasciae  latae,  extends  down  the  lateral  side  of  the  thigh  as 
two  layers,  one  superficial  to  and  the  other  beneath  this  muscle ;  at  the  lower  end 
of  the  muscle  these  two  layers  unite  and  form  a  strong  band,  having  first  received 
the  insertion  of  the  muscle.  This  band  is  continued  downward,  under  the  name 
of  the  iliotibial  band  (tradus  iliotihialis)  and  is  attached  to  the  lateral  condyle  of 
the  tibia.  The  part  of  the  iliotibial  band  which  lies  beneath  the  Tensor  fasciae 
latse  is  prolonged  upward  to  join  the  lateral  part  of  the  capsule  of  the  hip-joint. 
Below,  the  fasciae  lata  is  attached  to  all  the  prominent  points  around  the  knee- 
joint,  viz.,  the  condyles  of  the  femur  and  tibia,  and  the  head  of  the  fibula.  On 
either  side  of  the  patella  it  is  strengthened  by  transverse  fibers  from  the  lower  parts 
of  the  Vasti,  which  are  attached  to  and  support  this  bone.  Of  these  the  lateral 
are  the  stronger,  and  are  continuous  with  the  iliotibial  band.  The  deep  surface 
of  the  fascia  lata  gives  off  two  strong  intermuscular  septa,  which  are  attached 
to  the  whole  length  of  the  linea  aspera  and  its  prolongations  above  and  below; 
the  lateral  and  stronger  one,  which  extends  from  the  insertion  of  the  Glutseus 
maximus  to  the  lateral  condyle,  separates  the  Vastus  lateralis  in  front  from  the 
short  head  of  the  Biceps  femoris  behind,  and  gives  partial  origin  to  these  mus- 
cles; the  medial  and  thinner  one  separates  the  Vastus  medialis  from  the  Adduc- 


THE  ANTERIOR  FEMORAL  MUSCLES 


469 


tores  and  Pectineus.     Besides  these  there  are  numerous  smaller  septa,  separating 
the  individual  muscles,  and  enclosing  each  in  a  distinct  sheath. 

The  Fossa  Ovalis  (saphenous  opening)  (Fig.  431). — At  the  upper  and  medial 
part  of  the  thigh,  a  little  below  the  medial  end  of  the  inguinal  ligament,  is  a  large 
oval-shaped  aperture  in  the  fascia  lata;  it  transmits  the  great  saphenous  vein, 
and  other,  smaller  vessels,  and  is  termed  the  fossa  ovalis.  The  fascia  cribrosa, 
which  is  pierced  by  the  structures  passing  through  the  opening,  closes  the  aperture 
and  must  be  removed  to  expose  it.  The  fascia  lata  in  this  part  of  the  thigh  is 
described  as  consisting  of  a  superficial  and  a  deep  portion. 


Fig.  431. — The  fossa  ovalia. 


The  superficial  portion  of  the  fascia  lata  is  the  part  on  the  lateral  side  of  the  fossa 
ovalis.  It  is  attached,  laterally,  to  the  crest  and  anterior  superior  spine  of  the  ilium, 
to  the  whole  length  of  the  inguinal  ligament,  and  to  the  pectineal  line  in  con- 
junction with  the  lacunar  ligament.  From  the  tubercle  of  the  pubis  it  is  reflected 
downward  and  lateralward,  as  an  arched  margin,  the  falciform  margin,  forming 
the  lateral  boundary  of  the  fossa  ovalis;  this  margin  overlies  and  is  adherent  to  the 
anterior  layer  of  the  sheath  of  the  femoral  vessels :  to  its  edge  is  attached  the  fascia 
cribrosa.  The  upward  and  medial  prolongation  of  the  falciform  margin  is  named 
the  superior  comu ;  its  downward  and  medial  prolongation,  the  inferior  comu.  The 
latter  is  well-defined,  and  is  continuous  behind  the  great  saphenous  vein  with  the 
pectineal  fascia  4 

The  deep  portion  is  situated  on  the  medial  side  of  the  fossa  ovalis,  and  at  the 
lower  margin  of  the  fossa  is  continuous  with  the  superficial  portion;  traced  upward. 


470  MYOLOGY 

it 'covers  the  Pectineus,  Adductor  longus,  and  Gracilis,  and,  passing  behind  the 
sheath  of  the  femoral  vessels,  to  which  it  is  closely  united^  is  continuous  with  the 
iliopectineal  fascia,  and  is  attached  to  the  pectineal  line. 

From  this  description  it  may  be  observed  that  the  superficial  portion  of  the 
fascia  lata  lies  in  front  of  the  femoral  vessels,  and  the  deep  portion  behind  them, 
so  that  an  apparent  aperture  exists  between  the  two,  through  which  the  great 
saphenous  passes  to  join  the  femoral  vein. 

The  Sartorius,  the  longest  muscle  in  the  body,  is  narrow  and  ribbon-like;  it 
arises  by  tendinous  fibers  from  the  anterior  superior  iliac  spine  and  the  upper  half 
of  the  notch  below  it.  It  passes  obliquely  across  the  upper  and  anterior  part  of 
the  thigh,  from  the  lateral  to  the  medial  side  of  the  limb,  then  descends  vertically, 
as  far  as  the  medial  side  of  the  knee,  passing  behind  the  medial  condyle  of  the  femur 
to  end  in  a  tendon.  This  curves  obliquely  forward  and  expands  into  a  broad  apon- 
eurosis, which  is  inserted,  in  front  of  the  Gracilis  and  Semitendinous,  into  the  upper 
part  of  the  medial  surface  of  the  body  of  the  tibia,  nearly  as  far  forward  as  the 
anterior  crest.  The  upper  part  of  the  aponeurosis  is  curved  backward  over  the 
upper  edge  of  the  tendon  of  the  Gracilis  so  as  to  be  inserted  behind  it.  An  offset, 
from  its  upper  margin,  blends  with  the  capsule  of  the  knee-joint,  and  another 
from  its  lower  border,  with  the  fascia  on  the  medial  side  of  the  leg. 

Variations. — Slips  of  origin  from  the  outer  end  of  the  inguinal  ligament,  the  notch  of  the  ilium, 
the  ilio-pectineal  line  or  the  pubis  occur.  The  muscle  may  be  split  into  two  parts,  and  one  part 
may  be  inserted  into  the  fascia  lata,  the  femur,  the  ligament  of  the  patella  or  the  tendon  of  the 
Semitendinosus.  The  tendon  of  insertion  may  end  in  the  fascia  lata,  the  capsule  of  the  knee- 
joint,  or  the  fascia  of  the  leg.    The  muscle  may  be  absent. 

The  Quadriceps  femoris  (Quadriceps  extensor)  includes  the  four  remaining 
muscles  on  the  front  of  the  thigh.  It  is  the  great  extensor  muscle  of  the  leg,  forming 
a  large  fleshy  mass  which  covers  the  front  and  sides  of  the  femur.  It  is  subdivided 
into  separate  portions,  which  have  received  distinctive  names.  One  occupying 
the  middle  of  the  thigh,  and  connected  above  with  the  ilium,  is  called  from  its 
straight  course  the  Rectus  femoris.  The  other  three  lie  in  immediate  connection 
with  the  body  of  the  femur,  which  they  cover  from  the  trochanters  to  the  condyles. 
The  portion  on  the  lateral  side  of  the  femur  is  termed  the  Vastus  lateralis;  that 
covering  the  medial  side,  the  Vastus  medialis ;  and  that  in  front,  the  Vastus 
intermedius. 

The  Rectus  femoris  is  situated  in  the  middle  of  the  front  of  the  thigh;  it  is  fusi- 
form in  shape,  and  its  superficial  fibers  are  arranged  in  a  bipenniform  manner, 
the  deep  fibers  running  straight  down  to  the  deep  aponeurosis.  It  arises  by  two 
tendons:  one,  the  anterior  or  straight,  from  the  anterior  inferior  iliac  spine;  the 
other,  the  posterior  or  reflected,  fro;n  a  groove  above  the  brim  of  the  acetabulum. 
The  two  unite  at  an  acute  angle,  and  spread  into  an  aponeurosis  which  is  prolonged 
downward  on  the  anterior  surface  of  the  muscle,  and  from  this  the  muscular  flbers 
arise.  The  muscle  ends  in  a  broad  and  thick  aponeurosis  which  occupies  the  lower 
two-thirds  of  its  posterior  surface,  and,  gradually  becoming  narrowed  into  a  flat- 
tened tendon,  is  inserted  into  the  base  of  the  patella. 

The  Vastus  lateralis  (Vastus  externus)  is  the  largest  part  of  the  Quadriceps 
femoris.  It  arises  by  a  broad  aponeurosis,  which  is  attached  to  the  upper  part  of 
the  intertrochanteric  line,  to  the  anterior  and  inferior  borders  of  the  greater  tro- 
chanter, to  the  lateral  lip  of  the  gluteal  tuberosity,  and  to  the  upper  half  of  the 
lateral  lip  of  the  linea  aspera;  this  aponeurosis  covers  the  upper  three-fourths  of 
the  muscle,  and  from  its  deep  surface  many  fibers  take  origin.  A  few  additional 
fibers  arise  from  the  tendon  of  the  Gluta^us  maximus,  and  from  the  lateral  inter- 
muscular septum  between  the  Vastus  lateralis  and  short  head  of  the  Biceps  femoris. 
The  fibers  form  a  large  fleshy  mass,  which  is  attached  to  a  strong  aponeurosis, 
placed  on  the  deep  surface  of  the  lower  part  of  the  muscle:  this  aponeurosis  becomes 


41 


THE  MEDIAL  FEMORAL  MUSCLES  471 


^B I  contracted  and  thickened  into  a  flat  tendon  inserted  into  the  lateral  border  of  the 
patella,  blending  with  the  Quadriceps  femoris  tendon,  and  giving  an  expansion  to 
the  capsule  of  the  knee-joint. 

■I     The  Vastus  medialis  and  Vastus  intermedins  appear  to  be  inseparably  united, 
but  when  the  Rectus  femoris  has  been  reflected  a  narrow  interval  will  be  observed 
extending  upward  from  the  medial  border  of  the  patella  between  the  two  muscles, 
and  the  separation  may  be  continued  as  far  as  the  lower  part  of  the  intertrochan- 
teric line,  where,  however,  the  two  muscles  are  frequently  continuous. 
■I     The  Vastus  medialis  {VaMus  internus)  arises  from  the  lower  half  of  the  inter- 
"  trochanteric  line,  the  medial  lip  of  the  linea  aspera,  the  upper  part  of  the  medial 
supracondylar  line,  the  tendons  of  the  Adductor  longus  and  the  Adductor  magnus 
and  the  medial  intermuscular  septum.    Its  fibers  are  directed  downward  and  for- 
ward, and  are  chiefly  attached  to  an  aponeurosis  which  lies  on  the  deep  surface 
of  the  muscle  and  is  inserted  into  the  medial  border  of  the  patella  and  the  Quad- 
ra riceps  femoris  tendon,  an  expansion  being  sent  to  the  capsule  of  the  knee-joint. 
Hp     The  Vastus  intermedius  (Crureus)  arises  from  the  front  and  lateral  surfaces  of  the 
'       body  of  the  femur  in  its  upper  two-thirds  and  from  the  lower  part  of  the  lateral 
"intermuscular  septum.     Its  fibers  end  in  a  superficial  aponeurosis,  which  forms 
■■the  deep  part  of  the  Quadriceps  femoris  tendon. 

The  tendons  of  the  different  portions  of  the  Quadriceps  unite  at  the  lower  part  of  the  thigh, 
80  as  to  form  a  single  strong  tendon,  which  is  inserted  into  the  base  of  the  patella,  some  few  fibera 
passing  over  it  to  blend  with  the  ligamentum  patellae.  More  properly,  the  patella  may  be  regarded 
aa  a  sesamoid  bone,  developed  in  the  tendon  of  the  Quadriceps;  and  the  ligamentum  patellae, 
which  is  continued  from  the  apex  of  the  patella  to  the  tuberosity  of  the  tibia,  as  the  proper  tendon 
of  insertion  of  the  muscle,  the  medial  and  lateral  patellar  retinacula  (see  p.  338)  being  expan- 
sions from  its  borders.  A  bursa,  which  usually  communicates  with  the  cavity  of  the  knee-joint, 
is  situated  between  the  femur  and  the  portion  of  the  Quadriceps  tendon  above  the  patella;  another 
is  interposed  between  the  tendon  and  the  upper  part  of  the  front  of  the  tibia;  and  a  third,  the 
irepatellar  bursa,  is  placed  over  the  patella  itself. 


f 


The  Articularis  genu  (Subcrureus)  is  a  small  muscle,  usually  distinct  from  the 
astus  intermedius,  but  occasionally  blended  with  it;  it  arises  from  the  anterior 
surface  of  the  lower  part  of  the  body  of  the  femur,  and  is  inserted  into  the  upper 
part  of  the  synovial  membrane  of  the  knee-joint.  It  sometimes  consists  of  several 
separate  muscular  bundles. 


11. 


Nerves. — The  muscles  of  this  region  are  supplied  by  the  second,  third,  and  fourth  lumbar 
erves,  through  the  femoral  nerve. 

Actions. — The  Sartoriua  flexes  the  leg  upon  the  thigh,  and,  continuing  to  act,  flexes  the  thigh 
upon  the  pelvis;  it  next  abducts  and  rotates  the  thigh  outward.  When  the  knee  is  bent,  the 
Sartorius  assists  the  Semitendinosus,  Semimembranosus,  and  Popliteus  in  rotating  the  tibia  inward. 
Taking  its  fixed  point  from  the  leg,  it  flexes  the  pelvis  upon  the  thigh,  and,  if  one  muscle  acts,  assists 
in  rotating  the  pelvis.  The  Quadriceps  femoris  extends  the  leg  upon  the  thigh.  The  Rectus 
femoris  assists  the  Psoas  major  and  Iliacus  in  supporting  the  pelvis  and  trunk  upon  the  femur. 
It  also  assists  in  flexing  the  thigh  on  the  pelvis,  or  if  the  thigh  be  fixed  it  will  flex  the  pelvis.  The 
Vastus  medialis  draws  the  patella  medialward  as  well  as  upward. 


2.  The  Medial  Femoral  Muscles. 

Gracilis.  Adductor  longus.  Adductor  magnus. 

Pectineus.  Adductor  brevis. 


P  The  Gracilis  (Fig.  430)  is  the  most  superficial  muscle  on  the  medial  side  of  the 
thigh.  It  is  thin  and  flattened,  broad  above,  narrow  and  tapering  below.  It 
arises  by  a  thin  aponeurosis  from  the  anterior  margins  of  the  lower  half  of  the 
symphysis  pubis  and  the  upper  half  of  the  pubic  arch.  The  fibers  run  vertically 
downward,  and  end  in  a  rounded  tendon,  which  passes  behind  the  medial  condyle 
of  the  femur,  curves  around  the  medial  condyle  of  the  tibia,  where  it  becomes  flat- 


MYOLOGY 

tened,  and  is  inserted  into  the  upper  part  of  the  medial  surface  of  the  body  of  thfl 
tibia,  below  the  condyle.  A  few  of  the  fibers  of  the  lower  part  of  the  tendon  are 
prolonged  into  the  deep  fascia  of  the  leg.  At  its  insertion  the  tendon  is  situated 
immediately  above  that  of  the  Semitendinosus,  and  its  upper  edge  is  overlapped 
by  the  tendon  of  the  Sartorius,  with  which  it  is  in  part  blended.  It  is  separated 
from  the  tibial  collateral  ligament  of  the  knee-joint,  by  a  bursa  common  to  it  and 
the  tendon  of  the  Semitendinosus. 


Rectus  femoris  M. 


Femur 


Vasttis  intermedius 
M 


Linea  aspera 


Deep  femoral  artery 
and  vein 


Sartorius  M. 


^.Saphenous  nerve 


Femoral  vein 
and  artery 


Intermediate 
...  cutancjus 
nerve 


Great  saphenous 
vein 


^Adductor 
longus  M. 


^Gracilis  M. 


Intermuscular 

septum  of 
f'cdian  femoral 


.Perforating  artery 
arid  vein 


Vastus  lateralis  Al. 

Intermuscular  septu  m 
,  of  lateral  femoral 


^"^  Semimembranosus  M. 


Biceps  femoris  M.  \ 

[captit  breve]  ', 

Biceps  femoris  M. 
[caput  longum] 


Semitendinosus  M 


Isch  I 


1  'usitnur  femoral 
cutaneous  nerve 


Adductor  magnus  M. 
Fig.  432. — Cross-section  through  the  middle  of  the  thigh.      (Eycleshymer  and  Schoemaker.) 


•1 


The  Pectineus  (Fig.  430)  is  a  flat,  quadrangular  muscle,  situated  at  the  anterior 
part  of  the  upper  and  medial  aspect  of  the  thigh.  It  arises  from  the  pectineal  line, 
and  to  a  slight  extent  from  the  surface  of  bone  in  front  of  it,  between  the 
iliopectineal  eminence  and  tubercle  of  the  pubis,  and  from  the  fascia  covering  the 
anterior  surface  of  the  muscle;  the  fibers  pass  downward,  backward,  and  lateral- 
ward,  to  be  inserted  into  a  rough  line  leading  from  the  lesser  trochanter  to  the 
linea  aspera. 

The  Adductor  longus  (Fig.  433),  the  most  superficial  of  the  three  Adductores, 
is  a  triangular  muscle,  lying  in  the  same  plane  as  the  Pectineus.  It  arises  by  a 
flat,  narrow  tendon,  from  the  front  of  the  pubis,  at  the  angle  of  junction  of  the  crest 


THE  MEDIAL  FEMORAL 


with  the  symphysis;  and  soon  expands  into  a  broad  fleshy  belly.  This  passes 
downward,  backward,  and  lateralward,  and  is  inserted,  by  an  aponeurosis,  into  the 
linea  aspera,  between  the  Vastus  medialis  and  the  Adductor  magnus,  with  both 
of  which  it  is  usually  blended. 

The  Adductor  brevis  (Fig.  433)  is  situ- 
ated immediately  behind  the  two  preceding 
muscles.  It  is  somewhat  triangular  in  form, 
and  arises  by  a  narrow  origin  from  the 
outer  surfaces  of  the  superior  and  inferior 
rami  of  the  pubis,  between  the  Gracilis 
and  Obturator  externus.  Its  fibers,  passing 
backward,  lateralward,  and  downward,  are 
inserted,  by  an  aponeurosis,  into  the  line 
leading  from  the  lesser  trochanter  to  the 
linea  aspera  and  into  the  upper  part  of  the 
linea  aspera,  immediately  behind  the  Pectin- 
eus  and  upper  part  of  the  Adductor  longus. 

The  Adductor  magnus  (Fig.  433)  is  a  large 
triangular  muscle,  situated  on  the  medial  side 
of  the  thigh.  It  arises  from  a  small  part 
of  the  inferior  ramus  of  the  pubis,  from  the 
inferior  ramus  of  the  ischium,  and  from  the 
outer  margin  of  the  inferior  part  of  the 
tuberosity  of  the  ischium.  Those  fibers 
which  arise  from  the  ramus  of  the  pubis  are 
short,  horizontal  in  direction,  and  are  inserted 
into  the  rough  line  leading  from  the  greater 
trochanter  to  the  linea  aspera,  medial  to  the 
Glutseus  maximus;  those  from  the  ramus  of 
the  ischium  are  directed  downward  and  lat- 
eralward with  different  degrees  of  obliquity, 
to  be  inserted,  by  means  of  a  broad  aponeu- 
rosis, into  the  linea  aspera  and  the  upper 
part  of  its  medial  prolongation  below.  The 
medial  portion  of  the  muscle,  composed 
principally  of  the  fibers  arising  from  the 
tuberosity  of  the  ischium,  forms  a  thick 
fleshy  mass  consisting  of  coarse  bundles 
which  descend  almost  vertically,  and  end 
about  the  lower  third  of  the  thigh  in  a 
rounded  tendon  which  is  inserted  into  the 
adductor  tubercle  on  the  medial  condyle  of 
the  femur,  and  is  connected  by  a  fibrous 
expansion  to  the  line  leading  upward  from 
the  tubercle  to  the  linea  aspera.  At  the 
insertion  of  the  muscle,  there  is  a  series  of 
osseoaponeurotic  openings,  formed  by  tendi- 
nous arches  attached  to  the  bone.  The 
upper  four  openings  are  small,  and  give 
passage  to  the  perforating  branches  of  the 
profunda  femoris  artery.  The  lowest  is  of 
large  size,  and  transmits  the  femoral  vessels 

to  the  popliteal  fossa.  ^^°-  ^^S-Deep  musdes^of  the  medial  femoral 


474  i^^^^^^m        MYOLOGY 

Variations. — The  Pectineus  is  sometimes  divided  into  an  outer  part  supplied  by  the  femoral 
nerve  and  an  inner  part  supplied  by  the  obturator  nerve.  The  muscle  may  be  attached  to  or 
inserted  into  the  capsule  of  the  hip-joint.  The  Adductor  longus  may  be  double,  may  extend  to  the  , 
knee,  or  be  more  or  less  united  with  the  Pectineus.  The  Adductor  brevis  may  be  divided  into  two  ' 
or  three  parts,  or  it  may  be  united  to  the  Adductor  magnus.  The  Adductor  magnus  may  be  more 
or  less  segmented,  the  anterior  and  superior  portion  is  often  described  as  a  separate  muscle,  the 
Adductor  minimus.    The  muscle  may  be  fused  with  the  Quadratus  femoris. 

Nerves. — The  three  Adductores  and  the  Gracilis  are  supplied  by  the  third  and  fourth  lumbar 
nerves  through  the  obturator  nerve;  the  Adductor  magnus  receiving  an  additional  branch  from 
the  sacral  plexus  through  the  sciatic.  The  Pectineus  is  suppHed  by  the  second,  third,  and  fourth 
lumbar  nerves  through  the  femoral  nerve,  and  by  the  third  lumbar  through  the  accessory  obturator - 
when  this  latter  exists.    Occasionally  it  receives  a  branch  from  the  obturator  nerve.^  * 

Actions. — The  Pectineus  and  three  Adductores  adduct  the  thigh  powerfully;  they  are  especially 
used  in  horse  exercise,  the  sides  of  the  saddle  being  grasped  between  the  knees  by  the  contraction 
of  these  muscles.  In  consequence  of  the  obliquity  of  their  insertions  into  the  Unea  aspera,  they 
rotate  the  thigh  outward,  assisting  the  external  Rotators,  and  when  the  limb  has  been  abducted, 
they  draw  it  medialward,  carrying  the  thigh  across  that  of  the  opposite  side.  The  Pectineus 
and  Adductores  brevis  and  longus  assist  the  Psoas  major  and  Iliacus  in  flexing  the  thigh  upon 
the  pelvis.  In  progression,  all  these  muscles  assist  in  drawing  forward  the  lower  hmb.  The 
Gracilis  assists  the  Sartorius  in  flexing  the  leg  and  rotating  it  inward;  it  is  also  an  adductor  of  the 
thigh.  If  the  lower  extremities  be  fixed,  these  muscles,  taking  their  fixed  points  below,  may  act 
upon  the  pelvis,  serving  to  maintain  the  body  in  an  erect  posture;  or,  if  their  action  be  continued, 
flex  the  pelvis  forward  upon  the  femur. 

3.  The  Muscles  of  the  Gluteal  Region  (Fig.  434). 

Glutseus  maximus.  Obturator  internus. 

Glutseus  medius.  Gemellus  superior. 

Glutseus  minimus.  Gemellus  inferior. 

Tensor  fasciae  latae.  Quadratus  femoris. 

Piriformis.  Obturator  externus. 

The  Glutseus  maximus,  the  most  superficial  muscle  in  the  gluteal  region,  is  a 
broad  and  thick  fleshy  mass  of  a  quadrilateral  shape,  and  forms  the  prominence 
of  the  nates.  Its  large  size  is  one  of  the  most  characteristic  features  of  the  muscular 
system  in  man,  connected  as  it  is  with  the  power  he  has  of  maintaining  the  trunk 
in  the  erect  posture.  The  muscle  is  remarkably  coarse  in  structure,  being  made 
up  of  fasciculi  lying  parallel  with  one  another  and  collected  together  into  large 
bundles  separated  by  fibrous  septa.  It  arises  from  the  posterior  gluteal  line  of 
the  ilium,  and  the  rough  portion  of  bone  including  the  crest,  immediately  above 
and  behind  it;  from  the  posterior  surface  of  the  lower  part  of  the  sacrum  and  the 
side  of  the  coccyx;  from  the  aponeurosis  of  the  Sacrospinalis,  the  sacrotuberous 
ligament,  and  the  fascia  (gluteal  aponeurosis)  covering  the  Glutaeus  medius. 
The  fibers  are  directed  obliquely  downward  and  lateralward;  those  forming  the 
upper  and  larger  portion  of  the  muscle,  together  with  the  superficial  fibers  of  the 
lower  portion,  end  in  a  thick  tendinous  lamina,  which  passes  across  the  greater 
trochanter,  and  is  inserted  into  the  iliotibial  band  of  the  fascia  lata;  the  deeper 
fibers  of  the  lower  portion  of  the  muscle  are  inserted  into  the  gluteal  tuberosity 
between  the  Vastus  lateralis  and  Adductor  magnus. 

Bursse. — Three  bursse  are  usually  found  in  relation  with  the  deep  surface  of  this  muscle.  One 
of  these,  of  large  size,  and  generally  multilocular,  separates  it  from  the  greater  trochanter;  a 
second,  often  wanting,  is  situated  on  the  tuberosity  of  the  ischium;  a  third  is  found  between 
the  tendon  of  the  muscle  and  that  of  the  Vastus  lateralis. 

The  Glutaeus  medius  is  a  broad,  thick,  radiating  muscle,  situated  on  the  outer 
surface  of  the  pelvis.    Its  posterior  third  is  covered  by  the  Glutaeus  maximus,  its 

'  The  Pectineus  may  consist  of  two  incompletely  separated  strata;  the  lateral  or  dorsal  stratum,  which  is  constant, 
is  supplied  by  a  branch  from  the  femoral  nerve,  or  in  the  absence  of  this  branch  by  the  accessory  obturator  nerve; 
the  medial  or  ventral  stratum,  when  present,  is  supplied  by  the  obturator  nerve. — A.  M.  Paterson.  Journal  of  Anatomy 
and  Physiology,  xxvi,  43. 


I 


^Banterlor  two-thirds  by  the  gluteal 
aponeurosis,  which  separates  it 
from  the  superficial  fascia  and 
integument.  It  arises  from  the 
outer  surface  of  the  ilium  between 
the  iliac  crest  and  posterior  glu- 
teal line  above,  and  the  anterior 
gluteal  line  below;  it  also  arises 

Pfrom    the    gluteal     aponeurosis 
covering  its  outer  surface.    The 
fibers  converge  to  a  strong  flat- 
tened tendon,  which  is  inserted 
^^  into  the  oblique  ridge  which  runs 
^B  downward  and  forward   on  the 
^■lateral  surface  of  the  greater  tro- 
chanter.   A  bursa  separates  the 
tendon  of  the  muscle  from  the 

•  surface  of    the   trochanter  over 
[which  it  glides. 
I     Variations.  —  The  posterior  border 
Imay  be  more  or  less  closely  vmited  to 
the  Piriformis,  or  some  of  the  fibers  end 
on  its  tendon. 

The  Glutseus  minimus,  the  small- 
est of  the  three  Glutaji,  is  placed 
immediately  beneath  the  preced- 
ing. It  is  fan-shaped,  arising  from 
the  outer  surface  of  the  ilium, 
between  the  anterior  and  inferior 
gluteal  lines,  and  behind,  from 
the  margin  of  the  greater  sciatic 
notch.  The  fibers  converge  to 
the  deep  surface  of  a  radiated 
aponeurosis,  and  this  ends  in  a 
tendon  which  is  inserted  into  an 
impression  on  the  anterior  border 
of  the  greater  trochanter,  and 
gives  an  expansion  to  the  capsule 
of  the  hip-joint.  A  bursa  is 
interposed  between  the  tendon 
and  the  greater  trochanter.  Be- 
tween the  Glutseus  medius  and 
Glutseus  minimus  are  the  deep 
branches  of  the  superior  gluteal 
vessels  and  the  superior  gluteal 
nerve.  The  deep  surface  of  the 
Glutseus  minimus  is  in  relation 
with  the  reflected  tendon  of  the 
Rectus  femoris  and  the  capsule 
of  the  hip-joint. 

Variations. — The  muscle  may  be  di- 
vided into  an  anterior  and  a  posterior 
part,  or  it  may  send  slips  to  the  Piri- 
formis, the  Gemellus  superior  or  the 
outer  part  of  the  origm  of  the  Vastus 
lateralis. 


THE  MUSCLES  OF  THE  GLUTEAL  REGION 


475 


P 


t 

II 


Medial 
hamstring 

tendons 
Sartorius 

Cfracilis 

Semitendinosus 
Semi- 
membranosus 


Lateral 
^^hamstring 
tendon 

Biceps 
femoris 


Fia.  434. — Muscles  of  the  gluteal  and  posterior  femoral  regions. 


476 


MYOLOGY 


The  Tensor  fasciae  latae  {Tensor  fascice  femoris)  arises  from  flie~  anterior  "pari 
of  the  outer  lip  of  the  iliac  crest;  from  the  outer  surface  of  the  anterior  superior 
iliac  spine,  and  part  of  the  outer  border  of  the  notch  below  it,  between  the  Glutaeus 
medius  and  Sartorius;  and  from  the  deep  surface  of  the  fascia  lata.  It  is  inserted 
between  the  two  layers  of  the  iliotibial  band  of  the  fascia  lata  about  the  junction 
of  the  middle  and  upper  thirds  of  the  thigh. 

The  Piriformis  is  a  flat  muscle,  pyramidal  in  shape,  lying  almost  parallel  with 
the  posterior  margin  of  the  Glutseus  medius.  It  is  situated  partly  within  the  pelvis 
against  its  posterior  wall,  and  partly  at  the  back  of  the  hip-joint.  It  arises  from 
the  front  of  the  sacrum  by  three  fleshy  digitations,  attached  to  the  portions  of 
bone  between  the  first,  second,  third,  and  fourth  anterior  sacral  foramina,  and  to 
the  grooves  leading  from  the  foramina :  a  few  fibers  also  arise  from  the  margin  of 
the  greater  sciatic  foramen,  and  from  the  anterior  surface  of  the  sacrotuberous 
ligament.  The  muscle  passes  out  of  the  pelvis  through  the  greater  sciatic  fora- 
men, the  upper  part  of  which  it  fills',  and  is  inserted  by  a  rounded  tendon  into 
the  upper  border  of  the  greater  trochanter  behind,  but  often  partly  blended  with, 
the  common  tendon  of  the  Obturator  internus  and  Gemelli. 

Variations. — It  is  frequently  pierced  by  the  common  peroneal  nerve  and  thus  divided  more  or 
less  into  two  parts.  It  may  be  luiited  with  the  Glutaeus  medius,  or  send  fibers  to  the  Glutaeus 
minimus  or  receive  fibers  from  the  Gemellus  superior.  It  may  have  only  one  or  two  sacral  attach- 
ments or  be  inserted  in  to  the  capsule  of  the  hip-joint.    It  may  be  absent. 


Ant.  sup.  iliac  spine- 


Symphysis 
pubis 


Transverse  acetabular 
ligament 


Fig.  435. — The  obturator  membrane. 


^ 


Obturator  Membrane  (Fig.  435). — The  obturator  membrane  is  a  thin  fibrous  sheet, 
which  almost  completely  closes  the  obturator  foramen.  Its  fibers  are  arranged 
in  interlacing  bundles  mainly  transverse  in  direction;  the  uppermost  bundle  is 
attached  to  the  obturator  tubercles  and  completes  the  obturator  canal  for  the  pas- 
sage of  the  obturator  vessels  and  nerve.  The  membrane  is  attached  to  the  sharp 
margin  of  the  obturator  foramen  except  at  its  lower  lateral  angle,  where  it  is  fixed 


THE  MUSCLES  OF  THE  GLUTEAL  REGION  477 


I  to  the  pelvic  surface  of  the  inferior  ramus  of  the  ischium,  i.  e.,  within  the  margin. 
Both  obturator  muscles  are  connected  with  this  membrane. 
The  Obturator  intemus  is  situated  partly  within  the  lesser  pelvis,  and  partly 
at  the  back  of  the  hip-joint.  It  arises  from  the  inner  surface  of  the  antero-lateral 
wall  of  the  pelvis,  where  it  surrounds  the  greater  part  of  the  obturator  foramen, 
being  attached  to  the  inferior  rami  of  the  pubis  and  ischium,  and  at  the  side  to  the 
inner  surface  of  the  hip  bone  below  and  behind  the  pelvic  brim,  reaching  from  the 
upper  part  of  the  greater  sciatic  foramen  above  and  behind  to  the  obturator  fora- 
men below  and  in  front.  It  also  arises  from  the  pelvic  surface  of  the  obturator 
membrane  except  in  the  posterior  part,  from  the  tendinous  arch  which  completes  the 
canal  for  the  passage  of  the  obturator  vessels  and  nerve,  and  to  a  slight  extent  from 
the  obturator  fascia,  which  covers  the  muscle.  The  fibers  converge  rapidly  toward 
the  lesser  sciatic  foramen,  and  end  in  four  or  five  tendinous  bands,  which  are  found 
on  the  deep  surface  of  the  muscle;  these  bands  are  reflected  at  a  right  angle  over 
I        the  grooved  surface  of  the  ischium  between  its  spine  and  tuberosity.    This  bony 

II surface  is  covered  by  smooth  cartilage,  which  is  separated  from  the  tendon  by  a 
[bursa,  and  presents  one  or  more  ridges  corresponding  with  the  furrows  between 
the  tendinous  bands.  These  bands  leave  the  pelvis  through  the  lesser  sciatic  fora- 
men and  unite  into  a  single  flattened  tendon,  which  passes  horizontally  across  the 
capsule  of  the  hip-joint,  and,  after  receiving  the  attachments  of  the  Gemelli,  is 
inserted  into  the  forepart  of  the  medial  surface  of  the  greater  trochanter  above 
the  trochanteric  fossa.    A  bursa,  narrow  and  elongated  in  form,  is  usually  found 

I  between  the  tendon  and  the  capsule  of  the  hip-joint;  it  occasionally  communicates 
I  with  the  bursa  between  the  tendon  and  the  ischium. 
I     The  Gemelli  are  two  small  muscular  fasciculi,  accessories  to  the  tendon  of  the 
I  Obturator  internus  which  is  received  into  a  groove  between  them. 
I     The  Gemellus  superior,  the  smaller  of  the  two,  arises  from  the  outer  surface  of 
I  the  spine  of  the  ischium,  blends  with  the  upper  part  of  the  tendon  of  the  Obturator 
I  internus,  and  is  inserted  with  it  into  the  medial  surface  of  the  greater  trochanter. 
I  It  is  sometimes  wanting. 
I     The  Gemellus  inferior  arises  from  the  upper  part  of  the  tuberosity  of  the  ischium, 
:        immediately  below  the  groove  for  the  Obturator  internus  tendon.    It  blends  with 
-        the  lower  part  of  the  tendon  of  the  Obturator  internus,  and  is  inserted  with  it 
H I  it  into  the  medial  surface  of  the  greater  trochanter.     Rarely  absent. 
HI     The  Quadratus  femoris  is  a  flat,  quadrilateral  muscle,  between  the  Gemellus 

■  ■inferior  and  the  upper  margin  of  the  Adductor  magnus;  it  is  separated  from  the 
'        latter  by  the  terminal  branches  of  the  medial  femoral  circumflex  vessels.    It  arises 

from  the  upper  part  of  the  external  border  of  the  tuberosity  of  the  ischium,  and  is 
inserted  into  the  upper  part  of  the  linea  quadrata — that  is,  the  line  which  extends 
vertically  downward  from  the  intertrochanteric  crest.  A  bursa  is  often  found 
between  the  front  of  this  muscle  and  the  lesser  trochanter.  Sometimes  absent. 
The  Obturator  extemus  (Fig.  436)  is  a  flat,  triangular  muscle,  which  covers 
^    the  outer  surface  of  the  anterior  wall  of  the  pelvis.    It  arises  from  the  margin 

■  I  of  bone  immediately  around  the  medial  side  of  the  obturator  foramen,  viz.,  from 

the  rami  of  the  pubis,  and  the  inferior  ramus  of  the  ischium;  it  also  arises  from  the 
medial  two-thirds  of  the  outer  surface  of  the  obturator  membrane,  and  from  the 
tendinous  arch  which  completes  the  canal  for  the  passage  of  the  obturator  vessels 
and  nerves.  The  fibers  springing  from  the  pubic  arch  extend  on  to  the  inner  sur- 
face of  the  bone,  where  they  obtain  a  narrow  origin  between  the  margin  of  the 
foramen  and  the  attachment  of  the  obturator  membrane.  The  fibers  converge 
and  pass  backward,  lateralward,  and  upward,  and  end  in  a  tendon  which  runs 
across  the  back  of  the  neck  of  the  femur  and  lower  part  of  the  capsule  of  the  hip- 
joint  and  is  inserted  into  the  trochanteric  fossa  of  the  femur.  The  obturator  vessels 
lie  between  the  muscle  and  the  obturator  membrane;  the  anterior  branch  of  the 


l_ 


478 


MYOLOGY 


by  passing  in  front  of  the  muscle,  anc 


obturator  nerve  reaches  the  thigh 
posterior  branch  by  piercing  it. 

Nerves. — The  Glutseus  maximus  is  supplied  by  the  fifth  lumbar  and  first  and  second  sacra 
nerves  through  the  inferior  gluteal  nerve;  the  Gluta?i  medius  and  minimus  and  the  Tensor  fascdae 
latge  by  the  fourth  and  fifth  lumbar  and  first  sacral  nerves  through  the  superior  gluteal;  the  Piri- 
formis is  supplied  by  the  first  and  second  sacral  nerves;  the  Gemellus  inferior  and  Quadrat  us 
femoris  by  the  last  lumbar  and  first  sacral  nerves;  the  Gemellus  superior  and  Obturator  internus 
by  the  first,  second,  and  third  sacral  nerves,  and  the  Obturator  externus  by  the  third  and  fourth 
lumloar  nerves  through  the  obturator. 


Obturator  nerve 


Ant.  inf.  iliac  spine 


Fig.  436. — The  Obturator  externus. 


Actions. — When  the  Glutaeus  maximus  takes  its  fixed  point  from  the  pelvis,  it  extends  the 
femur  and  brings  the  bent  thigh  into  a  line  with  the  body.  Taking  its  fixed  point  from  below, 
it  acts  upon  the  pelvis,  supporting  it  and  the  trunk  upon  the  head  of  the  femur;  this  is  especially 
obvious  in  standing  on  one  leg.  Its  most  powerful  action  is  to  cause  the  body  to  regain  the  erect 
position  after  stooping,  by  drawing  the  pelvis  backward,  being  assisted  in  this  action  by  the 
Biceps  femoris,  Semitendinosus,  and  Semimembranosus.  The  Glutaeus  maximus  is  a  tensor  of 
the  fascia  lata,  and  by  its  connection  with  the  ihotibial  band  steadies  the  femur  on  the  articular 
surfaces  of  the  tibia  during  standing,  when  the  Extensor  muscles  are  relaxed.  The  lower  part 
of  the  muscle  also  acts  as  an  adductor  and  external  rotator  of  the  hmb.  The  Glutsei  medius  and 
minimus  abduct  the  thigh,  when  the  limb  is  extended,  and  are  principally  called  into  action  in 
supporting  the  body  on  one  hmb,  in  conjunction  with  the  Tensor  fasciae  latae.  Their  anterior 
fibers,  by  drawing  the  greater  trochanter  forward,  rotate  the  thigh  inward,  in  which  action  they 
are  also  assisted  by  the  Tensor  fasciae  latae.  The  Tensor  fasciae  latae  is  a  tensor  of  the  fascia  lata; 
continuing  its  action,  the  oblique  direction  of  its  fibers  enables  it  to  abduct  the  thigh  and  to  rotate 
it  inward.  In  the  erect  posture,  acting  from  below,  it  will  serve  to  steady  the  pelvis  upon  the  head 
of  the  femur;  and  by  means  of  the  iliotibial  band  it  steadies  the  condyles  of  the  femur  on  the 
articular  surfaces  of  the  tibia,  and  assists  the  Glutaeus  maximus  in  supporting  the  knee  in  the 
extended  position.  The  remaining  muscles  are  powerful  external  rotators  of  the  thigh.  In  the 
sitting  posture,  when  the  thigh  is  flexed  upon  the  pelvis,  their  action  as  rotators  ceases,  and  they 
become  abductors,  with  the  exception  of  the  Obturator  externus,  which  still  rotates  the  femur 
outward. 


4.  The  Posterior  Femoral  Muscles  (Hamstring  Muscles)  (Fig.  434). 
Biceps  femoris.  Semitendinosus.  Semimembranosus. 

The  Biceps  femoris  (Biceps)  is  situated  on  the  posterior  and  lateral  aspect  of  the 
thigh.     It  has  two  heads  of  origin ;  one,  the  long  head,  arises  from  the  lower  and  inner 


1 


THE  POSTERIOR  FEMORAL  MUSCLES  479 

impression  on  the  back  part  of  the  tuberosity  of  the  ischium,  by  a  tendon  common 
to  it  and  the  Semitendinosus,  and  from  the  lower  part  of  the  sacrotuberous  liga- 
ment; the  other,  the  short  head,  arises  from  the  lateral  lip  of  the  linea  aspera, 
between  the  Adductor  magnus  and  Vastus  lateralis,  extending  up  almost  as  high 
as  the  insertion  of  the  Glutgeus  maximus;  from  the  lateral  prolongation  of  the 
linea  aspera  to  within  5  cm.  of  the  lateral  condyle;  and  from  the  lateral  inter- 
muscular septum.  The  fibers  of  the  long  head  form  a  fusiform  belly,  which  passes 
obliquely  downward  and  lateralward  across  the  sciatic  nerve  to  end  in  an  aponeu- 
rosis which  covers  the  posterior  surface  of  the  muscle,  and  receives  the  fibers  of 
the  short  head;  this  aponeurosis  becomes  gradually  contracted  into  a  tendon, 
which  is  inserted  into  the  lateral  side  of  the  head  of  the  fibula,  and  by  a  small 
slip  into  the  lateral  condyle  of  the  tibia.  At  its  insertion  the  tendon  divides  into 
two  portions,  which  embrace  the  fibular  collateral  ligament  of  the  knee-joint. 
From  the  posterior  border  of  the  tendon  a  thin  expansion  is  given  off  to  the  fascia 
of  the  leg.  The  tendon  of  insertion  of  this  muscle  forms  the  lateral  hamstring; 
the  common  peroneal  nerve  descends  along  its  medial  border. 

Variations. — The  short  head  may  be  absent;  additional  heads  may  arise  from  the  ischial 
tuberosity,  the  linea  aspera,  the  medial  supracondylar  ridge  of  the  femur  or  from  various  other 
parts.    A  slip  may  pass  to  the  Gastrocnemius. 

The  Semitendinosus,  remarkable  for  the  great  length  of  its  tendon  of  insertion, 
is  situated  at  the  posterior  and  medial  aspect  of  the  thigh.  It  arises  from  the  lower 
and  medial  impression  on  the  tuberosity  of  the  ischium,  by  a  tendon  common 
to  it  and  the  long  head  of  the  Biceps  femoris;  it  also  arises  from  an  aponeurosis 
which  connects  the  adjacent  surfaces  of  the  two  muscles  to  the  extent  of  about 
7.5  cm.  from  their  origin.  The  muscle  is  fusiform  and  ends  a  little  below  the  middle 
of  the  thigh  in  a  long  round  tendon  which  lies  along  the  medial  side  of  the  popliteal 
fossa;  it  then  curves  around  the  medial  condyle  of  the  tibia  and  passes  over  the 
tibial  collateral  ligament  of  the  knee-joint,  from  which  it  is  separated  by  a  bursa, 
and  is  inserted  into  the  upper  part  of  the  medial  surface  of  the  body  of  the  tibia, 
nearly  as  far  forward  as  its  anterior  crest.  At  its  insertion  it  gives  off  from  its 
lower  border  a  prolongation  to  the  deep  fascia  of  the  leg  and  lies  behind  the  tendon 
of  the  Sartorius,  and  below  that  of  the  Gracilis,  to  which  it  is  united.  A  tendinous 
intersection  is  usually  observed  about  the  middle  of  the  muscle. 

The  Semimembranosus,  so  called  from  its  membranous  tendon  of  origin,  is  situ- 
ated at  the  back  and  medial  side  of  the  thigh.  It  arises  by  a  thick  tendon  from 
the  upper  and  outer  impression  on  the  tuberosity  of  the  ischium,  above  and  lateral 
to  the  Biceps  femoris  and  Semitendinosus.  The  tendon  of  origin  expands  into  an 
aponeurosis,  which  covers  the  upper  part  of  the  anterior  surface  of  the  muscle;  from 
this  aponeurosis  muscular  fibers  arise,  and  converge  to  another  aponeurosis  which 
covers  the  lower  part  of  the  posterior  surface  of  the  muscle  and  contracts  into  the 
tendon  of  insertion.  It  is  inserted  mainly  into  the  horizontal  groove  on  the  posterior 
medial  aspect  of  the  medial  condyle  of  the  tibia.  The  tendon  of  insertion  gives  off 
certain  fibrous  expansions :  one,  of  considerable  size,  passes  upward  and  lateralward 
to  be  inserted  into  the  back  part  of  the  lateral  condyle  of  the  femur,  forming  part 
of  the  oblique  popliteal  ligament  of  the  knee-joint ;  a  second  is  continued  downward 
to  the  fascia  which  covers  the  Popliteus  muscle;  while  a  few  fibers  join  the  tibial 
collateral  ligament  of  the  joint  and  the  fascia  of  the  leg.  The  muscle  overlaps  the 
upper  part  of  the  popliteal  vessels. 

Variations. — It  may  be  reduced  or  absent,  or  double,  arising  mainly  from  the  sacrotuberous 
ligament  and  giving  a  slip  to  the  femur  or  Adductor  magnus. 

The  tendons  of  insertion  of  the  two  preceding  muscles  form  the  medial  ham- 
strings. 


480  ^^^SSBKI^         MYOLOGY 

Nerves. — The  muscles  of  this  region  are  supplied  by  the  fourth  and  fifth  lumbar  and  the-ffifst 
second,  and  third  sacral  nerves;  the  nerve  to  the  short  head  of  the  Biceps  femoris  is  derived  frona 
the  common  peroneal,  the  other  muscles  are  supplied  through  the  tibial  nerve. 

Actions. — The  hamstring  muscles  flex  the  leg  upon  the  thigh.  When  the  knee  is  semiflexed, 
the  Biceps  femoris  in  consequence  of  its  oblique  direction  rotates  the  leg  slightly  outward;  and 
the  Semitendinosus,  and  to  a  slight  extent  the  Semimembranosus,  rotate  the  leg  inward,  assist- 
ing the  Popliteus.  Taking  their  fixed  point  from  below,  these  muscles  serve  to  support  the  pelvis 
upon  the  head  of  the  femur,  and  to  draw  the  trunk  directly  backward,  as  in  raising  it  from  the 
stooping  position  or  in  feats  of  strength,  when  the  body  is  thrown  backward  in  the  form  of  an 
arch.  As  already  indicated  on  page  285,  complete  flexion  of  the  hip  cannot  be  effected  unless 
the  knee-joint  is  also  flexed,  on  account  of  the  shortness  of  the  hamstring  muscles. 

m.    THE  MUSCLES  AND  FASCMl  OF  THE  LEG. 

The  muscles  of  the  leg  may  be  divided  into  three  groups:  anterior,  posterior, 
and  lateral. 

1.  The  Anterior  Crural  Muscles  (Fig.  437). 

Tibialis  anterior.  Extensor  digitorum  longus. 

Extensor  hallucis  longus.  Peronseus  tertius. 

Deep  Fascia  {fascia  cruris) . — The  deep  fascia  of  the  leg  forms  a  complete  invest- 
ment to  the  muscles,  and  is  fused  with  the  periosteum  over  the  subcutaneous 
surfaces  of  the  bones.  It  is  continuous  above  with  the  fascia  lata,  and  is  attached 
around  the  knee  to  the  patella,  the  ligamentum  patellae,  the  tuberosity  and  con- 
dyles of  the  tibia,  and  the  head  of  the  fibula.  Behind,  it  forms  the  popliteal  fascia, 
covering  in  the  popliteal  fossa;  here  it  is  strengthened  by  transverse  fibers,  and 
perforated  by  the  small  saphenous  vein.  It  receives  an  expansion  from  the  tendon 
of  the  Biceps  femoris  laterally,  and  from  the  tendons  of  the  Sartorius,  Gracilis, 
Semitendinosus,  and  Semimembranosus  medially;  in  front,  it  blends  with  the  peri- 
osteum covering  the  subcutaneous  surface  of  the  tibia,  and  with  that  covering 
the  head  and  malleolus  of  the  fibula;  below,  it  is  continuous  with  the  transverse 
crural  and  laciniate  ligaments.  It  is  thick  and  dense  in  the  upper  and  anterior 
part  of  the  leg,  and  gives  attachment,  by  its  deep  surface,  to  the  Tibialis  anterior 
and  Extensor  digitorum  longus;  but  thinner  behind,  where  it  covers  the  Gastroc- 
nemius and  Soleus.  It  gives  off  from  its  deep  surface,  on  the  lateral  side  of  the  leg, 
two  strong  intermuscular  septa,  the  anterior  and  posterior  peroneal  septa,  which 
enclose  the  Peronsei  longus  and  brevis,  and  separate  them  from  the  muscles  of 
the  anterior  and  posterior  crural  regions,  and  several  more  slender  processes  which 
enclose  the  individual  muscles  in  each  region.  A  broad  transverse  intermuscular 
septum,  called  the  deep  transverse  fascia  of  the  leg,  intervenes  between  the  super- 
ficial and  deep  posterior  crural  muscles. 

The  Tibialis  anterior  {Tibialis  anticus)  is  situated  on  the  lateral  side  of  the  tibia; 
it  is  thick  and  fleshy  above,  tendinous  below.  It  arises  from  the  lateral  condyle 
and  upper  half  or  two-thirds  of  the  lateral  surface  of  the  body  of  the  tibia;  from 
the  adjoining  part  of  the  interosseous  membrane;  from  the  deep  surface  of  the 
fascia;  and  from  the  intermuscular  septum  between  it  and  the  Extensor  digitorum 
longus.  The  fibers  run  vertically  downward,  and  end  in  a  tendon,  which  is  apparent 
on  the  anterior  surface  of  the  muscle  at  the  lower  third  of  the  leg.  After  passing 
through  the  most  medial  compartments  of  the  transverse  and  cruciate  crural 
ligaments,  it  is  inserted  into  the  medial  and  under  surface  of  the  first  cuneiform 
bone,  and  the  base  of  the  first  metatarsal  bone.  This  muscle  overlaps  the  anterior 
tibial  vessels  and  deep  peroneal  nerve  in  the  upper  part  of  the  leg. 

Variations. — A  deep  portion  of  the  muscle  is  rarely  inserted  into  the  talus,  or  a  tendinous  slip 
may  pass  to  the  head  of  the  first  metatarsal  bone  or  the  base  of  the  first  phalanx  of  the  great  toe. 
The  Tibiofascialis  anterior,  a  small  muscle  from  the  lower  part  of  the  tibia  to  the  transverse  or 
cruciate  crural  ligaments  or  deep  fascia. 


THE  ANTERIOR  CRURAL  MUSCLES 


481 


The  Extensor  hallucis  longus  {Extensor  proprius 
hallucis)  is  a  thin  muscle,  situated  between  the 
Tibialis  anterior  and  the  Extensor  digitorum 
longus.  It  arises  from  the  anterior  surface  of  the 
fibula  for  about  the  middle  two-fourths  of  its 
extent,  medial  to  the  origin  of  the  Extensor  digi- 
torum longus;  it  also  arises  from  the  interosseous 
membrane  to  a  similar  extent.  The  anterior 
tibial  vessels  and  deep  peroneal  nerve  lie  between 
it  and  the  Tibialis  anterior.  The  fibers  pass 
downward,  and  end  in  a  tendon,  which  occupies 
the  anterior  border  of  the  muscle,  passes  through 
a  distinct  compartment  in  the  cruciate  crural 
ligament,  crosses  from  the  lateral  to  the  medial 
side  of  the  anterior  tibial  vessels  near  the  bend  of 
the  ankle,  and  is  inserted  into  the  base  of  the  distal 
phalanx  of  the  great  toe.  Opposite  the  metatarso- 
phalangeal articulation,  the  tendon  gives  off  a  thin 
prolongation  on  either  side,  to  cover  the  surface 
of  the  joint.  An  expansion  from  the  medial  side 
of  the  tendon  is  usually  inserted  into  the  base  of 
the  proximal  phalanx. 

Variations. — Occasionally  united  at  its  origin  with  the 
Extensor  digitorum  longvis.  Extensor  ossis  metatarsi  hal- 
lucis, a  small  muscle,  sometimes  found  as  a  slip  from  the 
Extensor  hallucis  longus,  or  from  the  Tibialis  anterior,  or 
from  the  Extensor  digitorum  longus,  or  as  a  distinct  mus- 
cle; it  traverses  the  same  compartment  of  the  transverse 
ligament  with  the  Extensor  hallucis  longus. 

The  Extensor  digitonim  longus  is  a  penniform 
muscle,  situated  at  the  lateral  part  of  the  front 
of  the  leg.  It  arises  from  the  lateral  condyle  of 
the  tibia;  from  the  upper  three-fourths  of  the 
anterior  surface  of  the  body  of  the  fibula;  from 
the  upper  part  of  the  interosseous  membrane; 
from  the  deep  surface  of  the  fascia;  and  from  the 
intermuscular  septa  between  it  and  the  Tibialis 
anterior  on  the  medial,  and  the  Peronsei  on  the 
lateral  side.  Between  it  and  the  Tibialis  anterior 
are  the  upper  portions  of  the  anterior  tibial  vessels 
and  deep  peroneal  nerve.  The  tendon  passes  under 
the  transverse  and  cruciate  crural  ligaments  in 
company  with  the  Peronseus  tertius,  and  divides 
into  four  slips,  which  run  forward  on  the  dorsum 
of  the  foot,  and  are  inserted  into  the  second  and 
third  phalanges  of  the  four  lesser  toes.  The  ten- 
dons to  the  second,  third,  and  fourth  toes  are 
each  joined,  opposite  the  metatarsophalangeal 
articulation,  on  the  lateral  side  by  a  tendon  of 
the  Extensor  digitorum  brevis.  The  tendons  are 
inserted  in  the  following  manner:  each  receives  a 
fibrous  expansion  from  the  Interossei  and  Lum- 
bricalis,  and  then  spreads  out  into  a  broad  apon- 
eurosis, which  covers  the  dorsal  surface  of  the 


\ri6li 


xentt 


Fia.  437. — Muscles  of  the  front  of 
the  leg. 


k: 


482  MYOLOGY 


^1 

e  second 


first  phalanx:  this  aponeurosis,  at  the  articulation  of  the  first  with  the 
phalanx,  divides  into  three  slips — an  intermediate,  which  is  inserted  into  the  base 
of  the  second  phalanx;  and  two  collateral  slips,  which,  after  uniting  on  the  dorsal 
surface  of  the  second  phalanx,  are  continued  onward,  to  be  inserted  into  the  base 
of  the  third  phalanx. 

Variations. — This  muscle  varies  considerably  in  the  modes  of  origin  and  the  arrangement  of  itsi 
various  tendons.  The  tendons  to  the  second  and  fifth  toes  may  be  found  doubled,  or  extra  slips 
are  given  off  from  one  or  more  tendons  to  their  corresponding  metatarsal  bones,  or  to  the  short 
extensor,  or  to  one  of  the  interosseous  muscles.  A  slip  to  the  great  toe  from  the  innermost  tendon 
has  been  found. 

The  Peronseus  tertius  is  a  part  of  the  Extensor  digitorum  longus,  and  might 
be  described  as  its  fifth  tendon.  The  fibers  belonging  to  this  tendon  arise  from 
the  lower  third  or  more  of  the  anterior  surface  of  the  fibula;  from  the  lower  part 
of  the  interosseous  membrane;  and  from  an  intermuscular  septum  between  it 
and  the  Peronseus  brevis.  The  tendon,  after  passing  under  the  transverse  and 
cruciate  crural  ligaments  in  the  same  canal  as  the  Extensor  digitorum  longus, 
is  inserted  into  the  dorsal  surface  of  the  base  of  the  metatarsal  bone  of  the  little 
toe.    This  muscle  is  sometimes  wanting. 

Nerves. — These  muscles  are  supplied  by  the  fourth  and  fifth  lumbar  and  first  sacral  nerves 
through  the  deep  peroneal  nerve. 

Actions. — The  Tibialis  anterior  and  Peronajus  tertius  are  the  direct  flexors  of  the  foot  at  the 
ankle-joint;  the  former  muscle,  when  acting  in  conjunction  with  the  Tibialis  posterior,  raises  the 
medial  border  of  the  foot,  i.  e.,  inverts  the  foot;  and  the  latter,  acting  with  the  Perona?i  brevis 
and  longus,  raises  the  lateral  border  of  the  foot,  i.  e.,  everts  the  foot.  The  Extensor  digitorum 
longus  and  Extensor  hallucis  longus  extend  the  phalanges  of  the  toes,  and,  continuing  their 
action,  flex  the  foot  upon  the  leg.  Taking  their  fixed  points  from  below,  in  the  erect  posture, 
all  these  muscles  serve  to  fix  the  bones  of  the  leg  in  the  perpendicular  position,  and  give  increased 
strength  to  the  ankle-joint. 

2.  The  Posterior  Crural  Muscles. 

The  muscles  of  the  back  of  the  leg  are  subdivided  into  two  groups — superficial 
and  deep.  Those  of  the  superficial  group  constitute  a  pcf^verful  muscular  mass, 
forming  the  calf  of  the  leg.  Their  large  size  is  one  of  the  most  characteristic 
features  of  the  muscular  apparatus  in  man,  and  bears  a  direct  relation  to  his  erect 
attitude  and  his  mode  of  progression. 

The  Superficial  Group  (Fig.  438). 

Gastrocnemius.  Soleus.  Plantaris. 

The  Gastrocnemius  is  the  most  superficial  muscle,  and  forms  the  greater  part 
of  the  calf.  It  arises  by  two  heads,  which  are  connected  to  the  condyles  of  the 
femur  by  strong,  flat  tendons.  The  medial  and  larger  head  takes  its  origin  from  a 
depression  at  the  upper  and  back  part  of  the  medial  condyle  and  from  the  adjacent 
part  of  the  femur.  The  lateral  head  arises  from  an  impression  on  the  side  of  the 
lateral  condyle  and  from  the  posterior  surface  of  the  femur  immediately  above 
the  lateral  part  of  the  condyle.  Both  heads,  also,  arise  from  the  subjacent  part 
of  the  capsule  of  the  knee.  Each  tendon  spreads  out  into  an  aponeurosis,  which 
covers  the  posterior  surface  of  that  portion  of  the  muscle  to  which  it  belongs. 
From  the  anterior  surfaces  of  these  tendinous  expansions,  muscular  fibers  are 
given  off;  those  of  the  medial  head  being  thicker  and  extending  lower  than  those 
of  the  lateral.  The  fibers  unite  at  an  angle  in  the  middle  line  of  the  muscle  in  a 
tendinous  raphe,  which  expands  into  a  broad  aponeurosis  on  the  anterior  surface 
of  the  muscle,  and  into  this  the  remaining  fibers  are  inserted.  The  aponeurosis, 
gradually  contracting,  unites  with  the  tendon  of  the  Soleus,  and  forms  with  it 
the  tendo  calcaneus. 


I^^^^^^H        THE  POSTERIOR  CRURAL  MUSCLES  483 

P  \^Miafions.-^^-X1osence  of  the  outer  head  or  of  the  entire  muscle.  Extra  slips  from  the  popliteal 
[surface  of  the  femur. 
I  The  Soleus  is  a  broad  flat  muscle  situated  immediately  in  front  of  the  Gastroc- 
nemius. It  arises  by  tendinous  fibers  from  the  back  of  the  head  of  the  fibula, 
and  from  the  upper  third  of  the  posterior  surface  of  the  body  of  the  bone;  from  the 
popliteal  line,  and  the  middle  third  of  the  medial  border  of  the  tibia;  some  fibers 

■1  also  arise  from  a  tendinous  arch  placed  between  the  tibial  and  fibular  origins 
|of  the  muscle,  in  front  of  which  the  popliteal  vessels  and  tibial  nerve  run.  The 
fibers  end  in  an  aponeurosis  .which  covers  the  posterior  surface  of  the  muscle,  and, 
gradually  becoming  thicker  and  narrower,  joins  with  the  tendon  of  the  Gastroc- 
Inemius,  and  forms  with  it  the  tendo  calcaneus. 

Variations. — Accessory  head  to  its  lower  and  inner  part  usually  ending  in  the  tendocalcaneus,  or 
[the  calcaneus,  or  the  laciniate  ligament. 

The  Gastrocnemius  and  Soleus  together  form  a  muscular  mass  which  is  occa- 
sionally described  as  the  Triceps  surse;  its  tendon  of  insertion  is  the  tendo  calcaneus. 

Tendo  Calcaneus  {tendo  Achillis) . — The  tendo  calcaneus,  the  common  tendon  of  the 
Gastrocnemius  and  Soleus,  is  the  thickest  and  strongest  in  the  body.  It  is  about 
15  cm.  long,  and  begins  near  the  middle  of  the  leg,  but  receives  fleshy  fibers  on  its 
anterior  surface,  almost  to  its  lower  end.  Gradually  becoming  contracted  below, 
it  is  inserted  into  the  middle  part  of  the  posterior  surface  of  the  calcaneus,  a  bursa 
being  interposed  between  the  tendon  and  the  upper  part  of  this  surface.  The  ten- 
don spreads  out  somewhat  at  its  lower  end,  so  that  its  narrowest  part  is  about 
4  cm.  above  its  insertion.  It  is  covered  by  the  fascia  and  the  integument,  and  is 
separated  from  the  deep  muscles  and  vessels  by  a  considerable  interval  filled  up 
with  areolar  and  adipose  tissue.  Along  its  lateral  side,  but  superficial  to  it,  is  the 
small  saphenous  vein. 

The  Plantaris  is  placed  between  the  Gastrocnemius  and  Soleus.  It  arises  from 
the  lower  part  of  the  lateral  prolongation  of  the  linea  aspera,  and  from  the  oblique 
popliteal  ligament  of  the  knee-joint.  It  forms  a  small  fusiform  belly,  from  7  to 
10  cm.  long,  ending  in  a  long  slender  tendon  which  crosses  obliquely  between  the 
two  muscles  of  the  calf,  and  runs  along  the  medial  border  of  the  tendo  calcaneus, 
to  be  inserted  with  it  into  the  posterior  part  of  the  calcaneus.  This  muscle  is  some- 
times double,  and  at  other  times  wanting.  Occasionally,  its  tendon  is  lost  in  the 
laciniate  ligament,  or  in  the  fascia  of  the  leg. 

Nerves. — The  Gastrocnemius  and  Soleus  are  suppUed  by  the  first  and  second  sacral  nerves, 
and  the  Plantaris  by  the  fourth  and  fifth  lumbar  and  first  sacral  nerves,  through  the  tibial  nerve. 

Actions. — The  muscles  of  the  calf  are  the  chief  extensors  of  the  foot  at  the  ankle-joint.  They 
possess  considerable  power,  and  are  constantly  called  into  use  in  standing,  walking,  dancing, 
and  leaping;  hence  the  large  size  they  usually  present.  In  walking,  these  muscles  raise  the  heel 
from  the  ground;  the  body  being  thus  supported  on  the  raised  foot,  the  opposite  limb  can  be 
carried  forward.  In  standing,  the  Soleus,  taking  its  fixed  point  from  below,  steadies  the  leg  upon 
the  foot  and  prevents  the  body  from  falling  forward.  The  Gastrocnemius,  acting  from  below, 
serves  to  flex  the  femur  upon  the  tibia,  assisted  by  the  PopUteus.  The  Plantaris  is  the  rudiment 
of  a  large  muscle  which  in  some  of  the  lower  animals  is  continued  over  the  calcaneus  to  be  inserted 
into  the  plantar  aponeurosis.  In  man  it  is  an  accessory  to  the  Gastrocnemius,  extending  the 
ankle  if  the  foot  be  free,  or  bending  the  knee  if  the  foot  be  fixed. 


ki 


ir 


The  Deep  Group  (Fig.  439). 

Popliteus.  Flexor  digitorum  longus. 

Flexor  hallucis  longus.  Tibialis  posterior. 


Deep  Transverse  Fascia. — The  deep  transverse  fascia  of  the  leg  is  a  transversely 
placed,  intermuscular  septum,  between  the  superficial  and  deep  muscles  of  the 
back  of  the  leg.    At  the  sides  it  is  connected  to  the  margins  of  the  tibia  and 


484 


MYOLOGY 


fibula.    Above,  where  it  covers  the  PopHteus,  it  is  thick  and  dense,  and  receives 
an  expansion  from  the  tendon  of  the  Semimembranosus;  it  is  thinner  in  the  middle 


Tendons  of 

Peronae  longus 

et  brevis 


Fig.  438. — Muscles  of  the  back  of  the  leg. 
Superficial  layer. 


Fig.  439. — Muscles  of  the  back  of  the  leg. 
Deep  layer. 


of  the  leg;  but  below,  where  it  covers  the  tendons  passing  behind  the  malleoli, 
it  is  thickened  and  continuous  with  the  laciniate  ligament. 
The  Popliteus  is  a  thin,  flat,  triangular  muscle,  which  forms  the  lower  part  of 


THE  POSTERIOR  CRURAL  MUSCLES  485 


^Bithe  floor  of  the  popliteal  fossa.    It  arises  by  a  strong  tendon  about  2.5  em.  long, 

from  a  depression  at  the  anterior  part  of  the  groove  on  the  lateral  condyle  of  the 

femur,  and  to  a  small  extent  from  the  oblique  popliteal  ligament  of  the  knee-joint; 

^■Eand  is  inserted  into  the  medial  two-thirds  of  the  triangular  surface  above  the  pop- 

^■'  liteal  line  on  the  posterior  surface  of  the  body  of  the  tibia,  and  into  the  tendinous 

expansion  covering  the  surface  of  the  muscle. 

■I  Variations. — Additional  head  from  the  sesamoid  bone  in  the  outer  head  of  the  Gastrocnemius. 
'  Popliteus  minor,  rare,  origin  from  femur  on  the  inner  side  of  the  Plantaris,  insertion  into  the  pos- 
terior ligament  of  the  knee-joint.  Peroneotibialis,  14  per  cent.,  origin  inner  side  of  the  head  of  the 
fibula,  insertion  into  the  upper  end  of  the  oblique  line  of  the  tibia,  it  lies  beneath  the  Popliteus. 

The  Flexor  hallucis  longus  is  situated  on  the  fibular  side  of  the  leg.  It  arises 
from  the  inferior  two-thirds  of  the  posterior  surface  of  the  body  of  the  fibula,  with 
the  exception  of  2.5  cm.  at  its  lowest  part;  from  the  lower  part  of  the  interosseous 
embrane;  from  an  intermuscular  septum  between  it  and  the  Peronsei,  laterally, 
and  from  the  fascia  covering  the  Tibialis  posterior,  medially.  The  fibers  pass 
obliquely  downward  and  backward,  and  end  in  a  tendon  which  occupies  nearly 
;he  whole  length  of  the  posterior  surface  of  the  muscle.  This  tendon  lies  in  a  groove 
which  crosses  the  posterior  surface  of  the  lower  end  of  the  tibia,  the  posterior 
surface  of  the  talus,  and  the  under  surface  of  the  sustentaculum  tali  of  the  calca- 
neus; in  the  sole  of  the  foot  it  runs  forward  between  the  two  heads  of  the  Flexor 
hallucis  brevis,  and  is  inserted  into  the  base  of  the  last  phalanx  of  the  great  toe. 
The  grooves  on  the  talus  and  calcaneus,  which  contain  the  tendon  of  the  muscle, 
are  converted  by  tendinous  fibers  into  distinct  canals,  lined  by  a  mucous  sheath. 
As  the  tendon  passes  forward  in  the  sole  of  the  foot,  it  is  situated  above,  and 
crosses  from  the  lateral  to  the  medial  side  of  the  tendon  of  the  Flexor  digitorum 
longus,  to  which  it  is  connected  by  a  fibrous  slip. 

Variations. — -rsualiy  a  slip  runs  to  the  Flexor  digitorum  and  frequently  an  additional  slip  runs 
from  the  Flexor  digitorum  to  the  Flexor  hallucis.  Peroneocalcaneus  internus,  rare,  origin  below 
or  outside  the  Flexor  hallucis  from  the  back  of  the  fibula,  passes  over  the  sustentaculvun  tali  with 
ihe  Flexor  hallucis  and  is  inserted  into  the  calcaneum. 


■^ 


ir 


The  Flexor  digitorum  longus  is  situated  on  the  tibial  side  of  the  leg.  At  its 
origin  it  is  thin  and  pointed,  but  it  gradually  increases  in  size  as  it  descends.  It 
arises  from  the  posterior  surface  of  the  body  of  the  tibia,  from  immediately  below 
the  popliteal  line  to  within  7  or  8  cm.  of  its  lower  extremity,  medial  to  the  tibial 
origin  of  the  Tibialis  posterior;  it  also  arises  from  the  fascia  covering  the  Tibialis 
posterior.  The  fibers  end  in  a  tendon,  which  runs  nearly  the  whole  length  of  the 
posterior  surface  of  the  muscle.  This  tendon  passes  behind  the  medial  malleolus, 
in  a  groove,  common  to  it  and  the  Tibialis  posterior,  but  separated  from  the  latter 
by  a  fibrous  septum,  each  tendon  being  contained  in  a  special  compartment  lined 
by  a  separate  mucous  sheath.  It  passes  obliquely  forward  and  lateral  ward,  super- 
ficial to  the  deltoid  ligament  of  the  ankle-joint,  into  the  sole  of  the  foot  (Fig.  444), 
where  it  crosses  below  the  tendon  of  the  Flexor  hallucis  longus,  and  receives  from  it 
a  strong  tendinous  slip.  It  then  expands  and  is  joined  by  the  Quadratus  plants, 
and  finally  divides  into  four  tendons,  which  are  inserted  into  the  bases  of  the  last 
phalanges  of  the  second,  third,  fourth,  and  fifth  toes,  each  tendon  passing  through 
an  opening  in  the  corresponding  tendon  of  the  Flexor  digitorum  brevis  opposite 
the  base  of  the  first  phalanx. 

Variations. — Flexor  accessorius  longus  digitorum,  not  infrequent,  origin  from  fibula,  or  tibia, 
or  the  deep  fascia  and  ending  in  a  tendon  which,  after  passing  beneath  the  laciniate  ligament, 
joins  the  tendon  of  the  long  flexor  or  the  Quadratus  plantse. 

The  Tibialis  posterior  ( Tibialis  posticus)  lies  between  the  two  preceding  muscles, 
and  is  the  most  deeply  seated  of  the  muscles  on  the  back  of  the  leg.  It  begins 
above  by  two  pointed  processes,  separated  by  an  angular  interval  through  which 


» 


I- 


486  ^^       MYOLOGY 


I 


the  anterior  tibial  vessels  pass  forward  to  the  front  of  the  leg.  It  arises  from  the 
whole  of  the  posterior  surface  of  the  interosseous  membrane,  excepting  its  lowest 
part;  from  the  lateral  portion  of  the  posterior  surface  of  the  body  of  the  tibia, 
between  the  commencement  of  the  popliteal  line  above  and  the  junction  of  the 
middle  and  lower  thirds  of  the  body  below;  and  from  the  upper  two-thirds  of  the 
medial  surface  of  the  fibula ;  some  fibers  also  arise  from  the  deep  transverse  fascia, 
and  from  the  intermuscular  septa  separating  it  from  the  adjacent  muscles.  In 
the  lower  fourth  of  the  leg  its  tendon  passes  in  front  of  that  of  the  Flexor  digitorum 
longus  and  lies  with  it  in  a  groove  behind  the  medial  malleolus,  but  enclosed  in  a 
separate  sheath;  it  next  passes  under  the  laciniate  and  over  the  deltoid  ligament 
into  the  foot,  and  then  beneath  the  plantar  calcaneonavicular  ligament.  The 
tendon  contains  a  sesamoid  fibrocartilage,  as  it  runs  under  the  plantar  calcaneo- 
navicular ligament.  It  is  inserted  into  the  tuberosity  of  the  navicular  bone,  and 
gives  off  fibrous  expansions,  one  of  which  passes  backward  to  the  sustentaculum  tali 
of  the  calcaneus,  others  forward  and  lateralward  to  the  three  cuneiforms,  the 
cuboid,  and  the  bases  of  the  second,  third,  ^nd  fourth  metatarsal  bones. 

Nerves. — The  Popliteus  is  supplied  by  the  fourth  and  fifth  lumbar  and  first  sacral  nerves, 
the  Flexor  digitorum  longus  and  Tibiahs  posterior  by  the  fifth  lumbar  and  first  sacral,  and  the 
Flexor  haUucis  longus  by  the  fifth  lumbar  and  the  first  and  second  sacral  nerves,  through  the 
tibial  nerve. 

Actions. — The  PopHteus  assists  in  flexing  the  leg  upon  the  thigh;  when  the  leg  is  flexed,  it  will 
rotate  the  tibia  inward.  It  is  especially  called  into  action  at  the  beginning  of  the  act  of  bending 
the  knee,  inasmuch  as  it  produces  the  slight  inward  rotation  of  the  tibia  which  is  essential  in  the 
early  stage  of  this  movement.  The  Tibialis  posterior  is  a  direct  extensor  of  the  foot  at  the  ankle- 
joint;  acting  in  conjunction  with  the  Tibialis  anterior,  it  turns  the  sole  of  the  foot  upward  and 
medialward,  i.  e.,  inverts  the  foot,  antagonizing  the  Peronai,  which  turn  it  upward  and  lateral- 
ward  (evert  it).  In  the  sole  of  the  foot  the  tendon  of  the  TibiaUs  posterior  lies  directly  below  the 
plantar  calcaneonavicular  hgament,  and  is  therefore  an  important  factor  in  maintaining  the 
arch  of  the  foot.  The  Flexor  digitorum  longus  and  Flexor  hallucis  longus  are  the  direct  flexors  of 
the  phalanges,  and,  continuing  their  action,  extend  the  foot  upon  the  leg;  they  assist  the  Gastroc- 
nemius and  Soleus  in  extending  the  foot,  as  in  the  act  of  walking,  or  in  standing  on  tiptoe.  In 
consequence  of  the  oblique  direction  of  its  tendons  the  Flexor  digitorum  longus  would  draw  the 
toes  medialward,  were  it  not  for  the  Quadratus  plantae,  which  is  inserted  into  the  lateral  side 
of  the  tendon,  and  draws  it  to  the  middle  line  of  the  foot.  Taking  their  fixed  point  from  the 
foot,  these  muscles  serve  to  maintain  the  upright  posture  by  steadying  the  tibia  and  fibula 
perpendicularly  upon  the  talus. 

3.  The  Lateral  Crural  Muscles  (Fig.  439). 

Peronseus  longus.  Peronseus  brevis. 

The  Peronseus  longus  is  situated  at  the  upper  part  of  the  lateral  side  of  the 
leg,  and  is  the  more  superficial  of  the  two  muscles.  It  arises  from  the  head  and 
upper  two-thirds  of  the  lateral  surface  of  the  body  of  the  fibula,  from  the  deep 
surface  of  the  fascia,  and  from  the  intermuscular  septa  between  it  and  the  muscles 
on  the  front  and  back  of  the  leg;  occasionally  also  by  a  few  fibers  from  the  lateral 
condyle  of  the  tibia.  Between  its  attachments  to  the  head  and  to  the  body  of  the 
fibula  there  is  a  gap  through  which  the  common  peroneal  nerve  passes  to  the  front 
of  the  leg.  It  ends  in  a  long  tendon,  which  runs  behind  the  lateral  malleolus,  in 
a  groove  common  to  it  and  the  tendon  of  the  Peronseus  brevis,  behind  which  it 
lies;  the  groove  is  converted  into  a  canal  by  the  superior  peroneal  retinaculum,  and 
the  tendons  in  it  are  contained  in  a  common  mucous  sheath.  The  tendon  then 
extends  obliquely  forward  across  the  lateral  side  of  the  calcaneus,  below  the  troch- 
lear process,  and  the  tendon  of  the  Peronaeus  brevis,  and  under  cover  of  the  inferior 
peroneal  retinaculum.  It  crosses  the  lateral  side  of  the  cuboid,  and  then  runs  on  the 
under  surface  of  that  bone  in  a  groove  which  is  converted  into  a  canal  by  the  long 
plantar  ligament;  the  tendon  then  crosses  the  sole  of  the  foot  obliquely,  and  is 
inserted  into  the  lateral  side  of  the  base  of  the  first  metatarsal  bone  and  the  lateral 


THE  LATERAL  CRURAL  MUSCLES 


487 


side  of  the  first  cuneiform.  Occasionally  it  sends  a  slip  to  the  base  of  the  second 
metatarsal  bone.  The  tendon  changes  its  direction  at  two  points :  first,  behind  the 
lateral  malleolus;  secondly,  on  the  cuboid  bone;  in  both  of  these  situations  the  ten- 
don is  thickened,  and,  in  the -latter,  a  sesamoid  fibrocartilage  (sometimes  a  bone), 
is  usually  developed  in  its  substance. 


Tibialis  anterior  M.- 


Interosseous 
membram  '■ 


Tibia 


Extensores  longi  digi- 
toTum  et  hallucis  Mm. 


Flexor  digitorum 
/  longus  M. 


Deep  peroneal  nen 
and  anterior  tihi' 
artery  and  vein 

Peroncei  longzis 
and  brevis  Mm 


Superficial  peroneal •- '  \ 

nerve         V' 

Fibula'' 


Peroneal  artcri 
and  vein 


Great  saphenous  vein 
and  saphenous  nerve 


^Posterior  tibial  vein 
and  artery 


-Tibial  nerve 


Soleus  M. 


Tendo  m.  plantaris 


Gastrocnemius  M. 


Gastrocnemius  M/ 


^Median  cutaneous 

nerve 


isinuil  saphenous  vein 
Fig.  440. — Cross-section  through  middle  of  leg.     (Eycleshymer  and  Schoemaker.) 


Lateral  cuiuncuu^ 
nerve 


The  Peronaeus  brevis  lies  under  cover  of  the  Peronseus  longus,  and  is  a  shorter 
and  smaller  muscle.  It  arises  from  the  lower  two-thirds  of  the  lateral  surface  of 
the  body  of  the  fibula;  medial  to  the  Peronaeus  longus;  and  from  the  intermuscular 
septa  separating  it  from  the  adjacent  muscles  on  the  front  and  back  of  the  leg. 
The  fibers  pass  vertically  downward,  and  end  in  a  tendon  which  runs  behind  the 
lateral  malleolus  along  with  but  in  front  of  that  of  the  preceding  muscle,  the  two 
tendons  being  enclosed  in  the  same  compartment,  and  lubricated  by  a  common 
mucous  sheath.  It  then  runs  forward  on  the  lateral  side  of  the  calcaneus,  above 
the  trochlear  process  and  the  tendon  of  the  Peronaius  longus,  and  is  inserted  into 
the  tuberosity  at  the  base  of  the  fifth  metatarsal  bone,  on  its  lateral  side. 

On  the  lateral  surface  of  the  calcaneus  the  tendons  of  the  Peronsei  longus  and 
brevis  occupy  separate  osseoaponeurotic  canals  formed  by  the  calcaneus  and  the 
perineal  retinacula;  each  tendon  is  enveloped  by  a  forward  prolongation  of  the 
common  mucous  sheath. 

Variations. — Fusion  of  the  two  peronsei  is  rare.  A  slip  from  the  Peronaeus  longus  to  the  base 
of  the  third,  fourth  or  fifth  metatarsal  bone,  or  to  the  Adductor  hallucis  is  occasionally  seen. 

Peronaeus  accessarius,  origin  from  the  fibula  between  the  longus  and  brevis,  joins  the  tendon 
of  the  longus  in  the  sole  of  the  foot. 

PeroncBus  quinti  digiti,  rare,  origin  lower  fourth  of  the  fibula  imder  the  brevis,  insertion  into  the 
Extensor  aponeurosis  of  the  little  toe.  More  common  as  a  slip  of  the  tendon  of  the  Perona;us 
brevis. 

Peronaeus  quartus,  13  per  cent.  (Gniber),  origin  back  of  fibula  between  the  brevis  and  the  Flexor 
hallucis,  insertion  into  the  peroneal  spine  of  the  calcaneum,  {peroneocalcaneus  externum),  or  less 
frequently  into  the  tuberosity  of  the  cuboid  (peroneocuboideus). 

Nerves. — The  Peronaei  longus  and  brevis  are  supplied  by  the  fourth  and  fifth  lumbar  and 
first  sacral  nerves  through  the  superficial  peroneal  nerve. 


488 


MYOLOGY 


Actions. — The  Peronacf  longus  and  brevis  extend  the  foot  upon  fhe  leg,  in  conjuncfion  with 
the  Tibialis  posterior,  antagonizing  the  Tibiahs  anterior  and  Peronajus  tertius,  which  are  flexors 
of  the  foot.  The  Peronajus  longus  also  everts  the  sole  of  the  foot,  and  from  the  obhque  direction 
of  the  tendon  across  the  sole  of  the  foot  is  an  important  agent  in  the  maintenance  of  the  trans- 
verse arch.  Taking  their  fixed  points  below,  the  Perona^i  serve  to  steady  the  leg  upon  the  foot. 
This  is  especially  the  case  in  standing  upon  one  leg,  when  the  tendency  of  the  superincumbent 
weight  is  to  throw  the  leg  medialward ;  the  Peronajus  longus  overcomes  this  tendency  by  drawing 
on  the  lateral  side  of  the  leg. 


THE    FASCIA   AROUND    THE    ANKLE. 


Fibrous  bands,  or  thickened  portions  of  the  fascia,  bind  down  the  tendons 
front  of  and  behind  the  ankle  in  their  passage  to  the  foot.  They  comprise  three 
ligaments,  viz.,  the  transverse  crural,  the  cruciate  crural  and  the  laciniate;  and  the 
superior  and  inferior  peroneal  retinacula. 


IS  m^^ 


Tibialis  anterior 

/      Extensor  dig.  longus 


Ext.  hall.  long. 

Ext.  dig.  brevis 


Tendo  calcaneus 

Peronaua  longus 


PerontBus  brevis  Peronoetia  tertius 

Fia.  441. — The  mucous  sheaths  of  the  tendons  around  the  ankle. 


Lateral  aspect. 


Transverse  Crural  Ligament  (ligamentum  transversum  cruris;  upper  part  of  anterior 
annular  ligament)  (Fig.  441). — The  transverse  crural  ligament  binds  down  the 
tendons  of  Extensor  digitorum  longus,  Extensor  hallucis  longus,  Peronseus  tertius, 
and  Tibialis  anterior  as  they  descend  on  the  front  of  the  tibia  and  fibula;  under 
it  are  found  also  the  anterior  tibial  vessels  and  deep  peroneal  nerve.  It  is  attached 
laterally  to  the  lower  end  of  the  fibula,  and  medially  to  the  tibia;  above  it  is  con- 
tinuous with  the  fascia  of  the  leg. 

Cruciate  Crural  Ligament  (ligamentum  cruciatum  cruris;  lower  part  of  anterior 
annular  ligament)  (Figs.  441,  442). — The  cruciate  crural  ligament  is  a  Y-shaped 
band  placed  in  front  of  the  ankle-joint,  the  stem  of  the  Y  being  attached  laterally 
to  the  upper  surface  of  the  calcaneus,  in  front  of  the  depression  for  the  interosseous 
talocalcanean  ligament;  it  is  directed  medialward  as  a  double  layer,  one  lamina 
passing  in  front  of,  and  the  other  behind,  the  tendons  of  the  Peronseus  tertius 
and  Extensor  digitorum  longus.  At  the  medial  border  of  the  latter  tendon  these 
two  layers  join  together,  forming  a  compartment  in  which  the  tendons  are 
enclosed.  From  the  medial  extremity  of  this  sheath  the  two  limbs  of  the  Y  diverge : 
one  is  directed  upward  and  medialward,  to  be  attached  to  the  tibial  malleolus, 
passing  over  the  Extensor  hallucis  longus  and  the  vessels  and  nerves,  but  enclosing 


THE  FASCIA  AROUND  THE  ANKLE 


^■the  Tibialis  anterior  by  a  splitting  of  its  jSbers.    The  other  limb  extends  downward 
^*and  medialward,  to  be  attached  to  the  border  of  the  plantar  aponeurosis,  and  passes 

over  the  tendons  of  the  Extensor  hallucis  longus  and  Tibialis  anterior  and  also 

the  vessels  and  nerves. 
^^     Laciniate  Ligament  (ligamentum  laciniatum;   internal  annular  ligament). — The 
^■Jaciniate  ligament  is  a  strong  fibrous  band,  extending  from  the  tibial  malleolus 
^^  above  to  the  margin  of  the  calcaneus  below,  converting  a  series  of  bony  grooves 

in  this  situation  into  canals  for  the  passage  of  the  tendons  of  the  Flexor  muscles 

and  the  posterior  tibial  vessels  and  tibial  nerve  into  the  sole  of  the  foot.    It  is 

■  continuous  by  its  upper  border  with  the  deep  fascia  of  the  leg,  and  by  its  lower 
|)order  with  the  plantar  aponeurosis  and  the  fibers  of  origin  of  the  Abductor 
hallucis  muscle.  Enumerated  from  the  medial  side,  the  four  canals  which  it  forms 
transmit  the  tendon  of  the  Tibialis  posterior;  the  tendon  of  the  Flexor  digitorum 
longus;  the  posterior  tibial  vessels  and  tibial  nerve,  which  run  through  a  broad 
space  beneath  the  ligament;  and  lastly,  in  a  canal  formed  partly  by  the  talus,  the 
tendon  of  the  Flexor  hallucis  longus. 


The  mucous  sheaths  of  the  tendons  around  the  ankle. 


Bursa 

Tendocalcaneus 
Medial  aspect. 


1 

a 


Peroneal  Retinacula. —  The  peroneal  retinacula  are  fibrous  bands  which  bind 
down  the  tendons  of  the  Peronsei  longus  and  brevis  as  they  run  across  the  lateral 
side  of  the  ankle.  The  fibers  of  the  superior  retinaculum  {external  annular  ligament) 
are  attached  above  to  the  lateral  malleolus  and  below  to  the  lateral  surface  of  the 
calcaneus.  The  fibers  of  the  inferior  retinaculum  are  continuous  in  front  with  those 
of  the  cruciate  crural  ligament;  behind  they  are  attached  to  the  lateral  surface  of 
the  calcaneus;  some  of  the  fibers  are  fixed  to  the  peroneal  trochlea,  forming  a  septum 
between  the  tendons  of  the  Peronsei  longus  and  brevis. 

The  Mucous  Sheaths  of  the  Tendons  Aroimd  the  Ankle. — All  the  tendons  crossing 
the  ankle-joint  are  enclosed  for  part  of  their  length  in  mucous  sheaths  which  have 
an  almost  uniform  length  of  about  8  cm.  each.  On  the  front  of  the  ankle  (Fig.  441) 
;he  sheath  for  the  Tibialis  anterior  extends  from  the  upper  margin  of  the  trans- 
verse crural  ligament  to  the  interval  between  the  diverging  limbs  of  the  cruciate 
ligament;  those  for  the  Extensor  digitorum  longus  and  Extensor  hallucis  longus 
reach  upward  to  just  above  the  level  of  the  tips  of  the  malleoli,  the  former  being 
the  higher.  The  sheath  of  the  Extensor  hallucis  longus  is  prolonged  on  to  the  base 
of  the  first  metatarsal  bone,  while  that  of  the  Extensor  digitorum  longus  reaches 


490  ^^^^^^^-         MYOLOGY 


only  to  the  level  of  the  base  of  the  fifth  metatarsal.  On  the  medial  side  of  the  ankle 
(Fig.  442)  the  sheath  for  the  Tibialis  posterior  extends  highest  up — to  about 
4  cm.  above  the  tip  of  the  malleolus — while  below  it  stops  just  short  of  the  tuber- 
osity of  the  navicular.  The  sheath  for  Flexor  hallucis  longus  reaches  up  to  the  level 
of  the  tip  of  the  malleolus,  while  that  for  the  Flexor  digitorum  longus  is  slightly 
higher;  the  former  is  continued  to  the  base  of  the  first  metatarsal,  but  the  latter 
stops  opposite  the  first  cuneiform  bone. 

On  the  lateral  side  of  the  ankle  (Fig.  441)  a  sheath  which  is  single  for  the  greater 
part  of  its  extent  encloses  the  Peronsei  longus  and  brevis.  It  extends  upward 
for  about  4  cm,  above  the  tip  of  the  malleolus  and  downward  and  forward  for 
about  the  same  distance. 


•^ 


IV.    THE   MUSCLES    AND    FASCLffi   OF   THE   FOOT. 

1.  The  Dorsal  Muscle  of  the  Foot. 

Extensor  digitorum  brevis. 

The  fascia  on  the  dorsum  of  the  foot  is  a  thin  membranous  layer,  continuous 
above  with  the  transverse  and  cruciate  crural  ligaments;  on  either  side  it  blends 
with  the  plantar  aponeurosis;  anteriorly  it  forms  a  sheath  for  the  tendons  on  the 
dorsum  of  the  foot. 

The  Extensor  digitorum  brevis  (Fig.  441)  is  a  broad,  thin  muscle,  which  arises 
from  the  forepart  of  the  upper  and  lateral  surfaces  of  the  calcaneus,  in  front  of 
the  groove  for  the  Peronseus  brevis;  from  the  lateral  talocalcanean  ligament; 
and  from  the  common  limb  of  the  cruciate  crural  ligament.  It  passes  obliquely 
across  the  dorsum  of  the  foot,  and  ends  in  four  tendons.  The  most  medial,  which 
is  the  largest,  is  inserted  into  the  dorsal  surface  of  the  base  of  the  first  phalanx  of 
the  great  toe,  crossing  the  dorsalis  pedis  artery;  it  is  frequently  described  as  a 
separate  muscle — the  Extensor  hallucis  brevis.  The  other  three  are  inserted  into 
the  lateral  sides  of  the  tendons  of  the  Extensor  digitorum  longus  of  the  second, 
third,  and  fourth  toes. 

Variations. — ^Accessory  slips  of  origin  from  the  talus  and  navicular,  or  from  the  external  cunei- 
form and  third  metatarsal  bones  to  the  second  slip  of  the  muscle,  and  one  from  the  cuboid  to  the 
third  slip  have  been  observed.  The  tendons  vary  in  number  and  position;  they  may  be  reduced 
to  two,  or  one  of  them  may  be  doubled,  or  an  additional  slip  may  pass  to  the  little  toe.  A  super- 
numerary slip  ending  on  one  of  the  metatarsophalangeal  articulations,  or  joining  a  dorsal  inter- 
osseous muscle  is  not  uncommon.    Deep  slips  between  this  muscle  and  the  Dorsal  interossei  occur. 

Nerves. — It  is  suppUed  by  the  deep  peroneal  nerve. 

Actions. — The  Extensor  digitorum  brevis  extends  the  phalanges  of  the  four  toes  into  which 
it  is  inserted,  but  in  the  great  toe  acts  only  on  the  first  phalanx.  The  obhquity  of  its  direction 
counteracts  the  obUque  movement  given  to  the  toes  by  the  long  Extensor,  so  that  when  both 
muscles  act,  the  toes  are  evenly  extended. 

2.  The  Plantar  Muscles  of  the  Foot. 

Plantar  Aponeurosis  {aponeurosis  plantaris;  plantar  fascia). — The  plantar  apo- 
neurosis is  of  great  strength,  and  consists  of  pearly  white  glistening  fibers,  disposed, 
for  the  most  part,  longitudinally:  it  is  divided  into  central,  lateral,  and  medial 
portions. 

The  central  portion,  the  thickest,  is  narrow  behind  and  attached  to  the  medial 
process  of  the  tuberosity  of  the  calcaneus,  posterior  to  the  origin  of  the  Flexor 
digitorum  brevis;  and  becoming  broader  and  thinner  in  front,  divides  near  the 
heads  of  the  metatarsal  bones  into  five  processes,  one  for  each  of  the  toes.  Each 
of  these  processes  divides  opposite  the  metatarsophalangeal  articulation  into  two 
strata,  superficial  and  deep.    The  superficial  stratum  is  inserted  into  the  skin  of 


THE  PLANTAR  MUSCLES  OF  THE  FOOT 


491 


the  transverse  sulcus  which  separates  the  toes  from  the  sole.  The  deeper  stratum 
divides  into  two  slips  which  embrace  the  side  of  the  Flexor  tendons  of  the  toes, 
and  blend  with  the  sheaths  of  the  tendons,  and  with  the  transverse  metatarsal 
ligament,  thus  forming  a  series  of  arches  through  which  the  tendons  of  the  short 
and  long  Flexors  pass  to  the  toes.  The  intervals  left  between  the  five  processes 
allow  the  digital  vessels  and  nerves  and  the  tendons  of  the  Lumbricales  to  become 
superficial.  At  the  point  of  division  of  the  aponeurosis,  numerous  transverse 
fasciculi  are  superadded ;  these  serve  to  increase  the  strength  of  the  aponeurosis 
at  this  part  by  binding  the  processes  together,  and  connecting  them  with  the  integu- 
ment. The  central  portion  of  the  plantar  aponeurosis  is  continuous  with  the  lateral 
and  medial  portions  and  sends  upward  into  the  foot,  at  the  lines  of  junction,  two 
strong  vertical  intermuscular  septa,  broader  in  front  than  behind,  which  separate 
the  intermediate  from  the  lateral  and  medial  plantar  groups  of  muscles;  from  these 
again  are  derived  thinner  transverse  septa  which  separate  the  various  layers  of 
muscles  in  this  region.  The  upper  surface  of  this  aponeurosis  gives  origin  behind 
to  the  Flexor  digitorum  brevis. 

The  lateral  and  medial  portions  of  the  plantar  aponeurosis  are  thinner  than 
the  central  piece,  and  cover  the  sides  of  the  sole  of  the  foot. 

The  lateral  portion  covers  the  under  surface  of  the  Abductor  digiti  quinti;  it  is 
thin  in  front  and  thick  behind,  where  it  forms  a  strong  band  between  the  lateral 
process  of  the  tuberosity  of  the  calcaneus  and  the  base  of  the  fifth  metatarsal  bone; 
it  is  continuous  medially  with  the  central  portion  of  the  plantar  aponeurosis,  and 
laterally  with  the  dorsal  fascia. 

The  medial  portion  is  thin,  and  covers  the  under  surface  of  the  Abductor  hallucis; 
it  is  attached  behind  to  the  laciniate  ligament,  and  is  continuous  around  the  side 
of  the  foot  with  the  dorsal  fascia,  and  laterally  with  the  central  portion  of  the  plantar 
aponeurosis. 

The  muscles  in  the  plantar  region  of  the  foot  may  be  divided  into  three  groups, 
in  a  similar  manner  to  those  in  the  hand.  Those  of  the  medial  plantar  region 
are  connected  with  the  great  toe,  and  corrrespond  with  those  of  the  thumb;  those 
of  the  lateral  plantar  region  are  connected  with  the  little  toe,  and  correspond  with 
those  of  the  little  finger;  and  those  of  the  intermediate  plantar  region  are  connected 
with  the  tendons  intervening  between  the  two  former  groups.  But  in  order  to 
facilitate  the  description  of  these  muscles,  it  is  more  convenient  to  divide  them  into 
four  layers,  in  the  order  in  which  they  are  successively  exposed. 


Abductor  hallucis. 


The  First  Layer  (Fig.  443). 

Flexor  digitorum  brevis. 
Abductor  digiti  quinti. 


[■  The  Abductor  hallucis  lies  along  the  medial  border  of  the  foot  and  covers  the 
origins  of  the  plantar  vessels  and  nerves.  It  arises  from  the  medial  process  of  the 
tuberosity  of  the  calcaneus,  from  the  laciniate  ligament,  from  the  plantar  aponeu- 
rosis, and  from  the  intermuscular  septum  between  it  and  the  Flexor  digitorum 
brevis.  The  fibers  end  in  a  tendon,  which  is  inserted,  together  with  the  medial 
tendon  of  the  Flexor  hallucis  brevis,  into  the  tibial  side  of  the  base  of  the  first 
phalanx  of  the  great  toe. 

Variations. — Slip  to  the  base  of  the  first  phalanx  of  the  second  toe. 

The  Flexor  digitorum  brevis  lies  in  the  middle  of  the  sole  of  the  foot,  imme- 
diately above  the  central  part  of  the  plantar  aponeurosis,  with  which  it  is  firmly 
united.    Its  deep  surface  is  separated  from  the  lateral  plantar  vessels  and  nerves 


492 


MYOLOGY 


by  a  thin  layer  of  fascia.  It  arises  by  a  narrow  tendon,  from  the  medial  process 
of  the  tuberosity  of  the  calcaneus,  from  the  central  part  of  the  plantar  aponeurosis, 
and  from  the  intermuscular  septa  between  it  and  the  adjacent  muscles.  It  passes 
forward,  and  divides  into  four  tendons,  one  for  each  of  the  four  lesser  toes.  Oppo- 
site the  bases  of  the  first  phalanges,  each  tendon  divides  into  two  slips,  to  allow  of 
the  passage  of  the  corresponding  tendon  of  the  Flexor  digitorum  longus;  the  two 
portions  of  the  tendon  then  unite  and  form  a  grooved  channel  for  the  reception 
of  the  accompanying  long  Flexor  tendon.    Finally,  it  divides  a  second  time,  and 

is  inserted  into  the  sides  of  the  second  phalanx 
about  its  middle.     The  mode  of  division  of  the 
7UUWIM  tendons  of  the  Flexor  digitorum  brevis,  and  of 

their  insertion  into  the  phalanges,  is  analogous 
to  that  of  the  tendons  of  the  Flexor  digitorum 
sublimis  in  the  hand. 

Variations. — Slip  to  the  little  toe  frequently  wanting, 
23  per  cent.;  or  it  may  be  replaced  by  a  small  fusiform 
muscle  arising  from  the  long  flexor  tendon  or  from  the 
Quadratus  plantse. 

Fibrous  Sheaths  of  the  Flexor  Tendons. — The 

terminal  portions  of  the  tendons  of  the  long 
and  short  Flexor  muscles  are  contained  in 
osseoaponeurotic  canals  similar  in  their  ar- 
rangement to  those  in  .the  fingers.  These 
canals  are  formed  above  by  the  phalanges 
and  below  by  fibrous  bands,  which  arch  across 
the  tendons,  and  are  attached  on  either  side 
to  the  margins  of  the  phalanges.  Opposite 
the  bodies  of  the  proximal  and  second  pha- 
langes the  fibrous  bands  are  strong,  and  the 
fibers  are  transverse;  but  opposite  the  joints 
they  are  much  thinner,  and  the  fibers  are 
directed  obliquely.  Each  canal  contains  a 
mucous  sheath,  which  is  reflected  on  the  con- 
tained tendons. 

The  Abductor  digiti  quinti  {Abductor  minimi 
digiti)  lies  along  the  lateral  border  of  the  foot, 
and  is  in  relation  by  its  medial  margin  with 
the  lateral  plantar  vessels  and  nerves.  It  arises, 
by  a  broad  origin,  from  the  lateral  process  of 
the  tuberosity  of  the  calcaneus,  from  the  under 
surface  of  the  calcaneus  between  the  two  pro- 
cesses of  the  tuberosity,  from  the  forepart  of 
the  medial  process,  from  the  plantar  aponeu- 
rosis, and  from  the  intermuscular  septum 
between  it  and  the  Flexor  digitorum  brevis.  Its 
tendon,  after  gliding  over  a  smooth  facet  on  the 
under  surface  of  the  base  of  the  fifth  metatarsal  bone,  is  inserted,  with  the 
Flexor  digiti  quinti  brevis,  into  the  fibular  side  of  the  base  of  the  first  phalanx 
of  the  fifth  toe. 

Variations. — Slips  of  origin  from  the  tuberosity  at  the  base  of  the  fifth  metatarsal  Abdvctor 
osm  metatarsi  quinti,  origin  external  tubercle  of  the  calcaneus,  insertion  into  tuberosity  of  the 
fifth  metatarsalbone  in  common  with  or  beneath  the  outer  margin  of  the  plantar  fascia. 


I 


Fig.  443. — Muscles  of  the  sole  of  the  foot. 
First  layer. 


I 


THE  PLANTAR  MUSCLES  OF  THE  FOOT  493 

The  Second  Layer  (Fig.  444). 

Quadratus  plantae.  Lumbricales. 

The  Quadratus  plantse  (Flexor  accessoriiis)  is  separated  from  the  muscles  of 
the  first  layer  by  the  lateral  plantar  vessels  and  nerve.  It  arises  by  two  heads, 
which  are  separated  from  each  other  by  the  long  plantar  ligament:  the  medial 
or  larger  head  is  muscular,  and  is  attached  to  the  medial  concave  surface  of  the 
calcaneus,  below  the  groove  which  lodges  the  tendon  of  the  Flexor  hallucis  longus; 
the  lateral  head,  flat  and  tendinous,  arises  from  the  lateral  border  of  the  inferior 
surface  of  the  calcaneus,  in  front  of  the  lateral  process  of  its  tuberosity,  and  from 
the  long  plantar  ligament.  The  two  portions  join  at  an  acute  angle,  and  end  in  a 
flattened  band  which  is  inserted  into  the  lateral  margin  and  upper  and  under  sur- 

t  faces  of  the  tendon  of  the  Flexor  digitorum  longus,  forming  a  kind  of  groove,  in 
which  the  tendon  is  lodged.  It  usually  sends  slips  to  those  tendons  of  the  Flexor 
digitorum  longus  which  pass  to  the  second,  third,  and  fourth  toes. 

Variations. — Lateral  head  often  wanting;  entire  muscle  absent.  Variation  in  the  number  of 
digital  tendons  to  which  fibers  can  be  traced.  Most  frequent  offsets  are  sent  to  the  second,  third 
and  fourth  toes;  in  many  cases  to  the  fifth  as  well;  occasionally  to  two  toes  only. 

The  Lumbricales  are  four  small  muscles,  accessory  to  the  tendons  of  the  Flexor 
digitorum  longus  and  numbered  from  the  medial  side  of  the  foot;  they  arise  from 
these  tendons,  as  far  back  as  their  angles  of  division,  each  springing  from  two 
tendons,  except  the  first.  The  muscles  end  in  tendons,  which  pass  forward  on 
the  medial  sides  of  the  four  lesser  toes,  and  are  inserted  into  the  expansions  of 
the  tendons  of  the  Extensor  digitorum  longus  on  the  dorsal  surfaces  of  the  first 
phalanges. 

Variations. — Absence  of  one  or  more;  doubling  of  the  third  or  fourth.  Insertion  partly  or  wholly 
into  the  first  phalanges. 

The  Third  Layer  (Fig.  445). 

r  Flexor  hallucis  brevis.  Adductor  hallucis. 

Flexor  digiti  quinti  brevis. 

The  Flexor  hallucis  brevis  arises,  by  a  pointed  tendinous  process,  from  the  medial 
part  of  the  under  surface  of  the  cuboid  bone,  from  the  contiguous  portion  of  the 
third  cuneiform,  and  from  the  prolongation  of  the  tendon  of  the  Tibialis  posterior 
which  is  attached  to  that  bone.  It  divides  in  front  into  two  portions,  which  are 
inserted  into  the  medial  and  lateral  sides  of  the  base  of  the  first  phalanx  of  the 
great  toe,  a  sesamoid  bone  being  present  in  each  tendon  at  its  insertion.  The  medial 
portion  is  blended  with  the  Abductor  hallucis  previous  to  its  insertion;  the  lateral 
portion  with  the  Adductor  hallucis;  the  tendon  of  the  Flexor  hallucis  longus  lies 
in  a  groove  between  them;  the  lateral  portion  is  sometimes  described  as  the  first 
Interosseous  plantaris. 

Variations. — Origin  subject  to  considerable  variation;  it  often  receives  fibers  from  the  calcaneus 
lor  long  plantar  ligament.  Attachment  to  the  cuboid  sometimes  wanting.  Slip  to  first  phalanx 
I  of  the  second  toe. 

The  Adductor  hallucis  {Adductor  ohliquus  hallucis)  arises  by  two  heads — oblique 
and  transverse.  The  oblique  head  is  a  large,  thick,  fleshy  mass,  crossing  the  foot 
obliquely  and  occupying  the  hollow  space  under  the  first,  second,  third,  and  fourth 
metatarsal  bones.  It  arises  from  the  bases  of  the  second,  third,  and  fourth  meta- 
tarsal bones,  and  from  the  sheath  of  the  tendon  of  the  Peronseus  longus,  and  is 
inserted,  together  with  the  lateral  portion  of  the  Flexor  hallucis  brevis,  into  the 
lateral  side  of  the  base  of  the  first  phalanx  of  the  great  toe.  The  transverse  head 
( Transversus  pedis)  is  a  narrow,  flat  fasciculus  which  arises  from  the  plantar  meta- 


494 


MYOLOGY 


tarsophalangeal  ligaments  of  the  third,  fourth,  and  fifth  toes  (sometimes^fy 
from  the  third  and  fourth),  and  from  the  transverse  ligament  of  the  metatarsus. 
It  is  inserted  into  the  lateral  side  of  the  base  of  the  first  phalanx  of  the  great  toe, 
its  fibers  blending  with  the  tendon  of  insertion  of  the  oblique  head. 


I 


Fig.  444.— Muscles  of  the  sole  of  the  foot. 
Second  layer. 


Fia.  445. — Muscles  of  the  sole  of  the  foot. 
Third  layer. 


Opponens  hallucis,  occasional 


Variations. — Slips  to  the  base  of  the  first  phalanx  of  the  second  toe. 
slips  from  the  adductor  to  the  metatarsal  bone  of  the  great  toe. 

The  Abductor,  Flexor  brevis,  and  Adductor  of  the  great  toe,  like  the  similar 
muscles  of  the  thumb,  give  off,  at  their  insertions,  fibrous  expansions  to  blend 
with  the  tendons  of  the  Extensor  digitorum  longus. 

The  Flexor  digiti  quinti  brevis  (Flexor  brevis  minimi  digiti)  lies  under  the 
metatarsal  bone  of  the  little  toe,  and  resembles  one  of  the  Interossei.  It  arises 
from  the  base  of  the  fifth  metatarsal  bone,  and  from  the  sheath  of  the  Peronseus 
longus;  its  tendon  is  inserted  into  the  lateral  side  of  the  base  of  the  first  phalanx 
of  the  fifth  toe.  Occasionally  a  few  of  the  deeper  fibers  are  inserted  into  the 
lateral  part  of  the  distal  half  of  the  fifth  metatarsal  bone;  these  are  described  by 
some  as  a  distinct  muscle,  the  Opponens  digiti  quinti. 


THE  PLANTAR  MUSCLES  OF  THE  FOOT 


495 


The  Fourth  Layer. 
Interossei. 

The  titerossei  in  the  foot  are  similar  to  those  in  the  hand,  with  this  exception, 
that  they  are  grouped  around  the  middle  line  of  the  second  digit,  instead  of  that 
of  the  third.  They  are  seven  in  number,  and  consist  of  two  groups,  dorsal  and 
plantar. 

The  Interossei  dorsales  (Dorsal  interossei)  (Fig.  446), /owr  in  number,  are  situated 
between  the  metatarsal  bones.  They  are  bipenniform  muscles,  each  arising  by 
two  heads  from  the  adjacent  sides  of  the  metatarsal  bones  between  which  it  is 
placed ;  their  tendons  are  inserted  into  the  bases  of  the  first  phalanges,  and  into  the 
aponeurosis  of  the  tendons  of  the  Extensor  digitorum  longus.  In  the  angular 
interval  left  between  the  heads  of  each  of  the  three  lateral  muscles,  one  of  the 
perforating  arteries  passes  to  the  dorsum  of  the  foot;  through  the  space  between 
the  heads  of  the  first  muscle  the  deep  plantar  branch  of  the  dorsalis  pedis  artery 
enters  the  sole  of  the  foot.  The  first  is  inserted  into  the  medial  side  of  the  second 
toe;  the  other  three  are  inserted  into  the  lateral  sides  of  the  second,  third,  and 
fourth  toes. 


Fig.  446. — The  Interossei  dorsales.     Left  foot. 


Fio.  447. — -The  Interossei  plantares.     Left  foot. 


The  Interossei  plantares  {Plantar  interossei)  (Fig.  447),  three  in  nimiber,  lie 
beneath  rather  than  between  the  metatarsal  bones,  and  each  is  connected  with 
but  one  metatarsal  bone.  They  arise  from  the  bases  and  medial  sides  of  the  bodies 
of  the  third,  fourth,  and  fifth  metatarsal  bones,  and  are  inserted  into  the  medial 
sides  of  the  bases  of  the  first  phalanges  of  the  same  toes,  and  into  the  aponeuroses 
of  the  tendons  of  the  Extensor  digitorum  longus. 

Nerves. — The  Flexor  digitorum  brevis,  the  Flexor  hallucis  brevis,  the  Abductor  hallucis, 
and  the  first  Lumbricalis  are  supphed  by  the  medial  plantar  nerve;  all  the  other  muscles  in  the 
sole  of  the  foot  by  the  lateral  plantar.  The  first  Interosseous  dorsahs  frequently  receives  an 
extra  filament  from  the  medial  branch  of  the  deep  peroneal  nerve  on  the  dorsum  of  the  foot, 
and  the  second  Interosseous  dorsahs  a  twig  from  the  lateral  branch  of  the  same  nerve. 

Actions. — AU  the  muscles  of  the"  foot  act  upon  the  toes,  and  may  be  grouped  as  abductors, 
adductors,  flexors,  or  extensors.    The  abductors  are  the  Interossei  dorsales,  the  Abductor  hallucis, 


496  ^^^MSmSm  MYOLOGY 


■ 


and  the  Abductor  digiti  quinti.  The  Interossei  dorsales  are  abductors  from  an  imaginary  line 
passing  through  the  axis  of  the  second  toe,  so  that  the  first  muscle  draws  the  second  toe  medijil- 
ward,  toward  the  great  toe,  the  second  muscle  draws  the  same  toe  lateralward,  and  the  third 
and  fourth  draw  the  third  and  fourth  toes  in  the  same  direction.  Like  the  Interossei  in  the  hand, 
each  assists  in  flexing  the  first  phalanx  and  extending  the  second  and  third  phalanges.  Tlie 
Abductor  hallucis  abducts  the  great  toe  from  the  second,  and  also  flexes  its  proximal  phalanx. 
In  the  same  way  the  action  of  the  Abductor  digiti  quinti  is  twofold,  as  an  abductor  of  this  toe 
from  the  fourth,  and  also  as  a  flexor  of  its  proximal  phalanx.  The  adductors  are  the  Interossei 
plantares  and  the  Adductor  hallucis.  The  Interossei  plantares  adduct  the  third,  fourth,  and 
fifth  toes  toward  the  imaginary  Une  passing  through  the  second  toe,  and  by  means  of  their  inser- 
tions into  the  aponeuroses  of  the  Extensor  tendons  they  assist  in  flexing  the  proximal  phalanges 
and  extending  the  middle  and  terminal  phalanges.  The  oblique  head  of  the  Adductor  hallucis 
is  chiefly  concerned  in  adducting  the  great  toe  toward  the  second  one,  but  also  assists  in  flexing 
this  toe;  the  transverse  head  approximates  all  the  toes  and  thus  increases  the  curve  of  the  trans- 
verse arch  of  the  metatarsus.  The  ^xors  are  the  Flexor  digitorum  brevis,  the  Quadrat  us  planta?, 
the  Flexor  hallucis  brevis,  the  Flexor  digiti  quinti  brevis,  and  the  Lumbricales.  The  Flexor 
digitorum  brevis  flexes  the  second  phalanges  upon  the  first,  and,  continuing  its  action,  flexes  the 
first  phalanges  also,  and  brings  the  toes  together.  The  Quadratus  plants)  assists  the  Flexor  digi- 
torum longus  and  converts  the  obhque  puU  of  the  tendons  of  that  muscle  into  a  direct  backward 
puU  upon  the  toes.  The  Flexor  digiti  quinti  brevis  flexes  the  Uttle  toe  and  draws  its  metatarsal 
bone  downward  and  medialward.  The  Lumbricales,  like  the  corresponding  muscles  in  the  hand, 
assist  in  flexing  the  proximal  phalanges,  and  by  their  insertions  into  the  tendons  of  the  Extensor 
digitorum  longus  aid  that  muscle  in  straightening  the  middle  and  terminal  phalanges.  The 
Extensor  digitorum  brevis  extends  the  first  phalanx  of  the  great  toe  and  assists  the  long  Extensor 
in  extending  the  next  three  toes,  and  at  the  same  time  gives  to  the  toes  a  lateral  direction  when 
they  are  extended. 

BIBLIOGRAPHY. 

Bardeen,  C.  R.:  Development  and  Variation,  etc.,  of  the  Inferior  Extremity,  etc..  Am.  Jour. 
Anat.,  1907,  vi. 

Bardeen  and  Lewis:  Development  of  the  Back,  Body  Wall  and  Limbs  in  Man,  Am.  Jour. 
Anat.,  1901,  i. 

EiSLER,  P.:  Die  Muskeln  des  Stammes,  v.  Bardeleben's  Handbuch  der  Anatomic  des  MenscKen, 
Bd.  ii,  Abt.  ii,  Teil  1. 

FiCK,  R.:  Anatomie  und  Mechanik  der  Gelenke  unter  Benicksichtigimg  der  bewegenden 
Muskeln,  v.  Bardeleben's  Handbuch  der  Anatomie  des  Menschen,  Bd.  ii,  Abt.  i,  Teil  2  and  3. 

Frohse  and  Frankel:  Die  Muskeln  des  Menschlichen  Beines;  Die  Muskeln  des  Menschlichen 
Armes,  Handbuch  der  Anatomie  des  Menschen,  von  Bardeleben,  Bd.  ii,  Abt.  ii,  Teil  2,  A  and  B. 

Henle,  J.:    Handbuch  der  Systematischen  Anatomie  des  Menschen,  1871-79. 

Koch,  J.  C:    The  Laws  of  Bone  Architecture,  Am.  Jour.  Anat.,  1917,  xxi. 

Le  Double:    Traits  des  Variations  du  Systeme  Musculaire  de  L'Homme,  1897. 

Lewis,  W.  H.:    Development  of  the  Arm  in  Man,  Am.  Jour.  Anat.,  1901,  i. 

Lewis,  W.  H.:  Development  of  the  Muscular  System,  Keibel  and  Mall,  Manual  of  Human 
Embryology. 

PoiRiER,  P.,  et  Charpy,  a.:    Traits  d' Anatomie,  1899-1901. 

TbsTUT,  L. :    Traite  d' Anatomie  Humaine.  1893-94. 

Wolff,  J. :     Das  Gesetz  der  Transformation  der  Knochen,  Berlin,  1892. 


ANGIOLOGY. 


''PHE  vascular  system  is  divided  for  descriptive  purposes  into  (a)  the  blood 
J-  vascular  system,  which  comprises  the  heart  and  bloodvessels  for  the  circula- 
tion of  the  blood;  and  (6)  the  Ijrmph  vascular  system,  consisting  of  lymph  glands 
and  lymphatic  vessels,  through  which  a  colorless  fluid,  the  lymph,  circulates.  It 
must  be  noted,  however,  that  the  two  systems  communicate  with  each  other  and 

|9,re  intimately  associated  developmentally. 
t  The  heart  is  the  central  organ  of  the  blood  vascular  system,  and  consists  of  a 
hollow  muscle;  by  its  contraction  the  blood  is  pumped  to  all  parts  of  the  body 
through  a  complicated  series  of  tubes,  termed  arteries.  The  arteries  undergo 
enormous  ramification  in  their  course  throughout  the  body,  and  end  in  minute 
vessels,  called  arterioles,  which  in  their  turn  open  into  a  close-meshed  network 
of  microscopic  vessels,  termed  capillaries.  After  the  blood  has  passed  through  the 
capillaries  it  is  collected  into  a  series  of  larger  vessels,  called  veins,  by  which  it  is 
returned  to  the  heart.  The  passage  of  the  blood  through  the  heart  and  blood- 
vessels constitutes  what  is  termed  the  circulation  of  the  blood,  of  which  the  following 
is  an  outline. 

The  human  heart  is  divided  by  septa  into  right  and  left  halves,  and  each  half 
is  further  divided  into  two  cavities,  an  upper  termed  the  atrium  and  a  lower  the 
ventricle.  The  heart  therefore  consists  of  four  chambers,  two,  the  right  atrium 
and  right  ventricle,  forming  the  right  half,  and  two,  the  left  atrium  and  left  ventricle 
the  left  half.  The  right  half  of  the  heart  contains  venous  or  impure  blood;  the  left, 
arterial  or  pure  blood.  The  atria  are  receiving  chambers,  and  the  ventricles  dis- 
tributing ones.  From  the  cavity  of  the  left  ventricle  the  pure  blood  is  carried  into 
a  large  artery,  the  aorta,  through  the  numerous  branches  of  which  it  is  distributed 
to  all  parts  of  the  body,  with  the  exception  of  the  lungs.  In  its  passage  through 
the  capillaries  of  the  body  the  blood  gives  up  to  the  tissues  the  materials  necessary 
for  their  growth  and  nourishment,  and  at  the  same  time  receives  from  the  tissues 
the  waste  products  resulting  from  their  metabolism.  In  doing  so  it  is  changed 
from  arterial  into  venous  blood,  which  is  collected  by  the  veins  and  through  them 
returned  to  the  right  atrium  of  the  heart.  From  this  cavity  the  impure  blood 
passes  into  the  right  ventricle,  and  is  thence  conveyed  through  the  pulmonary 
arteries  to  the  lungs.  In  the  capillaries  of  the  lungs  it  again  becomes  arterialized, 
and  is  then  carried  to  the  left  atrium  by  the  pulmonary  veins.  From  the  left  atrium 
it  passes  into  the  left  ventricle,  from  which  the  cycle  once  more  begins. 

The  course  of  the  blood  from  the  left  ventricle  through  the  body  generally  to 
the  right  side  of  the  heart  constitutes  the  greater  or  systemic  circulation,  while  its 
passage  from  the  right  ventricle  through  the  lungs  to  the  left  side  of  the  heart  is 
termed  the  lesser  or  pulmonary  circulation. 

It  is  necessary,  however,  to  state  that  the  blood  which  circulates  through  the 
spleen,  pancreas,  stomach,  small  intestine,  and  the  greater  part  of  the  large  intes- 
tine is  not  returned  directly  from  these  organs  to  the  heart,  but  is  conveyed  by  the 
portal  vein  to  the  liver.  In  the  liver  this  vein  divides,  like  an  artery,  and  ultimately 
ends  in  capillary-like  vessels  (sinusoids),  from  which  the  rootlets  of  a  series  of  veins, 
called  the  hepatic  veins,  arise;  these  carry  the  blood  into  the  inferior  vena  cava, 
32  (497) 


498 


ANGIOLOGY 


I 


whence  it  is  conveyed  to  the  right  atrium.  From  this  it  will  be  seen  that  the 
blood  contained  in  the  portal  vein  passes  through  two  sets  of  vessels:  (1)  the 
capillaries  in  the  spleen,  pancreas,  stomach,  etc.,  and  (2)  the  sinusoids  in  the  liver. 
The  blood  in  the  portal  vein  carries  certain  of  the  products  of  digestion :  the  carbo- 
hydrates, which  are  mostly  taken  up  by  the  liver  cells  and  stored  as  glycogen,  and 
the  protein  products  which  remain  in  solution  and  are  carried  into  the  general 
circulation  to  the  various  tissues  and  organs  of  the  body. 

Speaking  generally,  the  arteries  may  be  said  to  contain  pure  and  the  veins 
impure  blood.  This  is  true  of  the  systemic,  but  not  of  the  pulmonary  vessels, 
since  it  has  been  seen  that  the  impure  blood  is  conveyed  from  the  heart  to  the  lungs 
by  the  pulmonary  arteries,  and  the  pure  blood  returned  from  the  lungs  to  the  heart 
by  the  pulmonary  veins.  Arteries,  therefore,  must  be  defined  as  vessels  which 
convey  blood  from  the  heart,  and  veins  as  vessels  which  return  blood  to  the  heart. 

Structure  of  Arteries  (Fig.  448). — The  arteries  are  composed  of  three  coats:  an  internal  or 
endothelial  coat  {tunica  intima  of  Kolliker);  a  middle  or  muscular  coat  {tunica  media);  and  an 

external  or  connective-tissue  coat  {tunica  adventitia). 
The  two  inner  coats  together  are  very  easily  separated 
from  the  external,  as  by  the  ordinary  operation  of 
tying  a  ligature  around  an  artery.  If  a  fine  string  be 
tied  forcibly  upon  an  artery  and  then  taken  off,  the 
external  coat  will  be  found  undivided,  but  the  two 
inner  coats  are  divided  in  the  track  of  the  ligature 
and  can  easily  be  further  dissected  from  the  outer 
coat. 

The  inner  coat  {tunica  intima)  can  be  separated 
from  the  middle  by  a  little  maceration,  or  it  may  be 
stripped  off  in  small  pieces;  but,  on  account  of  its 
friability,  it  cannot  be  separated  as  a  complete  mem- 
brane. It  is  a  fine,  transparent,  colorless  structure 
which  is  highly  elastic,  and,  after  death,  is  commonly 
corrugated  into  longitudinal  wrinkles.  The  inner  coat 
consists  of:  (1)  A  layer  of  pavement  endothelium, 
the  cells  of  which  are  polygonal,  oval,  or  fusiform, 
and  have  very  distinct  round  or  oval  nuclei.  This 
endothelium  is  brought  into  view  most  distinctly  by 
staining  with  nitrate  of  silver.  (2)  A  subendothelial 
layer,  consisting  of  deUcate  connective  tissue  with 
branched  cells  lying  in  the  interspaces  of  the  tissue; 
in  arteries  of  less  than  2  mm.  in  diameter  the  sub- 
endothelial layer  consists  of  a  single  stratum  of  stel- 
late cells,  and  the  connective  tissue  is  only  largely 
developed  in  vessels  of  a  considerable  size.  (3)  An 
elastic  or  fenestrated  layer,  which  consists  of  a  mem- 
brane containing  a  net-work  of  elastic  fibers,  having 
principally  a  longitudinal  direction,  and  in  which, 
imder  the  microscope,  small  elongated  apertures  or 
perforations  may  be  seen,  giving  it  a  fenestrated  ap- 
pearance. It  was  therefore  called  by  Henle  the  fenes- 
trated membrane.  This  membrane  forms  the  chief 
thickness  of  the  inner  coat,  and  can  be  separated  into 
several  layers,  some  of  which  present  the  appearance 
of  a  net-work  of  longitudinal  elastic  fibers,  and  others 
a  more  membranous  character,  marked  by  pale  lines 
having  a  longitudinal  direction.  In  minute  arteries 
the  fenestrated  membrane  is  a  very  thin  layer;  but  in  the  larger  arteries,  and  especially  in  the 
aorta,  it  has  a  very  considerable  thickness. 

The  middle  coat  {tunica  media)  is  distinguished  from  the  inner  by  its  color  and  by  the  trans- 
verse arrangement  of  its  fibers.  In  the  smaller  arteries  it  consists  principally  of  plain  muscle 
fibers  in  fine  bundles,  arranged  in  lamellae  and  disposed  circularly  around  the  vessel.  These 
lamellae  vary  in  number  according  to  the  size  of  the  vessel;  the  smallest  arteries  having  only  a 
single  layer  (Fig.  449),  and  those  slightly  larger  three  or  four  layers.  It  is  to  this  coat  that  the 
thickness  of  the  wall  of  the  artery  is  mainly  due  (Fig.  448^,  m).    In  the  larger  arteries,  as  the 


Fig.  448. — Transverse  section  through  a  small 
artery  and  vein  of  the  mucous  membrane  of  the 
epiglottis  of  a  child.  X  350.  (Klein  and  Noble 
Smith.)  A.  Artery,  showing  the  nucleated  endo- 
thelium, e,  which  lines  it;  the  vessel  being  con- 
tracted, the  endothelial  cells  appear  very  thick. 
Underneath  the  endothelium  is  the  wavy  elastic 
lamina.  _  The  chief  part  of  the  wall  of  the  vessel 
is  occupied  by  the  circular  muscle  coat  m;  the 
rod-shaped  nuclei  of  the  muscle  cells  are  well  seen. 
Outside  this  is  o,  part  of  the  adventitia.  This  is 
composed  of  bundles  of  connective  tissue  fibers, 
shown  in  section,  with  the  nuclei  of  the  connec- 
tive tissue  corpuscles.  The  adventitia  gradually 
merges  into  the  surrounding  connective  tissue. 
V.  Vein  showing  a  thin  endothelial  membrane, 
e,  raised  accidentally  from  the  intima,  which  on 
account  of  its  delicacy  is  seen  as  a  mere  line  on  the 
media  m.  This  latter  is  composed  of  a  few  circular 
unstriped  muscle  cells  o.  The  adventitia,  similar 
in  structure  to  that  of  an  artery. 


STRUCTURE  OF  ARTERIES 


499 


I  iliac,  femoral,  and  carotid,  elastic  fibers  unite  to  form  lamellae  which  alternate  with  the  layers 
of  muscular  fibers;  these  lamellae  are  united  to  one  another  by  elastic  fibers  which  pass  between 
the  muscular  bundles,  and  are  connected  with  the  fenestrated  membrane  of  the  inner  coat  (Fig. 

■  450).  In  the  largest  arteries,  as  the  aorta  and  innominate,  the  amount  of  elastic  tissue  is  very 
JBonsiderable;  in  these  vessels  a  few  bundles  of  white  connective  tissue  also  have  been  found  in 
the  middle  coat.  The  muscle  fiber  cells  are  about  oOu  in  length  and  contain  well-marked,  rod- 
shaped  nuclei,  which  are  often  slightly  curved. 

The  external  coat  (tunica  adventitia)  consists  mainly  of  fine  and  closely  felted  bundles  of  white 
connective  tissue,  but  also  contains  elastic  fibers  in  all  but  the  smallest  arteries.  The  elastic 
tissue  is  much  more  abundant  next  the  tunica  media, 
and  it  is  sometimes  described  as  forming  here,  between 
the  adventitia  and  media,  a  special  layer,  the  tunica 
elastica  externa  of  Henle.  This  layer  is  most  marked 
in  arteries  of  medium  size.  In  the  largest  vessels  the 
external  coat  is  relatively  thin;  but  in  small  arteries 
it  is  of  greater  proportionate  thickness.  In  the  smaller 
arteries  it  consists  of  a  single  layer  of  white  connec- 
tive tissue  and  elastic  fibers;  while  in  the  smallest 
arteries,  just  above  the  capillaries,  the  elastic  fibers 
are  wanting,  and  the  connective  tissue  of  which  the 
coat  is  composed  becomes  more  nearly  homogeneous 
tlie  nearer  it  approaches  the  capillaries,  and  is  grad- 
ually reduced  to  a  thin  membranous  envelope,  which 
finally  disappears. 

Some  arteries  have  extremely  thin  walls  in  propor- 
tion to  their  size;  this  is  especially  the  case  in  those 
situated  in  the  cavity  of  the  cranium  and  vertebral 
canal,  the  difference  depending  on  the  thinness  of  the 
external  and  middle  coats. 

The  arteries,  in  their  distribution  throughout  the 
body,  are  included  in  thin  fibro-areolar  investments, 
which  form  their  sheaths.  The  vessel  is  loosely  con- 
nected with  its  sheath  by  delicate  areolar  tissue;  and 
the  sheath  usually  encloses  the  accompanying  veins, 

and  sometimes  a  nerve.  Some  arteries,  as  those  in  the  cranium,  are  not  included  in  sheaths. 
All  the  larger  arteries,  like  the  other  organs  of  the  body,  are  supplied  with  bloodvessels.  These 
nutrient  vessels,  called  the  vasa  vasorum,  arise  from  a  branch  of  the  artery,  or  from  a  neighbor- 
ing vessel,  at  some  considerable  distance  from  the  point  at  which  they  are  distributed;  they 
ramify  in  the  loose  areolar  tissue  connecting  the  artery  with  its  sheath,  and  are  distributed  to 
the  external  coat,  but  do  not,  in  man,  penetrate  the  other  coats;  in  some  of  the  larger  mammals 
a  few  vessels  have  been  traced  into  the  middle  coat.  Minute  veins  return  the  blood  from  these 
vessels;  they  empty  themselves  into  the  vein  or  veins  accompanying  the  artery.     Lymphatic 

H  ^essels  are  also  present  in  the  outer  coat. 

m  W  Arteries  are  also  supplied  with  nerves,  which  are  derived  from  the  sympathetic,  but  may  pass 
through  the  cerebrospinal  nerves.  They  form  intricate  plexuses  upon  the  surfaces  of  the  larger 
trunks,  and  run  along  the  smaller  arteries  as  single  filaments,  or  bundles  of  filaments  which  twist 
around  the  vessel  and  unite  with  each  other  in  a  plexiform  manner.  The  branches  derived  from 
these  plexuses  penetrate  the  external  coat  and  are  distributed  principally  to  the  muscular  tissue 
of  the  middle  coat,  and  thus  regulate,  by  causing  the  contraction  and  relaxation  of  this  tissue 
the  amount  of  blood  sent  to  any  part. 

H  ■    The  Capillaries. — The  smaller  arterial  branches  (excepting  those  of  the  cavernous  structure 

■  fof  the  sexual  organs,  of  the  splenic  pulp,  and  of  the  placenta)  terminate  in  net-works  of  vessels 
which  pervade  nearly  every  tissue  of  the  body.  These  vessels,  from  their  minute  size,  are  termed 
capillaries.  They  are  interposed  between  the  smallest  branches  of  the  arteries  and  the  commenc- 
ing veins,  constituting  a  net-work,  the  branches  of  which  maintain  the  same  diameter  throughout; 
the  meshes  of  the  net-work  are  more  uniform  in  shape  and  size  than  those  formed  by  the  anasto- 
moses of  the  small  arteries  and  veins. 

The  diameters  of  the  capillaries  vary  in  the  different  tissues  of  the  body,  the  usual  size  being 
about  8,u.  The  smallest  are  those  of  the  brain  and  the  mucous  membrane  of  the  intestines; 
and  the  largest  those  of  the  skin  and  the  marrow  of  bone,  where  they  are  stated  to  be  as  large 
as  20/x  in  diameter.  The  form  of  the  capillary  net  varies  in  the  different  tissues,  the  meshes  being 
generally  rounded  or  elongated. 

The  rounded  form  of  mesh  is  most  common,  and  prevails  where  there  is  a  dense  network,  as  in 
the  lungs,  in  most  glands  and  mucous  membranes,  and  in  the  cutis;  the  meshes  are  not  of  an 
absolutely  circular  outhne,  but  more  or  less  angular,  sometimes  nearly  quadrangular,  or  polygonal, 
or  more  often  irregular. 


Fia.  449. — Small  artery  and  vein,  pia  mater  of 
sheep.  X  250.  Surface  view  above  the  inter- 
rupted line;  longitudinal  section  below.  Artery 
in  red;  vein  in  blue, 


I- 


500 


ANGIOLOGY 


I 


Elongated  meshes  are  observed  in  the  muscles  and  nerves,  the  meshes  resembling  parallelograms 
in  form,  the  long  axis  of  the  mesh  running  parallel  with  the  long  axis  of  the  nerve  or  muscle. 
Sometimes  the  capillaries  have  a  looped  arrangement;  a  single  vessel  projecting  from  the  common 
net-work  and  returning  after  forming  one  or  more  loops,  as  in  the  papillse  of  the  tongue  ar.d 
skin. 

The  number  of  the  capillaries  and  the  size  of  the  meshes  determine  the  degree  of  vascularity 
of  a  part.  The  closest  network  and  the  smallest  interspaces  are  found  in  the  lungs  and  in  the 
choroid  coat  of  the  eye.  In  these  situations  the  interspaces  are  smaller  than  the  capillary  vessels 
themselves.  In  the  intertubular  plexus  of  the  kidney,  in  the  conjunctiva,  and  in  the  cutis,  the 
interspaces  are  from  three  to  four  times  as  large  as  the  capillaries  which  form  them;  and  in  the 
brain  from  eight  to  ten  times  as  large  as  the  capillaries  in  their  long  diameters,  and  from  four 
to  six  times  as  large  in  their  transverse  diameters.  In  the  adventitia  of  arteries  the  width  of  the 
meshes  is  ten  times  that  of  the  capillary  vessels.  As  a  general  rule,  the  more  active  the  funo 
tion  of  the  organ,  the  closer  is  its  capillary  net  and  the  larger  its  supply  of  blood;  the  meshes  of 
the  network  are  very  narrow  in  all  growing  parts,  in  the  glands,  and  in  the  mucous  membranes, 
wider  in  bones  and  Ugaments  which  are  comparatively  inactive;  bloodvessels  are  nearly  alto- 
gether absent  in  tendons,  in  which  very  little  organic  change  occurs  after  their  formation.  In 
the  liver  the  capillaries  take  a  more  or  less  radial  course  toward  the  intralobular  vein,  and  their 
walls  are  incomplete,  so  that  the  blood  comes  into  direct  contact  with  the  liver  cells.  These 
vessels  in  the  liver  are  not  true  capillaries  but  "sinusoids;"  they  are  developed  by  the  growth 
of  columns  of  liver  cells  into  the  blood  spaces  of  the  embryonic  organ. 

Endothelial  and  svb- 
endothelial  layer  of 

inner  coat 

Elastic  layer 

Innermost  layers  of 
middle  coat 


Outermost  layers  of 
middle  coat 

Innermost  part  of 
outer  coat 


Outermost  part  of 
outer  coat 


Fig.  450. — Section  of  a  medium-sized  artery.     (After  Grilnstein.) 

Structure. — The  wall  of  a  capillary  consists  of  a  fine  transparent  endothelial  layer,  composed 
of  ceUs  joined  edge  to  edge  by  an  interstitial  cement  substance,  and  continuous  with  the  endo- 
thelial cells  which  hne  the  arteries  and  veins.  When  stained  with  nitrate  of  silver  the  edges  which 
boimd  the  epithehal  ceUs  are  brought  into  view  (Fig.  451).  These  cells  are  of  large  size  and  of 
an  irregular  polygonal  or  lanceolate  shape,  each  containing  an  oval  nucleus  which  may  be  dis- 
played by  carmine  or  hematoxyhn.  Between  their  edges,  at  various  points  of  their  meeting, 
roundish  dark  spots  are  sometimes  seen,  which  have  been  described  as  stomata.  though  they  are 
closed  by  intercellular  substance.  They  have  been  beUeved  to  be  the  situations  through  which 
the  colorless  corpuscles  of  the  blood,  when  migrating  from  the  bloodvessels,  emerge;  but  this 
view,  though  probable,  is  not  universally  accepted. 

Kolossow  describes  these  cells  as  having  a  rather  more  complex  structvu-e.     He  states  that 


I 


STRUCTURE  OF  VEINS 


501 


each  consists  of  two  parts:  of  hyaline  ground  plates,  and  of  a  protoplasmic  granular  part,  in 
which  is  imbedded  the  nucleus,  on  the  outside  of  the  ground  plates.  The  hyaline  internal  coat 
of  the  capillaries  does  not  form  a  complete  membrane,  but  consists  of  "plates"  which  are  inelastic, 

tand  though  in  contact  with  each  other  are  not  continuous;  when  therefore  the  capillaries  are  sub- 
jected to  intravascular  pressure,  the  plates  become  separated  from  each  other;  the  protoplasmic 
portions  of  the  cells,  on  the  other  hand,  are  united  together.  In  some  organs,  e.  g.,  the  glomeruH 
of  the  kidneys,  intercellular  cement  cannot  be  demonstrated  in  the  capillary  wall  and  the  cells 
are  beheved  to  form  a  syncytium. 

In  many  situations  a  delicate  sheath  or  envelope  of  branched  nucleated  connective  tissue  cells 
is  found  around  the  simple  capillary  tube,  particularly  in  the  larger  ones;  and  in  other  places, 
especially  in  the  glands,  the  capillaries  are  invested  with  retiform  connective  tissue. 

Sinusoids. — In  certain  organs,  viz.,  the  heart,  the  Uver,  the  suprarenal  and  parathyroid 
glands,  the  glomus  caroticum  and  glomus  coccygeum,  the  smallest  bloodvessels  present  various 
differences  from  true  capillaries.  They  are  wider,  with  an 
irregular  lumen,  and  have  no  connective  tissue  covering, 
their  endothehal  cells  being  in  direct  contact  with  the  cells  of 
the  organ.  Moreover,  they  are  either  arterial  or  venous  and 
not  intermediate  as  are  the  true  capillaries.  These  vessels 
have  been  called  sinusoids  by  Minot.  They  are  formed 
by  columns  of  cells  or  trabeculae  pushing  their  way  into  a 
large  bloodvessel  or  blood  space  and  carrying  its  endothe- 
lium before  them;  at  the  same  time  the  wall  of  the  vessel 
or  space  grows  out  between  the  cell  columns. 

Structure  of  Veins.— The  veins,  like  the  arteries,  are  com- 
posed of  three  coats:  internal,  middle,  and  external;  and 
these  coats  are,  with  the  necessary  modifications,  analogous 
to  the  coats  of  the  arteries;  the  internal  being  the  endo- 
thehal, the  middle  the  muscular,  and  the  external  the 
connective  tissue  or  areolar  (Fig.  452).  The  main  differ- 
ence between  the  veins  and  the  arteries  is  in  the  compara- 
tive weakness  of  the  middle  coat  in  the  former. 

In  the  smallest  veins  the  three  coats  are  hardly  to  be  dis- 
tinguished (Fig.  449).  The  endothelium  is  supported  on  a 
membrane  separable  into  two  layers,  the  outer  of  which 
is  the  thicker,  and  consists  of  a  delicate,  nucleated  mem- 
brane (adventitia) ,  while  the  inner  is  composed  of  a  network 
of  longitudinal  elastic  fibers  (media).  In  the  veins  next 
above  these  in  size  (0.4  mm.  in  diameter),  according  to 
Kolhker,  a  connective  tissue  layer  containing  numerous 
muscle  fibers  circularly  disposed  can  be  traced,  forming  the 

middle  coat,  while  the  elastic  and  connective  tissue  elements  of  the  outer  coat  become 
more  distinctly  perceptible.  In  the  middle-sized  veins  the  typical  structure  of  these  vessels 
becomes  clear.  The  endothelium  is  of  the  same  character  as  in  the  arteries,  but  its  cells 
are  more  oval  and  less  fusiform.  It  is  supported  by  a  connective  tissue  layer,  consisting  of 
a  deUcate  net-work  of  branched  cells,  and  external  to  this  is  a  layer  of  elastic  fibers  disposed 
in  the  form  of  a  net-work  in  place  of  the  definite  fenestrated  membrane  seen  in  the  arteries. 
This  constitutes  the  internal  coat.  The  middle  coat  is  composed  of  a  thick  layer  of  con- 
nective tissue  with  elastic  fibers,  intermixed,  in  some  veins,  with  a  transverse  layer  of  muscular 
tissue.  The  white  fibrous  element  is  in  considerable  excess,  and  the  elastic  fibers  are  in  much 
smaller  proportion  in  the  veins  than  in  the  arteries.  The  outer  coat  consists,  as  in  the  arteries, 
of  areolar  tissue,  with  longitudinal  elastic  fibers.  In  the  largest  veins  the  outer  coat  is  from 
two  to  five  times  thicker  than  the  middle  coat,  and  contains  a  large  number  of  longitudinal 
muscular  fibers.  These  are  most  distinct  in  the  inferior  vena  cava,  especially  at  the  termination 
of  this  vein  in  the  heart,  in  the  trunks  of  the  hepatic  veins,  in  all  the  large  tnmks  of  the  portal 
vein,  and  in  the  external  iliac,  renal,  and  azygos  veins.  In  the  renal  and  portal  veins  they  extend 
through  the  whole  thickness  of  the  outer  coat,  but  in  the  other  veins  mentioned  a  layer  of  con- 
nective and  elastic  tissue  is  found  external  to  the  muscular  fibers.  All  the  large  veins  which  open 
into  the  heart  are  covered  for  a  short  distance  with  a  layer  of  striped  muscular  tissue  continued 
on  to  them  from  the  heart.  Muscular  tissue  is  wanting:  (1)  in  the  veins  of  the  maternal  part 
of  the  placenta;  (2)  in  the  venous  sinuses  of  the  dura  mater  and  the  veins  of  the  pia  mater  of 
the  brain  and  medulla  spinaUs;  (3)  in  the  veins  of  the  retina;  (4)  in  the  veins  of  the  cancellous 
tissue  of  bones;  (5)  in  the  venous  spaces  of  the  corpora  cavernosa.  The  veins  of  the  above-men- 
tioned parts  consist  of  an  internal  endothehal  lining  supported  on  one  or  more  layers  of  areolar 
tissue. 

Most  veins  are  provided  with  valves  which  serve  to  prevent  the  reflux  of  the  blood.  Each 
valve  is  formed  by  a  reduplication  of  the  inner  coat,  strengthened  by  connective  tissue  and  elastic 


Fig.  451.— Capillaries  from  the  mesen- 
tery of  a  guinea-pig,  after  treatment  with 
solution  of  nitrate  of  silver,  a.  Cells. 
b.  Their  nuclei. 


502 


ANGIOLOGY 


I 


fibers,  and  is  covered  on  both  surfaces  with  endothehum,  the  arrangement  of  which  differs  on 
the  two  surfaces.  On  the  surface  of  the  valve  next  the  wall  of  the  vein  the  cells  are  arran^^ed 
transversely;  while  on  the  other  surface,  over  which  the  current  of  blood  flows,  the  cells  are 
arranged  longitudinally  in  the  direction  of  the  current.  Most  commonly  two  such  valves  are 
found  placed  opposite  one  another,  more  especially  in  the  smaller  veins  or  in  the  larger  trunks 
at  the  point  where  they  are  joined  by  smaller  branches;  occasionally  there  are  three  and  some- 
times only  one.  The  valves  are  semilunar.  They  are  attached  by  their  convex  edges  to  the 
wall  of  the  vein;  the  concave  margins  are  free,  directed  in  the  course  of  the  venous  current,  and 
Ue  in  close  apposition  with  the  wall  of  the  vein  as  long  as  the  current  of  blood  takes  its  natural 
course;  if,  however,  any  regurgitation  takes  place,  the  valves  become  distended,  their  opposed 
edges  are  brought  into  contact,  and  the  current  is  interrupted.  The  wall  of  the  vein  on  the 
cardiac  side  of  the  point  of  attachment  of  each  valve  ia  expanded  into  a  pouch  or  sinus,  which 
gives  to  the  vessel,  when  injected  or  distended  with  blood,  a  knotted  appearance.  The  valves 
are  very  numerous  in  the  veins  of  the  extremities,  especially  of  the  lower  extremities,  these  vessels 

Endothelium  •  - . 
Elastic  layer  x-^' 


Middle  coat  —  —  rft 


'0^'::% 


Ovier  coat ?^ 


Fig.  452. — Section  of  a  medium-sized  vein. 

having  to  conduct  the  blood  against  the  force  of  gravity.  They  are  absent  in  the  very  small 
veins,  i.  e.,  those  less  than  2  mm.  in  diameter,  also  in  the  venae  cavse,  hepatic,  renal,  uterine,  and 
ovarian  veins.  A  few  valves  are  found  in  each  spermatic  vein,  and  one  also  at  its  point  of  junc- 
tion with  the  renal  vein  or  inferior  vena  cava  respectively.  The  cerebral  and  spinal  veins,  the 
veins  of  the  cancellated  tissue  of  bone,  the  pulmonary  veins,  and  the  umbihcal  vein  and  its 
branches,  are  also  destitute  of  valves.  A  few  valves  are  occasionally  found  in  the  azygos  and 
intercostal  veins.  Rudimentary  valves  are  found  in  the  tributaries  of  the  portal  venous  system. 
The  veins,  like  the  arteries,  are  supplied  with  nutrient  vessels,  vasa  vasortun.  Nerves  also 
are  distributed  to  them  in  the  same  manner  as  to  the  arteries,  but  in  much  less  abundance. 


THE  BLOOD. 

The  blood  is  an  opaque,  rather  viscid  fluid,  of  a  bright  red  or  scarlet  color 
when  it  flows  from  the  arteries,  of  a  dark  red  or  purple  color  when  it  flows  from 
the  veins.  It  is  salt  to  the  taste,  and  has  a  peculiar  faint  odor  and  an  alkaline 
reaction.  Its  specific  gravity  is  about  1.06,  and  its  temperature  is  generally  about 
37°  C,  though  varying  slightly  in  different  parts  of  the  body. 


THE  BLOOD 


503 


I  General  Composition  of  the  Blood. — Blood  consists  of  a  faintly  yellow  fluid,  the 
plasma  or  liquor  sanguinis,  in  which  are  suspended  numerous  minute  particles, 
the  blood  corpuscles,  the  majority  of  which  are  colored  and  give  to  the  blood  its 
;red  tint.  If  a  drop  of  blood  be  placed  in  a  thin  layer  on  a  glass  slide  and  examined 
under  the  microscope,  a  number  of  these  corpuscles  will  be  seen  floating  in  the 
plasma 

6 


of 


Fig.  453. — Human  red  blo<xl  corpuscles.  Highly  magnified,  a. 
Seen  from  the  surface,  h.  Seen  in  profile  and  forming  rouleaux, 
c.  Rendered  spherical  by  water,  d.  Rendered  crenate  by  salt 
solution. 


W^ 


MTv, 


II 


The    Blood    Corpuscles    are 
three    kinds:      (1)     colored     cor- 
puscles or  erjrthrocytes ;  (2)  color- 
less corpuscles  or  leucocjrtes;  (3) 
blood  platelets. 

1.  Colored    or     red     corpuscles 

erythrocytes) ,     when     examined 
der  the  microscope,  are  seen 

o  be  circular  disks,  biconcave  in 
profile.  The  disk  has  no  nucleus, 
but,  in  consequence  of  its  bicon- 
cave shape,  presents,  according 
to  the  alterations  of  focus  under 
an  ordinary  high  power,  a  central 
part,  sometimes  bright,  sometimes 

dark,  which  has  the  appearance  of  a  nucleus  (Fig.  453,  a).    It  is  to  the  aggregation 
oi  the  red  corpuscles  that  the  blood  owes  its  red  hue,  although  when  examined 

ly  transmitted  light  their  color  appears  to  be  only  a  faint  reddish  yellow.  The 
corpuscles  vary  slightly  in  size  even  in  the  same  drop  of  blood,  but  the  average 
diameter  is  about  7.5^,^  and  the  thickness  about  2ju.  Besides  these  there  are 
found  certain  smaller  corpuscles  of  about  one-half  of  the  size  just  indicated; 
these  are  termed  microcjrtes,  and  are  very  scarce  in  normal  blood;  in  diseased  con- 
ditions {e.  g.,  anemia),  however,  they  are  more  numerous.     The  number  of  red 

orpuscles  in  the  blood  is  enormous;  between  4,000,000  and  5,000,000  are  con- 

ained  in  a  cubic  millimetre.     Power  states  that  the  red  corpuscles  of  an  adult 
ould  present  an  aggregate  surface  of  about  3000  square  yards. 
If  the  web  of  a  living  frog's  foot  be  spread  out  and  examined  under  the  micro- 
ope  the  blood  is  seen  to  flow  in  a  continuous  stream  through  the  vessels,  and  the 
corpuscles  show  no  tendency  to  adhere  to  each  other  or  to  the  wall  of  the  vessel. 
Doubtless  the  same  is  the  case  in  the  human  body;  but  when  human  blood  is  drawn 

nd  examined  on  a  slide  without  reagents  the  corpuscles  tend  to  collect  into  heaps 
like  rouleaux  of  coins  (Fig.  453,  6).  It  has  been  suggested  that  this  phenomenon 
may  be  explained  by  alteration  in  surface  tension.  During  life  the  red  corpuscles 
may  be  seen  to  change  their  shape  under  pressure  so  as  to  adapt  themselves,  to 
some  extent,  to  the  size  of  the  vessel.  They  are,  however,  highly  elastic,  and 
Speedily  recover  their  shape  when  the  pressure  is  removed.  They  are  readily 
influenced  by  the  medium  in  which  they  are  placed.  In  water  they  swell  up,  lose 
their  shape,  and  become  globular  (endosmosis)  (Fig.  453,  c).  Subsequently  the 
'hemoglobin  is  dissolved  out,  and  the  envelope  can  barely  be  distinguished  as  a 

aint  circular  outline.     Solutions  of  salt  or  sugar,  denser  than  the  plasma,  give 

em  a  stellate  or  crenated  appearance  (exosmosis)  (Fig.  453,  d),  but  the  usual 

shape  may  be  restored  by  diluting  the  solution  to  the  same  tonicity  as  the  plasma. 

The  crenated  outline  may  be  produced  as  the  first  effect  of  the  passage  of  an  elec- 

ric  shock:  subsequently,  if  sufficiently  strong,  the  shock  ruptures  the  envelope. 
A  solution  of  salt,  isotonic  with  the  plasma,  merely  separates  the  blood  corpuscles 
mechanically,  without  changing  their  shape.    Two  views  are  held  with  regard  to 

I  A  micromillimetre  {M  )  is  1/1000  of  a  millimetre  or  1/25000  of  an  inch. 


504 


ANGIOLOGY 


I 


the  structure  of  the  erythrocytes.  The  older  view,  that  of  Rollett,  supposes  that 
the  corpuscle  consists  of  a  sponge  work  or  stroma  permeated  by  a  solution  of  hemo- 
globin. Schafer,  on  the  other  hand,  believes  that  the  hemoglobin  solution  is  con- 
tained within  an  envelope  or  membrane,  and  the  facts  stated  above  with  regard 
to  the  osmotic  behavior  of  the  erythrocyte  support  this  belief.  The  envelope 
consists  mainly  of  lecithin,  cholesterin,  and  nucleoprotein. 

The  colorless  corpuscles  or  leucocytes  are  of  various  sizes,  some  no  larger,  others 
smaller,  than  the  red  corpuscles,  In  human  blood,  however,  the  majority  are 
rather  larger  than  the  red  corpuscles,  and  measure  about  10/i  in  diameter.  On  the 
average  from  7000  to  12,000  leucocytes  are  found  in  each  cubic  millimetre  of 
blood. 


n 


Fig.  454. — Varieties  of  leucocytes  found  in  human  blood.     Highly  magnified. 

They  consist  of  minute  masses  of  nucleated  protoplasm,  and  exhibit  several 
varieties,  which  are  differentiated  from  each  other  chiefly  by  the  occurrence  or 
non-occurrence  of  granules  in  their  protoplasm,  and  by  the  staining  reactions  of 
these  granules  when  present  (Fig.  454).  (1)  The  most  numerous  (60  per  cent.)  and 
important  are  irregular  in  shape,  possessed  of  the  power  of  ameboid  movement, 
and  are  characterized  by  nuclei  which  often  consist  of  two  or  three  parts  (multi- 
partite) connected  together  by  fine  threads  of  chromatin.  The  protoplasm  is 
clear,  and  contains  a  number  of  very  fine  granules,  which  stain  with  acid  dyes, 
such  as  eosin,  or  with  neutral  dyes,  and  are  therefore  called  oxyphil  or  neutrophil 
(Fig.  454,  P).  These  cells  are  termed  the  poljrmorphonuclear  leucocytes.  (2)  A 
second  variety  comprises  from  1  to  4  per  cent,  of  the  leucocytes;  they  are  larger 
than  the  previous  kind,  and  are  made  up  of  coarsely  granular  protoplasm,  the 
granules  being  highly  refractile  and  grouped  around  single  nuclei  of  horse-shoe 
shape  (Fig.  454,  E).  The  granules  stain  deeply  with  eosin,  and  the  cells  are  there- 
fore often  termed  eosinophil  corpuscles.  (3)  The  third  variety  is  called  the  hyaline 
cell  or  macrocjrte  (Fig.  454,  R).  This  is  usually  about  the  same  size  as  the  eosino- 
phil cell,  and,  when  at  rest,  is  spherical  in  shape  and  contains  a  single  round  or 
ov^  nucleus.  The  protoplasm  is  free  from  granules,  but  is  not  quite  transparent, 
having  the  appearance  of  ground  glass.  (4)  The  fourth  kind  of  colorless  corpuscle 
is  designated  the  Ijrmphocyte  (Fig.  454,  Z),  because  it  is  identical  with  the  cell  derived 
from  the  lymph  glands  or  other  lymphoid  tissue.  It  is  the  smallest  of  the  leuco- 
cytes, and  consists  chiefly  of  a  spheroidal  nucleus  with  a  very  little  surrounding 
protoplasm  of  a  homogeneous  nature;  it  is  regarded  as  the  immature  form  of  the 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM 


505 


hyaline  cell.  The  third  and  fourth  varieties  together  constitute  from  20  to  30 
per  cent,  of  the  colorless  corpuscles,  but  of  these  two  varieties  the  lymphocytes 
are  by  far  the  more  numerous.  Leucocytes  having  in  their  protoplasm  granules 
which  stain  with  basic  dyes  (basophil)  have  been  described  as  occurring  in  human 
blood,  but  they  are  rarely  found  except  in  disease. 

The  colorless  corpuscles  are  very  various  ip  shape  in  living  blood  (Fig.  455), 
because  many  of  them  have  the  power  of  constantly  changing  their  form  by  pro- 
truding finger-shaped  or  filamentous  processes  of  their  substance,  by  which  they 
move  and  take  up  granules  from  the  surrounding  medium.  In  locomotion  the 
corpuscle  pushes  out  a  process  of  its  substance — a  pseudopodium,  as  it  is  called 


ssi.  ^  S  t  ■*  6  ^ 


Fig.  455.- 


-Human  colorless  blood  corpuscle,  showing  its  successive  changes  of  outline  within  ten  minutes  when  kept 
moist  on  a  warm  stage.     (Schofield.) 


N» 


II 


II 


— and  then  shifts  the  rest  of  the  body  into  it.  In  the  same  way  when  any  granule 
or  particle  comes  in  its  way  the  corpuscle  wraps  a  pseudopodium  around  it,  and  then 
withdraws  the  pseudopodium  with  the  contained  particle  into  its  own  substance. 
By  means  of  these  ameboid  properties  the  cells  have  the  power  of  wandering 
or  emigrating  from  the  bloodvessels  by  penetrating  their  walls  and  thus  finding 
their  way  into  the  extravascular  spaces.  A  chemical  investigation  of  the  proto- 
plasm of  the  leucocytes  shows  the  presence  of  nucleoprotein  and  of  a  globulin. 
The  occurrence  of  small  amounts  of  fat,  lecithin,  and  glycogen  may  also  be 
demonstrated. 

The  blood  platelets  (Fig.  456)  are  discoid  or  irregularly  shaped,  colorless,  refractile 
bodies,  much  smaller  than  the  red  corpuscles.    Each  contains  a  central  chromatin 
mass  resembling  a  nucleus.    Blood  platelets  possess  the  power  of  ameboid  move- 
ment.   When  blood  is  shed  they  rapidly  disintegrate 
and  form  granular  masses,  setting  free  prothrombin 
and  the  substance  called  by  Howell  thromboplastin. 
It  is  doubtful  whether  they  exist  normally  in  circu- 
lating blood. 

DEVELOPMENT  OF  THE  VASCULAR  SYSTEM. 

Bloodvessels  first  make  their  appearance  in  sev- 
eral scattered  vascular  areas  which  are  developed 
simultaneously  between  the  entoderm  and  the  meso- 
derm of  the  yolk-sac,  i.  e.,  outside  the  body  of  the 
embryo.  Here  a  new  type  of  cell,  the  angioblast 
or  vasoformative  cell,  is  differentiated  from  the 
mesoderm.  These  cells  as  they  divide  form  small, 
dense  syncytial  masses  which  soon  join  with  similar 
masses  by  means  of  fine  processes  to  form  plexuses.  These  plexuses  increase 
both  by  division  and  growth  of  its  cells  and  by  the  addition  of  new  angioblasts 
which  differentiate  from  the  mesoderm.  Within  these  solid  plexuses  and  also 
within  the  isolated  masses  of  angioblasts  vacuoles  appear  through  liquefaction  of 
the  central  part  of  the  syncytium  into  plasma.  The  lumen  of  the  bloodvessels 
thus  formed  is  probably  intracellular.  The  flattened  cells  at  the  periphery  form 
the  endothelium.  The  nucleated  red  blood  corpuscles  develop  either  from  small 
masses  of  the  original  angioblast  left  attached  to  the  inner  wall  of  the  lumen  or 
directly  from  the  flat  endothelial  cells.     In  either  case  the  svncvtial  mass  thus 


Fig.  456.— Blood  platelets.     Highly 
magnified.     (After  Kopsch.) 


506 


ANGIOLOGY 


I 


eat 


formed  projects  from  and  is  attached  to  the  wall  of  the  vessel.  Such  a  mass  i^, 
known  as  a  blood  island  and  hemoglobin  gradually  accumulates  within  it.  Later 
the  cells  on  the  surface  round  up,  giving  the  mass  a  mulberry-like  appearance. 
Then  the  red  blood  cells  break  loose  and  are  carried  away  in  the  plasma.  Such 
free  blood  cells  continue  to  divide.  The  term  blood  island  was  originally  used  for 
the  syncytial  masses  of  angioblasts  found  in  the  area  vasculosa,  but  it  is  probably 
best  to  limit  the  term  to  the  masses  within  the  lumen  from  which  the  red  blood 
cells  arise  as  Sabin^  has  done.  Blood  islands  have  been  seen  in  the  area  vasculosa 
in  the  omphalomesenteric  vein  and  arteries,  and  in  the  dorsal  aorta. 

The  differentiation  of  angioblasts  from  the  mesoderm  occurs  not  only  in  the  area 
vasculosa  but  within  the  embryo  and  probably  most  of  the  larger  bloodvessels  are 
developed  in  situ  in  this  manner.  This  process  of  the  differentiation  of  angioblasts 
from  the  mesoderm  probably  ceases  in  diff  3rent  regions  of  the  embryo  at  different 

periods  and  after  its  cessation 
j\  ^^^^_  new  vessels  are  formed  by  sprouts 

from  vessels  already  laid  down  in 
the  form  of  capillary  plexuses. 

The  first  rudiment  of  the  heart 
appears  as  a  pair  of  tubular 
vessels  which  are  developed  in 
the  splanchnopleure  of  the  peri- 
cardial area  (Fig.  457).  These 
are  named  the  primitive  aortas, 
and  a  direct  continuity  is  soon 
established  between  them  and 
the  vessels  of  the  yolk-sac.  Each 
receives  anteriorly  a  vein — the 
vitelline  vein — from  the  yolk-sac, 
and  is  prolonged  backward  on 
the  lateral  aspect  of  the  noto- 
chord  under  the  name  of  the 
dorsal  aorta.  The  dorsal  aortse  give  branches  to  the  yolk-sac,  and  are  continued 
backward  through  the  body-stalk  as  the  umbilical  arteries  to  the  villi  of  the 
chorion. 

Eternod^  describes  the  circulation  in  an  embryo  which  he  estimated  to  be  about 
thirteen  days  old  (Fig.  458).  The  rudiment  of  the  heart  is  situated  immediately 
below  the  fore-gut  and  consists  of  a  short  stem.  It  gives  off  two  vessels,  the  primi- 
tive aortse,  which  run  backward,  one  on  either  side  of  the  notochord,  and  then  pass 
into  the  body-stalk  along  which  they  are  carried  to  the  chorion.  From  the  chorionic 
villi  the  blood  is  returned  by  a  pair  of  umbilical  veins  which  unite  in  the  body-stalk 
to  form  a  single  vessel  and  subsequently  encircle  the  mouth  of  the  yolk-sac  and 
open  into  the  heart.  At  the  junction  of  the  yolk-sac  and  body-stalk  each  vein 
is  joined  by  a  branch  from  the  vascular  plexus  of  the  yolk-sac.  From  his 
observations  it  seems  that,  in  the  human  embryo,  the  chorionic  circulation  is 
established  before  that  on  the  yolk-sac. 

By  the  forward  growth  and  flexure  of  the  head  the  pericardial  area  and  the 
anterior  portions  of  the  primitive  aortse  are  folded  backward  on  the  ventral  aspect 
of  the  fore-gut,  and  the  original  relation  of  the  somatopleure  and  splanchnopleure 
layers  of  the  pericardial  area  is  reversed.  Each  primitive  aorta  now  consists  of 
a  ventral  and  a  dorsal  part  connected  anteriorly  by  an  arch  (Fig.  459) ;  these  three 
parts  are  named  respectively  the  anterior  ventral  aorta,  the  dorsal  aorta,  and  the 
first  cephalic   arch.     The  vitelline  veins  which  enter  the  embryo  through  the 


Fig.  457. — Transverse  section  through  the  region  of  the  heart  in 
a  rabbit  embryo  of  nine  days.  X  80.  (Kolliker.)  j,  j.  Jugular 
veins,  ao.  Aorta,  ph.  Pharynx,  som.  Somatopleure.  bl.  Proamnion. 
ect.  Ectoderm,  ent.  Entoderm,  p.  Pericardium,  spl.  Splanchno- 
pleure. ah.  Outer  wall  of  heart,  i^.  Endothelial  lining  of  heart,  e'. 
Septum  between  heart  tubes. 


I  Anatomical  Record,  1917,  vol.  xiii,  p.  199. 


-  Anat.  Anzeiger,  1899,  vol.  xv. 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM 


507 


XJmhilical . 


anterior  wall  of  the  umbilical  orifice  are  now  continuous  with  the  posterior  ends  of 
the  anterior  ventral  aorta.  With  the  formation  of  the  tail-fold  the  posterior  parts 
of  the  primitive  aortse  are  carried  forward  in  a  ventral  direction  to  form  the  pos- 
terior ventral  aortae  and  primary  caudal  arches.^  In  the  pericardial  region  the  two 
primitive  aortse  grow  together,  and  fuse  to  form  a  single  tubular  heart  (Fig.  460), 
the  posterior  end  of  which  receives  the  two  vitelline  veins,  while  from  its  anterior 
end  the  two  anterior  ventral  aortse  emerge.^  The  first  cephalic  arches  pass  through 
the  mandibular  arches,  and  behind  them  five  additional  pairs  subsequently  develop, 
so  that  altogether  six  pairs  of  aortic  arches  are  formed;  the  fifth  arches  are  very 
transitory  vessels  connecting  the  ventral  aortse  with  the  dorsal  ends  of  the  sixth 
arches.  By  the  rhythmical  contraction  of  the  tubular  heart  the  blood  is  forced 
through  the  aortse  and  bloodvessels  of  the  vascular  area,  from  which  it  is  returned 
to  the  heart  by  the  vitelline  veins.  This  constitutes  the  vitelline  circulation  (Fig. 
459),  and  by  means  of  it  nutri- 
ment is  absorbed  from  the  yolk 
(vitellus.) 

The  vitelline  veins  at  first 
open  separately  into  the  poste- 
rior end  of  the  tubular  heart,  but 
after  a  time  their  terminal  por- 
tions fuse  to  form  a  single  ves- 
sel. The  vitelline  veins  ulti- 
mately drain  the  blood  from  the 
digestive  tube,  and  are  modified 
to  form  the  portal  vein.  This  is 
caused  by  the  growth  of  the  liver, 
which  interrupts  their  direct 
continuity  with  the  heart;  and 
the  blood  returned  by  them  cir- 
culates through  the  liver  before 
reaching  the  heart. 

With  the  atrophy  of  the  yolk- 
sac  the  vitelline  circulation  di- 
minishes and  ultimately  ceases, 
while  an  increasing  amount  of 
blood  is  carried  through  the  um- 
bilical arteries  to  the  villi  of  the 
chorion.  Subsequently,  as  the 
non-placental  chorionic  villi  atro- 
phy, their  vessels  disappear;  and 
then  the  umbilical  arteries  con- 
vey the  whole  of  their  contents 
to  the  placenta,  whence  it  is  re- 
turned to  the  heart  by  the  umbilical  veins.  In  this  manner  the  placental  circu- 
lation is  established,  and  by  means  of  it  nutritive  materials  are  absorbed  from, 
and  waste  products  given  up  to  the  maternal  blood. 

The  umbilical  veins,  like  the  vitelline,  undergo  interruption  in  the  developing 
liver,  and  the  blood  returned  by  them  passes  through  this  organ  before  reaching 
the  heart.    Ultimately  the  right  umbilical  vein  shrivels  up  and  disappears. 

During  the  occurrence  of  these  changes  great  alterations  take  place  in  the 
primitive  heart  and  bloodvessels. 


Neurenteric 
Canal 


Allantoic 
diverticulum 

Body-stalk 


Fig.  458. — Diagram  of  the  vascular  channels  in  a  human  embrj'o 
of  the  second  week.  (After  Eternod.)  The  red  lines  are  the  dorsal 
aortae  continued  into  the  umbilical  arteries.  The  red  dotted  linea 
are  the  ventral  aortse,  and  the  blue  dotted  lines  the  vitelline  veins. 


'  Young  and  Robinson,  .Journal  of  Anatomy  and  Physiology,  vol.  xxxii. 

*  In  most  fishes  and  in  the  amphibia  the  heart  originates  as  a  single  median  tube. 


508 


ANGIOLOGY 


I 


Further  Development  of  the  Heart. — Between  the  endothelial  hning  and  the 
outer  wall  of  the  heart  there  exists  for  a  time  an  intricate  trabecular  network  of 
mesodermal  tissue  from  w^hich,  at  a  later  stage,  the  musculi  papillares,  chordae 
tendineae,  and  trabeculse  carneae  are  developed.  The  simple  tubular  heart,  already 


Dorsal  aorta 

Primitive  jugular 
vein 


Amnion 

Cardinal  vein 

Dorsal  aorta 

Belly-stalk 

Chorionic  villi 

Fig.  459. — Human  embryo  of  about  fourteen  days,  with  yolk-sac.     (After  His.) 

described,  becomes  elongated  and  bent  on  itself  so  as  to  form  an  S-shaped  loop, 
the  anterior  part  bending  to  the  right  and  the  posterior  part  to  the  left  (Fig.  460) . 
The  intermediate  portion  arches  transversely  from  left  to  right,  and  then  turns 
sharply  forward  into  the  anterior  part  of  the  loop.  Slight  constrictions  make  their 
appearance  in  the  tube  and  divide  it  from  behind  forward  into  five  parts,  viz.: 


Forc-hrain 


Bidbus  cordis 


A  Irium  — 


Optic  vesicle 


Ventricle 


Vitelline  vein 


Fig.  460. — Head  of  chick  embryo  of  about  thirty-eight  hours'  incubation,  viewed  from  the  ventral  surface.     X  26 

(Duval.) 

(1)  the  sinus  venosus;  (2)  the  primitive  atrium;  (3)  the  primitive  ventricle;  (4)  the 
bulbus  cordis,  and  (5)  the  truncus  arteriosus  (Figs.  461,  462).  The  constriction 
between  the  atrium  and  ventricle  constitutes  the  atrial  canal,  and  indicates  the  site 
of  the  future  atrioventricular  valves. 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM 


509 


The  sinus  venosus  is  at  first  situated  in  the  septum  transversum  (a  layer  of 
mesoderm  in  which  the  liver  and  the  central  tendon  of  the  diaphragm  are  devel- 
oped) behind  the  primitive  atrium,  and  is  formed  by  the  union  of  the  vitelline 
veins.  The  veins  or  ducts  of  Cuvier  from  the  body  of  the  embryo  and  the  umbilical 
veins  from  the  placenta  subsequently  open  into  it  (Fig.  463) .  The  sinus  is  at  first 
place  transversely,  and  opens  by  a  median  aperture  into  the  primitive  atrium. 


BvJhus  cordis 
Ventricle 

Atrium 

Sinus  venosus 

Vitelline  veins 


Fia.  461. — Diagram  to  illustrate  the  simple  tubular 
condition  of  the  heart.  (Drawn  from  Ecker-Ziegler 
model.) 


Fio. 


462. — Heart  of  human  embryo  of  about  fourteen 
days.     (From  model  by  His.) 


Soon,  however,  it  assumes  an  oblique  position,  and  becomes  crescentic  in  form;  its 
right  half  or  horn  increases  more  rapidly  than  the  left,  and  the  opening  into  the 
atrium  now  communicates  with  the  right  portion  of  the  atrial  cavity.  The  right 
horn  and  transverse  portion  of  the  sinus  ultimately  become  incorporated  with  and 
form  a  part  of  the  adult  right  atrium,  the  line  of  union  between  it  and  the  auricula 
being  indicated  in  the  interior  of  the  atrium  by  a  vertical  crest,  the  crista  terminalis 
of  His.     The  left  horn,  which  ultimately  receives  only  the  left  duct  of  Cuvier, 


BvJbus  cordis 

Ventricle  — 
Duct  of  Cuvier 

Cardinal  vein 


Maxillary  process 
Stomodeum 
Mandibular  arch 


Atrium 

Bile-duct 
Umbilical  t'et'n 


Fig.  403. — Heart  of  human  embryo  of  about  fifteen  days.     (Reconstruction  by  His.) 

persists  as  the  coronary  sinus  (Fig.  464) .  The  vitelline  and  umbilical  veins  are  soon 
replaced  by  a  single  vessel,  the  inferior  vena  cava,  and  the  three  veins  (inferior  vena 
cava  and  right  and  left  Cuvierian  ducts)  open  into  the  dorsal  aspect  of  the  atrium 
by  a  common  slit-like  aperture  (Fig.  465).  The  upper  part  of  this  aperture  repre- 
sents the  opening  of  the  permanent  superior  vena  cava,  the  lower  that  of  the  inferior 
vena  cava,  and  the  intermediate  part  the  orifice  of  the  coronary  sinus.    The  slit- 


510 


ANGIOLOGY 


I 


like  aperture  lies  obliquely,  and  is  guarded  by  two  halves,  the  right  and  left  venous 
valves;  above  the  opening  these  unite  with  each  other  and  are  continuous  with  a 


Left  duct  of 
Cuvier 


Opening  into 
atrium 


Right  duct  of 
Cuvier 


Fig.  464. — Dorsal  surface  of  heart  of  human  embryo  of  thirty-five  days.     (From  model  by  Hi«.) 

ISeptum  6'pv/rium 

Opening  of  sinus  venosus 
Left  venous  valve 

Septum  primum 


Right  venous 
valve 


Spina  vestibvXi 

Posterior  endocardial 
cushion 

Atrial  canal 


Septum  inferius 

Fig.  465. — Interior  of  dorsal  half  of  heart  from  a  human  embryo  of  about  thirty  days.      (From  model  by  His.) 


fold  named  the  septum  spurium;  below  the  opening  they  fuse  to  form  a  triangular 
thickening — the  spina  vestibuli.     The  right  venous  valve  is  retained;  a  small 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM 


511 


hseptum,  the  sinus  septum,  grows  from  the  posterior  wall  of  the  sinus  venosus  to  fuse 
'with  the  valve  and  divide  it  into  two  parts — an  upper,  the  valve  of  the  inferior 
vena  cava,  and  a  lower,  the  valve  of  the  coronary  sinus  (Fig.  468).  The  extreme 
upper  portion  of  the  right  venous  valve,  together  with  the  septum  spurium,  form 


Bight  atriwm 
Bulbus  cordis 


Left  atrium 
Atrial  canal 

Ventricle 


Fig.  466. — Heart  showing  expansion  of  the  atria.     (Drawn  from  Ecker-Zeigler  model.) 

the  crista  terminalis  already  mentioned.  The  upper  and  middle  thirds  of  the  left 
/^enous  valve  disappear;  the  lower  third  is  continued  into  the  spina  vestibuli, 
md  later  fuses  with  the  septum  secundum  of  the  atria  and  takes  part  in  the  forma- 
tion of  the  limbus  fossae  ovalis. 


Septum  secundum 
Opening  of  coronary  sinu^ 

Septum  spurium 


Right  venous  volt 

night  atrioventricular 
opening 


Left  atrioventricular 

opening 
Septum  intermedium 


Septum  inferius 
Fig.  467. — Interior  of  dorsal  half  of  heart  of  human  embryo  of  about  thirty-five  days. 


(From  model  by  His.) 


The  atrial  canal  is  at  first  a  short  straight  tube  connecting  the  atrial  with  the 

ventricular  portion  of  the  heart,  but  its  growth  is  relatively  slow,  and  it  becomes 

[overlapped  by  the  atria  and  ventricles  so  that  its  position  on  the  surface  of  the  heart 

[is  indicated  only  by  an  annular  constriction  (Fig.  466).    Its  lumen  is  reduced  to  a 


512 


ANGIOLOGY 


I 


transverse  slit,  and  two  thickenings  appear,  one  on  its  dorsal  and  another  on  its 
ventral  wall.  These  thickenings,  or  endocardial  cushions  (Fig.  465)  as  they  are 
termed,  project  into  the  canal,  and,  meeting  in  the  middle  line,  unite  to  form  the 
septum  intermedium  which  divides  the  canal  into  two  channels,  the  future  right  and 
left  atrioventricular  orifices. 

The  primitive  atrium  grows  rapidly  and  partially  encircles  the  bulbus  cordis; 
the  groove  against  which  the  bulbus  cordis  lies  is  the  first  indication  of  a  division 
into  right  and  left  atria.  The  cavity  of  the  primitive  atrium  becomes  subdivided 
into  right  and  left  chambers  by  a  septum,  the  septum  primum  (Fig.  465),  which 
grows  downward  into  the  cavity.  For  a  time  the  atria  communicate  with  each 
other  by  an  opening,  the  ostium  primum  of  Bom,  below  the  free  margin  of  the  septum. 
This  opening  is  closed  by  the  union  of  the  septum  primum  with  the  septum  inter- 
medium, and  the  communication  between  the  atria  is  reestablished  through  an 
opening  which  is  developed  in  the  upper  part  of  the  septum  primum;  this  opening 
is  known  as  the  foramen  ovale  (ostium  secundum  of  Born)  and  persists  imtil  birth. 


Left  duct  of  Cuvier 


Opening  of  coronary 
sinus 


Foramen  ovale 
Probe  in  aorta 
Aortic  septum 

Septum 

intermedium 


Septum 
iuferius 


Fig.  468. — Same  heart  as  in  Fig.  467,  opened  on  right  side.      (From  model  by  His.) 

A  second  septum,  the  septum  secundum  (Figs,  467,  468),  semilunar  in  shape,  grows 
downward  from  the  upper  wall  of  the  atrium  immediately  to  the  right  of  the 
primary  septum  and  foramen  ovale.  Shortly  after  birth  it  fuses  with  the  primary 
septum,  and  by  this  means  the  foramen  ovale  is  closed,  but  sometimes  the  fusion 
is  incomplete  and  the  upper  part  of  the  foramen  remains  patent.  The  limbus  fossae 
ovalis  denotes  the  free  margin  of  the  septum  secundum.  Issuing  from  each  lung 
is  a  pair  of  pulmonary  veins;  each  pair  unites  to  form  a  single  vessel,  and  these  in 
turn  join  in  a  common  trunk  which  opens  into  the  left  atrium.  Subsequently 
the  common  trunk  and  the  two  vessels  forming  it  expand  and  form  the  vestibule 
or  greater  part  of  the  atrium,  the  expansion  reaching  as  far  as  the  openings  of  the 
four  vessels,  so  that  in  the  adult  all  four  veins  open  separately  into  the  left  atrium. 
The  primitive  ventricle  becomes  divided  by  a  septum,  the  septum  inferius  or 
ventricular  septiun  (Figs.  465,  466,  467),  which  grows  upward  from  the  lower  part 
of  the  ventricle,  its  position  being  indicated  on  the  surface  of  the  heart  by  a  furrow. 
Its  dorsal  part  increases  more  rapidly  than  its  ventral  portion,  and  fuses  with  the 
dorsal  part  of  the  "septum  intermedium.    For  a  time  an  interventricular  foramen 


I 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM 


513 


exists  above  its  ventral  portion  (Fig.  468),  but  this  foramen  is  ultimately  closed  by 
[the  fusion  of  the  aortic  septum  .with  the  ventricular  septum. 


Fig.  469. — Diagrams  to  illustrate  the  transformation  of  the  bulbus  cordis.     (Keith.)     Ao.  Truncus  arteriosus. 
Au.  Atrium.     B.  Bulbus  cordis.     RV.   Right  ventricle.     LV.  Left  ventricle.     P.  Pulmonary  artery. 

When  the  heart  assumes  its  S-shaped  form  the  bulbus  cordis  lies  ventral  to  and 
"in  front  of  the  primitive  ventricle.  The  adjacent  walls  of  the  bulbus  cordis  and 
ventricle  approximate,  fuse,  and  finally  disappear,  and  the  bulbus  cordis  now 


Aortic  septum 


Aortic  septum 


Common  atrio- 
ventricular aperture 


Right 
ventricle 


Puimonary 
artery 


Aorta 


Right  atrio- 
ventricular 
orifice 


Septum, 
inferiv^ 


Left 
ventricle 


Left  atrio- 
ventricular 
orifice 


Right 
ventricle 


Septum  inferius 


Left 
ventricle 


Fig.  470. — Diagrams  to  show  the  development  of  the  septum  of  the  aortic  bulb  and  of  the  ventricles.     (Born.) 

communicates  freely  with  the  right  ventricle,  while  the  junction  of  the  bulbus  with 
the  truncus  arteriosus  is  brought  directly  ventral  to  and  applied  to  the  atrial  canal. 
By  the  upgrowth  of  the  ventricular  septum  the  bulbus  cordis  is  in  great  measure 


Aorta 


Aorta 


Aorta 


f 

■  H      Fig.  471. — Transverse  sections  through  the  aortic  bulb  to  show  the  growth  of  the  aortic  septum.    The  lowest 
H  V  section  is  on  the  left,  the  highest  on  the  right  of  the  figure.      (After  His.) 


Pulmonary  artery 


Pulmo- 
nary artery 


Pulmonary  artery 


separated  from  the  left  ventricle,  but  remains  an  integral  part  otthe  right  ventricle, 
of  which  it  forms  the  infundibulum  (Fig.  469). 
33 


[N&IOLOGY 


I 


The  tnincus  arteriosus  and  bulbus  cordis  are  divided  by  the  aortic  septum  (Fig. 
470).  This  make.s  its  appearance  in  three  portions.  (1)  Two  distal  ridge-like 
thickenings  project  into  the  lumen  of  the  tube;  these  increase  in  size,  and  ultimately 
meet  and  fuse  to  form  a  septum,  which  takes  a  spiral  course  toward  the  proximal 
end  of  the  truncus  arteriosus.  It  divides  the  distal  part  of  the  truncus  into  t^^•o 
vessels,  the  aorta  and  pulmonary  artery,  which  lie  side  by  side  above,  but  near 
the  heart  the  pulmonary  artery  is  in  front  of  the  aorta.  (2)  Four  endocardial 
cushions  appear  in  the  proximal  part  of  the  truncus  arteriosus  in  the  region  of  the 
future  semilunar  valves;  the  manner  in  which  these  are  related  to  the  aortic  septum 
is  described  below.     (3)  Two  endocardial  thickenings — anterior  and  posterior — 


Second  aortic  arch 
Third  aortic  arch 


First  aortic  arch 


Avditory  vesicle 


Primitive  jugular  vein 
Fourth  aortic  arch 

Sixth  aortic  arch 
Dorsal  aorta 


Cardinal  vein 


Digestive  tube 


Hind-gut 


Umbilical  vein 


Olfactory  pit 


Maxillary  process 
First  branchial  groove 
Mandibular  arch 

BriUnis  cordis 
A  trium 
Duct  of  Cuvier 
Ventricle 


Allantoia 
Umbilical  artery 


Fig.  472. — Profile  view  of  a  human  embryo  estimated  at  twenty  or  twenty-one  days  old.     (After  His.) 


develop  in  the  bulbus  cordis  and  unite  to  form  a  short  septum;  this  joins  above  with 
the  aortic  septum  and  below  with  the  ventricular  septum.  The  septum  grows  down 
into  the  ventricle  as  an  oblique  partition,  which  ultimately  blends  with  the  ven- 
tricular septum  in  such  a  way  as  to  bring  the  bulbus  cordis  into  communication 
with  the  pulmonary  artery,  and  through  the  latter  with  the  sixth  pair  of  aortic 
arches;  while  the  left  ventricle  is  brought  into  continuity  with  the  aorta,  which 
communicates  with  the  remaining  aortic  arches. 

The  Valves  of  the  Heart. — The  atrioventricular  valves  are  developed  in  relation  to 
the  atrial  canal.  By  the  upward  expansion  of  the  bases  of  the  ventricles  the  canal 
becomes  invaginated  into  the  ventricular  cavities.  The  invaginated  margin  forms 
the  rudiments  of  the  lateral  cusps  of  the  atrioventricular  valves;  the  mesial  or 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM 


515 


^■septal  cusps  of  the  valves  are  developed  as  downward  prolongations  of  the  septum 

^'intermedium  (Fig.  467).    The  aortic  and  pulmonary  semilunar  valves  are  formed 

from  four  endocardial  thickenings — an  anterior,  a  posterior,  and  two  lateral — 

■which  appear  at  the  proximal  end  of  the  truncus  arteriosus.  As  the  aortic  septum 
^rows  downward  it  divides  each  of  the  lateral  thickenings  into  two,  thus  giving 
jHse  to  six  thickenings — the  rudiments  of  the  semilunar  valves — three  at  the  aortic 
and  three  at  the  pulmonary  orifice  (Fig.  471). 

Further  Development  of  the  Arteries. — Recent  observations  show  that  practi- 
cally none  of  the  main  vessels  of  the  adult  arise  as  such  in  the  embryo.  In  the  site 
of  each  vessel  a  capillary  network  forms,  and  by  the  enlargement  of  definite  paths 
in  this  the  larger  arteries  and  veins  are  developed.  The  branches  of  the  main 
arteries  are  not  always  simple  modifications  of  the  vessels  of  the  capillary  network, 
but  may  arise  as  new  outgrowths  from  the  enlarged  stem. 


Right  subclavian 
artery 


Rigid  pulmonary 
artery 


Trunk  of  pulmonary 
artery 


External  carotid 

Ventral  aorta 

Internal  carotid 
Common  carotid 

Aortic  arch 

Ductus  arteriosus 
Vertebral  artery 

Subclavian  artery 
Left  pulmonary  artery 


FiQ.  473. — Scheme  of  the  aortic  arches  and  their  destination.     (Modified  from  Kollmann.) 


It  has  been  seen  (page  506)  that  each  primitive  aorta  consists  of  a  ventral  and 
a  dorsal  part  w^hich  are  continuous  through  the  first  aortic  arch.  The  dorsal  aortae 
at  first  run  backward  separately  on  either  side  of  the  notochord,  but  about  the 
third  w^eek  they  fuse  from  about  the  level  of  the  fourth  thoracic  to  that  of  the  fourth 
lumbar  segment  to  form  a  single  trunk,  the  descending  aorta.  The  first  aortic 
arches  run  through  the  mandibular  arches,  and  behind  them  five  additional  pairs 
are  developed  within  the  visceral  arches;  so  that,  in  all,  six  pairs  of  aortic  arches 
are  formed  (Figs.  472,  473).  The  first  and  second  arches  pass  between  the  ventral 
and  dorsal  aortae,  while  the  others  arise  at  first  by  a  common  trunk  from  the  truncus 
arteriosus,  but  end  separately  in  the  dorsal  aortae.  As  the  neck  elongates,  the 
fVentral  aortae  are  draw^n  out,  and  the  third  and  fourth  arches  arise  directly  from 

ese  vessels. 

In  fishes  these  arches  persist  and  give  off  branches  to  the  gills,  in  which  the 
lood  is  oxygenated.    In  mammals  some  of  them  remain  as  permanent  structures, 

hile  others  disappear  or  become  obliterated  (Fig.  473) . 


516 


ANGIOLOGY 


I 


The  Anterior  Ventral  Aortae. — ^These  persist  on  both  sides.  The  right  forms  («) 
the  innominate  artery,  (b)  the  right  common  and  external  carotid  arteries.  The 
left  gives  rise  to  (a)  the  short  portion  of  the  aortic  arch,  which  reaches  from  the 
origin  of  the  innominate  artery  to  that  of  the  left  common  carotid  artery;  (6)  the 
left  common  and  external  carotid  arteries. 

The  Aortic  Arches. — The  first  and  second  arches  disappear  early,  but  the  dorsal 
end  of  the  second  gives  origin  to  the  stapedial  artery  (Fig.  474),  a  vessel  which 
atrophies  in  man  but  persists  in  some  mammals.  It  passes  through  the  ring  of  the 
stapes  and  divides  into  supraorbital,  infraorbital,  and  mandibular  branches  which 
follow  the  three  divisions  of  the  trigeminal  nerve.     The   infraorbital   and   mari- 

Post.  cerebral  a. 


Ant.  cerebral  a. 

Supraorbital  br 
of  stapedial  a. 

Trigeminal  nerve 

Maxillary  nerve 
Infraorbital  a. 

Mandibular  nerve 

Mandibular  a 
Ext.  max.  a. 


Stapedial  a. 


Int.  carotid  a. 


Common  carotid  a 


Aortic  arch 

PulmoTiary  arch 

Pulmonary  art. 

Dorsal  aorta 
FiQ.  474. — Diagram  showing  tiie  origins  of  tlie  main  branches  of  the  carotid  arteries.     (Founded  on  Tandler.) 

dibular  arise  from  a  common  stem,  the  terminal  part  of  which  anastomoses  with 
the  external  carotid.  On  the  obliteration  of  the  stapedial  artery  this  anastomosis 
enlarges  and  forms  the  internal  maxillary  artery,  and  the  branches  of  the  stapedial 
artery  are  now  branches  of  this  vessel.  The  common  stem  of  the  infraorbital  and 
mandibular  branches  passes  between  the  two  roots  of  the  auriculotemporal  nerve 
and  becomes  the  middle  meningeal  artery ;  the  original  supraorbital  branch  of  the 
stapedial  is  represented  by  the  orbital  twigs  of  the  middle  meningeal.  The  third 
aortic  arch  constitutes  the  commencement  of  the  internal  carotid  artery,  and  is 
therefore  named  the  carotid  arch.  The  fourth  right  arch  forms  the  right  sub- 
clavian as  far  as  the  origin  of  its  internal  mammary  branch ;  while  the  fourth  left 
arch  constitutes  the  arch  of  the  aorta  between  the  origin  of  the  left  carotid  artery 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM  517 


^|and  the  termination  of  the  ductus  arteriosus.  The  fifth  arch  disappears  on  both 
sides.  The  sixth  right  arch  disappears;  the  sixth  left  arch  gives  off  the  pulmonary 
arteries  and  forms  the  ductus  arteriosus;  this  duct  remains  pervious  during  the 
whole  of  fetal  life,  but  is  obliterated  a  few  days  after  birth.  His  showed  that  in  the 
early  embryo  the  right  and  left  arches  each  gives  a  branch  to  the  lungs,  but  that 
later  both  pulmonary  arteries  take  origin  from  the  left  arch. 

The  Dorsal  Aortse.— In  front  of  the  third  aortic  arches  the  dorsal  aortae  persist 
and  form  the  continuations  of  the  internal  carotid  arteries;  these  arteries  pass  to  the 
brain  and  each  divides  into  an  anterior  and  a  posterior  branch,  the  former  giving 
off  the  ophthalmic  and  the  anterior  and  middle  cerebral  arteries,  while  the  latter 
turns  back  and  joins  the  cerebral  part  of  the  vertebral  artery.  Behind  the  third 
arch  the  right  dorsal  aorta  disappears  as  far  as  the  point  where  the  two  dorsal 
.aortse  fuse  to  form  the  descending  aorta.    The  part  of  the  left  dorsal  aorta  between 

Ifche  third  and  fourth  arches  disappears,  while  the  remainder  persists  to  form 
phe  descending  part  of  the  arch  of  the  aorta.    A  constriction,  the  aortic  isthmus,  is 
jfeometimes  seen  in  the  aorta  between  the  origin  of  the  left  subclavian  and  the 
attachment  of  the  ductus  arteriosus. 

Sometimes  the  right  subclavian  artery  arises  from  the  aortic  arch  distal  to  the 
origin  of  the  left  subclavian  and  passes  upward  and  to  the  right  behind  the  trachea 
and  esophagus.  This  condition  may  be  explained  by  the  persistence-  of  the  right 
dorsal  aorta  and  the  obliteration  of  the  fourth  right  arch. 

In  birds  the  fourth  right  arch  forms  the  arch  of  the  aorta;  in  reptiles  the  fourth 

■  -arch  on  both  sides  persists  and  gives  rise  to  the  double  aortic  arch  in  these  animals. 
I  The  heart  originally  lies  on  the  ventral  aspect  of  the  pharynx,  immediately 
behind  the  stomodeum.  With  the  elongation  of  the  neck  and  the  development 
of  the  lungs  it  recedes  within  the  thorax,  and,  as  a  consequence,  the  anterior 
ventral  aortse  are  draw^n  out  and  the  original  position  of  the  fourth  and  fifth  arches 
is  greatly  modified.  Thus,  on  the  right  side  the  fourth  recedes  to  the  root  of  the 
neck,  while  on  the  left  side  it  is  withdrawn  within  the  thorax.  The  recurrent 
nerves  originally  pass  to  the  larynx  under  the  sixth  pair  of  arches,  and  are  there- 
fore pulled  backward  with  the  descent  of  these  structures,  so  that  in  the  adult  the 
left  nerve  hooks  around  the  ligamentum  arteriosum;  owing  to  the  disappearance  of 
the  fifth  and  the  sixth  right  arches  the  right  nerve  hooks  around  that  immediately 
above  them,  i.  e.,  the  commencement  of  the  subclavian  artery.  Segmental  arteries 
arise  from  the  primitive  dorsal  aortse  and  course  between  successive  segments. 
The  seventh  segmental  artery  is  of  special  interest,  since  it  forms  the  lower  end  of 
■  pthe  vertebral  artery  and,  when  the  forelimb  bud  appears,  sends  a  branch  to  it 
(the  subclavian  artery).  From  the  seventh  segmental  arteries  the  entire  left 
subclavian  and  the  greater  part  of  the  right  subclavian  are  formed.  The  second 
pair  of  segmental  arteries  accompany  the  hypoglossal  nerves  to  the  brain  and  are 
named  the  hypoglossal  arteries.  Each  sends  forward  a  branch  which  forms  the 
cerebral  part  of  the  vertebral  artery  and  anastomoses  with  the  posterior  branch 
of  the  internal  carotid.  The  two  vertebrals  unite  on  the  ventral  surface  of  the 
hind-brain  to  form  the  basilar  artery.  Later  the  hypoglossal  artery  atrophies 
and  the  vertebral  is  connected  with  the  first  segmental  artery.  The  cervical  part 
of  the  vertebral  is  developed  from  a  longitudinal  anastomosis  between  the  first 
seven  segmental  arteries,  so  that  the  seventh  of  these  ultimately  becomes  the  source 
of  the  artery.  As  a  result  of  the  growth  of  the  upper  limb  the  subclavian  artery 
increases  greatly  in  size  and  the  vertebral  then  appears  to  spring  from  it. 

Recent  observations  show  that  several  segmental  arteries  contribute  branches  to 
the  upper  limb-bud  and  form  in  it  a  free  capillary  anastomosis.  Of  these  branches, 
only  one,  viz.,  that  derived  from  the  seventh  segmental  artery,  persists  to  form 
the  subclavian  artery.  The  subclavian  artery  is  prolonged  into  the  limb  under 
the  names  of  the  axillary  and  brachial  arteries,  and  these  together  constitute  the 


518 


ANGIOLOGY 


I 


arterial  stem  for  the  upper  arm,  the  direct  continuation  of  this  stem  in  the  forearm 
is  the  volar  interosseous  artery.  A  branch  which  accompanies  the  median  nerA^e 
soon  increases  in  size  and  forms  the  main  vessel  (median  artery)  of  the  forearm, 
while  the  volar  interosseous  diminishes.  Later  the  radial  and  ulnar  arteries  are 
developed  as  branches  of  the  brachial  part  of  the  stem  and  coincidently  with  their 
enlargement  the  median  artery  recedes;  occasionally  it  persists  as  a  vessel  of  some 
considerable  size  and  then  accompanies  the  median  nerve  into  the  palm  of  the  hand. 
The  primary  arterial  stem  for  the  lower  limb  is  formed  by  the  inferior  gluteal 
(sciatic)  artery,  which  accompanies  the  sciatic  nerve  along  the  posterior  aspect  of 
the  thigh  to  the  back  of  the  knee,  whence  it  is  continued  as  the  peroneal  artery. 
This  arrangement  exists  in  reptiles  and  amphibians.  The  femoral  artery  arises 
later  as  a  branch  of  the  common  iliac,  and,  passing  down  the  front  and  medial 
side  of  the  thigh  to  the  bend  of  the  knee,  joins  the  inferior  gluteal  artery.  The 
femoral  quickly  enlarges,  and,  coincidently  with  this,  the  part  of  the  inferior  gluteal 
immediately  above  the  knee  undergoes  atrophy.  The  anterior  and  posterior  tibial 
arteries  are  branches  of  the  main  arterial  stem. 


Anterior  detacJied  portions 
of  umbilical  veins 


Venae  revehentes 


Stomach 
Venae  advehentes 
Pancreas 
Bile-duct 


Obliterated  portions 
of  venous  rings 

Right  umbilical  vein 


Ductus  venosus 


Liver 


Left  umbilical  vein 


Dicodenum 


Fig.  475. — The  liver  and  the  veins  in  connection  with  it,  of  a  human  embryo,  twenty-four  or  twenty-five  days  old, 

as  seen  from  the  ventral  surface.     (After  His.) 

Further  Development  of  the  Veins. — The  formation  of  the  great  veins  of  the 
embryo  may  be  best  considered  by  dividing  them  into  two  groups,  visceral  and 
parietal. 

The  Visceral  Veins. — The  visceral  veins  are  the  two  vitelline  or  omphalomesenteric 
veins  bringing  the  blood  from  the  yolk-sac,  and  the  two  umbilical  veins  returning 
the  blood  from  the  placenta;  these  four  veins  open  close  together  into  the  sinus 
venosus. 

The  Vitelline  Veins  run  upward  at  first  in  front,  and  subsequently  on  either 
side  of  the  intestinal  canal.  They  unite  on  the  ventral  aspect  of  the  canal,  and 
beyond  this  are  connected  to  one  another  by  two  anastomotic  branches,  one  on  the 
dorsal,  and  the  other  on  the  ventral  aspect  of  the  duodenal  portion  of  the  intestine, 
which  is  thus  encircled  by  two  venous  rings  (Fig.  475) ;  into  the  middle  or  dorsal 
anastomosis  the  superior  mesenteric  vein  opens.  The  portions  of  the  veins  above 
the  upper  ring  become  interrupted  by  the  developing  liver  and  broken  up  by  it  into 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM 


519 


I 

^■a  plexus  of  small  capillary-like  vessels  termed  sinusoids  (Minot).    The  branches 

^B conveying  the  blood  to  this  plexus  are  named  the  venae  advehentes,  and  become 

^■the  branches  of  the  portal  vein;  while  the  vessels  draining  the  plexus  into  the 

sinus  venosus  are  termed  the  venae  revehentes,  and  form  the  future  hepatic  veins 

■  (Figs.  475,  476).  Ultimately  the  left  vena  revehens  no  longer  communicates 
directly  with  the  sinus  venosus,  but  opens  into  the  right  vena  revehens.  The 
persistent  part  of  the  upper  venous  ring,  above  the  opening  of  the  superior  mes- 
enteric vein,  forms  the  trunk  of  the  portal  vein. 


Right  primitive  jugular  vein 
Right  cardinal  vein 

Right  ditx^t  of  Cuvier 

Sinus  venosus 
Right  hepatic  vein 

Portal  vein 

Portal  vein 
Right  umbilical  vein 

Umbilical  cord' 


Left  primitive 
jugular  vein 

Left  cardinal  vein 


Left  du£t  of  Cuvier 

Left  hepatic  vein 
Left  umbilical  vein 


Left  umbilical  vein 


Pig.  476. — Human  embryo  with  heart  and  anterior  bodv-wall  removed  to  show  the  sinus  venosus  and  its  tributaries. 

(After  His.) 

The  two  Umbilical  Veins  fuse  early  to  form  a  single  trunk  in  the  body-stalk, 
)ut  remain  separate  within  the  embryo  and  pass  forward  to  the  sinus  venosus 
in  the  side  walls  of  the  body.  Like  the  vitelline  veins,  their  direct  connection 
with  the  sinus  venosus  becomes  interrupted  by  the  developing  liver,  and  thus  at 
this  stage  the  whole  of  the  blood  from  the  yolk-sac  and  placenta  passes  through 
the  substance  of  the  liver  before  it  reaches  the  heart.  The  right  umbilical  and 
right  vitelline  veins  shrivel  and  disappear;  the  left  umbilical,  on  the  other  hand, 
becomes  enlarged  and  opens  into  the  upper  venous  ring  of  the  vitelline  veins;  with 
the  atrophy  of  the  yolk-sac  the  left  vitelline  vein  also  undergoes  atrophy  and 
disappears.  Finally  a  direct  branch  is  established  between  this  ring  and  the  right 
hepatic  vein;  this  branch  is  named  the  ductus  venosus,  and,  enlarging  rapidly, 
it  forms  a  wide  channel  through  which  most  of  the  blood,  returned  from  the 
placenta,  is  carried  direct  to  the  heart  without  passing  through  the  liver.  A  small 
proportion  of  the  blood  from  the  placenta  is,  however,  conveyed  from  the  left 
umbilical  vein  to  the  liver  through  the  left  vena  advehens.    The  left  umbilical 


520 


ANGIOLOGY 


I 


vein  and  the  ductus  venosus  undergo  atrophy  and  obliteration  after  birth,  ard 
form  respectively  the  ligamentum  teres  and  ligamentum  venosum  of  the  liver. 

The  Parietal  Veins. — ^The  first  indication  of  a  parietal  system  consists  in  tfie 
appearance  of  two  short  transverse  veins,  the  ducts  of  Cuvier,  which  open,  one 
on  either  side,  into  the  sinus  venosus.  Each  of  these  ducts  receives  an  ascending 
and  descending  vein.  The  ascending  veins  return  the  blood  from  the  parietes 
of  the  trunk  and  from  the  Wolffian  bodies,  and  are  called  cardinal  veins.  The 
descending  veins  return  the  blood  from  the  head,  and  are  called  primitive  jugular 
veins  (Fig.  477).  The  blood  from  the  lower  limbs  is  collected  by  the  right  and 
left  iliac  and  hypogastric  veins,  which,  in  the  earlier  stages  of  development,  open 
into  the  corresponding  right  and  left  cardinal  veins;  later,  a  transverse  branch  (the 
left  common  iliac  vein)  is  developed  between  the  lower  parts  of  the  two  cardinal 
veins  (Fig.  479),  and  through  this  the  blood  is  carried  into  the  right  cardinal  vein. 
The  portion  of  the  left  cardinal  vein  below  the  left  renal  vein  atrophies  and  dis- 
appears up  to  the  point  of  entrance  of  the  left  spermatic  vein;  the  portion  above 


Sinua  venosus 


Primitive  jugular 
Subclavian 

Duct  of  Cuvier 
Vitelline 
Umbilical 
Cardinal 

Svbcardinal 
Renal 


Uxtemal  iliac 
'-^ —  Hypogastric 


Internal  jugular 
External  jugular 
Subclavian 


Dujct  of  Cuvier 

Left  cardinal 
Ductus  venoeus 


Fig.  477. — Scheme  of  arrangement  of  parietal 
veins. 


_  Renal 
Svbcardinal 


EaAemal  iliac 
Hypogastric 


Fio.  478. — Scheme  showing  early  stages  of 
development  of  the  inferior  vena  cava. 


the  left  renal  vein  persists  as  the  hemiazygos  and  accessory  hemiazygos  veins 
and  the  lower  portion  of  the  highest  left  intercostal  vein.  The  right  cardinal  vein 
which  now  receives  the  blood  from  both  lower  extremities,  forms  a  large  venous 
trunk  along  the  posterior  abdominal  wall;  up  to  the  level  of  the  renal  veins  it 
forms  the  lower  part  of  the  inferior  vena  cava.  Above  the  level  of  the  renal  veins 
the  right  cardinal  vein  persists  as  the  azygos  vein  and  receives  the  right  intercostal 
veins,  while  the  hemiazygos  veins  are  brought  into  communication  with  it  by  the 
development  of  transverse  branches  in  front  of  the  vertebral  column  (Figs.  479,  480) 
Inferior  Vena  Cava. — The  development  of  the  inferior  vena  cava  is  associated 
with  the  formation  of  two  veins,  the  subcardinal  veins  (Figs.  477,  478).  These 
lie  parallel  to,  and  on  the  ventral  aspect  of,  the  cardinal  veins,  and  originate  as 
longitudinal  anastomosing  channels  which  link  up  the  tributaries  from  the  mes- 
entery to  the  cardinal  veins;  they  communicate  with  the  cardinal  veins  above  and 
below,  and  also  by  a  series  of  transverse  branches.  The  two  subcardinals  are  for 
a  time  connected  with  each  other  in  front  of  the  aorta  by  cross  branches,  but  these 
disappear  and  are  replaced  by  a  single  transverse  channel  at  the  level  where  the 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM 


521 


renal  veins  join  the  cardinals,  and  at  the  same  level  a  cross  communication  is 
established  on  either  side  between  the  cardinal  and  subcardinal  (Fig.  478).  The 
portion  of  the  right  subcardinal  behind  this  cross  communication  disappears,  while 


Left  innominate 


Internal  jugular 
External  jtugular 


Duct  of  Cuvier 


Left  cardinal 


Left  suprarenal 
Left  renal 


Bight  innominate 
Superior  vena  cava. 


Prerenal  part  of 
inferior  vena  cava 


Postrenal  pari  of 
inferior  vena  cava 


Left  common  iliac 
External  iliac 
Hypogastric 
'  FiG-  -179. — Diagram  showing  development  of  main  crosa  branches  between  jugulars  and  between  cardinala. 

that  in  front,  i.  e.,  the  prerenal  part,  forms  a  connection  with  the  ductus  venosus 
at  the  point  of  opening  of  the  hepatic  veins,  and,  rapidly  enlarging,  receives  the 


Left  innominate 

1 


Right  innominate- 


Superior  vena  cava 
Azygos  vein 


Prerenal  part  of 
inferior  vena  cava 


f Internal  jugular 

External  jugular 

Subclavian 

Highest  left  intercostal 

Ligament  of  left  vena  cava 

Obliqu£  vein  of  left  atrium 
Coronary  sinus 
Accessory  hemiazygos  vein 


Hemiazygos  vein 
Left  suprarenal 
Left  renal 
-Left  internal  spermatic 


Left  common  iliac  , 

External  iliac 
'Hypogastric 
Fig.  480. — Diagram  showing  completion  of  development  of  the  parietal  veins. 

blood  from  the  postrenal  part  of  the  right  cardinal  through  the  cross  communica- 
tion referred  to.  In  this  manner  a  single  trunk,  the  inferior  vena  cava  (Fig.  480),  is 
formed,  and  consists  of  the  proximal  part  of  the  ductus  venosus,  the  prerenal  part 


522  ANGIOLOGY 


I 


of  the  right  subcardinal  vein,  the  postrenal  part  of  the  right  cardinal  vein,  and  the. 
cross  branch  which  joins  these  two  veins.  The  left  subcardinal  disappears,  excepi: 
the  part  immediately  in  front  of  the  renal  vein,  which  is  retained  as  the  left  supra- 
renal vein.  The  spermatic  .(or  ovarian)  vein  opens  into  the  postrenal  part  of 
the  corresponding  cardinal  vein.  This  portion  of  the  right  cardinal,  as  already 
explained,  forms  the  lower  part  of  the  inferior  vena  cava,  so  that  the  right  spermatic 
opens  directly  into  that  vessel.  The  postrenal  segment  of  the  left  cardinal  dis- 
appears, with  the  exception  of  the  portion  between  the  spermatic  and  renal  vein, 
which  is  retained  as  the  terminal  part  of  the  left  spermatic  vein. 

In  consequence  of  the  atrophy  of  the  Wolffian  bodies  the  cardinal  veins  diminish 
in  size;  the  primitive  jugular  veins,  on  the  other  hand,  become  enlarged,  owing  to 
the  rapid  development  of  the  head  and  brain.  They  are  further  augmented  by 
receiving  the  veins  (siibclavian)  from  the  upper  extremities,  and  so  come  to  form 
the  chief  veins  of  the  Cuvierian  ducts;  these  ducts  gradually'  assume  an  almost 
vertical  position  in  consequence  of  the  descent  of  the  heart  into  the  thorax.  The 
right  and  left  Cuvierian  ducts  are  originally  of  the  same  diameter,  and  are  frequently 
termed  the  right  and  left  superior  venae  cavae.  By  the  development  of  a  transverse 
branch,  the  left  innominate  vein  between  the  two  primitive  jugular  veins,  the 
blood  is  carried  across  from  the  left  to  the  right  primitive  jugular  (Figs.  479,  480). 
The  portion  of  the  right  primitive  jugular  vein  between  the  left  innominate  and 
the  azygos  vein  forms  the  upper  part  of  the  superior  vena  cava  of  the  adult;  the 
lower  part  of  this  vessel,  i.  e.,  below  the  entrance  of  the  azygos  vein,  is  formed  by 
the  right  Cuvierian  duct.  Below  the  origin  of  the  transverse  branch  the  left 
primitive  jugular  vein  and  left  Cuvierian  duct  atrophy,  the  former  constituting 
the  upper  part  of  the  highest  left  intercostal  vein,  while  the  latter  is  represented 
by  the  ligament  of  the  left  vena  cava,  vestigial  fold  of  Marshall,  and  the  oblique 
vein  of  the  left  atrium,  oblique  vein  of  MarshaU  (Fig.  480).  Both  right  and  left 
superior  vense  cavae  are  present  in  some  animals,  and  are  occasionally  found  in  the 
adult  human  being.  The  oblique  vein  of  the  left  atrium  passes  downward  across 
the  back  of  the  left  atrium  to  open  into  the  coronary  sinus,  which,  as  already 
indicated,  repi^sents  the  persistent  left  horn  of  the  sinus  venosus. 

Venous  Sinuses  of  the  Dura  Mater.^ — ^The  primary  arrangement  for  drainage  of 
the  capillaries  of  the  head  (Figs.  481,  488)  consists  of  a  primary  head  vein  which 
starts  in  the  region  of  the  midbrain  and  runs  caudalward  along  the  side  of  the 
brain  tube  to  terminate  at  the  duct  of  Cuvier.  The  primary  head  vein  drains 
three  plexuses  of  capillaries :  the  anterior  dural  plexus,  the  middle  dural  plexus  and 
the  posterior  dural  plexus.  The  growth  of  the  cartilaginous  capsule  of  the  ear  and 
the  growth  and  alteration  in  form  of  the  brain  bring  about  changes  in  this  primary 
arrangement  (Figs.  483-488).  Owing  to  the  growth  of  the  otic  capsule  and  middle 
ear  the  course  of  the  primary  head  vein  becomes  unfavorable  and  a  segment  of  it 
becomes  obliterated.  To  make  the  necessary  adjustment  an  anastomosis  is  estab- 
lished above  the  otic  capsule  (Fig.  483)  and  the  middle  plexus  drains  into  the  poste- 
rior plexus.  Then  the  anteror  plexus  fuses  with  the  middle  plexus  (Fig.  484)  and 
drains  through  it  and  the  newly  estabished  channel,  dorsal  to  the  otic  capsule. 
All  that  remains  of  the  primary  head  vein  is  the  cardinal  portion  or  internal  jugular 
and  the  part  in  the  region  of  the  trigeminal  nerve  which  may  be  called  the  ca\ernous 
^inus.  Into  it  drain  the  orbital  veins.  The  drainage  from  the  cavernous  sinus  is 
now  upward  through  the  original  trunk  of  the  middle  plexus,  which  is  now  the 
superior  petrosal  sinus,  into  the  newly  established  dorsal  channel.  This  dorsal 
channel  is  the  transverse  sinus  (Figs.  485-488).  The  inferior  petrosal  sinus  appears 
later  (Fig.  486).  From  the  anterior  plexus  a  sagittal  plexus  extends  forward  from 
which  develops  the  superior  sagittal  sinus  (Figs.  484^88).     The  straight  sinus  is 

Streeter,  Am.  Jour.  Anat.,  1015.  vol.  xviii. 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM 


523 


Informed  in  the  ventral  part  of  the  sagittal  plexus.  As  the  hemispheres  extend  back- 
fward  these  sinuses  elongate  by  incorporating  the  more  caudal  loops  of  the  plexus. 
rThe  anterior  part  of  the  sinus  is  completed  first. 


PLEXUS  MEIMALIS 


CAPITIS  PRIMA 


SIN.  TRANS. 
PARS  SIGMOID. 


Figs.  481  to  488. — Profile  drawings  of  the  dural  veins  showing  principal  stages  in  their  development  in  human 
embryos  from  4  mm.  to  birth.  It  is  of  particular  interest  to  notice  their  adaptation  to  the  growth  and  changes  in  the 
form  of  the  central  nervous  system.  Fig.  481,  4  mm. ;  Fig.  482,  14  mm. ;  Fig.  483,  18  mm. ;  Fig.  484,  21  mm. ;  Fig.  485, 
,35  mm. ;  Fig.  480,  50  mm.  crown-rump  length;  Fig.  487,  Sb  mm.  crown-rump  length;  Fig.  488,  adult.     (After  StreeterJ 


^_  _  vv  Atiiii.  ,    A   lit,.   • 

I- 


524  ANGIOLOGV 


I 


The  external  jugular  vein  at  first  drains  the  region  behind  the  ear  (posterior 
auricular)  and  enters  the  primitive  jugular  as  a  lateral  tributary.  A  group  of  veins 
from  the  face  and  lingual  region  converge  to  form  a  common  vein,  the  linguo-facial/ 
which  also  terminates  in  the  primitive  jugular.  Later,  cross  communications 
develop  between  the  external  jugular  and  the  linguo-facial,  with  the  result  that 
the  posterior  group  of  facial  veins  is  transferred  to  the  external  jugular. 

THE  THORACIC  CAVITY. 

The  heart  and  lungs  are  situated  in  the  thorax,  the  walls  of  which  afford  them 
protection.  The  heart  lies  between  the  two  lungs,  and  is  enclosed  within  a  fibrous 
bag,  the  pericardium,  while  each  lung  is  invested  by  a  serous  membrane,  the  pleura. 
The  skeleton  of  the  thorax,  and  the  shape  and  boundaries  of  the  cavity,  have  already 
been  described  (page  117). 

The  Cavity  of  the  Thorax. — The  capacity  of  the  cavity  of  the  thorax  does  not 
correspond  with  its  apparent  size  externally,  because  (1)  the  space  enclosed  by 
the  lower  ribs  is  occupied  by  some  of  the  abdominal  viscera;  and  (2)  the  cavity 
extends  above  the  anterior  parts  of  the  first  ribs  into  the  neck.  The  size  of  the 
thoracic  cavity  is  constantly  varying  during  life  with  the  movements  of  the  ribs 
and  diaphragm,  and  with  the  degree  of  distention  of  the  abdominal  viscera. 
From  the  collapsed  state  of  the  lungs  as  seen  when  the  thorax  is  opened  in  the  dead 
body,  it  would  appear  as  if  the  viscera  only  partly  filled  the  cavity,  but  during 
life  there  is  no  vacant  space,  that  which  is  seen  after  death  being  filled  up  by  the 
expanded  lungs. 

The  Upper  Opening  of  the  Thorax. — The  parts  which  pass  through  the  upper 
opening  of  the  thorax  are,  from  before  backward,  in  or  near  the  middle  line,  the 
Sternohyoideus  and  Sternothyreoideus  muscles,  the  remains  of  the  thymus,  the 
inferior  thyroid  veins,  the  trachea,  esophagus,  thoracic  duct,  and  the  Longus 
colli  muscles;  at  the  sides,  the  innominate  artery,  the  left  common  carotid,  left 
subclavian  and  internal  mammary  arteries  and  the  costocervical  trunks,  the 
innominate  veins,  the  vagus,  cardiac,  phrenic,  and  sympathetic  nerves,  the  greater 
parts  of  the  anterior  divisions  of  the  first  thoracic  nerves,  and  the  recurrent  nerve 
of  the  left  side.  The  apex  of  each  lung,  covered  by  the  pleura,  also  projects 
through  this  aperture,  a  little  above  the  level  of  the  sternal  end  of  the  first  rib. 

The  Lower  Opening  of  the  Thorax. — The  lower  opening  of  the  thorax  is  wider 
transversely  than  from  before  backward.  It  slopes  obliquely  downward  and  back- 
ward, so  that  the  thoracic  cavity  is  much  deeper  behind  than  in  front.  The  dia- 
phragm (see  page  404)  closes  the  opening  and  forms  the  floor  of  the  thorax.  The 
floor  is  flatter  at  the  center  than  at  the  sides,  and  higher  on  the  right  side  than  on 
the  left;  in  the  dead  body  the  right  side  reaches  the  level  of  the  upper  border  of 
the  fifth  costal  cartilage,  while  the  left  extends  only  to  the  corresponding  part 
of  the  sixth  costal  cartilage.  From  the  highest  point  on  each  side  the  floor  slopes 
suddenly  downward  to  the  costal  and  vertebral  attachments  of  the  diaphragm; 
this  slope  is  more  marked  behind  than  in  front,  so  that  only  a  narrow  space  is  left 
between  the  diaphragm  and  the  posterior  wall  of  the  thorax. 

THE   PERICARDIUM. 

The  pericardium  (Fig.  489)  is  a  conical  fibro-serous  sac,  in  which  the  heart  and 
the  roots  of  the  great  vessels  are  contained.  It  is  placed  behind  the  sternum  and 
the  cartilages  of  the  third,  fourth,  fifth,  sixth,  and  seventh  ribs  of  the  left  side, 
in  the  mediastinal  cavity. 

Lewis,  American  Journa   of  Anatomy,  February,  1909,  No.  1,  vol.  ix. 


THE  PERICARDIUM 


525 


In  front,  it  is  separated  from  the  anterior  wall  of  the  thorax,  in  the  greater  part 
of  its  extent,  by  the  lungs  and  pleurae;  but  a  small  area, 'somewhat  variable  in  size, 
and  usually  corresponding  with  the  left  half  of  the  lower  portion  of  the  body  of 
Iphe  sternum  and  the  medial  ends  of  the  cartilages  of  the  fourth  and  fifth  ribs  of 
the  left  side,  comes  into  direct  relationship  with  the  chest  wall.  The  lower  extrem- 
ity of  the  thymus,  in  the  child,  is  in  contact  with  the  front  of  the  upper  part  of 
the  pericardium.  Behind,  it  rests  upon  the  bronchi,  the  esophagus,  the  descending 
thoracic  aorta,  and  the  posterior  part  of  the  mediastinal  surface  of  each  lung. 
Laterally,  it  is  covered  by  the  pleurae,  and  is  in  relation  with  the  mediastinal  sur- 
faces of  the  lungs;  the  phrenic  nerve,  with  its  accompanying  vessels,  descends 
between  the  pericardium  and  pleura  on  either  side. 


R.  common  carotid  a. 


JR.  subdavtan  a. 


L.  ccmmon  carotid  a. 


L.  subclavian  a. 


Cut  edges  of  se.rcnis 
'pericardium 


Sup,  vena  cava 


B.  'pulmonarii 
veins 


Fio.  4S9. — Posterior  wall  of  the  pericardial  sac,  showing  the  lines  of  reflection  of  the  serous  pericardium 

on  the  great  vessels. 


Structure  of  the  Pericardiiun. — Although  the  pericardium  is  usually  described  as  a  single  sac, 
an  examination  of  its  structure  shows  that  it  consists  essentially  of  two  sacs  intimately  connected 
with  one  another,  but  totally  different  in  structure.  The  outer  sac,  known  as  the  fibrous  peri- 
cardium, consists  of  fibrous  tissue.  The  inner  sac,  or  serous  pericardium,  is  a  deUcate  mem- 
brane which  Ues  within  the  fibrous  sac  and  lines  its  walls;  it  is  composed  of  a  single  layer  of 


526  ^^^K  ANGIOLOGY 


I 


flattened  cells  resting  on  loose  connective  tissue.  The  heart  invaginates  the  wall  of  the  serous 
sac  from  above  and  behind,  and  practically  obliterates  its  cavity,  the  space  being  merely  a 
potential  one. 

The  fibrous  pericardium  forms  a  flask-shaped  bag,  the  neck  of  which  is  closed  by  its  fusion 
with  the  external  coats  of  the  great  vessels,  while  its  base  is  attached  to  the  central  tendon  anil 
to  the  muscular  fibers  of  the  left  side  of  the  diaphragm.  In  some  of  the  lower  mammals  the 
base  is  either  completely  separated  from  the  diaphragm  or  joined  to  it  by  some  loose  areolar 
tissue;  in  man  much  of  its  diaphragmatic  attachment  consists  of  loose  fibrous  tissue  which  can 
be  readily  broken  down,  but  over  a  small  area  the  central  tendon  of  the  diaphragm  and  the 
pericardium  are  completely  fused.  Above,  the  fibrous  pericardium  not  only  blends  with  the 
external  coats  of  the  great  vessels,  but  is  continuous  with  the  pretracheal  layer  of  the  deep  cervical 
fascia.  By  means  of  these  upper  and  lower  connections  it  is  securely  anchored  within  the  thoracic 
cavity.  It  is  also  attached  to  the  posterior  surface  of  the  sternum  by  the  superior  and  inferior 
stemopericardiac  ligaments ;  the  upper  passing  to  the  manubrium,  and  the  lower  to  the  xiphoid 
process. 

The  vessels  receiving  fibrous  prolongations  from  this  membrane  are:  the  aorta,  the  superior 
vena  cava,  the  right  and  left  pulmonary  arteries,  and  the  four  pulmonary  veins.  The  inferior 
vena  cava  enters  the  pericardium  through  the  central  tendon  of  the  diaphragm,  and  receives 
no  covering  from  the  fibrous  layer. 

The  serous  pericardium  is,  as  already  stated,  a  closed  sac  which  lines  the  fibrous  pericardium 
and  is  invaginated  by  the  heart;  it  therefore  consists  of  a  visceral  and  a  parietal  portion.  The 
visceral  portion,  or  epicardium,  covers  the  heart  and  the  great  vessels,  and  from  the  latter  is 
continuous  with  the  parietal  layer  which  Unes  the  fibrous  pericardium.  The  portion  which 
covers  the  vessels  is  arranged  in  the  form  of  two  tubes.  The  aorta  and  pulmonary  artery  are 
enclosed  in  one  tube,  the  arterial  mesocardium.  The  superior  and  inferior  venae  cavae  and  the 
four  pulmonary  veins  are  enclosed  in  a  second  tube,  the  venous  mesocardium,  the  attachment 
of  which  to  the  parietal  layer  presents  the  shape  of  an  inverted  U.  The  cul-de-sac  enclosed  between 
the  limbs  of  the  U  lies  behind  the  left  atrium  and  is  known  as  the  oblique  sinus,  while  the  passage 
between  the  venous  and  arterial  mesocardia — i.  e.,  between  the  aorta  and  puhnonary  artery  in 
front  and  the  atria  behind — is  termed  the  transverse  sinus. 

The  Ligament  of  the  Left  Vena  Cava. — Between  the  left  pulmonary  artery  and  subjacent 
pulmonary  vein  is  a  triangular  fold  of  the  serous  pericardium;  it  is  known  as  the  ligament  of  the 
left  vena  cava  (vestigial  fold  of  Marshall) .  It  is  formed  by  the  duplicature  of  the  serous  layer 
over  the  remnant  of  the  lower  part  of  the  left  superior  vena  cava  (duct  of  Cuvier) ,  which  becomes 
obliterated  during  fetal  life,  and  remains  as  a  fibrous  band  stretching  from  the  highest  left  inter- 
costal vein  to  the  left  atrium,  where  it  is  continuous  with  a  small  vein,  the  vein  of  the  left  atrium 
(oblique  vein  of  Marshall),  which  opens  into  the  coronary  sinus. 

The  arteries  of  the  pericardium  are  derived  from  the  internal  mammary  and  its  musculo- 
phrenic branch,  and  from  the  descending  thoracic  aorta. 

The  nerves  of  the  percardium  are  derived  from  the  vagus  and  phrenic  nerves,  and  the  sympa- 
thetic trunks. 

THE  HEART  (COR). 

The  heart  is  a  hollow  muscular  organ  of  a  somewhat  conical  form;  it  lies  between 
the  lungs  in  the  middle  mediastinum  and  is  enclosed  in  the  pericardium  (Fig.  490). 
It  is  placed  obliquely  in  the  chest  behind  the  body  of  the  sternum  and  adjoining 
parts  of  the  rib  cartilages,  and  projects  farther  into  the  left  than  into  the  right 
half  of  the  thoracic  cavity,  so  that  about  one-third  of  it  is  situated  on  the  right 
and  two-thirds  on  the  left  of  the  median  plane. 

Size. — The  heart,  in  the  adult,  measures  about  12  cm.  in  length,  8  to  9  cm.  in 
breadth  at  the  broadest  part,  and  6  cm.  in  thickness.  Its  weight,  in  the  male, 
varies  from  280  to  340  grams;  in  the  female,  from  230  to  280  grams.  The  heart 
continues  to  increase  in  weight  and  size  up  to  an  advanced  period  of  life;  this 
increase  is  more  marked  in  men  than  in  women. 

Component  Parts.— As  has  already  been  stated  (page  497),  the  heart  is  sub- 
divided by  septa  into  right  and  left  halves,  and  a  constriction  subdivides  each 
half  of  the  organ  into  two  cavities,  the  upper  cavity  being  called  the  atrium,  the 
lower  the  ventricle.  The  heart  therefore  consists  of  four  chambers,  viz.,  right  and 
left  atria,  and  right  and  left  ventricles. 

The  division  of  the  heart  into  four  cavities  is  indicated  on  its  surface  by  grooves. 
The  atria  are  separated  from   the  ventricles    by  the  coronary  sulcus  (auriculo- 


THE  HEART 


527 


[ventricular  groove);  this  contains  the  trunks  of  the  nutrient  vessels  of  the  heart, 
and  is  deficient  in  front,  where  it  is  crossed  by  the  root  of  the  pulmonary  artery. 
The  interatrial  groove,  separating  the  two  atria,  is  scarcely  marked  on  the  posterior 
surface,  while  anteriorly  it  is  hidden  by  the  pulmonary  artery  and  aorta.  The 
ventricles  are  separated  by  two  grooves,  one  of  which,  the  anterior  longitudinal 
sulcus,  is  situated  on  the  sternocostal  surface  of  the  heart,  close  to  its  left  margin, 
the  other  posterior  longitudinal  sulcus,  on  the  diaphragmatic  surface  near  the  right 
margin ;  these  grooves  extend  from  the  base  of  the  ventricular  portion  to  a  notch, 
the  incisura  apicis  cordis,  on  the  acute  margin  of  the  heart  just  to  the  right  of  the 


i^pex. 


Cut  edge  of  pericardium 


Fig.  490. — Front  view  of  heart  and  lungs. 

The  base  {basis  cordis)  (Fig.  491),  directed  upward,  backward,  and  to  the  right, 
is  separated  from  the  fifth,  sixth,  seventh,  and  eighth  thoracic  vertebrae  by  the 
esophagus,  aorta,  and  thoracic  duct.  It  is  formed  mainly  by  the  left  atrium, 
and,  to  a  small  extent,  by  the  back  part  of  the  right  atrium.  Somewhat  quadri- 
lateral in  form,  it  is  in  relation  above  with  the  bifurcation  of  the  pulmonary  artery, 
and  is  bounded  below  by  the  posterior  part  of  the  coronary  sulcus,  containing  the 
coronary  sinus.  On  the  right  it  is  limited  by  the  sulcus  terminalis  of  the  right 
atrium,  and  on  the  left  by  the  ligament  of  the  left  vena  cava  and  the  oblique  vein 
of  the  left  atrium.  The  four  pulmonary  veins,  two  on  either  side,  open  into  the 
left  atrium,  while  the  superior  vena  cava  opens  into  the  upper,  and  the  anterior 
vena  cava  into  the  lower,  part  of  the  right  atrium. 

The  Apex  {a'pex  cordis). — The  apex  is  directed  downward,  forward,  and  to  the 
left,  and  is  overlapped  by  the  left  lung  and  pleura:  it  lies  behind  the  fifth  left 
intercostal  space,  8  to  9  cm.  from  the  mid-sternal  line,  or  about  4  cm.  below  and 
2  mm.  to  the  medial  side  of  the  left  mammary  papilla. 


528 


ANGIOLOGY 


I 


The  sternocostal  surface  (Fig.  492)  Is  directed  forward,  upward,  and  to  the  left. 
Its  lower  part  is  convex,  formed  chiefly  by  the  right  ventricle,  and  traversed  near 
its  left  margin  by  the  anterior  longitudinal  sulcus.  Its  upper  part  is  separated  from 
the  lower  by  the  coronary  sulcus,  and  is  formed  by  the  atria;  it  presents  a  deep 
concavity  (Fig.  494),  occupied  by  the  ascending  aorta  and  the  pulmonary  artery. 

The  diaphragmatic  surface  (Fig.  491),  directed  downward  and  slightly  backward., 
is  formed  by  the  ventricles,  and  rests  upon  the  central  tendon  and  a  small  part  of 
the  left  muscular  portion  of  the  diaphragm.  It  is  separated  from  the  base  by 
the  posterior  part  of  the  coronary  sulcus,  and  is  traversed  obliquely  by  the  posterior 
longitudinal  sulcus. 

The  right  margin  of  the  heart  is  long,  and  is  formed  by  the  right  atrium  above 
and  the  right  ventricle  below.  The  atrial  portion  is  rounded  and  almost  vertical; 
it  is  situated  behind  the  third,  fourth,  and  fifth  right  costal  cartilages  about 


■ygos  vein 


Left  'pulmonary  veins 

Oblique  vein  of  left  atrium 
Great  cardiac  vein 
Left  marginal  vein 


Sight  pulmonary 

veiTis 


——-^—^—  Small  cardiac  vein 

Posterior  vein  of  left  ventricle 

Middle  cardiac  vein 
Fig.  491. — Base  and  diaphragmatic  surface  of  heart. 

1.25  cm.  from  the  margin  of  the  sternum.  The  ventricular  portion,  thin  and  sharp, 
is  named  the  acute  margin;  it  is  nearly  horizontal,  and  extends  from  the  sternal 
end  of  the  sixth  right  costal  cartilage  to  the  apex  of  the  heart. 

The  left  or  obtuse  margin  is  shorter,  full,  and  rounded:  it  is  formed  mainly  by 
the  left  ventricle,  but  to  a  slight  extent,  above,  by  the  left  atrium.  It  extends 
from  a  point  in  the  second  left  intercostal  space,  about  2.5  mm.  from  the  sternal 
margin,  obliquely  downward,  with  a  convexity  to  the  left,  to  the  apex  of  the  heart. 

Right  Atrium  (atrium  dextrum;  right  auricle). — The  right  atrium  is  larger  than 
the  left,  but  its  walls  are  somewhat  thinner,  measuring  about  2  mm.;  its  cavity 
is  capable  of  containing  about  57c.c.  It  consists  of  two  parts:  a  principal  cavity, 
or  sinus  venarum,  situated  posteriorly,  and  an  anterior,  smaller  portion,  the  auricula. 

Sinus  Venarum  {sinus  venosus). — The  sinus  venarum  is  the  large  quadrangular 
cavity  placed  between  the  two  vense  cavae.    Its  walls,  which  are  extremely  thin, 


I 


THE  HEART 


529 


are  connected  below  with  the  right  ventricle,  and  medially  with  the  left  atrium, 
but  are  free  in  the  rest  of  their  extent. 

Auricula  {auricula  dextra;  right  auricular  appendix). — The  auricula  is  a  small 
conical  muscular  pouch,  the  margins  of  which  present  a  dentated  edge.  It  projects 
from  the  upper  and  front  part  of  the  sinus  forward  and  toward  the  left  side,  over- 
lapping the  root  of  the  aorta. 


Ant.  desc.  branch  of  left 
coronary  artery 


Pi 


Bight  corollary 
artery 


Fia.  492. — Sternocostal  surface  of  iiuan. 

The  separation  of  the  auricula  from  the  sinus  venarum  is  indicated  externally 
by  a  groove,  the  terminal  sulcus,  which  extends  from  the  front  of  the  superior  vena 
cava  to  the  front  of  the  inferior  vena  cava,  and  represents  the  line  of  union  of  the 
.sinus  venosus  of  the  embryo  with  the  primitive  atrium.  On  the  inner  wall  of  the 
atrium  the  separation  is  marked  by  a  vertical,  smooth,  muscular  ridge,  the  terminal 
crest.  Behind  the  crest  the  internal  surface  of  the  atrium  is  smooth,  while  in  front 
of  it  the  muscular  fibers  of  the  wall  are  raised  into  parallel  ridges  resembling  the 
teeth  of  a  comb,  and  hence  named  the  musculi  pectinati. 

Its  interior  (Fig.  493)  presents  the  following  parts  for  examination: 

Superior  vena  cava. 


Openings 


Inferior  vena  cava. 
Coronary  sinus. 
Foramina  venarum 

minimarum. 
,  Atrioventricular. 


Valves 


j  Valve  of  the  inferior  vena  cava. 
i  Valve  of  the  coronary  sinus. 


Fossa  oval  is. 
Limbus  fossae  ovalis. 
Intervenous  tubercle. 
Musculi  pectinati. 
Crista  terminalis. 

The  superior  vena  cava  returns  the  blood  from  the  upper  half  of  the  body,  and 
opens  into  the  upper  and  back  part  of  the  atrium,  the  direction  of  its  orifice  being 

I «  downward  and  forward.    Its  opening  has  no  valve. 
L. 


"530 


ANGIOLOGY 


The  inferior  vena  cava,  larger  than  the  superior,  returns  the  blood  from  the 
lower  half  of  the  body,  and  opens  into  the  lowest  part  of  the  atrium,  near  the 
atrial  septum,  its  orifice  being  directed  upward  and  backward,  and  guarded  h}> 
a  rudimentary  valve,  the  valve  of  the  inferior  vena  cava  {Eustachian  valve).  The 
blood  entering  the  atrium  through  the  superior  vena  cava  is  directed  downward 
and  forward,  i.  e.,  toward  the  atrioventricular  orifice,  while  that  entering  through 
the  inferior  vena  cava  is  directed  upward  and  backward,  toward  the  atrial  septum. 
This  is  the  normal  direction  of  the  two  currents  in  fetal  life. 

The  coronary  sinus  opens  into  the  atrium,  between  the  orifice  of  the  inferior 
vena  cava  and  the  atrioventricular  opening.  It  returns  blood  from  the  substance 
of  the  heart  and  is  protected  by  a  semicircular  valve,  the  valve  of  the  coronary 
sinus  (valve  of  Thebesius). 


Pulmonary  valve 


Opening  of  sup.  vena 
cava 
Crista  terminalis 
Atrial  septum 

Limbus  fossce  ovalis 

Opening  of  coronary 
sinus 


Opening  of  inf.  vaia 
cava 


Ant.  cusp  of  tricuspid 
valve 

Chordce  tendinece 

Papillary 
muscles 


A 


Valve  of  inf.  vena  cava 

Valve  of  coronary  sinus 


Fig.  493. — Interior  of  right  side  of  heart. 


The  foramina  venanim  minimarum  (foramina  Thehesii)  are  the  orifices  of  minute 
veins  (venoe  cordis  minimce),  which  return  blood  directly  from  the  muscular  sub-^ 
stance  of  the  heart.  H 

The  atrioventricular  opening  (tricuspid  orifice)  is  the  large  oval  aperture  of  com- 
munication between  the  atrium  and  the  ventricle;  it  will  be  described  with  the 
right  ventricle.  fl 

The  valve  of  the  inferior  vena  cava  (valvula  venoe  cavae  inferioris  [Eustachii];  ^ 
Eustachian  valve)  is  situated  in  front  of  the  orifice  of  the  inferior  vena  cava.  It 
is  semilunar  in  form,  its  convex  margin  being  attached  to  the  anterior  margin 
of  the  orifice;  its  concave  margin,  which  is  free,  ends  in  two  cornua,  of  which 
the  left  is  continuous  with  the  anterior  edge  of  the  limbus  fossse  ovalis  while 
the  right  is  lost  on  the  wall  of  the  atrium.  The  valve  is  formed  by  a  duplicature 
of  the  lining  membrane  of  the  atrium,  containing  a  few  muscular  fibers.  In  the 
fetus  this  valve  is  of  large  size,  and  serves  to  direct  the  blood  from  the  inferior 
vena  cava,  through  the  foramen  ovale,  into  the  left  atrium.  In  the  adidt  it  occa- 
sionally persists,  and  may  assist  in  preventing  the  reflux  of  blood  into  the  inferior 
vena  cava;  more  commonly  it  is  small,  and  may  present  a  cribriform  or  filamentous 
appearance;  sometimes  it  is  altogether  wanting. 


■to 

■^^■1  THE  HEART  531 

^H  The  valve  of  the  coronary  sinus  {valvula  sinus  coronarii  [Thebesii];  Thebesian 
■mhe)  is  a  semicircular  fold  of  the  lining  membrane  of  the  atrium,  at  the  orifice  of 
the  coronary  sinus.  It  prevents  the  regurgitation  of  blood  into  the  sinus  during  the 
contraction  of  the  atrium.     This  valve  may  be  double  or  it  may  be  cribriform. 

The  fossa  ovalis  is  an  oval  depression  on  the  septal  wall  of  the  atrium,  and  corre- 
sponds to  the  situation  of  the  foramen  ovale  in  the  fetus.  It  is  situated  at  the  lower 
part  of  the  septum,  above  and  to  the  left  of  the  orifice  of  the  inferior  vena  cava. 

The  limbus  fossae  ovalis  (annulus  ovalis)  is  the  prominent  oval  margin  of  the  fossa 
ovalis.  It  is  most  distinct  above  and  at  the  sides  of  the  fossa;  below,  it  is  deficient. 
A  small  slit-like  valvular  opening  is  occasionally  found,  at  the  upper  margin  of 
the  fossa,  leading  upward  beneath  the  limbus,  into  the  left  atrium;  it  is  the  remains 
of  the  fetal  aperture  between  the  two  atria. 

The  intervenous  tubercle  {tuherculum  intervenosum;  tubercle  of  Lower)  is  a  small 
projection  on  the  posterior  wall  of  the  atrium,  above  the  fossa  ovalis.  It  is  distinct 
in  the  hearts  of  quadrupeds,  but  in  man  is  scarcely  visible.  It  was  supposed  by 
Lower  to  direct  the  blood  from  the  superior  vena  cava  toward  the  atrioventricular 
opening. 

Right  Ventricle  (ventriculus  dexter). — The  right  ventricle  is  triangular  in  form, 
and  extends  from  the  right  atrium  to  near  the  apex  of  the  heart.  Its  antero- 
superior  surface  is  rounded  and  convex,  and  forms  the  larger  part  of  the  sterno- 
costal surface  of  the  heart.  Its  under  surface  is  flattened,  rests  upon  the  dia- 
phragm, and  forms  a  small  part  of  the  diaphragmatic  surface  of  the  heart.  Its 
posterior  wall  is  formed  by  the  ventricular  septum,  which  bulges  into  the  right 
ventricle,  so  that  a  transverse  section  of  the  cavity  presents  a  semilunar  outline. 
Its  upper  and  left  angle  forms  a  conical  pouch,  the  conus  arteriosus,  from  which 
the  pulmonary  artery  arises.  A  tendinous  band,  which  may  be  named  the  tendon 
of  the  conus  arteriosus,  extends  upward  from  the  right  atrioventricular  fibrous 
ring  and  connects  the  posterior  surface  of  the  conus  arteriosus  to  the  aorta.  The 
wall  of  the  right  ventricle  is  thinner  than  that  of  the  left,  the  proportion  between 
them  being  as  1  to  3;  it  is  thickest  at  the  base,  and  gradually  becomes  thinner 
tojvard  the  apex.  The  cavity  equals  in  size  that  of  the  left  ventricle,  and  is 
capable  of  containing  about  85  c.c. 

Its  interior  (Fig.  493)  presents  the  following  parts  for  examination: 

Q       .  (Right  atrioventricular.  y  ,         (Tricuspid. 

^        ^      i Pulmonary  artery.  iPulmonary. 

Trabeculse  carnese.  Chordae  tendinese. 

The  right  atrioventricular  orifice  is  the  large  oval  aperture  of  communication 
)etween  the  right  atrium  and  ventricle.  Situated  at  the  base  of  the  ventricle, 
it  measures  about  4  cm.  in  diameter  and  is  surrounded  by  a  fibrous  ring,  covered 
by  the  lining  membrane  of  the  heart;  it  is  considerably  larger  than  the  correspond- 
ing aperture  on  the  left  side,  being  sufficient  to  admit  the  ends  of  four  fingers 
It  is  guarded  by  the  tricuspid  valve. 

The  opening  of  the  pulmonary  artery  is  circular  in  form,  and  situated  at  the 
summit  of  the  conus  arteriosus,  close  to  the  ventricular  septum.  It  is  placed  above 
and  to  the  left  of  the  atrioventricular  opening,  and  is  guarded  by  the  pulmonary 
semilunar  valves. 

The  tricuspid  valve  {valvula  tricuspidalis)  (Figs.  493,  495)  consists  of  three  some- 
what triangular  cusps  or  segments.  The  largest  cusp  is  interposed  betw^een  the 
atrioventricular  orifice  and  the  conus  arteriosus  and  is  termed  the  anterioror  infundib- 
ular cusp.  A  second,  the  posterior  or  marginal  cusp,  is  in  relation  to  the  right  margin 
of  the  ventricle,  and  a  third,  the  medial  or  septal  cusp,  to  the  ventricular  septum. 
They  are  formed  by  duplicatures  of  the  lining  membrane  of  the  heart,  strengthened 


532 


ANGIOLOGY 


I 


by  intervening  layers  of  fibrous  tissue:  their  central  parts  are  thick  and  strong, 
their  marginal  portions  thin  and  translucent,  and  in  the  angles  between  the  latter 
small  intermediate  segments  are  sometimes  seen.  Their  bases  are  attached  to  a 
fibrous  ring  surrounding  the  atrioventricular  orifice  and  are  also  joined  to  each  other 
so  as  to  form  a  continuous  annular  membrane,  while  their  apices  project  into  the 
ventricular  cavity.  Their  atrial  surfaces,  directed  toward  the  blood  current  from 
the  atrium,  are  smooth;  their  ventricular  surfaces,  directed  toward  the  wall  of  the 
ventricle,  are  rough  and  irregular,  and,  together  with  the  apices  and  margins  of 
the  cusps,  give  attachment  to  a  number  of  delicate  tendinous  cords,  the  chordse 


tendinese. 


Right  auricula 


Right 
atrium 


Left 
auricula 


Left  pulmonary  veins 

FiQ.  494. — Heart  seen  from  above. 


Right  pulmonary 
veins 


Fia.  496. — Base  of  ventricles  exposed  by  removal 
of  the  atria. 


The  trabeculse  cameae  {columnae  carneoe)  are  rounded  or  irregular  muscular 
columns  which  project  from  the  whole  of  the  inner  surface. of  the  ventricle,  with 
the  exception  of  the  conus  arteriosus.  They  are  of  three  kinds:  some  are  attached 
along  their  entire  length  on  one  side  and  merely  form  prominent  ridges,  others 
are  fixed  at  their  extremities  but  free  in  the  middle,  while  a  third  set  {musculi 
papillares)  are  continuous  by  their  bases  with  the  wall  of  the  ventricle,  while  their 
apices  give  origin  to  the  chordae  tendinese  which  pass  to  be  attached  to  the  seg- 
ments of  the  tricuspid  valve.  There  are  two  papillary  muscles,  anterior  and  pos- 
terior :  of  these,  the  anterior  is  the  larger,  and  its  chordae  tendineae  are  connected 
with  the  anterior  and  posterior  cusps  of  the  valve :  the  posterior  papillary  muscle 
sometimes  consists  of  two  or  three  parts;  its  chordae  tendineae  are  connected 
with  the  posterior  and  medial  cusps.  In  addition  to  these,  some  chordae  tendineas 
spring  directly  from  the  ventricular  septum,  or  from  small  papillary  eminences  on  it, 
and  pass  to  the  anterior  and  medial  cusps.  A  muscular  band,  well-marked  in  sheep 
and  some  other  animals,  frequently  extends  from  the  base  of  the  anterior  papillary 
muscle  to  the  ventricular  septum.  From  its  attachments  it  may  assist  in  preventing 
overdistension  of  the  ventricle,  and  so  has  been  named  the  moderator  band. 

The  pulmonary  semilunar  valves  (Fig.  494)  are  three  in  number,  two  in  front 
and  one  behind,  formed  by  duplicatures  of  the  lining  membrane,  strengthened 
by  fibrous  tissue.  They  are  attached,  by  their  convex  margins,  to  the  wall  of  the 
artery,  at  its  junction  with  the  ventricle,  their  free  borders  being  directed  upward 
into  the  lumen  of  the  vessel.    The  free  and  attached  margins  of  each  are  strength- 


I 


THE  HEART 


533 


ened  by  tendinous  fibers,  and  the  former  presents,  at  its  middle,  a  thickened  nodule 
{corpus  Arantii).  From  this  nodule  tendinous  fibers  radiate  through  the  segment 
to  its  attached  margin,  but  are  absent  from  two  narrow  crescentic  portions,  the 
lunulse,  placed  one  on  either  side  of  the  nodule  immediately  adjoining  the  free 
margin.  Between  the  semilunar  valves  and  the  wall  of  the  pulmonary  artery  are 
three  pouches  or  sinuses  (sinuses  of  Valsalva) . 

Left  Atrium  {atrium  sinistum;  left  auricle). — The  left  atrium  is  rather  smaller 
than  the  right,  but  its  walls  are  thicker,  measuring  about  3  mm. ;  it  consists,  like 
the  right,  of  two  parts,  a  principal  cavity  and  an  auricula. 

The  principal  cavity  is  cuboidal  in  form,  and  concealed,  in  front,  by  the  pul- 
monary artery  and  aorta;  in  front  and  to  the  right  it  is  separated  from  the  right 
atrium  by  the  atrial  septum;  opening  into  it  on  either  side  are  the  two  pulmonary 

I  veins. 
I  Auricula  {auricula  sinistra;  left  auricular  appendix). — The  auricula  is  somewhat 
constricted  at  its  junction  with  the  principal  cavity;  it  is  longer,  narrower,  and  more 
curved  than  that  of  the  right  side,  and  its  margins  are  more  deeply  indented.  It 
is  directed  forward  and  toward  the  right  and  overlaps  the  root  of  the  pulmonary 
irtery. 


Fig.  496. — Interior  of  left  side  of  heart. 


The  interior 
examination : 


II 


atrium   (Fig.   496)   presents  the  following  parts  for 


Openings  of  the  four  pulmonary  veins. 
Left  atrioventricular  opening. 
Musculi  pectinati. 


The  pulmonary  veins,  four  in  number,  open  into  the  upper  part  of  the  posterior 
surface  of  the  left  atrium — two  on  either  side  of  its  middle  line:  they  are  not 
provided  with  valves.    The  two  left  veins  frequently  end  by  a  common  opening. 

The  left  atrioventricular  opening  is  the  aperture  between  the  left  atrium  and 
ventricle,  and  is  rather  smaller  than  the  corresponding  opening  on  the  right  side. 


534 


ANGIOLOGY 


I 


The  musculi  pectinati,  fewer  and  smaller  than  in  the  right  auricula,  are  confined 
to  the  inner  surface  of  the  auricula. 

On  the  atrial  septum  may  be  seen  a  lunated  impression,  bounded  below  by  a 
crescentic  ridge,  the  concavity  of  which  is  turned  upward.  The  depression  is 
just  above  the  fossa  ovalis  of  the  right  atrium. 

Left  Ventricle  (ventriculus  sinister). — The  left  ventricle  is  longer  and  more  conical 
in  shape  than  the  right,  and  on  transverse  section  its  concavity  presents  an  oval 
or  nearly  circular  outline.  It  forms  a  small  part  of  the  sternocostal  surface  and  a 
considerable  part  of  the  diaphragmatic  surface  of  the  heart;  it  also  forms  the  apex 
of  the  heart.    Its  walls  are  about  three  times  as  thick  as  those  of  the  right  ventricle. 

Its  interior  (Fig.  496)  presents  the  following  parts  for  examination: 


r\       '         (Left  atrioventricular. 
Openmgs   |^^^^.^ 

Trabeculse  carneae. 


vr  1         (Bicuspid  or  Mitral, 
valves   ^AQj.^ip 

Chordse  tendinese. 


1 


The  left  atrioventricular  opening  (jnitral  orifice)  is  placed  below  and  to  the  left 
of  the  aortic  orifice.  It  is  a  little  smaller  than  the  corresponding  aperture  of  the 
opposite  side,  admitting  only  two  fingers.  It  is  surrounded  by  a  dense  fibrous  ring, 
covered  by  the  lining  membrane  of  the  heart,  and  is  guarded  by  the  bicuspid  or 
mitral  valve. 


Aortic  sinus    Left  post. 
Nodulus  ^'"^^^ 

Lunula 


Origins  of  coronary  arteries 


Eight  post,  valve 


Ant.  valve 


Fia.  497. — Aorta  laid  open  to  show  the  seu 


valves. 


The  aortic  opening  is  a  circular  aperture,  in  front  and  to  the  right  of  the  atrio- 
ventricular, from  which  it  is  separated  by  the  anterior  cusp  of  the  bicuspid  valve. 
Its  orifice  is  guarded  by  the  aortic  semilunar  valves.  The  portion  of  the  ventricle 
immediately  below  the  aortic  orifice  is  termed  the  aortic  vestibule,  and  possesses 
fibrous  instead  of  muscular  walls. 

The  bicuspid  or  mitral  valve  (valvula  bicuspidalis  [metralis])  (Figs.  495,  496)  is 
attached  to  the  circumference  of  the  left  atrioventricular  orifice  in  the  same  way 
that  the  tricuspid  valve  is  on  the  opposite  side.  It  consists  of  two  triangular  cusps, 
formed  by  duplicatures  of  the  lining  membrane,  strengthened  by  fibrous  tissue, 
and  containing  a  few  muscular  fibers.  The  cusps  are  of  unequal  size,  and  are  larger, 
thicker,  and  stronger  than  those  of  the  tricuspid  valve.  The  larger  cusp  is  placed 
in  front  and  to  the  right  between  the  atrioventricular  and  aortic  orifices,  and  is 
known  as  the  anterior  or  aortic  cusp ;  the  smaller  or  posterior  cusp  is  placed  behind 
and  to  the  left  of  the  opening.  Two  smaller  cusps  are  usually  found  at  the  angles 
of  junction  of  the  larger.  The  cusps  of  the  bicuspid  valve  are  furnished  with  chordae 
tendinese,  which  are  attached  in  a  manner  similar  to  those  on  the  right  side;  they 
are,  however,  thicker,  stronger,  and  less  numerous. 


THE  HEART 


535 


The  aortic  semilunar  valves  (Figs.  494,  497)  are  three  in  number,  and  surround 
the  orifice  of  the  aorta;  two  are  anterior  (right  and  left)  and  one  posterior.  They 
are  similar  in  structure,  and  in  their  mode  of  attachment,  to  the  pulmonary  semi- 
lunar valves,  but  are  larger,  thicker,  and  stronger;  the  lunula  are  more  distinct, 
and  the  noduli  or  corpora  Arantii  thicker  and  more  prominent.  Opposite  the  valves 
the  aorta  presents  slight  dilatations,  the  aortic  sinuses  {sinuses  of  Valsalva),  which 
are  larger  than  those  at  the  origin  of  the  pulmonary  artery. 

The  trabeculse  carneae  are  of  three  kinds,  like  those  upon  the  right  side,  but 
they  are  more  numerous,  and  present  a  dense  interlacement,  especially  at  the 
apex,  and  upon  the  posterior  wall  of  the  ventricle.  The  musculi  papillares  are  two 
in  number,  one  being  connected  to  the  anterior,  the  other  to  the  posterior  wall; 
the}'  are  of  large  size,  and  end  in  rounded  extremities  from  which  the  chordae 
tendinese  arise.  The  chordse  tendineaj  from  each  papillary  muscle  are  connected 
to  both  cusps  of  the  bicuspid  valve. 


Left  auricula 


Inferior 
vena  cava 

Membranous' 
septum 
Musculi 
pectinati 


Aortic  valve 


^«      Papillary 
■muaclea 


Anterior  papillary  muscle 
Fig.  498. — Section  of  the  heart  showing  tne  ventricular  septum. 

Ventricular  Septum  {septum  ventricidorum;  interventricular  septum)  (Fig.  498). — • 
The  ventricular  septum  is  directed  obliquely  backward  and  to  the  right,  and  is 
curved  with  the  convexity  toward  the  right  ventricle:  its  margins  correspond 
with  the  anterior  and  posterior  longitudinal  sulci.  The  greater  portion  of  it  is 
thick  and  muscular  and  constitutes  the  muscular  ventricular  septum,  but  its  upper 
and  posterior  part,  which  separates  the  aortic  vestibule  from  the  lower  part  of 
the  right  atrium  and  upper  part  of  the  right  ventricle,  is  thin  and  fibrous,  and  is 
termed  the  membranous  ventricular  septum.  An  abnormal  communication  may 
exist  between  the  ventricles  at  this  part  owing  to  defective  development  of  the 
membranous  septum. 

Structure. — The  heart  consists  of  muscular  fibers,  and  of  fibrous  rings  which  serve  for  their 
attachment.  It  is  covered  by  the  visceral  layer  of'  the  serous  pericardium  (epicardium),  and 
lined  by  the  endocardium.    Between  these  two  membranes  is  the  muscular  wall  or  myocardium. 

The  endocardium  is  a  thin,  smooth  membrane  which  Unes  and  gives  the  ghstening  appear- 


536 


ANGIOLOGY 


I 


ance  to  the  inner  surface  of  the  heart;  it  assists  in  forming  the  valves  by  its  reduplications,  and 
is  continuous  with  the  hning  membrane  of  the  large  bloodvessels.  It  consists  of  connecti\e 
tissue  and  elastic  fibers,  and  is  attached  to  the  muscular  structure  by  loose  elastic  tissue  which 
contains  bloodvessels  and  nerves;  its  free  surface  is  covered  by  endothelial  cells. 

The  fibrous  rings  surround  the  atrioventricular  and  arterial  orifices,  and  are  stronger  upon 
the  left  than  on  the  right  side  of  the  heart.  The  atrioventricular  rings  serve  for  the  attachment 
of  the  muscular  fibers  of  the  atria  and  ventricles,  and  for  the  attachment  of  the  bicuspid  and 
tricuspid  valves.  The  left  atrioventricular  ring  is  closely  connected,  by  its  right  margin,  with 
the  aortic  arterial  ring;  between  these  and  the  right  atrioventricular  ring  is  a  triangular  mass  of 
fibrous  tissue,  the  trigonum  fibrosum,  which  represents  the  os  cordis  seen  in  the  heart  of  some  C'f 
the  larger  animals,  as  the  ox  and  elephant.  Lastly,  there  is  the  tendinous  band,  already  referred 
to,  the  posterior  surface  of  the  conus  arteriosus. 

The  fibrous  rings  surrounding  the  arterial  orifices  serve  for  the  attachment  of  the  great  vessels 
and  semilunar  valves.  Each  ring  receives,  by  its  ventricular  margin,  the  attachment  of  some 
of  the  muscular  fibers  of  the  ventricles;  its  opposite  margin  presents  three  deep  semicircular 
notches,  to  which  the  middle  coat  of  the  artery  is  firmly  fixed.  The  attachment  of  the  artery 
to  its  fibrous  ring  is  strengthened  by  the  external  coat  and  serous  membrane  externally,  and 
by  the  endocardium  internally.  From  the  margins  of  the  semicircular  notches  the  fibrous  structure 
of  the  ring  is  continued  into  the  segments  of  the  valves.  The  middle  coat  of  the  artery  in  this 
situation  is  thin,  and  the  vessel  is  dilated  to  form  the  sinuses  of  the  aorta  and  pulmonary  artery. 


m 


ri:^^T:,l     ^-.f=^_.      rfF' 


"1 


";  m  I 


>^  '  -f^  - 


Fig.  499. — Anastomosing  muscular  fibers  of  the  heart  seen 
in  a  longitudinal  section.  On  the  right  the  limits  of  the 
separate  cells  with  their  nuclei  are  exhibited  somewhat  dia- 
grammatically. 


Fig.  500. — Purkinje's  fibers  from  the  sheep's 
heart.  A.  In  longitudinal  section.  B.  In 
transverse  section. 


Cardiac  Muscular  Tissue. — The  fillers  of  the  heart  differ  very  remarkably  from  those  of  other 
striped  muscles.  They  are  smaller  by  one-third,  and  their  transverse  striae  are  by  no  means  so 
well-marked.  They  show  faint  longitudinal  striation.  The  fibers  are  made  up  of  distinct  quad- 
rangular cells,  joined  end  to  end  so  as  to  form  a  syncytium  (Fig.  499).  Each  cell  contains  a  clear 
oval  nucleus,  situated  near  its  center.  The  extremities  of  the  cells  have  a  tendency  to  branch  or 
divide,  the  subdivisions  uniting  with  offsets  from  other  cells,  and  thus  producing  an  anastomosis 
of  the  fibers.  The  connective  tissue  between  the  bundles  of  fibers  is  much  less  than  in  ordinary 
striped  muscle,  and  no  sarcolemma  has  been  proved  to  exist. 

Purkinje  Fibers  (Fig.  500). — Between  the  endocardium  and  the  ordinary  cardiac  muscle  are 
found,  imbedded  in  a  small  amount  of  connective  tissue,  peculiar  fibers  known  as  Purkinje  fibers. 
They  are  found  in  certain  mammals  and  in  birds,  and  can  be  best  seen  in  the  sheep's  heart,  where 


THE  HEART  ^  537 


I  they  form  a  considerable  portion  of  the  moderator  band  and  also  appear  as  gelatinoas-looking 
strands  on  the  inner  walls  of  the  atria  and  ventricles.  They  also  occur  in  the  human  heart  asso- 
ciated with  the  terminal  distributions  of  the  bundle  of  His^  The  fibers  are  very  much  larger  in 
size  than  the  cardiac  cells  and  difTer  from  thein  in  several  ways.  In  longitudinal  section  they  are 
quadrilateral  in  shape,  being  about  twice  as  long  as  they  are  broad.  The  central  portion  of  each 
fiber  contains  one  or  more  nuclei  and  is  made  up  of  granular  protoplasm,  with  no  indication  of 
striations,  while  the  peripheral  portion  is  clear  and  has  distinct  transverse  striations.  The  fibers 
are  intimately  connected  with  each  other,  possess  no  definite  sarcolemma,  and  do  not  branch. 

The  muscular  structure  of  the  heart  consists  of  bands  of  fibers,  which  present  an  exceedingly 
intricate  interlacement.  They  comprise  (a)  the  fibers  of  the  atria,  (6)  the  fibers  of  the  ventricles, 
and  (c)  the  atrioventricular  bundle  of  His. 

The  fibers  of  the  atria  are  arranged  in  two  layers — a  superficial,  common  to  both  cavities,  and 
a  deep,  proper  to  each.  The  superficial  fibers  are  most  distinct  on  the  front  of  the  atria,  across 
the  bases  of  which  they  run  in  a  transverse  direction,  forming  a  thin  and  incomplete  layer.  Some 
of  these  fibers  rim  into  the  atrial  septum.  The  deep  fibers  consist  of  looped  and  annular  fibers. 
The  looped  fibers  pass  upward  over  each  atrium,  being  attached  by  their  two  extremities  to  the 
corresponding  atrioventricular  ring,  in  front  and  behind.  The  annular  fibers  surround  the  auriculae, 
and  form  annular  bands  around  the  terminations  of  the  veins  and  around  the  fossa  ovalis. 

The  fibers  of  the  ventricles  are  arranged  in  a  complex  manner,  and  various  accounts  have 
been  given  of  their  course  and  connections;  the  following  description  is  based  on  the  work  of 
McCallum.i  They  consist  of  superficial  and  deep  layers,  all  of  which,  with  the  exception  of 
two,  are  inserted  into  the  papillary  muscles  of  the  ventricles.  The  superficial  layers  consist 
of  the  following:  (a)  Fibers  which  spring  from  the  tendon  of  the  conus  arteriosus  and  sweep 
downward  and  toward  the  left  across  the  anterior  longitudinal  sulcus  and  around  the  apex  of 
the  heart,  where  they  pass  upward  and  inward  to  terminate  in  the  papillary  muscles  of  the  left 
ventricle;  those  arising  from  the  upper  half  of  the  tendon  of  the  conus  arteriosus  pass  to  the 
anterior  papillary  muscle,  those  from  the  lower  half  to  the  posterior  papillary  muscle  and  the 
papillary  muscles  of  the  septum,  (b)  Fibers  which  arise  from  the  right  atrioventricular  ring  and 
run  diagonally  across  the  diaphragmatic  surface  of  the  right  ventricle  and  around  its  right  border 
on  to  its  costosternal  surface,  where  they  dip  beneath  the  fibers  just  described,  and,  crossing  the 
anterior  longitudinal  sulcus,  wind  around  the  apex  of  the  heart  and  end  in  the  posterior  papillary 
muscle  of  the  left  ventricle,  (c)  Fibers  which  spring  from  the  left  atrioventricular  ring,  and, 
crossing  the  posterior  longitudinal  sulcus,  pass  successively  into  the  right  ventricle  and  end  in 
its  papillary  muscles.  The  deep  layers  are  three  in  number;  they  arise  in  the  papillary  muscles 
of  one  ventricle  and,  curving  in  an  S-shaped  manner,  turn  in  at  the  longitudinal  sulcus  and  end 
in  the  papillary  muscles  of  the  other  ventricle.  The  layer  which  is  most  superficial  in  the  right 
ventricle  Ues  next  the  lumen  of  the  left,  and  vice  versa.  Those  of  the  first  layer  almost  encircle 
the  right  ventricle  and,  crossing  in  the  septum  to  the  left,  unite  with  the  superficial  fibers  from 
the  right  atrioventricular  ring  to  form  the  posterior  papillary  muscle.  Those  of  the  second 
layer  have  a  less  extensive  course  in  the  wall  of  the  right  ventricle,  and  a  correspondingly  greater 
course  in  the  left,  where  they  join  with  the  superficial  fibers  from  the  anterior  half  of  the  tendon 
of  the  conus  arteriosus  to  form  the  papillary  muscles  of  the  septum.  Those  of  the  third  layer 
pass  almost  entirely  around  the  left  ventricle  and  unite  with  the  superficial  fibers  from  the  lower 
half  of  the  tendon  of  the  conus  arteriosus  to  form  the  anterior  papillary  muscle.  Besides  the 
laj-^ers  just  described  there  are  two  bands  which  do  not  end  in  papillary  muscles.  One  springs 
from  the  right  atrioventricular  ring  and  crosses  in  the  atrioventricular  septum;  it  then  encircles 
the  deep  layers  of  the  left  ventricle  and  ends  in  the  left  atrioventricular  ring.  The  second  band 
•      is  apparently  confined  to  the  left  ventricle;  it  is  attached  to  the  left  atrioventricular  ring,  and 

■  fcencircles  the  portion  of  the  ventricle  adjacent  to  the  aortic  orifice. 

■  ■      The  atrioventricular  bundle  of  His  (Fig.  501),  is  the  only  direct  muscular  connection  known  to 

exist  between  the  atria  and  the  ventricles.  Its  cells  differ  from  ordinary  cardiac  muscle  cells  in 
l)eing  more  spindle-shaped.  They  are,  moreover,  more  loosely  arranged  and  have  a  richer  vascu- 
lar supply  than  the  rest  of  the  heart  muscle.  It  arises  in  connection  with  two  smaU  collections  of 
spindle-shaped  cells,  the  sinoatrial  and  atrioventricular  nodes.  The  sinoatrial  node  is  situated  on 
the  anterior  border  of  the  opening  of  the  superior  vena  cava;  from  its  strands  of  fusiform  fibers  run 
under  the  endocardium  of  the  wall  of  the  atrium  to  the  atrioventricular  node.  The  atrioventricidar 
node  lies  near  the  orifice  of  the  coronary  sinus  in  the  annular  and  septal  fibers  of  the  right  atrium; 
from  it  the  atrioventricular  bundle  passes  forward  in  the  lower  part  of  the  membranous  septum, 
and  divides  into  right  and  left  fascicuh.  These  run  down  in  the  right  and  left  ventricles,  one  on 
either  side  of  the  ventricular  septum,  covered  by  endocardium.  In  the  lower  parts  of  the  ventricles 
they  break  up  into  numerous  strands  which  end  in  the  papillary  muscles  and  in  the  ventricular 
muscle  generally.  The  greater  portion  of  the  atrioventricular  bundle  consists  of  narrow,  somewhat 
fusiform  fibers,  but  its  terminal  strands  are  composed  of  Purkinje  fibers. 

•  Johns  Hopkins  Hospital  Reports,  vo 


.OGY 


I 


Dr.  A.  Morison^  has  shown  that  in  the  sheep  and  pig  the  atrioventricular  bundle  "is  a  grea 
avenue  for  the  transmission  of  nerves  from  the  auricular  to  the  ventricular  heart;  large  and 
numerous  nerve  trunks  entering  the  bundle  and  coursing  with  it."     From  these,  branches  pasi 
off  and  form  plexuses  around  groups  of  Purkinje  cells,  and  from  these  plexuses  fine  fibrils  go  to 
innervate  individual  cells. 

Clinical  and  experimental  evidence  go  to  prove  that  this  bundle  conveys  the  impulse  to  sj^- 
tolic  contraction  from  the  atrial  septum  to  the  ventricles. 


Fig.  501. — Schematic  representation  of  the  atrioventricular  bundle  of  His.  The  bundle,  represented  in  red 
originates  near  the  orifice  of  1  he  coronary  sinus,  undergoes  slight  enlargement  to  form  a  node,  passes  forward  to 
the  ventricular  septum,  and  divides  into  two  limbs.  The  ultimate  distribution  cannot  be  completely  shown  in  this 
diagram. 

Vessels  and  Nerves. — The  arteries  supplying  the  heart  are  the  right  and  left  coronary  from 
the  aorta;  the  veins  end  in  the  right  atrium. 

The  lymphatics  end  in  the  thoracic  and  right  lymphatic  ducts. 

The  nerves  are  derived  from  the  cardiac  plexus,  which  are  formed  partly  from  the  vagi,  and 
partly  from  the  sympathetic  trunks.  They  are  freely  distributed  both  on  the  surface  and  in  the 
substance  of  the  heart,  the  separate  nerve  filaments  being  furnished  with  small  ganglia. 

The  Cardiac  Cycle  and  the  Actions  of  the  Valves. — By  the  contractions  of  the 
heart  the  blood  is  pumped  through  the  arteries  to  all  parts  of  the  body.  These 
contractions  occur  regularly  and  at  the  rate  of  about  seventy  per  minute.  Each 
wave  of  contraction  or  period  of  activity  is  followed  by  a  period  of  rest,  the  two 
periods  constituting  what  is  known  as  a  cardiac  cycle. 

Each  cardiac  cycle  consists  of  three  phases,  which  succeed  each  other  as  follows: 
(1)  a  short  simultaneous  contraction  of  both  atria,  termed  the  atrial  systole,  fol- 

*  Journal  of  Anatomy  and  Physiology,  vol.  xlvi. 


PECULIARITIES  IN  THE  VASCULAR  SYSTEM  OF  THE  FETUS52{ 

lowed,  after  a  slight  pause,  by  (2)  a  simultaneous,  but  more  prolonged,  contraction 
of  both  ventricles,  named  the  ventricular  systole,  and  (3)  a  period  of  rest,  during  which 
the  whole  heart  is  relaxed.  The  atrial  contraction  commences  around  the  venous 
openings,  and  sweeping  over  the  atria  forces  their  contents  through  the  atrio- 
ventricular openings  into  the  ventricles,  regurgitation  into  the  veins  being  pre- 
vented by  the  contraction  of  their  muscular  coats.  When  the  ventricles  contract, 
the  tricuspid  and  bicuspid  valves  are  closed,  and  prevent  the  passage  of  the  blood 
back  into  the  atria;  the  musculi  papillares  at  the  same  time  are  shortened,  and, 
pulling  on  the  chorda^  tendinese,  prevent  the  inversion  of  the  valves  into  the  atria. 
As  soon  as  the  pressure  in  the  ventricles  exceeds  that  in  the  pulmonary  artery  and 
aorta,  the  valves  guarding  the  orifices  of  these  vessels  are  opened  and  the  blood  is 
driven  from  the  right  ventricle  into  the  pulmonary  artery  and  from  the  left  into 
the  aorta.  The  moment  the  systole  of  the  ventricles  ceases,  the  pressure  of  the 
blood  in  the  pulmonary  artery  and  aorta  closes  the  pulmonary  and  aortic  semilunar 
valves  to  prevent  regurgitation  of  blood  into  the  ventricles,  the  valves  remaining 
shut  until  reopened  by  the  next  ventricular  systole.  During  the  period  of  rest  the 
tension  of  the  tricuspid  and  bicuspid  valves  is  relaxed,  and  blood  is  flowing  from 
the  veins  into  the  atria,  being  aspirated  by  negative  intrathoracic  pressure,  and 
slightly  also  from  the  atria  into  the  ventricles.  The  average  duration  of  a  cardiac 
cycle  is  about  ^^  of  a  second,  made  up  as  follows: 

Atrial  systole,  yV-  Atrial  diastole,  y^. 

Ventricular  systole,  ^.  Ventricular  diastole,  -^. 

Total  systole,  y%.  Complete  diastole,  ^^r- 


The  rhythmical  action  of  the  heart  is  muscular  in  origin — that  is  to  say,  the 
heart  muscle  itself  possesses  the  inherent  property  of  contraction  apart  from  any 
nervous  stimulation.  The  more  embryonic  the  muscle  the  better  is  it  able  to  initiate 
and  propagate  the  contraction  wave;  this  explains  why  the  normal  systole  of  the 
heart  starts  at  the  entrance  of  the  veins,  for  there  the  muscle  is  most  embryonic 
in  nature.  At  the  atrioventricular  junction  there  is  a  slight  pause  in  the  wave  of 
muscular  contraction.  To  obviate  this  so  far  as  possible  a  peculiar  band  of  marked 
embryonic  type  passes  across  the  junction  and  so  carries  on  the  contraction  wave 
to  the  ventricles.  This  band,  composed  of  special  fibers,  is  the  atrioventricular 
bundle  of  His  (p.  537).  The  nerves,  although  not  concerned  in  originating  the 
contractions  of  the  heart  muscle,  play  an  important  role  in  regulating  their  force 
and  frequency  in  order  to  subserve  the  physiological  needs  of  the  organism. 


PECULIARITIES   IN   THE   VASCULAR   SYSTEM   OF   THE   FETUS. 


The  chief  peculiarities  of  the  fetal  heart  are  the  direct  communication  between 
the  atria  through  the  foramen  ovale,  and  the  large  size  of  the  valve  of  the  inferior 
vena  cava.  Among  other  peculiarities  the  following  may  be  noted.  (1)  In  early 
fetal  life  the  heart  lies  immediately  below  the  mandibular  arch  and  is  relatively 
large  in  size.  As  development  proceeds  it  is  gradually  drawTi  w^thin  the  thorax,  but 
at  first  it  lies  in  the  middle  line ;  toward  the  end  of  pregnancy  it  gradually  becomes 
oblique  in  direction.  (2)  For  a  time  the  atrial  portion  exceeds  the  ventricular  in 
size,  and  the  walls  of  the  ventricles  are  of  equal  thickness :  toward  the  end  of  fetal 
life  the  ventricular  portion  becomes  the  larger  and  the  wall  of  the  left  ventricle 
exceeds  that  of  the  right  in  thickness.  (3)  Its  size  is  large  as  compared  with  that 
of  the  rest  of  the  body,  the  proportion  at  the  second  month  being  1  to  50,  and  at 
birth,  1  to  120,  while  in  the  adult  the  average  is  about  1  to  160. 

The  foramen  ovale,  situated  at  the  lower  part  of  the  atrial  septum,  forms  a  free 
communication  between  the  atria  until  the  end  of  fetal  life.  A  septum  {septum 
secundum)  grows  down  from  the  upper  wall  of  the  atrium  to  the  right  of  the  primary 


540  -^^^^^^^       ANGIOLOGY 


I 


septum  in  which  the  foramen  ovale  is  situated;  shortlj^  after  birth  it  fuses  with 
the  primary  septum  and  the  foramen  ovale  is  obliterated. 

The  valve  of  the  inferior  vena  cava  serves  to  direct  the  blood  from  that  vessel 
through  the  foramen  ovale  into  the  left  atrium. 

The  peculiarities  in  the  arterial  system  of  the  fetus  are  the  communication 
between  the  pulmonary  artery  and  the  aorta  by  means  of  the  ductus  arteriosus, 
and  the  continuation  of  the  hypogastric  arteries  as  the  umbilical  arteries  to  the 
placenta. 

The  ductus  arteriosus  is  a  short  tube,  about  1.25  cm.  in  length  at  birth,  and 
of  the  diameter  of  a  goose-quill.  In  the  early  condition  it  forms  the  continuation 
of  the  pulmonary  artery,  and  opens  into  the  aorta,  just  beyond  the  origin  of  the 
left  subclavian  artery;  and  so  conducts  the  greater  amount  of  the  blood  from  the 
right  ventricle  into  the  aorta.  When  the  branches  of  the  pulmonary  artery  have 
become  larger  relatively  to  the  ductus  arteriosus,  the  latter  is  chiefly  connected 
to  the  left  pulmonary  artery. 

The  hypogastric  arteries  run  along  the  sides  of  the  bladder  and  thence  upward 
on  the  back  of  the  anterior  abdominal  wall  to  the  umbilicus;  here  they  pass  out 
of  the  abdomen  and  are  continued  as  the  umbilical  arteries  in  the  umbilical  cord 
to  the  placenta.    They  convey  the  fetal  blood  to  the  placenta. 

The  peculiarities  in  the  venous  system  of  the  fetus  are  the  communications 
established  between  the  placenta  and  the  liver  and  portal  vein,  through  the  umbil- 
ical vein;  and  between  the  umbilical  vein  and  the  inferior  vena  cava  through  the 
ductus  venosus. 

Fetal  Circulation  (Fig.  502). — The  fetal  blood  is  returned  from  the  placenta  to 
the  fetus  by  the  umbilical  vein.  This  vein  enters  the  abdomen  at  the  umbilicus, 
and  passes  upward  along  the  free  margin  of  the  falciform  ligament  of  the  liver  to 
the  under  surface  of  that  organ,  where  it  gives  off  two  or  three  branches,  one  of 
large  size  to  the  left  lobe,  and  others  to  the  lobus  quadratus  and  lobus  caudatus. 
At  the  porta  hepatis  (transverse  fissure  of  the  liver)  it  divides  into  two  branches : 
of  these,  the  larger  is  joined  by  the  portal  vein,  and  enters  the  right  lobe;  the 
smaller  is  continued  upward,  under  the  name  of  the  ductus  venosus,  and  joins 
the  inferior  vena  cava.  The  blood,  therefore,  which  traverses  the  umbilical  vein, 
passes  to  the  inferior  vena  cava  in  three  different  ways.  A  considerable  quantity 
circulates  through  the  liver  with  the  portal  venous  blood,  before  entering  the 
inferior  vena  cava  by  the  hepatic  veins;  some  enters  the  liver  directly,  and  is 
carried  to  the  inferior  cava  by  the  hepatic  veins;  the  remainder  passes  directly 
into  the  inferior  vena  cava  through  the  ductus  venosus. 

In  the  inferior  vena  cava,  the  blood  carried  by  the  ductus  venosus  and  hepatic 
veins  becomes  mixed  with  that  returning  from  the  lower  extremities  and  abdominal 
wall.  It  enters  the  right  atrium,  and,  guided  by  the  valve  of  the  inferior  vena 
cava,  passes  through  the  foramen  ovale  into  the  left  atrium,  where  it  mixes  with 
a  small  quantity  of  blood  returned  from  the  lungs  by  the  pulmonary  veins.  From 
the  left  atrium  it  passes  into  the  left  ventricle;  and  from  the  left  ventricle  into  the 
aorta,  by  means  of  which  it  is  distributed  almost  entirely  to  the  head  and  upper 
extremities,  a  small  quantity  being  probably  carried  into  the  descending  aorta. 
From  the  head  and  upper  extremities  the  blood  is  returned  by  the  superior  vena 
cava  to  the  right  atrium,  where  it  mixes  with  a  small  portion  of  the  blood  from  the 
inferior  vena  cava.  From  the  right  atrium  it  descends  into  the  right  ventricle, 
and  thence  passes  into  the  pulmonary  artery.  The  lungs  of  the  fetus  being  inactive, 
only  a  small  quantity  of  the  blood  of  the  pulmonary  artery  is  distributed  to  them 
by  the  right  and  left  pulmonary  arteries,  and  returned  by  the  pulmonary  veins 
to  the  left  atrium:  the  greater  part  passes  through  the  ductus  arteriosus  into  the 
aorta,  where  it  mixes  with  a  small  quantity  of  the  blood  transmitted  by  the  left 
ventricle  into  the  aorta.    Through  this  vessel  it  descends,  and  is  in  part  distributed 


PECULIARITIES  IN  THE  VASCULAR  SYSTEM  OF  THE  FETUS      541 


fO  the  lower  extremities  and  the  viscera  of  the  abdomen  and  pelvis,  but  the  greater 
imount  is  conveyed  by  the  umbilical  arteries  to  the  placenta. 

From  the  preceding  account  of  the  circulation  of  the  blood  in  the  fetus  the  fol- 
lowing facts  will  be  evident:     (1)  The  placenta  serves  the  purposes  of  nutrition 


Hypogastric  arteries 


-Plan  of  the  fetal  circulation.     In  this  plan  the  figured  arrows  represent  the  kind  of  blood,  as  well  asthe 

direction  which  it  takes  in  the  vessles.     Thus — arterial  blood  is  figured   > >  ;  venous  blood,  > >  ;  mixed 

(arterial  and  venous)  blood,  > >. 

and  excretion,  receiving  the  impure  blood  from  the  fetus,  and  returning  it  purified 
and  charged  with  additional  nutritive  material.  (2)  Nearly  the  whole  of  the  blood 
of  the  umbilical  vein  traverses  the  liver  before  entering  the  inferior  vena  cava; 
hence  the  large  size  of  the  liver,  especially  at  an  early  period  of  fetal  life.  (3)  The 
right  atrium  is  the  point  of  meeting  of  a  double  current,  the  blood  in  the  inferior 


542  ANGIOLOGY 


I 


vena  cava  being  guided  by  the  valve  of  this  vessel  into  the  left  atrium,  while  that 
in  the  superior  vena  cava  descends  into  the  right  ventricle.  At  an  early  period 
of  fetal  life  it  is  highly  probable  that  the  two  streams  are  quite  distinct;  for  the 
inferior  vena  cava  opens  almost  directly  into  the  left  atrium,  and  the  valve  of  the 
inferior  vena  cava  would  exclude  the  current  from  the  right  ventricle.  At  a  later 
period,  as  the  separation  between  the  two  atria  becomes  more  distinct,  it  seems 
probable  that  some  mixture  of  the  two  streams  must  take  place.  (4)  The  pure 
blood  carried  from  the  placenta  to  the  fetus  by  the  umbilical  vein,  mixed  with  the 
blood  from  the  portal  vein  and  inferior  vena  cava,  passes  almost  directly  to  the 
arch  of  the  aorta,  and  is  distributed  by  the  branches  of  that  vessel  to  the  head 
and  upper  extremities.  (5)  The  blood  contained  in  the  descending  aorta,  chiefly 
derived  from  that  which  has  already  circulated  through  the  head  and  limbs, 
together  with  a  small  quantity  from  the  left  ventricle,  is  distributed  to  the 
abdomen  and  lower  extremities. 

Changes  in  the  Vascular  System  at  Birth. — At  birth,  when  respiration  is  estab- 
lished, an  increased  amount  of  blood  from  the  pulmonary  artery  passes  through  the 
lungs,  and  the  placental  circulation  is  cut  off.  The  foramen  ovale  is  closed  by  about 
the  tenth  day  after  birth :  the  valvular  fold  above  mentioned  adheres  to  the  margin 
of  the  foramen  for  the  greater  part  of  its  circumference,  but  a  slit-like  opening  is 
left  between  the  two  atria  above,  and  this  sometimes  persists. 

The  ductus  arteriosus  begins  to  contract  immediately  after  respiration  is  estab- 
lished, and  is  completely  closed  from  the  fourth  to  the  tenth  day;  it  ultimately 
degenerates  into  an  impervious  cord,  the  ligamentum  arteriosum,  which  connects 
the  left  pulmonary  artery  to  the  arch  of  the  aorta. 

Of  the  hypogastric  arteries,  the  parts  extending  from  the  sides  of  the  bladder 
to  the  umbilicus  become  obliterated  between  the  second  and  fifth  days  after  birth, 
and  project  as  fibrous  cords,  the  lateral  umbilical  ligaments,  toward  the  abdominal 
cavity,  carrying  on  them  folds  of  peritoneum. 

The  umbilical  vein  and  ductus  venosus  are  completely  obliterated  between  the 
second  and  fifth  days  after  birth;  the  former  becomes  the  ligamentum  teres,  the 
latter  the  ligamentum  venosum,  of  the  liver. 

BIBLIOGRAPHY. 

Bremer,  J.  L.:     The  Earliest  Bloodvessels  in  Man,  Am.  Jour.  Anat.,  1914,  xvi. 

Evans,  H.  M.:  On  the  Development  of  the  Aortae,  Cardinal  and  UmbiUcal  Veins  and  Other 
Bloodvessels  of  the  Vertebrate  Embryos  from  Capillaries,  Anat.  Rec,  1909,  iii. 

Evans,  H.  M.:  The  Development  of  the  Vascular  System,  Keibel  and  Mall,  Manual  of 
Human  Embryology. 

His,  W.:     Anatomic  Menschlicheu  Embryonen,  Leipzig,  1880-85. 

MacCallum,  J.  B.:  ,  On  the  Muscular  Ai-chitecture  and  Growth  of  the  Ventricles  of  the  Heart, 
Johns  Hop.  Hosp.  Rep.,  1900,  ix. 

Mall,  F.  P.:     A  Study  of  the  Structural  Unit  of  the  Liver,  Am.  Jour.  Anat.,  1906,  v. 

Mall,  F.  P. :  On  the  Muscular  Architecture  of  the  Ventricles  of  the  Human  Heart,  Am.  Jour. 
Anat.,  1911,  xi. 

Mall,  F.  P. :  The  Development  of  the  Internal  Mammary  and  Deep  Epigastric  Arteries  in 
^lan,  Johns  Hop.  Hosp.  Bulletin,  1898. 

Stockard,  C.  R.:  A  Study  of  Wandering  Mesenchymal  Cells  on  the  Living  Yolk  Sac  and 
Their  Developmental  Products:  Chromatophores,  Vascular  Endothelium  and  Blood  Cells,  Am. 
Jour.  Anat.,  1915,  xviii. 

Streeter,  G.  L.  :  The  Development  of  the  Venous  Sinuses  of  the  Dura  Mater  in  the  Human 
Embryo,  Am.  Jour.  Anat.,  1915,  xviii. 

Thoma,  R.  :  Text-book  of  General  Pathology  and  Pathological  Anatomy,  Translated  by  Bruce, 
London,  1896. 


THE  ARTERIES. 


■?..a  .-^Ki  iw>. ' 


THE  distribution  of  the  systematic  arteries  is  like  a  highly  ramified  tree,  the 
common  trunk  of  which,  formed  by  the  aorta,  commences  at  the  left  ventricle, 
while  the  smallest  ramifications  extend  to  the  peripheral  parts  of  the  body  and  the 
contained  organs.  Arteries  are  found  in  all  parts  of  the  body,  except  in  the  hairs, 
nails,  epidermis,  cartilages,  and  cornea;  the  larger  trunks  usually  occupy  the  most 
protected  situations,  running,  in  the  limbs,  along  the  flexor  surface,  where  they 
are  less  exposed  to  injury. 

There  is  considerable  variation  in  the  mode  of  division  of  the  arteries :  occasion- 
ally a  short  trunk  subdivides  into  several  branches  at  the  same  point,  as  may  be 
observed  in  the  celiac  artery  and  the  thyrocervical  trunk :  the  vessel  may  give  off 
several  branches  in  succession,  and  still  continue  as  the  main  trunk,  as  is  seen  in 
the  arteries  of  the  limbs;  or  the  division  may  be  dichotomous,  as,  for  instance,  when 
i:he  aorta  divides  into  the  two  common  iliacs. 

A  branch  of  an  artery  is  smaller  than  the  trunk  from  which  it  arises;  but  if  an 
artery  divides  into  two  branches,  the  combined  sectional  area  of  the  two  vessels 
is,  in  nearly  every  instance,  somewhat  greater  than  that  of  the  trunk;  and  the 
combined  sectional  area  of  all  the  arterial  branches  greatly  exceeds  that  of  the 
aorta;  so  that  the  arteries  collectively  may  be  regarded  as  a  cone,  the  apex  of 
which  corresponds  to  the  aorta,  and  the  base  to  the  capillary  system. 

The  arteries,  in  their  distribution,  communicate  with  one  another,  forming 
what  are  called  anastomoses,  and  these  communications  are  very  free  between 
the  large  as  well  as  between  the  smaller  branches.  The  anastomosis  between  trunks 
3f  equal  size  is  found  where  great  activity  of  the  circulation  is  requisite,  as  in  the 
brain;  here  the  two  vertebral  arteries  unite  to  form  the  basilar,  and  the  two  ante- 
rior cerebral  arteries  are  connected  by  a  short  communicating  trunk;  it  is  also 
round  in  the  abdomen,  where  the  intestinal  arteries  have  very  ample  anastomoses 
Detween  their  larger  branches.  In  the  limbs  the  anastomoses  are  most  numerous 
ind  of  largest  size  around  the  joints,  the  branches  of  an  artery  above  uniting 
with  branches  from  the  vessels  below.  These  anastomoses  are  of  considerable  in- 
terest to  the  surgeon,  as  it  is  by  their  enlargement  that  a  collateral  circulation  is 
established  after  the  application  of  a  ligature  to  an  artery.  The  smaller  branches 
oi  arteries  anastomose  more  frequently  than  the  larger;  and  between  the  smallest 
twigs  these  anastomoses  become  so  numerous  as  to  constitute  a  close  network 
that  pervades  nearly  every  tissue  of  the  body. 

Throughout  the  body  generally  the  larger  arterial  branches  pursue  a  fairly 
straight  course,  but  in  certain  situations  they  are  tortuous.  Thus  the  external 
maxillary  artery  in  its  course  over  the  face,  and  the  arteries  of  the  lips,  are  extremely 
tortuous  to  accommodate  themselves  to  the  movements  of  the  parts.  The  uterine 
arteries  are  also  tortuous,  to  accommodate  themselves  to  the  increase  of  size  which 
the  uterus  undergoes  during  pregnancy. 

The  Pulmonary  Artery  (A.  Pulmonalis)  (Figs.  503,  504). 

The  pulmonary  artery  conveys  the  venous  blood  from  the  right  ventricle  of  the 
heart  to  the  lungs.    It  is  a  short,  wide  vessel,  about  5  cm.  in  length  and  3  cm.  in 

(543) 


544 


ANGIOLOGY 


I 


diameter,  arising  from  the  conus  arteriosus  of  the  right  ventricle.     It  extends 
obliquely  upward  and  backward,  passing  at  first  in  front  and  then  to  the  left 


Traasversus  thoracis 
Internal  mammary  vessels 


Left  phrenic 
nerve 


Pulmonary  pleura 
Costal  pleura 


Sympathetic  trunk  /  V  \  ■^'^VQ^^  ^^^^ 

Thoracic  duct  Vagus  nerves 

Fig.  603. — Transverse  section  of  thorax,  showing  relations  of  pulmonary  artery. 


ENTRANCE    OF 
VENA     AZYGOS 
BHANCH    OF   PUL- 
MONARY  ARTERY 


Fig.  504. — Pulmonary  vessels,  seen  in  a  dorsal  view  of  the  heart  and  lungs.    The  lungs  have  been  pulled  away  from 
the  median  line,  and  a  part  of  the  right  lung  has  been  cut  away  to  display  the  air-ducts  and  bloodvessels. 


I 


THE  ASCENDING  AORTA  545 


II 


of  the  ascending  aorta,  as  far  as  the  under  surface  of  the  aortic  arch,  where  it 
divides,  about  the  level  of  the  fibrocartilage  between  the  fifth  and  sixth  thoracic 
vertebra?,  into  right  and  left  branches  of  nearly  equal  size.  — 

Relations. — The  whole  of  this  vessel  is  contained  within  the  pericardinna.  It  is  enclosed  with 
the  ascending  aorta  in  a  single  tube  of  the  visceral  layer  of  the  serous  pericardium,  which  is  con- 
tinued upward  upon  them  from  the  base  of  the  heart.  The  fibrous  layer  of  the  pericardium  is 
gradually  lost  upon  the  external  coats  of  the  two  branches  of  the  artery.  In  front,  the  pulmonary 
artery  is  separated  from  the  anterior  end  of  the  second  left  intercostal  space  by  the  pleura  and 
left  lung,  in  addition  to  the  pericardium;  it  rests  at  first  upon  the  ascending  aorta,  and  higher 
up  hes  in  front  of  the  left  atrium  on  a  plane  posterior  to  the  ascending  aorta.  On  either  side  of 
its  origin  is  the  auricula  of  the  corresponding  atrium  and  a  coronary  artery,  the  left  coronary 
artery  passing,  in  the  first  part  of  its  course,  behind  the  vessel.  The  superficial  part  of  the  cardiac 
plexus  lies  above  its  bifurcation,  between  it  and  the  arch  of  the  aorta. 

The  right  branch  of  the  puhnonary  artery  (ramus  dexter  a.  pulmonalis) ,  longer 
and  larger  than  the  left,  runs  horizontally  to  the  right,  behind  the  ascending  aorta 
and  superior  vena  cava  and  in  front  of  the  right  bronchus,  to  the  root  of  the  right 
lung,  where  it  divides  into  two  branches.  The  lower  and  larger  of  these  goes  to 
the  middle  and  lower  lobes  of  the  lung;  the  upper  and  smaller  is  distributed  to  the 
upper  lobe.  "" 

The  left  branch  of  the  pulmonary  artery  {ramus  sinister  a.  yulmonalis),  shorter 
and  somewhat  smaller  than  the  right,  passes  horizontally  in  front  of  the  descending 
aorta  and  left  bronchus  to  the  root  of  the  left  lung,  where  it  divides  into  two 
branches,  one  for  each  lobe  of  the  lung. 

Above,  it  is  connected  to  the  concavity  of  the  aortic  arch  by  the  ligamentum 
arteriosum,  on  the  left  of  which  is  the  left  recurrent  nerve,  and  on  the  right  the 
superficial  part  of  the  cardiac  plexus.     Below,  it  is  joined  to  the  upper  left  pul- 
.monary  vein  by  the  ligament  of  the  left  vena  cava. 

I  The  terminal  branches  of  the  pulmonary  arteries  will  be  described  with  the 
anatomy  of  the  lungs. 

THE  AORTA. 

The  aorta  is  the  main  trunk  of  a  series  of  vessels  which  convey  the  oxygenated 
blood  to  the  tissues  of  the  body  for  their  nutrition.  It  commences  at  the  upper 
part  of  the  left  ventricle,  where  it  is  about  3  cm.  in  diameter,  and  after  ascending 
for  a  short  distance,  arches  backward  and  to  the  left  side,  over  the  root  of  the  left 
lung;  it  then  descends  within  the  thorax  on  the  left  side  of  the  vertebral  column, 
passes  into  the  abdominal  cavity  through  the  aortic  hiatus  in  the  diaphragm, 
and  ends,  considerably  diminished  in  size  (about  1.75  cm.  in  diameter),  opposite 
the  lower  border  of  the  fourth  lumbar  vertebra,  by  dividing  into  the  right  and  left 
common  iliac  arteries.  Hence  it  is  described  in  several  portions,  viz.,  the  ascending 
aorta,  the  arch  of  the  aorta,  and  the  descending  aorta,  which  last  is  again  divided  into 
the  thoracic  and  abdominal  aortae. 


THE  ASCENDING  AORTA  (AORTA  ASCENDENS)  (Fig.  505). 


I 


The  ascending  aorta  is  about  5  cm.  in  length.  It  commences  at  the  upper  part 
of  the  base  of  the  left  ventricle,  on  a  level  with  the  lower  border  of  the  third  costal 
cartilage  behind  the  left  half  of  the  sternum;  it  passes  obliquely  upward,  forward, 
and  to  the  right,  in  the  direction  of  the  heart's  axis,  as  high  as  the  upper  border 
of  the  second  right  costal  cartilage,  describing  a  slight  curve  in  its  course,  and  being 
situated,  about  6  cm.  behind  the  posterior  surface  of  the  sternum.  At  its  origin 
it  presents,  opposite  the  segments  of  the  aortic  valve,  three  small  dilatations 
called  the  aortic  sinuses.  At  the  union  of  the  ascending  aorta  with  the  aortic  arch 
the  caliber  of  the  vessel  is  increased,  owing  to  a  bulging  of  its  right  wall.  This 
dilatation  is  termed  the  bulb  of  the  aorta,  and  on  transverse  section  presents  a  som,e- 
35 


546 


ANGIOLOGY 


I 


what  oval  figure.  The  ascending  aorta  is  contained  within  the  pericardium,  and 
is  enclosed  in  a  tube  of  the  serous  pericardium,  common  to  it  and  the  pulmonary- 
artery. 

Relations. — The  ascending  aorta  is  covered  at  its  commencement  by  the  trunk  of  the  pul- 
monary artery  and  the  right  auricula,  and,  higher  up,  is  separated  from  the  sternum  by  the 
pericardium,  the  right  pleura,  the  anterior  margin  of  the  right  lung,  some  loose  areolar  tissue, 
and  the  remains  of  the  thymus;  posteriorly,  it  rests  upon  the  left  atrium  and  right  pulmonary 
artery.  On  the  right  side,  it  is  in  relation  with  the  superior  vena  cava  and  right  atrium,  the 
former  lying  partly  behind  it;  on  the  left  side,  with  the  pulmonary  artery. 


Right  vagus 
Recurrent  nerve  ^\ 


Left  vagus 
I/eft  phrenic 
Thoracic  duct 


Fig.  505. — The  arch  of  the  aorta,  and  its  branches. 

Branches. — ^The  only  branches  of  the  ascending  aorta  are  the  two  coronary 
arteries  which  supply  the  heart;  they  arise  near  the  commencement  of  the  aorta 
immediately  above  the  attached  margins  of  the  semilunar  valves. 

The  Coronary  Arteries. — The  Right  Coronary  Artery  (a.  coronaria  [cordis]  dextra) 
arises  from  the  right  anterior  aortic  sinus.  It  passes  at  first  between  the  conus 
arteriosus  and  the  right  auricula  and  then  runs  in  the  right  portion  of  the  coronary 
sulcus,  coursing  at  first  from  the  left  to  right  and  then  on  the  diaphragmatic  surface 
of  the  heart  from  right  to  left  as  far  as  the  posterior  longitudinal  sulcus,  down 


I 


I 

I 


THE  ARCH  OF  THE  AORTA  547 

which  it  is  continued  to  the  apex  of  the  heart  as  the  posterior  descending  branch. 
It  gives  off  a  large  marginal  branch  which  follows  the  acute  margin  of  the  heart 
and  supplies  branches  to  both  surfaces  of  the  right  ventricle.  It  also  gives  twigs 
to  the  right  atrium  and  to  the  part  of  the  left  ventricle  which  adjoins  the 
posterior  longitudinal  sulcus. 

The  Left  Coronary  Artery  {a.  coronaria  [cordis]  sinistra),  larger  than  the  right, 
arises  from  the  left  anterior  aortic  sinus  and  divides  into  an  anterior  descending 
and  a  circumflex  branch.  The  anterior  descending  branch  passes  at  first  behind  the 
pulmonary  artery  and  then  comes  forward  between  that  vessel  and  the  left  auricula 
to  reach  the  anterior  longitudinal  sulcus,  along  which  it  descends  to  the  incisura 
apicis  cordis;  it  gives  branches  to  both  ventricles.  The  circumflex  branch  follows 
the  left  part  of  the  coronary  sulcus,  running  first  to  the  left  and  then  to  the  right, 
reaching  nearly  as  far  as  the  posterior  longitudinal  sulcus;  it  gives  branches  to  the 
left  atrium  and  ventricle.  There  is  a  free  anastomosis  between  the  minute 
branches  of  the  two  coronary  arteries  in  the  substance  of  the  heart. 

Peculiarities. — These  vessels  occasionally  arise  by  a  common  trunk,  or  their  number  may  be 
increased  to  three,  the  additional  branch  being  of  small  size.  More  rarely,  there  are  two  addi- 
tional branches. 


Ii  THE  ARCH  OF  THE  AORTA  (ARCUS  AORT^;  TRANSVERSE 

f  AORTA)   (Fig.  505). 

The  arch  of  the  aorta  begins  at  the  level  of  the  upper  border  of  the  second  sterno- 
costal articulation  of  the  right  side,  and  runs  at  first  upward,  backward,  and  to  the 
left  in  front  of  the  trachea ;  it  is  then  directed  backward  on  the  left  side  of  the  trachea 
and  finally  passes  downward  on  the  left  side  of  the  body  of  the  fourth  thoracic 
vertebra,  at  the  lower  border  of  which  it  becomes  continuous  with  the  descending 
^^   aorta.    It  thus  forms  two  curvatures:  one  with  its  convexity  upward,  the  other 
^M  \  with  its  convexity  forward  and  to  the  left.    Its  upper  border  is  usually  about  2.5 
^r  "  cm.  below  the  superior  border  to  the  manubrium  sterni. 

■  Relations. — The  arch  of  the  aorta  is  covered  anteriorly  by  the  pleurae  and  anterior  margins 

of  the  lungs,  and  by  the  remains  of  the  thymus.  As  the  vessel  runs  backward  its  left  side  is  in 
contact  with  the  left  lung  and  pleura.  Passing  downward  on  the  left  side  of  this  part  of  the  arch 
are  four  nerves;  in  order  from  before  backward  these  are,  the  left  phrenic,  the  lower  of  the  superior 
cardiac  branches  of  the  left  vagus,  the  superior  cardiac  branch  of  the  left  sympathetic,  and  the 
trunk  of  the  left  vagus.  As  the  last  nerve  crosses  the  arch  it  gives  off  its  recurrent  branch,  which 
hooks  around  below  the  vessel  and  then  passes  upward  on  its  right  side.  The  highest  left  inter- 
costal vein  runs  obUquely  upward  and  forward  on  the  left  side  of  the  arch,  between  the  phrenic 
and  vagus  nerves.  On  the  right  are  the  deep  part  of  the  cardiac  plexus,  the  left  recurrent  nerve, 
the  esophagus,  and  the  thoracic  duct;  the  trachea  Ues  behind  and  to  the  right  of  the  vessel. 

,  Above  are  the  innominate,  left  common  carotid,  and  left  subclavian  arteries,  which  arise  from 

the  convexity  of  the  arch  and  are  crossed  close  to  their  origins  by  the  left  innominate  vein.  Below 
are  the  bifurcation  of  the  pulmonary  artery,  the  left  bronchus,  the  hgamentum  arteriosum,  the 
superficial  part  of  the  cardiac  plexus,  and  the  left  recurrent  nerve.  As  already  stated,  the  hga- 
mentum arteriosum  connects  the  commencement  of  the  left  pulmonary  artery  to  the  aortic  arch. 

Between  the  origin  of  the  left  subclavian  artery  and  the  attachment  of  the  ductus 
arteriosus  the  lumen  of  the  fetal  aorta  is  considerably  narrowed,  forming  what  is 
termed  the  aortic  isthmus,  while  immediately  beyond  the  ductus  arteriosus  the 
vessel  presents  a  fusiform  dilation  which  His  has  named  the  aortic  spindle — the 
point  of  junction  of  the  two  parts  being  marked  in  the  concavity  of  the  arch  by  an 
indentation  or  angle.  These  conditions  persist,  to  some  extent,  in  the  adult,  where 
His  found  that  the  average  dianaeter  of  the  spindle  exceeded  that  of  the  isthmus 
by  3  mm. 

Distinct  from  this  diffuse  and  moderate  stenosis  at  the  isthmus  is  the  condition  known  as 
coarctation  of  the  aorta,  or  marked  stenosis  often  amounting  to  complete  obliteration  of  its  lumen, 
seen  in  adults  and  occurring  at  or  near,  oftenest  a  little  below,  the  insertion  of  the  ligamentum 


I 


548 


I 


arteriosum  into  the  aorta.  According  to  Bonnet^  this  coarctation  is  never  found  in  the  fetus  or 
at  birth,  and  is  due  to  an  abnormal  extension  of  the  pecuUar  tissue  of  the  ductus  into  the  aortic 
wall,  which  gives  rise  to  a  simultaneous  stenosis  of  both  vessels  as  it  contracts  after  birth — tae 
ductus  is  usually  obhterated  in  these  cases.  An  extensive  collateral  circulation  is  set  up,  by  tlie 
costocervicals,  internal  mammaries,  and  the  descending  branches  of  the  transverse  cervical 
above  the  stenosis,  and  below  it  by  the  first  four  aortic  intercostals,  the  pericardiaco-phrenics, 
and  the  superior  and  inferior  epigastrics. 

Peculiarities. — The  height  to  which  the  aorta  rises  in  the  thorax  is  usually  about  2.5  era. 
below  the  upper  border  of  the  sternum;  but  it  may  ascend  nearly  to  the  top  of  the  bone.  Occa- 
sionally it  is  found  4  cm.,  more  rarely  from  5  to  8  cm.  below  this  point.  Sometimes  the  aorta 
arches  over  the  root  of  the  right  lung  (right  aortic  arch)  instead  of  over  that  of  the  left,  and  pass(3S 
down  on  the  right  side  of  the  vertebral  column,  a  condition  which  is  found  in  birds.  In  such  easels 
all  the  thoracic  and  abdominal  viscera  are  transposed.  Less  frequently  the  aorta,  after  arching 
over  the  root  of  the  right  lung,  is  directed  to  its  usual  position  on  the  left  side  of  the  vertebral 
column;  this  peculiarity  is  not  accompanied  by  transposition  of  the  viscera.  The  aorta  occa- 
sionally divides,  as  in  some  quadrupeds,  into  an  ascending  and  a  descending  trunk,  the  former 
of  which  is  directed  vertically  upward,  and  subdivides  into  three  branches,  to  supply  the  head 
and  upper  extremities.  Sometimes  the  aorta  subdivides  near  its  origin  into  two  branches,  which 
soon  reunite.  In  one  of  these  cases  the  esophagus  and  trachea  were  found  to  pass  through  the 
interval  between  the  two  branches;  this  is  the  normal  condition  of  the  vessel  in  the  reptilia. 

Branches  (Figs.  505,  506). — The  branches  given  off  from  the  arch  of  the  aorta 
are  three  in  number:  the  innominate,  the  left  common  carotid,  and  the  left  subclavian. 

Peculiarities. — Position  of  the  Branches. — The  branches,  instead  of  arising  from  the  highest 
part  of  the  arch,  may  spring  from  the  commencement  of  the  arch  or  upper  part  of  the  ascending 
aorta;  or  the  distance  between  them  at  their  origins  may  be  increased  or  diminished,  the  most 
frequent  change  in  this  respect  being  the  approximation  of  the  left  carotid  toward  the  innominate 
artery. 

The  number  of  the  primary  branches  may  be  reduced  to  one,  or  more  commonly  two;  the  left 
carotid  arising  from  the  innominate  artery;  or  (more  rarely)  the  carotid  and  subclavian  arteries 
of  the  left  side  arising  from  a  left  innominate  artery.  But  the  number  may  be  increased  to  four, 
from  the  right  carotid  and  subclavian  arteries  arising  directly  from  the  aorta,  the  innominate 
being  absent.  In  most  of  these  latter  cases  the  right  subclavian  has  been  found  to  arise  from  the 
left  end  of  the  arch;  in  other  cases  it  is  the  second  or  third  branch  given  off,  instead  of  the  first. 
Another  common  form  in  which  there  are  four  primary  branches  is  that  in  which  the  left  vertebral 
artery  arises  from  the  arch  of  the  aorta  between  the  left  carotid  and  subclavian  arteries.  Lastly, 
the  number  of  trunks  from  the  arch  may  be  increased  to  five  or  six;  in  these  instances,  the  external 
and  internal  carotids  arise  separately  from  the  arch,  the  common  carotid  being  absent  on  one  or 
both  sides.  In  some  few  cases  six  branches  have  been  found,  and  this  condition  is  associated 
with  the  origin  of  both  vertebral  arteries  from  the  arch. 

Number  Usual,  Arrangement  Different. — When  the  aorta  arches  over  to  the  right  side,  the 
three  branches  have  an  arrangement  the  reverse  of  what  is  usual;  the  innominate  artery  is  a  left 
one,  and  the  right  carotid  and  subclavian  arise  separately.  In  other  cases,  where  the  aorta  takes 
its  usual  course,  the  two  carotids  may  be  joined  in  a  common  trunk,  and  the  subclavians  arise 
separately  from  the  arch,  the  right  subclavian  generally  arising  from  the  left  end  of  the  arch. 

In  some  instances  other  arteries  spring  from  the  arch  of  the  aorta.  Of  these  the  most  common 
are  the  bronchial,  one  or  both,  and  the  thyreoidea  ima;  but  the  internal  mammary  and  the  inferior 
thjrroid  have  been  seen  to  arise  from  this  vessel. 

The  Innominate  Artery  (A.  Anonyma;  Brachiocephalic  Artery)  (Fig.  505). 

The  innominate  artery  is  the  largest  branch  of  the  arch  of  the  aorta,  and  is  from 
4  to  5  cm.  in  length.  It  arises,  on  a  level  with  the  upper  border  of  the  second 
right  costal  cartilage,  from  the  commencement  of  the  arch  of  the  aorta,  on  a  plane 
anterior  to  the  origin  of  the  left  carotid;  it  ascends  obliquely  upward,  backward, 
and  to  the  right  to  the  level  of  the  upper  border  of  the  right  sternoclavicular 
articulation,  where  it  divides  into  the  right  common  carotid  and  right  subclavian 
arteries. 

Relations. — Anteriorly,  it  is  separated  from  the  manubrium  sterni  by  the  Sternohyoideus  and 
Sternothyreoideus,  the  remains  of  the  thymus,  the  left  innominate  and  right  inferior  thyroid  veins 
which  cross  its  root,  and  sometimes  the  superior  cardiac  branches  of  the  right  vagus.    Posterior 

1  Rev.  de  M6d.,  Paris,  1903. 


p 


p 


f 


THE  COMMON  CAROTID  ARTERY  549 

to  it  is  the  trachea,  which  it  crosses  obUquely.  On  the  right  side  are  the  right  innominate  vein, 
the  superior  vena  cava,  the  right  phrenic  nerve,  and  the  pleura;  and  on  the  left  side,  the  remains 
of  the  thymus,  the  origin  of  the  left  common  carotid  artery,  the  inferior  thyroid  veins,  and  the 
trachea. 

Branches. — The  innominate  artery  usually  gives  off  no  branches;  but  occasion- 
ally a  small  branch,  the  thjn-eoidea  ima,  arises  from  it.  Sometimes  it  gives  off  a 
thymic  or  bronchial  branch. 

The  thyreoidea  ima  (a.  thyreoidea  ima)  ascends  in  front  of  the  trachea  to  the 
lower  part  of  the  thyroid  gland,  which  it  supplies.  It  varies  greatly  in  size,  and 
appears  to  compensate  for  deficiency  or  absence  of  one  of  the  other  thyroid 
vessels.  It  occasionally  arises  from  the  aorta,  the  right  common  carotid,  the 
subclavian  or  the  internal  mammary. 

Point  of  Division. — The  innominate  artery  sometimes  divides  above  the  level  of  the  sterno- 
clavicular joint,  less  frequently  below  it. 

Position. — When  the  aortic  arch  is  on  the  right  side,  the  innominate  is  directed  to  the  left  side 
of  the  neck.  * 

Collateral  Circulation. — Allan  Burns  demonstrated,  on  the  dead  subject,  the  possibility  of  the 
estabhshment  of  the  collateral  circulation  after  Ugature  of  the  innominate  artery,  by  tying  and 
dividing  that  artery.  He  then  found  that  "Even  coarse  injection,  impelled  into  the  aorta,  passed 
freely  by  the  anastomosing  branches  into  the  arteries  of  the  right  arm,  fiUing  them  and  all  the 
vessels  of  the  head  completely. "^  The  branches  by  which  this  circulation  would  be  carried  on 
are  very  numerous;  thus,  all  the  communications  across  the  middle  line  between  the  branches 
of  the  carotid  arteries  of  opposite  sides  would  be  available  for  the  supply  of  blood  to  the  right 
side  of  the  head  and  neck;  while  the  anastomosis  between  the  costocervical  of  the  subclavian  and 
the  first  aortic  intercostal  (see  infra  on  the  collateral  circulation  after  obhteration  of  the  thoracic 
aorta)  would  bring  the  blood,  by  a  free  and  direct  course,  into  the  right  subclavian.  The  numerous 
connections,  also,  between  the  intercostal  arteries  and  the  branches  of  the  axillary  and  internal 
mammary  arteries  would,  doubtless,  assist  in  the  supply  of  blood  to  the  right  arm,  while  the 
inferior  epigastric  from  the  external  ihac  would,  by  means  of  its  anastomosis  with  the  internal 
mammary,  compensate  for  any  deficiency  in  the  vascularity  of  the  wall  of  the  chest. 


THE  ARTERIES  OF  THE  HEAD  AND  NECK. 


The  principal  arteries  of  supply  to  the  head  and  neck  are  the  two  common 
carotids;  they  ascend  in  the  neck  and  each  divides  into  two  branches,  viz.,  (1)  the 
external  carotid,  supplying  the  exterior  of  the  head,  the  face,  and  the  greater  part 
of  the  neck;  (2)  the  internal  carotid,  supplying  to  a  great  extent  the  parts  within 
the  cranial  and  orbital  cavities. 


THE  COMMON  CAROTID  ARTERY  (A.  CAROTIS  COMMUNIS). 

The  common  carotid  arteries  differ  in  length  and  in  their  mode  of  origin.  The 
right  begins  at  the  bifurcation  of  the  innominate  artery  behind  the  sternoclavicular 
joint  and  is  confined  to  the  neck.  The  left  springs  from  the  highest  part  of  the 
arch  of  the  aorta  to  the  left  of,  and  on  a  plane  posterior  to  the  innominate  artery, 
and  therefore  consists  of  a  thoracic  and  a  cervical  portion. 

The  thoracic  portion  of  the  left  common  carotid  artery  ascends  from  the  arch  of 
the  aorta  through  the  superior  mediastinum  to  the  level  of  the  left  sternoclavicular 
joint,  where  it  is  continuous  wdth  the  cervical  portion. 

Relations. — In  front,  it  is  separated  from  the  manubrium  stemi  by  the  Sternohyoideus  and 
Sternothyreoideus,  the  anterior  portions  of  the  left  pleura  and  lung,  the  left  innominate  vein, 
and  the  remains  of  the  thymus;  behind,  it  lies  on  the  trachea,  esophagus,  left  recurrent  nerve, 
and  thoracic  duct.  To  its  right  side  below  is  the  innominate  artery,  and  above,  the  trachea,  the 
inferior  thyroid  veins,  and  the  remains  of  the  thymus;  to  its  left  side  are  the  left  vagus  and  phrenic 
nerves,  left  pleura,  and  lung.    The  left  subclavian  artery  is  posterior  and  sUghtly  lateral  to  it. 

'  Surgical  Anatomy  of  t'le  Head  and  Xeck,  p.  62. 


550 


ANGIOLOGY 


The  cervical  portions  of  the  common  carotids  resemble  each  other  so  closely 
that  one  description  will  apply  to  both  (Fig.  507).  Each  vessel  passes  obliquely 
upward,  from  behind  the  sternoclavicular  articulation,  to  the  level  of  the  upper 
border  of  the  thyroid  cartilage,  where  it  divides  into  the  external  and  internal 
carotid  arteries. 


I 


Fig.  507. — Superficial  dissection  of  the  right  side  of  the  neck,  showing  the  carotid  and  subclavian  arteries. 

At  the  lower  part  of  the  neck  the  two  common  carotid  arteries  are  separated 
from  each  other  by  a  very  narrow  interval  which  contains  the  trachea;  but  at  the 
upper  part,  the  thyroid  gland,  the  larynx  and  pharynx  project  forward  between 
the  two  vessels.  The  common  carotid  artery  is  contained  in  a  sheath,  which  is 
derived  from  the  deep  cervical  fascia  and  encloses  also  the  internal  jugular  vein 
and  vagus  nerve,  the  vein  lying  lateral  to  the  artery,  and  the  nerve  between  the 
artery  and  vein,  on  a  plane  posterior  to  both.  On  opening  the  sheath,  each  of 
these  three  structures  is  seen  to  have  a  separate  fibrous  investment. 


I 


THEEXfERNALCAROTID  ARTERY  551 


Relations. — At  the  lower  part  of  the  neck  the  common  carotid  artery  is  very  deeply  seated, 
being  covered  by  the  integument,  superficial  fascia,  Platysma,  and  deep  cervical  fascia,  the  Sterno- 
cleidomastoideus,  Sternohyoideus,  Sternothyreoideus,  and  Omohyoideus;  in  the  upper  part  of 
its  course  it  is  more  superficial,  being  covered  merely  by  the  integument,  the  superficial  fascia, 
Platysma,  deep  cervical  fascia,  and  medial  margin  of  the  Sternocleidomastoideus.  When  the 
latter  muscle  is  drawn  backward,  the  artery  is  seen  to  be  contained  in  a  triangular  space,  the 
carotid  triangle,  bounded  behind  by  the  Sternocleidomastoideus,  above  by  the  Stylohyoideus 
and  posterior  belly  of  the  Digastricus,  and  below  by  the  superior  belly  of  the  Omohyoideus. 
This  part  of  the  artery  is  crossed  obUquely,  from  its  medial  to  its  lateral  side,  by  the  sterno- 
cleidomastoid branch  of  the  superior  thyroid  artery;  it  is  also  crossed  by  the  superior  and  middle 
thyroid  veins  which  end  in  the  internal  jugular;  descending  in  front  of  its  sheath  is  the  descending 
branch  of  the  hypoglossal  nerve,  this  filament  being  joined  by  one  or  two  branches  from  the 
cervical  nerves,  which  cross  the  vessel  obhquely.  Sometimes  the  descending  branch  of  the  hypo- 
glossal nerve  is  contained  within  the  sheath.  The  superior  thyroid  vein  crosses  the  artery  near 
its  termination,  and  the  middle  thyroid  vein  a  Uttle  below  the  level  of  the  cricoid  cartilage;  the 
anterior  jugular  vein  crosses  the  artery  just  above  the  clavicle,  but  is  separated  from  it  by  the 
Sternohyoideus  and  Sternothyreoideus.  Behind,  the  artery  is  seps rated  from  the  transverse 
processes  of  the  cervical  vertebrae  by  the  Longus  colli  and  Longus  capitis,  the  sympathetic  trunk 
being  interposed  between  it  and  the  muscles.  The  inferior  thyroid  artery  crosses  behind  the 
lower  part  of  the  vessel.  Medially,  it  is  in  relation  with  the  esophagus,  trachea,  and  thyroid 
gland  (which  overlaps  it),  the  inferior  thyroid  artery  and  recurrent  nerve  being  interposed;  higher 
up,  with  the  larynx  and  pharynx.  Lateral  to  the  artery  are  the  internal  jugular  vein  and  vagus 
nerve. 

At  the  lower  part  of  the  neck,  the  right  recurrent  nerve  crosses  obUquely  behind  the  artery; 
the  right  internal  jugular  vein  diverges  from  the  artery,  but  the  left  approaches  and  often  over- 
laps the  lower  part  of  the  artery. 

Behind  the  angle  of  bifurcation  of  the  common  carotid  artery  is  a  reddish-brown  oval  body, 
known  as  the  glomus  caroticum  (carotid  body).  It  is  similar  in  structiu-e  to  the  glomus  coccygeum 
(coccygeal  body)  which  is  situated  on  the  middle  sacral  artery. 

Peculiarities  as  to  Origin. — The  right  common  carotid  may  arise  above  the  level  of  the  upper 
border  of  the  sternoclavicular  articulation;  this  variation  occurs  in  about  12  per  cent,  of  cases. 
In  other  cases  the  artery  may  arise  as  a  separate  branch  from  the  arch  of  the  aorta,  or  in  con- 
junction with  the  left  carotid.  The  left  common  carotid  varies  in  its  origin  more  than  the  right. 
In  the  majority  of  abnormal  cases  it  arises  with  the  innominate  artery;  if  that  artery  is  absent, 
the  two  carotids  arise  usually  by  a  single  trunk.  It  is  rarely  joined  with  the  left  subclavian^, 
except  in  cases  of  transposition  of  the  aortic  arch. 

Peculiarities  as  to  Point  of  Division. — In  the  majority  of  abnormal  cases  this  occurs  higher 
than  usual,  the  artery  dividing  opposite  or  even  above  the  hyoid  bone;  more  rarely,  it  occurs 
below,  opposite  the  middle  of  the  larynx,  or  the  lower  border  of  the  cricoid  cartilage;  one  case 
is  related  by  Morgagni,  where  the  artery  was  only  4  cm.  in  length  and  divided  at  the  root  of  the 
neck.  Very  rarely,  the  common  carotid  ascends  in  the  neck  without  any  subdivision,  either  the 
external  or  the  internal  carotid  being  wanting;  and  in  a  few  cases  the  common  carotid  has  been 
found  to  be  absent,  the  external  and  internal  carotids  arising  directly  from  the  arch  of  the  aorta. 
This  pecuharity  existed  on  both  sides  in  some  instances,  on  one  side  in  others. 

Occasional  Branches. — The  common  carotid  usually  gives  off  no  branch  previous  to  its  bif urea- 
ion,  but  it  occasionally  gives  origin  to  the  superior  thjrroid  or  its  laryngeal  branch,  the  ascend- 
ing pharyngeal,  the  inferior  thyroid,  or,  more  rarely,  the  vertebral  artery. 

Collateral  Circulation. — After  hgature  of  the  common  carotid,  the  collateral  circulation  can 
be  perfectly  estabhshed,  by  the  free  communication  which  exists  between  the  carotid  arteries 
of  opposite  sides,  both  without  and  within  the  cranium,  and  by  enlargement  of  the  branches  of 
the  subclavian  artery  on  the  side  corresponding  to  that  on  which  the  vessel  has  been  tied.  The 
chief  communications  outside  the  skull  take  place  between  the  superior  and  inferior  thyroid 
arteries,  and  the  profimda  cervicis  and  ramus  descendens  of  the  occipital;  the  vertebral  takes 
the  place  of  the  internal  carotid  within  the  cranium. 


The  External  Carotid  Artery  (A.  Carotis  Externa)  (Fig.  507). 


I  The  external  carotid  artery  begins  opposite  the  upper  border  of  the  thyroid 
cartilage,  and,  taking  a  slightly  curved  course,  passes  upward  and  forward,  and 
then  inclines  backward  to  the  space  behind  the  neck  of  the  mandible,  where  it 
^divides  into  the  superficial  temporal  and  internal  maxillary  arteries.  It  rapidly 
■■diminishes  in  size  in  its  course  up  the  neck,  owing  to  the  number  and  large  size 
"  of  the  branches  given  oft"  from  it.  In  the  child,  it  is  somewhat  smaller  than  the 
internal  carotid;  but  in  the  adult,  the  two  vessels  are  of  nearly  equal  size.    At  its 


k 


552 


ANGIOLOGY 


origin,  this  artery  is  more  superficial,  and  placed  nearer  the  middle  line  than  the 
internal  carotid,  and  is  contained  within  the  carotid  triangle. 

Relations. — The  external  carotid  artery  is  covered  by  the  skin,  superficial  fascia,  Platysma, 
deep  fascia,  and  anterior  margin  of  the  Sternocleidomastoideus;  it  is  crossed  by  the  hypoglossal 
nerve,  by  the  lingual,  ranine,  common  facial,  and  superior  thyroid  veins;  and  by  the  Digastricus 
and  Stylohyoideus;  higher  up  it  passes  deeply  into  the  substance  of  the  parotid  gland,  where 
it  lies  deep  to  the  facial  nerve  and  the  junction  of  the  terhporal  and  internal  maxillary  veins. 
Medial  to  it  are  the  hyoid  bone,  the  wall  of  the  pharynx,  the  superior  laryngeal  nerve,  and  a 
portion  of  the  parotid  gland.  Lateral  to  it,  in  the  lower  part  of  its  course,  is  the  internal  carotid 
artery.  Posterior  to  it,  near  its  origin,  is  the  superior  laryngeal  nerve;  and  higher  up,  it  is  sepa- 
rated from  the  internal  carotid  by  the  Styloglossus  and  Stylopharyngeus,  the  glossopharyngeal 
nerve,  the  pharyngeal  branch  of  the  vagus,  and  part  of  the  parotid  gland. 

Branches. — The  branches  of  the  external  carotid  artery  may  be  divided  into  four 
sets. 


I 


Anterior. 
Superior  Thyroid. 
Lingual. 
External  Maxillary. 


Posterior. 
Occipital. 
Posterior  Auricular. 


Ascending. 
Ascending 
Pharyngeal. 


Terminal. 
Superficial  Temporal. 
Internal  Maxillary. 


1.  The  superior  th3n:oid  artery  (a.  thyreoidea  superior)  (Fig.  507)  arises  from 
the  external  carotid  artery  just  below  the  level  of  the  greater  cornu  of  the  hyoid 
bone  and  ends  in  the  thyroid  gland. 

Relations. — From  its  origin  under  the  anterior  border  of  the  Sternocleidomastoideus  it  runs 
upward  and  forward  for  a  short  distance  in  the  carotid  triangle,  where  it  is  covered  by  the  skin, 
Platysma,  and  fascia;  it  then  arches  downward  beneath  the  Omohyoideus,  Sternohyoideus,  and 
Sternothyreoideus.  To  its  medial  side  are  the  Constrictor  pharyngis  inferior  and  the  external 
branch  of  the  superior  laryngeal  nerve. 

Branches. — It  distributes  twigs  to  the  adjacent  muscles,  and  numerous  branches 
to  the  thyroid  gland,  anastomosing  with  its  fellow  of  the  opposite  side,  and  with 
the  inferior  thyroid  arteries.  The  branches  to  the  gland  are  generally  two  in 
number;  one,  the  larger,  supplies  principally  the  anterior  surface;  on  the  isthmus 
of  the  gland  it  anastomoses  with  the  corresponding  artery  of  the  opposite  side: 
a  second  branch  descends  on  the  posterior  surface  of  the  gland  and  anastomoses 
with  the  inferior  thyroid  artery. 

Besides  the  arteries  distributed  to  the  muscles  and  to  the  thyroid  gland,  the 
branches  of  the  superior  thyroid  are : 


Hyoid. 
Sternocleidomastoid . 


Superior  Laryngeal. 
Cricothyroid. 


The  Hyoid  Branch  {ramibs  hyoideus;  infrahyoid  branch)  is  small  and  runs  along 
the  lower  border  of  the  hyoid  bone  beneath  the  Thyreohyoideus  and  anastomoses 
with  the  vessel  of  the  opposite  side. 

The  Sternocleidomastoid  Branch  {ramus  sternocleidomastoideus;  sternomastoid 
branch)  runs  downward  and  lateralward  across  the  sheath  of  the  common  carotid 
artery,  and  supplies  the  Sternocleidomastoideus  and  neighboring  muscles  and 
integument;  it  frequently  aris'es  as  a  separate  branch  from  the  external  carotid. 

The  Superior  Laryngeal  Artery  (a.  laryngea  superior),  larger  than  either  of  the 
preceding,  accompanies  the  internal  laryngeal  branch  of  the  superior  laryngeal 
nerve,  beneath  the  Thyreohyoideus;  it  pierces  the  hyothyroid  membrane,  and 
supplies  the  muscles,  mucous  membrane,  and  glands  of  the  larynx,  anastomosing 
with  the  branch  from  the  opposite  side. 

The  Cricothyroid  Branch  {ramus  cricothyreoideus)  is  small  and  runs  transversely 
across  the  cricothyroid  membrane,  communicating  with  the  artery  of  the  opposite 
side. 


N 


^ 
¥ 


I 


I 


THE  EXTERNAL  CAROTID  ARTERY  553 

2.  The  lingual  artery  (a.  lingualis)  (Fig.  513")  ame*  from  the  external  carotid 
between  the  superior  thyroid  and  external  maxillary;  it  first  runs  obliquely  upward 
and  medialward  to  the  greater  cornu  of  the  hyoid  bone;  it  then  curves  downward 
and  forward,  forming  a  loop  which  is  crossed  by  the  hypoglossal  nerve,  and  passing 
beneath  the  Digastricus  and  Stylohyoideus  it  runs  horizontally  forward,  beneath 
the  Hyoglossus,  and  finally,  ascending  almost  perpendicularly  to  the  tongue,  turns 
forward  on  its  lower  surface  as  far  as  the  tip,  under  the  name  of  the  profunda 
linguae. 

Relations. — Its  first,  or  oblique,  portion  is  superficial,  and  is  contained  within  the  carotid 
triangle;  it  rests  upon  the  Constrictor  pharyngis  medius,  and  is  covered  by  the  Platysma  and 
the  fascia  of  the  neck.  Its  second,  or  curved,  portion  also  lies  upon  the  Constrictor  pharyngis 
medius,  being  covered  at  first  by  the  tendon  of  the  Digastricus  and  by  the  Stylohyoideus,  and 
afterward  by  the  Hyoglossus.  Its  third,  or  horizontal,  portion  lies  between  the  Hyoglossus  and 
Genioglossus.  The  fourth,  or  terminal  part,  under  the  name  of  the  profunda  linguae  {ranine 
artery)  runs  along  the  under  surface  of  the  tongue  to  its  tip;  here  it  is  superficial,  being  covered 
only  by  the  mucous  membrane;  above  it  is  the  Longitudinalis  inferior,  and  on  the  medial  side 
the  Genioglossus.  The  hypoglossal  nerve  crosses  the  first  part  of  the  Ungual  artery,  but  is  sepa- 
rated from  the  second  part  by  the  Hyoglossus. 

Branches. — The  branches  of  the  lingual  artery  are: 

L   .  Hyoid.  Sublingual. 

P  Dorsales  linguce.  Profunda  linguae. 

The  Hyoid  Branch  {ramus  hyoideus;  suprahyoid  branch)  runs  along  the  upper 
border  of  the  hyoid  bone,  supplying  the  muscles  attached  to  it  and  anastomosing 

.  with  its  fellow  of  the  opposite  side. 

'  The  Arteriae  Dorsales  Linguae  (rami  dorsales  linguw)  consist  usually  of  two  or 
three  small  branches  which  arise  beneath  the  Hyoglossus;  they  ascend  to  the  back 
part  of  the  dorsum  of  the  tongue,  and  supply  the  mucous  membrane  in  this  situa- 
tion, the  glossopalatine  arch,  the  tonsil,  soft  palate,  and  epiglottis;  anastomosing 
with  the  vessels  of  the  opposite  side. 

The  Sublingual  Artery  (a.  sublingualis)  arises  at  the  anterior  margin  of  the  Hyo- 

I  glossus,  and  runs  forward  between  the  Genioglossus  and  Mylohyoideus  to  the  sub- 

'  lingual  gland.  It  supplies  the  gland  and  gives  branches  to  the  Mylohyoideus  and 
neighboring  muscles,  and  to  the  mucous  membrane  of  the  mouth  and  gums.  One 
branch  runs  behind  the  alveolar  process  of  the  mandible  in  the  substance  of  the 

,  gum  to  anastomose  with  a  similar  artery  from  the  other  side;  another  pierces 

I  the  Mylohyoideus  and  anastomoses  with  the  submental  branch  of  the  external 
maxillary  artery. 

The  Arteria  Profunda  Linguae  (ranine  artery;  deep  lingual  artery)  is  the  terminal 
portion  of  the  lingual  artery;  it  pursues  a  tortuous  coufse  and  runs  along  the  under 
surface  of  the  tongue,  below  the  Longitudinalis  inferior,  and  above  the  mucous 

I  membrane;  it  lies  on  the  lateral  side  of  the  Genioglossus,  accompanied  by  the 
lingual  nerve.  At  the  tip  of  the  tongue,  it  is  said  ta  anastomose  wdth  the  artery 
of  the  opposite  side,  but  this  is  denied  by  Hyrtl.    In  the  mouth,  these  vessels  are 

(placed  one  on  either  side  of  the  frenulum  linguae.  ^ 
yr  3.  The  external  maxillary  artery  (a.  maxillaris  externa;  facial  artery)  (l^ig.  508), 
arises  in  the  carotid  triangle  a  little  above  the  lingual  artery  and,  sheltered  by  the 
ramus  of  the  mandible,  passes  obliquely  up  beneath  the  Digastricus  and  Stylo- 
hyoideus, over  which  it  arches  to  enter  a  groove  on  the  posterior  surface  of  the 
submaxillary  gland.  It  then  curves  upward  over  the  body  of  the  mandible  at  the 
.  antero-inferior  angle  of  the  ^lasseter;  passes  forward  and  upward  across  the  cheek 
I  to  the  angle  of  the  mouth,  then  ascends  along  the  side  of  the  nose,  and  ends  at 
the  medial  commissure  of  the  eye,  under  the  name  of  the  angular  artery.  This 
vessel,  both  in  the  neck  and  on  the  face,  is  remarkably  tortuous:  in  the  former 


554 


ANGIOLOGY 


situation,  to  accommodate  itself  to  the  movements  of  the  pharynx  in  deglutition; 
and  in  the  latter,  to  the  movements  of  the  mandible,  lips,  and  cheeks. 

Relations. — In  the  neck,  its  origin  is  superficial,  being  covered  by  the  integument,  Platysma, 
and  fascia;  it  then  passes  beneath  the  Digastricus  and  Stylohyoideus  muscles  and  part  of  the 
submaxillary  gland,  and  frequently  beneath  the  hypoglossal  nerve.  It  lies  upon  the  Constrictores 
pharyngis  medius  and  superior,  the  latter  of  which  separates  it,  at  the  summit  of  its  arch,  from 
the  lower  and  back  part  of  the  tonsil.  On  the  face,  where  it  passes  over  the  body  of  the  mandible, 
it  is  comparatively  superficial,  lying  immediately  beneath  the  Platysma.  In  its  course  over  the 
face,  it  is  covered  by  the  integument,  the  fat  of  the  cheek,  and,  near  the  angle  of  the  mouth, 
by  the  Platysma,  Risorius,  and  Zygomaticus.  It  rests  on  the  Buccinator  and  Caninus,  and 
passes  either  over  or  under  the  infraorbital  head  of  the  Quadratus  labii  superioris.  The  anterior 
facial  vein  lies  lateral  to  the  artery,  and  takes  a  more  direct  course  across  the  face,  where  it  is 
separated  from  the  artery  by  a  considerable  interval.  In  the  neck  it  lies  superficial  to  the  artery. 
The  branches  of  the  facial  nerve  cross  the  artery  from  behind  forward. 


Angular 


\       Lateral 


Septal 
Superior  labial 


Inferior  labial 


Fig.  508. — The  arteries  of  the  face  and  scalp.' 

Branches. — The  branches  of  the  artery  may  be  divided  into  two  sets:  those 
given  off  in  the  neck  {cervical),  and  those  on  the  face  {facial). 

Cervical  Branches.  Facial  Branches. 

Ascending  Palatine.  Inferior  Labial. 

Tonsillar.  Superior  Labial. 

Glandular.  Lateral  Nasal. 

Submental.  J  Angular. 

Muscular.  Muscular. 

'  The  muscular  tissue  of  the  lips  must  be  supposed  to  have  been  cut  away,  in  order  to  show  the  course  of  the  labial 
arteries. 


THE  EXTERNAL  CAROTID  ARTERY 


555 


I  The  Ascending  Palatine  Artery  (a.  palatina  ascendens)  (Fig.  513)  arises  close  to 
the  origin  of  the  external  maxillary  artery  and  passes  up  between  the  Styloglossus 
and  Stylopharyngeus  to  the  side  of  the  pharynx,  along  which  it  is  continued  between 
iJhe  Constrictor  pharyngis  superior  and  the  Pterygoideus  internus  to  near  the  base 
of  the  skull.  It  divides  near  the  Levator  veli  palatini  into  two  branches:  one  fol- 
lows the  course  of  this  muscle,  and,  winding  over  the  upper  border  of  the  Constrictor 
pharyngis  superior,  supplies  the  soft  palate  and  the  palatine  glands,  anastomosing 
with  its  fellow  of  the  opposite  side  and  with  the  descending  palatine  branch  of  the 
internal  maxillary  artery;  the  other  pierces  the  Constrictor  pharyngis  superior 
and  supplies  the  palatine  tonsil  and  auditory  tube,  anastomosing  with  the  tonsillar 
and  ascending  pharyngeal  arteries. 

The  Tonsillar  Branch  (ramus  tonsillaris)  (Fig.  513)  ascends  between  the  Ptery- 
goideus internus  and  Styloglossus,  and  then  along  the  side  of  the  pharynx, 
perforating  the  Constrictor  pharyngis  superior,  to  ramify  in  the  substance  of  the 
palatine  tonsil  and  root  of  the  tongue. 

The  Glandular  Branches  {rami  glandulares;  submaxillary  branches)  consist  of  three 
or  four  large  vessels,  which  supply  the  submaxillary  gland,  some  being  prolonged 
to  the  neighboring  muscles,  lymph  glands,  and  integument. 

The  Submental  Artery  (a.  submentalis)  the  largest  of  the  cervical  branches,  is 
given  off  from  the  facial  artery  just  as  that  vessel  quits  the  submaxillary  gland: 
it  runs  forward  upon  the  Mylohyoideus,  just  below  the  body  of  the  mandible, 
and  beneath  the  Digastricus.  It  supplies  the  surrounding  muscles,  and  anastomoses 
with  the  sublingual  artery  and  with  the  mjdohyoid  branch  of  the  inferior  alveolar; 
at  the  symphysis  menti  it  turns  upward  over  the  border  of  the  mandible  and 
divides  into  a  superficial  and  a  deep  branch.  The  superficial  branch  passes  between 
the  integument  and  Quadratus  labii  inferioris,  and  anastomoses  with  the  inferior 
labial  artery;  the  deep  branch  runs  between  the  muscle  and  the  bone,  supplies 
he  lip,  and  anastomoses  with  the  inferior  labial  and  mental  arteries. 


Fig.  509 — The  labial  coronary  arteries,  the  glands  of  the  lips,  and  the  nerves  of  the  right  side  seen  from  the 
posterior  surface  after  removal  of  the  mucous  membrane.     (Poirier  and  Charpy.) 

The  Inferior  Labial  Artery  (a.  labialis  inferior;  inferior  coronary  artery)  arises  near 
the  angle  of  the  mouth;  it  passes  upward  and  forward  beneath  the  Triangularis 
and,  penetrating  the  Orbicularis  oris,  runs  in  a  tortuous  course  along  the  edge  of 
the  lower  lip  between  this  muscle  and  the  mucous  membrane.  It  supplies  the 
labial  glands,  the  mucous  membrane,  and  the  muscles  of  the  lower  lip;  and  anas- 
tomoses with  the  artery  of  the  opposite  side,  and  with  the  mental  branch  of  the 
inferior  alveolar  artery. 

The  Superior  Labial  Artery  (a.  labialis  superior;  superior  coronary  artery)  is  larger 
and  more  tortuous  than  the  inferior.  It  follows  a  similar  course  along  the  edge 
of  the  upper  lip,  lying  between  the  mucous  membrane  and  the  Orbicularis  oris, 
md  anastomoses  with  the  artery  of  the  opposite  side.    It  supplies  the  upper  lip. 


^nd  anast' 


556  ^      ANGIOLOGY 


I 


and  gives  off  in  its  course  two  or  three  vessels  which  ascend  to  the  nose;  a  septal 
branch  ramifies  on  the  nasal  septum  as  far  as  the  point  of  the  nose,  and  an  alar 
branch  supplies  the  ala  of  the  nose. 

The  Lateral  Nasal  branch  is  derived  from  the  external  maxillary  as  that  vessel 
ascends  along  the  side  of  the  nose.  It  supplies  the  ala  and  dorsum  of  the  nose,  anas- 
tomosing with  its  fellow,  with  the  septal  and  alar  branches,  with  the  dorsal  ijasal 
branch  of  the  ophthalmic,  and  with  the  infraorbital  branch  of  the  internal  maxillary. 

The  Angular  Artery  (a.  angularis)  is  the  terminal  part  of  the  external  maxillary; 
it  ascends  to  the  medial  angle  of  the  orbit,  imbedded  in  the  fibers  of  the  angular 
head  of  the  Quadratus  labii  superioris,  and  accompanied  by  the  angular  vein. 
On  the  cheek  it  distributes  branches  which  anastomose  with  the  infraorbital; 
after  supplying  the  lacrimal  sac  and  Orbicularis  oculi,  it  ends  by  anastomosing 
with  the  dorsal  nasal  branch  of  the  ophthalmic  artery. 

The  Muscular  Branches  in  the  neck  are  distributed  to  the  Pterygoideus  internus  and 
Stylohyoideus,  and  on  the  face  to  the  Masseter  and  Buccinator.  The  anastomoses 
of  the  external  maxillary  artery  are  very  numerous,  not  only  with  the  vessel  of 
the  opposite  side,  but,  in  the  neck,  with  the  sublingual  branch  of  the  lingual,  with 
the  ascending  pharyngeal,  and  by  its  ascending  palatine  and  tonsillar  branches 
with  the  palatine  branch  of  the  internal  maxillary ;  on  the  face,  with  the  mental 
branch  of  the  inferior  alveolar  as  it  emerges  from  the  mental  foramen,  with  the 
transverse  facial  branch  of  the  superficial  temporal,  with  the  infraorbital  branch 
of  the  internal  maxillary,  and  with  the  dorsal  nasal  branch  of  the  ophthalmic. 

Peculiarities. — The  external  maxillary  artery  not  infrequently  arises  in  common  with  the 
lingual.  It  varies  in  its  size  and  in  the  extent  to  which  it  supplies  the  face^  it  occasionally  ends 
as  the  submental,  and  not  infrequently  extends  only  as  high  as  the  angle  of  the  mouth  or  nose. 
The  deficiency  is  then  compensated  for  by  enlargement  of  one  of  the  neighboring  arteries. 

4.  The  occipital  artery  (a.  occipitalis)  (Fig.  508)  arises  from  the  posterior  part 
of  the  external  carotid,  opposite  the  external  maxillary,  near  the  lower  margin 
of  the  posterior  belly  of  the  Digastricus,  and  ends  in  the  posterior  part  of  the  scalp. 

Course  and  Relations. — At  its  origin,  it  is  covered  by  the  posterior  belly  of  the  Digastricus 
and  the  Stylohyoideus,  and  the  hypoglossal  nerve  winds  around  it  from  behind  forward;  higher 
up,  it  crosses  the  internal  carotid  artery,  the  internal  jugular  vein,  and  the  vagus  and  accessory 
nerves.  It  next  ascends  to  the  interval  between  the  transverse  process  of  the  atlas  and  the  mastoid 
process  of  the  temporal  bone,  and  passes  horizontally  backward,  grooving  the  surface  of  the 
latter  bone,  being  covered  by  the  Stemocleidomastoideus,  Splenius  capitis,  Longissimus  capitis, 
and  Digastricus,  and  resting  upon  the  Rectus  capitis  lateralis,  the  Obliquus  superior,  and  Semi- 
spinaUs  capitis.  It  then  changes  its  course  and  runs  vertically  upward,  pierces  the  fascia  con- 
necting the  cranial  attachment  of  the  Trapezius  with  the  Stemocleidomastoideus,  and  ascends 
in  a  tortuous  course  in  the  superficial  fascia  of  the  scalp,  where  it  divides  into  numerous  branches, 
which  reach  as  high  as  the  vertex  of  the  skull  and  anastomose  with  the  posterior  auricular  and 
superficial  temporal  arteries.    Its  terminal  portion  is  accompanied  by  the  greater  occipital  nerve. 

Branches.^ — The  branches  of  the  occipital  artery  are: 

Muscular.  Sternocleidomastoid.  Auricular. 

Meningeal.  Descending. 

The  Muscular  Branches  {ravii  musculares)  supply  the  Digastricus,  Stylohyoideus, 
Splenius,  and  Longissimus  capitis. 

The  Sternocleidomastoid  Artery  (a.  sternocleidomastoidea;  sternomastoid  artery) 
generally  arises  from  the  occipital  close  to  its  commencement,  but  sometimes 
springs  directly  from  the  external  carotid.  It  passes  downward  and  backward 
over  the  hypoglossal  nerve,  and  enters  the  substance  of  the  muscle,  in  company 
with  the  accessory  nerve. 

The  Auricular  Branch  {ramus  auricularis)  supplies  the  back  of  the  concha  and 
frequently  gives  off  a  branch,  which  enters  the  skull  through  the  mastoid  foramen 


THE  EXTERNAL  CAROTID  ARTERY  557 


^Pftnd  supplies  the  dura  mater,  the  diploe,  and  the  mastoid  cells;  this  latter  branch 
I       sometimes  arises  from  the  occipital  artery,  and  is  then  known  as  the  mastoid  branch. 

The  Meningeal  Branch  (ramus  meningeiis;  dural  branch)  ascends  with  the  internal 
jugular  vein,  and  enters  the  skull  through  the  jugular  foramen  and  condyloid 
canal,  to  supply  the  dura  mater  in  the  posterior  fossa. 

The  Descending  Branch  {ramus  descendens;  arteria  princeps  cervicis)  (Fig.  513), 
the  largest  branch  of  the  occipital,  descends  on  the  back  of  the  neck,  and  divides 
into  a  superficial  and  deep  portion.  The  superficial  portion  runs  beneath  the 
Splenius,  giving  off  branches  which  pierce  that  muscle  to  supply  the  Trapezius  and 
anastomose  with  the  ascending  branch  of  the  transverse  cervical :  the  deep  portion 
runs  down  between  the  Semispinales  capitis  and  colli,  and  anastomoses  with  the 
vertebral  and  with  the  a.  profunda  cervicalis,  a  branch  of  the  costocervical  trunk. 
The  anastomosis  between  these  vessels  assists  in  establishing  the  collateral  circu- 
lation after  ligature  of  the  common  carotid  or  subclavian  artery. 

The  terminal  branches  of  the  occipital  artery  are  distributed  to  the  back  of  the 
head:  they  are  very  tortuous,  and  lie  between  the  integument  and  Occipitalis, 
anastomosing  with  the  artery  of  the  opposite  side  and  with  the  posterior  auricular 
and  temporal  arteries,  and  supplying  the  Occipitalis,  the  integument,  and  peri- 
cranium. One  of  the  terminal  branches  may  give  off  a  meningeal  twig  which  passes 
through  the  parietal  foramen. 

5.  The  posterior  auricular  artery  (a.  auricularis  posterior)  (Fig.  508)  is  small 
and  arises  from  the  external  carotid,  above  the  Digastricus  and  Stylohyoideus, 
opposite  the  apex  of  the  styloid  process.  It  ascends,  under  cover  of  the  parotid 
gland,  on  the  styloid  process  of  the  temporal  bone,  to  the  groove  between  the 
cartilage  of  the  ear  and  the  mastoid  process,  immediately  above  which  it  divides 
into  its  auricular  and  occipital  branches. 

Branches.— Besides  several  small  branches  to  the  Digastricus,  Stylohyoideus, 
and  Sternocleidomastoideus,  and  to  the  parotid  gland,  this  vessel  gives  off  three 
branches: 


» 


Stylomastoid.  Auricular.  Occipital. 


The  Stylomastoid  Artery  (a.  siylomastoidea)  enters  the  stylomastoid  foramen  and 
supplies  the  tympanic  cavity,  the  tympanic  antrum  and  mastoid  cells,  and  the 
semicircular  canals.  In  the  young  subject  a  branch  from  this  vessel  forms,  with 
the  anterior  tympanic  artery  from  the  internal  maxillary,  a  vascular  circle,  which 
surrounds  the  tympanic  membrane,  and  from  which  delicate  vessels  ramify  on  that 
membrane.  It  anastomoses  with  the  superficial  petrosal  branch  of  the  middle 
meningeal  artery  \>y  a  twig  which  enters  the  hiatus  canalis  facialis. 

The  Auricular  Branch  (ramus  auricularis)  ascends  behind  the  ear,  beneath  the 
Auricularis  posterior,  and  is  distributed  to  the  back  of  the  auricula,  upon  which 
it  ramifies  minutely,  some  branches  curving  around  the  margin  of  the  cartilage, 
others  perforating  it,  to  supply  the  anterior  surface.  It  anastomoses  with  the 
parietal  and  anterior  auricular  branches  of  the  superficial  temporal. 

The  Occipital  Branch  (ramus  occipitalis)  passes  backward,  over  the  Sternocleido- 
mastoideus, to  the  scalp  above  and  behind  the  ear.  It  supplies  the  Occipitalis 
and  the  scalp  in  this  situation  and  anastomoses  with  the  occipital  artery. 

6.  The  ascending  pharyngeal  artery  (a.  pharyngea  ascendens)  (Fig.  513),  the 
smallest  branch  of  the  external  carotid,  is  a  long,  slender  vessel,  deeply  seated  in 
the  neck,  beneath  the  other  branches  of  the  external  carotid  and  under  the  Stylo- 
pharyngeus.  It  arises  from  the  back  part  of  the  external  carotid,  near  the  com- 
mencement of  that  vessel,  and  ascends  vertically  between  the  internal  carotid 
and  the  side  of  the  pharynx,  to  the  under  surface  of  the  base  of  the  skull,  lying 
on  the  Longus  capitis. 


558  ANGIOLOGY 

Branches. — Its  branches  are : 

Pharyngeal.  Prevertebral. 

Palatine.  Inferior  Tympanic. 

Posterior  Meningeal. 

The  Pharyngeal  Branches  {rami  pharyngei)  are  three  or  four  in  number.  Two 
of  these  descend  to  supply  the  Constrictores  pharyngis  medius  and  inferior  and 
the  Stylopharyngeus,  ramifying  in  their  substance  and  in  the  mucous  membrane 
lining  them. 

The  Palatine  Branch  varies  in  size,  and  may  take  the  place  of  the  ascending 
palatine  branch  of  the  facial  artery,  when  that  vessel  is  small.  It  passes  inward 
upon  the  Constrictor  pharyngis  superior,  sends  ramifications  to  the  soft  palate 
and  tonsil,  and  supplies  a  branch  to  the  auditory  tube. 

The  Prevertebral  Branches  are  numerous  small  vessels,  which  supply  the  Longi 
capitis  and  colli,  the  sympathetic  trunk,  the  hypoglossal  and  vagus  nerves,  and  the 
lymph  glands;  they  anastomose  with  the  ascending  cervical  artery. 

The  Inferior  Tympanic  Artery  (a.  tympanica  inferior)  is  a  small  branch  which 
passes  through  a  minute  foramen  in  the  petrous  portion  of  the  temporal  bone,  in 
company  with  the  tympanic  branch  of  the  glossopharyngeal  nerve,  to  supply  the 
medial  wall  of  the  tympanic  cavity  and  anastomose  with  the  other  tympanic  arteries. 

The  Meningeal  Branches  are  several  small  vessels,  which  supply  the  dura  mater. 
One,  the  posterior  meningeal,  enters  the  cranium  through  the  jugular  foramen; 
a  second  passes  through  the  foramen  lacerum;  and  occasionally  a  third  through 
the  canal  for  the  hypoglossal  nerve. 

7.  The  superficial  temporal  artery  (a.  temporalis  siiperficialis)  (Fig.  508),  the 
smaller  of  the  two  terminal  branches  of  the  external  carotid,  appears,  from  its 
direction,  to  be  the  continuation  of  that  vessel.  It  begins  in  the  substance  of  the 
parotid  gland,  behind  the  neck  of  the  mandible,  and  crosses  over  the  posterior  root 
of  the  zygomatic  process  of  the  temporal  bone;  about  5  cm.  above  this  process 
it  divides  into  two  branches,  a  frontal  and  a  parietal. 

Relations. — As  it  crosses  the  zygomatic  process,  it  is  covered  by  the  Auricularis  anterior  muscle, 
and  by  a  dense  fascia;  it  is  crossed  by  the  temporal  and  zygomatic  branches  of  the  facial  nerve 
and  one  or  two  veins,  and  is  accompanied  by  the  auriculotemporal  nerve,  which  lies  immediately 
behind  it. 

Branches. — Besides  some  twigs  to  the  parotid  gland,  to  the  temporomandibular 
joint,  and  to  the  Masseter  muscle,  its  branches  are: 

Transverse  Facial.  Anterior  Auricular. 

Middle  Temporal.  Frontal. 

Parietal. 

The  Transverse  Facial  Artery  (a.  transversa  faciei)  is  given  off  from  the  superficial 
temporal  before  that  vessel  quits  the  parotid  gland;  running  forward  through  the 
substance  of  the  gland,  it  passes  transversely  across  the  side  of  the  face,  between 
the  parotid  duct  and  the  lower  border  of  the  zygomatic  arch,  and  divides  into  numer- 
ous branches,  which  supply  the  parotid  gland  and  duct,  the  Masseter,  and  the 
integument,  and  anastomose  with  the  external  maxillary,  masseteric,  buccinator, 
and  infraorbital  arteries.  This  vessel  rests  on  the  Masseter,  and  is  accompanied 
by  one  or  two  branches  of  the  facial  nerve. 

The  Middle  Temporal  Artery  (a.  temporalis  media)  arises  immediately  above  the 
zygomatic  arch,  and,  perforating  the  temporal  fascia,  gives  branches  to  the  Tem- 
poralis, anastomosing  with  the  deep  temporal  branches  of  the  internal  maxillary. 
It  occasionally  gives  off  a  zygomaticoorbital  branch,  which  runs  along  the  upper 
border  of  the  zygomatic  arch,  between  the  two  layers  of  the  temporal  fascia,  to 
the  lateral  angle  of  the  orbit.    This  branch,  which  may  arise  directly  from  the 


THE  EXTERNAL  CAROTID  ARTERY 


559 


•superficial  temporal  artery,  supplies  the  Orbicularis  ocull,  and  anastomoses  with 
;  the  lacrimal  and  palpebral  branches  of  the  ophthalmic  artery. 

iThe  Anterior  Auricular  Branches  {rami  auriculares  anteriores)  are  distributed  to 
the  anterior  portion  of  the  auricula,  the  lobule,  and  part  of  the  external  meatus, 
,  anastomosing  with  the  posterior  auricular. 

The  Frontal  Branch  (ramus  frontalis;  anterior  temporal)  runs  tortuously  upward 
and  forward  to  the  forehead,  supplying  the  muscles,  integument,  and  pericranium 

I  in  this  region,  and  anastomosing  with  the  supraorbital  and  frontal  arteries. 
I     The  Parietal  Branch  (ramus  parietalis;  posterior  temporal)  larger  than  the  frontal, 
curves  upward  and  backward  on  the  side  of  the  head,  lying  superficial  to  the  tem- 
poral fascia,  and  anastomosing  with  its  fellow  of  the  opposite  side,  and  wdth  the 
posterior  auricular  and  occipital  arteries. 


Incisor  branch 


Fig.  510. — Plan  of  branches  of  internal  maxillarj'  artery. 


d 


I 


8.  The  internal  maxillary  artery  (a.  maxillaris  interna)  (Fig.  510),  the  larger 
of  the  two  terminal  branches  of  the  external  carotid,  arises  behind  the  neck  of  the 
mandible,  and  is  at  first  imbedded  in  the  substance  of  the  parotid  gland;  it  passes 
forward  between  the  ramus  of  the  mandible  and  the  sphenomandibular  ligament, 
nd  then  runs,  either  superficial  or  deep  to  the  Pterygoideus  externus,  to  the 
pterygopalatine  fossa.  It  supplies  the  deep  structures  of  the  face,  and  may  be 
divided  into  mandibular,  pterygoid,  and  pterygopalatine  portions. 

The  first  or  mandibular  portion  passes  horizontally  forward,  between  the  ramus 
of  the  mandible  and  the  sphenomandibular  ligament,  where  it  lies  parallel  to  and 

little  below  the  auriculotemporal  nerve;  it  crosses  the  inferior  alveolar  nerve, 
and  runs  along  the  lower  border  of  the  Pterygoideus  externus. 

The  second  or  pterygoid  portion  runs  obliquely  forward  and  upward  under  cover 
f  the  ramus  of  the  mandible  and  insertion  of  the  Temporalis,  on  the  superficial 
(very  frequently  on  the  deep)  surface  of  the  Pterygoideus  externus;  it  then  passes 
between  the  two  heads  of  origin  of  this  muscle  and  enters  the  fossa. 

The  third  or  pterygopalatine  portion  lies  in  the  pterygopalatine  fossa  in  relation 
with  the  sphenopalatine  ganglion. 


560 


ANGIOLOGY 


I 


The  branches  of  this  vessel  may  be  divided  into  three  groups  (Fig.  511),  corre 
sponding  with  its  three  divisions. 

Branches  of  the  First  or  Mandibular  Portions. — 


Anterior  Tympanic. 
Deep  Auricular. 


Inferior  Alveolar. 


Middle  Meningeal. 
Accessory  Meningeal 


II 


The  Anterior  Tympanic  Artery  (a.  tympanica  anterior;  tympanic  artery)  passes 
upward  behind  the  temporomandibular  articulation,  enters  the  tympanic  cavity 
through  the  petrotympanic  fissure,  and  ramifies  upon  the  tympanic  membrane, 
forming  a  vascular  circle  around  the  membrane  with  the  stylomastoid  branch  of 
the  posterior  auricular,  and  anastomosing  with  the  artery  of  the  pterygoid  canal 
and  with  the  caroticotympanic  branch  from  the  internal  carotid. 


Art.  ofPte^^i^^ 
■pharyngectl 


Sphenopalatine 
fraorbital 


Post.  sup.  alveolar 


Fig.  511. — Plan  of  branches  of  internal  maxillary- artery. 

The  Deep  Auricular  Artery  (a.  auricularis  profunda)  often  arises  in  common  with 
the  preceding.  It  ascends  in  the  substance  of  the  parotid  gland,  behind  the  tem- 
poromandibular articulation,  pierces  the  cartilaginous  or  bony  wall  of  the  external 
acoustic  meatus,  and  supplies  its  cuticular  lining  and  the  outer  surface  of  the 
tympanic  membrane.    It  gives  a  branch  to  the  temporomandibular  joint. 

The  Middle  Meningeal  Artery  (a.  meningea  media;  medidural  artery)  is  the  largest 
of  the  arteries  which  supply  the  dura  mater.  It  ascends  between  the  spheno- 
mandibular  ligament  and  the  Pterygoideus  externus,  and  between  the  two  roots 
of  the  auriculotemporal  nerve  to  the  foramen  spinosum  of  the  sphenoid  bone, 
through  which  it  enters  the  cranium;  it  then  runs  forward  in  a  groove  on  the  great 
wing  of  the  sphenoid  bone,  and  divides  into  two  branches,  anterior  and  posterior. 
The  anterior  branch,  the  larger,  crosses  the  great  wing  of  the  sphenoid,  reaches  the 
groove,  or  canal,  in  the  sphenoidal  angle  of  the  parietal  bone,  and  then  divides 
into  branches  which  spread  out  between  the  dura  mater  and  internal  surface  of 
the  cranium,  some  passing  upward  as  far  as  the  vertex,  and  others  backward  to 
the  occipital  region.  The  posterior  branch  curves  backward  on  the  squama  of  the 
temporal  bone,  and,  reaching  the  parietal  some  distance  in  front  of  its  mastoid 
angle,  divides  into  branches  which  supply  the  posterior  part  of  the  dura  mater  and 


^ 


THE  EXTERNAL  CAROTID  ARTERY  561 

cranium.  The  branches  of  the  middle  meningeal  artery  are  distributed  partly 
to  the  dura  mater,  but  chiefly  to  the  bones;  they  anastomose  with  the  arteries  of 
the  opposite  side,  and  with  the  anterior  and  posterior  meningeal. 

The  middle  meningeal  on  entering  the  cranium  gives  off  the  following  branches:  (1)  Numerous 
small  vessels  supply  the  semilunar  ganglion  and  the  dura  mater  in  this  situation.  (2)  A  superficial 
petrosal  branch  enters  the  hiatus  of  the  facial  canal,  suppHes  the  facial  nerve,  and  anastomoses 
with  the  stylomastoid  branch  of  the  posterior  auricular  artery.     (3)  A  superior  tympanic  artery 

(runs  in  the  canal  for  the  Tensor  tympani,  and  suppUes  this  muscle  and  the  lining  membrane  of 
the  canal.  (4)  Orbital  branches  pass  through  the  superior  orbital  fissure  or  through  separate 
canals  in  the  great  wing  of  the  sphenoid,  to  anastomose  with  the  lacrimal  or  other  branches  of 
the  ophthalmic  artery.  (5)  Temporal  branches  pass  through  foramina  in  the  great  wing  of  the 
sphenoid,  and  anastomose  in  the  temporal  fossa  with  the  deep  temporal  arteries. 

The  Accessory  Meningeal  Branch  (ramus  meningeus  accessorius;  small  meningeal 
or  parndural  branch)  is  sometimes  derived  from  the  preceding.  It  enters  the 
skull  through  the  foramen  ovale,  and  supplies  the  semilunar  ganglion  and  dura 

.  mater. 

h  The  Inferior  Alveolar  Artery  (a.  alveolaris  inferior;  inferior  dental  artery)  descends 
with  the  inferior  alveolar  nerve  to  the  mandibular  foramen  on  the  medial  surface 
of  the  ramus  of  the  mandible.  It  runs  along  the  mandibular  canal  in  the  substance 
of  the  bone,  accompanied  by  the  nerve,  and  opposite  the  first  premolar  tooth  divides 
into  two  branches,  incisor  and  mental.  The  incisor  branch  is  continued  forward 
beneath  the  incisor  teeth  as  far  as  the  middle  line,  where  it  anastomoses  with  the 
artery  of  the  opposite  side;  the  mental  branch  escapes  with  the  nerve  at  the  mental 
foramen,  supplies  the  chin,  and  anastomoses  with  the  submental  and  inferior 
labial  arteries.  Near  its  origin  the  inferior  alveolar  artery  gives  off  a  lingual  branch 
which  descends  with  the  lingual  nerve  and  supplies  the  mucous  membrane  of  the 
outh.  As  the  inferior  alveolar  artery  enters  the  foramen,  it  gives  off  a  mylohyoid 
branch  which  runs  in  the  mylohyoid  groove,  and  ramifies  on  the  under  surface  of 
the  Mylohyoideus.  The  inferior  alveolar  artery  and  its  incisor  branch  during 
their  course  through  the  substance  of  the  bone  give  off  a  few  twigs  which  are  lost 
in  the  cancellous  tissue,  and  a  series  of  branches  which  correspond  in  number  to 
the  roots  of  the  teeth :  these  enter  the  minute  apertures  at  the  extremities  of  the 
roots,  and  supply  the  pulp  of  the  teeth. 

»    Branches  of  the  Second  or  Pterygoid  Portion. — 
[  Deep  Temporal.  Masseteric. 

Pterygoid.  Buccinator. 

The  Deep  Temporal  Branches,  two  in  number,  anterior  and  posterior,  ascend 
between  the  Temporalis  and  the  pericranium;  they  supply  the  muscle,  and  anasto- 
mose with  the  middle  temporal  artery ;  the  anterior  communicates  with  the  lacrimal 
artery  by  means  of  small  branches  which  perforate  the  zygomatic  bone  and  great 
wing  of  the  sphenoid. 

The  Pterygoid  Branches  (rami  pterygoidei) ,  irregular  in  their  number  and  origin, 
supply  the  Pterygoidei. 

The  Masseteric  Artery  (a.  masseterica)  is  small  and  passes  lateral  ward  through 
the  mandibular  notch  to  the  deep  surface  of  the  Masseter.  It  suppHes  the  muscle, 
and  anastomoses  with  the  masseteric  branches  of  the  external  maxillary  and  with 
the  transverse  facial  artery. 

The  Buccinator  Artery  (a.  buccinatoria;  buccal  artery)  is  small  and  runs  obliquely 
forward,  between  the  Pterygoideus  internus  and  the  insertion  of  the  Temporalis, 
to  the  outer  surface  of  the  Buccinator,  to  which  it  is  distributed,  anastomosing 
with  branches  of  the  external  maxillary  and  with  the  infraorbital. 
^H      Branches  of  the  Third  or  Pterygopalatine  Portion. — 

IB  Posterior  Superior  Alveolar.  Artery  of  the  Pterygoid  Canal. 

■B  Infraorbital.  Pharyngeal. 

IB  Descending  Palatine.  Sphenopalatine. 


562  ^^^^^^"^       ANGIOLOGY 


The  Posterior  Superior  Alveolar  Artery  (a.  alveolaris  superior  posterior;  alveoM-or 
posterior  dental  artery)  is  given  off  from  the  internal  maxillary,  frequently  in  con- 
junction with  the  infraorbital  just  as  the  trunk  of  the  vessel  is  passing  into  the 
pterygopalatine  fossa.  Descending  upon  the  tuberosity  of  the, maxilla,  it  divides 
into  numerous  branches,  some  of  which  enter  the  alveolar  canals,  to  supply  the 
molar  and  premolar  teeth  and  the  lining  of  the  maxillary  sinus,  while  others  are 
continued  forward  on  the  alveolar  process  to  supply  the  gums. 

The  Infraorbital  Artery  (a.  infraorbitalis)  appears,  from  its  direction,  to  be  the 
continuation  of  the  trunk  of  the  internal  maxillary,  but  often  arises  in  conjunction 
with  the  posterior  superior  alveolar.  It  runs  along  the  infraorbital  groove  and 
canal  with  the  infraorbital  nerve,  and  emerges  on  the  face  through  the  infraorbital 
foramen,  beneath  the  infraorbital  head  of  the  Quadratus  labii  superioris.  While 
in  the  canal,  it  gives  off  (a)  orbital  branches  which  assist  in  supplying  the  Rectus 
inferior  and  Obliquus  inferior  and  the  lacrimal  sac,  and  (6)  anterior  superior  alveolar 
branches  which  descend  through  the  anterior  alveolar  canals  to  supply  the  upper 
incisor  and  canine  teeth  and  the  mucous  membrane  of  the  maxillary  sinus.  On 
the  face,  some  branches  pass  upward  to  the  medial  angle  of  the  orbit  and  the 
lacrimal  sac,  anastomosing  with  the  angular  branch  of  the  external  maxillary 
artery;  others  run  toward  the  nose,  anastomosing  with  the  dorsal  nasal  branch  of 
the  ophthalmic;  and  others  descend  between  the  Quadratus  labii  superioris  and 
the  Caninus,  and  anastomose  with  the  external  maxillary,  transverse  facial,  and 
buccinator  arteries.  The  four  remaining  branches  arise  from  that  portion  of  the 
internal  maxillary  which  is  contained  in  the  pterygopalatine  fossa. 

The  Descending  Palatine  Artery  (a.  palatina  descendens)  descends  through  the 
pterygopalatine  canal  with  the  anterior  palatine  branch  of  the  sphenopalatine 
ganglion,  and,  emerging  from  the  greater  palatine  foramen,  runs  forward  in  a  groove 
on  the  medial  side  of  the  alveolar  border  of  the  hard  palate  to  the  incisive  canal; 
the  terminal  branch  of  the  artery  passes  upward  through  this  canal  to  anastomose 
with  the  sphenopalatine  artery.  Branches  are  distributed  to  the  gums,  the  palatine 
glands,  and  the  mucous  membrane  of  the  roof  of  the  mouth;  while  in  the  pterygo- 
palatine canal  it  gives  off  twigs  which  descend  in  the  lesser  palatine  canals  to  supply 
the  soft  palate  and  palatine  tonsil,  anastomosing  with  the  ascending  palatine  artery. 

The  Artery  of  the  Pterygoid  Canal  (a.  canalis  pterygoidei;  Vidian  artery)  passes 
backward  along  the  pterygoid  canal  with  the  corresponding  nerve.  It  is  distributed 
to  the  upper  part  of  the  pharynx  and  to  the  auditory  tube,  sending  into  the  tympanic 
cavity  a  small  branch  which  anastomoses  with  the  other  tympanic  arteries. 

The  Pharyngeal  Branch  is  very  small;  it  runs  backward  through  the  pharyngeal 
canal  with  the  pharyngeal  nerve,  and  is  distributed  to  the  upper  part  of  the  pharynx 
and  to  the  auditory  tube. 

The  Sphenopalatine  Artery  (a.  sphenopalatina;  nasopalatine  artery)  passes  through 
the  sphenopalatine  foramen  into  the  cavity  of  the  nose,  at  the  back  part  of  the 
superior  meatus.  Here  it  gives  off  its  posterior  lateral  nasal  branches  which  spread 
forward  over  the  conchae  and  meatuses,  anastomose  with  the  ethmoidal  arteries 
and  the  nasal  branches  of  the  descending  palatine,  and  assist  in  supplying  the 
frontal,  maxillary,  ethmoidal,  and  sphenoidal  sinuses.  Crossing  the  under  surface  of 
the  sphenoid  the  sphenopalatine  artery  ends  on  the  nasal  septum  as  the  posterior 
septal  branches;  these  anastomose  with  the  ethmoidal  arteries  and  the  septal 
branch  of  the  superior  labial;  one  branch  descends  in  a  groove  on  the  vomer  to 
the  incisive  canal  and  anastomoses  with  the  descending  palatine  artery. 

THE  TRIANGLES  OF  THE  NECK   (Fig.  512). 

The  side  of  the  neck  presents  a  somewhat  quadrilateral  outline,  limited,  above, 
by  the  lower  border  of  the  body  of  the  mandible,  and  an  imaginary  line  extending 


I 


I 


THE  TRIANGLES  OF  THE  NECK 


from  the  angle  of  the  mandible  to  the  mastoid  process;  below,  by  the  upper  border 
of  the  clavicle;  in  front,  by  the  middle  line  of  the  neck;  behind,  by  the  anterior 
margin  of  the  Trapezius.  This  space  is  subdivided  into  two  large  triangles  by  the 
Sternocleidomastoideus,  which  passes  obliquely  across  the  neck,  from  the  sternum 
and  clavicle  below,  to  the  mastoid  process  and  occipital  bone  above.  Tlie  triangular 
space  in  front  of  this  muscle  is  called  the  anterior  triangle ;  and  that  behind  it,  the 
posterior  triangle. 

Anterior  Triangle. — The  anterior  triangle  is  bounded,  in  front,  by  the  middle  line 
of  the  neck;  behind,  by  the  anterior  margin  of  the  Sternocleidomastoideus;  its 
base,  directed  upward,  is  formed  by  the  lower  border  of  the  body  of  the  mandible, 
and  a  line  extending  from  the  angle  of  the  mandible  to  the  mastoid  process;  its 
apex  is  below,  at  the  sternum.  This  space  is  subdivided  into  four  smaller  triangles 
by  the  Digastricus  above,  and  the  superior  belly  of  the  Omohyoideus  below. 
These  smaller  triangles  are  named  the  inferior  carotid,  the  superior  carotid,  the 
■submaxillary,  and  the  suprahyoid. 


Suprahyoid  triangle 
Submaxillary  triangle 

Superior  carotid  triangle 


Inferior  carotid  triangle 


Occipital  triangle 


Subclavian  triangle 
Fig.  512. — The  triangles  of  the  neck. 

The  Inferior  Carotid,  or  Muscular  Triangle,  is  bounded,  in  front,  by  the  median 
line  of  the  neck  from  the  hyoid  bone  to  the  sternum ;  behind,  by  the  anterior  margin 
of  the  Sternocleidomastoideus;  above,  by  the  superior  belly  of  the  Omohyoideus. 
It  is  covered  by  the  integument,  superficial  fascia,  Platysma,  and  deep  fascia, 
ramifying  in  which  are  some  of  the  branches  of  the  supraclavicular  nerves.  Be- 
neath these  superficial  structures  are  the  Sternohyoideus  and  Sternothyreoideus, 
which,  together  with  the  anterior  margin  of  the  Sternocleidomastoideus,  conceal 
the  lower  part  of  the  common  carotid  artery.^  This  vessel  is  enclosed  within  its 
sheath,  together  with  the  internal  jugular  vein  and  vagus  nerve;  the  vein  lies 
lateral  to  the  artery  on  the  right  side  of  the  neck,  but  overlaps  it  below  on  the  left 
side;  the  nerve  lies  between  the  artery  and  vein,  on  a  plane  posterior  to  both. 

■  Therefore  the  common  carotid  artery  and  internal  jugular  vein  are  not,  strictly  speaking,  contained  in  this  tri- 
angle, since  they  are  covered  by  the  Sternocleidomastoideus:  that  is  to  say,  they  lie  under  that  muscle,  which  forms 
the  posterior  border  of  the  triangle.  But  as  they  lie  very  close  to  the  structures  which  are  really  contained  in  the 
triangle,  and  whose  position  it  is  essential  to  remember  in  operating  on  this  part  of  the  artery,  it  is  e.xpedient  to  study 
the  relations  of  all  these  parts  together. 


564  ANGIOLOGY 


I 


In  front  of  the  sheath  are  a  few  descending  filaments  from  the  ansa  hypoglossi; 
behind  the  sheath  are  the  inferior  thyroid  artery,  the  recurrent  nerve,  and  the  sym- 
pathetic trunk;  and  on  its  medial  side,  the  esophagus,  the  trachea,  the  thyroid 
gland,  and  the  lower  part  of  the  larynx.  By  cutting  into  the  upper  part  of  this 
space,  and  slightly  displacing  the  Sternocleidomastoideus,  the  common  carotid 
artery  may  be  tied  below  the  Omohyoideus. 

The  Superior  Carotid,  or  Carotid  Triangle,  is  bounded,  behind  by  the  Sternocleido- 
mastoideus; below,  by  the  superior  belly  of  the  Omohyoideus;  and  above,  by  the 
Stylohyoideus  and  the  posterior  belly  of  the  Digastricus.  It  is  covered  by  the  integu- 
ment, superficial  fascia,  Platysma  and  deep  fascia;  ramifying  in  which  are  branches 
of  the  facial  and  cutaneous  cervical  nerves.  Its  floor  is  formed  by  parts  of  the  Thyro- 
hyoideus,  Hyoglossus,  and  the  Constrictores  pharyngis  medius  and  inferior.  This 
space  when  dissected  is  seen  to  contain  the  upper  part  of  the  common  carotid 
artery,  which  bifurcates  opposite  the  upper  border  of  the  thyroid  cartilage  into  the 
external  and  internal  carotid.  These  vessels  are  somewhat  concealed  from  view 
by  the  anterior  margin  of  the  Sternocleidomastoideus,  which  overlaps  them. 
The  external  and  internal  carotids  lie  side  by  side,  the  external  being  the  more 
anterior  of  the  two.  The  following  branches  of  the  external  carotid  are  also  met 
with  in  this  space:  the  superior  thyroid,  running  forward  and  downward;  the 
lingual,  directly  forward ;  the  external  maxillary,  forward  and  upward ;  the  occipital, 
backward;  and  the  ascending  pharyngeal,  directly  upward  on  the  medial  side  of  the 
internal  carotid.  The  veins  met  with  are:  the  internal  jugular,  which  lies  on  the 
lateral  side  of  the  common  and  internal  carotid  arteries;  and  veins  corresponding 
to  the  above-mentioned  branches  of  the  external  carotid — viz.,  the  superior  thyroid, 
the  lingual,  common  facial,  ascending  pharyngeal,  and  sometimes  the  occipital — 
all  of  which  end  in  the  internal  jugular.  The  nerves  in  this  space  are  the  following. 
In  front  of  the  sheath  of  the  common  carotid  is  the  ramus  descendens  hypoglossi. 
The  hypoglossal  nerve  crosses  both  the  internal  and  external  carotids  above, 
curving  around  the  origin  of  the  occipital  artery.  Within  the  sheath,  between  the 
artery  and  vein,  and  behind  both,  is  the  vagus  nerve;  behind  the  sheath,  the  sym- 
pathetic trunk.  On  the  lateral  side  of  the  vessels,  the  accessory  nerve  runs  for  a 
short  distance  before  it  pierces  the  Sternocleidomastoideus;  and  on  the  medial 
side  of  the  external  carotid,  just  below  the  hyoid  bone,  may  be  seen  the  internal 
branch  of  the  superior  laryngeal  nerve;  and,  still  more  inferiorly,  the  external 
branch  of  the  same  nerve.  The  upper  portion  of  the  larynx  and  lower  portion  of 
the  pharynx  are  also  found  in  the  front  part  of  this  space. 

The  Submaxillary  or  Digastric  Triangle  corresponds  to  the  region  of  the  neck 
immediately  beneath  the  body  of  the  mandible.  It  is  bounded,  above,  by  the  lower 
border  of  the  body  of  the  mandible,  and  a  line  drawn  from  its  angle  to  the  mastoid 
process;  below,  by  the  posterior  belly  of  the  Digastricus  and  the  Stylohyoideus; 
in  front,  by  the  anterior  belly  of  the  Digastricus.  It  is  covered  by  the  integument, 
superficial  fascia,  Platysma,  and  deep  fascia,  ramifying  in  which  are  branches 
of  the  facial  nerve  and  ascending  filaments  of  the  cutaneous  cervical  nerve.  Its 
floor  is  formed  by  the  Mylohyoideus,  Hyoglossus,  and  Constrictor  pharyngis 
superior.  It  is  divided  into  an  anterior  and  a  posterior  part  by  the  stylomandibular 
ligament.  The  anterior  part  contains  the  submaxillary  gland,  superficial  to  which 
is  the  anterior  facial  vein,  while  imbedded  in  the  gland  is  the  external  maxillary 
artery  and  its  glandular  branches;  beneath  the  gland,  on  the  surface  of  the  Mylo- 
hyoideus, are  the  submental  artery  and  the  mylohyoid  artery  and  nerve.  The 
posterior  part  of  this  triangle  contains  the  external  carotid  artery,  ascending  deeply 
in  the  substance  of  the  parotid  gland;  this  vessel  lies  here  in  front  of,  and  super- 
ficial to,  the  internal  carotid,  being  crossed  by  the  facial  nerve,  and  gives  off  in 
its  course  the  posterior  auricular,  superficial  temporal,  and  internal  maxillary 
branches:  more  deeply  are  the  internal  carotid,  the  internal  jugular  vein,  and  the 


THE  TRIANGLES  OF  THE  NECK  565 


^B\ragus  nerve,  separated  from  the  external  carotid  by  the  Styloglossus  and  Stylo- 
pharyngeus,  and  the  glossopharyngeal  nerve.^ 

The  Suprahyoid  Triangle  is  limited  behind  by  the  anterior  belly  of  the  Digastricus, 
in  front  by  the  middle  line  of  the  neck  between  the  mandible  and  the  hyoid  bone ; 
below,  by  the  body  of  the  hyoid  bone;  its  floor  is  formed  by  the  Mylohyoideus. 
t  contains  one  or  two  lymph  glands  and  some  small  veins;  the  latter  unite  to  form 
the  anterior  jugular  vein. 

Posterior  Triangle. — ^The  posterior  triangle  is  bounded,  in  front,  by  the  Sterno- 
cleidomastoideus;  behind,  by  the  anterior  margin  of  the  Trapezius;  its  base  is  formed 

(by  the  middle  third  of  the  clavicle;  its  apex,  by  the  occipital  bone.  The  space 
is  crossed,  about  2.5  cm.  above  the  clavicle,  by  the  inferior  belly  of  the  Omo- 
hyoideus,  which  divides  it  into  two  triangles,  an  upper  or  occipital,  and  a  lower  or 
subclavian. 

The  Occipital  Triangle,  the  larger  division  of  the  posterior  triangle,  is  bounded, 
in  front,  by  the  Sternocleidomastoideus;  behind,  by  the  Trapezius;  below,  by  the 
Omohyoideus.  Its  floor  is  formed  from  above  downward  by  the  Splenius  capitis. 
Levator  scapulae,  and  the  Scaleni  medius  and  posterior.  It  is  covered  by  the  skin, 
the  superficial  and  deep  fasciae,  and  by  the  Platysma  below.  The  accessory  nerve 
is  directed  obliquely  across  the  space  from  the  Sternocleidomastoideus,  which  it 
pierces,  to  the  under  surface  of  the  Trapezius;  below,  the  supraclavicular  nerves 
and  the  transverse  cervical  vessels  and  the  upper  part  of  the  brachial  plexus  cross 
the  space.  A  chain  of  lymph  glands  is  also  found  running  along  the  posterior  border 
of  the  Sternocleidomastoideus,  from  the  mastoid  process  to  the  root  of  the  neck. 

The  Subclavian  Triangle,  the  smaller  division  of  the  posterior  triangle,  is  bounded, 
above,  by  the  inferior  belly  of  the  Omohyoideus;  below,  by  the  clavicle;  its  base  is 
formed  by  the  posterior  border  of  the  Sternocleidomastoideus.  Its  floor  is  formed 
by  the  first  rib  with  the  first  digitation  of  the  Serratus  anterior.  The  size  of  the 
subclavian  triangle  varies  with  the  extent  of  attachment  of  the  clavicular  portions 
of  the  Sternocleidomastoideus  and  Trapezius,  and  also  with  the  height  at  which 
the  Omohyoideus  crosses  the  neck.  Its  height  also  varies  according  to  the  position 
of  the  arm,  being  diminished  by  raising  the  limb,  on  account  of  the  ascent  of  the 
clavicle,  and  increased  by  drawing  the  arm  downward,  when  that  bone  is  depressed. 
This  space  is  covered  by  the  integument,  the  superficial  and  deep  fasciae  and  the 
Platysma,  and  crossed  by  the  supraclavicular  nerves.  Just  above  the  level  of  the 
clavicle,  the  third  portion  of  the  subclavian  artery  curves  lateralward  and  downward 
from  the  lateral  margin  of  the  Scalenus  anterior,  across  the  first  rib,  to  the  axilla, 
and  this  is  the  situation  most  commonly  chosen  for  ligaturing  the  vessel.  Some- 
times this  vessel  rises  as  high  as  4  cm.  above  the  clavicle;  occasionally,  it  passes 
in  front  of  the  Scalenus  anterior,  or  pierces  the  fibers  of  that  muscle.  The  sub- 
clavian vein  lies  behind  the  clavicle,  and  is  not  usually  seen  in  this  space;  but  in 
some  cases  it  rises  as  high  as  the  artery,  and  has  even  been  seen  to  pass  with  that 
vessel  behind  the  Scalenus  anterior.  The  brachial  plexus  of  nerves  lies  above 
the  artery,  and  in  close  contact  with  it.  Passing  transversely  behind  the  clavicle 
are  the  transverse  scapular  vessels;  and  traversing  its  upper  angle  in  the  same 
direction,  the  transverse  cervical  artery  and  vein.  The  external  jugular  vein  runs 
vertically  downward  behind  the  posterior  border  of  the  Sternocleidomastoideus, 
to  terminate  in  the  subclavian  vein;  it  receives  the  transverse  cervical  and  trans- 
verse scapular  veins,  which  form  a  plexus  in  front  of  the  artery,  and  occasionally 
a  small  vein  which  crosses  the  clavicle  from  the  cephalic.  The  small  nerve  to  the 
Subclavius  also  crosses  this  triangle  about  its  middle,  and  some  lymph  glands  are 
usually  found  in  the  space. 

1  The  remark  made  about  the  inferior  carotid  triangle  applies  also  to  this  one.  The  structures  enumerated  as  con- 
tained in  its  posterior  part  lie,  strictly  speaking,  beneath  the  muscles  which  form  the  posterior  boundary  of  the  tri- 
angle; but  as  it  is  very  important  to  bear  in  mind  their  close  relation  to  the  parotid  gland,  all  these  parts  are  spoken 
fOf  together. 


I_ 


566  ANGIOLOGY 

The  Internal  Carotid  Artery  (A.  Carotis  Interna)  (Fig.  513). 

The  internal  carotid  artery  supplies  the  anterior  part  of  the  brain,  the  eye  and  its 
appendages,  and  sends  branches  to  the  forehead  and  nose.  Its  size,  in  the  adult, 
is  equal  to  that  of  the  external  carotid,  though,  in  the  child,  it  is  larger  than  that 


First  aortic  intercoatal 

Fig.  513. — The  internal  carotid  and  vertebral  arteries.     Right  side. 

vessel.  It  is  remarkable  for  the  number  of  curvatures  that  it  presents  in  different 
parts  of  its  course.  It  occasionally  has  one  or  two  flexures  near  the  base  of  the  skull, 
while  in  its  passage  through  the  carotid  canal  and  along  the  side  of  the  body  of 
the  sphenoid  bone  it  describes  a  double  curvature  and  resembles  the  italic  letter  S. 


I 

I 


^» 


r 


I 


THE  INTERNAL  CAROTID  ARTERY  567 

Course  and  Relations.— In  considering  the  course  and  relations  of  this  vessel 
it  may  be  divided  into  four  portions:  cervical,  petrous,  cavernous,  and  cerebral. 

Cervical  Portion.— This  portion  of  the  internal  carotid  begins  at  the  bifurca- 
tion of  the  common  carotid,  opposite  the  upper  border  of  the  thyroid  cartilage, 
and  runs  perpendicularly  upward,  in  front  of  the  transverse  processes  of  the  upper 
three  cervical  vertebrae,  to  the  carotid  canal  in  the  petrous  portion  of  the  temporal 
bone.  It  is  comparatively  superficial  at  its  commencement,  where  it  is  contained 
in  the  carotid  triangle,  and  lies  behind  and  lateral  to  the  external  carotid,  over- 
lapped by  the  Sternocleidomastoideus,  and  covered  by  the  deep  fascia,  Platysma, 
and  integument:  it  then  passes  beneath  the  parotid  gland,  being  crossed  by  the 
hypoglossal  nerve,  the  Digastricus  and  Stylohyoideus,  and  the  occipital  and  pos- 
terior auricular  arteries.  Higher  up,  it  is  separated  from  the  external  carotid  by 
the  Styloglossus  and  Stylopharyngeus,  the  tip  of  the  styloid  process  and  the  stylo- 
hyoid ligament,  the  glossopharyngeal  nerve  and  the  pharyngeal  branch  of  the  vagus. 
It  is  in  relation,  behind,  with  the  Longus  capitis,  the  superior  cervical  ganglion  of 
the  sympathetic  trunk,  and  the  superior  laryngeal  nerve;  laterally,  with  the  internal 
jugular  vein  and  vagus  nerve,  the  nerve  lying  on  a  plane  posterior  to  the  artery; 
medially,  with  the  pharynx,  superior  laryngeal  nerve,  and  ascending  pharyngeal 
artery.  At  the  base  of  the  skull  the  glossopharyngeal,  vagus,  accessory,  and  hypo- 
glossal nerves  lie  between  the  artery  and  the  internal  jugular  vein. 

Petrous  Portion. — When  the  internal  carotid  artery  enters  the  canal  in  the 
petrous  portion  of  the  temporal  bone,  it  first  ascends  a  short  distance,  then  curves 
forward  and  medialward,  and  again  ascends  as  it  leaves  the  canal  to  enter  the 
cavity  of  the  skull  between  the  lingula  and  petrosal  process  of  the  sphenoid.  The 
artery  lies  at  first  in  front  of  the  cochlea  and  tympanic  cavity;  from  the  latter 
cavity  it  is  separated  by  a  thin,  bony  lamella,  which  is  cribriform  in  the  young 
subject,  and  often  partly  absorbed  in  old  age.  Farther  forward  it  is  separated 
from  the  semilunar  ganglion  by  a  thin  plate  of  bone,  which  forms  the  floor  of  the 
fossa  for  the  ganglion  and  the  roof  of  the  horizontal  portion  of  the  canal.  Fre- 
quently this  bony  plate  is  more  or  less  deficient,  and  then  the  ganglion  is  separated 
from  the  artery  by  fibrous  membrane.  The  artery  is  separated  from  the  bony  wall 
of  the  carotid  canal  by  a  prolongation  of  dura  mater,  and  is  surrounded  by  a  number 
of  small  veins  and  by  filaments  of  the  carotid  plexus,  derived  from  the  ascending 
branch  of  the  superior  cervical  ganglion  of  the  sympathetic  trunk. 

Cavernous  Portion. — In  this  part  of  its  course,  the  artery  is  situated  between 
the  layers  of  the  dura  Inater  forming  the  cavernous  sinus,  but  covered  by  the  lining 
membrane  of  the  sinus.  It  at  first  ascends  toward  the  posterior  clinoid  process, 
then  passes  forward  by  the  side  of  the  body  of  the  sphenoid  bone,  and  again  curves 
upward  on  the  medial  side  of  the  anterior  clinoid  process,  and  perforates  the  dura 
mater  forming  the  roof  of  the  sinus.  This  portion  of  the  artery  is  surrounded  by 
filaments  of  the  sympathetic  nerve,  and  on  its  lateral  side  is  the  abducent  nerve. 

Cerebral  Portion. — Having  perforated  the  dura  mater  on  the  medial  side  of 
the  anterior  clinoid  process,  the  internal  carotid  passes  between  the  optic  and  oculo- 
motor nerves  to  the  anterior  perforated  substance  at  the  medial  extremity  of  the 
lateral  cerebral  fissure,  where  it  gives  off  its  terminal  or  cerebral  branches. 

Peculiarities. — The  length  of  the  internal  carotid  varies  according  to  the  length  of  the  neck, 
and  also  according  to  the  point  of  bifurcation  of  the  common  carotid.  It  arises  sometimes  from 
the  arch  of  the  aorta;  in  such  rare  instances,  this  vessel  has  been  found  to  be  placed  nearer  the 
middle  line  of  the  neck  than  the  external  carotid,  as  far  upward  as  the  larynx,  when  the  latter 
vessel  crossed  the  internal  carotid.  The  course  of  the  artery,  instead  of  being  straight,  may  be 
very  tortuous.  A  few  instances  are  recorded  in  which  this  vessel  was  altogether  absent;  in  one 
of  these  the  common  carotid  passed  up  the  neck,  and  gave  off  the  usual  branches  of  the  external 
carotid;  the  cranial  portion  of  the  internal  carotid  was  replaced  by  two  branches  of  the  internal 
maxillary,  which  entered  the  skull  through  the  foramen  rotundum  and  foramen  ovale,  and  joined 
to  form  a  single  vessel- 


ANGIOLOGY 


I 


Branches. — The  cervical  portion  of  the  internal  carotid  gives  off  no  branches. 
Those  from  the  other  portions  are: 


From  the  Petrous  Portion 


From  the  Cavernous  Portion 


From  the  Cerebral  Portion 


\  Caroticotympanic. 

lArtery  of  the  Pterygoid  Canal. 

Cavernous. 
Hypophyseal. 
Semilunar. 
Anterior  Meningeal. 
Ophthalmic. 

Anterior  Cerebral. 
Middle  Cerebral. 
Posterior  Communicating. 
Choroidal. 


1.  The  caroticotympanic  branch  (ramus  caroticotympanicus;  tympanic  branch) 
is  small;  it  enters  the  tympanic  cavity  through  a  minute  foramen  in  the  carotid 
canal,  and  anastomoses  with  the  anterior  tympanic  branch  of  the  internal  maxillary, 
and  with  the  stylomastoid  artery. 

2.  The  artery  of  the  pterygoid  canal  (a.  canilis  pterygoidei  [Vidii];  Vidian  artery) 
is  a  small,  inconstant  branch  which  passes  into  the  pterj^goid  canal  and  anas- 
tomoses with  a  branch  of  the  internal  maxillary  artery. 

3.  The  cavernous  branches  are  numerous  small  vessels  which  supply  the 
hypophysis,  the  semilunar  ganglion,  and  the  walls  of  the  cavernous  and  inferior 
petrosal  sinuses.    Some  of  them  anastomose  with  branches  of  the  middle  meningeal. 

4.  The  hjrpophyseal  branches  are  one  or  two  minute  vessels  supplying  the 
hypophysis. 

5.  The  semilunar  branches  are  small  vessels  to  the  semilunar  ganglion. 

6.  The  anterior  meningeal  branch  (a.  meningea  anterior)  is  a  small  branch  which 
passes  over  the  small  w  ing  of  the  sphenoid  to  supply  the  dura  mater  of  the  anterior 
cranial  fossa;  it  anastomoses  with  the  meningeal  branch  from  the  posterior  eth- 
moidal artery. 

7.  The  ophthalmic  artery  (a.  ophthalmica)  (Fig.  514)  arises  from  the  internal 
carotid,  just  as  that  vessel  is  emerging  from  the  cavernous  sinus,  on  the  medial 
side  of  the  anterior  clinoid  process,  and  enters  the  orbital  cavity  through  the  optic 
foramen,  below  and  lateral  to  the  optic  nerve.  It  then  passes  over  the  nerve  to 
reach  the  medial  wall  of  the  orbit,  and  thence  horizontally  forward,  beneath  the 
lower  border  of  the  Obliquus  superior,  and  divides  it  into  two  terminal  branches, 
the  frontal  and  dorsal  nasal.  As  the  artery  crosses  the  optic  nerve  it  is  accompanied 
by  the  nasociliary  nerve,  and  is  separated  from  the  frontal  nerve  by  the  Rectus 
superior  and  Levator  palpebrse  superioris. 

Branches. — The  branches  of  the  ophthalmic  artery  may  be  divided  into  an  orbital 
group,  distributed  to  the  orbit  and  surrounding  parts;  and  an  ocular  group,  to  the 
muscles  and  bulb  of  the  eye. 


Orbital  Group. 

Lacrimal. 
Supraorbital. 
Posterior  Ethmoidal. 
Anterior  Ethmoidal. 
Medial  Palpebral. 
Frontal. 
Dorsal  Nasal. 


Ocular  Group. 

Central  Artery  of  the  Retina. 
Short  Posterior  Ciliary. 
Long  Posterior  Ciliary. 
Anterior  Ciliary. 
Muscular. 


THE  INTERNAL  CAROTID  ARTERY 


569 


I  The  Lacrimal  Artery  (a.  lacrimalis)  arises  close  to  the  optic  foramen,  and  is  one 
of  the  largest  branches  derived  from  the  ophthalmic:  not  infrequently  it  is  given 
off  before  the  artery  enters  the  orbit.  It  accompanies  the  lacrimal  nerve  along 
the  upper  border  of  the  Rectus  lateralis,  and  supplies  the  lacrimal  gland.  Its 
terminal  branches,  escaping  from  the  gland,  are  distributed  to  the  eyelids  and  con- 
junctiva :  of  those  supplying  the  eyelids,  two  are  of  considerable  size  and  are  named 
the  lateral  palpebral  arteries;  they  run  mediaiward  in  the  upper  and  lower  lids 
respectively  and  anastomose  with  the  medial  palpebral  arteries,  forming  an  arterial 
circle  in  this  situation.  The  lacrimal  artery  give  off  one  or  two  zygomatic  branches, 
^^  one  of  which  passes  through  the  zygomatico-temporal  foramen,  to  reach  the  tem- 
^H^poral  fossa,  and  anastomoses  with  the  deep  temporal  arteries;  another  appears 
^^  on  the  cheek  through  the  zygomatico-facial  foramen,  and  anastomoses  with  the 
transverse  facial.  A  recurrent  branch  passes  backward  through  the  lateral  part  of 
the  superior  orbital  fissure  to  the  dura  mater,  and  anastomoses  with  a  branch  of 
the  middle  meningeal  artery.  The  lacrimal  artery  is  sometimes  derived  from  one 
of  the  anterior  branches  of  the  middle  meningeal  artery. 

Dorsal  nasal        Medial  'palpebral 

'/IV.  I    Frontal  Supraorbital 


Anterior  ethmoidal 


Posterior  ethmoidal 


y  Zygomatic  branches 
of  lacrimal 


Mitacular 


Lacrimal 


Ophthalmic 


Internal  carotid 


Fig.  514. — The  ophthalmic  artery  and  its  branches. 


hi 


m 

m  The  Supraorbital  Artery  (a.  supraorbitalis)  springs  from  the  ophthalmic  as  that 
vessel  is  crossing  over  the  optic  nerve.  It  passes  upward  on  the  medial  borders 
of  the  Rectus  superior  and  Levator  palpebrse,  and  meeting  the  supraorbital  nerve 
accompanies  it  between  the  periosteum  and  Levator  palpebrse  to  the  supraorbital 
foramen;  passing  through  this  it  divides  into  a  superficial  and  a  deep  branch, 
which  supply  the  integument,  the  muscles,  and  the  pericranium  of  the  forehead, 
anastomosing  with  the  frontal,  the  frontal  branch  of  the  superficial  temporal,  and 
the  artery  of  the  opposite  side.  This  artery  in  the  orbit  supplies  the  Rectus  superior 
and  the  Levator  palpebrse,  and  sends  a  branch  across  the  pulley  of  the  Obliquus 
superior,  to  supply  the  parts  at  the  medial  palpebral  commissure.  At  the  supra- 
orbital foramen  it  frequently  transmits  a  branch  to  the  diploe. 


i_ 


ANGIOLOGY 


I 


The  Ethmoidal  Arteries  are  two  in  number:  posterior  and  anterior.  The  posterior 
ethmoidal  artery,  the  smaller,  passes  through  the  posterior  ethmoidal  canal,  supplies 
the  posterior  ethmoidal  cells,  and,  entering  the  cranium,  gives  off  a  meningeal 
branch  to  the  dura  mater,  and  nasal  branches  which  descend  into  the  nasal  cavity 
through  apertures  in  the  cribriform  plate,  anastomosing  with  branches  of  the 
sphenopalatine.  The  anterior  ethmoidal  artery  accompanies  the  nasociliary  nerve 
through  the  anterior  ethmoidal  canal,  supplies  the  anterior  and  middle  ethmoidal 
cells  and  frontal  sinus,  and,  entering  the  cranium,  gives  off  a  meningeal  branch 
to  the  dura  mater,  and  nasal  branches;  these  latter  descend  into  the  nasal  cavity 
through  the  slit  by  the  side  of  the  crista  galli,  and,  running  along  the  groove  on 
the  inner  surface  of  the  nasal  bone,  supply  branches  to  the  lateral  wall  and  septum 
of  the  nose,  and  a  terminal  branch  which  appears  on  the  dorsum  of  the  nose  between 
the  nasal  bone  and  the  lateral  cartilage. 


Fig.  515. — Bloodvessels  of  the  eyelids,  front  view.  1,  supraorbital  artery  and  vein;  2,  nasal  artery;  3,  angular  artery, 
the  terminal  branch  of  4,  the  facial  artery;  5,  suborbital  artery;  6,  anterior  branch  of  the  superficial  temporal  artery; 
6',  malar  branch  of  the  transverse  artery  of  the  face ;  7,  lacrimal  artery ;  8,  superior  palpebral  artery  with  8',  its  external 
arch;  9,  anastomoses  of  the  superior  palpebral  with  the  superficial  temporal  and  lacrimal;  10,  inferior  palpebral  artery; 
11,  facial  vein;  12,  angular  vein;  13,  branch  of  the  superficial  temporal  vein.     (Teetut.) 

The  Medial  Palpebral  Arteries  {aa.  palpebrales  mediates;  internal  'palpebral 
arteries),  two  in  number,  superior  and  inferior,  arise  from  the  ophthalmic,  opposite 
the  pulley  of  the  Obliquus  superior;  they  leave  the  orbit  to  encircle  the  eyelids 
near  their  free  margins,  forming  a  superior  and  an  inferior  arch,  which  lie  between 
the  Orbicularis  oculi  and  the  tarsi.  The  superior  palpebral  anastomoses,  at  the 
lateral  angle  of  the  orbit,  with  the  zygomaticoorbital  branch  of  the  temporal  artery 
and  with  the  upper  of  the  two  lateral  palpebral  branches  from  the  lacrimal  artery; 
the  inferior  palpebral  anastomoses,  at  the  lateral  angle  of  the  orbit,  with  the  lower 
of  the  two  lateral  palpebral  branches  from  the  lacrimal  and  with  the  transverse 
facial  artery,  and,  at  the  medial  part  of  the  lid,  with  a  branch  from  the  angular 
artery.  From  this  last  anastomoses  a  branch  passes  to  the  nasolacrimal  duct, 
ramifying  in  its  mucous  membrane,  as  far  as  the  inferior  meatus  of  the  nasal 
cavity. 

The  Frontal  Artery  (a.  frontalis),  one  of  the  terminal  branches  of  the  ophthalmic, 
leaves  the  orbit  at  its  medial  angle  with  the  supratrochlear  nerve,  and,  ascending 


h 


N 


k» 


THE  INTERNAL  CAROTW^IWEKY  571 

on  the  forehead,  supplies  the  integument,  muscles,  and  pericranium,  anastomosing 
with  the  supraorbital  artery,  and  with  the  artery  of  the  opposite  side. 

The  Dorsal  Nasal  Artery  {a.  dorsalis  nasi;  nasal  artery),  the  other  terminal  branch 
of  the  ophthalmic,  emerges  from  the  orbit  above  the  medial  palpebral  ligament, 
and,  after  giving  a  twig  to  the  upper  part  of  the  lacrimal  sac,  divides  into  tAvo 
branches,  one  of  which  crosses  the  root  of  the  nose,  and  anastomoses  with  the 
angular  artery,  the  other  runs  along  the  dorsum  of  the  nose,  supplies  its  outer 
surface ;  and  anastomoses  with  the  artery  of  the  opposite  side,  and  with  the  lateral 
nasal  branch  of  the  external  maxillary. 

The  Central  Artery  of  the  Retina  (a.  centralis  retinoe)  is  the  first  and  one  of  the 
smallest  branches  of  the  ophthalmic  artery.  It  runs  for  a  short  distance  within 
the  dural  sheath  of  the  optic  nerve,  but  about  1.25  cm.  behind  the  eyeball  it  pierces 
the  nerve  obliquely,  and  runs  forward  in  the  center  of  its  substance  to  the  retina. 
Its  mode  of  distribution  will  be  described  with  the  anatomy  of  the  eye. 

The  Ciliary  Arteries  (aa.  ciliares)  are  divisible  into  three  groups,  the  long  and  short, 
f posterior,  and  the  anterior.  The  short  posterior  ciliary  arteries  from  six  to  twelve 
in  number,  arise  from  the  ophthalmic,  or  its  branches;  they  pass  forward  around  the 
optic  nerve  to  the  posterior  part  of  the  eyeball,  pierce  the  sclera  around  the  entrance 
of  the  nerve,  and  supply  the  choroid  and  ciliary  processes.  The  long  posterior 
ciliary  arteries,  two  in  number,  pierce  the  posterior  part  of  the  sclera  at  some  little 
distance  from  the  optic  nerve,  and  run  forward,  along  either  side  of  the  eyeball, 
between  the  sclera  and  choroid,  to  the  ciliary  muscle,  where  they  divide  into  two 
branches;  these  form  an  arterial  circle,  the  circulus  arteriosus  major,  around  the 
circumference  of  the  iris,  from  which  numerous  converging  branches  run,  in  the 
substance  of  the  iris,  to  its  pupillary  margin,  w  here  they  form  a  second  arterial 
circle,  the  circulus  arteriosus  minor.  The  anterior  ciliary  arteries  are  derived  from 
the  muscular  branches;  they  run  to  the  front  of  the  eyeball  in  company  with  the 
tendons  of  the  Recti,  form  a  vascular  zone  beneath  the  conjunctiva,  and  then  pierce 
I  the  sclera  a  short  distance  from  the  cornea  and  end  in  the  circulus  arteriosus  major. 

The  Muscular  Branches,  {rami  musculares),  two  in  number,  superior  and  inferior, 
frequently  spring  from  a  common  trunk.  The  superior,  often  wanting,  supplies 
the  Levator  palpebrse  superioris,  Rectus  superior,  and  Obliquus  superior.  The 
inferior,  more  constantly  present,  passes  forward  between  the  optic  nerve  and  Rectus 
inferior,  and  is  distributed  to  the  Recti  lateralis,  medialis,  and  inferior,  and  the 
Obliquus  inferior.  This  vessel  gives  off  most  of  the  anterior  ciliary  arteries.  Addi- 
tional muscular  branches  are  given  off  from  the  lacrimal  and  supraorbital  arteries, 
or  from  the  trunk  of  the  ophthalmic. 

8.  The  anterior  cerebral  artery  (a.  cerebri  anterior)  (Figs,  516,  517,  518)  arises 
from  the  internal  carotid,  at  the  medial  extremity  of  the  lateral  cerebral  fissure. 
It  passes  forward  and  medialward  across  the  anterior  perforated  substance,  above 
the  optic  nerve,  to  the  commencement  of  the  longitudinal  fissure.  Here  it  comes 
into  close  relationship  with  the  opposite  artery,  to  which  it  is  connected  by  a  short 
trunk,  the  anterior  communicating  artery.  From  this  point  the  two  vessels  run  side 
by  side  in  the  longitudinal  fissure,  curve  around  the  genu  of  the  corpus  callosum, 
and  turning  backward  continue  along  the  upper  surface  of  the  corpus  callosum 
to  its  posterior  part,  where  they  end  by  anastomosing  with  the  posterior  cerebral 
arteries. 

Branches. — In  its  course  the  anterior  cerebral  artery  gives  off  the  following 
branches : 

Antero-medial  Ganglionic.  Anterior.  Posterior. 

Inferior.  Middle. 

The  Antero-medial  Ganglionic  Branches  are  a  group  of  small  arteries  which  arise 
at  the  commencement  of  the  anterior  cerebral  artery;  they  pierce  the  anterior 


572 


ANGIOLOGY 


I 


perforated  substance  and  lamina  terminalis,  and  supply  the  rostrum  of  the  corpus 
callosum,  the  septum  pellucidum,  and  the  head  of  the  caudate  nucleus.  The 
inferior  branches,  two  or  three  in  number,  are  distributed  to  the  orbital  surface  of 
the  frontal  lobe,  where  they  supply  the  olfactory  lobe,  gyrus  rectus,  and  interna] 
orbital  gyrus.  The  anterior  branches  supply  a  part  of  the  superior  frontal  gyrus, 
and  send  twigs  over  the  edge  of  the  hemisphere  to  the  superior  and  middle  frontal 
gyri  and  upper  part  of  the  anterior  central  gyrus.  The  middle  branches  supply 
the  corpus  callosum,  the  cingulate  gyrus,  the  medial  surface  of  the  superior  frontal 
gyrus,  and  the  upper  part  of  the  anterior  central  gyrus.  The  posterior  branches 
supply  the  precuneus  and  adjacent  lateral  surface  of  the  hemisphere. 


l 


Fio.  516. — The  arteries  of  the  base  of  the  brain.    The  tempora  pole  of  the  cerebrum  and  a  portion  of  the  cerebellar 
hemisphere  have  been  removed  on  the  right  side. 

The  Anterior  Communicating  Artery  (a.  communicans  anterior)  connects  the  two 
anterior  cerebral  arteries  across  the  commencement  of  the  longitudinal  fissure. 
Sometimes  this  vessel  is  wanting,  the  two  arteries  joining  together  to  form  a 
single  trunk,  which  afterward  divides ;  or  it  may  be  wholly,  or  partially,  divided 
into  two.  Its  length  averages  about  4  mm.,  but  varies  greatly.  It  gives  off  some 
of  the  antero-medial  ganglionic  vessels,  but  these  are  principally  derived  from  the 
anterior  cerebral. 

9.  The  middle  cerebral  artery  (a.  cerebri  media)  (Figs.  516,  '517),  the  largest 
branch  of  the  internal  carotid,  runs  at  first  lateralward  in  the  lateral  cerebral  or 
Sylvian  fissure  and  then  backward  and  upward  on  the  surface  of  the  insula,  where 


I 


THE  INTERNAL  CAROTID  ARTERY 


573 


it  divides  into  a  number  of  branches  which  are  distributed  to  the  lateral  surface 
of  the  cerebral  hemisphere. 
Branches. — ^The  branches  of  this  vessel  are  the : 


Antero-lateral  Ganglionic. 
Inferior  Lateral  Frontal. 
Ascending  Frontal. 


Ascending  Parietal. 
Parietotemporal . 
Temporal. 


^If  The  Antero-lateral  Ganglionic  Branches,  a  group  of  small  arteries  which  arise  at 
the  commencement  of  the  middle  cerebral  artery,  are  arranged  in  two  sets:  one, 
the  internal  striate,  passes  upward  through  the  inner  segments  of  the  lentiform 
nucleus,  and  supplies  it,  the  caudate  nucleus,  and  the  internal  capsule;  the  other, 
the  external  striate,  ascends  through  the  outer  segment  of  the  lentiform  nucleus, 
and  supplies  the  caudate  nucleus  and  the  thalamus.  One  artery  of  this  group 
is  of  larger  size  than  the  rest,  and  is  of  special  importance,  as  being  the  artery  in 
the  brain  most  frequently  ruptured;  it  has  been  termed  by  Charcot  the  artery 
of  cerebral  hemorrhage.  It  ascends  between  the  lentiform  nucleus  and  the  external 
capsule,  and  ends  in  the  caudate  nucleus.     The  inferior  lateral  frontal  supplies 


Fig.  517. — Outer  surface  of  cerebral  hemisphere,  showing  areas  supplied  by  cerebral  arteries. 


FiQ.  518. — Medial  surface  of  cerebral  hemisphere,  showing  areas  supplied  by  cerebral  arteries. 


the  inferior  frontal  gyrus  {Broca's  convolution)  and  the  lateral  part  of  the  orbital 
surface  of  the  frontal  lobe.  The  ascending  frontal  supplies  the  anterior  central 
gyrus.  The  ascending  parietal  is  distributed  to  the  posterior  central  gyrus  and  the 
lower  part  of  the  superior  parietal  lobule.  The  parietotemporal  supplies  the  supra- 
marginal  and  angular  gyri,  and  the  posterior  parts  of  the  superior  and  middle 
temporal  gyri.  The  temporal  branches,  two  or  three  in  number,  are  distributed 
to  the  lateral  surface  of  the  temporal  lobe. 

10.  The  posterior  communicating  artery  (a.  communicans  'posterior)  (Fig.  516) 
Ifcruns  backward  from  the  internal  carotid,  and  anastomoses  with  the  posterior 


574 


ANGIOLOGY 


cerebral,  a  branch  of  the  basilar.  It  varies  in  size,  being  sometimes  small,  and  occa- 
sionally so  large  that  the  posterior  cerebral  may  be  considered  as  arising  from  the 
internal  carotid  rather  than  from  the  basilar.  It  is  frequently  larger  on  one  side 
than  on  the  other.  From  its  posterior  half  are  given  off  a  number  of  small  branches, 
the  postero-medial  ganglionic  branches,  which,  with  similar  vessels  from  the  posterior 
cerebral,  pierce  the  posterior  perforated  substance  and  supply  the  medial  surface 
of  the  thalami  and  the  walls  of  the  third  ventricle. 

11.  The  anterior  choroidal  (a.  chorioidea;  choroid  artery)  is  a  small  but  constant 
branch,  which  arises  from  the  internal  carotid,  near  the  posterior  communicating 
artery.  Passing  backward  and  lateralward  between  the  temporal  lobe  and  the 
cerebral  peduncle,  it  enters  the  inferior  horn  of  the  lateral  ventricle  through  the 
choroidal  fissure  and  ends  in  the  choroid  plexus.  It  is  distributed  to  the  hippo- 
campus, fimbria,  tela  chorioidea  of  the  third  ventricle,  and  choroid  plexus. 


I 


Int.  carotid 


ArU,  commwiicating 
Ant.  cerebral 


Po3t  com- 
municating 


THE    ARTERIES    OF   THE   BRAIN. 

Since  the  mode  of  distribution  of  the  vessels  of  the  brain  has  an  important 
bearing  upon  a  considerable  number  of  the  pathological  lesions  which  may  occur 

in  this  part  of  the  nervous  system,  it  is  im- 
portant to  consider  a  little  more  in  detail  the 
manner  in  which  the  vessels  are  distributed. 
The  cerebral  arteries  are  derived  from  the 
internal  carotid  and  vertebral,  which  at  the 
base  of  the  brain  form  a  remarkable  anasto- 
mosis known  as  the  arterial  circle  of  Willis. 
It  is  formed  in  front  by  the  anterior  cere- 
bral arteries,  branches  of  the  internal  carotid, 
which  are  connected  together  by  the  anterior 
communicating;  behind  by  the  two  posterior 
cerebral  arteries,  branches  of  the  basilar, 
which  are  connected  on  either  side  with  the 
internal  carotid  by  the  posterior  commu- 
nicating (Figs.  516,  519).  The  parts  of  the 
brain  included  within  this  arterial  circle  are 
the  lamina  terminalis,  the  optic  chiasma, 
the  infundibulum,  the  tuber  cinereum,  the 
corpora  mammillaria,  and  the  posterior 
perforated  substance. 

The  three  trunks  which  together  supply 
each  cerebral  hemisphere  arise  from  the 
arterial  circle  of  Willis.  From  its  anterior 
part  proceed  the  two  anterior  cerebrals, 
from  its  antero-lateral  parts  the  middle 
cerebrals,  and  from  its  posterior  part  the^ 
posterior  cerebrals.  Each  of  these  prin- 
cipal arteries  gives  origin  to  two  different 
systems  of  secondary  vessels.  One  of  these  is  named  the  ganglionic  system,  and  the 
vessels  belonging  to  it  supply  the  thalami  and  corpora  striata ;  the  other  is  the  cortical 
system,  and  its  vessels  ramify  in  the  pia  mater  and  supply  the  cortex  and  subjacent 
brain  substance.  These  two  systems  do  not  communicate  at  any  point  of  their 
peripheral  distribution,  but  are  entirely  independent  of  each  other,  and  there  is 
between  the  parts  supplied  by  the  two  systems  a  borderland  of  diminished 
nutritive  activity,  where,  it  is  said,  softening  is  especially  liable  to  occur  in  the 
brains  of  old  people. 


Posterior 
inferior 
cerebellar 

Fig.  519. — Diagram  of  the  arterial  circulation  at 
the  base  of  the  brain.  A.L.  Antero-lateral.  A.M. 
Antero-medial.  P.L.  Postero-lateral.  P.M.  Postero- 
medial ganglionic  branches. 


I 


THE  SUBCLAVIAN  ARTERY  "^^"^  575 


I 


The  Ganglionic  System. — All  the  vessels  of  this  system  are  given  off  from  the 
arterial  circle  of  Willis,  or  from  the  vessels  close  to  it.  They  form  six  principal 
groups:  (I)  the  antero-medial  group,  derived  from  the  anterior  cerebrals  and  anterior 
communicating;  (II)  the  postero-medial  group,  from  the  posterior  cerebrals  and 
j)osterior  communicating;  (III  and  IV)  the  right  and  left  antero-lateral  groups, 
from  the  middle  cerebrals;  and  (V  and  VI)  the  right  and  left  postero-lateral 
groups,  from  the  posterior  cerebrals,  after  they  have  wound  around  the  cerebral 
peduncles.  The  vessels  of  this  system  are  larger  than  those  of  the  cortical  system, 
and  are  what  Cohnheim  designated  terminal  arteries — that  is  to  say,  vessels  which 
from  their  origin  to  their  termination  neither  supply  nor  receive  any  anastomotic 
branch,  so  that,  through  any  one  of  the  vessels  only  a  limited  area  of  the  thalamus 
or  corpus  striatum  can  be  injected,  and  the  injection  cannot  be  driven  beyond  the 
area  of  the  part  supplied  by  the  particular  vessel  which  is  the  subject  of  the 
experiment. 

The  Cortical  Arterial  System. — The  vessels  forming  this  system  are  the  terminal 
branches  of  the  anterior,  middle,  and  posterior  cerebral  arteries.  They  divide 
and  ramify  in  the  substance  of  the  pia  mater,  and  give  off  branches  which  penetrate 
the  brain  cortex,  perpendicularly.  These  branches  are  divisible  into  two  classes, 
long  and  short.  The  long,  or  medullary  arteries,  pass  through  the  gray  substance 
and  penetrate  the  subjacent  white  substance  to  the  depth  of  3  or  4  cm.,  without 
intercommunicating  otherwise  than  by  very  fine  capillaries,  and  thus  constitute 
so  many  independent  small  systems.  The  short  vessels  are  confined  to  the  cortex, 
where  they  form  with  the  long  vessels  a  compact  net-work  in  the  middle  zone 
of  the  gray  substance,  the  outer  and  inner  zones  being  sparingly  supplied  with 
blood.  The  vessels  of  the  cortical  arterial  system  are  not  so  strictly  "terminal" 
as  those  of  the  ganglionic  system,  but  they  approach  this  type  very  closely,  so 
that  injection  of  one  area  from  the  vessel  of  another  area,  though  possible,  is 
frequently  very  difficult,  and  is  onlj^  effected  through  vessels  of  small  caliber.  As 
a  result  of  this,  obstruction  of  one  of  the  main  branches,  or  its  divisions,  may  have 

e  effect  of  producing  softening  in  a  limited  area  of  the  cortex. 


f 


THE  ARTERIES  OF  THE  UPPER  EXTREMITY. 


The  artery  which  supplies  the  upper  extremity  continues  as  a  single  trunk 
from  its  commencement  down  to  the  elbow;  but  different  portions  of  it  have  received 
different  names,  according  to  the  regions  through  which  they  pass.  That  part 
of  the  vessel  which  extends  from  its  origin  to  the  outer  border  of  the  first  rib  is 
termed  the  subclavian;  beyond  this  point  to  the  lower  border  of  the  axilla  it  is 
named  the  axillary;  and  from  the  lower  margin  of  the  axillary  space  to  the  bend 
of  the  elbow  it  is  termed  brachial ;  here  the  trunk  ends  by  dividing  into  two  branches 
the  radial  and  ulnar. 

THE   SUBCLAVIAN   ARTERY   (A.  SUBCLAVIA)  (Fig.  520). 

On  the  right  side  the  subclavian  artery  arises  from  the  innominate  artery  behind 
the  right  sternoclavicular  articulation;  on  the  left  side  it  springs  from  the  arch 
of  the  aorta.  The  two  vessels,  therefore,  in  the  first  part  of  their  course,  differ 
in  length,  direction,  and  relation  with  neighboring  structures. 

In  order  to  facilitate  the  description,  each  subclavian  artery  is  divided  into 
three  parts.  The  first  portion  extends  from  the  origin  of  the  vessel  to  the  medial 
border  of  the  Scalenus  anterior;  the  second  lies  behind  this  muscle;  and  the  third 
extends  from  the  lateral  margin  of  the  muscle  to  the  outer  border  of  the  first  rib, 
where  it  becomes  the  axillary  artery.  The  first  portions  of  the  two  vessels  require 
separate  descriptions ;  the  second  and  third  parts  of  the  two  arteries  are  practically 
alike. 


I 


576 


ANGIOLOGY 


First  Part  of  the  Right  Subclavian  Artery  (Figs.  505,  520).— The  first  "part  cf 
the  right  subclavian  artery  arises  from  the  innominate  artery,  behind  the  upper 
part  of  the  right  sternoclavicular  articulation,  and  passes  upward  and  lateralward 
to  the  medial  margin  of  the  Scalenus  anterior.  It  ascends  a  little  above  the  clavicle, 
the  extent  to  which  it  does  so  varying  in  different  cases. 


Fig.  520. — Superficial  dissection  of  the  right  side  of  the  necli,  showing  the  ckrotid  and  subclavian  arteries. 


Relations. — It  is  covered,  in  front,  by  the  integument,  superficial  fascia,  Platysma,  deep  fascia, 
the  clavicular  origin  of  the  Stemocleidomastoideus,  the  Sternohyoideus,  and  Sternothyreoideus, 
and  another  layer  of  the  deep  fascia.  It  is  crossed  by  the  internal  jugular  and  vertebral  veins, 
by  the  vagus  nerve  and  the  cardiac  branches  of  the  vagus  and  sympathetic,  and  by  the  sub- 
clavian loop  of  the  sympathetic  trunk  which  forms  a  ring  ai'ound  the  vessel.  The  anterior  jugular 
vein  is  directed  lateralward  in  front  of  the  artery,  but  is  separated  from  it  by  the  Sternohyoideus 
and  Sternothyreoideus.  Below  and  behind  the  artery  is  the  pleura,  which  separates  it  from  the 
apex  of  the  lung;  behind  is  the  sympathetic  trunk,  the  Longus  colli  and  the  first  thoracic  vertebra. 
The  right  recurrent  nerve  winds  around  the  lower  and  back  part  of  the  vessel. 


I 


THE  SUBCLAVIAN  ARTERY  577 


First  Part  of  the  Left  Subclavian  Artery  (Fig.  505). — The  first  part  of  the  left 
subclavian  artery  arises  from  the  arch  of  the  aorta,  behind  the  left  common  carotid, 
and  at  the  level  of  the  fourth  thoracic  vertebra;  it  ascends  in  the  superior  medias- 
tinal cavity  to  the  root  of  the  neck  and  then  arches  lateralward  to  the  medial 
border  of  the  Scalenus  anterior. 

Relations. — It  is  in  relation,  in  front,  with  the  vagus,  cardiac,  and  phrenic  nerves,  which  he 
parallel  with  it,  the  left  common  carotid  artery,  left  internal  jugular  and  vertebral  veins,  and 
the  commencement  of  the  left  innominate  vein,  and  is  covered  by  the  Sternothyreoideus,  Sterno- 
hyoideus,  and  Sternocleidomastoideus;  behind,  it  is  in  relation  with  the  esophagus,  thoracic 
duct,  left  recurrent  nerve,  inferior  cervical  gangUon  of  the  sympathetic  trunk,  and  Longus  colli; 
higher  up,  however,  the  esophagus  and  thoracic  duct  lie  to  its  right  side;  the  latter  ultimately 
arching  over  the  vessel  to  join  the  angle  of  union  between  the  subclavian  and  internal  jugular 
veins.  Medial  to  it  are  the  esophagus,  trachea,  thoracic  duct,  and  left  recurrent  nerve;  lateral 
to  it,  the  left  pleura  and  lung. 

[  Second  and  Third  Parts  of  the  Subclavian  Artery  (Fig.  520). — The  second 
portion  of  the  subclavian  artery  lies  behind  the  Scalenus  anterior;  it  is  very  short, 
and  forms  the  highest  part  of  the  arch  described  by  the  vessel. 

Relations. — It  is  covered,  in  front,  by  the  skin,  superficial  fascia,  Platysma,  deep  cervical 
fascia,  Sternocleidomastoideus,  and  Scalenus  anterior.  On  the  right  side  of  the  neck  the 
phrenic  nerve  is  separated  from  the  second  part  of  the  artery  by  the  Scalenus  anterior,  while 
on  the  left  side  it  crosses  the  first  part  of  the  artery  close  to  the  medial  edge  of  the  muscle. 
Behind  the  vessel  are  the  pleura  and  the  Scalenus  medius;  above,  the  brachial  plexus  of  nerves; 
below,  the  pleura.  The  subclavian  vein  lies  below  and  in  front  of  the  artery,  separated  from  it 
by  the  Scalenus  anterior. 

The  third  portion  of  the  subclavian  artery  runs  downward  and  lateralward  from 
the  lateral  margin  of  the  Scalenus  anterior  to  the  outer  border  of  the  first  rib, 
where  it  becomes  the  axillary  artery.  This  is  the  most  superficial  portion  of  the 
vessel,  and  is  contained  in  the  subclavian  triangle  (see  page  565). 

Relations. — It  is  covered,  in  front,  by  the  skin,  the  superficial  fascia,  the  Platysma,  the  supra- 
clavicular nerves,  and  the  deep  cervical  fascia.  The  external  jugular  vein  crosses  its  medial 
part  and  receives  the  transverse  scapular,  transverse  cervical,  and  anterior  jugular  veins,  which 
frequently  form  a  plexus  in  front  of  the  artery.  Behind  the  veins,  the  nerve  to  the  Subclavius 
descends  in  front  of  the  artery.  The  terminal  part  of  the  artery  lies  behind  the  clavicle  and  the 
Subclavius  and  is  crossed  by  the  transverse  scapular  vessels.  The  subclavian  vein  is  in  front 
of  and  at  a  slightlj^  lower  level  than  the  artery.  Behind,  it  lies  on  the  lowest  trunk  of  the  brachial 
plexus,  which  intervenes  between  it  and  the  Scalenus  medius.  Above  and  to  its  lateral  side  are 
the  upper  trunks  of  the  brachial  plexus  and  the  Omohyoideus.  Below,  it  rests  on  the  upper 
surface  of  the  first  rib. 

Peculiarities. — The  subclavian  arteries  vary  in  their  origin,  their  course,  and  the  height  to 
which  they  rise  in  the  neck. 

The  origin  of  the  right  subclavian  from  the  innominate  takes  place,  in  some  cases,  above  the 
sternoclavicular  articulation,  and  occasionally,  but  less  frequently,  below  that  joint.  The  artery 
may  arise  as  a  separate  trunk  from  the  arch  of  the  aorta,  and  in  such  cases  it  may  be  either  the 
first,  second,  third,  or  even  the  last  branch  derived  from  that  vessel;  in  the  majority,  however, 
it  is  the  first  or  last,  rarely  the  second  or  third.  When  it  is  the  first  branch,  it  occupies  the  ordinary 
position  of  the  innominate  artery;  when  the  second  or  third,  it  gains  its  usual  position  by  passing 
behind  the  right  carotid;  and  when  the  last  branch,  it  arises  from  the  left  extremity  of  the  arch, 
and  passes  obliquely  toward  the  right  side,  usually  behind  the  trachea,  esophagus,  and  right 
carotid,  sometimes  between  the  esophagus  and  trachea,  to  the  upper  border  of  the  first  rib, 
whence  it  follows  its  ordinary  course.  In  very  rare  instances,  this  vessel  arises  from  the  thoracic 
aorta,  as  low  down  as  the  fourth  thoracic  vertebra.  Occasionally,  it  perforates  the  Scalenus 
anterior;  more  rarely  it  passes  in  front  of  that  muscle.  Sometimes  the  subclavian  vein  passes 
with  the  artery  behind  the  Scalenus  anterior.  The  artery  may  ascend  as  high  as  4  cm.  above 
the  clavicle,  or  any  intermediate  point  between  this  and  the  upper  border  of  the  bone,  the  right 
subclavian  usually  ascending  higher  than  the  left. 

The  left  subclavian  is  occasionally  joined  at  its  origin  with  the  left  carotid. 

The  left  subclavian  artery  is  more  deeply  placed  than  the  right  in  the  first  part  of  its  course, 
and,  as  a  rule,  does  not  reach  quite  as  high  a  level  in  the  neck.  The  posterior  border  of  the  Sterno- 
cleidomastoideus corresponds  pretty  closely  to  the  lateral  border  of  the  Scalenus  anterior,  so 
that  the  third  portion  of  the  artery,  the  part  most  accessible  for  operation,  lies  immediately 
lateral  to  the  posterior  border  of  the  Sternocleidomastoideus. 
37 


kl 


578  ^^^^^^^^^AmiOLOGY 

Collateral  Circulation. — Afler  ligature  of  the  third  part  of  the  subclavian  artery,  the  collateral 
circulation  is  established  mainly  by  three  sets  of  vessels,  thus  described  in  a  dissection: 

1.  A  posterior  set,  consisting  of  the  transverse  scapular  and  the  descending  ramus  of  the  trans- 
verse cervical  branches  of  the  subclavian,  anastomosing  with  the  subscapular  from  the  axillary. 

2.  A  medial  set,  produced  by  the  connection  of  the  internal  mammary  on  the  one  hand,  with 
the  highest  intercostal  and  lateral  thoracic  arteries,  and  the  branches  from  the  subscapular  on 
the  other. 

3.  A  middle  or  axillary  set,  consisting  of  a  number  of  small  vessels  derived  from  branches  of 
the  subclavian,  above,  and,  passing  through  the  axilla,  terminating  either  in  the  main  trunk, 
or  some  of  the  branches  of  the  axillary  below.  This  last  set  presented  most  conspicuously  the 
pecuhar  character  of  newly  formed  or,  rather,  dilated  arteries,  being  excessively  tortuous,  and 
forming  a  complete  plexus. 

The  chief  agent  in  the  restoration  of  the  axillary  artery  below  the  tumor  was  the  subscapular 
artery,  which  communicated  most  freely  with  the  internal  mammary,  transverse  scapular  and 
descending  ramus  of  the  transverse  cervical  branches  of  the  subclavian,  from  all  of  whkh  it 
received  so  great  an  influx  of  blood  as  to  dilate  it  to  three  times  its  natural  size.i 

When  a  ligature  is  appHed  to  the  first  part  of  the  subclavian  artery,  the  collateral  circulation  is 
carried  on  by:  (1)  the  anastomosis  between  the  superior  and  inferior  thyroids;  (2)  the  anastomosis 
of  the  two  vertebrals;  (3)  the  anastomosis  of  the  internal  mammary  with  the  inferior  epigastric 
and  the  aortic  intercostals;  (4)  the  costocervical  anastomosing  with  the  aortic  intercostals;  (5) 
the  profunda  cervicis  anastomosing  with  the  descending  branch  of  the  occipital;  (6)  the  scapular 
branches  of  the  thyrocervical  tnmk  anastomosing  with  the  branches  of  the  axillary,  and  (7)  the 
thoracic  branches  of  the  axillary  anastomosing  with  the  aortic  intercostals. 

Branches. — The  branches  of  the  subclavian  artery  are: 

Vertebral.  Internal  mammary. 

Thyrocervical.  Costocervical. 

On  the  left  side  all  four  branches  generally  arise  from  the  first  portion  of  the 
vessel;  but  on  the  right  side  (Fig.  520)  the  costocervical  trunk  usually  springs 
from  the  second  portion  of  the  vessel.  On  both  sides  of  the  neck,  the  first  three 
branches  arise  close  together  at  the  medial  border  of  the  Scalenus  anterior;  in 
the  majority  of  cases,  a  free  interval  of  from  1.25  to  2.5  cm.  exists  between  the 
commencement  of  the  artery  and  the  origin  of  the  nearest  branch. 

1.  The  vertebral  artery  (a.  vertebralis)  (Fig.  514),  is  the  first  branch  of  the  sub- 
clavian, and  arises  from  the  upper  and  back  part  of  the  first  portion  of  the  vessel. 
It  is  surrounded  by  a  plexus  of  nerve  fibers  derived  from  the  inferior  cervical 
ganglion  of  the  sympathetic  trunk,  and  ascends  through  the  foramina  in  the 
transverse  processes  of  the  upper  six  cervical  vertebrae  ;2  it  then  winds  behind  the 
superior  articular  process  of  the  atlas  and,  entering  the  skull  through  the  foramen 
magnum,  unites,  at  the  lower  border  of  the  pons,  with  the  vessel  of  the  opposite 
side  to  form  the  basilar  artery. 

Relations. — The  vertebral  artery  may  be  divided  into  four  parts:  The  first  part  runs  upward 
and  backward  between  the  Longus  coUi  and  the  Scalenus  anterior.  In  front  of  it  are  the  internal 
jugular  and  vertebral  veins,  and  it  is  crossed  by  the  inferior  thyroid  artery;  the  left  vertebral 
is  crossed  by  the  thoracic  duct  also.  Behind  it  are  the  transverse  process  of  the  seventh  cervical 
vertebra,  the  sympathetic  trunk  and  its  inferior  cervical  gangUon.  The  second  part  runs  upward 
through  the  foramina  in  the  transverse  processes  of  the  upper  six  cervical  vertebrse,  and  is  sur- 
rounded by  branches  from  the  inferior  cervical  sympathetic  gangUon  and  by  a  plexus  of  veins 
which  unite  to  form  the  vertebral  vein  at  the  lower  part  of  the  neck.  It  is  situated  in  front  of 
the  trimks  of  the  cervical  nerves,  and  pursues  an  almost  vertical  course  as  far  as  the  transverse 
process  of  the  atlas,  above  which  it  runs  upward  and  lateralward  to  the  foramen  in  the  trans- 
verse process  of  the  atlas.  The  third  part  issues  from  the  latter  foramen  on  the  medial  side  of 
the  Rectus  capitis  lateraUs,  and  curves  backward  behind  the  superior  articular  process  of  the 
atlas,  the  anterior  ramus  of  the  first  cervical  nerve  being  on  its  medial  side;  it  then  Hes  in  the 
groove  on  the  upper  surface  of  the  posterior  arch  of  the  atlas,  and  enters  the  vertebral  canal 
by  passmg  beneath  the  posterior  atlantooccipital  membrane.  This  part  of  the  artery  is  covered 
by  the  Semispinahs  capitis  and  is  contained  in  the  suboccipital  triangle — a  triangular  space 

1  Guy's  Hospital  Reports,  vol.  i,  1836.  Case  of  axillary  aneurism,  in  which  Aston  Key  had  tied  the  subclavian 
artery  on  the  lateral  edge  of  the  Scalenus  anterior,  twelve  years  previously. 

"  The  vertebral  artery  sometimes  enters  the  foramen  in  the  transverse  process  of  the  fifth  vertebra,  and  has  been 
seen  entering  that  of  the  seventh  vertebra. 


THE  SUBCLAVIAN  ARTERY  579 


bounded  by  the  Rectus  capitis  posterior  major,  the  ObHquus  superior,  and  the  Obliquus  inferior. 
The  first  cervical  or  suboccipital  nerve  lies  between  the  artery  and  the  posterior  arch  of  the  atlas. 
The  fourth  part  pierces  the  dura  mater  and  inclines  medialward  to  the  front  of  the  medulla 
oblongata;  it  is  placed  between  the  hypoglossal  nerve  and  the  anterior  root  of  the  first  cervical 
nerve  and  beneath  the  first  digitation  of  the  ligamentum  denticulatum.  At  the  lower  border 
of  the  pons  it  unites  with  the  vessel  of  the  opposite  side  to  form  the  basilar  artery. 

Branches. — The  branches  of  the  vertebral  artery  may  be  divided  into  two  sets: 
those  given  off  in  the  neck,  and  those  within  the  cranium. 

i  Cervical  Branches.  Cranial  Branches. 

r  Spinal.  Meningeal. 

■  Muscular.  Posterior  Spinal. 

^^L.  Anterior  Spinal. 

HP  Posterior  Inferior  Cerebellar. 

f  Medullary, 

pinal  Branches  {rami  sjyinales)  enter  the  vertebral  canal  through  the  interverte- 
bral foramina,  and  each  divides  into  two  branches.  Of  these,  one  passes  along 
the  roots  of  the  nerves  to  supply  the  medulla  spinalis  and  its  membranes,  anasto- 
mosing with  the  other  arteries  of  the  medulla  spinalis;  the  other  divides  into  an 
ascending  and  a  descending  branch,  which  unite  with  similar  branches  from  the 
arteries  above  and  below,  so  that  two  lateral  anastomotic  chains  are  formed  on  the 
posterior  surfaces  of  the  bodies  of  the  vertebrae,  near  the  attachment  of  the  pedicles. 
From  these  anastomotic  chains  branches  are  supplied  to  the  periosteum  and  the 
bodies  of  the  vertebrae,  and  others  form  communications  with  similar  branches  from 
the  opposite  side;  from  these  communications  small  twigs  arise  which  join  similar 
branches  above  and  below,  to  form  a  central  anastomotic  chain  on  the  posterior 
surface  of  the  bodies  of  the  vertebrae. 

Muscular  Branches  are  given  off  to  the  deep  muscles  of  the  neck,  where  the 
vertebral  artery  curves  around  the  articular  process  of  the  atlas.  They  anastomose 
with  the  occipital,  and  with  the  ascending  and  deep  cervical  arteries. 

The  Meningeal  Branch  {ramus  meningeus;  'posterior  meningeal  branch)  springs 
from  the  vertebral  opposite  the  foramen  magnum,  ramifies  between  the  bone 
and  dura  mater  in  the  cerebellar  fossa,  and  supplies  the  falx  cerebelli.  It  is  fre- 
quently represented  by  one  or  two  small  branches. 

The  Posterior  Spinal  Artery  (a.  spinalis  posterior;  dorsal  spinal  artery)  arises 
from  the  vertebral,  at  the  side  of  the  medulla  oblongata;  passing  backward,  it 

1^  descends  on  this  structure,  lying  in  front  of  the  posterior  roots  of  the  spinal  nerves. 
Band  is  reinforced  by  a  succession  of  small  branches,  which  enter  the  vertebral 
canal  through  the  intervertebral  foramina;  by  means  of  these  it  is  continued  to 
the  lower  part  of  the  medulla  spinalis,  and  to  the  cauda  equina.  Branches  from 
the  posterior  spinal  arteries  form  a  free  anastomosis  around  the  posterior  roots 
of  the  spinal  nerves,  and  communicate,  by  means  of  very  tortuous  transverse 
branches,  with  the  vessels  of  the  opposite  side.  Close  to  its  origin  each  gives  off 
an  ascending  branch,  which  ends  at  the  side  of  the  fourth  ventricle. 

The  Anterior  Spinal  Artery  (a.  spinalis  anterior;  ventral  spinal  artery)  is  a  small 
branch,  which  arises  near  the  termination  of  the  vertebral,  and,  descendmg  in 
front  of  the  medulla  oblongata,  unites  with  its  fellow  of  the  opposite  side  at  the 
level  of  the  foramen  magnum.  One  of  these  vessels  is  usually  larger  than  the  other, 
but  occasionally  they  are  about  equal  in  size.    The  single  trunk,  thus  formed, 

(descends  on  the  front  of  the  medulla  spinalis,  and  is  reinforced  by  a  succession 
Bof  small  branches  which  enter  the  vertebral  canal  through  the  intervertebral 
foramina ;  these  branches  are  derived  from  the  vertebral  and  the  ascending  cervical 
of  the  inferior  thyroid  in  the  neck;  from  the  intercostals  in  the  thorax;  and  from 
the  lumbar,  iliolumbar,  and  lateral  sacral  arteries  in  the  abdomen  and  pelvis. 
They  unite,  by  means  of  ascending  and  descending  branches,  to  form  a  single 


580 


ANGIOLOGY 


anterior  median  artery,  which  extend  as  far  as  the  lower  part  of  the  medulla  spinalis, 
and  is  continued  as  a  slender  twig  on  the  filum  terminale.  This  vessel  is  placed 
in  the  pia  mater  along  the  anterior  median  fissure ;  it  supplies  that  membrane,  and 
the  substance  of  the  medulla  spinalis,  and  sends  off  branches  at  its  lower  part  to 
be  distributed  to  the  cauda  equina. 

The  Posterior  Inferior  Cerebellar  Artery  (a.  cerebelli  inferior  posterior)  (Fig.  516), 
the  largest  branch  of  the  vertebral,  winds  backward  around  the  upper  part  of  the 
medulla  oblongata,  passing  between  the  origins  of  the  vagus  and  accessory  nerves, 
over  the  inferior  peduncle  to  the  under  surface  of  the  cerebellum,  where  it  divides 
into  two  branches.  The  medial  branch  is  continued  backward  to  the  notch  between 
the  two  hemispheres  of  the  cerebellum;  while  the  lateral  supplies  the  under  surface 
of  the  cerebellum,  as  far  as  its  lateral  border,  where  it  anastomoses  with  the  anterior 
inferior  cerebellar  and  the  superior  cerebellar  branches  of  the  basilar  artery. 
Branches  from  this  artery  supply  the  choroid  plexus  of  the  fourth  ventricle. 

The  Medullary  Arteries  (bulbar  arteries)  are  several  minute  vessels  which  spring 
from  the  vertebral  and  its  branches  and  are  distributed  to  the  medulla  oblongata. 

The  Basilar  Artery  (a.  basilaris)  (Fig.  516),  so  named  from  its  position  at  the 
base  of  the  skull,  is  a  single  trunk  formed  by  the  junction  of  the  two  vertebral 
arterieg:  it  extends  from  the  lower  to  the  upper  border  of  the  pons,  lying  in  its 
median  groove,  under  cover  of  the  arachnoid.  It  ends  by  dividing  into  the  two 
posterior  cerebral  arteries. 

Its  branches,  on  either  side,  are  the  following: 


Pontine. 
Internal  Auditory. 


Anterior  Inferior  Cerebellar. 
Superior  Cerebellar. 
Posterior  Cerebral. 


The  pontine  branches  {rami  ad  pontem;  transverse  branches)  are  a  number  of  small 
vessels  which  come  off  at  right  angles  from  either  side  of  the  basilar  artery  and 
supply  the  pons  and  adjacent  parts  of  the  brain. 

The  internal  auditory  artery  (a.  auditiva  interna;  auditory  artery),  a  long  slender 
branch,  arises  from  near  the  middle  of  the  artery;  it  accompanies  the  acoustic  nerve 
through  the  internal  acoustic  meatus,  and  is  distributed  to  the  internal  ear. 

The  anterior  inferior  cerebellar  artery  (a.  cerebelli  inferior  anterior)  passes  back- 
ward to  be  distributed  to  the  anterior  part  of  the  under  surface  of  the  cerebellum,, 
anastomosing  with  the  posterior  inferior  cerebellar  branch  of  the  vertebral. 

The  superior  cerebellar  artery  (a.  cerebelli  superior)  arises  near  the  termination 
of  the  basilar.  It  passes  lateralward,  immediately  below  the  oculomotor  nerve, 
which  separates  it  from  the  posterior  cerebral  artery,  winds  around  the  cerebral 
peduncle,  close  to  the  trochlear  nerve,  and,  arriving  at  the  upper  surface  of  the 
cerebellum,  divides  into  branches  which  ramify  in  the  pia  mater  and  anastomose 
with  those  of  the  inferior  cerebellar  arteries.  Several  branches  are  given  to  the 
pineal  body,  the  anterior  medullary  velum,  and  the  tela  chorioidea  of  the  third 
ventricle. 

The  posterior  cerebral  artery  (a.  cerebri  posterior)  (Figs.  516,  517,  518)  is  larger 
than  the  preceding,  from  which  it  is  separated  near  its  origin  by  the  oculomotor 
nerve.  Passing  lateralward,  parallel  to  the  superior  cerebellar  artery,  and  receiving 
the  posterior  communicating  from  the  internal  carotid,  it  winds  around  the  cerebral 
peduncle,  and  reaches  the  tentorial  surface  of  the  occipital  lobe  of  the  cerebrum, 
where  it  breaks  up  into  branches  for  the  supply  of  the  temporal  and  occipital  lobes. 

The  branches  of  the  posterior  cerebral  artery  are  divided  into  two  sets,  ganglionic 
and  cortical: 

r Posterior-medial.  rAnterior  Temporal. 

Ganglionic   ]  Posterior  Choroidal.       n    f'    1       Posterior  Temporal. 
IPostero-lateral.  °^  ^^^        Calcarine. 

Parietooccipital. 


1^ 


THE  SUBCLAVIAN  ARTERY  ^^^  581 

Ganglionic. — The  postero-medial  ganglionic  branches  (Fig.  519)  are  a  group  of 
smaD  arteries  which  arise  at  the  commencement  of  the  posterior  cerebral  artery; 
:hese,  with  similar  branches  from  the  posterior  communicating,  pierce  the  pos- 
terior perforated  substance,  and  supply  the  medial  surfaces  of  the  thalami  and  the 
walls  of  the  third  ventricle.  The  posterior  choroidal  branches  run  forward  beneath 
he  splenium  of  the  corpus  callosum,  and  supply  the  tela  chorioidea  of  the  third 
ventricle  and  the  choroid  plexus.  The  postero-lateral  ganglionic  branches  are  small 
arteries  which  arise  from  the  posterior  cerebral  artery  after  it  has  turned  around  the 
jCerebral  peduncle;  they  supply  a  considerable  portion  of  the  thalamus. 

Cortical. — The  cortical  branches  are:  the  anterior  temporal,  distributed  to  the 
uncus  and  the  anterior  part  of  the  fusiform  gyrus;  the  posterior  temporal,  to  the 
fusiform  and  the  inferior  temporal  gyri;  the  calcarine,  to  the  cuneus  and  gyrus 
ingualis  and  the  back  part  of  the  convex  surface  of  the  occipital  lobe;  and  the 
parietooccipital,  to  the  cuneus  and  the  precuneus. 

2.  The  thyrocervical  trunk  (truncus  ihyreocervicalis;  thyroid  axis)  (Fig.  520)  is 
a  short  thick  trunk,  which  arises  from  the  front  of  the  first  portion  of  the  subclavian 
artery,  close  to  the  medial  border  of  the  Scalenus  anterior,  and  divides  almost 
immediately  into  three  branches,  the  inferior  thyroid,  transverse  scapular,  and  trans- 
verse cervical. 

The  Inferior  Thyroid  Artery  (a.  thyreoidea  inferior)  passes  upward,  in  front  of  the 
ertebral  artery  and  Longus  colli ;  then  turns  medialward  behind  the  carotid  sheath 
and  its  contents,  and  also  behind  the  sympathetic  trunk,  the  middle  cervical 
ganglion  resting  upon  the  vessel.  Reaching  the  lower  border  of  the  thyroid  gland 
it  divides  into  two  branches,  which  supply  the  postero-inferior  parts  of  the  gland, 
and  anastomose  with  the  superior  thyroid,  and  with  the  corresponding  artery  of 
the  opposite  side.  The  recurrent  nerve  passes  upward  generally  behind,  but  occa- 
sionally in  front,  of  the  artery. 

The  branches  of  the  inferior  thyroid  are : 


h 


Inferior  Laryngeal..  Esophageal. 

Tracheal.  Ascending  Cervical. 

Muscular. 


ife 


li 


The  inferior  larjmgeal  artery  (a.  laryngea  inferior)  ascends  upon  the  trachea  to 
the  back  part  of  the  larynx  under  cover  of  the  Constrictor  pharyngis  inferior,  in 
company  with  the  recurrent  nerve,  and  supplies  the  muscles  and  mucous  mem- 
brane of  this  part,  anastomosing  with  the  branch  from  the  opposite  side,  and  with 
the  superior  laryngeal  branch  of  the  superior  thyroid  artery. 

The  tracheal  branches  (rami  tracheales)  are  distributed  upon  the  trachea,  and 
anastomose  below  with  the  bronchial  arteries. 

The  esophageal  branches  (rami  cesophagei)  supply  the  esophagus,  and  anasto- 
mose with  the  esophageal  branches  of  the  aorta. 

The  ascending  cervical  artery  (a.  cervicalis  ascendens)  is  a  small  branch  which 
rises  from  the  inferior  thyroid  as  that  vessel  is  passing  behind  the  carotid  sheath; 
it  runs  up  on  the  anterior  tubercles  of  the  transverse  processes  of  the  cervical 
vertebrae  in  the  interval  between  the  Scalenus  anterior  and  Longus  capitis.  To 
the  muscles  of  the  neck  it  gives  twigs  which  anastomose  with  branches  of  the  ver- 
tebral, and  it  sends  one  or  two  spinal  branches  into  the  vertebral  canal  through 
he  intervertebral  foramina  to  be  distributed  to  the  medulla  spinalis  and  its  mem- 
branes, and  to  the  bodies  of  the  vertebrae,  in  the  same  manner  as  the  spinal  branches 
from  the  vertebral.  It  anastomoses  with  the  ascending  pharyngeal  and  occipital 
arteries. 

The  muscular  branches  supply  the  depressors  of  the  hyoid  bone,  and  the  Longus 
colli,  Scalenus  anterior,  and  Constrictor  pharyngis  inferior. 


582 


ANGIOLOGY 


Desc.  hr.  of_ 
transverse  cervical 


Transverse  scapular 


Am'omial  branch 
of  thoracoacromial 


Fig.  521. — The  scapular  and  circumflex  arteries. 


The  Transverse  Scapular  Artery  («.  transversa  scayulas;  suprascapular  artery)  passes 
at    first    downward  and  lateralward  across  the  Scalenus  anterior   and  phrenic 

nerve,  being  covered  by  the 
Sternocleidomastoideus;  it  then 
crosses  the  subclavian  artery 
and  the  brachial  plexus,  and 
runs  behind  and  parallel  with 
the  clavicle  and  Subclavius, 
and  beneath  the  inferior  belly 
of  the  Omohyoideus,  to  the 
superior  border  of  the  scapula; 
it  passes  over  the  superior 
transverse  ligament  of  the 
scapula  which  separates  it  from 
the  suprascapular  nerve,  and 
enters  the  supraspinatous  fossa 
(Fig.  521).  In  this  situation  it 
lies  close  to  the  bone,  and  rami- 
fies between  it  and  the  Supra- 
spinatus,  to  which  it  supplies 
branches.  It  then  descends  be- 
hind the  neck  of  the  scapula, 
through  the  great  scapular 
notch  and  under  cover  of  the 
inferior  transverse  ligament,  to 
reach  the  infraspinatous  fossa,  where  it  anastomoses  with  the  scapular  circumflex 
and  the  descending  branch  of  the  transverse  cervical .  Besides  distributing  branches 
to  the  Sternocleidomastoideus,  Subclavius,  and  neighboring  muscles,  it  gives  off  a 
suprasternal  branch,  which  crosses  over  the  sternal  end  of  the  clavicle  to  the  skin  of 
the  upper  part  of  the  chest;  and  an  acromial  branch,  which  pierces  the  Trapezius 
and  supplies  the  skin  over  the  acromion,  anastomosing  with  the  thoracoacromial 
artery.  As  the  artery  passes  over  the  superior  transverse  ligament  of  the  scapula, 
it  sends  a  branch  into  the  subscapular  fossa,  where  it  ramifies  beneath  the  Sub- 
scapularis,  and  anastomoses  with  the  subscapular  artery  and  with  the  descending 
branch  of  the  transverse  cervical.  It  also  sends  articular  branches  to  the  acro- 
mioclavicular and  shoulder-joints,  and  a  nutrient  artery  to  the  clavicle. 

The  Transverse  Cervical  Artery  (a.  transversa  colli;  transversalis  colli  artery)  lies 
at  a  higher  level  than  the  transverse  scapular;  it  passes  transversely  above  the 
inferior  belly  of  the  Omohyoideus  to  the  anterior  margin  of  the  Trapezius,  beneath 
which  it  divides  into  an  ascending  and  a  descending  branch.  It  crosses  in  front  of 
the  phrenic  nerve  and  the  Scaleni,  and  in  front  of  or  between  the  divisions  of  the 
brachial  plexus,  and  is  covered  by  the  Platysma  and  Sternocleidomastoideus,  and 
crossed  by  the  Omohyoideus  and  Trapezius. 

The  ascending  branch  {ramus  ascendens;  superficial  cervical  artery)  ascends  be- 
neath the  anterior  margin  of  the  Trapezius,  distributing  branches  to  it,  and  to  the 
neighboring  muscles  and  lymph  glands  in  the  neck,  and  anastomosing  with  the 
superficial  branch  of  the  descending  ramus  of  the  occipital  artery. 

The  descending  branch  {ramus  descendens;  posterior  scapular  artery)  (Fig.  521)  • 
passes  beneath  the  Levator  scapulae  to  the  medial  angle  of  the  scapula,  and  then 
descends  under  the  Rhomboidei  along  the  vertebral  border  of  that  bone  as  far  as 
the  inferior  angle.  It  supplies  the  Rhomboidei,  Latissimus  dorsi  and  Trapezius, 
and  anastomoses  with  the  transverse  scapular  and  subscapular  arteries,  and  with 
the  posterior  branches  of  some  of  the  intercostal  arteries. 


THE  SUBCLAVIAN  ARTERY 


583 


Peculiarities. — The  ascending  branch  of  the  transverse  cervical  frequently  arises  directly 
from  the  th^Tocervical  trunk;  and  the  descending  branch  from  the  third,  more  rarely  from  the 
second,  part  of  the  subclavian.  . 


Thyrocervical  artery 


Scalenus  anterior 


MusciUophrenic  artery 


Common  carotid  artery 
Innominate  artery 
Internal  mammary  artery 


Perforating  branches 


Superior  epigastric  artery 


? —  Inferior  epigastric  artery 


^- —  External  iliac  artery 


'  — i' 
Fia.  522. — The  internal  mammary  artery  and  lu  branches. 


The  internal  mammary  artery  (a.  mammaria  interna)  (Fig.  522)  arises  from 
le  under  surface  of  the  first  portion  of  the  subclavian,  opposite  the  thyro- 
jrvical  trunk.    It  descends  behind  the  cartilages  of  the  upper  six  ribs  at  a  distance 


584  ^^^^^^^^       ANGIOLOGY 


of  about  1.25  cm.  from  the  margin  of  the  sternum,  and  at  the  level  of  the  sixth 
intercostal  space  divides  into  the  musculophrenic  and  superior  epigastric  arteries. 

Relations. — It  is  directed  at  first  downward,  forward,  and  medialward  behind  the  sternal 
end  of  the  clavicle,  the  subclavian  and  internal  jugular  veins,  and  the  first  costal  cartilage,  and 
passes  forward  close  to  the  lateral  side  of  the  innominate  vein.  As  it  enters  the  thorax  the  phrenic; 
nerve  crosses  from  its  lateral  to  its  medial  side.  Below  the  first  costal  cartilage  it  descends  almost 
vertically  to  its  point  of  bifurcation.  It  is  covered  in  front  by  the  cartilages  of  the  upper  six 
ribs  and  the  intervening  Intercostales  interni  and  anterior  intercostal  membranes,  and  is  crossed 
by  the  terminal  portions  of  the  upper  six  intercostal  nerves.  It  rests  on  the  pleura,  as  far  as  the 
third  costal  cartilage;  below  this  level,  upon  the  Transvei'sus  thoracis.  It  is  accompanied  by  a 
pair  of  veins;  these  unite  above  to  form  a  single  vessel,  which  runs  medial  to  the  artery  and  ends 
in  the  corresponding  innominate  vein. 


I 


Branches. — The  branches  of  the  internal  mammary  are: 

Pericardiacophrenic.  Intercostal. 

Anterior  Mediastinal.  Perforating. 

Pericardial.  Musculophrenic. 

Sternal.  Superior  Epigastric. 


■^ 


The  Pericardiacophrenic  Artery  (a.  pericardiacophrenica;  a.  comes  nervi  phrenici) 
is  a  long  slender  branch,  which  accompanies  the  phrenic  nerve,  between  the  pleura 
and  pericardium,  to  the  diaphragm,  to  which  it  is  distributed;  it  anastomoses 
with  the  musculophrenic  and  inferior  phrenic  arteries. 

The  Anterior  Mediastinal  Arteries  (aa.  mediastinales  anterior es;  mediastinal  arter- 
ies) are  small  vessels,  distributed  to  the  areolar  tissue  and  lymph  glands  in  the 
anterior  mediastinal  cavity,  and  to  the  remains  of  the  thymus. 

The  Pericardial  Branches  supply  the  upper  part  of  the  anterior  surface  of  the 
pericardium;  the  lower  part  receives  branches  from  the  musculophrenic  artery. 

The  Sternal  Branches  {rami  sternales)  are  distributed  to  the  Transversus  thoracis, 
and  to  the  posterior  surface  of  the  sternum. 

The  anterior  mediastinal,  pericardial,  and  sternal  branches,  together  with  some 
twigs  from  the  pericardiacophrenic,  anastomose  with  branches  from  the  intercostal 
and  bronchial  arteries,  and  form  a  subpleural  mediastinal  plexus. 

The  Intercostal  Branches  .{rami  intercostales;  anterior  intercostal  arteries)  supply 
the  upper  five  or  six  intercostal  spaces.  Two  in  number  in  each  space,  these  small 
vessels  pass  lateral  ward,  one  lying  near  the  lower  margin  of  the  rib  above,  and  the 
other  near  the  upper  margin  of  the  rib  below,  and  anastomose  with  the  intercostal 
arteries  from  the  aorta.  They  are  at  first  situated  between  the  pleura  and  the 
Intercostales  interni,  and  then  between  the  Intercostales  interni  and  externi. 
They  supply  the  Intercostales  and,  by  branches  which  perforate  the  Intercostales 
externi,  the  Pectorales  and  the  mamma. 

The  Perforating  Branches  {rami  perforantes)  correspond  to  the  five  or  six  inter- 
costal spaces.  They  pass  forward  through  the  intercostal  spaces,  and,  curving 
lateralward,  supply  the  Pectoralis  major  and  the  integument.  Those  which  corre- 
spond to  the  second,  third,  and  fourth  spaces  give  branches  to  the  mamma,  and 
during  lactation  are  of  large  size. 

The  Musculophrenic  Artery  {a.  musculophrenica)  is  directed  obliquely  downward 
and  lateralward,  behind  the  cartilages  of  the  false  ribs;  it  perforates  the  dia- 
phragm at  the  eighth  or  ninth  costal  cartilage,  and  ends,  considerably  reduced 
in  size,  opposite  the  last  intercostal  space.  It  gives  off  intercostal  branches 
to  the  seventh,  eighth,  and  ninth  intercostal  spaces;  these  diminish  in  size  as  the 
spaces  decrease  in  length,  and  are  distributed  in  a  manner  precisely  similar  to  the 
intercostals  from  the  internal  mammary.  The  musculophrenic  also  gives  branches 
to  the  lower  part  of  the  pericardium,  and  others  which  run  backward  to  the  dia- 
phragm, and  downward  to  the  abdominal  muscles. 


THE  AXILLA  imom^  585 

The  Superior  Epigastric  Artery  {a.  epigasirica  superior)  continues  in  the  original 
direction  of  the  internal  mammary;  it  descends  through  the  interval  between  the 
costal  and  sternal  attachments  of  the  diaphragm,  and  enters  the  sheath  of  the 
Rectus  abdominis,  at  first  lying  behind  the  muscle,  and  then  perforating  and  sup- 
plying it,  and  anastomosing  with  the  inferior  epigastric  artery  from  the  external 
iliac.  Branches  perforate  the  anterior  wall  of  the  sheath  of  the  Rectus,  and  supply 
the  muscles  of  the  abdomen  and  the  integument,  and  a  small  branch  passes  in 
front  of  the  xiphoid  process  and  anastomoses  with  the  artery  of  the  opposite  side. 
It  also  gives  some  twigs  to  the  diaphragm,  while  from  the  artery  of  the  right 
side  small  branches  extend  into  the  falciform  ligament  of  the  liver  and  anastomose 
with  the  hepatic  artery. 

4.  The  costocervical  trunk  {truncus  costocervicalis;  superior  intercostal  artery) 
(Fig.  513)  arises  from  the  upper  and  back  part  of  the  subclavian  artery,  behind 
the  Scalenus  anterior  on  the  right  side,  and  medial  to  that  muscle  on  the  left  side. 
Passing  backward,  it  gives  off  the  profunda  cervicalis,  and,  continuing  as  the  highest 
intercostal  artery,  descends  behind  the  pleura  in  front  of  the  necks  of  the  first  and 
second  ribs,  and  anastomoses  with  the  first  aortic  intercostal.  As  it  crosses  the 
neck  of  the  first  rib  it  lies  medial  to  the  anterior  division  of  the  first  thoracic  nerve, 
and  lateral  to  the  first  thoracic  ganglion  of  the  sympathetic  trunk. 

In  the  first  intercostal  space,  it  gives  off  a  branch  which  is  distributed  in  a 
manner  similar  to  the  distribution  of  the  aortic  intercostals.  The  branch  for  the 
second  intercostal  space  usually  joins  with  one  from  the  highest  aortic  intercostal 
artery.  This  branch  is  not  constant,  but  is  more  commonly  found  on  the  right 
side;  when  absent,  its  place  is  supplied  by  an  intercostal  branch  from  the  aorta. 
Each  intercostal  gives  off  a  posterior  branch  which  goes  to  the  posterior  vertebral 
muscles,  and  sends  a  small  spinal  branch  through  the  corresponding  intervertebral 
_  _  foramen  to  the  medulla  spinalis  and  its  membranes. 

IB     The  Profunda  Cervicalis  (a.  cervicalis  profunda;  deep  cervical  branch)  arises,  in 
most  cases,  from  the  costocervical  trunk,  and  is  analogous  to  the  posterior  branch 
of  an  aortic  intercostal  artery:  occasionally  it  is  a  separate  branch  from  the  sub- 
IB  clavian  artery.    Passing  backward,  above  the  eighth  cervical  nerve  and  between 
I H  the  transverse  process  of  the  seventh  cervical  vertebra  and  the  neck  of  the  first  rib, 
I H  it  runs  up  the  back  of  the  neck,  between  the  Semispinales  capitis  and  colli,  as  high 
as  the  axis  vertebra,  supplying  these  and  adjacent  muscles,  and  anastomosing  with 
the  deep  division  of  the  descending  branch  of  the  occipital,  and  with  branches  of 
the  vertebral.    It  gives  off  a  spinal  twig  which  enters  the  canal  through  the  inter- 
vertebral foramen  between  the  seventh  cervical  and  first  thoracic  vertebrae. 


I 


THE    AXILLA. 


The  axilla  is  a  pyramidal  space,  situated  between  the  upper  lateral  part  of  the 
chest  and  the  medial  side  of  the  arm. 

Boundaries. — The  apex,  which  is  directed  upward  toward  the  root  of  the  neck, 
corresponds  to  the  interval  between  the  outer  border  of  the  first  rib,  the  superior 

I  border  of  the  scapula,  and  the  posterior  surface  of  the  clavicle,  and  through  it 
B  the  axillary  vessels  and  nerves  pass.  The  base,  directed  downward,  is  broad  at 
^  the  chest  but  narrow  and  pointed  at  the  arm;  it  is  formed  by  the  integument  and  a 
•thick  layer  of  fascia,  the  axillary  fascia,  extending  between  the  lower  border  of  the 
Pectoralis  major  in  front,  and  the  lower  border  of  the  Latissimus  dorsi  behind. 
The  anterior  wall  is  formed  by  the  Pectorales  major  and  minor,  the  former  covering 
the  whole  of  this  wall,  the  latter  only  its  central  part.  The  space  between  the  upper 
border  of  the  Pectoralis  minor  and  the  clavicle  is  occupied  by  the  coracoclavicular 
fascia.  The  posterior  ivall,  which  extends  somewhat  lower  than  the  anterior,  is 
formed  by  the  Subscapularis  above,  the  Teres  major  and  Latissimus  dorsi  below. 


586  T^^^^^^^^«     ANGIOLOGY 

On  the  medial  side  are  the  first  four  ribs  with  their  corresponding  Intercostales, 
and  part  of  the  Serratus  anterior.  On  the  lateral  side,  where  the  anterior  and 
posterior  walls  converge,  the  space  is  narrow,  and  bounded  by  the  humerus,  the 
Coracobrachialis,  and  the  Biceps  brachii. 

Contents. — It  contains  the  axillar}^  vessels,  and  the  brachial  plexus  of  nerves, 
with  their  branches,  some  branches  of  the  intercostal  nerves,  and  a  large  number 
of  lymph  glands,  together  with  a  quantity  of  fat  and  loose  areolar  tissue.  The 
axillary  artery  and  vein,  with  the  brachial  plexus  of  nerves,  extend  obliquely  along 
the  lateral  boundary  of  the  axilla,  from  its  apex  to  its  base,  and  are  placed  much 
nearer  to  the  anterior  than  to  the  posterior  wall,  the  vein  lying  to  the  thoracic  side 
of  the  artery  and  partially  concealing  it.  At  the  forepart  of  the  axilla,  in  contact 
with  the  Pectorales,  are  the  thoracic  branches  of  the  axillary  artery,  and  along 
the  lower  margin  of  the  Pectoral  is  minor  the  lateral  thoracic  artery  extends  to  the 
side  of  the  chest.  At  the  back  part,  in  contact  with  the  lower  margin  of  the  Sub- 
scapularis,  are  the  subscapular  vessels  and  nerves;  winding  around  the  lateral 
border  of  this  muscle  are  the  scapular  circumflex  vessels;  and,  close  to  the  neck 
of  the  humerus,  the  posterior  humeral  circumflex  vessels  and  the  axillary  nerve 
curve  backward  to  the  shoulder.  Along  the  medial  or  thoracic  side  no  vessel  of 
any  importance  exists,  the  upper  part  of  the  space  being  crossed  merely  by  a  few 
small  branches  from  the  highest  thoracic  artery.  There  are  some  important  nerves, 
however,  in  this  situation,  viz.,  the  long  thoracic  nerve,  descending  on  the  surface 
of  the  Serratus  anterior,  to  which  it  is  distributed;  and  the  intercostobrachial 
nerve,  perforating  the  upper  and  anterior  part  of  this  wall,  and  passing  across  the 
axilla  to  the  medial  side  of  the  arm. 

The  position  and  arrangement  of  the  lymph  glands  are  described  on  pages  699 
and  700. 

The  Axillary  Artery  (A.  Axillaris)  (Fig.  523). 

The  axillary  artery,  the  continuation  of  the  subclavian,  commences  at  the  outer 
border  of  the  first  rib,  and  ends  at  the  lower  border  of  the  tendon  of  the  Teres 
major,  where  it  takes  the  name  of  brachial.  Its  direction  varies  with  the  position 
of  the  limb;  thus  the  vessel  is  nearly  straight  w^hen  the  arm  is  directed  at  right 
angles  with  the  trunk,  concave  upward  when  the  arm  is  elevated  above  this,  and 
convex  upward  and  lateralward  when  the  arm  lies  by  the  side.  At  its  origin  the 
artery  is  very  deeply  situated,  but  near  its  termination  is  superficial,  being  covered 
only  by  the  skin  and  fascia.  To  facilitate  the  description  of  the  vessel  it  is  divided 
into  three  portions;  the  first  part  lies  above,  the  second  behind,  and  the  third 
below  the  Pectoralis  minor. 

Relations. — The  first  portion  of  the  axillary  artery  is  covered  anteriorly  by  the  clavicular 
portion  of  the  Pectoralis  major  and  the  coracoclavicular  fascia,  and  is  crossed  by  the  lateral 
anterior  thoracic  nerve,  arjd  the  thoracoacromial  and  cephalic  veins;  -posterior  to  it  are  the  first 
intercostal  space,  the  corresponding  Intercostalis  externus,  the  first  and  second  digitations  of 
the  Serratus  anterior,  and  the  long  thoracic  and  medial  anterior  thoracic  nerves,  and  the  medial 
cord  of  the  brachial  plexus;  on  its  lateral  side  is  the  brachial  plexus,  from  which  it  is  separated 
by  a  little  areolar  tissue;  on  its  medial,  or  thoracic  side,  is  the  axillary  vein  which  overlaps  the 
artery.  It  is  enclosed,  together  with  the  axillary  vein  and  the  brachial  plexus,  in  a  fibrous  sheath 
— the  axillary  sheath — continuous  above  with  the  deep  cervical  fascia. 

The  second  portion  of  the  axillary  artery  is  covered,  anteriorly,  by  the  Pectorales  major  and 
minor;  posterior  to  it  are  the  posterior  cord  of  the  brachial  plexus,  and  some  areolar  tissue  which, 
intervenes  between  it  and  the  Subscapularis;  on  the  medial  side  is  the  axillary  vein,  separated 
from  the  artery  by  the  medial  cord  of  the  brachial  plexus  and  the  medial  anterior  thoracic  nerve; 
on  the  lateral  side  is  the  lateral  cord  of  the  brachial  plexus.  The  brachial  plexus  thus  surrounds 
the  artery  on  three  sides,  and  separates  it  from  direct  contact  with  the  vein  and  adjacent  muscles. 

The  third  portion  of  the  axillary  artery  extends  from  the  lower  border  of  the  Pectoralis  minor 
to  the  lower  border  of  the  tendon  of  the  Teres  major.  In  front,  it  is  covered  by  the  lower  part 
of  the  Pectoralis  major  a'bove,  but  only  by  the  integument  and  fascia  below;  behind,  it  is  in  rela- 
tion with  the  lower  part  of  the  Subscapularis,  and  the  tendons  of  the  Latissimus  dorsi  and  Teres 


I 


THE  AXILLARY  ARTERY 


587 


lajor;  on  its  lateral  side  is  the  Coracobrachialis,  and  on  its  medial  or  thoracic  side,  the  axillary 
Fvein.  The  nerves  of  the  brachial  plexus  bear  the  following  relations  to  this  part  of  the  artery: 
on  the  lateral  side  are  the  lateral  head  and  the  trunk  of  the  median,  and  the  musculocutaneous 
for  a  short  distance;  on  the  medial  side  the  ulnar  (between  the  vein  and  artery)  and  medial  brachial 
cutaneous  (to  the  medial  side  of  the  vein) ;  in  front  are  the  medial  head  of  the  median  and  the 
medial  antibrachial  cutaneous,  and  behind,  the  radial  and  axillary,  the  latter  only  as  far  as  the 
lower  border  of  the  Subscapularis. 

Collateral  Circulation  after  Ligature  of  the  Axillary  Artery. — If  the  artery  be  tied  above  the 
origin  of  the  thoracoacromial,  the  collateral  circulation  will  be  carried  on  by  the  same  branches 
as  after  the  ligatm-e  of  the  third  part  of  the  subclavian;  if  at  a  lower  point,  between  the 
thoracoacromial  and  the  subscapular,  the  latter  vessel,  by  its  free  anastomosis  with  the  trans- 
verse scapular  and  transverse  cervical  branches  of  the  subclavian,  will  become  the  chief  agent 
in  carrj-ing  on  the  circulation ;  the  lateral  thoracic,  if  it  be  below  the  Mgature,  will  materially  contrib- 
ute by  its  anastomoses  with  the  intercostal  and  internal  mammary  arteries.  If  the  point  included 
in  the  ligature  is  below  the  origin  of  the  subscapular  artery,  it  will  most  probably  also  be  below 
the  origins  of  the  two  humeral  circumflex  arteries.  The  chief  agents  in  restoring  the  circulation 
will  then  be  the  subscapular  and. the  two  humeral  circumflex  arteries  anastomosing  with  the 
a.  profunda  brachii. 


Fig.  523. — The  axillary  artery  and  its  branches. 


Branches. — The  branches  of  the  axillary  are: 


r,  7        .    f Thoracoacromial. 

Z*  rom  second  part  ir    4.      ^  n^-u 

^         (Lateral  ihoracic. 


^From  first  part,  Highest  Thoracic. 
fSubscapular. 
^  From  third  part    I  Posterior  Humeral  Circumflex. 

B  [Anterior  Humeral  Circumflex. 

1.  The  highest  thoracic  artery  (a.  ihoracalis  suprema;  superior  thoracic  artery) 
io  a  small  vessel,  which  may  arise  from  the  thoracoacromial.  Running  forward 
and  medialward  along  the  upper  border  of  the  Pectoralis  minor,  it  passes  between 
it  and  the  Pectoralis  major  to  the  side  of  the  chest.    It  supplies  branches  to  these 


588 


I 


muscles,  and  to  the  parietes  of  the  thorax,  and  anastomoses  with  the  internal  mam- 
mary and  intercostal  arteries. 

2.  The  thoracoacromial  artery  (a.  thoracoacromialis ;  acromiothoracic  artery;  tho- 
racic axis)  is  a  short  trunk,  which  arises  from  the  forepart  of  the  axillary  artery, 
its  origin  being  generally  overlapped  by  the  upper  edge  of  the  Pectoralis  minor 
Projecting  forward  to  the  upper  border  of  this  muscle,  it  pierces  the  coracoclavicular 
fascia  and  divides  into  four  branches — pectoral,  acromial,  clavicular,  and  deltoid. 
The  pectoral  branch  descends  between  the  two  Pectorales,  and  is  distributed  to 
them  and  to  the  mamma,  anastomosing  with  the  intercostal  branches  of  the  internal 
mammary  and  with  the  lateral  thoracic.  The  acromial  branch  runs  lateralward 
over  the  coracoid  process  and  under  the  Deltoideus,  to  which  it  gives  branches; 
it  then  pierces  that  muscle  and  ends  on  the  acromion  in  an  arterial  network  formed 
by  branches  from  the  transverse  scapular,  thoracoacromial,  and  posterior  humeral 
circumflex  arteries.  The  clavicular  branch  runs  upward  and  medial  ward  to  the 
sternoclavicular  joint,  supplying  this  articulation,  and  the  Subclavius.  The  deltoid 
{humeral)  branch,  often  arising  with  the  acromial,  crosses  over  the  Pectoralis  minor 
and  passes  in  the  same  groove  as  the  cephalic  vein,  between  the  Pectoralis  major 
and  Deltoideus,  and  gives  branches  to  both  muscles. 

3.  The  lateral  thoracic  artery  (a.  thoracalis  lateralis;  long  thoracic  artery;  external 
mammary  artery)  follows  the  lower  border  of  the  Pectoralis  minor  to  the  side  of 
the  chest,  supplying  the  Serratus  anterior  and  the  Pectoralis,  and  sending  branches 
across  the  axilla  to  the  axillary  glands  and  Subscapularis;  it  anastomoses  with  the 
internal  mammary,  subscapular,  and  intercostal  arteries,  and  with  the  pectoral 
branch  of  the  thoracoacromial.  In  the  female  it  supplies  an  external  mammary 
branch  which  turns  round  the  free  edge  of  the  Pectoralis  major  and  supplies  the 
mamma. 

4.  The  subscapular  artery  (a.  subscapidaris)  the  largest  branch  of  the  axillary 
artery,  arises  at  the  lower  border  of  the  Subscapularis,  which  it  follows  to  the  in- 
ferior angle  of  the  scapula,  where 
it  anastomoses  with  the  lateral 
thoracic  and  intercostal  arteri^ 
and  with  the  descending  branch 
of  the  transverse  cervical,  and 
ends  in  the  neighboring  muscles. 
About  4  cm.  from  its  origin  it 
gives  off  a  branch,  the  scapular 
circumflex  artery. 

The  Scapular  Circumflex  Artery 
(a.  circumfiexa  scapula^;  dorsalis 
scajndce  artery)  is  generally  larger 
than  the  continuation  of  the  sub- 
scapular. It  curves  around  the 
axillary  border  of  the  scapula, 
traversing  the  space  between 
the  Subscapularis  above,  the 
Teres  major  below,  and  the  long 
head  of  the  Triceps  laterally 
(Fig.  524);  it  enters  the  infra- 
spinatous  fossa  under  cover  of 
the  Teres  minor,  and  anasto- 
moses with  the  transverse  scap- 
ular artery  and  the  descending  branch  of  the  transverse  cervical.  In  its  course 
it  gives  off  two  branches:  one  (infrascapular)  enters  the  subscapular  fossa  beneath 
the  Subscapularis,  which  it  supplies,  anastomosing  with  the  transverse  scapular 


Dese.  br.  of 
transverse  cervical 


Transverse  scapular 


Acromial  branch 
'  thoraco-acromial 


Fig.  524. — The  scapular  and  circumflex  arteries. 


11^ 


THE  BRACHIAL  ARTERY  ^^^  589 

artery  and  the  descending  branch  of  the  transverse  cervical ;  the  other  is  continued 
-Along  the  axillary  border  of  the  scapula,  between  the  Teres  major  and  minor, 
nd  at  the  dorsal  surface  of  the  inferior  angle  anastomoses  with  the  descending 
branch  of  the  transverse  cervical.  In  addition  to  these,  small  branches  are  dis- 
tributed to  the  back  part  of  the  Deltoideus  and  the  long  head  of  the  Triceps 
brachii,  anastomosing  with  an  ascending  branch  of  the  a.  profunda  brachii. 

5.  The  posterior  humeral  circumflex  artery  (a.  circumflexa  humeri  jjosterior;  pos- 
terior circumiiex  artery)  (Fig.  52-4)  arises  from  the  axillary  artery  at  the  lower  border 
of  the  Subscapularis,  and  runs  backward  with  the  axillary  nerve  through  the  quad- 
rangular space  bounded  by  the  Subscapularis  and  Teres  minor  above,  the  Teres 
major  below,  the  long  head  of  the  Triceps  brachii  medially,  and  the  surgical  neck 
of  the  humerus  laterally.  It  winds  around  the  neck  of  the  humerus  and  is  dis- 
tributed to  the  Deltoideus  and  shoulder-joint,  anastomosing  with  the  anterior 
humeral  circumflex  and  profunda  brachii. 

6.  The  anterior  humeral  circumflex  artery  (a.  circumflexa  humeri  anterior;  anterior 
circumflex  artery)  (Fig.  524),  considerably  smaller  than  the  posterior,  arises  nearly 
opposite  it,  from  the  lateral  side  of  the  axillary  artery.   It  runs  horizontally,  beneath 

he  Coracobrachialis  and  short  head  of  the  Biceps  brachii,  in  front  of  the  neck  of 
the  humerus.  On  reaching  the  intertubercular  sulcus,  it  gives  off  a  branch  which 
ascends  in  the  sulcus  to  supply  the  head  of  the  humerus  and  the  shoulder-joint. 
The  trunk  of  the  vessel  is  then  continued  onward  beneath  the  long  head  of  the 
Biceps  brachii  and  the  Deltoideus,  and  anastomoses  with  the  posterior  humeral 
circumflex  artery. 

Peculiarities. — The  branches  of  the  axillary  artery  vary  considerably  in  different  subjects. 
Occasionally  the  subscapular,  humeral  circumflex,  and  profunda  arteries  arise  from  a  common 
trunk,  and  when  this  occurs  the  branches  of  the  brachial  plexus  surroimd  this  trunk  instead  of 
the  main  vessel.  Sometimes  the  axillary  artery  divides  into  the  radial  and  ulnar  arteries,  and 
occasionally  it  gives  origin  to  the  volar  interosseous  artery  of  the  forearm. 

The  Brachial  Artery  (A.  Brachialis)  (Fig.  525). 

The  brachial  artery  commences  at  the  lower  margin  of  the  tendon  of  the  Teres 
major,  and,  passing  down  the  arm,  ends  about  1  cm.  below  the  bend  of  the  elbow, 
where  it  divides  into  the  radial  and  ulnar  arteries.  At  first  the  brachial  artery  lies 
medial  to  the  humerus;  but  as  it  runs  down  the  arm  it  gradually  gets  in  front  of 
the  bone,  and  at  the  bend  of  the  elbow  it  lies  midway  between  its  two  epicondyles. 

Relations. — The  artery  is  superficial  throughout  its  entire  extent,  being  covered,  in  front, 
by  the  integument  and  the  superficial  and  deep  fascise;  the  lacertus  fibrosus  (bicipital  fascia) 
hes  in  front  of  it  opposite  the  elbow  and  separates  it  from  the  vena  mediana  cubiti;  the  median 
nerve  crosses  from  its  lateral  to  its  medial  side  opposite  the  insertion  of  the  CoracobrachiaUs. 
Behind,  it  is  separated  from  the  long  head  of  the  Triceps  brachii  by  the  radial  nerve  and  a.  pro- 
funda brachii.  It  then  lies  upon  the  medial  head  of  the  Triceps  brachii,  next  upon  the  insertion 
of  the  CoracobrachiaHs,  and  lastly  on  the  Brachialis.  Laterally,  it  is  in  relation  above  with  the 
median  nerve  and  the  Coracobrachialis,  below  with  the  Biceps  brachii,  the  two  muscles  over- 
lapping the  artery  to  a  considerable  extent.  Medially,  its  upper  half  is  in  relation  with  the  medial 
antibrachial  cutaneous  and  ulnar  nerves,  its  lower  half  with  the  median  nerve.  The  basilic  vein 
lies  on  its  medial  side,  but  is  separated  from  it  in  the  lower  part  of  the  arm  by  the  deep  fascia. 
The  artery  is  accompanied  by  two  venae  comitantes,  which  lie  in  close  contact  with  it,  and  are 
connected  together  at  intervals  by  short  transverse  branches. 

The  Anticubital  Fossa. — At  the  bend  of  the  elbow  the  brachial  artery  sinks 
deeply  into  a  triangular  interval,  the  anticubital  fossa.  The  base  of  the  triangle 
is  directed  upward,  and  is  represented  by  a  line  connecting  the  two  epicondyles 
of  the  humerus;  the  sides  are  formed  by  the  medial  edge  of  the  Brachioradialis 
and  the  lateral  margin  of  the  Pronator  teres;  the  floor  is  formed  by  the  Brachialis 
and  Supinator.  This  space  contains  the  brachial  artery,  with  its  accompanying 
veins;  the  radial  and  ulnar  arteries;  the  median  and  radial  nerves;  and  the  tendon 
of  the  Biceps  brachii.    The  brachial  artery  occupies  the  middle  of  the  space,  and 


590 


ANGIOLOGY 


Med.  antihrach 
cutan.  nerve 

Badial  nerve 

A.  profunda 
brachii 


divides  opposite  the  neck  of  the  radius  into  the  radial  and  ulnar  arteries ;  it  is  covered, 
in  front,  by  the  integument,  the  superficial  fascia,  and  the  vena  mediana  cubiti, 
the  last  being  separated  from  the  artery  by  the  lacertus  fibrosus.  Behind  it  is 
the  Brachialis  which  separates  it  from  the  elbow-joint.    The  median  nerve  lien 

close  to  the  medial  side  of  th(; 
artery,  above,  but  is  separated 
from  it  below  by  the  ulnar  head  of 
the  Pronator  teres.  The  tendon  of 
the  Biceps  brachii  lies  to  the  lateral 
side  of  the  artery;  the  radial  nerve 
is  situated  upon  the  Supinator,  and 
concealed  by  the  Brachioradialis. 

Peculiarities  of  the  Brachial  Artery  as 
Regards  its  Course.— The  brachial  artery, 
accompanied  by  the  median  nerve,  may 
leave  the  medial  border  of  the  Biceps 
brachii,  and  descend  toward  the  medial 
epicondyle  of  the  humerus;  in  such  cases 
it  usually  passes  behind  the  supracondylar 
■process  of  the  humerus,  from  which  a 
fibrous  arch  is  in  most  cases  thrown 
over  the  artery;  it  then  runs  beneath  or 
through  the  substance  of  the  Pronator 
teres,  to  the  bend  of  the  elbow.  This 
variation  bears  considerable  analogy  with 
the  normal  condition  of  the  artery  in 
some  of  the  carnivora;  it  has  been  re- 
ferred to  in  the  description  of  the  hu- 
merus (p.  212). 

As  Regards  its  Division. — Occasionally, 
the  artery  is  divided  for  a  short  distance 
at  its  upper  part  into  two  trunks,  which 
are  vmited  below.  Frequently  the  arteiy 
divides  at  a  higher  level  than  usual,  and 
the  vessels  concerned  in  this  high  division 
are  three,  viz.,  radial,  ulnar,  and  inter- 
osseous. Most  frequently  the  radial  is 
given  off  high  up,  the  other  limb  of  the 
bifurcation  consisting  of  the  ulnar  and 
interosseous;  in  some  instances  the  ulnar 
arises  above  the  ordinary  level,  and  the 
radial  and  interosseous  form  the  other 
limb  of  the  division;  occasionally  the  in- 
terosseous arises  high  up. 

Sometimes,  long  slender  vessels,   va^a 

aherrantia,    connect   the  brachial  or   the 

axillary  artery   with  one  of  the  arteries 

of  the  forearm,  or  branches  from  them. 

These  vessels  usually  join  the  radial. 

Varieties  in  Muscular  Relations. — The  brachial  artery  is  occasionally  concealed,  in  some  part 

of  its  course,  by  muscular  or  tendinous  slips  derived  from  the  Coracobrachialis,  Biceps  brachii, 

Brachialis,  or  Pronator  teres. 

Collateral  Circulation. — After  the  appUcation  of  a  ligature  to  the  brachial  artery  in  the  upper 
third  of  the  arm,  the  circulation  is  carried  on  by  branches  from  the  humeral  circumflex  and  sub- 
scapular arteries  anastomosing  with  ascending  branches  from  the  profunda  brachii.  If  the 
artery  be  tied  helow  the  origin  of  the  profunda  brachii  and  superior  ulnar  collateral,  the  circula- 
tion is  maintained  by  the  branches  of  these  two  arteries  anastomosing  with  the  inferior  ulnar 
collateral,  the  radial  and  ulnar  recurrents,  and  the  dorsal  interosseous. 

Branches. — The  branches  of  the  brachial  artery  are: 

Profunda  Brachii.  Superior  Ulnar  Collateral. 

Nutrient.  Inferior  Ulnar  Collateral. 

Muscular. 


Sup.  idnar  collateral 
artery 


Inf.  ulnar  collateral 
artery 


Fig.  525. — The  brachial  artery 


THE  BRACHIAL  ARTERY 


591 


1.  The  arteria  profunda  brachii  {superior  profunda  artery)  is  a  large  vessel  which 
'arises  from  the  medial  and  back  part  of  the  brachial,  just  below  the  lower  border 

of  the  Teres  major.  It  follows  closeh^  the  radial  nerve,  running  at  first  backAvard 
between  the  medial  and  lateral  heads  of  the  Triceps  brachii,  then  along  the  groove 
for  the  radial  nerve,  where  it  is  covered  by  the  lateral  head  of  the  Triceps  brachii, 
to  the  lateral  side  of  the  arm;  there  it  pierces  the  lateral  intermuscular  septum, 
and,  descending  between  the  Brachioradialis  and  the  Brachialis  to  the  front  of 
the  lateral  epicondyle  of  the  humerus,  ends  by  anastomosing  with  the  radial  recur- 
rent artery.  It  gives  branches  to  the  Deltoideus  and  to  the  muscles  between  which 
it  lies;  it  supplies  an  occasional  nutrient  artery  which  enters  the  humerus  behind  the 
deltoid  tuberosity.  A  branch  ascends  between  the  long  and  lateral  heads  of  the 
Triceps  brachii  to  anastomose  with  the  posterior  humeral  circumflex  artery;  a 
middle  collateral  branch  descends  in  the  middle  head  of  the  Triceps  brachii  and 
assists  in  forming  the  anastomosis  above  the  olecranon;  and,  lastly,  a  radial  collateral 
branch  runs  down  behind  the  lateral  intermuscular  septum  to  the  back  of  the  lateral 
epicondyle  of  the  humerus,  where  it  anastomoses  with  the  interosseous  recurrent 
and  the  inferior  ulnar  collateral  arteries. 

2.  The  nutrient  artery  {a.  nutricia  humeri)  of  the  body  of  the  humerus  arises 
about  the  middle  of  the  arm  and  enters  the  nutrient  canal  near  the  insertion  of  the 
Coracobrachialis. 

A.  profunda  brachii 

Sup,  ulnar  collateral 
Brachial 


Anterior  branch  of  profunda 


^Radial  collateral  branch 
of  profunda 


Bodied  recurrent 


Interosseous  recurrent 
Radial 


Inf.  ulnar  collateral 


Anterior  ulnar  recurrent 


Posterior  ulnar  recurrent 

Interosseous 
Dorsal  interosseous 

Ulnar 

Volar  interosseous 


Fig.  526. — Diagram  of  the  anastomosis  around  the  elbow-joint. 


3.  The  superior  ulnar  collateral  artery  (a.  collateralis  ulnar  is  superior;  inferior 
profunda  artery),  of  small  size,  arises  from  the  brachial  a  little  below  the  middle 
of  the  arm;  it  frequently  springs  from  the  upper  part  of  the  a.  profunda  brachii. 
It  pierces  the  medial  intermuscular  septum,  and  descends  on  the  surface  of  the  medial 
head  of  the  Triceps  brachii  to  the  space  between  the  medial  epicondyle  and 


592  ANGIOLOGY 

olecranon,  accompanied  by  the  ulnar  nerve,  and  ends  under  the  Flexor  carpi  ulnaris 
by  anastomosing  with  the  posterior  ulnar  recurrent,  and  inferior  ulnar  collateral. 
It  sometimes  sends  a  branch  in  front  of  the  medial  epicondyle,  to  anastomose 
with  the  anterior  ulnar  recurrent. 

4.  The  inferior  ulnar  collateral  artery  (a.  collateralis  ulnaris  inferior;  anastomotica 
magna  artery)  arises  about  5  cm.  above  the  elbow.  It  passes  medialward  upon  the 
Brachialis,  and  piercing  the  medial  intermuscular  septum,  winds  around  the  back  of 
the  humerus  between  the  Triceps  brachii  and  the  bone,  forming,  by  its  junction  with 
the  profunda  brachii,  an  arch  above  the  olecranon  fossa.  As  the  vessel  lies  on  the 
Brachialis,  it  gives  off  branches  which  ascend  to  join  the  superior  ulnar  collateral: 
others  descend  in  front  of  the  medial  epicondyle,  to  anastomose  with  the  anterior 
ulnar  recurrent.  Behind  the  medial  epicondyle  a  branch  anastomoses  with  the 
superior  ulnar  collateral  and  posterior  ulnar  recurrent  arteries. 

5.  The  muscular  branches  (rami  musculares)  three  or  four  in  number,  are  dis- 
tributed to  the  Coracobrachialis,  Biceps  brachii,  and  Brachialis. 

The  Anastomosis  Around  the  Elbow-joint  (Fig.  526).— The  vessels  engaged  in 
this  anastomosis  may  be  conveniently  divided  into  those  situated  in  front  of  and 
those  behind  the  medial  and  lateral  epicondyles  of  the  humerus.  The  branches 
anastomosing  iji  front  of  the  medial  epicondyle  are :  the  anterior  branch  of  the 
inferior  ulnar  collateral,  the  anterior  ulnar  recurrent,  and  the  anterior  branch  of 
the  superior  ulnar  collateral.  Those  behind  the  medial  epicondyle  are:  the  inferior 
ulnar  collateral,  the  posterior  ulnar  recurrent,  and  the  posterior  branch  of  the  supe- 
rior ulnar  collateral.  The  branches  anastomosing  in  front  of  the  lateral  epicondyle 
are:  the  radial  recurrent  and  the  terminal  part  of  the  profunda  brachii.  Those 
behind  the  lateral  epicondyle  (perhaps  more  properly  described  as  being  situated 
between  the  lateral  epicondyle  and  the  olecranon)  are:  the  inferior  ulnar  collateral, 
the  interosseous  recurrent,  and  the  radial  collateral  branch  of  the  profunda  brachii. 
There  is  also  an  arch  of  anastomosis  above  the  olecranon,  formed  by  the  interosseous 
recurrent  joining  with  the  inferior  ulnar  collateral  and  posterior  ulnar  recurrent 
(Fig.  529). 

The  Radial  Artery  (A.  Radialis)  (Fig.  527). 

The  radial  artery  appears,  from  its  direction,  to  be  the  continuation  of  the  brachial, 
but  it  is  smaller  in  caliber  than  the  ulnar.  It  commences  at  the  bifurcation  of  the 
brachial,  just  below  the  bend  of  the  elbow,  and  passes  along  the  radial  side  of  the 
forearm  to  the  wrist.  It  then  winds  backward,  around  the  lateral  side  of  the  carpus, 
beneath  the  tendons  of  the  Abductor  pollicis  longus  and  Extensores  pollicis  longus 
and  brevis  to  the  upper  end  of  the  space  between  the  metacarpal  bones  of  the  thumb 
and  index  finger.  Finally  it  passes  forward  between  the  two  heads  of  the  first 
Interosseous  dorsalis,  into  the  palm  of  the  hand,  where  it  crosses  the  metacarpal 
bones  and  at  the  ulnar  side  of  the  hand  unites  with  the  deep  volar  branch  of  the 
ulnar  artery  to  form  the  deep  volar  arch.  The  radial  artery  therefore  consists 
of  three  portions,  one  in  the  forearm,  a  second  at  the  back  of  the  wrist,  and  a  third 
in  the  hand. 

Relations. — (a)  In  the  forearm  the  artery  extends  from  the  neck  of  the  radius  to  the  forepart 
of  the  styloid  process,  being  placed  to  the  medial  side  of  the  body  of  the  bone  above,  and  in  front 
of  it  below.  Its  upper  part  is  overlapped  by  the  fleshy  belly  of  the  Brachioradiahs;  the  rest  of 
the  artery  is  superficial,  being  covered  by  the  integument  and  the  superficial  and  deep  fasciie. 
In  its  course  downward,  it  lies  upon  the  tendon  of  the  Biceps  brachii,  the  Supinator,  the  Pronator 
teres,  the  radial  origin  of  the  Flexor  digitorum  subUmis,  the  Flexor  pollicis  longus,  the  Pronator 
quadratus,  and  the  lower  end  of  the  radius.  In  the  upper  third  of  its  course  it  hes  between  the 
Brachioradiahs  and  the  Pronator  teres;  in  the  lower  two-thirds,  between  the  tendons  of  the 
Brachioradiahs  and  Flexor  carpi  radiahs.  The  superficial  branch  of  the  radial  nerve  is, close  to 
the  lateral  side  of  the  artery  in  the  middle  third  of  its  course;  and  some  filaments  of  the  lateral 
antibrachial  cutaneous  nerve  run  along  the  lower  part  of  the  artery  as  it  winds  around  the  wrist. 
The  vessel  is  accompanied  by  a  pair  of  venai  conaitantes  throughout  its  whole  course. 


THE  RADIAL  ARTERY 


593 


(6)  At  the  wrist  the  artery  reaches  the  back  of  the  carpus  by  passing  between  the  radial  collateral 
ligament  of  the  wrist  and  the  tendons  of  the  Abductor  pollicis  longus  and  Extensor  polUcis  brevis. 


Radial 
recurrent 


Eadiai 
recurrent 


Dorsal 
interosseous 


Mvscvlar 


Deep  vdar   yolar  radial  carpal 

.  ^r^'"^«  Super Acial  volar 

of  ulnar 


Inferior  ulnar 
collateral 


Anterior  vlrmr 

recurrent 
Posterior  ulnar 

recurrent 


MuscuUlT 


Volar  ulnar  carpal 

Deep  volar  branch 
of  ulnar 


Fig.  527. — The  radial  and  ulnar  arteries. 


Fia.  528. — Ulnar  and  radial  arteries.     Deep  view. 


It  then  descends  on  the  navicular  and  greater  multangular  bones,  and  before  disappearing  be- 
tween the  heads  of  the  first  Interosseus  dorsahs  is  crossed  by  the  tendon  of  the  Extensor  pollicis 

38 


594 


ANGIOLOGY 


I 


longus.  In  the  interval  between  the  two  Extensores  pollicis  it  is  crossed  by  the  digital  rami  of 
the  superficial  branch  of  the  radial  nerve  which  go  to  the  thumb  and  index  finger. 

(c)  In  the  hand,  it  passes  from  the  upper  end  of  the  first  interosseous  space,  between  the  heads 
of  the  first  Interosseus  dorsalis,  transversely  across  the  palm  between  the  Adductor  pollicis 
obliquus  and  Adductor  pollicis  transversus,  but  sometimes  piercing  the  latter  muscle,  to  the 
base  of  the  metacarpal  bone  of  the  httle  finger,  where  it  anastomoses  with  the  deep  volar  branch 
from  the  ulnar  artery,  completing  the  deep  volar  arch  (Fig.  528). 

Peculiarities. — The  origin  of  the  radial  artery  is,  in  nearly  one  case  in  eight,  higher  than  usual; 
more  often  it  arises  from  the  axillary  or  upper  part  of  the  brachial  than  from  the  lower  part  of 
the  latter  vessel.  In  the  forearm  it  deviates  less  frequently  from  its  normal  position  than  the 
ulnar.  It  has  been  found  lying  on  the  deep  fascia  instead  of  beneath  it.  It  has  also  been  observed 
on  the  surface  of  the  Brachioradialis,  instead  of  under  its  medial  border;  and  in  turning  around 
the  wrist,  it  has  been  seen  lying  on,  instead  of  beneath,  the  Extensor  tendons  of  the  thumb. 

Branches. — The  branches  of  the  radial  artery  may  be  divided  into  three  groups, 
corresponding  with  the  three  regions  in  which  the  vessel  is  situated. 


In  the  Forearm. 
Radial  Recurrent. 
Muscular. 
Volar  Carpal. 
Superficial  Volar. 


At  the  J] Wist. 
Dorsal  Carpal. 
First  Dorsal  Metacarpal. 


In  the  Hand. 
Princeps  Pollicis. 
Volaris  Indicis  Radialis. 
Volar  Metacarpal. 
Perforating. 
Recurrent. 


The  radial  recurrent  artery  (a.  recurrens  radialis)  arises  immediately  below  the 
elbow.  It  ascends  between  the  branches  of  the  radial  nerve,  lying  on  the  Supinator 
and  then  between  the  Brachioradialis  and  Brachialis,  supplying  these  muscles 
and  the  elbow-joint,  and  anastomosing  with  the  terminal  part  of  the  profunda 
brachii. 

The  muscular  branches  (rami  mnsculares)  are  distributed  to  the  muscles  on  the 
radial  side  of  the  forearm. 

The  volar  carpal  branch  {ramus  carpeus  volaris;  anterior  radial  carpal  artery) 
is  a  small  vessel  which  arises  near  the  lower  border  of  the  Pronator  quadratus, 
and,  running  across  the  front  of  the  carpus,  anastomoses  with  the  volar  carpal 
branch  of  the  ulnar  artery.  This  anastomosis  is  joined  by  a  branch  from  the  volar 
interosseous  above,  and  by  recurrent  branches  from  the  deep  volar  arch  below, 
thus  forming  a  volar  carpal  net-work  which  supplies  the  articulations  of  the  wrist 
and  carpus. 

The  superficial  volar  branch  {ramus  volaris  superficialis ;  superficialis  voice  artery) 
arises  from  the  radial  artery,  just  where  this  vessel  is  about  to  wind  around  the 
lateral  side  of  the  wrist.  Running  forward,  it  passes  through,  occasionally  over, 
the  muscles  of  the  ball  of  the  thumb,  which  it  supplies,  and  sometimes  anastomoses 
with  the  terminal  portion  of  the  ulnar  artery,  completing  the  superficial  volar  arch. 
This  vessel  varies  considerably  in  size:  usually  it  is  very  small,  and  ends  in  the 
muscles  of  the  thumb ;  sometimes  it  is  as  large  as  the  continuation  of  the  radial 

The  dorsal  carpal  branch  {ramus  carpeus  dorsalis;  posterior  radial  carpal  artery) 
is  a  small  vessel  which  arises  beneath  the  Extensor  tendons  of  the  thumb ;  crossing 
the  carpus  transversely  toward  the  medial  border  of  the  hand,  it  anastomoses  with 
the  dorsal  carpal  branch  of  the  ulnar  and  with  the  volar  and  dorsal  interosseous 
arteries  to  form  a  dorsal  carpal  network.  From  this  network  are  given  off  three 
slender  dorsal  metacarpal  arteries,  which  run  downward  on  the  second,  third,  and 
fourth  Interossei  dorsales  and  bifurcate  into  the  dorsal  digital  branches  for  the 
supply  of  the  adjacent  sides  of  the  middle,  ring,  and  little  fingers  respectively, 
communicating  with  the  proper  volar  digital  branches  of  the  superficial  volar 
arch.  Near  their  origins  they  anastomose  with  the  deep  volar  arch  by  the  superior 
perforating  arteries,  and  near  their  points  of  bifurcation  with  the  common  volar 
digital  vessels  of  the  superficial  volar  arch  by  the  inferior  perforating  arteries. 


* 


THE  ULNAR  ARTERY  ^^^^^T^'        595 

The  first  dorsal  metacarpal  arises  just  before  the  radial  artery  passes  between 
the  two  heads  of  the  first  Interosseous  dorsalis  and  divides  almost  immediately 
into  two  branches  which  supply  the  adjacent  sides  of  the  thumb  and  index  finger ; 
'■  the  radial  side  of  the  thumb  receives  a  branch  directly  from  the  radial  artery. 

The  arteria  princeps  pollicis  arises  from  the  radial  just  as  it  turns  medialward 
to  the  deep  part  of  the  hand ;  it  descends  between  the  first  Interosseous  dorsalis  and 
Adductor  pollicis  obliquus,  along  the  ulnar  side  of  the  metacarpal  bone  of  the 
thumb  to  the  base  of  the  first  phalanx,  where  it  lies  beneath  the  tendon  of  the 
Flexor  pollicis  longus  and  divides  into  two  branches.  These  make  their  appear- 
ance between  the  medial  and  lateral  insertions  of  the  Adductor  pollicis  obliquus, 
I  and  run  along  the  sides  of  the  thumb,  forming  on  the  volar  surface  of  the  last 
'  phalanx  an  arch,  from  which  branches  are  distributed  to  the  integument  and 
subcutaneous  tissue  of  the  thumb. 

The  arteria  volaris  indicis  radialis  (radialis  indicis  artery)  arises  close  to  the  pre- 
ceding, descends  between  the  first  Interosseus  dorsalis  and  Adductor  pollicis  trans- 
versus,  and  runs  along  the  radial  side  of  the  index  finger  to  its  extremity,  where  it 
anastomoses  with  the  proper  digital  artery,  supplying  the  ulnar  side  of  the  finger.  At 
the  lower  border  of  the  Adductor  pollicis  transversus  this  vessel  anastomoses  with 
the  princeps  pollicis,  and  gives  a  communicating  branch  to  the  superficial  volar  arch. 
The  a.  princeps  pollicis  and  a.  volaris  indicis  radialis  may  spring  from  a  common 
trunk  termed  the  first  volar  metacarpal  artery. 

The  deep  volar  arch  {arcus  volaris  'profundus;  deep  palmar  arch)  (Fig.  528)  is 
formed  by  the  anastomosis  of  the  terminal  part  of  the  radial  artery  with  the  deep 
volar  branch  of  the  ulnar.  It  lies  upon  the  carpal  extremities  of  the  metacarpal 
bones  and  on  the  Interossei,  being  covered  by  the  Adductor  pollicis  obliquus,  the 
Flexor  tendons  of  the  fingers,  and  the  Lumbricales.  Alongside  of  it,  but  running 
in  the  opposite  direction — that  is  to  say,  toward  the  radial  side  of  the  hand— is 

I  the  deep  branch  of  the  ulnar  nerve. 

■  ■      The  volar  metacarpal  arteries   {aa.    metacarpeae    volares;   palmar    interosseous 

■  I  arteries),  three  or  four  in  number,  arise  from  the  convexity  of  the  deep  volar  arch; 

II  they  run  distally  upon  the  Interossei,  and  anastomose  at  the  clefts  of  the  fingers 

■  I  with  the  common  digital  branches  of  the  superficial  volar  arch. 

■  B  The  perforating  branches  (rami  perforantes) ,  three  in  number,  pass  backward 
I  p  from  the  deep  volar  arch,  through  the  second,  third,  and  fourth  interosseous  spaces 
P  and  between  the  heads  of  the  corresponding  Interossei  dorsalis,  to  anastomose 
,         with  the  dorsal  metacarpal  arteries. 

■  K  The  recurrent  branches  arise  from  the  concavity  of  the  deep  volar  arch.  They 
P"  ascend  in  front  of  the  wrist,  supply  the  intercarpal  articulations,  and  end  in  the 

volar  carpal  network. 

The  Ulnar  Artery  (A.  Ulnaris)  (Fig.  528). 

The  ulnar  artery,  the  larger  of  the  two  terminal  branches  of  the  brachial,  begins 
a  little  below  the  bend  of  the  elbow,  and,  passing  obliquely  downward,  reaches 
the  ulnar  side  of  the  forearm  at  a  point  about  midway  between  the  elbow  and  the 
wrist.  It  then  runs  along  the  ulnar  border  to  the  wrist,  crosses  the  transverse 
carpal  ligament  on  the  radial  side  of  the  pisiform  bone,  and  immediately  beyond 
this  bone  divides  into  two  branches,  which  enter  into  the  formation  of  the  superficial 
and  deep  volar  arches. 

Relations. — (a)  hi  the  forearm. — In  its  upper  half,  it  is  deeply  seated,  being  covered  by  the 
Pronator  teres,  Flexor  carpi  radialis,  Palmaris  longus,  and  Flexor  digitorum  sublimis;  it  lies 
upon  the  Brachiahs  and  Flexor  digitorum  profundus.  The  median  nerve  is  in  relation  with  the 
medial  side  of  the  artery  for  about  2.5  cm.  and  then  crosses  the  vessel,  being  separated  from  it 
by  the  ulnar  head  of  the  Pronator  teres.  In  the  lower  half  of  the  forearm  it  lies  upon  the  Flexor 
digitorum  profundus,  being  covered  by  the  integument  and  the  superficial  and  deep  fasciae, 


k> 


II 


596 


ANGIOLOGY 


In  the  Forearm   ^ 


and  placed  between  the  Flexor  carpi  ulnaris  and  Flexor  digitorum  sublimis.  It  is  accompanied 
by  two  venae  comitantes,  and  is  overlapped  in  its  middle  third  by  the  Flexor  carpi  uhiaris;  tha 
ulnar  nerve  hes  on  the  medial  side  of  the  lower  two-thirds  of  the  artery,  and  the  palmar  cutaneous 
branch  of  the  nerve  descends  on  the  lower  part  of  the  vessel  to  the  palm  of  the  hand. 

(b)  At  the  wrist  (Fig.  527)  the  ulnar  artery  is  covered  by  the  integument  and  the  volar  carpal 
hgament,  and  hes  upon  the  transverse  carpal  ligament.  On  its  medial  side  is  the  pisiform  bone, 
and,  somewhat  behind  the  artery,  the  ulnar  nerve. 

Peculiarities. — The  ulnar  artery  varies  in  its  origin  in  the  proportion  of  about  one  in  thirteen 
cases;  it  may  arise  about  5  to  7  cm.  below  the  elbow,  but  more  frequently  higher,  the  brachial 
being  more  often  the  source  of  origin  than  the  axillary.  Variations  in  the  position  of  this  vessel 
are  more  common  than  in  the  radial.  When  its  origin  is  normal,  the  course  of  the  vessel  is  rarely 
changed.  When  it  arises  high  up,  it  is  almost  invariably  superficial  to  the  Flexor  muscles  in  the 
forearm,  lying  commonly  beneath  the  fascia,  more  rarely  between  the  fascia  and  integument. 
In  a  few  cases,  its  position  was  subcutaneous  in  the  upper  part  of  the  forearm,  and  subaponeurotic 
in  the  lower  part. 

Branches. — The  branches  of  the  uhiar  artery  may  be  arranged  in  the  following 
groups : 

Anterior  Recurrent.  ^^  ^^^  Wrist    i  ^^^^^  Carpal. 

Posterior  Recurrent.  \  Dorsal  Carpal. 

Common  Interosseous,     i^i  the  Hand    f^^^^J^^^f:,  ,      ,     , 
Muscular.  \  Superficial  Volar  Arch. 

The  anterior  ulnar  recurrent  artery  (a.  recurrentes  ulnaris  anterior)  arises  imme- 
diately below  the  elbow-joint,  runs  upward  between  the  Brachialis  and  Pronator 
teres,  supplies  twigs  to  those  muscles,  and,  in  front  of  the  medial  epicondyle,  anasto- 
moses with  the  superior  and  inferior  ulnar  collateral  arteries. 

The  posterior  ulnar  recurrent  artery  (a.  recurrentes  ulnaris  posterior)  is  much 
larger,  and  arises  somewhat  lower  than  the  preceding.  It  passes  backward  and 
medialward  on  the  Flexor  digitorum  profundus,  behind  the  Flexor  digitorum  sub- 
limis, and  ascends  behind  the  medial  epicondyle  of  the  humerus.  In  the  interval 
between  this  process  and  the  olecranon,  it  lies  beneath  the  Flexor  carpi  ulnaris, 
and  ascending  between  the  heads  of  that  muscle,  in  relation  with  the  ulnar  nerve, 
it  supplies  the  neighboring  muscles  and  the  elbow-joint,  and  anastomoses  with 
the  superior  and  inferior  ulnar  collateral  and  the  interosseous  recurrent  arteries 
(Fig.  529). 

The  common  interosseous  artery  (a.  interossea  communis)  (Fig.  528),  about  1  cm. 
in  length,  arises  immediately  below  the  tuberosity  of  the  radius,  and,  passing 
backward  to  the  upper  border  of  the  interosseous  membrane,  divides  into  two 
branches,  the  volar  and  dorsal  interosseous  arteries. 

The  Volar  Interosseous  Artery  (a.  interossea  volaris;  anterior  interosseous  artery) 
(Fig.  528),  passes  down  the  forearm  on  the  volar  surface  of  the  interosseous  mem- 
brane. It  is  accompanied  by  the  volar  interosseous  branch  of  the  median  nerve, 
and  overlapped  by  the  contiguous  margins  of  the  Flexor  digitorum  profundus  and 
Flexor  pollicis  longus,  giving  off  in  this  situation  muscular  branches,  and  the  nutrient 
arteries  of  the  radius  and  ulna.  At  the  upper  border  of  the  Pronator  quadratus  it 
pierces  the  interosseous  membrane  and  reaches  the  back  of  the  forearm,  where  it 
anastomoses  with  the  dorsal  interosseous  artery  (Fig.  529).  It  then  descends,  in 
company  with  the  terminal  portion  of  the  dorsal  interosseous  nerve,  to  the  back 
of  the  wrist  to  join  the  dorsal  carpal  net-work.  The  volar  interosseous  artery  gives 
oflF  a  slender  branch,  the  arteria  mediana,  which  accompanies  the  median  nerve,  and 
gives  offsets  to  its  substance;  this  artery  is  sometimes  much  enlarged,  and  runs 
with  the  nerve  into  the  palm  of  the  hand.  Before  it  pierces  the  interosseous 
membrane  the  volar  interosseous  sends  a  branch  downward  behind  the  Pronator 
quadratus  to  join  the  volar  carpal  network. 

The  Dorsal  Interosseous  Artery  (a.  interossea  dorsalis;  posterior  interosseous  artery) 
(Fig.  529)  passes  backward  between  the  oblique  cord  and  the  upper  border  of  the 
interosseous  membrane .   It  appears  between  the  contiguous  borders  of  the  Supinator 


I 


THE  ULNAR  ARTERY 


597 


and  the  Abductor  pollicis  longus,  and  runs  down  the  back  of  the  forearm  between 
the  superficial  and  deep  layers  of  muscles,  to  both  of  which  it  distributes  branches. 
Where  it  lies  upon  the  Abductor  pollicis  longus  and  the  Extensor  pollicis  brevis, 


A.  profunda  brachii 


Inf.  uhmr  collateral 


Posterior  ulnar  recurrent  — ' 


Dorsal  interosseous 


Dorsal  ulnar  carpal 


Termination  of  volar 
interosseoits 


Dorsal  radial  carpal 


Fig.  529. — Arteries  of  the  back  of  the  forearm  and  hand. 


it  is  accompanied  by  the  dorsal  interosseous  nerve.  At  the  lower  part  of  the  fore- 
arm it  anastomoses  with  the  termination  of  the  volar  interosseous  artery,  and  with 
the  dorsal  carpal  network.  It  gives  off,  near  its  origin,  the  interosseous  recurrent 
artery,  which  ascends  to  the  interval  between  the  lateral  epicondyle  and  olecranon, 


II 


598  -^^^^^^m       ANGIOLOGY 


on  or  through  the  fibers  of  the  Supinator,  but  beneath  the  Anconseus,  and  anasto 
moses  with  the  radial  collateral  branch  of  the  profunda  brachii,  the  posterior 
ulnar  recurrent  and  the  inferior  ulnar  collateral. 

The  muscular  branches  {rami  musculares)  are  distributed  to  the  muscles  along 
the  ulnar  side  of  the  forearm. 

The  volar  carpal  branch  {ramus  carpeus  volares;  anterior  ulnar  carpal  artery)  is  a 
small  vessel  which  crosses  the  front  of  the  carpus  beneath  the  tendons  of  the  Flexor 
digitorum  profundus,  and  anastomoses  with  the  corresponding  branch  of  the  radial 
artery. 

The  dorsal  carpal  branch  {ramus  carpeus  dorsalis;  posterior  ulnar  carpal  artery) 
arises  immediately  above  the  pisiform  bone,  and  winds  backward  beneath  the 
tendon  of  the  Flexor  carpi  ulnaris;  it  passes  across  the  dorsal  surface  of  the  carpus 
beneath  the  Extensor  tendons,  to  anastomose  with  a  corresponding  branch  of  the 
radial  artery.  Immediately  after  its  origin,  it  gives  off  a  small  branch,  which  runs 
along  the  ulnar  side  of  the  fifth  metacarpal  bone,  and  supplies  the  ulnar  side  of  the 
dorsal  surface  of  the  little  finger. 

The  deep  volar  branch  {ramus  volaris  profundus;  profunda  branch)  (Fig.  528) 
passes  between  the  Abductor  digiti  quinti  and  Flexor  digiti  quinti  brevis  and 
through  the  origin  of  the  Opponens  digiti  quinti;  it  anastomoses  with  the  radial 
artery,  and  completes  the  deep  volar  arch. 

The  superficial  volar  arch  {arcus  volaris  superficialis;  superficial  palmar  arch) 
(Fig.  527)  is  formed  by  the  ulnar  artery,  and  is  usually  completed  by  a  branch 
from  the  a.  volaris  indicis  radialis,  but  sometimes  by  the  superficial  volar  or  by 
a  branch  from  the  a.  princeps  pollicis  of  the  radial  artery.  The  arch  passes  across 
the  palm,  describing  a  curve,  with  its  convexity  downward. 

Relations. — The  superficial  volar  arch  is  covered  by  the  skin,  the  Palmaris  brevis,  and  the 
palmar  aponeurosis.  It  lies  upon  the  transverse  carpal  ligament,  the  Flexor  digiti  quinti  brevis 
and  Opponens  digiti  quinti,  the  tendons  of  the  Flexor  digitorum  sublimis,  the  Lumbricales,  and 
the  divisions  of  the  median  and  ulnar  nerves. 

Three  Common  Volar  Digital  Arteries  {aa.  digitales  volares  communes;  palmar  digital 
arteries)  (Fig.  527)  arise  from  the  convexity  of  the  arch  and  proceed  downward 
on  the  second,  third,  and  fourth  Lumbricales.  Each  receives  the  corresponding 
volar  metacarpal  artery  and  then  divides  into  a  pair  of  proper  volar  digital  arteries 
{aa.  digitales  volares  propriae;  collateral  digital  arteries)  which  run  along  the  con- 
tiguous sides  of  the  index,  middle,  ring,  and  little  fingers,  behind  the  corresponding 
digital  nerves;  they  anastomose  freely  in  the  subcutaneous  tissue  of  the  finger  tips 
and  by  smaller  branches  near  the  interphalangeal  joints.  Each  gives  off  a  couple 
of  dorsal  branches  which  anastomose  with  the  dorsal  digital  arteries,  and  supply 
the  soft  parts  on  the  back  of  the  second  and  third  phalanges,  including  the  matrix 
of  the  finger-nail.  The  proper  volar  digital  artery  for  medial  side  of  the  little 
finger  springs  from  the  ulnar  artery  under  cover  of  the  Palmaris  brevis. 

THE   ARTERIES   OF   THE    TRUNK. 

THE   DESCENDING    AORTA. 

The  descending  aorta  is  divided  into  two  portions,  the  thoracic  and  abdominal, 
in  correspondence  with  the  two  great  cavities  of  the  trunk  in  which  it  is  situated 

The  Thoracic  Aorta  (Aorta  Thoracahs)  (Fig.  530). 

The  thoracic  aorta  is  contained  in  the  posterior  mediastinal  cavity.  It  begins 
at  the  lower  border  of  the  fourth  thoracic  vertebra  where  it  is  continuous  with 
the  aortic  arch,  and  ends  in  front  of  the  lower  border  of  the  twelfth  at  the  aortic 


I 


THE  THORACIC  AORTA 


599 


hiatus  in  the  diaphragm.  At  its  commencement,  it  is  situated  on  the  left  of  the 
vertebral  column;  it  approaches  the  median  line  as  it  descends;  and,  at  its  termina- 
tion, lies  directly  in  front  of  the  column.  The  vessel  describes  a  curve  which  is 
concave  forward,  and  as  the  branches  given  off  from  it  are  small,  its  diminution 
in  size  is  inconsiderable. 


Highest  intercostal  artery 


Highest  intercostal  vein 


Rami  communicantes 
Lig.  arteriosum 


Fig.  530. — The  thoracic  aorta,  viewed  from  the  left  side. 

Relations. — It  is  in  relation,  anteriorly,  from  above  downward,  with  the  root  of  the  left  lung, 
the  pericardium,  the  esophagus,  and  the  diaphragm;  posteriorly,  with  the  vertebral  column 
and  the  hemiazygos  veins;  on  the  right  side,  with  the  azygos  vein  and  thoracic  duct;  on  the  lejt 
side,  with  the  left  pleura  and  lung.  The  esophagus,  with  its  accompanying  plexus  of  nerves, 
lies  on  the  right  side  of  the  aorta  above ;  but  at  the  lower  part  of  the  thorax  it  is  placed  in  front 
of  the  aorta,  and,  close  to  the  diaphragm,  is  situated  on  its  left  side. 

Peculiarities. — The  aorta  is  occasionally  found  to  be  obliterated  at  the  jimction  of  the  arch 
with  the  thoracic  aorta,  just  below  the  ductus  arteriosus.  Whether  this  is  the  result  of  disease, 
or  of  congenital  malformation,  is  immaterial  to  our  present  purpose;  it  affords  an  interesting 
opportunity  of  observing  the  resources  of  the  collateral  circulation.    The  course  of  the  anastomos- 


l_ 


600 


ANGIOLOGY 


ing  vessels,  by  which  the  blood  is  brought  from  the  upper  to  the  lower  part  of  the  artery,  will  be 
found  well  described  in  an  account  of  two  cases  in  the  Pathological  Transactions,  vols,  viii  and  x. 
In  the  former,  Sydney  Jones  thus  sums  up  the  detailed  description  of  the  anastomosing  vessels: 
The  principal  communications  by  which  the  circulation  was  carried  on  were:  (1)  The  internal 
mammary,  anastomosing  with  the  intercostal  arteries,  with  the  inferior  phrenic  of  the  abdominal 
aorta  by  means  of  the  musculophrenic  and  pericardiacophrenic,  and  largely  with  the  inferior 
epigastric.  (2)  The  costocervical  trunk,  anastomosing  anteriorly  by  means  of  a  large  branch 
with  the  first  aortic  intercostal,  and  posteriorly  with  the  posterior  branch  of  the  same  artery. 
(3)  The  inferior  thyroid,  by  means  of  a  branch  about  the  size  of  an  ordinary  radial,  forming  a 
communication  with  the  first  aortic  intercostal.  (4)  The  transverse  cervical,  by  means  of  very 
large  communications  with  the  posterior  branches  of  the  intercostals.  (5)  The  branches  (of 
the  subclavian  and  axillary)  going  to  the  side  of  the  chest  were  large,  and  anastomosed  freely 
with  the  lateral  branches  of  the  intercostals.  In  the  second  case  Wood  describes  the  anastomoses 
in  a  somewhat  similar  manner,  adding  the  remark  that  "the  blood  which  was  brought  into  the 
aorta  through  the  anastomosis  of  the  intercostal  arteries  appeared  to  be  expended  principally 
in  supplying  the  abdomen  and  pelvis;  while  the  supply  to  the  lower  extremities  had  passed  through 
the  internal  mammary  and  epigastrics." 

In  a  few  cases  an  apparently  double  descending  thoracic  aorta  has  been  found,  the  two  vessels 
lying  side  by  side,  and  eventually  fusing  to  form  a  single  tube  in  the  lower  part  of  the  thorax  or 
in  the  abdomen.  One  of  them  is  the  aorta,  the  other  represents  a  dissecting  aortic  aneurism 
which  has  become  canalized;  opening  above  and  below  into  the  true  aorta,  and  at  first  sight 
presenting  the  appearances  of  a  proper  bloodvessel. 


Branches  of  the  Thoracic  Aorta. — 


Visceral 


Pericardial. 
Bronchial. 
Esophageal. 
Mediastinal. 


r  Intercostal. 
Parietal   -l  Subcostal. 

(  Superior  Phrenic. 


The  pericardial  branches  (rami  pericardiaci)  consist  of  a  few  small  vessels  which 
are  distributed  to  the  posterior  surface  of  the  pericardium. 

The  bronchial  arteries  (aa.  bronchioles)  vary  in  number,  size,  and  origin.  There 
is  as  a  rule  only  one  right  bronchial  artery,  which  arises  from  the  first  aortic  inter- 
costal, or  from  the  upper  left  bronchial  artery.  The  left  bronchial  arteries  are  usually 
two  in  number,  and  arise  from  the  thoracic  aorta.  The  upper  left  bronchial  arises 
opposite  the  fifth  thoracic  vertebra,  the  lower  just  below  the  level  of  the  left  bron- 
chus. Each  vessel  runs  on  the  back  part  of  its  bronchus,  dividing  and  subdividing 
along  the  bronchial  tubes,  supplying  them,  the  areolar  tissue  of  the  lungs,  the 
bronchial  l>Tnph  glands,  and  the  esophagus. 

The  esophageal  arteries  {aa.  oBsophagece)  four  or  five  in  number,  arise  from 
the  front  of  the  aorta,  and  pass  obliquely  downward  to  the  esophagus,  forming 
a  chain  of  anastomoses  along  that  tube,  anastomosing  with  the  esophageal  branches 
of  the  inferior  thyroid  arteries  above,  and  with  ascending  branches  from  the  left 
inferior  phrenic  and  left  gastric  arteries  below. 

The  mediastinal  branches  (rami  mediastinales)  are  numerous  small  vessels  which 
supply  the  lymph  glands  and  loose  areolar  tissue  in  the  posterior  mediastinum. 

Intercostal  Arteries  {aa,  intercostales) . — There  are  usually  nine  pairs  of  aortic 
intercostal  arteries.  They  arise  from  the  back  of  the  aorta,  and  a  redistributed 
to  the  lower  nine  intercostal  spaces,  the  first  two  spaces  being  supplied  by  the  highest 
intercostal  artery,  a  branch  of  the  costocervical  trunk  of  the  subclavian.  The 
right  aortic  intercostals  are  longer  than  the  left,  on  account  of  the  position  of  the 
aorta  on  the  left  side  of  the  vertebral  column;  they  pass  across  the  bodies  of  the 
vertebrae  behind  the  esophagus,  thoracic  duct,  and  vena  azygos,  and  are  covered 
by  the  right  lung  and  pleura.  The  left  aortic  intercostals  run  backward  on  the 
sides  of  the  vertebrae  and  are  covered  by  the  left  lung  and  pleura;  the  upper  two 
vessels  are  crossed  by  the  highest  left  intercostal  vein,  the  lower  vessels  by  the 
hemiazygos  veins.  The  further  course  of  the  intercostal  arteries  is  practically 
the  same  on  both  sides.    Opposite  the  heads  of  the  ribs  the  sympathetic  trunk 


I 


THE  THORACIC  AORTA  ^^^  gOl 

passes  downward  in  front  of  them,  and  the  splanchnic  nerves  also  descend  in  front 
by  the  lower  arteries.  Each  artery  then  divides  into  an  anterior  and  a  posterior 
ramus. 

The  Anterior  Ramus  crosses  the  corresponding  intercostal  space  obliquely  toward 
the  angle  of  the  upper  rib,  and  thence  is  continued  forward  in  the  costal  groove.  It 
is  placed  at  first  between  the  pleura  and  the  posterior  intercostal  membrane,  then 
it  pierces  this  membrane,  and  lies  between  it  and  the  Intercostalis  externus  as  far  as 
the  angle  of  the  rib;  from  this  onward  it  runs  between  the  Intercostales  externus 
and  internus,  and  anastomoses  in  front  with  the  intercostal  branch  of  the  internal 
mammary  or  musculophrenic.  Each  artery  is  accompanied  by  a  vein  and  a  nerve, 
the  former  being  above  and  the  latter  below  the  artery,  except  in  the  upper  spaces, 
where  the  nerve  is  at  first  above  the  artery.  The  first  aortic  intercostal  artery 
anastomoses  with  the  intercostal  branch  of  the  costocervical  trunk,  and  may  form 
the  chief  supply  of  the  second  intercostal  space.  The  lower  two  intercostal  arteries 
are  continued  anteriorly  from  the  intercostal  spaces  into  the  abdominal  wall,  and 
anastomose  with  the  subcostal,  superior  epigastric,  and  lumbar  arteries. 

Branches. — ^The  anterior  rami  give  off  the  following  branches: 

Collateral  Intercostal.  Lateral  Cutaneous. 

Muscular.  Mammary. 

The  collateral  intercostal  branch  comes  off  from  the  intercostal  artery  near  the 
angle  of  the  rib,  and  descends  to  the  upper  border  of  the  rib  below,  along  which  it 
courses  to  anastomose  with  the  intercostal  branch  of  the  internal  mammary. 

Muscular  branches  are  given  to  the  Intercostales  and  Pectorales  and  to  the 
Serratus  anterior;  they  anastomose  with  the  highest  and  lateral  thoracic  branches 
of  the  axillary  artery. 

The  lateral  cutaneous  branches  accompany  the  lateral  cutaneous  branches  of  the 
thoracic  nerves. 

Mammary  branches  are  given  oi^  by  the  vessels  in  the  third,  fourth,  and  fifth 
spaces.  They  supply  the  mamma,  and  increase  considerably  in  size  during  the 
period  of  lactation. 

The  Posterior  Ramus  runs  backward  through  a  space  which  is  bounded  above 
and  below  by  the  necks  of  the  ribs,  medially  by  the  body  of  a  vertebra,  and  laterally 
by  an  anterior  costotransverse  ligament.  It  gives  off  a  spinal  branch  which  enters 
the  vertebral  canal  through  the  intervertebral  foramen  and  is  distributed  to  the 
medulla  spinalis  and  its  membranes  and  the  vertebrae.  It  then  courses  over 
the  transverse  process  with  the  posterior  division  of  the  thoracic  nerve,  supplies 
branches  to  the  muscles  of  the  back  and  cutaneous  branches  which  accompany 
the  corresponding  cutaneous  branches  of  the  posterior  division  of  the  nerve. 

The  subcostal  arteries,  so  named  because  they  lie  below  the  last  ribs,  constitute 
the  lowest  pair  of  branches  derived  from  the  thoracic  aorta,  and  are  in  series  with 
the  intercostal  arteries.  Each  passes  along  the  lower  border  of  the  twelfth  rib 
behind  the  kidney  and  in  front  of  the  Quadratus  lumborum  muscle,  and  is  accom- 
panied by  the  twelfth  thoracic  nerve.  It  then  pierces  the  posterior  aponeurosis 
of  the  Transversus  abdominis,  and,  passing  forward  between  this  muscle  and  the 
Obliquus  internus,  anastomoses  with  the  superior  epigastric,  lower  intercostal,  and 
lumbar  arteries.  Each  subcostal  artery  gives  off  a  posterior  branch  which  has  a 
similar  distribution  to  the  posterior  ramus  of  an  intercostal  artery. 

The  superior  phrenic  branches  are  small  and  arise  from  the  lower  part  of  the 
thoracic  aorta;  they  are  distributed  to  the  posterior  part  of  the  upper  surface  of 
the  diaphragm,  and  anastomose  with  the  musculophrenic  and  pericardiacophrenic 
arteries. 

A  small  aberrant  artery  is  sometimes  found  arising  from  the  right  side  of  the  tho- 
racic aorta  near  the  origin  of  the  right  bronchial.    It  passes  upward  and  to  the  right 


602 


ANGIOLOGY 


behind  the  trachea   and   the  esophagus,  and  may  anastomose  with  the  highes? 
right  intercostal  artery.  It  represents  the  remains  of  the  right  dorsal  aorta,  and  in  a  ;| 
small  proportion  of  cases  is  enlarged  to  form  the  first  part  of  the  right  subclavian  i 
artery.  \ 

The  Abdominal  Aorta  (Aorta  Abdominalis)  (Fig.  531).  \ 

The  abdominal  aorta  begins  at  the  aortic  hiatus  of  the  diaphragm,  in  front 
of  the  lower  border  of  the  body  of  the  last  thoracic  vertebra,  and,  descending  in 


O  V  ^  P  H  R  A  Cjvj 


Inferior  phrenic  arteries 


Internal 

spermatic 

vessels 


Fig.  531. — The  abdominal  aorta  and  its  bwnches. 

front  of  the  vertebral  column,  ends  on  the  body  of  the  fourth  lumbar  vertebra, 
commonly  a  little  to  the  left  of  the  middle  line,^  by  dividing  into  the  two  common 
iliac  arteries.  It  diminishes  rapidly  in  size,  in  consequence  of  the  many  large 
branches  which  it  gives  off.  As  it  lies  upon  the  bodies  of  the  vertebrae,  the  curve 
which  it  describes  is  convex  forward,  the  summit  of  the  convexity  corresponding 
to  the  third  lumbar  vertebra. 


1  Lord  Lister,  having  accurately  examined  30  bodies  in  order  to  ascertain  the  exact  point  of  termination  of  thia 
vessel,  found  it  "either  absolutely,  or  almost  absolutely,  mesial  in  15,  while  in  13  it  deviated  more  or  less  to  the  left, 
and  in  2  was  slightly  to  the  right. "    System  of  Surgery,  edited  by  T.  Holmes,  2d  ed.,  v,  652. 


t- 


THE  ABDOMINAL  AORTA  603 


k 


II 


II 


II 


Relations. — The  abdominal  aorta  is  covered,  anteriorly,  by  the  lesser  omentum  and  stomach, 
behind  which  are  the  branches  of  the  celiac  artery  and  the  celiac  plexus;  below  these,  by  the 
lienal  vein,  the  pancreas,  the  left  renal  vein,  the  inferior  part  of  the  duodenum,  the  mesentery, 
and  aortic  plexus.  Posteriorly,  it  is  separated  from  the  lumbar  vertebrae  and  intervertebral 
fibrocartilages  by  the  anterior  longitudinal  ligament  and  left  lumbar  veins.  On  the  right  side 
it  is  in  relation  above  with  the  azygos  vein,  cisterna  chyh,  thoracic  duct,  and  the  right  crus  of 
the  diaphragm— the  last  separating  it  from  the  upper  part  of  the  inferior  vena  cava,  and  from 
the  right  celiac  ganglion;  the  inferior  vena  cava  is  in  contact  with  the  aorta  below.  On  the 
left  side  are  the  left  crus  of  the  diaphragm,  the  left  ceUac  ganglion,  the  ascending  part  of  the 
duodemma,  and  some  coils  of  the  small  intestine. 

Collateral  Circulation. — The  collateral  circulation  would  be  carried  on  by  the  anastomoses 
between  the  internal  mammary  and  the  inferior  epigastric;  by  the  free  communication  between 
the  superior  and  inferior  mesenteries,  if  the  Ugature  were  placed  between  these  vessels;  or  by  the 
anastomosis  between  the  inferior  mesenteric  and  the  internal  pudendal,  when  (as  is  more  common) 
the  point  of  ligature  is  below  the  origin  of  the  inferior  mesenteric;  and  possibly  by  the  anastomoses 
of  the  lumbar  arteries  with  the  branches  of  the  hypogastric. 

Branches. — The  branches  of  the  abdominal  aorta  may  be  divided  into  three 
sets:  visceral,  parietal,  and  terminal. 

Visceral  Branches.  Parietal  Branches. 

Celiac.  Inferior  Phrenics. 

Superior  Mesenteric.  Lumbars. 

Inferior  Mesenteric.  Middle  Sacral. 
Middle  Suprarenals. 
Renals. 

Internal  Spermatics.  Terminal  Branches. 

Ovarian  (in  the  female) .  Common  Iliacs. 

Of  the  visceral  branches,  the  celiac  artery  and  the  superior  and  inferior  mes- 
enteric arteries  are  unpaired,  while  the  suprarenals,  renals,  internal  spermatics, 
and  ovarian  are  paired.  Of  the  parietal  branches  the  inferior  phrenics  and  lumbars 
are  paired;  the  middle  sacral  is  unpaired.    The  terminal  branches  are  paired. 

The  celiac  artery  (a.  coeliaca;  celiac  axis)  (Figs.  532,  533)  is  a  short  thick  trunk, 
about  1.25  cm.  in  length,  which  arises  from  the  front  of  the  aorta,  just  below 
the  aortic  hiatus  of  the  diaphragm,  and,  passing  nearly  horizontally  forward, 
divides  into  three  large  branches,  the  left  gastric,  the  hepatic,  and  the  splenic;  it 
occasionally  gives  off  one  of  the  inferior  phrenic  arteries. 

Relations. — The  cehac  artery  is  covered  by  the  lesser  omentum.  On  the  right  side  it  is  in 
relation  with  the  right  celiac  ganglion  and  the  caudate  process  of  the  liver;  on  the  left  side,  with 
the  left  cehac  ganghon  and  the  cardiac  end  of  the  stomach.  Below,  it  is  in  relation  to  the  upper 
border  of  the  pancreas,  and  the  lienal  vein. 

1.  The  Left  Gastric  Artery  (a.  gastrica  sinistra;  gastric  or  coronary  artery),  the 
smallest  of  the  three  branches  of  the  celiac  artery,  passes  upward  and  to  the  left, 
posterior  to  the  omental  bursa,  to  the  cardiac  orifice  of  the  stomach.  Here  it  dis- 
tributes branches  to  the  esophagus,  which  anastomose  with  the  aortic  esophageal 
arteries ;  others  supply  the  cardiac  part  of  the  stomach,  anastomosing  with  branches 
of  the  lienal  artery.  It  then  runs  from  left  to  right,  along  the  lesser  curvature  of  the 
stomach  to  the  pylorus,  between  the  layers  of  the  lesser  omentum ;  it  gives  branches 
to  both  surfaces  of  the  stomach  and  anastomoses  with  the  right  gastric  artery. 

2.  The  Hepatic  Artery  (a.  hepatica)  in  the  adult  is  intermediate  in  size  between 
the  left  gastric  and  lienal;  in  the  fetus,  it  is  the  largest  of  the  three  branches  of 
the  celiac  artery.  It  is  first  directed  forward  and  to  the  right,  to  the  upper  margin 
of  the  superior  part  of  the  duodenum,  forming  the  lower  boundary  of  the  epiploic 
foramen  {foramen  of  Winslow).  It  then  crosses  the  portal  vein  anteriorly  and 
ascends  between  the  layers  of  the  lesser  omentum,  and  in  front  of  the  epiploic  fora- 
men, to  the  porta  hepatis,  where  it  divides  into  two  branches,  right  and  left,  which 
supply  the  corresponding  lobes  of  the  liver,  accompanying  the  ramifications  of  the 


604 


ANGIOLOGY 


portal  vein  and  hepatic  ducts.    The  hepatic  artery,  in  its  course  along  the  right 
border  of  the  lesser  omentum,  is  in  relation  with  the  common  bile-duct  and  portal 
vein,  the  duct  lying  to  the  right  of  the  artery,  and  the  vein  behind. 
Its  branches  are: 

Right  Gastric. 

Gastroduodenal  |^^g^^^^J*^«^P^Pj«i^-      ^       , 
[  buperior  rancreaticoduodenal. 

Cystic. 


Cystic  artery 


n    in     e     n 


Fio.  532. — The  celiac  artery  and  its  branches;  the  liver  has  been  raised,  and  the  lesser  omentum  and  anterior 

layer  of  the  greater  omentum  removed. 

The  right  gastric  artery  (a.  gastrica  dextra;  pyloric  artery)  arises  from  the  hepatic, 
above  the  pylorus,  descends  to  the  pyloric  end  of  the  stomach,  and  passes  from 
right  to  left  along  its  lesser  curvature,  supplying  it  with  branches,  and  anastomosing 
with  the  left  gastric  artery. 

The  gastroduodenal  artery  (a.  gastroduodenalis)  (Fig.  533)  is  a  short  but  large 
branch,  which  descends,  near  the  pylorus,  between  the  superior  part  of  the  duo- 
denum and  the  neck  of  the  pancreas,  and  divides  at  the  lower  border  of  the  duodenum 
into  two  branches,  the  right  gastroepiploic  and  the  superior  pancreaticoduodenal. 
Previous  to  its  division  it  gives  off  two  or  three  small  branches  to  the  pyloric  end 
of  the  stomach  and  to  the  pancreas. 

The  right  gastroepiploic  artery  (a.  gastroepiploica  dextra)  runs  from  right  to  left 
along  the  ^greater  curvature  of  the  stomach,  between  the  layers  of  the  greater 
omentum,  anastomosing  with  the  left  gastroepiploic  branch  of  the  lienal  artery. 
Except  at  the  pylorus,  where  it  is  in  contact  with  the  stomach,  it  lies  about  a  finger's 


THE  ABDOMINAL  AORTA 


605 


breadth  from  the  greater  curvature.  This  vessel  gives  off  numerous  branches, 
some  of  which  ascend  to  supply  both  surfaces  of  the  stomach,  while  others  descend 
to  supply  the  greater  omentum  and  anastomose  with  branches  of  the  middle  colic. 
The  superior  pancreaticoduodenal  artery  (a.  pancreaticoduodenalis  superior) 
descends  between  the  contiguous  margins  of  the  duodenum  and  pancreas.  It 
supplies  both  these  organs,  and  anastomoses  with  the  inferior  pancreaticoduodenal 
branch  of  the  superior  mesenteric  artery,  and  with  the  pancreatic  branches  of  the 
lienal  artery. 

Branches  to  greater  omentum 


The  celiac  artery  and  its  branches;  the  stomach  has  been  raised  and  the  peritoneum  removed. 

The  cystic  artery  (a.  cystica)  (Fig.  532),  usually  a  branch  of  the  right  hepatic, 
passes  downward  and  forward  along  the  neck  of  the  gall-bladder,  and  divides  into 
two  branches,  one  ot  which  ramifies  on  the  free  surface,  the  other  on  the  attached 
surface  of  the  gall-bladder. 

3.  The  Lienal  or  Splenic  Artery  (a.  lienalis),  the  largest  branch  of  the  celiac 
artery,  is  remarkable  for  the  tortuosity  of  its  course.  It  passes  horizontally  to 
the  left  side,  behind  the  stomach  and  the  omental  bursa  of  the  peritoneum,  and 
along  the  upper  border  of  the  pancreas,  accompanied  by  the  lienal  vein,  which 
lies  below  it;  it  crosses  in  front  of  the  upper  part  of  the  left  kidney,  and,  on  arriving 
near  the  spleen,  divides  into  branches,  some  of  which  enter  the  hilus  of  that  organ 
between  the  two  layers  of  the  phrenicolienal  ligament  to  be  distributed  to  the  tissues 

I  of  the  spleen ;  some  are  given  to  the  pancreas,  while  others  pass  to  the  greater  curva- 
ture of  the  stomach  between  the  layers  of  the  gastrolienal  ligament.    Its  branches  are : 
Pancreatic.  Short  Gastric.  Left  Gastroepiploic. 

I 


h 


tt 


606 


ANGIOLOGY 


The  pancreatic  branches  (ravii  pancreatici)  are  numerous  small  vessels  derived 
from  the  lienal  as  it  runs  behind  the  upper  border  of  the  pancreas,  supplying  its 
body  and  tail.  One  of  these,  larger  than  the  rest,  is  sometimes  given  off  near  the 
tail  of  the  pancreas;  it  runs  from  left  to  right  near  the  posterior  surface  of  the  gland,  H 
following  the  course  of  the  pancreatic  duct,  and  is  called  the  arteria  pancreatica 
magna.  These  vessels  anastomose  with  the  pancreatic  branches  of  the  pancreatico- 
duodenal and  superior  mesenteric  arteries. 


Fig.  534. — The  superior  mesenteric  artery  and  its  branches. 

The  short  gastric  arteries  {aa.  gastriccs  breves;  vasa  brevia)  consist  of  from  jfive  to 
seven  small  branches,  which  arise  from  the  end  of  the  lienal  artery,  and  from  its 
terminal  divisions.  They  pass  from  left  to  right,  between  the  layers  of  the  gastro- 
lienal ligament,  and  are  distributed  to  the  greater  curvature  of  the  stomach,  anasto- 
mosing with  branches  of  the  left  gastric  and  left  gastroepiploic  arteries. 

The  left  gastroepiploic  artery  (a.  gastroepiploica  sinistra)  the  largest  branch  of  the 
lienal,  runs  from  left  to  right  about  a  finger's  breadth  or  more  from  the  greater 
curvature  of  the  stomach,  between  the  layers  of  the  greater  omentum,  and  anasto- 
moses with  the  right  gastroepiploic.  In  its  course  it  distributes  several  ascending 
branches  to  both  surfaces  of  the  stomach;  others  descend  to  supply  the  greater 
omentum  and  anastomose  with  branches  of  the  middle  colic. 

The  superior  mesenteric  artery  (a.  mesenterica  superior)  (Fig.  534)  is  a  large 


THE  ABDOMINAL  AORTA  607 


vessel  which  supplies  the  whole  length  of  the  small  intestine,  except  the  superior 
part  of  the  duodenum;  it  also  supplies  the  cecum  and  the  ascending  part  of  the  colon 
and  about  one-half  of  the  transverse  part  of  the  colon.  It  arises  from  the  front 
of  the  aorta,  about  1.25  cm.  below  the  celiac  artery,  and  is  crossed  at  its  origin  by 
the  lienal  vein  and  the  neck  of  the  pancreas.  It  passes  downward  and  forward, 
anterior  to  the  processus  uncinatus  of  the  head  of  the  pancreas  and  inferior  part 
of  the  duodenum,  and  descends  between  the  layers  of  the  mesentery  to  the  right 
iliac  fossa,  where,  considerably  diminished  in  size,  it  anastomoses  with  one  of 
its  own  branches,  viz.,  the  ileocolic.  In  its  course  it  crosses  in  front  of  the  inferior 
vena  cava,  the  right  ureter  and  Psoas  major,  and  forms  an  arch,  the  convexity  of 
which  is  directed  forward  and  downward  to  the  left  side,  the  concavity  backward 
and  upward  to  the  right.  It  is  accompanied  by  the  superior  mesenteric  vein, 
which  lies  to  its  right  side,  and  it  is  surrounded  by  the  superior  mesenteric  plexus 
of  nerves. 

»  Branches. — Its  branches  are: 
Inferior  Pancreaticoduodenal.  Ileocolic. 

Intestinal.  Right  Colic. 

Middle  Colic. 
The  Inferior  Pancreaticoduodenal  Artery  (a.  pancreaticoduodenalis  inferior)  is  given 
off  from  the  superior  mesenteric  or  from  its  first  intestinal  branch,  opposite  the 
upper  border  of  the  inferior  part  of  the  duodenum.  It  courses  to  the  right 
between  the  head  of  the  pancreas  and  duodenum,  and  then  ascends  to  anastomose 
with  the  superior  pancreaticoduodenal  artery.  It  distributes  branches  to  the  head 
of  the  pancreas  and  to  the  descending  and  inferior  parts  of  the  duodenum. 

The  Intestinal  Arteries  {aa.  intestinales;  xasa  intestini  tenuis)  arise  from  the  convex 
side  of  the  superior  mesenteric  artery.  They  are  usually  from  twelve  to  fifteen 
in  number,  and  are  distributed  to  the  jejunum  and  ileum.  They  run  nearly  parallel 
with  one  another  between  the  layers  of  the  mesentery,  each  vessel  dividing  into 
two  branches,  which  unite  with  adjacent  branches,  forming  a  series  of  arches,  the 
convexities  of  which  are  directed  toward  the  intestine  (Fig.  535) .  From  this  first 
set  of  arches  branches  arise,  which  unite  with  similar  branches  from  above  and  below 
and  thus  a  second  series  of  arches  is  formed ;  from  the  lower  branches  of  the  artery, 
a  third,  a  fourth,  or  even  a  fifth  series  of  arches  may  be  formed,  diminishing  in 
size  the  nearer  they  approach  the  intestine.  In  the  short,  upper  part  of  the  mesen- 
tery only  one  set  of  arches  exists,  but  as  the  depth  of  the  mesentery  increases, 
second,  third,  fourth,  or  even  fifth  groups  are  developed.  From  the  terminal 
arches  numerous  small  straight  vessels  arise  which  encircle  the  intestine,  upon 
which  they  are  distributed,  ramifying  between  its  coats..  From  the  intestinal 
arteries  small  branches  are  given  off  to  the  lymph  glands  and  other  structures 
between  the  layers  of  the  mesentery. 

The  Ileocolic  Artery  (a.  ileocolica)  is  the  lowest  branch  arising  from  the  concavity 
of  the  superior  mesenteric  artery.  It  passes  downward  and  to  the  right  behind  the 
peritoneum  toward  the  right  iliac  fossa,  where  it  divides  into  a  superior  and  an 
inferior  branch;  the  inferior  anastomoses  with  the  end  of  the  superior  mesenteric 
artery,  the  superior  with  the  right  colic  artery. 

The  inferior  branch  of  the  ileocolic  runs  toward  the  upper  border  of  the  ileo- 
colic junction  and  supplies  the  following  branches  (Fig.  536) : 

(a)  colic,  which  pass  upward  on  the  ascending  colon;  (6)  anterior  and  posterior 
cecal,  which  are  distributed  to  the  front  and  back  of  the  cecum ;  (c)  an  appendicular 
artery,  which  descends  behind  the  termination  of  the  ileum  and  enters  the  mesen- 
teriole  of  the  vermiform  process;  it  runs  near  the  free  margin  of  this  mesenteriole 
and  ends  in  branches  which  supply  the  vermiform  process ;  and  (d)  ileal,  which  run 
upward  and  to  the  left  on  the  lower  part  of  the  ileum,  and  anastomose  with  the 
ermination  of  the  superior  mesenteric. 


I 


608 


ANGIOLOGY 


Fig.  535. — Loop  of  small  intestine  showing  distribution  of  intestinal  arteries.  (From  a  preparation  by  Mr.  Hamilton 
Drummond.)  The  vessels  were  injected  while  the  gut  was  in  situ;  the  gut  was  then  removed,  and  an  x-ray  photograph 
taken. 


Terminal  part  of  ileocolic 

Cecal  branches 

Ileal  branches 


Appendictdar 
artery 


^■^^rmjprocess 
Fig.  536. — Arteries  of  cecum  and  vermiform  process. 


THE  ABDOMINAL  AORTA 


609 


The  Right  Colic  Artery  (a.  colica  dextra)  arises  from  about  the  middle  of  the  con- 
cavity of  the  superior  mesenteric  artery,  or  from  a  stem  common  to  it  and  the  ileo- 
colic. It  passes  to  the  right  behind  the  peritoneum,  and  in  front  of  the  right 
internal  spermatic  or  ovarian  vessels,  the  right  ureter  and  the  Psoas  major,  toward 
the  middle  of  the  ascending  colon;  sometimes  the  vessel  lies  at  a  higher  level, 
and  crosses  the  descending  part  of  the  duodenum  and  the  lower  end  of  the  right 
kidney.  At  the  colon  it  divides  into  a  descending  branch,  which  anastomoses  with 
the  ileocolic,  and  an  ascending  branch,  which  anastomoses  with  the  middle  colic. 
These  branches  form  arches,  from  the  convexity  of  which  vessels  are  distributed 
to  the  ascending  colon. 


Middle  Hemorrhoidal 
Inferior  Hemorrhoidal 


Fia.  537. — The  inferior  mesenteric  artery  and  its  branches. 

The  Middle  Colic  Artery  (a.  colica  media)  arises  from  the  superior  mesenteric 
just  below  the  pancreas  and,  passing  downward  and  forward  between  the  layers  of 
the  transverse  mesocolon,  divides  into  two  branches,  right  and  left;  the  former 
anastomoses  with  the  right  colic;  the  latter  with  the  left  colic,  a  branch  of  the  in- 
ferior mesenteric.  The  arches  thus  formed  are  placed  about  two  jBngers'  breadth 
from  the  transverse  colon,  to  which  they  distribute  branches. 

The  inferior  mesenteric  artery  (a.  mesenterica  inferior)  (Fig.  537)  supplies  the 
left  half  of  the  transverse  part  of  the  colon,  the  whole  of  the  descending  and  iliac 
parts  of  the  colon,  the  sigmoid  colon,  and  the  greater  part  of  the  rectum.  It  is 
smaller  than  the  superior  mesenteric,  and  arises  from  the  aorta,  about  3  or  4  cm. 
39 


610  ^^^^^^"       ANGIOLOGY 

above  its  division  into  the  common  iliacs  and  close  to  the  lower  border  of  the 
inferior  part  of  the  duodenum.  It  passes  downward  posterior  to  the  peritoneum, 
lying  at  first  anterior  to  and  then  on  the  left  side  of  the  aorta.  It  crosses  the 
left  common  iliac  artery  and  is  continued  into  the  lesser  pelvis  under  the  name  of 
the  superior  hemorrhoidal  artery,  which  descends  between  the  two  layers  of  the 
sigmoid  mesocolon  and  ends  on  the  upper  part  of  the  rectum 
Branches. — Its  branches  are: 


Left  Colic.  Sigmoid.  Superior  Hemorrhoidal 

The  Left  Colic  Artery  (a.  colica  sinistra)  runs  to  the  left  behind  the  peritoneum 
and  in  front  of  the  Psoas  major,  and  after  a  short,  but  variable,  course  divides 
into  an  ascending  and  a  descending  branch;  the  stem  of  the  artery  or  its  branches 
cross  the  left  ureter  and  left  internal  spermatic  vessels.  The  ascending  branch 
crosses  in  front  of  the  left  kidney  and  ends,  between  the  two  layers  of  the  transverse 
mesocolon,  by  anastomosing  with  the  middle  colic  artery;  the  descending  branch 
anastomoses  with  the  highest  sigmoid  artery.  From  the  arches  formed  by  these 
anastomoses  branches  are  distributed  to  the  descending  colon  and  the  left  part 
of  the  transverse  colon. 

The  Sigmoid  Arteries  {aa.  sigmoideae)  (Fig.  538),  two  or  three  in  number,  run 
obliquely  downward  and  to  the  left  behind  the  peritoneum  and  in  front  of  the 
Psoas  major,  ureter,  and  internal  spermatic  vessels.  Their  branches  supply  the  lower 
part  of  the  descending  colon,  the  iliac  colon,  and  the  sigmoid  or  pelvic  colon;  anasto- 
mosing above  with  the  left  colic,  and  below  with  the  superior  hemorrhoidal  artery. 

The  Superior  Hemorrhoidal  Artery  (a.  hoBmorrhoidalis  superior)  (Fig.  538),  the 
continuation  of  the  inferior  mesenteric,  descends  into  the  pelvis  between  the  layers 
of  the  mesentery  of  the  sigmoid  colon,  crossing,  in  its  course,  the  left  common 
iliac  vessels.  It  divides,  opposite  the  third  sacral  vertebra,  into  two  branches, 
which  descend  one  on  either  side  of  the  rectum,  and  about  10  or  12  cm.  from  the 
anus  break  up  into  several  small  branches.  These  pierce  the  muscular  coat  of  the 
bowel  and  run  downward,  as  straight  vessels,  placed  at  regular  intervals  from  each 
other  in  the  wall  of  the  gut  between  its  muscular  and  mucous  coats,  to  the  level 
of  the  Sphincter  ani  internus ;  here  they  form  a  series  of  loops  around  the  lower  end 
of  the  rectum,  and  communicate  with  the  middle  hemorrhoidal  branches  of  the 
hypogastric,  and  with  the  inferior  hemorrhoidal  branches  of  the  internal  pudendal. 

The  middle  suprarenal  arteries  (aa.  suprarenales  media;  middle  capsular  arteries; 
suprarenal  arteries)  are  two  small  vessels  which  arise,  one  from  either  side  of  the 
aorta,  opposite  the  superior  mesenteric  artery.  They  pass  lateralward  and  slightly 
upward,  over  the  crura  of  the  diaphragm,  to  the  suprarenal  glands,  where  they 
anastomose  with  suprarenal  branches  of  the  inferior  phrenic  and  renal  arteries.  In 
the  fetus  these  arteries  are  of  large  size. 

The  renal  arteries  {aa.  renales)  (Fig.  531),  are  two  large  trunks,  which  arise 
from  the  side  of  the  aorta,  immediately  below  the  superior  mesenteric  artery. 
Each  is  directed  across  the  crus  of  the  diaphragm,  so  as  to  form  nearly  a  right 
angle  with  the  aorta.  The  right  is  longer  than  the  left,  on  account  of  the  position 
of  the  aorta;  it  passes  behind  the  inferior  vena  cava,  the  right  renal  vein,  the  head 
of  the  pancreas,  and  the  descending  part  of  the  duodenum.  The  left  is  somewhat 
higher  than  the  right;  it  lies  behind  the  left  renal  vein,  the  body  of  the  pancreas 
and  the  lienal  vein,  and  is  crossed  by  the  inferior  mesenteric  vein.  Before  reaching 
the  hilus  of  the. kidney,  each  artery  divides  into  four  or  five  branches;  the  greater 
number  of  these  lie  between  the  renal  vein  and  ureter,  the  vein  being  in  front, 
the  ureter  behind,  but  one  or  more  branches  are  usually  situated  behind  the  ureter. 
Each  vessel  gives  off  some  small  inferior  suprarenal  branches  to  the  suprarenal 
gland,  the  ureter,  and  the  surrounding  cellular  tissue  and  muscles.  One  or  two 
accessory  renal  arteries  are  frequently  found,  more  especially  on  the  left  side 


;um  ■ 


THE  ABDOMINAL  AORTA 


611 


they  usually  arise  from  the  aorta,  and  may  come  off  above  or  below  the  main  artery, 
the  former  being  the  more  common  position.  Instead  of  entering  the  kidney  at  the 
hilus,  they  usually  pierce  the  upper  or  lower  part  of  the  gland. 

The  internal  spermatic  arteries  (aa.  spermaticoe  internee;  spermatic  arteries) 
(Fig.  531)  are  distributed  to  the  testes.  They  are  two  slender  vessels  of  consid- 
erable length,  and  arise  from  the  front  of  the  aorta  a  little  below  the  renal  arteries. 
Each  passes  obliquely  downward  and  laterahvard  behind  the  peritoneum,  resting 
on  the  Psoas  major,  the  right  spermatic  lying  in  front  of  the  inferior  vena  cava 
and  behind  the  middle  colic  and  ileocolic  arteries  and  the  terminal  part  of  the 
ileum,  the  left  behind  the  left  colic  and  sigmoid  arteries  and  the  iliac  colon.  Each 
crosses  obliquely  over  the  ureter  and  the  lower  part  of  the  external  iliac  artery 


Fig.  53S. — Sigmoid  colon  and  rectum,   showing  distribution  of   branches  of  inferior  mesenteric  artery  and  their 
anastomoses.     (From  a  preparation  by  Mr.  Hamilton  Drummond.)    Prepared  in  same  manner  as  Fig.  535. 

to  reach  the  abdominal  inguinal  ring,  through  which  it  passes,  and  accompanies 
the  other  constituents  of  the  spermatic  cord  along  the  inguinal  canal  to  the 
scrotum,  where  it  becomes  tortuous,  and  divides  into  several  branches.  Two  or 
three  of  these  accompany  the  ductus  deferens,  and  supply  the  epididymis,  anasto- 
mosing with  the  artery  of  the  ductus  deferens ;  others  pierce  the  back  part  of  the 
tunica  albuginea,  and  supply  the  substance  of  the  testis.  The  internal  spermatic 
artery  supplies  one  or  two  small  branches  to  the  ureter,  and  in  the  inguinal  canal 
gives  one  or  two  twigs  to  the  Cremaster. 

The  ovarian  arteries  {aa.  ovaricce)  are  the  corresponding  arteries  in  the  female 
to  the  internal  spermatic  in  the  male.  They  supply  the  ovaries,  are  shorter  than  the 
internal  spermatics,  and  do  not  pass  out  of  the  abdominal  cavity.  The  origin 
and  course  of  the  first  part  of  each  artery  are  the  same  as  those  of  the  internal 


ANGIOLOGY 

spermatic,  but  on  arriving  at  the  upper  opening  of  the  lesser  pelvis  the  ovarian 
artery  passes  inward,  between  the  two  layers  of  the  ovariopelvic  ligament  and  of 
the  broad  ligament  of  the  uterus,  to  be  distributed  to  the  ovary.  Small  branches 
are  given  to  the  ureter  and  the  uterine  tube,  and  one  passes  on  to  the  side  of  the 
uterus,  and  unites  with  the  uterine  artery.  Other  offsets  are  continued  on  the  round 
ligament  of  the  uterus,  through  the  inguinal  canal,  to  the  integument  of  the  labium 
majus  and  groin. 

At  an  early  period  of  fetal  life,  when  the  testes  or  ovaries  lie  by  the  side  of  the 
vertebral  column,  below  the  kidneys,  the  internal  spermatic  or  ovarian  arteries 
are  short;  but  with  the  descent  of  these  organs  into  the  scrotum  or  lesser  pelvis, 
the  arteries  are  gradually  lengthened. 

The  inferior  phrenic  arteries  {aa.  phrenicoe  inferiores)  (Fig.  531)  are  two  small 
vessels,  which  supply  the  diaphragm  but  present  much  variety  in  their  origin. 
They  may  arise  separately  from  the  front  of  the  aorta,  immediately  above  the  celiac 
artery,  or  by  a  common  trunk,  which  may  spring  either  from  the  aorta  or  from  the 
celiac  artery.  Sometimes  one  is  derived  from  the  aorta,  and  the  other  from  one  of 
the  renal  arteries;  they  rarely  arise  as  separate  vessels  from  the  aorta.  They 
diverge  from  one  another  across  the  crura  of  the  diaphragm,  and  then  run  ob- 
liquely upward  and  lateralward  upon  its  under  surface.  The  left  phrenic  passes 
behind  the  esophagus,  and  runs  forward  on  the  left  side  of  the  esophageal  hiatus. 
The  right  phrenic  passes  behind  the  inferior  vena  cava,  and  along  the  right  side 
of  the  foramen  which  transmits  that  vein.  Near  the  back  part  of  the  central 
tendon  each  vessel  divides  into  a  medial  and  a  lateral  branch.  The  medial  branch 
curves  forward,  and  anastomoses  with  its  fellow  of  the  opposite  side,  and  with 
the  musculophrenic  and  pericardiacophrenic  arteries.  The  lateral  branch  passes 
toward  the  side  of  the  thorax,  and  anastomoses  with  the  lower  intercostal  arteries, 
and  with  the  musculophrenic.  The  lateral  branch  of  the  right  phrenic  gives  off 
a  few  vessels  to  the  inferior  vena  cava;  and  the  left  one,  some  branches  to  the 
esophagus.  Each  vessel  gives  off  superior  suprarenal  branches  to  the  suprarenal 
gland  of  its  own  side.  The  spleen  and  the  liver  also  receive  a  few  twigs  from  the 
left  and  right  vessels  respectively. 

The  lumbar  arteries  {aa.  lumhales)  are  in  series  with  the  intercostals.  They 
are  usually  four  in  number  on  either  side,  and  arise  from  the  back  of  the  aorta, 
opposite  the  bodies  of  the  upper  four  lumbar  vertebrae.  A  fifth  pair,  small  in  size, 
is  occasionally  present:  they  arise  from  the  middle  sacral  artery.  They  run  lateral- 
ward  and  backward  on  the  bodies  of  the  lumbar  vertebrae,  behind  the  sympathetic 
trunk,  to  the  intervals  between  the  adjacent  transverse  processes,  and  are  then 
continued  into  the  abdominal  wall.  The  arteries  of  the  right  side  pass  behind  the 
inferior  vena  cava,  and  the  upper  two  on  each  side  run  behind  the  corresponding 
crus  of  the  diaphragm.  The  arteries  of  both  sides  pass  beneath  the  tendinous 
arches  which  give  origin  to  the  Psoas  major,  and  are  then  continued  behind  this 
muscle  and  the  lumbar  plexus.  They  now  cross  the  Quadratus  lumborum,  the  upper 
three  arteries  running  behind,  the  last  usually  in  front  of  the  muscle.  At  the  lateral 
border  of  the  Quadratus  lumborum  they  pierce  the  posterior  aponeurosis  of  the 
Transversus  abdominis  and  are  carried  forward  between  this  muscle  and  the 
Obliquus  internus.  They  anastomose  Avith  the  lower  intercostal,  the  subcostal, 
the  iliolumbar,  the  deep  iliac  circumflex,  and  the  inferior  epigastric  arteries. 

Branches. — In  the  interval  between  the  adjacent  transverse  processes  each  lumbar 
artery  gives  off  a  posterior  ramus  which  is  continued  backward  between  the  trans- 
verse processes  and  is  distributed  to  the  muscles  and  skin  of  the  back;  it  furnishes 
a  spinal  branch  which  enters  the  vertebral  canal  and  is  distributed  in  a  manner 
similar  to  the  spinal  branches  of  the  posterior  rami  of  the  intercostal  arteries 
(page  601).  Muscular  branches  are  supplied  from  each  lumbar  artery  and  from  its 
posterior  ramus  to  the  neighboring  muscles. 


THE  COMMON  ILIAC  ARTERIES 


613 


The  middle  sacral  artery  (a.  sacralis  media)  (Fig.  531)  is  a  small  vessel,  which 
arises  from  the  back  of  the  aorta,  a  little  above  its  bifurcation.  It  descends  in 
the  middle  line  in  front  of  the  fourth  and  fifth  lumbar  vertebrae,  the  sacrum  and 
coccjrx,  and  ends  in  the  glomus  coccygeum  {coccygeal  gland).  From  it,  minute 
branches  are  said  to  pass  to  the  posterior  surface  of  the  rectum.  On  the  last 
lumbar  vertebra  it  anastomoses  with  the  lumbar  branch  of  the  iliolumbar  artery; 
in  front  of  the  sacrum  it  anastomoses  with  the  lateral  sacral  arteries,  and  sends 
offsets  into  the  anterior  sacral  foramina.  It  is  crossed  by  the  left  common  iliac 
vein,  and  is  accompanied  by  a  pair  of  venae  comitantes;  these  unite  to  form  a  single 
vessel,  which  opens  into  the  left  common  iliac  vein. 


Middle  sacral 

Sup.  hemorrhoidal 


Fio.  539. — The  arteries  of  the  pelvis. 


li^ 


THE  COMMON  ILIAC  ARTERIES    (AA.  HJACffi  COMMUNES)    (Figs.  531,  539). 

The  abdominal  aorta  divides,  on  the  left  side  of  the  body  of  the  fourth  lumbar 
ertebra,  into  the  two  common  iliac  arteries.  Each  is  about  5  cm.  in  length.  They 
diverge  from  the  termination  of  the  aorta,  pass  downward  and  lateralward,  and 
divide,  opposite  the  intervertebral  fibrocartilage  between  the  last  lumbar  vertebra 
and  the  sacrum,  into  two  branches,  the  external  iliac  and  hypogastric  arteries; 
the  former  supplies  the  lower  extremity ;  the  latter,  the  viscera  and  parietes  of  the 
pelvis. 


614  AmidLOi 

The  right  common  iliac  artery  (Fig.  539)  is  somewhat  longer  than  the  left,  and 
passes  more  obliquely  across  the  body  of  the  last  lumbar  vertebra.  In  front  of 
it  are  the  peritoneum,  the  small  intestines,  branches  of  the  sympathetic  nerves, 
and,  at  its  point  of  division,  the  ureter.  Behind,  it  is  separated  from  the  bodies  of 
the  fourth  and  fifth  lumbar  vertebrae,  and  the  intervening  fibrocartilage,  by  the 
terminations  of  the  two  common  iliac  veins  and  the  commencement  of  the  inferior 
vena  cava.  Laterally,  it  is  in  relation,  above,  with  the  inferior  vena  cava  and  the 
right  common  iliac  vein;  and,  below,  with  the  Psoas  major.  Medial  to  it,  above, 
is  the  left  common  iliac  vein. 

The  left  common  iliac  artery  is  in  relation,  in  front,  with  the  peritoneum,  the 
small  intestines,  branches  of  the  sympathetic  nerves,  and  the  superior  hemorrhoidal 
artery;  and  is  crossed  at  its  point  of  bifurcation  by  the  ureter.  It  rests  on  the 
bodies  of  the  fourth  and  fifth  lumbar  vertebrae,  and  the  intervening  fibrocartilage. 
The  left  common  iliac  vein  lies  partly  medial  to,  and  partly  behind  the  artery; 
laterally,  the  artery  is  in  relation  with  the  Psoas  major. 

Branches. — The  common  iliac  arteries  give  off  small  branches  to  the  peritoneum, 
Psoas  major,  ureters,  and  the  surrounding  areolar  tissue,  and  occasionally  give 
origin  to  the  iliolumbar,  or  accessory  renal  arteries. 

Peculiarities. — ^The  point  of  origin  varies  according  to  the  bifurcation  of  the  aorta.  In  three- 
fourths  of  a  large  number  of  cases,  the  aorta  bifurcated  either  upon  the  fourth  lumbar  vertebra, 
or  upon  the  fibrocartilage  between  it  and  the  fifth;  the  bifurcation  being,  in  one  case  out  of  nine, 
below,  and  in  one  out  of  eleven,  above  this  point.  In  about  80  per  cent,  of  the  cases  the  aorta 
bifurcated  within  1.25  cm.  above  or  below  the  level  of  the  crest  of  the  ihum;  more  frequently 
below  than  above. 

The  -point  of  division  is  subject  to  great  variety.  In  two-thirds  of  a  large  number  of  cases  it 
was  between  the  last  lumbar  vertebra  and  the  upper  border  of  the  sacrum;  being  above  that  point 
in  one  case  out  of  eight,  and  below  it  in  one  case  out  of  six.  The  left  common  iUac  artery  divides 
lower  down  more  frequently  than  the  right. 

The  relative  lengths,  also,  of  the  two  common  ihac  arteries  vary.  The  right  common  iliac  was 
the  longer  in  sixty-three  cases;  the  left  in  fifty-two;  while  they  were  equal  in  fifty-three.  The 
length  of  the  arteries  varied,  in  five-sevenths  of  the  cases  examined,  from  3.5  to  7.5  cm.;  in  about 
half  of  the  remaining  cases  the  artery  was  longer,  and  in  the  other  half,  shorter;  the  minimum 
length  being  less  than  1.25  cm.,  the  maximum,  11  cm.  In  rare  instances,  the  right  common 
iliac  has  been  found  wanting,  the  external  iliac  and  hypogastric  arising  directly  from  the  aorta. 

Collateral  Circulation. — The  principal  agents  in  carrying  on  the  collateral  circulation  after  the 
application  of  a  ligature  to  the  common  iliac  are :  the  anastomoses  of  the  hemorrhoidal  branches 
of  the  hypogastric  with  the  superior  hemorrhoidal  from  the  inferior  mesenteric;  of  the  uterine, 
ovarian,  and  vesical  arteries  of  the  opposite  sides;  of  the  lateral  sacral  with  the  middle  sacral 
artery;  of  the  inferior  epigastric  with  the  internal  mammary,  inferior  intercostal,  and  lumbar 
arteries;  of  the  deep  iUac  circumflex  with  the  lumbar  arteries;  of  the  iliolumbar  with  the  last 
lumbar  artery;  of  the  obturator  artery,  by  means  of  its  pubic  branch,  with  the  vessel  of  the 
opposite  side  and  with  the  inferior  epigastric. 

The  Hypogastric  Artery  (A.  Hypogastrica;  Internal  Iliac  Artery)  (Fig.  539). 

The  hypogastric  artery  supplies  the  walls  and  viscera  of  the  pelvis,  the  buttock, 
the  generative  organs,  and  the  medial  side  of  the  thigh.  It  is  a  short,  thick  vessel, 
smaller  than  the  external  iliac,  and  about  4  cm.  in  length.  It  arises  at  the  bifur- 
cation of  the  common  iliac,  opposite  the  lumbosacral  articulation,  and,  passing 
downward  to  the  upper  margin  of  the  greater  sciatic  foramen,  divides  into  two 
large  trunks,  an  anterior  and  a  posterior. 

Relations. — It  is  in  relation  in  front  with  the  m-eter;  behind,  with  the  internal  ihac  vein,  the 
lumbosacral  trunk,  and  the  Piriformis  muscle;  laterally,  near  its  origin,  with  the  external  ihac 
vein,  which  lies  between  it  and  the  Psoas  major  muscle;  lower  down,  with  the  obturator  nerve. 

In  the  fetus,  the  hypogastric  artery  is  twice  as  large  as  the  external  iliac,  and  is 
the  direct  continuation  of  the  common  iliac.  It  ascends  along  the  side  of  the 
bladder,  and  runs  upward  on  the  back  of  the  anterior  wall  of  the  abdomen  to  the 
umbilicus,  converging  toward  its  fellow  of  the  opposite  side.    Having  passed  through 


i 


THE  HYPOGASTRIC  ARTEUY 


615 


the  umbilical  opening,  the  two  arteries,  now  termed  umbilical,  enter  the  umbiUcal 
cord,  where  they  are  coiled  around  the  umbilical  vein,  and  ultimately  ramify  in 
the  placenta. 

At  birth,  when  the  placental  circulation  ceases,  the  pelvic  portion  only  of  the 
artery  remains  patent  and  constitute  the  hypogastric  and  the  first  part  of  the 
superior  vesical  artery  of  the  adult;  the  remainder  of  the  vessel  is  converted  into 
a  solid  fibrous  cord,  the  lateral  umbilical  ligament  {obliterated  hypogastric  artery) 
which  extends  from  the  pelvis  to  the  umbilicus. 

Peculiarities  as  Regards  Length. — In  two-thirds  of  a  large  number  of  cases,  the  length  of  the 
hypogastric  varied  between  2.25  and  3.4  cm.;  in  the  remaining  third  it  was  more  frequently 
longer  than  shorter,  the  maximum  length  being  about  7  cm.  the  minimum  about  1  cm. 

The  lengths  of  the  common  iUac  and  hypogastric  arteries  bear  an  inverse  proportion  to  each 
other,  the  hypogastric  artery  being  long  when  the  common  iliac  is  short,  and  vice  versa. 

As  Regards  its  Place  of  Division. — The  place  of  division  of  the  hypogastric  varies  between 
the  upper  margin  of  the  sacrum  and  the  upper  border  of  the  greater  sciatic  foramen. 

The  right  and  left  hypogastric  arteries 'in  a  series  of  cases  often  diflfered  in  length,  but  neither 
seemed  constantly  to  exceed  the  other. 

Collateral  Circulation. — The  circulation  after  Ugature  of  the  hypogastric  artery  is  carried  on 
by  the  anastomoses  of  the  uterine  and  ovarian  arteries;  of  the  vesical  arteries  of  the  two  sides; 
of  the  hemorrhoidal  branches  of  the  hypogastric  with  those  from  the  inferior  mesenteric;  of  the 
obturator  artery,  by  means  of  its  pubic  branch,  with  the  vessel  of  the  opposite  side,  and  with  the 
inferior  epigastric  and  medial  femoral  circumflex;  of  the  circumflex  and  perforating  branches  of 
the  profunda  femoris  with  the  inferior  gluteal;  of  the  superior  gluteal  with  the  posterior  branches 
of  the  lateral  sacral  arteries;  of  the  iUolumbar  with  the  last  lumbar;  of  the  lateral  sacral  with  the 
middle  sacral;  and  of  the  ihac  circumflex  with  the  iUolumbar  and  superior  gluteal.^ 

Branches. — The  branches  of  the  hypogastric  artery  are: 


From  the  Posterior  Trunk. 
Iliolumbar. 
Lateral  Sacral. 
Superior  Gluteal. 


From  the  Anterior  Trunk. 
Superior  Vesical. 
Middle  Vesical. 
Inferior  Vesical. 
Middle  Hemorrhoidal. 
Obturator. 
Internal  Pudendal. 
Inferior  Gluteal. 

TT     •     1    [in  the  Female. 
Vagmal   j 

The  superior  vesical  artery  (a.  vesicalis  superior)  supplies  numerous  branches 
to  the  upper  part  of  the  bladder.  From  one  of  these  a  slender  vessel,  the  artery 
to  the  ductus  deferens,  takes  origin  and  accompanies  the  duct  in  its  course  to  the 
testis,  where  it  anastomoses  with  the  internal  spermatic  artery.  Other  branches 
supply  the  ureter.  The  first  part  of  the  superior  vesical  artery  represents  the 
terminal  section  of  the  pervious  portion  of  the  fetal  hypogastric  artery. 

The  middle  vesical  artery  (a.  vesicalis  mediali^),  usually  a  branch  of  the  superior, 
is  distributed  to  the  fundus  of  the  bladder  and  the  vesiculse  seminales. 

The  inferior  vesical  artery  (a.  vesicalis  inferior)  frequently  arises  in  common 
with  the  middle  hemorrhoidal,  and  is  distributed  to  the  fundus  of  the  bladder,  the 
prostate,  and  the  vesiculfe  seminales.  The  branches  to  the  prostate  communicate 
with  the  corresponding  vessels  of  the  opposite  side. 

The  middle  hemorrhoidal  artery  (a.  hcemorrhoidalis  media)  usually  arises  with 
the  preceding  vessel.  It  is  distributed  to  the  rectum,  anastomosing  with  the 
inferior  vesical  and  with  the  superior  and  inferior  hemorrhoidal  arteries.  It  gives 
offsets  to  the  vesiculse  seminales  and  prostate. 

The  uterine  artery  (a.  uierina)  (Fig.  540)  springs  from  the  anterior  division  of 

1  For  a  description  of  a  case  in  which  Owen  made  a  dissection  ten  years  after  ligature  of  the  hypogastric  artery, 
see  Med.-Chir.  Trans.,  vol.  rvi. 


616 


ANGIOLOGY 


the  hypogastric  and  runs  medialward  on  the  Levator  ani  and  toward  the  cervi 
uteri;  about  2  cm.  from  the  cervix  it  crosses  above  and  in  front  of  the  ureter,  to' 
which  it  suppHes  a  small  branch.  Reaching  the  side  of  the  uterus  it  ascends  in  a 
tortuous  manner  between  the  two  layers  of  the  broad  ligament  to  the  junction 
of  the  uterine  tube  and  uterus.  It  then  runs  lateralw^ard  toward  the  hilus  of  the 
ovary,  and  ends  by  joining  with  the  ovarian  artery.  It  supplies  branches  to  the 
cervix  uteri  and  others  which  descend  on  the  vagina;  the  latter  anastomose  with 
branches  of  the  vaginal  arteries  and  form  with  them  two  median  longitudinal 
vessels — the  azygos  arteries  of  the  vagina — one  of  which  runs  down  in  front  of 
and  the  other  behind  the  vagina.  It  supplies  numerous  branches  to  the  body  of  the 
uterus,  and  from  its  terminal  portion  twigs  are  distributed  to  the  uterine  tube  and 
the  round  ligament  of  the  uterus. 

The  vaginal  artery  (a.  vaginalis)  usually  corresponds  to  the  inferior  vesical  in 
the  male ;  it  descends  upon  the  vagina,  supplying  its  mucous  membrane,  and  sends 
branches  to  the  bulb  of  the  vestibule,  the  fundus  of  the  bladder,  and  the  contiguous 
part  of  the  rectum.  It  assists  in  forming  the  azygos  arteries  of  the  vagina,  and 
is  frequently  represented  by  two  or  three  branches. 


Branches  to  tvbe 


Branches  to  fundus 


Fig.  540. — The  arteries  of  the  internal  organs  of  generation  of  the  female,  seen  from  behind.     (After  Hyrtl.) 


The  obturator  artery  (a.  ohturatoria)  passes  forward  and  downward  on  the  lateral 
wall  of  the  pelvis,  to  the  upper  part  of  the  obturator  foramen,  and,  escaping  from 
the  pelvic  cavity  through  the  obturator  canal,  it  divides  into  an  anterior  and  a 
posterior  branch.  In  the  pelvic  cavity  this  vessel  is  in  relation,  laterally,  with  the 
obturator  fascia;  medially,  with  the  ureter,  ductus  deferens,  and  peritoneum; 
while  a  little  below  it  is  the  obturator  nerve. 

Branches. — Inside  the  pelvis  the  obturator  artery  gives  off  iliac  branches  to  the 
iliac  fossa,  which  supply  the  bone  and  the  Iliacus,  and  anastomose  with  the  ilio- 
lumbar artery;  a  vesical  branch,  which  runs  backward  to  supply  the  bladder;  and 
a  pubic  branch,  which  is  given  off  from  the  vessel  just  before  it  leaves  the  pelvic 
cavity.    The  pubic  branch  ascends  upon  the  back  of  the  pubis,  communicating 


THE  HYPOGASTRIC  ARTERY 


617 


ki 


with  the  corresponding  vessel  of  the  opposite  side,  and  with  the  inferior  epigastric 
artery. 

Outside  the  pelvis,  the  obturator  artery  divides  at  the  upper  margin  of  the  obtur- 
ator foramen,  into  an  anterior  and  a  posterior  branch  which  encircle  the  foramen 
under  cover  of  the  Obturator  externus. 

The  anterior  branch  runs  forward  on  the  outer  surface  of  the  obturator  mem- 
brane and  then  curves  downward  along  the  anterior  margin  of  the  foramen.  It 
distributes  branches  to  the  Obturator  externus,  Pectineus,  Adductores,  and  Gracilis, 
and  anastomoses  with  the  posterior  branch  and  with  the  medial  femoral  circum- 
flex artery. 

The  posterior  branch  follows  the  posterior  margin  of  the  foramen  and  turns  for- 
ward on  the  inferior  ramus  of  the  ischium,  where  it  anastomoses  with  the  anterior 
branch.  It  gives  twigs  to  the  muscles  attached  to  the  ischial  tuberosity  and  anas- 
tomoses with  the  inferior  gluteal.  It  also  supplies  an  articular  branch  which 
enters  the  hip-joint  through  the  acetabular  notch,  ramifies  in  the  fat  at  the  bottom 
of  the  acetabulum*  and  sends  a  twig  along  the  ligamentum  teres  to  the  head  of  the 
femur. 

Peculiarities. — The  obturator  artery  sometimes  arises  from  the  main  stem  or  from  the  posterior 
trunk  of  the  hypogastric,  or  it  may  spring  from  the  superior  gluteal  artery;  occasionally  it  arises 
from  the  external  iUac.  In  about  two  out  of  every  seven  cases  it  springs  from  the  inferior  epi- 
gastric and  descends  almost  vertically  to  the  upper  part  of  the  obturator  foramen.  The  artery 
in  this  course  usually  lies  in  contact  with  the  external  iUac  vein,  and  on  the  lateral  side  of  the 
femoral  ring  (Fig.  541^1) ;  in  such  cases  it  would  not  be  endangered  in  the  operation  for  strangulated 
femoral  hernia.  Occasionally,  however,  it  curves  along  the  free  margin  of  the  lacunar  ligament 
(Fig.  541 JB),  and  if  in  such  circumstances  a  femoral  hernia  occurred,  the  vessel  would  almost 
completely  encircle  the  neck  of  the  hernial  sac,  and  would  be  in  great  danger  of  being  wounded 
if  an  operation  were  performed  for  strangulation. 


II 


Fig.  541. — Variations  in  origin  and  course  of  obturator  artery. 

The  internal  pudendal  artery  (a.  pudenda  interna;  internal  pudic  artery)  is  the 
smaller  of  the  two  terminal  branches  of  the  anterior  trunk  of  the  hypogastric,  and 
supplies  the  external  organs  of  generation.  Though  the  course  of  the  artery  is 
the  same  in  the  two  sexes,  the  vessel  is  smaller  in  the  female  than  in  the  male,  and 
the  distribution  of  its  branches  somewhat  different.  The  description  of  its  arrange- 
ment in  the  male  will  first  be  given,  and  subsequently  the  differences  which  it 
presents  in  the  female  will  be  mentioned. 

The  internal  pudendal  artery  in  the  male  passes  downward  and  outward  to  the 
lower  border  of  the  greater  sciatic  foramen,  and  emerges  from  the  pelvis  between 
the  Piriformis  and  Coccygeus;  it  then  crosses  the  ischial  spine,  and  enters  the  peri- 
neum through  the  lesser  sciatic  foramen.  The  artery  now  crosses  the  Obturator 
internus,  along  the  lateral  wall  of  the  ischiorectal  fossa ,  being  situated  about  4  cm. 
above  the  lower  margin  of  the  ischial  tuberosity.  It  gradually  approaches  the 
margin  of  the  inferior  ramus  of  the  ischium  and  passes  forward  between  the  two 
layers  of  the  fascia  of  the  urogenital  diaphragm;  it  then  runs  forward  along  the 
medial  margin  of  the  inferior  ramus  of  the  pubis,  and  about  1.25  cm.  behind  the 
pubic  arcuate  ligament  it  pierces  the  inferior  fascia  of  the  urogenital  diaphragm 
and  divides  into  the  dorsal  and  deep  arteries  of  the  penis. 


618 


ANGIOLOGY 


Relations. — Within  the  pelvis,  it  lies  in  front  of  the  Piriformis  muscle,  the  sacral  plexus  of 
nerves,  and  the  inferior  gluteal  artery.  As  it  crosses  the  ischial  spine,  it  is  covered  by  the  Gluta^us 
maximus  and  overlapped  by  the  sacrotuberous  ligament.  Here  the  pudendal  nerve  lies  to  the 
medial  side  and  the  nerve  to  the  Obturator  internus  to  the  lateral  side  of  the  vessel.  In  the  peri- 
neum it  lies  on  the  lateral  waU  of  the  ischiorectal  fossa,  in  a  canal  (Alcock's  canal)  formed  by  the 
splitting  of  the  obturator  fascia.  It  is  accompanied  by  a  pair  of  vense  comitantes  and  the  pudendal 
nerve. 

Peculiarities. — The  internal  pudendal  artery  is  sometimes  smaller  than  usual,  or  fails  to  give 
off  one  or  two  of  its  usual  branches;  in  such  cases  the  deficiency  is  supplied  by  branches  derived 
from  an  additional  vessel,  the,  accessory  pudendal,  which  generally  arises  from  the  internal 
pudendal  artery  before  its  exit  from  the  greater  sciatic  foramen.  It  passes  forward  along  the 
lower  part  of  the  bladder  and  across  the  side  of  the  prostate  to  the  root  of  the  penis,  where  it 
perforates  the  urogenital  diaphragm,  and  gives  off  the  branches  usually  derived  from  the  internal 
pudendal  artery.  The  deficiency  most  frequently  met  with  is  that  in  which  the  internal  pudendal 
ends  as  the  artery  of  the  urethral  bulb,  the  dorsal  and  deep  arteries  of  the  penis  being  derived 
from  the  accessory  pudendal.  The  internal  pudendal  artery  may  also  end  as  the  perineal,  the 
artery  of  the  urethral  bulb  being  derived,  with  the  other  two  branches,  from  the  accessory  vessel. 
Occasionally  the  accessory  pudendal  artery  is  derived  from  one  of  the  other  branches  of  the 
hypogastric  artery,  most  frequently  the  inferior  vesical  or  the  obturator. 

Branches. — ^The  branches  of  the  internal  pudendal  artery  (Figs.  542,  54.3)  are: 


Muscular. 

Inferior  Hemorrhoidal. 

Perineal. 


Dorsal  Artery  of  the  Penis. 


Artery  of  the  Urethral  Bulb. 

Urethral. 

Deep  Artery  of  the  Penis. 


Posterior  scrotal  arteries 
Posterior  scrotal  iierves 

Pudendal  nerve 
Internal  pudendal  artery 


Fig.  542. — The  superficial  branches  of  the  internal  pudendal  artery. 


«l 


The  Muscular  Branches  consist  of  two  sets:  one  given  off  in  the  pelvis;  the  other, 
as  the  vessel  crosses  the  ischial  spine.  The  former  consists  of  several  small  ofi'sets 
which  supply  the  Levator  ani,  the  Obturator  internus,  the  Piriformis,  and  the 
Coccygeus.  The  branches  given  off  outside  the  pelvis  are  distributed  to  the 
adjacent  parts  of  the  Glutjeus  maximus  and  external  rotator  muscles.  They 
anastomose  with  branches  of  the  inferior  gluteal  artery. 


THE  HYPOGASTRIC  ARTERY 


619 


The  Inferior  Hemorrhoidal  Artery    (a.  hwmorrhoidalis  inferior)   arises  from  the 

■•internal  pudendal  as  it  passes  above  the  ischial  tuberosity.  Piercing  the  wall 
lof  Alcock's  canal  it  divides  into  two  or  three  branches  which  cross  the  ischiorectal 
fossa,  and  are  distributed  to  the  muscles  and  integument  of  the  anal  region,  and 
send  offshoots  around  the  lower  edge  of  the  Glutseus  maximus  to  the  skin  of  the 
buttock.  They  anastomose  with  the  corresponding  vessels  of  the  opposite  side,  with 
the  superior  and  middle  hemorrhoidal,  and  with  the  perineal  artery. 

The  Perineal  Artery  (a.  perinei;  superficial  perineal  artery)  arises  from  the  internal 
pudendal,  in  front  of  the  preceding  branches,  and  turns  upward,  crossing  either 
over  or  under  the  Transversus  perinsei  superficialis,  and  runs  forward,  parallel 
Hko  the  pubic  arch,  in  the  interspace  between  the  Bulbocavernosus  and  Ischiocaver- 
niosus,  both  of  which  it  supplies,  and  finally  divides  into  several  posterior  scrotal 
branches  which  are  distributed  to  the  skin  and  dartos  tunic  of  the  scrotum.  As 
it  crosses  the  Transversus  perina?i  superficialis  it  gives  off  the  transverse  perineal 

■  artery  which  runs  transversely  on  the  cutaneous  surface  of  the  muscle,  and  anasto- 
hjioses  with  the  corresponding  vessel  of  the  opposite  side  and  with  the  perineal 
^nd  inferior  hemorrhoidal  arteries.     It  supplies  the  Transversus  perinsei  super- 
ficialis and  the  structures  between  the  anus  and  the  urethral  bulb. 


Deep  artei-y  of  penis 
Dorsal  artery  of  penis 


Artery  of  urethral  hxdb 

Internal  pudendal  artery 

Bulbo-urethral  gland 


Fia.  543. — The  deeper  branches  of  the  internal  pudendal  artery. 

The  Artery  of  the  Urethral  Bulb  (a.  hulhi  urethrce)  is  a  short  vessel  of  large  caliber 
which  arises  from  the  internal  pudendal  between  the  two  layers  of  fascia  of  the  uro- 
genital diaphragm;  it  passes  medialward,  pierces  the  inferior  fascia  of  the  urogenital 
diaphragm,  and  gives  off  branches  which  ramify  in  the  bulb  of  the  urethra  and  in 
the  posterior  part  of  the  corpus  cavernosum  urethrse.  It  gives  oft'  a  small  branch 
to  the  bulbo-urethral  gland. 

The  Urethral  Artery  (a.  urethralis)  arises  a  short  distance  in  front  of  the  artery 
of  the  urethral  bulb.  It  runs  forward  and  medialward,  pierces  the  inferior  fascia 
of  the  urogenital  diaphragm  and  enters  the  corpus  cavernosum  urethrse,  in  which 


620  ^^^^^^       ANGIOLOGY 

The  Deep  Artery  of  the  Penis  (a.  profunda  penis;  artery  to  the  corpus  cavernosum), 
one  of  the  terminal  branches  of  the  internal  pudendal,  arises  from  that  vessel 
while  it  is  situated  between  the  two  fascise  of  the  urogenital  diaphragm;  it 
pierces  the  inferior  fascia,  and,  entering  the  crus  penis  obliquely,  runs  forward 
in  the  center  of  the  corpus  cavernosum  penis,  to  which  its  branches  are  distributed. 

The  Dorsal  Artery  of  the  Penis  (a.  dorsalis  penis)  ascends  between  the  crus  penis 
and  the  pubic  symphysis,  and,  piercing  the  inferior  fascia  of  the  urogenital  dia- 
phragm, passes  between  the  two  layers  of  the  suspensory  ligament  of  the  penis, 
and  runs  forward  on  the  dorsum  of  the  penis  to  the  glans,  where  it  divides  into  two 
branches,  which  supply  the  glans  and  prepuce.  On  the  penis,  it  lies  between  the 
dorsal  nerve  and  deep  dorsal  vein,  the  former  being  on  its  lateral  side.  It  supplies 
the  integument  and  fibrous  sheath  of  the  corpus  cavernosum  penis,  sending  branches 
through  the  sheath  to  anastomose  with  the  preceding  vessel. 

The  internal  pudendal  artery  in  the  female  is  smaller  than  in  the  male.  Its  origin 
and  course  are  similar,  and  there  is  considerable  analogy  in  the  distribution  of  its 
branches.  The  perineal  artery  supplies  the  labia  pudendi;  the  artery  of  the  bulb 
supplies  the  bulbus  vestibuli  and  the  erectile  tissue  of  the  vagina;  the  deep  artery 
of  the  clitoris  supplies  the  corpus  cavernosum  clitoridis;  and  the  dorsal  artery  of 
the  clitoris  supplies  the  dorsum  of  that  organ,  and  ends  in  the  glans  and  prepuce 
of  the  clitoris. 

The  inferior  gluteal  artery  (a.  glutoea  inferior;  sciatic  artery)  (Fig.  544),  the 
larger  of  the  two  terminal  branches  of  the  anterior  trunk  of  the  hypogastric,  is 
distributed  chiefly  to  the  buttock  and  back  of  the  thigh.  It  passes  down  on  the 
sacral  plexus  of  nerves  and  the  Piriformis,  behind  the  internal  pudendal  artery, 
to  the  lower  part  of  the  greater  sciatic  foramen,  through  which  it  escapes  from  the 
pelvis  between  the  Piriformis  and  Coccygeus.  It  then  descends  in  the  interval 
between  the  greater  trochanter  of  the  femur  and  tuberosity  of  the  ischium,  accom- 
panied by  the  sciatic  and  posterior  femoral  cutaneous  nerves,  and  covered  by  the 
Gluteus  maximus,  and  is  continued  down  the  back  of  the  thigh,  supplying  the 
skin,  and  anastomosing  with  branches  of  the  perforating  arteries. 

Inside  the  pelvis  it  distributes  branches  to  the  Piriformis,  Coccygeus,  and  Levator 
ani;  some  branches  which  supply  the  fat  around  the  rectum,  and  occasionally 
take  the  place  of  the  middle  hemorrhoidal  artery;  and  vesical  branches  to  the 
fundus  of  the  bladder,  vesiculse  seminales,  and  prostate.  Outside  the  pelvis  it  gives 
off  the  following  branches: 

Muscular.  Anastomotic. 

Coccygeal.  Articular. 

Comitans  Nervi  Ischiadici.  Cutaneous. 

The  Muscular  Branches  supply  the  Glutseus  maximus,  anastomosing  with  the 
superior  gluteal  artery  in  the  substance  of  the  muscle;  the  external  rotators, 
anastomosing  with  the  internal  pudendal  artery;  and  the  muscles  attached  to 
the  tuberosity  of  the  ischium,  anastomosing  with  the  posterior  branch  of  the 
obturator  and  the  medial  femoral  circumflex  arteries. 

The  Coccygeal  Branches  run  medialward,  pierce  the  sacrotuberous  ligament,  and 
supply  the  Glutseus  maximus,  the  integument,  and  other  structures  on  the  back 
of  the  coccyx. 

The  Arteria  Comitans  Nervi  Ischiadici  is  a  long,  slender  vessel,  which  accom- 
panies the  sciatic  nerve  for  a  short  distance ;  it  then  penetrates  it,  and  runs  in  its 
substance  to  the  lower  part  of  the  thigh. 

The  Anastomotic  is  directed  downward  across  the  external  rotators,  and  assists 
in  forming  the  so-called  crucial  anastomosis  by  joining  with  the  first  perforating 
and  medial  and  lateral  femoral  circumflex  arteries. 

The  Articular  Branch,  generally  derived  from  the  anastomotic,  is  distributed  to 
the  capsule  of  the  hip-joint. 


THE  HYPOGASTRIC  ARTERY 


621 


The  Cutaneous  Branches  are  distributed  to  the  skin  of  the  buttock  and  back  of 
I  the  thigh. 

The  iliolumbar  artery  (a.  iliolumhalis)  a  branch  of  the  posterior  trunk  of  the 
hypogastric,  turns  upward  behind  the  obturator  nerve  and  the  external  iliac  vessels, 
to  the  medial  border  of  the  Psoas  major,  behind  which  it  divides  into  a  lumbar  and 
an  iliac  branch. 

The  Lumbar  Branch  {ramus  lumhalis)  supplies  the  Psoas  major  and  Quadratus 
lumborum,  anastomoses  with  the  last  lumbar  artery,  and  sends  a  small  spinal 
branch  through  the  intervertebral 
foramen  between  the  last  lumbar 
vertebra  and  the  sacrum,  into  the 
vertebral  canal,  to  supply  the 
Cauda  equina. 

The  Iliac  Branch  {ramus  iliacus) 
descends  to  supply  the  Iliacus; 
some  offsets,  running  between  the 
muscle  and  the  bone,  anastomose 
with  the  iliac  branches  of  the  ob- 
turator; one  of  these  enters  an 
oblique  canal  to  supply  the  bone, 
while  others  run  along  the  crest  of 
the  ilium,  distributing  branches  to 
the  gluteal  and  abdominal  muscles, 
and  anastomosing  in  their  course 
with  the  superior  gluteal,  iliac 
circumflex,  and  lateral  femoral 
circumflex  arteries. 

The  lateral  sacral  arteries  {aa. 
sacrales  laterales)  (Fig.  539)  arise 
from  the  posterior  division  of  the 
hypogastric;  there  are  usually  two, 
a  superior  and  an  inferior. 

The  superior,  of  large  size,  passes 
medialward,  and,  after  anastomos- 
ing with  branches  from  the  middle 
sacral,  enters  the  first  or  second 
anterior  sacral  foramen,  supplies 
branches  to  the  contents  of  the 
sacral  canal,  and,  escaping  by  the 
corresponding  posterior  sacral  fora- 
men, is  distributed  to  the  skin  and 
muscles  on  the  dorsum  of  the 
sacrum,  anastomosing  with  the 
superior  gluteal. 

The  inferior  runs  obliquely  across 
the  front  of  the  Piriformis  and  the 
sacral  nerves  to  the  medial  side  of 
t  the  anterior  sacral  foramina,  de- 
f  scends  on  the  front  of  the  sacrum, 
and  anastomoses  over  the  coccyx 
with  the  middle  sacral  and  opposite 
■  lateral  sacral  artery.    In  its  course  it  gives  off  branches,  which  enter  the  anterior 
sacral  foramina;  these,  after  supplying  the  contents  of  the  sacral  canal,  escapes 
by  the  posterior  sacral  foramina,  and  are  distributed  to  the  muscles  and  skin  on 
the  dorsal  surface  of  the  sacrum,  anastomosing  with  the  gluteal  arteries. 


Termination  oj 

medial  femoral 

circumflex 


First 

perforating 


Lateral 
superior 
genicular 


Fig.  544. 


Second 

perforating 

' Third 

perforating 


Termination 
of  profunda 


Superior  muscular 


Medial  superior  genicvlaT 


—  Sural 


-The  arteries  of  the  gluteal  and  posterior 
femoral  regions. 


i 


ANGIOLOGY 

The  superior  gluteal  artery  (a.  glutwa  superior;  gluteal  artery)  (Fig.  544)  is  the 
largest  branch  of  the  hypogastric,  and  appears  to  be  the  continuation  of  the  pos- 
terior division  of  that  vessel.  It  is  a  short  artery  which  runs  backward  between 
the  lumbosacral  trunk  and  the  first  sacral  nerve,  and,  passing  out  of  the  pelvis 
above  the  upper  border  of  the  Piriformis,  immediately  divides  into  a  superficial 
and  a  deep  branch.  Within  the  pelvis  it  gives  off  a  few  branches  to  the  Iliacus, 
Piriformis,  and  Obturator  internus,  and  just  previous  to  quitting  that  cavity,  a 
nutrient  artery  which  enters  the  ilium. 

The  superficial  branch  enters  the  deep  surface  of  the  Glutteus  maximus,  and 
divides  into  numerous  branches,  some  of  which  supply  the  muscle  and  anastomose 
with  the  inferior  gluteal,  while  others  perforate  its  tendinous  origin,  and  supply 
the  integument  covering  the  posterior  surface  of  the  sacrum,  anastomosing  with 
the  posterior  branches  of  the  lateral  sacral  arteries. 

The  deep  branch  lies  under  the  Gluta^us  medius  and  almost  immediately  sub- 
divides into  two.  Of  these,  the  superior  division,  continuing  the  original  course 
of  the  vessel,  passes  along  the  upper  border  of  the  Gluteus  minimus  to  the  anterior 
superior  spine  of  the  ilium,  anastomosing  with  the  deep  iliac  circumflex  artery  and 
the  ascending  branch  of  the  lateral  femoral  circumflex  artery.  The  inferior  division 
crosses  the  Glutseus  minimus  obliquely  to  the  greater  trochanter,  distributing 
branches  to  the  Glutsei  and  anastomoses  with  the  lateral  femoral  circumflex  artery. 
Some  branches  pierce  the  Gluta^us  minimus  and  supply  the  hip-joint. 

The  External  Hiac  Artery  (A.  Iliaca  Externa)  (Fig.  539). 

The  external  iliac  artery  is  larger  than  the  hypogastric,  and  passes  obliquely 
downward  and  lateralward  along  the  medial  border  of  the  Psoas  major,  from  the 
bifurcation  of  the  common  iliac  to  a  point  beneath  the  inguinal  ligament,  midway 
between  the  anterior  superior  spine  of  the  ilium  and  the  symphysis  pubis,  where 
it  enters  the  thigh  and  becomes  the  femoral  artery. 

Relations. — In  front  and  medially,  the  artery  is  in  relation  with  the  peritoneum,  subperitoneal 
areolar  tissue,  the  termination  of  the  ileum  and  frequently  the  vermiform  process  on  the  right 
side,  and  the  sigmoid  colon  on  the  left,  and  a  thin  layer  of  fascia,  derived  from  the  ihac  fascia, 
which  surrounds  the  artery  and  vein.  At  its  origin  it  is  crossed  by  the  ovarian  vessels  in  the 
female,  and  occasionally  by  the  ureter.  The  internal  spermatic  vessels  lie  for  some  distance 
upon  it  near  its  termination,  and  it  is  crossed  in  this  situation  by  the  external  spermatic  branch 
of  the  genitofemoral  nerve  and  the  deep  iliac  circumflex  vein;  the  ductus  deferens  in  the  male, 
and  the  round  ligament  of  the  uterus  in  the  female,  curve  down  across  its  medial  side.  Behind, 
it  is  in  relation  with  the  medial  border  of  the  Psoas  major,  from  which  it  is  separated  by  the 
iliac  fascia.  At  the  upper  part  of  its  course,  the  external  ihac  vein  lies  partly  behind  it,  but  lower 
down  hes  entirely  to  its  medial  side.  Laterally,  it  rests  against  the  Psoas  major,  from  which  it 
is  separated  by  the  iliac  fascia.  Nimaerous  lymphatic  vessels  and  lymph  glands  lie  on  the  front 
and  on  the  medial  side  of  the  vessel. 

Collateral  Circulation. — The  principal  anastomoses  in  carrying  on  the  collateral  circulation, 
after  the  application  of  a  ligature  to  the  external  iliac,  are:  the  iholumbar  with  the  iliac  circum- 
flex; the  superior  gluteal  with  the  lateral  femoral  circumflex;  the  obturator  with  the  medial  femoral 
circumflex;  the  inferior  gluteal  with  the  first  perforating  and  circumflex  branches  of  the  profunda 
artery;  and  the  internal  pudendal  with  the  external  pudendal.  When  the  obturator  arises  from 
the  inferior  epigastric,  it  is  supplied  with  blood  by  branches,  from  either  the  hypogastric,  the 
lateral  sacral,  or  the  internal  pudendal.  The  inferior  epigastric  receives  its  supply  from  the 
internal  mammary  and  lower  intercogtal  arteries,  and  from  the  hypogastric  by  the  anastomoses 
of  its  branches  with  the  obturator.^ 

Branches. — Besides  several  small  branches  to  the  Psoas  major  and  the  neighbor- 
ing lymph  glands,  the  external  iliac  gives  off  two  branches  of  considerable  size: 

Inferior  Epigastric.  Deep  Iliac  Circumflex. 

'  Sir  Astley  Cooper  describes  in  Guy '5  Hospital  Reports,  vol.  i,  the  dissection  of  a  limb  eighteen  years  after  successful 
ligature  of  the  external  iliac  artery. 


»l 


I 

I 


THE  FEMORAL  ARTERY 

The  inferior  epigastric  artery  (a.  epigaMrica  inferior;  deep  epigastric  artery) 
(Fig.  547)  arises  from  the  external  iliac,  immediately  above  the  inguinal  ligament. 
It  curves  forward  in  the  subperitoneal  tissue,  and  then  ascends  obliquely  along 
the  medial  margin  of  the  abdominal  inguinal  ring;  continuing  its  course  upward, 
it  pierces  the  transversalis  fascia,  and,  passing  in  front  of  the  linea  semicircularis, 
ascends  between  the  Rectus  abdominis  and  the  posterior  lamella  of  its  sheath. 
It  finally  divides  into  numerous  branches,  which  anastomose,  above  the  umbilicus, 
with  the  superior  epigastric  branch  of  the  internal  mammary  and  with  the  lower 
intercostal  arteries  (Fig.  522).  As  the  inferior  epigastric  artery  passes  obliquely 
upward  from  its  origin  it  lies  along  the  lower  and  medial  margins  of  the  abdominal 
inguinal  ring,  and  behind  the  commencement  of  the  spermatic  cord.  The  ductus 
deferens,  as  it  leaves  the  spermatic  cord  in  the  male,  and  the  round  ligament  of  the 
uterus  in  the  female,  winds  around  the  lateral  and  posterior  aspects  of  the  artery. 

Branches.^ — The  branches  of  the  vessel  are :  the  external  spermatic  artery  {cremasteric 
artery),  which  accompanies  the  spermatic  cord,  and  supplies  the  Cremaster  and 
other  coverings  of  the  cord,  anastomosing  with  the  internal  spermatic  artery  (in 
the  female  it  is  very  small  and  accompanies  the  round  ligament);  a  pubic  branch 
which  runs  along  the  inguinal  ligament,  and  then  descends  along  the  medial  margin 
of  the  femoral  ring  to  the  back  of  the  pubis,  and  there  anastomoses  w^ith  the  pubic 
branch  of  the  obturator  artery ;  muscular  branches,  some  of  which  are  distributed  to 
the  abdominal  muscles  and  peritoneum,  anastomosing  with  the  iliac  circumflex 
and  lumbar  arteries;  branches  which  perforate  the  tendon  of  the  Obliquus 
externus,  and  supply  the  integument,  anastomosing  with  branches  of  the  super- 
ficial epigastric. 

Peculiarities. — The  origin  of  the  inferior  epigastric  may  take  place  from  any  part  of  the  external 
iHac  between  the  inguinal  ligament  and  a  point  6  cm.  above  it;  or  it  may  arise  below  this  ligament, 
from  the  femoral.  It  frequently  springs  from  the  external  iliac,  by  a  common  trunk  with  the 
obturator.  Sometimes  it  arises  from  the  obturator,  the  latter  vessel  being  furnished  by  the 
hypogastric,  or  it  may  be  formed  of  two  branches,  one  derived  from  tho  external  iUac,  the  other 
from  the  hypogastric. 

The  deep  iliac  circumflex  artery  (a.  circumflexa  ilium  profunda)  arises  from  the 
lateral  aspect  of  the  external  iliac  nearly  opposite  the  inferior  epigastric  artery. 
It  ascends  obliquely  lateralward  behind  the  inguinal  ligament,  contained  in  a 
fibrous  sheath  formed  by  the  junction  of  the  transversalis  fascia  and  iliac  fascia, 
to  the  anterior  superior  iliac  spine,  where  it  anastomoses  with  the  ascending  branch 
of  the  lateral  femoral  circumflex  artery.  It  then  pierces  the  transversalis  fascia 
and  passes  along  the  inner  lip  of  the  crest  of  the  ilium  to  about  its  middle,  where 
it  perforates  the  Transversus,  and  runs  backward  between  that  muscle  and  the 
Obliquus  internus,  to  anastomose  with  the  iliolumbar  and  superior  gluteal  arteries. 
Opposite  the  anterior  superior  spine  of  the  ilium  it  gives  off  a  large  branch,  which 
ascends  between  the  Obliquus  internus  and  Transversus  muscles,  supplying  them, 
and  anastomosing  with  the  lumbar  and  inferior  epigastric  arteries. 

THE  ARTERIES   OF  THE  LOWER  EXTREMITY. 

The  artery  which  supplies  the  greater  part  of  the  lower  extremity  is  the  direct 
continuation  of  the  external  iliac.  It  runs  as  a  single  trunk  from  the  inguinal 
ligament  to  the  lower  border  of  the  Popliteus,  where  it  divides  into  two  branches, 
the  anterior  and  posterior  tibial.  The  upper  part  of  the  main  trunk  is  named  the 
femoral,  the  lower  part  the  popliteal. 

THE  FEMORAL  ARTERY  (A.   FEMORALIS)   (Figs.  549,  550). 

The  femoral  artery  begins  immediately  behind  the  inguinal  ligament,  midway 
between  the  anterior  superior  spine  of  the  ilium  and  the  symphysis  pubis,  and 


ANGIOLOGY 


Fro.  545. — Femoral  sheath  laid  open  to  show  its  three  compartments. 


Lat.fem.  cutan.  nerve 


Femoral  nerve 

Lumho-inguinal  nerve 
i  Femoral  artery 

I  Femoral  sheath 
J    I  Femoral  vein 
C>'l   I     Femoral  ring 
W^^K^/^^^jL^  Lacunar  ligament 


Fia.  546. — Structures  passing  behind  the  inguinal  ligament. 


THE  FEMORAL  ARTERY 


625 


passes  down  the  front  and  medial  side  of  the  thigh.  It  ends  at  the  junction  of  the 
middle  with  the  lower  third  of  the  thigh,  where  it  passes  through  an  opening  in 
the  Adductor  magnus  to  become  the  popliteal  artery.  The  vessel,  at  the  upper  part 
of  the  thigh,  lies  in  front  of  the  hip-joint;  in  the  lower  part  of  its  course  it  lies  to 
the  medial  side  of  the  body  of  the  femur,  and  between  these  two  parts,  where  it 
crosses  the  angle  between  the  head  and  body,  the  vessel  is  some  distance  from  the 
bone.  The  first  4  cm.  of  the  vessel  is  enclosed,  together  with  the  femoral  vein, 
in  a  fibrous  sheath — the  femoral  sheath.  In  the  upper  third  of  the  thigh  the  femoral 
artery  is  contained  in  the  femoral  triangle  {Scarpa's  triangle),  and  in  the  middle 
third  of  the  thigh,  in  the  adductor  canal  (Hunter's  canal). 

The  femoral  sheath  (crural  sheath)  (Figs.  545,  546)  is  formed  by  a  prolongation 
downward,  behind  the  inguinal  ligament,  of  the  fasciae  which  line  the  abdomen, 
the  transversalis  fascia  being  continued  down  in  front  of  the  femoral  vessels  and 
the  iliac  fascia  behind  them.  The  sheath  assumes  the  form  of  a  short  funnel,  the 
wide  end  of  which  is  directed  upward,  while  the  lower,  narrow  end  fuses  with  the 


Fia.  547. — The  relations  of  the  femoral  and  abdominal  inguinal  rings,  seen  from  within  the  abdomen.     Right  side. 

fascial  investment  of  the  vessels,  about  4  cm.  below  the  inguinal  ligament.  It  is 
strengthened  in  front  by  a  band  termed  the  deep  crural  arch  (page  419) .  The  lateral 
wall  of  the  sheath  is  vertical  and  is  perforated  by  the  lumboinguinal  nerve;  the 
medial  wall  is  directed  obliquely  downward  and  lateralward,  and  is  pierced  by  the 
great  saphenous  vein  and  by  some  lymphatic  vessels.  The  sheath  is  divided  by 
two  vertical  partitions  which  stretch  between  its  anterior  and  posterior  walls. 
The  lateral  compartment  contains  the  femoral  artery,  and  the  intermediate  the 
femoral  vein,  while  the  medial  and  smallest  compartment  is  named  the  femoral 
canal,  and  contains  some  lymphatic  vessels  and  a  lymph  gland  imbedded  in  a  small 
amount  of  areolar  tissue.  The  femoral  canal  is  conical  and  measures  about  1.25 
cm.  in  length.  Its  base,  directed  upward  and  named  the  femoral  ring,  is  oval  in 
form,  its  long  diameter  being  directed  transversely  and  measuring  about  1.25  cm. 
The  femoral  ring  (Figs.  546,  547)  is  bounded  in  front  by  the  inguinal  ligament, 
behind  by  the  Pectineus  covered  by  the  pectineal  fascia,  medially  by  the  crescentic 
base  of  the  lacunar  ligament,  and  laterally  by  the  fibrous  septum  on  the  medial 
side  of  the  femoral  vein.  The  spermatic  cord  in  the  male  and  the  round  ligament 
40 


626 


ANGIOLOGY 


of  the  uterus  in  the  female  lie  immediately  above  the  anterior  margin  of  the  ring, 
while  the  inferior  epigastric  vessels  are  close  to  its  upper  and  lateral  angle.  The 
femoral  ring  is  closed  by  a  somewhat  condensed  portion  of  the  extraperitoneal 
fatty  tissue,  named  the  septum  femorale  (crural  septum),  the  abdominal  surface 
of  which  supports  a  small  lymph  gland  and  is  covered  by  the  parietal  layer  of  the 
peritoneum.  The  septum  femorale  is  pierced  by  numerous  lymphatic  vessels 
passing  from  the  deep  inguinal  to  the  external  iliac  lymph  glands,  and  the  parietal 
peritoneum  immediately  above  it  presents  a  slight  depression  named  the  femoral 
fossa. 


SUPERFICIAL 
EPIGASTRIC 

SUPERFICIAL  CIR- 
CUMFLEX ILIAC 

COMMON 
FEMORAL' 


EXTERNA 
CIRCUMFLEX 

DESCENDING 
RAMUS  OF 
EXTERNAL 

CIRCUMFLEX 


SUPERIOR  EXTER- 
NAL ARTICULAR 
BRANCH  OF 
POPLITEAL 


SUPERFICIAL 

EXTERNAL 

PUOIC 

DEEP 
^1     EXTERNAL 
PUDIC 
INTERNAL 
CIRCUMFLEX 


ANASTOMOTICA 
MAGNA 


SUPERIOR    INTERNAL 
ARTICULAR 
—  BRANCH   OF 
POPLITEAL 


Fig.  548. — Scheme  of  the  femoral  artery.     (Poirier  and  Charpy.) 


The  femoral  triangle  {trigonum  femorale;  Scarpa's  triangle)  (Fig.  549)  corre- 
sponds to  the  depression  seen  immediately  below  the  fold  of  the  groin.  Its  apex 
is  directed  downward,  and  the  sides  are  formed  laterally  by  the  medial  margin 
of  the  Sartorius,  medially  by  the  medial  margin  of  the  Adductor  longus,  and  above 
by  the  inguinal  ligament.  The  floor  of  the  space  is  formed  from  its  lateral  to  its 
medial  side  by  the  Iliacus,  Psoas  major,  Pectineus,  in  some  cases  a  small  part  of 


THE  FEMORAL  ARTERY 


627 


I  the  Adductor  brevis,  and  the  Adductor  longus;  and  it  is  divided  into  two  nearly 
equal  parts  by  the  femoral  vessels,  which  extend  from  near  the  middle  of  its  base 
to  its  apex:  the  arterj^  giving  off  in  this  situation  its  superficial  and  profunda 
branches,  the  vein  receiving  the  deep  femoral  and  great  saphenous  tributaries. 
On  the  lateral  side  of  the  femoral  artery  is  the  femoral  nerve  dividing  into  its 
branches.     Besides    the    vessels   and  nerves,  this  space  contains  some  fat  and 

■  lymphatics. 
I  The  adductor  canal  {canalis  adductorius;  Hunter's  canal)  is  an  aponeurotic 
tunnel  in  the  middle  third  of  the  thigh,  extending  from  the  apex  of  the  femoral 
triangle  to  the  opening  in  the  Adductor  magnus.  It  is  bounded,  in  front  and  later- 
ally, by  the  Vastus  medialis;  behind  by  the  Adductores  longus  and  magnus;  and 
is  covered  in  by  a  strong  aponeurosis  which  extends  from  the  Vastus  medialis, 
across  the  femoral  vessels  to  the  Adductores  longus  and  magnus;  lying  on  the 
aponeurosis  is  the  Sartorius  muscle.  The  canal  contains  the  femoral  artery  and 
vein,  the  saphenous  nerve,  and  the  nerve  to  the  Vastus  medialis. 

Superficial  iliac  circumflex  ve 
Femoral  nerve 
Superficial  epigastric  vessels 

Superficial  external  pudendal  vessels 
Deep  external  pudendal  vessels 


Great  sapJiencnut  vein 

Fig.  549. — The  left  femoral  triangle. 


I  Relations  of  the  Femoral  Artery. — In  the  femoral  triangle  (Fig.  549)  the  artery  is  superficial. 
In  front  of  it  are  the  skin  and  superficial  fascia,  the  superficial  subinguinal  lymph  glands,  the 
superficial  iliac  circumflex  vein,  the  superficial  layer  of  the  fascia  lata  and  the  anterior  part  of 
the  femoral  sheath.  The  lumboinguinal  nerve  courses  for  a  short  distance  within  the  lateral 
compartment  of  the  femoral  sheath,  and  lies  at  first  in  front  and  then  lateral  to  the  artery.  Near 
the  apex  of  the  femoral  triangle  the  medial  branch  of  the  anterior  femoral  cutaneous  nerve 
crosses  the  artery  from  its  lateral  to  its  medial  side. 


I 


628 


ANGIOLOGY 


Behind  the  artery  are  the  posterior  part  of  the  femoral  sheath,  the  pectineal  fascia,  the  medial 
part  of  the  tendon  of  the  Psoas  major,  the  Pectineus  and  the  Adductor  longus.  The  artery  is 
separated  from  the  capsule  of  the  hip-joint  by  the  tendon  of  the  Psoas  major,  from  the  Pectineus 
by  the  femoral  vein  and  profunda  vessels,  and  from  the  Adductor  longus  by  the  femoral' vein. 
The  nerve  to  the  Pectineus  passes  medialward  behind  the  artery.  On  the  lateral  side  of  the 
artery,  but  separated  from  it  by  some  fibers  of  the  Psoas  major,  is  the  femoral  nerve.  The  femoral 
vein  is  on  the  medial  side  of  the  upper  part  of  the  artery,  but  is  behind  the  vessel  in  the  lower 
part  of  the  femoral  triangle. 


Anterior  tibial  recurrent 


Scrotum 


—  Saphenous  nerve 

I 

—  Highest  genicular 


Lateral  sup.  genicular 


Lateral  inf.  genicular — -^ 


MiLsculo-arlicvlar  br.  of 

highest  genicular 
Medial  sup.  genicidar 


I    /A —  Medial  inf.  genicular 


Fia.  550. — The  femoral  artery. 


In  the  adductor  canal  (Fig.  550)  the  femoral  artery  is  more  deeply  situated,  being  covered  by 
the  integument,  the  superficial  and  deep  fascia;,  the  Sartorius  and  the  fibrous  roof  of  the  canal; 
the  saphenous  nerve  crosses  from  its  lateral  to  its  medial  side.    Behind  the  artery  are  the  Adduc- 


m 


THE  FEMORAL  ARTERY  WfKm  629 

tores  longus  and  magnus;  in  front  and  lateral  to  it  is  the  Vastus  medialis.  The  femoral  vein 
lies  posterior  to  the  upper  part,  and  lateral  to  the  lower  part  of  the  artery. 

Peculiarities. — Several  cases  are  recorded  in  which  the  femoral  artery  divided  into  two  trunks 
below  the  origin  of  the  profunda,  and  became  reunited  near  the  opening  in  the  Adductor  magnus, 
so  as  to  form  a  single  popliteal  artery.  One  occurred  in  a  patient  who  was  operated  upon  for 
popliteal  aneurism.  A  few  cases  have  been  recorded  in  which  the  femoral  artery  was  absent, 
its  place  being  supplied  by  the  inferior  gluteal  artery  which  accompanied  the  sciatic  nerve  to  the 
popliteal  fossa.  The  external  iliac  in  these  cases  was  small,  and  terminated  in  the  profunda. 
The  femoral  vein  is  occasionally  placed  along  the  medial  side  of  the  artery  throughout  the  entire 
extent  of  the  femoral  trangle;  or  it  may  be  split  so  that  a  large  vein  is  placed  on  either  side  of 
the  artery  for  a  greater  or  lesser  distance. 

Collateral  Circulation. — After  ligature  of  the  femoral  artery,  the  main  channels  for  carrying 
on  the  circulation  are  the  anastomoses  between — (1)  the  superior  and  inferior  gluteal  branches 
of  the  hypogastric  with  the  medial  and  lateral  femoral  circumflex  and  first  perforating  branches 
of  the  profunda  f  em  oris;  (2)  the  obturator  branch  of  the  hypogastric  with  the  medial  femoral 
circumflex  of  the  profunda;  (3)  the  internal  pudendal  of  the  hypogastric  with  the  superficial 
and  deep  external  pudendal  of  the  femoral;  (4)  the  deep  iUac  circumflex  of  the  external  iliac  with 
the  lateral  femoral  circumflex  of  the  profunda  and  the  superficial  iliac  circumflex  of  the  femoral, 
and  (5)  the  inferior  gluteal  of  the  hypogastric  with  the  perforating  branches  of  the  profunda. 

Branches. — The  branches  of  the  femoral  artery  are: 

Superficial  Epigastric.  Deep  External  Pudendal. 

Superficial  Iliac  Circumflex.  Muscular. 

Superficial  External  Pudendal.  Profunda  Femoris. 

Highest  Genicular. 

The  superficial  epigastric  artery  (a.  epigastrica  superficialis)  arises  from  the 
front  of  the  femoral  artery  about  1  cm.  below  the  inguinal  ligament,  and,  passing 
through  the  femoral  sheath  and  the  fascia  cribrosa,  turns  upward  in  front  of  the 
inguinal  ligament,  and  ascends  between  the  two  layers  of  the  superficial  fascia  of 
the  abdominal  wall  nearly  as  far  as  the  umbilicus.  It  distributes  branches  to  the 
superficial  subinguinal  lymph  glands,  the  superficial  fascia,  and  the  integument; 
it  anastomoses  with  branches  of  the  inferior  epigastric,  and  with  its  fellow  of  the 
opposite  side. 

The  superficial  iliac  circumflex  artery  (a.  circumflexa  ilium  superficialis),  the 
smallest  of  the  cutaneous  branches,  arises  close  to  the  preceding,  and,  piercing 
the  fascia  lata,  runs  lateralward,  parallel  with  the  inguinal  ligament,  as  far  as  the 
crest  of  the  ilium;  it  divides  into  branches  which  supply  the  integument  of  the 
Hkroin,  the  superficial  fascia,  and  the  superficial  subinguinal  lymph  glands,  anas- 
^  ^omosing  with  the  deep  iliac  circumflex,  the  superior  gluteal  and  lateral  femoral 
circumflex  arteries. 

The   superficial   external  pudendal  artery    (a.   pudenda  externa  superficialis; 

■  superficial  external  pudic  artery)  arises  from  the  medial  side  of  the  femoral  artery, 
■close  to  the  preceding  vessels,  and,  after  piercing  the  femoral  sheath  and  fascia 
cribrosa,  courses  medialward,  across  the  spermatic  cord  (or  round  ligament  in  the 
female),  to  be  distributed  to  the  integument  on  the  lower  part  of  the  abdomen, 
the  penis  and  scrotum  in  the  male,  and  the  labium  majus  in  the  female,  anasto- 

■  r  mosing  with  branches  of  the  internal  pudendal. 
I  The  deep  external  pudendal  artery  (a.  pudenda  externa  profunda;  deep  external 
pudic  artery),  more  deeply  seated  than  the  preceding,  passes  medialward  across 
the  Pectineus  and  the  Adductor  longus  muscles;  it  is  covered  by  the  fascia  lata, 
which  it  pierces  at  the  medial  side  of  the  thigh,  and  is  distributed,  in  the  male, 
to  the  integument  of  the  scrotum  and  perineum,  in  the  female  to  the  labium  majus; 
its  branches  anastomose  with  the  scrotal  (or  labial)  branches  of  the  perineal  artery. 
Muscular  branches  (rami  muscnlares)  are  supplied  by  the  femoral  artery  to  the 
Sartorius,  Vastus  medialis,  and  Adductores. 

The  profunda  femoris  artery  (a.  profunda  femoris;  deep  femoral  artery)  (Fig. 
550)  is  a  large  vessel  arising  from  the  lateral  and  back  part  of  the  femoral  artery, 


I 


II 


630  ^K^m  ANGIOWGY 

from  2  to  5  cm.  below  the  inguinal  ligament.  At  first  it  lies  lateral  to  the  femoral 
artery ;  it  then  runs  behind  it  and  the  femoral  vein  to  the  medial  side  of  the  femur, 
and,  passing  dowuAvard  behind  the  Adductor  longus,  ends  at  the  lower  third  of  the 
thigh  in  a  small  branch,  which  pierces  the  Adductor  magnus,  and  is  distributed 
on  the  back  of  the  thigh  to  the  hamstring  muscles.  The  terminal  part  of  the  pro-  ■■ 
funda  is  sometimes  named  the  fourth  perforating  artery.  Il 

Relations. — Behind  it,  from  above  downward,  are  the  Iliacus,  Pectineus,  Adductor  brevis, 
and  Adductor  magnus.  In  front  it  is  separated  from  the  femoral  artery  by  the  femoral  and  pro- 
funda veins  above  and  by  the  Adductor  longus  below.  Laterally,  the  origin  of  the  Vastus  medialia 
intervenes  between  it  and  the  femur. 

Peculiarities. — This  vessel  sometimes  arises  from  the  medial  side,  and,  more  rarely,  from  the 
back  of  the  femoral  artery;  but  a  more  important  peculiarity,  from  a  surgical  point  of  view,  is 
that  relating  to  the  height  at  which  the  vessel  arises.  In  three-fourths  of  a  large  number  of  cases 
it  arose  from  2.25  to  5  cm.  below  the  inguinal  ligament;  in  a  few  cases  the  distance  was  less  than 
2.25  cm.;  more  rarely,  opposite  the  hgament;  and  in  one  case  above  the  inguinal  ligament,  from 
the  external  ihac.  Occasionally  the  distance  between  the  origin  of  the  vessel  and  the  inguinal 
ligament  exceeds  5  cm. 

Branches. — The  profunda  gives  off  the  following  branches: 

Lateral  Femoral  Circumflex.  Perforating. 

Medial  Femoral  Circumflex.  Muscular. 

The  Lateral  Femoral  Circumflex  Artery  (a.  circumflexa  femoris  lateralis;  external 
circumflex  artery)  arises  from  the  lateral  side  of  the  profunda,  passes  horizontally 
between  the  divisions  of  the  femoral  nerve,  and  behind  the  Sartorius  and  Rectus 
femoris,  and  divides  into  ascending,  transverse,  and  descending  branches. 

The  ascending  branch  passes  upward,  beneath  the  Tensor  fascise  latse,  to  the 
lateral  aspect  of  the  hip,  and  anastomoses  with  the  terminal  branches  of  the  superior 
gluteal  and  deep  iliac  circumflex  arteries. 

The  descending  branch  runs  downward,  behind  the  Rectus  femoris,  upon  the 
Vastus  lateralis,  to  which  it  gives  offsets;  one  long  branch  descends  in  the  muscle 
as  far  as  the  knee,  and  anastomoses  with  the  superior  lateral  genicular  branch  of 
the  popliteal  artery.  It  is  accompanied  by  the  branch  of  the  femoral  nerve  to  the 
Vastus  lateralis. 

The  transverse  branch,  the  smallest,  passes  lateralward  over  the  Vastus  inter- 
medins, pierces  the  Vastus  lateralis,  and  winds  around  the  femur,  just  below  the 
greater  trochanter,  anastomosing  on  the  back  of  the  thigh  with  the  medial  femoral 
circumflex,  inferior  gluteal,  and  first  perforating  arteries. 

The  Medial  Femoral  Circumflex  Artery  (a.  circumflexa  femoris  medialis;  internal 
circumflex  artery)  arises  from  the  medial  and  posterior  aspect  of  the  profunda, 
and  winds  around  the  medial  side  of  the  femur,  passing  first  between  the  Pectineus 
and  Psoas  major,  and  then  between  the  Obturator  externus  and  the  Adductor 
brevis.  At  the  upper  border  of  the  Adductor  brevis  it  gives  off  two  branches: 
one  is  distributed  to  the  Adductores,  the  Gracilis,  and  Obturator  externus,  and 
anastomoses  with  the  obturator  artery;  the  other  descends  beneath  the  Adductor 
brevis,  to  supply  it  and  the  Adductor  magnus;  the  continuation  of  the  vessel 
passes  backward  and  divides  into  superficial,  deep,  and  acetabular  branches.  The 
superficial  branch  appears  between  the  Quadratus  femoris  and  upper  border  of  the 
Adductor  magnus,  and  anastomoses  with  the  inferior  gluteal,  lateral  femoral 
circumflex,  and  first  perforating  arteries  (crucial  anastomosis).  The  deep  branch 
runs  obliquely  upward  upon  the  tendon  of  the  Obturator  externus  and  in  front 
of  the  Quadratus  femoris  toward  the  trochanteric  fossa,  where  it  anastomoses 
with  twigs  from  the  gluteal  arteries.  The  acetabular  branch  arises  opposite  the 
acetabular  notch  and  enters  the  hip-joint  beneath  the  transverse  ligament  in  com- 
pany with  an  articular  branch  from  the  obturator  artery ;  it  supplies  the  fat  in  the 
bottom  of  the  acetabulum,  and  is  continued  along  the  round  ligament  to  the  head 
of  the  femur. 


I 


I 


I 
I 

I 


THE  POPLITEAL  FOSSA  631 

The  Perforating  Arteries  (Pig.  544),  usually  three  in  number,  are  so  named  because 
they  perforate  the  tendon  of  the  Adductor  magnus  to  reach  the  back  of  the  thigh. 
They  pass  backward  close  to  the  linea  aspera  of  the  femur  under  cover  of  small 
tendinous  arches  in  the  muscle.  The  first  is  given  off  above  the  Adductor  brevis, 
the  second  in  front  of  that  muscle,  and  the  third  immediately  below  it. 

The  first  perforating  artery  (a.  perforans  'prima)  passes  backward  between  the  Pec- 
tineus  and  Adductor  brevis  (sometimes  it  perforates  the  latter);  it  then  pierces 
the  Adductor  magnus  close  to  the  linea  aspera.  It  gives  branches  to  the  Adductores 
brevis  and  magnus.  Biceps  femoris,  and  Glutseus  maximus,  and  anastomoses  with 
the  inferior  gluteal,  medial  and  lateral  femoral  circumflex  and  second  perforating 
arteries. 

The  second  perforating  artery  {a.  perforans  seciinda) ,  larger  than  the  first,  pierces 
the  tendons  of  the  Adductores  brevis  and  rhagnus,  and  divides  into  ascending 
and  descending  branches,  which  supply  the  posterior  femoral  muscles,  anasto- 
mosing with  the  first  and  third  perforating.  The  second  artery  frequently  arises 
in  common  with  the  first.  The  nutrient  artery  of  the  femur  is  usually  given  off 
from  the  second  perforating  artery;  when  two  nutrient  arteries  exist,  they  usually 
spring  from  the  first  and  third  perforating  vessels. 

The  third  perforating  artery  (a.  perforans  tertia)  is  given  off  below  the  Adductor 
brevis;  it  pierces  the  Adductor  magnus,  and  divides  into  branches  which  supply 
the  posterior  femoral  muscles;  anastomosing  above  with  the  higher  perforating 
arteries,  and  below  with  the  terminal  branches  of  the  profunda  and  the  muscular 
branches  of  the  popliteal.  The  nutrient  artery  of  the  femur  may  arise  from  this 
branch.  The  termination  of  the  profunda  artery,  already  described,  is  sometimes 
termed  the  fourth  perforating  artery. 

Numerous  muscular  branches  arise  from  the  profunda;  some  of  these  end  in  the 
Adductores,  others  pierce  the  Adductor  magnus,  give  branches  to  the  hamstrings, 
and  anastomose  with  the  medial  femoral  circumflex  artery  and  with  the  superior 
muscular  branches  of  the  popliteal. 

The  highest  genicular  artery  (a.  genu  suprema;  anastomotica  magna  artery)  (Fig. 
550)  arises  from  the  femoral  just  before  it  passes  through  the  opening  in  the 
tendon  of  the  Adductor  magnus,  and  immediately  divides  into  a  saphenous  and  a 
musculo-articular  branch. 

The  saphenous  branch  pierces  the  aponeurotic  covering  of  the  adductor  canal, 
and  accompanies  the  saphenous  nerve  to  the  medial  side  of  the  knee.  It  passes 
between  the  Sartorius  and  Gracilis,  and,  piercing  the  fascia  lata,  is  distributed  to 
the  integument  of  the  upper  and  medial  part  of  the  leg,  anastomosing  with  the 
medial  inferior  genicular  artery. 

The  musculo-articular  branch  descends  in  the  substance  of  the  Vastus  medialis, 
and  in  front  of  the  tendon  of  the  Adductor  magnus,  to  the  medial  side  of  the  knee, 
where  it  anastomoses  with  the  medial  superior  genicular  artery  and  anterior  recur- 
rent tibial  artery.  A  branch  from  this  vessel  crosses  above  the  patellar  surface 
of  the  femur,  forming  an  anastomotic  arch  with  the  lateral  superior  genicular 
artery,  and  supplying  branches  to  the  knee-joint. 

THE  POPLITEAL   FOSSA  (Fig.   551). 

Boundaries. — The  popliteal  fossa  or  space  is  a  lozenge-shaped  space,  at  the 
back  of  the  knee-joint.  Laterally  it  is  bounded  by  the  Biceps  femoris  above, 
and  by  the  Plantaris  and  the  lateral  head  of  the  Gastrocnemius  below;  medially 
it  is  limited  by  the  Semitendinous  and  Semimembranosus  above,  and  by  the  medial 
head  of  the  Gastrocnemius  below.  The  floor  is  formed  by  the  popliteal  surface 
of  the  femur,  the  oblique  popliteal  ligament  of  the  knee-joint,  the  upper  end  of  the 
tibia,  and  the  fascia,  covering  the  Popliteus]  the  fossa  is  covered  in  by  the  fascia  lata. 


ANGIOLOGY 


Contents. — The  popliteal  fossa  contains  the  popliteal  vessels,  the  tibial  and  the 
common  peroneal  nerves,  the  termination  of  the  small  saphenous  vein,  the  lower 
part  of  the  posterior  femoral  cutaneous  nerve,  the  articular  branch  from  the  obtur- 
ator nerve,  a  few  small  lymph  glands,  and 
a  considerable  quantity  of  fat.  The  tibial 
nerve  descends  through  the  middle  of  the 
fossa,  lying  under  the  deep  fascia  and  cross- 
ing the  vessels  posteriorly  from  the  lateral 
to  the  medial  side.  The  common  peroneal 
nerve  descends  on  the  lateral  side  of  the 
upper  part  of  the  fossa,  close  to  the  tendon 
of  the  Biceps  femoris.  On  the  floor  of  the 
fossa  are  the  popliteal  vessels,  the  vein 
being  superficial  to  the  artery  and  united 
to  it  by  dense  areolar  tissue;  the  vein  is  a 
thick-walled  vessel,  and  lies  at  first  lateral 
to  the  artery,  and  then  crosses  it  posteriorly 
to  gain  its  medial  side  below;  sometimes 
it  is  double,  the  artery  lying  between  the 
two  veins,  which  are  usually  connected  by 
short  transverse  branches.  The  articular 
branch  from  the  obturator  nerve  descends 
upon  the  artery  to  the  knee-joint.  The 
popliteal  Ij^mph  glands,  six  or  seven  in 
number,  are  imbedded  in  the  fat;  one  lies 
beneath  the  popliteal  fascia  near  the  termi- 
nation of  the  external  saphenous  vein, 
another  between  the  popliteal  artery  and 
the  back  of  the  knee-joint,  while  the  others 
are  placed  at  the  sides  of  the  popliteal 
vessel.  Arising  from  the  artery,  and  pass- 
ing off  from  it  at  right  angles,  are  its  genic- 
ular branches. 


The  Popliteal  Artery  (A.  Poplitea)  (Fig.  551). 

The  popliteal  artery  is  the  continuation  of 
the  femoral,  and  courses  through  the  poplit- 
eal fossa.  It  extends  from  the  opening  in 
the  Adductor  magnus,  at  the  junction  of  the 
middle  and  lower  thirds  of  the  thigh,  down- 
ward and  lateral  ward  to  the  intercondyloid 
fossa  of  the  femur,  and  then  vertically  down- 
ward to  the  lower  border  of  the  Popliteus, 
where  it  divides  into  anterior  and  posterior 
tibial  arteries. 

Relations.— In  front  of  the  artery  from  'above 
downward  are  the  popliteal  surface  of  the  femur 
(which  is  separated  from  the  vessel  by  some  fat), 
the  back  of  the  knee-joint,  and  the  fascia  cover- 
ing the  Popliteus.  Behind,  it  is  overlapped  by  the 
Semimembranosus  above,  ai>d  is  covered  by  the 
Gastrocnemius  and  Plantaris  below.  In  the  middle 
part  of  its  course  the  artery  is  separated  from  the 
integument  and  fasciae  by  a  (quantity  of  fat,  and  is 


Perf.  branch 
of  peroneal 


Fig.  551. — The  popliteal,  posterior  tibial,  and 
peroneal  arteries. 


I 


THE  POPLITEAL  ARTERY  ^^^  633 

crossed  from  the  lateral  to  the  medial  side  by  the  tibial  nerve  and  the  popliteal  vein,  the  vein 
being  between  the  nerve  and  the  artery  and  closely  adherent  to  the  latter.  On  its  lateral  side, 
above,  are  the  Biceps  femoris,  the  tibial  nerve,  the  popliteal  vein,  and  the  lateral  condyle  of  the 
femur;  below,  the  Plantaris  and  the  lateral  head  of  the  Gastrocnemius.  On  its  medial  side,  above, 
are  the  Semimembranosus  and  the  medial  condyle  of  the  femur;  below,  the  tibial  nerve,  the 
popliteal  vein,  and  the  medial  head  of  the  Gastrocnemius.  The  relations  of  the  popliteal  lymph 
glands  to  the  artery  are  described  above. 

Peculiarities  in  Point  of  Division. — Occasionally  the  popliteal  artery  divides  into  its  terminal 
branches  opposite  the  knee-joint.  The  anterior  tibial  under  these  circumstances  usually  passes 
in  front  of  the  Popliteus. 

Unusual  Branches. — The  artery  sometimes  divides  into  the  anterior  tibial  and  peroneal,  the 
posterior  tibial  being  wanting,  or  very  small.  Occasionally  it  divides  into  three  branches,  the 
anterior  and  posterior  tibial,  and  peroneal. 

Branches. — The  branches  of  the  popliteal  artery  are : 

,  y        ,       f  Superior  Lateral  Superior  Genicular. 

\  Sural.  Middle  Genicular. 

Cutaneous.  Medial  Inferior  Genicular. 

Medial  Superior  Genicular  Lateral  Inferior  Genicular. 

The  superior  muscular  branches,  two  or  three  in  number,  arise  from  the  upper 
part  of  the  artery,  and  are  distributed  to  the  lower  parts  of  the  Adductor  magnus 
and  hamstring  muscles,  anastomosing  with  the  terminal  part  of  the  profunda 
femoris. 

The  sural  arteries  {aa.  surales;  inferior  muscular  arteries)  are  two  large  branches, 
which  are  distributed  to  the  Gastrocnemius,  Soleus,  and  Plantaris.  They  arise 
from  the  popliteal  artery  opposite  the  knee-joint. 

The  cutaneous  branches  arise  either  from  the  popliteal  artery  or  from  some  of 
its  branches;  they  descend  between  the  two  heads  of  the  Gastrocnemius,  and, 
piercing  the  deep  fascia,  are  distributed  to  the  skin  of  the  back  of  the  leg.  One 
branch  usually  accompanies  the  small  saphenous  vein. 

The  superior  genicular  arteries  {aa.  genu  superior es;  superior  articular  arteries) 
(Figs.  550,  551),  two  in  number,  arise  one  on  either  side  of  the  popliteal,  and  wind 
around  the  femur  immediately  above  its  condyles  to  the  front  of  the  knee-joint.  The 
medial  superior  genicular  runs  in  front  of  the  Semimembranosus  and  Semitendinosus, 
above  the  medial  head  of  the  Gastrocnemius,  and  passes  beneath  the  tendon  of  the 
Adductor  magnus.  It  divides  into  two  branches,  one  of  which  supplies  the  Vastus 
medialis,  anastomosing  with  the  highest  genicular  and  medial  inferior  genicular 
arteries;  the  other  ramifies  close  to  the  surface  of  the  femur,  supplying  it  and  the 
knee-joint,  and  anastomosing  with  the  lateral  superior  genicular  artery.  The  medial 
superior  genicular  artery  is  frequently  of  small  size,  a  condition,  which  is  associated 
with  an  increase  in  the  size  of  the  highest  genicular.  The  lateral  superior  genicular 
passes  above  the  lateral  condyle  of  the  femur,  beneath  the  tendon  of  the  Biceps 
femoris,  and  divides  into  a  superficial  and  a  deep  branch;  the  superficial  branch 
supplies  the  Vastus  lateralis,  and  anastomoses  with  the  descending  branch  of  the 
lateral  femoral  circumflex  and  the  lateral  inferior  genicular  arteries;  the  deep 
branch  supplies  the  lower  part  of  the  femur  and  knee-joint,  and  forms  an  anasto- 
motic arch  across  the  front  of  the  bone  with  the  highest  genicular  and  the  medial 
inferior  genicular  arteries. 

The  middle  genicular  artery  (a.  genu  media;  azygos  articular  artery)  is  a  small 
branch,  arising  opposite  the  back  of  the  knee-joint.  It  pierces  the  oblique  popliteal 
ligament,  and  supplies  the  ligaments  and  synovial  membrane  in  the  interior  of 
the  articulation. 

The  inferior  genicular  arteries  (aa.  genu  inferiores;  inferior  articular  arteries)  (Figs. 
550,  551),  two  in  number,  arise  from  the  popliteal  beneath  the  Gastrocnemius.  The 
medial  inferior  genicular  first  descends  along  the  upper  margin  of  the  Popliteus,  to 
which  it  gives  branches;  it  then  passes  below  the  medial  condyle  of  the  tibia,  beneath 


634 


ANGIOLOGY 


the  tibial  collateral  ligament,  at  the  anterior  border  of  which  it  ascends  to  the  front 
and  medial  side  of  the  joint,  to  supply  the  upper  end  of  the  tibia  and  the  articula- 
tion of  the  knee,  anastomosing  with  the  lateral  inferior  and  medial  superior  genic- 
ular arteries.  The  lateral  inferior  genicular  runs  lateralward  above  the  head  of  the 
fibula  to  the  front  of  the  knee-joint,  passing  in  its  course  beneath  the  lateral  head 
of  the  Gastrocnemius,  the  fibular  collateral  ligament,  and  the  tendon  of  the  Biceps 
femoris.  It  ends  by  dividing  into  branches,  which  anastomose  with  the  medial 
inferior  and  lateral  superior  genicular  arteries,  and  with  the  anterior  recurrent 
tibial  artery. 


Descending  branch  of 
lateral  femoral  circumflex 


Highest  genicular 


Musculo-articular  branch  of 
highest  genicular 

Saphenous  branch  of  highest 
genicular 

Medial  superior  genicular 


Lateral  superior  genicvloT 


Lateral  inferior  genicvlar 


Fibular  -\£ 


Anterior  recurrent  tibial 


Anterior  tibial 


Fig.  552. — Circumpatellar  anastomosis. 


The  Anastomosis  Around  the  Knee-joint  (Fig.  552) . — Around  and  above  the  patella, 
and  on  the  contiguous  ends  of  the  femur  and  tibia,  is  an  intricate  net- work  of  vessels 
forming  a  superficial  and  a  deep  plexus.  The  superficial  plexus  is  situated  between 
the  fascia  and  skin  around  about  the  patella,  and  forms  three  well-defined  arches: 
one,  above  the  upper  border  of  the  patella,  in  the  loose  connective  tissue  over  the 
Quadriceps  femoris;  the  other  two,  below  the  level  of  the  patella,  are  situated  in 
the  fat  behind  the  ligamentum  patellae.  The  deep  plexus,  which  forms  a  close 
net-work  of  vessels,  lies  on  the  lower  end  of  the  femur  and  upper  end  of  the  tibia 
around  their  articular  surfaces,  and  sends  numerous  offsets  into  the  interior  of  the 
joint.  The  arteries  which  form  this  plexus  are  the  two  medial  and  the  two  lateral 
genicular  branches  of  the  popliteal,  the  highest  genicular,  the  descending  branch 
of  the  lateral  femoral  circumflex,  and  the  anterior  recurrent  tibial. 


*l 


I 


The  Anterior  Tibial  Artery  (A.  Tibialis  Anterior)  (Fig.  553). 

The  anterior  tibial  artery  commences  at  the  bifurcation  of  the  popliteal,  at  the 
lower  border  of  the  Popliteus,  passes  forward  between  the  two  heads  of  the  Tibialis 


THE  ANTERIOR  TIBIAL  ARTERY  ^^^        635 

posterior,  and  through  the  aperture  above  the  upper  border  of  the  interosseous 
membrane,  to  the  deep  part  of  the  front  of  the  leg:  it  here  Ues  close  to  the  medial 
side  of  the  neck  of  the  fibula.  It  then  descends  on  the  anterior  surface  of  the  inter- 
osseous membrane,  gradually  approaching  the  tibia;  at  the  lower  part  of  the  leg 
it  lies  on  this  bone,  and  then  on  the  front  of  the  ankle-joint,  where  it  is  more 
superficial,  and  becomes  the  dorsalis  pedis. 

Relations. — In  the  upper  two-thirds  of  its  extent,  the  anterior  tibial  artery  rests  upon  the  inter- 
osseous membrane;  in  the  lower  third,  upon  the  front  of  the  tibia,  and  the  anterior  ligament  of 
the  ankle-joint.  In  the  upper  third  of  its  course,  it  lies  between  the  Tibialis  anterior  and  Extensor 
digitorum  longus;  in  the  middle  third  between  the  Tibialis  anterior  and  Extensor  hallucis  longus. 
At  the  ankle  it  is  crossed  from  the  lateral  to  the  medial  side  by  the  tendon  of  the  Extensor  hallucis 
longus,  and  hes  between  it  and  the  first  tendon  of  the  Extensor  digitorum  longus.  It  is  covered 
in  the  upper  two-thirds  of  its  course,  by  the  muscles  which  lie  on  either  side  of  it,  and  by  the  deep 
fascia;  in  the  lower  third,  by  the  integument  and  fascia,  and  the  transverse  and  cruciate  crural 
ligaments. 

The  anterior  tibial  artery  is  accompanied  by  a  pair  of  venae  comitantes  which  lie  one  on  either 
side  of  the  artery;  the  deep  peroneal  nerve,  coursing  around  the  lateral  side  of  the  neck  of  the 
fibula,  comes  into  relation  with  the  lateral  side  of  the  artery  shortly  after  it  has  reached  the 
front  of  the  leg;  about  the  middle  of  the  leg  the  nerve  is  in  front  of  the  artery;  at  the  lower  part 
it  is  generally  again  on  the  lateral  side. 

Peciiliarities  in  Size. — This  vessel  may  be  diminished  in  size,  may  be  deficient  to  a  greater 
or  less  extent,  or  may  be  entirely  wanting,  its  place  being  supplied  by  perforating  branches  from 
the  posterior  tibial,  or  by  the  perforating  branch  of  the  peroneal  artery. 

Course. — The  artery  occasionally  deviates  toward  the  fibular  side  of  the  leg,  regaining  its 
usual  position  at  the  front  of  the  ankle.  In  rare  instances  the  vessel  has  been  found  to  approach 
the  surface  in  the  middle  of  the  leg,  being  covered  merely  by  the  integument  and  fascia  below 
that  point. 

Branches. — The  branches  of  the  anterior  tibial  artery  are: 

Posterior  Tibial  Recurrent.  Muscular. 

Fibular.  Anterior  Medial  Malleolar. 

Anterior  Tibial  Recurrent.  Anterior  Lateral  Malleolar. 

The  posterior  tibial  recurrent  artery  (a.  recurrens  tibialis  posterior)  an  inconstant 
branch,  is  given  off  from  the  anterior  tibial  before  that  vessel  passes  through  the 
interosseous  space.  It  ascends  in  front  of  the  Popliteus,  which  it  supplies,  and 
anastomoses  with  the  inferior  genicular  branches  of  the  popliteal  artery,  giving 
an  offset  to  the  tibiofibular  joint. 

The  fibular  artery  is  sometimes  derived  from  the  anterior  tibial,  sometimes  irom 
the  posterior  tibial.  It  passes  lateralward,  around  the  neck  of  the  fibula,  through 
the  Soleus,  which  it  supplies,  and  ends  in  the  substance  of  the  Peroneus  longus. 

The  anterior  tibial  recurrent  artery  (a.  recurrens  tibialis  anterior)  arises  from 
the  anterior  tibial,  as  soon  as  that  vessel  has  passed  through  the  interosseous 
space;  it  ascends  in  the  Tibialis  anterior,  ramifies  on  the  front  and  sides  of  the 
knee-joint,  and  assists  in  the  formation  of  the  patellar  plexus  by  anastomosing 
with  the  genicular  branches  of  the  popliteal,  and  with  the  highest  genicular  artery. 

The  muscular  branches  {rami  muscidares)  are  numerous;  they  are  distributed  to 
the  muscles  which  lie  on  either  side  of  the  vessel,  some  piercing  the  deep  fascia  to 
supply  the  integument,  others  passing  through  the  interosseous  membrane,  and 
anastomosing  with  branches  of  the  posterior  tibial  and  peroneal  arteries. 

The  anterior  medial  malleolar  artery  (a.  malleolaris  anterior  medialis;  internal 
malleolar  artery)  arises  about  5  cm.  above  the  ankle-joint,  and  passes  behind  the 
tendons  of  the  Extensor  hallucis  longus  and  Tibialis  anterior,  to  the  medial  side  of 
the  ankle,  upon  which  it  ramifies,  anastomosing  with  branches  of  the  posterior  tibial 
^B  and  medial  plantar  arteries  and  with  the  medial  calcaneal  from  the  posterior  tibial. 
I^B  The  anterior  lateral  malleolar  artery  (a.  malleolaris  anterior  lateralis;  exter- 
^^B  nal  malleolar  artery)   passes   beneath   the  tendons   of  the   Extensor  digitorum 


636 


ANGIOLOGY 


Lateral 
inferior  .J 
genicular 


Medial 
■  inferior 
genicular 


longus  and  Peronseus  tertius  and  supplies  the  lateral  side  of  the  ankle,  anas- 
tomosing with  the  perforating  branch  of  the  peroneal  artery,  and  with  ascend- 
ing twigs  from  the  lateral  tarsal  artery. 
The  arteries  around  the  ankle-joint 
anastomose  freely  with  one  another 
and  form  net-works  below  the  corre- 
sponding malleoli.  The  medial  malleolar 
net-work  is  formed  by  the  anterior 
medial  malleolar  branch  of  the  anterior 
tibial,  the  medial  tarsal  branches  of 
the  dorsalis  pedis,  the  posterior  medial 
malleolar  and  medial  calcaneal  branches 
of  the  posterior  tibial  and  branches 
from  the  medial  plantar  artery.  The 
lateral  malleolar  net-work  is  formed  by 
the  anterior  lateral  malleolar  branch  of 
the  anterior  tibial,  the  lateral  tarsal 
branch  of  the  dorsalis  pedis,  the  per- 
forating and  the  lateral  calcaneal 
branches  of  the  peroneal,  and  twigs 
from  the  lateral  plantar  artery. 


The  Arteria  Dorsalis  Pedis  (Dorsalis 
Pedis  Artery)  (Fig.  553). 

The  arteria  dorsalis  pedis,  the  contin- 
uation of  the  anterior  tibial,  passes  for- 
ward from  the  ankle-joint  along  the 
tibial  side  of  the  dorsum  of  the  foot  to 
the  proximal  part  of  the  first  inter- 
metatarsal  space,  where  it  divides  into 
two  branches,  the  first  dorsal  metatarsal 
and  the  deep  plantar. 

Relations. — This  vessel,  in  its  course  for- 
ward, rests  upon  the  front  of  the  articular 
capsule  of  the  ankle-joint,  the  talus,  navic- 
ular, and  second  cuneiform  bones,  and  the 
ligaments  connecting  them,  being  covered  by 
the  integument,  fascia  and  cruciate  ligament, 
and  crossed  near  its  termination  by  the  first 
tendon  of  the  Extensor  digitorum  brevis.  On 
its  tibial  side  is  the  tendon  of  the  Extensor 
hallucis  longus;  on  its  fibular  side,  the  first 
tendon  of  the  Extensor  digitorum  longus, 
and  the  termination  of  the  deep  peroneal 
nerve.    It  is  accompanied  by  two  veins. 

Peculiarities  in  Size. — The  dorsal  artery  of 
the  foot  may  be  larger  than  usual,  to  com- 
pensate for  a  deficient  plantar  artery;  or  its 
terminal  branches  to  the  toes  may  be  absent, 
the  toes  then  being  supplied  by  the  medial 
plantar;  or  its  place  may  be  taken  altogether 
by  a  large  perforating  branch  of  the  peroneal 
artery. 

Position. — ^This  artery  frequently  curves 
lateralward,  lying  lateral  to  the  line  between 
the  middle  of  the  ankle  and  the  back  part  of 
the  first  interosseous  space. 


Ant.  med, 
malleolar 


Deep 
plantar 


Fig.  553. — Anterior  tibial  and  dorsalis  pedis  arterioa 


ir 


I 


THE  POSTERIOR  TIBIAL  ARTERY  637 

Branches. — The  branches  of  the  arteria  dorsalis  pedis  are: 

Lateral  Tarsal.  Arcuate. 

Medial  Tarsal.  First  Dorsal  Metatarsal. 

Deep  Plantar. 

The  lateral  tarsal  artery  (a.  tar  sea  lateralis;  tarsal  artery)  arises  from  the  dorsalis 
pedis,  as  that  vessel  crosses  the  navicular  bone;  it  passes  in  an  arched  direction 
lateralward,  lying  upon  the  tarsal  bones,  and  covered  by  the  Extensor  digitorum 
brevis;  it  supplies  this  muscle  and  the  articulations  of  the  tarsus,  and  anastomoses 
with  branches  of  the  arcuate,  anterior  lateral  malleolar  and  lateral  plantar  arteries, 
and  with  the  perforating  branch  of  the  peroneal  artery. 

The  medial  tarsal  arteries  {aa.  tarseoe  mediales)  are  two  or  three  small  branches 
which  ramify  on  the  medial  border  of  the  foot  and  join  the  medial  malleolar  net-work. 

The  arcuate  artery  (a.  arcuata;  metatarsal  artery)  arises  a  little  anterior  to  the 
lateral  tarsal  artery;  it  passes  lateralward,  over  the  bases  of  the  metatarsal  bones, 
beneath  the  tendons  of  the  Extensor  digitorum  brevis,  its  direction  being  influenced 
by  its  point  of  origin ;  and  it  anastomoses  with  the  lateral  tarsal  and  lateral  plantar 
arteries.  This  vessel  gives  off  the  second,  third,  and  fourth  dorsal  metatarsal  arteries, 
which  run  forward  upon  the  corresponding  Interossei  dorsales;  in  the  clefts  between 
the  toes,  each  divides  into  two  dorsal  digital  branches  for  the  adjoining  toes.  At 
the  proximal  parts  of  the  interosseous  spaces  these  vessels  receive  the  posterior 
perforating  branches  from  the  plantar  arch,  and  at  the  distal  parts  of  the  spaces 
they  are  joined  by  the  anterior  perforating  branches,  from  the  plantar  metatarsal 
arteries.  The  fourth  dorsal  metatarsal  artery  gives  off  a  branch  which  supplies 
the  lateral  side  of  the  fifth  toe. 

The  first  dorsal  metatarsal  artery  (a.  dorsalis  halluds)  runs  forward  on  the  first 
Interosseous  dorsalis,  and  at  the  cleft  between  the  first  and  second  toes  divides 
into  two  branches,  one  of  which  passes  beneath  the  tendon  of  the  Extensor  hallucis 
longus,  and  is  distributed  to  the  medial  border  of  the  great  toe;  the  other  bifurcates 
to  supply  the  adjoining  sides  of  the  great  and  second  toes. 

The  deep  plantar  artery  {ramus  plantaris  ^profundus;  communicating  artery) 
descends  into  the  sole  of  the  foot,  between  the  two  heads  of  the  first  Interosseous 
dorsalis,  and  unites  with  the  termination  of  the  lateral  plantar  artery,  to  complete 
the  plantar  arch.  It  sends  a  branch  along  the  medial  side  of  the  great  toe,  and  is 
continued  forward  along  the  first  interosseous  space  as  the  first  plantar  metatarsal 
artery,  which  bifurcates  for  the  supply  of  the  adjacent  sides  of  the  great  and  second 
toes. 

The  Posterior  Tibial  Artery  (A.  Tibialis  Posterior)  (Fig.  551). 

The  posterior  tibial  artery  begins  at  the  lower  border  of  the  Popliteus,  opposite 
the  interval  between  the  tibia  and  fibula;  it  extends  obliquely  downward,  and,  as 
it  descends,  it  approaches  the  tibial  side  of  the  leg,  lying  behind  the  tibia,  and  in 
the  lower  part  of  its  course  is  situated  midway  between  the  medial  malleolus  and 
the  medial  process  of  the  calcaneal  tuberosity.  Here  it  divides  beneath  the  origin 
of  the  Adductor  hallucis  into  the  medial  and  lateral  plantar  arteries. 

Relations. — The  posterior  tibial  artery  lies  successively  upon  the  Tibialis  posterior,  the  Flexor 
digitorum  longus,  the  tibia,  and  the  back  of  the  ankle-joint.  It  is  covered  by  the  deep  trans- 
verse fascia  of  the  leg,  which  separates  it  above  from  the  Gastrocnemius  and  Soleus;  at  its  termi- 
nation it  is  covered  by  the  Abductor  hallucis.  In  the  lower  third  of  the  leg,  where  it  is  more 
superficial,  it  is  covered  only  by  the  integument  and  fascia,  and  runs  parallel  with  the  medial 
border  of  the  tendo  calcaneus.  It  is  accompanied  by  two  veins,  and  by  the  tibial  nerve,  which 
lies  at  first  to  the  medial  side  of  the  artery,  but  soon  crosses  it  posteriorly,  and  is  in  the  greater 
part,  of  its  course  on  its  lateral  side. 

Behind  the  medial  malleolus,  the  tendons,  bloodvessels,  and  nerve  are  arranged,  under  cover 
of  the  laciniate  ligament,  in  the  following  order  from  the  medial  to  the  lateral  side:     (1)  the 


638  ANGJOLOGY 

tendons  of  the  Tibialis  posterior  and  Flexor  digitorum  longus,  lying  in  the  same  groove,  behind 
the  malleolus,  the  former  being  the  more  medial.  Next  is  the  posterior  tibial  artery,  with  a  vein 
on  either  side  of  it;  and  lateral  to  the  vessels  is  the  tibial  nerve;  about  1.25  cm.  nearer  the  heel 
is  the  tendon  of  the  Flexor  hallucis  longus. 

Peculiarities  in  Size. — The  posterior  tibial  is  not  infrequently  smaller  than  usual,  or  absent, 
its  place  being  supplied  by  a  large  peroneal  artery,  which  either  joins  the  small  posterior  tibial 
artery,  or  continues  alone  to  the  sole  of  the  foot. 

Branches. — The  branches  of  the  posterior  tibial  artery  are : 

Peroneal.  Posterior  Medial  ^Malleolar. 

Nutrient.  Communicating. 

Muscular.  Medial  Calcaneal. 

The  peroneal  artery  (a.  peroncBo)  is  deeply  seated  on  the  back  of  the  fibular 
side  of  the  leg.  It  arises  from  the  posterior  tibial,  about  2.5  cm.  below  the  lower 
border  of  the  Popliteus,  passes  obliquely  toward  the  fibula,  and  then  descends 
along  the  medial  side  of  that  bone,  contained  in  a  fibrous  canal  between  the  Tibialis 
posterior  and  the  Flexor  hallucis  longus,  or  in  the  substance  of  the  latter  muscle. 
It  then  runs  behind  the  tibiofibular  syndesmosis  and  divides  into  lateral  calcaneal 
branches  which  ramify  on  the  lateral  and  posterior  surfaces  of  the  calcaneus. 

It  is  covered,  in  the  upper  part  of  its  course,  by  the  Soleus  and  deep  transverse 
fascia  of  the  leg;  below,  by  the  Flexor  hallucis  longus. 

Peculiarities  in  Orifinin. — The  peroneal  artery  may  arise  7  or  8  cm.  below  the  Popliteus,  or  from 
the  posterior  tibial  high  up,  or  even  from  the  popliteal. 

Its  size  is  more  frequently  increased  than  diminished;  and  then  it  either  reinforces  the  posterior 
tibial  by  its  jimction  with  it,  or  altogether  takes  the  place  of  the  posterior  tibial  in  the  lower 
part  of  the  leg  and  foot,  the  latter  vessel  only  existing  as  a  short  muscular  branch.  In  those 
rare  cases  where  the  peroneal  artery  is  smaller  than  usual,  a  branch  from  the  posterior  tibial 
supplies  its  place;  and  a  branch  from  the  anterior  tibial  compensates  for  the  diminished  anterior 
peroneal  artery.    In  one  case  the  peroneal  artery  was  entirely  wanting. 

Branches. — The  branches  of  the  peroneal  are : 

Muscular.  Perforating. 

Nutrient.  Communicating. 

Lateral  Calcaneal. 

Muscular  Branches. — The  peroneal  artery,  in  its  course,  gives  off  branches  to 
the  Soleus,  Tibialis  posterior,  Flexor  hallucis  longus,  and  Peronei. 

The  Nutrient  Artery  (a.  nutricia  fibulce)  supplies  the  fibula,  and  is  directed 
downward. 

The  Perforating  Branch  (ramus  perforans;  anterior  peroneal  artery)  pierces  the 
interosseous  membrane,  about  5  cm.  above  the  lateral  malleolus,  to  reach  the  front 
of  the  leg,  where  it  anastomoses  with  the  anterior  lateral  malleolar;  it  then  passes 
down  in  front  of  the  tibiofibular  syndesmosis,  gives  branches  to  the  tarsus,  and 
anastomoses  with  the  lateral  tarsal.  The  perforating  branch  is  sometimes  enlarged, 
and  takes  the  place  of  the  dorsalis  pedis  artery. 

The  Communicating  Branch  (ramus  communicans)  is  given  off  from  the  peroneal 
about  2.5  cm.  from  its  lower  end,  and  joins  the  communicating  branch  of  the 
posterior  tibial. 

The  Lateral  Calcaneal  (ramus  calcaneus  lateralis;  external  calcaneal)  are  the  ter- 
minal branches  of  the  peroneal  artery;  they  pass  to  the  lateral  side  of  the  heel, 
and  communicate  with  the  lateral  malleolar  and,  on  the  back  of  the  heel,  with  the 
medial  calcaneal  arteries. 

The  nutrient  artery  (a.  nutricia  tibice)  of  the  tibia  arises  from  the  posterior 
tibial,  near  its  origin,  and  after  supplying  a  few  muscular  branches  enters  the 
nutrient  canal  of  the  bone,  which  it  traverses  obliquely  from  above  downward. 
This  is  the  largest  nutrient  artery  of  bone  in  the  body. 


THE  POSTERIOR  TIBIAL  ARTERY 


639 


The  muscular  branches  of  the  posterior  tibial  are  distributed  to  the  Soleus  and 
deep  muscles  along  the  back  of  the  leg. 

The  posterior  medial  malleolar  artery  (a.  malleolaris  posterior  viedialis;  internal 
malleolar  artery)  is  a  small  branch  which  winds  around  the  tibial  malleolus  and 
ends  in  the  medial  malleolar  net-work. 

The  communicating  branch  {ramus  communicans)  runs  transversely  across  the 
back  of  the  tibia,  about  5  cm.  above  its  lower  end,  beneath  the  Flexor  hallucis 
longus,  and  joins  the  communicating  branch  of  the  peroneal. 

The  medial  calcaneal  (raini  calcanei  mediales;  internal  calcaneal)  are  several 
large  arteries  which  arise  from  the  posterior  tibial  just  before  its  division;  they 
pierce  the  laciniate  ligament  and  are  distributed  to  the  fat  and  integument  behind 
the  tendo  calcaneus  and  about  the  heel,  and  to  the  muscles  on  the  tibial  side  of 
the  sole,  anastomosing  with  the  peroneal  and  medial  malleolar  and,  on  the  back 
of  the  heel,  with  the  lateral  calcaneal  arteries. 


Deep  plantar 


\st  plantar 
metatarsal 


Fia.  554.- — The  plantar  arteries.      Superficial  view. 


FiQ.  555. — The  plantar  arteries.     Deep  view. 


II 


The  medial  plantar  artery  (a.  plantaris  medialis;  internal  plantar  artery)  (Figs, 
554:  and  555),  much  smaller  than  the  lateral,  passes  forward  along  the  medial  side 
of  the  foot.  It  is  at  first  situated  above  the  Abductor  hallucis,  and  then  between 
it  and  the  Flexor  digitorum  brevis,  both  of  which  it  supplies.  At  the  base  of  the 
first  metatarsal  bone,  where  it  is  much  diminished  in  size,  it  passes  along  the  medial 
border  of  the  first  toe,  anastomosing  with  the  first  dorsal  metatarsal  artery.  Small 
superficial  digital  branches  accompany  the  digital  branches  of  the  medial  plantar 
nerve  and  join  the  plantar  metatarsal  arteries  of  the  first  three  spaces. 

The  lateral  plantar  artery  (a.  plantaris  lateralis;  external  plantar  artery),  much 
larger  than  the  medial,  passes  obliquely  lateral  ward  and  forward  to  the  base  of 
the  fifth  metatarsal  bone.  It  then  turns  medialward  to  the  interval  between  the 
bases  of  the  first  and  second  metatarsal  bones,  where  it  unites  with  the  deep  plantar 
branch  of  the  dorsalis  pedis  artery,  thus  completing  the  plantar  arch.  As  this  artery 
passes  lateralward,  it  is  first  placed  between  the  calcaneus  and  Abductor  hallucis, 


i_ 


i 

II 


640  ^  ANGIOLOGY 

and  then  between  the  Flexor  digitorum  brevis  and  Quadratus  plantse;  as  it  run 
forward  to  the  base  of  the  little  toe  it  lies  more  superficially  between  the  Flexor 
digitorum  brevis  and  Abductor  digiti  quinti,  covered  by  the  plantar  aponeurosis 
and  integument.  The  remaining  portion  of  the  vessel  is  deeply  situated;  it  extends 
from  the  base  of  the  fifth  metatarsal  bone  to  the  proximal  part  of  the  first  inter-^ 
osseous  space,  and  forms  the  plantar  arch;  it  is  convex  forward,  lies  below  the  base: 
of  the  second,  third,  and  fourth  metatarsal  bones  and  the  corresponding  Interossei 
and  upon  the  oblique  part  of  the  Adductor  hallucis. 

Branches. — The  plantar  arch,  besides  distributing  numerous  branches  to  the 
muscles,  integument,  and  fasciae  in  the  sole,  gives  off  the  following  branches: 

Perforating.  Plantar  Metatarsal. 

The  Perforating  Branches  {rami  perforantes)  are  three  in  number;  they  ascend 
through  the  proximal  parts  of  the  second,  third,  and  fourth  interosseous  spaces, 
between  the  heads  of  the  Interossei  dorsales,  and  anastomose  with  the  dorsal 
metatarsal  arteries. 

The  Plantar  Metatarsal  Arteries  {aa.  metatarsece  plantares;  digital  branches)  are 
four  in  number,  and  run  forward  between  the  metatarsal  bones  and  in  contact 
with  the  Interossei.  Each  divides  into  a  pair  of  plantar  digital  arteries  which  sup- 
ply the  adjacent  sides  of  the  toes.  Near  their  points  of  division  each  sends  upward 
an  anterior  perforating  branch  to  join  the  corresponding  dorsal  metatarsal  artery. 
The  first  plantar  metatarsal  artery  {arteria  yrinceps  hallucis)  springs  from  the  junc- 
tion between  the  lateral  plantar  and  deep  plantar  arteries  and  sends  a  digital 
branch  to  the  medial  side  of  the  first  toe.  The  digital  branch  for  the  lateral  side 
of  the  fifth  toe  arise  from  the  lateral  plantar  artery  near  the  base  of  the  fifth 
metatarsal  bone. 

BIBLIOGRAPHY. 

Bean,  R.  B.:     A  Composite  Study  of  the  Subclavian  Artery  in  Man,  Am.  Jour.  Anat.,  1905,  iv. 

Bremer,  J.  L. :  On  the  Origin  of  the  Renal  Artery  in  Mammals  and  its  Anomalies,  Am.  Jour. 
Anat.,  1915,  xviii. 

Broman,  Ivar:  Ueber  die  Entwickelung  "  Wanderung, "  und  Variation  der  Bauchaortenzweige 
bei  den  Wirbeltieren,  Ergebnisse  der  Anat.  u.  Entwick.,  1906,  xvi. 

Eaton,  P.  B.:    The  Celiac  Axis,  Anat.  Rec,  1917,  xiii. 

Henle,  J. :    Anatomie  des  Menschen. 

HiTZROT,  J.  M.:  A  Composite  Study  of  the  Axillary  Artery  in  Man,  Johns  Hop.  Hosp.  Bull., 
1901,  xii. 

LiPSHUTZ,  B.  B.:  Studies  on  the  Blood  Vascular  Tree.  I.  A  Composite  Study  of  the  Femoral 
Artery,  Anat.  Rec,  1916,  x. 

PoiRiER  et  Charpy:     Trait6  d' Anatomie  Humaine. 

Quain's  Anatomy. 


THE  VEmS. 


THE  Veins  convey  the  blood  from  the  capillaries  of  the  different  parts  of  the 
body  to  the  heart.     They  consist  of  two  distinct  sets  of  vessels,  the  pulmonary 
and  systemic. 

The  Pulmonary  Veins,  unlike  other  veins,  contain  arterial  blood,  which  they  return 
from  the  lungs  to  the  left  atrium  of  the  heart. 

The  Systemic  Veins  return  the  venous  blood  from  the  body  generally  to  the 
right  atrium  of  the  heart. 

The  Portal  Vein,  an  appendage  to  the  systemic  venous  system,  is  confined  to 
the  abdominal  cavity,  and  returns  the  venous  blood  from  the  spleen  and  the  viscera 
of  digestion  to  the  liver.  This  vessel  ramifies  in  the  substance  of  the  liver  and  there 
breaks  up  into  a  minute  network  of  capillary-like  vessels,  from  which  the  blood 
is  conveyed  by  the  hepatic  veins  to  the  inferior  vena  cava. 

The  veins  commence  by  minute  plexuses  which  receive  the  blood  from  the  capil- 
laries. The  branches  arising  from  these  plexuses  unite  together  into  trunks,  and 
these,  in  their  passage  toward  the  heart,  constantly  increase  in  size  as  they  receive 
tributaries,  or  join  other  veins.  The  veins  are  larger  and  altogether  more  numerous 
than  the  arteries;  hence,  the  entire  capacity  of  the  venous  system  is  much  greater 
than  that  of  the  arterial;  the  capacity  of  the  pulmonary  veins,  however,  only 
slightly  exceeds  that  of  the  pulmonary  arteries.  The  veins  are  cylindrical  like  the 
arteries;  their  walls,  however,  are  thin  and  they  collapse  when  the  vessels  are 
empty,  and  the  uniformity  of  their  surfaces  is  interrupted  at  intervals  by  slight 
constrictions,  which  indicate  the  existence  of  valves  in  their  interior.  They  com- 
municate very  freely  with  one  another,  especially  in  certain  regions  of  the  body; 
and  these  communications  exist  between  the  larger  trunks  as  well  as  between  the 
smaller  branches.  Thus,  between  the  venous  sinuses  of  the  cranium,  and  between 
the  veins  of  the  neck,  where  obstruction  would  be  attended  with  imminent  danger 
to  the  cerebral  venous  system,  large  and  frequent  anastomoses  are  found.  The 
same  free  communication  exists  between  the  veins  throughout  the  whole  extent 
of  the  vertebral  canal,  and  between  the  veins  composing  the  various  venous  plexuses 
in  the  abdomen  and  pelvis,  e.  g.,  the  spermatic,  uterine,  vesical,  and  pudendal. 

The  systemic  venous  channels  are  subdivided  into  three  sets,  viz.,  superficial 
and  deep  veins,  and  venous  sinuses. 

The  Superficial  Veins  {cutaneous  veins)  are  found  between  the  layers  of  the 
superficial  fascia  immediately  beneath  the  skin;  they  return  the  blood  from  these 
structures,  and  communicate  with  the  deep  veins  by  perforating  the  deep  fascia. 

The  Deep  Veins  accompany  the  arteries,  and  are  usually  enclosed  in  the  same 
sheaths  with  those  vessels.  With  the  smaller  arteries — as  the  radial,  ulnar,  brachial, 
tibial,  peroneal — they  exist  generally  in  pairs,  one  lying  on  each  side  of  the  vessel, 
and  are  called  venae  comitantes.  The  larger  arteries — such  as  the  axillary,  sub- 
clavian, popliteal,  and  femoral — have  usually  only  one  accompanying  vein.  In 
certain  organs  of  the  body,  however,  the  deep  veins  do  not  accompany  the  arteries; 
for  instance,  the  veins  in  the  skull  and  vertebral  canal,  the  hepatic  veins  in  the  liver, 
and  the  larger  veins  returning  blood  from  the  bones. 

Venous  Sinuses  are  found  only  in  the  interior  of  the  skull,  and  consist  of  canals 
formed  by  a  separation  of  the  two  layers  of  the  dura  mater;  their  outer  coat  con- 
sists of  fibrous  tissue,  their  inner  of  an  endothelial  layer  continuous  with  the  lining 
membrane  of  the  veins. 

41  •  (641) 


642  '^^^^^^^        ANGIOLOGY 


THE   PULMONARY  VEINS   (VEN^  PULMONALES). 

The  pulmonary  veins  return  the  arteriahzed  blood  from  the  lungs  to  the  Text 
atrium  of  the  heart.  They  are  four  in  number,  two  from  each  lung,  and  are  desti- 
tute of  valves.  The  commence  in  a  capillary  net-work  upon  the  walls  of  the  air  sacs, 
where  they  are  continuous  with  the  capillary  ramifications  of  the  pulmonary  artery, 
and,  joining  together,  form  one  vessel  for  each  lobule.  These  vessels  uniting 
successively,  form  a  single  trunk  for  each  lobe,  three  for  the  right,  and  two  fo'r 
the  left  lung.  The  vein  from  the  middle  lobe  of  the  right  lung  generally  unites—, 
with  that  from  the  upper  lobe,  so  that  ultimately  two  trunks  from  each  lung  ar^l 
formed;  they  perforate  the  fibrous  layer  of  the  pericardium  and  open  separately 
into  the  upper  and  back  part  of  the  left  atrium.  Occasionally  the  three  veins 
on  the  right  side  remain  separate.  Not  infrequently  the  two  left  pulmonary 
veins  end  by  a  common  opening. 

At  the  root  of  the  lung,  the  superior  pulmonary  vein  lies  in  front  of  and  a  little 
below  the  pulmonary  artery;  the  inferior  is  situated  at  the  lowest  part  of  the  hilus 
of  the  lung  and  on  a  plane  posterior  to  the  upper  vein.  Behind  the  pulmonary 
artery  is  the  bronchus. 

Within  the  pericardium,  their  anterior  surfaces  are  invested  by  the  serous  layer  • 
of  this  membrane. 

The  right  pulmonary  veins  pass  behind  the  right  atrium  and  superior  vena  cava; 
the  left  in  front  of  the  descending  thoracic  aorta. 


THE  SYSTEMIC  VEINS. 

The  systemic  veins  may  be  arranged  into  three  groups :  (1)  The  veins  of  the  heart. 
(2)  The  veins  of  the  upper  extremities,  head,  neck,  and  thorax,  which  end  in  the 
superior  vena  cava.  (3)  The  veins  of  the  lower  extremities,  abdomen,  and  pelvis, 
which  end  in  the  inferior  vena  cava. 

THE  VEINS  OF  THE  HEART   (VV.  Cordis)    (Fig.   556). 

Coronary  Sinus  {sinus  coronarius), — Most  of  the  veins  of  the  heart  open  into 
the  coronary  sinus.  This  is  a  wide  venous  channel  about  2.25  cm.  in  length 
situated  in  the  posterior  part  of  the  coronary  sulcus,  and  covered  by  muscular 
fibers  from  the  left  atrium.  It  ends  in  the  right  atrium  between  the  opening  of 
the  inferior  vena  cava  and  the  atrioventricular  aperture,  its  orifice  being  guarded 
by  a  semilunar  valve,  the  valve  of  the  coronary  sinus  {valve  of  Thehesius) . 

Tributaries. — Its  tributaries  are  the  great,  small,  and  middle  cardiac  veins,  the 
posterior  vein  of  the  left  ventricle,  and  the  oblique  vein  of  the  left  atrium,  all  of 
which,  except  the  last,  are  provided  with  valves  at  their  orifices. 

1.  The  Great  Cardiac  Vein  {v.  cordis  magna;  left  coronary  vein)  begins  at  the  apex 
of  the  heart  and  ascends  along  the  anterior  longitudinal  sulcus  to  the  base  of  the 
ventricles.  It  then  curves  to  the  left  in  the  coronary  sulcus,  and  reaching  the 
back  of  the  heart,  opens  into  the  left  extremity  of  the  coronary  sinus.  It  receives 
tributaries  from  the  left  atrium  and  from  both  ventricles:  one,  the  left  marginal 
vein,  is  of  considerable  size,  and  ascends  along  the  left  margin  of  the  heart. 

2.  The  Small  Cardiac  Vein  {v.  cordis  parva;  right  coronary  vein)  runs  in  the  coronary 
sulcus  between  the  right  atrium  and  ventricle,  and  opens  into  the  right  extremity 
of  the  coronary  sinus.  It  receives  blood  from  the  back  of  the  right  atrium  and 
ventricle;  the  right  marginal  vein  ascends  along  the  right  margin  of  the  heart  and 
ioins  it  in  the  coronary  sulcus,  or  opens  directly  into  the  right  atrium. 


THE  VEINS  OF  THE  HEAD  AND  NECK 


643 


3.  The  Middle  Cardiac  Vein  {v.  cordis  media)  commences  at  the  apex  of  the  heart, 
ascends  in  the  posterior  longitudinal  sulcus,  and  ends  in  the  coronary  sinus  near 
its  right  extremity. 

4.  The  Posterior  Vein  of  the  Left  Ventricle  (v.  ijosterior  mntriculi  sinistri)  runs  on 
the  diaphragmatic  surface  of  the  left  ventricle  to  the  coronary  sinus,  but  may  end 
in  the  great  cardiac  vein. 

5.  The  Oblique  Vein  of  the  Left  Atrium  {v.  ohliqua  atrii  sinistri  [Marshalli] ;  oblique 
vein  of  Marshall)  is  a  small  vessel  which  descends  obliquely  on  the  back  of  the  left 
atrium  and  ends  in  the  coronary  sinus  near  its  left  extremity;  it  is  continuous  above 
with  the  ligament  of  the  left  vena  cava  {lig.  venoe  cavoe  sinistroe;  vestigial  fold  of 
Marshall),  and  the  two  structures  form  the  remnant  of  the  left  Cuvierian  duct. 

Azygos  vein 


Left  fulmonary  veins 

Oblique  vein  of  left  atrium 
Cheat  cardiac  vein 
Left  marginal  vein 


Right  pulmonary 
veins 


Small  cardiac  vein 


Posterior  vein  of  left  ventricle 

Middle  cardiac  vein 
Fig.  556. — Base  and  diaphragmatic  surface  of  heart. 


The  following  cardiac  veins  do  not  end  in  the  coronary  sinus:  (1)  the  anterior 
cardiac  veins,  comprising  three  or  four  small  vessels  which  collect  blood  from  the 
front  of  the  right  ventricle  and  open  into  the  right  atrium ;  the  right  marginal  vein 
frequently  opens  into  the  right  atrium,  and  is  therefore  sometimes  regarded  as 
belonging  to  this  group;  (2)  the  smallest  cardiac  veins  {veins  of  Thebesius),  con- 
sisting of  a  number  of  minute  veins  which  arise  in  the  muscular  wall  of  the  heart; 
the  majority  open  into  the  atria,  but  a  few  end  in  the  ventricles. 


THE  VEINS  OF  THE  HEAD  AND  NECK. 

The  veins  of  the  head  and  neck  may  be  subdivided  into  three  groups:  (1)  The 
veins  of  the  exterior  of  the  head  and  face.  (2)  The  veins  of  the  neck.  (3)  The  diploic 
veins,  the  veins  of  the  brain,  and  the  venous  sinuses  of  the  dura  mater. 


64^ 


ANGIOLOGY 


The  Veins  of  the  Exterior  of  the  Head  and  Face  (Fig.  557). 
The  veins  of  the  exterior  of  the  head  and  face  are : 


Frontal. 
Supraorbital. 
Angular. 
Anterior  Facial. 


Superficial  Temporal 
Internal  Maxillary. 
Posterior  Facial. 
Posterior  Auricular. 


Occipital. 


Frontal 

Communicating  branch 
with  ophthalmic  vein 

Angular 


Lhigual 
^~  Pharyngeal 


Fig.  557. — Veins  of  the  head  and  neck. 


The  frontal  vein  {v.  frontalis)  begins  on  the  forehead  in  a  venous  plexus  which 
communicates  with  the  frontal  branches  of  the  superficial  temporal  vein.  The 
veins  converge  to  form  a  single  trunk,  which  runs  downward  near  the  middle  line 
of  the  forehead  parallel  with  the  vein  of  the  opposite  side.  The  two  veins  are  joined, 
at  the  root  of  the  nose,  by  a  transverse  branch,  called  the  nasal  arch,  which  receives 
some  small  veins  from  the  dorsum  of  the  nose.  At  the  root  of  the  nose  the  veins 
diverge,  and,  each  at  the  medial  angle  of  the  orbit,  joins  the  supraorbital  vein,  to 


THE  VEINS  OF  THE  EXTERIOR  OF  THE  HEAD  AND  FACE         645 

form  the  angular  vein.  Occasionally  the  frontal  veins  join  to  form  a  single  trunk, 
which  bifurcates  at  the  root  of  the  nose  into  the  two  angular  veins. 

The  supraorbital  vein  (v.  swpraorhiialis)  begins  on  the  forehead  where  it  com- 
municates with  the  frontal  branch  of  the  superficial  temporal  vein.  It  runs  down- 
ward superficial  to  the  Frontalis  muscle,  and  joins  the  frontal  vein  at  the  medial 
angle  of  the  orbit  to  form  the  angular  vein.  Previous  to  its  junction  with  the  frontal 
vein,  it  sends  through  the  supraorbital  notch  into  the  orbit  a  branch  which  com- 
municates with  the  ophthalmic  vein;  as  this  vessel  passes  through  the  notch,  it 
receives  the  frontal  diploic  vein  through  a  foramen  at  the  bottom  of  the  notch. 

The  angular  vein  {v.  angularis)  formed  by  the  junction  of  the  frontal  and  supra- 
orbital veins,  runs  obliquely  downward,  on  the  side  of  the  root  of  the  nose,  to  tlje 
level  of  the  lower  margin  of  the  orbit,  where  it  becomes  the  anterior  facial  vein. 
It  receives  the  veins  of  the  ala  nasi,  and  communicates  with  the  superior  ophthalmic 
vein  through  the  nasofrontal  vein,  thus  establishing  an  important  anastomosis 
between  the  anterior  facial  vein  and  the  cavernous  sinus. 

The  anterior  facial  vein  (v.  facialis  anterior;  facial  vein)  commences  at  the  side 
of  the  root  of  the  nose,  and  is  a  direct  continuation  of  the  angular  vein.  It  lies 
behind  the  external  maxillary  (facial)  artery  and  follows  a  less  tortuous  course. 
It  runs  obliquely  downward  and  backward,  beneath  the  Zygomaticus  and  zygo- 
matic head  of  the  Quadratus  labii  superioris,  descends  along  the  anterior  border 
and  then  on  the  superficial  surface  of  the  Masseter,  crosses  over  the  body  of  the 
mandible,  and  passes  obliquely  backward,  beneath  the  Platysma  and  cervical 
fascia,  superficial  to  the  submaxillary  gland,  the  Digastricus  and  Stylohyoideus. 
It  unites  with  the  posterior  facial  vein  to  form  the  common  facial  vein,  which 
crosses  the  external  carotid  artery  and  enters  the  internal  jugular  vein  at  a  vari- 
able point  below  the  hyoid  bone.  From  near  its  termination  a  communicating 
branch  often  runs  down  the  anterior  border  of  the  Sternocleidomastoideus  to  join 
the  lower  part  of  the  anterior  jugular  vein.  The  facial  vein  has  no  valves,  and  its 
walls  are  not  so  flaccid  as  most  superficial  veins. 

Tributaries. — The  anterior  facial  vein  receives  a  branch  of  considerable  size, 
the  deep  facial  vein,  from  the  pter^'goid  venous  plexus.  It  is  also  joined  by  the 
superior  and  inferior  palpebral,  the  superior  and  inferior  labial,  the  buccinator 
and  the  masseteric  veins.  Below  the  mandible  it  receives  the  submental,  palatine, 
and  submaxillary  veins,  and,  generally,  the  vena  comitans  of  the  hypoglossal  nerve. 

The  superficial  temporal  vein  (v.  temporalis  superficialis)  begins  on  the  side  and 
vertex  of  the  skull  in  a  plexus  which  communicates  with  the  frontal  and  supra- 
orbital veins,  with  the  corresponding  vein  of  the  opposite  side,  and  with  the  pos- 
terior auricular  and  occipital  veins.  From  this  net-work  frontal  and  parietal  branches 
arise,  and  unite  above  the  zygomatic  arch  to  form  the  trunk  of  the  vein,  which  is 
joined  in  this  situation  by  the  middle  temporal  vein,  from  the  substance  of  the  Tem- 
poralis. It  then  crosses  the  posterior  root  of  the  zygomatic  arch,  enters  the  sub- 
stance of  the  parotid  gland,  and  unites  with  the  internal  maxillary  vein  to  form  the 
posterior  facial  vein. 

Tributaries. — The  superficial  temporal  vein  receives  in  its  course  some  parotid 
veins,  articular  veins  from  the  temporomandibular  joint,  anterior  auricular  veins 
from  the  auricula,  and  the  transverse  facial  from  the  side  of  the  face.  The  middle 
temporal  vein  receives  the  orbital  vein,  which  is  formed  by  some  lateral  palpebral 
branches,  and  passes  backward  between  the  layers  of  the  temporal  fascia  to  join 
the  superficial  temporal  vein. 

The  pterygoid  plexus  (plexus  pterygoideus)  is  of  considerable  size,  and  is  situated 
between  the  Temporalis  and  Pterygoideus  externus,  and  partly  between  the  two 
Pterygoidei.  It  receives  tributaries  corresponding  with  the  branches  of  the  internal 
maxillary  artery.  Thus  it  receives  the  sphenopalatine,  the  middle  meningeal,  the 
deep  temporal,  the  pterygoid,  masseteric,  buccinator,  alveolar,  and  some  palatine 


646  ^^^^^^^^       ANGIOLOGY 

veins,  and  a  branch  which  communicates  with  the  ophthalmic  vein  through  the 
inferior  orbital  fissure.  This  plexus  communicates  freely  with  the  anterior  facial 
vein;  it  also  communicates  with  the  cavernous  sinus,  by  branches  through  the 
foramen  Vesalii,  foramen  ovale,  and  foramen  lacerum. 

The  internal  maxillary  vein  {v.  maxillaris  interna)  is  a  short  trunk  which  accom- 
panics  the  first  part  of  the  internal  maxillary  artery.  It  is  formed  by  a  confluence 
of  the  veins  of  the  pterygoid  plexus,  and  passes  backward  between  the  spheno- 
mandibular  ligament  and  the  neck  of  the  mandible,  and  unites  with  the  temporal 
vein  to  form  the  posterior  facial  vein. 

The  posterior  facial  vein  (v.  facialis  posterior;  temporomaxillary  vein),  formed 
by  the  union  of  the  superficial  temporal  and  internal  maxillary  veins,  descends  in 
the  substance  of  the  parotid  gland,  superficial  to  the  external  carotid  artery  but 
beneath  the  facial  nerve,  between  the  ramus  of  the  mandible  and  the  Sternocleido- 
mastoideus  muscle.  It  divides  into  two  branches,  an  anterior,  which  passes  forward 
and  unites  with  the  anterior  facial  vein  to  form  the  common  facial  vein  and  a  pos- 
terior, which  is  joined  by  the  posterior  auricular  vein  and  becomes  the  external 
jugular  vein. 

The  posterior  auricular  vein  {v.  auricularis  posterior)  begins  upon  the  side  of 
the  head,  in  a  plexus  which  communicates  with  the  tributaries  of  the  occipital, 
and  superficial  temporal  veins.  It  descends  behind  the  auricula,  and  joins  the 
posterior  division  of  the  posterior  facial  vein  to  form  the  external  jugular.  It 
receive  the  stylomastoid  vein,  and  some  tributaries  from  the  cranial  surface  of  the 
auricula. 

The  occipital  vein  {v.  occipitalis)  begins  in  a  plexus  at  the  back  part  of  the  vertex 
of  the  skull,  From  the  plexus  emerges  a  single  vessel,  which  pierces  the  cranial 
attachment  of  the  Trapezius  and,  dipping  into  the  suboccipital  triangle,  joins  the 
deep  cervical  and  vertebral  veins.  Occasionally  it  follows  the  course  of  the  occipital 
artery  and  ends  in  the  internal  jugular;  in  other  instances,  it  joins  the  posterior 
auricular  and  through  it  opens  into  the  external  jugular.  The  parietal  emissary 
vein  connects  it  with  the  superior  sagittal  sinus ;  and  as  it  passes  across  the  mastoid 
portion  of  the  temporal  bone,  it  receives  the  mastoid  emissary  vein  which  connects 
it  with  the  transverse  sinus.    The  occipital  diploic  vein  sometimes  joins  it. 

The  Veins  of  the  Neck  (Fig.  558). 

The  veins  of  the  neck,  which  return  the  blood  from  the  head  and  face,  are : 

External  Jugular.  Anterior  Jugular. 

Posterior  External  Jugular.  Internal  Jugular. 

Vertebral. 

The  external  jugular  vein  {v.  jugularis  externa)  receives  the  greater  part  of  the 
blood  from  the  exterior  of  the  cranium  and  the  deep  parts  of  the  face,  being  formed 
by  the  junction  of  the  posterior  division  of  the  posterior  facial  with  the  posterior 
auricular  vein.  It  commences  in  the  substance  of  the  parotid  gland,  on  a  level 
with  the  angle  of  the  mandible,  and  runs  perpendicularly  down  the  neck,  in  the 
direction  of  a  line  drawn  from  the  angle  of  the  mandible  to  the  middle  of  the  clavicle 
at  the  posterior  border  of  the  Sternocleidomastoideus.  In  its  course  it  crosses 
the  Sternocleidomastoideus  obliquely,  and  in  the  subclavian  triangle  perforates 
the  deep  fascia,  and  ends  in  the  subclavian  vein,  lateral  to  or  in  front  of  the  Scalenus 
anterior.  It  is  separated  from  the  Sternocleidomastoideus  by  the  investing  layer 
of  the  deep  cervical  fascia,  and  is  covered  by  the  Platysma,  the  superficial  fascia, 
and  the  integument;  it  crosses  the  cutaneous  cervical  nerve,  and  its  upper  half 
runs  parallel  with  the  great  auricular  nerve.  The  external  jugular  vein  varies  in 
size,  bearing  an  inverse  proportion  to  the  other  veins  of  the  neck,  it  is  occasionally 


I 
I 


THE  VEINS  OF  THE  NECK 


647 


double.  It  is  provided  with  two  pairs  of  valves,  the  lower  pair  being  placed  at 
its  entrance  into  the  subclavian  vein,  the  upper  in  most  cases  about  4  cm,  above  the 
clavicle.  The  portion  of  vein  between  the  two  sets  of  valves  is  often  dilated,  and 
is  termed  the  sinus.  These  valves  do  not  prevent  the  regurgitation  of  the  blood, 
or  the  passage  of  injection  from  below  upward. 

Tributaries. — This  vein  receives  the  occipital  occasionally,  the  posterior  external 
jugular,  and,  near  its  termination,  the  transverse  cervical,  transverse  scapular,  and 
anterior  jugular  veins;  in  the  substance  of  the  parotid,  a  large  branch  of  commu- 
nication from  the  internal  jugular  joins  it. 


b 


Fia.  558.- 


Svbclavian  vein 
-The  veins  of  the  neck,  viewed  from  in  front. 


(Spalteholz.) 


The  posterior  external  jugular  vein  {v.  jugularis  posterior)  begins  in  the  occipital 
region  and  returns  the  blood  from  the  skin  and  superficial  muscles  in  the  upper  and 
back  part  of  the  neck,  lying  between  the  Splenius  and  Trapezius.  It  runs  down 
the  back  part  of  the  neck,  and  opens  into  the  external  jugular  vein  just  below  the 
middle  of  its  course. 

The  anterior  jugular  vein  (i'.  jugularis  anterior)  begins  near  the  hyoid  bone  by 
the  confluence  of  several  superficial  veins  from  the  submaxillary  region.  It  descends 
between  the  median  line  and  the  anterior  border  of  the  Sternocleidomastoideus, 
and,  at  the  lower  part  of  the  neck,  passes  beneath  that  muscle  to  open  into  the  ter- 
mination of  the  external  jugular,  or,  in  some  instances,  into  the  subclavian  vein 
(Figs.  557,  558).    It  varies  considerably  in  size,  bearing  usually  an  inverse  propor- 


648 


ANGIOLOGY 


tion  to  the  external  jugular;  most  frequently  there  are  two  anterior  jugulars, 
right  and  left;  but  sometimes  only  one.  Its  tributaries  are  some  laryngeal  veins,] 
and  occasionally  a  small  thyroid  vein.  Just  above  the  sternum  the  two  anterior! 
jugular  veins  communicate  by  a  transverse  trunk,  the  venous  jugular  arch,  which! 
receive  tributaries  from  the  inferior  thyroid  veins;  each  also  communicates  with  thej 
internal  jugular.    There  are  no  valves  in  this  vein. 

The  internal  jugular  vein  (v.  jugularis  interna)  collects  the  blood  from  the  brain,  I 
from  the  superficial  parts  of  the  face,  and  from  the  neck.  It  is  directly  continuous' 
with  the  transverse  sinus,  and  begins  in  the  posterior  compartment  of  the  jugular 
foramen,  at  the  base  of  the  skull.  At  its  origin  it  is  somewhat  dilated,  and  this 
dilatation  is  called  the  superior  bulb.  It  runs  down  the  side  of  the  neck  in  a  vertical 
direction,  lying  at  first  lateral  to  the  internal  carotid  artery,  and  then  lateral 
to  the  common  carotid,  and  at  the  root  of  the  neck  unites  with  the  subclavian  vein 
to  form  the  innominate  vein;  a  little  above  its  termination  is  a  second  dilatation, 
the  inferior  bulb.  Above,  it  lies  upon  the  Rectus  capitis  lateralis,  behind  the  internal 
carotid  artery  and  the  nerves  passing  through  the  jugular  foramen;  lower  down, 
the  vein  and  artery  lie  upon  the  same  plane,  the  glossopharyngeal  and  hypoglossal 
nerves  passing  forward  between  them;  the  vagus  descends  between  and  behind 
the  vein  and  the  artery  in  the  same  sheath,  and  the  accessory  runs  obliquely 
backward,  superficial  or  deep  to  the  vein.  At  the  root  of  the  neck  the  right  internal 
jugular  vein  is  placed  at  a  little  distance  from  the  common  carotid  artery,  and 


DORSALIS 

LINGUjE  ARTCRV. 

LINGUAL  VEIN 

VEINS  OF 

DORSUM   OF 

TONGUE 


\ 


HYPOGLOSSAL  NERVE 


Fig.  659. — Veins  of  the  tongue.     The  hypoglossal  nerve  has  been  displaced  downward  in  this  preparation. 

(.Testut  after  Hirschfeld.) 


crosses  the  first  part  of  the  subclavian  artery,  while  the  left  internal  jugular  vein 
usually  overlaps  the  common  carotid  artery.  The  left  vein  is  generally  smaller 
than  the  right,  and  each  contains  a  pair  of  valves,  which  are  placed  about  2.5  cm. 
above  the  termination  of  the  vessel. 

Tributaries. — This  vein  receives  in  its  course  the  inferior  petrosal  sinus,  the  common 
facial,  lingual,  pharyngeal,  superior  and  middle  thyroid  veins,  and  sometimes  the 
occipital.  The  thoracic  duct  on  the  left  side  and  the  right  lymphatic  duct  on  the 
right  side  open  into  the  angle  of  union  of  the  internal  jugular  and  subclavian  veins. 

The  Inferior  Petrosal  Sinus  (simis  petrostis  inferior)  leaves  the  skull  through  the 
anterior  part  of  the  jugular  foramen,  and  joins  the  superior  bulb  of  the  internal 
jugular  vein. 

The  Lingual  Veins  (w.  linguales)  begin  on  the  dorsum,  sides,  and  under  surface 
of  the  tongue,  and,  passing  backward  along  the  course  of  the  lingual  artery,  end 
in  the  internal  jugular  vein.    The  vena  comitans  of  the  hypoglossal  nerve  (ranine 


THE  VEINS  OF  THE  NECK 


649 


vein),  a  branch  of  considerable  size,  begins  below  the  tip  of  the  tongue,  and  may 
join  the  lingual;  generally,  however,  it  passes  backward  on  the  Hyoglossus,  and 
joins  the  common  facial. 

The  Pharyngeal  Veins  (vv.  j^haryngece)  begin  in  the  pharyngeal  plexus  on  the  outer 
surface  of  the  pharynx,  and,  after  receiving  some  posterior  meningeal  veins  and  the 
vein  of  the  pterygoid  canal,  end  in  the  internal  jugular.  They  occasionally  open 
into  the  facial,  lingual,  or  superior  thyroid  vein. 

The  Superior  Thyroid  Vein  (v.  thyreoidea  swperioris)  (Fig.  560)  begins  in  the  sub- 
stance and  on  the  surface  of  the  thyroid  gland,  by  tributaries  corresponding  with 
the  branches  of  the  superior  thyroid  artery,  and  ends  in  the  upper  part  of  the 
internal  jugular  vein.    It  receives  the  superior  laryngeal  and  cricothyroid  veins. 

The  IVfiddle  Thjrroid  Vein  (Figs.  561,  562)  collects  the  blood  from  the  lower  part 
of  the  thyroid  gland,  and  after  being'  joined  by  some  veins  from  the  larynx  and 
trachea,  ends  in  the  lower  part  of  the  internal  jugular  vein. 

The  common  facial  and  occipital  veins  have  been  described.  • 


External  carotid  artery 


Vagtis  nerve 


Superior  thyroid  artery 
Superior  thyroid  vein 


Middle  thyroid  vein 


FiQ.  5G0. — The  veins  of  the  thyroid  gland. 


The  vertebral  vein  (v.  vertebralis)  is  formed  in  the  suboccipital  triangle,  from 
numerous  small  tributaries  which  spring  from  the  internal  vertebral  venous  plexuses 
and  issue  from  the  vertebral  canal  above  the  posterior  arch  of  the  atlas.  They 
unite  with  small  veins  from  the  deep  muscles  at  the  upper  part  of  the  back  of 
the  neck,  and  form  a  vessel  which  enters  the  foramen  in  the  transverse  process 
of  the  atlas,  and  descends,  forming  a  dense  plexus  around  the  vertebral  artery, 
in  the  canal  formed  by  the  foramina  transversaria  of  the  cervical  vertebrae.  This 
plexus  ends  in  a  single  trunk,  which  emerges  from  the  foramen  transversarium  of 
the  sixth  cervical  vertebra,  and  opens  at  the  root  of  the  neck  into  the  back  part 
of  the  innominate  vein  near  its  origin,  its  mouth  being  guarded  by  a  pair  of  valves. 
On  the  right  side,  it  crosses  the  first  part  of  the  subclavian  artery. 


Tributaries. — The  vertebral  vein  communicates  with  the  transverse  sinus  by 
a  vein  which  passes  through  the  condyloid  canal,  when  that  canal  exists.      It 


SUPERIOR 

THYROID 

ARTERY 


INFERIOR 

THYROID 

VEIN 


Fig.  561. — Diagram  showing  common  arrangement  of  thyroid  veins.     (Kocher.) 


STERNO- 
THYROID 
MUSCLE 


INFERIOR 
THYROID 


Fio.  562.— The  fascia  and  middle  thyroid  veins.     The  veins  here  desitcnated  the  inferior  thyroid  are  called  by 
Kocher  the  thyroidea  ima.      (Poirier  and  Charpy.) 


receives  branches  from  the  occipital  vein  and  from  the  prevertebral  muscles,  from 
the  internal  and  external  vertebral  venous  plexuses,  from  the  anterior  vertebral 


THE  DIPLOIC  VEINS 


651 


and  the  deep  cervical  veins;  close  to  its  termination  it  is  sometimes  joined  by  the 
first  intercostal  vein. 

The  Anterior  Vertebral  Vein  commences  in  a  plexus  around  the  transverse  pro- 
cesses of  the  upper  cervical  vertebrae,  descends  in  company  with  the  ascending 
cervical  artery  between  the  Scalenus  anterior  and  Longus  capitis  muscles,  and 
opens  into  the  terminal  part  of  the  vertebral  vein. 


VERTEBRAL- 


VERTEBRAL 


ASCENDING 
CERVICAL 


Fig.  563. — The  vertebral  vein.     (Poirier  and  Charpy.) 

The  Deep  Cervical  Vein  {v.  cervicalis  profunda;  posterior  vertebral  or  posterior 
deep  cervical  vein)  accompanies  its  artery  between  the  Semispinales  capitis  and 
colli.  It  begins  in  the  suboccipital  region  by  communicating  branches  from  the 
occipital  vein  and  by  small  veins  from  the  deep  muscles  at  the  back  of  the  neck. 
It  receives  tributaries  from  the  plexuses  around  the  spinous  processes  of  the  cer- 
vical vertebrae,  and  terminates  in  the  lower  part  of  the  vertebral  vein. 


I 


The  Diploic  Veins  (Venae  Diploicae)  (Fig.  564). 

The  diploic  veins  occupy  channels  in  the  diploe  of  the  cranial  bones.  They  are 
large  and  exhibit  at  irregular  intervals  pouch-like  dilatations;  their  walls  are  thin, 
and  formed  of  endothelium  resting  upon  a  layer  of  elastic  tissue. 

So  long  as  the  cranial  bones  are  separable  from  one  another,  these  veins  are 
confined  to  the  particular  bones;  but  when  the  sutures  are  obliterated,  they  unite 
with  each  other,  and  increase  in  size.  They  communicate  with  the  meningeal 
veins  and  the  sinuses  of  the  dura  mater,  and  with  the  veins  of  the  pericranium. 
They  consist  of  (1)  the  frontal,  which  opens  into  the  supraorbital  vein  and  the 
superior  sagittal  sinus;  (2)  the  anterior  temporal,  which  is  confined  chiefly  to  the 
frontal  bone,  and  opens  into  the  sphenoparietal  sinus  and  into  one  of  the  deep 
temporal  veins,  through  an  aperture  in  the  great  wing  of  the  sphenoid;  (3)  the 
posterior  temporal,  which  is  situated  in  the  parietal  bone,  and  ends  in  the  transverse 
sinus,  through  an  aperture  at  the  mastoid  angle  of  the  parietal  bone  or  through  the 


ANGIOLOGY 

mastoid  foramen;  and  (4)  the  occipital,  the  largest  of  the  four,  which  is  confined 
to  the  occipital  bone,  and  opens  either  externally  into  the  occipital  vein,  or  inter- 
nally into  the  transverse  sinus  or  into  the  confluence  of  the  sinuses  (torcular 
Herophili). 


I 


Fia.  564. — Veins  of  the  diploe  as  displayed  by  the  removal  of  the  outer  table  of  the  skull. 


The  Veins  of  the  Brain. 

The  veins  of  the  brain  possess  no  valves,  and  their  walls,  owing  to  the  absence 
of  muscular  tissue,  are  extremely  thin.  They  pierce  the  arachnoid  membrane  and 
the  inner  or  meningeal  layer  of  the  dura  mater,  and  open  into  the  cranial  venous 
sinuses.    They  may  be  divided  into  two  sets,  cerebral  and  cerebellar. 

The  cerebral  veins  (vv.  cerebri)  are  divisible  into  external  and  internal  groups 
according  as  they  drain  the  outer  surfaces  or  the  inner  parts  of  the  hemispheres. 

The  external  veins  are  the  superior,  inferior,  and  middle  cerebral. 

The  Superior  Cerebral  Veins  (vv.  cerebri  swperiores) ,  eight  to  twelve  in  number, 
drain  the  superior,  lateral,  and  medial  surfaces  of  the  hemispheres,  and  are  mainly 
lodged  in  the  sulci  between  the  gyri,  but  some  run  across  the  gyri.  They  open  into 
the  superior  sagittal  sinus;  the  anterior  veins  runs  nearly  at  right  angles  to  the 
sinus;  the  posterior  and  larger  veins  are  directed  obliquely  forward  and  open  into 
the  sinus  in  a  direction  more  or  less  opposed  to  the  current  of  the  blood  contained 
within  it. 

The  Middle  Cerebral  Vein  {v.  cerebri  media;  superficial  Sylvian  vein)  begins  on  the 
lateral  surface  of  the  hemisphere,  and,  running  along  the  lateral  cerebral  fissure, 
ends  in  the  cavernous  or  the  sphenoparietal  sinus.  It  is  connected  (a)  with  the 
superior  sagittal  sinus  by  the  great  anastomotic  vein  of  Trolard,  which  opens  into  one 
of  the  superior  cerebral  veins;  (6)  with  the  transverse  sinus  by  the  posterior  anasto- 
motic vein  of  Labbe,  which  courses  over  the  temporal  lobe. 

The  Inferior  Cerebral  Veins  {vv.  cerebri  inferiores),  of  small  size,  drain  the  under 
surfaces  of  the  hemispheres.  Those  on  the  orbital  surface  of  the  frontal  lobe  join 
the  superior  cerebral  veins,  and  through  these  open  into  the  superior  sagittal 
sinus;  those  of  the  temporal  lobe  anastomose  with  the  middle  cerebral  and  basal 
veins,  and  join  the  cavernous,  sphenoparietal,  and  superior  petrosal  sinuses. 


THE  VEINS  OF  THE  BRAIN 


653 


I 


n 


The  basal  vein  is  formed  at  the  anterior  perforated  substance  by  the  union  of  (a) 
a  small  anterior  cerebral  vein  which  accompanies  the  anterior  cerebral  artery,  (b) 
the  deep  middle  cerebral  vein  (deej)  Sylvian  vein),  which  receives  tributaries  from 
the  insula  and  neighboring  gyri,  and  runs  in  the  lower  part  of  the  lateral  cerebral 
fissure,  and  (c)  the  inferior  striate  veins,  which  leave  the  corpus  striatum  through 
the  anterior  perforated  substance.  The  basal  vein  passes  backward  around  the 
cerebral  peduncle,  and  ends  in  the  internal  cerebral  vein  (vein  of  Galen) ;  it  receives 
tributaries  from  the  interpeduncular  fossa,  the  inferior  horn  of  the  lateral  ventricle, 
the  hippocampal  gyrus,  and  the  mid-brain. 

The  Internal  Cerebral  Veins  (vv.  cerebri  internee;  veins  of  Galen;  deep  cerebral 
veins)  drain  the  deep  parts  of  the  hemisphere  and  are  two  in  number;  each  is  formed 
near  the  interventricular  foramen  by  the  union  of  the  terminal  and  choroid  veins. 
They  run  backward  parallel  with  one  another,  between  the  layers  of  the  tela 
chorioidea  of  the  third  ventricle,  and  beneath  the  splenium  of  the  corpus  callosum, 
where  they  unite  to  form  a  short  trunk,  the  great  cerebral  vein;  just  before  their 
union  each  receives  the  corresponding  basal  vein. 

The  terminal  vein  (v.  terminalis;  vena  corporis  striati)  commences  in  the  groove 
between  the  corpus  striatum  and  thalamus,  receives  numerous  veins  from  both 
of  these  parts,  and  unites  behind  the  crus  fornicis  with  the  choroid  vein,  to  form 
one  of  the  internal  cerebral  veins.  The  choroid  vein  runs  along  the  whole  length  of 
the  choroid  plexus,  and  receives  veins  from  the  hippocampus,  the  fornix,  and  the 
corpus  callosum. 


k\        CAUDATE 
NUCLEUS 


Pig.  565. — Velum  interpositum.     (Poirier  and  Charpy.) 


GREAT 
CEREBRAL  VEIN 


The  Great  Cerebral  Vein  {v.  cerebri -magna  [Galeni];  great  vein  of  Galen)  (Fig.  565), 
formed  by  the  union  of  the  two  internal  cerebral  veins,  is  a  short  median  trunk 
which  curves  backward  and  upward  around  the  splenium  of  the  corpus  callosum 
and  ends  in  the  anterior  extremity  of  the  straight  sinus. 

The  cerebellar  veins  are  placed  on  the  surface  of  the  cerebellum,  and  are  dis- 
posed in  two  sets,  superior  and  inferior.  The  superior  cerebellar  veins  {vv.  cerebelli 
superiores)  pass  partly  forward  and  medialward,  across  the  superior  vermis,  to  end 
in  the  straight  sinus  and  the  internal  cerebral  veins,  partly  lateralward  to  the  trans- 
verse and  superior  petrosal  sinuses.  The  inferior  cerebellar  veins  {vv.  cerebelli  infe- 
rioreg)  of  large  size,  end  in  the  transverse,  superior  petrosal,  and  occipital  sinuses. 


654 


ANGIOLOGY 


The  Sinuses  of  the  Dura  Mater  (Sinus  Durse  Matris). 

Emissary  Veins. 


Ophthahnic  Veins  and 


The  sinuses  of  the  dura  mater  are  venous  channels  which  drain  the  blood  from  the 
brain;  they  are  devoid  of  valves,  and  are  situated  between  the  two  layers  of  the 
dura  mater  and  lined  by  endothelium  continuous  with  that  which  lines  the  veins. 
They  may  be  divided  into  two  groups:  (1)  a  postero-superior,  at  the  upper  and  back, 
part  of  the  skull,  and  (2)  an  antero-inferior,  at  the  base  of  the  skull. 

The  postero-superior  group  comprises  the 


41 


Superior  Sagittal. 
Inferior  Sagittal. 


Straight. 

Two  Transverse. 


Occipital. 


Dural  vein 


Superior  sagittal 
sinus 


Venous 
lacuna 


Venous  lacuna 


Fig.  566.  —  Superior  sagittal  sinus  laid  open  after  remova  of  the  skull  cap.  Thechordse  Willisii  are  clearly  seen. 
The  venous  lacunae  are  also  well  shown;  from  two  of  them  probes  are  passed  into  the  superior  sagittal  sinus. 
(Poirier  and  Charpy.) 

The  superior  sagittal  sinus  {sinus  sagittalis  superior;  superior  longitudinal  sinu^) 
(Figs.  566,  567)  occupies  the  attached  or  convex  margin  of  the  falx  cerebri.  Com- 
mencing at  the  foramen  cecum,  through  which  it  receives  a  vein  from  the  nasal 
cavity,  it  runs  from  before  backward,  grooving  the  inner  surface  of  the  frontal, 
the  adjacent  margins  of  the  two  parietals,  and  the  superior  division  of  the  cruciate 
eminence  of  the  occipital;  near  the  internal  occipital  protuberance  it  deviates  to 
one  or  other  side  (usually  the  right),  and  is  continued  as  the  corresponding  trans- 
verse sinus.  It  is  triangular  in  section,  narrow  in  front,  and  gradually  increases  in 
size  as  it  passes  backward.  Its  inner  surface  presents  the  openings  of  the  superior 
cerebral  veins,  which  run,  for  the  most  part,  obliquely  forward,  and  open  chiefly 
at  the  back  part  of  the  sinus,  their  orifices  being  concealed  by  fibrous  folds ;  numerous 


THE  SINUSES  OF  THE  DURA  MATER 


655 


fibrous  bands  {chordae  Willisii)  extend  transversely  across  the  inferior  angle  of 
the  sinus;  and,  lastly,  small  openings  communicate  with  irregularly  shaped  venous 
spaces  {venous  lacunoe)  in  the  dura  mater  near  the  sinus.  There  are  usually  three 
lacunae  on  either  side  of  the  sinus :  a  small  frontal,  a  large  parietal,  and  an  occipital, 
intermediate  in  size  between  the  other  two  (Sargent^.  Most  of  the  cerebral 
veins  from  the  outer  surface  of  the  hemisphere  open  into  these  lacunae,  and  numer- 
ous arachnoid  granulations  {Pacchionian  bodies)  project  into  them  from  below. 
The  superior  sagittal  sinus  receives  the  superior  cerebral  veins,  veins  from  the  diploe 
and  dura  mater,  and,  near  the  posterior  extremity  of  the  sagittal  suture,  veins  from 
the  pericranium,  which  pass  through  the  parietal  foramina. 

The  numerous  communications  exist  between  this  sinus  and  the  veins  of  the 
nose,  scalp,  and  diploe. 


Great  cerebral  vein 

Glossopharyngeal  nerve 

Vagus  nerce 
Accessory  iierve 

Acoustic  nerve 

Facial  nerve 


Optic  nerves 
Ophthalmic  artery 
Diaphragma  sellce 
Oculomotor  nerves 
Trochlear  nerve 


Abducent  nerve    Trigeminal  nerve 
Fia.  567. — Dura  mater  and  its  processes  exposed  by  removing  part  of  the  right  half  of  the  skull,  and  the  brain. 


The  inferior  sagittal  sinus  {sinus  sagittalis  inferior;  inferior  longitudinal  sinus) 
(Fig.  567)  is  contained  in  the  posterior  half  or  two-thirds  of  the  free  margin  of  the 
falx  cerebri.  It  is  of  a  cylindrical  form,  increases  in  size  as  it  passes  backward,  and 
ends  in  the  straight  sinus.  It  receives  several  veins  from  the  falx  cerebri,  and 
occasionally  a  few  from  the  medial  surfaces  of  the  hemispheres. 

The  straight  sinus  {sinus  rectus;  tentorial  sinus)  (Figs,  567,  569)  is  situated  at 
the  line  of  junction  of  the  falx  cerebri  with  the  tentorium  cerebelli.    It  is  triangular 

1  Journal  of  Anatomy  and  Physiology,  vol.  xlv. 


656 


ANGIOLOGY 


in  section,  increases  in  size  as  it  proceeds  backward,  and  runs  dowTiward  and  back- 
ward from  the  end  of  the  inferior  sagittal  sinus  to  the  transverse  sinus  of  the  oppo- 


Torcular  herophili 


amen  cecum. 


Fig.  568. — Sagittal  section  o^  the  skuUi  showing  the  sinuses  of  the  dura. 


Optic  nerve 
Diaphragma  sellce 
Free  margin  of  tentorium 


Internal  earotid  artery 
Oculomotor  nerve 

Attached  margin  of  tentorium 


Comfluence  of  the  sinuses 
Fta.  569. — Tentorium  cerebelli  from  above. 


« 


site  side  to  that  into  which  the  superior  sagittal  sinus  is  prolonged.    Its  terminal 
part  communicates  by  a  cross  branch  with  the  confluence  of  the  sinuses.    Besides 


I 


THE  SINUSES  OF  THl 


>UR^ 


I 


the  inferior  sagittal  sinus,  it  receives  the  great  cerebral  vein  (great  vein  of  Galen) 
and  the  superior  cerebellar  veins.    A  few  transverse  bands  cross  its  interior. 

The  transverse  sinuses  (sinus  transversus;  lateral  sinuses)  (Figs.  569,  570)  are 
of  large  size  and  begin  at  the  internal  occipital  protuberance ;  one,  generally  the 
right,  being  the  direct  continuation  of  the  superior  sagittal  sinus,  the  other  of  the 
straight  sinus.  Each  transverse  sinus  passes  lateralward  and  forward,  describing 
a  slight  curve  with  its  convexity  upward,  to  the  base  of  the  petrous  portion  of 
the  temporal  bone,  and  lies,  in  this  part  of  its  course,  in  the  attached  margin  of 
the  tentorium   cerebelli;    it  then  leaves  the  tentorium  and  curves  downward  and 

^^  >7?'i*L'^?5-'?^^^^fe^^^^    Levator  palpebrcB 

■  *'"  '^       "^^^       -™r    I      -      -^        ,  ^ggf JJ5  superior 


Sup.  oph- 
thalmic vein 


Sphenoparietal 
sinua 


I 


End  of  straight  sinus'  Vertebral  artery 

Superior  sagittal  sinus 
Fig.  570. — The  sinuses  at  the  base  of  the  skull. 

medialward  to  reach  the  jugular  foramen,  where  it  ends  in  the  internal  jugular 
vein.  In  its  course  it  rests  upon  the  squama  of  the  occipital,  the  mastoid  angle 
of  the  parietal,  the  mastoid  part  of  the  temporal,  and,  just  before  its  termination, 
the  jugular  process  of  the  occipital;  the  portion  which  occupies  the  groove  on  the 
mastoid  part  of  the  temporal  is  sometimes  termed  the  sigmoid  sinus.  The  trans- 
verse sinuses  are  frequently  of  unequal  size,  that  formed  by  the  superior  sagittal 
sinus  being  the  larger;  they  increase  in  size  as  they  proceed  from  behind  forward. 
On  transverse  section  the  horizontal  portion  exhibits  a  prismatic,  the  curved 
portion  a  semicyUndrical  form.  They  receive  the  blood  from  the  superior  petrosal 
42 


658 


ANGIOLOGY 


sinuses  at  the  base  of  the  petrous  portion  of  the  temporal  bone ;  they  communicate 
with  the  veins  of  the  pericranium  by  means  of  the  mastoid  and  condyloid  emissary 
veins;  and  they  receive  some  of  the  inferior  cerebral  and  inferior  cerebellar  veins, 
and  some  veins  from  the  diploe.  The  petrosquamous  sinus,  when  present,  runs 
backward  along  the  junction  of  the  squama  and  petrous  portion  of  the  temporal, 
and  opens  into  the  transverse  sinus. 

The  occipital  sinus  (sinus  occipitalis)  (Fig.  570)  is  the  smallest  of  the  cranial 
sinuses.  It  is  situated  in  the  attached  margin  of  the  falx  cerebelli,  and  is  generally 
single,  but  occasionally  there  are  two.  It  commences  around  the  margin  of  the  for- 
amen magnum  by  several  small  venous  channels,  one  of  which  joins  the  terminal 
part  of  the  transverse  sinus ;  it  communicates  with  the  posterior  internal  vertebral 
venous  plexuses  and  ends  in  the  confluence  of  the  sinuses. 

The  Confluence  of  the  Sinuses  {confluens  sinuum;  torcular  Herophili)  is  the  term 
applied  to  the  dilated  extremity  of  the  superior  sagittal  sinus.  It  is  of  irregular 
form,  and  is  lodged  on  one  side  (generally  the  right)  of  the  internal  occipital  pro- 
tuberance. From  it  the  transverse  sinus  of  the  same  side  is  derived.  It  receives 
also  the  blood  from  the  occipital  sinus,  and  is  connected  across  the  middle  line  with 
the  commencement  of  the  transverse  sinus  of  the  opposite  side. 

The  antero-inferior  group  of  sinuses  comprises  the 


Two  Cavernous. 
Two  Intercavernous 


Two  Superior  Petrosal. 
Two  Inferior  Petrosal. 


Basilar  Plexus. 


The  cavernous  sinuses  {sinus  cavernosus)  (Figs.  570,  571)  are  so  named  because 
they  present  a  reticulated  structure,  due  to  their  being  traversed  by  numerous  inter- 
lacing filaments.   They  are  of  irregular 
Internal  carotid  artery 
Cavernous  sinus 


Oculomotor  nerve 
Trochlear  nerve 

Ophthalmic  nerve 
Abducent  nerve 


Maxillary  nerve 


Fig.  571. — Oblique  section  through  the  cavernous  sinus. 


form,  larger  behind  than  in  front,  and 
are  placed  one  on  either  side  of  the 
body  of  the  sphenoid  bone,  extending 
from  the  superior  orbital  fissure  to 
the  apex  of  the  petrous  portion  of 
the  temporal  bone.  Each  opens  be- 
hind into  the  petrosal  sinuses.  On 
the  medial  wall  of  each  sinus  is  the 
internal  carotid  artery,  accompanied 
by  filaments  of  the  carotid  plexus; 
near  the  artery  is  the  abducent  nerve; 
on  the  lateral  wall  are  the  oculomotor 
and  trochlear  nerves,  and  the  oph- 
thalmic and  maxillary  divisions  of 
the  trigeminal  nerve  (Fig.  571).  These  structures  are  separated  from  the  blood 
flowing  along  the  sinus  by  the  lining  membrane  of  the  sinus.  The  cavernous 
sinus  receives  the  superior  ophthalmic  vein  through  the  superior  orbital  fissure, 
some  of  the  cerebral  veins,  and  also  the  small  sphenoparietal  sinus,  which  courses 
along  the  under  surface  of  the  small  wing  of  the  sphenoid.  It  communicates  with 
the  transverse  sinus  by  means  of  the  superior  petrosal  sinus;  with  the  internal 
jugular  vein  through  the  inferior  petrosal  sinus  and  a  plexus  of  veins  on  the  inter- 
nal carotid  artery;  with  the  pterygoid  venous  plexus  through  the  foramen  Vesalii, 
foramen  ovale,  and  foramen  lacerum,  and  with  the  angular  vein  through  the 
ophthalmic  vein.  The  two  sinuses  also  communicate  with  each  other  by  means 
of  the  anterior  and  posterior  intercavernous  sinuses. 

The  ophthalmic   veins   (Fig.  572),  two  in   number,  superior  and  inferior,   are 
devoid  of  valves. 


THE  SINUSES  OF  THE  DURA  MATER 


659 


The  Superior  Ophthalmic  Vein  (v.  ophthalmica  superior)  begins  at  the  inner  angle 
of  the  orbit  in  a  vein  named  the  nasofrontal  which  communicates  anteriorly  with  the 
angular  vein;  it  pursues  the  same  course  as  the  ophthalmic  artery,  and  receives 
tributaries  corresponding  to  the  branches  of  that  vessel.  Forming  a  short  single 
trunk,  it  passes  between  the  two  heads  of  the  Rectus  lateralis  and  through  the  medial 
part  of  the  superior  orbital  fissure,  and  ends  in  the  cavernous  sinus. 

The  Inferior  Ophthalmic  Vein  (v.  ophthalmica  inferior)  begins  in  a  venous  net-work 
at  the  forepart  of  the  floor  and  medial  wall  of  the  orbit;  it  receives  some  veins  from 
the  Rectus  inferior,  Obliquus  inferior,  lacrimal  sac  and  eyelids,  runs  backward  in 
the  lower  part  of  the  orbit  and  divides  into  two  branches.  One  of  these  passes 
through  the  inferior  orbital  fissure  and  joins  the  pterygoid  venous  plexus,  while 
the  other  enters  the  cranium  through  the  superior  orbital  fissure  and  ends  in  the 
cavernous  sinus,  either  by  a  separate  opening,  or  more  frequently  in  common  with 
the  superior  ophthalmic  vein. 


Inferior 
ophthalmic 


Fia.  572. — Veins  of  orbit.     (Poirier  and  Charpy.) 


The  intercavernous  sinuses  (sini  intercavernosi)  (Fig.  570)  are  two  in  number,  an 
anterior  and  a  posterior,  and  connect  the  two  cavernous  sinuses  across  the  middle 
line.  The  anterior  passes  in  front  of  the  hypophysis  cerebri,  the  posterior  behind  it, 
and  they  form  with  the  cavernous  sinuses  a  venous  circle  (circular  sinus)  around  the 
hypophysis.  The  anterior  one  is  usually  the  larger  of  the  two,  and  one  or  other  is 
occasionally  absent. 

The  superior  petrosal  sinus  (sinus  petrosus  superior)  (Fig.  570)  small  and  narrow, 
connects  the  cavernous  with  the  transverse  sinus.  It  runs  lateralward  and  back- 
ward, from  the  posterior  end  of  the  cavernous  sinus,  over  the  trigeminal  nerve, 
and  lies  in  the  attached  margin  of  the  tentorium  cerebelli  and  in  the  superior 
petrosal  sulcus  of  the  temporal  bone;  it  joins  the  transverse  sinus  where  the  latter 
curves  downward  on  the  inner  surface  of  the  mastoid  part  of  the  temporal.  It 
receives  some  cerebellar  and  inferior  cerebral  veins,  and  veins  from  the  tympanic 
cavity. 

The  inferior  petrosal  sinus  (sinus  petrosus  inferior)  (Fig.  570)  is  situated  in  the 
inferior  petrosal  sulcus  formed  by  the  junction  of  the  petrous  part  of  the  temporal 
with  the  basilar  part  of  the  occipital.  It  begins  in  the  postero-inferior  part  of  the 
cavernous  sinus,  and,  passing  through  the  anterior  part  of  the  jugular  foramen, 
ends  in  the  superior  bulb  of  the  internal  jugular  vein.    The  inferior  petrosal  sinus 


660  ANGIOLOGY 

receives  the  internal  auditory  veins  and  also  veins  from  the  medulla  oblongata, 
pons,  and  under  surface  of  the  cerebellum. 

The  exact  relation  of  the  parts  to  one  another  in  the  jugular  foramen  is  as  follows : 
the  inferior  petrosal  sinus  lies  medially  and  anteriorly  with  the  meningeal  branch 
of  the  ascending  pharyngeal  artery,  and  is  directed  obliquely  downward  and  back- 
ward; the  transverse  sinus  is  situated  at  the  lateral  and  back  part  of  the  foramen 
with  a  meningeal  branch  of  the  occipital  artery,  and  between  the  two  sinuses  are 
the  glossopharyngeal,  vagus,  and  accessory  nerves.  These  three  sets  of  structures 
are  divided  from  each  other  by  two  processes  of  fibrous  tissue.  The  junction  of  the 
inferior  petrosal  sinus  with  the  internal  jugular  vein  takes  place  on  the  lateral 
aspect  of  the  nerves. 

The  basilar  plexus  {plexus  hasilaris;  transverse  or  basilar  sinus)  (Fig.  571)  con- 
sists of  several  interlacing  venous  channels  between  the  layers  of  the  dura  mater 
over  the  basilar  part  of  the  occipital  bone,  and  serves  to  connect  the  two  inferior 
petrosal  sinuses.    It  communicates  with  the  anterior  vertebral  venous  plexus. 

Emissary  Veins  (emissaria). — The  emissary  veins  pass  through  apertures  in  the 
cranial  wall  and  establish  communication  between  the  sinuses  inside  the  skull  and 
the  veins  external  to  it.  Some  are  always  present,  others  only  occasionally  so. 
The  principal  emissary  veins  are  the  following:  (1)  A  mastoid  emissary  vein, 
usually  present,  runs  through  the  mastoid  foramen  and  unites  the  transverse  sinus 
with  the  posterior  auricular  or  with  the  occipital  vein.  (2)  A  parietal  emissary 
vein  passes  through  the  parietal  foramen  and  connects  the  superior  sagittal  sinus 
with  the  veins  of  the  scalp.  (3)  A  net-work  of  minute  veins  {rete  canalis  hypoglossi) 
traverses  the  hypoglossal  canal  and  joins  the  transverse  sinus  with  the  vertebral 
vein  and  deep  veins  of  the  neck.  (4)  An  inconstant  condyloid  emissary  vein  passes 
through  the  condyloid  canal  and  connects  the  transverse  sinus  with  the  deep  veins 
of  the  neck.  (5)  A  net-work  of  veins  {rete  foraminis  ovalis)  unites  the  cavernous 
sinus  with  the  pterygoid  plexus  through  the  foramen  ovale.  (6)  Two  or  three  small 
veins  run  through  the  foramen  lacerum  and  connect  the  cavernous  sinus  with  the 
pterygoid  plexus.  (7)  The  emissary  vein  of  the  foramen  of  Vesalius  connects  the 
same  parts.  (8)  An  internal  carotid  plexus  of  veins  traverses  the  carotid  canal  and 
unites  the  cavernous  sinus  with  the  internal  jugular  vein.  (9)  A  vein  is  trans- 
mitted through  the  foramen  cecum  and  connects  the  superior  sagittal  sinus  with 
the  veins  of  the  nasal  cavity. 

THE   VEINS    OF   THE   UPPER   EXTREMITY   AND   THORAX. 

The  veins  of  the  upper  extremity  are  divided  into  two  sets,  superficial  and  deep; 
the  two  sets  anastomose  frequently  with  each  other.  The  superficial  veins  are 
placed  immediately  beneath  the  integument  between  the  two  layers  of  superficial 
fascia.  The  deep  veins  accompany  the  arteries,  and  constitute  the  vense  comi- 
tantes  of  those  vessels.  Both  sets  are  provided  with  valves,  which  are  more 
numerous  in  the  deep  than  in  the  superficial  veins. 

The  Superficial  Veins  of  the  Upper  Extremity. 

The  superficial  veins  of  the  upper  extremity  are  the  digital,  metacarpal,  cephalic, 
basilic,  median. 

'Digital  Veins. — The  dorsal  digital  veins  pass  along  the  sides  of  the  fingers  and 
are  joined  to  one  another  by  oblique  communicating  branches.  Those  from  the 
adjacent  sides  of  the  fingers  unite  to  form  three  dorsal  metacarpal  veins  (Fig. 
573),  which  end  in  a  dorsal  venous  net-work  opposite  the  middle  of  the  meta- 
carpus. The  radial  part  of  the  net-work  is  joined  by  the  dorsal  digital  vein  from  the . 
radial  side  of  the  index  finger  and  by  the  dorsal  digital  veins  of  the  thumb,  and 
is  prolonged  upward  as  the  cephalic  vein.    The  ulnar  part  of  the  net- work  receives 


I 
I 


i 


I 


THE  SUPERFICIAL  VEINS  OF  THE  UPPER  EXTREMITY 


661 


the  dorsal  digital  vein  of  the  ulnar  side  of  the  little  finger  and  is  continued  upward 
the  basilic  vein.     A  communicating  branch  frequently  connects  the  dorsal 


as 


venous  network  with  the  cephalic  vein  about  the  middle  of  the  forearm. 

The  volar  digital  veins  on  each  finger  are  connected  to  the  dorsal  digital  veins 
by  oblique  intercapitular  veins.  They  drain  into  a  venous  plexus  which  is  situated 
over  the  thenar  and  hypothenar  eminences  and  across  the  front  of  the  wrist. 


Cephalic 


Dorsal  venous 
neiioork 


Fig.  573. — The  veins  on  the  dorsum  of  the  hand.     (Bourgery.) 

The  cephalic  vein  (Fig.  574)  begins  in  the  radial  part  of  the  dorsal  venous  net- 
work and  winds  upward  around  the  radial  border  of  the  forearm,  receiving  tribu- 
taries from  both  surfaces.  Below  the  front  of  the  elbow  it  gives  off  the  vena  mediana 
cubiti  {median  basilic  vein),  which  receives  a  communicating  branch  from  the  deep 
veins  of  the  forearm  and  passes  across  to  join  the  basilic  vein.  The  cephalic  vein 
then  ascends  in  front  of  the  elbow  in  the  groove  between  the  Brachioradialis  and 
the  Biceps  brachii.  It  crosses  superficial  to  the  musculocutaneous  nerve  and  ascends 
in  the  groove  along  the  lateral  border  of  the  Biceps  brachii.  In  the  upper  third 
of  the  arm  it  passes  between  the  Pectoralis  major  and  Deltoideus,  where  it  is  accom- 


662 


ANGIOLOGY 


panied  by  the  deltoid 
clavicular  fascia  and 
below  the  clavicle. 


Cephalic  vein 


branch  of  the  thoracoacromial  artery.    It  pierces  the  corac" 
,  crossing  the  axillary  artery,  ends  in  the  axillary  vein  just 
Sometimes  it  communicates  with  the  external  jugular  vein 

by  a  branch  which  ascends  in  front 
of  the  clavicle. 

The  accessory  cephalic  vein  {v. 
cephalica  accessoria)  arises  either 
from  a  small  tributory  plexus  on 
the  back  of  the  forearm  or  from 
the  ulnar  side  of  the  dorsal  venous 
net-work;  it  joins  the  cephalic  be- 
low the  elbow.  In  some  cases  the 
accessory  cephalic  springs  from 
the  cephalic  above  the  wrist  and 
joins  it  again  higher  up.  A  large 
oblique  branch  frequently  con- 
nects the  basilic  and  cephalic  veins 
on  the  back  of  the  forearm. 

The  basilic  vein  (v.  basilica) 
(Fig.  574)  begins  in  the  ulnar  part 
of  the  dorsal  venous  network.  It 
runs  up  the  posterior  surface  of 
the  ulnar  side  of  the  forearm  and 
inclines  forward  to  the  anterior 
surface  below  the  elbow,  where  it 
is  joined  by  the  vena  mediana 
cubiti.  It  ascends  obliquely  in 
the  groove  between  the  Biceps 
brachii  and  Pronator  teres  and 
crosses  the  brachial  artery,  from 
which  it  is  separated  by  thelacertus 
fibrosus;  filaments  of  the  medial 
antibrachial  cutaneous  nerve  pass 
both  in  front  of  and  behind  this 
portion  of  the  vein.  It  then  runs 
upward  along  the  medial  border 
of  the  Biceps  brachii,  perforates 
the  deep  fascia  a  little  below  the 
middle  of  the  arm,  and,  ascending 
on  the  medial  side  of  the  brachial 
artery  to  the  lower  border  of  the 
Teres  major,  is  continued  onward 
as  the  axillary  vein. 

The  median  antibrachial  vein 
{v.  mediana  antibrachii)  drains  the 
venous  plexus  on  the  volar  surface 
of  the  hand.  It  ascends  on  the 
ulnar  side  of  the  front  of  the  fore- 
arm and  ends  in  the  basilic  vein  or 
in  the  vena  mediana  cubiti;  in  a 
small  proportion  of  cases  it  divides 
into  two  branches,  one  of  which 
joins  the  basilic,  the  other  the 
cephalic,  below  the  elbow. 


Basilic  vein 


Vena  mediana 
cubiti 


Basilic  vein 


Medial  anti- 
brachial cutane- 
ous nerve 
Median  anti- 
brachial vein 


Fig.  574. — The  superficial  veins  of  the  upper  extremity 


THE  DEEP  VEINS  OF  THE  UPPER  EXTREMITY 


663 


The  Deep  Veins  of  the  Upper  Extremity. 

The  deep  veins  follow  the  course  of  the  arteries,  forming  their  venae  comitantes. 
They  are  generally  arranged  in  pairs,  and  are  situated  one  on  either  side  of  the 
corresponding  artery,  and  connected  at  intervals  by  short  transverse  branches. 

Deep  Veins  of  the  Hand. — ^The  superficial  and  deep  volar  arterial  arches  are 
each  accompanied  by  a  pair  of  venae  comitantes  which  constitute  respectively 
the  superficial  and  deep  volar  venous  arches,  and  receive  the  veins  corresponding 
to  the  branches  of  the  arterial  arches;  thus  the  common  volar  digital  veins,  formed  by 
the  union  of  the  proper  volar  digital  veins,  open  into  the  superficial,  and  the  volar 
metacarpal  veins  into  the  deep  volar  venous  arches.  The  dorsal  metacarpal  veins 
perforating    branches 


volar  metacarpal 
and  end  in  the  radial 
and  in  the  superficial 
the  dorsum  of   the 


receive 
from    the 
veins 
veins 
veins  on 
wrist. 

The  deep  veins  of  the  fore- 
arm are  the  venae  comitantes 
of  the  radial  and  ulnar  veins 
and  constitute  respectively  the 
upward  continuations  of  the 
deep  and  superficial  volar 
venous  arches;  they  unite  in 
front  of  the  elbow  to  form 
the  brachial  veins.  The  radial 
veins  are  smaller  than  the  ulnar 
and  receive  the  dorsal  meta- 
carpal veins.  The  ulnar  veins 
receive  tributaries  from  the 
deep  volar  venous  arches  and 
communicate  with  the  super- 
ficial veins  at  the  wrist;  near 
the  elbow  they  receive  the  volar 
and  dorsal  interosseous  veins 
and  send  a  large  communicat- 
ing branch  (profunda  vein)  to 
the  vena  mediana  cubiti. 

The  brachial  veins  (vv. 
hrachiales)  are  placed  one  on 
either  side  of  the  brachial 
artery,    receiving    tributaries 


INTEROSSEOUS 


ULNAR  DEEP 
VEINS 


VENAE  COMITES 
OF    BRACHIAL 
ARTERY 


ANASTOMOSIS 

OF  RADIAL 

\        AND  ULNAR 


RADIAL  DEEP 
VEINS 


Fig.  575. — The  deep  vtii  i  it  ihc  upper  extremity      (Bourgery.) 


I  corresponding  with  the  branches  given  off  from  that  vessel ;  near  the  lower  margin 
of  the  Subscapularis,  they  join  the  axillary  vein;  the  medial  one  frequently  joins 
the  basilic  vein. 
These  deep  veins  have  numerous  anastomoses,  not  only  with  each  other,  but 
also  with  the  superficial  veins. 
The  axillary  vein  {v.  axillaris)  begins  at  the  lower  border  of  the  Teres  major, 
as  the  continuation  of  the  basilic  vein,  increases  in  size  as  it  ascends,  and  ends  at  the 
outer  border  of  the  first  rib  as  the  subclavian  vein.  Near  the  lower  border  of 
bthe  Subscapularis  it  receives  the  brachial  veins  and,  close  to  its  termination,  the 
cephalic  vein;  its  other  tributaries  correspond  with  the  branches  of  the  axillary 
artery.  It  lies  on  the  medial  side  of  the  artery,  which  it  partly  overlaps;  between 
the  two  vessels  are  the  medial  cord  of  the  brachial  plexus,  the  median,  the  ulnar, 


I 


664 


ANGIOLOGY 


and  the  medial  anterior  thoracic  nerves.  It  is  provided  with  a  pair  of  valves  oppo- 
site the  lower  border  of  the  Subscapularis;  valves  are  also  found  at  the  ends  of  the 
cephalic  and  subscapular  veins.  jl 

The  subclavian  vein  (v.  suhclavia),  the  continuation  of  the  axillary,  extends]  B 
from  the  outer  border  of  the  first  rib  to  the  sternal  end  of  the  clavicle,  where  it'l 
unites  with  the  internal  jugular  to  form  the  innominate  vein.  It  is  in  relation,  in 
front,  with  the  clavicle  and  Subclavius;  behind  and  above,  with  the  subclavian 
artery,  from  which  it  is  separated  medially  by  the  Scalenus  anterior  and  the  phrenic 
nerve.  Below,  it  rests  in  a  depression  on  the  first  rib  and  upon  the  pleura.  '  It  is 
usually  provided  with  a  pair  of  valves,  which  are  situated  about  2.5  cm.  from  its 
termination. 

AXIU:.ARY 
ARTERY 
MUSCULO- 
CUTANEUS  NERVE 
MEDIAN   NERVE 

ANTERIOR 
CIRCUMFLEX 


COSTOAXILLARY 


LONG  THORACIC 

Fig.  576.— The  veins  of  the  right  axilla,  viewed  from  in  front.     (Spalteholz.) 

The  subclavian  vein  occasionally  rises  in  the  neck  to  a  level  with  the  third  part 
of  the  subclavian  artery,  and  occasionally  passes  with  this  vessel  behind  the  Scalenus 
anterior. 

Tributaries. — This  vein  receives  the  external  jugular  vein,  sometimes  the  anterior 
jugular  vein,  and  occasionally  a  small  branch,  which  ascends  in  front  of  the  clavicle, 
from  the  cephalic.  At  its  angle  of  junction  with  the  internal  jugular,  the  left 
subclavian  vein  receives  the  thoracic  duct,  and  the  right  subclavian  vein  the  right 
lymphatic  duct. 

The  Veins  of  the  Thorax  (Fig.  577) 

The  innominate  veins  {m.  anonymoe;  brachiocephalic  veins)  are  two  large  trunks, 
placed  one  on  either  side  of  the  root  of  the  neck,  and  formed  by  the  union  of  the 
internal  jugular  and  subclavian  veins  of  the  corresponding  side;  they  are  devoid 
of  valves. 

The  Right  Innominate  Vein  (v.  anonyma  dextra)  is  a  short  vessel,  about  2.5  cm. 
in  length,  which  begins  behind  the  sternal  end  of  the  clavicle,  and,  passing  almost 
vertically  downward,  joins  with  the  left  innominate  vein  just  below  the  cartilage 


I 


THE  VEINS  OF  THE  THORAX 


665 


of  the  first  rib,  close  to  the  right  border  of  the  sternum,  to  form  the  superior  vena 
cava.    It  lies  in  front  and  to  the  right  of  the  innominate  artery;  on  its  right  side 


itf^  Anterior  jugvXar 


Superior  thyroid  - 


Middle 
thyroid 


External  juguiar 


Suprarenal 


FiQ.  577. — The  vense  cavse  and  azygos  veins,  with  their  tributaries. 


are 


the 


phrenic  nerve  and  the  pleura,  which  are  interposed  between  it  and  the  apex 
of  the  lung.    This  vein,  at  its  commencement,  receives  the  right  vertebral  vein;  and, 


666  ANGIOLOGY 


I 


lower  down,  the  right  internal  mammary  and  right  inferior  thyroid  veins,  and  some- 
times the  vein  from  the  first  intercostal  space. 

The  Left  Innominate  Vein  (v.  anonyma  sinistra),  about  6  cm.  in  length,  begins 
behind  the  sternal  end  of  the  clavicle  and  runs  obliquely  downward  and  to  the 
right  behind  the  upper  half  of  the  manubrium  sterni  to  the  sternal  end  of  the  first 
right  costal  cartilage,  where  it  unites  with  the  right  innominate  vein  to  form  the 
superior  vena  cava.  It  is  separated  from  the  manubrium  sterni  by  the  Sterno- 
hyoideus  and  Sternothyreoideus,  the  thymus  or  its  remains,  and  some  loose  areolar 
tissue.  Behind  it  are  the  three  large  arteries,  innominate,  left  common  carotid,  and 
left  subclavian,  arising  from  the  aortic  arch,  together  with  the  vagus  and  phrenic 
nerves.  The  left  innominate  vein  may  occupy  a  higher  level,  crossing  the  jugular 
notch  and  lying  directly  in  front  of  the  trachea. 

Tributaries. — Its  tributaries  are  the  left  vertebral,  left  internal  mammary,  left 
inferior  thyroid,  and  the  left  highest  intercostal  veins,  and  occasionally  some 
thymic  and  pericardiac  veins. 

Peculiarities. — Sometimes  the  innominate  veins  open  separately  into  the  right  atrium;  in 
such  cases  the  right  vein  takes  the  ordinary  course  of  the  superior  vena  cava;  the  left  vein — 
left  superior  vena  cava,  as  it  is  then  termed — which  may  communicate  by  a  small  branch  with 
the  right  one,  passes  in  front  of  the  root  of  the  left  lung,  and,  turning  to  the  back  of  the  heart, 
ends  in  the  right  atrium.  This  occasional  condition  in  the  adult  is  due  to  the  persistence  of  the 
early  fetal  condition,  and  is  the  normal  state  of  things  in  birds  and  some  mammalia. 

The  internal  mammary  veins  (ct,  mammarioe  internee)  are  venae  comitantes 
to  the  lower  half  of  the  internal  mammary  artery,  and  receive  tributaries  corre- 
sponding to  the  branches  of  the  artery.  They  then  unite  to  form  a  single  trunk, 
which  runs  up  on  the  medial  side  of  the  artery  and  ends  in  the  corresponding 
innominate  vein.  The  superior  phrenic  vein,  i.  e.,  the  vein  accompanying  the  peri- 
cardiacophrenic artery,  usually  opens  into  the  internal  mammary  vein. 

The  inferior  thyroid  veins  (m.  thyreoidece  inferiores)  two,  frequently  three  or 
four,  in  number,  arise  in  the  venous  plexus  on  the  thyroid  gland,  communicating 
with  the  middle  and  superior  thyroid  veins.  They  form  a  plexus  in  front  of  the 
trachea,  behind  the  Sternothyreoidei.  From  this  plexus,  a  left  vein  descends  and 
joins  the  left  innominate  trunk,  and  a  right  vein  passes  obliquely  downward  and  to 
the  right  across  the  innominate  artery  to  open  into  the  right  innominate  vein, 
just  at  its  junction  with  the  superior  vena  cava;  sometimes  the  right  and  left  veins 
open  by  a  common  trunk  in  the  latter  situation.  These  veins  receive  esophageal 
tracheal,  and  inferior  laryngeal  veins,  and  are  provided  with  valves  at  their 
terminations  in  the  innominate  veins. 

The  highest  intercostal  vein  (v.  intercostalis  suprema;  superior  intercostal  veins) 
(right  and  left)  drain  the  blood  from  the  upper  three  or  four  intercostal  spaces. 
The  right  vein  (v.  intercostalis  suprema  dextra)  passes  downward  and  opens  into  the 
vena  azygos;  the  left  vein  {v.  intercostalis  suprema  sinistra)  runs  across  the  arch 
of  the  aorta  and  the  origins  of  the  left  subclavian  and  left  common  carotid 
arteries  and  opens  into  the  left  innominate  vein.  It  usually  receives  the  left 
bronchial  vein,  and  sometimes  the  left  superior  phrenic  vein,  and  communicates 
below  with  the  accessory  hemiazygos  vein. 

The  superior  vena  cava  {v.  cava  superior)  drains  the  blood  from  the  upper  half 
of  the  body.  It  measures  about  7  cm.  in  length,  and  is  formed  by  the  junction  of 
the  two  innominate  veins.  It  begins  immediately  below  the  cartilage  of  the  right 
first  rib  close  to  the  sternum,  and,  descending  vertically  behind  the  first  and  second 
intercostal  spaces,  ends  in  the  upper  part  of  the  right  atrium  opposite  the  upper 
border  of  the  third  right  costal  cartilage :  the  lower  half  of  the  vessel  is  within  the 
pericardium.  In  its  course  it  describes  a  slight  curve,  the  convexity  of  which  is 
to  the  right  side. 


THE  VEINS  OF  THE  VERTEBRAL  COLUMN  667 

telations. — In  front  are  the  anterior  margins  of  the  right  lung  and  pleura  with  the  pericardium 
intervening  below;  these  separate  it  from  the  first  and  second  intercostal  spaces  and  from  the 
second  and  third  right  costal  cartilages;  behind  it  are  the  root  of  the  right  lung  and  the  right 
vagus  nerve.  On  its  right  side  are  the  phrenic  nerve  and  right  pleura;  on  its  left  side,  the  com- 
mencement of  the  innominate  artery  and  the  ascending  aorta,  the  latter  overlapping  it.  Just 
before  it  pierces  the  pericardium,  it  receives  the  azygos  vein  and  several  small  veins  from  the 
pericardium  and  other  contents  of  the  mediastinal  cavity.  The  portion  contained  within  the 
pericardium  is  covered,  in  front  and  laterally,  by  the  serous  layer  of  the  membrane.  The  superior 
vena  cava  has  no  valves. 

The  azygos  vein  (».  azygos;  vena  azygos  major)  begins  opposite  the  first  or  second 
lumbar  vertebra,  by  a  branch,  the  ascending  lumbar  vein  (page  678) ;  sometimes  by 
a  branch  from  the  right  renal  vein,  or  from  the  inferior  vena  cava.  It  enters  the 
thorax  through  the  aortic  hiatus  in  the  diaphragm,  and  passes  along  the  right  side 
of  the  vertebral  column  to  the  fourth  thoracic  vertebra,  where  it  arches  forward 
over  the  root  of  the  right  lung,  and  ends  in  the  superior  vena  cava,  just  before 
that  vessel  pierces  the  pericardium.  In  the  aortic  hiatus,  it  lies  with  the  thoracic 
duct  on  the  right  side  of  the  aorta ;  in  the  thorax  it  lies  upon  the  intercostal  arteries, 
on  the  right  side  of  the  aorta  and  thoracic  duct,  and  is  partly  covered  by  pleura. 

Tributaries. — It  receives  the  right  subcostal  and  intercostal  veins,  the  upper  three 
or  four  of  these  latter  opening  by  a  common  stem,  the  highest  superior  intercostal 
vein.  It  receives  the  hemiazygos  veins,  several  esophageal,  mediastinal,  and  peri- 
cardial veins,  and,  near  its  termination,  the  right  bronchial  vein.  A  few  imperfect 
valves  are  found  in  the  azygos  vein;  but  its  tributaries  are  provided  with  complete 
valves. 

The  intercostal  veins  on  the  left  side,  below  the  upper  three  intercostal  spaces, 
usually  form  two  trunks,  named  the  hemiazygos  and  accessory  hemiazygos  veins. 

The  Hemiazygos  Vein  (v.  hemiazygos;  vena  azygos  minor  inferior)  begins  in  the 
left  ascending  lumbar  or  renal  vein.  It  enters  the  thorax,  through  the  left  crus 
of  the  diaphragm,  and,  ascending  on  the  left  side  of  the  vertebral  column,  as  high 
as  the  ninth  thoracic  vertebra,  passes  across  the  column,  behind  the  aorta,  esoph- 
agus, and  thoracic  duct,  to  end  in  the  azygos  vein.  It  receives  the  lower  four 
or  five  intercostal  veins  and  the  subcostal  vein  of  the  left  side,  and  some  esophageal 
and  mediastinal  veins. 

The  Accessory  Hemiazygos  Vein  (v.  hemiazygos  accessoria;  vena  azygos  minor  supe- 
rior) descends  on  the  left  side  of  the  vertebral  column,  and  varies  inversely  in  size 
with  the  highest  left  intercostal  vein.  It  receives  veins  from  the  three  or  four 
intercostal  spaces  between  the  highest  left  intercostal  vein  and  highest  tributary 
of  the  hemiazygos;  the  left  bronchial  vein  sometimes  opens  into  it.  It  either  crosses 
the  body  of  the  eighth  thoracic  vertebra  to  join  the  azygos  vein  or  ends  in  the 
hemiazygos.  When  this  vein  is  small,  or  altogether  wanting,  the  left  highest 
intercostal  vein  may  extend  as  low  as  the  fifth  or  sixth  intercostal  space. 

In  obstruction  of  the  superior  vena  cava,  the  azygos  and  hemiazygos  veins  are  one  of  the 
principal  means  by  which  the  venous  circulation  is  carried  on,  connecting  as  they  do  the  superior 
and  inferior  venae  cavae,  and  communicating  with  the  common  iliac  vein?  by  the  ascending  lumbar 
veins  and  with  many  of  the  tributaries  of  the  inferior  vena  cava. 

The  Bronchial  Veins  {vv.  bronchioles)  return  the  blood  from  the  larger  bronchi,  and 
from  the  structures  at  the  roots  of  the  lungs;  that  of  the  right  side  opens  into  the 
azygos  vein,  near  its  termination;  that  of  the  left  side,  into  the  highest  left  inter- 
costal or  the  accessory  hemiazygos  vein.  A  considerable  quantity  of  the  blood  which 
is  carried  to  the  lungs  through  the  bronchial  arteries  is  returned  to  the  left  side  of 
the  heart  through  the  pulmonary  veins. 

The  Veins  of  the  Vertebral  Column  (Figs.  578,  579). 

The  veins  which  drain  the  blood  from  the  vertebral  column,  the  neighboring 
muscles,  and  the  meninges  of  the  medulla  spinalis  form  intricate  plexuses  extending 


668 


ANGIOLOGY 


along  the  entire  length  of  the  column;  these  plexuses  may  be  divided  into  two 
groups,  external  and  internal,  according  to  their  positions  inside  or  outside  the 
vertebral  canal.  The  plexuses  of  the  two  groups  anastomose  freely  with  each  other 
and  end  in  the  intervertebral  veins. 

The  external  vertebral  venous  plexuses  {plexus  venosi  rertebrales  externi;  extra- 
spinal  veins)  best  marked  in  the  cervical  region,  consist  of  anterior  and  posterior 
plexuses  which  anastomose  freely  with  each  other.  The  anterior  external  plexuses 
lie  in  front  of  the  bodies  of  the  vertebrae,  communicate  with  the  basivertebral  and 
intervertebral  veins,  and  receive  tributaries  from  the  vertebral  bodies.  The  pos- 
terior external  plexuses  are  placed  partly  on  the  posterior  surfaces  of  the  vertebral 
arches  and  their  processes,  and  partly  between  the  deep  dorsal  muscles.  They  are 
best  developed  in  the  cervical  region,  and  there  anastomose  with  the  vertebral, 
occipital,  and  deep  cervical  veins. 

The  internal  vertebral  venous  plexuses  (plexus  venosi  vertebrales  inierni;  intra- 
spinal veins)  lie  within  the  vertebral  canal  between  the  dura  mater  and  the  verte- 
brae, and  receive  tributaries  from  the  bones  and  from  the  medulla  spinalis.    They 


Posterior  external  plexuses 


I 

I 


Fig.  578. — Transverse  section  of  a  thoracic  vertebra, 
showing  the  vertebral  venous  plexuses. 


Fig.  679. — Median  sagittal  section  of  two  thoracic  verte- 
brae, showing  the  vertebral  venous  plexuses. 


form  a  closer  net-work  than  the  external  plexuses,  and,  running  mainly  in  a  vertical 
direction,  form  four  longitudinal  veins,  two  in  front  and  two  behind ;  they  therefore 
may  be  divided  into  anterior  and  posterior  groups.  The  anterior  internal  plexuses 
consist  of  large  veins  which  lie  on  the  posterior  surfaces  of  the  vertebral  bodies  and 
intervertebral  fibrocartilages  on  either  side  of  the  posterior  longitudinal  ligament; 
under  cover  of  this  ligament  they  are  connected  by  transverse  branches  into  which 
the  basivertebral  veins  open.  The  posterior  internal  plexuses  are  placed,  one  on 
either  side  of  the  middle  line  in  front  of  the  vertebral  arches  and  ligamenta  flava, 
and  anastomose  by  veins  passing  through  those  ligaments  with  the  posterior  exter- 
nal plexuses.  The  anterior  and  posterior  plexuses  communicate  freely  with  one 
another  by  a  series  of  venous  rings  {retia  venosa  vertebrarum) ,  one  opposite  each 
vertebra.  Around  the  foramen  magnum  they  form  an  intricate  net-work  which 
opens  into  the  vertebral  veins  and  is  connected  above  with  the  occipital  sinus, 
the  basilar  plexus,  the  condyloid  emissary  vein,  and  the  rete  canalis  hypoglossi. 

The  basivertebral  veins  (vv.  basivertebrales)  emerge  from  the  foramina  on  the 
posterior  surfaces  of  the  vertebral  bodies.    They  are  contained  in  large,  tortuous 


I 


It 

ir 
II 


THE  SUPERFICIAL  VEINS  OF  THE  LOWER  EXTREMITY  66'9 

channels  in  the  substance  of  the  bones,  similar  in  every  respect  to  those  found  in 
the  diploe  of  the  cranial  bones.  They  communicate  through  small  openings  on  the 
front  and  sides  of  the  bodies  of  the  vertebrae  with  the  anterior  external  vertebral 
plexuses,  and  converge  behind  to  the  principal  canal,  which  is  sometimes  double 
toward  its  posterior  part,  and  open  by  valved  orifices  into  the  transverse  branches 
which  unite  the  anterior  internal  vertebral  plexuses.  They  become  greatly  enlarged 
in  advanced  age. 

The  intervertebral  veins  (vv.  intervertebrales)  accompany  the  spinal  nerves 
through  the  intervertebral  foramina;  they  receive  the  veins  from  the  medulla 
spinalis,  drain  the  internal  and  external  vertebral  plexuses  and  end  in  the  vertebral, 
intercostal,  lumbar,  and  lateral  sacral  veins,  their  orifices  being  provided  with 
valves. 

The  veins  of  the  medulla  spinalis  (vv.  spinales;  veins  of  the  spinal  cord)  are 
situated  in  the  pia  mater  and  form  a  minute,  tortuous,  venous  plexus.  They 
emerge  chiefly  from  the  median  fissures  of  the  medulla  spinalis  and  are  largest  in 
the  lumbar  region.  In  this  plexus  there  are  (1)  two  median  longitudinal  veins, 
one  in  front  of  the  anterior  fissure,  and  the  other  behind  the  posterior  sulcus  of  the 
cord,  and  (2)  four  lateral  longitudinal  veins  which  run  behind  the  nerve  roots. 
They  end  in  the  intervertebral  veins.  Near  the  base  of  the  skull  they  unite,  and 
form  two  or  three  small  trunks,  which  communicate  with  the  vertebral  veins, 
and  then  end  in  the  inferior  cerebellar  veins,  or  in  the  inferior  petrosal  sinuses. 


THE  VEINS   OF  THE  LOWER  EXTREMITY,  ABDOMEN,  AND  PELVIS. 

The  veins  of  the  lower  extremity  are  subdivided,  like  those  of  the  upper,  into 
two  sets,  superficial  and  deep ;  the  superficial  veins  are  placed  beneath  the  integument 
between  the  two  layers  of  superficial  fascia;  the  deep  veins  accompany  the  arteries. 
Both  sets  of  veins  are  provided  with  valves,  which  are  more  numerous  in  the  deep 
than  in  the  superficial  set.  Valves  are  also  more  numerous  in  the  veins  of  the 
lower  than  in  those  of  the  upper  limb. 

The  Superficial  Veins  of  the  Lower  Extremity. 

The  superficial  veins  of  the  lower  extremity  are  the  great  and  small  saphenous 
veins  and  their  tributaries. 

On  the  dorsum  of  the  foot  the  dorsal  digital  veins  receive,  in  the  clefts  between  the 
toes,  the  intercapitular  veins  from  the  plantar  cutaneous  venous  arch  and  join  to 
form  short  common  digital  veins  which  unite  across  the  distal  ends  of  the  metatarsal 
bones  in  a  dorsal  venous  arch.  Proximal  to  this  arch  is  an  irregular  venous  net- 
work which  receives  tributaries  from  the  deep  veins  and  is  joined  at  the  sides  of  the 
foot  by  a  medial  and  a  lateral  marginal  vein,  formed  mainly  by  the  union  of  branches 
from  the  superficial  parts  of  the  sole  of  the  foot. 

On  the  sole  of  the  foot  the  superficial  veins  form  a  plantar  cutaneous  venous  arch 
which  extends  across  the  roots  of  the  toes  and  opens  at  the  sides  of  the  foot  into 
the  medial  and  lateral  marginal  veins.  Proximal  to  this  arch  is  a  plantar  cutaneous 
venous  net- work  which  is  especially  dense  in  the  fat  beneath  the  heel ;  this  net-work 
communicates  with  the  cutaneous  venous  arch  and  with  the  deep  veins,  but  is 
chiefly  drained  into  the  medial  and  lateral  marginal  veins. 

The  great  saphenous  vein  (v.  saphena  magna;  internal  or  long  saphenous  vein) 
(Fig.  581),  the  longest  vein  in  the  body,  begins  in  the  medial  marginal  vein  of  the 
dorsum  of  the  foot  and  ends  in  the  femoral  vein  about  3  cm.  below  the  inguinal 
ligament.  It  ascends  in  front  of  the  tibial  malleolus  and  along  the  medial  side  of 
the  leg  in  relation  with  the  saphenous  nerve.    It  runs  upward  behind  the  medial 


670 


[NGIOLOGY 


condyles  of  the  tibia  and  femur  and  along  the  medial  side  of  the  thigh  and,  passing 
through  the  fossa  ovalis,  ends  in  the  femoral  vein. 

Tributaries. — At  the  ankle  it  receives  branches  from  the  sole  of  the  foot  through 
the  medial  marginal  vein;  in  the  leg  it  anastomoses  freely  with  the  small  saphenous 
vein,  communicates  with  the  anterior  and  posterior  tibial  veins  and  receives  many 
cutaneous  veins;  in  the  thigh  it  communicates  with  the  femoral  vein  and  receives 
numerous  tributaries;  those  from  the  medial  and  posterior  parts  of  the  thigh 
frequently  unite  to  form  a  large  accessory  saphenous  vein  which  joins  the  main 
vein  at  a  variable  level.  Near  the  fossa  ovalis  (Fig.  580)  it  is  joined  by  the  super- 
ficial epigastric,  superficial  iliac  circumflex,  and  superficial  external  pudendal  veins. 
A  vein,  named  the  thoracoepigastric,  runs  along  the  lateral  aspect  of  the  trunk 
between  the  superficial  epigastric  vein  below  and  the  lateral  thoracic  vein  above 
and  establishes  an  important  communication  between  the  femoral  and  axillary 
veins. 


Fio.  580. — The  great  saphenous  vein  and  its  tributaries  at  the  fossa  ovalis. 


The  valves  in  the  great  saphenous  vein  vary  from  ten  to  twenty  in  number; 
they  are  more  numerous  in  the  leg  than  in  the  thigh. 

The  small  saphenous  vein  (v.  saphena  parva;  external  or  short  saphenous  vein) 
(Fig.  582)  begins  behind  the  lateral  malleolus  as  a  continuation  of  the  lateral 
marginal  vein;  it  first  ascends  along  the  lateral  margin  of  the  tendocalcaneus, 
and  then  crosses  it  to  reach  the  middle  of  the  back  of  the  leg.  Running  directly 
upward,  it  perforates  the  deep  fascia  in  the  lower  part  of  the  popliteal  fossa,  and 
ends  in  the  popliteal  vein,  between  the  heads  of  the  Gastrocnemius.     It  commu- 


THE  DEEP  VEINS  OF  THE  LOWER  EXTREMITY 


671 


nicates  with  the  deep  veins  on  the  dorsum  of  the  foot,  and  receives  numerous  large 
tributaries  from  the  back  of  the  leg.    Before  it  pierces  the  deep  fascia,  it  gives  off 

a  branch  which  runs  upward  and  forward  to  join 
the  great  saphenous  vein.  The  small  saphenous 
vein  possesses  from  nine  to  twelve  valves,  one  of 
which  is  always  found  near  its  termination  in  the 
popliteal  vein.  In  the  lower  third  of  the  leg  the 
small  saphenous  vein  is  in  close  relation  with 
the  sural  nerve,  in  the  upper  two-thirds  with 
the  medial  sural  cutaneous  nerve. 


\ 


1^%} 


^^IFS 


The  Deep  Veins  of  the  Lower  Extremity. 

The  deep  veins  of  the  lower  extremity  accom- 
pany the  arteries  and  their  branches;  they  possess 
numerous  valves. 


V 


Fig.  581. — The  great  saphenous)  vein  and 
its  tributaries. 


FiQ.  582. — The  small  saphenous  vein. 


The  plantar  digital  veins    {vv.  digitales  plantares)  arise  from  plexuses  on  the 
1  plantar  surfaces  of  the  digits,  and,  after  sending  intercapitular  veins  to  join  the 


672 


ANGIOLOGY 


dorsal  digital  veins,  unite  to  form  four  metatarsal  veins;  these  run  backward  in 
the  metatarsal  spaces,  communicate,  by  means  of  perforating  veins,  with  the 
veins  on  the  dorsum  of  the  foot,  and  unite  to  form  the  deep  plantar  venous  arch 
which  lies  alongside  the  plantar  arterial  arch.  From  the  deep  plantar  venous  arch 
the  medial  and  lateral  plantar  veins  run  backward  close  to  the  corresponding 
arteries  and,  after  communicating  with  the  great  and  small  saphenous  veins,  unite 
behind  the  medial  malleolus  to  form  the  posterior  tibial  veins. 

The  posterior  tibial  veins  (vv.  tihiales  posteriores)  accompany  the  posterior 
tibial  artery,  and  are  joined  by  the  peroneal  veins. 

The  anterior  tibial  veins  (vv.  tihiales  anteriores)  are 
the  upward  continuation  of  the  venae  comitantes  of  the 
dorsalis  pedis  artery.  They  leave  the  front  of  the 
leg  by  passing  between  the  tibia  and  fibula,  over  the 
interosseous  membrane,  and  unite  with  the  posterior 
tibial,  to  form  the  popliteal  vein. 

The  Popliteal  Vein  {v.  poplitea)  (Fig.  583)  is  formed 
by  the  junction  of  the  anterior  and  posterior  tibial  veins 
at  the  lower  border  of  the  Popliteus;  it  ascends  through 
the  popliteal  fossa  to  the  aperture  in  the  Adductor  mag- 
nus,  where  it  becomes  the  femoral  vein.  In  the  lower 
part  of  its  course  it  is  placed  medial  to  the  artery; 
between  the  heads  of  the  Gastrocnemius  it  is  super- 
ficial to  that  vessel;  but  above  the  knee-joint,  it  is  close 
to  its  lateral  side.  It  receives  tributaries  corresponding 
to  the  branches  of  the  popliteal  artery,  and  it  also 
receives  the  small  saphenous  vein.  The  valves  in  the 
popliteal  vein  are  usually  four  in  number. 

The  femoral  vein  (v.  femoralis)  accompanies  the 
femoral  artery  through  the  upper  two-thirds  of  the 
thigh.  In  the  lower  part  of  its  course  it  lies  lateral  to 
the  artery;  higher  up,  it  is  behind  it;  and  at  the  inguinal 
ligament,  it  lies  on  its  medial  side,  and  on  the  same 
plane.  It  receives  numerous  muscular  tributaries,  and 
about  4  cm.  below  the  inguinal  ligament  is  joined  by 
thev.  profunda  femoris;  near  its  termination  it  is  joined 
by  the  great  saphenous  vein.  The  valves  in  the  femoral 
vein  are  three  in  number. 
The  Deep  Femoral  Vein  {v.  profunda  femoris)  receives 
tributaries  corresponding  to  the  perforating  branches  of  the  profunda  artery,  and 
through  these  establishes  communications  with  the  popliteal  vein  below  and  the 
inferior  gluteal  vein  above.  It  also  receives  the  medial  and  lateral  femoral  circum- 
flex veins. 

The  Veins  of  the  Abdomen  and  Pelvis  (Figs.  585,  586,  587). 

The  external  iliac  vein  {v.  iliaca  externa),  the  upward  continuation  of  the  femoral 
vein,  begins  behind  the  inguinal  ligament,  and,  passing  upward  along  the  brim 
of  the  lesser  pelvis,  ends  opposite  the  sacroiliac  articulation,  by  uniting  with  the 
hypogastric  vein  to  form  the  common  iliac  vein.  On  the  right  side,  it  lies  at  first 
medial  to  the  artery:  but,  as  it  passes  upward,  gradually  inclines  behind  it.  On 
the  left  side,  it  lies  altogether  on  the  medial  side  of  the  artery.  It  frequently 
contains  one,  sometimes  two,  valves. 

Tributaries. — The  external  iliac  vein  receives  the  inferior  epigastric,  deep  iliac 
circumflex,  and  pubic  veins. 

The  Inferior  Epigastric  Vein  (v.  epigastrica  inferior;  deep  epigastric  vein)  is  formed 


Fig.  583. — The  popliteal  vein. 


THE  VEINS  OF  THE  ABDOMEN  AND  PELVIS 


673 


)y  the  union  of  the  venae  comitantes  of  the  inferior  epigastric  artery,  which  com- 
municate above  with  the  superior  epigastric  vein;  it  joins  the  external  iliac  about 
1.25  cm.  above  the  inguinal  ligament. 

The  Deep  Iliac  Circumflex  Vein  (v.  circumfiexa  ilium  profunda)  is  formed  by  the 
union  of  the  venae  comitantes  of  the  deep  iliac  circumflex  artery,  and  joins  the 
external  iliac  vein  about  2  cm.  above  the  inguinal  ligament. 

The  Pubic  Vein  communicates  with  the  obturator  vein  in  the  obturator  foramen, 
and  ascends  on  the  back  of  the  pubis  to  the  external  iliac  vein. 

The  hypogastric  vein  (v.  hypogastrica;  internal  iliac  vein)  begins  near  the  upper 
part  of  the  greater  sciatic  foramen,  passes  upward  behind  and  slightly  medial  to 
the  hypogastric  artery  and,  at  the  brim  of  the  pelvis,  joins  with  the  external  iliac 
to  form  the  common  iliac  vein. 


UMBItfCUS 


SUPERFICIAL 
EPIGASTRIC 


SUPERFICIAL 

INTERNAL 

CIRCUMFLEX 


SUPERFICIAL 

EXTERNAL 

PUOIC 


^y 


-^       CIRCUMFLEX 


Fig.  584. — The  femoral  vein  and  its  tributaries.     (Poirier  and  Charpy.) 


Tributaries. — With  the  exception  of  the  fetal  umbilical  vein  which  passes  upward 
and  backward  from  the  umbilicus  to  the  liver,  and  the  iliolumbar  vein  which  usually 
joins  the  common  iliac  vein,  the  tributaries  of  the  hypogastric  vein  correspond 
with  the  branches  of  the  hypogastric  artery.  It  receives  (a)  the  gluteal,  internal 
pudendal,  and  obturator  veins,  which  have  their  origins  outside  the  pelvis;  (6)  the 
lateral  sacral  veins,  which  lie  in  front  of  the  sacrum;  and  (c)  the  middle  hemorrhoidal, 
vesical,  uterine,  and  vaginal  veins,  which  originate  in  venous  plexuses  connected 
with  the.  pelvic  viscera. 
43 


674 


ANGIOLOGY 


1.  The  Superior  Gluteal  Veins  (vv.  glutaeac  superiores;  gluteal  veins)  are  vense 
comitantes  of  the  superior  gluteal  artery ;  they  receive  tributaries  from  the  buttock 
corresponding  with  the  branches  of  the  artery,  and  enter  the  pelvis  through  the 
greater  sciatic  foramen,  above  the  Piriformis,  and  frequently  unite  before  ending 
in  the  hypogastric  vein. 

Third  lumbar 


Prostatic  plexus 


Middle 
hemorrhoidal 


Inferior 
hemorrhoidal 


Deep  dorsal  vein 
of  penis 


_  )le3Ma  Internal  pudendal 

Fig.  585. — The  veins  of  the  right  half  of  the  male  pelvis.     (Spalteholz). 

2.  The  Inferior  Gluteal  Veins  {vv.  glutaeoB  mferiores;  sciatic  veins),  or  vense  comi- 
tantes of  the  inferior  gluteal  artery,  begin  on  the  upper  part  of  the  back  of  the 
thigh,  where  they  anastomose  with  the  medial  femoral  circumflex  and  first  perfo- 
rating veins.  _  They  enter  the  pelvis  through  the  lower  part  of  the  greater  sciatic 
foramen  and  join  to  form  a  single  stem  which  opens  into  the  lower  part  of  the  hypo- 
gastric vein. 

3.  The  Internal  Pudendal  Veins  (internal  pudic  veins)  are  the  venae  comitantes 
of  the  internal  pudendal  artery.  They  begin  in  the  deep  veins  of  the  penis  which 
issue  from  the  corpus  cavernosum  penis,  accompany  the  internal  pudendal  artery, 
and  uriite  to  form  a  single  vessel,  which  ends  in  the  hypogastric  vein.  They  receive 
the  veins  from  the  urethral  bulb,  and  the  perineal  and  inferior  hemorrhoidal  veins. 


THE  VEINS  OF  THE  ABDOMEN  AND  PELVIS 


675 


LATERAL 
SACRAL 


MiDOL 
SACRAL 


DEEP 

CIRCUMFLEX 

ILIAC 


INFERIOR 
EPIGASTRIC 


FiQ.  586. — The  iliac  veina.     (Poirier  and  Charpy.) 


MIDDLE 
HEMORRHOIDAL' 


Fig.  587. — Scheme  of  the  anastomosis  of  the  veins  of  tde  rectimi.      (Poirier  and  Charpy.) 


676  ANGIOLOGY 

The  deep  dorsal  vein  of  the  penis  communicates  with  the  internal  pudendal  veins, 
but  ends  mainly  in  the  pudendal  plexus. 

4.  The  Obturator  Vein  {v.  ohturatoria)  begins  in  the  upper  portion  of  the  adductor 
region  of  the  thigh  and  enters  the  pelvis  through  the  upper  part  of  the  obturator 
foramen.  It  runs  backward  and  upward  on  the  lateral  wall  of  the  pelvis  below  the 
obturator  artery,  and  then  passes  between  the  ureter  and  the  hypogastric  artery, 
to  end  in  the  hypogastric  vein. 

5.  The  Lateral  Sacral  Vems  (w.  sacrales  laterales)  accompany  the  lateral  sacral 
arteries  on  the  anterior  surface  of  the  sacrum  and  end  in  the  hypogastric  vein. 

6.  The  Middle  Hemorrhoidal  Vein  {v.  hcemorrhoidalis  media)  takes  origin  in  the 
hemorrhoidal  plexus  and  receives  tributaries  from  the  bladder,  prostate,  and 
seminal  vesicle;  it  runs  lateralward  on  the  pelvic  surface  of  the  Levator  ani  to 
end  in  the  hypogastric  vein. 

The  hemorrhoidal  plexus  (plexus  hoemonhoidalis)  surrounds  the  rectum,  and 
communicates  in  front  with  the  vesical  plexus  in  the  male,  and  the  uterovaginal 
plexus  in  the  female.  It  consists  of  two  parts,  an  internal  in  the  submucosa,  and  an 
external  outside  the  muscular  coat.  The  internal  plexus  presents  a  series  of  dilated 
pouches  which  are  arranged  in  a  circle  around  the  tube,  immediately  above  the 
anal  orifice,  and  are  connected  by  transverse  branches. 

The  lower  part  of  the  external  plexus  is  drained  by  the  inferior  hemorrhoidal 
veins  into  the  internal  pudendal  vein;  the  middle  part  by  the  middle  hemorrhoidal 
vein  which  joins  the  hypogastric  vein;  and  the  upper  part  by  the  superior  hemor- 
rhoidal vein  which  forms  the  commencement  of  the  inferior  mesenteric  vein, 
a  tributary  of  the  portal  vein.  A  free  communication  between  the  portal  and  sys- 
temic venous  systems  is  established  through  the  hemorrhoidal  plexus. 

The  veins  of  the  hemorrhoidal  plexus  are  contained  in  very  loose,  connective 
tissue,  so  that  they  get  less  support  from  surrounding  structures  than  most  other 
veins,  and  are  less  capable  of  resisting  increased  blood-pressure. 

The  pudendal  plexus  (plexus  pudendalis;  vesicoprostatic  plexus)  lies  behind  the 
arcuate  pubic  ligament  and  the  lower  part  of  the  symphysis  pubis,  and  in  front  of 
the  bladder  and  prostate.  Its  chief  tributary  is  the  deep  dorsal  vein  of  the  penis, 
but  it  also  receives  branches  from  the  front  of  the  bladder  and  prostate.  It  com- 
municates with  the  vesical  plexus  and  with  the  internal  pudendal  vein  and  drains 
into  the  vesical  and  hypogastric  veins.  The  prostatic  veins  form  a  well-marked 
prostatic  plexus  which  lies  partly  in  the  fascial  sheath  of  the  prostate  and  partly 
between  the  sheath  and  the  prostatic  capsule.  It  communicates  with  the  pudendal 
and  vesical  plexuses. 

The  vesical  plexus  (plexus  vesicalis)  envelops  the  lower  part  of  the  bladder  and 
the  base  of  the  prostate  and  communicates  with  the  pudendal  and  prostatic  plexuses. 
It  is  drained,  by  means  of  several  vesical  veins,  into  the  hypogastric  veins. 

The  Dorsal  Veins  of  the  Penis  (vv.  dor  sales  penis)  are  two  in  number,  a  superficial 
and  a  deep.  The  superficial  vein  drains  the  prepuce  and  skin  of  the  penis,  and, 
running  backward  in  the  subcutaneous  tissue,  inclines  to  the  right  or  left,  and  opens 
into  the  corresponding  superficial  external  pudendal  vein,  a  tributary  of  the  great 
saphenous  vein.  The  deep  vein  lies  beneath  the  deep  fascia  of  the  penis;  it  receives 
the  blood  from  the  glans  penis  and  corpora  cavernosa  penis  and  courses  backward 
in  the  middle  line  between  the  dorsal  arteries;  near  the  root  of  the  penis  it  passes 
between  the  two  parts  of  the  suspensory  ligament  and  then  through  an  aperture 
between  the  arcuate  pubic  ligament  and  the  transverse  ligament  of  the  pelvis, 
and  divides  into  two  branches,  which  enter  the  pudendal  plexus.  The  deep  vein 
also  communicates  below  the  symphysis  pubis  with  the  internal  pudendal  vein. 

The  uterine  plexuses  lie  along  the  sides  and  superior  angles  of  the  uterus  between 
the  two  layers  of  the  broad  ligament,  and  communicate  with  the  ovarian  and 
vaginal  plexuses.    They  are  drained  by  a  pair  of  uterine  veins  on  either  side :  these 


I 


VEINS  OF  THE  ABDOMEN  AND  PELVIS 


677 


SUPERFICIAL  DOR* 
SAL  VEIN 
DORSAL  ARTERY   1  .DEEP  DORSAL  VEIN 
CORPUS  CAVER  NOSUM; 


SKIN 

SUPERFICIAL 

FASCIA 

cav::rnous. 

ARTERV 


arise  from  the  lower  part  of  the  plexuses,  opposite  the  external  orifice  of  the  uterus, 
and  open  into  the  corresponding  hypogastric  vein. 

The  vaginal  plexuses  are  placed  at  the  sides  of  the  vagina;  they  communicate 
with  the  uterine,  vesical,  and  hemorrhoidal  plexuses,  and  are  drained  by  the 
vaginal  veins,  one  on  either  side,  into  the  hypogastric  veins. 

The  common  iliac  yeins  {vv.  iliacoe 
communes)  are  formed  by  the  union 
of  the  external  iliac  and  hypogastric 
veins,  in  front  of  the  sacroiliac  artic- 
ulation; passing  obliquely  upward 
toward  the  right  side,  they  end  upon 
the  fifth  lumbar  vertebra,  by  uniting 
with  each  other  at  an  acute  angle  to 
form  the  inferior  vena  cava.  The 
right  common  iliac  is  shorter  than 
the  left,  nearly  vertical  in  its  di- 
rection, and  ascends  behind  and  then 
lateral  to  its  corresponding  artery. 
The  left  common  iliac,  longer  than 
the  right  and  more  oblique  in  its 
course,  is  at  first  situated  on  the  medial  side  of  the  corresponding  artery,  and  then 
behind  the  right  common  iliac.  Each  common  iliac  receives  the  iliolumbar,  and 
sometimes  the  lateral  sacral  veins.  The  left  receives,  in  addition,  the  middle  sacral 
vein.    No  valves  are  found  in  these  veins. 

The  Middle  Sacral  Veins  {m.  sacrales  mediales)  accompany  the  corresponding 
artery  along  the  front  of  the  sacrum,  and  join  to  form  a  single  vein,  which  ends  in 
the  left  common  iliac  vein;  sometimes  in  the  angle  of  junction  of  the  two  iliac  veins. 


DEEP 
FASCIA 


BULBO-CAVERNOUS    ARTER\,  

—ANTERIOR    BRANCH  i      URETHRA 

CORPUS 
SPONGIOSUM 


Fig.  588.- 


-The  penis  in  transverse  section,  showing  the 
bloodveasels.     (Testut.) 


ANASTOMOSIS  OF 
UTERINE    AND 


FALLOPIAN 
TUBE 


UTERINE   ARTERY 


UPERIOR    VAGINAL 
ARTERIES 


OS    UTERI         VAGINA    CUT   OPEN    BEHIND 

Fig.  589. — Vessels  of  the  uterus  and  its  appendages,  rear  view.     (Testut.) 

Peculiarities. — The  left  common  iliac  vein,  instead  of  joining  with  the  right  in  its  usual  posi- 
tion, occasionally  ascends  on  the  left  side  of  the  aorta  as  high  a's  the  kidney,  where,  after  receiving 
the  left  renal  vein,  it  crosses  over  the  aorta,  and  then  joins  with  the  right  vein  to  foim  the  vena 
cava.  In  these  cases,  the  two  common  iliacs  are  connected  by  a  small  communicating  branch 
at  the  spot  where  they  are  usually  united. 

The  inferior  vena  cava  (v.  cava  inferior)  (Fig.  577),  returns  to  the  heart  the  blood 
from  the  parts  below  the  diaphragm.  It  is  formed  by  the  junction  of  the  two 
common  iliac  veins,  on  the  right  side  of  the  fifth  lumbar  vertebra.    It  ascends  along 


678  ^^^^^^"       ANGIOLOGY 

the  front  of  the  vertebral  column,  on  the  right  side  of  the  aorta,  and,  having  reached 
the  liver,  is  continued  in  a  groove  on  its  posterior  surface.  It  then  perforates 
the  diaphragm  between  the  median  and  right  portions  of  its  central  tendon; 
it  subsequently  inclines  forward  and  medialward  for  about  2.5  cm.,  and,  piercing 
the  fibrous  pericardium,  passes  behind  the  serous  pericardium  to  open  into  the 
lower  and  back  part  of  the  right  atrium.  In  front  of  its  atrial  orifice  is  a  semilunar 
valve,  termed  the  valve  of  the  inferior  vena  cava :  this  is  rudimentary  in  the  adult, 
but  is  of  large  size  and  exercises  an  important  function  in  the  fetus  (see  page  540) . 

Relations. — The  abdominal  portion  of  the  inferior  vena  cava  is  in  relation  in  front,  from  below 
upward,  with  the  right  common  ihac  artery,  the  mesentery,  the  right  internal  spermatic  artery,  ^_ 
the  inferior  part  of  the  duodenum,  the  pancreas,  the  common  bile  duct,  the  portal  vein,  and  the  ^| 
posterior  surface  of  the  liver;  the  last  partly  overlaps  and  occasionally  completely  surrounds  it;  ^^ 
behind,  with  the  vertebral  column,  the  right  Psoas  major,  the  right  crus  of  the  diaphragm,  the 
right  inferior  phrenic,  suprarenal,  renal  and  lumbar  arteries,  right  sympathetic  trunk  and  right 
celiac  ganglion,  and  the  medial  part  of  the  right  suprarenal  gland;  on  the  right  side,  with  the 
right  kidney  and  ureter;  on  the  left  side,  with  the  aorta,  right  crus  of  the  diaphragm,  and  the 
caudate  lobe  of  the  liver. 

The  thoracic  portion  is  only  about  2.5  cm.  in  length,  and  is  situated  partly  inside  and  partly 
outside  the  pericardial  sac.  The  extrapericardial  part  is  separated  from  the  right  pleura  and 
lung  by  a  fibrous  band,  named  the  right  phrenicopericardiac  ligament.  This  ligament,  often 
feebly  marked,  is  attached  below  to  the  margin  of  the  vena-caval  opening  in  the  diaphragm,  and 
above  to  the  pericardium  in  front  of  and  behind  the  root  of  the  right  lung.  The  intrapericardiac  ■ 
part  is  very  short,  and  is  covered  antero-lateraUy  by  the  serous  layer  of  the  pericardium. 

Pectiliarities. — In  Position. — This  vessel  is  sometimes  placed  on  the  left  side  of  the  aorta, 
aa  high  as  the  left  renal  vein,  and,  after  receiving  this  vein,  crosses  over  to  its  usual  position  on 
the  right  side;  or  it  may  be  placed  altogether  on  the  left  side  of  the  aorta,  and  in  such  a  case  the 
abdominal  and  thoracic  viscera,  together  with  the  great  vessels,  are  aU  transposed. 

Point  of  Termination. — Occasionally  the  inferior  vena  cava  joins  the  azygos  vein,  which  is 
then  of  large  size.  In  such  cases,  the  superior  vena  cava  receives  the  whole  of  the  blood  from 
the  body  before  transmitting  it  to  the  right  atrium,  except  the  blood  from  the  hepatic  veins, 
which  passes  directly  into  the  right  atrium. 

Tributaries. — ^The  inferior  vena  cava  receives  the  following  veins: 

Lumbar.  Renal.  Inferior  Phrenic. 

Right  Spermatic  or  Ovarian.  Suprarenal.  Hepatic. 

The  Lumbar  Veins  (vv.  lumhales)  four  in  number  on  each  side,  collect  the  blood 
by  dorsal  tributaries  from  the  muscles  and  integument  of  the  loins,  and  by  abdomi- 
nal tributaries  from  the  walls  of  the  abdomen,  where  they  communicate  with  the 
epigastric  veins.  At  the  vertebral  column,  they  receive  veins  from  the  vertebral 
plexuses,  and  then  pass  forward,  around  the  sides  of  the  bodies  of  the  vertebrae, 
beneath  the  Psoas  major,  and  end  in  the  back  part  of  the  inferior  cava.  The  left 
lumbar  veins  are  longer  than  the  right,  and  pass  behind  the  aorta.  The  lumbar 
veins  are  connected  together  by  a  longitudinal  vein  which  passes  in  front  of  the 
transverse  processes  of  the  lumbar  vertebrae,  and  is  called  the  ascending  lumbar; 
it  forms  the  most  frequent  origin  of  the  corresponding  azygos  or  hemiazygos  vein, 
and  serves  to  connect  the  common  iliac,  iliolumbar,  and  azygos  or  hemiazygos 
veins  of  its  own  side  of  the  body. 

The  Spermatic  Veins  {vv.  spermaticce)  (Fig.  590)  emerge  from  the  back  of  the 
testis,  and  receive  tributaries  from  the  epididymis;  they  unite  and  form  a  convo- 
luted plexus,  called  the  pampiniform  plexus,  which  constitutes  the  greater  mass  of 
the  spermatic  cord;  the  vessels  composing  this  plexus  are  very  numerous,  and 
ascend  along  the  cord,  in  front  of  the  ductus  deferens.  Below  the  subcutaneous 
inguinal  ring  they  unite  to  form  three  or  four  veins,  which  pass  along  the  inguinal 
canal,  and,  entering  the  abdomen  through  the  abdominal  inguinal  ring,  coalesce 
to  form  two  veins,  which  ascend  on  the  Psoas  major,  behind  the  peritoneum,  lying 
one  on  either  side  of  the  internal  spermatic  artery.  These  unite  to  form  a  single 
vein,  which  opens  on  the  right  side  into  the  inferior  vena  cava,  at  an  acute  angle; 
on  the  left  side  into  the  left  renal  vein,  at  a  right  angle.     The  spermatic  veins 


THE  VEINS  OF  THE  ABDOMEN  AND  PELVIS 


679 


are  provided  with  valves.^    The  left  spermatic  vein  passes  behind  the  iliac  colon, 
and  is  thus  exposed  to  pressure  from  the  contents  of  that  part  of  the  bowel. 

The  Ovarian  Veins  {vv.  ovaricoe)  correspond  with  the  spermatic  in  the  male;  they 
form  a  plexus  in  the  broad  ligament  near  the  ovary  and  uterine  tube,  and  communi- 
cate with  the  uterine  plexus.  They  end  in  the  same  way  as  the  spermatic  veins 
in  the  male.  Valves  are  occasionally  found  in  these  veins.  Like  the  uterine  veins, 
they  become  much  enlarged  during  pregnancy. 


...U.H. 


Fig.  590. — Spermatic  veins.     (Testut.) 

The  Renal  Veins  (vv.  renales)  are  of  large  size,  and  placed  in  front  of  the  renal 
arteries.  The  left  is  longer  than  the  right,  and  passes  in  front  of  the  aorta,  just 
below  the  origin  of  the  superior  mesenteric  artery.  It  receives  the  left  spermatic 
and  left  inferior  phrenic  veins,  and,  generally,  the  left  suprarenal  vein.  It  opens 
into  the  inferior  vena  cava  at  a  slightly  higher  level  than  the  right. 

The  Suprarenal  Veins  {vv.  swprarenales)  are  two  in  number:  the  right  ends  in  the 
inferior  vena  cava;  the  left,  in  the  left  renal  or  left  inferior  phrenic  vein. 

The  Inferior  Phrenic  Veins  {m.  phrenicce  inferiores)  follow  the  course  of  the  inferior 
phrenic  arteries;  the  right  ends  in  the  inferior  vena  cava;  the  left  is  often  repre- 
sented by  two  branches,  one  of  which  ends  in  the  left  renal  or  suprarenal  vein, 
while  the  other  passes  in  front  of  the  esophageal  hiatus  in  the  diaphragm  and 
opens  into  the  inferior  vena  cava. 

'  Rivington  has  pointed  out  that  valvps  are  usually  found  at  the  orifices  of  both  the  right  and  left  spermatic  veins. 
When  no  valves  exist  at  the  opening  of  the  left  spermatic  vein  into  the  left  renal  vein,  valves  are  generally  present  in 
the  left  renal  vein  within  6  mm   from  the  orifice  of  the  spermatic  vein. — Journal  of  Anatomy  and  Physiology,  vii,  163. 


680 


ANGIOLOGY 


The  Hepatic  Veins  {vv.  hepaticcp)  commence  in  the  substance  of  the  liver,  in  the 
terminations  of  the  portal  vein  and  hepatic  artery,  and  are  arranged  in  two  groups, 
upper  and  lower.  The  upper  group  usually  consists  of  three  large  veins,  which 
converge  toward  the  posterior  surface  of  the  liver,  and  open  into  the  inferior 
vena  cava,  while  that  vessel  is  situated  in  the  groove  on  the  back  part  of  the  liver. 
The  veins  of  the  lower  group  vary  in  number,  and  are  of  small  size;  they  come 
from  the  right  and  caudate  lobes.  The  hepatic  veins  run  singly,  and  are  in  direct 
contact  with  the  hepatic  tissue.     They  are  destitute  of  valves. 


Fig.  591. — The  portal  vein  and  its  tributaries. 

THE   PORTAL   SYSTEM   OF   VEINS    (Fig.    591). 

The  portal  system  includes  all  the  veins  which  drain  the  blood  from  the  abdominal 
part  of  the  digestive  tube  (with  the  exception  of  the  lower  part  of  the  rectum) 
and  from  the  spleen,  pancreas,  and  gall-bladder.  From  these  viscera  the  blood 
is  conveyed  to  the  liver  by  the  portal  vein.  In  the  liver  this  vein  ramifies  like  an 
artery  and  ends  in  capillary-like  vessels  termed  sinusoids,  from  which  the  blood  is 


»" 


THE  PORTAL  SYSTEM  OF  VEINS  681 

conveyed  to  the  inferior  vena  cava  by  the  hepatic  veins.  From  this  it  will  be  seen 
that  the  blood  of  the  portal  system  passes  through  two  sets  of  minute  vessels, 
iz.,  (a)  the  capillaries  of  the  digestive  tube,  spleen,  pancreas,  and  gall-bladder; 
and  (b)  the  sinusoids  of  the  liver.  In  the  adult  the  portal  vein  and  its  tributaries 
are  destitute  of  valves ;  in  the  fetus  and  for  a  short  time  after  birth  valves  can  be 
demonstrated  in  the  tributaries  of  the  portal  vein;  as  a  rule  they  soon  atrophy 
and  disappear,  but  in  some  subjects  they  persist  in  a  degenerate  form. 

The  portal  vein  (vena  portce)  is  about  8  cm.  in  length,  and  is  formed  at  the  level 
of  the  second  lumbar  vertebra  by  the  junction  of  the  superior  mesenteric  and  lienal 
veins,  the  union  of  these  veins  taking  place  in  front  of  the  inferior  vena  cava  and 
behind  the  neck  of  the  pancreas.  It  passes  upward  behind  the  superior  part  of 
the  duodenum  and  then  ascends  in  the  right  border  of  the  lesser  omentum  to  the 
right  extremity  of  the  porta  hepatis,  where  it  divides  into  a  right  and  a  left  branch, 
which  accompany  the  corresponding  branches  of  the  hepatic  artery  into  the  sub- 
stance of  the  liver.  In  the  lesser  omentum  it  is  placed  behind  and  between  the 
common  bile  duct  and  the  hepatic  artery,  the  former  lying  to  the  right  of  the  latter. 
It  is  surrounded  by  the  hepatic  plexus  of  nerves,  and  is  accompanied  by  numerous 
lymphatic  vessels  and  some  lymph  glands.  The  right  branch  of  the  portal  vein 
enters  the  right  lobe  of  the  liver,  but  before  doing  so  generally  receives  the  cystic 
vein.  The  left  branch,  longer  but  of  smaller  caliber  than  the  right,  crosses  the  left 
sagittal  fossa,  gives  branches  to  the  caudate  lobe,  and  then  enters  the  left  lobe  of 
the  liver.  As  it  crosses  the  left  sagittal  fossa  it  is  joined  in  front  by  a  fibrous  cord, 
the  ligamentum  teres  (obliterated  umbilical  vein) ,  and  is  united  to  the  inferior  vena 
cava  by  a  second  fibrous  cord,  the  ligamentum  venosum  (obliterated  ductus  venosus). 

Tributaries. — The  tributaries  of  the  portal  vein  are: 


Lienal.  Pyloric. 

Superior  Mesenteric.  Cystic. 

Coronary.  Parumbilical. 


The  Lienal  Vein  (v.  lienalis;  splenic  vein)  commences  by  five  or  six  large  branches 
which  return  the  blood  from  the  spleen.  These  unite  to  form  a  single  vessel,  which 
passes  from  left  to  right,  grooving  the  upper  and  back  part  of  the  pancreas,  below 
the  lineal  artery,  and  ends  behind  the  neck  of  the  pancreas  by  uniting  at  a  right 
angle  with  the  superior  mesenteric  to  form  the  portal  vein.  The  lienal  vein  is 
of  large  size,  but  is  not  tortuous  like  the  artery. 

Tributaries. — The  lineal  vein  receives  the  short  gastric  veins,  the  left  gastro- 
epiploic vein,  the  pancreatic  veins,  and  the  inferior  mesenteric  veins. 

The  short  gastric  veins  {vv.  gastricce  breves)  Joutot  five  in  number,  drain  the  fundus 
and  left  part  of  the  greater  curvature  of  the  stom-ach,  and  pass  between  the  two 
layers  of  the  gastrolienal  ligament  to  end  in  the  lienal  vein  or  in  one  of  its  large 
tributaries. 

The  left  gastroepiploic  vein  (v.  gastroepiploica  sinistra)  receives  branches  from 
the  antero-superior  and  postero-inferior  surfaces  of  the  stomach  and  from  the  greater 
omentum;  it  runs  from  right  to  left  along  the  greater  curvature  of  the  stomach 
and  ends  in  the  commencement  of  the  lienal  vein. 

The  pancreatic  veins  (vv.  pancreaticos)  consist  of  several  small  vessels  which  drain 
the  body  and  tail  of  the  pancreas,  and  open  into  the  trunk  of  the  lienal  vein. 

The  inferior  mesenteric  vein  (v.  mesenterica  inferior)  returns  blood  from  the  rectum 
and  the  sigmoid,  and  descending  parts  of  the  colon.  It  begins  in  the  rectum  as 
the  superior  hemorrhoidal  vein,  which  has  its  origin  in  the  hemorrhoidal  plexus, 
and  through  this  plexus  communicates  with  the  middle  and  inferior  hemor- 
rhoidal veins.  The  superior  hemorrhoidal  vein  leaves  the  lesser  pelvis  and  crosses 
the  left  common  iliac  vessels  with  the  superior  hemorrhoidal  artery,  and  is  con- 
tinued upward  as  the  inferior  mesenteric  vein.  This  vein  lies  to  the  left  of  its 
artery,  and  ascends  behind  the  peritoneum  and  in  front  of  the  left  Psoas  major; 


■Larterv,  ai 


682  ^^^^^^^^^      ANGIOLOGY 

it  then  passes  behind  the  body  of  the  pancreas  and  opens  into  the  lienal  vein; 
sometimes  it  ends  in  the  angle  of  union  of  the  lienal  and  superior  mesenteric  veins. 

Tributaries. — The  inferior  mesenteric  vein  receives  the  sigmoid  veins  from  the 
sigmoid  colon  and  iliac  colon,  and  the  left  colic  vein  from  the  descending  colon  and 
left  colic  flexure. 

The  Superior  Mesenteric  Vein  {v.  mesenierica  superior)  returns  the  blood  from  the 
small  intestine,  from  the  cecum,  and  from  the  ascending  and  transverse  portions 
of  the  colon.  It  begins  in  the  right  iliac  fossa  by  the  union  of  the  veins  which  drain 
the  terminal  part  of  the  ileum,  the  cecum,  and  vermiform  process,  and  ascends 
between  the  two  layers  of  the  mesentery  on  the  right  side  of  the  superior  mes- 
enteric artery.  In  its  upward  course  it  passes  in  front  of  the  right  ureter,  the 
inferior  vena  cava,  the  inferior  part  of  the  duodenum,  and  the  lower  portion  of 
the  head  of  the  pancreas.  Behind  the  neck  of  the  pancreas  it  unites  with  the  lienal 
vein  to  form  the  portal  vein. 

Tributaries. — Besides  the  tributaries  which  correspond  with  the  branches  of  the 
superior  mesenteric  artery,  viz.,  the  intestinal,  ileocolic,  right  colic,  and  middle  colic 
veins,  the  superior  mesenteric  vein  is  joined  by  the  right  gastroepiploic  and  pan- 
creaticoduodenal veins. 

The  right  gastroepiploic  vein  {v.  gastroepiploica  dextra)  receives  branches  from  the 
greater  omentum  and  from  the  lower  parts  of  the  antero-superior  and  postero- 
inferior  surfaces  of  the  stomach;  it  runs  from  left  to  right  along  the  greater  curva- 
ture of  the  stomach  between  the  two  layers  of  the  greater  omentum. 

The  pancreaticoduodenal  veins  {vv.  pancreaticoduodenales)  accompany  their  corre- 
sponding arteries;  the  lower  of  the  two  frequently  joins  the  right  gastroepiploic 
vein. 

The  Coronary  Vein  {v.  coronaria  ventriculi;  gastric  vein)  derives  tributaries  from 
both  surfaces  of  the  stomach;  it  runs  from  right  to  left  along  the  lesser  curvature 
of  the  stomach,  between  the  two  layers  of  the  lesser  omentum,  to  the  esophageal 
opening  of  the  stomach,  where  it  receives  some  esophageal  veins.  It  then  turns 
backward  and  passes  from  left  to  right  behind  the  omental  bursa  and  ends  in  the 
portal  vein. 

The  Pyloric  Vein  is  of  small  size,  and  runs  from  left  to  right  along  the  pyloric 
portion  of  the  lesser  curvature  of  the  stomach,  between  the  two  layers  of  the  lesser 
omentum,  to  end  in  the  portal  vein. 

The  Cystic  Vein  {v.  cystica)  drains  the  blood  from  the  gall-bladder,  and,  accom- 
panying the  cystic  duct,  usually  ends  in  the  right  branch  of  the  portal  vein. 

Parumbilical  Veins(OT.  parumbilicales) . — In  the  course  of  the  ligamentum  teres 
of  the  liver  and  of  the  middle  umbilical  ligament,  small  veins  {parumbilical)  are 
found  which  establish  an  anastomosis  between  the  veins  of  the  anterior  abdominal 
wall  and  the  portal,  hypogastric,  and  iliac  veins.  The  best  marked  of  these  small 
veins  is  one  which  commences  at  the  umbilicus  and  runs  backward  and  upward 
in,  or  on  the  surface  of,  the  ligamentum  teres  between  the  layers  of  the  falciform 
ligament  to  end  in  the  left  portal  vein. 

Collateral  venous  circulation  to  relieve  portal  obstruction  in  the  liver  may  be  effected  by- 
communications  between  (a)  the  gastric  veins  and  the  esophageal  veins  which  often  project 
as  a  varicose  bunch  into  the  stomach,  emptying  themselves  into  the  hemiazygos  vein;  (b)  the 
veins  of  the  colon  and  duodenum  and  the  left  renal  vein;  (c)  the  accessory  portal  system  of 
Sappey,  branches  of  which  pass  in  the  round  and  falciform  hgaments  (particularly  the  latter) 
to  unite  with  the  epigastric  and  internal  mammary  veins,  and  through  the  diaphragmatic 
veins  with  the  azygos;  a  single  large  vein,  shown  to  be  a  parumbilical  vein,  may  pass  from 
the  hilus  of  the  liver  by  the  round  hgament  to  the  umbihcus,  producing  there  a  bunch  of 
prominent  varicose  veins  known  as  the  caput  medusw.;  (d)  the  veins  of  Retzius,  which  connect 
the  intestinal  veins  with  the  inferior  vena  cava  and  its  retroperitoneal  branches;  (e)  the  inferior 
mesenteric  veins,  and  the  hemorrhoidal  veins  that  open  into  the  hypogastrics;  (/)  very  rarely 
the  ductus  venosus  remains  patent,  affording  a  direct  connection  between  the  portal  vein  and 
the  inferior  vena  cava. 


THE  LYMPHATIC  SYSTEM. 


THE  lymphatic  system  consists  (1)  of  complex  capillary  networks  which  collect  the 
lymph  in  the  various  organs  and  tissues;  (2)  of  an  elaborate  system  of  collecting 
yessels  which  conduct  the  lymph  from  the  capillaries  to  the  large  veins  of  the  neck 
at  the  junction  of  the  internal  jugular  and  subclavian  veins,  where  the  hinph  is 
poured  into  the  blood  stream;  and  (3)  IjTnph  glands  or  nodes  which  are  inter- 
spaced in  the  pathways  of  the  collecting  vessels  filtering  the  lymph  as  it  passes 
through  them  and  contributing  lymphocytes  to  it.  The  lymphatic  capillaries  and 
collecting  vessels  are  lined  throughout  by  a  continuous  layer  of  endothelial  cells, 
forming  thus  a  closed  system.  The  lymphatic  vessels  of  the  small  intestine  receive 
the  special  designation  of  lacteals  or  chyliferous  vessels;  they  differ  in  no  respect 
from  the  lymphatic  vessels  generally  excepting  that  during  the  process  of  digestion 
thev  contain  a  milk-white  fluid,  the  chyle. 


Lejt  innominate 


Jugular  lymph-sac 
Sight  innominate 

Superior  vena  cava 


Prerenal  part  of 
inferior  vena  cava 


Postrenal  part  of 
inferior  vena  cava 


Posterior  lymph-sac 


Internal  jugular 
External  jugular 


Duct  of  Cuvier 
Left  cardinal 


Cistema  chyli 
Left  renal 
Retro-peritoneal 
lymph-sac 


Left  common  iliac 
External  iliac 
Hypogastric 


Fig.  592.- 


-Scheme  showing  relative  positions  of  primary  lymph  sacs  based  on  the  description  given  by 
Florence  Sabin. 


The  Development  of  the  Lymphatic  Vessels. — The  lymphatic  system  begins  as 
a  series  of  sacs^  at  the  points  of  junction  of  certain  of  the  embryonic  veins.  These 
lymph-sacs  are  developed  by  the  confluence  of  numerous  venous  capillaries,  which 
at  first  lose  their  connections  with  the  venous  system,  but  subsequently,  on  the 
formation  of  the  sacs,  regain  them.  The  lymphatic  system  is  therefore  develop- 
mentally  an  offshoot  of  the  venous  system,  and  the  lining  walls  of  its  vessels  are 
always  endothelial. 

In  the  human  embryo  the  lymph  sacs  from  which  the  lymphatic  vessels  are 


>  Sabin,  Am.  Jour.  Anat.,  1909,  vol.  ix;  Johns  Hopkins  Hospital  Reports,  1913. 


(  683 ) 


684  ^^^^^^^      ANGIOLOGY 

derived  are  six  in  number;  two  paired,  the  jugular  and  the  posterior  lymph-sacs; 
and  two  unpaired,  the  retroperitoneal  and  the  cisterna  chj'li.  In  lower  mammals 
an  additional  pair,  subclavian,  is  present,  but  in  the  human  embryo  these  are 
merely  extensions  of  the  jugular  sacs. 

The  position  of  the  sacs  is  as  follows:  (1)  jugular  sac,  the  first  to  appear,  at 
the  junction  of  the  subclavian  vein  with  the  primitive  jugular;  (2)  posterior  sac, 
at  the  junction  of  the  iliac  vein  with  the  cardinal;  (3)  retroperitoneal,  in  the  root 
of  the  mesentery  near  the  suprarenal  glands;  (4)  cisterna  chyli,  opposite  the  third 
and  fourth  lumbar  vertebrae  (Fig.  592).  From  the  lymph-sacs  the  lymphatic 
vessels  bud  out  along  fixed  lines  corresponding  more  or  less  closely  to  the  course 
of  the  embryonic  bloodvessels.  Both  in  the  body-wall  and  in  the  wall  of  the 
intestine,  the  deeper  plexuses  are  the  first  to  be  developed;  by  continued  growth 
of  these  the  vessels  in  the  superficial  layers  are  gradually  formed.  The  thoracic 
duct  is  probably  formed  from  anastomosing  outgrowths  from  the  jugular  sac  and 
cisterna  chyli.  At  its  connection  with  the  cisterna  chyli  it  is  at  first  double,  but 
the  two  vessels  soon  join. 

All  the  Ij'mph-sacs  except  the  cisterna  chyli  are,  at  a  later  stage,  divided  up  by 
slender  connective  tissue  bridges  and  transformed  into  groups  of  lymph  glands. 
The  lower  portion  of  the  cisterna  chyli  is  similarly  converted,  but  its  upper  portion 
remains  as  the  adult  cisterna. 

Ljrmphatic  Capillaries. — ^The  complex  capillary  plexuses  which  consist  of  a 
single  layer  of  thin  flat  endothelial  cells  lie  in  the  connective-tissue  spaces  in  the 
various  regions  of  the  body  to  which  the\'^  are  distributed  and  are  bathed  by  the 
intercellular  tissue  fluids.  Two  views  are  at  present  held  as  to  the  mode  in  which 
the  IjTiiph  is  formed :  one  being  by  the  physical  processes  of  filtration,  diffusion,  and 
osmosis,  and  the  other,  that  in  addition  to  these  physical  processes  the  endothelial 
cells  have  an  active  secretory  function.  The  colorless  liquid  honph  has  about  the 
same  composition  as  the  blood  plasma.  It  contains  many  hniiphocytes  and  fre- 
quently red  blood  corpuscles.  Granules  and  bacteria  are  also  taken  up  by  the  lymph 
from  the  connective-tissue  spaces,  partly  by  the  action  of  hniphocytes  which  pass 
into  the  hinph  between  the  endothelial  cells  and  partly  by  the  direct  passage  of  the 
granules  through  the  endothelial  cells. 

The  lytnphatic  capillary  plexuses  vary  greatly  in  form;  the  anastomoses  are 
usually  numerous;  blind  ends  or  cul-de-sacs  are  especially  common  in  the  intestinal 
villi,  the  dermal  papillae  and  the  filiform  papilla?  of  the  tongue.  The  plexuses  are 
often  in  two  layers :  a  superficial  and  a  deep,  the  superficial  being  of  smaller  caliber 
than  the  deep.  The  caliber,  however,  varies  greatly  in  a  given  plexus  from  a  few 
micromillimeters  to  one  millimeter.    The  capillaries  are  without  valves. 

Distribution. — The  Skin. — Ljmphatic  capillaries  are  abundant  in  the  dermis 
where  they  form  superficial  and  deep  plexuses,  the  former  sending  blind  ends  into 
the  dermal  papillae.  The  plexuses  are  especially  rich  over  the  palmar  surface  of  the 
hands  and  fingers  and  over  the  plantar  surface  of  the  feet  and  toes.  The  epidermis 
is  without  capillaries.    The  conjunctiva  has  an  especially  rich  plexus. 

The  subcutaneous  tissue  is  without  capillaries. 

The  tendons  of  striated  muscle  and  viuscle  sheaths  are  richlj-  supplied.  In  muscle, 
however,  their  existence  is  still  disputed. 

The  'periosteum  of  bone  is  richly  supplied  and  they  have  been  described  in  the 
Haversian  canals.    They  are  absent  in  cartilage  and  probably  in  bone  marrow. 

The  joint  capsules  are  richly  supplied  with  l^tTnphatic  capillaries,  they  do  not, 
however,  open  into  the  joint  cavities. 

Beneath  the  mesothelium  lining  of  the  pleural,  peritoneal  and  pericardial  cavities 
are  rich  plexuses;  they  do  not  open  into  these  cavities. 

The  alimentary  canal  is  supplied  with  rich  plexuses  beneath  the  epithelium,  often 
as  a  superficial  plexus  in  the  mucosa  and  a  deeper  submucosal  plexus.    Cul-de-sacs 


LYMPHATIC  CAPILLARIES 


685 


extend  into  the  filiform  papillae  of  the  tongue  and  the  villi  of  the  small  intestine. 
Those  portions  of  the  alimentary  canal  covered  by  peritoneum,  have  in  addition 
[a  subserous  lymphatic  capillary  plexus  beneath  the  mesothelium. 


Tig.  593. — Lymph  capillaries  of  the  human  conjunctiva:  a,  conjunctiva  corneae;  b,  conjunctiva  scleroticse. 

X  40  dia.     (Teichmann.) 


Fig.  594. — Lymph  capillaries  from  the  human  scrotum,  showing  also  transition  from  capillaries  to  the  collecting 
vessels  a,  a.      X  20  dia.     (Teichmann.) 

The  salivary  glands  are  supplied  with  Ijinphatic  capillaries. 

The  liver  has  a  rich  subserous  plexus  in  the  capsule  and  also  extensive  plexuses 
which  accompany  the  hepatic  artery  and  portal  vein.  The  Ijinphatic  capillaries 
have  not  been  followed  into  the  liver  lobules.    The  lymph  from  the  liver  forms  a 


686 


ANGIOLOGY 


large  part  of  that  which  flows  through  the  thoracic  duct.    The  gall-bladder  and  Mk 
ducts  have  rich  subepithehal  plexuses  and  the  former  a  subserous  plexus. 

The  syJeen  has  a  rich  subserous  set  and  a  capsular  set  of  lymphatic  capillaries. 
Iheir  presence  m  the  parenchyma  is  uncertain. 


Yia.  595. — Lymph  capillaries  of  the  cutis  from  the  inner  border  of  the  sole  of  the  human  foot. 
b,  b,  inner  layer.      X  30  dia.     (Teichmann.) 


o,  o,  outer  layer; 


The  nasal  cavity  has  extensive  capillary  plexuses  in  the  mucosa  and  submucosa. 

The  trachea  and  bronchi  have  plexuses  in  the  mucosa  and  submucosa  but  the 
smaller  bronchi  have  only  a  single  layer.  The  capillaries  do  not  extend  to  the 
air-cells.  The  plexuses  around  the  smaller  bronchi  connect  with  the  rich  subserous 
plexus  of  the  lungs  in  places  where  the  veins  reach  the  surface. 


Fig.  596.- 


-Vertical  section  through  human  tongue;  o,  a,  blind  lyniij 
lying  lymphatic  plexus.      X  45. 


tapillaiitoiii  the  liUtoriii  papillse  with  the  under- 
(Teichmann.) 


Lymphatics  have  been  described  in  the  thyroid  gland  and  in  the  thymus. 

The  adrenal  has  a  superficial  plexus  divided  into  two  layers,  one  in  the  loose  tissue 
about  the  gland  and  the  other  beneath  the  capsule.  Capillaries  have  also  been 
described  within  the  parenchyma. 


I 


STRUCTURE  OF  LYMPHATIC  VESSELS 

The  kidney  is  supplied  with  a  coarse  subserous  plexus  and  a  deeper  plexus  of 
finer  capillaries  in  the  capsule.  Lymphatics  have  been  described  within  the  sub- 
stance of  the  kidney  surrounding  the  tubules. 

The  urinary  bladder  has  a  rich  plexus  of  l.Mnphatic  capillaries  just  beneath  the 
epithelial  lining,  also  a  subserous  set  which  anastomoses  with  the  former  through 
the  muscle  layer.  The  submucous  plexus  is  continuous  with  the  submucous  plexus 
of  the  urethra. 

The  prostate  has  a  rich  lymphatic  plexus  surrounding  the  gland  and  a  wide- 
meshed  subcapsular  plexus. 

The  testis  has  a  rich  superficial  plexus  beneath  the  tunica  albuginea.  The  pres- 
ence of  deep  lymphatics  is  disputed. 

The  uterus  is  provided  with  a  subserous  plexus,  the  deeper  lymphatics  are 
uncertain.     Subepithelial  plexuses  are  found  in  the  vagina. 

The  ovary  has  a  rich  superficial  plexus  and  a  deep  interstitial  plexus. 

The  heart  has  a  rich  subserous  plexus  beneath  the  epicajdium.  Lymphatic 
capillaries  have  also  been  described  beneath  the  endocardium  and  throughout 
the  muscle. 

Lymphatic  capillaries  are  probably  absent  in  the  central  nervous  system,  the 
meninges,  the  eyeball  (except  the  conjunctiva),  the  orbit,  the  internal  ear,  within 
striated  muscle,  the  liver  lobule,  the  spleen  pulp  and  kidney  parenchyma.  They 
are  entirely  absent  in  cartilage.    In  many  places  further  investigation  is  needed.    . 

L3miphatic  Vessels. — ^The  hmphatic  vessels  are  exceedingly  delicate,  and  their 
coats  are  so  transparent  that  the  fluid  they  contain  is  readily  seen  through  them. 
They  are  interrupted  at  intervals  by  constrictions,  which  give  them  a  knotted 
or  beaded  appearance;  these  constrictions  correspond  to  the  situations  of  valves 
in  their  interior.  Lymphatic  vessels  have  been  found  in  nearly  every  texture 
and  organ  of  the  body  which  contains  bloodvessels.  Such  non-vascular  structures 
as  cartilage,  the  nails,  cuticle,  and  hair  have  none,  but  with  these  exceptions  it  is 
probable  that  eventually  all  parts  will  be  found  to  be  permeated  by  these  vessels. 

Structure  of  Lymphatic  Vessels. — The  larger  lymphatic  vessels  are  each  composed  of  three 
coats.  The  internal  coat  is  thin,  transparent,  slightly  elastic,  and  consists  of  a  layer  of  elongated 
endothehal  cells  with  wavy  margins  by  which  the  contiguous  cells  are  dovetailed  into  one  another; 
the  cells  are  supported  on  an  elastic  membrane.  The  middle  coat  is  composed  of  smooth  muscular 
and  fine  elastic  fibers,  disposed  in  a  transverse  direction.  The  external  coat  consists  of  connective 
tissue,  intermixed  with  smooth  muscular  fibers  longitudinally  or  obUquely  disposed;  it  forms 
a  protective  covering  to  the  other  coats,  and  serves  to  connect  the  vessel  with  the  neighboring 
structures.  In  the  smaller  vessels  there  are  no  muscular  or  elastic  fibers,  and  the  wall  consists 
only  of  a  connective-tissue  coat,  lined  by  endothehum.  The  thoracic  duct  has  a  more  complex 
structure  than  the  other  lymphatic  vessels;  it  presents  a  distinct  subendothelial  layer  of  branched 
corpuscles,  similar  to  that  found  in  the  arteries;  in  the  middle  coat  there  is,  in  addition  to  the 
muscular  and  elastic  fibers,  a  layer  of  connective  tissue  with  its  fibers  arranged  longitudinally. 
The  lymphatic  vessels  are  supphed  by  nutrient  vessels,  which  are  distributed  to  their  outer 
and  middle  coats;  and  here  also  have  been  traced  many  non-medullated  nerves  in  the  form  of 
a  fine  plexus  of  fibrils. 

The  valves  of  the  Ijonphatic  vessels  are  formed  of  thin  layers  of  fibrous  tissue  covered  on  both 
surfaces  by  endothelium  which  presents  the  same  arrangement  as  on  the  valves  of  veins  (p.  501). 
In  form  the  valves  are  semilunar;  they  are  attached  by  their  convex  edges  to  the  wall  of  the 
vessel,  the  concave  edges  being  free  and  directed  along  the  course  of  the  contained  current. 
Usuall}^  two  such  valves,  of  equal  size,  are  found  opposite  one  another;  but  occasionally  excep- 
tions occur,  especially  at  or  near  the  anastomoses  of  lymphatic  vessels.  Thus,  one  valve  may 
be  of  small  size  and  the  other  increased  in  proportion. 

In  the  lymphatic  vessels  the  valves  are  placed  at  much  shorter  intervals  than  in  the  veins. 
They  are  most  numerous  near  the  lymph  glands,  and  are  found  more  frequently  in  the  lymphatic 
vessels  of  the  neck  and  upper  extremity  than  in  those  of  the  lower  extremity.  The  wall  of 
the  lymphatic  vessel  immediately  above  the  point  of  attachment  of  each  segment  of  a  valve  is 
expanded  into  a  pouch  or  sinus  which  gives  to  these  vessels,  when  distended,  the  knotted  or 
beaded  appearance  already  referred  to.  Valves  are  wanting  in  the  vessels  composing  the  plexi- 
form  net-work  in  which  the  lymphatic  vessels  usually  originate  on  the  surface  of  the  body. 


I 


688 


ANGIOLOGY 


Lympn  Glands  (lymphoglandulce) . — The  lymph  glands  are  small  oval  or  bean- 
shaped  bodies,  situated  in  the  course  of  lymphatic  and  lacteal  vessels  so  that  the 
lymph  and  chyle  pass  through  them  on  their  way  to  the  blood.  Each  generally 
presents  on  one  side  a  slight  depression — the  hilus — through  which  the  bloodvessels 
enter  and  leave  the  interior.  The  efferent  lymphatic  vessel  also  emerges  from  the 
gland  at  this  spot,  while  the  afferent  vessels  enter  the  organ  at  different  parts  of  Jl 
the  periphery.  On  section  (Fig.  597)  a  lymph  gland  displays  two  different  struc-" 
tures:  an  external,  of  lighter  color — the  cortical;  and  an  internal,  darker — the 
medullary.  The  cortical  structure  does  not  form  a  complete  investment,  but  is 
deficient  at  the  hilus,  where  the  medullary  portion  reaches  the  surface  of  the 
gland;  so  that  the  efferent  vessel  is  derived  directly  from  the  medullary  structures, 
while  the  afferent  vessels  empty  themselves  into  the  cortical  substance. 


Lymphoid 

tissue  in 

cortex 


ips 
lymph-path 


Lymph-path 
in  medulla 


Fio.   597. — Section  of  small  lymph  gland  of  rabbit.      X  100. 


Structure  of  Lymph  Glands. — A  lymph  gland  consists  of  (1)  a  fibrous  envelope,  or  capsule, 
from  which  a  frame-work  of  processes  (irabeculce)  proceeds  inward,  imperfectly  dividing  the 
gland  into  open  spaces  freely  communicating  with  each  other;  (2)  a  quantity  of  lymphoid  tissue 
occupying  these  spaces  without  completely  filling  them;  (3)  a  free  supply  of  bloodvessels,  which 
are  supported  in  the  trabeculae;  and  (4)  the  afferent  and  efferent  vessels  communicating  through 
the  lymph  paths  in  the  substance  of  the  gland.  The  nerves  passing  into  the  hilus  are  few  in 
number  and  are  chiefly  distributed  to  the  bloodvessels  supplying  the  gland. 

The  capsule  is  composed  of  connective  tissue  with  some  plain  muscle  fibers,  and  from  its  internal 
surface  are  given  off  a  number  of  membranous  processes  or  trabeculae,  consisting,  in  man,  of 
connective  tissue,  with  a  small  admixture  of  plain  muscle  fibers;  but  in  many  of  the  lower  animals 
composed  almost  entirely  of  involuntary  muscle.  They  pass  inward,  radiating  toward  the  center 
of  the  gland,  for  a  certain  distance — that  is  to  say,  for  about  one-third  or  one-fourth  of  the  space 
between  the  circumference  and  the  center  of  the  gland.  In  some  animals  they  are  sufficiently 
well-marked  to  divide  the  peripheral  or  cortical  portion  of  the  gland  into  a  number  of  compart- 
ments (so-called  foUicles),  but  in  man  this  arrangement  is  not  obvious.  The  larger  trabeculae 
springing  from  the  capsule  break  up  into  finer  bands,  and  these  interlace  to  form  a  mesh-work 
in  the  central  or  medullary  portion  of  the  gland.  In  these  spaces  formed  by  the  interlacing 
trabeculae  is  contained  the  proper  gland  substance  or  lymphoid  tissue.  The  gland  pulp  does 
not,  however,  completely  fill  the  spaces,  but  leaves,  between  its  outer  margin  and  the  enclosing 
trabeculae,  a  channel  or  space  of  uniform  width  throughout.    This  is  termed  the  lymph  path 


II 


STRUCTURE  OF  LYMPH  GLANDS 


689 


or  lymph  sihus  (Fig.  597).  Running  across  it  are  a  number  of  finer  trabeculse  of  retiform  con- 
nective tissue,  the  fibers  of  which  are,  for  the  most  part,  covered  by  ramifying  cells. 

On  account  of  the  pecuhar  arrangement  of  the  frame-work  of  the  organ,  the  gland  pulp  in  the 
cortical  portion  is  disposed  in  the  form  of  nodules,  and  in  the  medullary  part  in  the  form  of  rounded 
cords.  It  consists  of  ordinary  lymphoid  tissue  (Fig.  598),  being  made  up  of  a  delicate  net-work 
of  retiform  tissue,  which  is  continuous  with  that  in  the  lymph  paths,  but  marked  off  from  it 
by  a  closer  reticulation;  it  is  probable,  moreover,  that  the  reticular  tissue  of  the  gland  pulp  and 
the  lymph  paths  is  continuous  with  that  of  the  trabeculse,  and  ultimately  with  that  of  the  capsule 
of  the  gland.  In  its  meshes,  in  the  nodules  and  cords  of  lymphoid  tissue,  are  closely  packed 
lymph  corpuscles.  The  gland  pulp  is  traversed  by  a  dense  plexus  of  capiUary  bloodvessels. 
The  nodules  or  follicles  in  the  cortical  portion  of  the  gland  frequently  show,  in  their  centers, 
areas  where  karyokinetic  figures  indicate  a  division  of  the  lymph  corpuscles.  These  areas  are 
termed  germ  centers.  The  cells  composing  them  have  more  abimdant  protoplasm  than  the 
peripheral  cells. 

The  afferent  vessels,  as  stated  above,  enter  at  afl  parts  of  the  periphery  of  the  gland,  and  after 
branching  and  forming  a  dense  plexus  in  the  substance  of  the  capsule,  open  into  the  lymph  sinuses 
of  the  cortical  part.  In  doing  this  they  lose  all  their  coats  except  their  endothelial  lining,  which 
is  continuous  with  a  layer  of  similar  cells  lining  the  lymph  paths.  In  like  manner  the  efferent 
vessel  commences  from  the  lymph  sinuses  of  the  medullary  portion.  The  stream  of  lymph  carried 
to  the  glajid  by  the  afferent  vessels  thus  passes  through  the  plexus  in  the  capsule  to  the  lymph 


II 


Fig.  598. — Lymph  gland  tissue.     Highly  magnified,     a,  Trabeculse.    6.  Small  artery  in  substance  of  same, 
c.  Lymph  paths,     d.  Lymph  corpuscles,     e.  Capillary  plexus. 


paths  of  the  cortical  portion,  where  it  is  exposed  to  the  action  of  the  gland  pulp;  flowing  through 
these  it  enters  the  paths  or  sinuses  of  the  medullary  portion,  and  finally  emerges  from  the  hilus 
by  means  of  the  efferent  vessel.  The  stream  of  lymph  in  its  passage  through  the  lymph  sinuses 
is  much  retarded  by  the  presence  of  the  reticulmn,  hence  morphological  elements,  either  normal 
or  morbid,  are  easily  arrested  and  deposited  in  the  sinuses.  Many  lymph  corpuscles  pass  with 
the  efferent  lymph  stream  to  join  the  general  blood  stream.  The  arteries  of  the  gland  enter 
at  the  hilus,  and  either  go  at  once  to  the  gland  pulp,  to  break  up  into  a  capillary  plexus,  or  else 
run  along  the  trabeculae,  partly  to  supply  them  and  partly  running  across  the  lymph  paths, 
to  assist  in  forming  the  capiUary  plexus  of  the  gland  pulp.  This  plexus  traverses  the  lymphoid 
tissue,  but  does  not  enter  into  the  lymph  sinuses.  From  it  the  veins  commence  and  emerge 
from  the  organ  at  the  same  place  as  that  at  which  the  arteries  enter. 


The  lymphatic  vessels  are  arranged  into  a  superficial  and  a  deep  set.  On  the 
surface  of  the  body  the  superficial  lymphatic  vessels  are  placed  immediately 
beneath  the  integument,  accompanying  the  superficial  veins;  they  join  the  deep 
lymphatic  vessels  in  certain  situations  by  perforating  the  deep  fascia.  In  the 
interior  of  the  body  they  lie  in  the  submucous  areolar  tissue,  throughout  the  whole 
length  of  the  digestive,  respiratory,  and  genito-urinary  tracts;  and  in  the- subserous 
tissue  of  the  thoracic  and  abdominal  walls.  Plexiform  networks  of  minute  lym- 
phatic  vessels  are  found  interspersed  among  the  proper  elements  and  bloodvessels 

■  of  the  several  tissues;  the  vessels  composing  the  net- work,  as  well  as  the  meshes 

■  44 


690  ANGJOLOGY 


I 


between  them,  are  much  larger  than  those  of  the  capillary  plexus.  From  these 
net-works  small  vessels  emerge,  which  pass,  either  to  a  neighboring  gland,  or  to 
join  some  larger  lymphatic  trunk.  The  deep  lymphatic  vessels,  fewer  in  number, 
but  larger  than  the  superficial,  accompany  the  deep  bloodvessels.  Their  mode  of 
origin  is  probably  similar  to  that  of  the  superficial  vessels.  The  lymphatic  vessels 
of  any  part  or  organ  exceed  the  veins  in  number,  but  in  size  they  are  much  smaller. ' 
Their  anastomoses  also,  especially  those  of  the  large  trunks,  are  more  frequent, 
and  are  effected  by  vessels  equal  in  diameter  to  those  which  they  connect,  the  con- 
tinuous trunks  retaining  the  same  diameter,  ]| 

Hemolymph  nodes  or  glands  and  hemal  nodes  which  are  so  abundant  in  some 
mammals  are  probably  not  present  in  man. 

Lymph. — LAonph,  found  only  in  the  closed  l\Tnphatic  vessels,  is  a  transparent, 
colorless,  or  slightly  yellow,  watery  fluid  of  specific  gravity  about  1.015;  it  closely 
resembles  the  blood  plasma,  but  is  more  dilute.  When  it  is  examined  under  the 
microscope,  leucocytes  of  the  lymphocyte  class  are  found  floating  in  the  transparent 
fluid ;  they  are  always  increased  in  number  after  the  passage  of  the  Ij-mph  through 
lymphoid  tissue,  as  in  lymph  glands.  Lymph  should  be  distinguished  from  "  tissue 
fluid"^  which  is  found  outside  the  lymphatic  vessels  in  the  tissue  spaces. 


THE   THORACIC   DUCT. 

The  thoracic  duct  (duciiis  thoracicus)  (Fig.  599)  conveys  the  greater  part  of  the 
lymph  and  chyle  into  the  blood.  It  is  the  common  trunk  of  all  the  lymphatic 
vessels  of  the  body,  excepting  those  on  the  right  side  of  the  head,  neck,  and  thorax, 
and  right  upper  extremity,  the  right  lung,  right  side  of  the  heart,  and  the  convex 
surface  of  the  liver.  In  the  adult  it  varies  in  length  from  38  to  45  cm.  and  extends 
from  the  second  lumbar  vertebra  to  the  root  of  the  neck.  It  begins  in  the  abdomen 
by  a  triangular  dilatation,  the  cistema  chyli,  which  is  situated  on  the  front  of  the 
body  of  the  second  lumbar  vertebra,  to  the  right  side  of  and  behind  the  aorta, 
by  the  side  of  the  right  crus  of  the  diaphragm.  It  enters  the  thorax  through  the 
aortic  hiatus  of  the  diaphragm,  and  ascends  through  the  posterior  mediastinal 
cavity  between  the  aorta  and  azygos  vein.  Behind  it  in  this  region  are  the  vertebral 
column,  the  right  intercostal  arteries,  and  the  hemiazygos  veins  as  they  cross  to 
open  into  the  azygos  vein;  in  front  of  it  are  the  diaphragm,  esophagus,  and  peri- 
cardium, the  last  being  separated  from  it  by  a  recess  of  the  right  pleural  cavity. 
Opposite  the  fifth  thoracic  vertebra,  it  inclines  toward  the  left  side,  enters  the  supe- 
rior mediastinal  cavity,  and  ascends  behind  the  aortic  arch  and  the  thoracic  part 
of  the  left  subclavian  artery  and  between  the  left  side  of  the  esophagus  and  the 
left  pleura,  to  the  upper  orifice  of  the  thorax.  Passing  into  the  neck  it  forms  an 
arch  which  rises  about  3  or  4  cm.  above  the  clavicle  and  crosses  anterior  to  the 
subclavian  artery,  the  vertebral  artery  and  vein,  and  the  thyrocervical  trunk  or 
its  branches.  It  also  passes  in  front  of  the  phrenic  nerve  and  the  medial  border 
of  the  Scalenus  anterior,  but  is  separated  from  these  two  structures  by  the  pre- 
vertebral fascia.  In  front  of  it  are  the  left  common  carotid  artery,  vagus  nerve, 
and  internal  jugular  vein;  it  ends  by  opening  into  the  angle  of  junction  of  the  left 
subclavian  vein  with  the  left  internal  jugular  vein.  The  thoracic  duct,  at  its  com- 
mencement, is  about  equal  in  diameter  to  a  goose-quill,  but  it  diminishes  consid- 
erably in  caliber  in  the  middle  of  the  thorax,  and  is  again  dilated  just  before  its 
termination.  It  is  generally  flexuous,  and  constricted  at  intervals  so  as  to  present 
a  varicose  appearance.  Not  infrequently  it  divides  in  the  middle  of  its  course  into 
two  vessels  of  unequal  size  which  soon  reunite,  or  into  several  branches  which  form 

*  Sabin,  Harvey  Lecture,  Series  ix.  New  York,  1915-16. 


THE  THORACIC  DUCT 


691 


H 


a  plexiform  interlacement.  It  occasionally  divides  at  its  upper  part  into  two 
branches,  right  and  left;  the  left  ending  in  the  usual  manner,  while  the  right  opens 
into  the  right   subclavian  vein,  in 


connection  with  the  right  lymphatic 
duct.  The  thoracic  duct  has  several 
valves;  at  its  termination  it  is  pro- 
vided with  a  pair,  the  free  borders 
of  which  are  turned  toward  the  vein, 
so  as  to  prevent  the  passage  of 
venous  blood  into  the  duct. 

The  cisterna  chyli  (receptaculum 
chyli)  (Fig.  600)  receives  the  two 
lumbar  lymphatic  trunks,  right  and 
left,  and  the  intestinal  lymphatic 
trunk.  The  lumbar  trunks  are  formed 
by  the  union  of  the  efferent  vessels 
from  the  lateral  aortic  lymph  glands. 
They  receive  the  lymph  from  the 
lower  limbs,  from  the  walls  and 
viscera  of  the  pelvis,  from  the  kid- 
neys and  suprarenal  glands  and  the 
deep  lymphatics  of  the  greater  part 
of  the  abdominal  wall.  The  intes- 
tinal trunk  receives  the  lymph  from 
the  stomach  and  intestine,  from  the 
pancreas  and  spleen,  and  from  the 
lower  and  front  part  of  the  liver. 

Tributaries.  —  Opening  into  the 
commencement  of  the  thoracic  duct, 
on  either  side,  is  a  descending  trunk 
from  the  posterior  intercostal  lymph 
glands  of  the  lower  six  or  seven  in- 
tercostal spaces.  In  the  thorax  the 
duct  is  joined,  on  either  side,  by  a 
trunk  which  drains  the  upper  lumbar 
lymph  glands  and  *pierces  the  crus 
of  the  diaphragm.  It  also  receives 
the  efferents  from  the  posterior 
mediastinal  lymph  glands  and  from 
the  posterior  intercostal  lymph 
glands  of  the  upper  six  left  spaces. 
In  the  neck  it  is  joined  by  the  left 
jugular  and  left  subclavian  trunks, 
and  sometimes  by  the  left  broncho- 
mediastinal trunk;  the  last-named, 
however,  usually  opens  indepen- 
dently into  the  junction  of  the  left 
subclavian  and  internal  jugular 
veins. 

The  right  Ijrmphatic  duct  {ductus  lymphaticus  dexter)  (Fig.  601),  about  1.25  cm. 
in  length,  courses  along  the  medial  border  of  the  Scalenus  anterior  at  the  root  of 
the  neck  and  ends  in  the  right  subclavian  vein,  at  its  angle  of  junction  with  the  right 
internal  jugular  vein.  Its  orifice  is  guarded  by  two  semilunar  valves,  which  prevent 
the  passage  of  venous  blood  into  the  duct. 


599. — The  thoracic  and  right  lymphatic  ducts. 


692 


ANGIOLOGY 


Tributaries. — The  right  lymphatic  duct  receives  the  lymph  from  the  right  side 
of  the  head  and  neck  through  the  right  jugular  trunk;  from  the  right  upper  extremity 
through  the  right  subclavian  trunk;  from  the  right  side  of  the  thorax,  right  lung, 


Fig.  600. — Modes  of  origin  of  thoracic  duct.  (Poirier  and  Charpy.)  a.  Thoracic  duct.  a'.  Cistefna  chyli.  6,  c 
Efferent  trunlcs  from  lateral  aortic  glands,  d.  An  efferent  vessel  which  pierces  the  left  crus  of  the  aiaphragm.  e.  f. 
Lateral  aortic  glands,   h.  Retroaortic  glands,    i.  Intestinal  trunk,    j.  Descending  branch  from  intercostal  lymphatics. 

right  side  of  the  heart,  and  part  of  the  convex  surface  of  the  liver,  through  the 
right  bronchomediastinal  trunk.  These  three  collecting  trunks  frequently  open 
separately  in  the  angle  of  union  of  the  two  veins. 


Fia.  601. — Terminal  collecting  trunks  of  right  side.  a.  Jugular  trunk,  b.  Subclavian  trunk,  c.  Broncho- 
mediastinal trunk,  d.  Right  lymphatic  trunk,  e.  Gland  of  internal  mammary  chain.  /.  Gland  of  deep  cervical 
chain.     (Poirier  and  Charpy.) 

THE  LYMPHATICS  OF  THE  HEAD,.  FACE,  AND  NECK. 


The  Lymph  Glands  of  the  Head  (Fig.  602). 

The  lymph  glands  of  the  head  are  arranged  in  the  following  groups: 
Occipital.  Facial. 

Posterior  Auricular.  Deep  Facial, 

Anterior  Auricular.  Lingual. 

Parotid.  Retropharyngeal. 

The  occipital  glands  (lymphoglandulcB  occipitales),  one  to  three  in  nu  her,  are 
placed  on  the  back  of  the  head  close  to  the  margin  of  the  Trapezius  and  resting 
on  the  insertion  of  the  Semispinalis  capitis.  Their  afferent  vessels  drain  the  occipi- 
tal region  of  the  scalp,  while  their  efferents  pass  to  the  superior  deep  cervical 
glands. 


LYMPH  GLANDS 


693 


The  posterior  auricular  glands  {lyynphoglandulcB  auricidares;  mastoid  glands), 
usually  two  in  number,  are  situated  on  the  mastoid  insertion  of  the  Sternocleido- 
mastoideus,  beneath  the  Auricularis  posterior.  Their  afferent  vessels  drain  the 
posterior  part  of  the  temporoparietal  region,  the  upper  part  of  the  cranial  surface 
of  the  auricula  or  pinna,  and  the  back  of  the  external  acoustic  meatus;  their 
efFerents  pass  to  the  superior  deep  cervical  glands. 


Maxillary  glands 


Parotid  glands 
Buccinator  glands 


Supramandibular 

glands 
Svhmaxillary 
glands 

8vJbmenlal  glands 


Inferior  deep 
cervical  glands 


and  neck. 


I 


The  anterior  auricular  glands  {lyviphoglanduloe  auriculares  anteriores;  superficial 
parotid  or  preauricular  glands),  from  one  to  three  in  number,  lie  immediately  in 
front  of  the  tragus.  Their  afferents  drain  the  lateral  surface  of  the  auricula  and  the 
skin  of  the  adjacent  part  of  the  temporal  region;  their  efferents  pass  to  the  superior 
deep  cervical  glands. 

The  parotid  glands  {lymphoglandulce  parotideo'),  form  two  groups  in  relation 
with  the  parotid  salivary  gland,  viz.,  a  group  imbedded  in  the  substance  of  the  gland, 
and  a  group  of  subparotid  glands  lying  on  the  lateral  wall  of  the  pharynx.  Occa- 
sionally small  glands  are  found  in  the  subcutaneous  tissue  over  the  parotid  gland. 
Their  afferent  vessels  drain  the  root  of  the  nose,  the  eyelids,  the  frontotemporal 
region,  the  external  acoustic  meatus  and  the  tympanic  cavity,  possibly  also  the 
posterior  parts  of  the  palate  and  the  floor  of  the  nasal  cavity.    The  efferents  of 

ese  glands  pass  to  the  superior  deep  cervical  glands.    The  afferents  of  the  sub- 


694 


ANGIOLOGY 


parotid  glands  drain  the  nasal  part  of  the  pharynx  and  the  posterior  parts  of  t 
nasal  cavities;  their  efferents  pass  to  the  superior  deep  cervical  glands. 

The  facial  glands  comprise  three  groups :  (a)  infraorbital  or  maxillary,  scattered 
over  the  infraorbital  region  from  the  groove  between  the  nose  and  cheek  to  the 
zygomatic  arch;  (6)  buccinator,  one  or  more  placed  on  the  Buccinator  opposite  the 
angle  of  the  mouth;  (c)  supramandibular,  on  the  outer  surface  of  the  mandible, 
in  front  of  the  Masseter  and  in  contact  with  the  external  maxillary  artery  and 
anterior  facial  vein.  Their  efferent  vessels  drain  the  eyelids,  the  conjunctiva 
and  the  skin  and  mucous  membrane  of  the  nose  and  cheek;  their  efferents  pass  t 
the  submaxillary  glands. 

The  deep  facial  glands  {lymyhoglandulae  faciales  ^profunda;  internal  maxillary 
glands)  are  placed  beneath  the  ramus  of  the  mandible,  on  the  outer  surface  of  the 
Pterygoideus  externus,  in  relation  to  the  internal  maxillary  artery.  Their  afferent 
vessels  drain  the  temporal  and  infratemporal  fossse  and  the  nasal  part  of  the  pharynx 
their  efferents  pass  to  the  superior  deep  cervical  glands. 

The  lingual  glands  {lymphoglandulw  linguales)  are  two  or  three  small  nodules 
lying  on  the  Hyoglossus  and  under  the  Genioglossus.  They  form  merely  glandular 
substations  in  the  course  of  the  lymphatic  vessels  of  the  tongue. 


% 


Afferent  vessel  to  deep 
cervical  glands 


Olandular  nodule 

Gland  of  deep  cervical 

chain 
Efferent  vessels  of  retro- 
phai~)jngeal  glands 


Fig.   603. — Lymphatics  of  pharj'nx.     (Poirier  and  Charpy. 


The  retropharyngeal  glands  (Fig.  603),  from  one  to  three  in  number,  lie  in  the 
buccopharyngeal  fascia,  behind  the  upper  part  of  the  pharynx  and  in  front  of  the 
arch  of  the  atlas,  being  separated,  however,  from  the  latter  by  the  Longus  capitis. 
Their  afferents  drain  the  nasal  cavities,  the  nasal  part  of  the  pharynx,  and  the 
auditory  tubes;  their  efferents  pass  to  the  superior  deep  cervical  glands. 

The  l3rmphatic  vessels  of  the  scalp  are  divisible  into  (a)  those  of  the  frontal  region, 
which  terminate  in  the  anterior  auricular  and  parotid  glands;  {h)  those  of  the 
temporoparietal  region,  which  end  in  the  parotid  and  posterior  auricular  glands; 
and  (c)  those  of  the  occipital  region,  which  terminate  partly  in  the  occipital 
glands  and  partly  in  a  trunk  which  runs  down  along  the  posterior  border  of  the 
Sternocleidomastoideus  to  end  in  the  inferior  deep  cervical  glands. 

The  Ijrmphatic  vessels  of  the  auricula  and  external  acoustic  meatus  are  also  divisible 
into  three  groups:  (a)  an  anterior,  from  the  lateral  surface  of  the  auricula  and 
anterior  wall  of  the  meatus  to  the  anterior  auricular  glands;  (b)  a  posterior,  from 
the  margin  of  the  auricula,  the  upper  part  of  its  cranial  surface,  the  internal  surface 


THE  LYMPH  GLANDS  OF  THE  HEAD 


695 


and  posterior  wall  of  the  meatus  to  the  posterior  auricular  and  superior  deep  cervical 
glands;  (c)  an  inferior,  from  the  floor  of  the  meatus  and  from  the  lobule  of  the  auric- 
ula to  the  superficial  and  superior  deep  cervical  glands. 

The  lymphatic  vessels  of  the  face  (Fig.  604)  are  more  numerous  than  those  of  the 
scalp.  Those  from  the  eyelids  and  conjunctiva  terminate  partly  in  the  submaxillary 
but  mainly  in  the  parotid  glands.  The  vessels  from  the  posterior  part  of  the  cheek 
also  pass  to  the  parotid  glands,  while  those  from  the  anterior  portion  of  the  cheek, 
the  side  of  the  nose,  the  upper  lip,  and  the  lateral  portions  of  the  lower  lip  end  in 
the  submaxillary  glands.  The  deeper  vessels  from  the  temporal  and  infratemporal 
fossae  pass  to  the  deep  facial  and  superior  deep  cervical  glands.  The  deeper  vessels 
of  the  cheek  and  lips  end,  like  the  superficial,  in  the  submaxillary  glands.  Both 
superficial  and  deep  vessels  of  the  central  part  of  the  lower  lip  run  to  the  submental 
glands. 


Parotid  glands 


Superficial  cervi- 
cal glands 


Facial  glands 
Svbmaxillary  glands 

Deep  cervical  glands 


Fig.  604. — The  lymphatics  of  the  face.     (After  Kuttner.) 

Lymphatic  Vessels  of  the  Nasal  Cavities. — ^Those  from  the  anterior  parts  of  the 
nasal  cavities  communicate  with  the  vessels  of  the  integument  of  the  nose  and 
end  in  the  submaxillary  glands;  those  from  the  posterior  two-thirds  of  the  nasal 
cavities  and  from  the  accessory  air  sinuses  pass  partly  to  the  retropharyngeal 
and  partly  to  the  superior  deep  cervical  glands. 

Lymphatic  Vessels  of  the  Mouth. — The  vessels  of  the  gums  pass  to  the  submaxillary 
glands;  those  of  the  hard  palate  are  continuous  in  front  with  those  of  the  upper 
gum,  but  pass  backward  to  pierce  the  Constrictor  pharyngis  superior  and  end  in 
the  superior  deep  cervical  and  subparotid  glands;  those  of  the  soft  palate  pass 
backward  and  lateralward  and  end  partly  in  the  retropharyngeal  and  subparotid, 
and  partly  in  the  superior  deep  cervical  glands.  The  vessels  of  the  anterior  part 
of  the  floor  of  the  mouth  pass  either  directly  to  the  inferior  glands  of  the  superior 
deep  cervical  group,  or  indirectly  through  the  submental  glands;  from  the  rest 
of  the  floor  of  the  mouth  the  vessels  pass  to  the  submaxillary  and  superior  deep 
[cervical  glands. 

The  l3rmphatic  vessels  of  the  palatine  tonsil,  usually  three  to  five  in  number, 
[pierce  the  buccopharyngeal  fascia  and  constrictor  pharyngis  superior  and  pass 


696 


ANGIOLOGY 


between  the  Stylohyoideus  and  internal  jugular  vein  to  the  uppermost  of  the 
superior  deep  cervical  glands.  They  end  in  a  gland  which  lies  at  the  side  of  the 
posterior  belly  of  the  Digastricus,  on  the  internal  jugular  vein;  occasionally  one 
or  two  additional  vessels  run  to  small  glands  on  the  lateral  side  of  the  vein  under 
cover  of  the  Sternocleidomastoideus. 


Vessels  from 
root  of  tongue 


Vessels  from 

margin  of 

tongue 


Principal 
gland  of 
tongue 


XVefsda  from 
■*     *  ajpex 


Submental 

gland 

~>  Trunks  front 

r    margin  of 

tongue 


Interrupting  nodule 


Supra-omohyoid 

gland 


Fig.  605. — Lymphatics  of  the  tongue.     (Poirier  and  Charpy.) 


The  lymphatic  vessels  of  the  tongue  (Fig.  605)  are  drained  chiefly  into  the  deep 
cervical  glands  lying  between  the  posterior  belly  of  the  Digastricus  and  the  superior 
belly  of  the  Omohyoideus;  one  gland  situated  at  the  bifurcation  of  the  common 
carotid  artery  is  so  intimately  associated  with  these  vessels  that  it  is  known  as  the 
principal  gland  of  the  tongue.  The  lymphatic  vessels  of  the  tongue  may  be  divided 
into  four  groups:  (1)  apical,  from  the  tip  of  the  tongue  to  the  suprahyoid  glands 
and  principal  gland  of  the  tongue;  (2)  lateral,  from  the  margin  of  the  tongue — 
some  of  these  pierce  the  Mylohyoideus  to  end  in  the  submaxillary  glands,  others 
pass  down  on  the  Hyoglossus  to  the  superior  deep  cervical  glands;  (3)  basal,  from 
the  region  of  the  vallate  papillae  to  the  superior  deep  cervical  glands;  and  (4) 
median,  a  few  of  which  perforate  the  Mylohyoideus  to  reach  the  submaxillary 
glands,  while  the  majority  turn  around  the  posterior  border  of  the  muscle  to 
enter  the  superior  deep  cervical  glands. 


THE  LYMPH  GLANDS  OF  THE  NECK 


697 


The  Lymph  Glands  of  the  Neck. 


Nb 


lelymph  glands  of  the  neck  include  the  following  groups; 


Submaxillary.  Superficial  Cervical. 

Submental.  Anterior  Cervical. 

Deep  Cervical, 

The  submaxillary  glands  {lymphoglandulcp  submaxillar es)  (Fig.  604),  three  to 
six  in  number,  are  placed  beneath  the  body  of  the  mandible  in  the  submaxillary 
triangle,  and  rest  on  the  superficial  surface  of  the  submaxillary  salivary  gland. 
One  gland,  the  middle  gland  of  Stahr,  which  lies  on  the  external  maxillary  artery 
as  it  turns  over  the  mandible,  is  the  most  constant  of  the  series;  small  lymph  glands 
are  sometimes  found  on  the  deep  surface  of  the  submaxillary  salivary  glands.  The 
afferents  of  the  submaxillary  glands  drain  the  medial  palpebral  commissure, 
the  cheek,  the  side  of  the  nose,  the  upper  lip,  the  lateral  part  of  the  lower  lip, 
the  gums,  and  the  anterior  part  of  the  margin  of  the  tongue;  efferent  vessels 
from  the  facial  and  submental  glands  also  enter  the  submaxillary  glands.  Their 
effefent  vessels  pass  to  the  superior  deep  cervical  glands. 

The  submental  or  suprahyoid  glands  are  situated  between  the  anterior  bellies 
of  the  Digastrici.  Their  afferents  drain  the  central  portions  of  the  lower  lip  and 
floor  of  the  mouth  and  the  apex  of  the  tongue;  their  efferents  pass  partly  to  the 
submaxillary  glands  and  partly  to  a  gland  of  the  deep  cervical  group  situated  on 
the  internal  jugular  vein  at  the  level  of  the  cricoid  cartilage. 

The  superficial  cervical  glands  {lymphoglandulw  cervicales  swperficiales)  lie  in 
close  relationship  with  the  external  jugular  vein  as  it  emerges  from  the  parotid 
gland,  g,nd,  therefore,  superficial  to  the  Sternocleidomastoideus.  Their  afferents 
drain  the  lower  parts  of  the  auricula  and  parotid  region,  while  their  efferents  pass 
around  the  anterior  margin  of  the  Sternocleidomastoideus  to  join  the  superior  deep 
cervical  glands. 

The  anterior  cervical  glands  form  an  irregular  and  inconstant  group  on  the  front 
of  the  larynx  and  trachea.  They  may  be  divided  into  (a)  a  superficial  set,  placed 
on  the  anterior  jugular  vein;  (6)  a  deeper  set,  which  is  further  subdivided  into 
prelaryngeal,  on  the  middle  cricothyroid  ligament,  and  pretracheal,  on  the  front 
of  the  trachea.  This  deeper  set  drains  the  lower  part  of  the  larynx,  the  thyroid 
gland,  and  the  upper  part  of  the  trachea;  its  efferents  pass  to  the  lowest  of  the 
superior  deep  cervical  glands. 

The  deep  cervical  glands  {lymphoglanduloe  cervicales  profundcp)  (Figs.  602, 
605)  are  numerous  and  of  large  size:  they  form  a  chain  along  the  carotid  sheath, 
lying  by  the  side  of  the  pharynx,  esophagus,  and  trachea,  and  extending  from  the 
base  of  the  skull  to  the  root  of  the  neck.  They  are  usually  described  in  two  groups : 
(1)  the  superior  deep  cer/ical  glands  lying  under  the  Sternocleidomastoideus  in 
close  relation  with  the  accessory  nerve  and  the  internal  jugular  vein,  some  of  the 
glands  lying  in  front  of  and  others  behind  the  vessel ;  (2)  the  inferior  deep  cervical 
glands  extending  beyond  the  posterior  margin  of  the  Sternocleidomastoideus 
into  the  supraclavicular  triangle,  where  they  are  closely  related  to  the  brachial 
plexus  and  subclavian  vein.  A  few  minute  paratracheal  glands  are  situated  along- 
side the  recurrent  nerves  on  the  lateral  aspects  of  the  trachea  and  esophagus. 
The  superior  deep  cervical  glands  drain  the  occipital  portion  of  the  scalp,  the 
auricula,  the  back  of  the  neck,  a  considerable  part  of  the  tongue,  the  larynx,  thyroid 
gland,  trachea,  nasal  part  of  the  pharynx,  nasal  cavities,  palate,  and  esophagus. 
They  receive  also  the  efferent  vessels  from  all  the  other  glands  of  the  head  and 
neck,  except  those  from  the  inferior  deep  cervical  glands.  The  inferior  deep  cervical 
glands  drain  the  back  of  the  scalp  and  neck,  the  superficial  pectoral  region,  part 
of  the  arm  (see  page  701),  and,  occasionally,  part  of  the  superior  surface  of  the 


698 


ANGIOLOGY 


liver,  In  addition,  they  receive  vessels  from  the  superior  deep  cervical  glands. 
The  efFerents  of  the  superior  deep  cervical  glands  pass  partly  to  the  inferior  deep 
cervical  glands  and  partly  to  a  trunk  which  unites  with  the  efferent  vessel  of  the 
inferior  deep  cervical  glands  and  forms  the  jugular  trunk.  On  the  right  side,  this 
trunk  ends  in  the  junction  of  the  internal  jugular  and  subclavian  veins;  on  the  left 
side  it  joins  the  thoracic  duct. 

Deltoideo. 
pectoral 
glands 


AziUary  glands 


Fig.  606. — The  superficial  lymph  glanas  and  lymphatic  vessels  of  the  upper  extremity. 


The  lymphatic  vessels  of  the  skin  and  muscles  of  the  neck  pass  to  the  deep  cervical 
glands.  From  the  upper  part  of  the  pharynx  the  lymphatic  vessels  pass  to  the  retro- 
pharyngeal, from  the  lower  part  to  the  deep  cervical  glands.  From  the  larynx 
two  sets  of  vessels  arise,  an  upper  and  a  lower.  The  vessels  of  the  upper  set  pierce 
the  hyothyroid  membrane  and  join  the  superior  deep  cervical  glands.  Of  the 
lower  set,  some  pierce  the  conus  elasticus  and  join  the  pretracheal  and  pre- 
laryngeal glands;  others  run  between  the  cricoid  and  first  tracheal  ring  and  enter 
the  inferior  deep  cervical  glands.  The  lymphatic  vessels  of  the  thyroid  gland  con- 
sist of  two  sets,  an  upper,  which  accompanies  the  superior  thyroid  artery  and  enters 
the  superior  deep  cervical  glands^  and  a  lower,  which  runs  partly  to  the  pretracheal 


THE  LYMPH  GLANDS  OF  THE  UPPER  EXTREMITY 


699 


glands  and  partly  to  the  small  paratracheal  glands  which  accompany  the  recurrent 
nerves.  These  latter  glands  receive  also  the  lymphatic  vessels  from  the  ce^^ical 
portion  of  the  trachea. 


THE   LYMPHATICS   OF  THE   UPPER   EXTREMITY. 
The  Lymph  Glands  of  the  Upper  Extremity  (Fig.  606). 


HI     The  lymph  glands  of  the  upper  extremity  are  divided  into  two  sets,  superficial 

IP  and  deep. 

The  superficial  lymph  glands  are  few  and  of  small  size.  One  or  two  supra- 
trochlear glands  are  placed  above  the  medial  epicondyle  of  the  humerus,  medial 
to  the  basilic  vein.  Their  afferents  drain  the  middle,  ring,  and  little  fingers,  the 
medial  portion  of  the  hand,  and  the  superficial  area  over  the  ulnar  side  of  the  fore- 
arm; these  vessels  are,  however,  in  free  communication  with  the  other  lymphatic 
vessels  of  the  forearm.  Their  efferents  accompany  the  basilic  vein  and  join  the 
deeper  vessels.  One  or  two  deltoideopectoral  glands  are  found  beside  the  cephalic 
vein,  between  the  Pectoralis  major  and  Deltoideus,  immediately  below  the  clavicle. 
They  are  situated  in  the  course  of  the  external  collecting  trunks  of  the  arm. 


Deltoideopectoral  glands 


Lateral  group 


Central  grotip 
Subscapular  group 


Mammary  lymphatic 

ending  in 
svbclavicidar  glands 


1^    Pectoral  group 

Mammary  collecting 

trunks 


Subareolar  plexus 


Pectoral  group 


Cutam  ous  collecting  trunk    >  ^ 
/row  the  thoracic  wall 


Cutaneous  collecting  -%         ^<^  Collecting  trunks 

trunks  passing  to  internal 

mammary  glands 
Fio.  607. — Lymphatics  of  the  mamma,  and  the  axillary  glands  (semidiagrammatic) .     (Poirier  and  Charpy.) 


The  deep  lymph  glands  are  chiefly  grouped  in  the  axilla,  although  a  few  may 
be  found  in  the  forearm,  in  the  course  of  the  radial,  ulnar,  and  interosseous  vessels, 
and  in  the  arm  along  the  medial  side  of  the  brachial  artery. 

The  Axillary  Glands  {lyrnphoglandulae  axillares)  (Fig.  607)  are  of  large  size,  vary 
from  twenty  to  thirty  in  number,  and  may  be  arranged  in  the  following  groups: 

1.  A  lateral  group  of  from  four  to  six  glands  lies  in  relation  to  the  medial  and 
posterior  aspects  of  the  axillary  vein;  the  afferents  of  these  glands  drain  the  whole 

IKjfU'm  with  the  exception  of  that  portion  whose  vessels  accompany  the  cephalic 


700 


ANGIOLOGY 


vein.    The  efferent  vessels  pass  partly  to  the  central  and  subclavicular  groups  of 
axillary  glands  and  partly  to  the  inferior  deep  cervical  glands. 

2.  An  anterior  or  pectoral  group  consists  of  four  or  five  glands  along  the  lower 
border  of  the  Pectoralis  minor,  in  relation  with  the  lateral  thoracic  artery.  Their 
afferents  drain  the  skin  and  muscles  of  the  anterior  and  lateral  thoracic  walls, 
and  the  central  and  lateral  parts  of  the  namma ;  their  eff erents  pass  partly  to  the 
central  and  partly  to  the  subclavicular  groups  of  axillary  glands. 

3.  A  posterior  or  subscapular  group  of  six  or  seven  glands  is  placed  along  the  lower 
margin  of  the  posterior  wall  of  the  axilla  in  the  course  of  the  subscapular  artery. 
The  aff erents  of  this  group  drain  the  skin  and  muscles  of  the  lower  part  of  the  back 
of  the  neck  and  of  the  posterior  thoracic  wall;  their  eff  erents  pass  to  the  central 
group  of  axillary  glands. 

4.  A  central  or  intermediate  group  of  three  or  four  large  glands  is  imbedded  in 
the  adipose  tissue  near  the  base  of  the  axilla.  Its  afferents  are  the  efferent  vessels 
of  all  the  preceding  groups  of  axillary  glands;  its  eff  erents  pass  to  the  subclavicular 
group. 

5.  A  medial  or  subclavicular  group  of  six  to  twelve  glands  is  situated  partly 
posterior  to  the  upper  portion  of  the  Pectoralis  minor  and  partly  above  the  upper 
border  of  this  muscle.  Its  only  direct  territorial  afferents  are  those  which  accompany 
the  cephalic  vein  and  one  which  drains  the  upper  peripheral  part  of  the  mamma, 
but  it  receives  the  afferents  of  all  the  other  axillary  glands.    The  efferent  vessels 

of  the  subclavicular  group  unite  to 
J  -  11'  ^^i}^Miia  form  the  subclavian  trunk,  which  opens 

either  directly  into  the  junction  of 
the  internal  jugular  and  subclavian 
veins  or  into  the  jugular  lymphatic 
trunk;  on  the  left  side  it  may  end  in 
the  thoracic  duct.  A  few  efferents 
from  the  subclavicular  glands  usually 
pass  to  the  inferior  deep  cervical 
glands. 

The  Lymphatic  Vessels  of  the 
Upper  Extremity. 

The  lymphatic  vessels  of  the  upper 
extremity  are  divided  into  two  sets, 
superficial  and  deep. 

The  superficial  lymphatic  vessels 
commence  (Fig.  60S)  in  the  lymphatic 
plexus  which  everywhere  pervades 
the  skin;  the  meshes  of  the  plexus  are 
much  finer  in  the  palm  and  on  the 
flexor  aspect  of  the  digits  than  else- 
where. The  digital  plexuses  are  drained 
by  a  pair  of  vessels  which  run  on 
the  sides  of  each  digit,  and  incline 
backward  to  reach  the  dorsum  of  the 
hand.  From  the  dense  plexus  of  the 
palm,  vessels  pass  in  different  direc- 
tions, viz.,  upward  toward  the  wTist, 
downward  to  join  the  digital  vessels, 
medialward  to  join  the  vessels  on  the  ulnar  border  of  the  hand,  and  latefalward  to 
those  on  the  thumb.    Several  vessels  from  the  central  part  of  the  plexus  unite  to 


Fig 


*• — Lymphatic  vessels  of   the  dorsal    surface  of  the 
hand.     (Sappey.) 


THE  LYMPH  GLANDS  OF  THE  LOWER  EXTREMITY 


701 


form  a  trunk,  which  passes  around  the  metacarpal  bone  of  the  index  finger  to  join 
the  vessels  on*  the  back  of  that  digit  and  on  the  back  of  the  thumb.  Running 
upward  in  front  of  and  behind  the  wrist,  the  lymphatic  vessels  are  collected 
into  radial,  median,  and  ulnar  groups,  which  accompany  respectively  the  cephalic, 
median,  and  basilic  veins  in  the  forearm.  A  few  of  the  ulnar  lymphatics  end  in 
the  supratrochlear  glands,  but  the  majority  pass  directly  to  the  lateral  group  of 
axillary  glands.  Some  of  the  radial  vessels  are  collected  into  a  trunk  which 
ascends  with  the  cephalic  vein  to  the  deltoideopectoral  glands;  the  efferents  from 
this  group  pass  either  to  the  subclavicular  axillary  glands  or  to  the  inferior  cervical 
glands. 

The  deep  lymphatic  vessels  accompany  the  deep  bloodvessels.  In  the  fore- 
arm, they  consist  of  four  sets,  corresponding  with  the  radial,  ulnar,  volar,  and 
dorsal  interosseous  arteries;  they  communicate  at  intervals  with  the  superficial 
lymphatics,  and  some  of  them  end  in  the  glands  which  are  occasionally  found  beside 
the  arteries.  In  their  course  upward,  a  few  end  in  the  glands  which  lie  upon  the 
brachial  artery;  but  most  of  them  pass  to  the  lateral  group  of  axillary  glands. 


Tibial  nerve 
Poplitecd  vein 

Popliteal  artery 
Common  peronoeal  nerve 
Gland  at  side  of  popliteal 

^_y  ill 

iiAxilll'l  Gland  on  back  of  knee 

joint 
Gland  at  termination  of 
small  saph.  vein 


Fig.  609. — Lymph  glands  of  popliteal  fossa.      (Poirier  and  Charpy.) 


THE  LYMPHATICS   OF  THE  LOWER  EXTREMITY. 


The  Lymph  Glands  of  the  Lower  Extremity. 

The  lymph  glands  of  the  lower  extremity  consist  of  the  anterior  tibial  gland 
and  the  popliteal  and  inguinal  glands. 

The  anterior  tibial  gland  {lymphoglandula  tibialis  anterior)  is  small  and  incon- 
stant. It  lies  on  the  interosseous  membrane  in  relation  to  the  upper  part  of  the 
anterior  tibial  vessels,  and  constitutes  a  substation  in  the  course  of  the  anterior 
tibial  lymphatic  trunlvs. 

The  popliteal  glands  (lymphoglandulcB  poplitea)  (Fig.  609), 'small  in  size  and 
some  six  or  seven  in  number,  are  imbedded  in  the  fat  contained  in  the  popliteal 


702 


ANGIOLOGY 


t=^ 


.^ 


Superficial 
inguinal  - 
glands 


Superficial 

svbinguinal- 

glands 


Fig. 


610. — The  superficial  lymph  glands  and  lymphatic 

vessels  of  the  lower  extremity. 


fossa.  One  lies  immediately  beneath 
the  popliteal  fascia,  near  the  terminal 
part  of  the  small  saphenous  vein,  and 
drains  the  region  from  which  this  vein 
derives  its  tributaries.  Another  is  placed 
between  the  popliteal  artery  and  the 
posterior  surface  of  the  knee-joint;  it 
receives  the  lymphatic  vessels  from  the 
knee-joint  together  with  those  which 
accompany  the  genicular  arteries.  The 
others  lie  at  the  sides  of  the  popliteal 
vessels,  and  receive  as  efferents  the 
trunks  which  accompany  the  anterior 
and  posterior  tibial  vessels.  The  effer- 
ents of  the  popliteal  glands  pass  almost 
entirely  alongside  the  femoral  vessels  to 
the  deep  inguinal  glands,  but  a  few  may 
accompany  the  great  saphenous  vein, 
and  end  in  the  glands  of  the  superficial 
subinguinal  group. 

The  inguinal  glands  (lymphoglandula 
inguinales)  (Fig.  610),  from  twelve  to 
twenty  in  number,  are  situated  at  the 
upper  part  of  the  femoral  triangle.  They 
may  be  divided  into  two  groups  by  a 
horizontal  line  at  the  level  of  the  termi- 
nation of  the  great  saphenous  vein; 
those  lying  above  this  line  are  termed 
the  superficial  inguinal  glands,  and  those 
below  it  the  subinguinal  glands,  the  latter 
group  consisting  of  a  superficial  and  a 
deej)  set. 

The  Superficial  Inguinal  Glands  form 
a  chain  immediately  below  the  inguinal 
Hgament.  They  receive  as  afferents  lym- 
phatic vessels  from  the  integument  of 
the  penis,  scrotum,  perineum,  buttock, 
and  abdominal  wall  below  the  level  of 
the  umbilicus. 

The  Superficial  Subinguinal  Glands 
(lymphoglanduloB  suhinguinaJes  super- 
ficiales)  are  placed  on  either  side  of  the 
upper  part  of  the  great  saphenous  vein; 
their  efferents  consist  chiefly  of  the 
superficial  lymphatic  vessels  of  the 
lower  extremity;  but  they  also  receive 
some  of  the  vessels  which  drain  the  in- 
tegument of  the  penis,  scrotum,  peri- 
neum, and  buttock. 

The  Deep  Subinguinal  Glands  {lympho- 
glanduloB suhinguinales  profundoe)  vary 
from  one  to  three  in  number,  and  are 
placed  under  the  fascia  lata,  on  the 
medial  side  of  the  femoral  vein.   When 


w 


THE  LYMPH  GLANDS  OF  THE  ABDOMEN  AND  PELVIS  703 


three  are  present,  the  lowest  is  situated  just  below  the  junction  of  the  great  saphe- 
nous and  femoral  veins,  the  middle  in  the  femoral  canal,  and  the  highest  in  the 
lateral  part  of  the  femoral  ring.  The  middle  one  is  the  most  inconstant  of  the 
three,  but  the  highest,  the  gland  of  Cloquet  or  Rosenmiiller,  is  also  frequently  absent. 
They  receive  as  afferents  the  deep  lymphatic  trunks  which  accompany  the  femoral 
vessels,  the  lymphatics  from  the  glans  penis  vel  clitoridis,  and  also  some  of  the 
efferents  from  the  superficial  subinguinal  glands. 


IT 


The  Lymphatic  Vessels  of  the  Lower  Extremity. 


The  lymphatic  vessels  of  the  lower  extremity  consist  of  two  sets,  superficial 
and  deep,  and  in  their  distribution  correspond  closely  with  the  veins. 

The  superficial  Ijrmphatic  vessels  lie  in  the  superficial  fascia,  and  are  divisible 
into  tw^o  groups:  a  medial,  which  follows  the  course  of  the  great  saphenous  vein, 
and  a  lateral,  which  accompanies  the  small  saphenous  vein.  The  vessels  of  the 
medial  group  (Fig.  610)  are  larger  and  more  numerous  than  those  of  the  lateral 
group,  and  commence  on  the  tibial  side  and  dorsum  of  the  foot;  they  ascend  both 
in  front  of  and  behind  the  medial  malleolus,  run  up  the  leg  with  the  great  saphe- 
nous vein,  pass  with  it  behind  the  medial  condyle  of  the  femur,  and  accompany 
it  to  the  groin,  where  they  end  in  the  subinguinal  group  of  superficial  glands. 
The  vessels  of  the  lateral  group  arise  from  the  fibular  side  of  the  foot;  some  ascend 
in  front  of  the  leg,  and,  just  below  the  knee,  cross  the  tibia  to  join  the  lymphatics 
on  the  medial  side  of  the  thigh;  others  pass  behind  the  lateral  malleolus,  and, 
accompanying  the  small  saphenous  vein,  enter  the  popliteal  glands. 

The  deep  lymphatic  vessels  are  few  in  number,  and  accompany  the  deep  blood- 
Vessels.  In  the  leg,  they  consist  of  three  sets,  the  anterior  tibial,  posterior  tibial, 
and  peroneal,  which  accompany  the  corresponding  bloodvessels,  two  or  three  with 
each  artery;  they  enter  the  popliteal  lymph  glands. 

The  deep  lymphatic  vessels  of  the  gluteal  and  ischial  regions  follow  the  course 
of  the  corresponding  bloodvessels.  Those  accompanying  the  superior  gluteal 
vessels  end  in  a  gland  which  lies  on  the  intrapelvic  portion  of  the  superior  gluteal 
artery  near  the  upper  border  of  the  greater  sciatic  foramen.  Those  following 
the  inferior  gluteal  vessels  traverse  one  or  two  small  glands  which  lie  below  the 
Piriformis  muscle,  and  end  in  the  hypogastric  glands. 


THE  LYMPHATICS   OF   THE  ABDOMEN  AND  PELVIS. 


H^^H  The  Lymph  Glands  of  the  Abdomen  and  Pelvis. 

The  lymph  glands  of  the  abdomen  and  pelvis  may  be  divided,  from  their  situa- 
tions, into  (a)  parietal,  lying  behind  the  peritoneum  and  in  close  association  with 
the  larger  bloodvessels;  and  (6)  visceral,  which  are  found  in  relation  to  the  visceral 
arteries. 

The  parietal  glands  (Figs.  611,  612)  include  the  following  groups: 

H I       External  Iliac.  Iliac  Circumflex.  ^Lateral  Aortic. 


Common  Iliac.  Hypogastric.  Lumbar  ^  Preaortic. 

Epigastric.  Sacral.  iRetroaortic. 


The  External  Iliac  Glands,  from  eight  to  ten  in  number,  lie  along  the  external 
iliac  vessels.  They  are  arranged  in  three  groups,  one  on  the  lateral,  another 
on  the  medial,  and  a  third  on  the  anterior  aspect  of  the  vessels;  the  third  group  is, 
however,  sometimes  absent.  Their  principal  afi"erents  are  derived  from  the  inguinal 
and  subinguinal  glands,  the  deep  lymphatics  of  the  abdominal  wall  below  the  umbili- 
cus and  of  the  adductor  region  of  the  thigh,  and  the  lymphatics  from  the  glans 


704 


ANGIOLOGY 


I 


penis  vel  clitoridis,  the  membranous  urethra,  the  prostate,  the  fundus  of  the  bladder, 
the  cervix  uteri,  and  upper  part  of  the  vagina. 

The  Common  Iliac  Glands,  four  to  six  in  number,  are  grouped  behind  and  on  the 
sides  of  the  common  ihae  artery,  one  or  two  being  placed  below  the  bifurcation 
of  the  aorta,  in  front  of  the  fifth  lumbar  vertebra.  They  drain  chiefly  the  hypo- 
gastric and  external  iliac  glands,  and  their  efferents  pass  to  the  lateral  aortic  glands. 

The  Epigastric  Glands  (lymphoglandulcB  epigastricce) ,  three  or  four  in  number, 
are  placed  alongside  the  lower  portion  of  the  inferior  epigastric  vessels. 


Hight  lateral  aoHtc 
/. 


Left  lateral  aortic 

Common  iliac 


Gland  in 

front  of  sacral  — 

promontory 

Corrtmon  iliac  — 


External  iliac 


External  iliac 


Obturator  artery 


\ 

Obturator  gland 


Fig.  611. — The  parietal  lymph  glands  of  the  pelvis.     (Cun6o  and  Marcille.) 

The  Iliac  Circumflex  Glands,  two  to  four  in  number,  are  situated  along  the  course 
of  the  deep  iliac  circumflex  vessels;  they  are  sometimes  absent. 

The  Hypogastric  Glands  (lymphoglandulcE  hypogastricce;  internal  iliac  gland) 
(Fig.  612)  surround  the  hypogastric  vessels,  and  receive  the  lymphatics  corre- 
sponding to  the  distribution  of  the  branches  of  the  hypogastric  artery,  i.  e.,  they 
receive  lymphatics  from  all  the  pelvic  viscera,  from  the  deeper  parts  of  the  perineum, 
including  the  membranous  and  cavernous  portions  of  the  urethra,  and  from  the 
buttock  and  back  of  the  thigh.  An  obturator  gland  is  sometimes  seen  in  the  upper 
part  of  the  obturator  foramen. 

The  Sacral  Glands  are  placed  in  the  concavity  of  the  sacrum,  in  relation  to  the 


THE  LYMPH  GLANDS  OF  THE  ABDOMEN  AND 


middle  and  lateral  sacral  arteries;  they  receive  lymphatics  from  the  rectum  and 
posterior  wall  of  the  pelvis. 

The  efferents  of  the  hypogastric  group  end  in  the  common  iliac  glands. 

The  Lumbar  Glands  (lymphoglanduloB  lumhales)  are  very  numerous,  and  consist 
of  right  and  left  lateral  aortic,  preaortic,  and  retroaortic  groups. 

The  right  lateral  aortic  glands  are  situated  partly  in  front  of  the  inferior  vena 
cava,  near  the  termination  of  the  renal  vein,  and  partly  behind  it  on  the  origin  of  the 
Psoas  major,  and  on  the  right  crus  of  the  diaphragm.  The  left  lateral  aortic 
glands  form  a  chain  on  the  left  side  of  the  abdominal  aorta  in  front  of  the  origin 
of  the  Psoas  major  and  left  crus  of  the  diaphragm.  The  glands  on  either  side 
receive  {a)  the  efferents  of  the  common  iliac  glands,  (6)  the  lymphatics  from  the 
testis  in  the  male  and  from  the  ovary,  uterine  tube,  and  body  of  the  uterus  in  the 


Hypogastric 


Gland  in  front  of 
sacral  promontory 


External  iliac 
ff  lands 


Internal  lymphatics  of 

bladder 

ymphatic  from  glans 

penis 


Lymphatics  of  bladder  ^^  _ 

Prostatic  collecting  trunk 
Urethral  collecting  trunks 

Glandular  nodule  in  front  of  symphysis  Prostatic  collecting  trunk 

Fig,  612. — Iliopelvic  glands  (lateral  view).     (Cunfio  and  Marcille.) 


Lateral  sacral 


Hypogastric 

Satellite  trunk  of 
internal  puden- 
dal vessels. 
Trunk  of  middle 
hcemorrhoidal 


female;  (c)  the  lymphatics  from  the  kidney  and  suprarenal  gland;  and  (d)  the 

lymphatics  draining  the  lateral  abdominal  muscles  and  accompanying  the  lumbar 

-—veins.    Most  of  the  efferent  vessels  of  the  lateral  aortic  glands  converge  to  form 

IB  the  right  and  left  lumbar  trunks  which  join  the  cisterna  chyli,  but  some  enter  the 

pre-  and  retroaortic  glands,  and  others  pierce  the  crura  of  the  diaphragm  to  join 

the  lower  end  of  the  thoracic  duct.    The  preaortic  glands  lie  in  front  of  the  aorta, 

and  may  be  divided  into  celiac,  superior  mesenteric,  and  inferior  mesenteric  groups, 

arranged  around  the  origins  of  the  corresponding  arteries.    They  receive  a  few 

vessels  from  the  lateral  aortic  glands,  but  their  principal  afferents  are  derived  from 

the  viscera  supplied  by  the  three  arteries  with  which  they  are  associated.    Some 

of  their  efferents  pass  to  the  retroaortic  glands,  but  the  majority  unite  to  form 

IB  the  intestinal  trunk,  which  enters  the  cisterna  chyli.   The  retroaortic  glands  are  placed 

B  45 


706  '^^^^^^^     ANGIOLOGY 

below  the  cisterna  chyli,  on  the  bodies  of  the  third  and  fourth  lumbar  vertebrae. 
They  receive  lymphatic  trunks  from  the  lateral  and  preaortic  glands,  while  their 
efferents  end  in  the  cisterna  chyli. 

The  Lymphatic  Vessels  of  the  Abdomen  and  Pelvis. 

The  lymphatic  vessels  of  the  walls  of  the  abdomen  ahd  pelvis  may  be  divided 
into  two  sets,  superficial  and  deep. 

The  superficial  vessels  follow  the  course  of  the  superficial  bloodvessels  and 
converge  to  the  superficial  inguinal  glands;  those  derived  from  the  integument 
of  the  front  of  the  abdomen  below  the  umbilicus  follow  the  course  of  the  superficial 
epigastric  vessels,  and  those  from  the  sides  of  the  lumbar  part  of  the  abdominal 
wall  pass  along  the  crest  of  the  ilium,  with  the  superficial  iliac  circumflex  vessels. 
The  superficial  lymphatic  vessels  of  the  gluteal  region  turn  horizontally  around  the 
buttock,  and  join  the  superficial  inguinal  and  subinguinal  glands. 

The  deep  vessels  run  alongside  the  principal  bloodvessels.  Those  of  the  parietes 
of  the  pelvis,  which  accompany  the  superior  and  inferior  gluteal,  and  obturator 
vessels,  follow  the  course  of  the  hypogastric  artery,  and  ultimately  join  the  lateral 
aortic  glands. 

Lymphatic  Vessels  of  the  Perineum  and  External  Genitals. — The  lymphatic  vessels 
of  the  perineum,  of  the  integument  of  the  penis,  and  of  the  scrotum  (or  vulva), 
follow  the  course  of  the  external  pudendal  vessels,  and  end  in  the  superficial  ingui- 
nal and  subinguinal  glands.  Those  of  the  glans  penis  vel  clitoridis  terminate 
partly  in  the  deep  subinguinal  glands  and  partly  in  the  external  iliac  glands. 

The  visceral  glands  are  associated  with  the  branches  of  the  celiac,  superior 
and  inferior  mesenteric  arteries.  Those  related  to  the  branches  of  the  celiac 
artery  form  three  sets,  gastric,  hepatic,  and  pancreaticolienal. 

The  Gastric  Glands  (Figs.  613,  614)  consist  of  two  sets,  superior  and  inferior. 

The  Superior  Gastric  Glands  (lymphoglanduloB  gastricce  superiores)  accompany 
the  left  gastric  artery  and  are  divisible  into  three  groups,  viz.:  (a)  upper,  on  the 
stem  of  the  artery;  (6)  lower,  accompanying  the  descending  branches  of  the  artery 
along  the  cardiac  half  of  the  lesser  curvature  of  the  stomach,  between  the  two  layers 
of  the  lesser  omentum;  and  (c)  paracardial  outlying  members  of  the  gastric  glands, 
disposed  in  a  manner  comparable  to  a  chain  of  beads  around  the  neck  of  the  stomach 
(Jamieson  and  Dobson^.  They  receive  their  afferents  from  the  stomach;  their 
efferents  pass  to  the  celiac  group  of  preaortic  glands. 

The  Inferior  Gastric  Glands  (lymphoglandulcB  gastricoe  inferiores;  right  gastro- 
epiploic gland),  four  to  seven  in  number,  lie  between  the  two  layers  of  the  greater 
omentum  along  the  pyloric  half  of  the  greater  curvature  of  the  stomach. 

The  Hepatic  Glands  (lymphoglandulcB  hepaticoe)  (Fig.  613),  consist  of  the  follow- 
ing groups:  (a)  hepatic,  on  the  stem  of  the  hepatic  artery,  and  extending  upward 
along  the  common  bile  duct,  between  the  two  layers  of  the  lesser  omentum,  as 
far  as  the  porta  hepatis;  the  cystic  gland,  a  member  of  this  group,  is  placed  near 
the  neck  of  the  gall-bladder;  (6)  subpyloric,  four  or  five  in  number,  in  close  relation 
to  the  bifurcation  of  the  gastroduodenal  artery,  in  the  angle  between  the  superior 
and  descending  parts  of  the  duodenum;  an  outlying  member  of  this  group  is  some- 
times found  above  the  duodenum  on  the  right  gastric  (pyloric)  artery.  The  glands 
of  the  hepatic  chain  receive  afferents  from  the  stomach,  duodenum,  liver,  gall- 
bladder, and  pancreas ;  their  efferents  join  the  celiac  group  of  preaortic  glands. 

The  Pancreaticolienal  Glands  (lymphoglandidoe  pancreaticolienales;  splenic 
glands)  (Fig.  614)  accompany  the  lienal  (splenic)  artery,  and  are  situated  in  rela- 
tion to  the  posterior  surface  and  upper  border  of  the  pancreas;  one  or  two  members 

I  Lancet,  April  20  and  27,  1907. 


I 
I 


THE  LYMPHATIC  VESSELS  OF  THE  ABDOMEN  AND  PELVIS       707 


Paracardial  glands 
Superior  gastric  glands 
Hepatic  glands 


Svbpylortc 
glands 


Pancreaticolienal  glcnda 


Inferior  gastric  glands 
Fig.  613. — Lymphatics  of  stomach,  etc.     (Jamieson  and  Dobson.) 


Subpylo 
glands 


Fig.  614. — Lymphatics  of  stomach,  etc.    The  stomach  has  been  turned  upward.     (Jamieson  and  Dobson.) 


708 


ANGIOLOGY 


of  this  group  are  found  in  the  gastrolienal  h'gament  (Jamieson  and  Dobson,  op.  cit.). 
Their  afferents  are  derived  from  the  stomach,  spleen,  and  pancreas,  their  efferents 
join  the  celiac  group  of  preaortic  glands. 


I 


Duodenum 


Upper  group  of 
ileocolic  glands 


Lower  group  of 
ileocolic  glands 


Cecum  Vermiform  process 

FiQ.  615.— The  lymphatics  of  cecum  and  vermiform  process  from  the  front.     (Jamieson  and  Dobson.) 


Upper  group  of 
ileocolic  glands 


Lower  group  of 
ileocolic  glands 


Vermiform  process  Cecum 

Fig.  616. — The  lymphatics  of  cecum  and  vermiform  process  from  behind.     (Jamieson  and  Dobson.; 


THE  LYMPHATIC  VESSELS  OF  ABDOMEN  AND  PELVIS 


709 


R 


The  superior  mesenteric  glands  may  be  divided  into  three  principal  groups: 
mesenteric,  ileocolic,  and  mesocolic. 

The  Mesenteric  Glands  (lymphoglanduloB  mesenteric^)  lie  between  the  layers  of 
the  mesentery.  They  vary  from  one  hundred  to  one  hundred  and  fifty  in  number, 
and  may  be  grouped  into  three  sets,  viz. :  one  lying  close  to  the  wall  of  the  small 
intestine,  among  the  terminal  twigs  of  the  superior  mesenteric  artery;  a  second, 
in  relation  to  the  loops  and  primary  branches  of  the  vessels;  and  a  third  along 
the  trunk  of  the  artery. 

The  Ileocolic  glands  (Figs.  615,  616),  from  ten  to  twenty  in  number,  form  a  chain 
around  the  ileocolic  artery,  but  show  a  tendency  to  subdivision  into  two  groups, 
one  near  the  duodenum  and  another  on  the  lower  part  of  the  trunk  of  the  artery. 


(Jamieson  and  DobsonO 

Where  the  vessel  divides  into  its  terminal  branches  the  chain  is  broken  up  into  sev- 
eral groups,  viz.:  (a)  ileal,  in  relation  to  the  ileal  branch  of  the  artery;  (6)  anterior 
ileocolic,  usually  of  three  glands,  in  the  ileocolic  fold,  near  the  wall  of  the  cecum; 
(c)  posterior  ileocolic,  mostly  placed  in  the  angle  between  the  ileum  and  the  colon, 
but  partly  lying  behind  the  cecum  at  its  junction  with  the  ascending  colon;  (d) 
a  single  gland,  between  the  layers  of  the  mesenteriole  of  the  vermiform  process; 
(e)  right  colic,  along  the  medial  side  of  the  ascending  colon. 

The  Mesocolic  Glands  {lymphoglandulce  mesocolicce)  are  numerous,  and  lie  between 
the  layers  of  the  transverse  mesocolon,  in  close  relation  to  the  transverse  colon ;  they 
are  best  developed  in  the  neighborhood  of  the  right  and  left  colic  flexures.  One  or 
two  small  glands  are  occasionally  seen  along  the  trunk  of  the  right  colic  artery  and 
others  are  found  in  relation  to  the  trunk  and  branches  of  the  middle  colic  artery. 


710  ANGIOLOGY 

The  superior  mesenteric  glands  receive  afferents  from  the  jejunum,  ileum,  cecum, 
vermiform  process,  and  the  ascending  and  transverse  parts  of  the  colon;  theiri« 
efferents  pass  to  the  preaortic  glands.  || 

The  inferior  mesenteric  glands  (Fig.  617)  consist  of:  (a)  small  glands  on  the 
branches  of  the  left  colic  and  sigmoid  arteries;  (6)  a  group  in  the  sigmoid  mesocolon, 
around  the  superior  hemorrhoidal  artery;  and  (c)  a  pararectal  group  in  contact  with 
the  muscular  coat  of  the  rectum.  They  drain  the  descending  iliac  and  sigmoid 
parts  of  the  colon  and  the  upper  part  of  the  rectum;  their  efferents  pass  to  the 
preaortic  glands. 


The  Lymphatic  Vessels  of  the  Abdominal  and  Pelvic  Viscera. 


4 

thosefj 


The  lymphatic  vessels  of  the  abdominal  and  pelvic  viscera  consist  of  (1)  thosef| 
of  the  subdiaphragmatic  portion  of  the  digestive  tube  and  its  associated  glands, 
the  liver  and  pancreas;  (2)  those  of  the  spleen  and  suprarenal  glands;  (3)  those  of 
the  urinary  organs;  (4)  those  of  the  reproductive  organs. 

1.  The  lymphatic  vessels  of  the  subdiaphragmatic  portion  of  the  digestive  tube 
are  situated  partly  in  the  mucous  membrane  and  partly  in  the  seromuscular  coats, 
but  as  the  former  system  drains  into  the  latter,  the  two  may  be  considered  as  one. 

The  Lymphatic  Vessels  of  the  Stomach  (Figs.  613,  614)  are  continuous  at  the 
cardiac  orifice  with  those  of  the  esophagus,  and  at  the  pylorus  with  those  of  the  • 
duodenum.  They  mainly  follow  the  bloodvessels,  and  may  be  arranged  in  four 
sets.  Those  of  the  first  set  accompany  the  branches  of  the  left  gastric  artery, 
receiving  tributaries  from  a  large  area  on  either  surface  of  the  stomach,  and  ter- 
minate in  the  superior  gastric  glands.  Those  of  the  second  set  drain  the  fundus 
and  body  of  the  stomach  on  the  left  of  a  line  drawn  vertically  from  the  esophagus; 
they  accompany,  more  or  less  closely,  the  short  gastric  and  left  gastroepiploic 
arteries,  and  end  in  the  pancreaticolienal  glands.  The  vessels  of  the  third  set  drain 
the  right  portion  of  the  greater  curvature  as  far  as  the  pyloric  portion,  and  end  in 
the  inferior  gastric  glands,  the  efferents  of  which  pass  to  the  subpyloric  group. 
Those  of  the  fourth  set  drain  the  pyloric  portion  and  pass  to  the  hepatic  and 
subpyloric  glands,  and  to  the  superior  gastric  glands. 

The  Ljrmphatic  Vessels  of  the  Duodenum  consist  of  an  anterior  and  a  posterior 
set,  which  open  into  a  series  of  small  pancreaticoduodenal  glands  on  the  anterior 
and  poisterior  aspects  of  the  groove  between  the  head  of  the  pancreas  and  the  duo- 
denum. The  efferents  of  these  glands  run  in  two  directions,  upward  to  the  hepatic 
glands  and  downward  to  the  preaortic  glands  around  the  origin  of  the  superior^ 
mesenteric  artery.  " 

The  Lymphatic  Vessels  of  the  Jejunum  and  Ileum  are  termed  lacteals,  from  the 
milk-white  fluid  they  contain  during  intestinal  digestion.  They  run  between  the 
layers  of  the  mesentery  and  enter  the  mesenteric  glands,  the  efferents  of  which 
end  in  the  preaortic  glands.  fl 

The  Lymphatic  Vessels  of  the  Vermiform  Process  and  Cecum  (Figs.  615,  616)  are  " 
numerous,  since  in  the  wall  of  this  process  there  is  a  large  amount  of  adenoid  tissue. 
From  the  body  and  tail  of  the  vermiform  process  eight  to  fifteen  vessels  ascend 
between  the  layers  of  the  mesenteriole,  one  or  two  being  interrupted  in  the  gland 
which  lies  between  the  layers  of  this  peritoneal  fold.  They  unite  to  form  three 
or  four  vessels,  which  end  partly  in  the  lower  and  partly  in  the  upper  glands  of  the 
ileocolic  chain.  The  vessels  from  the  root  of  the  vermiform  process  and  from  the 
cecum  consist  of  an  anterior  and  a  posterior  group.  The  anterior  vessels  pass  in 
front  of  the  cecum,  and  end  in  the  anterior  ileocolic  glands  and  in  the  upper  and 
lower  glands  of  the  ileocolic  chain;  the  posterior  vessels  ascend  over  the  back  of  the 
cecum  and  terminate  in  the  posterior  ileocolic  glands  and  in  the  lower  glands  of  the 
ileocolic  chain. 


I 


II 


II 


II 


THE  LYMPHATIC  VESSELS  OF  ABDOMINAL  AND  PELVIC  VISCERA     711 

Lymphatic  Vessels  of  the  Colon  (Fig.  617). — ^The  lymphatic  vessels  of  the  ascend- 
ing and  transverse  parts  of  the  colon  finally  end  in  the  mesenteric  glands,  after 
traversing  the  right  colic  and  mesocolic  glands.  Those  of  the  descending  and  iliac 
sigmoid  parts  of  the  colon  are  interrupted  by  the  small  glands  on  the  branches 
of  the  left  colic  and  sigmoid  arteries,  and  ultimately  end  in  the  preaortic  glands 
around  the  origin  of  the  inferior  mesenteric  artery. 

L3rmphatic  Vessels  of  the  Anus,  Anal  Canal,  and  Rectum. — ^The  lymphatics  from 
the  anus  pass  forward  and  end  with  those  of  the  integument  of  the  perineum  and 
scrotum  in  the  superficial  inguinal  glands;  those  from  the  anal  canal  accompany 
the  middle  and  inferior  hemorrhoidal  arteries,  and  end  in  the  hypogastric  glands; 
while  the  vessels  from  the  rectum  traverse  the  pararectal  glands  and  pass  to  those 
in  the  sigmoid  mesocolon;  the  eft'erents  of  the  latter  terminate  in  the  preaortic 
glands  around  the  origin  of  the  inferior  mesenteric  artery. 

The  Lymphatic  Vessels  of  the  Liver  are  divisible  into  two  sets,  superficial  and  deep. 
The  former  arise  in  the  subperitoneal  areolar  tissue  over  the  entire  surface  of  the 
organ,  and  may  be  grouped  into  (a)  those  on  the  convex  surface,  (b)  those  on  the 
inferior  surface. 

(a)  On  the  convex  surface :  The  vessels  from  the  back  part  of  this  surface  reach 
their  terminal  glands  by  three  different  routes;  the  vessels  of  the  middle  set,  five 
or  six  in  number,  pass  through  the  vena-caval  foramen  in  the  diaphragm  and  end 
in  one  or  two  glands  which  are  situated  around  the  terminal  part  of  the  inferior 
vena  cava;  a  few  vessels  from  the  left  side  pass  backward  toward  the  esophageal 
hiatus,  and  terminate  in  the  paracardial  group  of  superior  gastric  glands;  the  vessels 
from  the  right  side,  one  or  two  in  number,  run  on  the  abdominal  surface  of  the 
diaphragm,  and,  after  crossing  its  right  crus,  end  in  the  preaortic  glands  which 
surround  the  origin  of  the  celiac  artery.  From  the  portions  of  the  right  and  left 
lobes  adjacent  to  the  falciform  ligament,  the  lymphatic  vessels  converge  to  form 
two  trunks,  one  of  which  accompanies  the  inferior  vena  cava  through  the  dia- 
phragm, and  ends  in  the  glands  around  the  terminal  part  of  this  vessel;  the  other 
runs  downward  and  forward,  and,  turning  around  the  anterior  sharp  margin  of  the 
liver,  accompanies  the  upper  part  of  the  ligamentum  teres,  and  ends  in  the  upper 
hepatic  glands.  From  the  anterior  surface  a  few  additional  vessels  turn  around  the 
anterior  sharp  margin  to  reach  the  upper  hepatic  glands. 

(6)  On  the  inferior  surface :  The  vessels  from  this  surface  mostly  converge 
to  the  porta  hepatis,  and  accompany  the  deep  lymphatics,  emerging  from  the 
porta  to  the  hepatic  glands;  one  or  tw^o  from  the  posterior  parts  of  the  right  and 
caudate  lobes  accompany  the  inferior  vena  cava  through  the  diaphragm,  and 
end  in  the  glands  around  the  terminal  part  of  this  vein. 

The  deep  lymphatics  converge  to  ascending  and  descending  trunks.  The  ascend- 
ing trunks  accompany  the  hepatic  veins  and  pass  through  the  diaphragm  to  end 
in  the  glands  around  the  terminal  part  of  the  inferior  vena  cava.  The  descending 
trunks  emerge  from  the  porta  hepatis,  and  end  in  the  hepatic  glands. 

The  Lymphatic  Vessels  of  the  Gall-bladder  pass  to  the  hepatic  glands  in  the  porta 
hepatis;  those  of  the  common  bile  duct  to  the  hepatic  glands  alongside  the  duct 
and  to  the  upper  pancreaticoduodenal  glands. 

The  Lymphatic  Vessels  of  the  Pancreas  follow  the  course  of  its  bloodvessels. 
Most  of  them  enter  the  pancreaticolienal  glands,  but  some  end  in  the  pancreatico- 
duodenal glands,  and  others  in  the  preaortic  glands  near  the  origin  of  the  superior 
mesenteric  artery. 

2.  The  l3miphatic  vessels  of  the  spleen  and  suprarenal  glands. 

The  Lymphatic  Vessels  of  the  Spleen,  both  superficial  and  deep,  pass  to  the  pan- 
creaticolienal glands. 

The  Lymphatic  Vessels  of  the  Suprarenal  Glands  usually  accompany  the  supra- 
renal veins,  and  end   in  the   lateral  aortic  glands;  occasionally  some  of  them 


712 


ANGIOLOGY 


pierce  the  crura  of  the  diaphragm  and  end  in  the  glands  of  the  postenoF 
tinum. 

3.  The  lymphatic  vessels  of  the  urinary  organs. 

The  Lymphatic  Vessels  of  the  Kidney  form  three  plexuses:  one  in  the  substance*' 
of  the  kidney,  a  second  beneath  its  fibrous  capsule,  and  a  third  in  the  perinephric 
fat;  the  second  and  third  communicate  freely  with  each  other.  The  vessels  from 
the  plexus  in  the  kidney  substance  converge  to  form  four  or  five  trunks  which 
issue  at  the  hilum.  Here  they  are  joined  by  vessels  from  the  plexus  under  the 
capsule,  and,  following  the  course  of  the  renal  vein,  end  in  the  lateral  aortic  glands. 
The  perinephric  plexus  is  drained  directly  into  the  upper  lateral  aortic  glands. 

The  Lymphatic  Vessels  of  the  Ureter  run  in  different  directions.  Those  from 
its  upper  portion  end  partly  in  the  efferent  vessels  of  the  kidney  and  partly  in  the 
lateral  aortic  glands;  those  from  the  portion  immediately  above  the  brim  of  the 
lesser  pelvis  are  drained  into  the  common  iliac  glands;  while  the  vessels  from  the 
intrapelvic  portion  of  the  tube  either  join  the  eft'erents  from  the  bladder,  or  end 
in  the  hypogastric  glands. 


Common  iliac 
artery 


External  iliac 
glands 

Lymphatics 
from  bladder 


Gland  in  front  of 
sacral  promontort/ 


Hypogastric 
glands 

Ureter 

Lymphatics  from 
bladder 


•I 


Fig.  618. — Lymphatics  of  the  bladder.     (Cun6o  and  Marcille.)  •  fl 

The  Lymphatic  Vessels  of  the  Bladder  (Fig.  618)  originate  in  two  plexuses,  an 
intra-  and  an  extramuscular,  it  being  generally  admitted  that  the  mucous  mem- 
brane is  devoid  of  lymphatics.^  The  efferent  vessels  are  arranged  in  two  groups, 
one  from  the  anterior  and  another  from  the  posterior  surface  of  the  bladder.  The 
vessels  from  the  anterior  surface  pass  to  the  external  iliac  glands,  but  in  their  course 
minute  glands  are  situated.  These  minute  glands  are  arranged  in  two  groups, 
an  anterior  vesical,  in  front  of  the  bladder,  and  a  lateral  vesical,  in  relation  to  the 
lateral  umbilical  ligament.  The  vessels  from  the  posterior  surface  pass  to  the  hypo- 
gastric, external,  and  common  iliac  glands;  those  draining  the  upper  part  of  this 
surface  traverse  the  lateral  vesical  glands. 


'  Some  authorities  maintain  that  a  plexus  of  lymphatic  vessels  does  exist  in  the  mucous  membrane  of  the  bladder 
(consult  M6decine  op6ratoire  des  Voies  urinaires,  par  J.  Albarran,  Paris.  1909). 


THE  LYMPHATIC  VESSELS  OF  ABDOMINAL  AND  PELVIC  VISCERA     713 


I 


The  Lymphatic  Vessels  of  the  Prostate  (Fig.  619)  terminate  chiefly  in  the  hypo- 
gastric and  sacral  glands,  but  one  trunk  from  the  posterior  surface  ends  in  the  exter- 
nal iliac  glands,  and  another  from  the  anterior  surface  joins  the  vessels  which  drain 
the  membranous  part  of  the  urethra. 

Lymphatic  Vessels  of  the  Urethra. — The  lymphatics  of  the  cavernous  portion  of 
the  urethra. accompany  those  of  the  glans  penis,  and  terminate  with  them  in  the  deep 
subinguinal  and  external  iliac  glands.  Those  of  the  membranous  and  prostatic 
portions,  and  those  of  the  whole  urethra  in  the  female, pass  to  the  hypogastric  glands. 


_  ^Sxt.  iliac  glands  \  ^       , 

ir     :::::;>^ 

Vessels  draining ^> 

into  ext.  iliac  \J\' 

glands  f   >    \  .    ,X^  ^ 

■  ^1  ( I  ^:^^™^ 

W  ^p  Reiroprostatic 
lymph-nodes 
Vessels  draining 
into  gland  on 

sacral  prom-  f^^ft^A 

ontory  ,  il^gMi,> 


Fig.  619. — Lymphatics  of  the  prostate.     (Cun6o  and  Marcille.) 

(4)  The  lymphatic  vessels  of  the  reproductive  organs. 

The  Lsrmphatic  Vessels  of  the  Testes  consist  of  two  sets,  superficial  and  deep, 
the  former  commencing  on  the  surface  of  the  tunica  vaginalis,  the  latter  in  the 
epididymis  and  body  of  the  testis.  They  form  from  four  to  eight  collecting  trunks 
which  ascend  with  the  spermatic  veins  in  the  spermatic  cord  and  along  the  front 
of  the  Psoas  major  to  the  level  where  the  spermatic  vessels  cross  the  ureter  and  end 
in  the  lateral  and  preaortic  groups  of  lumbar  glands.^ 

The  Lsrmphatic  Vessels  of  the  Ductus  Deferens  pass  to  the  external  iliac  glands; 
those  of  the  vesiculae  seminales  partly  to  the  hypogastric  and  partly  to  the  external 
glands. 

^  "The  Lymphatics  of  the  Testicle,"  by  Jamieson  and  Dobson,  Lancet,  February  19,  1900. 


714 


ANGIOLOGY 


The  Lymphatic  Vessels  of  the  Ovary  are  similar  to  those  of  the  testis,  and  ascend 
'with  the  ovarian  artery  to  the  lateral  and  preaortic  glands. 

The  Lymphatic  Vessels  of  the  Uterine  Tube  pass  partly  with  those  of  the  ovary 
and  partly  with  those  of  the  uterus. 

The  L3rmphatic  Vessels  of  the  Uterus  (Fig.  620)  consist  of  two  sets,  superficial 
and  deep,  the  former  being  placed  beneath  the  peritoneum,  the  latter  in  the  sub- 
stance of  the  organ.  The  lymphatics  of  the  cervix  uteri  run  in  three  directions: 
transversely  to  the  external  iliac  glands,  postero-laterally  to  the  hypogastric  glands, 
and  posteriorly  to  the  common  iliac  glands.    The  majority  of  the  vessels  of  the  body 


Efferents  to  lat., 
aortic  glands 


Efferents  to  ext.  J 
iliac  glands    1  " 

Network  in  lateral 
aspect  of  cervix' 
uteri 


A 


Glands  in  front 
of  sacral  prom- 
ontory 


Efferents  to  glands 
■"*     in  front  of  sa- 
cral promontory 
...Hypogastric 
glands 

—  Lat.  sacral  ^| 

glands  ^5 

Vessels  draining 

—  into  hypogastric 
glands 

--■Vessels  passing 
to  lat.  sacral 
glands 


Fig.  620. — Lymphatics  of  the  uterus.    (Cun^oand  Maroille.) 

and  fundus  of  the  uterus  pass  lateralward  in  the  broad  ligaments,  and  are  continued 
up  with  the  ovarian  vessels  to  the  lateral  and  preaortic  glands;  a  few,  however, 
run  to  the  external  iliac  glands,  and  one  or  two  to  the  superficial  inguinal  glands. 
In  the  unimpregnated  uterus  the  lymphatic  vessels  are  very  small,  but  during 
gestation  they  are  greatly  enlarged. 

The  Lymphatic  Vessels  of  the  Vagina  are  carried  in  three  directions:  those  of 
the  upper  part  of  the  vagina  to  the  external  iliac  glands,  those  of  the  middle  part 
to  the  hypogastric  glands,  and  those  of  the  lower  part  to  the  common  iliac  glands. 
On  the  course  of  the  vessels  from  the  middle  and  lower  parts  small  glands  are 
situated.  Some  lymphatic  vessels  from  the  lower  part  of  the  vagina  join  those 
of  the  vulva  and  pass  to  the  superficial  inguinal  glands.  The  lymphatics  of  the 
vagina  anastomose  with  those  of  the  cervix  uteri,  vulva,  and  rectum,  but  not  with 
those  of  the  bladder. 


THE  LYMPHATICS  OF  THE  THORAX  715 

THE   LYMPHATICS  OF  THE   THORAX. 

The  lymph  glands  of  the  thorax  may  be  divided  into  parietal  and  visceral — the 
former  being  situated  in  the  thoracic  wall,  the  latter  in  relation  to  the  viscera. 

The  parietal  lymph  glands  include  the  sternal,  intercostal,  and  diaphragmatic 
glands. 

1.  The  Sternal  Glands  {lymphoglandido;  sternales;  internal  mammary  glands)  are 
placed  at  the  anterior  ends  of  the  intercostal  spaces,  by  the  side  of  the  internal 

ammary  artery.  They  derive  afferents  from  the  mamma,  from  the  deeper  struc- 
tures of  the  anterior  abdominal  wall  above  the  level  of  the  umbilicus,  from  the 
upper  surface  of  the  liver  through  a  small  group  of  glands  which  lie  behind  the 
xiphoid  process,  and  from  the  deeper  parts  of  the  anterior  portion  of  the  thoracic 
wall.  Their  efferents  usually  unite  to  form  a  single  trunk  on  either  side;  this  may 
open  directly  into  the  junction  of  the  internal  jugular  and  subclavian  veins,  or 
that  of  the  right  side  may  join  the  right  subclavian  trunk,  and  that  of  the  left 
the  thoracic  duct. 

2.  The  Intercostal  Glands  (lymphoglandulce  intercosiales)  occupy  the  posterior 
parts  of  the  intercostal  spaces,  in  relation  to  the  intercostal  vessels.  They  receive 
the  deep  lymphatics  from  the  posterolateral  aspect  of  the  chest;  some  of  these 
vessels  are  interrupted  by  small  lateral  intercostal  glands.  The  efferents  of  the 
glands  in  the  lower  four  or  five  spaces  unite  to  form  a  trunk,  which  descends  and 
opens  either  into  the  cisterna  chyli  or  into  the  commencement  of  the  thoracic  duct. 
The  efferents  of  the  glands  in  the  upper  spaces  of  the  left  side  end  in  the  thoracic 
duct;  those  of  the  corresponding  right  spaces,  in  the  right  lymphatic  duct. 

3.  The  Diaphragmatic  Glands  lie  on  the  thoracic  aspect  of  the  diaphragm, 
and  consist  of  three  sets,  anterior,  middle,  and  posterior. 

The  anterior  set  comprises  (a)  two  or  three  small  glands  behind  the  base  of  the 
xiphoid  process,  which  receive  afferents  from  the  convex  surface  of  the  liver,  and 
(&)  one  or  two  glands  on  either  side  near  the  junction  of  the  seventh  rib  with  its 
cartilage,  which  receive  lymphatic  vessels  from  the  front  part  of  the  diaphragm. 
The  efferent  vessels  of  the  anterior  set  pass  to  the  sternal  glands. 

The  middle  set  consists  of  two  or  three  glands  on  either  side  close  to  where  the 
phrenic  nerves  enter  the  diaphragm.  On  the  right  side  some  of  the  glands  of  this 
group  lie  within  the  fibrous  sac  of  the  pericardium,  on  the  front  of  the  termination 
of  the  inferior  vena  cava.  The  afferents  of  this  set  are  derived  from  the  middle 
part  of  the  diaphragm,  those  on  the  right  side  also  receiving  afferents  from  the 

nvex  surface  of  the  liver.   Their  efferents  pass  to  the  posterior  mediastinal  glands. 

The  posterior  set  consists  of  a  few  glands  situated  on  the  back  of  the  crura  of 
the  diaphragm,  and  connected  on  the  one  hand  with  the  lumbar  glands  and  on 
the  other  with  the  posterior  mediastinal  glands. 

The  superficial  lymphatic  vessels  of  the  thoracic  wall  ramify  beneath  the  skin 
and  converge  to  the  axillary  glands.  Those  over  the  Trapezius  and  Latissimus 
dorsi  run  forward  and  unite  to  form  about  ten  or  twelve  trunks  which  end  in  the 
subscapular  group.  Those  over  the  pectoral  region,  including  the  vessels  from  the 
skin  covering  the  peripheral  part  of  the  mamma,  run  backward,  and  those  over 
the  Serratus  anterior  upward,  to  the  pectoral  group.  Others  near  the  lateral  margin 
of  the  sternum  pass  inward  between  the  rib  cartilages  and  end  in  the  sternal  glands, 
while  the  vessels  of  opposite  sides  anastomose  across  the  front  of  the  sternum.  A 
few  vessels  from  the  upper  part  of  the  pectoral  region  ascend  over  the  clavicle  to 
the  supraclavicular  group  of  cetvical  glands. 

The  Ljrmphatic  Vessels  of  the  Mamma  originate  in  a  plexus  in  the  interlobular 
spaces  and  on  the  walls  of  the  galactophorous  ducts.  Those  from  the  central  part 
of  the  gland  pass  to  an  intricate  plexus  situated  beneath  the  areola,  a  plexus  which 
receives  also  the  lymphatics  from  the  skin  over  the  central  part  of  the  gland  and 


716 


ANGIOLOGY 


those  from  the  areola  and  nipple.  Its  efFerents  are  collected  into  two  trunkswnicli 
pasf  to  the  pectoral  group  of  axillary  glands.  The  vessels  which  drain  the  medial 
part  of  the  mamma  pierce  the  thoracic  wall  and  end  in  the  sternal  glands,  while 
a  vessel  has  occasionally  been  seen  to  emerge  from  the  upper  part  of  the  mamma 
and,  piercing  the  Pectoralis  major,  terminate  in  the  subclavicular  glands  (Fig.  607). 


I 


DEEP  CERVICAL 
SCALENUS  ANTICUS 
MUSCLE 
THORACIC  DUCT 


MEDIASTINAL 

NODES  AND 

VESSELS 


INTERCOSTAL 

NODES  AND 

VESSELS 


RECEPTACULUM 
CHYLI 


COMMON    INTES- 
TINAL TRUNK 

PREAORTIC 
NODES  AND 
VESSELS 


COMMON    INTES- 
TINAL TRUNK 


INTERNAL  ILIAC 
EXTERNAL  ILIAC 


Fia.  621. — Deep  lymph  nodes  and  vessels  of  the  thorax  and  abdomen  (diagrammatic).     Afferent  vessels  are 
represented  by  continuous  lines,  and  efferent  and  internodular  vessels  by  dotted  lines.      (Cunningham.) 

The  deep  lymphatic  vessels  of  the  thoracic  wall  (Fig.  621)  consist  of: 

1.  The  lymphatics  of  the  muscles  which  lie  on  the  ribs:  most  of  these  end  in 

the  axillary  glands,  but  some  from  the  Pectoralis  major  pass  to  the  sternal  glands. 

2.  The  intercostal  vessels  which  drain  the  Intercostales  and  parietal  pleura.    Those 

draining  the  Intercostales  cxterni  run  backward  and,  after  receiving  the  vessels 


■r 

w 


¥ 


THE  LYMPHATICS  OF  THE  THORAX  717 

which  accompany  the  posterior  branches  of  the  intercostal  arteries,  end  in  the 
intercostal  glands.  Those  of  the  Intercostales  interni  and  parietal  pleura  consist 
of  a  single  trunk  in  each  space.  These  trunks  run  forward  in  the  subpleural  tissue 
and  the  upper  six  open  separately  into  the  sternal  glands  or  into  the  vessels  which 
unite  them ;  those  of  the  lower  spaces  unite  to  form  a  single  trunk  which  terminates 
in  the  lowest  of  the  sternal  glands.  3.  The  lymphatic  vessels  of  the  diaphragm, 
which  form  two  plexuses,  one  on  its  thoracic  and  another  on  its  abdominal  surface. 
These  plexuses  anastomose  freely  with  each  other,  and  are  best  marked  on  the 
parts  covered  respectively  by  the  pleurse  and  peritoneum.  That  on  the  thoracic 
surface  communicates  with  the  lymphatics  of  the  costal  and  mediastinal  parts  of 
the  pleura,  and  its  efferents  consist  of  three  groups :  (a)  anterior,  passing  to  the  gland 
which  lie  near  the  junction  of  the  seventh  rib  with  its  cartilage;  (b)  middle,  to  the 
glands  on  the  esophagus  and  to  those  around  the  termination  of  the  inferior  vena 
ava;  and  (e)  posterior,  to  the  glands  which  surround  the  aorta  at  the  point  where 
his  vessel  leaves  the  thoracic  cavity. 

The  plexus  on  the  abdominal  surface  is  composed  of  fine  vessels,  and  anasto- 
moses with  the  lymphatics  of  the  liver  and,  at  the  periphery  of  the  diaphragm, 
with  those  of  the  subperitoneal  tissue.  The  efferents  from  the  right  half  of  this 
rolexus  terminate  partly  in  a  group  of  glands  on  the  trunk  of  the  corresponding 
inferior  phrenic  artery,  while  others  end  in  the  right  lateral  aortic  glands.  Those 
from  the  left  half  of  the  plexus  pass  to  the  pre-  and  lateral  aortic  glands  and  to  the 
glands  on  the  terminal  portion  of  the  esophagus. 

The  visceral  Isnnph  glands  consist  of  three  groups,  viz.:  anterior  mediastinal, 
posterior  mediastinal,  and  tracheobronchial. 

The  Anterior  Mediastinal  Glands  {lymyhoglandidcB  mediastinales  anteriores)  are 
placed  in  the  anterior  part  of  the  superior  mediastinal  cavity,  in  front  of  the  aortic 
arch  and  in  relation  to  the  innominate  veins  and  the  large  arterial  trunks  which 
arise  from  the  aortic  arch.  They  receive  afferents  from  the  thymus  and  pericar- 
dium, and  from  the  sternal  glands;  their  efferents  unite  with  those  of  the  tracheo- 
bronchial glands,  to  form  the  right  and  left  bronchomediastinal  trunks. 

The  Posterior  Mediastinal  Glands  (lymphoglandulcB  inediastinales  posteriores) 
lie  behmd  the  pericardium  in  relation  to  the  esophagus  and  descending  thoracic 
aorta.  Their  afferents  are  derived  from  the  esophagus,  the  posterior  part  of  the 
pericardium,  the  diaphragm,  and  the  convex  surface  of  the  liver.  Their  efferents 
mostly  end  in  the  thoracic  duct,  but  some  join  the  tracheobronchial  glands. 

The  Tracheobronchial  Glands  (Fig.  622)  form  four  main  groups:  (a)  tracheal, 
on  either  side  of  the  trachea;  (6)  bronchial,  in  the  angles  between  the  lower  part 
of  the  trachea  and  bronchi  and  in  the  angle  between  the  two  bronchi ;  (c)  broncho- 
pulmonary, in  the  hilus  of  each  lung;  and  (d)  pulmonary,  in  the  lung  substance,  on 
the  larger  branches  of  the  bronchi.  The  afferents  of  the  tracheobronchial  glands 
drain  the  lungs  and  bronchi,  the  thoracic  part  of  the  trachea  and  the  heart;  some 
of  the  efferents  of  the  posterior  mediastinal  glands  also  end  in  this  group.  Their 
efferent  vessels  ascend  upon  the  trachea  and  unite  with  efferents  of  the  internal 
mammary  and  anterior  mediastinal  glands  to  form  the  right  and  left  broncho- 
mediastinal trunks.  The  right  bronchomediastinal  trunk  may  join  the  right 
lymphatic  duct,  and  the  left  the  thoracic  duct,  but  more  frequently  they  open 
independently  of  these  ducts  into  the  junction  of  the  internal  jugular  and 
subclavian  veins  of  their  own  side. 

In  all  town  dwellers  there  are  continually  being  swept  into  these  glands  from  the  bronchi 
and  alveoli  large  quantities  of  the  dust  and  black  carbonaceous  pigment  that  are  so  freely 
inhaled  in  cities.  At  first  the  glands  are  moderately  enlarged,  firm,  "inky  black,  and  gritty  on 
section;  later  they  enlarge  still  further,  often  becoming  fibrous  from  the  irritation  set  up  by 
the  minute  foreign  bodies  with  which  they  are  crammed,  and  may  break  down  into  a  soft  slimy 
mass  or  may  calcify. 


k 


718 


ANGIOLOGY 


The  lymphatic  vessels  of  the  thoracic  viscera  comprise  those  of  the  heart 
pericardium,  lungs  and  pleura,  thymus,  and  esophagus. 

The  Lymphatic  Vessels  of  the  Heart  consist  of  two  plexuses:  (a)  deep,  immediately 
under  the  endocardium;  and  (6)  superficial,  subjacent  to  the  visceral  pericardium. 
The  deep  plexus  opens  into  the  superficial,  the  efferents  of  which  form  right  and 
left  collecting  trunks.  The  left  trunks,  two  or  three  in  number,  ascend  in  the  anterior 
longitudinal  sulcus,  receiving,  in  their  course,  vessels  from  both  ventricles.  On 
reaching  the  coronary  sulcus  they  are  joined  by  a  large  trunk  from  the  diaphragmatic 
surface  of  the  heart,  and  then  unite  'to  form  a  single  vessel  which  ascends  between 
the  pulmonary  artery  and  the  left  atrium  and  ends  in  one  of  the  tracheobronchial 


Parairacheal  glands 


R.  recurrent  nerve 

Parairacheal  glands 
Innominate  artery 


L.  tracJieobronchial 


L,  ironchoptdmo- 
nary  glands 


E.  tracheobronchial 
glands 


R.  bronchopulmo- 
nary glands 


Fig.  622. — The  tracheobronchial  lymph  glands.     (From  a  figure  designed  by  M.  Hall6.) 


glands.  The  right  tnmk  receives  its  afferents  from  the  right  atrium  and  from  the 
right  border  and  diaphragmatic  surface  of  the  right  ventricle.  It  ascends  in  the 
posterior  longitudinal  sulcus  and  then  runs  forward  in  the  coronary  sulcus,  and 
passes  up  behind  the  pulmonary  artery,  to  end  in  one  of  the  tracheobronchial 
glands. 

The  Lymphatic  Vessels  of  the  Lungs  originate  in  two  plexuses,  a  superficial  and  a 
deep.  The  superficial  plexus  is  placed  beneath  the  pulmonary  pleura.  The  deep 
accompanies  the  branches  of  the  pulmonary  vessels  and  the  ramifications  of  the 
bronchi.  In  the  case  of  the  larger  bronchi  the  deep  plexus  consists  of  two  net-works 
— one,  submucous,  beneath  the  mucous  membrane,  and  another,  peribronchial, 
outside  the  walls  of  the  bronchi.  In  the  smaller  bronchi  there  is  but  a  single  plexus, 
which  extends  as  far  as  the  bronchioles,  but  fails  to  reach  the  alveoli,  in  the  walls 


THE  LYMPHATICS  OF  THE  THORAX 


719 


I 


of  which  there  are  no  traces  of  lymphatic  vessels.  The  superficial  efferents  turn 
around  the  borders  of  the  lungs  and  the  margins  of  their  fissures,  and  converge  to 
end  in  some  glands  situated  at  the  hilus;  the  deep  efferents  are  conducted  to  the 
hilus  along  the  pulmonary  vessels  and  bronchi,  and  end  in  the  tracheobronchial 
glands.  Little  or  no  anastomosis  occurs  between  the  superficial  and  deep  lym- 
phatics of  the  lungs,  except  in  the  region  of  the  hilus. 

The  Lymphatic  Vessels  of  the  Pleura  consist  of  two  sets — one  in  the  visceral 
and  another  in  the  parietal  part  of  the  membrane.  Those  of  the  visceral  pleura 
drain  into  the  superficial  efferents  of  the  lung,  while  the  lymphatics  of  the  parietal 
pleura  have  three  modes  of  ending,  viz.:  (a)  those  of  the  costal  portion  join  the 
lymphatics  of  the  Intercostales  interni  and  so  reach  the  sternal  glands;  (6)  those 
of  the  diaphragmatic  part  are  drained  by  the  efferents  of  the  diaphragm;  while 
(c)  those  of  the  mediastinal  portion  terminate  in  the  posterior  mediastinal  glands. 

The  Lymphatic  Vessels  of  the  Thymus  end  in  the  anterior  mediastinal,  tracheo- 
bronchial, and  sternal  glands. 

The  Lymphatic  Vessels  of  the  Esophagus  form  a  plexus  around  that  tube,  and  the 
collecting  vessels  from  the  plexus  drain  into  the  posterior  mediastinal  glands. 


BIBLIOGRAPHY. 


IBartels,  p.  :     Das  Lymphgefasssystem,  Bardeleben's  Handbuch  der  Anatomie  des  Menschen, 
1909. 
Clark,  E.  R.  :     Observations  on  Living,  Growing  Lymphatics  in  the  Tail  of  the  Frog  Larva, 
Anat.  Rec,  1909,  iii. 
Huntington,  G.:    The  Genetic  Principles  of  the  Development  of  the  Systemic  Lymphatic 
Vessels  in  the  Mammalian  Embryo,  Anat.  Rec,  1910,  iv. 

Huntington  and  McClure:     The  Anatomy  and  Development  of  the  Jugular  Lymph  Sacs 
in  the  Domestic  Cat,  Am.  Jour.  Anat.,  1910,  x. 

Sappy  :     Description  et  Iconographie  des  Vaisseaux  Lymphatiques,  Paris,  1885. 
Sabin,  F.  R.  :    The  Development  of  the  Lymphatic  System,  Keibel  and   Mall,  Manual  of 
Human  Embryology,  1912. 

Teichman:     Das  Saugadermsystem,  Leipzig,  1861. 


NEUROLOGY. 


I 

II 


II 


t  npHE  Nervous  System  is  the  most  complicated  and  highly  organized  of  the  various 
P  -L  systems  which  make  up  the  human  body.  It  is  the  mechanism  concerned 
with  the  correlation  and  integration  of  various  bodily  processes  and  the  reactions 
and  adjustments  of  the  organism  to  its  environment.  In  addition  the  cerebral 
cortex  is  concerned  with  conscious  life.  It  may  be  divided  into  two  parts,  central 
and  peripheral. 

The  central  nervous  system  consists  of  the  encephalon  or  brain,  contained  within 
the  cranium,  and  the  medulla  spinalis  or  spinal  cord,  lodged  in  the  vertebral  canal ; 
the  two  portions  are  continuous  with  one  another  at  the  level  of  the  upper  border 
of  the  atlas  vertebra. 

The  peripheral  nervous  system  consists  of  a  series  of  nerves  by  which  the  central 
nervous  system  is  connected  with  the  various  tissues  of  the  body.  For  descriptive 
purposes  these  nerves  may  be  arranged  in  two  groups,  cerebrospinal  and  sjrmpathetic, 
the  arrangement,  however,  being  an  arbitrary  one,  since  the  two  groups  are  inti- 
mately connected  and  closely  intermingled.  Both  the  cerebrospinal  and  sym- 
pathetic ner^•es  have  nuclei  of  origin  (the  somatic  efferent  and  s;yTiipathetic  efferent) 
as  well  as  nuclei  of  termination  (somatic  afferent  and  sympathetic  afferent)  in  the 
central  nervous  system.  The  cerebrospinal  nerves  are  forty-three  in  number  on 
either  side — twelve  cranial,  attached  to  the  brain,  and  thirty-one  spinal,  to  the 
medulla  spinalis.  They  are  associated  with  the  functions  of  the  special  and  gen- 
eral senses  and  with  the  voluntary  movements  of  the  body.  The  sympathetic 
nerves  transmit  the  impulses  which  regulate  the  movements  of  the  viscera, 
determine  the  caliber  of  the  bloodvessels,  and  control  the  phenomena  of  secre- 
tion. In  relation  with  them  are  two  rows  of  central  ganglia,  situated  one  on 
either  side  of  the  middle  line  in  front  of  the  vertebral  column;  these  ganglia  are 
intimately  connected  with  the  medulla  spinalis  and  the  spinal  nerves,  and  are  also 
joined  to  each  other  by  vertical  strands  of  nerve  fibers  so  as  to  constitute  a  pair 
of  knotted  cords,  the  sympathetic  trunks,  which  reach  from  the  base  of  the  skull 
to  the  coccyx.  The  sympathetic  nerves  issuing  from  the  ganglia  form  three  great 
prevertebral  plexuses  which  supply  the  thoracic,  abdominal,  and  pelvic  viscera; 
in  relation  to  the  walls  of  these  viscera  intricate  nerve  plexuses  and  numerous 
peripheral  ganglia  are  found. 


STRUCTURE  OF  THE  NERVOUS  SYSTEM. 

The  nervous  tissues  are  composed  of  nerve  cells  and  their  various  processes, 
together  with  a  supporting  tissue  called  neuroglia,  which,  however,  is  found  only 
in  the  brain  and  medulla  spinalis.  Certain  long  processes  of  the  nerve  cells  are  of 
special  importance,  and  it  is  convenient  to  consider  them  apart  from  the  cells; 
they  are  known  as  nerve  fibers. 

To  the  naked  eye  a  difference  is  obvious  between  certain  portions  of  the  brain 
and  medulla  spinalis,  viz.,  the  gray  substance  and  the  white  substance.  The  gray 
substance  is  largely  composed  of  nerve  cells,  W'hile  the  white  substance  contains 
only  their  long  processes,  the  nerve  fibers.  It  is  in  the  former  that  nervous  impres- 
sions are  received,  stored,  and  transformed  into  efferent  impulses,  and  by  the  latter 

(721) 


k: 


722 


NEUROLOGY 


that  they  are  conducted.  Hence  the  gray  substance  forms  the  essential  constituen 
of  all  the  ganglionic  centers,  both  those  in  the  isolated  ganglia  and  those  aggregated 
in  the  brain  and  medulla  spinalis;  while  the  white  substance  forms  the  bulk  of  the 
commissural  portions  of  the  nerve  centers  and  the  peripheral  nerves. 

Neuroglia. — Neuroglia,  the  peculiar  ground.substance  in  which  are  imbedded  the 
true  nervous  constituents  of  the  brain  and  medulla  spinalis,  consists  of  cells  and 
fibers.  Some  of  the  cells  are  stellate  in  shape,  with  ill-defined  cell  body,  and  their 
fine  processes  become  neuroglia  fibers,  which  extend  radially  and  unbranched 
(Fig.  623,  B)  among  the  nerve  cells  and  fibers  which  they  aid  in  supporting.  Other 
cells  give  off  fibers  which  branch  repeatedly  (Fig.  623,  A).  Some  of  the  fibers  start 
from  the  epithelial  cells  lining  the  ventricles  of  the  brain  and  central  canal  of 
the  medulla  spinalis,  and  pass  through  the  nervous  tissue,  branching  repeatedly 
to  end  in  slight  enlargements  on  the  pia  mater.  Thus,  neuroglia  is  evidently  a 
connective  tissue  in  function  but  is  not  so  in  development;  it  is  ectodermal  in 
origin,  whereas  all  connective  tissues  are  mesodermal. 


Fio.  623. — Neuroglia  cells  of  brain  shown  by  Golgi's  method.    A.  Cell  with  branched  processes, 
with  unbranched  processes.     (After  Andriezen.) 


B.  Spider  cell 


Nerve  Cells  (Fig.  624). — Nerve  cells  are  largely  aggregated  in  the  gray  substance 
of  the  brain  and  medulla  spinalis,  but  smaller  collections  of  these  cells  also  form 
the  swellings,  called  ganglia,  seen  on  many  nerves.  These  latter  are  found  chiefly 
upon  the  spinal  and  cranial  nerve  roots  and  in  connection  with  the  sympathetic 
nerves. 

The  nerve  cells  vary  in  shape  and  size,  and  have  one  or  more  processes.  They 
may  be  divided  for  purposes  of  description  into  three  groups,  according  to  the 
number  of  processes  which  they  possess:  (1)  Unipolar  cells,  which  are  found  in 
the  spinal  ganglia;  the  single  process,  after  a  short  course,  divides  in  a  T-shaped 
manner  (Fig.  624,  E).  (2)  Bipolar  cells,  also  found  in.  the  spinal  ganglia  (Fig.  625), 
when  the  cells  are  in  an  embryonic  condition.  They  are  best  demonstrated  in  the 
spinal  ganglia  of  fish.  Sometimes  the  processes  come  off  from  opposite  poles  of 
the  cell,  and  the  cell  then  assumes  a  spindle  shape;  in  other  cells  both  processes 
emerge  at  the  same  point.  In  some  cases  where  two  fibers  are  apparently  con- 
nected with  a  cell,  one  of  the  fibers  is  really  derived  from  an  adjoining  nerve  cell 
and  is  passing  to  end  in  a  ramification  around  the  ganglion  cell,  or,  again,  it  may 
be  coiled  spirally  around  the  nerve  process  which  is  issuing  from  the  cell.  (3) 
Multipolar  cells,  which  are  pyramidal  or  stellate  in  shape,  and  characterized  by 
their  large  size  and  by  the  numerous  processes  which  issue  from  them.     The 


STRUCTURE  OF  THE  NERVOUS  SYSTEM 


723 


processes  are  of  two  kinds:  one  of  them  is  termed  the  axis-cylinder  process  or  axon 
because  it  becomes  the  axis-cyhnder  of  a  nerve  fiber  (Figs.  626,  627,  628).  The 
others  are  termed  the  protoplasmic  processes  or  dendrons ;  they  begin  to  divide  and 


Fio.  624. — Various  forms  of  nerve  cells.  A.  Pyramidal  cell.  B.  Small  multipolar  cell,  in  which  the  axon  quickly 
divides  into  numerous  branches.  C.  Small  fusiform  cell.  D  and  E.  Ganglion  cells  (E  shows  T-shaped  division  <if 
axon),      ax.  Axon,     c    Capsule. 


Sheaih  of 
cell  body 


Nvcleus 


Cell  protoplasm 


—  Axon 


NtuUeolua 

Fig.  626. — Motor  nerve  cell  from  ventral  horn  of  medulla 
spinalis  of  rabbit.  The  angular  and  spindle-shaped  Nissl 
bodies  are  well  shown.     (After  Nissl.) 


subdivide  soon  after  they  emerge  from  the 
U  ■       "W^^^^^^^^^f  ^^^^'  ^^^  finally  end  in  minute  twigs  and  be- 

■  ■  \:^^^:f^^W  come  lost  among  the  other  elements  of  the 

■  ■  X^^^V^^  nervous  tissue. 

B^  ^^^Mf  The  body  of  the  nerve  cell,  known  as  the 

I^H|.  ^l^^-Oendron.  c3rton,  consists  of  a  finely  fibrillated  proto- 

H  ^^B_  ^^j^^Myelin  sheath  plasmic  material,  of  a  reddish  or  yellowish- 

H^|H[  ^^  brown   color,   which   occasionally   presents 

patches  of  a  deeper  tint,  caused  by  the  ag- 
gregation of  pigment  granules  at  one  side  of 
the  nucleus,  as  in  the  substantia  nigra  and 
locus  cseruleus  of  the  brain.  The  protoplasm  also  contains  peculiar  angular  gran- 
ules, w^hich  stain  deeply  with  basic  dyes,  such  as  methylene  blue;  the.se  are  known 
as  Nissl's  granules  (Fig.  626).  They  extend  into  the  dendritic  processes  but  not 
into  the  axis-cylinder;  the  small  clear  area  at  the  point  of  exit  of  the  axon  in 


Fig.  625.; — Bipolar  nerve  cell  from  the  spinal  gan- 
glion of  the  pike.     (After  Kolliker.) 


k 


724 


NEUROLOGY 


some  cell  tx^^es  is  termed  the  cone  of  origin.  These  granules  disappear  {chromato-\ 
lysis)  during  fatigue  or  after  prolonged  stimulation  of  the  nerve  fibers  connected 
with  the  cells.  They  are  supposed  to  represent  a  store  of  nervous  energy,  and 
in  various  mental  diseases  are  deficient  or  absent.  The  nucleus  is,  as  a  rule,  a 
large,^  well-defined,  spherical  body,  often  presenting  an  intranuclear  network,  and 
containing  a  well-marked  nucleolus. 


Fig.  627. — Pyramidal  cell  from  the  cerebral  cortex 
of  a  mouse.    (After  Ramon  y  Cajal.) 


Fio.  628. — Cell  of  Purkinje  from  the  cerebellum.  Golgi 
method.  (Cajal.)  4.  Axon.  b.  Collateral,  c  and  d. 
Dendrons. 


In  addition  to  the  protoplasmic  network  described  above,  each  nerve  cell  may 
be  shown  to  have  delicate  neurofibrils  running  through  its  substance  (Fig.  629); 
these  fibrils  are  continuous  wdth  the  fibrils  of  the  axon,  and  are  believed  to 
convey  nerve  impulses.  Golgi  has  also  described  an  extracellular  network,  which 
is  probably  a  supporting  structure. 

Nerve  Fibers. — Nerve  fibers  are  found  universally  in  the  peripheral  nerves 
and  in  the  white  substance  of  the  brain  and  medulla  spinalis.  They  are  of  two 
kinds — viz.,  meduUated  or  white  fibers,  and  non-meduUated  or  gray  fibers. 

The  medullated  fibers  form  the  white  part  of  the  brain  and  medulla  spinalis,  and 
also  the  greater  part  of  every  cranial  and  spinal  nerve^  and  give  to  these  structures 


STRUCTURE  OF  THE  NERVOUS  SYSTEM 


725 


their  opaque,,  white  aspect.  When  perfectly  fresh  they  appear  to  be  homogeneous; 
but  soon  after  removal  from  the  body  each  fiber  presents,  when  examined  by  trans- 
mitted light,  a  double  outline  or  contour,  as  if  consisting  of  two  parts  (Fig.  630). 
The  central  portion  is  named  the  axis-cylinder;  around  this  is  a  sheath  of  fatty 
material,  staining  black  with  osmic  acid,  named  the  white  substance  of  Schwann 
I*  or  medullary  sheath,  which  gives  to  the  fiber  its  double  contour,  and  the  whole 
is  enclosed  in  a  delicate  membrane,  the  neurolemma,  primitive  sheath,  or  nucleated 
sheath  of  Schwann  (Fig.  633) 


-e 


Fig.  629. — Nerve  cells  of  kitten,  showing  neurofibrils.       (Cajal.)     a.  Axon.     6.  Cyton.    c.   Nucleus,     d.  Neurofibrils. 

The  axis-cylinder  is  the  essential  part  of  the  nerve  fiber,  and  is  always  present; 
the  medullary  sheath  and  the  neurolemma  are  occasionally  absent,  expecially  at 
the  origin  and  termination  of  the  nerve  fiber.  The  axis-cylinder  undergoes  no 
interruption  from  its  origin  in  the  nerve  center  to  its  peripheral  termination,  and 
must  be  regarded  as  a  direct  prolongation  of  a  nerve  cell.  It  constitutes  about 
one-half  or  one-third  of  the  nerve  fiber,  being  greater  in  proportion  in  the  fibers 
of  the  central  organs  than  in  those  of  the  nerves.  It  is  quite  transparent,  and  is 
therefore  indistinguishable  in  a  perfectly  fresh  and  natural  state  of  the  nerve. 
It  is  made  up  of  exceedingly  fine  fibrils,  which  stain  darkly  with  gold  chloride 
(Fig.  632),  and  at  its  termination  may  be  seen  to  break  up  into  these  fibrillse.  The 
fibrillse  have  been  termed  the  primitive  fibrillse  of  Schultze.  The  axis-cylinder  is 
said  by  some  to  be  enveloped  in  a  special  reticular  sheath,  which  separates  it  from 
the  medullary  sheath,  and  is  composed  of  a  substance  called  neurokeratin.  The 
more  common  opinion  is  that  this  network  or  reticulum  is  contained  in  the  white 


726 


NEUROLOGY 


matter  of  Schwann,  and  by  some  it  is    believed  to  be  produced  by  the  action  oJ' 
the  reagents  employed  to  show  it. 

The  medullary  sheath,  or  white  matter  of  Schwami  (Fig.  631),  is  regarded  as  being  a 
fatty  matter  in  a  fluid  state,  which  insulates  and  protects  the  essential  part  of  the; 
nerve — the  axis-cylinder.    It  varies  in  thickness,  in  some  forming  a  layer  of  extreme 


-Incisure 


— Node  of  Ranirier 


\  '   ' 


\i  y  lU 


Fig.  030.— Medullated  nerve  fibers.      X  3-50. 


Incisure 


ATucZeus— l«||jli  I    !11 Node  of  Ranvier 

Neurolemma 

Medullary  sheath 
Axis-cylinder 

Fig.  631. — Diagram  of  longitudinal  sections  of  medullated 
nerve  fibers.     Osmic  acid. 


Axis-cylinder 
Neurolemma 
Medullary  sheath 


Fig.  632. — Transverse  sections  of  medullated  nerve  fibers. 
Osmic  acid. 


Fig.  633. — Diagram  of  medullated  nerve  fibers 
stained  with  osmic  acid.  X  425.  (Schafer.)  R. 
Nodes  of  Ranvier.  a.  Neurolemma,  c.  Nucleus. 


thinness,  so  as  to  be  scarcely  distinguishable,  in  others  forming  about  one-half  the 
nerve  fiber.  The  variation  in  diameter  of  the  nerve  fibers  (from  2  to  IQix)  depends 
mainly  upon  the  amount  of  the  white  substance,  though  the  axis  cylinder  also 
varies  within  certain  limits.  The  medullary  sheath  undergoes  interruptions  in  its 
continuity  at  regular  intervals,  giving  to  the  fiber  the  appearance  of  constriction 


STRUCTURE  OF  THE  NERVOUS  SYSTEM 


727 


ta 


at  these  points:  these  are  known  as  the  nodes  of  Ranvier  (Figs.  631  and  633).  The 
portion  of  nerve  fiber  between  two  nodes  is  called  an  intemodal  segment.  The 
neurolemma  or  primitive  sheath  is  not  interrupted  at  the  nodes,  but  passes  over 
them  as  a  continuous  membrane.  If  the  fiber  be  treated  with  silver  nitrate  the 
reagent  penetrates  the  neurolemma  at  the  nodes,  and  on  exposure  to  light  reduction 
takes  place,  giving  rise  to  the  appearance  of  black  crosses,  Ranvier's  crosses,  on  the 
axis-cylinder.  There  may  also  be  seen  transverse  lines  beyond  the  nodes  termed 
Frommann's  lines  (Fig.  634);  the  significance  of  these  is  not  understood.  In  addi- 
tion to  these  interruptions  oblique  clefts  may  be  seen  in  the  medullary  sheath, 
subdividing  it  into  irregular  portions,  which  are  termed  medullary  segments,  or 
segments  of  Lantermann  (Fig.  631);  there  is  reason  to  believe  that  these  clefts  are 
artificially  produced  in  the  preparation  of  the  specimens.  Medullated  nerve 
fibers,  when  examined  in  the  fresh  condition,  frequently  present  a  beaded  or  vari- 
cose appearance :  this  is  due  to  manipulation  and  pressure  causing  the  oily  matter 
to  collect  into  drops  and  in  consequence  of  the  extreme  delicacy  of  the  primitive 
sheath,  even  slight  pressure  will  cause  the  transudation  of  the  fatty  matter,  which 
collects  as  drops  of  oil  outside  the  membrane. 


Node  of 
Ranvier 


Frommann's 

lines 


Fig.   634. — Medullated  nerve  fibers  stained  with  silver  nitrate 


Fig.  635. — A  small  nervous  branch 
from  the  sympathetic  of  a  mammal. 
a.  Two  medullated  nerve  fibers  among 
a  number  of  gray  nerve  fibers,  h. 


n 


The  neurolemma  or  primitive  sheath  presents  the  appearance  of  a  delicate, 
structureless  membrane.  Here  and  there  beneath  it,  and  situated  in  depressions 
in  the  white  matter  of  Schwann,  are  nuclei  surrounded  by  a  small  amount  of 
protoplasm.  The  nuclei  are  oval  and  somewhat  flattened,  and  bear  a  definite 
relation  to  the  nodes  of  Ranvier,  one  nucleus  generally  lying  in  the  center  of  each 
internode.  The  primitive  sheath  is  not  present  in  all  medullated  nerve  fibers, 
being  absent  in  those  fibers  which  are  found  in  the  brain  and  medulla  spinalis. 

Wallerian  Degeneration. — When  nerve  fibers  are  cut  across,  the  central  ends  of  the  fibers 
degenerate  as  far  as  the  first  node  of  Ranvier;  but  the  peripheral  ends  degenerate  simultaneously 
throughout  their  whole  length.  The  axons  break  up  into  fragments  and  become  surrounded  by 
drops  of  fatty  substance  which  are  formed  from  the  breaking  down  of  the  medullary  sheath. 
The  nuclei  of  the  primitive  sheath  prohferate,  and  finally  absorption  of  the  axons  and  fatty 
substance  occurs.  If  the  cut  ends  of  the  nerve  be  sutured  together  regeneration  of  the  nerve 
fibers  takes  place  by  the  downgrowth  of  axons  from  the  central  end  of  the  nerve.  At  one  time 
it  was  beUeved  that  the  regeneration  was  peripheral  in  origin,  but  this  has  been  disproved,  the 
proUferated  nuclei  in  the  peripheral  portions  taJsing  part  merely  in  the  formation  of  the  so-called 
scaffolding  along  which  the  new  axons  pass. 


728  ^^^^^^  NEUROLOGY 

Non-medullated  Fibers. — Most  of  the  fibers  of  the  sympathetic  system,  and 
some  of  the  cerebrospinal,  consist  of  the  gray  or  gelatinous  nerve  fibers  {fibers  of 
Remak)  (Fig.  635) .  Each  of  these  consists  of  an  axis-cylinder  to  which  nuclei  are 
applied  at  intervals.  These  nuclei  are  believed  to  be  in  connection  with  a  delicate 
sheath  corresponding  with  the  neurolemma  of  the  medullated  nerve  fiber.  In 
external  appearance  the  non-medullated  nerve  fibers  are  semitransparent  and  gray 
or  yellowish  gray.  The  individual  fibers  vary  in  size,  generally  averaging  about 
half  the  size  of  the  medullated  fibers. 

Structure  of  the  Peripheral  Nerves  and  Ganglia. — ^The  cerebrospinal  nerves  con- 
sist of  numerous  nerve  fibers  collected  together  and  enclosed  in  membranous  sheaths 
(Fig.  636).  A  small  bundle  of  fibers,  enclosed  in  a  tubular  sheath,  is  called  a 
funiculus;  if  the  nerve  is  of  small  size,  it  may  consist  only  of  a  single  funiculus;  but 
if  large,  the  funiculi  are  collected  together  into  larger  bundles  or  fasciculi,  which 
are  bound  together  in  a  common  membranous  investment.  In  structure  the 
common  membranous  investment,  or  sheath  of  the  whole  nerve  (epineurium),  as 
well  as  the  septa  given  off  from  it  to  separate  the  fasciculi,  consist  of  connective 
tissue,  composed  of  white  and  yellow  elastic  fibers,  the  latter  existing  in  great 
abundance.  The  tubular  sheath  of  the  funiculi  (perineurium)  is  a  fine,  smooth, 
transparent  membrane,  which  ma}'  be  easily  separated,  in  the  form  of  a  tube,  from 
the  fibers  it  encloses;  in  structure  it  is  made  up  of  connective  tissue,  which  has  a 
distinctly  lamellar  arrangement.  The  nerve  fibers  are  held  together  and  supported 
within  the  funiculus  by  delicate  connective  tissue,  called  the  endoneurium.  It  is 
continuous  with  septa  which  pass  inward  from  the  innermost  layer  of  the  peri- 
neurium, and  shows  a  ground  substance  in  which  are  imbedded  fine  bundles  of 
fibrous  connective  tissue  running  for  the  most  part  longitudinally.  It  serves  to 
support  capillary  vessels,  arranged  so  as  to  form  a  net-work  with  elongated  meshes. 
The  cerebrospinal  nerves  consist  almost  exclusively  of  medullated  nerve  fibers, 
only  a  very  small  proportion  of  non-medullated  being  present. 

The  bloodvessels  supplying  a  nerve  end  in  a  minute  capillary  plexus,  the  vessels 
composing  which  pierce  the  perineurium,  and  run,  for  the  most  part,  parallel  with 
the  fibers;  they  are  connected  together  by  short,  transverse  vessels,  forming  narrow, 
oblong  meshes,  similar  to  the  capillary  system  of  muscle.  P'ine  non-medullated 
nerve  fibers,  vasomotor  fibers,  accompany  these  capillary  vessels,  and  break  up  into 
elementary  fibrils,  which  form  a  network  around  the  vessels.  Horsley  has  demon- 
strated certain  medullated  fibers  running  in  the  epineurium  and  terminating  in 
small  spheroidal  tactile  corpuscles  or  end  bulbs  of  Krause.  These  nerve  fibers,  which 
Marshall  believes  to  be  sensory,  and  which  he  has  termed  nervi  nervonmi,  are  con- 
sidered by  him  to  have  an  important  bearing  upon  certain  neuralgic  pains. 

The  nerve  fibers,  so  far  as  is  at  present  known,  do  not  coalesce,  but  pursue  an 
uninterrupted  course  from  the  center  to  the  periphery.  In  separating  a  nerve, 
however,  into  its  component  funiculi,  it  may  be  seen  that  these  do  not  pursue  a 
perfectly  insulated  course,  but  occasionally  join  at  a  very  acute  angle  with  other 
funiculi  proceeding  in  the  same  direction;  from  this,  branches  are  given  off,  to  joint 
again  in  like  manner  with  other  funiculi.  It  must  be  distinctly  understood,  however, 
that  in  these  communications  the  individual  nerve  fibers  do  not  coalesce,  but 
merely  pass  into  the  sheath  of  the  adjacent  nerve,  become  intermixed  with  its  nerve 
fibers,  and  again  pass  on  to  intermingle  with  the  nerve  fibers  in  some  adjoining 
funiculus. 

Nerves,  in  their  course,  subdivide  into  branches,  and  these  frequently  conununi- 
cate  with  branches  of  a  neighboring  nerve.  The  communications  which  thus  take 
place  form  what  is  called  a  plexus.  Sometimes  a  plexus  is  formed  by  the  primary 
branches  of  the  trunks  of  the  nerves — as  the  cervical,  brachial,  lumbar,  and  sacral 
plexuses — and  occasionally  by  the  terminal  funiculi,  as  in  the  plexuses  formed  at 
the  periphery  of  the  body.    In  the  formation  of  a  plexus,  the  component  nerves 


STRUCTURE  OF  THE  NERVOUS  SYSTEM 


729 


divide,  then  join,  and  again  subdivide  in  such  a  complex  manner  that  the  individual 
funiculi  become  interlaced  most  intricately;  so  that  each  branch  leaving  a  plexus 
may  contain  filaments  from  all  the  primary  nervous  trunks  which  form  the  plexus. 
In  the  formation  also  of  smaller  plexuses  at  the  periphery  of  the  body  there  is  a 
free  interchange  of  the  funiculi  and  primitive  fibers.  In  each  case,  however,  the 
individual  fibers  remain  separate  and  distinct. 

It  is  probable  that  through  this  interchange  of  fibers,  every  branch  passing  off 
from  a  plexus  has  a  more  extensive  connection  with  the  spinal  cord  than  if  it  had 
proceeded  to  its  distribution  without  forming  connections  with  other  nerves. 
Consequently  the  parts  supplied  by  these  nerves  have  more  extended  relations 
with  the  nervous  centers;  by  this  means,  also,  groups  of  muscles  may  be  associated 
for  combined  action. 


/ 


/ 


Epineurium 

Perineurium 


II 


y?^&^ 


FiQ.  63b. — Transverse  section  of  human  tibial  nerve. 

The  sympathetic  nerves  are  constructed  in  the  same  manner  as  the  cerebrospinal 
nerves,  but  consist  mainly  of  non-medullated  fibers,  collected  in  funiculi  and  enclosed 
in  sheaths  of  connective  tissue.  There  is,  however,  in  these  nerves  a  certain  admix- 
ture of  medullated  fibers.  The  number  of  the  latter  varies  in  different  nerves,  and 
may  be  estimated  by  the  color  of  the  nerve.  Those  branches  of  the  sjTnpathetic, 
which  present  a  well-marked  gray  color,  are  composed  chiefly  of  non-medullated 
nerve  fibers,  intermixed  with  a  few  medullated  fibers;  while  those  of  a  white  color 
contain  many  of  the  latter  fibers,  and  few  of  the  former. 

The  cerebrospinal  and  sjTnpathetic  nerve  fibers  convey  various  impressions. 
The  sensory  nerves,  called  also  centripetal  or  afferent  nerves,  transmit  to  the  nervous 
centers  impressions  made  upon  the  peripheral  extremities  of  the  nerves,  and  in  this 
way  the  mind,  through  the  medium  of  the  brain,  becomes  conscious  of  external 
objects.  The  centrifugal  or  efferent  nerves  transmit  impressions  from  the  nervous 
centers  to  the  parts  to  which  the  nerves  are  distributed,  these  impressions  either 
exciting  muscular  contraction  or  influencing  the  processes  of  nutrition,  growth, 
and  secretion. 

Origins  and  Terminations  of  Nerves. — By  the  expression  "the  terminations  of 
nerve  fibers"  is  signified  their  connections  with  the  nerve  centers  and  with  the  parts 


730  ^^^^^  NEUROLOGY 


they  supply.  Th?  former  are  sometimes  called  their  origins  or  central  terminations ; 
the  latter  their  peripheral  terminations. 

Origins  of  Nerves. — The  origin  in  some  cases  is  single — that  is  to  say,  the  whole 
nerve  emerges  from  the  nervous  center  by  a  single  root ;  in  other  instances  the  nerve 
arises  by  two  or  more  roots  which  come  off  from  different  parts  of  the  nerve  center, 
sometimes  widely  apart  from  each  other,  and  it  often  happens,  when  a  nerve  arises 
in  this  way  by  two  roots,  that  the  functions  of  these  two  roots  are  different;  as,  for 
example,  in  the  spinal  nerves,  each  of  which  arises  by  two  roots,  the  anterior  of 
which  is  motor,  and  the  posterior  sensory.  The  point  where  the  nerve  root  or 
roots  emerge  from  the  surface  of  the  nervous  center  is  named  the  superficial  or 
apparent  origin,  but  the  fibers  of  the  nerve  can  be  traced  for  a  certain  distance  into 
the  substance  of  the  ner\'ous  center  to  some  portion  of  the  gray  matter,  which 
constitutes  the  deep  or  real  origin  of  the  nerve.  The  centrifugal  or  efferent  nerve 
fibers  originate  in  the  nerve  cells  of  the  gray  substance,  the  axis-cylinder  processes 
of  these  cells  being  prolonged  to  form  the  fibers.  In  the  case  of  the  centripetal  or 
afferent  nerves  the  fibers  grow  inward  either  from  nerve  cells  in  the  organs  of  special 
sense,  e.  g.,  the  retina,  or  from  nerve  cells  in  the  ganglia.  Having  entered  the  nerve 
center  they  branch  and  send  their  ultimate  twigs  among  the  cells,  without,  however, 
uniting  with  them. 

Peripheral  Terminations  of  Nerves. — Nerve  fibers  terminate  peripherally  in  various 
ways,  and  these  may  be  conveniently  studied  in  the  sensory  and  motor  nerves 
respectively.  The  terminations  of  the  sensory  nerves  are  dealt  with  in  the  section 
on  Sense  Organs. 

Motor  nerves  can  be  traced  into  either  unstriped  or  striped  muscular  fibers.  In 
the  unstriped  or  involuntary  muscles  the  nerves  are  derived  from  the  sympathetic, 
and  are  composed  mainly  of  non-medullated  fibers.  Near  their  terminations  they 
divide  into  numerous  branches,  which  communicate  and  form  intimate  plexuses. 
At  the  junction  of  the  branches  small  triangular  nuclear  bodies  (ganglion  cells)  are 
situated.  From  these  plexuses  minute  branches  are  given  off  which  divide  and 
break  up  into  the  ultimate  fibrillse  of  which  the  nerves  are  composed.  These 
fibrillse  course  between  the  involuntary  muscle  cells,  and,  according  to  Elischer, 
terminate  on  the  surfaces  of  the  cells,  opposite  the  nuclei,  in  minute  swellings. 

In  the  striped  or  voluntary  muscle  the  nerves  supplying  the  muscular  fibers  are 
derived  from  the  cerebrospinal  nerves,  and  are  composed  main'y  of  medullated 
fibers.  The  nerve,  after  entering  the  sheath  of  the  muscle,  breaks  up  into  fibers  or 
bundles  of  fibers,  which  form  plexuses,  and  gradually  divide  until,  as  a  rule,  a  single 
nerve  fiber  enters  a  single  muscular  fiber.  Sometimes,  however,  if  the  muscular 
fiber  be  long,  more  than  one  nerve  fiber  enters  it.  Within  the  muscular  fiber  the 
nerve  terminates  in  a  special  expansion,  called  by  Kiihne,  who  first  accurately 
described  it,  a  motor  end-plate  (Fig.  637).  The  nerve  fiber,  on  approaching  the  mus- 
cular fiber,  suddenly  loses  its  medullary  sheath,  the  neurolemma  becomes  continuous 
with  the  sarcolemma  of  the  muscle,  and  only  the  axis-cylinder  enters  the  muscular 
fiber.  There  it  at  once  spreads  out,  ramifying  like  the  roots  of  a  tree,  immediately 
beneath  the  sarcolemma,  and  becomes  imbedded  in  a  layer  of  granular  matter, 
containing  a  number  of  clear,  oblong  nuclei,  the  whole  constituting  an  end-plate 
from  which  the  contractile  wave  of  the  muscular  fiber  is  said  to  start. 

Ganglia  are  small  aggregations  of  nerve  cells.  They  are  found  on  the  posterior 
roots  of  the  spinal  nerves;  on  the  sensory  roots  of  the  trigeminal,  facial,  glosso- 
pharyngeal, and  vagus  nerves,  and  on  the  acoustic  nerves.  They  are  also  lound  in 
connection  with  the  sympathetic  nerves.  On  section  they  are  seen  to  consist  of  a 
reddish-gray  substance,  traversed  b}-  numerous  white  nerve  fibers;  they  vary  con- 
siderably in  form  and  size;  the  largest  are  found  in  the  cavity  of  the  abdomen; 
the  smallest,  not  visible  to  the  naked  eye,  exist  in  considerable  numbers  upon  the 
nerves  distributed  to  the  different  viscera.    Each  ganglion  is  invested  by  a  smooth 


I 


STRUCTURE  OF  THE  NERVOUl 


and  firm,  closely  adhering,  membranous  envelope,  consisting  of  dense  areolar 
tissue;  this  sheath  is  continuous  with  the  perineurium  of  the  nerves,  and  sends 
numerous  processes  into  the  interior  to  support  the  bloodvessels  supplying  the 
substance  of  the  ganglion. 


II 


Fig.  637. — Muscular  fibers  of  Lacerta  viridis  with  the  terminations  of  nerves,  a.  Seen  in  profile.  P,  P.  The  nerve 
end-plates.  S,  S.  The  base  of  the  plate,  consisting  of  a  granular  mass  with  nuclei,  b.  The  same  as  seen  in  looking  at 
a  perfectly  fresh  fiber,  the  nervous  ends  being  probably  still  excitable.  (The  forms  of  the  variously  divided  plate  can 
hardly  be  represented  in  a  woodcut  by  sufficiently  delicate  and  pale  contours  to  reproduce  correctly  what  is  seen  in 
nature.)    c.  The  same  as  seen  two  hours  after  death  from  poisonmg  by  curare. 

In  structure  all  ganglia  are  essentially  similar,  consisting  of  the  same  structural 
elements — viz.,  ner\e  cells  and  nerve  fibers.  Each  nerve  cell  has  a  nucleated  sheath 
which  is  continuous  with  the  neurolemma  of  the  nerve  fiber  with  which  the  cell  is 
connected.  The  nerve  cells  in  the  ganglia  of  the  spinal  nerves  (Fig.  638)  are  pyri- 
form  in  shape,  and  have  each  a  single  process.  A  short  distance  from  the  cell  and 
while  still  within  the  ganglion  this  process  divides  in  a  T-shaped  manner,  one 
limb  of  the  cross-bar  turning  into  the  medulla  spinalis,  the  other  limb  passing  out- 


X 


li 


Fig.  638. — Transverse  section  of  spinal  ganglion  of  rabbit.  A.  Ganglion.  X  30.  o.  Large  clear  nerve  cell.  6. 
Small  deeply  staining  nerve  cell.  c.  Nuclei  of  capsule.  X  250.  The  lines  in  the  center  point  to  the  corresponding 
cells  in  the  ganglion. 

ward  to  the  periphery.  In  the  sympathetic  ganglia  (Fig.  639)  the  nerve  cells  are 
multipolar  and  each  has  one  axis-cylinder  process  and  several  dendrons;  the  axon 
emerges  from  the  ganglion  as  a  non-medullated  nerve  fiber.  Similar  cells  are  found 
in  the  ganglia  connected  with  the  trigeminal  nerve,  and  these  ganglia  are  therefore 


732 


NEUROLOGY 


regarded  as  the  cranial  portions  of  the  sympathetic  system.  The  "symp 
nervous  system  includes  those  portions  of  the  nervous  mechanism  in  which  a  medul- 
lated  nerve  fiber  from  the  central  system  passes  to  a  ganglion,  sympathetic  or 
peripheral,  from  which  fibers,  usually  non-medullated,  are  distributed  to  such 
structures,  e.  g.,  bloodvessels,  as  are  not  under  voluntary  control.  The  spinal  and 
sympathetic  ganglia  differ  somewhat  in  the  size  and  disposition  of  the  cells  and  in 
the  number  of  nerve  fibers  entering  and  leaving  them.  In  the  spinal  ganglia  (Fig. 
638)  the  nerve  cells  are  much  larger  and  for  the  most  part  collected  in  groups  near 
the  periphery,  while  the  fibers,  which  are  mostly  medullated,  traverse  the  central 

portion  of  the  ganglion;  whereas  in 
Nerve-cells  of  ganglion  the  sympathetic  ganglia  (Fig.  639) 

the  cells  are  smaller  and  distributed 
in  irregular  groups  throughout  the 
whole  ganglion;  the  fibers  also  are 
irregularly  scattered;  some  of  the 
entering  ones  are  medullated,  while 
many  of  those  leaving  the  ganglion 
are  non-medullated. 

Neuron  Theory. — The  nerve  cell 
and  its  processes  collectively  con- 
stitute what  is  termed  a  neuron,  and 
Waldeyer  formulated  the  theory 
that  the  nervous  system  is  built  up 
of  niunerous  neurons,  "  anatomically 
and  genetically  independent  of  one 
another."  According  to  this  theory 
{neuron  tJieory)  the  processes  of 
one  neuron  only  come  into  con- 
tact, and  are  never  in  direct  con- 
tinuity, with  those  of  other  neu- 
rons; while  impulses  are  transmitted  from  one  nerve  cell  to  another  through 
these  points  of  contact,  the  synapses.  The  synapse  or  synaptic  membrane  seems 
to  allow  nervous  impulses  to  pass  in  one  direction  only,  namely,  from  the  terminals 
of  the  axis-cylinder  to  the  dendrons.  This  theory  is  based  on  the  following  facts, 
viz. :  (1)  embryonic  nerve  cells  or  neuroblasts  are  entirely  distinct  from  one  another; 
(2)  when  nervous  tissues  are  stained  by  the  Golgi  method  no  continuity  is  seen  even 
between  neighboring  neurons;  and  (3)  w^hen  degenerative  changes  occur  in  nervous 
tissue,  either  as  the  result  of  disease  or  experiment,  they  never  spread  from  one 
neuron  to  another,  but  are  limited  to  the  individual  neurons,  or  groups  of  neurons, 
primarily  affected.  It  must,  however,  be  added  that  within  the  past  few  years  the 
validity  of  the  neuron  theory  has  been  called  in  question  by  certain  eminent  histol- 
ogists,  who  maintain  that  by  the  employment  of  more  delicate  histological  methods, 
minute  fibrils  can  be  followed  from  one  nerve  cell  into  another.  Their  existence, 
however,  in  the  living  is  open  to  question.  Mott  and  Marinesco  made  careful 
examinations  of  living  cells,  using  even  the  ultramicroscope  and  agree  that  neither 
Nissl  bodies  nor  neurofibrils  are  present  in  the  living  state. 

For  the  present  we  may  look  upon  the  neurons  as  the  units  or  structural  elements 
of  the  nervous  system.  All  the  neurons  are  present  at  birth  which  are  present  in 
the  adult,  their  division  ceases  before  birth;  they  are  not  all  functionally  active 
at  birth,  but  gradually  assume  functional  activity.  There  is  no  indication  of  any 
regeneration  after  the  destruction  of  the  cell-body  of  any  individual  neuron. 

Fasciculi,  tracts  or  fiber  systems  are  groups  of  axons  having  homologous  origin 
and  homologous  distribution  (as  regards  their  collaterals,  subdivisions  and  ter- 
minals) and  are  often  named  in  accordance  with  their  origin  and  termination,  the 


I 


FiQ.  639. — Transverse  section  of  sympathetic  ganglion  of  cat. 
A.  Ganglion.     X  50.    a.  A  nerve  cell.     X  250. 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 


733 


name  of  the  nucleus  or  the  location  of  the  cell  body  from  which  the  axon  or  fiber 
arises  preceding  that  of  the  nucleus  or  location  of  its  termination.  A  given  topo- 
graphical area  seldom  represents  a  pure  tract,  as  in  most  cases  fibers  of  different 
systems  are  mixed. 

DEVELOPMENT  OF  THE  NERVOUS  SYSTEM. 

The  entire  nervous  system  is  of  ectodermal  origin,  and  its  first  rudiment  is  seen 
in  the  neural  groove  which  extends  along  the  dorsal  aspect  of  the  embryo  (Fig. 
17).  By  the  elevation  and  ultimate  fusion  of  the  neural  folds,  the  groove  is  con- 
verted into  the  neural  tube  (Fig.  19).  The  anterior  end  of  the  neural  tube  becomes 
expanded  to  form  the  three  primary  brain-vesicles;  the  cavity  of  the  tube  is  sub- 
sequently modified  to  form  the  ventricular  cavities  of  the  brain,  and  the  central 
canal  of  the  medulla  spinalis;  from  the  wall  the  nervous  elements  and  the  neuroglia 
of  the  brain  and  medulla  spinalis  are  developed. 


Roof-plate 

Oval  bundle 
Posterior  nerve  root 

Central  canal 
Ependymal  layer 

Mantle  layer 

Anterior  nerve-  rootn 

■Marginal  layer 
-Floor-plate 


fh 


Fig.  640. — Section  of  medulla  spinalis  of  a  four  weeks'  embryo.     (His.) 


The  Medulla  Spinalis. — At  first  the  wall  of  the  neural  tube  is  composed  of  a 
single  layer  of  columnar  ectodermal  cells.  Soon  the  side-walls  become  thickened, 
while  the  dorsal  and  ventral  parts  remain  thin,  and  are  named  the  roof-  and  floor- 
plates  (Figs.  640,  642,  643).    A  transverse  section  of  the  tube  at  this  stage  presents 

n  oval  outline,  while  its  lumen  has  the  appearance  of  a  slit.  The  cells  which 
constitute  the  wall  of  the  tube  proliferate  rapidly,  lose  their  cell-boundaries  and 
form  a  syncytium.  This  syncytium  consists  at  first  of  dense  protoplasm  with 
closely  packed  nuclei,  but  later  it  opens  out  and  forms  a  looser  meshwork  with 
the  cellular  strands  arranged  in  a  radiating  manner  from  the  central  canal.    Three 

ayers  may  now  be  defined — an  internal  or  ependymal,  an  intermediate  or  mantle, 
and  an  external  or  marginal.  The  ependymal  layer  is  ultimately  converted  into  the 
ependyma  of  the  central  canal;  the  processes  of  its  cells  pass  outward  toward 
the  periphery  of  the  medulla  spinalis.  The  marginal  layer  is  devoid  of  nuclei,  and 
later  forms  the  supporting  framework  for  the  white  funiculi  of  the  medulla  spinalis. 
The  mantle  layer  represents  the  whole  of  the  future  gray  columns  of  the  medulla 
spinalis;  in  it  the  cells  are  differentiated  into  two  sets,  viz.,  (a)  spongioblasts  or 
young  neuroglia  cells,  and  (6)  germinal  cells,  which  are  the  parents  of  the  neuroblasts 


k 


734 


NEUROLOGY 


I 


or  young  nerve  cells  (Fig.  641).  The  spongioblasts  are  at  first  connected  to  ono 
another  by  filaments  of  the  syncytium ;  in  these,  fibrils  are  developed,  so  that  as  the 
neuroglial  cells  become  defined  they  exhibit  their  characteristic  mature  appearance 
with  multiple  processes  proceeding  from  each  cell.    The  germinal  cells  are  large. 


Germinal  cell 


Neuroblast 


'Nuclei  of  spongioblasts 


Syncytium. 


Fia.  641. 


-Transverse  section  of  the  medulla  spinalis  of  a  human  embryo  at  the  beginning  of  the  fourth  week. 
The  left  edge  of  the  figure  corresponds  to  the  lining  of  the  central  canal.     (His.) 


round  or  oval,  and  first  make  their  appearance  between  the  ependymal  cells  on 
the  sides  of  the  central  canal.  They  increase  rapidly  in  number,  so  that  by  the 
fourth  week  they  form  an  almost  continuous  layer  on  each  side  of  the  tube.  No 
germinal  cells  are  found  in  the  roof-  or  floor-plates;  the  roof-plate  retains,  in  certain 


Roof-plate 

Alar  lamina 


Oval  bundle 


Posterior 

nerve-root 
Central  canal 

Ependymal 

layer 
Lateral 

funiculus 
Basal  lamina 


Floor-plate 


^  Anterior 
nerve-root 


Anterior  funiculus 


Fasciculus  gracilis  [Posterior 

Fascicidus  cuneatuJ     fv-nicvlua 


Post,  nerve-root 


Lateral 
funiculus 

Central  canal 

Anterior 
column 


Anterior  funiculus 


Fias.  642,  643. — Transverse  sections  through  the  medullse  spinales  of  human  embryos.      (His.) 
Fig.  642,  aged  about  four  and  a  half  weeks.     Fig.  643,  aged  about  three  months. 


regions  of  the  brain,  its  epithelial  character;  elsewhere,  its  cells  become  spongio- 
blasts. By  subdivision  the  germinal  cells  give  rise  to  the  neuroblasts  or  young 
nerve  cells,  which  migrate  outward  from  the  sides  of  the  central  canal  into  the 
mantle  layer  and  neural  crest,  and  at  the  same  time  become  pear-shaped;  the 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM  735 


Hptapering  part  of  the  cell  undergoes  still  further  elongation,  and  forms  the  axis- 
cylinder  of  the  cell. 

The  lateral  walls  of  the  medulla  spinalis  continue  to  increase  in  thickness,  and 
|the  canal  widens  out  near  its  dorsal  extremity,  and  assumes  a  somewhat  lozenge- 
shaped  appearance. .  The  widest  part  of  the  canal  serves  to  subdivide  the  lateral 
wall  of  the  neural  tube  into  a  dorsal  or  alar,  and  a  ventral  or  basal  lamina  (Figs.  642, 
643) ,  a  subdivision  which  extends  forward  into  the  brain.  At  a  later  stage  the  ventral 
part  of  the  canal  widens  out,  while  the  dorsal  part  is  first  reduced  to  a  mere  slit 
■■and  then  becomes  obliterated  by  the  approximation  and  fusion  of  its  walls;  the 
^ventral  part  of  the  canal  persists  and  forms  the  central  canal  of  the  adult  medulla 
spinalis.  The  caudal  end  of  the  canal  exhibits  a  conical  expansion  which  is  known 
as  the  terminal  ventricle. 

The  ventral  part  of  the  mantle  layer  becomes  thickened,  and  on  cross-section 
appears  as  a  triangular  patch  between  the  marginal  and  ependymal  layers.  This 
thickening  is  the  rudiment  of  the  anterior  column  of  gray  substance,  and  contains 
-many  neuroblasts,  the  axis-cylinders  of  which  pass  out  through  the  marginal  layer 
and  form  the  anterior  roots  of  the  spinal  nerves  (Figs.  640,642, 643) .  The  thickening 
of  the  mantle  layer  gradually  extends  in  a  dorsal  direction,  and  forms  the  posterior 
column  of  gray  substance.  The  axons  of  many  of  the  neuroblasts  in  the  alar  lamina 
run  forward,  and  cross  in  the  floor-plate  to  the  opposite  side  of  the  medulla  spinalis; 
these  form  the  rudiment  of  the  anterior  white  commissure. 

About  the  end  of  the  fourth  week  nerve  fibers  begin  to  appear  in  the  marginal 
layer.  The  first  to  develop  are  the  short  intersegmental  fibers  from  the  neuro- 
blasts in  the  mantle  zone,  and  the  fibers  of  the  dorsal  nerve  roots  which  grow  into 
the  medulla  spinalis  from  the  cells  of  the  spinal  ganglia.  By  the  sixth  week  these 
dorsal  root  fibers  form  a  well-defined  oval  bundle  in  the  peripheral  part  of  the  alar 
lamina;  this  bundle  gradually  increases  in  size,  and  spreading  toward  the  middle 
line  forms  the  rudiment  of  the  posterior  funiculus.  The  long  intersegmental  fibers 
begin  to  appear  about  the  third  month  and  the  cerebrospinal  fibers  about  the  fifth 
month.  All  nerve  fibers  are  at  first  destitute  of  medullary  sheaths.  Different 
groups  of  fibers  receive  their  sheaths  at  different  times — the  dorsal  and  ventral 
nerve  roots  about  the  fifth  month,  the  cerebrospinal  fibers  after  the  ninth  month. 
By  the  growth  of  the  anterior  columns  of  gray  substance,  and  by  the  increase 
in  size  of  the  anterior  funiculi,  a  furrow  is  formed  between  the  lateral  halves  of  the 
cord  anteriorly;  this  gradually  deepens  to  form  the  anterior  median  fissure.  The 
_  -mode  of  formation  of  the  posterior  septum  is  somewhat  uncertain.  Many  believe 
I  fchat  it  is  produced  by  the  growing  together  of  the  walls  of  the  posterior  part  of  the 
central  canal  and  by  the  development  from  its  ependymal  cells  of  a  septum  of 
fibrillated  tissue  which  separates  the  future  funiculi  graciles. 

■  k     Up  to  the  third  month  of  fetal  life  the  medulla  spinalis  occupies  the  entire 

■  Hength  of  the  vertebral  canal,  and  the  spinal  nerves  pass  outward  at  right  angles 

to  the  medulla  spinalis.  From  this  time  onward,  the  vertebral  column  grows  more 
rapidly  than  the  medulla  spinalis,  and  the  latter,  being  fixed  above  through  its 
continuity  with  the  brain,  gradually  assumes  a  higher  position  within  the  canal. 
By  the  sixth  month  its  lower  end  reaches  only  as  far  as  the  upper  end  of  the  sacrum; 
at  birth  it  is  on  a  level  with  the  third  lumbar  vertebra,  and  in  the  adult  with  the 
lower  border  of  the  first  or  upper  border  of  the  second  lumbar  vertebra.  A  delicate 
filament,  the  filum  terminale,  extends  from  its  lower  end  as  far  as  the  coccyx. 

The  Spinal  Nerves. — Each  spinal  nerve  is  attached  to  the  medulla  spinalis  by 
an  anterior  or  ventral  and  a  posterior  or  dorsal  root. 

■I  The  fibers  of  the  anterior  roots  are  formed  by  the  axons  of  the  neuroblasts 
pwrhich  lie  in  the  ventral  part  of  the  mantle  layer;  these  axons  grow  out  through  the 
overlying  marginal  laver  and  become  grouped  to  form  the  anterior  nerve  root 
(Fig.  641). 


I 


736 


NEUROLOGY 


The  fibers  of  the  posterior  roots  are  developed  from  the  cells  of  the  spinal  ganglia. 
Before  the  neural  groove  is  closed  to  form  the  neural  tube  a  ridge  of  ectodermal 
cells,  the  ganglion  ridge  or  neural  crest  (Fig.  644),  appears  along  the  prominent 
margin  of  each  neural  fold.  When  the  folds  meet  in  the  middle  line  the  two  gan- 
glion ridges  fuse  and  form  a  wedge-shaped  area  along  the  line  of  closure  of  the  tube. 
The  cells  of  this  area  proliferate  rapidly  opposite  the  primitive  segments  and  then 
migrate  in  a  lateral  and  ventral  direction  to  the  sides  of  the  neural  tube,  where  they 
ultimately  form  a  series  of  oval-shaped  masses,  the  future  spinal  ganglia.  These 
ganglia  are  arranged  symmetrically  on  the  two  sides  of  the  neural  tube  and,  except 
in  the  region  of  the  tail,  are  equal  in  number  to  the  primitive  segments.  The  cells 
of  the  ganglia,  like  the  cells  of  the  mantle  layer,  are  of  two  kinds,  viz.,  spongio- 
blasts and  neuroblasts.  The  spongioblasts  develop  into  the  neuroglial  cells  of  the 
ganglia.  The  neuroblasts  are  at  first  round  or  oval  in  shape,  but  soon  assume 
the  form  of  spindles  the  extremities  of  which  gradually  elongate  into  central  and 

peripheral  processes.  The  central 
processes  grow  medialward  and,  be- 
coming connected  with  the  neural 
tube,  constitute  the  fibers  of  the 
posterior  nerve  roots,  while  the  per- 
ipheral processes  grow  lateralward  to 
mingle  with  the  fibers  of  the  anterior 
root  in  the  spinal  nerve.  As  de- 
velopment proceeds  the  original 
bipolar  form  of  the  cells  changes; 
the  two  processes  become  approxi- 
mated until  they  ultimately  arise 
from  a  single  stem  in  a  T-shaped 
manner.  Only  in  the  ganglia  of  the 
acoustic  nerve  is  the  bipolar  form 
retained.  More  recent  observers  hold, 
however,  that  the  T-form  is  derived 
from  the  branching  of  a  single  pro- 
cess which  grows  out  from  the  cell. 

The  anterior  or  ventral  and  the  pos- 
terior or  dorsal  nerve  roots  join  imme- 
diately beyond  the  spinal  ganglion  to  form  the  spinal  nerve,  which  then  divides  into 
anterior,  posterior,  and  visceral  divisions.  The  anterior  and  posterior  divisions 
proceed  directly  to  their  areas  of  distribution  without  further  association  with 
ganglion  cells  (Fig.  645).  The  visceral  divisions  are  distributed  to  the  thoracic, 
abdominal,  and  pelvic  viscera,  to  reach  which  they  pass  through  the  sympathetic 
trunk,  and  many  of  the  fibers  form  arborizations  around  the  ganglion  cells  of  this 
trunk.  Visceral  branches  are  not  given  off  from  all  the  spinal  nerves;  they  form 
two  groups,  viz.,  (a)  thoracico-lumbar,  from  the  first  or  second  thoracic,  to  the 
second  or  third  lumbar  nerves;  and  {h)  pelvic,  from  the  second  and  third,  or 
third  and  fourth  sacral  nerves. 

The  Brain. — The  brain  is  developed  from  the  anterior  end  of  the  neural  tube, 
which  at  an  early  period  becomes  expanded  into  three  vesicles,  the  primary  cerebral 
vesicles  (Fig.  18).  These  are  marked  off  from  each  other  by  intervening  con- 
strictions, and  are  named  the  fore-brain  or  prosencephalon,  the  mid-brain  or 
mesencephalon,  and  the  hind-brain  or  rhombencephalon — the  last  being  continuous 
with  the  medulla  spinalis.  As  the  result  of  unequal  growth  of  these  different 
parts  three  flexures  are  formed  and  the  embryonic  brain  becomes  bent  on  itself 
in  a  somewhat  zigzag  fashion;  the  two  earliest  flexures  are  concave  ventrally 
and  are  associated  with  corresponding  flexures  of  the  whole  head.    The  first  flexure 


Fia.  644. — Two  stages  in  the  development  of  the  neural 
crest  in  the  human  embryo.     (Lenhossdk.) 


DEVELOPMEm 

appears  in  the  region  of  the  mid-brain,  and  is  named  the  ventral  cephalic  flexure 
(Fig.  650).  By  means  of  it  the  fore-brain  is  bent  in  a  ventral  direction  around 
the  anterior  end  of  the  notochord  and  fore-gut,  with  the  result  that  the  floor  of 
the  fore-brain  comes  to  lie  almost  parallel  with  that  of  the  hind-brain.  This 
flexure  causes  the  mid-brain  to  become,  for  a  time,  the  most  prominent  part  of 
the  brain,  since  its  dorsal  surface  corresponds  with  the  convexity  of  the  curve. 


Audilory  vesicle 


Facial  and  acoustic  Ns. 
Trigeminal  N. 


Trochlear  N. 


Glossopharyngeal  N. 
Vagus  N. 

Accessory  N. 
Hypoglossal  N. 


Mesencephalon —  ' 
Oculomotor  N.~^ 


Dieticephalon 


Cerebral 
hemisphere 


Froriep's 
ganglion 

I.  Cervieal 


Phrenic  N. 


)f^L::,sm\—  I.  Thoracic 


Vitelline  loop 
Tail 


I.  Coccygeal 


I.  Lumbar 


Sacral 


Fig.  645. — Reconstruction  of  periphera   nerves  of  a  human  embryo  of  10.2  mm.     (After  His.)     The  abducent  nerve 
is  not  labelled,  but  is  seen  passing  forward  to  the  eye  under  the  mandibular  and  maxillary  nerves. 


t 

I 


The  second  bend  appears  at  the  junction  of  the  hind-brain  and  medulla  spinalis. 
This  is  termed  the  cervical  flexure  (Fig.  652),  and  increases  from  the  third  to  the 
end  of  the  fifth  week,  when  the  hind-brain  forms  nearly  a  right  angle  with  the 
medulla  spinalis;  after  the  fifth  week  erection  of  the  head  takes  place  and  the  cervi- 
cal flexure  diminishes  and  disappears.  The  third  bend  is  named  the  pontine  flexure 
(Fig.  652),  because  it  is  found  in  the  region  of  the  future  pons  Varoli,  It  differs 
from  the  other  two  in  that  (a)  its  convexity  is  forward,  and  (b)  it  does  not  affect 

47 


738 


NEUROLOGY 


the  head.  The  lateral  walls  of  the  brain-tube,  like  those  of  the  medulla  spmaiie" 
are  divided  by  internal  furrows  into  alar  or  dorsal  and  basal  or  ventral  laminse 
(Fig.  646). 

The  Hind-brain  or  Rhombencephalon. — The  cavity  of  the  hind-brain  becomes 
the  fourth  ventricle.     At  the  time  when  the  ventral  cephalic  flexure  makes  its 


I 


jk 


Fig.  646. — Diagram  to  illustrate  the  alar  and 
basal  laminse  of  brain  vesicles.     (His.) 


Roof-plate 


Alar  lamina 

Furrow  between 
alar  and  basal 
h  1       lamince 

'^j1 — Basal  lamina 


Vagtis  nerve 
Hypoglossal  nerve 
Floor-plate 

Fig.  647. — Transverse  section  of  medulla  oblongata  of  human 
embryo.      X  32.     (KoUmann.) 


appearance,  the  length  of  the  hind-brain  exceeds  the  combined  lengths  of  the  other 
two  vesicles.  Immediately  behind  the  mid-brain  it  exhibits  a  marked  constriction, 
the  isthmus  rhombencephali  (Fig.  650,  Isthmus),  which  is  best  seen  when  the  brain  is 
viewed  from  the  dorsal  aspect.  From  the  isthmus  the  anterior  medullary  velum 
and  the  superior  peduncle  of  the  cerebellum   are  formed.      It  is  customary  to 


Rhombic  lip 


Vagus  nerve 


Hypoglossal  nerve 


Floor-plate 
Fig.  648. — Transverse  section  of  medulla  oblongata  of  human  embryo.     (After  His.) 


divide  the  rest  of  the  hind-brain  into  two  parts,  viz.,  an  upper,  called  the  meten- 
cephalon,  and  a  lower,  the  myelencephalon.  The  cerebellum  is  developed  by  a 
thickening  of  the  roof,  and  the  pons  by  a  thickening  in  the  floor  and  lateral  walls 
of  the  metencephalon.  The  floor  and  lateral  walls  of  the  myelencephalon  are 
thickened  to  form  the  medulla  oblongata;  its  roof  remains  thin,  and,  retaining  to 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 


739 


'•  a  great  extent  its  epithelial  nature,  is  expanded  in  a  lateral  direction.  Later,  by 
the  growth  and  backward  extension  of  the  cerebellum,  the  roof  is  folded  inward 
toward  the  cavity  of  the  fourth  ventricle;  it  assists  in  completing  the  dorsal  wall 

[of  this  cavity,  and  is  also  invaginated  to  form  the  ependymal  covering  of  its  choroid. 

'plexuses.    Above  it  is  continuous  with  the  posterior  medullary  velum;  below%  with. 

[the  obex  and  ligulse. 

The  development  of  the  medulla  oblongata  resembles  that  of  the  medulla  spinalis, 

I  but  at  the  same  time  exhibits  one  or  two  interesting  modifications.   On  transverse 

[section  the  myelencephalon  at  an  early  stage  is  seen  to  consist  of  two  lateral  walls, 
connected  across  the  middle  line  by  floor-  and  roof-plates  (Figs.  647  and  648). 
Each  lateral  wall  consists  of  an  alar  and  a  basal  lamina,  separated  by  an  internal 
furrow,  the  remains  of  which  are  represented  in  the  adult  brain  by  the  sulcus 
limitans  on  the  rhomboid  fossa.    The  contained  cavity  is  more  or  less  triangular 


TcEnia  j  WLfercbf '  hi  '•; 

Bhombic  lip     \  ^^KHSt 


V.  N.  Motor  roct 
V.  N.  Sensory  root 

Oanglia  of  VII.  and 
VIII.  Ns. 

Auditory  vesicle 


Fia.  649. — Hind-brain  of  a  human  embryo  of  three 
months — viewed  from  behind  and  partly  from  left  side. 
(From  model  by  His.) 


FiQ.  650. — Exterior  of  brain  of  human  embryo  of  four 
and  a  half  weeks.     (From  model  by  His.) 


II 


in  outline,  the  base  being  formed  by  the  roof-plate,  which  is  thin  and  greatly 
expanded  transversely.  Pear-shaped  neuroblasts  are  developed  in  the  alar  and 
basal  laminae,  and  their  narrow  stalks  are  elongated  to  form  the  axis-cylinders  of 
the  nerve  fibers.  Opposite  the  furrow  or  boundary  between  the  alar  and  basal 
laminae  a  bundle  of  nerve  fibers  attaches  itself  to  the  outer  surface  of  the  alar 
lamina.  This  is  named  the  tractus  solitarius  (Fig.  648),  and  is  formed  by  the  sensory 
fibers  of  the  glossopharyngeal  and  vagus  nerves.  It  is  the  homologue  of  the  oval 
bundle  seen  in  the  medulla  spinalis,  and,  like  it,  is  developed  by  an  ingrowth  of 
fibers  from  the  ganglia  of  the  neural  crest.  At  first  it  is  applied  to  the  outer  surface 
of  the  alar  lamina,  but  it  soon  becomes  buried,  owing  to  the  growth  over  it  of  the 
neighboring  parts.  By  the  fifth  week  the  dorsal  part  of  the  alar  lamina  bends 
in  a  lateral  direction  along  its  entire  length,  to  form  what  is  termed  the  rhombic 
lip  (Figs.  648,  649).    Within  a  few  days  this  lip  becomes  applied  to,  and  unites 


i_ 


740 


NEUROLOGY 


with,  the  outer  surface  of  the  main  part  of  the  alar  lamina,  and  so  covers  in  th<; 
tractus  solitarius  and  also  the  spinal  root  of  the  trigeminal  nerve;  the  nodulus 
and  flocculus  of  the  cerebellum  are  developed  from  the  rhombic  lip. 

Neuroblasts  accumulate  in  the  mantle  layer;  those  in  the  basal  lamina  corre- 
spond with  the  cells  in  the  anterior  gray  column  of  the  medulla  spinalis,  and,  like 
them,  give  origin  to  motor  nerve  fibers;  in  the  medulla  oblongata  they  are,  however, 
arranged  in  groups  or  nuclei,  instead  of  forming  a  continuous  column.  From  th(; 
alar  lamina  and  its  rhombic  lip,  neuroblasts  migrate  into  the  basal  lamina,  and 
become  aggregated  to  form  the  olivary  nuclei,  while  many  send  their  axis-cylinders 
through  the  floor-plate  to  the  opposite  side,  and  thus  constitute  the  rudiment  of 
the  raphe  of  the  medulla  oblongata.  By  means  of  this  thickening  of  the  ventral 
portion,  the  motor  nuclei  are  buried  deeply  in  the  interior,  and,  in  the  adult,  are 
found  close  to  the  rhomboid  fossa.    This  is  still  further  accentuated:  (a)  by  the 

development  of  the  pyramids,  which 
are  formed  about  the  fourth  month 
by  the  downward  growth  of  the 
motor  fibers  from  the  cerebral  cortex; 
and  (6)  by  the  fibers  which  pass  to 
and  from  the  cerebellum.  On  the 
rhomboid  fossa  a  series  of  six  tem- 
porary furrows  appears;  these  are 
termed  the  rhombic  grooves.  They 
bear  a  definite  relationship  to  certain 
of  the  cranial  nerves;  thus,  from 
before  backw^ard  the  first  and  second 
grooves  overlie  the  nucleus  of  the 
trigeminal;  the  third,  the  nucleus  of 
the  facial;  the  fourth,  that  of  the  ab- 
ducent; the  fifth,  that  of  the  glosso- 
pharyngeal; and  the  sixth,  that  of 
the  vagus. 

The  pons  is  developed  from  the 
ventro-lateral  wall  of  the  meten- 
cephalon  by  a  process  similar  to  that 
which  has  been  described  for  the 
medulla  oblongata. 

The  cerebellum  is  developed  in 
the  roof  of  the  anterior  part  of 
the  hind-brain  (Figs.  649  to  654). 
The  alar  laminae  of  this  region 
become  thickened  to  form  two 
lateral  plates  which  soon  fuse  in  the  middle  line  and  produce  a  thick  lamina  which 
roofs  in  the  upper  part  of  the  cavity  of  the  hind-brain  vesicle;  this  constitutes 
the  rudiment  of  the  cerebellum,  the  outer  surface  of  which  is  originally  smooth 
and  convex.  The  fissures  of  the  cerebellum  appear  first  in  the  vermis  and  floccular 
region,  and  traces  of  them  are  found  during  the  third  month;  the  fissures  on  the 
cerebellar  hemispheres  do  not  appear  until  the  fifth  month.  The  primitive  fissures 
are  not  developed  in  the  order  of  their  relative  size  in  the  adult — thus  the  hori- 
zontal sulcus  in  the  fifth  month  is  merely  a  shallow  groove.  The  best  marked 
of  the  early  fissures  are:  (a)  the  fissura  prima  between  the  developing  culmen  and 
declive,  and  {h)  the  fissura  secunda  between  the  future  pyramid  and  uvula.  The 
flocculus  and  nodule  are  developed  from  the  rhombic  lip,  and  are  therefore  recog- 
nizable as  separate  portions  before  any  of  the  other  cerebellar  lobules.  The 
groove  produced  by  the  bending  over  of  the  rhombic  lip  is  here  known  as  the 


I 


Fio.  651.— Brain  of  human  embryo  of  four  and  a  half  weeks, 
showing  interior  of  fore-brain.  (From  model  by  Hia.) 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 


741 


floccular  fissure;  when  the  two  lateral  walls  fuse,  the  right  and  left  floccular  fissures 
join  in  the  middle  line  and  their  central  part  becomes  the  post-nodular  fissure. 

On  the  ventricular  surface  of  the  cerebellar  lamina  a  transverse  furrow,  the 
incisura  fastigii,  appears,  and  deepens  to  form  the  tent-like  recess  of  the  roof  of  the 
fourth  ventricle.  The  rudiment  of  the  cerebellum  at  first  projects  in  a  dorsal 
direction;  but,  by  the  backward  growth  of  the  cerebrum,  it  is  folded  downward  and 
somewhat  flattened,  and  the  thin  roof-plate  of  the  fourth  ventricle,  originally 
continuous  with  the  posterior  border  of  the  cerebellum,  is  projected  inward  toward 
the  cavity  of  the  ventricle. 

The  Mid-brain  or  Mesencephalon. — The  mid-brain  (Figs.  650  to  654)  exists  for  a 
time  as  a  thin-walled  cavity  of  some  size,  and  is  separated  from  the  isthmus  rhomb- 
encephali  behind,  and  from  the  fore-brain  in  front,  by  slight  constrictions.  Its 
cavity  becomes  relatively  reduced  in  diameter,  and  forms  the  cerebral  aqueduct 
of  the  adult  brain.  Its  basal  laminae  increase  in  thickness  to  form  the  cerebral 
peduncles,  which  are  at  first  of  small  size,  but  rapidly  enlarge  after  the  fourth  month. 

Oanglion  habemdce 


Fig.  652. — Exterior  of  brain  of  human  embryo  of  five  weeks.     (From  model  by  His.) 


The  neuroblasts  of  these  laminae  are  grouped  in  relation  to  the  sides  and  floor 
of  the  cerebral  aqueduct,  and  constitute  the  nuclei  of  the  oculomotor  and  trochlear 
nerves,  and  of  the  mesencephalic  root  of  the  trigeminal  nerve.  By  a  similar 
thickening  process  its  alar  laminae  are  developed  into  the  quadrigeminal  lamina. 
The  dorsal  part  of  the  wall  for  a  time  undergoes  expansion,  and  presents  an  internal 
median  furrow  and  a  corresponding  external  ridge;  these,  however,  disappear, 
and  the  latter  is  replaced  by  a  groove.  Subsequently  two  oblique  furrows  extend 
medialward  and  backward,  and  the  thickened  lamina  is  thus  subdivided  into  the 
superior  and  inferior  colliculi. 

The  Fore-brain  or  Prosencephalon. — A  transverse  section  of  the  early  fore-brain 
shows  the  same  parts  as  are  displayed  in  similar  sections  of  the  medulla  spinalis 
and  medulla  oblongata,  viz.,  a  pair  of  thick  lateral  walls  connected  by  thin  floor- 
and  roof-plates.  Moreover,  each  lateral  wall  exhibits  a  division  into  a  dorsal  or 
alar  and  a  ventral  or  basal  lamina  separated  internally  by  a  furrow  termed  the  sulcus 


742 


NEUROLOGY 


I 


of  Monro.  This  sulcus  ends  anteriorly  at  the  medial  end  of  the  optic  stalk,  and  in 
the  adult  brain  is  retained  as  a  slight  groove  extending  backward  from  the  inter- 
ventricular foramen  to  the  cerebral  aqueduct. 

At  a  very  early  period — in  some  animals  before  the  closure  of  the  cranial  part  of 
the  neural  tube — two  lateral  diverticula,  the  optic  vesicles,  appear,  one  on  either 
side  of  the  fore-brain;  for  a  time  they  communicate  with  the  cavity  of  the  fore-brain 
by  relatively  wide  openings.  The  peripheral  parts  of  the  vesicles  expand,  while 
the  proximal  parts  are  reduced  to  tubular  stalks,  the  optic  stalks.  The  optic  vesicle 
gives  rise  to  the  retina  and  the  epithelium  on  the  back  of  the  ciliary  body  and  iris; 
the  optic  stalk  is  invaded  by  nerve  fibers  to  form  the  optic  nerve.  The  fore-brain 
then  grows  forward,  and  from  the  alar  laminae  of  this  front  portion  the  cerebral 
hemispheres  originate  as  diverticula  which  rapidly  expand  to  form  two  large 
pouches,  one  on  either  side.  The  cavities  of  these  diverticula'  are  the  rudiments  of 
the  lateral  ventricles;  they  communicate  with  the  median  part  of  the  fore-brain 
cavity  by  relatively  wide  openings,  which  ultimately  form  the  interventricular 


Choroidal  fissure 
Hypophysis 

Recessus  infundibuli 

Tuber  cinereum 

Corpus  mamiUare 


Cervical  flexure 
Fig.  653. — Interior  of  brain  of  human  embryo  of  five  weeks.     (From  model  by  His.) 

foramen.  The  median  portion  of  the  wall  of  the  fore-brain  vesicle  consists  of  a 
thin  lamina,  the  lamina  terminalis  (Figs.  654,  657),  which  stretches  from  the 
interventricular  foramen  to  the  recess  at  the  base  of  the  optic  stalk.  The 
anterior  part  of  the  fore-brain,  including  the  rudiments  of  the  cerebral  hemi- 
spheres, is  named  the  telencephalon,  and  its  posterior  portion  is  termed  the 
diencephalon ;  both  of  these  contribute  to  the  formation  of  the  third  ventricle. 

The  Diencephalon. — From  the  alar  lamina  of  the  diencephalon,  the  thalamus, 
metathalamus,  and  epithalamus  are  developed.  The  thalamus  (Figs.  650  to  654) 
arises  as  a  thickening  which  involves  the  anterior  two-thirds  of  the  alar  lamina. 
The  two  thalami  are  visible,  for  a  time,  on  the  surface  of  the  brain,  but  are  subse- 
quently hidden  by  the  cerebral  hemispheres  which  grow  backward  over  them. 
The  thalami  extend  medialward  and  gradually  narrow  the  cavity  between  them, 
into  a  slit-like  aperture  which  forms  the  greater  part  of  the  third  ventricle;  their 
medial  surfaces  ultimately  adhere,  in  part,  to  each  other,  and  the  intermediate 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 


743 


mass  of  the  ventricle  is  developed  across  the  area  of  contact.  The  metathalamus 
comprises  the  geniculate  bodies  which  originate  as  slight  outward  bulgings  of  the 
alar  lamina.  In  the  adult  the  lateral  geniculate  body  appears  as  an  eminence  on 
the  lateral  part  of  the  posterior  end  of  the  thalamus,  while  the  medial  is  situated 
on  the  lateral  aspect  of  the  mid-brain.  The  epithalamus  includes  the  pineal 
body,  the  posterior  commissure,  and  the  trigonum  habenulse.  The  pineal  body 
arises  as  an  upward  the  evagination  of  roof-plate  immediately  in  front  of  the  mid- 
brain; this  evagination  becomes  solid  with  the  exception  of  its  proximal  part, 
which  persists  as  the  recessus  pinealis.  In  lizards  the  pineal  evagination  is  elongated 
into  a  stalk,  and  its  peripheral  extremity  is  expanded  into  a  vesicle,  in  which  a 
rudimentary  lens  and  retina  are  formed;  the  stalk  becomes  solid  and  nerve  fibers 
make  their  appearance  in  it,  so  that  in  these  animals  the  pineal  body  forms  a 
rudimentary  eye.  The  posterior  commissure  is  formed  by  the  ingrowth  of  fibers 
into  the  depression  behind  and  below  the  pineal  evagination,  and  the  trigonum 
^habenulse  is  developed  in  front  of  the  pineal  recess. 

Choroidal  fissure 


Rhinencephalcm, 

Lamina  tenninalis 

Corptis  striatum 

Optic  recess 

Ckiasma 

Hypophysis 

Recessus  infundibtdi 


Fig.  654. — Median  sagittal  section  of  brain  of  human  embrj'o  of  three  months.      (From  model  by  His.) 


11 


From  the  basal  laminae  of  the  diencephalon  the  pars  mamillaris  hypothalami 
is  developed;  this  comprises  the  corpora  mamillaria  and  the  posterior  part  of 
the  tuber  cinereum.  The  corpora  mamillaria  arise  as  a  single  thickening, 
which  becomes  divided  into  two  by  a  median  furrow  during  the  third  month. 

The  roof-plate  of  the  diencephalon,  in  front  of  the  pineal  body,  remains  thin  and 
epithelial  in  character,  and  is  subsequently  invaginated  by  the  choroid  plexuses 
of  the  third  ventricle. 

The  Telencephalon. — This  consists  of  a  median  portion  and  two  lateral  diver- 
ticula. The  median  portion  forms  the  anterior  part  of  the  cavity  of  the  third 
ventricle,  and  is  closed  below  and  in  front  by  the  lamina  terminalis.  The  lateral 
diverticula  consist  of  outward  pouchings  of  the  alar  laminae;  the  cavities  represent 
the  lateral  ventricles,  and   their  walls  become  thickened  to  form  the  nervous 


I 


744 


NEUROLOGY 


matter  of  the  cerebral  hemispheres.  The  roof-plate  of  the  telencephalon  remains 
thin,  and  is  continuous  in  front  with  the  lamina  terminalis  and  behind  with  th(; 
roof-plate  of  the  diencephalon.  In  the  basal  laminae  and  floor-plate  the  pars 
optica  hypothalami  is  developed;  this  comprises  the  anterior  part  of  the  tuber 
cinereum,  the  infundibulum  and  posterior  lobe  of  the  hypophysis,  and  the  opticj 
chiasma.  The  anterior  part  of  the  tuber  cinereum  is  derived  from  the  posterior 
part  of  the  floor  of  the  telencephalon;  the  infundibulum  and  posterior  lobe  of  the 
hypophysis  arise  as  a  downward  diverticulum  from  the  floor.  The  most  depen- 
dent part  of  the  diverticulum  becomes  solid  and  forms  the  posterior  lobe  of  the 
hypophysis;  the  anterior  lobe  of  the  hypophysis  is  developed  from  a  diverticulum 
of  the  ectodermal  lining  of  the  stomodeum.  The  optic  chiasma  is  formed 
by  the  meeting  and  partial  decussation  of  the  optic  nerves,  which  subsequently 
grow  backward  as  the  optic  tracts  and  end  in  the  diencephalon. 

The  cerebral  hemispheres  arise  as  diverticula  of  the  alar  laminae  of  the  telen-. 
cephalon  (Figs.  650  to  654);  they  increase  rapidly  in  size  and  ultimately  overlap 
the  structures  developed  from  the  mid-  and  hind-brains.    This  great  expansion 

of  the  hemispheres  is  a  char- 
acteristic feature  of  the  brains 
of  mammals,  and  attains  its 
maximum  development  in 
the  brain  of  man.  Elliott- 
Smith  divides  each  cerebral 
hemisphere  into  three  funda- 
mental parts,  viz.,  the  rhinen- 
cephalon,  the  corpus  striatum, 
and  the  neopallium. 

The  rhinencephalon  (Fig. 
655)  represents  the  oldest 
part  of  the  telencephalon, 
and  forms  almost  the  whole 
of  the  hemisphere  in  fishes, 
amphibians,  and  reptiles.  In 
man  it  is  feebly  developed 
in  comparison  with  the  rest 
of  the  hemisphere,  and  com- 
prises the  following  parts, 
viz.,  the  olfactory  lobe  {q6\\- 
sisting  of  the  olfactory  tract  and  bulb  and  the  trigonum  olfactorium),  the  anterior 
perforated  substance,  the  septum  pellucidum,  the  subcallosal,  supracallosal,  and 
dentate  gyri,  the  fornix,  the  hippocampus,  and  the  uncus.  The  rhinencephalon 
appears  as  a  longitudinal  elevation,  with  a  corresponding  internal  furrow,  on  the 
under  surface  of  the  hemisphere  close  to  the  lamina  terminalis;  it  is  separated 
from  the  lateral  surface  of  the  hemisphere  by  a  furrow,  the  external  rhinal  fissure, 
and  is  continuous  behind  with  that  part  of  the  hemisphere,  which  will  ultimately 
form  the  anterior  end  of  the  temporal  lobe.  The  elevation  becomes  divided  by 
a  groove  into  an  anterior  and  a  posterior  part.  The  anterior  grows  forward  as 
a  hollow  stalk  the  lumen  of  which  is  continuous  with  the  anterior  part  of  the  ven- 
tricular cavity.  During  the  third  month  the  stalk  becomes  solid  and  forms  the 
rudiment  of  the  olfactory  bulb  and  tract;  a  strand  of  gelatinous  tissue  in  the  interior 
of  the  bulb  indicates  the  position  of  the  original  cavity.  From  the  posterior  part  the 
anterior  perforated  substance  and  the  pyriform  lobe  are  developed;  at  the  begin- 
ning of  the  fourth  month  the  latter  forms  a  curved  elevation  continuous  behind 
with  the  medial  surface  of  the  temporal  lobe,  and  consisting,  from  before  backward, 
of  the  gyrus  olfactorius  lateralis,  gyrus  ambiens,  and  gyrus  semilunaris,  parts  which 


I 


Oyr.  df.  med. 
Gyr.  olf.  lat. 


Gyr.  ambiens 

Gyr.  diagonalis 

Gyr,  semilunaris 


Cerebellum, 

Olive 


Fig.  655. — Inferior  surface  of  brain  of  embryo  at  beginning  of  fourth 
month.     (From  KoUmann.) 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 


745 


in  the  adult  brain  are  represented  by  the  lateral  root  of  the  olfactory  tract  and  the 
uncus.  The  position  and  connections  of  the  remaining  portions  of  the  rhinen- 
cephalon  are  described  with  the  anatomy  of  the  brain. 

The  corpus  striatum  (Figs.  651  and  653)  appears  in  the  fourth  week  as  a  triangular 
thickening  of  the  floor  of  the  telencephalon  between  the  optic  recess  and  the 
interventricular  foramen,  and  continuous  behind  with  the  thalamic  part  of  the 
diencephalon.  It  increases  in  size,  and  by  the  second  month  is  seen  as  a  swelling 
in  the  floor  of  the  future  lateral  ventricle;  this  swelling  reaches  as  far  as  the  posterior 
end  of  the  primitive  hemisphere,  and  when  this  part  of  the  hemisphere  grows 
backward  and  downward  to  form  the  temporal  lobe,  the  posterior  part  of  the  corpus 
striatum  is  carried  into  the  roof  of  the  inferior  horn  of  the  ventricle,  where  it  is 
seen  as  the  tail  of  the  caudate  nucleus  in  the  adult  brain.  During  the  fourth  and 
fifth  months  the  corpus  striatum  becomes  incompletely  subdivided  by  the  fibers  of 
the  internal  capsule  into  two  masses,  an  inner,  the  caudate  nucleus,  and  an  outer, 
the  lentiform  nucleus.  In  front,  the  corpus  striatum  is  continuous  with  the  anterior 
perforated  substance;  laterally  it  is  confluent  for  a  time  with  that  portion  of  the 
wall  of  the  vesicle  which  is  developed  into  the  insula,  but  this  continuity  is  sub- 
sequently interrupted  by  the  fibers  of  the  external  capsule. 

Falx  cerebri 


Fig.  656.- 


Edge  of  uhite  substance 
^Edge  ofqrey  cortical 
subhtance 
Jlippocainpal  fissure 

Cs.  Corpus  striatum.    Th.  Thalamus. 

-Diagrammatic  coronal  section  of  brain  to  show  relations  of  neopallium.    (After  His.)    Cs.  Corpus  striatum. 

Th.  Thalamus. 


The  neopallium  (Fig.  656)  forms  the  remaining,  and  by  far  the  greater,  part  of  the 
cerebral  hemisphere.  It  consists,  at  an  early  stage,  of  a  relatively  large,  more  or 
less  hemispherical  cavity — the  primitive  lateral  ventricle — enclosed  by  a  thin  wall 
from  which  the  cortex  of  the  hemisphere  is  developed.  The  vesicle  expands  in  all 
directions,  but  more  especially  upward  and  backward,  so  that  by  the  third  month 
the  hemispheres  cover  the  diencephalon,  by  the  sixth  they  overlap  the  mid-brain, 
and  by  the  eighth  the  hind-brain. 

The  median  lamina  uniting  the  two  hemispheres  does  not  share  in  their  expan- 
sion, and  thus  the  hemispheres  are  separated  by  a  deep  cleft,  the  forerunner  of 
the  longitudinal  fissure,  and  this  cleft  is  occupied  by  a  septum  of  mesodermal 
tissue  which  constitutes  the  primitive  falx  cerebri.'  Coincidently  with  the  expan- 
sion of  the  vesicle,  its  cavity  is  drawn  out  into  three  prolongations  which  represent 


746 


NEUROLOGY 


I 


the  horns  of  the  future  lateral  ventricle;  the  hinder  end  of  the  vesicle  is  carried  down- 
ward and  forward  and  forms  the  inferior  horn;  the  posterior  horn  is  produced 
somewhat  later,  in  association  with  the  backward  growth  of  the  occipital  lobe  of 
the  hemisphere.  The  roof-plate  of  the  primitive  fore-brain  remains  thin  and  of  an 
epithelial  character;  it  is  invaginated  into  the  lateral  ventricle  along  the  medial 
wall  of  the  hemisphere.  This  invagination  constitutes  the  choroidal  fissure,  and 
extends  from  the  interventricular  foramen  to  the  posterior  end  of  the  vesicle.  Meso- 
dermal tissue,  continuous  with  that  of  the  primitive  falx  cerebri,  and  carrying 
bloodvessels  with  it,  spreads  between  the  two  layers  of  the  invaginated  fold  and 
forms  the  rudiment  of  the  tela  choroidea;  the  margins  of  the  tela  become  highly 
vascular  and  form  the  choroid  plexuses  which  for  some  months  almost  completely 
fill  the  ventricular  cavities;  the  tela  at  the  same  time  invaginates  the  epithelial 
roof  of  the  diencephalon  to  form  the  choroid  plexuses  of  the  third  ventricle.  By 
the  downward  and  forward  growth  of  the  posterior  end  of  the  vesicle  to  form  the 
temporal  lobe  the  choroidal  fissure  finally  reaches  from  the  interventricular  fora- 
men to  the  extremity  of  the  inferior  horn  of  the  ventricle. 


Gynia  dentatus 
TcBnia  thoLami 


Thalamus 


Choroidal  fissure 


Post,  commissure 

Corpora  quadrigemina 

Cerebral  aqueduct  — j 
Cerebral  peduncle  — L 

Cerebellum 


Corpus  callosum 
Septum  pellucidum 
Anterior  commissure 

Lamina  terminalia 


IV.  ventricle 


Rhinencephalon 
Optic  chiasmO) 
Hypophysis 

k_J\  ///.  ventricle 
j  Pons 

/\  Medulla  oblongata 
Fig.  657. — Median  sagittal  section  of  brain  of  human  embryo  of  four  months.     (Marchand.) 

Parallel  with  but  above  and  in  front  of  the  choroidal  fissure  the  medial  wall  of 
the  cerebral  vesicle  becomes  folded  outward  and  gives  rise  to  the  hippocampal 
fissure  on  the  medial  surface  and  to  a  corresponding  elevation,  the  hippocampus, 
within  the  ventricular  cavity.  The  gray  or  ganglionic  covering  of  the  wall  of  the 
vesicle  ends  at  the  inferior  margin  of  the  fissure  is  a  thickened  edge;  beneath  this 
the  marginal  or  reticular  layer  (future  white  substance)  is  exposed  and  its  lower 
thinned  edge  is  continuous  with  the  epithelial  invagination  covering  the  choroid 
plexus  (Fig.  656).  As  a  result  of  the  later  downward  and  forward  growth  of  the 
temporal  lobe  the  hippocampal  fissure  and  the  parts  associated  with  it  extend  from 
the  interventricular  foramen  to  the  end  of  the  inferior  horn  of  the  ventricle. 
The  thickened  edge  of  gray  substance  becomes  the  gyrus  dentatus,  the  fasciola 
cinerea  and  the  supra-  and  subcallosal  gyri,  while  the  free  edge  of  the  white  sub- 
stance forms  the  fimbria  hippocampi  and  the  body  and  crus  of  the  fornix.  The 
corpus  callosum  is  developed  within  the  arch  of  the  hippocampal  fissure,  and  the 
upper  part  of  the  fissure  forms,  in  the  adult  brain,  the  callosal  fissure  on  the  medial 
surface  of  the  hemisphere. 

The  .Commissures  (Fig.  657). — The  development  of  the  posterior  commissure 
has  already  been  referred  to  (page  743).    The  great  commisssures  of  the  hemi- 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 


747 


Parietal 
opercvlum 


spheres,  viz.,  the  corpus  callosum,  the  fornix,  and  anterior  commissures,  arise  from 
the  lamina  terminahs.  About  the  fourth  month  a  small  thickening  appears  in 
this  lamina,  immediately  in  front  of  the  interventricular  foramen.  The  lower 
part  of  this  thickening  is  soon  constricted  off,  and  fibers  appear  in  it  to  form 
the  anterior  commissure.  The  upper  part  continues  to  grow  with  the  hemispheres, 
and  is  invaded  by  two  sets  of  fibers.  Transverse  fibers,  extending  between  the 
hemispheres,  pass  into  its  dorsal  part,  which  is  now  differentiated  as  the  corpus 
callosum  (in  rare  cases  the  corpus  callosum  is  not  developed).  Into  the  ventral 
part  longitudinal  fibers  from  the  hippocampus  pass  to  the  lamina  terminalis,  and 
through  that  structure  to  the  corpora  mamillaria;  these  fibers  constitute  the 
fornix.  A  small  portion,  lying  antero-inferiorly  between  .the  corpus  callosum  and 
fornix,  is  not  invaded  by  the  commissural  fibers;  it  remains  thin,  and  later  a 
;avity,  the  cavity  of  the  septum  pellucidum,  forms  in  its  interior. 

Fissures  and  Sulci. — The  outer  surface  of  the  cerebral  hemisphere  is  at  first  smooth, 
)ut  later  it  exhibits  a  number  of  elevations  or  convolutions,  separated  from  each 
)ther  by  fissures  and  sulci,  most  of  which 
make  their  appearance  during  the  sixth 
or  seventh  months  of  fetal  life.  The 
term  fissure  is  applied  to  such  grooves  as 
involve  the  entire  thickness  of  the  cere- 
bral wall,  and  thus  produce  correspond- 
ing eminences  in  the  ventricular  cavity, 
while  the  sulci  affect  only  the  superficial 
part  of  the  wall,  and  therefore  leave  no 
impressions  in  the  ventricle.  The  fissures 
comprise  the  choroidal  and  hippocampal 
already  described,  and  two  others,  viz., 
the  calcarine  and  collateral,  which  pro- 
duce the  swellings  known  respectively 
as  the  calcar  avis  and  the  collateral 
eminence  in  the  ventricular  cavity.  Of 
the  sulci  the  following  may  be  referred 
to,  viz.,  the  central  sulcus  (fissure  of 
Rolando),  which  is  developed  in  two 
parts;  the  intraparietal  sulcus  in  four 
parts;  and  the  cingulate   sulcus  in  two 

or  three  parts.  The  lateral  cerebral  or  Sylvian  fissure  differs  from  all  the  other 
fissures  in  its  mode  of  development.  It  appears  about  the  third  month  as  a  depres- 
sion, the  Sylvian  fossa,  on  the  lateral  surface  of  the  hemisphere  (Fig.  658);  this 
fossa  corresponds  with  the  position  of  the  corpus  striatum,  and  its  floor  is  moulded 
to  form  the  insula.  The  intimate  connection  which  exists  between  the  cortex 
of  the  insula  and  the  subjacent  corpus  striatum  prevents  this  part  of  the  hemi- 
sphere wall  from  expanding  at  the  same  rate  as  the  portions  which  surround  it. 
The  neighboring  parts  of  the  hemisphere  therefore  gradually  grow  over  and  cover 
in  the  insula,  and  constitute  the  temporal,  parietal,  frontal,  and  orbital  opercula 
of  the  adult  brain.  The  frontal  and  orbital  opercula  are  the  last  to  form,  but  by  the 
end  of  the  first  year  after  birth  the  insula  is  completely  submerged  by  the  approxi- 
mation of  the  opercula.  The  fissures  separating  the  opposed  margins  of  the  oper- 
cula constitute  the  composite  lateral  cerebral  fissure. 

If  a  section  across  the  wall  of  the  hemisphere  about  the  sixth  week  be  examined 
microscopically  it  will  be  found  to  consist  of  a  thin  marginal  or  reticular  layer,  a 
thick  ependymal  layer,  and  a  thin  intervening  mantle  layer.  Neuroblasts  from  the 
ependymal  and  mantle  layers  migrate  into  the  deep  part  of  the  marginal  layer  and 
form  the  cells  of  the  cerebral  cortex.  The  nerve  fibers  which  form  the  underlying 
white  substance  of  the  hemispheres  consist  at  first  of  outgrowths  from  the  cells  of 


Temporal  operculum 

Sylvian  fossa 
Frontal  operculum 

Fig.  658. — Outer  surface  of  cerebral  hemisphere  of 
human  embryo  of  about  five  months. 


748 


NEUROLOGY 


I 


the  corpora  striata  and  thalami;  later  the  fibers  from  the  cells  of  the  cortex  are 
added.  Medullation  of  these  fibers  begins  about  the  time  of  birth  and  continues 
until  puberty.  A  summary  of  the  parts  derived  from  the  brain  vesicles  is  given  in 
the  following  table : 


Hind-brain  or 
Rhombencephalon 


1.  Myelencephalon 


2.  Metencephalon 


3.  Isthmus  rhomb- 
encephali 


Mid-brain  or  Mesencephalon 


Fore-brain  or 
Prosencephalon 


1.  Diencephalon 


2.  Telencephalon 


Medulla  oblongata 

Lower  part  of  fourth 
ventricle. 

Pons 

Cerebellum 

Intermediate  part  of  fourth 
ventricle. 

Anterior  medullary  velum 

Brachia  conjunctiva 
cerebelli. 

Upper  part  of  fourth 
ventricle. 

Cerebral  peduncles 

Lamina  quadrigemina 

Cerebral  aqueduct. 

Thalamus 

Metathalamus 

Epithalamus 

Pars  mamillaris  hypo- 
thalami 

Posterior  part  of  third 
ventricle, 
f  Anterior  part  of  third 
ventricle 

Pars  optica  hypo- 
thalami 

Cerebral  hemispheres 

Lateral  ventricles 

Interventricular  foramen. 


11 


The  Cranial  Nerves. — With  the  exception  of  the  olfactory,  optic,  and  acoustic 
nerves,  which  will  be  especially,  considered,  the  cranial  nerves  are  developed  in  a 

similar  manner  to  the  spinal  nerves 
(see  page  735).  The  sensory  or 
afferent  nerves  are  derived  from 
the  cells  of  the  ganglion  rudiments 
of  the  neural  crest.  The  central 
processes  of  these  cells  grow  into 
the  brain  and  form  the  roots  of  the 
nerves,  while  the  peripheral  pro- 
cesses extend  outward  and  consti- 
tute their  fibers  of  distribution 
(Fig.  645).  It  has  been  seen,  in 
considering  the  development  of  the 
medulla  oblongata  (page  739),  that 
the  tractus  solitarius  (Fig.  660),  de- 
rived from  the  fibers  which  grow 
Vagus  nerve  inward  from  the  ganglion  rudiments 

Hypoglossal  nerve  of  the  glossopharyngeal  and  vagus 

Floor-plate  ucrves,  is   the   homologue    of  the 

Fio.  659. — Transverse  section  of  medulla  oblongata  of  i   i.       ji       •      j.i  j        i_  •    i      i.    j 

human  embryo.     X  32.     (KoUmann )  OVal   DUndle    m  the    COrd    WhlCh    had 


■Boof-plate 


■Alar  lamina 


Furrow  between 
alar  and  basal 
lamincB 

■Basal  lamina 


THE  MEDULLA  SPINALIS  OR  SPINAL  CORD 


749 


HKts  origin  in  the  posterior  nerve  roots.  The  motor  or  efferent  nerves  arise  as  out 
growtlis  of  the  neuroblasts  situated  in  the  basal  laminae  of  the  mid-  and  hind- 
brain.  While,  however,  the  spinal  motor  nerve  roots  arise  in  one  series  from  the 
H| basal  lamina,  the  cranial  motor  nerves  are  grouped  into  two  sets,  according  as 
"*  they  spring  from  the  medial  or  lateral  parts  of  the  basal  lamina.  To  the  former 
set  belong  the  oculomotor,  trochlear,  abducent,  and  hypoglossal  nerves;  to  the 
latter,  the  accessory  and  the  motor  fibers  of  the  trigeminal,  facial,  glossopharyn- 
geal, vagus  nerves  (Figs.  659,  660). 


Rhombic  lip 


I 


Vagus  nerve 


Hypoglossal  nervs 

Floor-plate 
Fig.  660. — Transverse  section  of  medulla  oblongata  of  human  embryo.     (After  His.) 

THE  MEDULLA   SPINALIS   OR   SPINAL   CORD. 

The  medulla  spinalis  or  spinal  cord  forms  the  elongated,  nearly  cylindrical,  part 
of  the  central  nervous  system  which  occupies  the  upper  two-thirds  of  th^  vertebral 
canal.  Its  average  length  in  the  male  is  about  45  cm.,  in  the  female  from  42  to  43 
cm.,  while  its  weight  amounts  to  about  30  gms.  It  extends  from  the  level  of  the 
upper  border  of  the  atlas  to  that  of  the  lower  border  of  the  first,  or  upper  border 
of  the  second,  lumbar  vertebra.  Above,  it  is  continuous  with  the  brain;  below,  it 
ends  in  a  conical  extremity,  the  conus  medullaris,  from  the  apex  of  which  a  delicate 
filament,  the  filum  terminale,  descends  as  far  as  the  first  segment  of  the  coccyx 
i<Fig.  661). 

The  position  of  the  medulla  spinalis  varies  with  the  movements  of  the  vertebral 
column,  its  lower  extremity  being  drawn  slightly  upward  when  the  column  is 
flexed.  It  also  varies  at  different  periods  of  life;  up  to  the  third  month  of  fetal 
life  the  medulla  spinalis  is  as  long  as  the  vertebral  canal,  but  from  this  stage  onward 
the  vertebral  column  elongates  more  rapidly  than  the  medulla  spinalis,  so  that  by 
the  end  of  the  fifth  month  the  medulla  spinalis  terminates  at  the  base  of  the  sacrum, 
and  at  birth  about  the  third  lumbar  vertebra. 

The  medulla  spinalis  does  not  fill  the  part  of  the  vertebral  canal  in  which  it  lies; 
it  is  ensheathed  by  three  protective  membranes,  separated  from  each  other  by  two 
concentric  spaces.  The  three  membranes  are  named  from  without  inward,  the 
dura  mater,  the  arachnoid,  and  the  pia  mater.  The  dura  mater  is  a  strong,  fibrous 
membrane  which  forms  a  wide,  tubular  sheath;  this  sheath  extends  below  the  ter- 
mination of  the  medulla  spinalis  and  ends  in  a  pointed  cul-de-sac  at  the  level  of  the 
lower  border  of  the  second  sacral  vertebra.  The  dura  mater  is  separated  from  the 
wall  of  the  vertebral  canal  by  the  epidural  cavity,  which  contains  a  quantity  of  loose 
areolar  tissue  and  a  plexus  of  veins;  between  the  dura  mater  and  the  subjacent 
arachnoid  is  a  capillary  interval,  the  subdural  cavity,  which  contains  a  small  quan- 
ity  of  fluid,  probably  of  the  nature  of  lymph.    The  arachnoid  is  a  thin,  transparent 


750 


NEUROLOGY 


sheath,  separated  from  the  pia  mater  by  a  comparatively  wide  interval,  the  sub- 
arachnoid cavity,  which  is  filled  with  cerebrospinal  fluid.  The  pia  mater  closely 
invests  the  medulla  spinalis  and  sends  delicate  septa  into  its  substance;  a  narrow 
band,  the  ligamentum  denticulatum,  extends  along  each  of  its  lateral  surfaces 
and  is  attached  by  a  series  of  pointed  processes  to  the  inner  surface  of  the  dura 
mater. 

Thirty-one  pairs  of  spinal  nerves  spring  from  the  medulla  spinalis,  each  nerve 
having  an  anterior  or  ventral,  and  a  posterior  or  dorsal  root,  the  latter  being  dis- 
tinguished by  the  presence  of  an  oval  swelling, 
the  spinal  ganglion,  which  contains  numerous 
nerve  cells.  Each  root  consists  of  several 
bundles  of  nerve  fibers,  and  at  its  attachment 
extends  for  some  distance  along  the  side  of 
the  medulla  spinalis.  The  pairs  of  spinal 
nerves  are  grouped  as  follows:  cervical  8, 
thoracic  12,  lumbar  5,  sacral  5,  coccygeal  1, 
and,  for  convenience  of  description,  the 
medulla  spinalis  is  divided  into  cervical, 
thoracic,  lumbar  and  sacral  regions,  corre- 
sponding with  the  attachments  of  the  different 
groups  of  nerves. 

Although  no  trace  of  transverse  segmen- 
tation is  visible  on  the  surface  of  the  medulla 
spinalis,  it  is  convenient  to  regard  it  as  being 
built  up  of  a  series  of  superimposed  spinal 
segments  or  neuromeres,  each  of  which  has 
a  length  equivalent  to  the  extent  of  attach- 
ment of  a  pair  of  spinal  nerves.  Since  the  ex- 
tent of  attachment  of  the  successive  pairs  of 
nerves  varies  in  different  parts,  it  follows  that 
the  spinal  segments  are  of  varying  lengths; 
thus,  in  the  cervical  region  they  average  about 
13  mm.,  in  the  mid-thoracic  region  about  26 
mm.,  while  in  the  lumbar  and  sacral  regions 
they  diminish  rapidly  from  about  15  mm.  at 
the  level  of  the  first  pair  of  lumbar  nerves  to 
about  4  mm.  opposite  the  attachments  of  the 
lower  sacral  nerves. 

As  a  consequence  of  the  relative  inequality 
in  the  rates  of  growth  of  the  medulla  spinalis 
and  vertebral  column,  the  nerve  roots,  which 
in  the  early  embryo  passed  transversely  out- 
ward to  reach  their  respective  intervertebral  foramina,  become  more  and  more 
oblique  in  direction  from  above  downward,  so  that  the  lumbar  and  sacral  nerves 
descend  almost  vertically  to  reach  their  points  of  exit.  From  the  appearance  these 
nerves  present  at  their  attachment  to  the  medulla  spinalis  and  from  their  great 
length  they  are  collectively  termed  the  cauda  equina  (Fig.  C62). 

The  filum  terminate  is  a  delicate  filament,  about  20  cm.  in  length,  prolonged 
downward  from  the  apex  of  the  conus  medullaris.  It  consists  of  two  parts,  an  upper 
and  a  lower.  The  upper  part,  or  filum  terminate  internum,  measures  about  15  cm. 
in  length  and  reaches  as  far  as  the  lower  border  of  the  second  sacral  vertebra.  It 
is  contained  within  the  tubular  sheath  of  dura  mater,  and  is  surrounded  by  the 
nerves  forming  the  cauda  equina,  from  which  it  can  be  readily  recognized  by  its 
bluish-white  color.    The  lower  part,  or  filum  terminale  externum,  is  closely  invested 


I 


Fig.  661. — Sagittal  section  of  vertebral  canal 
to  show  the  lower  end  of  the  medulla  spinalis 
and  the  filum  terminale.  Li,  Lv.  First  and  fifth 
lumbar  vertebrae.  Sii.  Second  sacral  vertebra. 
1.  Dura  mater.  2.  Lower  part  of  tube  of 
dura  mater.  3.  Lower  extremity  of  medulla 
spinalis.  4.  Intradural,  and  5,  Extradural  por- 
tions of  filum  terminale.  6.  Attachment 
of  filum  terminale  to  first  segment  of  coccyx. 
(Testut.) 


THE  MEDULLA  SPINALIS  OR  SPINAL  CORD 


751 


)y,  and  is  adherent  to,  the  dura  mater;  it  extends  downward  from  the  apex  of  the 

tubular  sheath  and  is  attached  to  the  back  of  the  first  segment  of  the  coccyx. 

[The  filum  terminale  consists  mainly  of 

brous  tissue,  continuous  above  with 

hat  of  the  pia  mater.    Adhering  to  its 

uter  surface,  however,  are  a  few  strands 
of  nerve  fibers  which  probably  represent 
rudimentary  second  and  third  coccygeal 

■■nerves;  further,  the  central  canal  of  the 


Decussation  of 
the  pyramids 


medulla  spinalis  extends  downward  into 
it  for  5  or  6  cm. 

Enlargements. — The  medulla  spinalis 
is  not  quite  cylindrical,  being  slightly 
flattened  from  before  backward;  it  also 


Anterior  median 
fissure 


Dura  mater 

Conns  medullaris 
Posterior  nerveroots 


Filum  terminale 


Postero- 
■  intermediate 

sulcus 


Cervical 
enlargement 


Posterior 
median  sulcus 

Postero- 
lateral sulcus 


Lniinhar 
enlargement 


•Gonus 


—  Filum  - — 


I 


Fio.  662. — Cauda  equina  and  filum  terminale  seen 
from  behind.  The  dura  mater  has  been  opened  and 
spread  out,  and  the  arachnoid  has  been  removed. 


Ventral  aspect        Dorsal  aspect 
FiQ.  663. — Diagrams  of  the  medulla  spinalis^ 


752 


NEUROLOGY 


presents  two  swellings  or  enlargements,  an  upper  or  cervical,  and  a  lower  orTumD^r 
(Fig.  663). 

The  cervical  enlargement  is  the  more  pronounced,  and  corresponds  with  the  attach- 
ments of  the  large  nerves  which  supply  the  upper  limbs.  It  extends  from  about 
the  third  cervical  to  the  second  thoracic  vertebra,  its  maximum  circumference 
(about  38  mm.)  being  on  a  level  with  the  attachment  of  the  sixth  pair  of  cervical 
nerves. 

The  lumbar  enlargement  gives  attachment  to  the  nerves  which  supply  the  lower 
limbs.  It  commences  about  the  level  of  the  ninth  thoracic  vertebra,  and  reaches 
its  maximum  circumference,  of  about  33  mm.,  opposite  the  last  thoracic  vertebra, 
below  which  it  tapers  rapidly  into  the  conus  medullaris. 

Fissures  and  Sulci  (Fig.  664). — An  anterior  median  fissure  and  a  posterior 
median  sulcus  incompletely  divide  the  medulla  spinalis  into  two  symmetrical 
parts,  which  are  joined  across  the  middle  line  by  a  commissural  band  of  nervous 
matter. 

Posterior  median  sulcus 

Posterior  median  septum 


Posterior 
lervp  roots 


ostcro-lateral  sulcus 


Format  io 
reticularis 
Lateral 
column 


Anterior  nerve  roots        Anterior  median  fissure 
Fig.  664. — Transverse  section  of  the  medulla  spinalis  in  the  mid-thoracic  region. 

The  Anterior  Median  Fissure  {fissura  mediana  anterior)  has  an  average  depth  of 
about  3  mm.,  but  this  is  increased  in  the  lower  part  of  the  medulla  spinalis.  It 
contains  a  double  fold  of  pia  mater,  and  its  floor  is  formed  by  a  transverse  band 
of  white  substance,  the  anterior  white  commissure,  which  is  perforated  by  blood- 
vessels on  their  way  to  or  from  the  central  part  of  the  medulla  spinalis. 

The  Posterior  Median  Sulcus  (sulcus  medianus  posterior)  is  very  shallow;  from  it 
a  septum  of  neuroglia  reaches  rather  more  than  half-way  into  the  substance  of  the 
medulla  spinalis;  this  septum  varies  in  depth  from  4  to  6  mm.,  but  diminishes 
considerably  in  the  lower  part  of  the  medulla  spinalis. 

On  either  side  of  the  posterior  median  sulcus,  and  at  a  short  distance  from  it, 
the  posterior  nerve  roots  are  attached  along  a  vertical  furrow  named  the  postero- 
lateral sulcus.  The  portion  of  the  medulla  spinalis  which  lies  between  this  and  the 
posterior  median  sulcus  is  named  the  posterior  funiculus.  In  the  cervical  and  upper 
thoracic  regions  this  funiculus  presents  a  longitudinal  furrow,  the  postero-inter- 
mediate  sulcus;  this  marks  the  position  of  a  septum  which  extends  into  the  posterior 
funiculus  and  subdivides  it  into  two  fasciculi— a  medial,  named  the  fasciculus 
gracilis  {tract  of  Goll);  and  a  lateral,  the  fasciculus  cuneatus  {tract  of  Burdach) 


THE  MEDULLA  SPIN  ALT ft^U 


(Fig.  672).  The  portion  of  the  medulla  spinalis  which  lies  in  front  of  the  postero- 
lateral sulcus  is  termed  the  antero-lateral  region.  The  anterior  nerve  roots,  unlike 
the  posterior,  are  not  attached  in  linear  series,  and  their  position  of  exit  is  not 
marked  by  a  sulcus.  They  arise  by  separate  bundles  which  spring  from  the  anterior 
column  of  gray  substance  and,  passing  forward  through  the  white  substance, 
emerge  over  an  area  of  some  slight  width.  The  most  lateral  of  these  bundles  is 
generally  taken  as  a  dividing  line  which  separates  the  antero-lateral  region  into 
two  parts,  viz.,  an  anterior  funiculus,  between  the  anterior  median  fissure  and  the 
most  lateral  of  the  anterior  nerve  roots;  and  a  lateral  funiculus,  between  the  exit 
of  these  roots  and  the  postero-lateral  sulcus.  In  the  upper  part  of  the  cervical 
region  a  series  of  nerve  roots  passes  outward  through  the  lateral  funiculus  of  the 
medulla  spinalis;  these  unite  to  form  the  spinal  portion  of  the  accessory  nerve, 
which  runs  upward  and  enters  the  cranial  cavity  through  the  foramen  magnum. 


-White  maH"er 


Gray  motter. 


-CnHre  secMon. 


h 


Fig.  665. — Ciirves  showing  the  sectional  area  at  different  levels  of  the  cord.    The  ordinates  show  the  area  in  sq.  mm. 

(Donaldson  and  Davis.) 


II 


)l 
II 

It 


u 


The  Internal  Structure  of  the  Medulla  Spinalis. — On  examining  a  transverse 
section  of  the  medulla  spinalis  (Fig.  664)  it  is  seen  to  consist  of  gray  and  white 
nervous  substance,  the  former  being  enclosed  within  the  latter. 

Gray  Substance  {substantia  grisea  centralis). — ^The  gray  substance  consists  of 
two  symmetrical  portions,  one  in  each  half  of  the  medulla  spinalis:  these  are 
joined  across  the  middle  line  by  a  transverse  commissure  of  graj'  substance,  through 
which  runs  a  minute  canal,  the  central  canal,  just  visible  to  the  naked  eye.  In  a 
transverse  section  each  half  of  the  gray  substance  is  shaped  like  a  comma  or 
crescent,  the  concavity  of  which  is  directed  laterally;  and  these,  together  with 
the  intervening  gray  commissure,  present  the  appearance  of  the  letter  H.  An 
imaginary  coronal  plane  through  the  central  canal  serves  to  divide  each  crescent 
into  an  anterior  or  ventral,  and  a  posterior  or  dorsal  column. 

The  Anterior  Column  {columna  anterior;  anterior  cornu),  directed  forward,  is 
broad  and  of  a  rounded  or  quadrangular  shape.  Its  posterior  part  is  termed  the 
base,  and  its  anterior  part  the  head,  but  these  are  not  differentiated  from  each  other 
by  any  well-defined  constriction.  It  is  separated  from  the  surface  of  the  medulla 
spinalis  by  a  layer  of  white  substance  which  is  traversed  by  the  bundles  of  the 
anterior  nerve  roots.  In  the  thoracic  region,  the  postero-lateral  part  of  the  anterior 
column  projects  lateralward  as  a  triangular  field,  which  is  named  the  lateral  column 
{columna  lateralis;  lateral  cornu). 

The  Posterior  Column  {columna  posterior;  posterior  cornu)  is  long  and  slender, 
and  is  directed  backward  and  lateralward:  it  reaches  almost  as  far  as  the'postero- 
lateral  sulcus,  from  which  it  is  separated  by  a  thin  layer  of  white  substance,  the 
tract  of  Lissauer.  It  consists  of  a  base,  directly  continuous  with  the  base  of  the 
anterior  horn,  and  a  neck  or  slightly  constricted  portion,  which  is  succeeded  by 
'an  oval  or  fusiform  area,  termed  the  head,  of  which  the  apex  approaches  the  postero- 
lateral sulcus.  The  apex  is  capped  by  a  V-shaped  or  crescentic  mass  of  trans- 
lucent, gelatinous  neuroglia,  termed  the  substantia  gelatinosa  of  Rolando,  which 
48 


754 


NEUROLOGY 


contains  both  neuroglia  cells,  and  small  nerve  cells, 
posterior  columns  the  gray  substance  extends 


CI 


C2. 


C5, 


C8. 


ThZ 


ThS, 


Th.m 


L.3. 


S.2. 


Coa 


FiQ.  666. — Transverse  sections  of  the 
medulla  spinalis  at  different  levels. 


Between  the  anten^ 
as  a  series  of  processes  into  the 
lateral  funiculus,  to  form  a  net-work  called  the  for- 
matio  reticularis. 

The  quantity  of  gray  substance,  as  well  as  the  form 
which  it  presents  on  transverse  section,  varies  mark- 
edly at  different  levels.  In  the  thoracic  region  it  is 
small,  not  only  in  amount  but  relatively  to  the  sur- 
rounding white  substance.  In  the  cervical  and  lum- 
bar enlargements  it  is  greatly  increased :  in  the  latter, 
and  especially  in  the  conus  medullaris,  its  proportion 
to  the  white  substance  is  greatest  (Fig.  665).  In 
the  cervical  region  its  posterior  column  is  compara- 
tively narrow,  while  its  anterior  is  broad  and  ex- 
panded; in  the  thoracic  region,  both  columns  are 
attenuated,  and  the  lateral  column  is  evident;  in 
the  lumbar  enlargement,  both  are  expanded;  while 
in  the  conus  medullaris  the  gray  substance  assumes 
the  form  of  two  oval  masses,  one  in  each  half  of  the 
cord,  connected  together  by  a  broad  gray  commissure. 

The  Central  Canal  (canalis  centralis)  runs  through- 
out the  entire  length  of  the  medulla  spinalis.  The 
portion  of  gray  substance  in  front  of  the  canal  is 
named  the  anterior  gray  commissure ;  that  behind  it, 
the  posterior  gray  commissure.  The  former  is  thin, 
and  is  in  contact  anteriorly  with  the  anterior  white 
commissure:  it  contains  a  couple  of  longitudinal 
veins,  one  on  either  side  of  the  middle  line.  The 
posterior  gray  commissure  reaches  from  the  central 
canal  to  the  posterior  median  septum,  and  is  thin- 
nest in  the  thoracic  region,  and  thickest  in  the  conus 
medullaris.  The  central  canal  is  continued  upward 
through  the  lower  part  of  the  medulla  oblongata,  and 
opens  into  the  fourth  ventricle  of  the  brain;  below, 
it  reaches  for  a  short  distance  into  the  filum  termi- 
nale.  In  the  lower  part  of  the  conus  medullaris  it 
exhibits  a  fusiform  dilatation,  the  terminal  ventricle; 
this  has  a  vertical  measurement  of  from  8  to  10 
mm.,  is  triangular  on  cross-section  with  its  base 
directed  forward,  and  tends  to  undergo  obliteration 
after  the  age  of  forty  years. 

Throughout  the  cervical  and  thoracic  regions  the 
central  canal  is  situated  in  the  anterior  third  of  the 
medulla  spinalis;  in  the  lumbar  enlargement  it  is 
near  the  middle,  and  in  the  conus  medullaris  it 
approaches  the  posterior  surface.  It  is  filled  with 
cerebrospinal  fluid,  and  lined  by  ciliated,  columnar 
epithelium,  outside  of  which  is  an  encircling  band 
of  gelatinous  substance,  the  substantia  gelatinosa 
centralis.  This  gelatinous  substance  consists  mainly 
of  neuroglia,  but  contains  a  few  nerve  cells  and 
fibers;  it  is  traversed  by  processes  from  the  deep  ends 
of  the  columnar  ciliated  cells  which  line  the  central 
canal  (Fig.  667). 


THE  MEDtJLLA  SPINALIS  OR  SPINAL  CORD 


755 


Structure  of  the  Gray  Substance. — The  gray  substance  consists  of  numerous  nerve 
cells  and  nerve  fibers  held  together  by  neuroglia.  Throughout  the  greater  part 
of  the  gray  substance  the  neuroglia  presents  the  appearance  of  a  sponge-like  net- 
work, but  around  the  central  canal  and  on  the  apices  of  the  posterior  columns 
it  consists  of  the  gelatinous  substance  already  referred  to.  The  nerve  cells  are 
multipolar,  and  vary  greatly  in  size  and  shape.  They  consist  of  (1)  motor  cells  of 
large  size,  which  are  situated  in  the  anterior  horn,  and  are  especially  numerous  in 
the  cervical  and  lumbar  enlargements;  the  axons  of  most  of  these  cells  pass  out  to 
form  the  anterior  nerve  roots,  but  before  leaving  the  white  substance  they  fre- 
quently give  off  collaterals,  which  reenter  and  ramify  in  the  gray  substance.^  (2) 
Cells  of  small  or  medium  size,  whose 
axons  pass  into  the  white  matter, 
where  some  pursue  an  ascending. 


Hb  and  others  a  descending  course,  but 
"■  most  of  them  divide  in  a  T-shape 
manner  into  descending  and  ascend- 
ing processes.    They  give  off  col- 
laterals which  enter  and  ramify  in 
the  gray  substance,  and  the  termi- 
nations of  the  axons  behave  in  a 
similar  manner.    The   lengths  of 
these    axons   vary   greatly:   some 
L     are  short   and  pass  only  between 
Bp  adjoining    spinal  segments,    while 
"     others  are  longer  and  connect  more 


'.J 


—  Collateral 


■  Ascending 


Fig.  667. — Section  of  central  canal  of  medulla 
spinalis,  showing  ependymal  and  neuroglial  cells. 

(v.  Lenhossek.) 


~  Descending 


•Arborisation 


Fig.  668. — Cells  of  medulla  spinalis.  Diagram  showing 
in  longitudinal  section  the  intersegmental  neurons  of  the 
medulla  spinalis.  The  gray  and  white  parts  correspond 
respectively  to  the  gray  and  white  substance  of  the  medulla 
spinalis.     (Poirier.) 


» 


I 
I 


distant  segments.  These  cells  and  their  processes  constitute  a  series  of  association 
or  intersegmental  neurons  (Fig.  668),  which  link  together  the  different  parts  of 
the  medulla  spinalis.  The  axons  of  most  of  these  cells  are  confined  to  that  side 
of  the  medulla  spinalis  in  which  the  nerve  cells  are  situated,  but  some  cross  to  the 
opposite  side  through  the  anterior  commissure,  and  are  termed  crossed  commissural 
fibers.  Some  of  these  latter  end  directly  in  the  gray  substance,  while  others  enter 
the  white  substance,  and  ascend  or  descend  in  it  for  varying  distances,  before  finally 
terminating  in  the  gray  substance.    (3)  Cells  of  the  type  II  of  Golgi,  limited  for  the 


'  Lenhossek  and  Cajal  found  that  in  the  chick  embryo  the  axons  of  a  few  of  these  nerve  cells  passed  backward  through 
the  posterior  column,  and  emerged  as  the  motor  fibers  of  the  posterior  nerve  roots.  These  fibers  are  said  to  control  the 
peristaltic  movements  of  the  intestine.     Their  presence,  in  man,  has  not  yet  been  determined. 


756 


NEUROLOGY 


most  part  to  the  posterior  column,  are  found  also  in  the  substantia  gelatinosa  of 
Rolando;  their  axons  are  short  and  entirely  confined  to  the  gray  substance,  in  which 


I 


or 

I 


Ventral 

spinocerebellar 

fasciculus 

Posterior 

'  spinothalamie 

fasciculus 

Spinotectal 

fasciculus 

Ventral 

spinothalamic 

fasciculus 

Fiq.  669. — Diagram  showing  a  few  of  the  connections  of  afferent  (sensory)  fibers  of  the  posterior  root  with  the  efferent 
fibers  from  the  ventral  column  and  with  the  various  long  ascending  fasciculi. 

they  break  up  into  numerous  fine  filaments.    Most  of  the  nerve  cells  are  arranged  in 
longitudinal  columns,  and  appear  as  groups  on  transverse  section  (Figs.  669, 670, 671). 


— Lateral  cerebrospinal 
fasciculus 

-Rubrospinal  fasciculus 
-Tectospinal  fasciculus 


—Vestibulospinal  fasciculus 


Fig.  670. — Diagram  showing  possible  connection  of  long  descending  fibers  from  higher  centers  with  the  motor 
cells  of  the  ventral  column  through  association  fibers. 

Nerve  Cells  in  the  Anterior  Column. — The  nerve  cells  in  the  anterior  column  are 
arranged  in  columns  of  varying  length.  The  longest  occupies  the  medial  part  of 
the  anterior  column,  and  is  named  the  antero-medial  column:  it  is  well  marked  in 
C 4,  Co,  again  from  C 8  to  L 4,  it  disappears  in  L 5  and  S 1  but  is  well  marked  in 


THE  MEDULLA  SPINALIS  OR  SPINAL  CORD 


757 


II 


p» 


I 


S2,  S3  and  S4  (Bruce). ^  Behind  it 
is  not  represented  in  L 5,  SI,  S 2  nor 
dorsal  rami  of  the  spinal  nerves  to 
column.  In  the  cervical  and  lumbar 
I  enlargements,  where  the  anterior 
i  column  is  expanded  in  a  lateral  direc- 
tion, the  following  additional  col- 
umns are  present,  viz.:  (a)  antero- 
j  lateral,  which  consists  of  two  groups, 
one  in  C4,  C5,  C6  the  other  in  C6, 
[C7,  C8  in  the  cervical  enlargement 
[and  of  a  group  from  L2  to  S2  in 
the  lumbo-sacral  enlargement;  (b) 
postero-lateral,  in  the  lower  five  cer- 
vical, lower  four  lumbar,  and  upper 
three  sacral  segments;  (c)  post-postero- 
lateral,  in  the  last  cervical,  first  tho- 
racic, and  upper  three  sacral  seg- 
ments; and  (d)  a  central,  in  the  lower 
four  lumbar  and  upper  two  sacral 
segments.  These  cell  groups  are  evi- 
dently related  to  the  nerve  roots  of 
tlie  brachial  and  sacral  plexuses  and 
supply  fibers  to  the  muscles  of  the 
arm  and  leg.  Throughout  the  base 
of  the  anterior  column  are  scattered 
solitary  cells,  the  axons  of  some  of 
which  form  crossed  commissural 
fibers,  Avhile  others  constitute  the 
motor  fibers  of  the  posterior  nerve 
roots.     (See  footnote,  page  755.) 

Nerve  Cells  in  the  Lateral  Column. 

These  form  a  column  which  is 
best  marked  where  the  lateral  gray 
column  is  differentiated,  viz.,  in  the 
thoracic  region  ;2  but  it  can  be  traced 
throughout  the  entire  length  of  the 
medulla  spinalis  in  the  form  of 
groups  of  small  cells  which  are  situ- 
ated in  the  anterior  part  of  the 
formatio  reticularis.  In  the  upper 
part  of  the  cervical  region  and  lower 
part  of  the  medulla  oblongata  as 
well  as  in  the  third  and  fourth  sac- 
ral segments  this  column  is  again 
differentiated.  In  the  medulla  it  is 
known  as  the  lateral  nucleus.  The 
cells  of  this  column  are  fusiform  or 
star-shaped,  and  of  a  medium  size: 
the  axons  of  some  of  them  pass  into 

-  Topographical  Atlas  of  the  Spinal  Cord,  1901. 

'  According  to  Bruce  and  Pirie  (B.  M.  J.,  Novem- 
ber 17,  1906)  this  column  extends  from  the  middle 
of  the  eighth  cervical  segment  to  the  lower  part  of 
the  second  lumbar  or  the  upper  part  of  the  third 
lumbar  segment. 


is  a  dorso-medial  column  of  small  cells,  which 
below  S4.  Its  axons  probably  pass  into  the 
supply  the  dorsal  musculature  of  the  spinal 


Lateral 
column' 

Postero- 
lateral 

column 


Antero-lateral 
column 


Dorso-medial 
column 

,Aniero-medial 
column 


Dorsal  nude 


Lateral  column 


Anterior  column' 


Postero- 
lateral 
column 


Antero-lateral, 
column 


Antero-medial 
column 


Central  column 


Postero-lateral 
column 


Central 
column 


Fia.  671. — Transverse  sections  of  the  medulla  spinalis  at 
different  levels  to  show  the  arrangement  of  the  principal  ceil 
columns. 


758  ^  NEUROLOGY 


I 


the  anterior  nerve  roots,  by  which  they  are  carried  to  the  sympathetic  nerves: 
they  constitute  the  white  rami  and  are  sympathetic  or  visceral  efferent  fibers;  they 
are  also  known  as  preganglionic  fibers  of  the  sympathetic  system;  the  axons  of  others 
pass  into  the  anterior  and  lateral  funiculi,  where  they  become  longitudinal. 

Nerve  Cells  in  the  Posterior  Colunm. — 1 .  The  dorsal  nucleus  (nucleus  dorsalis;  col- 
umn of  Clarke)  occupies  the  medial  part  of  the  base  of  the  posterior  column,  and 
appears  on  the  transverse  section  as  a  well-defined  oval  area.  It  begins  below 
at  the  level  of  the  second  or  third  lumbar  nerve,  and  reaches  its  maximum  size 
opposite  the  twelfth  thoracic  nerve.  Above  the  level  of  the  ninth  thoracic  nerve 
its  size  diminishes,  and  the  column  ends  opposite  the  last  cervical  or  first  thoracic 
nerve.  It  is  represented,  however,  in  the  other  regions  by  scattered  cells,  which 
become  aggregated  to  form  a  cervical  nucleus  opposite  the  third  cervical  nerve, 
and  a  sacral  nucleus  in  the  middle  and  lower  part  of  the  sacral  region.  Its  cells 
are  of  medium  size,  and  of  an  oval  or  pyrif orm  shape ;  their  axons  pass  into  the 
peripheral  part  of  the  lateral  funiculus  of  the  same  side,  and  there  ascend,  prob- 
ably in  dorsal  spinocerebellar  {direct  cerebellar)  fasciculus.  2.  The  nerve  cells  in  the 
substantia  gelatinosa  of  Rolando  are  arranged  in  three  zones :  a  posterior  or  margi- 
nal, of  large  angular  or  fusiform  cells;  an  intermediate,  of  small  fusiform  cells;  and 
an  anterior,  of  star-shaped  cells.  The  axons  of  these  cells  pass  into  the  lateral 
and  posterior  funiculi,  and  there  assume  a  vertical  course.  In  the  anterior  zone 
some  Golgi  cells  are  found  whose  short  axons  ramify  in  the  gray  substance.  3. 
Solitary  cells  of  varying  form  and  size  are  scattered  throughout  the  posterior 
column.  Some  of  these  are  grouped  to  form  the  posterior  basal  column  in  the  base 
of  the  posterior  column,  lateral  to  the  dorsal  nucleus;  the  posterior  basal  column 
is  well-marked  in  the  gorilla  (Waldeyer),  but  is  ill-defined  in  man.  The  axons  of 
its  cells  pass  partly  to  the  posterior  and  lateral  funiculi  of  the  same  side,  and 
partly  through  the  anterior  white  commissure  to  the  lateral  funiculus  of  the 
opposite  side.  Golgi  cells,  type  II,  located  in  this  region  send  axons  to  the  lateral 
and  ventral  columns. 

A  few  star-shaped  or  fusiform  nerve  cells  of  varying  size  are  found  in  the  sub- 
stantia gelatinosa  centralis.  Their  axons  pass  into  the  lateral  funiculus  of  the 
same,  or  of  the  opposite  side. 

The  nerve  fibers  in  the  gray  substance  form  a  dense  interlacement  of  minute 
fibrils  among  the  nerve  cells.  This  interlacement  is  formed  partly  of  axons  which 
pass  from  the  cells  in  the  gray  substance  to  enter  the  white  funiculi  or  nerve  roots; 
partly  of  the  axons  of  Golgi's  cells  which  ramify  only  in  the  gray  substance;  and 
partly  of  collaterals  from  the  nerve  fibers  in  the  white  funiculi  which,  as  already 
stated,  enter  the  gray  substance  and  ramify  within  it. 

White  Substance  {substantia  alba). — The  white  substance  of  the  medulla  spinalis 
consists  of  medullated  nerve  fibers  imbedded  in  a  spongelike  net-work  of  neuroglia, 
and  is  arranged  in  three  funiculi :  anterior,  lateral,  and  posterior.  The  anterior 
funiculus  lies  between  the  anterior  median  fissure  and  the  most  lateral  of  the  ante- 
rior nerve  roots :  the  lateral  funiculus  between  these  nerve  roots  and  the  postero- 
lateral sulcus;  and  the  posterior  funiculus  between  the  postero-lateral  and  the  pos- 
terior median  sulci  (Fig.  672).  The  fibers  vary  greatly  in  thickness,  the  smallest 
being  found  in  the  fasciculus  gracilis,  the  tract  of  Dssauer,  and  inner  part  of  the 
lateral  funiculus;  while  the  largest  are  situated  in  the  anterior  funiculus,  and  in  the 
peripheral  part  of  the  lateral  funiculus.  Some  of  the  nerve  fibers  assume  a  more 
or  less  transverse  direction,  as  for  example  those  which  cross  from  side  to  side 
in  the  anterior  white  commissure,  but  the  majority  pursue  a  longitudinal  course 
and  are  divisible  into  (1)  those  connecting  the  medulla  spinaHs  with  the  brain  and 
conveying  impulses  to  or  from  the  latter,  and  (2)  those  which  are  confined  to  the 
medulla  spinalis  and  link  together  its  different  segments,  i.  e.,  intersegmental  or 
association  fibers. 


THE  MEDULLA  SPINALIS  OR  SPINAL  CORD 


'59 


Nerve  Fasciculi. — ^The  longitudinal  fibers  are  grouped  into  more  or  less  definite 
bundles  or  fasciculi.  These  are  not  recognizable  from  each  other  in  the  normal 
state,  and  their  existence  has  been  determined  by  the  following  methods:  (1) 
A.  Waller  discovered  that  if  a  bundle  of  nerve  fibers  be  cut,  the  portions  of  the 
fibers  which  are  separated  from  their  cells  rapidly  degenerate  and  become  atrophied, 
while  the  cells  and  the  parts  of  the  fibers  connected  with  them  undergo  little  alter- 
ation.^ This  is  known  as  Wallerian  degeneration.  Similarly,  if  a  group  of  nerve 
cells  be  destroyed,  the  fibers  arising  from  them  undergo  degeneration.  Thus, 
if  the  motor  cells  of  the  cerebral  cortex  be  destroyed,  or  if  the  fibers  arising  from 
these  cells  be  severed,  a  descending  degeneration  from  the  seat  of  injury  takes 
place  in  the  fibers.  In  the  same  manner,  if  a  spinal  ganglion  be  destroyed,  or  the 
fibers  which  pass  from  it  into  the  medulla  spinalis  be  cut,  an  ascending  degenera- 
tion will  extend  along  these  fibers.  (2)  Pathological  changes,  especially  in  man, 
have  given  important  information  by  causing  ascending  and  descending  degenera- 


Fasciculus  gracilis-,^ 
(Goll.) 
Fasciculus  cuneatus^ 
(Burdach) 


I. 

■  V        Lateral  proper 
H  V  fascicidus  -  ^ 

.Dorsal 
spinocerebellar 
^  -  fascicidus 

H  ■  (Flechsig) 

Ventro 

spinocerebellar 

fasciculus 

(Gowers) 

Posterior  y 
spinothalamic 
fasciculus 

Spinotectal ' 
fasciculus 


Septomarginal  fasciculus 
I  Comma  fasciculus 

'osterior  proper  fasciculus 

Juissauer's  fasciculus 


Lateral  cerebrospinal 
fasciculus 


Rubrospinal 

fasciculus 
(Monakow) 

Tectospinal  i 
fasciculus 


Anterior  spinothalamic 
fasciculus 


VestibulospinoH 
*  fasciculus 


Anterior  cerebrospinal  fasciculus 


I 


Sulcomarginal  fasciculus 
''Anterior  proper  fasciculus 
Fig.  672. — Diagram  of  the  principal  fasciculi  of  the  spinal  cord. 


tions.  (3)  By  tracing  the  development  of  the  nervous  system,  it  has  been  observed 
that  at  first  the  nerve  fibers  are  merely  naked  axis-cylinders,  and  that  they  do  not 
all  acquire  their  medullary  sheaths  at  the  same  time;  hence  the  fibers  can  be  grouped 
into  different  bundles  according  to  the  dates  at  which  they  receive  their  medullary 
sheaths.  (4)  Various  methods  of  staining  nervous  tissue  are  of  great  value  in 
tracing  the  course  and  mode  of  termination  of  tlie  axis-cylinder  processes. 

Fasciculi  in  the  Anterior  Funiculus. —  Descending  Fasciculi. — ^The  anterior  cerebro- 
spinal {fasciciihis  cerebrospinalis  anterior;  direct  pyramidal  tract),  which  is  usually 
small,  but  varies  inversely  in  size  with  the  lateral  cerebrospinal  fasciculus.  It 
lies  close  to  the  anterior  median  fissure,  and  is  present  only  in  the  upper  part 
of  the  medulla  spinalis;  gradually  diminishing  in  size  as  it  descends,  it  ends  about 
the  middle  of  the  thoracic  region.    It  consists  of  descending  fibers  which  arise 

*  Somewhat  later  a  change,  termed  chromatolysis,  takes  place  in  the  nerve  cells,  and  consists  of  a  breaking  down  and 
an  ultimate  disappearance  of  the  Nissl  bodies.  Further,  tne  body  of  the  cell  is  swollen,  the  nucleus  displaced  toward 
the  periphery,  and  the  part  of  the  axon  still  attached  to  the  altered  cell  is  diminished  in  size  and  somewhat  atrophied. 
Under  favorable  conditions  the  cell  is  capable  of  reassuming  its  normal  appearance,  and  its  axon  jnay  grow  agaio. 


760  ^^         NEUROLOGY 


I 


from  cells  in  the  motor  area  of  the  cerebral  hemisphere  of  the  same  side,  an<i 
which,  as  they  run  downward  in  the  medulla  spinalis,  cross  in  succession  through 
the  anterior  white  commissure  to  the  opposite  side,  where  the}'  end,  either  directly 
or  indirectly,  by  arborizing  around  the  motor  cells  in  the  anterior  column.  A  few 
of  its  fibers  are  said  to  pass  to  the  lateral  column  of  the  same  side  and  to  the 
gray  matter  at  the  base  of  the  posterior  column.  They  conduct  voluntary  motor 
impulses  from  the  precentral  gyrus  to  the  motor  centers  of  the  cord. 

The  vestibulospinal  fasciculus,  situated  chiefly  in  the  marginal  part  of  the  funiculus 
and  mainly  derived  from  the  cells  of  Deiters'  nucleus,  of  the  same  and  the  opposite 
side,  i.  e.,  the  chief  terminal  nucleus  of  the  vestibular  nerve.  Fibers  are  also 
contributed  to  this  fasciculus  from  scattered  cells  of  the  articular  formation  of  the 
medulla  oblongata,  the  pons  and  the  mid-brain  (tegmentum).  The  other  terminal 
nuclei  of  the  vestibular  nerve  also  contribute  fibers.  In  the  brain  stem  these  fibers 
form  part  of  the  median  longitudinal  bundle.  The  fasciculus  can  be  traced  to  the 
sacral  region.  Its  terminals  and  collaterals  end  either  directly  or  indirectly  among 
the  motor  cells  of  the  anterior  column.  This  fasciculus  is  probably  concerned  with 
equilibratory  reflexes. 

The  tectospinal  fasciculus,  situated  partly  in  the  anterior  and  partly  in  the  lateral 
funiculus,  is  mainly  derived  from  the  opposite  superior  colliculus  of  the  mid-brain. 
The  fibers  from  the  superior  colliculus  cross  the  median  raphe  in  the  fountain 
decussation  of  Mejoiert  and  descend  as  the  ventral  longitudinal  bundle  in  the 
reticular  formation  of  the  brain-stem.  Its  collaterals  and  terminals  end  either 
directly  or  indirectly  among  the  motor  cells  of  the  anterior  column  of  the  same  side. 
Since  the  superior  colliculus  is  an  important  visual  reflex  center,  the  tectospinal 
fasciculus  is  probably  concerned  with  visual  reflexes. 

Ascending  Fasciculi. — The  ventral  spinothalamic  fasciculus,  situated  in  the 
marginal  part  of  the  funiculus  and  intermingled  more  or  less  with  the  vestibulo- 
spinal fasciculus,  is  derived  from  cells  in  the  posterior  column  or  intermediate  gray 
matter  of  the  opposite  side.  Their  axons  cross  in  the  anterior  commissure.  This 
is  a  somewhat  doubtful  fasciculus  and  its  fibers  are  supposed  to  end  in  the  thalamus 
and  to  conduct  certain  of  the  touch  impulses. 

The  remaining  fibers  of  the  anterior  funiculus  constitute  what  is  termed  the 
anterior  proper  fasciculus  {fasciculus  anterior  proprius;  anterior  basis  bundle).  It 
consists  of  (a)  longitudinal  intersegmental  fibers  which  arise  from  cells  in  the  gray 
substance,  more  especially  from  those  of  the  medial  group  of  the  anterior  column, 
and,  after  a  longer  or  shorter  course,  reenter  the  gray  substance;  (6)  fibers  which 
cross  in  the  anterior  white  commissure  from  the  gray  substance  of  the  opposite 
side. 

Fasciculi  in  the  Lateral  Funiculus.  —  1 .  Descending  Fasciculi.  —  (a)  The  lateral 
cerebrospinal  fasciculus  (fasciculus  cerebrospinalis  lateralis;  crossed  pyramidal 
tract)  extends  throughout  the  entire  length  of  the  medulla  spinalis,  and  on  trans- 
verse section  appears  as  an  oval  area  in  front  of  the  posterior  column  and  medial 
to  the  cerebellospinal.  Its  fibers  arise  from  cells  in  the  motor  area  of  the  cerebral 
hemisphere  of  the  opposite  side.  They  pass  downward  in  company  with  those 
of  the  anterior  cerebrospinal  fasciculus  through  the  same  side  of  the  brain  as  that 
from  which  they  originate,  but  they  cross  to  the  opposite  side  in  the  medulla  oblon- 
gata and  descend  in  the  lateral  funiculus  of  the  medulla  spinalis. 

It  is  probable^  that  the  fibers  of  the  anterior  and  lateral  cerebrospinal  fasciculi 
are  not  related  in  this  direct  manner  with  the  cells  of  the  anterior  column,  but  ter- 
minate by  arborizing  around  the  cells  at  the  base  of  the  posterior  column  and  the 
cells  of  Clarke's  column,  which  in  turn  link  them  to  the  motor  cells  in  the  anterior 
column,  usually  of  several  segments  of  the  cord.    In  consequence  of  these  interposed 

I  Schfifer,  Proc.  Physiolog.  Hoc,  1899. 


n 


n 


IP 


I 


THE  MEDULLA  SPINALIS  OR  SPINAL  CORD  761 

neurons  the  fibers  of  the  cerebrospinal  fasciculi  correspond  not  to  individual  muscles, 
hut  to  associated  groups  of  muscles. 

The  anterior  and  lateral  cerebrospinal  fasciculi  constitute  the  motor  fasciculi 
iof  the  medulla  spinalis  and  have  their  origins  in  the  motor  cells  of  the  cerebral 
cortex.  They  descend  through  the  internal  capsule  of  the  cerebrum,  traverse  the 
cerebral  peduncles  and  pons  and  enter  the  pyramid  of  the  medulla  oblongata. 
In  the  lower  part  of  the  latter  about  two-thirds  of  them  cross  the  middle  line  and 
run  downward  in  the  lateral  funiculus  as  the  lateral  cerebrospinal  fasciculus,  while 
the  remaining  fibers  do  not  cross  the  middle  line,  but  are  continued  into  the  same 
side  of  the  medulla  spinalis,  where  they  form  the  anterior  cerebrospinal  fasciculus. 
The  fibers  of  the  latter,  however,  cross  the  middle  line  in  the  anterior  white  com- 
missure, and  thus  all  the  motor  fibers  from  one  side  of  the  brain  ultimately  reach 
the  opposite  side  of  the  medulla  spinalis.  The  proportion  of  fibers  which  cross 
in  the  medulla  oblongata  is  not  a  constant  one,  and  thus  the  anterior  and  lateral 
cerebrospinal  fasciculi  vary  inversely  in  size.  Sometimes  the  former  is  absent, 
and  in  such  cases  it  may  be  presumed  that  the  decussation  of  the  motor  fibers  in 
the  medulla  oblongata  has  been  complete.  The  fibers  of  these  two  fasciculi  do 
not  acquire  their  medullary  sheaths  until  after  birth.  In  some  animals  the  motor 
fibers  are  situated  in  the  posterior  funiculus. 

(6)  The  rubrospinal  fasciculus  (Monakow)  {prepyramidal  tract),  lies  on  the  ventral 
aspect  of  the  lateral  cerebrospinal  fasciculus  and  on  transverse  section  appears 
as  a  somewhat  triangular  area.  Its  fibers  descend  from  the  mid-brain,  where  they 
have  their  origin  in  the  red  nucleus  of  the  tegmentum  of  the  opposite  side.  Its 
terminals  and  collaterals  end  either  directly  or  indirectly  in  relation  with  the  motor 
cells  of  the  anterior  column.  The  rubrospinal  fasciculus  is  supposed  to  be  concerned 
with  cerebellar  reflexes  since  fibers  which  pass  from  the  cerebellum  through  the 
superior  peduncle  send  many  collaterals  and  terminals  to  the  red  nucleus. 

(c)  The  olivospinal  fasciculus  (Helweg)  arises  in  the  vicinity  of  the  inferior 
olivary  nucleus  in  the  medulla  oblongata,  and  is  seen  only  in  the  cervical  region 
of  the  medulla  spinalis,  where  it  forms  a  small  triangular  area  at  the  periphery, 
close  to  the  most  lateral  of  the  anterior  nerve  roots.  Its  exact  origin  and  its  mode 
f  ending  have  not  yet  been  definitely  made  out. 

2.  Ascending  Fascicidi. — (a)  The  dorsal  spinocerebellar  fasciculus  {fasciculus 
cerehellospinalis;  direct  cerebellar  tract  of  Flechsig)  is  situated  at  the  periphery  of  the 
posterior  part  of  the  lateral  funiculus,  and  on  transverse  section  appears  as  a 
flattened  band  reaching  as  far  forward  as  a  line  drawn  transversely  through  the 
central  canal.  Medially,  it  is  in  contact  with  the  lateral  cerebrospinal  fasciculus, 
behind,  with  the  fasciculus  of  Lissauer.  It  begins  about  the  level  of  the  second  or 
third  lumbar  nerve,  and  increasing  in  size  as  it  ascends,  passes  to  the  vermis  of  the 
cerebellum  through  the  inferior  peduncle.  Its  flbers  are  generally  regarded  as 
being  formed  by  the  axons  of  the  cells  of  the  dorsal  nucleus  {Clarke's  column) ;  they 
receive  their  medullar}-  sheatlis  about  the  sixth  or  seventh  month  of  fetal  life.  Its 
fibers  are  supposed  to  conduct  impulses  of  unconscious  muscle  sense. 

The  superficial  antero-lateral  fasciculus  {tract  of  Gowers)  consists  of  four  fasciculi, 
the  ventral  spinocerebellar,  the  lateral  spinothalamic,  the  spinotectal  and  the 
ventral  spinothalamic. 

(6)  The  ventral  spinocerebellar  fasciculus  {Gowers)  skirts  the  periphery  of  the 
lateral  funiculus  in  front  of  the  dorsal  spinocerebellar  fasciculus.  In  transverse 
section  it  is  shaped  somewhat  like  a  comma,  the  expanded  end  of  which  lies  in  front 
of  the  dorsal  spinocerebellar  fasciculus  while  the  tail  reaches  forward  into  the 
anterior  funiculus.  Its  fibers  come  from  the  same  but  mostly  from  the  opposite 
side  of  the  medulla  spinalis  and  cross  both  in  the  anterior  white  commissure  and 
in  the  gray  commissure;  they  are  probably  derived  from  the  cells  of  the  dorsal 
nucleus  and  from  other  cells  of  the  posterior  column  and  the  intermediate  portion 


11^ 


762  NEUROLOGY 


I 


of  the  gray  matter.  The  ventral  spinocerebellar  fasciculus  begins  about  the  level 
of  the  tliird  pair  of  lumbar  nerves,  and  can  be  followed  into  the  medulla  oblongata 
and  pons  almost  to  the  level  of  the  inferior  colliculus  where  it  crosses  over  the 
superior  peduncle  and  then  passes  backward  along  its  medial  border  to  reach  the 
vermis  of  the  cerebellum.  In  the  pons  it  lies  along  the  lateral  edge  of  the  lateral 
lemniscus.  Some  of  its  fibers  join  the  dorsal  spinocerebellar  fasciculus  at  the  level 
of  the  inferior  peduncle  and  pass  with  them  into  the  cerebellum.  Other  fibers  are 
said  to  continue  upward  in  the  dorso-lateral  part  of  the  tegmentum  of  the  mid-braift 
probably  as  far  as  the  thalamus.  Hj 

(c)  The  lateral  spinothalamic  fasciculus  is  supposed  to  come  from  cells  in  the  dors^ 
column  and  the  intermediate  gray  matter  whose  axons  cross  in  the  anterior  com- 
missure to  the  opposite  lateral  funiculus  where  they  pass  upward  on  the  medial 
side  of  the  ventral  spinocerebellar  fasciculus;  on  reaching  the  medulla  oblongata 
they  continue  in  the  formatio  reticularis  near  the  median  fillet  and  probably  ter- 
minate in  the  ventro-lateral  region  of  the  thalamus.  It  is  supposed  to  conduct 
impulses  of  pain  and  temperature.  The  lateral  and  ventral  spinothalamic  fasciculi 
are  sometimes  termed  the  secondary  sensory  fasciculus  or  spinal  lemniscus. 

(d)  The  spinotectal  fasciculus  is  supposed  to  arise  in  the  dorsal  column  and 
terminate  in  the  (inferior  ?)  and  superior  colliculi.  It  is  situated  ventral  to  the 
lateral  spmothalamic  fasciculus,  but  its  fibers  are  more  or  less  intermingled  with  it. 
It  is  also  known  as  the  spino-quadrigeminal  system  of  Mott.  In  the  brain-stem  the 
fibers  run  lateral  from  the  inferior  olive,  ventro-lateral  from  the  superior  olive,  then 
ventro-medial  from  the  spinal  tract  of  the  trigeminal;  the  fibers  come  to  lie  in  the 
medial  portion  of  the  lateral  lemniscus. 

(e)  The  fasciculus  of  Lissauer  is  a  small  strand  situated  in  relation  to  the  tip 
of  the  posterior  column  close  to  the  entrance  of  the  posterior  nerve  roots.  It 
consists  of  fine  fibers  which  do  not  receive  their  medullary  sheaths  until  toward 
the  close  of  fetal  life.  It  is  usually  regarded  as  being  formed  by  some  of  the  fibers 
of  the  posterior  nerve  roots,  which  ascend  for  a  short  distance  in  the  tract  and  then 
enter  the  posterior  column,  but  since  its  fibers  are  myelinated  later  than  those  of 
the  posterior  nerve  roots,  and  do  not  undergo  degeneration  in  locomotor  ataxia, 
they  are  probably  intersegmental  in  character. 

In  addition  the  fasciculus  or  tract  of  Lissauer  contains  great  numbers  of  fine 
non-medullated  fibers  derived  mostly  from  the  dorsal  roots  but  partly  endogenous 
in  origin.  These  fibers  are  intimately  related  to  the  substantia  gelatinosa  which  is 
probably  the  terminal  nucleus.  The  non-medullated  fibers  ascend  or  descend  for 
short  distances  not  exceeding  one  or  two  segments,  but  most  of  them  enter  the 
substantia  gelatinosa  at  or  near  the  level  of  their  origin.  Ransom^  suggests  that 
these  non-medullated  fibers  and  the  substantia  gelatinosa  are  concerned  with  the 
reflexes  associated  with  pain  impulses. 

(/)  The  lateral  proper  fasciculus  (fasciculus  lateralis  proprius;  lateral  basis  bundle) 
constitutes  the  remainder  of  the  lateral  column,  and  is  continuous  in  front  with  the 
anterior  proper  fasciculus.  It  consists  chiefly  of  intersegmental  fibers  which  arise 
from  cells  in  the  gray  substance,  and,  after  a  longer  or  shorter  course,  reenter  the 
gray  substance  and  ramify  in  it.  Some  of  its  fibers  are,  however,  continued  upward 
into  the  brain  under  the  name  of  the  medial  longitudinal  fasciculus. 

Fasciculi  in  the  Posterior  Funiculus. — This  funiculus  comprises  two  main  fasciculi, 
viz.,  the  fasciculus  gracilis,  and  the  fasciculus  cuneatus.  These  are  separated  from 
each  other  in  the  cervical  and  upper  thoracic  regions  by  the  postero-intermediate 
septum,  and  consist  mainly  of  ascending  fibers  derived  from  the  posterior  nerve  roots. 

The  fasciculus  gracilis  {tract  of  Goll)  is  wedge-shaped  on  transverse  section,  and 
lies  next  the  posterior  median  septum,  its  base  being  at  the  surface  of  the  medulla 

'  Ransom,  Am.  Jour.  Anat.,  1914;  Brain,  1913. 


THE  MEDULLA  SPINALIS  OR  SPINAL  CORD 


763 


spinalis,  and  Its  apex  directed  toward  the  posterior  gray  commissure.  It  increases 
in  size  from  below  upward,  and  consists  of  long  thin  fibers  which  are  derived  from 
the  posterior  nerve  roots,  and  ascend  as  far  as  the  medulla  oblongata,  where  they 
end  in  the  nucleus  gracilis. 

The  fasciculus  cuneatus  (tract  of  Burdach)  is  triangular  on  transverse  section, 
and  lies  between  the  fasciculus  gracilis  and  the  posterior  column,  its  base  corre- 
sponding with  the  surface  of  the  medulla  spinalis.    Its  fibers,  larger  than  those  of 


First 

thoracic 

nerve 


Descending  comma  fascicvlua 


Posterior 
column 


Oval  area  of  Flechsig. 


Sacral 
nerves 


Fig.  673. — Formation  of  the  fasciculus  gracilis.  Medulla 
■apinalis  viewed  from  behind.  To  the  left,  the  fasciculus 
gracilis  is  shaded.  To  the  right,  the  drawing  shows  that 
the  fasciculus  gracilis  is  formed  by  the  long  fibers  of  the 
posterior  roots,  and  that  in  this  tract  the  sacral  nerves 
lie  next  the  ■  median  plane,  the  lumbar  to  their  lateral 
side,  and  the  thoracic  still  more  laterally.     (Poirier.) 


Posterior 
\       column 


\      Posterior 
column 


Fig.  _  674. — Descending  fibers  in  the  posterior 
funiculi,  shown  at  different  levels.  A.  In  the  conus 
medullaris.  B.  In  the  lumbar  region.  C.  In  the 
lower  thoracic  region.  D.  In  the  upper  thoracic 
region.     (After  Testut.) 


I 


the  fasciculus  gracilis,  are  mostly  derived  from  the  same  source,  viz.,  the  posterior 
nerve  roots.  Some  ascend  for  only  a  short  distance  in  the  tract,  and,  entering 
the  gray  matter,  come  into  close  relationship  with  the  cells  of  the  dorsal  nucleus; 
while  others  can  be  traced  as  far  as  the  medulla  oblongata,  where  they  end  in  the 
gracile  and  cuneate  nuclei. 

The  fasciculus  gracilis  and  fasciculus  cuneatus  conduct  (1)  impulses  of  conscious 
muscle  sense,  neurons  of  the  second  order  from  the  nucleus  gracilis  and  nucleus 
cuneatus,  pass  in  the  median  lemniscus  to  the  thalamus  and  neurons  of  the  third 


764 


TUOLOm 


I 


order  from  the  thalamus  to  the  cerebral  cortex ;  (2)  impulses  of  unconscious  muscle 
sense,  via  neurons  of  the  second  order  from  the  nucleus  gracilis  and  nucleus  cuneatu:? 
pass  in  the  internal  and  external  arcuate  fibers  of  the  medulla  oblongata  to  th(^ 
inferior  peduncle  and  through  it  to  the  cerebellum ;  (3)  impulses  of  tactile  discrimina- 
tion, via  neurons  of  the  second  order  from  the  nucleus  cuneatus  and  nucleus  gracilis 
pass  in  the  median  lemniscus  to  the  thalamus,  neurons  of  the  third  order  pass  from 
the  thalamus  to  the  cortex. 

The  Posterior  Proper  Fasciculus  {posterior  ground  bundle;  posterior  basis  bundle) 
arises  from  cells  in  the  posterior  column;  their  axons  bifurcate  into  ascending  and 
descending  branches  which  occupy  the  ventral  part  of  the  funiculus  close  to  th(; 
gray  column.  They  are  intersegmental  and  run  for  varvang  distances  sending  off 
collaterals  and  terminals  to  the  gray  matter. 

Some  descending  fibers  occupy  different  parts  at  different  levels.  In  the  cer- 
vical and  upper  thoracic  regions  they  appear  as  a  comma-shaped  fasciculus  in 
the  lateral  part  of  the  fasciculus  cuneatus,  the  blunt  end  of  the  comma  being 
directed  toward  the  posterior  gray  commissure;  in  the  lower  thoracic  region  they 
form  a  dorsal  peripheral  band  on  the  posterior  surface  of  the  funiculus;  in  the  lumbar 
region,  they  are  situated  by  the  side  of  the  posterior  median  septum,  and  appear 
on  section  as  a  semi-elliptical  bundle,  which,  together  with  the  corresponding 
bundle  of  the  opposite  side,  forms  the  oval  area  of  Flechsig;  while  in  the  conus 
medullaris  they  assume  the  form  of  a  triangular  strand  in  the  postero-medial  part 
of  the  fasciculus  gracilis.  These  descending  fibers  are  mainly  intersegmental 
in  character  and  derived  from  cells  in  the  posterior  column,  but  some  consist 
of  the  descending  branches  of  the  posterior  nerve  roots.  The  comma-shaped 
fasciculus  was  supposed  to  belong  to  the  second  category,  but  against  this  view 
is  the  fact  that  it  does  not  undergo  descending  degeneration  when  the  posterior 
nerve  roots  are  destroyed. 

Roots  of  the  Spinal  Nerves. — As  already  stated,  each  spinal  nerve  possesses 
two  roots,  an  anterior  and  a  posterior,  which  are  attached  to  the  surface  of  the 

medulla    spinalis    opposite    the 
Lateral  column  Corresponding    column   of    gray 

substance  (Fig.  675) ;  their  fibers 
become  medullated  about  the 
fifth  month  of  fetal  life. 

The  Anterior  Nerve  Root  (radix 
anterior)  consists  of  eiferent  fibers, 
which  are  the  axons  of  the  nerve 
cells  in  the  ventral  part  of  the 
anterior  and  lateral  columns.  A 
short  distance  from  their  origins, 
tliese  axons  are  invested  by  medul- 
lary sheaths  and,  passing  forward, 
emerge  in  two  or  three  irregular 
rows  over  an  area  Avhich  meas- 
ures about  3  mm.  in  width. 

The  Posterior  Root  (radix  pos- 
terior) comprises  some  six  or  eight 
fasciculi,  attached  in  linear  series 
along  the  postero-lateral  sulcus. 
It  consists  of  afferent  fibers  which 
arise  from  the  nerve  cells  in  a  spinal  ganglion.  Each  ganglion  cell  gives  off  a  single 
fiber  which  divides  in  a  T-shaped  manner  into  two  processes,  medial  and  lateral. 
The  lateral  processes  extend  to  the  sensory  end-organs  of  the  skin,  muscles,  tendons, 
joints,  etc.  (somatic  receptors),  and  to  the  sensory  end-organs  of  the  viscera  (visceral 


Ant.  med.  fissure 
Anterior  column'*' 


Anterior  root 


Fia.  675. — A  spinal  nerve  with  its  anterior  and  posterior  roots. 


THE  MEDULLA  SPINALIS  OR  SPINAL  CORD 


'65 


l)> 


eceptors).    The  medial  processes  of  the  ganglion  cells  grow  into  the  medulla  spinalis 
s  the  posterior  roots  of  the  spinal  nerves. 

The  posterior  nerve  root  enters  the  medulla  spinalis  in  three  chief  bundles, 

edial,  intermediate,  and  lateral.  The  medial  strand  passes  directly  into  the  fas- 
ciculus cuneatus :  it  consists  of  coarse  fibers,  which  acquire  their  medullary  sheaths 
about  the  fifth  month  of  intrauterine  life;  the  intermediate  strand  consists  of  coarse 
fibers,  which  enter  the  gelatinous  substance  of  Rolando;  the  lateral  is  composed 
of  fine  fibers,  which  assume  a  longitudinal  direction  in  the  tract  of  Lissauer,  and 
iio  not  acquire  their  medullary  sheaths  until  after  birth.  In  addition  to  these 
tnedullated  fibers  there  are  great  numbers  of  non-meduUated  fibers  winch  enter 
Brith  the  lateral  bundle.  They  are  more  numerous  than  the  myelinated  fibers. 
They  arise  from  the  small  cells  of  the  spinal  ganglia  by  T-shaped  axons  similar 
to  the  myelinated.  They  are  distributed  with  the  peripheral  nerves  chiefly  to  the 
jkin,  only  a  few  are  found  in  the  nerves  to  the  muscles.^ 

Having  entered  the  medulla  spinalis,  all  the  fibers  of  the  posterior  nerve  roots 
iivide  into  ascending  and  descending  branches,  and  these  in  their  turn  give  off 
collaterals  which  enter  the  gray 
substance  (Fig.  676).  The  de- 
scending fibers  are  short,  and 
soon  enter  the  gray  substance. 
The  ascending  fibers  are  grouped 
into  long,  short,  and  intermedi- 
ate: the  long  fibers  ascend  in 
the  fasciculus  cuneatus  and  fas- 
ciculus gracilis  as  far  as  the  me- 
dulla oblongata,  where  they  end 
by  arborizing  around  the  cells  of 
the  cuneate  and  gracile  nuclei; 
the  short  fibers  run  upward  for 
a  distance  of  only  5  or  6  mm. 
and  enter  the  gray  substance; 
while  the  intermediate  fibers, 
after  a  somewhat  longer  course, 
have  a  similar  destination.  All 
fibers  entering  the  gray  sub- 
stance end  by  arborizing  around 
its  nerve  cells  or  the  dendrites 
of  cells,  those  of  intermediate 
length  being  especially  associated 
with  the  cells  of  the  dorsal  nu- 
cleus. 

The  long  fibers  of  the  posterior  nerve  roots  pursue  an  oblique  course  upward,  being 
situated  at  first  in  the  lateral  part  of  the  fasciculus  cuneatus :  higher  up,  they  occupy 
the  middle  of  this  fasciculus,  having  been  displaced  by  the  accession  of  other 
entering  fibers;  while  still  higher,  they  ascend  in  the  fasciculus  gracilis.  The  upper 
cervical  fibers  do  not  reach  this  fasciculus,  but  are  entirely  confined  to  the  fascic- 
ulus cuneatus.  The  localization  of  these  fibers  is  very  precise:  the  sacral  nerves 
lie  in  the  medial  part  of  the  fasciculus  gracilis  and  near  its  periphery,  the  lumbar 
nerves  lateral  to  them,  the  thoracic  nerves  still  more  laterally;  while  the  cervical 
nerves  are  confined  to  the  fasciculus  cuneatus  (Fig.  673). 


Fig.  676. — Posterior  roots  entering  medulla  spinalis  and  dividing 
into  ascending  and  descending  branches.  (Van  Gehuchten.)  o. 
Stem  fiber,  b,  b.  Ascending  and  descending  limbs  of  bifurcation, 
c.  Collateral  arising  from  stem  fiber. 


1  Ransom,  Brain,  1915,  38. 


NEUROLOGY 


THE   ENCEPHALON   OR   BRAIN. 

General  Considerations  and  Divisions. — The  brain,  is  contained  within  the 
cranium,  and  constitutes  the  upper,  greatly  expanded  part  of  the  central  nervous 

system.  In  its  early  embryonic 
condition  it  consists  of  three  hollow 
vesicles,  termed  the  hind-brain  or 
rhombencephalon,  the  mid-brain  or 
mesencephalon,  and  the  fore-brain 
or  prosencephalon;  and  the  parts 
derived  from  each  of  these  can 
be  recognized  in  the  adult  (Fig. 
677).  Thus  in  the  process  of  de- 
velopment the  wall  of  the  hind- 
brain  undergoes  modification  to 
form  the  medulla  oblongata,  the 
pons,  and  cerebellum,  while  its 
cavity  is  expanded  to  form  the 
fourth  ventricle.  The  mid-brain 
forms  only  a  small  part  of  the 
adult  brain;  its  cavity  becomes 
the   cerebral  aqueduct  {aqueduct  of 


Middle  peduncle 
Inferior  peduncle 

Medulla  oblongata 


Fig.  677. — Scheme  showing  the  connections  of  the  several 
parts  of  the  brain.     (After  Schwalbe.) 


c.eR"JS£iZ,£o^ 


BASAL   GANGLIA 
OF   FORE-BRAIN 


CORPORA 
QUAORIGCMINA 


TT    RETICULAR    GANGLIONI 

*■*■'  MASS   WITX    CRANIA 

NERVE   NUCLE 


NTRAL    GRAY  (FLOOR    OF 
URTH      VENTRICLE      AND 
ROUND    aqueduct) 


NTRAL  GRAY  OF  I. 
INAL   CORD 


Fig.  C78. — Schematic  representation  of  the  chief  ganglionic  categories  (I  to  V).     (Spitzka.) 


n 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON  767 

Sylvius),  which  serves  as  a  tubular  communication  between  the  third  and  fourth 
'ventricles;  Avhile  its  walls  are  thickened  to  form  the  corpora  quadrigemina  and 
cerebral  peduncles.  The  fore-brain  undergoes  great  modification:  its  anterior  part 
or  telencephalon  expands  laterally  in  the  form  of  two  hollow  vesicles,  the  cavities 
of  which  become  the  lateral  ventricles,  while  the  surrounding  walls  form  the  cere- 
bral hemispheres  and  their  commissures ;  the  cavity  of  the  posterior  part  or  dien- 
cephalon  forms  the  greater  part  of  the  third  ventricle,  and  from  its  walls  are  devel- 
oped most  of  the  structures  which  bound  that  cavity. 


THE   HIND-BRAIN    OR   RHOMBENCEPHALON. 


I 


The  hind-brain  or  rhombencephalon  occupies  the  posterior  fossa  of  the  cranial 
cavity  and  lies  below  a  fold  of  dura  mater,  the  tentorium  cerebelli.  It  consists 
of  (a)  the  myelencephalon,  comprising  the  medulla  oblongata  and  the  lower  part 
of  the  fourth  ventricle;  (6)  the  metencephalon,  consisting  of  the  pons,  cerebellum, 
and  the  intermediate  part  of  the  fourth  ventricle;  and  (c)  the  isthmus  rhomben- 
cephali,  a  constricted  portion  immediately  adjoining  the  mid-brain  and  includ- 
ing the  superior  peduncles  of  the  cerebellum,  the  anterior  medullary  velum,  and 
the  upper  part  of  the  fourth  ventricle. 

The  Medulla  Oblongata  {spinal  bulb). — The  medulla  oblongata  extends  from 
the  lower  margin  of  the  pons  to  a  plane  passing  transversely  below  the  pyram- 
idal decussation  and  above  the  first  pair  of  cervical  nerves;  this  plane  corre- 
sponds with  the  upper  border  of  the  atlas  behind,  and  the  middle  of  the  odontoid 
process  of  the  axis  in  front;  at  this  level  the  medulla  oblongata  is  continuous 
with  the  medulla  spinalis.  Its  anterior  surface  is  separated  from  the  basilar  part  of 
the  occipital  bone  and  the  upper  part  of  the  odontoid  process  by  the  membranes 
of  the  brain  and  the  occipitoaxial  ligaments.  Its  posterior  surface  is  received  into 
the  fossa  between  the  hemispheres  of  the  cerebellum,  and  the  upper  portion  of  it 
forms  the  lower  part  of  the  floor  of  the  fourth  ventricle. 

The  medulla  oblongata  is  pyramidal  in  vshape,  its  broad  extremity  being  directed 
upward  toward  the  pons,  while  its  narrow,  lower  end  is  continuous  with  the  medulla 
spinalis.  It  measures  about  3  cm.  in  length,  about  2  cm.  in  breadth  at  its  widest 
part,  and  about  1.25  cm.  in  thickness.  The  central  canal  of  the  medulla  spinalis 
is  prolonged  into  its  lower  half,  and  then  opens  into  the  cavity  of  the  fourth  ven- 
tricle; the  meduUa  oblongata  may  therefore  be  divided  into  a  lower  closed  part 
containing  the  central  canal,  and  an  upper  open  part  corresponding  with  the  lower 
portion  of  the  fourth  ventricle. 

The  Anterior  Median  Fissure  ifissura  mediana  anterior;  ventral  or  ventromedian 
fissure)  contains  a  fold  of  pia  mater,  and  extends  along  the  entire  length  of  the 
medulla  oblongata:  it  ends  at  the  lower  border  of  the  pons  in  a  small  triangular 
expansion,  termed  the  foramen  cecum.  Its  lower  part  is  interrupted  by  bundles 
of  fibers  which  cross  obliquely  from  one  side  to  the  other,  and  constitute  the  P3rram- 
idal  decussation.  Some  fibers,  termed  the  anterior  external  arcuate  fibers,  emerge 
from  the  fissure  above  this  decussation  and  curve  lateralward  and  upward  over 
the  surface  of  the  medulla  oblongata  to  join  the  inferior  peduncle. 

The  Posterior  Median  Fissure  (fissura  mediana  posterior;  dorsal  or  dorsomedian 
fissure)  is  a  narrow  groove;  and  exists  only  in  the  closed  part  of  the  medulla  oblon- 
gata; it  becomes  gradually  shallower  from  below  upward,  and  finally  ends  about 
the  middle  of  the  medulla  oblongata,  where  the  central  canal  expands  into  the 
cavity  of  the  fourth  ventricle. 

These  two  fissures  divide  the  closed  part  of  the  medulla  oblongata  into  sym- 
metrical halves,  each  presenting  elongated  eminences  which,  on  surface  view, 
are  continuous  with  the  funiculi  of  the  medulla  spinalis.  In  the  open  part  the 
halves  are  separated  by  the  anterior  median  fissure,  and  by  a  median  raphe  which 


768 


NEUROLOGY 


extends  from  the  bottom  of  the  fissure  to  the  floor  of  the  fourth  ventric^.  Furtner, 
certain  of  the  cranial  nerves  pass  through  the  substance  of  the  medulla  oblongata, 
and  are  attached  to  its  surface  in  series  with  the  roots  of  the  spinal  nerves;  thus, 
the  fibers  of  the  hypoglossal  nerve  represent  the  upward  continuation  of  the 
anterior  nerve  roots,  and  emerge  in  linear  series  from  a  furrow  termed  the 
antero-lateral  sulcus.  Similarly,  the  accessory,  vagus,  and  glossopharyngeal  nerves 
correspond  with  the  posterior  nerve  roots,  and  are  attached  to  the  bottom  of  a  sulcus 
named  the  postero-lateral  sulcus.  Advantage  is  taken  of  this  arrangement  to  sub- 
divide each  half  of  the  medulla  oblongata  into  three  districts,  anterior,  middle, 
and  posterior.  Although  these  three  districts  appear  to  be  directly  continuous 
with  the  corresponding  funiculi  of  the  medulla  spinalis,  they  do  not  necessarily 
contain  the  same  fibers,  since  some  of  the  fasciculi  of  the  medulla  spinalis  end  in 
the  medulla  oblongata,  while  others  alter  their  course  in  passing  through  it. 

The  anterior  district  (Fig.  679)  is  named  the  pjrramid  {yyramis  medullce  oblongatce) 
and  lies  between  the  anterior  median  fissure  and  the  antero-lateral  sulcus.  Its 
upper  end  is  slightly  constricted, 
and  between  it  and  the  pons 
the  fibers  of  the  abducent  nerve 
emerge;  a  little  below  the  pons  it 
becomes  enlarged  and  prominent, 
and  finally  tapers  into  the  anterior 
funiculus  of  the  medulla  spinalis, 
with  which,  at  first  sight,  it  ap- 
pears to  be  directly  continuous. 

The  two  pyramids  contain  the 
motor  fibers  which  pass  from  the 
brain  to  the  medulla  oblongata  and 
medulla  spinalis,  corticobulbar  and 
corticospinal  fibers.  When  these 
pyramidal  fibers  are  traced  down- 


Brachium 

pontis 
cerebeUi 


I 


Fig.  679. — Medulla  oblongata  and  pons. 
Anterior  surface. 


l-'iG.  680. — Decussation  of  pyramids.  Scheme  showing  pas- 
sage of  various  fasciculi  from  medulla  spinalis  to  medulla  ob- 
longata, o.  Pons.  b.  Medulla  oblongata,  c.  Decussation  of 
the  pyramids,  d.  Section  of  cervical  part  of  medulla  spinalis. 
i.  Anterior  cerebrospinal  fasciculus  (in  red).  2.  Lateral 
cerebrospinal  fasciculus  (in  red).  3.  Sensory  tract  (fasciculi 
gracilis  et  cuneatus)  (in  blue).  3'.  Gracile  and  cuneate  nuclei. 
4.  Antero-lateral  proper  fasciculus  (in  dotted  line).  5.  Pyra- 
mid. 6.  Lemniscus.  7.  Medial  longitudinal  fasciculus.  8. 
Ventral  spinocerebellar  fasciculus  (in  blue).  9.  Dorsal  spino- 
cerebellar fasciculus  (in  yellow).     (Testut.) 


ward  it  is  found  that  some  two-thirds  or  more  of  them  leave  the  pyramids  in 
successive  bundles,  and  decussate  in  the  anterior  median  fissure,  forming  what  is 
termed  the  pyramidal  decussation.  Having  crossed  the  middle  line,  they  pass  down 
in  the  posterior  part  of  the  lateral  funiculus  as  the  lateral  cerebrospinal  fascic- 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON 


769 


ulus.  The  remaining  fibers^ — i.  e.,  those  which  occupy  the  lateral  part  of  the 
pyramid — do  not  cross  the  middle  line,  but  are  carried  downward  as  the  anterior 
cerebrospinal  fasciculus  (Fig.  680)  into  the  anterior  funiculus  of  the  same  side. 

The  greater  part  of  the  anterior  proper  fasciculus  of  the  medulla  spinalis  is  con- 
tinued upward  through  the  medulla  oblongata  under  the  name  of  the  medial 
longitudinal  fasciculus. 

SupeHor  hrachiiim     Lateral  geniculate  body 


Inferior  hrachium 
Pulvinar    I  A 
Pineal  body    \     M 

\ 


Medial  geniculate  body 

02>tic  tract 


Superior  collie v/i  -! — 
Inferior  collicidi .  \ 

Frenulum  veli 

Trochlear  -nerve 

Lateral  lemniscus 

Superior  peduncle 

Middle  peduncle 
Rhomboid  fossa 


Clava  — 


Glossopharyngeal  aivl  vagus  nerves 


Accessory  nerve 


Optic  commissure 


Oculomotor  nerve 


Trigeminal  nerve 


Acoustic  nerve 
Facial  nerce 


Abducent  nerve 


Hypoglossal  nerve 


Fia.  681. — Hind-  and  mid-brains;  posterolateral  view. 

The  lateral  district  (Fig.  681)  is  limited  in  front  by  the  antero-lateral  sulcus 
and  the  roots  of  the  hypoglossal  nerve,  and  behind  by  the  postero-lateral  sulcus 
and  the  roots  of  the  accessory,  vagus,  and  glossopharyngeal  nerves.  Its  upper  part 
consists  of  a  prominent  oval  mass  which  is  named  the  olive,  while  its  lower  part 
is  of  the  same  width  as  the  lateral  funiculus  of  the  medulla  spinalis,  and  appears 
on  the  surface  to  be  a  direct  continuation  of  it.  As  a  matter  of  fact,  only  a  portion 
of  the  lateral  funiculus  is  continued  upward  into  this  district,  for  the  lateral  cerebro- 
spinal fasciculus  passes  into  the  pyramid  of  the  opposite  side,  and  the  dorsal 
spinocerebellar  fasciculus  is  carried  into  the  inferior  peduncle  in  the  posterior 
district.  The  ventral  spinocerebellar  fasciculus  is  continued  upward  on  the  lateral 
surface  of  the  medulla  oblongata  in  the  same  relative  position  it  occupies  in  the 
spinal  cord  until  it  passes  under  cover  of  the  external  arcuate  fibers.  It  passes 
beneath  these  fibers  just  dorsal  to  the  olive  and  ventral  to  the  roots  of  the  vagus 
and  glossopharyngeal  nerves;  it  continues  upward  through  the  pons  along  the 
dorso-lateral  edge  of  the  lateral  lemniscus.  The  remainder  of  the  lateral  funiculus 
consists  chiefly  of  the  lateral  proper  fasciculus.  Most  of  these  fibers  dip  beneath 
the  olive  and  disappear  from  the  surface;  but  a  small  strand  remains  superficial  to 
the  olive.    In  a  depression  at  the  upper  end  of  this  strand  is  the  acoustic  nerve. 

The  olive  (oliva;  olivary  body)  is  situated  lateral  to  the  pyramid,  from  which  it 
is  separated  by  the  antero-lateral  sulcus,  and  the  fibers  of  the  hypoglossal  nerve. 
Behind,  it  is  separated  from  the  postero-lateral  sulcus  by  the  ventral  spinocerebellar 
fasciculus.  In  the  depression  between  the  upper  end  of  the  olive  and  the  pons  lies 
the  acoustic  nerve.  It  measures  about  1.25  cm.  in  length,  and  between  its  upper 
49 


770 


NEUROLOGY 


Ventral  spinocere- 
bellar fasciculus 


Mn. 


Fig.  682. — Superficial  dissection  of  brain-stem.     Lateral  vipw. 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON 


771 


lateral  geniculate 
Superior  coUiculus 


I 


Stria  terminalis 


External  arcuate 
fibers 

Dorsal  external 
arcuate  fibers 


Pyramidal  tract 


Fig.  G83. — Dissection  of  brain-stem.     Lateral  view. 


72 


NEUROLOGY 


Stria  terminalis 


Medial  O^niculate  ■^^^^^i^minx.    ■■■ 
Cortico-tectal  J^^piEL'IffcviV 

fibers        _Z—^"'mnr,-i 
Superior  colliculus  y?   ••.■7////  o-^/ 


Ventral  spinocerebellar 
fasciculus 


Pyramidal  de- 
cussation 


FiQ.  684. — Deep  dissection  of  brain-stem.     I^ateral  view. 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON 


773 


Medial  geniculate 
Superior  coUiculus 


Inferior  coUiculus 


Ventral  spinocere- 
bellar fas. 


Fig.  685. — Deep  dissection  of  brain-stem.     Lateral  view. 


774 


NEUROLOGY 


I 


end  and  the  pons  there  is  a  slight  depression  to  which  the  roots  of  the  facial  nerve 
are  attached.  The  external  arcuate  fibers  wind  across  the  lower  part  of  the  pyra- 
mid and  olive  and  enter  the  inferior  peduncle. 

The  posterior  district  (Fig.  686)  lies  behind  the  postero-lateral  sulcus  and  the 
roots  of  the  accessory,  vagus,  and  the  glossopharyngeal  nerves,  and,  like  the  lateral 
district,  is  divisible  into  a  lower  and  an  upper  portion. 


Trochlear  nerve 


Trigeminal  nerve 


Facial  -nerve 
Acmistic  nerve 


Cerebral  peduncle 


Superior  peduncle 
Middle  peduncle 
Inferior  peduncle 


Glossopharyngeal 
nerve 

Vagus  nerve 
Accessory  nerve 
(cerebral  part) 
Hypoglossal  nerve 

Accessory  nerve 
[spinal  part) 


Post,  roots  of  first 
cervical  nerve 


Medulla  spinalis  — 


Vertebral  artery 
Clava 
Fasciculus  cuneatus 

Fasciculus  gracUia 


Dura  mater 
(laid  open) 


Fig.  686. — Upper  part  of  medulla  spinalis  and  hind-  and  mid-brains;  posterior  aspect,  exposed  in  situ. 

The  lower  part  is  limited  behind  by  the  posterior  median  fissure,  and  consists 
of  the  fasciculus  gracilis  and  the  fasciculus  cuneatus.  The  fasciculus  gracilis  is 
placed  parallel  to  and  along  the  side  of  the  posterior  median  fissure,  and  separated 
from  the  fasciculus  cuneatus  by  the  postero-intermediate  sulcus  and  septum. 
The  gracile  and  cuneate  fasciculi  are  at  first  vertical  in  direction ;  but  at  the  lower 
part  of  the  rhomboid  fossa  they  diverge  from  the  middle  line  in  a  V-shaped  manner, 
and  each  presents  an  elongated  swelling.  That  on  the  fasciculus  gracilis  is  named 
the  clava,  and  is  produced  by  a  subjacent  nucleus  of  gray  matter,  the  nucleus 
gracilis ;  that  on  the  fasciculus  cuneatus  is  termed  the  cuneate  tubercle,  and  is  like- 
wise caused  by  a  gray  nucleus,  named  the  nucleus  cuneatus.  The  fibers  of  these 
fasciculi  terminate  by  arborizing  around  the  cells  in  their  respective  nuclei.  A 
third  elevation,  produced  by  the  substantia  gelatinosa  of  Rolando,  is  present  in 
the  lower  part  of  the  posterior  district  of  the  medulla  oblongata.    It  lies  on  the 


1^ 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON  lib 

ateral  aspect  of  the  fasciculus  cuneatus,  and  is  separated  from  the  surface  of  the 
medulla  oblongata  by  a  band  of  nerve  fibers  which  form  the  spinal  tract  (spinal 
root)  of  the  trigeminal  nerve.  Narrow  below,  this  elevation  gradually  expands 
above,  and  ends,  about  1.25  cm.  below  the  pons,  in  a  tubercle,  the  tubercle  of 
Rolando  {iuher  cinereum). 

The  upper  part  of  the  posterior  district  of  the  medulla  oblongata  is  occupied 
y  the  inferior  peduncle,  a  thick  rope-like  strand  situated  between  the  lower  part 
of  the  fourth  ventricle  and  the  roots  of  the  glossopharyngeal  and  vagus  nerves. 
The  inferior  peduncles  connect  the  medulla  spinalis  and  medulla  oblongata  with 
the  cerebellum,  and  are  sometimes  named  the  restiform  bodies.  As  they  pass 
upward,  they  diverge  from  each  other,  and  assist  in  forming  the  lower  part  of  the 
lateral  boundaries  of  the  fourth  ventricle;  higher  up,  they  are  directed  backward, 
each  passing  to  the  corresponding  cerebellar  hemisphere.  Near  their  entrance, 
into  the  cerebellum  they  are  crossed  by  several  strands  of  fibers,  which  run 
to  the  median  sulcus  of  the  rhomboid  fossa,  and  are  named  the  striae  medullares. 
The  inferior  peduncle  appears  to  be  the  upward  continuation  of  the  fasciculus  gra- 
cilis and  fasciculus  cuneatus;  this,  however,  is  not  so,  as  the  fibers  of  these  fasciculi 
end  in  the  gracile  and  cuneate  nuclei.  The  constitution  of  the  inferior  peduncle 
will  be  subsequently  discussed. 

Caudal  to  the  striae  medullares  the  inferior  peduncle  is  partly  covered  by  the 
corpus  pontobulbare  (Essick') ,  a  thin  mass  of  cells  and  fibers  extending  from  the 
pons  between  the  origin  of  the  VII  and  VIII  cranial  nerves. 

Internal  Structure  of  the  Medulla  Oblongata. — Although  the  external  form  of  the 
medulla  oblongata  bears  a  certain  resemblance  to  that  of  the  upper  part  of  the 
medulla  spinalis,  its  internal  structure  differs  widely  from  that  of  the  latter,  and 
this  for  the  following  principal  reasons:  (1)  certain  fasciculi  which  extend  from  the 
medulla  spinalis  to  the  brain,  and  vice  versa,  undergo  a  rearrangement  in  their 
passage  through  the  medulla  oblongata;  (2)  others  which  exist  in  the  medulla  spin- 
alis end  in  the  medulla  oblongata;  (3)  new  fasciculi  originate  in  the  gray  substance 
of  the  medulla  oblongata  and  pass  to  different  parts  of  the  brain;  (4)  the  gray 
substance,  which  in  the  medulla  spinalis  forms  a  continuous  H-shaped  column, 
becomes  greatly  modified  and  subdivided  in  the  medulla  oblongata,  where  also 
new  masses  of  gray  substance  are  added ;  (5)  on  account  of  the  opening  out  of  the 
central  canal  of  the  medulla  spinalis,  certain  parts  of  the  gray  substance,  which 
in  the  medulla  spinalis  were  more  or  less  centrally  situated,  are  displayed  in  the 
rhomboid  fossa;  (6)  the  medulla  oblongata  is  intimately  associated  with  many 
of  the  cranial  nerves,  some  arising  form,  and  others  ending  in,  nuclei  within  its 
substance. 

The  Cerebrospinal  Fasciculi.— The  downward  course  of  these  fasciculi  from  the 
pyramids  of  the  medulla  oblongata  and  their  partial  decussation  have  already 
been  described  (page  761).  In  crossing  to  reach  the  lateral  funiculus  of  the  oppo- 
site side,  the  fibers  of  the  lateral  cerebrospinal  fasciculi  extend  backward  through 
the  anterior  columns,  and  separate  the  head  of  each  of  these  columns  from  its 
base  (Figs.  687,  688).  The  base  retains  its  position  in  relation  to  the  ventral 
aspect  of  the  central  canal,  and,  when  the  latter  opens  into  the  fourth  ventricle, 
appears  in  the  rhomboid  fossa  close  to  the  middle  line,  where  it  forms  the  nuclei 
of  the  hypoglossal  and  abducent  nerves;  while  above  the  level  of  the  ventricle  it 
exists  as  the  nuclei  of  the  trochlear  and  oculomotor  nerves  in  relation  to  the  floor 
of  the  cerebral  aqueduct.  The  head  of  the  column  is  pushed  lateralward  and  forms 
the  nucleus  ambiguus,  which  gives  origin  from  below  upward  to  the  cranial  part 
of  the  accessory  and  the  motor  fibers  of  the  vagus  and  glossopharyngeal,  and  still 
iiigher  to  the  motor  fibers  of  the  facial  and  trigeminal  nerves. 

'  Essick,   Am.  Jour.  Anat.,   1907. 


776 


NEUROLOGY 


I 


The  fasciculus  gracilis  and  fasciculus  cuneatus  constitute  the  posterior  sensory 
fasciculi  of  the  medulla  spinalis;  they  are  prolonged  upward  into  the  lower  part 


4— 


Fia.  687. — Section  of  the  medulla  oblongata  through 
the  lower  part  of  the  decussation  of  the  pyramids.  (Tes- 
tut.)  1.  Anterior  median  fissure.  2.  Posterior  median 
sulcus.  3.  Anterior  column  (in  red),  with  3',  anterior 
root.  4.  Posterior  column  (in  blue),  with  4',  posterior 
roots.  5.  Lateral  cerebrospinal  fasciculus.  6.  Posterior 
funiculus.  The  red  arrow,  a,  a',  indicates  the  course  the 
lateral  cerebrospinal  fasciculus  takes  at  the  level  of  the 
decussation  of  the  pyramids;  the  blue  arrow,  b,  h',  indi- 
cates the  course  which  the  sensory  fibers  take. 


FiQ.  G8S. — Section  of  the  medulla  oblongata  at  the 
level  of  the  decussation  of  the  pyramids.  (Testut.)  1 
Anterior  median  fissure.  2.  Posterior  median  sulcus. 
3.  Motor  roots.  4.  Sensory  roots.  5.  Base  of  the 
anterior  column,  from  which  the  head  (5')  has  been 
detached  by  the  lateral  cerebrospinal  fasciculus.  6. 
Decussation  of  the  lateral  cerebrospinal  fasciculus.  7. 
Posterior  columns  (in  blue).    8.  Gracile  nucleus. 


N.  VI 
Nn.  VII,  VIII 


1h 


■Decussation 


Fio.  689. — Superficial  dissection  of  brain-stem.     Ventral  view. 

of  the  medulla  oblongata,  where  they  end  respectively  in  the  nucleus  gracilis  and 
nucleus  cuneatus.    These  two  nuclei  are  continuous  with  the  central  gray  substance 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON 


777 


of  the  medulla  spinalis,  and  may  be  regarded  as  dorsal  projections  of  this,  each 
being  covered  siiperjQcially  by  the  fibers  of  the  corresponding  fasciculus.  On 
transverse  section  (Fig.  694)  the  nucleus  gracilis  appears  as  a  single,  more  or  less 
quadrangular  mass,  while  the  nucleus  cuneatus  consists  of  two  parts:  a  larger, 
'  somewhat  triangular,  medial  nucleus,  composed  of  small  or  medium-sized  cells, 
and  a  smaller  lateral  nucleus  containing  large  cells. 


Decussation  of 
svtperior  pe- 
duncle 


NtLcleus    of 
lateral 
lemniscus 

Decussation  of 
lemniscus 


Internal  arcu- 
ate fibers 


Fig.  690. — Deep  dissection  of  brain-stem. .    Ventral  view. 


I 


The  fibers  of  the  fasciculus  gracilis  and  fasciculus  cuneatus  end  by  arborizing 
around  the  cells  of  these  nuclei  (Fig.  692).  From  the  cells  of  the  nuclei  new  fibers 
arise;  some  of  these  are  continued  as  the  posterior  external  arcuate  fibers  into  the 
inferior  peduncle,  and  through  it  to  the  cerebellum,  but  most  of  them  pass  forward 
through  the  neck  of  the  posterior  column,  thus  cutting  off  its  head  from  its  base 
(Fig.  693) .  Curving  forward,  they  decussate  in  the  middle  line  with  the  correspond- 
ing fibers  of  the  opposite  side,  and  run  upward  immediately  behind  the  cerebro- 
spinal fibers,  as  a  flattened  band,  named  the  lemniscus  or  fillet.  The  decussation 
of  these  sensory  fibers  is  situated  above  that  of  the  motor  fibers,  and  is  named 
the  decussation  of  the  lemniscus  or  sensory  decussation.  The  lemniscus  is  joined  by 
the  spinothalamic  fasciculus  (page  762),  the  fibers  of  which  are  derived  from  the 
cells  of  the  gray  substance  of  the  opposite  side  of  the  medulla  spinalis. 

The  base  of  the  posterior  column  at  first  lies  on  the  dorsal  aspect  of  the  central 
canal,  but  when  the  latter  opens  into  the  fourth  ventricle,  it  appears  in  the  lateral 
part  of  the  rhomboid  fossa.    It  forms  the  terminal  nuclei  of  the  sensorv  fibers  of 


778 


NEUROLOGY 


I 


the  vagus  and  glossopharyngeal  nerves,  and  is  associated  with  the  vestibular  part 
of  the  acoustic  nerve  and  the  sensory  root  of  the  facial  nerve.  Still  higher,  it  forms  a 
mass  of  pigmented  cells — the  locus  csenileus — in  which  some  of  the  sensory  fibers 
of  the  trigeminal  nerve  appear  to  end.  The  head  of  the  posterior  column  forms  a 
long  nucleus,  in  which  the  fibers  of  the  spinal  tract  of  the  trigeminal  nerve  largely 
end. 


Auditory  radiation 
Medial  geniculate 


Stria  terminalis 


Inferior  colliculus 

N.  V 
Nucleus  incertv^ 

Vestibular  nucleus 
Cochlear  nucleus 

Nucleus  cinerea 
Nucleus  cuneatv^ 

Nucleus  gracilis 

Nucleus  spinal 
tract,  trigem- 
inal 


Lateral  lemniscus 


l7iferior  peduncle 

Dorsal  external 
arcuate  fibers 

External  arcuate 
fibers 


Fig.  691. — Dissection  of  brain-stem. 


Dorsal  view.     The  nuclear  masses  of  the  medulla  are  taken  from  model  by 
Weed,  Carnegie  Publication,  No.  19. 


The  dorsal  spinocerebellar  fasciculus  {fasciculus  cerebellospinalis;  direct  cerebellar 
tract)  lea  ves  the  lateral  district  of  the  medulla  oblongata ;  most  of  its  fibers  are  carried 
backward  into  the  inferior  peduncle  of  the  same  side,  and  through  it  are  conveyed 
to  the  cerebellum;  but  some  run  upward  with  the  fibers  of  the  lemniscus,  and, 
reaching  the  inferior  colliculus,  undergo  decussation,  and  are  carried  to  the 
cerebellum  through  the  superior  peduncle. 

The  proper  fasciculi  (basis  bundles)  of  the  anterior  and  lateral  funiculi  largely 
consist  of  intersegmental  fibers,  which  link  together  the  different  segments  of  the 
medulla  spinalis;  they  assist  in  the  production  of  the  formatio  reticularis  of  the 
medulla  oblongata,  and  many  of  them  are  accumulated  into  a  fasciculus  which 
runs  up  close  to  the  median  raphe  between  the  lemniscus  and  the  rhomboid  fossa; 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON 


779 


^Hthis  strand  is  named  the  medial   longitudinal  fasciculus,  and  will  be    again  re- 
ferred to. 

Gray  Substance  of  the  Medulla  Oblongata  (Figs.  694,  695). — In  addition  to  the 
gracile  and  cuneate  nuclei,  there  are  several  other  nuclei  to  be  considered.  Some 
of  these  are  traceable  from  the  gray  substance  of  the  medulla  spinalis,  while  others 
are  unrepresented  in  it. 

1.  The  hypoglossal  nucleus  is  derived  from  the  base  of  the  anterior  column; 
in  the  lower  closed  part  of  the  medulla  oblongata  it  is  situated  on  the  ventro- 
lateral aspect  of  the  central  canal;  but 
in  the  upper  part  it  approaches  the 
rhomboid  fossa,  where  it  lies  close  to 
the  middle  line,  under  an  eminence 
named  the  trigonum  hypoglossi  (Fig.  709). 
Numerous  fibers  connect  the  two  nuclei, 
both  nuclei  send  long  dendrons  across  the 
midline  to  the  opposite  nucleus;  commis- 
sure fibers  also  connect  them.  The  nucleus 
measures  about  2  cm.  in  length,  and  con- 


' 


_  Fig.  692. — Superior  terminations  of  the  posterior  fas- 
ciculi of  the  medulla  spinalis.  1.  Posterior  median 
sulcus.  2.  Fasciculus  gracilis.  3.  Fasciculus  cujieatus. 
4.  Gracile  nucleus.  5.  Cuneate  nucleus.  6,  6',  6". 
Sensory  fibers  forming  the  lemniscus.  7.  Sensory 
decussation.  8.  Cerebellar  fibers  uncrossed  (in  black). 
9.  Cerebellar  fibers  crossed  (in  black).     (Testut.) 


Fig.  693. — Transverse  section  passing  through  the 
sensory  decussation.  (Schematic.)  1.  Anterior  median 
fissure.  2.  Posterior  median  sulcus.  3,  3.  Head  and 
base  of  anterior  column  (in  red) .  4.  Hypoglossal  nerve. 
5.  Bases  of  posterior  columns.  6.  Gracile  nucleus.  7. 
Cuneate  nucleus.  8,  8.  Lemniscus.  9.  Sensory  decus- 
sation.    10.  Cerebrospinal  fasciculus.     (Testut.) 


sists  of  large  multipolar  nerve  cells,  similar  to  those  in  the  anterior  column  of  the 
spinal  cord,  whose  axons  constitute  the  roots  of  the  hypoglossal  nerve.  These 
nerve  roots  leave  the  ventral  side  of  the  nucleus,  pass  forward  between  the  white 
reticular  formation  and  the  gray  reticular  formation,  some  between  the  inferior 
olivary  nucleus  and  the  medial  accessory  olivary  nucleus,  and  emerge  from  the 
antero-lateral  sulcus. 

2.  The  nucleus  ambiguus  (Figs.  696,  697),  the  somatic  motor  nucleus  of  the  glosso- 
pharvTigeal,  vagus  and  cranial  portion  of  the  accessory  nerves,  is  the  continuation 
into  the  medulla  oblongata  of  the  dorso-lateral  cell  group  of  the  anterior  column 
of  the  spinal  cord.  Its  large  multipolar  cells  are  like  those  in  the  anterior  column 
of  the  cord ;  they  form  a  slender  column  in  the  deep  part  of  the  formatio  reticularis 
grisea  about  midway  between  the  dorsal  accessory  olive  and  the  nucleus  of  the 
spinal  tract  of  the  trigeminal.  It  extends  from  the  level  of  the  decussation  of  the 
median  fillet  to  the  upper  end  of  the  medulla  oblongata.  Its  fibers  first  pass  back- 
ward toward  the  floor  of  the  fourth  ventricle  and  then  curve  rather  abruptly 
lateralward  and  ventrally  to  join  the  fibers  from  the  dorsal  nucleus. 


I 


780 


NEUROLOGY 


I 


3.  The  dorsal  nucleus   (Figs.  696,  698),  nucleus  ala  cinerea,  often  called  the 
sensory  nucleus  or  the  terminal  nucleus  of  the  sensory  fibers  of  the  glossopharyng(ial 


-  ^         nuclei 


Nucleiis  of  medial  eminence   nucleus 


Raphe  — 
Torm/Uio  reticularis  grisea  — ■ 

Formatio  reticularis  alba 

Accessory  olivary  nuclei  ^ 


Nucleus  gracilis 

Nucleus  cuneattis 

Inferior  peduncle 


Spinal  tract  of 
trigeminal  nerve 


Vagus  nerve 
Arcuate  fibers 


^  Inferior  olivary  nucleus 

Hypoglossal  nerve 
Anterior  median  fissure 
Fig.  G94. — Section  of  the  medulla  oblongata  at  about  the  middle  of  the  olive.     (Schwalbe.) 

Nucleus  of  vagus 
Ligula       J      Medial  longitudinal  fasciculus 

Nucleus  intercalatus    I        7        /     rr      •     ,         ,  -^     . 
rr        ,       ,        ,  \       I       /      Masciculus  solitanus 

■Hypoglossal  nucleus         \      J      /       , 

Descending  root  of  vestibular  nerve 

Mestiforin  body 

Nucleus  lateralis 


Spinal  tract  of  tru 
geminal  nerve 


Vagus  nerve 

Nticleus  amhiquus 
Dorsal  accessory 
olivary  nucleus 


Inferior  olivary  nucleus 
Hypoglossal  nerve 


CerehrospiiMl  fasciculus  /  \         Medial  accessory  olivary  nucleus 

Lemniscus  med.       Nucleus  arcuatus 
Fig.  C95. — Transverse  section  of  medulla  oblongata  below  the  middle  of  the  olive. 

and  vagus  nerves,  is  probably  a  mixed  nucleus  and  contains  not  only  the  terminations 
of  the  sympathetic  afferent  or  sensory  fibers  and  the  cells  connected  with  them  but 
contains  also  cells  which  give  rise  to  sympathetic  efferent  or  preganglionic  fibers. 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON 


'781 


I  These  preganglionic  fibers  terminate  in  sympathetic  gangUa  from  which  the  impulses 
are  carried  by  other  neurons.  The  cells  of  the  dorsal  nucleus  are  spindle-shaped, 
like  those  of  the  posterior  column  of  the  spinal  cord,  and  the  nucleus  is  usually 
considered  as  representing  the  base  of  the  posterior  column.  It  measures  about  2 
cm.  in  length,  and  in  the  lower,  closed  part  of  the  medulla  oblongata  is  situated 
behind  the  hypoglossal  nucleus;  whereas  in  the  upper,  open  part  it  lies  lateral  to 
that  nucleus,  and  corresponds  to  an  eminence,  named  the  ala  cinerea  {trigonum 
vagi),  in  the  rhomboid  fossa. 
I     4.  The  nuclei  of  the  cochlear  and  vestibular  nerves  are  described  on  page  788. 

5.  The  olivary  nuclei  (Fig.  694) 
are  three  in  number  on  either  side 
of  the  middle  line,  viz.,  the  inferior 
olivary  nucleus,  and  the  medial 
and  dorsal  accessory  olivary  nu- 
clei; they  consist  of  small,  round, 
yellowish  cells  and  numerous  fine 
nerve  fibers,  (a)  The  inferior  oli- 
vary nucleus  is  the  largest,  and  is 
situated  within  the  olive.  It  con- 
sists of  a  gray  folded  lamina  ar- 
ranged in  the  form  of  an  incom- 
plete capsule,  opening  medially 
by  an  aperture  called  the  hilum; 
emerging  from  the  hilum  are  num- 
erous fibers  which  collectively 
constitute  the  peduncle  of  the 
olive.  The  axons,  olivocerebellar 
fibers,  which  leave  the  olivary 
nucleus  pass  out  through  the 
hilum  and  decussate  with  those 
from  the  opposite  olive  in  the 
raphe,  then  as  internal  arcuate 
fibers  they  pass  partly  through 
and  partly  around  the  opposite 
olive  and  enter  the  inferior 
peduncle  to  be  distributed  to 
the  cerebellar  hemisphere  of  the 
opposite  side  from  which  they 
arise.  The  fibers  are  smaller 
than  the  internal  arcuate  fibers 
connected  with  the  median  lem- 
niscus. Fibers  passing  in  the  op- 
posite direction  from  the  cerebel- 
lum to  the  olivary  nucleus  are 
often  described  but  their  existence 
isdoubtful.  Much  uncertainty  also 
exists  in  regard  to  the  connections 

of  the  olive  and  the  spinal  cord.  Important  connections  between  the  cerebrum  and 
the  olive  of  the  same  side  exist  but  the  exact  pathway  is  unknown.  Many  collaterals 
from  the  reticular  formation  and  from  the  pyramids  enter  the  inferior  olivary 
nucleus.  Removal  of  one  cerebellar  hemisphere  is  followed  by  atrophy  of  the 
jopposite  olivary  nucleus.  (6)  The  medial  accessory  olivary  nucleus  lies  between 
.the  inferior  olivary  nucleus  and  the  pyramid,  and  forms  a  curved  lamina,  the  con- 
«cavity  of  which  is  directed  laterally.    The  fibers  of  the  hypoglossal  nerve,  as  they 


Nucleus  ambiguus 
{IX  and  X) 


Nuclevs  of 
solitary  tract 


Fig.  696. — The  cranial  nerve  nuclei  schematically  represented; 
dorsal  view.  Motor  nuclei  in  red;  sensory  in  blue.  (The  olfactory 
and  optic  centers  are  not  represented.) 


782 


I 


traverse  the  medulla,  pass  between  the  medial  accessory  and  the  inferior  olivary 
nuclei,  (c)  The  dorsal  accessory  olivary  nucleus  is  the  smallest,  and  appears  on 
transverse  section  as  a  curved  lamina  behind  the  inferior  olivary  nucleus. 

6.  The  nucleus  arcuatus  is  described  below  with  the  anterior  external  arcuate  fibers. 

Inferior  Peduncle  (restiform  body). — The  position  of  the  inferior  peduncles  has 
already  been  described  (page  775).    Each  comprises: 

(1)  Fibers  from  the  dorsal  spinocerebellar  fascicidus,  which  ascends  from  the  latei-al 
funiculus  of  the  medulla  spinalis. 

(2)  The  olivocerebellar  fibers  from  the  opposite  olivary  nucleus. 

(3)  Internal  arcuate  fibers  from  the  gracile  and  cuneate  nuclei  of  the  opposite  side ; 
these  fibers  form  the  deeper  and  larger  part  of  the  inferior  peduncle. 


Cervical  nerves 
Fig.   697. — Nuclei  of  origin  of  cranial  motor  nerves  schematically  represented;  lateral  view. 

(4)  The  anterior  external  arcuate  fibers  vary  as  to  their  prominence  in  different  cases : 
in  some  they  form  an  almost  continuous  layer  covering  the  pyramid  and  olive, 
while  in  others  they  are  barely  visible  on  the  surface.  They  arise  from  the  cells 
of  the  gracile  and  cuneate  nuclei,  and  passing  forward  through  the  formatio  reticu- 
laris, decussate  in  the  middle  line.  Most  of  them  reach  the  surface  by  way  of  the 
anterior  median  fissure,  and  arch  backward  over  the  pyramid.  Reinforced  by 
others  which  emerge  between  the  pyramid  and  olive,  they  pass  backward  over 
the  olive  and  lateral  district  of  the  medulla  oblongata,  and  enter  the  inferior 
peduncle.  They  thus  connect  the  cerebellum  with  the  gracile  and  cuneate  nuclei  of 
the  opposite  side.  As  the  fibers  arch  across  the  pyramid,  they  enclose  a  small 
nucleus  which  lies  in  front  of  and  medial  to  the  pyramid.  This  is  named  the  nucleus 
arcuatus,  and  is  serially  continuous  above  with  the  nuclei  pontis  in  the  pons;  it 
contains  small  fusiform  cells,  around  which  some  of  the  arcuate  fibers  end,  and 
from  which  others  arise. 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON 


783 


(5)  The  posterior  external  arcuate  fibers  also  take  origin  in  the  gracile  and  cuneate 
luclei;  they  pass  to  the  inferior  peduncle  of  the  same  side.    It  is  uncertain  whether 


Fia.   698. — Primary    terminal    nuclei    of    the    aflFerent   (sensory)    cranial    nerves    schematically  represented;    lateral 
view.     The  olfactory  and  optic  centers  are  not  represented. 


h 


Fig.  699. — Diagram  showing  the  course  of  the  arcuate  fibers.  (Testut.)  1.  Medulla  oblongata  anterior  surface. 
il.  Anterior  median  fissure.  3.  Fourth  ventricle.  4.  Inferior  olivary  nucleus,  with  the  accessory  olivary  nuclei.  5. 
(iracile  nucleus.  6.  Cuneate  nucleus.  7.  Trigeminal.  8.  Inferior  peduncles,  seen  from  in  front.  9.  Posterior  external 
:-rcuate  fibers.  10.  Anterior  external  arcuate  fibers.  11.  Internal  arcuate  fibers.  12.  Peduncle  of  inferior  olivary 
nucleus.    13.  Nucleus  arcuatus.     14.  Vagus.     15.  Hypoglossal. 


784 


NEUROLOGY 


fibers  are  continued  directly  from  the  gracile  and  cuneate  fasciculi  into  the  infenol 
peduncle. 

(6)  Fibers  from  the  terminal  sensory  nuclei  of  the  cranial  nerves,  especially  the 
vestibular.  Some  of  the  fibers  of  the  vestibular  nerve  are  thought  to  continue 
directly  into  the  cerebellum. 

(7)  Fibers  from  the  ventral  spinocerebellar  fasciculus. 

(8)  The  existence  of  fibers  from  the  cerebellum  (cerebellobulbar,  cerebelloolivs 
and  cerebellospinal)  to  the  medulla  and  spinal  cord  is  very  uncertain. 


Fig.  700. — The  formatio  reticularis  of  the  medulla  oblongata,  .showa  by  a  traasverse  section  passing  through  the 
middle  of  the  oUve.  (Testut.)  1.  Anterior  median  fissure.  2.  Fourth  ventricle.  3.  Formatio  reticularis,  with  3', 
itsinternalpart  (reticularisalba),  and3",it3externalpart  (reticularisgrisea).  4.  Raph6.  5.  Pyramid.  6.  Lenmiscus. 
7.  Inferior  olivary  nucleus  with  the  two  accessory  olivary  nuclei.  8.  Hypoglossal  nerve,  with  8',  its  nucleus  of  origin. 
9.  Vagus  nerve,  with  9',  its  nucleus  of  termination.  10.  Lateral  dorsal  acoustic  nucleus.  11.  Nucleus  ambiguus 
(nucleus  of  origin  of  motor  fibers  of  glossopharyngeal,  vagus,  and  cerebral  portion  of  spinal  accessory).  12.  Gracile 
nucleus.  _  13.  Cuneate  nucleus.  14.  Head  of  posterior  column,  with  14',  the  lower  sensory  root  of  trigeminal  nerve. 
16.  Fasciculus  soUtarius.  16.  Anterior  external  arcuate  fibers,  with  16',  the  nucleus  arcuatus.  17.  Nucleus  lateralis 
18.  Nucleus  of  fasciculus  teres.     19.  Ligula. 

Formatio  Reticularis  (Fig.  700). — This  term  is  applied  to  the  coarse  reticulum 
which  occupies  the  anterior  and  lateral  districts  of  the  medulla  oblongata.  It 
is  situated  behind  the  pyramid  and  olive,  extending  laterally  as  far  as  the  inferior 
peduncles,  and  dorsally  to  within  a  short  distance  of  the  rhomboid  fossa.  The 
reticulum  is  caused  by  the  intersection  of  bundles  of  fibers  running  at  right  angles 
to  each  other,  some  being  longitudinal,  others  more  or  less  transverse  in  direction. 
The  formatio  reticularis  presents  a  different  appearance  in  the  anterior  district  from 
what  it  does  in  the  lateral ;  in  the  former,  there  is  an  almost  entire  absence  of  ner\'e 
cells,  and  hence  this  part  is  known  as  the  reticularis  alba;  whereas  in  the  lateral 
district  nerve  cells  are  numerous,  and  as  a  consequence  it  presents  a  gray  appear- 
ance, and  is  termed  the  reticularis  grisea. 

In  the  substance  of  the  formatio  reticularis  are  two  small  nuclei  of  gray  matter: 
one,  the  inferior  central  nucleus  (nucleus  of  Roller),  near  the  dorsal  aspect  of  the  hilus 
of  the  inferior  olivary  nucleus;  the  other,  the  nucleus  lateralis,  between  the  olive 
and  the  spinal  tract  of  the  trigeminal  nerve. 

In  the  reticularis  alba  the  longitudinal  fibers  form  two  well-defined  fasciculi, 
viz.:  (1)  the  lemniscus,  which  lies  close  to  the  raphe,  immediately  behind  the 
fibers  of  the  pyramid;  and  (2)  the  medial  longitudinal  fasciculus,  which  is  continued 
upward  from  the  anterior  and  lateral  proper  fasciculi  of  the  medulla  spinalis,  and, 


I 

I 


I 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON  785 

in  the  upper  part  of  the  medulla  oblongata,  lies  between  the  lemniscus  and  the  gray 
substance  of  the  rhomboid  fossa.  The  longitudinal  fibers  in  the  reticularis  grisea 
are  derived  from  the  lateral  funiculus  of  the  medulla  spinalis  after  the  lateral 
cerebrospinal  fasciculus  has  passed  over  to  the  opposite  side,  and  the  dorsal  spino- 
cerebellar fasciculus  has  entered  the  inferior  peduncle.  They  form  indeterminate 
fibers,  with  the  exception  of  a  bimdle  named  the  fasciculus  solitarius,  which  is  made  up 
of  descending  fibers  of  the  vagus  and  glossopharyngeal  nerves.  The  transverse 
fibers  of  the  formatio  reticularis  are  the  arcuate  fibers  already  described  (page  782). 

The  Pons  {pons  Varoli). — The  pons  or  forepart  of  the  hind-brain  is  situ- 
ated in  front  of  the  cerebellum.  From  its  superior  surface  the  cerebral  peduncles 
emerge,  one  on  either  side  of  the  middle  line.  Curving  around  each  peduncle,  close 
to  the  upper  surface  of  the  pons,  a  thin  white  band,  the  taenia  pontis,  is  frequently 
seen;  it  enters  the  cerebellum  between  the  middle  and  superior  peduncles.  Behind 
and  below,  the  pons  is  continuous  with  the  medulla  oblongata,  but  is  separated 
from  it  in  front  by  a  furrow  in  which  the  abducent,  facial,  and  acoustic  nerves 
appear. 

Its  ventral  or  anterior  surface  {pars  hasilaris  pontis)  is  very  prominent,  markedly 
convex  from  side  to  side,  less  so  from  above  downward.  It  consists  of  transverse 
fibers  arched  like  a  bridge  across  the  middle  line,  and  gathered  on  either  side  into 
a  compact  mass  which  forms  the  middle  peduncle.  It  rests  upon  the  clivus  of  the 
sphenoidal  bone,  and  is  limited  above  and  below  by  well-defined  borders.  In  the 
middle  line  is  the  sulcus  basilaris  for  the  lodgement  of  the  basilar  artery;  this  sulcus 
is  bounded  on  either  side  by  an  eminence  caused  by  the  descent  of  the  cerebrospinal 
fibers  through  the  substance  of  the  pons.  Outside  these  eminences,  near  the  upper 
border  of  the  pons,  the  trigeminal  nerves  make  their  exit,  each  consisting  of  a 
smaller,  medial,  motor  root,  and  a  larger,  lateral,  sensor}^  root;  vertical  lines 
drawn  immediately  beyond  the  trigeminal  nerves,  may  be  taken  as  the  boundaries 
between  the  ventral  surface  of  the  pons  and  the  middle  cerebellar  peduncle. 

Its  dorsal  or  posterior  surface  {pars  dorsalis  pontis),  triangular  in  shape,  is  hidden 
by  the  cerebellum,  and  is  bounded  laterally  by  the  superior  peduncle;  it  forms 
the  upper  part  of  the  rhomboid  fossa,  with  which  it  will  be  described. 

Structure  (Fig.  701). — Transverse  sections  of  the  pons  show  it  to  be  composed 
of  two  parts  which  differ  in  appearance  and  structure :  thus,  the  basilar  or  ventral 
portion  consists  for  the  most  part  of  fibers  arranged  in  transverse  and  longitudinal 
bundles,  together  with  a  small  amount  of  gray  substance;  while  the  dorsal  tegmental 
portion  is  a  continuation  of  the  reticular  formation  of  the  medulla  oblongata, 
and  most  of  its  constituents  are  continued  into  the  tegmenta  of  the  cerebral 
peduncles. 

The  basilar  part  of  the  pons  consists  of — (a)  superficial  and  deep  transverse 
fibers,  (6)  longitudinal  fasciculi,  and  (c)  some  small  nuclei  of  gray  substance, 
termed  the  nuclei  pontis  which  gi\'e  rise  to  the  transverse  fibers. 

The  superficial  transverse  fibers  {fibrw  pontis  superficiales)  constitute  a  rather 
thick  layer  on  the  ventral  surface  of  the  pons,  and  are  collected  into  a  large 
rounded  bundle  on  either  side  of  the  middle  line.  This  bundle,  with  the  addition 
of  some  transverse  fibers  from  the  deeper  part  of  the  pons,  forms  the  greater  part 
of  the  brachium  pontis. 

The  deep  transverse  fibers  {fihros  pontis  profunda)  partly  intersect  and  partly 
lie  on  the  dorsal  aspect  of  the  cerebrospinal  fibers.  They  course  to  the  lateral 
border  of  the  pons,  and  form  part  of  the 'middle  peduncle;  the  further  connections 
of  this  brachium  will  be  discussed  with  the  anatomy  of  the  cerebellum. 

The  longitudinal  fasciculi  {fasciculi  longitudinales)  are  derived  from  the  cerebral 
peduncles,  and  enter  the  upper  surface  of  the  pons.  They  stream  downward  on 
either  side  of  the  middle  line  in  larger  or  smaller  bundles,  separated  from  each 
other  by  the  deep  transverse  fibers;  these  longitudinal  bundles  cause  a  forward 
50 


786 


NEUROLOGY 


projection  of  the  superficial  transverse  fibers,  and  thus  give  rise  to  the  eminence;? 
on  the  anterior  surface.  Some  of  these  fibers  end  in,  or  give  off  collateral  to,  the; 
nuclei  pontis.  An  important  pathway  is  thus  formed  between  the  cerebral  cortex 
and  the  cerebellum,  the  first  neuron  having  its  cell  body  in  the  cortex  and  sending 
its  axon  through  the  internal  capsule  and  cerebral  peduncle  to  form  synapses  eithei- 
by  terminals  or  collaterals  with  cell  bodies  situated  in  the  nuclei  pontis.  Axons 
from  these  cells  form  the  transverse  fibers  which  pass  through  the  middle  peduncle 
into  the  cerebellum.  Others  after  decussating,  terminate  either  directly  or  indi- 
rectly in  the  motor  nuclei  of  the  trigeminal,  abducent,  facial,  and  hypoglossal 
nerves;  but  most  of  them  are  carried  through  the  pons,  and  at  its  lower  surface 
are  collected  into  the  pyramids  of  the  medulla.  The  fibers  which  end  in  the  motor 
nuclei  of  the  cranial  nerves  are  derived  from  the  cells  of  the  cerebral  cortex,  and 
bear  the  same  relation  to  the  motor  cells  of  the  cranial  nerves  that  the  cerebro- 


I 


Superior  peduncle 


Mesencephalic  root  V. 
Nn.  mes.  root 


Med.  long,  fas 

Lateral  lemniscus 

Formatio  reticularis-^ 


Ant.  med, 
velum 

White        \ 
stratum      .1    Gray  stratum 


Fourth  ventricle 


Medial 
lemniscus 


Transverse 
fibers 


Cerebrospinal 
fasciculi 


Trigemiruii- 


Raphi 
Fig.  701. — Coronal  section  of  the  pons,  at  its  upper  part. 


spinal  fibers  bear  to  the  motor  cells  in  the  anterior  column  of  the  medulla  spinalis. 
Probably  none  of  the  collaterals  or  terminals  of  the  cerebrospinal  and  cerebro- 
bulbar  fibers  end  directly  in  the  motor  nuclei  of  the  spinal  and  cranial  nerves,  one  or 
more  association  neurons  are  probably  interpolated  in  the  pathway. 

The  nuclei  pontis  are  serially  continuous  with  the  arcuate  nuclei  in  the  medulla, 
and  consist  of  small  groups  of  multipolar  nerve  cells  which  are  scattered  between 
the  bundles  of  transverse  fibers. 

The  dorsal  or  tegmental  part  of  the  pons  is  chiefly  composed  of  an  upward  con- 
tinuation of  the  reticular  formation  and  gray  substance  of  the  medulla  oblongata. 
It  consists  of  transverse  and  longitudinal  fibers  and  also  contains  important  gray 
nuclei,  and  is  subdivided  by  a  median  raphe,  which,  however,  does  not  extend  into 
the  basilar  part,  being  obliterated  by  the  transverse  fibers.  The  transverse  fibers 
the  lower  part  of  the  pons  are  collected  into  a  distinct  strand,  named  the 


in 


I 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON  787 


* 
I 


h 


I 


trapezoid  body.  This  consists  of  fibers  which  arise  from  the  cells  of  the  cochlear 
nucleus,  and  will  be  referred  to  in  connection  with  the  cochlear  division  of  the 
acoustic  nerve.  In  the  substance  of  the  trapezoid  body  is  a  collection  of  nerve 
tells,  which  constitutes  the  trapezoid  nucleus.  The  longitudinal  fibers,  which  are 
continuous  with  those  of  the  medulla  oblongata,  are  mostly  collected  into  two 
fasciculi  on  either  side.  One  of  these  lies  between  the  trapezoid  body  and 
the  reticular  formation,  and  forms  the  upward  prolongation  of  the  lemniscus; 
the  second  is  situated  near  the  floor  of  the  fourth  ventricle,  and  is  the  medial 
longitudinal  fasciculus.  Other  longitudinal  fibers,  more  diffusely  distributed,  arise 
from  the  cells  of  the  gray  substance  of  the  pons. 

The  rest  of  the  dorsal  part  of  the  pons  is  a  continuation  upward  of  the  formatio 
{reticularis  of  the  medulla  oblongata,  and,  like  it,  presents  the  appearance  of  a  net- 
'work,  in  the  meshes  of  which  are  numerous  nerve  cells.  Besides  these  scattered 
nerve  cells,  there  are  some  larger  masses  of  gray  substance,  viz.,  the  superior 
olivary  nucleus  and  the  nuclei  of  the  trigeminal,  abducent,  facial,  and  acoustic 
nerves  (Fig.  696). 

1.  The  superior  olivary  nucleus  {nucleus  olivaris  superior)  is  a  small  mass  of  gray 
substance  situated  on  the  dorsal  surface  of  the  lateral  part  of  the  trapezoid  body. 
Rudimentary  in  man,  but  well  developed  in  certain  animals,  it  exhibits  the  same 
structure  as  the  inferior  olivary  nucleus,  and  is  situated  immediately  above  it. 
Some  of  the  fibers  of  the  trapezoid  body  end  by  arborizing  around  the  cells  of 
this  nucleus,  while  others  arise  from  these  cells. 

2.  The  nuclei  of  the  trigeminal  nerve  {nuclei  n.  trigemini)  in  the  pons  are  two  in 
number :  a  motor  and  a  sensory.  The  motor  nucleus  is  situated  in  the  upper  part  of 
the  pons,  close  to  its  posterior  surface  and  along  the  line  of  the  lateral  margin  of  the 
fourth  ventricle.  It  is  serially  homologous  with  the  nucleus  ambiguus  and  the 
dorso-lateral  cell  group  of  the  anterior  column  of  the  spinal  cord.  The  axis-cylinder 
processes  of  its  cells  form  the  motor  root  of  the  trigeminal  nerve.  The  mesen- 
cephalic root  arises  from  the  gray  substance  of  the  floor  of  the  cerebral  aqueduct, 
joins  the  motor  root  and  probably  conveys  fibers  of  muscle  sense  from  the  tem- 
poral, masseter  and  pterygoid  muscles.  It  is  not  altogether  clear  whether  the 
mesencephalic  root  is  motor  or  sensory.    The  sensory  nucleus  is  lateral  to  the 

-motor  one,  and  beneath  the   superior  peduncle.    Some  of  the  sensory  fibers  of 

■the  trigeminal  nerve  end  in  this  nucleus;  but  the  greater  number  descend,  under  the 

name  of  the  spinal  tract  of  the  trigeminal  nerve,  to  end  in  the  substantia  gelatinosa 

of  liolando.    The  roots,  motor  and  sensory,  of  the  trigeminal  nerve  pass  through 

the  substance  of  the  pons  and  emerge  near  the  upper  margin  of  its  anterior  surface. 

3.  The  nucleus  of  the  abducent  nerve  {nucleus  n.  ahducentis)  is  a  circular  mass  of 
gray  substance  situated  close  to  the  floor  of  the  fourth  ventricle,  above  the  striae 
medullares  and  subjacent  to  the  medial  eminence:  it  lies  a  little  lateral  to  the 
ascending  part  of  the  facial  nerve.  The  fibers  of  the  abducent  nerve  pass  forward 
through  the  entire  thickness  of  the  pons  on  the  medial  side  of  the  superior  olivary 
nucleus,  and  between  the  lateral  fasciculi  of  the  cerebrospinal  fibers,  and  emerge 
in  the  furrow  between  the  lower  border  of  the  pons  and  the  pyramid  of  the 
medulla  oblongata. 

4.  The  nucleus  of  the  facial  nerve  {nucleus  n.  fascialis)  is  situated  deeply  in  the 
reticular  formation  of  the  pons,  on  the  dorsal  aspect  of  the  superior  olivary  nucleus, 
and  the  roots  of  the  nerve  derived  from  it  pursue  a  remarkably  tortuous  course  in 
the  substance  of  the  pons.  At  first  they  pass  backward  and  medialward  until  they 
reach  the  rhomboid  fossa,  close  to  the  median  sulcus,  where  they  are  collected  into 
a  round  bundle;  this  passes  upward  and  forward,  producing  an  elevation,  the 
colliculus  facialis,  in  the  rhomboid  fossa,  and  then  takes  a  sharp  bend,  and  arches 
lateralward  through  the  substance  of  the  pons  to  emerge  at  its  lower  border  in 
the  interval  between  the  olive  and  the  inferior  peduncle  of  the  medulla  oblongata. 


788  ^^^^^  NEUROLOGY 


5.  The  nucleus  of  the  cochlear  nerve  consists  of:  (a)  the  lateral  cochlear  nucleu:;, 
corresponding  to  the  tuberculum  acusticum  on  the  dorso-lateral  surface  of  the 
inferior  peduncle;  and  (6)  the  ventral  or  accessory  cochlear  nucleus,  placed  between 
the  two  divisions  of  the  nerve,  on  the  ventral  aspect  of  the  inferior  jjeduncle. 

The  nuclei  of  the  vestibiilar  nerve,  (a)  The  medial  (dorsal  or  chief  vestibula.r 
nucleus),  corresponding  to  the  lower  part  of  the  area  acustica  in  the  rhomboid 
fossa ;  the  caudal  end  of  this  nucleus  is  sometimes  termed  the  descending  or  spinal 
vestibular  nucleus.  (6)  The  lateral  or  nucleus  of  Deiters,  consisting  of  large  cells 
and  situated  in  the  lateral  angle  of  the  rhomboid  fossa;  the  dorso-lateral  part  of 
this  nucleus  is  sometimes  termed  the  nucleus  of  Bechterew. 

The  fibers  of  the  vestibular  nerve  enter  the  medulla  oblongata  on  the  medial 
side  of  those  of  the  cochlear,  and  pass  between  the  inferior  peduncle  and  the  spinal 
tract  of  the  trigeminal.  They  then  divide  into  ascending  and  descending  fibers. 
The  latter  end  by  arborizing  around  the  cells  of  the  medial  nucleus,  which  is  situ- 
ated in  the  area  acustica  of  the  rhomboid  fossa.  The  ascending  fibers  either  end 
in  the  same  manner  or  in  the  lateral  nucleus,  which  is  situated  lateral  to  the  area 
acustica  and  farther  from  the  ventricular  floor.  Some  of  the  axons  of  the  cells  of 
the  lateral  nucleus,  and  possibly  also  of  the  medial  nucleus,  are  continued  upward 
through  the  inferior  peduncle  to  the  roof  nuclei  of  the  opposite  side  of  the  cere- 
bellum, to  which  also  other  fibers  of  the  vestibular  root  are  prolonged  without 
interruption  in  the  nuclei  of  the  medulla  oblongata.  A  second  set  of  fibers  from 
the  medial  and  lateral  nuclei  end  partly  in  the  tegmentum,  while  the  remainder 
ascend  in  the  medial  longitudinal  fasciculus  to  arborize  around  the  cells  of  the 
nuclei  of  the  oculomotor  nerve. 

The  Cerebellum. — The  cerebellum  constitutes  the  largest  part  of  the  hind- 
brain.  It  lies  behind  the  pons  and  medulla  oblongata;  between  its  central  portion 
and  these  structures  is  the  cavity  of  the  fourth  ventricle.  It  rests  on  the  inferior 
occipital  fossae,  while  above  it  is  the  tentorium  cerebelli;  a  fold  of  dura  mater 
which  separates  it  from  the  tentorial  surface  of  the  cerebrum.  It  is  somewhat 
oval  in  form,  but  constricted  medially  and  flattened  from  above  downward,  its 
greatest  diameter  being  from  side  to  side.  Its  surface  is  not  convoluted  like  that 
of  thp  cerebrum,  but  is  traversed  by  numerous  curved  furrows  or  sulci,  which 
vary  in  depth  at  different  parts,  and  separate  the  laminae  of  which  it  is  composed. 
Its  average  weight  in  the  male  is  about  150  gms.  In  the  adult  the  propor- 
tion between  the  cerebellum  and  cerebrum  is  about  1  to  8,  in  the  infant  about 
1  to  20. 

Lobes  of  the  Cerebellum. — The  cerebellum  consists  of  three  parts,  a  median  and 
two  lateral,  which  are  continuous  with  each  other,  and  are  substantially  the  same 
in  structure.  The  median  portion  is  constricted,  and  is  called  the  vermis,  from  its 
annulated  appearance  which  it  owes  to  the  transverse  ridges  and  furrows  upon  it; 
the  lateral  expanded  portions  are  named  the  hemispheres.  On  the  upper  surface 
of  the  cerebellum  the  vermis  is  elevated  above  the  level  of  the  hemispheres,  but 
on  the  under  surface  it  is  sunk  almost  out  of  sight  in  the  bottom  of  a  deep  depres- 
sion between  them;  this  depression  is  called  the  vallecula  cerebelli,  and  lodges  the 
posterior  part  of  the  medulla  oblongata.  The  part  of  the  vermis  on  the  upper 
surface  of  the  cerebellum  is  named  the  superior  vermis;  that  on  the  lower  surface, 
the  inferior  vermis.  The  hemispheres  are  separated  below  and  behind  by  a  deep 
notch,  the  posterior  cerebellar  notch,  and  in  front  by  a  broader  shallower  notch, 
the  anterior  cerebellar  notch.  The  anterior  notch  lies  close  to  the  pons  and  upper 
part  of  the  medulla,  and  its  superior  edge  encircles  the  inferior  colliculi  and  the 
superior  cerebellar  peduncle.  The  posterior  notch  contains  the  upper  part  of  the 
falx  cerebelli,  a  fold  of  dura  mater. 

The  cerebellum  is  characterized  by  a  laminated  or  foliated  appearance;  it  is 
marked  by  deep,  somewhat  curved  fissures,  which  extend  for  a  considerable  dis- 


I 


THE  HIXD-BRAIN  OR  RHOMBENCEPHALON 


789 


Ijtance  into  its  substance,  and  divide  it  into  a  series  of  layers  or  leaves.  The  largest 
|ind  deepest  fissure  is  named  the  horizontal  sulcus.  It  commences  in  front  of  the 
pons,  and  passes  horizontally  around  the  free  margin  of  the  hemisphere  to  the 
middle  line  behind,  and  divides  the  cerebellum  into  an  upper  and  a  lower  portion. 
Several  secondary  but  deep  fissures  separate  the  cerebellum  into  lobes,  and  these 
are  further  subdivided  by  shallower  sulci,  which  separate  the  individual  folia  or 
laminae  from  each  other.  Sections  across  the  laminae  show  that  the  folia,  though 
differing  in  appearance  from  the  convolutions  of  the  cerebrum,  are  analogous 
to  them,  inasmuch  as  they  consist  of  central  white  substance  covered  by  gray 
substance. 

f  The  cerebellum  is  connected  to  the  cerebrum,  pons,  and  medulla  oblongata; 
;o  the  cerebrum  by  the  superior  peduncle,  to  the  pons  by  the  middle  peduncle, 
,nd  to  the  medulla  oblongata  by  the  inferior  peduncles. 


Ala  lohuli  centralis 


Ldbulus  centralis 


Horizontal 
sulcus 


PrcBclival  fissure 

Postclival 
fissure 

f 


I 


Upper  surface  of  the  cerebellum.     (SchMer.) 

The  upper  surface  of  the  cerebellum  (Fig.  702)  is  elevated  in  the  middle  and  sloped 
toward  the  circumference,  the  hemispheres  being  connected  together  by  the  supe- 
rior vermis,  which  assumes  the  form  of  a  raised  median  ridge,  most  prominent 
in  front,  but  not  sharply  defined  from  the  hemispheres.  The  superior  vermis  is 
subdivided  from  before  backward  into  the  lingula,  the  lobulus  centralis,  the  mon- 
ticulus  and  the  folium  vermis,  and  each  of  these,  with  the  exception  of  the  lingula, 
is  continuous  with  the  corresponding  parts  of  the  hemispheres — the  lobulus 
centralis  with  the  alse,  the  monticulus  with  the  quadrangular  lobules,  and  the 
folium  vermis  with  the  superior  semilunar  lobules. 

The  lingula  {lingula  cereheUi)  is  a  small  tongue-shaped  process,  consisting  of 
four  or  five  folia;  it  lies  in  front  of  the  lobulus  centralis,  and  is  concealed  by  it. 
Anteriorly,  it  rests  on  the  dorsal  surface  of  the  anterior  medullary  velum,  and  its 
white  substance  is  continuous  with  that  of  the  velum. 

The  Lobulus  Centralis  and  Alse. — The  lobulus  centralis  is  a  small  square  lobule, 
situated  in  the  anterior  cerebellar  notch.  It  overlaps  the  lingula,  from  which  it 
is  separated  by  the  precentral  fissure;  laterally,  it  extends  along  the  upper  and 
anterior  part  of  each  hemisphere,  where  it  forms  a  wing-like  prolongation,  the  ala 
lobuli  centralis. 

The  Monticulus  and  Quadrangular  Lobules. — ^The  monticulus  is  the  largest  part 
of  the  superior  vermis.  Anteriorly,  it  overlaps  the  lobulus  centralis,  from  which 
it  is  separated  by  the  postcentral  fissure ;  laterally,  it  is  continuous  with  the  quad- 
rangular lobule  in  the  hemispheres.    It  is  divided  by  the  precUval  fissure  into  an 


m 


NEUROLOGY 


I 


anterior,  raised  part,  the  culmen  or  summit,  and  a  posterior  sloped  part,  the  clivu»; 
the  quadrangular  lobule  is  similarly  divided.  The  culmen  and  the  anterior  parts 
of  the  quadrangular  lobules  form  the  lobus  culminis;  the  clivus  and  the  posterior 
parts,  the  lobus  clivi. 

The  Folium  Vermis  and  Superior  Semilunar  Lobule. — The  folium  vermis  (folium 
cacuminis;  cacuminal  lobe)  is  a  short,  narrow,  concealed  band  at  the  posterior 
extremity  of  the  vermis,  consisting  apparently  of  a  single  folium,  but  in  reality 
marked  on  its  upper  and  under  surfaces  by  secondary  fissures.  Laterally,  it 
expands  in  either  hemisphere  into  a  considerable  lobule,  the  superior  semilimar 
lobule  (lobulns  semilunaris  superior;  postero-superior  lobules),  which  occupies  the 
posterior  third  of  the  upper  surface  of  the  hemisphere,  and  is  bounded  below  by 
the  horizontal  sulcus.  The  superior  semilunar  lobules  and  the  folium  vermis  form 
the  lobus  semilunaris. 


Ala  lohuK  centralis       Flocculus 


Postnodular  fissure 


Ant.  medullary  vdum 
Lobulus  centralis 


Hm-izontal  sulcus 


Tuber  vermis 
Fig.  703. — Ujider  surface  of  the  cerebellum,     (Schafer. 

The  under  surface  of  the  cerebellum  (Fig.  703)  presents,  in  the  middle  line,  the 
inferior  vermis,  buried  in  the  vallecula,  and  separated  from  the  hemisphere  on  either 
side  by  a  deep  groove,  the  sulcus  valleculse.  Here,  as  on  the  upper  surface,  there 
are  deep  fissures,  dividing  it  into  separate  segments  or  lobules ;  but  the  arrangement 
is  more  complicated,  and  the  relation  of  the  segments  of  the  vermis  to  those  of  the 
hemispheres  is  less  clearly  marked.  The  inferior  vermis  is  subdivided  from  before 
backward,  into  (1)  the  nodule,  (2)  the  uvula,  (3)  the  pyramid,  and  (4)  the  tuber 
vermis;  the  corresponding  parts  on  the  hemispheres  are  (1)  the  flocculus,  (2)  the 
tonsilla  cerebelli,  (3)  the  biventral  lobule,  and  (4)  the  inferior  semilunar  lobule.  The 
three  main  fissures  are  (1)  the  postnodular  fissure,  which  runs  transversely  across 
the  vermis,  between  the  nodule  and  the  uvula.  In  the  hemispheres  this  fissure 
passes  in  front  of  the  tonsil,  crosses  between  the  flocculus  in  front  and  the  biventral 
lobule  behind,  and  joins  the  anterior  end  of  the  horizontal  sulcus.  (2)  The  pre- 
pyramidal  fissure  crosses  the  vermis  between  the  uvula  in  front  and  the  pyramid 
behind,  then  curves  forward  between  the  tonsil  and  the  biventral  lobe,  to  join 
the  postnodular  fissure.  (3)  The  postpyramidal  fissure  passes  across  the  vermis 
between  the  pyramid  and  the  tuber  vermis,  and,  in  the  hemispheres,  courses 
behind  the  tonsil  and  biventral  lobules,  and  then  along  the  lateral  border  of  the 
biventral  lobule  to  the  postnodular  sulcus ;  in  the  hemisphere  it  forms  the  anterior 
boundary  of  the  inferior  semilunar  lobule. 

The  Nodule  and  Flocculus. — The  nodule  (nodulus  vermis;  riodular  lobe),  or  anterior 
end  of  the  inferior  vermis,  abuts  against  the  roof  of  the  fourth  ventricle,  and  can 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON  791 


^^  only  be  distinctly  seen  after  the  cerebellum  has  been  separated  from  the  medulla 
oblongata  and  pons.  On  either  side  of  the  nodule  is  a  thin  layer  of  white  sub- 
stance, named  the  posterior  medullary  velum.  It  is  semilunar  in  form,  its  convex 
border  being  continuous  with  the  white  substance  of  the  cerebellum;  it  extends 
on  either  side  as  far  as  the  flocculus.  The  flocculus  is  a  prominent,  irregular 
lobule,  situated  in  front  of  the  biventral  lobule,  between  it  and  the  middle  cere- 
bellar peduncle.  It  is  subdivided  into  a  few  small  laminae,  and  is  connected  to 
the  inferior  medullary  velum  by  its  central  white  core.  The  flocculi,  together 
with  the  posterior  medullary  velum  and  nodule,  constitute  the  lobus  noduli. 

The  Uvula  and  Tonsilla. — The  uvula  (uvula  vermis;  uvular  lobe)  forms  a  consid- 
erable portion  of  the  inferior  vermis;  it  is  separated  on  either  side  from  the  tonsil 
by  the  sulcus  valleculae,  at  the  bottom  of  which  it  is  connected  to  the  tonsil  by  a 
ridge  of  gray  matter,  indented  on  its  surface  by  shallow  furrows,  and  hence  called 
the  furrowed  band.  The  tonsilla  (tonsilla  cerebelli;  amygdaline  nucleus)  is  a  rounded 
mass,  situated  in  the  hemispheres.  Each  lies  in  a  deep  fossa,  termed  the  bird's 
nest  (nidus  avis),  between  the  uvula  and  the  biventral  lobule.  The  uvula  and  ton- 
sillae  form  the  lobus  uvulae. 

kThe  Pyramid  and  Biventral  lobules  constitute  the  lobus  pyramidis.    The  pyramid 
lis  a  conical  projection,  forming  the  largest  prominence  of  the  inferior  vermis. 
It  is  separated  from  the  hemispheres  by  the  sulcus  valleculae,  across  which  it  is 
connected  to  the  biventral  lobule  by  an  indistinct  gray  band,  analogous  to  the 
furrowed  band  already  described.      The  biventral  lobule  is  triangular  in  shape; 
its  apex  points  backward,  and  is  joined  by  the  gray  band  to  the  pyramid.    The 
lateral  border  is  separated  from  the  inferior  semilunar  lobule  by  the  postpyramidal 
fissure.    The  base  is  directed  forward,  and  is  on  a  line  with  the  anterior  border  of 
I     J  the  tonsil,  and  is  separated  from  the  flocculus  by  the  postnodular  fissure. 
H I     The  Tuber  Vermis  (tuber  valvulcB)  and  the  Inferior  Semilunar  Lobule  (lobulus  semi- 
^    lunaris  inferior;  postero-superior  lobule)  collectively  form  the  lobus  tuberus  (tuberce 
lobe).    The  tuber  vermis,  the  most  posterior  division  of  the  inferior  vermis,  is  of 
small  size,  and  laterally  spreads  out  into  the  large  inferior  semilunar  lobules, 
which  comprise  at  least  two-thirds  of  the  inferior  surface  of  the  hemisphere. 

Internal  Structiu-e  of  the  Cerebellum. — ^The  cerebellum  consists  of  white  and  gray 
substance. 

White  Substance. — If  a  sagittal  section  (Fig.  704)  be  made  through  either  hemi- 
sphere, the  interior  will  be  found  to  consist  of  a  central  stem  of  white  substance, 
in  the  middle  of  which  is  a  gray  mass,  the  dentate  nucleus.  From  the  surface  of  this 
central  white  stem  a  series  of  plates  is  prolonged;  these  are  covered  with  gray 
substance  and  form  the  laminae.  In  consequence  of  the  main  branches  from  the 
central  stem  dividing  and  subdividing,  a  characteristic  appearance,  named  the 
arbor  vitse,  is  presented.  If  the  sagittal  section  be  made  through  the  middle  of 
the  vermis,  it  will  be  found  that  the  central  stem  divides  into  a  vertical  and  a  hor- 
izontal branch.  The  vertical  branch  passes  upward  to  the  culmen  monticuli, 
where  it  subdivides  freely,  one  of  its  ramifications  passing  forward  and  upward 
to  the  central  lobule.  The  horizontal  branch  passes  backward  to  the  folium  vermis, 
greatly  diminished  in  size  in  consequence  of  having  given  off  large  secondary 
branches;  one,  from  its  upper  surface,  ascends  to  the  clivus  monticuli;  the  others 
descend,  and  enter  the  lobes  in  the  inferior  vermis,  viz.,  the  tuber  vermis,  the 
pyramid,  the  uvula,  and  the  nodule. 

The  white  substance  of  the  cerebellum  includes  two  sets  of  nerve  fibers:  (1) 
projection  fibers,  (2)  fibrae  propriae. 

Projection  Fibers. — The  cerebellum  is  connected  to  the  other  parts  of  the  brain 
by  three  large  bundles  of  projection  fibers,  viz.,  to  the  cerebrum  by  the  superior 
peduncle,  to  the  pons  by  the  middle  peduncle,  and  to  the  medulla  oblongata  by 
the  inferior  peduncles  (Fig.  705). 


I 


NEUROLOGY 

The  superior  cerebellar  peduncles  (brack >'a  conjunctiva),  two  in  numb(^r,  emerge 
from  the  upper  and  medial  part  of  the  white  substance  of  the  hemispheres  and 
are  placed  under  cover  of  the  upper  part  of  the  cerebellum.  They  are  joined  to  each 
other  across  the  middle  line  by  the  anterior  medullary  velum,  and  can  be  followed 


,,^^  °i^:^^^Q_ 


°s^   Ala  lobidt  centralis 
Lingula 


Superior  peduncle 


Horizontal         '^ 
sulcus 

TONSIl- 

Nodule        Fourth  ventricle 
Fia.  704. — Sagittal  section  of  the  cerebellum,  near  the  junction  of  the  vermia  with  the  hemisphere.    (SchSfer.) 


Superior  peduncle 


Inferior  peduncle 


Middle  peduncle 
/ 


Trigeminal 

nerve 


Inferior  peduncle 
Fia.  705. — Dissection  showing  the  projection  fibers  of  the  cerebellum.      (After  E.  B.  Jamieson.) 

upward  as  far  as  the  inferior  colliculi,  under  which  they  disappear.  Below,  they 
form  the  upper  lateral  boundaries  of  the  fourth  ventricle,  but  as  they  ascend  they 
converge  on  the  dorsal  aspect  of  the  ventricle  and  thus  assist  in  roofing  it  in. 

The  fibers  of  the  superior  peduncle  are  mainly  derived  from  the  cells  of  the 


I  THE  HIND-BRAIN  OR  RHOMBENCEPHALON  793 

entate  nucleus  of  the  cerebellum  and  emerge  from  the  hilus  of  this  nucleus; 
a  few  arise  from  the  cells  of  the  smaller  gray  nuclei  in  the  cerebellar  white  sub- 
stance, and  others  from  the  cells  of  the  cerebellar  cortex.  They  are  continued 
upward  beneath  the  corpora  quadrigemina,  and  the  fibers  of  the  two  peduncles  under- 
go a  complete  decussation  ventral  to  the  Sylvian  aqueduct.  Having  crossed  the 
middle  line  they  divide  into  ascending  and  descending  groups  of  fibers,  the  former 
ending  in  the  red  nucleus,  the  thalamus,  and  the  nucleus  of  the  oculomotor  nerve, 
while  the  descending  fibers  can  be  traced  as  far  as  the  dorsal  part  of  the  pons; 
Cajal  believes  them  to  be  continued  into  the  anterior  funiculus  of  the  medulla 
spinalis. 

As  already  stated  (page  762),  the  majority  of  the  fibers  of  the  ventral  spino- 
cerebellar fasciculus  of  the  medulla  spinalis  pass  to  the  cerebellum,  which  they 
reach  b;s'  way  of  the  superior  peduncle. 

The  middle  cerebellar  ped^lncles  (brachia  pontis)  (Fig.  705)  are  composed  entirely  of 
centripetal  fibers,  which  arise  from  the  cells  of  the  nuclei  pontis  of  the  opposite  side 
and  end  in  the  cerebellar  cortex;  the  fibers  are  arranged  in  three  fasciculi,  superior, 
inferior,  and  deep.  The  superior  fasciculus,  the  most  superficial,  is  derived  from 
the  upper  transverse  fibers  of  the  pons;  it  is  directed  backward  and  lateralward 
superficial  to  the  other  two  fasciculi,  and  is  distributed  mainly  to  the  lobules  on 
the  inferior  surface  of  the  cerebellar  hemisphere  and  to  the  parts  of  the  superior 
surface  adjoining  the  posterior  and  lateral  margins.  •  The  inferior  fasciculus  is 
formed  by  the  lowest  transverse  fibers  of  the  pons;  it  passes  under  cover  of  the 
superior  fasciculus  and  is  continued  downward  and  backward  more  or  less  parallel 
with  it,  to  be  distributed  to  the  folia  on  the  under  surface  close  to  the  vermis. 

The  deep  fasciculus  comprises  most  of  the  deep  transverse  fibers  of  the  pons. 
It  is  at  first  covered  by  the  superior  and  inferior  fasciculi,  but  crosses  obliquely 
and  appears  on  the  medial  side  of  the  superior,  from  which  it  receives  a  bundle; 
its  fibers  spread  out  and  pass  to  the  upper  anterior  cerebellar  folia.  The  fibers 
of  this  fasciculus  cover  those  of  the  restiform  body.^ 

The  inferior  cerebellar  peduncles  (restiform  bodies)  pass  at  first  upward  and  lateral- 
ward,  forming  part  of  the  lateral  walls  of  the  fourth  ventricle,  and  then  bend 
abruptly  backward  to  enter  the  cerebellum  between  the  superior  and  middle 
peduncles.  Each  contains  the  following  fasciculi:  (1)  the  dorsal  spinocerebellar 
fasciculus  of  the  medulla  spinalis,  Avhich  ends  mainly  in  the  superior  vermis;  (2) 
fibers  from  the  gracile  and  cuneate  nuclei  of  the  same  and  of  the  opposite  sides; 
(3)  fibers  from  the  opposite  olivary  nuclei;  (4)  crossed  and  uncrossed  fibers  from  the 
reticular  formation  of  the  medulla  oblongata;  (5)  vestibular  fibers,  derived  partly 
from  the  vestibular  division  of  the  acoustic  nerve  and  partly  from  the  nuclei  in 
which  this  division  ends — these  fibers  occupy  the  medial  segment  of  the  inferior 
peduncle  and  divide  into  ascending  and  descending  groups  of  fibers,  the  ascending 
fibers  partly  end  in  the  roof  nucleus  of  the  opposite  side  of  the  cerebellum;  (6) 
cerebellobulbar  fibers  A\'hich  come  from  the  opposite  roof  nucleus  and  probably 
from  the  dentate  nucleus,  and  are  said  to  end  in  the  nucleus  of  Deiters  and  in  the 
formatio  reticularis  of  the  medulla  oblongata;  (7)  some  fibers  from  the  ventral 
spinocerebellar  fasciculus  are  said  to  join  the  dorsal  spinocerebellar  fasciculus. 

The  anterior  medullary  velum  {velum  medidlare  anterius;  valve  of  Vieussens;  superior 
medullary  velum)  is  a  thin,  transparent  lamina  of  white  substance,  which  stretches 
between  the  superior  peduncle;  on  the  dorsal  surface  of  its  lower  half  the  folia 
and  lingula  are  prolonged.  It  forms,  together  with  the  superior  peduncle,  the 
roof  of  the  upper  part  of  the  fourth  ventricle ;  it  is  narrow  above,  where  it  passes 
beneath  the  inferior  colliculi,  and  broader  below,  where  it  is  continuous  with  the 
white  substance  of  the  superior  vermis.    A  slightly  elevated  ridge,  the  frsenulum 

'  See  article  by  E.  B.  Jamieson,  Journal  of  Anatomy  and  Physiology,  vol.  xliv. 


794  NEUROLOGY 


veli,  descends  upon  its  upper  part  from  between  the  inferior  colliculi,  and  on  either 
side  of  this  the  trochlear  nerve  emerges. 

The  posterior  medullary  velum  {velum  medullare  posterius;  inferior  medullary  velutt) 
is  a  thin  layer  of  white  Substance,  prolonged  from  the  white  center  of  the  cerebelluia, 
above  and  on  either  side  of  the  nodule;  it  forms  a  part  of  the  roof  of  the  fouri:h 
ventricle.  Somewhat  semilunar  in  shape,  its  convex  edge  is  continuous  with  the 
white  substance  of  the  cerebellum,  while  its  thin  concave  margin  is  apparently 
free;  in  reality,  however,  it  is  continuous  wuth  the  epithelium  of  the  ventricle, 
which  is  prolonged  downward  from  the  posterior  medullary  velum  to  the  liguke. 

The  two  medullary  vela  are  in  contact  with  each  other  along  their  line  of  emer- 
gence from  the  white  substance  of  the  cerebellum;  and  this  line  of  contact  forms 
the  summit  of  the  roof  of  the  fourth  ventricle,  which,  in  a  vertical  section  through 
the  cavity,  appears  as  a  pointed  angle. 

The  Fibrae  Propriae  of  the  cerebellum  are  6i  two  kinds:  (1)  commissural  fibers, 
which  cross  the  middle  line  at  the  anterior  and  posterior  parts  of  the  vermis  and 
connect  the  opposite  halves  of  the  cerebellum;  (2)  arcuate  or  association  fibers, 
which  connect  adjacent  laminae  with  each  other. 

Gray  Substance. — ^The  gray  substance  of  the  cerebellum  is  found  in  two  situations: 
(1)  on  the  surface,  forming  the  cortex;  (2)  as  independent  masses  in  the  anterior. 

(1)  The  gray  substance  of  the  cortex  presents  a  characteristic  foliated  appearance, 
due  to  the  series  of  laminae  which  are  given  off  from  the  central  white  substance; 
these  in  their  turn  give  off  secondary  laminae,  which  are  covered  by  gray  substance. 
Externally,  the  cortex  is  covered  by  pia  mater;  internally  is  the  medullary  center, 
consisting  mainly  of  nerve  fibers. 

Microscopic  Appearance  of  the  Cortex  (Fig.  706). — The  cortex  consists  of  two 
layers,  viz.,  an  external  gray  molecular  layer,  and  an  internal  rust-colored  nuclear 
layer;  between  these  is  an  incomplete  stratum  of  cells  which  are  characteristic  of 
the  cerebellum,  viz.,  the  cells  of  Purkinje. 

The  external  gray  or  molecular  layer  consists  of  fibers  and  cells.  The  nerve  fibers 
are  delicate  fibrillae,  and  are  derived  from  the  following  sources:  (a)  the  dendrites 
and  axon  collaterals  of  Purkinje's  cells;  (6)  fibers  from  cells  in  the  nuclear  layer; 
(c)  fibers  from  the  central  white  substance  of  the  cerebellum;  (d)  fibers  derived 
from  cells  in  the  molecular  layer  itself.  In  addition  to  these  are  other  fibers,  which 
have  a  vertical  direction,  and  are  the  processes  of  large  neuroglia  cells,  situated 
in  the  nuclear  layer.  They  pass  outward  to  the  periphery  of  the  gray  matter, 
where  they  expand  into  little  conical  enlargements  which  form  a  sort  of  limiting 
membrane  beneath  the  pia  mater,  analogous  to  the  membrana  limitans  interna 
in  the  retina,  formed  by  the  sustentacular  fibers  of  Miiller. 

The  cells  of  the  molecular  layer  are  small,  and  are  arranged  in  two  strata,  an 
outer  and  an  inner.  They  all  possess  branched  axons;  those  of  the  inner  layer 
are  termed  basket  cells ;  they  run  for  some  distance  parallel  with  the  surface  of  the 
folium — giving  off  collaterals  which  pass  in  a  vertical  direction  toward  the  bodies 
of  Purkinje's  cells,  around  which  they  become  enlarged,  and  form  basket-like 
net-works. 

The  cells  of  Purkinje  form  a  single  stratum  of  large,  flask-shaped  cells  at  the 
junction  of  the  molecular  and  nuclear  layers,  their  bases  resting  against  the  latter; 
in  fishes  and  reptiles  they  are  arranged  in  several  layers.  The  cells  are  flattened 
in  a  direction  transverse  to  the  long  axis  of  the  folium,  and  thus  appear  broad 
in  sections  carried  across  the  folium,  and  fusiform  in  sections  parallel  to  the  long 
axis  of  the  folium.  From  the  neck  of  the  flask  one  or  more  dendrites  arise  and  pass 
into  the  molecular  layer,  where  they  subdivide  and  form  an  extremely  rich  arbores- 
cence,  the  various  subdivisions  of  the  dendrites  being  covered  by  lateral  spine- 
like processes.  This  arborescence  is  not  circular,  but,  like  the  cell,  is  flattened  at 
right  angles  to  the  long  axis  of  the  folium;  in  other  words,  it  does  not  resemble 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON 


795 


a  round  bush,  but  has  been  aptly  compared  by  Obersteiner  to  the  branches  of  a 
fruit  tree  trained  against  a  trellis  or  a  wall.  Hence,  in  sections  carried  across 
the  folium  the  arborescence  is  broad  and  expanded ;  whereas  in  those  "which  are 
parallel  to  the  long  axis  of  the  folium,  the  arborescence,  like  the  cell  itself,  is 
seen  in  profile,  and  is  limited  to  a  narrow  area. 

From  the  bottom  of  the  flask-shaped  cell  the  axon  arises;  this  passes  through 
the  nuclear  layer,  and,  becoming  medullated,  is  continued  as  a  nerve  fiber  in  the 
subjacent  white  substance.  As  this  axon  traverses  the  granular  layer  it  gives  off 
fine  collaterals,  some  of  which  run  back  into  the  molecular  layer. 


Cell  of  Purkinje 


Molecular 
layer 


Axons  of 
granule  cells 
cut  trans- 
versely 


Small  cell 

of  molecular. 

layer 


Basket  cell. 


Golgi  cell 


Nuclear 
layer 


j  Axon  of  cell  of  Purkinje 


Neuroglia  cell 
Fig.  706. — Transverse  section  of  a  cerebellar  folium.     (Diagrammatic^  after  Cajal  and  Kolliker.) 


Tendril  fiber 
Moss  fiber 


The  internal  rust-colored  or  nuclear  layer  (Fig.  706)  is  characterized  by  containing 
numerous  small  nerve  cells  of  a  reddish-brown  color,  together  with  many  nerve 
fibrils.  Most  of  the  cells  are  nearly  spherical  and  provided  with  short  dendrites 
which  spread  out  in  a  spider-like  manner  in  the  nuclear  layer.  Their  axons  pass 
outward  into  the  molecular  layer,  and,  bifurcating  at  right  angles,  run  for  some 
distance  parallel  with  the  surface.    In  the  outer  part  of  the  nuclear  layer  are  some 

II       larger  cells,  of  the  type  II  of  Golgi.    Their  axons  undergo  frequent  division  as  soon 
as  they  leave  the  nerve  cells,  and  pass  into  the  nuclear  layer;  while  their  dendrites 


796 


NEUROLOGY 


I 


Finally,  in  the  gray  substance  of  the  cerebellar  cortex  there  are  fibers  whicli 
come  from  the  white  center  and  penetrate  the  cortex.  The  cell-origin  of  these 
fibers  is  unknown,  though  it  is  believed  that  it  is  probably  in  the  gray  substance 
of  the  medulla  spinalis.  Some  of  these  fibers  end  in  the  nuclear  layer  by  dividing 
into  numerous  branches,  on  which  are  to  be  seen  peculiar  moss-like  appendages; 
hence  they  have  been  termed  by  Ramon  y  Cajal  the  moss  fibers;  they  form  an 
arborescence  around  the  cells  of  the  nuclear  layer  and  are  said  to  come  from  fibers 
in  the  inferior  peduncle.  Other  fibers,  the  clinging  or  tendril  fibers,  derived  from  th(5 
medullary  center  can  be  traced  into  the  molecular  layer,  where  their  branches 
cling  around  the  dendrites  of  Purkinje's  cells.  They  are  said  to  come  from  fibers 
of  the  middle  peduncle. 

(2)  The  independeiit  centers  of  gray  substance  in  the  cerebellum  are  four  in 
number  on  either  side :  one  is  of  large  size,  and  is  known  as  the  nucleus  dentatus ; 
the  other  three,  much  smaller,  are  situated  near  the  middle  of  the  cerebellum,  and 
are  known  as  the  nucleus  emboliformis,  nucleus  globosus,  and  nucleus  fastigii. 

Nucleus  dentatus  Superior  peduncle 

Corpora  qvadrigemina 


Inferior  olivary  nucleus 
Fig.  707. — Sagittal  section  through  right  cerebellar  hemisphere.     The  right  olive  has  also  been  cut  sagitally. 

The  nucleus  dentatus  (Fig.  707)  is  situated  a  little  to  the  medial  side  of  the  center 
of  the  stem  of  the  white  substance  of  the  hemisphere.  It  consists  of  an  irregularly 
folded  lamina,  of  a  grayish-yellow  color,  containing  white  fibers,  and  presenting 
on  its  antero-medial  aspect  an  opening,  the  hilus,  from  which  most  of  the  fibers  of 
the  superior  peduncle  emerge  (page  792). 

The  nucleus  emboliformis  lies  immediately  to  the  medial  side  of  the  nucleus 
dentatus,  and  partly  covering  its  hilus.  The  nucleus  globosus  is  an  elongated 
mass,  directed  antero-posteriorly,  and  placed  medial  to  preceding.  The  nucleus 
fastigii  is  somewhat  larger  than  the  other  two,  and  is  situated  close  to  the  middle 
line  at  the  anterior  end  of  the  superior  vermis,  and  immediately  over  the  roof 
of  the  fourth  ventricle,  from  which  it  is  separated  by  a  thin  layer  of  white  substance. 

The  cerebellum  is  concerned  with  the  coordination  of  movements  necessary  in  equilibration, 
locomotion  and  prehension.  In  it  terminate  pathways  conducting  impulses  of  mugcle  sense, 
tendon  sense,  joint  sense  and  equilibratory  disturbances.  With  the  exception  of  the  ventral 
spinocerebellar  fasciculus  these  impulses  enter  through  the  inferior  peduncle.  The  reflex  arc  is 
completed  by  fibers  in  the  superior  peduncle  which  pass  to  the  red  nucleus  and  the  thalamus  and 
thence  by  additional  neurons  (rubrospinal  tract)  to  the  motor  centers.  The  exact  functions  of  its 
different  parts  are  still  quite  uncertain,  owing  to  the  contradictory  nature  of  the  evidence  furnished 
by  (1)  ablation  experiments  upon  animals,  and  (2)  clinical  observations  in  man  of  the  effects 
produced  by  abscesses  or  tumors  affecting  different  portions  of  the  organ. 


I 


THE  HJND-BRAIN  OR  RHOMBENCEPHALON  797 


The  Fourth  Ventricle  (ventriculiis  quarins). — The  fourth  ventricle,  or  cavity 
of  the  hind-brain,  is  situated  in  front  of  the  cerebellum  and  behind  the  pons 
and  upper  half  of  the  medulla  oblongata.  Developmentally  considered,  the  fourth 
ventricle  consists  of  three  parts :  a  superior  belonging  to  the  isthmus  rhombencephali, 
an  intermediate,  to  the  metencephalon,  and  an  inferior,  to  the  myelencephalon. 
It  is  lined  by  ciliated  epithelium,  and  is  continuous  below  with  the  central  canal 
of  the  medulla  oblongata;^  above,  it  communicates,  by  means  of  a  passage  termed 
the  cerebral  aqueduct,  with  the  cavity  of  the  third  ventricle.  It  presents  four 
angles,  and  possesses  a  roof  or  dorsal  wall,  a  floor  or  ventral  wall,  and  lateral 
boundaries. 

Angles. — The  superior  angle  is  on  a  level  with  the  upper  border  of  the  pons, 
and  is  continuous  with  the  lower  end  of  the  cerebral  aqueduct.  The  inferior  angle 
is  on  a  level  with  the  lower  end  of  the  olive,  and  opens  into  the  central  canal  of  the 
medulla  oblongata.  Each  lateral  angle  corresponds  with  the  point  of  meeting 
of  the  brachia  and  inferior  peduncle.  A  little  below  the  lateral  angles,  on  a  level 
with  the  striae  medullares,  the  ventricular  cavity  is  prolonged  outward  in  the  form 
of  two  narrow  lateral  recesses,  one  on  either  side;  these  are  situated  between  the 
inferior  peduncles  and  the  flocculi,  and  reach  as  far  as  the  attachments  of  the  glosso- 
pharyngeal and  vagus  nerves. 

Lateral  Boundaries. — The  lower  part  of  each  lateral  boundary  is  constituted 
by  the  clava,  the  fasciculus  cuneatus,  and  the  inferior  peduncle;  the  upper  part  by 
the  middle  and  the  superior  peduncle. 

Roof  or  Dorsal  Wall  (Fig.  708). — The  upper  portion  of  the  roof  is  formed  by 
the  superior  peduncle  and  the  anterior  medullary  velum;  the  lower  portion, 
by  the  posterior  medullary  velum,  the  epithelial  lining  of  the  ventricle  covered 
by  the  tela  chorioidea  inferior,  the  tsenise  of  the  fourth  ventricle,  and  the  obex. 

The  superior  peduncle  (page  792),  on  emerging  from  the  central  white  sub- 
stance of  the  cerebellum,  pass  upward  and  forward,  forming  at  first  the  lateral 
boundaries  of  the  upper  part  of  the  cavity;  on  approaching  the  inferior  colliculi, 
they  converge,  and  their  medial  portions  overlap  the  cavity  and  form  part  of  its 
roof. 

The  anterior  medullary  velum  (page  793)  fills  in  the  angular  interval  between 
the  superior  peduncle,  and  is  continuous  behind  with  the  central  white  sub- 
stance of  the  cerebellum;  it  is  covered  on  its  dorsal  surface  by  the  lingula  of  the 
superior  vermis. 

The  posterior  medullary  velum  (page  794)  is  continued  downward  and  forward 
from  the  central  white  substance  of  the  cerebellum  in  front  of  the  nodule  and 
tonsils,  and  ends  inferiorly  in  a  thin,  concave,  somewhat  ragged  margin.  Below 
this  margin  the  roof  is  devoid  of  nervous  matter  except  in  the  immediate  vicinity 
of  the  lower  lateral  boundaries  of  the  ventricle,  where  two  narrow  white  bands,  the 
taeniae  of  the  fourth  ventricle  (ligylce),  appear;  these  bands  meet  over  the  inferior 
angle  of  the  ventricle  in  a  thin  triangular  lamina,  the  obex.  The  non-nervous  part 
of  the  roof  is  formed  by  the  epithelial  lining  of  the  ventricle,  which  is'prolonged 
downward  as  a  thin  membrane,  from  the  deep  surface  of  the  posterior  medullary 
velum  to  the  corresponding  surface  of  the  obex  and  taeniae,  and  thence  on  to  the 
floor  of  the  ventricular  cavity;  it  is  covered  and  strengthened  by  a  portion  of  the 
pia  mater,  which  is  named  the  tela  chorioidea  of  the  fourth  ventricle. 

The  taeniae  of  the  fourth  ventricle  (tcenia  ventriculi  quarti;  ligula)  are  two  narrow 
bands  of  white  matter,  one  on  either  side,  which  complete  the  lower  part  of  the  roof 
of  the  cavity.  Each  consists  of  a  vertical  and  a  horizontal  part.  The  vertical  part 
;S  continuous  below  the  obex  with  the  clava,  to  which  it  is  adherent  by  its  lateral 


\i 


I 


'  J.  T.  Wilson  (Journal  of  Anatomy  and  Physiology,  vol.  xl)  has  pointed  out  that  the  central  cana  .'of  the  medulla 
oblongata,  immediately  below  its  entrance  into  the  fourth  ventricle,  retains  the  cleft-like  form  presented  by  the  fetal 
medulla  spinalis,  and  that  it  is  marked  by  dorso-  and  ventro-Iateral  sulci. 


798 


NEUROLOGY 


I 


border.  The  horizontal  portion  extends  transversely  across  the  inferior  peduncle, 
below  the  strife  medullares,  and  roofs  in  the  lower  and  posterior  part  of  the  lateral 
recess;  it  is  attached  by  its  lower  margin  to  the  inferior  peduncle,  and  partly  enclos<iS 
the  choroid  plexus,  which,  however,  projects  beyond  it  like  a  cluster  of  grapes;  and 
hence  this  part  of  the  taenia  has  been  termed  the  cornucopia  (Bochdalek).  The  obex 
is  a  thin,  triangular,  gray  lamina,  which  roofs  in  the  lower  angle  of  the  ventricle  and 
is  attached  by  its  lateral  margins  to  the  clavse.  The  tela  chorioidea  of  the  fourth 
ventricle  is  the  name  applied  to  the  triangular  fold  of  pia  mater  which  is  carried 
upward  between  the  cerebellum  and  the  medulla  oblongata.  It  consists  of  two 
layers,  which  are  continuous  with  each  other  in  front,  and  are  more  or  less  adherent 
throughout.  The  posterior  layer  covers  the  antero-inferior  surface  of  the  cere- 
bellum, while  the  anterior  is  applied  to  the  structures  Avhich  form  the  lower  part 
of  the  roof  of  the  ventricle,  and  is  continuous  inferiorly  with  the  pia  mater  on  the 
inferior  peduncles  and  closed  part  of  the  medulla. 

Corpora 

quadrigemina 

Cerebral 

peduncle 

Anterior 

"medullary 

velum 

Ependymal 

lining  of 

ventricle 

PONS 

Posterior 
medullary  velum 


Choroid  plexus 

Cisterna  cerebellomedullaris  of 
subarachnoid  cavity 

Central  canal 


Fio.  708. — Scheme  of  roof  of  fourth  ventricle. 


Cisterna  pontis  of 
subarachnoid  cavity 

The  arrow  ia  i  n  the  foramen  of  Majendie. 


Choroid  Plexuses. — These  consist  of  two  highly  vascular  inflexions  of  the  tela 
chorioidea,  which  invaginate  the  lower  part  of  the  roof  of  the  ventricle  and  are 
everywhere  covered  by  the  epithelial  lining  of  the  cavity.  Each  consists  of  a  ver- 
tical and  a  horizontal  portion:  the  former  lies  close  to  the  middle  line,  and  the  latter 
passes  into  the  lateral  recess  and  projects  beyond  its  apex.  The  vertical  parts  of 
the  plexuses  are  distinct  from  each  other,  but  the  horizontal  portions  are  joined 
in  the  middle  line;  and  hence  the  entire  structure  presents  the  form  of  the  letter  T, 
the  vertical  limb  of  which,  however,  is  double. 

Openings  in  the  Roof. — In  the  roof  of  the  fourth  ventricle  there  are  three  openings, 
a  medial  and  two  lateral :  the  medial  aperture  {foramen  Majendii),  is  situated  imme- 
diately above  the. inferior  angle  of  the  ventricle;  the  lateral  apertures,  {foramina 
of  Luschka  are  found  at  the  extremities  of  the  lateral  recesses.  By  means  of  these 
three  openings  the  ventricle  communicates  with  the  subarachnoid  cavity,  and  the 
cerebrospinal  fluid  can  circulate  from  the  one  to  the  other. 

Rhomboid  Fossa  {fossa  rhomhoidea;  "floor"  of  the  fourth  ventricle)  (Fig.  709). — 
The  anterior  part  of  the  fourth  ventricle  is  named,  from  its  shape,  the  rhomboid 
fossa,  and  its  anterior  wall,  formed  by  the  back  of.  the  pons  and  medulla  oblongata, 
constitutes  the  floor  of  the  fourth  ventricle.    It  is  covered  by  a  thin  layer  of  gray 


I 


THE  HIND-BRAIN  OR  RHOMBENCEPHALON 


799 


substance  continuous  with  that  of  the  medulla  spinalis;  superficial  to  this  is  a  thin 
lamina  of  neuroglia  which  constitutes  the  ependyma  of  the  ventricle  and  supports 
ji  layer  of  ciliated  epithelium.  The  fossa  consists  of  three  parts,  superior,  inter- 
mediate, and  inferior.  The  superior  part  is  triangular  in  shape  and  limited  laterally 
by  the  superior  cerebellar  peduncle;  its  apex,  directed  upward,  is  continuous  with 
the  cerebral  aqueduct ;  its  base  it  represented  by  an  imaginary  line  at  the  level  of  the 
upper  ends  of  the  superior  fovese.  The  intermediate  part  extends  from  this  level 
to  that  of  the  horizontal  portions  of  the  taenise  of  the  ventricle;  it  is  narrow  above 
where  it  is  limited  laterally  by  the  middle  peduncle,  but  widens  below  and  is  pro- 
longed into  the  lateral  recesses  of  the  ventricle.  The  inferior  part  is  triangular, 
and  its  downw^ardly  directed  apex,  named  the  calamus  scriptorius,  is  continuous 
with  the  central  canal  of  the  closed  part  of  the  medulla  oblongata. 


Frenvlum  veil 


Taenia  pontis^ 


Trochlear  nerve 
Ant.  medullary  velum 
Superior  peduncle 

Nucleus  dentatus 


Superior  fovea 
Collicvlus  facialis 
Striae  medullares 
Area  acustica 
Trigonum  hypoglossi 
Ala  cinerea 
Tcenia  of  fourth  ventricle 


P 


^  Funiculus  separana 
iArea  postrema 
^Obex 
'  Clava 
Fig.  709. — Rhomboid  fossa. 


The  rhomboid  fossa  is  divided  into  symmetrical  halves  by  a  median  sulcus 
which  reaches  from  the  upper  to  the  lower  angles  of  the  fossa  and  is  deeper  below 
than  above.  On  either  side  of  this  sulcus  is  an  elevation,  the  medial  eminence, 
bounded  laterally  by  a  sulcus,  the  sulcus  limitans.  In  the  superior  part  of  the  fossa 
the  medial  eminence  has  a  width  equal  to  that  of  the  corresponding  half  of  the 
fossa,  but  opposite  the  superior  fovea  it  forms  an  elongated  swelling,  the  coUiculus 
facialis,  which  overlies  the  nucleus  of  the  abducent  nerve,  and  is,  in  part  at  least, 
produced  by  the  ascending  portion  of  the  root  of  the  facial  nerve.  In  the  inferior 
part  of  the  fossa  the  medial  eminence  assumes  the  form  of  a  triangular  area,  the 
trigonum  hypoglossi.  When  examined  under  water  with  a  lens  this  trigone  is  seen 
to  consist  of  a  medial  and  a  lateral  area  separated  by  a  series  of  oblique  furrows; 
the  medial  area  corresponds  with  the  upper  part  of  the  nucleus  of  the  hypoglossal 
nerve,  the  lateral  with  a  small  nucleus,  the  nucleus  intercalatus. 

The  sulcus  limitans  forms  the  lateral  boundary  of  the  medial  eminence.  In 
the  superior  part  of  the  rhomboid  fossa  it  corresponds  with  the  lateral  limit  of  the 


I 


800 


NEUROLOGY 


I 


fossa  and  presents  a  bluish-gray  area,  the  locus  caeruleus,  which  owes  its  color 
to  an  underlying  patch  of  deeply  pigmented  nerve  cells,  termed  the  substantia 
ferruginea.  At  the  level  of  the  colliculus  facialis  the  sulcus  limitans  widens  into 
a  flattened  depression,  the  superior  fovea,  and  in  the  inferior  part  of  the  fossa  appears 
as  a  distinct  dimple,  the  inferior  fovea.  Lateral  to  the  foveae  is  a  rounded  elevation 
named  the  area  acustica,  which  extends  into  the  lateral  recess  and  there  forms  a 
feebly  marked  swelling,  the  tuberculum  acusticum.  Winding  around  the  inferior 
peduncle  and  crossing  the  area  acustica  and  the  medial  eminence  are  a  number  of 
white  strands,  the  striae  medullares,  which  form  a  portion  of  the  cochlear  division  of 
the  acoustic  nerve  and  disappear  into  the  median  sulcus.  Below  the  inferior  fovea, 
and  between  the  trigonum  hypoglossi  and  the  lower  part  of  the  area  acustica  is  a 
triangular  dark  field,  the  ala  cinerea,  which  corresponds  to  the  sensory  nucleus 
of  the  vagus  and  glossopharyngeal  nerves.  The  lower  end  of  the  ala  cinerea  is 
crossed  by  a  narrow  translucent  ridge,  the  funiculus  separans,  and  between  this 
funiculus  and  the  clava,  is  a  small  tongue-shaped  area,  the  area  postrema.  On 
section  it  is  seen  that  the  funiculus  separans  is  formed  by  a  strip  of  thickened 
ependyma,  and  the  area  postrema  by  loose,  highly  vascular,  neuroglial  tissue  con- 
taining nerve  cells  of  moderate  size. 

THE   MID-BRAIN    OR   MESENCEPHALON. 

The  mid-brain  or  mesencephalon  (Fig.  681)  is  the  short,  constricted  portion  which 
connects  the  pons  and  cerebellum  with  the  thalamencephalon  and  cerebral  hemi- 
spheres. It  is  directed  upward  and  for- 
ward, and  consists  of  (1)  a  ventro- 
lateral portion,  composed  of  a  pair  of 
cylindrical  bodies,  named  the  cerebral 
peduncles;  (2)  a  dorsal  portion,  consist- 
ing of  four  rounded  eminences,  named 
the  corpora  quadrigemina;  and  (3)  an 
intervening  passage  or  tunnel,  the  cere- 
bral aqueduct,  which  represents  the 
original  cavity  of  the  mid-brain  and 
connects  the  third  with  the  fourth  ven- 
tricle (Fig.  710). 

The  cerebral  peduncles  (pedunculus 
cerebri;  crus  cerebri)  are  two  cylindrical 
masses  situated  at  the  base  of  thetibrain, 
and  largely  hidden  by  the  t^nliBoral 
lobes  of  the  cerebrum,  which  hiuet  be 
drawn  aside  or  removed  in  order  to 
expose  them.  They  emerge  from  the 
upper  surface  of  the  pons,  one  on  either 
side  of  the  middle  line,  and,  diverging 
as  they  pass  upward  and  forward,  dis- 
appear into  the  substance  of  the  cere- 
bral hemispheres.  The  depressed  area 
between  the  crura  is  termed  the  inter- 
peduncular fossa,  and  consists  of  a  lajer 
of  grayish  substance,  the  posterior 
perforated  substance,  which  is  pierced  by  small  apertures  for  the  transmission  of 
bloodvessels;  its  lower  part  lies  on  the  ventral  aspect  of  the  medial  portions  of  the 
tegmenta,  and  contains  a  nucleus  named  the  interpeduncular  ganglion  (page  802) ; 
its  upper  part  assists  in  forming  the  floor  of  the  third  ventricle.    The  ventral  sur- 


....3 


L..-8 


Fig.  710. — Coronal  section  through  mid-brain.  (Sche- 
matic.) (Testut.)  1.  Corpora  quadrigemina.  2.  Cere- 
bral aqueduct.  3.  Central  gray  stratum.  4.  Interpedun- 
cular space.  5.  Sulcus  lateralis,  b.  Substantia  nigra.  7. 
Red  nucleus  of  tegmentum.  8.  Oculomotor  nerve,  with  8', 
its  nucleus  of  origin,  a.  Lemniscus  (in  blue)  with  a'  the 
medial  lemniscus  and  a"  the  lateral  lemniscus.  6. 
Medial  longitudinal  fasciculus,  f.  Raph6.  d.  Temporo- 
pontine fibers,  e.  Portion  of  medial  lemniscus,  which  runs 
to  the  lentiform  nucleus  and  insula.  /.  Cerebrospinal 
fibers,     g.  Frontopontine  fibers. 


THE  MID-BRAIN  OR  MESENCEPHALON 


801 


face  of  each  peduncle  is  crossed  from  the  medial  to  the  lateral  side  by  the  superior 
cerebellar  and  posterior  cerebral  arteries;  its  lateral  surface  is  in  relation  to  the 
gyrus  hippocampi  of  the  cerebral  hemisphere  and  is  crossed  from  behind  forward 
by  the  trochlear  nerve.  Close  to  the  point  of  disappearance  of  the  peduncle  into 
le  cerebral  hemisphere,  the  optic  tract  winds  forward  around  its  ventro-lateral 


Inferior  coUiculi 


Cerebral  aquediict 

Nticleus  of  ocvlomotor 
nerve 


Lateral  lemniscus 

Medial  longitudinal 
fasciculus 

Medial  lemnisc^is 


^  _  ^  FkK.  711. — Transverse  section  of  mid-brain  at  level  of  inferior  colliculi. 

^  '  surface.  The  medial  surface  of  the  peduncle  forms  the  lateral  boundary 
of  the  interpeduncular  fossa,  and  is  marked  by  a  longitudinal  furrow,  the  oculo- 
motor sulcus,  from  which  the  roots  of  the  oculomotor  nerve  emerge.  On  the  lateral 
surface  of  each  peduncle  there  is^&  second  longitudinal  furrow,  termed  the  lateral 
sulcus ;  the  fibers  of  the  lateraf  3pmniscus  come  to  the  surface  in  this  sulcus,  and 


)ass  backward  and  upwa 


under  the  Inferior  colliculus. 


Cerebral  aqueduct 


Nucleus  ofoeulomotor  nerve 
Medial  longitudinal 
fasciculus 


Transverse  section  of  mid-brain  at  level  of  superior  colliculi. 


I 


Structure  of  the  Cerebral  Peduncles  (Figs.  711,  712). — On  transverse  section,  each 
peduncle  is  seen  to  consist  of  a  dorsal  and  a  ventral  part,  separated  by  a  deeply 
pigmented  lamina  of  gray  substance,  termed  the  substantia  nigra.     The  dorsal  part 
51 


802  NEUROLOGY 


I 


is  named  the  tegmentum;  the  ventral,  the  base  or  crusta;  the  two  bases  are  separated 
from  each  other,  but  the  tegmenta  are  joined  in  the  median  plane  by  a  forward 
prolongation  of  the  raphe  of  the  pons.  Laterally,  the  tegmenta  are  free;  dorsally, 
they  blend  with  the  corpora  quadrigemina. 

The  base  {basis  pedunculi;  crusta  or  pes)  is  semilunar  on  transverse  section,  and 
consists  almost  entirely  of  longitudinal  bundles  of  efferent  fibers,  which  arise  from 
the  cells  of  the  cerebral  cortex  and  are  grouped  into  three  principal  sets,  viz., 
cerebrospinal,  frontopontine,  and  temporopontine  (Fig.  710).  The  cerebrospinal 
fibers,  derived  from  the  cells  of  the  motor  area  of  the  cerebral  cortex,  occupy 
the  middle  three-fifths  of  the  base;  they  are  continued  partly  to  the  nuclei  of  the 
motor  cranial  nerves,  but  mainly  into  the  pyramids  of  the  medulla  oblongata. 
The  frontopontine  fibers  are  situated  in  the  medial  fifth  of  the  base;  they  arise  from 
the  cells  of  the  frontal  lobe  and  end  in  the  nuclei  of  the  pons.  The  temporopontine 
fibers  are  lateral  to  the  cerebrospinal  fibers;  they  originate  in  the  temporal  lobe 
and  end  in  the  nuclei  pontis.^ 

The  substantia  nigra  (intercalatum)  is  a  layer  of  gray  substance  containing 
numerous  deeply  pigmented,  multipolar  nerve  cells.  It  is  semilunar  on  transverse 
section,  its  concavity  being  directed  toward  the  tegmentum;  from  its  convexity, 
prolongations  extend  between  the  fibers  of  the  base  of  the  peduncle.  Thicker 
medially  than  laterally,  it  reaches  from  the  oculomotor  sulcus  to  the  lateral  sulcus, 
and  extends  from  the  upper  surface  of  the  pons  to  the  subthalamic  region;  its 
medial  part  is  traversed  by  the  fibers  of  the  oculomotor  nerve  as  these  stream  for- 
ward to  reach  the  oculomotor  sulcus.  The  connections  of  the  cells  of  the  substantia 
nigra  have  not  been  definitely  established.  It  receives  collaterals  from  the  medial 
lemniscus  and  the  pyramidal  bundles.  Bechterew  is  of  the  opinion  that  the  fibers 
from  the  motor  area  of  the  cerebral  cortex  form  synapses  with  cells  whose  axons 
pass  to  the  motor  nucleus  of  the  trigeminal  nerve  and  serve  for  the  coordination 
of  the  muscles  of  mastication. 

The  tegmentum  is  continuous  below  with  the  reticular  formation  of  the  pons, 
and,  like  it,  consists  of  longitudinal  and  transverse  fibers,  together  with  a  consider- 
able amount  of  gray  substance.  The  principal  gray  masses  of  the  tegmentum 
are  the  red  nucleus  and  the  interpeduncular  ganglion;  of  its  fibers  the  chief  longi- 
tudinal tracts  are  the  superior  peduncle,  the  medial  longitudinal  fasciculus,  and 
the  lemniscus. 

Gray  Substance. — ^The  red  nucleus  is  situated  in  the  anterior  part  of  the  teg- 
mentum, and  is  continued  upward  into  the  posterior  part  of  the  subthalamic  region. 
In  sections  at  the  level  of  the  superior  colliculus  it  appears  as  a  circular  mass 
which  is  traversed  by  the  fibers  of  the  oculomotor  nerve.  It  receives  many  terminals 
and  collaterals  from  the  superior  cerebellar  peduncle  also  collaterals  from  the 
ventral  longitudinal  bundle,  from  Gudden's  bundle  and  the  median  lemniscus. 
The  axons  of  its  larger  cells  cross  the  middle  line  and  are  continued  downward 
into  the  lateral  funiculus  of  the  medulla  spinalis  as  the  rubrospinal  tract  (page  761) ; 
those  of  its  smaller  cells  end  mainly  in  the  thalamus.  The  rubrospinal  tract  forms 
an  important  part  of  the  pathway  from  the  cerebellum  to  the  lower  motor  centers. 

The  interpedimcular  ganglion  is  a  median  collection  of  nerve  cells  situated  in 
the  ventral  part  of  the  tegmentum.  The  fibers  of  the  fasciculus  retroflexus  of 
Meynert,  which  have  their  origin  in  the  cells  of  the  ganglion  habenulae  (page  812), 
end  in  it. 

Besides  the  two  nuclei  mentioned,  there  are  small  collections  of  cells  which 
form  the  dorsal  and  ventral  nuclei  and  the  central  nucleus  or  nucleus  of  the  raphe. 

*  A  band  of  fibers,  the  tractus  peduneularis  transverSus,  is  sometimes  seen  emerging  from  in  front  of  the  superior  collic- 
ulus; it  passes  around  the  ventral  aspect  of  the  peduncle  about  midway  between  the  pons  and  the  optic  tract,  and 
dips  into  the  oculomotor  sulcus.  This  band  is  a  constant  structure  in  many  mammals,  but  is  only  present  in  about 
30  per  cent,  of  human  brains.  Since  it  undergoes  atrophy  after  enucleation  of  the  eyeballs,  it  may  be  considered  as 
forming  a  path  for  visual  sensations. 


I  THE  MID-BRAIN  OR  MESENCEPHALON  80^ 


^H     White  Substance. — (1)  The  origin  and  course  of  the  superior  peduncle  have 
already  been  described  (page  792). 

(2)  The  medial  (posterior)  longitudinal  fasciculus  is  continuous  below  with  the 
proper  fasciculi  of  the  anterior  and  lateral  funiculi  of  the  medulla  spinalis.  In 
the  medulla  oblongata  and  pons  it  runs  close  to  the  middle  line,  near  the  floor 
of  the  fourth  ventricle;  in  the  mid-brain  it  is  situated  on  the  ventral  aspect 
of  the  cerebral  aqueduct,  below  the  nuclei  of  the  oculomotor  and  trochlear 
nerves.  Its  connections  are  imperfectly  known,  but  it  consists  largely  of  ascend- 
ing and  descending  intersegmental  or  association  fibers,  which  connect  the 
nuclei  of  the  hind-brain  and  mid-brain  to  each  other.  Many  of  the  fibers  arise 
in  Deiters's  nucleus  (lateral  vestibular  nucleus)  and  divide  into  ascending  and  descend- 
ing branches  which  send  terminals  and  collaterals  to  the  motor  nuclei  of  the  cranial 
■  and  spinal  nerves.  Its  spinal  portion  is  located  in  the  anterior  funiculus  and  is 
jknown  as  the  vestibulospinal  fasciculus.  Other  fibers  pass  to  the  median  longitudinal 
bundle  from  cells  in  the  reticular  formation  of  the  medulla,  pons  and  mid-brain 
and  also  from  certain  large  cells  in  the  terminal  nucleus  of  the  trigeminal  nerve. 
According  to  Edinger  it  extends  to  the  so-called  nucleus  of  the  posterior  longi- 
tudinal bundle  in  the  hypothalamic  region,  but  this  is  uncertain  and  the  fibers 
above  the  nucleus  of  the  oculomotor  are  smaller  in  diameter  than  the  rest  of  the 
bundle.  According  to  Held  fibers  from  the  posterior  commissure  can  be  traced 
into  the  posterior  longitudinal  bundle,  and  according  to  the  same  author  many 
of  the  descending  fibers  arise  in  the  superior  colliculus,  and,  after  decussating  in 
the  middle  line,  end  in  the  motor  nuclei  of  the  pons  and  medulla  oblongata.  These 
fibers  from  the  superior  colliculus  probably  pass  into  the  ventral  longitudinal 
bundle.  Fibers  are  said  to  pass  through  the  medial  longitudinal  fasciculus  from  the 
nucleus  of  the  abducent  nerve  into  the  oculomotor  nerve  of  the  opposite  side,  and 
through  this  nerve  to  the  Rectus  medialis  oculi.  Fraser,  however,  denies  the  exist- 
ence of  such  fibers.  Again,  fibers  are  said  to  be  prolonged  through  this  fasciculus 
from  the  nucleus  of  the  oculomotor  nerve  into  the  facial  nerve,  and  are  distributed 
to  the  Orbicularis  oculi,  the  Corrugator,  and  the  Frontalis.^ 

The  ventral  longitudinal  bundle  consists  for  the  most  part  of  the  tectospinal  fas- 
ciculus, and  arises  from  the  superior 'colliculus,  the  fibers  arch  ventrally  around  the 
central  gray  matter  and  cross  the  midline  in  the  fountain-decussation  of  MejTiert. 
They  then  descend  in  the  tegmentum,  part  of  them  passing  through  the  red  nucleus 
ventral  to  the  medial  longitudinal  bundle.     In  the  medulla  oblongata  and  spinal 

■  ,  cord  its  fibers  are  more  or  less  intermingled  with  the  medial  longitudinal  bundle 
iftnd  the  rubrospinal  tract.  It  descends  in  the  adjoining  region  of  the  ventral 
and  lateral  funiculi.  Collaterals  and  terminals  are  given  off  to  the  red  nucleus  and 
probably  other  nuclei  of  the  brain  stem  and  to  the  anterior  column  of  the  spinal 

■  ■cord.  It  is  probably  concerned  in  optic  reflexes. 
"  (3)  The  medial  lemniscus  or  medial  fillet  (Fig.  713). — ^The  fibers  of  tha  medial 
lemniscus  take  origin  in  the  gracile  and  cuneate  nuclei  of  the  medulla  oblongata, 
and  as  internal  arcuate  fibers  they  cross  to  the  opposite  side  in  the  sensory  decussa- 
tion (page  777).  They  then  paSs  in  the  interolivary  stratum  upward  through 
the  medulla  oblongata,  in  which  they  are  situated  behind  the  cerebrospinal  fibers 

■  ■and  between  the  olives.    In  the  pons  and  lower  part  of  the  mid-brain  it  occupies 
pthe  ventral  part  of  the  reticular  formation  and  tegmentum  close  to  the  raphe,  while 
above  it  gradually  shifts  to  the  dorso-lateral  part  of  the  tegmentum  in  the  angle 
between  the  red  nucleus  and  the  substantia  nigra.     In  the  pons  it  assumes  a  flattened 
ribbon-like  appearance,  and  is  placed  dorsal  to  the  trapezium.    As  the  lemniscus 
^■ascends,  it  receives  additional  fibers  from  the  terminal  sensory  nuclei  of  the* cranial 


I 


I  A.  Bruce  and  J.  H.  Harvey  Pirrie,  "On  the  Origin  of  the  Facial  Nerve,"  Review  of  Neurology  and  Psychiatry, 
December,  1908,  No.  12,  vol.  vi,  produce  weighty  evidence  against  the  view  that  the  facial  nerve  derives  fibers  from 
the  nucleus  of  the  oculomotor  nerve." 


804 


NEUROLOGY 


nerves  of  the  opposite  side.  Many  of  the  fibers  which  arise  from  the  terminal 
sensors'  nuclei  of  the  cranial  nerves  pass  upward  in  the  formatio  reticularis  as  a 
separate  bundle,  known  as  the  central  tract  of  the  cranial  nerves,  to  the  thalamus. 

Many  fibers  either  terminate  in  or  send  off  collaterals  to  the  gray  matter  of  the 
medulla,  the  pons,  and  the  mid-brain.  Large  numbers  of  fibers  pass  to  or  from  tfie 
substantia  nigra.  Many  collaterals  enter  the  red  nucleus  and  other  fibers  are  said 
to  run  to  the  superior  colliculus.  The  great  bulk  of  the  fibers,  however,  enter  the 
ventro-lateral  portion  of  the  thalamus,  give  off  collaterals  to  the  posterior  semi- 
lunar nucleus  and  then  terminate  in  the  principal  sensory  nucleus  of  the  thalamus. 


I 


Corpora 
quadrigemina 


Superior  olivary 
mtcleus 


Cochlear  nucleus 
-  Sensory  cerebral  nuclei 

Nucleus  gracilis 
Nucleus  cuneatus 


Fig.  713. — Scheme  showing  the  course  of  the  fibers  of  the  lemniscus;  medial  lemniscus  in  blue,  lateral  in  red. 

In  the  cerebral  peduncle,  a  few  of  its  fibers  pass  upward  in  the  lateral  part 
of  the  base  of  the  peduncle,  on  the  dorsal  aspect  of  the  temporopontine  fibers, 
and  reach  the  lentiform  nucleus  and  the  insula.  The  greater  part  of  the  medial 
lemniscus,  on  the  other  hand,  is  prolonged  through  the  tegmentum,  and  most 
of  its  fibers  end  in  the  thalamus;  probably  some  are  continued  directly  through 
the  occipital  part  of  the  internal  capsule  to  the  cerebral  cortex.  From  the  cells  of 
the  thalamus  a  relay  of  fibers  is  prolonged  to  the  cerebral  cortex. 

The  medial  lemniscus  may  be  considered  as  the  upward  continuation  of  the 
posterior  funiculus  of  the  spinal  cord  and  to  convey  conscious  impulses  of  muscle 
sense  and  tactile  discrimination. 


THE  MID-BRAIN  OR  MESENCEPHALON 


805 


6   2 


Fig.  714. — 'I^ransverse  section  passing  through 
the  sensory  decussation.  Schematic.  (Testut.) 
1.  Anterior  median  fissure.  2.  Posterior  median 
sulcus.  3,  3'.  Head  and  base  of  anterior  column 
(in  red).  4.  Hypoglossal  nerve.  5.  Bases  of 
posterior  column.  6.  Gracile  nucleus.  7.  Cune- 
ate  nucleus.  8,  8.  Lemniscus.  9.  Sensory 
decussation.      10.  Cerebrospinal  fasciculus. 


The  central  or  thalamic  tract  of  the  cranial  nerves  is  closely  associated  with  the 
medial  lemniscus.  The  fibers  of  the  spinothalamic  fasciculi  are  continued  from  the 
ispinal  cord  into  this  tract  which  passes  upward  in  the  reticular  formation  and  the 
tegmentum  to  the  thalamus  along  the  dor.sal  side  of  the  median  lemniscus.  It 
receives  fibers  from  the  opposite  terminal  sensory  nuclei  of  the  vagus,  glossopharyn- 
geal, facial,  trigeminal  and  probably  the  vestibular  nerves.  IMany  of  the  secondary 
sensory  fibers  of  the  trigeminal  cross  the  raphe  from  its  terminal  nucleus  and  pass 
upward  to  the  thalamus  by  a  more  or  less  separate  but  closely  associated  pathway 
knowTi  as  the  central  tract  of  the  trigeminal  nerve 
which  also  lies  on  the  dorsal  aspect  of  the  lemnis- 

^^  eus.   These  two  tracts  give  off  collaterals  to  the 

^■toosterior  semilunar  nucleus  of  the  thalamus  and 

^^' terminate  in  the  anterior  semilunar  nucleus  of 
the  ventro-lateral  region  of  the  thalamus  sending 
collaterals  into  the  zona  incerta. 

The  fibers  of  the  rubrospinal  tract  {bundle  of 
Monahow)  arise  in  the  red  nucleus,  cross  the 
midline  in  the  decussation  of  Forel  and  pass 
downward  in  the  f  ormatio  reticularis  of  the  brain- 
stem into  the  lateral  funiculus  of  the  spinal  cord 
ventral  to  the  crossed  pyramidal  tract. 

The  lateral  lemniscus  {lemniscus  lateralis) 
comes  to  the  surface  of  the  mid-brain  along 
its  lateral  sulcus,  and  disappears  under  the 
inferior  colliculus.  It  consists  of  fibers  from 
the  terminal  nuclei  of  the  cochlear  division 
of  the  acoustic  nerve,  together  with  others  from 
the  superior  olivary  and  trapezoid  nuclei.    Most 

of  these  fibers  are  crossed,  but  some  are  uncrossed.  Many  of  them  pass  to  the 
inferior  colliculus  of  the  same  or  opposite  side,  but  others^  are  prolonged  to 
the  thalamus,  and  thence  through  the  occipital  part  of  the  internal  capsule  to 
the  middle  and  superior  temporal  gyri. 

The  corpora  quadrigemina  (Fig.  720)  are  four  rounded  eminences  which  form 
the  dorsal  part  of  the  mid-brain.  They  are  situated  above  and  in  front  of 
the  anterior  medullary  velum  and  superior  peduncle,  and  below  and  behind  the 
third  ventricle  and  posterior  commissure.  They  are  covered  by  the  splenium  of  the 
corpus  callosum,  and  are  partly  overlapped  on  either  side  by  the  medial  angle, 
or  pulvinar,  of  the  posterior  end  of  the  thalamus;  on  the  lateral  aspect,  under 

■  cover  of  the  pulvinar,  is  an  oval  eminence,  named  the  medial  geniculate  body. 
Prhe  corpora  quadrigemina  are  arranged  in  pairs  (superior  and  inferior  colliculi), 
and  are  separated  from  one  another  by  a  crucial  sulcus.  The  longitudinal  part 
of  this  sulcus  expands  superiorly  to  form  a  slight  depression  which  supports  the 
pineal  body,  a  cone-like  structure  which  projects  backward  from  the  thalam- 
encephalon  and  partly  obscures  the  superior  colliculi.  From  the  inferior  end  of 
the  longitudinal  sulcus,  a  white  band,  termed  the  frenulum  veli,  is  prolonged  down- 
ward to  the  anterior  medullary  velum;  on  either  side  of  this  band  the  trochlear 
nerve  emerges,  and  passes  forward  on  the  lateral  aspect  of  the  cerebral  peduncle 
to  reach  the  base  of  the  brain.  The  superior  colliculi  are  larger  and  darker  in  color 
than  the  inferior,  and  are  oval  in  shape.  The  inferior  colliculi  are  hemispherical, 
and  somewhat  more  prominent  than  the  superior.  The  superior  colliculi  are 
associated  with  the  sense  of  sight,  the  inferior  with  that  of  hearing. 

I  From  the  lateral  aspect  of  each  colliculus  a  white  band,  termed  the  brachium, 
ris  prolonged  upward  and  forward.  The  superior  brachium  extends  lateralward 
^~"' — """■■■ 


806  NEUROLOGY 


I 


late  body,  is  partly  continued  into  an  eminence  called  the  lateral  §:eniculate  body, 
and  partly  into  the  optic  tract.  The  inferior  brachium  passes  forward  and  upward 
from  the  inferior  colliculus  and  disappears  under  cover  of  the  medial  geniculate  body. 

In  close  relationship  with  the  corpora  quadrigemina  are  the  superior  peduncles, 
w^hich  emerge  from  the  upper  and  medial  parts  of  the  cerebellar  hemispheres. 
They  run  upward  and  forward,  and,  passing  under  the  inferior  colliculi,  enter  the 
tegmenta  as  already  described  (page  792). 

Structure  of  the  Corpora  Quadrigemina. — The  inferior  colliculus  {colliculus  inferior; 
inferior  quadrigeminal  body;  postgemina)  consists  of  a  compact  nucleus  of  gray 
substance  containing  large  and  small  multipolar  nerve  cells,  and  more  or  less 
completely  surrounded  by  white  fibers  derived  from  the  lateral  lemniscus. 
Most  of  these  fibers  end  in  the  gray  nucleus  of  the  same  side,  but  some  cross  the 
middle  line  and  end  in  that  of  the  opposite  side.  From  the  cells  of  the  gray 
nucleus,  fibers  are  prolonged  through  the  inferior  brachium  into  the  tegmentum 
of  the  cerebral  peduncle,  and  are  carried  to  the  thalamus  and  the  cortex  of  the 
temporal  lobe;  other  fibers  cross  the  middle  line  and  end  in  the  opposite  colliculus. 

The  superior  colliculus  {colliculus  superior;  superior  quadrigeminal  body; 
pregemina)  is  covered  by  a  thin  stratum  (stratum  zonale)  of  white  fibers, 
the  majority  of  which  are  derived  from  the  optic  tract.  Beneath  this  is  the 
stratum  cinereum,  a  cap-like  layer  of  gray  substance,  thicker  in  the  center  than 
at  the  circumference,  and  consisting  of  numerous  small  multipolar  ^nerve  cells, 
imbedded  in  a  fine  network  of  nerve  fibers.  Still  deeper  is  the  stratum  opticum, 
containing  large  multipolar  nerve  cells,  separated  by  numerous  fine  nerve  fibers. 
Finally,  there  is  the  stratum  lemnisci,  consisting  of  fibers  derived  partly  from  the 
lemniscus  and  partly  from  the  cells  of  the  stratum  opticum;  interspersed  among 
these  fibers  are  many  large  multipolar  nerve  cells.  The  two  last-named  strata 
are  sometimes  termed  the  gray-white  layers,  from  the  fact  that  they  consist  of  both 
gray  and  white  substance.  Of  the  afferent  fibers  which  reach  the  superior  colliculus, 
some  are  derived  from  the  lemniscus,  but  the  majority  have  their  origins  in  the 
retina  and  are  conveyed  to  it  through  the  superior  brachium;  all  of  them  end  by 
arborizing  around  the  cells  of  the  gray  substance.  Of  the  efferent  fibers,  some 
cross  the  middle  line  to  the  opposite  colliculus;  many  ascend  through  the  superior 
brachium,  and  finally  reach  the  cortex  of  the  occipital  lobe  of  the  cerebrum;  while 
others,  after  undergoing  decussation  (fountain  decussation  of  Meynert)  form  the 
tectospinal  fasciculus  which  descends  through  the  formatio  reticularis  of  the  mid- 
brain, pons,  and  medulla  oblongata  into  the  medulla  spinalis,  where  it  is  found 
partly  in  the  anterior  funiculus  and  partly  intermingled  with  the  fibers  of  the 
rubrospinal  tract. 

The  corpora  quadrigemina  are  larger  in  the  lower  animals  than  in  man.  In 
fishes,  reptiles,  and  birds  they  are  hollow,  and  only  two  in  number  (corpora 
bigemina) ;  they  represent  the  superior  colliculi  of  mammals,  and  are  frequently 
termed  the  optic  lobes,  because  of  their  intimate  connection  with  the  optic  tracts. 

The  cerebral  aqueduct  {aqueductus  cerebri;  aqueduct  of  Sylvius)  is  a  narrow 
canal,  about  15  mm.  long,  situated  between  the  corpora  quadrigemina  and  teg- 
menta, and  connecting  the  third  with  the  fourth  ventricle.  Its  shape,  as  seen  in 
transverse  section^  varies  at  different  levels,  being  T-shaped,  triangular  above, 
and  oval  in  the  middle;  the  central  part  is  slightly  dilated,  and  was  named  by 
Retzius  the  ventricle  of  the  mid-brain.  It  is  lined  by  ciliated  columnar  epithelium, 
and  is  surrounded  by  a  layer  of  gray  substance  named  the  central  gray  stratum: 
this  is  continuous  below  with  the  gray  substance  in  the  rhomboid  fossa,  and  above 
with  that  of  the  third  ventricle.  Dorsally,  it  is  partly  separated  from  the  gray 
substance  of  the  quadrigeminal  bodies  by  the  fibers  of  the  lemniscus;  ventral  to 
it  are  the  medial  longitudinal  fasciculus,  and  the  formatio  reticularis  of  the  teg- 
mentum.    Scattered  throughout  the  central  gray  stratum  are  numerous  nerve 


I- 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


807 


cells  of  various  sizes,  interlaced,  by  a  net-work  of  fine  fibers.  Besides  these  scattered 
cells  it  contains  three  groups  which  constitute  the  nuclei  of  the  oculomotor  and 
trochlear  nerves,  and  the  nucleus  of  the  mesencephalic  root  of  the  trigeminal  nerve. 
The  nucleus  of  the  trigeminal  nerve  extends  along  the  entire  length  of  the  aqueduct, 
and  occupies  the  lateral  part  of  the  gray  stratum,  while  the  nuclei  of  the  oculo- 
motor and  trochlear  nerves  are  situated  in  its  ventral  part.  The  nucleus  of  the 
oculomotor  nerve  is  about  10  cm.  long,  and  lies  under  the  superior  colliculus,  beyond 
which,  however,  it  extends  for  a  short  distance  into  the  gray  substance  of  the  third 
ventricle.  The  nucleus  of  the  trochlear  nerve  is  small  and  nearly  circular,  and  is  on 
a  level  with  a  plane  carried  transversely  through  the  upper  part  of  the  inferior 
colliculus. 

THE   FORE-BRAIN   OR   PROSENCEPHALON. 

The  fore-brain  or  prosencephalon  consists  of:  (1)  the  diencephalon,  corresponding 
[in  a  large  measure  to  the  third  ventricle  and  the  structures  which  bound  it;  and 
1(2)  the  telencephalon,  comprising  the  largest  part  of  the  brain,  viz.,  the  cerebral 
hemispheres;  these  hemispheres  are  intimately  connected  with  each  other  across 
the  middle  line,  and  each  contains  a  large  cavity,  named  the  lateral  ventricle. 
The  lateral  ventricles  communicate  through  the  interventricular  foramen  with  the 
third  ventricle,  but  are  separated  from  each  other  by  a  medial  septum,  the  septum 
pellucidum;  this  contains  a  slit-like  cavity,  which  does  not  communicate  with  the 
ventricles. 


FORAMEN  OF  MONRO 


MIDDLE  COMMISSURE. 

CHOROID   PLEXUS  OF 
THI  RD  VENTRICLE 

TAENIA  THALAMt 

HABENULAR 
COMMISSURE 

POSTERIOR 
COMMISSURE 


lOSTRUW  - 

COPULA 
ANTERIOR 
COMMISSURE 
LAMINA  TERMINALIS 

OPTIC  CHIASM 
^H    r  OPTIC 

^H  ■; 

^H  H|  PITUITARY  BO 


QUADRIGEMINAL 
LA  M  I  N  A 


AQUEDUCT 


SUP.  MEDULLARt 
VELUM 
\  FOURTH 
VENTRICLE 


Fig.  715. — Mesal  aspect  of  a  brain  sectioned  in  the  median  sagittal  plane. 


I 


The  Diencephalon. — The  diencephalon  is  connected  above  and  in  front  with 
the  cerebral  hemispheres;  behind  with  the  mid-brain.  Its  upper  surface  is  con- 
cealed by  the  corpus  callosum,  and  is  covered  by  a  fold  of  pia  mater,  named  the 
tela  chorioidea  of  the  third  ventricle;  inferiorly  it  reaches  to  the  base  of  the  brain. 

The  diencephalon  comprises:  (1)  the  thalamencephalon;  (2)  the  pars  mamillaris 


808 


NEUROLOGY 


hypothalami ;  and  (3)  the  posterior  part  of  the  third  ventricle.  For  descriptive  purposes, 
however,  it  is  more  convenient  to  consider  the  whole  of  the  third  ventricle  and  its 
boundaries  together;  this  necessitates  the  inclusion,  under  this  heading,  of  the  pars 
optica  hypothalami  and  the  corresponding  part  of  the  third  ventricle — structures 
which  properly  belong  to  the  telencephalon. 

The  Thalamencephalon. — The  thalamencephalon  comprises:  (1)  the  thalamus; 
(2)  the  metathalamus  or  corpora  geniculata;  and  (3)  the  epithalamus,  consisting  of 
the  trigonum  habenulae,  the  pineal  body,  and  the  posterior  commissure. 


I 


Fia.  716. — Dissection  showing  the  ventricles  of  the  brain. 

The  Thalami  {o^tic  thalamus)  (Figs.  716,  717)  are  two  large  ovoid  masses,  situated 
one  on  either  side  of  the  third  ventricle  and  reaching  for  some  distance  behind  that 
cavity.  Each  measures  about  4  cm.  in  length,  and  presents  two  extremities,  an 
anterior  and  a  posterior,  and  four  surfaces,  superior,  inferior,  medial,  and  lateral. 

The  anterior  extremity  is  narrow;  it  lies  close  to  the  middle  line  and  forms  the 
posterior  boundary  of  the  interventricular  foramen. 

The  posterior  extremity  is  expanded,  directed  backward  and  lateralward,  and 
overlaps  the  superior  colliculus.  Medially  it  presents  an  angular  prominence, 
the  pulvinar,  which  is  continued  laterally  into  an  oval  swelling,  the  lateral  geniculate 
body,  while  beneath  the  pulvinar,  but  separated  from  it  by  the  superior  brachium, 
is  a  second  oval  swelling,  the  medial  geniculate  body. 

The  superior  surface  is  free,  slightly  convex,  and  covered  by  a  layer  of  white 
substance,  termed  the  stratum  zonale.  It  is  separated  laterally  from  the  caudate 
nucleus  by  a  white  band,  the  stria  terminalis,  and  by  the  terminal  vein.  It  is  divided 
into  a  medial  and  a  lateral  portion  by  an  oblique  shallow  furrow  which  runs  from 
behind  forward  and  medialward  and  corresponds  with  the  lateral  margin  of  the 
fornix;  the  lateral  part  forms  a  portion  of  the  floor  of  the  lateral  ventricle,  and  is 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


809 


covered  by  the  epithelial  lining  of  this  cavity;  the  medial  part  is  covered  by  the 
tela  chorioidea  of  the  third  ventricle,  and  is  destitute  of  an  epithelial  covering. 
In  front,  the  superior  is  separated  from  the  medial  surface  by  a  salient  margin, 
the  taenia  thalami,  along  which  the  epithelial  lining  of  the  third  ventricle  is  reflected 
on  to  the  under  surface  of  the  tela  chorioidea.  Behind,  it  is  limited  medially  by 
la  groove,  the  sulcus  habenulse,  which  intervenes  between  it  and  a  small  triangular 
area,  termed  the  trigonum  habenulse. 

The  inferior  surface  rests  upon  and  is  continuous  with  the  upward  prolongation 
of  the  tegmentum  (subthalamic  tegmental  region) ,  in  front  of  which  it  is  related  to 
the  substantia  innominata  of  Meyaert. 


Thalamus 

Lateral  ventricle 
Caudate  nucleus 
Internal  capsule 

Lentiform  nucleus 

Claustrum 
Insula 


Corpus  callosum 
Choroid  plexu.1  of 
lateral  ventricle 
Fornix 

Choroid  plexus  of 
third  ventricle 

Third  ventricle 


lied  nucleus 


Substantia  nigra 
Post.  perf.  substance 


Fio. 


Base  of  peduncle 
Nucleus  of  Luys 
Tcenia  hippocampi 

Gyrus  dentatus 
717. — Coronal  section  of  brain  immediately  in  front  of  pons. 


Inferior  comu  of  lateral  ventricle 
Hippocampus 
Caudate  nucleus 


HI  The  medial  surface  constitutes  the  upper  part  of  the  lateral  wall  of  the  third 
B  Ventricle,  and  is  connected  to  the  corresponding  surface  of  the  opposite  thalamus 
by  a  flattened  gray  band,  the  massa  intermedia  (middle  or  gray  commissure).  This 
mass  averages  about  1  cm.  in  its  antero-posterior  diameter:  it  sometimes  consists 
of  two  parts  and  occasionally  is  absent.  It  contains  nerve  cells  and  nerve  fibers; 
a  few  of  the  latter  may  cross  the  middle  line,  but  most  of  them  pass  toward  the 

■  middle  line  and  then  curve  lateralward  on  the  same  side. 
m    The  lateral  surface  is  in  contact  with  a  thick  band  of  white  substance  which 
^forms  the  occipital  part  of  the  internal  capsule  and  separates  the  thalamus  from 
the  lentiform  nucleus  of  the  corpus  striatum. 


I 


810 


NEUROLOGY 


I 


Structure. — The  thalamus  consists  chiefly  of  gray  substance,  but  its  upper  sur- 
face is  covered  by  a  layer  of  white  substance,  named  the  stratum  zonale,  and  ii:s 
lateral  surface  by  a  similar  layer  termed  the  lateral  medullary  lamina.  Its  gray 
substance  is  incompletely  subdivided  into  three  parts — anterior,  medial,  and  lateral 
— by  a  white  layer,  the  medial  medullary  lamina.  The  anterior  part  comprises  the 
anterior  tubercle,  the  medial  part  lies  next  the  lateral  wall  of  the  third  ventricle 
while  the  lateral  and  largest  part  is  interposed  between  the  medullary  laminae 
and  includes  the  pulvinar.  The  lateral  part  is  traversed  by  numerous  fibers  which 
radiate  from  the  thalamus  into  the  internal  capsule,  and  pass  through  the  latter 
to  the  cerebral  cortex.  These  three  parts  are  built  up  of  numerous  nuclei,  the 
connections  of  many  of  which  are  imperfectly  known. 


Thalamus 

Caudate  nucleus 

Internal  capsule 
Globus  pallidus 
Putamen 
Claustrum 
Insula, 


Corpus  callosum 

Lateral  ventricle 

Choroid  plexus 

Fornix 

Third  ventricle 
Medial  medullary  lamina 

Intermediate  mass 

Third  ventricle 

Optic  tract 


n 


Amygdaloid  nucleus 
Fig.   718. — Coronal  section  of  brain  through  intermediate  mass  of  third  ventricle. 

Ck)miections.^ — The  thalamus  may  be  regarded  as  a  large  ganglionic  mass  in  which 
the  ascending  tracts  of  the  tegmentum  and  a  considerable  proportion  of  the  fibers 
of  the  optic  tract  end,  and  from  the  cells  of  which  numerous  fibers  (thalamocortical) 
take  origin,  and  radiate  to  almost  every  part  of  the  cerebral  cortex.  The  lemniscus, 
together  with  the  other  longitudinal  strands  of  the  tegmentum,  enters  its  ventral 
part:  the  thalamomammillary  fasciculus  {bundle  of  Vicq  d'Azyr),  from  the  corpus 
mammillare,  enters  in  its  anterior  tubercle,  while  many  of  the  fibers  of  the  optic 
tract  terminate  in  its  posterior  end.  The  thalamus  also  receives  numerous  fibers 
(corticothalamic)  from  the  cells  of  the  cerebral  cortex.    The  fibers  that  arise  from 


THE  FC 


OR  PROSENCEPHALON 


[the  cells  of  the  thalamus  form  four  principal  groups  or  stalks:  (a)  those  of  the  ante- 
rior stalk  pass  through  the  frontal  part  of  the  internal  capsule  to  the  frontal  lobe ; 
(b)  the  fibers  of  the  posterior  stalk  (oiJtic  radiations)  arise  in  the  pulvinar  and  are 
conveyed  through  the  occipital  part  of  the  internal  capsule  to  the  occipital  lobe;  (c) 
the  fibers  of  the  inferior  stalk  leave  the  under  and  medial  surfaces  of  the  thalamus, 
and  pass  beneath  the  lentiform  nucleus  to  the  temporal  lobe  and  insula;  (d)  those 
of  the  parietal  stalk  pass  from  the  lateral  nucleus  of  the  thalamus  to  the  parietal 
lobe.  Fibers  also  extend  from,  the  thalamus  into  the  corpus  striatum — those 
destined  for  the  caudate  nucleus  leave  the  lateral  surface,  and  those  for  the  lenti- 
form nucleus,  the  inferior  surface  of  the  thalamus. 

Superior  brachium      Lateral  geniculate  body 


Inferior  brachium 
Pulvinar 
PineaVhody    \ 


Medial  geniculate  body 

Optic  tract 


Superior  collieuli- 
Inferior  collieul; 

Frenulum  veli 

Trochlear  nerve 

Lateral  lemniscus 

Superior  peduncle 

Middle  peduncle^— 
Jlhoinhoid  fossa 


Clava 
Glossophai-yngeal  and  vagus  ner 


Optic  commissure 


Oculomotor  nei-ve 


Trigeminal  nerve 


Acoustic  nerve 
Facial  nerve 


Abducent  nerve 
Hypoglossal  nerve 


Accessory  nerve 

Fib.  719. — Hind-  and  mid-braina;  postero-lateral  view. 

The  TYletathalamus  (Fig.  719)  comprises  the  geniculate  bodies,  which  are  two  in 
number — a  medial  and  a  lateral — on  each  side. 

The  medial  geniculate  body  {corpus  geniculatum  mediate;  internal  geniculate  body; 
'postgeniculatum)  lies  under  cover  of  the  pulvinar  of  the  thalamus  and  on  the  lateral 
aspect  of  the  corpora  quadrigemina.  Oval  in  shape,  with  its  long  axis  directed 
forward  and  lateralward,  it  is  lighter  in  color  and  smaller  in  size  than  the  lateral. 
The  inferior  brachium  from  the  inferior  colliculus  disappears  under  cover  of  it 
while  from  its  lateral  extremity  a  strand  of  fibers  passes  to  join  the  optic  tract. 
Entering  it  are  many  acoustic  fibers  from  the  lateral  lemniscus.  The  medial 
geniculate  bodies  are  connected  with  one  another  by  the  commissure  of  Gudden, 
which  passes  through  the  posterior  part  of  the  optic  chiasma. 

The  lateral  geniculate  body  (corpus  geniculatum  later  ale;  external  geniculate  body; 
pregeniculatum)  is  an  oval  elevation  on  the  lateral  part  of  the  posterior  end  of  the 
thalamus,  and  is  connected  with  the  superior  colliculus  by  the  superior  brachium. 
It  is  of  a  dark  color,  and  presents  a  laminated  arrangement  consisting  of  alternate 
layers  of  gray  and  white  substance.  It  receives  numerous  fibers  from  the  optic 
tract,  while  other  fibers  of  this  tract  pass  over  or  through  it  into  the  pulvinar. 
Its  cells  are  large  and  pigmented;  their  axons  pass  to  the  visual  area  in  the  occipital 
part  of  the  cerebral  cortex. 


8i2  NEUROLOGY 


I 


The  superior  colliculus,  the  pulvinar,  and  the  lateral  geniculate  body  receive 
many  fibers  from  the  optic  tracts,  and  are  therefore  intimately  connected  with 
sight,  constituting  what  are  termed  the  lower  visual  centers.  Extirpation  of  tlie 
eyes  in  a  newly  born  animal  entails  an  arrest  of  the  development  of  these  centers, 
but  has  no  effect  on  the  medial  geniculate  bodies  or  on  the  inferior  colliculi.  More- 
over, the  latter  are  well-developed  in  the  mole,  an  animal  in  which  the  superior 
colliculi  are  rudimentary. 

The  Epithalamus  comprises  the  trigonum  habenulse,  the  pineal  body,  and  the 
posterior  commissure. 

The  trigonum  habenulse  is  a  small  depressed  triangular  area  situated  in  front 
of  the  superior  colliculus  and  on  the  lateral  aspect  of  the  posterior  part  of  the  taenia 
thalami.  It  contains  a  group  of  nerve  cells  termed  the  ganglion  habenulse.  Fibers 
enter  it  from  the  stalk  of  the  pineal  body,  and  others,  forming  what  is  termed  the 
habenular  commissure,  pass  across  the  middle  line  to  the  corresponding  ganglion 
of  the  opposite  side.  Most  of  its  fibers  are,  however,  directed  downward  and  form 
a  bundle,  the  fasciculus  retrofiexus  of  Meynert,  which  passes  medial  to  the  red 
nucleus,  and,  after  decussating  with  the  corresponding  fasciculus  of  the  opposite 
side,  ends  in  the  interpeduncular  ganglion. 

The  pineal  body  (corpus  pineale;  epiphysis)  is  a  small,  conical,  reddish-gray  body 
which  lies  in  the  depression  between  the  superior  colliculi.  It  is  placed  beneath  the 
splenium  of  the  corpus  callosum,  but  is  separated  from  this  by  the  tela  chorioidea 
of  the  third  ventricle,  the  lower  layer  of  which  envelops  it.  It  measures  about 
8  mm.  in  length,  and  its  base,  directed  forward,  is  attached  by  a  stalk  or  peduncle 
of  white  substance.  The  stalk  of  the  pineal  body  divides  anteriorly  into  two 
laminae,  a  dorsal  and  a  ventral,  separated  from  one  another  by  the  pineal  recess 
of  the  third  ventricle.  The  ventral  lamina  is  continuous  with  the  posterior  com- 
missure; the  dorsal  lamina  is  continuous  with  the  habenular  commissure  and 
divides  into  two  strands  the  medullary  striae,  which  run  forward,  one  on  either 
side,  along  the  junction  of  the  medial  and  upper  surfaces  of  the  thalamus  to  blend 
in  front  with  the  columns  of  the  fornix. 

The  posterior  commissure  is  a  rounded  band  of  white  fibers  crossing  the  middle 
line  on  the  dorsal  aspect  of  the  upper  end  of  the  cerebral  aqueduct.  Its  fibers 
acquire  their  medullary  sheaths  early,  but  their  connections  have  not  been  definitely 
determined.  Most  of  them  have  their  origin  in  a  nucleus,  the  nucleus  of  the  poste- 
rior commissure  (nucleus  of  Darkschewitsch) ,  which  lies  in  the  central  gray  substance 
of  the  upper  end  of  the  cerebral  aqueduct,  in  front  of  the  nucleus  of  the  oculomotor 
nerve.  Some  are  probably  derived  from  the  posterior  part  of  the  thalamus  and  from 
the  superior  colliculus,  while  others  are  believed  to  be  continued  downward  into 
the  medial  longitudinal  fasciculus. 

The  Hypothalamus  (Fig.  720)  includes  the  subthalamic  tegmental  region  and 
the  structures  forming  the  greater  part  of  the  floor  of  the  third  ventricle^  viz.,  the 
corpora  mammillaria,  tuber  cinereum,  infundibulum,  hypophysis,  and  optic  chiasma. 

The  subthalamic  tegmental  region  consists  of  the  upward  continuation  of  the 
tegmentum;  it  lies  on  the  ventro-lateral  aspect  of  the  thalamus  and  separates 
it  from  the  fibers  of  the  internal  capsule.  The  red  nucleus  and  the  substantia 
nigra  are  prolonged  into  its  lower  part;  in  front  it  is  continuous  with  the  substantia 
innominata  of  Meynert,  medially  with  the  gray  substance  of  the  floor  of  the  third 
ventricle. 

It  consists  from  above  downward  of  three  strata:  (1)  stratum  dorsale,  directly 
applied  to  the  under  surface  of  the  thalamus  and  consisting  of  fine  longitudinal 
fibers;  (2)  zona  incerta,  a  continuation  forward  of  the  formatio  reticularis  of  the 
tegmentum;  and  (3)  the  corpus  subthalamicum  (nucleus  of  Luys),  a  brownish  mass 
presenting  a  lenticular  shape  on  transverse  section,  and  situated  on  the  dorsal 
aspect  of  the  fibers  of  the  base  of  the  cerebral  peduncle;  it  is  encapsuled  by  a  lamina 


I- 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


813 


of  nerve  fibers  and  contains  numerous  medium-sized  nerve  cells,  the  connections 
I  of  which  are  as  yet  not  fully  determined. 

It  The  corpora  mammillaria  (corpus  albicantia)  are  two  round  white  masses,  each 
about  the  size  of  a  small  pea,  placed  side  by  side  below  the  gray  substance  of  the 
floor  of  the  third  ventricle  in  front  of  the  posterior  perforated  substance.  They 
consist  of  white  substance  externally  and  of  gray  substance  internally,  the  cells  of 
the  latter  forming  two  nuclei,  a  medial  of  smaller  and  a  lateral  of  larger  cells.  The 
white  substance  is  mainly  formed  by  the  fibers  of  the  columns  of  the  fornix,  which 
descend  to  the  base  of  the  brain  and  end  partly  in  the  corpora  mammillaria.  From 
the  cells  of  the  gray  substance  of  each  mammillary  body  two  fasciculi  arise :  one, 
the  thalamomammillary  fasciculus  {bundle  of  Vicq  d'Azyr),  passes  upward  into  the 
anterior  nucleus  of  the  thalamus;  the  other  is  directed  downward  into  the  tegmen- 
tum. Afferent  fibers  are  believed  to  reach  the  corpus  mammillare  from  the  medial 
jmniscus  and  from  the  tegmentum. 


Tela  chorioidea  of  third  ventricle     Posterior  commissure 


Intermediate  mass 
Inter  vent  ricviar  foramen 


Corpora  quadrigemina 
Pineal  body 

Splenium 

Pia  mater 


Genvs         / 
Rostrum 
Anterior  commissure  /   ,     / 
Lamina,  terminalis  /  / 
Optic  recess  / 


Optic  chiasma 
Infundibulum 
Corpiis  mamillare 

Oculomotor  nerve 
Cerebral  aqueduct 


Choroid  plexus 


Fourth  ventricle 
Fig.  720. — Median  sagittal  section  of  brain.     The  relations  of  the  pia  mater  are  indicated  by  the  red  color. 

The  tuber  cinereum  is  a  hollow  eminence  of  gray  substance  situated  between 
the  corpora  mammillaria  behind,  and  the  optic  chiasma  in  front.  Laterally  it  is 
continuous  with  the  anterior  perforated  substances  and  anteriorly  with  a  thin 
lamina,  the  lamina  terminalis.  From  the  under  surface  of  the  tuber  cinereum  a 
hollow  conical  process,  the  infundibulum,  projects  downward  and  forward  and  is 
attached  to  the  posterior  lobe  of  the  hypophysis. 

^IP  In  the  lateral  part  of  the  tuber  cinereum  is  a  nucleus  of  nerve  ceUs,  the  basal  optic  nucleus 
of  Me3mert,  while  close  to  the  cavity  of  the  third  ventricle  are  three  additional  nuclei.  Between 
the  tuber  cinereum  and  the  corpora  mammillaria  a  small  elevation,  with  a  corresponding  de- 
pression in  the  third  ventricle,  is  sometimes  seen.  Retzius  has  named  it  the  eminentia  saccularis, 
and  regards  it  as  a  representative  of  the  saccus  vasculosus  found  in  this  situation  in  some  of 
the  lower  vertebrates. 


NEUROLOGY 


I 


The  hypophysis  {pituitary  body)  (Fig.  721)  is  a  reddish-gray,  somewhat  o\al 
mass,  measuring  about  12.5  mm.  in  its  transverse,  and  about  8  mm.  in  its  antero- 
posterior diameter.  It  is  attached  to  the  end  of  the  infundibulum,  and  is  situated 
in  the  fossa  hypophyseos  of  the  sphenoidal  bone,  where  it  is  retained  by  a  circular 
fold  of  dura  mater,  the  diaphragma  sella;  this  fold  almost  completely  roofs  in  the 
fossa,  leaving  only  a  small  central  aperture  through  which  the  infundibulum  passes. 


Lamina 
terminalis 


Anterior     Optic 
commissure    recess 


Ant.  cerebral  artery. 


Optic  chiasma.. 


Anterior  lobe 
of  hypophysis 


^Jnfundibulum 
■Circular  sinv^ 


Cerebral  peduncle 


Corpus  mammiUare 
Post,  cerebral  artery 
Basilar  artery 

Pons 


Posterior  lobe 
Fig.  721. — The  hypophysis  cerebri,  in  position. 


Shown  in  sagittal  section. 


Optic  Chiasma  {chiasma  optioum;  optic  commissure). — The  optic  chiasma  is  a 
flattened,  somewhat  quadrilateral  band  of  fibers,  situated  at  the  junction  of  the 
floor  and  anterior  wall  of  the  third  ventricle.  Most  of  its  fibers  have  their  origins 
in  the  retina,  and  reach  the  chiasma  through  the  optic  nerves,  which  are  continuous 
with  its  antero-lateral  angles.  In  the  chiasma,  they  undergo  a  partial  decussation 
(Fig.  722) ;  the  fibers  from  the  nasal  half  of  the  retina  decussate  and  enter  the  optic 
tract  of  the  opposite  side,  while  the  fibers  from  the  temporal  half  of  the  retina  do 
not  undergo  decussation,  but  pass  back  into  the  optic  tract  of  the  same  side. 
Occupying  the  posterior  part  of  the  commissure,  however,  is  a  strand  of  fibers, 
the  commissure  of  Gudden,  which  is  not  derived  from  the  optic  nerves;  it  forms  a 
connecting  link  between  the  medial  geniculate  bodies. 

Optic  Tracts. — ^The  optic  tracts  are  continued  backward  and  lateral  ward  from 
the  posterolateral  angles  of  the  optic  chiasma.  Each  passes  between  the  anterior 
perforated  substance  and  the  tuber  cinereum,  and,  winding  around  the  ventro- 
lateral aspect  of  the  cerebral  peduncle,  divides  into  a  medial  and  a  lateral  root. 
The  former  comprises  the  fibers  of  Gudden's  commissure.  The  lateral  root  consists 
mainly  of  afferent  fibers  which  arise  in  the  retina  and  undergo  partial  decussation 
in  the  optic  chiasma,  as  described;  but  it  also  contains  a  few  fine  efferent  fibers 
which  have  their  origins  in  the  brain  and  their  terminations  in  the  retina.  When 
traced  backward,  the  afferent  fibers  of  the  lateral  root  are  found  to  end  in  the  lateral 
geniculate  body  and  pulvinar  of  the  thalamus,  and  in  the  superior  colliculus;  and 
these  three  structures  constitute  the  lower  visual  centers.  Fibers  arise  from  the 
nerve  cells  in  these  centers  and  pass  through  the  occipital  part  of  the  internal 
capsule,  under  the  name  of  the  optic  radiations,  to  the  cortex  of  the  occipital  lobe 
of  the  cerebrum,  where  the  higher  or  cortical  visual  center  is  situated.  Some  of  the 
fibers  of  the  optic  radiations  take  an  opposite  course,  arising  from  the  cells  of  the 
occipital  cortex  and  passing  to  the  lower  visual  centers.  Some  fibers  are  detached 
from  the  optic  tract,  and  pass  through  the  cerebral  peduncle  to  the  nucleus  of 
the  oculomotor  nerve.     These  may  be  regarded  as  the  afferent  branches  for  the 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


815 


Sphincter  pupillse  and    Ciliaris    muscles.     Other  fibers  have  been  described  as 
reaching  the  cerebellum  through  the  superior  peduncle;  while  others,  again,  are 

I  lost  in  the  pons. 

The  Third  Ventricle  {ventriculus  tertius)  (Figs.  716,  720).— The  third  ventricle  is 
a  median  cleft  between  the  two  thalami.  Behind,  it  communicates  with  the  fourth 
ventricle  through  the  cerebral  aqueduct,  and  in  front  with  the  lateral  ventricles 
through  the  interventricular  foramen.    Somewhat  triangular  in  shape,  with  the 

I  apex  directed  backward,  it  has  a  roof,  a  floor,  an  anterior  and  a  posterior  boundary 

||and  a  pair  of  lateral  walls. 


Optic  nerve 

-J Crossed  fibers 

~  Uncrossed  fibers 

Optic  chiasma 

—  Optic  tract 
Commissure  of  Gvdden 


Pvlvinar 

Lateral  genicidate  body 
Superior  coUicvlus 
Medial  geniculate  body 

Nucleus  of  oeidomotor  nerve 
Nucleus  of  trochlear  nerve 
Nudev^  of  abducent  nerve 


Cortex  of  occipital  lobes 
Fia.  722. — Scheme  showing  central  connections  of  the  optic  nerves  and  optic  tracts. 

The  roof  (Fig.  723)  is  formed  by  a  layer  of  epithelium,  which  stretches  between 
the  upper  edges  of  the  lateral  walls  of  the  cavity  and  is  continuous  with  the  epithe- 
hal  lining  of  the  ventricle.  It  is  covered  by  and  adherent  to  a  fold  of  pia  mater, 
named  the  tela  chorioidea  of  the  third  ventricle,  from  the  under  surface  of  which 
a  pair  of  vascular  fringed  processes,  the  choroid  plexuses  of  the  third  ventricle, 
project  downward,  one  on  either  side  of  the  middle  line,  and  invaginate  the 
epithelial  roof  into  the  ventricular  cavity. 

The  floor  slopes  downward  and  forward  and  is  formed  mainly  by  the  structures 
which  constitute  the  hypothalamus:  from  before  backward  these  are:  the  optic 


816 


NEUROLOGY 


I 


chiasma,  the  tuber  cinereum  and  infundibulum,  and  the  corpora  mammillaria. 
Behind  the  last,  the  floor  is  formed  by  the  interpeduncular  fossa  and  the  tegmen-a 
of  the  cerebral  peduncles.  The  ventricle  is  prolonged  downward  as  a  funnel- 
shaped  recess,  the  recessus  infundibuli,  into  the  infundibulum,  and  to  the  apex  of 
the  latter  the  hypophysis  is  attached. 

The  anterior  boundary  is  constituted  below  by  the  lamina  terminalis,  a  thin  layer 
of  gray  substance  stretching  from  the  upper  surface  of  the  optic  chiasma  to  the 
rostrum  of  the  corpus  callosum;  above  by  the  Columns  of  the  fornix  and  the  anterior 
commissure.  At  the  junction  of  the  floor  and  anterior  wall,  immediately  aboA^e 
the  optic  chiasma,  the  ventricle  presents  a  small  angular  recess  or  diverticulum, 
the  optic  recess.  Between  the  columns  of  the  fornix,  and  above  the  anterior 
commissure,  is  a  second  recess  termed  the  vulva.  At  the  junction  of  the  roof  and 
anterior  wall  of  the  ventricle,  and  situated  between  the  thalami  behind  and  the 
columns  of  the  fornix  in  front,  is  the  interventricular  foramen  {foramen  of  Monro) 
through  which  the  third  communicates  with  the  lateral  ventricles. 


Lateral  / 
ventricle 


EpitJielial  lining 

of  ventricle 
Terminal  vein 
Choroid  'plexus  of 
lateral  ventricle 


Tela  chorioidea/    Ssr 
Internal  cerebral  wins  ^ 
Epithelial  lining  of  ventricle 


Choroid  plexuses  of  third  veniricle 
Third  ventricle 


Fig.  723. — Coronal  section  of  lateral  and  third  ventricles.     (Diagrammatic.) 

The  posterior  boundary  is  constituted  by  the  pineal  body,  the  posterior  commissure 
and  the  cerebral  aqueduct.  A  small  recess,  the  recessus  pinealis,  projects  into  the 
stalk  of  the  pineal  body,  while  in  front  of  and  above  the  pineal  body  is  a  second 
recess,  the  recessus  suprapinealis,  consisting  of  a  diverticulum  of  the  epithelium 
which  forms  the  ventricular  roof. 

Each  lateral  wall  consists  of  an  upper  portion  formed  by  the  medial  surface  of 
the  anterior  two-thirds  of  the  thalamus,  and  a  lower  consisting  of  an  upward 
continuation  of  the  gray  substance  of  the  ventricular  floor.  These  two  parts 
correspond  to  the  alar  and  basal  laminae  respectively  of  the  lateral  wall  of  the 
fore-brain  vesicle  and  are  separated  from  each  other  by  a  furrow,  the  sulcus  of 
Monro,  which  extends  from  the  interventricular  foramen  to  the  cerebral  aqueduct 
(pages  741  and  742).  The  lateral  wall  is  limited  above  by  the  taenia  thalami.  The 
columns  of  the  fornix  curve  downward  in  front  of  the  interventricular  foramen,  and 
then  run  in  the  lateral  walls  of  the  ventricle,  where,  at  first,  they  form  distinct 
prominences,  but  subsequently  are  lost  to  sight.  The  lateral  walls  are  joined  to 
each  other  across  the  cavity  of  the  ventricle  by  a  band  of  gray  matter,  the  massa 
intermedia  (page  S09). 

Interpeduncular  Fossa  (Fig.  724). — This  is  a  somewhat  lozenge-shaped  area  of  the 
base  of  the  brain,  limited  in  front  by  the  optic  chiasma,  behind  by  the  antero- 
superior  surface  of  the  pons,  antero-laterally  by  the  converging  optic  tracts, 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


817 


I  and  postero-Iaterally  by  the  diverging  cerebral  peduncles.  The  structures  con- 
tained in  it  have  already  been  described;  from  behind  forward,  they  are  the  pos- 
terior perforated  substance,  corpora  mamillaria,  tuber  cinereum,  infundibulum, 
and  hypophysis. 


Frontal  lobe 


Temporal 
lobe 


Occipital  lobe 


Fig.   724. — Base  of  brain. 


The  Telencephalon. — The  telencephalon  includes:  (1)  the  cerebral  hemispheres 
with  their  cavities,  the  lateral  ventricles ;  and  (2)  the  pars  optica  hypothalami  and 
the  anterior  portion  of  the  third  ventricle  (already  described  under  the  dienceph- 
alon).  As  previously  stated  (see  page  744),  each  cerebral  hemisphere  may  be 
divided  into  three  fundamental  parts,  viz.,  the  rhinencephalon,  the  corpus 
striatum,  and  the  neopallium.  The  rhinencephalon,  associated  with  the  sense 
of  smell,  is  the  oldest  part  of  the  telencephalon,  and  forms  almost  the  whole  of 
the  hemisphere  in  some  of  the  lower  animals,  e.  g.,  fishes,  amphibians,  and 
reptiles.  In  man  it  is  rudimentary,  whereas  the  neopallium  undergoes  great 
development  and  forms  the  chief  part  of  the  hemisphere. 

The  Cerebral  Hemispheres. — The  cerebral  hemispheres  constitute  the  largest 
part  of  the  brain,  and,  when  viewed  together  from  above,  assume  the  form  of 
an  ovoid  mass  broader  behind  than  in  front,  the  greatest  transverse  diameter 
corresponding  with  a  line  connecting  the  two  parietal  eminences.  The  hemispheres 
are  separated  medially  by  a  deep  cleft,  named  the  longitudinal  cerebral  fissure, 
and  each  possesses  a  central  cavity,  the  lateral  ventricle. 


I 


52 


818 


NEUROLOGY 


■ 


The  Longitudinal  Cerebral  Fissure  (fissura  cerebrilongitudinalis;  great  longitudinal 
fissure)  contains  a  sickle-shaped  process  of  dura  mater,  the  falx  cerebri.  It  front 
and  behind,  the  fissure  extends  from  the  upper  to  the  under  surfaces  of  the  hemi- 
spheres and  completely  separates  them,  but  its  middle  portion  separates  them  for 
only  about  one-half  of  their  vertical  extent ;  for  at  this  part  they  are  connected  acrc>ss 
the  middle  line  by  a  great  central  white  commissure,  the  corpus  callosum. 

In  a  median  sagittal  section  (Fig.  720)  the  cut  corpus  callosum  presents  the 
appearance  of  a  broad,  arched  band.  Its  thick  posterior  end,  termed  the  splenium, 
overlaps  the  mid-brain,  but  is  separated  from  it  by  the  tela  chorioidea  of  the  third 

ventricle  and  ihc  pineal  body.  Its  anterior 
curved  end,  termed  the  genu,  gradually  tapers 
into  a  thinner  portion,  the  rostrum,  which  is 
continued  downward  and  backward  in  front  of 
the  anterior  commissure  to  join  the  lamina 
terminalis .  Arching  backward  from  immediately 
behind  the  anterior  commissure  to  the  under 
surface  of  the  splenium  is  a  second  white  band 
named  the  fornix:  between  this  and  the  corpus 
callosum  are  the  laminae  and  cavity  of  the 
septum  pellucidum. 

Surfaces  of  the  Cerebral  Hemispheres. — Each 
hemisphere  presents  three  surfaces:  lateral, 
medial,  and  inferior. 

The  lateral  surface  is  convex  in  adaptation  to 
the  concavity  of  the  corresponding  half  of  the 
vault  of  the  cranium.  The  medial  surface  is 
flat  and  vertical,  and  is  separated  from  that 
of  the  opposite  hemisphere  by  the  great  longi- 
tudinal fissure  and  the  falx  cerebri.  The  inferior 
surface  is  of  an  irregular  form,  and  may  be  divided 
into  three  areas :  anterior,  middle,  and  posterior. 
The  anterior  area,  formed  by  the  orbital  sur- 
face of  the  frontal  lobe,  is  concave,  and  rests  on 
the  roof  of  the  orbit  and  nose;  the  middle  area 
is  convex,  and  consists  of  the  under  surface  of 
the  temporal  lobe:  it  is  adapted  to  the  corre- 
sponding half  of  the  middle  cranial  fossa.  The 
posterior  area  is  concave,  directed  medialward 
as  well  as  downward,  and  is  named  the  tentorial 
surface,  since  it  rests  upon  the  tentorium  cere- 
belli,  which  intervenes  between  it  and  the  upper 
surface  of  the- cerebellum. 

These  three  surfaces  are  separated  from 
each  other  by  the  following  borders:  (a) 
supero-medial,  between  the  lateral  and  medial  surfaces;  (6)  infero-lateral,  between 
the  lateral  and  inferior  surfaces;  the  anterior  part  of  this  border  separating  the 
lateral  from  the  orbital  surface,  is  known  as  the  superciliary  border;  (c)  medial 
occipital,  separating  the  medial  and  tentorial  surfaces;  and  (d)  medial  orbital, 
separating  the  orbital  from  the  medial  surface.  The  anterior  end  of  the  hemi- 
sphere is  named  the  frontal  pole ;  the  posterior,  the  occipital  pole ;  and  the  anterior 
end  of  the  temporal  lobe,  the  temporal  pole.  About  5  cm.  in  front  of  the  occipital 
pole  on  the  infero-lateral  border  is  an  indentation  or  notch,  named  the  preoccipital 
notch. 

The  surfaces  of  the  hemispheres  are  moulded  into  a  number  of  irregular  emi- 


Fia.  725. — Lateral  surface  of  left  cerebral 
hemisphere,  viewed  from  above. 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


819 


nences,  named  gyri  or  convolutions,  and  separated  by  furrows  termed  fissures  and 
sulci.  The  furrows  are  of  two  kinds,  complete  and  incomplete.  The  former  appear 
early  in  fetal  life,  are  few  in  number,  and  are  produced  by  infoldings  of  the  entire 
thickness  of  the  brain  wall,  and  give  rise  to  corresponding  elevations  in  the  interior 
of  the  ventricle.  They  comprise  the  hippocampal  fissure,  and  parts  of  the  calcarine 
and  collateral  fissures.  The  incomplete  furrows  are  very  numerous,  and  only  indent 
the  subjacent  white  substance,  without  producing  any  corresponding  elevations  in 
the  ventricular  cavity. 

The  gyri  and  their  intervening  fissures  and  the  sulci  are  fairly,  constant  in  their 
arrangement;  at  the  same  time  they  vary  within  certain  limits,  not  only  in  different 
individuals,  but  on  the  two  hemispheres  of  the  same  brain.  The  convoluted  con- 
dition of  the  surface  permits  of  a  great  increase  of  the  gray  matter  without  the 
sacrifice  of  much  additional  space.  The  number  and  extent  of  the  gyri,  as  well 
as  the  depth  of  the  intervening  furrows,  appear  to  bear  a  direct  relation  to  the 
intellectual  powers  of  the  individual. 

Certain  of  the  fissures  and  sulci  are  utilized  for  the  purpose  of  dividing  the  hemi- 
sphere into  lobes,  and  are  therefore  termed  interlobular;  included  under  this  category 
are  the  lateral  cerebral,  parietooccipital,  calcarine,  and  collateral  fissures,  the 
central  and  cingulate  sulci,  and  the  sulcus  circularis. 


Fig.   726. — Lateral  surface  of  left  cerebral  hemisphere,  viewed  from  the  side. 


r  The  Lateral  Cerebral  Fissure  (fissura  cerebri  lateralis  [Sylvii] ;  fissure  of  Sylvius)  (Fig. 
726)  is  a  well-marked  cleft  on  the  inferior  and  lateral  surfaces  of  the  hemisphere, 
and  consists  of  a  short  stem  which  divides  into  three  rami.  The  stem  is  situated 
on  the  base  of  the  brain,  and  commences  in  a  depression  at  the  lateral  angle  of  the 
anterior  perforated  substance.  From  this  point  it  extends  between  the  anterior 
part  of  the  temporal  lobe  and  the  orbital  surface  of  the  frontal  lobe,  and  reaches 
,  the  lateral  surface  of  the  hemisphere.  Here  it  divides  into  three  rami :  an  anterior 
I  horizontal,  an  anterior  ascending,  and  a  posterior.  The  anterior  horizontal  ramus 
passes  forward  for  about  2.5  cm.  into  the  inferior  frontal  gyrus,  while  the  anterior 
ascending  ramus  extends  upward  into  the  same  convolution  for  about  an  equal 
distance.    The  posterior  ramus  is  the  longest;  it  runs  backward  and  slightly  upward 

tfor  about  7  cm.,  and  ends  by  an  upward  inflexion  in  the  parietal  lobe. 
The  Central  Sulcus  (sulcus  centralis  [Rolandi] ;  fissure  of  Rolando;  central  fissure) 


N 


820 


NEUROLOGY 


I 


(Figs.  725, 726)  is  situated  about  the  middle  of  the  lateral  surface  of  the  hemisphere:, 
and  begins  in  or  near  the  longitudinal  cerebral  fissure,  a  little  behind  its  mid-point,. 
It  runs  sinuously  downward  and  forward,  and  ends  a  little  above  the  posterior 
ramus  of  the  lateral  fissure,  and  about  2.5  cm.  behind  the  anterior  ascending  ramus 
of  the  same  fissure.  It  described  two  chief  curves:  a  superior  genu  with  its  con- 
cavity directed  forward,  and  an  inferior  genu  with  its  concavity  directed  backward . 
The  central  sulcus  forms  an  angle  opening  forward  of  about  70°  with  the  median 
plane. 

The  Parietooccipital  Fissure  {fissura  parietodccipitalis) . — Only  a  small  part  of  this 
fissure  is  seen  on  the  lateral  surface  of  the  hemisphere,  its  chief  part  being  on  the 
medial  surface. 

The  lateral  part  of  the  parietooccipital  fissure  (Fig.  726)  is  situated  about  5  cm. 
in  front  of  the  occipital  pole  of  the  hemisphere,  and  measures  about  1.25  cm.  in 
length. 


Fig.  727. — Medial  surface  of  left  cerebral  hemisphere. 

The  medial  part  of  the  parietooccipital  fissure  (Fig.  727)  runs  downward  and  for- 
ward as  a  deep  cleft  on  the  medial  surface  of  the  hemisphere,  and  joins  the  calcarine 
fissure  below  and  behind  the  posterior  end  of  the  corpus  callosum.  In  most  cases 
it  contains  a  submerged  gyrus. 

The  Calcarine  Fissure  (fissura  calcarina)  (Fig.  727)  is  on  the  medial  surface  of 
the  hemisphere.  It  begins  near  the  occipital  pole  in  two  converging  rami,  and  runs 
forward  to  a  point  a  little  below  the  splenium  of  the  corpus  callosum,  where  it  is 
joined  at  an  acute  angle  by  the  medial  part  of  the  parietooccipital  fissure.  The 
anterior  part  of  this  fissure  gives  rise  to  the  prominence  of  the  calcar  avis  in  the 
posterior  cornu  of  the  lateral  ventricle. 

The  Cingulate  Sulcus  {sulcus  cinguli;  callosomarginal  fissure)  (Fig.  727)  is  on  the 
medial  surface  of  the  hemisphere;  it  begins  below  the  anterior  end  of  the  corpus 
callosum  and  runs  upward  and  forward  nearly  parallel  to  the  rostrum  of  this  body 
and,  curving  in  front  of  the  genu,  is  continued  backward  above  the  corpus  callosum, 
and  finally  ascends  to  the  supero-medial  border  of  the  hemisphere  a  short  distance 
behind  the  upper  end  of  the  central  sulcus.  It  separates  the  superior  frontal  from 
the  cingulate  gyrus. 

The  Collateral  Fissure  (fissura  collateralis)  (Fig.  727)  is  on  the  tentorial  surface 
of  the  hemisphere  and  extends  from  near  the  occipital  pole  to  within  a  short  dis- 
tance of  the  temporal  pole.    Behind,  it  lies  below  and  lateral  to  the  calcarine  fissure. 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


821 


from  which  it  is  separated  by  the  lingual  gyms;  in  front,  it  is  situated  between  the 
hippocampal  gyrus  and  the  anterior  part  of  the  fusiform  gyrus. 

The  Sulcus  Circularis  {circuminsular  fissure)  (Fig.  731)  is  on  the  lower  and  lateral 
surfaces  of  the  hemisphere:  it  surrounds  the  insula  and  separates  it  from  the 
frontal,  parietal,  and  temporal  lobes. 

Lobes  of  the  Hemispheres. — By  means  of  these  fissures  and  sulci,  assisted  by 
certain  arbitrary  lines,  each  hemisphere  is  divided  into  the  following  lobes:  the 
frontal,  the  parietal,  the  temporal,  the  occipital,  the  limbic,  and  the  insula. 

Frontal  Lobe  {lohus  frontalis) . — On  the  lateral  surface  of  the  hemisphere  this  lobe 
extends  from  the  frontal  pole  to  the  central  sulcus,  the  latter  separating  it  from 
the  parietal  lobe.  Below,  it  is  limited  by  the  posterior  ramus  of  the  lateral 
fissure,  which  intervenes  between  it  and  the  central  lobe.  On  the  medial  sur- 
face, it  is  separated  from  the  cingulate  gyrus  by  the  cingulate  sulcus;  and  on  the 
inferior  surface,  it  is  bounded  behind  by  the  stem  of  the  lateral  fissure. 


w 


OCCIPITAL  F. 


I 


Fig.  728. — Principal  fissures  and  lobes  of  the  cerebrum  viewed  laterally. 

The  lateral  surface  of  the  frontal  lobe  (Fig.  726)  is  traversed  by  three  sulci  which 
divide  it  into  four  gyri:  the  sulci  are  named  the  precentral,  and  the  superior  and 
inferior  frontal;  the  gyri  are  the  anterior  central,  and  the  superior,  middle,  and 
inferior  frontal.  The  precentral  sulcus  runs  parallel  to  the  central  sulcus,  and  is 
usually  divided  into  an  upper  and  a  lower  part;  between  it  and  the  central  sulcus  is 
the  anterior  central  gyrus.  From  the  precentral  sulcus,  the  superior  and  inferior 
frontal  sulci  run  forward  and  downward,  and  divide  the  remainder  of  the  lateral 
surface  of  the  lobe  into  three  parallel  gyri,  named,  respectively  the  superior,  middle, 
and  inferior  frontal  gyri. 

The  anterior  central  gyrus  {gyrus  centralis  anterior;  ascending  frontal  convolution; 
precentral  gyre)  is  bounded  in  front  by  the  precentral  sulcus,  behind  by  the  central 
sulcus;  it  extends  from  the  supero-medial  border  of  the  hemisphere  to  the  posterior 
ramus  of  the  lateral  fissure. 

The  superior  frontal  g3rrus  (gyrus  frontalis  superior;  superfrontal  gyre)  is  situated 
above  the  superior  frontal  sulcus  and  is  continued  on  to  the  medial  surface  of  the 
hemisphere.  The  portion  on  the  lateral  surface  of  the  hemisphere  is  usually  more 
or  less  completely  subdivided  into  an  upper  and   a  lower  part  by  an  antero- 


822 


NEUROLOGY 


I 


posterior  sulcus,  the  paramedial  sulcus,  which,  however,  is  frequently  interrupteti 
by  bridging  gyri. 

The  middle  frontal  gyrus  {gyrus  frontalis  medius;  medifrontal  gyre),  between  the 
superior  and  inferior  frontal  sulci,  is  continuous  with  the  anterior  orbital  gyrus  on 
the  inferior  surface  of  the  hemisphere;  it  is  frequently  subdivided  into  two  by  a 
horizontal  sulcus,  the  medial  frontal  sulcus  of  Eberstaller,  which  ends  anteriorly  in 
a  wide  bifurcation. 

The  inferior  frontal  gyrus  {gyrus  frontalis  inferior;  suhfrontal  gyre)  lies  below  the 
inferior  frontal  sulcus,  and  extends  forward  from  the  lower  part  of  the  precentral 
sulcus;  it  is  continuous  with  the  lateral  and  posterior  orbital  gyri  on  the  under 
surface  of  the  lobe.  It  is  subdivided  by  the  anterior  horizontal  and  ascending  rami 
of  the  lateral  fissure  into  three  parts,  viz.,  (1)  the  orbital  part,  below  the  anterior 
horizontal  ramus  of  the  fissure;  (2)  the  triangular  part  {cap  of  Broca),  between 
the  ascending  and  horizontal  rami;  and  (3)  the  basilar  part,  behind  the  anterior 
ascending  ramus.  The  left  inferior  frontal  gyrus  is,  as  a  rule,  more  highly 
developed  than  the  right,  and  is  named  the  gjmis  of  Broca,  from  the  fact  that 
Broca  described  it  as  the  center  for  articulate  speech. 

The  inferior  or  orbital  surface  of  the  frontal  lobe  is  concave,  and  rests  on  the  orbital 
plate  of  the  frontal  bone  (Fig.  729).  It  is  divided  into  four  orbital  gyri  by  a  well- 
marked  H-shaped  orbital  sulcus.  These  are 
named,  from  their  position,  the  medial,  anterior, 
lateral,  and  posterior  orbital  gyri.  The  medial 
orbital  gyrus  presents  a  well-marked  antero- 
posterior sulcus,  the  olfactory  sulcus,  for  the 
olfactory  tract;  the  portion  medial  to  this  is 
named  the  straight  gyrus,  and  is  continuous  with 
the  superior  frontal  gyrus  on  the  medial  surface. 
The  medial  surface  of  the  frontal  lobe  is  occu- 
pied by  the  medial  part  of  the  superior  frontal 
gyrus  {marginal  gyrus)  (Fig.  727).  It  lies  be- 
tween the  cingulate  sulcus  and  the  supero-medial 
margin  of  the  hemisphere.  The  posterior  part 
of  this  gyrus  is  sometimes  marked  off  by  a  ver- 
tical sulcus,  and  is  distinguished  as  the  paracen- 
tral lobule,  because  it  is  continuous  with  the 
anterior  and  posterior  central  gyri. 

Parietal  Lobe  {lobus  jparietalis) . — The  parietal 
lobe  is  separated  from  the  frontal  lobe  by  the 
central  sulcus,  but  its  boundaries  below  and 
behind  are  not  so  definite.  Posteriorly,  it  is  limited  by  the  parietooccipital  fissure, 
and  by  a  line  carried  across  the  hemisphere  from  the  end  of  this  fissure  toward 
the  preoccipital  notch.  Below,  it  is  separated  from  the  temporal  lobe  by  the 
posterior  ramus  of  the  lateral  fissure,  and  by  a  line  carried  backward  from  it  to 
meet  the  line  passing  downward  to  the  preoccipital  notch. 

The  lateral  surface  of  the  parietal  lobe  (Fig.  726)  is  cleft  by  a  well-marked  furrow, 
the  intraparietal  sulcus  of  Turner,  which  consists  of  an  oblique  and  a  horizontal 
portion.  The  oblique  part  is  named  the  postcentral  sulcus,  and  commences  below, 
about  midw^ay  between  the  low^er  end  of  the  central  sulcus  and  the  upturned  end 
of  the  lateral  fissure.  It  runs  upward  and  backward,  parallel  to  the  central  sulcus, 
and  is  sometimes  divided  into  an  upper  and  a  lower  ramus.  It  forms  the  hinder 
limit  of  the  posterior  central  gyrus. 

From  about  the  middle  of  the  postcentral  sulcus,  or  from  the  upper  end  of  its 
inferior  ramus,  the  horizontal  portion  of  the  intraparietal  sulcus  is  carried  backward 
and  slightly  upward  on  the  parietal  lobe,  and  is  prolonged,  under  the  name  of  the 


Fio.  729. — Orbital  surface  of  left  frontal  lobe. 


THE  FORE-BRAIN  OR  PROSENCEPHALON  823 


Ibccipital  ramus,  on  to  the  occipital  lobe,  where  it  divides  into  two  parts,  which  form 
nearly  a  right  angle  with  the  main  stem  and  constitute  the  transverse  occipital  sulcus. 
[The  part  of  the  parietal  lobe  above  the  horizontal  portion  of  the  intraparietal 
sulcus  is  named  the  superior  parietal  lobule ;  the  part  below,  the  inferior  parietal  lobule. 

The  posterior  central  gyrus  {gyrus  centralis  posterior;  ascending  parietal  convolution; 
postcentral  gyre)  extends  from  the  longitudinal  fissure  above  to  the  posterior  ramus 
^^of  the  lateral  fissure  below.  It  lies  parallel  with  the  anterior  central  gyrus,  with 
^Biehich  it  is  connected  below,  and  also,  sometimes,  above,  the  central  sulcus. 

The  superior  parietal  lobule  (lobulus  parietalis  superior)  is  bounded  in  front  by 
the  upper  part  of  the  postcentral  sulcus,  but  is  usually  connected  with  the  pos- 
terior central  gyrus  above  the  end  of  the  sulcus;  behind  it  is  the  lateral  part  of 
■the  parietooccipital  fissure,  around  the  end  of  which  it  is  joined  to  the  occipital 
lobe  by  a  curved  gyrus,  the  arcus  parietooccipitalis ;  below,  it  is  separated  from  the 
inferior  parietal  lobule  by  the  horizontal  portion  of  the  intraparietal  sulcus. 

The  inferior  parietal  lobule  {lobulus  parietalis  inferior;  suhparietal  district  or  lobule) 
lies  below  the  horizontal  portion  of  the  intraparietal  sulcus,  and  behind  the  lower 
part  of  the  postcentral  sulcus.  It  is  divided  from  before  backward  into  two  gyri. 
One,  the  supramarginal,  arches  over  the  upturned  end  of  the  lateral  fissure;  it  is 
continuous  in  front  with  the  postcentral  gyrus,  and  behind  wdth  the  superior  tem- 
poral gyrus.  The  second,  the  angular,  arches  over  the  posterior  end  of  the  superior 
temporal  sulcus,  behind  which  it  is  continuous  with  the  middle  temporal  gyrus. 

The  medial  surface  of  the  parietal  lobe  (Fig.  727)  is  bounded  behind  by  the 
medial  part  of  the  parietooccipital  fissure;  in  front,  by  the  posterior  end  of  the  cin- 
gulate  sulcus;  and  below,  it  is  separated  from  the  cingulate  gyrus  by  the  subparietal 
sulcus.  It  is  of  small  size,  and  consists  of  a  square-shaped  convolution,  which  is 
termed  the  precuneus  or  quadrate  lobe. 

Occipital  Lobe  {lobus  occipitalis). — The  occipital  lobe  is  small  and  pyramidal 
in  shape;  it  presents  three  surfaces:  lateral,  medial,  and  tentorial. 

The  lateral  surface  is  limited  in  front  by  the  lateral  part  of  the  parietooccipital 
fissure,  and  by  a  line  carried  from  the  end  of  this  fissure  to  the  preoccipital  notch; 
it  is  traversed  by  the  transverse  occipital  and  the  lateral  occipital  sulci.  The 
transverse  occipital  sulcus  is  continuous  with  the  posterior  end  of  the  occipital 
ramus  of  the  intraparietal  sulcus,  and  runs  across  the  upper  part  of  the  lobe,  a 
short  distance  behind  the  parietooccipital  fissure.  The  lateral  occipital  sulcus 
extends  from  behind  forward,  and  divides  the  lateral  surface  of  the  occipital  lobe 
into  a  superior  and  an  inferior  gsnns,  which  are  continuous  in  front  with  the  parietal 
and  temporal  lobes. ^ 

The  medial  surface  of  the  occipital  lobe  is  bounded  in  front  by  the  medial  part 
of  the  parietooccipital  fissure,  and  is  traversed  by  the  calcarine  fissure,  which 
subdivides  it  into  the  cuneus  and  the  lingual  gyrus.  The  cuneus  is  a  wedge-shaped 
area  between  the  calcarine  fissure  and  the  medial  part  of  the  parietooccipital 
fissure.  The  lingual  gyrus  lies  between  the  calcarine  fissure  and  the  posterior  part 
of  the  collateral  fissure;  behind,  it  reaches  the  occipital  pole;  in  front,  it  is  con- 
tinued on  to  the  tentorial  surface  of  the  temporal  lobe,  and  joins  the  hippocampal 
gyrus. 

The  tentorial  surface  of  the  occipital  lobe  is  limited  in  front  by  an  imaginary 
transverse  line  through  the  preoccipital  notch,  and  consists  of  the  posterior  part 
of  the  fusiform  gyvi&  {occipitotemporal  convolution)  and  the  lower  part  of  the  lingual 
gyrus,  which  are  separated  from  each  other  by  the  posterior  segment  of  the 
collateral  fissure. 

Temporal  Lobe  {lobus  temporalis). — ^The  temporal  lobe  presents  superior,  lateral, 
and  inferior  surfaces. 


I 


'  Elliot  Siaith  has  named  the  lateral  occipital  sulcus  the  sulcus  lunatus;  he  regards  it  as  the  representative,  in  the 
human  brain,  of  the  "Affenapalte"  of  the  brain  of  the  ape. 


824 


NEUROLOGY 


I 


The  superior  surface  forms  the  lower  Hmit  of  the  lateral  fissure  and  overlaps 
the  insula.  On  opening  out  the  lateral  fissure,  three  or  four  gyri  will  be  seen  spring- 
ing from  the  depth  of  the  hinder  end  of  the  fissure,  and  running  obliquely  forward 
and  outward  on  the  posterior  part  of  the  upper  surface  of  the  superior  temporal 
gyrus;  these  are  named  the  transverse  temporal  gyri  (Heschl)  (Fig.  730). 

The  lateral  surface  (Fig.  726)  is  bounded  above  by  the  posterior  ramus  of. the 
lateral  fissure,  and  by  the  imaginary  line  continued  backward  from  it;  below, 
it  is  limited  by  the  infero-lateral  border  of  the  hemisphere.  It  is  divided  into 
superior,  middle,  and  inferior  gyri  by  the  superior  and  middle  temporal  suhn. 
The  superior  temporal  sulcus  runs  from  before  backward  across  the  temporal  lobe, 
some  little  distance  below,  but  parallel  with,  the  posterior  ramus  of  the  lateral 
fissure;  and  hence  it  is  often  termed  the  parallel  sulcus.  The  middle  temporal  sulcus 
takes  the  same  direction  as  the  superior,  but  is  situated  at  a  lower  level,  and  is 
usually  subdivided  into  two  or  more  parts.    The  superior  temporal  gyrus  lies  between 


Clauslrum  • — ^ 
Insvia 

Transverse  temporal  gyri'^l 


Optic  tract 

Lentiforin,  nuclezis 
Internal  capsule 

Thalamus 

Firnbria 

Tail  of  caudate  nucleus 

Inferior  cornu  of  lateral 

ventricle 


Fia.  730. — Section  of  brain  showing  upper  surface  of  temporal  lobe. 

the  posterior  ramus  of  the  lateral  fissure  and  the  superior  temporal  sulcus,  and  is 
continuous  behind  with  the  supramarginal  and  angular  gyri.  The  middle  temporal 
gyrus  is  placed  between  the  superior  and  middle  temporal  sulci,  and  is  joined  pos- 
teriorly with  the  angular  gyrus.  The  inferior  temporal  gyrus  is  placed  below  the 
middle  temporal  sulcus,  and  is  connected  behind  with  the  inferior  occipital  gyrus; 
it  also  extends  around  the  infero-lateral  border  on  to  the  inferior  surface  of  the 
temporal  lobe,  where  it  is  limited  by  the  inferior  sulcus. 

The  inferior  surface  is  concave,  and  is  continuous  posteriorly  with  the  tentorial 
surface  of  the  occipital  lobe.  It  is  traversed  by  the  inferior  temporal  sulcus,  which 
extends  from  near  the  occipital  pole  behind,  to  within  a  short  distance  of  the  tem- 
poral pole  in  front,  but  is  frequently  subdivided  by  bridging  gyri.  Lateral  to  this 
fissure  is  the  narrow  tentorial  part  of  the  inferior  temporal  gyrus,  and  medial  to 
it  the  fusiform  gyrus,  which  extends  from  the  occipital  to  the  temporal  pole;  this 
gyrus  is  limited  mediallj^  by  the  collateral  fissure,  which  separates  it  from  the 
lingual  gyrus  behind  and  from  the  hippocampal  gyrus  in  front. 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


825 


^Mi     The  Insula  {island  of  Red;  central  lobe)   (Fig.  731)  lies  deeply  in  the  lateral  or 
^"  Sylvian  fissure,  and  can  only  be  seen  when  the  lips  of  that  fissure  are  widely  sep- 
arated, since  it  is  overlapped  and  hidden  by  the  gyri  which  bound  the  fissure. 
These  gyri  are  termed  the  opercula  of  the  insula ;  they  are  separated  from  each  other 
by  the  three  rami  of  the  lateral  fissure,  and  are  named  the  orbital,  frontal,  fronto- 
parietal, and  temporal  opercula.     The  orbital  operculum  lies  below  the  anterior 
horizontal  ramus  of  the  fissure,  the  frontal  between  this  and  the  anterior  ascending 
ramus,  the  parietal  between  the  anterior  ascending  ramus  and  the  upturned  end 
of  the  posterior  ramus,  and  the  temporal  below  the  posterior  ramus.    The  frontal 
^^,  operculum  is  of  small  size  in  those  cases  where  the  anterior  horizontal  and  ascending 
^■bami  of  the  lateral  fissure  arise  from  a  common  stem.    The  insula  is  surrounded 
^^  by  a  deep  circular  sulcus  which  separates  it  from  the  frontal,  parietal,  and  temporal 
lobes.    When  the  opercula  have  been  removed,  the  insula  is  seen  as  a  triangular 
eminence,  the  apex  of  which  is  directed  toward  the  anterior  perforated  substance. 

Ijit  is  divided  into  a  larger  anterior  and  a  smaller  posterior  part  by  a  deep  sulcus, 
■which  runs  backward  and  upward  from  the  apex  of  the  insula.  The  anterior 
■part  is  subdivided  by  shallow  sulci  into  three  or  four  short  gyri,  while  the  posterior 
f  part  is  formed  by  one  long  gjmis,  which  is  often  bifurcated  at  its  upper  end.  The 
cortical  gray  substance  of  the  insula  is  continuous  with  that  of  the  dift'erent  opercula, 
.while  its  deep  surface  corresponds  with  the  lentiform  nucleus  of  the  corpus  striatum. 


N 


Fia.  731. — The  insula  of  the  left  side,  exposed  by  removing  the  opercula. 


Limbic  Lobe  (Fig.  727). — ^The  term  limbic  lobe  was  introduced  by  Broca,  and 
under  it  he  included  the  cingulate  and  hippocampal  gyri,  which  together  arch 
around  the  corpus  callosum  and  the  hippocampal  fissure.  These  he  separated  on 
the  morphological  ground  that  they  are  well-developed  in  animals  possessing  a 
keen  sense  of  smell  (osmatic  animals),  such  as  the  dog  and  fox.  They  were  thus 
regarded  as  a  part  of  the  rhinencephalon,  but  it  is  now  recognized  that  they  belong 
to  the  neopallium;  the  cingulate  gyrus  is  therefore  sometimes  described  as  a  part 
of  the  frontal  lobe,  and  the  hippocampal  as  a  part  of  the  temporal  lobe. 

The  cingulate  gyrus  (gyrus  cinguli;  callosal  convolution)  is  an  arch-shaped  convo- 
lution, lying  in  close  relation  to  the  superficial  surface  of  the  corpus  callosum, 
from  which  it  is  separated  by  a  slit-like  fissure,  the  callosal  fissure.  It  commences 
below  the  rostrum  of  the  corpus  callosum,  curves  around  in  front  of  the  genu, 
extends  along  the  upper  surface  of  the  body,  and  finally  turns  downward  behind 
the  splenium,  where  it  is  connected  by  a  narrow  isthmus  with  the  hippocampal 


NEUROLOGY 


I 


gyrus.  It  is  separated  from  the  medial  part  of  the  superior  frontal  gyrus  by  tbe 
cingulate  sulcus,  and  from  the  precuneus  by  the  subparietal  sulcus. 

The  hippocampal  gyrus  {gyrus  hippocampi)  is  bounded  above  by  the  hippocampul 
fissure,  and  below  by  the  anterior  part  of  the  collateral  fissure.  Behind,  it  is  con- 
tinuous superiorly,  through  the  isthmus,  with  the  cingulate  gyrus  and  inferiorly 
with  the  lingual  gyrus.  Running  in  the  substance  of  the  cingulate  and  hippocampal 
gyri,  and  connecting  them  together,  is  a  tract  of  arched  fibers,  named  the  cinguluin 
(page  843) .  The  anterior  extremity  of  the  hippocampal  g^Tus  is  recurved  in  th  e 
form  of  a  hook  (uncus) ,  which  is  separated  from  the  apex  of  the  temporal  lobe  by 
a  slight  fissure,  the  incisura  temporalis.  Although  superficially  continuous  with  the 
hippocampal  gyrus,  the  uncus  forms  morphologically  a  part  of  the  rhinencephalon. 

The  Hippocampal  Fissure  {fissura  hippocampi;  dentate  fissure)  begins  immediately 
behind  the  splenium  of  the  corpus  callosum,  and  runs  forward  between  the  hippo- 
campal and  dentate  gyri  to  end  in  the  uncus.  It  is  a  complete  fissure  (page  819), 
and  gives  rise  to  the  prominence  of  the  hippocampus  in  the  inferior  cornu  of  the 
lateral  ventricle. 

Gyrus  supracallcsuf! 


Fascia  denlata 
hippocampi 


Uncus 
Anterior  perforated  substance    J  Band  of  Giacomini 

Fig.  732. — Scheme  of  rhinencephalon. 

Rhinencephalon  (Fig.  732). — The  rhinencephalon  comprises  the  olfactory  lobe, 
the  uncus,  the  subcallosal  and  supracallosal  gyri,  the  fascia  dentata  hippocampi, 
the  septum  pellucidum,  the  fornix,  and  the  hippocampus. 

1 .  The  Olfactory  Lobe  (lobus  olfactoritis)  is  situated  under  the  inferior  or  orbital 
surface  of  the  frontal  lobe.  In  many  vertebrates  it  constitutes  a  well-marked 
portion  of  the  hemisphere  and  contains  an  extension  of  the  lateral  ventricle;  but 
in  man  and  some  other  mammals  it  is  rudimentary.  It  consists  of  the  olfactory 
bulb  and  tract,  the  olfactory  trigone,  the  parolfactory  area  of  Broca,  and  the  anterior 
perforated  substance. 

(a)  The  olfactory  bulb  (bulbus  olfactoritis)  is  an  oval,  reddish-gray  mass  which 
rests  on  the  cribriform  plate  of  the  ethmoid  and  forms  the  anterior  expanded 
extremity  of  the  olfactory  tract.  Its  under  surface  receives  the  olfactory  nerves, 
which  pass  upward  through  the  cribriform  plate  from  the  olfactory  region  of  the 
nasal  cavity.    Its  minute  structure  is  described  on  page  848. 

(b)  The  olfactory  tract  (iractus  olfactorius)  is  a  narrow  white  band,  triangular 
on  coronal  section,  the  apex  being  directed  upward.  It  lies  in  the  olfactory  sulcus 
on  the  inferior  surface  of  the  frontal  lobe,  and  divides  posteriorly  into  two  strise, 
a  medial  and  a  lateral.    The  lateral  stria  is  directed  across  the  lateral  part  of  the 


I 


THE  FORE-BRAIN  ORPROSENCEPHALON 


kan 
qu 


anterior  perforated  substance  and  then  bends  abruptly  medialward  toward  the 
uncus  of  the  hippocampal  gyrus.  The  medial  stria  turns  medialward  behind 
the  parolfactory  area  and  ends  in  the  subcallosal  gyrus;  in  some  cases  a  small 
intermediate  stria  is  seen  running  backward  to  the  anterior  perforated  substance. 

(c)  The  olfactory  trigone  {trigonum  olfactorium)  is  a  small  triangular  area  in  front 
of  the  anterior  perforated  substance.  Its  apex,  directed  forward,  occupies  the 
posterior  part  of  the  olfactory  sulcus,  and  is  brought  into  view  by  throwing  back 
the  olfactory  tract. 

(d)  The  parolfactory  area  of  Broca  (area  parolfactoria)  is  a  small  triangular  field 
on  the  medial  surface  of  the  hemisphere  in  front  of  the  subcallosal  gyrus,  from  which 
it  is  separated  by  the  posterior  parolfactory  sulcus;  it  is  continuous  below^  with 
the  olfactory  trigone,  and  above  and  in  front  w^ith  the  cingulate  gyrus;  it  is  limited 
anteriorly  by  the  anterior  parolfactory  sulcus. 

i  (e)  The  anterior  perforated  substance  (substantia  perforata  anterior)  is  an  irregularly 
adrilateral  area  in  front  of  the  optic  tract  and  behind  the  olfactory  trigone, 
from  which  it  is  separated  by  the  fissure  prima ;  medially  and  in  front  it  is  continuous 
with  the  subcallosal  gyrus;  laterally  it  is  bounded  by  the  lateral  stria  of  the  olfactory 
tract  and  is  continued  into  the  uncus.  Its  gray  substance  is  confluent  above 
with  that  of  the  corpus  striatum,  and  is  perforated  anteriorly  by  numerous  small 
bloodvessels. 

2.  The  Uncus  has  already  been  described  (page  826)  as  the  recurved,  hook-like 
portion  of  the  hippocampal  gyrus. 

3.  The  Subcallosal,  Supracallosal,  and  Dentate  Gyri  form  a  rudimentary  arch- 
shaped  lamina  of  gray  substance  extending  over  the  corpus  callosum  and  above 
the  hippocampal  gyrus  from  the  anterior  perforated  substance  to  the  uncus. 

(a)  The  subcallosal  gyms  (gyrus  suhcallosus;  peduncle  of  the  corpus  callosum)  is 
a  narrow  lamina  on  the  medial  surface  of  the  hemisphere  in  front  of  the  lamina 
terminalis,  behind  the  parolfactory  area,  and  below  the  rostrum  of  the  <;orpus 
3allosum.  It  is  continuous  around  the  genu  of  the  corpus  callosum  with  the  supra- 
callosal gyrus. 

(h)  The  supracallosal  gyms  (indusium  griseum;  gyrus  epicallosus)  consists  of  a 
thin  layer  of  gray  substance  in  contact  with  the  upper  surface  of  the  corpus 
callosum  and  continuous  laterally  with  the  gray  substance  of  the  cingulate  gyrus. 
It  contains  two  longitudinally  directed  strands  of  fibers  termed  respectively  the 
medial  and  lateral  longitudinal  striae.  The  supracallosal  gyrus  is  prolonged  around 
the  splenium  of  the  corpus  callosum  as  a  delicate  lamina,  the  fasciola  cinerea, 
which  is  continuous  below  with  the  fascia  dentata  hippocampi. 

(c)  The  fascia  dentata  hippocampi  (gyrus  dentatus)  is  a  narrow  band  extending 
downward  and  forward  above  the  hippocampal  gyrus  but  separated  from  it  by 
the  hippocampal  fissure;  its  free  margin  is  notched  and  overlapped  by  the  fimbria 
— the  fimbriodentate  fissure  intervening.  Anteriorly  it  is  continued  into  the  notch 
of  the  uncus,  where  it  forms  a  sharp  bend  and  is  then  prolonged  as  a  delicate  band, 
the  band  of  Giacomini,  over  the  uncus,  on  the  lateral  surface  of  which  it  is  lost. 

The  remaining  parts  of  the  rhinencephalon,  viz.,  the  septum  pellucidum,  fornix, 
and  hippocampus,  will  be  described  in  connection  with  the  lateral  ventricle. 

Interior  of  the  Cerebral  Hemispheres. — If  the  upper  part  of  either  hemisphere  be 
removed,  at  a  level  about  1.25  cm.  above  the  corpus  callosum,  the  central  white  sub- 
stance will  be  exposed  as  an  oval-shaped  area,  the  centrum  ovale  minus,  surrounded 
by  a  narrow  convoluted  margin  of  gray  substance,  and  studded  with  numerous 
minute  red  dots  (puncta  vasculosa) ,  produced  by  the  escape  of  blood  from  divided 
bloodvessels.  If  the  remaining  portions  of  the  hemispheres  be  slightly  drawn  apart  • 
a  broad  band  of  white  substance,  the  corpus  callosum,  will  be  observed,  connecting 
them  at  the  bottom  of  the  longitudinal  fissure;  the  margins  of  the  hemispheres 
which  overlap  the  corpus  callosum  are  called  the  labia  cerebri.    Each  labrium  is 


I 


828 


NEUROLOGY 


I 


part  of  the  cingulate  gyrus  already  described;  and  the  slit-like  interval  between 
it  and  the  upper  surface  of  the  corpus  callosum  is  termed  the  callosal  fissure  (Fig. 
727) .  If  the  hemispheres  be  sliced  off  to  a  level  with  the  upper  surface  of  the  corpus 
callosum,  the  white  substance  of  that  structure  w  ill  be  seen  connecting  the  two 
hemispheres.  The  large  expanse  of  medullary  matter  now  exposed,  surrounded  by 
the  convoluted  margin  of  gray  substance,  is  called  the  centnun  ovale  majus. 

The  Corpus  Callosum  (Fig.  733)  is  the  great  transverse  commissure  which  unites 
the  cerebral  hemispheres  and  roofs  in  the  lateral  ventricles.  A  good  conception 
of  its  position  and  size  is  obtained  by  examining  a  median  sagittal  section  of  the 
brain  (Fig.  720),  when  it  is  seen  to  form  an  arched  structure  about  10  cm.  long. 
Its  anterior  end  is  about  4  cm.  from  the  frontal  pole,  and  its  posterior  end  about 
6  cm.  from  the  occipital  pole  of  the  hemisphere. 


Fig.  733. — Corpus  callosum  from  above. 

The  anterior  end  is  named  the  genu,  and  is  bent  downward  and  backward  in  frontj 
of  the  septum  pellucidum;  diminishing  rapidly  in  thickness,  it  is  prolonged  backward! 
under  the  name  of  the  rostrum,  which  is  connected  below  with  the  lamina  terminalis. 
The  anterior  cerebral  arteries  are  in  contact  with  the  under  surface  of  the  rostrum; 
they  then  arch  over  the  front  of  the  genu,  and  are  carried  backward  above  the  body 
of  the  corpus  callosum. 

The  posterior  end  is  termed  the  splenium  and  constitutes  the  thickest  part  of  the 
corpus  callosum.  It  overlaps  the  tela  chorioidea  of  the  third  ventricle  and  the 
mid-brain,   and   ends   in   a   thick,   convex,   free   border.    A   sagittal  section  of 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


829 


U 


the  splenium  shows  that  the  posterior  end  of  the  corpus  callosum  is  acutely  bent 
forward,  the  upper  and  lower  parts  being  applied  to  each  other. 

The  superior  surface  is  convex  from  before  backward,  and  is  about  2.5  cm.  wide. 
Its  medial  part  forms  the  bottom  of  the  longitudinal  fissure,  and  is  in  contact 
posteriorly  with  the  lower  border  of  the  falx  cerebri.  Laterally  it  is  overlapped  by 
ihe  cingulate  gyrus,  but  is  separated  from  it  by  the  slit-like  callosal  fissure.  It  is 
traversed  by  numerous  transverse  ridges  and  furrows,  and  is  covered  by  a  thin 
\siyeT  of  gray  matter,  the  supracallosal  gjmis,  which  exhibits  on  either  side  of  the 
middle  line  the  medial  and  lateral  longitudinal  striae,  already  described  (page  827). 

The  inferior  surface  is  concave,  and  forms  on  either  side  of  the  middle  line  the 
roof  of  the  lateral  ventricle.  Medially,  this  surface  is  attached  in  front  to  the 
septum  pellucidum;  behind  this  it  is  fused  with  the  upper  surface  of  the  body 
of  the  fornix,  while  the  splenium  is  in  contact  with  the  tela  chorioidea. 
i  On  either  side,  the  fibers  of  the  corpus  callosum  radiate  in  the  white  substance 
and  pass  to  the  various  parts  of  the  cerebral  cortex;  those  curving  forward  from  the 
genu  into  the  frontal  lobe  constitute  the  forceps  anterior,  and  those  curving  backward 
into  the  occipital  lobe,  the  forceps  posterior.  Between  these  two  parts  is  the  main 
body  of  the  fibers  which  constitute  the  tapetiim  and  extend  laterally  on  either  side 
into  the  temporal  lobe,  and  cover  in  the  central  part  of  the  lateral  ventricle. 


Fourth  ventricle 
Fig.   734. — Scheme  showing  relations  of  the  ventricles  to  the  surface  of  the  brain. 

The  Lateral  Ventricles  (ventriculus  lateralis)  (Fig.  734) . — The  two  lateral  ventricles 
are  irregular  cavities  situated  in  the  lower  and  medial  parts  of  the  cerebral  hemi- 
spheres, one  on  either  side  of  the  middle  line.  They  are  separated  from  each  other 
by  a  median  vertical  partition,  the  septum  pellucidum,  but  communicate  with  the 
third  ventricle  and  indirectly  with  each  other  through  the  interventricular  foramen. 
They  are  lined  by  a  thin,  diaphanous  membrane,  the  ependyma,  covered  by  ciliated 
epithelium,  and  contain  cerebrospinal  fluid,  which,  even  in  health,  may  be  secreted 
in  considerable  amount.  Each  lateral  ventricle  consists  of  a  central  part  or  body, 
and  three  prolongations  from  it,  termed  comua  (Figs.  735,  736). 

The  central  part  (pars  centralis  ventriculi  lateralis;  cella)  (Fig.  737)  of  the  lateral 
ventricle  extends  from  the  interventricular  foramen  to  the  splenium  of  the  corpus 


830 


NEUROLOGY 


h 


callosum.  It  is  an  irregularly  curved  cavity,  triangular  on  transverse  section, 
with  a  roof,  a  floor,  and  a  medial  wall.  The  roof  is  formed  b}'  the  under  surface  of 
the  corpus  callosum;  the  floor  by  the  following  parts,  enumerated  in  their  order  of 
position,  from  before  backward:  the  caudate  nucleus  of  the  corpus  striatum,  the 


Third  ventricle 


Suprapineal  recess 


Fig.  735. — Drawing  of  a  cast  of  the  ventricular  cavities,  viewed  from  above.      (Retzius.J 

stria  terminalis  and  the  terminal  vein,  the  lateral  portion  of  the  upper  surface  of 
the  thalamus,  the  choroid  plexus,  and  the  lateral  part  of  the  fornix;  the  medial 
wall  is  the  posterior  part  of  the  septum  pellucidum,  which  separates  it  from  the 
opposite  ventricle. 

Interventricular  foramen 


Ant.  commissure 


Suprapineal  recess 
Cerebral  aqueduct 


Optic  recess 
Infundibulum 


Lateral  recess 
Fia    736. — Drawing  of  a  cast  of  the  ventricular  cavities,  viewed  from  the  .side.      (Retzius.) 

The  anterior  comu  {cornu  anierius;  anterior  horn;  yrecornu)  (Fig.  736)  passes 
forward  and  lateralward,  with  a  slight  inclination  downward,  from  the  interventric- 
ular foramen  into  the  frontal  lobe,  curving  around  the  anterior  end  of  the  caudate 
nucleus.    Its  floor  is  formed  by  the  upper  surface  of  the  reflected  portion  of  the 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


831 


corpus  callosum,  the  rostrum.  It  is  bounded  medially  by  the  anterior  portion 
of  the  septum  pellucidum,  and  laterally  by  the  head  of  the  caudate  nucleus.  Its 
apex  reaches  the  posterior  surface  of  the  genu  of  the  corpus  callosum. 

The  posterior  comu  (cornu  posterivs;  postcormi)  (Figs,  737,  738)  passes  into  the 
occipital  lobe,  its  direction  being  backward  and  lateralward,  and  then  mediahvard. 
Its  roof  is  formed  by  the  fibers  of  the  corpus  callosum  passing  to  the  temporal  and 
occipital  lobes.  On  its  medial  wall  is  a  longitudinal  eminence,  the  calcar  avis 
(hippocampus  mmor),  which  is  an  involution  of  the  ventricular  wall  produced  by 
the  calcarine  fissure.  Above  this  the  forceps  posterior  of  the  corpus  callosum, 
sweeping  around  to  enter  the  occipital  lobe,  causes  another  projection,  termed  the 
bulb  of  the  posterior  comu.  The  calcar  avis  and  bulb  of  the  posterior  cornu  are 
extremely  variable  in  their  degree  of  development;  in  some  cases  they  are  ill- 
defined,  in  others  prominent. 


FiQ.  737. — Central  part  and  anterior  and  posterior  cornua  of  lateral  ventricles  exposed  from  above. 

The  inferior  cornu  (cornu  inferior;  descending  horn;  middle  horn;  medicornu)  (Fig. 
739),  the  largest  of  the  three,  traverses  the  temporal  lobe  of  the  brain,  forming 
in  its  course  a  curve  around  the  posterior  end  of  the  thalamus.  It  passes  at  first 
backward,  lateralward,  and  downward,  and  then  curves  forward  to  within  2.5  cm. 
of  the  apex  of  the  temporal  lobe,  its  direction  being  fairly  well  indicated  on  the 
surface  of  the  brain  by  that  of  the  superior  temporal  sulcus.  Its  roof  is  formed 
chiefly  by  the  inferior  surface  of  the  tapetum  of  the  corpus  callosum,  but  the  tail 
of  the  caudate  nucleus  and  the  stria  terminalis  also  extend  forward  in  the  roof  of 
the  inferior  cornu  to  its  extremity;  the  tail  of  the  caudate  nucleus  ioins  the 


832 


NEUROLOGY 


I 


putamen.    Its  floor  presents  the  following  parts:  the  hippocampus,  the  fimbria 
hippocampi,    the    collateral    eminence,    and    the    choroid    plexus.      When    the 


Bulb  of  posterior  cornu 

Posterior  cornu 

Calcar  avis 

Collateral  eminence 

Calcarine  fissure 


Collateral  fissure 


Fig.  738. — Coronal  section  through  posterior  cornua  of  lateral  ventricle 

choroid  plexus  is  removed,  a  cleft-like  opening  is  left  along  the  medial  wall  of 
the  inferior  cornu;  this  cleft  constitutes  the  lower  part  of  the  choroidal  fissure. 

Choroid  plexus 

Bulb  of  posterior  cornu 
Calcar  avis 


Lateral 
cerebral 
fissure 

Collateral  eminence 
Fimbria  hippocampi 
Uippocampus 
Fio.  739. — Posterior  and  inferior  comua  of  left  lateral  ventricle  exposed  from  the  side. 


The  hippocampus  (hippocampus  major)  (Figs.  739,  740)  is  a  curved  eminence, 
about  5  cm.  long,  which  extends  throughout  the  entire  length  of  the  floor  of  the 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


833 


I 


inferior  cornu.  Its  lower  end  is  enlarged,  and  presents  two  or  three  rounded  eleva- 
tions or  digitations  which  give  it  a  paw-like  appearance,  and  hence  it  is  named 
the  pes  hippocampi.  If  a  transverse  section  be  made  through  the  hippocampus, 
it  will  be  seen  that  this  eminence  is  produced  by  the  folding  of  the  wall  of  the 
hemisphere  to  form  the  hippocampal  fissure.  The  main  mass  of  the  hippocampus 
consists  of  gray  substance,  but  on  its  ventricular  surface  is  a  thin  white  layer, 
the  alveus,  which  is  continuous  with  the  fimbria  hippocampi. 

The  collateral  eminence  (emineniia  collaieralis)  (Fig.  740)  is  an  elongated 
swelling  lying  lateral  to  and  parallel  with  the  hippocampus.  It  corresponds  with 
ihe  middle  part  of  the  collateral  fissure,  and  its  size  depends  on  the  depth  and 
jdirection  of  this  fissure.  It  is  continuous  behind  with  a  flattened  triangular  area, 
the  trigonum  coUaterale,  situated  between  the  posterior  and  inferior  cornua. 

The  fimbria  hippocampi  is  a  continuation  of  the  crus  of  the  fornix,  and  will  be 
discussed  with  that  body;  a  description  of  the  choroid  plexus  will  be  found  on 
page  840. 


Fig.  740. — Inferior  and  posterior  cornua, 
viewed  from  above. 


Fig.  741. — ^Two  views  of  a  model  of  the  striatum:  A, 
lateral  aspect;  B,  mesal  aspect. 


The  corpus  striatum  has  received  its  name  from  the  striped  appearance  which 
a  section  of  its  anterior  part  presents,  in  consequence  of  diverging  white  fibers 
being  mixed  with  the  gray  substance  which  forms  its  chief  mass.  A  part  of  the 
icorpus  striatum  is  imbedded  in  the  white  substance  of  the  hemisphere,  and  is 
■therefore  external  to  the  ventricle;  it  is  termed  the  extraventricular  portion,  or  the 
lentiform  nucleus ;  the  remainder,  however,  projects  into  the  ventricle,  and  is  named 
the  intraventricular  portion,  or  the  caudate  nucleus  (Fig.  737) . 

The  caudate  nucleus  (nucleus  caudatus;  caudatum)  (Figs.  741, 742)  is  a  pear-shaped, 
highly  arched  gray  mass;  its  broad  extremity,  or  head,  is  directed  forward  into  the 
anterior  cornu  of  the  lateral  ventricle,  and  is  continuous  with  the  anterior  perforated 
substance  and  with  the  anterior  end  of  the  lentiform  nucleus;  its  narrow  end, 
pr  tail,  is  directed  backward  on  the  lateral  side  of  the  thalamus,  from  which  it  is 
53 


NEUROLOGY 


I 


separated  by  the  stria  terminalis  and  the  terminal  vein.  It  is  then  continued 
downward  into  the  roof  of  the  inferior  cornu,  and  ends  in  the  putamen  near  the 
apex  of  the  temporal  lobe.  It  is  covered  by  the  lining  of  the  ventricle,  and  crossed 
by  some  veins  of  considerable  size.  It  is  separated  from  the  lentiform  nucleus, 
in  the  greater  part  of  its  extent,  by  a  thick  lamina  of  white  substance,  called  the 
internal  capsule,  but  the  two  portions  of  the  corpus  striatum  are  united  in  front 
(Figs.  743,  744). 


Genu  of  corpus  callosum  _J. 
Anterior  cornu  of  lateral  ventricle j^. 

Caudate  nucleus      '' 

Septum  x>ellueidtim 

Internal  capsule  (Jrontal  part) 

Column  of  fornix 

Genu  of  internal  capsule 

Putamen 

Globus  pallidus 

Internal  capsule  (occipital  part) 

Thalamus 


Tail  of  caudate  nucleus 
Hippocampus 

Inferior  cornu  oj  lateral  ventricle 


Area,  striata 


Posterior  cornu  of  lateral  ventrici 


External  cwpsuLe 
Claustrum 
Insula 


Optic  radiation 


Fio.  742. — Horizontal  section  of  right  cerebral  hemisphere. 

The  lentiform  nucleus  (nucleus  lerdiformis;  lenticular  nucleus;  lenticula)  (Fig.  741) 
is  lateral  to  the  caudate  nucleus  and  thalamus,  and  is  seen  only  in  sections  of  the 
hemisphere.  When  divided  horizontally,  it  exhibits,  to  some  extent,  the  appearance 
of  a  biconvex  lens  (Fig.  742),  while  a  coronal  section  of  its  central  part  presents  a 
somewhat  triangular  outline.  It  is  shorter  than  the  caudate  nucleus  and  does  not 
extend  as  far  forward.  It  is  bounded  laterally  by  a  lamina  of  white  substance 
called  the  external  capsule,  and  lateral  to  this  is  a  thin  layer  of  gray  substance 
termed  the  claustrum.  Its  anterior  end  is  continuous  with  the  lower  part  of  the 
head  of  the  caudate  nucleus  and  with  the  anterior  perforated  substance. 

In  a  coronal  section  through  the  middle  of  the  lentiform  nucleus,  two  medullary 
laminae  are  seen  dividing  it  into  three  parts.  The  lateral  and  largest  part  is  of  a 
reddish  color,  and  is  known  as  the  putamen,  w  hile  the  medial  and  intermediate  are  of 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


a  yellowish  tint,  and  together  constitute  the  globus  pallidus;  all  three  are  marked  by 
fine  radiating  white  fibers,  which  are  most  distinct  in  the  putamen  (Fig.  744) . 

The  gray  substance  of  the  corpus  striatum  is  traversed  by  nerve  fibers,  some 

of  which  originate  in  it.    The  cells  are  multipolar,  both  large  and  small;  those  of 

^^the  lentiform  nucleus  contain  yellow  pigment.    The  caudate  and  lentiform  nuclei 

^Bfire  not  only  directly  continuous  with  each  other  anteriorly,  but  are  connected  to 

^^each  other  by  numerous  fibers.    The  corpus  striatum  is  also  connected:  (1)  to  the 

cerebral  cortex,  by  what  are  termed  the  corticostriate  fibers;  (2)  to  the  thalamus, 

by  fibers  which  pass  through  the  internal  capsule,  and  by  a  strand  named  the 

ansa  lentiformis;  (3)  to  the  cerebral  peduncle,  by  fibers  which  leave  the  lower 

,spect  of  the  caudate  and  lentiform  nuclei. 


r 


Superior  frontal  gynis 


Middle  fronial 
gyrus 


Corpus  caUosum 

Anterior  comu 

Septum  pelluddum 

Caudate  nucleus 

Internal  capsule 

Lentiform  nucleus 


I 


Sulcus  olfactoriv^ 

Insula 
Temporal  lobe 
Inferior  frontal  gyrus 

Fig.  743. — Coronal  section  through  anterior  comua  of  lateral  ventricles. 

The  claustnun  (Figs.  742,  744)  is  a  thin  layer  of  gray  substance,  situated  on  the 
lateral  surface  of  the  external  capsule.  Its  transverse  section  is  triangular,  with 
the  apex  directed  upward.  Its  medial  surface,  contiguous  to  the  external  capsule, 
is  smooth,  but  its  lateral  surface  presents  ridges  and  furrows  corresponding  with 
the  gyri  a  nd  sulci  of  the  insula,  with  which  it  is  in  close  relationship.  The  claustrum 
is  regarded  as  a  detached  portion  of  the  gray  substance  of  the  insula,  from  which 
it  is  separated  by  a  layer  of  white  fibers,  the  capsula  extrema  {band  of  Baillarger). 
Its  cells  are  small  and  spindle-shaped,  and  contain  yellow  pigment;  they  are  similar 
to  those  of  the  deepest  layer  of  the  cortex. 

The  nucleus  amygdalae  {amygdala)  (Fig.  741),  is  an  ovoid  gray  mass,  situated  at  the 
lower  end  of  the  roof  of  the  inferior  cornu.    It  is  merely  a  localized  thickening  of  the 


836 


NEUROLOGY 


gray  cortex,  continuous  with  that  of  the  uncus;  in  front  it  is  continuous  with  the 
putamen,  behind  with  the  stria  terminahs  and  the  tail  of  the  caudate  nucleus. 

The  internal  capsule  (capsula  interna)  (Figs.  745, 746)  is  a  flattened  band  of  white 
fibers,  between  the  lentiform  nucleus  on  the  lateral  side  and  the  caudate  nucleus 
and  thalamus  on  the  medial  side.  In  horizontal  section  (Figs.  742)  it  is  seen  to  be 
somewhat  abruptly  curved,  with  its  convexity  inward;  the  prominence  of  the  curve 
is  called  the  genu,  and  projects  between  the  caudate  nucleus  and  the  thalamus. 
The  portion  in  front  of  the  genu  is  termed  the  frontal  part,  and  separates  the  len- 
tiform from  the  caudate  nucleus ;  the  portion  behind  the  genu  is  the  occipital  part, 
and  separates  the  lentiform  nucleus  from  the  thalamus. 


Corpus  ccdlosum 

Anterior  corn' 
Cavity  of  septum 
pellucidum 

Columns  of 
fornix 

Anterior 
commissure 

Third  ventricle 

Optic 
chiasmd 


Caudate  nvx^ev^ 
Internal  capsule 

Putamen 

Globus  pallidus 
Claustrum 
Insula 


Fig.  744. — Coronal  section  of  brain  through  anterior  commissure. 


The  frontal  part  of  the  internal  capsule  contains:  (1)  fibers  running  from  the 
thalamus  to  the  frontal  lobe;  (2)  fibers  connecting  the  lentiform  and  caudate 
nuclei;  (3)  fibers  connecting  the  cortex  with  the  corpus  striatum;  and  (4)  fibers 
passing  from  the  frontal  lobe  through  the  medial  fifth  of  the  base  of  the  cerebral 
peduncle  to  the  nuclei  pontis.  The  fibers  in  the  region  of  the  genu  are  named 
the  geniculate  fibers ;  they  originate  in  the  motor  part  of  the  cerebral  cortex,  and, 
after  passing  downward  through  the  base  of  the  cerebral  peduncle  with  the  cerebro- 
spinal fibers,  undergo  decussation  and  end  in  the  motor  nuclei  of  the  cranial 
nerves  of  the  opposite  side.  The  anterior  two-thirds  of  the  occipital  part  of  the 
internal  capsule  contains  the  cerebrospinal  fibers,  which  arise  in  the  motor  area 
of  the  cerebral  cortex  and,  passing  downward  through  the  middle  three-fifths  of 
the  base  of  the  cerebral  peduncle,  are  continued  into  the  pyramids  of  the  medulla 
oblongata.  The  posterior  third  of  the  occipital  part  contains:  (1)  sensory  fibers, 
largely  derived  from  the  thalamus,  though  some  may  be  continued  upward  from 


I 


THE  FORE-BRAIN  OR  PROSE! 


i 


the  medial  lemniscus;  (2)  the  fibers  of  optic  radiation,  from  the  lower  visual  centers 
to  the  cortex  of  the  occipital  lobe;  (3)  acoustic  fibers,  from  the  lateral  lemniscus  to 
the  temporal  lobe;  and  (4)  fibers  which  pass  from  the  occipital  and  temporal  lobes 
to  the  nuclei  pontis. 

The  fibers  of  the  internal  capsule  radiate  widely  as  they  pass  to  and  from  the 
arious  parts  of  the  cerebral  cortex,  forming  the  corona  radiata  (Fig.  745)  and 

termingling  with  the  fibers  of  the  corpus  callosum. 

The  external  capsule  {capsula  externa)  (Fig.  742)  is  a  lamina  of  white  substance, 
situated  lateral  to  the  lentiform  nucleus,  between  it  and  the  claustrum,  and  con- 
tinuous with  the  internal  capsule  below  and  behind  the  lentiform  nucleus.  It 
probably  contains  fibers  derived  from  the  thalamus,  the  anterior  commissure,  and 

e  subthalamic  region. 


B.  oculomotor  nerve 

L.  oculomotor  nerve 

Superior  peduncle     / 

"Pyramid 

Olivi 
Fig.  745. — Dissection  showing  the  course  of  the  cerebrospinal  fibers.      (E.  B.  Jamieson.) 


Inferior  peduncle 


I 


The  substantia  innominata  of  Meynert  is  a  stratum  consisting  partly  of  gray  and 
partly  of  white  substance,  which  lies  below  the  anterior  part  of  the  thalamus 
and  lentiform  nucleus.  It  consists  of  three  layers,  superior,  middle,  and  inferior. 
The  superior  layer  is  named  the  ansa  lentiformis,  and  its  fibers,  derived  from  the 
medullary  lamina  of  the  lentiform  nucleus,  pass  medially  to  end  in  the  thalamus 
and  subthalamic  region,  while  others  are  said  to  end  in  the  tegmentum  and  red 
nucleus.  The  middle  layer  consists  of  nerve  cells  and  nerve  fibers;  fibers  enter  it 
from  the  parietal  lobe  through  the  external  capsule,  while  others  are  said  to  con- 
nect it  with  the  medial  longitudinal  fasciculus.  The  inferior  layer  forms  the  main 
part  of  the  inferior  stalk  of  the  thalamus,  and  connects  this  body  wuth  the  temporal 
lobe  and  the  insula. 

The  stria  terminalis  {toenia  semicircularis)  is  a  narrow  band  of  white  substance 
situated  in  the  depression  between  the  caudate  nucleus  and  the  thalamus.  Ante- 
riorly, its  fibers  are  partly  continued  into  the  column  of  the  fornix;  some,  however, 
ass  over  the  anterior  commissure  to  the  gray  substance  between  the  caudate 


838 


I 


NEUROLOGY 


GCNICULAT 

PORTION  O 

MOTOR  THAC 

(for   MUSCLE 

OF  FACE  AN 

TONGUE 


nucleus  and  septum  pellueidum,  while  others  are  said  to  enter  the  caudate  nucleus. 
Posteriorly,  it  is  continued  into  the  roof  of  the  inferior  cornu  of  the  lateral  ventricle, 
at  the  extremity  of  which  it  enters  the  nucleus  amygdalae.  Superficial  to  it  is  a 
large  vein,  the  terminal  vein  {vein  of  the  corpus  striatum),  which  receives  numerous 
tributaries  from  the  corpus  striatum  and  thalamus;  it  runs  forward  to  the  inter- 
ventricular foramen  and  there  joins  with  the  vein  of  the  choroid  plexus  to  form 

the  corresponding  internal  cerebral 
vein.  On  the  surface  of  the  ter- 
minal vein  is  a  narrow  white  band, 
named  the  lamina  affixa. 

The  Fornix  (Figs.  720,  747,  748) 
is  a  longitudinal,  arch-shaped  lam- 
ella of  white  substance,  situated 
below  the  corpus  callosum,  and 
continuous  with  it  behind,  but 
separated  from  it  in  front  by  the 
septum  pellueidum.  It  may  be 
described  as  consisting  of  two 
symmetrical  bands,  one  for  either 
hemisphere.  The  two  portions  are 
not  united  to  each  other  in  front 
and  behind,  but  their  central  parts 
are  joined  together  in  the  middle 
line.  The  anterior  parts  are  called 
the  columns  of  the  fornix;  the  inter- 
mediate united  portions,  the  body; 
and  the  posterior  parts,  the  crura. 

The  body  (corpus  fornicis)  of  the 
fornix  is  triangular,  narrow  in  front, 
and  broad  behind.  The  medial  part 
of  its  upper  surface  is  connected  to 
the  septum  pellueidum  in  front  and 
to  the  corpus  callosum  behind.  The 
lateral  portion  of  this  surface  forms 
part  of  the  floor  of  the  lateral  ven- 
tricle, and  is  covered  by  the  ven- 
tricular epithelium.  Its  lateral  edge 
overlaps  the  choroid  plexus,  and  is 
continuous  with  the  epithelial  cov- 
ering of  this  structure.  The  under 
surface  rests  upon  the  tela  chori- 
oidea  of  the  third  ventricle,  which 
separates  it  from  the  epithelial  roof 
of  that  cavity,  and  from  the  medial 
portions  of  the  upper  surfaces  of  the 
thalami.  Below,  the  lateral  portions 
of  the  body  of  the  fornix  are  joined 
by  a  thin  triangular  lamina,  named  the  psalterium  (lyra).  This  lamina  contains 
some  transverse  fibers  which  connect  the  two  hippocampi  across  the  middle  line 
and  constitute  the  hippocampal  commissure.  Between  the  psalterium  and  the  corpus 
callosum  a  horizontal  cleft,  the  so-called  ventricle  of  the  fornix  (ventricle  of  Verga), 
is  sometimes  found. 

The  columns  (columna  fornicis;  anterior  pillars;  fornicolumns)  of  the  fornix  arch 
downward  in  front  of  the  interventricular  foramen  and  behind  the  anterior  commis- 


FiG.  746. — Diagram  of  the  tracts  in  the  internal  capsule. 
Motor  tract  red.  The  sensory  tract  (blue)  is  not  direct,  but 
formed  of  neurons  receiving  impulses  from  below  in  the  thala- 
mus and  transmitting  them_  to  the  cortex.  The  optic  radiation 
(occipitothalamic)  is  shown  in  violet. 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


839 


sure,  and  each  descends  through  the  gray  substance  in  the  lateral  wall  of  the  third 
ventricle  to  the  base  of  the  brain,  where  it  ends  in  the  corpus  mammillare.  From 
I  the  cells  of  the  corpus  mammillare  the  thalamomammillary  fasciculus  (bundle  of  Vicq 


ANT.    PILLARS 
OF    FORNIX 


IPPOCAMPU8 


Fig.  747. — Diagram  of  the  fornix.     (Spitzka.) 


Cavttp  of  septum  pellucidum 
Optic  chiasma 

Optic  nerve 

Tuber  cinereum 

Optic  tract 


Corpora 
mammiUaria 


Corpus 

callosum 

(wider  gurf ace) 

Fimbria 
hippocampi 


Fig.  748. — The  fornix  and  corpus  callosum  from  below.    (From  a  specimen  in  the  Department  of  Human 
Anatomy  of  the  University  of  Oxford.) 

d'Azyr)  takes  origin  and  is  prolonged  into  the  anterior  nucleus  of  the  thalamus. 
>        The  column  of  the  fornix  and  the  thalamomammillarv  fasciculus  together  form  a  loop 

r —— 


'840  ^  NEUROLOGY 


I 


mammillare.  The  column  of  the  fornix  is  joined  by  the  stria  medullaris  of  the  pineal 
body  and  by  the  superficial  fibers  of  the  stria  terminaUs,  and  is  said  to  recei\e 
also  fibers  from  the  septum  pellucidum.  Zuckerkandl  describes  an  olfactory  fascic- 
ulus which  becomes  detached  from  the  main  portion  of  the  column  of  the  fornix, 
and  passes  downward  in  front  of  the  anterior  commissure  to  the  base  of  the  brain, 
where  it  divides  into  two  bundles,  one  joining  the  medial  stria  of  the  olfactory 
tract ;  the  other  joins  the  subcallosal  gyrus,  and  through  it  reaches  the  hippocampal 
gyrus. 

The  crura  {cms  fornicis;  posterior  pillars)  of  the  fornix  are  prolonged  backward 
from  the  body.  They  are  flattened  bands,  and  at  their  commencement  are  inti- 
mately connected  with  the  under  surface  of  the  corpus  callosum.  Diverging  from 
one  another,  each  curves  around  the  posterior  end  of  the  thalamus,  and  passes 
downward  and  forward  into  the  inferior  cornu  of  the  lateral  ventricle  (Fig.  750). 
Here  it  lies  along  the  concavity  of  the  hippocampus,  on  the  surface  of  which  some 
of  its  fibers  are  spread  out  to  form  the  alveus,  while  the  remainder  are  continued 
as  a  narrow  white  band,  the  fimbria  hippocampi,  which  is  prolonged  into  the  uncus 
of  the  hippocampal  gyrus.  The  inner  edge  of  the  fimbria  overlaps  the  fascia 
dentata  hippocampi  (dentate  gyrus)  (page  827),  from  which  it  is  separated  by  the 
fimbriodentate  fissure;  from  its  lateral  margin,  which  is  thin  and  ragged,  the  ventric- 
ular epithelium  is  reflected  over  the  choroid  plexus  as  the  latter  projects  into  the 
chorioidal  fissure. 

Interventricular  Foramen  (foramen  of  Monro). — Between  the  columns  of  the  fornix 
and  the  anterior  ends  of  the  thalami,  an  oval  aperture  is  present  on  either  side: 
this  is  the  interventricular  foramen,  and  through  it  the  lateral  ventricles  communi- 
cate with  the  third  ventricle.  Behind  the  epithelial  lining  of  the  foramen  the  choroid 
plexuses  of  the  lateral  ventricles  are  joined  across  the  middle  line. 

The  Anterior  Commissure  (precommissure)  is  a  bundle  of  white  fibers,  connecting 
the  two  cerebral  hemispheres  across  the  middle  line,  and  placed  in  front  of  the 
columns  of  the  fornix.  On  sagittal  section  it  is  oval  in  shape,  its  long  diameter 
being  vertical  and  measuring  about  5  mm.  Its  fibers  can  be  traced  lateral  ward 
and  backward  on  either  side  beneath  the  corpus  striatum  into  the  substance  of 
the  temporal  lobe.  It  serves  in  this  way  to  connect  the  two  temporal  lobes,  but 
it  also  contains  decussating  fibers  from  the  olfactory  tracts. 

The  Septum  Pellucidum  (septum  lucidum)  (Fig.  720)  is  a  thin,  vertically  placed 
partition  consisting  of  two  laminae,  separated  in  the  greater  part  of  their  extent 
by  a  narrow  chink  or  interval,  the  cavity  of  the  septum  pellucidum.  It  is  attached, 
above,  to  the  under  surface  of  the  corpus  callosum;  below,  to  the  anterior  part  of 
the  fornix  behind,  and  the  reflected  portion  of  the  corpus  callosum  in  front.  It  is 
triangular  in  form,  broad  in  front  and  narrow  behind;  its  inferior  angle  corre- 
sponds with  the  upper  part  of  the  anterior  commissure.  The  lateral  surface  of  each 
lamina  is  directed  toward  the  body  and  anterior  cornu  of  the  lateral  ventricle, 
and  is  covered  by  the  ependyma  of  that  cavity. 

The  cavity  of  the  septum  pellucidum  (cavum  septi  pellucidi;  pseudocele;  fifth 
ventricle)  is  generally  regarded  as  part  of  the  longitudinal  cerebral  fissure,  which 
has  become  shut  off  by  the  union  of  the  hemispheres  in  the  formation  of  the  corpus 
callosum  above  and  the  fornix  below.  Each  half  of  the  septum  therefore  forms 
part  of  the  medial  wall  of  the  hemisphere,  and  consists  of  a  medial  layer  of  gray 
substance,  derived  from  that  of  the  cortex,  and  a  lateral  layer  of  white  substance 
continuous  with  that  of  the  cerebral  hemispheres.  This  cavity  is  not  developed 
from  the  cavity  of  the  cerebral  vesicles,  and  never  communicates  with  the  ventricles 
of  the  brain. 

The  Choroid  Plexus  of  the  Lateral  Ventricle  (plexus  chorioideus  ventriculus  later- 
alis; paraplexus)  (Fig.  750)  is  a  highly  vascular,  fringe-like  process  of  pia  mater, 
which  projects  into  the  ventricular  cavity.     The  plexus,  however,  is  everywhere 


I 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


841 


m 


covered  by  a  layer  of  epithelium  continuous  with  the  epithelial  lining  of  the 
ventricle.  It  extends  from  the  interventricular  foramen,  where  it  is  joined 
ith  the  plexus  of  the  opposite  ventricle,  to  the  end  of  the  inferior  cornu.  The 
part  in  relation  to  the  body  of  the  ventricle  forms  the  vascular  fringed  margin 
of  a  triangular  process  of  pia  mater,  named  the  tela  chorioidea  of  the  third 
ventricle,  and  projects  from  under  cover  of  the  lateral  edge  of  the  fornix.  It 
lies  upon  the  upper  surface  of  the  thalamus,  from  which  the  epithelium  is  reflected 
over  the  plexus  on  to  the  edge  of  the  fornix  (Fig.  723) .  The  portion  in  relation 
to  the  inferior  cornu  lies  in  the  concavity  of  the  hippocampus  and  overlaps  the 
fimbria  hippocampi :  from  the  lateral  edge  of  the  fimbria  the  epithelium  is  reflected 
over  the  plexus  on  to  the  roof  of  the  cornu  (Fig.  749) .  It  consists  of  minute  and 
highly  vascular  villous  processes,  each  with  an  alTerent  and  an  efferent  vessel.  The 
arteries  of  the  plexus  are:  (a)  the  anterior  choroidal,  a  branch  of  the  internal  carotid, 
which  enters  the  plexus  at  the  end  of  the  inferior  cornu;  and  (b)  the  posterior 
choroidal,  one  or  two  small  branches  of  the  posterior  cerebral,  which  pass  forward 
lender  the  splenium.  The  vei7is  of  the  choroid  plexus  unite  to  form  a  tortuous  vein, 
which  courses  from  behind  forward  to  the  interventricular  foramen  and  there  joins 
with  the  terminal  vein  to  form  the  corresponding  internal  cerebral  vein. 


Tail  of  caudate  nudeus 


Choroid  plexus 

Epithelial  lining  of  ventricle 


b» 


If 


Pia  mater 

Fimbria 
Fimbriodentate 
fissure 

Alveus 

Fascia  devtata 
hippocampi 

Dentate  fissure 


Fig.  749. — Coronal  section  of  inferior  horn  of  lateral  ventricle.      (Diagrammatic.) 


When  the  choroid  plexus  is  pulled  away,  the  continuity  between  its  epithelial 
overing  and  the  epithelial  lining  of  the  ventricle  is  severed,  and  a  cleft-like  space 
is  produced.  This  is  named  the  choroidal  fissure;  like  the  plexus,  it  extends  from 
the  interventricular  foramen  to  the  end  of  the  inferior  cornu.  The  upper  part  of 
the  fissure,  i.  e.,  the  part  nearest  the  interventricular  foramen  is  situated  between 
the  lateral  edge  of  the  fornix  and  the  upper  surface  of  the  thalamus;  farther  back 
at  the  beginning  of  the  inferior  cornu  it  is  between  the  commencement  of  the  fim- 
bria hippocampi  and  the  posterior  end  of  the  thalamus,  Avhile  in  the  inferior  cornu  it 
lies  between  the  fimbria  in  the  floor  and  the  stria  terminalis  in  the  roof  of  the  cornu. 

The  tela  chorioidea  of  the  third  ventricle  {tela  chorioidea  ventriculi  tertii;  velum 
interpositum)  (Fig.  750)  is  a  double  fold  of  pia  mater,  triangular  in  shape,  which 
lies  beneath  the  fornix.  The  lateral  portions  of  its  lower  surface  rest  upon  the 
thalami,  while  its  medial  portion  is  in  contact  with  the  epithelial  roof  of  the  third 
ventricle.  Its  apex  is  situated  at  the  interventricular  foramen;  its  base  corresponds 
with  the  splenium  of  the  corpus  callosum,  and  occupies  the  interval  between  that 

ructure  above  and  the  corpora  quadrigemina  and  pineal  body  below.     This 


842 


NEUROLOGY 


I 


interval,  together  with  the  lower  portions  of  the  choroidal  fissures,  is  sometimtis 
spoken  of  as  the  transverse  fissure  of  the  brain.  At  its  base  the  two  layers  of  the 
velum  separate  from  each  other,  and  are  continuous  with  the  pia  mater  investing 
the  brain  in  this  region.  Its  lateral  margins  are  modified  to  form  the  highly  vas- 
cular choroid  plexuses  of  the  lateral  ventricles.  It  is  supplied  by  the  anterior  and 
posterior  choroidal  arteries  already  described.  The  veins  of  the  tela  chorioidea  are 
named  the  internal  cerebral  veins  {vence  Galeni);  they  are  two  in  number,  and  run 
backward  between  its  layers,  each  being  formed  at  the  interventricular  foramen  by 
the  union  of  the  terminal  vein  with  the  choroidal  vein.  The  internal  cerebral 
veins  unite  posteriorly  in  a  single  trunk,  the  great  cerebral  vein  {vena  magna  Galeni), 
which  passes  backward  beneath  the  splenium  and  ends  in  the  straight  sinus. 


4 


Fig.  750. — Tela  chorioidea  of  the  third  ventricle,  and  the  choroid   plexus  of  the  left  lateral  ventricle,  exposed 

from  above. 

Structure  of  the  Cerebral  Hemispheres. — The  cerebral  hemispheres  are  composed 
of  gray  and  white  substance:  the  former  covers  their  surface,  and  is  termed  the 
cortex;  the  latter  occupies  the  interior  of  the  hemispheres. 

The  white  substance  consists  of  medullated  fibers,  varying  in  size,  and  arranged 
in  bundles  separated  by  neuroglia.  They  may  be  divided,  according  to  their 
course  and  connections,  into  three  distinct  systems.  (1)  Projection  fibers  connect 
the  hemisphere  with  the  lower  parts  of  the  brain  and  with  the  medulla  spinalis. 
(2)  Transverse  or  commissural  fibers  unite  the  two  hemispheres.  (3)  Association 
fibers  connect  different  structures  in  the  same  hemisphere;  these  are,  in  many 


I 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


843 


^ 


instances,  collateral  branches  of  the  projection  fibers,  but  others  are  the  axons 
of  independent  cells. 

1  The  projection  fibers  consist  of  efferent  and  afferent  fibers  uniting  the  cortex 
with  the  lower  parts  of  the  brain  and  with  the  medulla  spinalis.  The  principal 
efferent  strands  are:  (1)  the  motor  tract,  occupying  the  genu  and  anterior  two-thirds 
of  the  occipital  part  of  the  internal  capsule,  and  consisting  of  (a)  the  geniculate 
fibers,  which  decussate  and  end  in  the  motor  nuclei  of  the  cranial  nerves  of  the 
opposite  side;  and  (b)  the  cerebrospinal  fibers,  which  are  prolonged  through  the 
pyramid  of  the  medulla  oblongata  into  the  medulla  spinalis :  (2)  the  corticopontine 
fibers,  ending  in  the  nuclei  pontis.  The  chief  afferent  fibers  are:  (1)  those  of  the 
lemniscus  which  are  not  interrupted  in  the  thalamus;  (2)  those  of  the  superior 
cerebellar  peduncle  which  are  not  interrupted  in  the  red  nucleus  and  thalamus; 
■(3)  numerous  fibers  arising  within  the  thalamus,  and  passing  through  its  stalks 
^o  the  different  parts  of  the  cortex  (page  810);  (4)  optic  and  acoustic  fibers,  the 
(former  passing  to  the  occipital,  the  latter  to  the  temporal  lobe. 
[  2.  The  transverse  or  commissural  fibers  connect  the  two  hemispheres.  They 
include :  (a)  the  transverse  fibers  of  the  corpus  callosum,  (6)  the  anterior  commissure, 
(c)  the  posterior  commissure,  and  (d)  the  lyra  or  hippocampal  commissure;  they 
have  already  been  described. 


Fig.  751. — Diagram  showing  principal  systems  of  association  fibers  in  the  cerebnim. 

3.  The  association  fibers  (Fig.  751)  unite  different  parts  of  the  same  hemi- 
sphere, and  are  of  two  kinds:  (1)  those  connecting  adjacent  gyri,  short  association 
fibers ;  (2)  those  passing  between  more  distant  parts,  long  association  fibers. 

The  short  association  fibers  lie  immediately  beneath  the  gray  substance  of  the 
cortex  of  the  hemispheres,  and  connect  together  adjacent  gyri. 

The  long  association  fibers  include  the  following:  (a)  the  uncinate  fasciculus; 
(6)  the  cingulum;  (c)  the  superior  longitudinal  fasciculus;  (d)  the  inferior  longi- 
tudinal fasciculus;  (e)  the  perpendicular  fasciculus;  (/)  the  occipitofrontal 
fasciculus;  and  (g)  the  fornix. 

(a)  The  uncinate  fasciculus  passes  across  the  bottom  of  the  lateral  fissure,  and 
unites  the  gyri  of  the  frontal  lobe  with  the  anterior  end  of  the  temporal  lobe. 

(6)  The  cingulum  is  a  band  of  white  matter  contained  within  the  cingulate 
gyrus.  Beginning  in  front  at  the  anterior  perforated  substance,  it  passes  forward 
and  upward  parallel  with  the  rostrum,  winds  around  the  genu,  runs  backward  above 
the  corpus  callosum,  turns  around  the  splenium,  and  ends  in  the  hippocampal  gyrus. 


I 


NEUROLOGY 


I 


(c)  The  superior  longitudinal  fasciculus  passes  backward  from  the  frontal  lobe 
above  the  lentiform  nucleus  and  insula;  some  of  its  fibers  end  in  the  occipital 
lobe,  and  others  curve  downward  and  forward  into  the  temporal  lobe. 


Fig.  752. — Dissection  of  cortex  and  brain-stem  showing  association  fibers  and  island  of  Reil  after  removal  of  its  super- 
ficial gray  substance. 

{d)  The  inferior  longitudinal  fasciculus  connects  the  temporal  and  occipital 
lobes,  running  along  the  lateral  walls  of  the  inferior  and  posterior  cornua  of  the 
lateral  ventricle. 


Olivo-cerebellar  fiberk 
Nuclei   grac.  et 

cuneatvs 
Vent,  spinocere- 
bellar fas. 


Fig.  753. — Deep  dissection  of  cortex  and  brain-stem. 


(e)  The  perpendicular  fasciculus  runs  vertically  through  the  front  part  of  the 
occipital  lobe,  and  connects  the  inferior  parietal  lobule  with  the  fusiform  gyrus. 

(/)  The  occipitofrontal  fasciculus  passes  backward  from  the  frontal  lobe,  along 
the  lateral  border  of  the  caudate  nucleus,  and  on  the  mesial  aspect  of  the  corona 


I 


THE  FORE-BRAIN  OR  PROSENCEPHALON  845 

Iradiata;  its  fibers  radiate  in  a  fan-like  manner  and  pass  into  the  occipital  and  tem- 
poral lobes  lateral  to  the  posterior  and  inferior  cornua.  Dejerine  regards  the  fibers 
of  the  tapetum  as  being  derived  from  this  fasciculus,  and  not  from  the  corpus 

icallosum. 

(g)  The  fornix  connects  the  hippocampal  gyrus  with  the  corpus  mammillare 
iind,  by  means  of  the  thalamomammillar}^  fasciculus,  witn  the  thalamus  (see  page 

I|B39).    Through  the  fibers  of  the  hippocampal  commissure  it  probably  also  unites 

(the  opposite  hippocampal  gyri. 

The  gray  substance  of  the  hemisphere  is  divided  into:  (1)  that  of  the  cerebral 
cortex,  and  (2)  that  of  the  caudate  nucleus,  the  lentiform  nucleus,  the  claustrum, 
and  the  nucleus  amygdalae. 

I  Structure  of  the  Cerebral  Cortex  (Fig.  754). — The  cerebral  cortex  differs  in  thickness  and 
■tructure  in  different  parts  of  the  hemisphere.  It  is  thinner  in  the  occipital  region  than  in  the 
anterior  and  posterior  central  gyri,  and  it  is  also  much  thinner  at  the  bottom  of  the  sulci  than 
on  the  top  of  the  gyri.  Again,  the  minute  structure  of  the  anterior  central  differs  from  that  of 
the  posterior  central  gyrus,  and  areas  possessing  a  specialized  type  of  cortex  can  be  mapped  out 
in  the  occipital  lobe. 

On  examining  a  section  of  the  cortex  with  a  lens,  it  is  seen  to  consist  of  alternating  white  and 
gray  layers  thus  disposed  from  the  surface  inward:  (1)  a  thin  layer  of  white  substance;  (2)  a 
layer  of  gray  substance;  (3)  a  second  white  layer  (outer  band  of  Baillarger  or  band  of  Gennari); 
(4)  a  second  gray  layer;  (5)  a  third  white  layer  (inner  band  of  Baillarger);  (6)  a  third  gray  layer, 
which  rests  on  the  medullary  substance  of  the  gyrus. 

The  cortex  is  made  up  of  nerve  cells  of  varying  size  and  shape,  and  of  nerve  fibers  which  are 
either  medullated  or  naked  axis- cylinders,  imbedded  in  a  matrix  of  neurogha. 

Nerve  Cells. — According  to  Cajal,  the  nerve  cells  are  arranged  in  four  layers,  named  from  the 
surface  inward  as  follows:  (1)  the  molecular  layer,  (2)  the  layer  of  small  pyramidal  cells,  (3) 
the  layer  of  large  pyramidal  cells,  (4)  the  layer  of  polymorphous  cells. 

The  Molecular  Layer. — In  this  layer  the  cells  are  polygonal,  triangular,  or  fusiform  in  shape. 
Each  polygonal  cell  gives  off  some  four  or  five  dendrites,  while  its  axon  may  arise  directly  from 
the  cell  or  from  one  of  its  dendrites.  Each  triangular  cell  gives  off  two  or  three  dendrites,  from 
one  of  which  the  axon  arises.  The  fusiform  cells  are  placed  with  their  long  axes  parallel  to  the 
surface  and  are  mostly  bipolar,  each  pole  being  prolonged  into  a  dendrite,  which  runs  horizontally 
for  somp  distance  and  furnishes  ascending  branches.  Their  axons,  two  or  three  in  number,  arise 
from  the  dendrites,  and,  like  them,  take  a  horizontal  course,  giving  off  numerous  ascending, 
collaterals.  The  distribution  of  the  axons  and  dendrites  of  all  three  sets  of  cells  is  limited  to  the 
molecular  layer. 

The  Layer  of  Small  and  the  Layer  of  Large  Pyramidal  Cells. — The  cells  in  these  two  layers 
may  be  studied  together,  since,  with  the  exception  of  the  difference  in  size  and  the  more  super- 
ficial position  of  the  smaller  cells,  they  resemble  each  other.  The  average  length  of  the  small 
cells  is  from  10  to  15m;  that  of  the  large  cells  from  20  to  30,".  The  body  of  each  cell  is  pyramidal 
in  shape,  its  base  being  directed  to  the  deeper  parts  and  its  apex  toward  the  surface.  It  contains 
granular  pigment,  and  stains  deeply  with  ordinary  reagents.  The  nucleus  is  of  large  size,  and 
round  or  oval  in  shape.  The  base  of  the  cell  gives  off  the  axis  cylinder,  and  this  runs  into  the 
central  white  substance,  giving  off  collaterals  in  its  course,  and  is  distributed  as  a  projection, 
commissural,  or  association  fiber.  The  apical  and  basal  parts  of  the  cell  give  off  dendrites;  the 
apical  dendrite  is  directed  toward  the  surface,  and  ends  in  the  molecular  layer  by  dividing  into 
numerous  branches,  aU  of  which  may  be  seen,  when  prepared  by  the  silver  or  methylene-blue 
method,  to  be  studded  with  projecting  bristle-Uke  processes.  The  largest  pyramidal  cells  are 
found  in  the  upper  part  of  the  anterior  central  gjTus  and  in  the  paracentral  lobule;  they  are 
often  arranged  in  groups  or  nests  of  from  three  to  five,  and  are  named  the  giant  cells  of  Betz. 
In  the  former  situation  they  may  exceed  50m  in  length  and  40m  in  breadth,  while  in  the  para- 
central lobule  they  may  attain  a  length  of  65m. 

Layer  of  Polymorphous  Cells. — The  cells  in  this  layer,  as  their  name  impUes,  are  very  irregular 
in  contour;  they  may  be  fusiform,  oval,  triangular,  or  star-shaped.  Their  dendrites  are  directed 
outward,  but  do  not  reach  so  far  as  the  molecular  layer;  their  axons  pass  into  the  subjacent  white 
matter. 

There  are  two  other  kinds  of  cells  in  the  cerebral  cortex.  They  are:  (a)  the  cells  of  Golgi, 
the  axons  of  which  divide  immediately  after  their  origins  into  a  large  number  of  branches,  which 
are  directed  toward  the  surface  of  the  cortex;  (b)  the  cells  of  Martinotti,  which  are  chiefly  found 
in  the  polymorphous  layer;  their  dendrites  are  short,  and  may  have  an  ascending  or  descending 
course,  while  their  axons  pass  out  into  the  molecular  layer  and  form  an  extensive  horizontal 
arborization. 


846 


NEUROLOGY 


Nerve  Fibers. — These  fill  up  a  large  part  of  the  intervals  between  the  cells,  and  may  be  med . 
lated  or  non-medullated — the  latter  comprising  the  axons  of  the  smallest  pyramidal  cells  aad 
the  cells  of  Golgi.  In  their  direction  the  fibers  may  be  either  tangential  or  radial.  The  tangential 
fibers  run  parallel  to  the  surface  of  the  hemisphere,  intersecting  the  radial  fibers  at  a  right  angle. 
They  constitute  several  strata,  of  which  the  following  are  the  more  important:  (1)  a  stratum 
of  white  fibers  covering  the  superficial  aspect  of  the  molecular  layer  (plexus  of  Exner) ;  (2)  the 
band  of  Bechterew,  in  the  outer  part  of  the  layer  of  small  pyramidal  cells;  (3)  the  band  of  Gennari 


Molecular 
layer 


Layer  of 

small 

pyramidal 

cells 


Layer  of 

large 

pyramidal 

cells 


Layer  of 

2>olymorphous 

cells 


""  Plexus  of  Exner 


Ji 


Band  of  Bechterew 


Outer  band  of  Bail- 
larger,  or  band  of 
Gennari 


— Vertical  fibers . 


Internal  band  of 
Baillarger 


Deep  tangential 
fibers 


White  medullary 
substance 


Fig.  754. — Cerebral  cortex.    (Poirier.)    To  the  left,  the  groups  of  cells;  to  the  right,  the  systems  of  fibers.    Quite 
to  the  left  of  the  figure  a  sensory  nerve  fiber  is  shown. 


or  external  band  of  Baillarger,  rimning  through  the  layer  of  large  pyramidal  cells;  (4)  the  internal 
band  of  Baillarger,  between  the  layer  of  large  pyramidal  cells  and  the  polymorphous  layer;  (5) 
the  deep  tangential  fibers,  in  the  lower  part  of  the  polymorphous  layer.  The  tangential  fibers 
consist  of  (a)  the  collaterals  of  the  pyramidal  and  polymorphous  cells  and  of  the  cells  of  Martinotti; 
(&)  the  branching  axons  of  Golgi's  cells;  (c)  the  collaterals  and  terminal  arborizations  of  the 
projection,  commissural,  or  association  fibers.  The  radial  fibers. — Some  of  these,  viz.,  the  axons 
of  the  pyramidal  and  polymorphous  cells,  descend  into  the  central  white-matter,  while  others, 


I 


THE  FORE-BRAIN  OR  PROSENCEPHALON 


the  terminations  of  the  projection,  commissural,  or  association  fibers,  ascend  to  end  in  the  cortex. 
The  axons  of  the  cells  of  Martinotti  are  also  ascending  fibers. 

Special  Tsrpes  of  Cerebral  Cortex. — It  has  been  already  pointed  out  that  the  minute  structure 
of  the  cortex  differs  in  different  regions  of  the  hemisphere;  and  A.  W.  CampbelP  has  endeavored 
to  prove,  as  the  result  of  an  exhaustive  examination  of  a  series  of  human  and  anthropoid  brains, 
"that  there  e.xists  a  direct  correlation  between  physiological  function  and  histological  structure." 
The  principal  regions  where  the  "typical"  structure  is  departed  from  will  now  be  referred  to. 

1.  In  the  calcarine  fissure  and  the  gyri  bounding  it,  the  internal  band  of  Baillarger  is  absent, 
while  the  band  of  Gennari  is  of  considerable  thickness,  and  forms  a  characteristic  feature  of  this 
region  of  the  cortex.  If  a  section  be  examined  microscopically,  an  additional  layer  of  cells  is 
seen  to  be  interpolated  between  the  molecular  layer  and  the  layer  of  small  pyramidal  cells.  This 
extra  layer  consists  of  two  or  three  strata  of  fusiform  cells,  the  long  axes  of  which  are  at  right 
angles  to  the  surface;  each  cell  gives  off  two  dendrites,  external  and  internal,  from  the  latter  of 
which  the  axon  arises  and  passes  into  the  white  central  substance.  In  the  layer  of  small  pyramidal 
cells,  fusiform  cells,  identical  with  the  above,  are  seen,  as  well  as  ovoid  or  star-hke  cells  with 
ascending  axons  {cells  of  Martinotti).  This  is  the  visual  area  of  the  cortex,  and  it  has  been  shown 
by  J.  S.  Bolton^  that  in  old-standing  cases  of  optic  atrophy  the  thickness  of  Gennari's  band  is 
reduced  by  nearly  50  per  cent. 

White  svbstnnce   dorsal  pari) 

Neuroglia 

White  substance  {ventral 
part) 

,'  Medtdlary  layer 

.■'Mitral  cells 

Molecular 
layer 


'^Glomerular  layer 


Layer  of  olfactory  nerve  fibers 
Fig.  755. — Coronal  section  of  olfactory  bulb.     (Schwalbe.) 

A.  W.  Campbell  says:  "Histologically,  two  distinct  types  of  cortex  can  be  made  out  in  the 
occipital  lobe.  The  first  of  these  coats  the  walls  and  bounding  convolutions  of  the  calcarine 
fissure,  and  is  distinguished  by  the  well-known  line  of  Gennari  or  Vicq  d'Azyr;  the  second  area 
forms  an  investing  zone  a  centimetre  or  more  broad  around  the  first,  and  is  characterized  by  a 
remarkable  wealth  of  fibers,  as  well  as  by  curious  pyriform  cells  of  large  size  richly  stocked  with 
chromophilic  elements — cells  which  seem  to  have  escaped  the  observation  of  Ramon  y  Cajal, 
Bolton,  and  others  who  have  worked  at  this  region.  As  to  the  functions  of  these  two  regions 
there  is  abundant  evidence,  anatomical,  embryological,  and  pathological,  to  show  that  the  first 
or  calcarine  area  is  that  to  which  visual  sensations  primarily  pass,  and  we  are  gradually  obtain- 
ing proof  to  the  effect  that  the  second  investing  area  is  constituted  for  the  interpretation  and 
further  elaboration  of  these  sensations.  These  areas  therefore  deserve  the  names  visuo-sensory 
and  visuo-psychic." 

2.  The  anterior  central  gyrus  is  characterized  by  the  presence  of  the  giant  cells  of  Betz  and 
by  "a  wealth  of  nerve  fibers  immeasurably  superior  to  that  of  any  other  part"  (Campbell),  and 
in  these  respects  differs  from  the  posterior  central  gyrus.  These  two  gyri,  together  with  the 
paracentral  lobule,  were  long  regarded  as  constituting  the  "motor  areas"  of  the  hemisphere; 
but  Sherrington  and  Grunbaum  have  shown^  that  in  the  chimpanzee  the  motor  area  never  extends 
on  to  the  free  face  of  the  posterior  central  gyrus,  but  occupies  the  entire  length  of  the  anterior 
central  gyrus,  and  in  most  cases  the  greater  part  or  the  whole  of  its  width.  It  extends  into  the 
depth  of  the  central  sulcus,  occupying  the  anterior  wall,  and  in  some  places  the  floor,  and  in 
some  extending  even  into  the  deeper  part  of  the  posterior  wall  of  the  sulcus. 

I  Histological  Studies  on  the  Localization  of  Cerebral  Function,  Cambridge  University  Press. 
'  Philosophical  Transactions  of  Royal  Society,  Series  B,  cxciii,  165. 
•  Transactions  of  the  Pathological  Society  of  London,  vol.  liii. 


848 


NEUROLOGY 


I 


3.  In  the  hippocampus  the  molecular  layer  is  very  thick  and  contains  a  large  number  of  Golgi 
cells.  It  has  been  divided  into  three  strata:  (a)  s.  convolutum  or  s.  granulosum,  containing 
many  tangential  fibers;  (6)  s.  lacunosum,  presenting  numerous  vascular  spaces;  (c)  s.  radialum, 
exhibiting  a  rich  plexus  of  fibrils.  The  two  layers  of  pyramidal  cells  are  condensed  into  one, 
and  the  cells  are  mostly  of  large  size.  The  axons  of  the  cells  in  the  polymorphous  layer  may 
run  in  an  ascending,  a  descending,  or  a  horizontal  direction.  Between  the  polymorphous  layer 
and  the  ventricular  ependyma  is  the  white  substance  of  the  alveus. 

4.  In  the  fascia  dentata  hippocampi  or  dentate  gyrus  the  molecular  layer  contains  some  pyrami- 
dal cells,  while  the  layer  of  pyramidal  cells  is  almost  entirely  represented  by  small  ovoid  cells. 

5.  The  Olfactory  Bulb. — In  many  of  the  lower  animals  this  contains  a  cavity  which  communi- 
cates through  the  olfactory  tract  with  the  lateral  ventricle.  In  man  the  original  cavity  is  filled 
up  by  neuroglia  and  its  wall  becomes  thickened,  but  much  more  so  on  its  ventral  than  on  its 
dorsal  aspect.  Its  dorsal  part  contains  a  small  amount  of  gray  and  white  substance,  but  it  is 
scanty  and  ill-defined.  A  section  through  the  ventral  part  (Fig.  755)  shows  it  to  consist  of  the 
foUowmg  layers  from  without  inward: 


Fig.  756. — Areas  of  localization  on  lateral  surface  of  hemisphere.     Motor  area  in  red.    Area  of  general  sensations 
in  blue.     Auditory  area  in  green.     Visual  area  in  yellow.     The  psychic  portions  are  in  lighter  tints. 

1.  A  layer  of  olfactory  nerve  fibers,  which  are  the  non-meduUated  axons  prolonged  from  the 
olfactory  cells  of  the  nasal  cavity,  and  reach  the  bulb  by  passing  through  the  cribriform  plate 
of  the  ethmoid  bone.  At  first  they  cover  the  bulb,  and  then  penetrate  it  to  end  by  forming 
synapses  with  the  dendrites  of  the  mitral  cells,  presently  to  be  described. 

2.  Glomerular  Layer. — This  contains  numerous  spheroidal  reticulated  enlargements,  termed 
glomeruli,  produced  by  the  branching  and  arborization  of  the  processes  of  the  olfactory  nerve 
fibres  with  the  descending  dendrites  of  the  mitral  cells. 

3.  Molecular  Layer. — This  is  formed  of  a  matrix  of  neurogUa,  imbedded  in  which  are  the  mitral 
cells.  These  cells  are  pyramidal  in  shape,  and  the  basal  part  of  each  gives  oflf  a  thick  dendrite 
which  descends  into  the  glomerular  layer,  where  it  arborizes  as  indicated  above,  and  others  which 
interlace  with  similar  dendrites  of  neighboring  mitral  cells.  The  axons  pass  through  the  next 
layer  into  the  white  matter  of  the  bulb,  and  after  becoming  bent  on  themselves  at  a  right  angle, 
are  continued  into  the  olfactory  tract. 

4.  Nerve  Fiber  Layer. — This  hes  next  the  central  core  of  neurogUa,  and  its  fibers  consist  of 
the  axons  or  afferent  processes  of  the  mitral  cells  passing  to  the  brain;  some  eflferent  fibers  are, 
however,  also  present,  and  end  in  the  molecular  layer,  but  nothing  is  known  as  to  their  exact 
origin. 

Weight  of  the  Encephalon. — The  average  weight  of  the  brain,  in  the  adult  male,  is  about  1380 
gms.;  that  of  the  female,  about  1250  gms.  In  the  male,  the  maximum  weight  out  of  278  cases 
was  1840  gms.  and  the  minimum  weight  964  gms.  The  maximum  weight  of  the  adult  female 
brain,  out  of  191  cases,  was  1585  gms.  and  the  minimum  weight  879  gms.  The  brain  increases 
rapidly  during  the  first  four  years  of  life,  and  reaches  its  maximum  weight  by  about  the  twentieth 
year.  As  age  advances,  the  brain  decreases  slowly  in  weight;  in  old  age  the  decrease  takes  place 
more  rapidly,  to  the  extent  of  about  28  gms. 


I 


^COMPOSITION  AND  CENTRAL  CONNECTIONS  OF  SPINAL  NERVES    849 


The  human  brain  is  heavier  than  that  of  any  of  the  lower  animals,  except  the  elephant  and 
whale.  The  brain  of  the  former  weighs  from  3.5  to  5.4  kilogm.,  and  that  of  a  whale,  in  a  speci- 
men 19  metres  long,  weighed  rather  more  than  6.7  kilogm. 

Cerebral  Localization. — Physiological  and  pathological  research  have  now  gone  far  to  prove 
that  a  considerable  part  of  the  surface  of  the  brain  may  be  mapped  out  into  a  series  of  more 
or  less  definite  areas,  each  of  which  is  intimately  connected  with  some  well-defined  function. 

The  chief  areas  are  indicated  in  Figs.  756  and  757. 

Motor  Areas. — The  motor  area  occupies  the  anterior  central  and  frontal  gyri  and  the  para- 
central lobule.  The  centers  for  the  lower  limb  are  located  on  the  uppermost  part  of  the  anterior 
central  gyrus  and  its  continuation  on  to  the  paracentral  lobule;  those  for  the  trimk  are  on  the 
upper  portion,  and  those  for  the  upper  hmb  on  the  middle  portion  of  the  anterior  central  gyrus. 
The  facial  centers  are  situated  on  the  lower  part  of  the  anterior  central  gyrus,  those  for  the  tongue, 
larynx,  muscles  of  mastication,  and  pharynx  on  the  frontal  operculum,  while  those  for  the  head 
Land  neck  occupy  the  posterior  end  of  the  middle  frontal  gyrus. 


II 


jFia.  757. — Areas  of  localization  on  medial  surface  of  hemisphere.     Motor  area  in  red.    Area  of  general  sensations 
in  blue.     Visual  area  in  yellow.     Olfactory  area  in  purple.     The  psychic  portions  are  in  lighter  tints. 

Sensory  Areas. — Tactile  and  temperature  senses  are  located  on  the  posterior  central  gyrus, 
while  the  sense  of  form  and  sohdity  is  on  the  superior  parietal  lobule  and  precuneus.  With 
regard  to  the  special  senses,  the  area  for  the  sense  of  taste  is  probably  related  to  the  imcus  and 
hippocampal  gyrus.  The  auditory  area  occupies  the  middle  third  of  the  superior  temporal  gyrus 
and  the  adjacent  gyri  in  the  lateral  fissure;  the  visual  area,  the  calcarine  fissure  and  cuneus;  the 
olfactory  area,  the  rhinencephalon.  As  special  centers  of  much  importance  may  be  noted:  the 
emissive  center  for  speech  on  the  left  inferior  frontal  and  anterior  central  g3Ti  (Broca) ;  the  auditory 
receptive  center  on  the  transverse  and  superior  temporal  gyri,  and  the  visual  receptive  center 
on  the  lingual  gyrus  and  cuneus. 

COMPOSITION  AND  CENTRAL  CONNECTIONS  OF  THE  SPINAL  NERVES. 


The  typical  spinal  nerve  consists  of  at  least  four  types  of  fibers,  the  somatic  sensory, 
sympathetic  afferent  or  sensory,  somatic  motor  and  sympathetic  efferent  or  pregan- 
glionic. The  somatic  sensory  fibers,  afferent  fibers,  arise  from  cells  in  the  spinal 
ganglia  and  are  found  in  all  the  spinal  nerves,  except  occasionally  the  first  cervical, 
and  conduct  impulses  of  pain,  touch  and  temperature  from  the  surface  of  the  body 

F+hrough  the  posterior  roots  to  the  spinal  cord  and  impulses  of  muscle  sense,  tendon 
nse  and  joint  sense  from  the  deeper  structures.    The  sympathetic  afferent  fibers, 
conduct  sensory  impulses  from  the  viscera  through  the  rami  communicantes  and 
posterior  roots  to  the  spinal  cord.    They  are  probably  limited  to  the  white  rami 
■fconnected  with  the  spinal  nerves  in  two  groups,  viz.,  the  first  thoracic  to  the  second 

i 


I 


850 


NEUROLOGY 


I 


lumbar  and  the  second  sacral  to  the  fourth  sacral  nerves.  The  somatic  motor 
fibers,  efferent  fibers,  arise  from  cells  in  the  anterior  column  of  the  spinal  cord  and 
pass  out  through  the  anterior  roots  to  the  voluntary  muscles.  The  sympathetic 
efferent  fibers,  probably  arise  from  cells  in  the  lateral  column  or  the  base  of  the 
anterior  column  and  emerge  through  the  anterior  roots  and  white  rami  communi- 
cantes.  These  are  preganglionic  fibers  which  end  in  various  sympathetic  ganglia 
from  which  postganglionic  fibers  conduct  the  motor  impulses  to  the  smooth  muscles 
of  the  viscera  and  vessels  and  secretory  impulses  to  the  glands.  These  fibers  are 
also  limited  to  two  regions,  the  first  thoracic  to  the  second  lumbar  and  the  second 
sacral  to  the  fourth  sacral  nerves. 

The  afferent  fibers  which  pass  into  the  spinal  cord  establish  various  types  of 
connections,  some  within  the  cord  itself  for  spinal  reflexes,  others  for  reflexes  con- 
nected with  higher  centers  in  the  brain,  while  still  others  conduct  impulses  of 
conscious  sensation  by  a  series  of  neurons  to  the  cerebral  cortex. 

pinal   lemniscus 
orrelation  neuronel 
funiculus    dorsali5 

C)    sp.g.1 
correlation  neuroneS 
^T)  sp.g.2 


sKin 
spg.5 

correJation  neurone^ 


Fig.  758. — Diagram  of  the  spinal  cord  reflex  apparatus.  Some  of  the  connections  of  a  single  aflferent  neuron  from 
the  skin  (d.r.2)  are  indicated:  d.r.2,  dorsal  root  from  second  spinal  ganglion;  m,  muscles;  sp.g.l  to  sp.qA,  spinal 
ganglia;  v.r.V^  to  v.r.A,  ventral  roots.     (After  Herrick.) 

The  Intrinsic  Spinal  Reflex  Paths.^ — ^The  collaterals  and  terminals  of  the  ascend- 
ing and  descending  branches  of  the  posterior  root  fibers  which  leave  the  fasciculus 
cuneatus  to  enter  the  gray  matter  of  the  spinal  cord  end  in  various  ways.  Many  end 
in  the  dorsal  column,  some  near  its  apex,  others  in  the  substance  of  Rolando,  others 
in  the  intermediate  region  between  the  dorsal  and  ventral  columns,  others  traverse 
the  whol  3  thickness  of  the  gray  matter  to  reach  the  ventral  column,  others  end  in  the 
dorsal  nucleus,  and  others  pass  through  the  gray  commissure  to  the  dorsal  column 
of  the  opposite  side.  All  of  these  collaterals  and  terminals  end  in  connection  with 
cells  or  dendrites  of  cells  in  the  gray  columns.  The  axons  of  these  cells  ha\'e  various 
destinations,  some  pass  out  into  the  lateral  and  ventral  funiculi  and  turn  upward 
to  reach  the  brain.  Those  concerned  with  the  intrinsic  spinal  reflexes  come  into 
relation  either  directly  or  indirectly  with  motor  cells  in  the  anterior  column.  It  is 
very  unlikely  that  either  the  terminals  or  collaterals  of  the  dorsal  root  fibers  effect 
simple  direct  connections  with  the  motor  cells  of  the  ventral  column,  there  is  at 
least  one  if  not  several  intercalated  neurons  in  the  path.  These  intercalated  or 
correlation  neurons  may  have  short  axons  that  do  not  pass  out  of  the  gray  matter 
or  the  axons  may  pass  out  into  the  proper  fasciculi  and  extend  for  varying  distances 


COMPOSITION  AND  CENTRAL  CONNECTIONS  OF  SPINAL  NERVES    851 

I  up  and  do\vTi  or  in  both  directions  giving  off  collaterals  and  finally  terminating  in 
the  gray  matter  of  the  same  or  the  opposite  side.  The  shortest  fibers  of  the  proper 
fasciculi  lie  close  to  the  gray  matter,  the  longest  ones  are  nearer  the  periphery  of 
the  proper  fasciculi  and  are  more  or  less  intermingled  with  the  long  ascending  and 
descending  fasciculi  which  occupy  the  more  marginal  regions  of  the  spinal  cord. 
Each  sensory  neuron,  with  its  ascending  and  descending  branches,  giving  off  as 
it  does  many  collaterals  into  the  gray  matter,  each  one  of  which  may  form  a  synapse 
with  one  or  several  correlation  neurons,  is  thus  brought  into  relation  with  many 
r       correlation  neurons  and  each  one  of  these  in  turn,  with  its  ascending  and  descending 

. branches  and  their  numerous  collaterals,  is  brought  into  relation,  either  directly 

^■or  through  the  intercalation  of  additional  correlation  neurons,  with  great  numbers 
^■of  motor  cells  in  the  anterior  column.  The  great  complexity  of  these  so-called 
^H^imple  reflex  mechanisms,  in  the  least  complex  portion  of  the  nervous  system  the 
^^spinal  cord,  renders  them  extremely  difficult  of  exact  analysis. 

The  association  or  correlation  neurons  are  concerned  not  only  with  the  reflex 
mechanisms  of  the  spinal  cord  but  play  an  equally  important  role  in  the  trans- 
mission of  impulses  from  the  higher  centers  in  the  brain  to  the  motor  neurons  of  the 
spinal  cord. 
^m  The  complex  mechanisms  just  described  are  probably  concerned  not  so  much  in 
^Bthe  contraction  of  indi^•idual  muscles  as  in  the  complicated  action  of  groups  of 
muscles  concerned  in  the  enormous  number  of  movements,  which  the  limbs  and 

P  trunk  exhibit  in  the  course  of  our  daily  life. 
\  Sensory  Pathways  from  the  Spinal  Cord  to  the  Brain. — ^The  posterior  root  fibers 
conducting  the  impulses  of  conscious  muscle  sense,  tendon  sense  and  joint  sense, 
those  impulses  which  have  to  do  with  the  coordination  and  adjustment  of  muscular 
movements,  ascend  in  the  fasciculus  gracilis  and  fasciculus  cuneatus  to  the  nucleus 
gracilis  and  nucleus  cuneatus  in  the  medulla  oblongata  (Fig.  759). 

In  the  nucleus  gracilis  and  nucleus  cuneatus  sjTiaptic  relations  are  found  with 
nem-ons  whose  cell  bodies  are  located  in  these  nuclei  and  whose  axons  pass  by  way 
of  the  internal  arcuate  fibers,  cross  in  the  raphe  to  the  opposite  side  in  the  region 
between  the  olives  and  turn  abruptly  upward  to  form  the  medial  lemniscus  or  medial 
fillet.  The  medial  fillet  passes  upward  in  the  ventral  part  of  the  formatio  reticularis 
through  the  medulla  oblongata,  pons  and  mid-brain  to  the  principal  sensory  nucleus 
of  the  ventro-lateral  region  of  the  thalamus.  Here  the  terminals  form  synapses 
^  with  neurons  of  the  third  order  whose  axons  pass  through  the  internal  capsule  and 
H  porona  radiata  to  the  somatic  sensory  area  of  the  cortex  in  the  post-central  gyrus. 
Fibers  conducting  the  impulses  of  unconscious  muscle  sense  pass  to  the  cerebellum 
partly  by  way  of  the  fasciculus  gracilis  and  fasciculus  cuneatus  to  the  nucleus 
gracilis  and  nucleus  cuneatus,  thence  neurons  of  the  second  order  convey  the 
impulses  either  via  the  dorsal  external  arcuate  fibers  directly  into  the  inferior 
peduncle  of  the  cerebellum  or  via  the  ventral  external  arcuate  fibers  which  are 
continued  from  the  internal  arcuate  fibers  through  the  ventral  part  of  the  raphe 
and  after  crossing  the  midline  emerge  on  the  surface  of  the  medulla  in  the  ventral 
sulcus  between  the  pyramids  or  in  the  groove  between  the  pjTamid  and  the  olive. 
They  pass  oxer  the  lateral  surface  of  the  medulla  and  olive  to  reach  the  inferior 
peduncle  through  which  they  pass  to  the  cerebellum. 

IL  Other  fibers  conducting  impulses  of  unconscious  muscle  sense  pass  upward  in  the 
dorsal  spinocerebellar  fasciculus,  which  arises  from  cells  in  the  nucleus  dorsalis. 
The  posterior  root  fibers  conducting  these  impulses  pass  into  the  fasciculus  cuneatus 
and  the  collaterals  from  them  to  the  nucleus  dorsalis  are  said  to  come  almost 
exclusively  from  the  middle  area  of  the  fasciculus  cuneatus.  They  form  by  their 
multiple  division  baskets  about  the  individual  cells  of  the  nucleus  dorsalis,  each 
fiber  coming  in  relation  with  the  bodies  and  dendrites  of  several  cells.  The  axons 
•f  the  second  order  pass  into  the  dorsal  spinocerebellar  fasciculus  of  the  same  side 


852 


NEUROLOGY 


I 


and  ascend  along  the  lateral  surface  of  the  spinal  cord  and  medulla  oblongata  until 
they  arrive  at  the  level  of  the  olive,  they  then  curve  backward  beneath  the  exterr  al 
arcuate  fibers  into  the  inferior  peduncle  and  pass  into  the  cerebellum.  Here  th<3y 
give  oft'  collaterals  to  the  dentate  nucleus  and  finally  terminate  in  the  cortex  of  t  le 
dorsal  and  superior  portion  of  the  vermis,  partly  on  the  same  side,  but  to  a  great 


Medial  lemniscus- 


Sensory  decussaium 


Nuclezis  cuneaiua 
Nucleus  gracilis 


—  -  Posterior  nerve  roots 


-The  sensory  tract.     (Modified  from  Poirier.) 


extent  by  way  of  a  large  commissure  to  the  opposite  side.  The  fibers  lose  their 
myelin  sheaths  as  they  enter  the  gray  substance  and  terminate  by  end  ramifications 
among  the  nerve  cells  and  their  processes.  Some  of  the  fibers  are  said  to  end  in 
the  nucleus  dentatus  and  the  roof  nuclei  of  the  cerebellum  (the  nucleus  globosus, 
nucleus  emboliformis  and  nucleus  fastigius)  and  others  pass  through  them  to  ter- 
minate in  the  inferior  vermis.    A  few  fibers  of  the  dorsal  spinocerebellar  fasciculus 


H     COMPOSITION  AND  CENTRAL  CONNECTIONS  OF  SPINAL  NERVES    853 

^Hare  said  not  to  enter  the  inferior  peduncle  but  to  pass  with  the  ventral  spinocere- 
^^  bellar  fasciculus.  The  cerebellar  reflex  arc  is  supposed  to  be  completed  by  the  fibers 
of  the  superior  peduncle  which  pass  from  the  cerebellum  to  the  red  nucleus  of  the 
mid-brain  where  some  of  their  terminals  and  collaterals  form  s\Tiapses  with  neurons 
whose  axons  descend  to  the  spinal  cord  in  the  rubrospinal  fasciculus.  The  terminal 
and  collaterals  of  this  fasciculus  end  either  directly  or  indirectly  about  the  motor 
cells  in  the  anterior  column. 
The  ventral  spinocerebellar  fasciculus,  since  most  of  its  fibers  pass  to  the  cere- 

Pbellum,  is  also  supposed  to  be  concerned  in  the  conduction  of  unconscious  muscle 
sense.  The  location  of  its  cells  of  origin  is  uncertain.  They  are  probably  in  or  near 
the  dorsal  nucleus  of  the  same  and  the  opposite  side;  various  other  locations  are 
given,  the  dorsal  column,  the  intermediate  zone  of  the  gray  matter  and  the  central 
portion  of  the  anterior  column.  The  neurons  of  the  first  order  whose  central  fibers 
enter  the  fasciculus  cuneatus  from  the  dorsal  roots  send  collaterals  and  terminals 
to  form  sjTiapses  with  these  cells.  The  fibers  which  come  from  the  opposite  gray 
columns  cross  some  in  the  white  and  some  in  the  gi-ay  commissure  and  pass  with 
fibers  from  the  same  side  through  the  lateral  funiculus  to  the  marginal  region 
ventral  to  the  dorsal  spinocerebellar  fasciculus.  The  fasciculus  begins  about  the 
level  of  the  third  lumbar  nerve  and  continues  upward  on  the  lateral  surface  of 
the  spinal  cord  and  medulla  oblongata  until  it  passes  under  cover  of  the  external 
arcuate  fibers.  It  passes  just  dorsal  to  the  olive  and  above  this  joins  the  lateral 
edge  of  the  lateral  lemniscus  along  which  it  runs,  ventral  to  the  roots  of  the  trigem- 
inal nerve,  almost  to  the  \e\e\  of  the  superior  colliculus,  it  then  crosses  over  the 
superior  peduncle,  turns  abruptly  backward  along  its  medial  border,  enters  the 
cerebellum  with  it  and  ends  in  the  vermis  of  the  same  and  the  opposite  side.  Some 
of  its  fibers  are  said  to  join  the  dorsal  spinocerebellar  fasciculus  in  the  medulla 
oblongata  and  enter  the  cerebellum  through  the  inferior  peduncle.  A  number  of 
fibers  are  said  to  continue  upward  in  the  dorsolateral  part  of  the  tegmentum  as 

ar  as  the  superior  colliculus  and  a  few  pass  to  the  thalamus.    They  probably  form 
rt  of  the  sensory  or  higher  reflex  path. 

The  posterior  root  fibers  conducting  impulses  of  pain  and  temperature  probably 
rminate  in  the  posterior  column  or  the  intermediate  region  of  the  gray  matter 
soon  after  they  enter  the  spinal  cord.  The  neurons  of  the  second  order  are  supposed 
to  pass  through  the  anterior  commissure  to  the  superficial  antero-lateral  fasciculus 
(tract  of  Gowers)  and  pass  upward  in  that  portion  of  it  known  as  the  lateral  spino- 
thalamic fasciculus.  This  fasciculus  lies  along  the  medial  side  of  the  ventral  spino- 
cerebellar fasciculus.  It  is  stated  by  some  authors  that  the  pain  fibers  pass  upward 
in  the  antero-lateral  ground  bundles.  In  some  of  the  lower  mammals  this  pathway 
carries  the  pain  fibers  upward  by  a  series  of  neurons  some  of  which  cross  to  the 
opposite  side,  so  that  in  part  there  is  a  double  path.  In  man,  however,  the  lateral 
spinot  .alamic  fasciculus  is  probably  the  most  important  pathway.  On  reaching  the 
meduila  these  fibers  continue  upward  through  the  formatio  reticularis  in  the  neigh- 
borhood of  the  median  fillet  to  the  thalamus,  probably  its  ventro-lateral  region. 
\Yhether  higher  neurons  convey  the  pain  impulses  to  the  cortex  through  the  internal 
capsule  is  uncertain.  The  pathway  is  probably  more  complex  and  Head  is  of  the 
opinion  that  our  sensations  of  pain  are  essentially  thalamic.  The  pain  and  temper- 
ature pathways  in  the  lateral  spinothalamic  fasciculus  are  not  so  closely  inter- 
ingled  but  that  one  can  be  destroyed  without  injury  to  the  other. 
Ransom  suggests  that  the  non-medullated  fibers  of  the  posterior  roots,  which 

urn  into  Lissauer's  tract  and  ascend  or  descend  for  short  distances  not  exceeding 
one  or  two  segments  and  finally  end  in  the  substantia  gelatinosa,  are  in  part  at 
least  pain  fibers  and  that  the  fasciculus  of  Lissauer  and  the  substantia  gelatinosa 
represent  part  of  the  mechanism  for  reflexes  associated  with  pain  conduction  and 
reception  while  the  fibers  to  the  higher  centers  pass  up  in  the  spinothalamic  tract. 


I 


ir 


I 


854  NEUROLOGY 


I 


The  fibers  of  tactile  discrimination,  according  to  Head  and  Thompson,  pass  up  in 
the  fasciculus  cuneatus  and  fasciculus  gracilis  of  the  same  side  and  follow  the  pa~h 
of  the  muscle-sense  fibers.  The  axons  of  the  second  order  arising  in  the  nucleus 
cuneatus  and  gracilis  cross  with  the  internal  arcuate  fibers  and  ascend  to  the  thalamus 
with  the  medial  lemniscus,  thence  by  neurons  of  higher  order  the  impulses  are  carrit;d 
to  the  somatic  sensory  area  of  the  cortex  through  the  internal  capsule.  The  other 
touch  fibers,  shortly  after  entering  the  spinal  cord,  terminate  in  the  dorsal  colunm 
or  intermediate  gray  matter.  Neurons  of  the  second  order  send  their  axons  through 
the  anterior  commissure  to  pass  upward  in  the  antero-lateral  funiculus  probably 
in  the  ventral  spinothalamic  fasciculus.  In  the  medulla  they  join  or  pass  upwai'd 
in  the  neighborhood  of  the  medial  lemniscus  to  the  thalamus  and  thence  by  neurons 
of  higher  order  to  the  somatic  sensory  area  of  the  cortex. 

The  remaining  ascending  fasciculi  form  a  part  of  the  complex  known  as  the  super- 
ficial antero-lateral  fasciculus  {tract  of  Gowers).  The  spinotectal  fasciculus,  as  its 
name  indicates,  is  supposed  to  have  its  origin  in  the  gray  matter  of  the  cord  and 
terminations  in  the  superior  and  inferior  (?)  colliculi  of  the  mid-brain  serving  for 
reflexes  between  the  cord  and  the  visceral  and  auditory  centers  of  the  mid-brain. 

The  spino-olivary  fasciculus  {olivospinal;  bulbospinal,  Helweg's  bundle)  is  likewise 
of  unknown  constitution  and  function;  there  is  uncertainty  even  in  regard  to  the 
direction  of  its  fibers. 

Sympathetic  afferent  fibers  {visceral  afferent;  viscerosensory;  splanchnic  afferent) 
enter  the  spinal  cord  by  the  posterior  roots  of  the  thoracic  and  first  two  or  three 
lumbar  nerves  and  the  second  to  the  fourth  sacral  nerves.  The  fibers  pass  to  these 
nerves  from  the  peripheral  sympathetic  system  through  the  white  rami  communi- 
cantes.  Some  of  the  cell  bodies  of  these  aft'erent  fibers  are  located  in  the  spinal 
ganglia  and  others  are  in  the  sympathetic  ganglia.  Some  of  the  afferent  sj-mpa- 
thetic  fibers  end  about  the  cell  bodies  of  somatic  sensory  neurons  and  visceral 
impulses  are  thus  transmitted  to  these  neurons  which  conduct  them  as  well  as  their 
own  special  impulses  to  the  spinal  cord.  Other  sympathetic  afferent  neurons 
whose  cell  bodies  are  located  in  the  spinal  ganglia  send  collaterals  to  neighboring 
cells  of  somatic  sensory  neurons  and  thus  have  a  double  path  of  transmission  to 
the  spinal  cord.  Such  an  arrangement  provides  a  mechanism  for  some  of  the 
referred  pains. 

These  sympathetic  afferent  fibers  presumably  divide  on  entering  the  spinal  cord 
into  ascending  and  descending  branches.  Their  distribution  and  termination 
within  the  spinal  cord  are  unknown.  Some  of  them  probably  eventually  come  into 
relation  with  the  sympathetic  efferent  fibers  whose  cell  bodies  are  located  in  the 
lateral  column.  Our  knowledge  concerning  both  the  termination  and  origin  of 
these  fibers  is  very  unsatisfactory. 

The  S3rmpathetic  efferent  fibers  {splanchnic  motor;  viscero-motor;  preganglionic  fibers) 
are  supposed  to  arise  from  cells  in  the  intermediate  zone  between  the  dorsal 
and  ventral  gray  columns  and  in  the  intermedio-lateral  column  at  the  margin  of 
the  lateral  column.  These  preganglionic  sjTnpathetic  fibers  are  not  distributed 
throughout  the  entire  series  of  spinal  nerves  but  are  confined  to  two  groups,  the 
thoraco-lumbar  from  the  first  thoracic  to  the  second  or  third  lumbar  nerves  and 
the  sacral  group  from  the  second  to  the  fourth  sacral  nerves.  They  pass  out  with 
the  anterior  root  fibers  and  through  the  rami  communicantes  to  end  in  sympathetic 
ganglia.  The  impulses  are  distributed  from  cells  in  these  ganglia  through  post- 
ganglionic fibers  to  the  smooth  muscles  and  glands.  The  thoraco-lumbar  outflow 
and  the  sacral  outflow  form  two  distinct  functional  groups  which  are  considered 
more  fully  under  the  sympathetic  system. 


p 


COMPOSITION  AND  CENTRAL   CONNECTIONS  OF   CRANIAL  NERVES    855 

COMPOSITION    AND   CENTRAL   CONNECTIONS    OF    THE   CRANIAL   NERVES. 

The  cranial  nerves  are  more  varied  in  their  composition  than  the  spinal  nerves. 
Some,  for  example,  contain  somatic  motor  fibers  only,  others  contain  the  various 
types  of  fibers  found  in  the  spinal  nerves,  namely,  somatic  motor,  sjTiipathetic 
efferent,  somatic  sensory  and  sympathetic  sensory.  In  addition  there  are  included 
the  nerves  of  the  special  senses,  namely,  the  nerves  of  smell,  sight,  hearing,  equili- 
bration and  taste. 

The  Hypoglossal  Nerve  (XII  cranial)  consists  of  somatic  motor  fibers  only  and 
supplies  the  muscles  .of  the  tongue.  Its  axons  arise  from  cells  in  the  hypoglossal 
nucleus  and  pass  forward  between  the  white  reticular  formation  and  the  gray 
reticular  formation  to  emerge  from  the  antero-lateral  sulcus  of  the  medulla.  The 
hypoglossal  nuclei  of  the  two  sides  are  connected  by  many  commissural  fibers  and 
also  by  dendrites  of  motor  cells  which  extend  across  the  midline  to  the  opposite 
nucleus.  The  hypoglossal  nucleus  receives  either  directly  or  indirectly  numerous 
collaterals  and  terminals  from  the  opposite  p^Tamidal  tract  (cortico-bulbar  or  cerebro- 
bulbar  fibers)  which  convey  voluntary  motor  impulses  from  the  cerebral  cortex. 
Many  reflex  collaterals  enter  the  nucleus  from  the  secondary  sensory  paths  of  the 
trigeminal  and  vagus  and  probably  also  from  the  nervus  intermedius  and  the  glosso- 
pharyngeal. Collaterals  from  the  posterior  longitudinal  bundle  and  the  ventral 
longitudinal  bundle  are  said  to  pass  to  the  nucleus. 

The  Accessory  Nerve  ( XI  cranial)  contains  somatic  motor  fibers.  The  spinal  part 
arises  from  lateral  cell  groups  in  the  anterior  column  near  its  dorso-lateral  margin  in 
the  upper  five  or  six  segments  of  the  cord,  its  roots  pass  through  the  lateral  funiculus 
to  the  lateral  surface  of  the  cord.  It  supplies  the  Trapezius  and  Sternocleido- 
mastoideus.  The  cranial  part  arises  from  the  nucleus  ambiguus,  the  continuation  in 
the  medulla  oblongata  of  the  lateral  cell  groups  of  the  anterior  column  of  the  spinal 
cord  from  which  the  spinal  part  has  origin.  The  upper  part  of  the  nucleus  ambiguus 
gives  motor  fibers  to  the  vagus  and  glossopharyngeal  nerves.  The  cranial  part 
sends  it  fibers  through  the  vagus  to  the  laryngeal  nerves  to  supply  the  muscles  of 
the  larynx.  The  root  fibers  of  the  cranial  part  of  the  accessory  nerve  pass  anterior 
to  the  spinal  tract  of  the  trigeminal  while  those  of  the  vagus  pass  through  or  dorsal 
to  the  trigeminal  root,  and  emerge  in  the  line  of  the  postero-lateral  sulcus.  The 
nucleus  of  origin  of  the  spinal  part  undoubtedly  receives  either  directly  or  indirectly 
terminals  and  collaterals  controlling  voluntary  movements  from  the  pyramidal 
tracts.  It  is  probable  that  terminals  and  collaterals  reach  the  nucleus  either  directly 
or  indirectly  from  the  rubrospinal  and  the  vestibulospinal  tracts.  It  is  also  con- 
nected indirectly  with  the  spinal  somatic  sensory  nerves  by  association  fibers  of  the 
proper  fasciculi.  The  cranial  part  receives  indirectly  or  directly  terminals  and  col- 
laterals from  the  opposite  pjTamidal  tract  and  form  the  terminal  sensory  nuclei  of 
the  cranial  nerves.  A  few  fibers  of  the  cranial  part  are  said  to  arise  in  the  dorsal 
nucleus  of  the  vagus  and  are  thus  s\Tnpathetic  efferent.  They  are  said  to  join  the 
vagus  nerve. 

The  Vagus  Nerve  (A'  cranial)  contains  somatic  sensory,  sympathetic  afferent, 
somatic  motor,  sj-mpathetic  efferent  and  (taste  fibers?) .  The  afferent  fibers  (somatic 
sensory,  sympathetic,  and  taste)  have  their  cells  of  origin  in  the  jugular  ganglion 
and  in  the  nodosal  ganglion  (ganglion  of  the  trunk)  and  on  entering  the  medulla 
divide  into  ascending  and  descending  branches  as  do  the  sensory  fibers  of  the  pos- 
terior roots  of  the  spinal  nerves  after  they  enter  the  spinal  cord. 

(1)  The  somatic  sensory  fibers  are  few  in  number,  convey  impulses  from  a  limited 
area  of  the  skin  on  the  back  of  the  ear  and  posterior  part  of  the  external  auditory 
meatus,  and  probably  join  the  spinal  tract  of  the  trigeminal  nerve  to  terminate  in 

»its  nucleus.     Connections  are  probably  established  through  the  central  path  of 
the  trigeminal  with  the  thalamus  and  somatic  sensory  area  of  the  cortex  for  the 


^ 


856  NEUROLOGY 


I 


conscious  recognition  of  impulses.  The  descending  fibers  in  the  spinal  tract  of  the 
trigeminal  terminating  in  the  nucleus  of  the  tract  probably  establish  relations 
through  connecting  neurons  with  motor  nuclei  in  the  anterior  column  of  the  spin;il 
cord  and  with  motor  nuclei  of  the  medulla. 

(2)  The  sympathetic  afferent  fibers  are  usually  described  as  terminating  in  the 
dorsal  nucleus  of  the  vagus  and  glossopharyngeal.  Some  authors,  however,  believe 
they  join  the  tractus  solitarius  and  terminate  in  its  nucleus.  These  afferent  fibers 
convey  impulses  from  the  heart,  the  pancreas,  and  probably  from  the  stomach, 
esophagus  and  respiratory  tract.  Their  terminals  in  the  dorsal  nucleus  come  into 
relation  with  neurons  whose  axons  probably  descend  into  the  spinal  cord,  conveying 
impulses  to  the  motor  nuclei  supplying  fibers  to  the  muscles  of  respiration,  i.  e., 
the  phrenic  nerve  and  the  nerves  to  the  intercostal  and  levatores  costarum  muscles. 
Other  axons  probably  convey  vasomotor  impulses  to  certain  sympathetic  efferent 
neurons  throughout  the  spinal  cord.  The  dorsal  nucleus  (nucleus  of  the  ala  cinerea) 
and  the  posterior  continuation  of  it  into  the  commissural  nucleus  of  the  ala  cinerea 
constitute  probably  the  so-called  respiratory  and  vaso-motor  center  of  the  medulla. 
The  shorter  reflex  neurons  of  the  dorsal  nucleus  probably  eft'ect  connections 
either  directly  or  indirectly  with  motor  cells  of  the  vagus  itself  and  other  cranial 
nerves. 

(3)  Taste  fibers  conducting  impulses  from  the  epiglottis  and  larynx  are  supposed 
to  pass  in  the  vagus  and  to  join  the  tractus  solitarius,  finally  terminating  in  the 
nucleus  of  the  tractus  solitarius.  It  is  not  certain  that  this  nucleus  represents  the 
primary  terminal  center  for  taste  and  some  authors  maintain  that  the  taste  fibers 
terminate  in  the  dorsal  nucleus.  The  secondary  ascending  pathways  from  the 
primary  gustatory  nucleus  to  the  cortex  as  well  as  the  location  of  the  cortical 
center  for  taste  are  unknown.  A  gustatory  center  has  been  described  near  the  ante- 
rior end  of  the  temporal  lobe.  The  nucleus  of  the  tractus  solitarius  is  connected 
with  motor  centers  of  the  pons,  medulla  and  spinal  cord  for  the  reactions  of  mastica- 
tion and  swallowing. 

(4)  Somatic  motor  fibers  to  the  cross  striated  muscles  of  the  pharynx  and  larynx 
arise  in  the  nucleus  ambiguus.  This  nucleus  undoubtedly  receives  either  directly 
or  indirectly  collaterals  or  terminals  from  the  opposite  pyramidal  tract  controlling 
the  voluntary  movements  of  the  pharynx  and  larynx.  The  reflex  pathways  con- 
veying impulses  from  the  terminal  sensory  nuclei  are  unknown,  but  probably  form 
part  of  the  intricate  maze  of  fibers  constituting  the  reticular  formation. 

(5)  Sympathetic  efferent  fibers  arise  from  cells  in  the  dorsal  nucleus  (nucleus  of 
the  ala  cinerea).  These  are  preganglionic  fibers  of  the  sympathetic  system  and  all 
terminate  in  sympathetic  ganglia  from  which  postganglionic  fibers  are  distributed  to 
various  organs,  i.  e.,  motor  fibers  to  the  esophagus,  stomach,  small  intestine,  gall- 
bladder, and  to  the  lungs;  inhibitory  fibers  to  the  heart;  secretory  fibers  to  the 
stomach  and  pancreas.  The  dorsal  nucleus  not  only  receives  terminals  of  sym- 
pathetic afferent  fibers  for  reflexes  but  undoubtedly  receives  terminals  and  collaterals 
from  many  other  sources,  but  the  exact  pathways  are  at  present  unknown. 

The  Glossopharyngeal  Nerve  {IX  cranial)  is  similar  to  the  vagus  nerve  as  regards 
its  central  connections  and  is  usually  described  with  it.  It  contains  somatic  sensory, 
sympathetic  afferent,  taste,  somatic  motor  and  sympathetic  efferent  fibers.  The 
afferent  sensory  fibers  arise  from  cells  in  the  superior  ganglion  and  in  the  petrosal 
ganglion.  The  same  uncertainty  exists  concerning  the  nuclei  of  termination  and 
nuclei  of  origin  of  the  various  components  as  for  the  vagus. 

(1)  The  somatic  sensory  fibers  are  few  in  number.  Some  are  distributed  with 
the  auricular  branch  of  the  vagus  to  the  external  ear;  others  probably  pass  to  the 
pharynx  and  fauces.  They  are  supposed  to  join  the  spinal  tract  of  the  trigeminal 
and  terminate  in  its  nucleus.  The  connections  are  similar  to  those  of  the  somatic 
sensory  fibers  of  the  vagus. 


COMPOSITION  AND  CENTRAL  CONNECTIONS  OF  CRANIAL   NERVES    857 


I 


(2)  Ssrmpathetic  afferent  fibers  from  the  pharynx  and  middle  ear  are  supposed  to 
terminate  in  the  dorsal  nucleus.  Connections  are  probably  established  with  motor 
nuclei  concerned  in  chewing  and  swallowing;  ^■ery  little  is  known,  however,  about 
|Jie  connections  with  other  parts  of  the  brain. 

*  (3)  Taste  fibers  from  the  tongue  probably  terminate  in  the  nucleus  of  the  tractus 
solitarius.  These  fibers  together  with  similar  fibers  from  the  facial  (nervus  inter- 
medins) and  the  vagus  are  supposed  to  form  the  tractus  solitarius  and  terminate 
in  its  nucleus.  The  central  connections  have  been  considered  under  the  ^'agus. 
\  (4)  Somatic  motor  fibers  to  the  Stylopharyngeus  muscle  arise  in  the  upper  end 
of  the  nucleus  ambiguus.  The  existence  of  these  fibers  in  the  roots  of  the  glosso- 
pharyngeal is  uncertain,  as  there  are  other  paths  by  which  such  fibers  might  reach 
the  glossopharyngeal  from  the  \-agus.  The  sources  of  impulses  passing  to  the 
nucleus  ambiguus  are  considered  under  the  vagus. 

(5)  Sympathetic  efferent  fibers  {motor  and  secretory  fibers)  arise  from  the  nucleus 
dorsalis.  Some  authors  believe  that  the  secretory  fibers  to  the  parotid  gland  arise 
from  a  distinct  nucleus,  the  inferior  salivatory  nucleus,  situated  near  the  dorsal 

Fucleus.    The  preganglionic  fibers  from  this  nucleus  terminate  in  the  otic  ganglion; 
le  postganglionic  fibers  from  the  otic  ganglion  pass  to  the  parotid  gland. 
The  Acoustic  Nerve  {VIII  cranial)  consists  of  two  distinct  nerves  the  cochlear 
nerve,  the  nerve  of  hearing,  and  the  vestibular  nerve,  the  nerve  of  equilibration. 


6    14 


...A 


— _:wi.5 


Fia.  760. — Terminal  nuclei  of  the  cochlear  nerve,  with  their  upper  coanectiona.  (Schematic.)  The  vestibular 
nerve  with  it3  terminal  nuclei  and  their  efferent  fibers  have  been  suppressed.  On  the  other  hand,  in  order  not  to 
obscure  the  trapezoid  body,  the  efferent  fibers  of  the  terminal  nuclei  on  the  right  side  have  been  resected  in  a  consid- 
erable portion  of  their  extent.  The  trapezoid  body,  therefore,  shows  only  one-half  of  its  fibers,  viz.,  those  which 
come  from  the  left.  1.  Vestibular  nerve,  divided  at  its  entrance  into  the  medulla  oblongata.  2.  Cochlear  nerve.  3. 
Accessory  nucleus  of  acoustic  nerve.  4.  Tubenulum  acusticum.  5.  Efferent  fibers  of  accessory  nucleus.  6.  Efferent 
fibers  of  tubercuhini  acusticum,  forming  the  striae  medullares,  with  6',  their  direct  bundle  going  to  the  superior 
olivary  nucleus  of  the  same  side;  6",  their  decussating  bundles  going  to  the  superior  olivary  nucleus  of  the  opposite 
side.  7.  Superior  olivary  nucleus.  8.  Trapezoid  body.  9.  Trapezoid  nucleus.  10.  Central  acoustic  tract  (lateral 
lemniscus).     11.  Raph6.     12.  Cerebrospinal  fasciculus.    13.  Fourth  ventricle.    14.  Inferior  peduncle.     (Testut.) 

Hi  The  Cochlear  Nerve  arises  from  bipolar  cells  in  the  spiral  ganglion  of  the  cochlea; 
the  peripheral  fibers  end  in  the  organ  of  Corti,  the  central  fibers  bifurcate  as  they 
enter  the  cochlear  nucleus ;  the  short  ascending  branches  end  in  the  ventral  portion 
of  the  nucleus,  the  longer  descending  branches  terminate  in  the  dorsal  portion  of 

■  the  nucleus.  From  the  dorsal  portion  of  the  cochlear  nucleus  axons  arise  which 
^ass  across  the  dorsal  aspect  of  the  inferior  peduncle  and  the  floor  of  the  fourth 
A'entricle,  the  striae  medullares,  to  the  median  sulcus.  Here  they  dip  into  the  sub- 
stance of  the  pons,  cross  the  median  plane,  and  join  the  lateral  lemniscus.    Some 


I 


858  NEUROLOGY 

of  the  fibers  terminate  in  the  superior  oh  vary  nucleus.  The  fibers  of  the  striae 
meduHares  are  not  always  visible  on  the  floor  of  the  rhomboid  fossa.  From  the 
ventral  portion  of  the  cochlear  nucleus  axons  pass  into  the  trapezoid  body,  here 
some  of  them  end  in  the  superior  olivary  nucleus  of  the  same  side,  others  cross  the 
midline  and  end  in  the  superior  olivary  nucleus  of  the  opposite  side  or  pass  by  these 
nuclei,  giving  off  collaterals  to  them,  and  join  the  lateral  lemniscus.  Other  fibers 
either  terminate  in  or  give  off  collaterals  to  the  nucleus  of  the  trapezoid  body  of 
the  same  or  the  opposite  side.  Other  fibers  from  the  ventral  portion  of  the  cochlear 
nucleus  pass  dorsal  to  the  inferior  peduncle  and  then  dip  into  the  substance  of  tlie 
pons  to  join  the  trapezoid  body  or  the  superior  olivary  nucleus  of  the  same  side. 
From  the  superior  olivary  nucleus  of  the  same  and  opposite  sides  axons  join  the 
lateral  lemniscus.  Collaterals  and  probably  terminals  also  pass  from  the  lateral 
lemniscus  to  other  nuclei  in  its  path  and  receive  in  turn  axons  from  these  nuclei. 
They  are  the  accessory  nucleus,  the  medial  preolivary  nucleus,  the  lateral  pre- 
olivary  or  semilunar  nucleus  and  the  nucleus  of  the  lateral  lemniscus. 

The  trapezoid  body  consists  of  horizontal  fibers  in  the  ventral  part  of  the  formatia 
reticularis  of  the  lower  part  of  the  pons  behind  its  deep  transverse  fibers  and  the 
pyramid  bundles.  The  axons  come  from  the  dorsal  and  ventral  portions  of  the 
cochlear  nucleus.  After  crossing  the  raphe,  where  they  decussate  with  those  from 
the  opposite  side,  they  turn  upward  to  form  the  lateral  lemniscus.  Fibers  from  the 
striae  medullares  contribute  to  the  trapezoid  body,  in  addition  it  sends  terminals 
or  collaterals  to  and  receives  axons  from  the  superior  olivary  nucleus,  the  nucleus 
of  the  trapezoid  body,  the  lateral  preolivary  or  semilunar  nucleus  and  the  mesial 
preolivary  nucleus. 

The  cochlear  nucleus,  the  terminal  nucleus  for  the  nerve  of  hearing,  is  usually 
described  as  consisting  of  a  larger  dorsal  nucleus  on  the  dorsal  and  lateral  aspect  of 
the  inferior  peduncle  forming  a  prominent  projection,  the  acoustic  tubercle,  and  a 
ventral  or  accessory  cochlear  nucleus  more  ventral  to  the  inferior  peduncle.  The 
two  nuclei  are  continuous  and  are  merely  portions  of  one  large  nucleus.  The  axons 
from  cells  of  the  spiral  ganglion  of  the  cochlear  nerve  on  reaching  the  nucleus 
divide  into  ascending  and  descending  branches  which  enter  the  ventral  and  dorsal 
nuclei  respectively.  Axons  from  the  large  fusiform  cells  of  the  dorsal  nucleus  pass 
partly  by  way  of  the  striae  medullares  to  the  trapezoid  body  and  lateral  lemniscus 
and  the  nuclei  associated  with  the  former,  and  partly  transversely  beneath  the 
inferior  peduncle  and  spinal  tract  of  the  trigeminal  to  the  trapezoid  body.  Axons 
from  the  ventral  cochlear  nucleus  pass  partly  by  the  striae  medullares  but  for  the 
most  part  horizontally  to  the  trapezoid  body. 

The  superior  olivary  nucleus  is  a  small  mass  of  gray  matter  situated  on  the  dorsal 
surface  of  the  lateral  part  of  the  trapezoid  body.  Some  of  its  axons  pass  backward 
to  the  abducent  nucleus,  this  bundle  is  known  as  the  peduncle  of  the  superior 
olivary  nucleus.  Other  fibers  from  the  nucleus  join  the  posterior  longitudinal 
bundle  and  terminate  in  the  nuclei  of  the  trochlear  and  oculomotor  nerves.  The 
majority  of  its  axons,  after  giving  off  collaterals  to  the  nucleus  itself  join  the  lateral 
lemniscus  of  the  same  side,  other  axons  pass  in  the  trapezoid  body  toward  the  ven- 
tral portion  of  the  cochlear  nucleus. 

The  nucleus  of  the  trapezoid  body  lies  between  the  root  fibers  of  the  abducent  nerve 
and  the  superior  olivary  nucleus.  Its  cells  lie  among  the  fibers  of  the  trapezoid 
body.  In  it  terminate  fibers  and  collaterals  of  the  trapezoid  body  which  come 
from  the  cochlear  nucleus  of  the  opposite  and  probably  the  same  side  and  from  the 
opposite  trapezoid  nucleus.  They  terminate  in  the  nucleus  of  the  trapezoid  body 
in  diffuse  arborizations  and  peculiar  end  plaques  or  acoustic  calyces  of  yellowish 
color  which  fuse  with  the  cell  bodies.  Its  cells  are  round  and  of  medium  size ;  their 
axons  pass  into  the  trapezoid  body,  cross  the  median  line  and  probably  join  the 
lateral  fillet. 


COMPOSITION  AND  CENTRAL  CONNECTIONS  OF  CRANIAL  NERVES    859 


l.._._ 

^H  nucleus.     In  it  end  terminals  and  collaterals  of  the  trapezoid  body  and  probably 

^H  fibers  of  the  opposite  cochlear  nucleus.     Its  axons  mingle  with  the  trapezoid  body 

^H  and  join  the  lateral  fillet. 

^H     The  mesial  preolivary  nucleus  is  in  contact  with  the  ventral  side  of  the  nucleus 

^f  of  the  trapezoid  body.    It  receives  many  collaterals  from  the  trapezoid  body.    Its 

''        cells  are  smaller  than  those  of  the  trapezoid  nucleus,  their  axons  join  the  lateral 

r       fillet. 

^B     The  lateral  lemniscus  {lateral  fillet),  the  continuation  upward  of  the  central  path 

^H  of  hearing,  consists  of  fibers  which  come  from  the  cochlear  nuclei  of  the  same  and 

^P  the  opposite  side  by  way  of  the  trapezoid  body  and  from  the  preolivary  nuclei.    It 

^       lies  in  the  ventral  or  ventro-lateral  part  of  the  reticular  formation  of  the  pons,  at 

)  first  ventral  then  lateral  to  the  median  fillet.  Above  the  pons  these  ascending  fibers 
^come  to  the  surface  at  the  side  of  the  reticular  formation  in  the  trigonum  lemnisci 
fand  are  coxered  by  a  layer  of  ependyma.  This  part  of  the  lateral  lemniscus  is 
'known  as  the  fillet  of  Reil,  On  reaching  the  level  of  the  inferior  colliculus  the  dorsal 
fibers  which  overlie  the  superior  peduncle  decussate  in  the  velum  medullare  anterius 
with  similar  fibers  of  the  opposite  side.  Numerous  small  masses  of  cells  are  scattered 
along  the  path  of  the  lateral  lemniscus  above  the  superior  olivary  nucleus  and  con- 
stitute lower  and  upper  nuclei  of  the  lateral  lemniscus.  They  are  supplied  with 
many  collaterals  and  possibly  terminals  from  the  fibers  of  the  lemniscus.  The  axons 
of  the  lower  nucleus  of  the  lateral  lemniscus,  which  arise  from  the  larger  stellate  or 
spindle-shaped  cells,  with  long,  smooth,  much  branched  dendrites,  are  said  by  some 
authors  to  join  the  lateral  lemniscus,  but  according  to  Cajal  they  pass  medially 
toward  the  raphe;  their  termination  is  unknoAvn.  The  cells  of  the  upper  nucleus 
of  the  lateral  lemniscus  are  more  scattered.  The  same  uncertainty  exists  in  regard 
to  their  termination. 

The  fibers  of  the  lateral  lemniscus  end  by  terminals  or  collaterals  in  the  inferior 
colliculus  and  the  medial  geniculate  body.  A  few  of  the  fibers  are  said  to  pass  by 
the  inferior  colliculus  to  terminate  in  the  middle  portion  of  the  stratum  griseum  of 
the  superior  colliculus,  and  are  probably  concerned  with  reflex  movements  of  the 
eyes  depending  on  acoustic  stimuli. 

The  inferior  colliculi  (lower  or  posterior  qiiadrigeminal  bodies)  are  important 
auditory  reflex  centers.  Each  consists  of  a  compact  nucleus  of  gray  matter  covered 
by  a  superficial  white  layer  and  separated  from  the  central  gray  matter  about 
the  aqueduct  by  a  thin,  deep,  white  layer.  Many  of  the  axons  which  appear  in  the 
superficial  white  layer  ascend  through  the  inferior  brachium  to  the  medial  genicu- 
late body.  Others  mainly  from  large  cells  in  the  dorso-mesial  part  of  the  nucleus 
pass  through  the  deep  white  layer  into  the  tegmentum  of  the  same  and  the  opposite 
side  and  descend.  Their  termination  is  unknown,  but  they  probably  constitute  an 
auditory  reflex  path  to  the  lower  motor  centers,  perhaps  descending  into  the  spinal 
cord  with  the  tectospinal  fasciculus.  Other  axons  are  said  to  descend  in  the  lateral 
lemniscus  to  the  various  nuclei  in  the  auditory  path  (Held)  and  probably  to  motor 
nuclei  of  the  medulla  and  spinal  cord. 
Hb  The  medial  geniculate  body  receives  terminals  and  collaterals  from  the  lateral 
^•lemniscus  (the  central  auditory  path)  and  also  large  numbers  of  axons  from  the 
inferior  colliculus  of  the  same  side  and  a  few  from  the  opposite  side.  It  is  thus  a 
station  in  the  central  auditory  path.  A  large  proportion  of  its  axons  pass  forward 
beneath  the  optic  tract  to  join  the  corona  radiata  and  then  sweep  backward  and 
lateralward  as  the  auditory  radiation  to  terminate  in  the  cortex  of  the  superior 
temporal  gyrus.  V.  Monakow  holds  that  Golgi  cells  type  II  are  interpolated  between 
the  terminations  of  the  incoming  fibers  to  the  medial  geniculate  body  and  the  cells 
located  there  which  give  rise  to  the  fibers  of  the  auditory  radiation.  The  medial 
geniculate  bodies  are  united  by  the  long,  slender  commissure  of  Gudden.    These 


I 


860 


NEUROLOGY 


I 


J 


fibers  join  the  optic  tract  as  it  passes  over  the  edge  of  the  medial  geniculate  ard 
passes  through  the  posterior  part  of  the  optic  chiasma.  It  is  probablj'  a  commissure 
connected  with  the  auditory  system. 

The  Vestibular  Nerve  {vestibular  root,  VIII  cranial)  arise  from  the  bipolar  cells 
in  the  vestibular  ganglion  (Scarpa's  ganglion).  The  peripheral  fibers  end  in  the 
semicircular  canals,  the  saccule  and  the  utricle,  the  end-organs  concerned  with 
mechanism  for  the  maintenance  of  bodily  equilibrium.  The  central  fibers  ent(;r 
the  medulla  oblongata  and  pass  between  the  inferior  peduncle  and  the  spinal  tra(;t 
of  the  trigeminal.  They  bifurcate  into  ascending  and  descending  branches  as  do 
the  dorsal  root  fibers  of  all  the  spinal  nerves  and  all  afferent  cranial  nerves.  The 
descending  branches  terminate  in  the  dorsal  (medial)  vestibular  nucleus,  the 
principal  nucleus  of  the  vestibular  nerve.  This  nucleus  is  prolonged  downward 
into  a  descending  portion  in  which  end  terminals  and  collaterals  of  the  descending 
branch.    The  ascending  branches  pass  to  Deiters's  nucleus,  to  Bechterew's  nucleus 

and  through  the  inferior  peduncle 
c  of  the  cerebellum  to  the  nucleus 

tecti  of  the  opposite  side. 

The  dorsal  vestibular  nucleus 
(medial  or  principal  nucleus)  is  a 
large  mass  of  small  cells  in  the 
floor  of  the  fourth  ventricle  under 
the  area  acustica,  located  partly 
in  the  medulla  and  partly  in  the 
pons.  The  striae  medullares  cross 
the  upper  part  of  it.  It  is  sepa- 
rated from  the  median  plane  by 
the  nucleus  intercalatus.  Its  axons 
pass  into  the  posterior  longitudi- 
nal bundle  of  the  same  and  the 
opposite  side  and  ascend  to  ter- 
minate in  the  nucleus  abducens 
of  the  same  side  and  in  the  troch- 
lear nucleus  and  the  oculo-motor 
nucleus  of  the  opposite  side,  and 
to  the  motor  nuclei  of  the  trigem- 
inal on  both  sides.  The  descending 
portion,  the  nucleus  of  the  descend- 
ing tract  extends  downward  as  far  as  the  upper  end  of  the  nucleus  gracilis,  and  the 
decussation  of  the  medial  lemniscus.  It  is  sometimes  called  the  inferior  vestibulax 
nucleus.  Many  of  its  axons  cross  the  midline  and  probably  ascend  with  the  medial 
lemniscus  to  the  ventro-lateral  region  of  the  thalamus. 

The  lateral  vestibular  nucleus  (Deiters's  nucleus)  is  the  continuation  upward  and 
lateralward  of  the  principal  nucleus,  and  in  it  terminate  many  of  the  ascending 
branches  of  the  vestibular  nerve.  It  consists  of  very  large  multipolar  cells  whose 
axons  form  an  important  part  of  the  posterior  longitudinal  bundle  of  the  same  and 
the  opposite  sids.  The  axons  bifurcate  as  they  enter  the  posterior  longitudinal 
bundle,  the  ascending  branches  send  terminals  and  collaterals  to  the  motor  nuclei 
of  the  abducens,  trochlear  and  oculomotor  nerves,  and  are  concerned  in  coordinating 
the  movements  of  the  eyes  wath  alterations  in  the  position  of  the  head ;  the  descending 
branches  pass  down  in  the  posterior  longitudinal  bundle  into  the  anterior  funiculus 
of  the  spinal  cord  as  the  vestibulospinal  fasciculus  (anterior  marginal  bundle)  and 
are  distributed  to  motor  nuclei  of  the  anterior  column  by  terminals  and  collaterals. 
Other  fibers  are  said  to  pass  directly  to  the  vestibulospinal  fasciculus  without 
passing  into  the  posterior  longitudinal  bundle.     The  fibers  which  pass  into  the 


P^G.  761. — Terminal  nuclei  of  the  vestibular  nerve,  with  their 
upper  connections.  (Schematic.)  1.  Cochlear  nerve,  with  its 
two  nuclei.  2.  Accessory  nucleus.  3.  Tuberculum  acusticum. 
4.  Vestibular  nerve.  5.  Internal  nucleus.  6.  Nucleus  of  Deiters. 
7.  Nucleus  of  Bechterew.  8.  Inferior  or  descending  root  of 
acoustic.  9.  Ascending  cerebellar  fibers.  10.  Fibers  going  to 
raph6.  11.  Fibers  taking  an  oblique  course.  12.  Lemniscus.  13. 
Inferior  sensory  root  of  trigeminal.  14.  Cerebrospinal  fasciculus. 
15.  Raph6.  16.  Fourth  ventricle.  17.  Inferior  peduncle.  Origin 
of  striae  medullares.     (Testut.) 


I 


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i 


COMPOSITION  AND  CENTRAL  CONNECTIONS  OF  CRANIAL   NERVES    861 

N'estibulospinal  fasciculus  are  intimately  concerned  with  equilibratory  reflexes. 
Other  axons  from  Deiters's  nucleus  are  supposed  to  cross  and  ascend  in  the  opposite 
medial  lemniscus  to  the  ventro-lateral  nuclei  of  the  thalamus ;  still  other  fibers  pass 
into  the  cerebellum  with  the  inferior  peduncle  and  are  distributed  to  the  cortex  of 
the  vermis  and  the  roof  nuclei  of  the  cerebellum;  according  to  Cajal  they  merely 
|)ass  through  the  nucleus  fastigii  on.  their  way  to  the  cortex  of  the  vermis  and  the 
|hemisphere. 

i  The  superior  vestibular  nucleus  {Bechterew's  nucleus)  is  the  dorso-lateral  part  of 
the  vestibular  nucleus  and  receives  collaterals  and  terminals  from  the  ascending 
branches  of  the  vestibular  nerve.  Its  axons  terminate  in  much  the  same  manner 
hs  do  those  from  the  lateral  nucleus. 

I  The  Facial  Nerve  {VII  cranial)  consists  of  somatic  sensory,  sympathetic  afferent, 
llaste,  somatic  motor  and  sympathetic  efferent  fibers.  The  afferent  or  sensory 
fibers  arise  from  cells  in  the  geniculate  ganglion.  This  portion  of  the  nerve  is  often 
described  as  the  nervus  intermedins. 

I  (1)  The  somatic  sensory  fibers  are  few  in  number  and  convey  sensory  impulses 
from  the  middle  ear  region.  Their  existence  has  not  been  fully  confirmed.  Their 
central  termination  is  likewise  uncertain,  it  is  possible  that  they  join  the  spinal 
tract  of  the  trigeminal  as  do  the  somatic  sensory  fibers  of  the  vagus  and  glosso- 
pharyngeal. 

I  (2)  The  ssrmpathetic  afferent  fibers  are  likewise  few  in  number  and  of  unknown 
lermination. 

■  (3)  Taste  fibers  convey  impulses  from  the  anterior  two-thirds  of  the  tongue  via 
the  chorda  tympani.  They  are  supposed  to  join  the  tractus  solitarius  and  termi- 
nate in  its  nucleus.  The  central  connections  of  this  nucleus  have  already  been 
considered. 

(4)  Somatic  motor  fibers,  supplying  the  muscles  derived  from  the  hyoid  arch, 
»rise  from  the  large  multipolar  cells  of  the  nucleus  of  the  facial  nerve.  This  nucleus 
is  serially  homologous  with  the  nucleus  ambiguus  and  lateral  part  of  the  anterior 
column  of  the  spinal  cord.  Voluntary  impulses  from  the  cerebral  cortex  are  con- 
veyed by  terminals  and  collaterals  of  the  pyramidal  tract  of  the  opposite  side, 
indirectly,  that  is  with  the  interpolation  of  a  connecting  neuron,  to  the  facial 
nucleus.  This  nucleus  undoubtedly  receives  many  reflex  fibers  from  various 
sources,  i.  e.,  from  the  superior  colliculus  via  the  ventral  longitudinal  bundle 
{tectospinal  fasciculus)  for  optic  reflexes;  from  the  inferior  colliculus  via  the  auditory 
reflex  path;  and  indirectly  from  the  terminal  sensory  nuclei  of  the  brain-stem. 
Through  the  posterior  longitudinal  bundle  it  is  intimately  connected  with  other 
.motor  nuclei  of  the  brain-stem. 

(5)  Sympathetic  efferent  fibers  {preganglionic  fibers)  arise  according  to  some 
"authors  from  the  small  cells  of  the  facial  nucleus,  or  according  to  others  from  a 
special  nucleus  of  cells  scattered  in  the  reticular  formation,  dorso-medial  to  the 
facial  nucleus.  This  is  sometimes  called  the  superior  salivatory  nucleus.  These 
preganglionic  fibers  are  distributed  partly  via  the  chorda  tympani  and  lingual  nerves 
to  the  submaxillary  ganglion,  thence  by  postganglionic  (vasodilator)  fibers  to  the 
submaxillary  and  sublingual  glands.  Some  of  the  preganglionic  fibers  pass  to  the 
sphenopalatine  ganglion  via  the  great  superficial  petrosal  nerve. 

k  The  Abducens  Nerve  (T'Z  cranial)  contains  somatic  motor  fibers  only  which 
Bupply  the  lateral  rectus  muscle  of  the  eye.  The  fibers  arise  from  the  nucleus  of 
Ithe  abducens  nerve  and  pass  ventrally  through  the  formatio  reticularis  of  the  pons 
to  emerge  in  the  transverse  groove  between  the  caudal  edge  of  the  pons  and  the 
p}Tamid.  The  nucleus  is  serially  homologous  with  the  nuclei  of  the  trochlear  and 
oculomotor  above  and  with  the  hypoglossal  and  medial  part  of  the  anterior  column 
of  the  spinal  cord  below.  It  is  situated  close  to  the  floor  of  the  fourth  ventricle, 
just  above  the  level  of  the  striae  medullares.    Voluntary  impulses  from  the  cerebral 


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862  iKI^KKm  NEUROLOGY 

cortex  are  conducted  by  the  pyramidal  tract  fibers  (corticopontine  fibers).  The;i 
fibers  probably  terminate  in  relation  with  association  neurons  which  control  the 
coordinated  action  of  all  the  eye  muscles.  This  association  and  coordination 
mechanism  is  interposed  between  the  terminals  and  collaterals  of  the  voluntary 
fibers  and  the  neurons  within  the  nuclei  of  origin  of  the  motor  fibers  to  the  eye 
muscles.  The  fibers  of  the  posterior  longitudinal  bundle  are  supposed  to  play  an 
important  role  in  the  coordination  of  the  movements  of  the  eyeball.  Whether  it  is 
concerned  only  with  coordinations  between  the  vestibular  apparatus  and  the  eye 
or  with  more  extensive  coordinations  is  unknown.  Many  fibers  of  the  posterior 
longitudinal  bundle  have  their  origin  in  the  terminal  nuclei  of  the  vestibular  nerve 
and  from  the  posterior  longitudinal  bundle  many  collaterals  and  terminals  are 
given  oft*  to  the  abducent  nucleus  as  well  as  to  the  trochlear  and  oculomotor  nuclei. 
The  abducens  nucleus  probably  receives  collaterals  and  terminals  from  the  ventral 
longitudinal  bundle  (tectospinal  fasciculus);  fibers  which  have  their  origin  in  the 
superior  coUiculus,  the  primary  visual  center,  and  are  concerned  with  visual  reflexes. 
Others  probably  come  from  the  reflex  auditory  center  in  the  inferior  colliculus  and 
from  other  sensory  nuclei  of  the  brain-stem. 

The  Trigeminal  Nerve  (I^  cranial)  contains  somatic  motor  and  somatic  sensory 
fibers.  The  motor  fibers  arise  in  the  motor  nucleus  of  the  trigeminal  and  pass 
ventro-laterally  through  the  pons  to  supply  the  muscles  of  mastication.  The  sensory 
fibers  arise  from  the  unipolar  cells  of  the  semilunar  ganglion;  the  peripheral  branches 
of  the  T-shaped  fibers  are  distributed  to  the  face  and  anterior  two-thirds  of  the 
head;  the  central  fibers  pass  into  the  pons  with  the  motor  root  and  bifurcate  into 
ascending  and  descending  branches  which  terminate  in  the  sensory  nuclei  of  the 
trigeminal. 

The  motor  nucleus  of  the  trigeminal  is  situated  in  the  upper  part  of  the  pons 
beneath  the  lateral  angle  of  the  fourth  ventricle.  It  is  serially  homologous  with 
the  facial  nucleus  and  the  nucleus  ambiguus  (motor  nucleus  of  the  vagus  and  glosso- 
pharyngeal) which  belong  to  the  motor  nuclei  of  the  lateral  somatic  group.  The 
axons  arise  from  large  pigmented  multipolar  cells.  The  motor  nucleus  receives 
reflex  collaterals  and  terminals,  (1)  from  the  terminal  nucleus  of  the  trigeminal  of 
the  same  and  a  few  from  the  opposite  side,  via  the  central  sensory  tract  (trigemino- 
thalamic tract) ;  (2)  from  the  mesencephalic  root  of  the  trigeminal ;  (3)  from  the 
posterior  longitudinal  bundle;  (4)  and  probably  from  fibers  in  the  formatio  reticu- 
laris. It  also  receives  collaterals  and  terminals  from  the  opposite  pyramidal  tract 
(corticopontine  fibers)  for  voluntary  movements.  There  is  probably  a  connecting 
or  association  neuron  interposed  between  these  fibers  and  the  motor  neurons. 

The  terminal  sensory  nucleus  consists  of  an  enlarged  upper  end,  the  main  sensory 
nucleus,  and  a  long  more  slender  descending  portion  which  passes  dowTi  through 
the  pons  and  medulla  to  become  continuous  with  the  dorsal  part  of  the  posterior 
column  of  the  gray  matter  especially  the  substantia  gelatinosa  of  the  spinal  cord. 
This  descending  portion  consists  mainly  of  substantia  gelatinosa  and  is  called  the 
nucleus  of  the  spinal  tract  of  the  trigeminal  nerve. 

The  main  sensory  nucleus  lies  lateral  to  the  motor  nucleus  beneath  the  superior 
peduncle.  It  receives  the  short  ascending  branches  of  the  sensory  root.  The 
descending  branches  which  form  the  tractus  spinalis,  pass  down  through  the  pons 
and  medulla  on  the  lateral  side  of  the  nucleus  of  the  tractus  spinalis,  in  which  they 
end  by  collaterals  and  terminals,  into  the  spinal  cord  on  the  level  of  the  second 
cervical  segment.  It  decreases  rapidly  in  size  as  it  descends.  At  first  it  is  located 
between  the  emergent  part  of  the  facial  nerve  and  the  vestibular  nerve,  then  between 
the  nucleus  of  the  facial  nerve  and  the  inferior  peduncle.  Lower  down  in  the  upper 
part  of  the  medulla  it  lies  beneath  the  inferior  peduncle  and  is  broken  up  into 
bundles  by  the  olivocerebellar  fibers  and  the  roots  of  the  ninth  and  tenth  cranial 
nerves.     Finally  it  comes  to  the  surface  of  the  medulla  under  the  tubercle  of 


I 


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'OM POSITION  AND  CENTRAL  CONNECTIONS  OF  CRANIAL   NERVES    863 

Rolando  and  continues  in  this  position  lateral  to  the  fasciculus  cuneatus  as  far  as 

I  the  upper  part  of  the  cervical  region  where  it  disappears. 
I  The  cells  of  the  sensory  nucleus  are  of  large  and  medium  size  and  send  their 
axons  into  the  formatio  reticularis  where  they  form  a  distinct  bundle,  the  central 
path  of  the  trigeminal  [trigeminothalaimc  iraci),  which  passes  upward  through  the 
formatio  reticularis  and  tegmentum  to  the  ventro-lateral  part  of  the  thalamus. 
Most  of  the  fibers  cross  to  the  trigeminothalamic  tract  of  the  opposite  side.  This 
tract  lies  dorsal  to  the  medial  fillet;  approaches  close  to  it  in  the  tegmentum  and 
terminates  in  a  distinct  part  of  the  thalamus.  From  the  thalamus  impulses  are 
conveyed  to  the  somatic  sensory  area  of  the  cortex  by  axons  of  cells  in  the  thalamus 
through  the  internal  capsule  and  corona  radiata.  Many  collaterals  are  given  off 
in  the  medulla  and  pass  from  the  trigeminothalamic  tract  to  the  motor  nuclei, 
especially  to  the  nucleus  ambiguus,  the  facial  nucleus  and  the  motor  nucleus  of  the 
trigeminal. 

The  somatic  sensory  fibers  of  the  \'agus,  the  glossopharyngeal  and  the  facial 
nerves  probably  end  in  the  nucleus  of  the  descending  tract  of  the  trigeminal  and 
their  cortical  impulses  are  probably  carried  up  in  the  central  sensory  path  of  the 
trigeminal. 

The  mesencephalic  root  {descending  root  of  the  trigeminal)  arises  from  unipolar 
cells  arranged  in  scattered  groups  in  a  column  at  the  lateral  edge  of  the  central 
gray  matter  surrounding  the  upper  end  of  the  fourth  ventricle  and  the  cerebral 
aqueduct.  They  have  usually  been  considered  as  motor  fibers  that  join  the  motor 
root,  but  Johnston  claims  that  they  join  the  sensory  root  of  the  trigeminal,  that  they 
develop  in  the  alar,  not  in  the  basal  lamina,  and  that  the  pear-shaped  unipolar 
eells  are  sensor\^  in  type. 

I  The  Trochlear  Nerve  {IV  cranial)  contains  somatic  motor  fibers  only.  It  supplies 
the  superior  oblique  muscle  of  the  eye.  Its  nucleus  of  origin,  trochlear  nucleus, 
is  a  small,  o^•al  mass  situated  in  the  ventral  part  of  the  central  gra>'  matter  o^  the 
cerebral  aqueduct  at  the  level  of  the  upper  part  of  the  inferior  coUiculus.  The 
axons  from  the  nucleus  pass  do\\Tiward  in  the  tegmentum  toward  the  pons,  but 
turn  abruptly  dorsalward  before  reaching  it,  and  pass  into  the  superior  medullary 
v'elum,  in  which  they  cross  horizontally,  to  decussate  with  the  nerve  of  the  opposite 
side,  and  emerges  from  the  surface  of  the  velum,  immediately  behind  the  inferior 
colliculus.  The  cells  of  the  trochlear  nucleus  are  large,  irregular  and  yellowish  in 
color.  The  nuclei  of  the  two  sides  are  separated  by  the  raphe  through  which 
dendrites  extend  from  one  nucleus  to  the  other.  They  receive  many  collaterals 
and  terminals  from  the  posterior  longitudinal  bundle  which  lies  on  the  ventral 
side  of  the  nucleus. 

There  are  no  branches  from  the  fibers  of  the  pyramidal  tracts  to  these  nuclei; 
the  volitional  pathway  must  be  an  indirect  one,  as  is  the  case  with  other  motor 
nuclei. 

The  Oculomotor  Nerve  (///  cranial)  contains  somatic  motor  fibers  to  the  Obliquus 
inferior,  Rectus  inferior,  Rectus  superior,  Levator  palpebrse  superioris  and  Rectus 
medialis  muscles  and  sympathetic  efferent  fibers  (preganglionic  fibers)  to  the 
ciliary  ganglion.  The  postganglionic  fibers  connected  with  these  supply  the  ciliary 
muscle  and  the  sphincter  of  the  iris.  The  axons  arise  from  the  nucleus  of  the 
oculomotor  ner\'e  and  pass  in  bundles  through  the  posterior  longitudinal  bundle, 
the  tegmentum,  the  red  nucleus  and  the  medial  margin  of  the  substantia  nigra  in  a 
series  of  curves  and  finalh'  emerge  from  the  oculomotor  sulcus  on  the  medial  side 
of  the  cerebral  peduncle. 

The  oculomotor  nucleus  lies  in  the  gray  substance  of  the  floor  of  the  cerebral 
aqueduct  subjacent  to  the  superior  colliculus  and  extends  in  front  of  the  aqueduct 
a  short  distance  into  the  floor  of  the  third  ventricle.  The  inferior  end  is  continuous 
with  the  trochlear  nucleus.    It  is  from  6  to  10  mm.  in  length.    It  is  intimately 


864 


NEUROLOGY 


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i    ^ 
4  a/ 


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related  to  the  posterior  longitudinal  bundle  which  lies  against  its  ventro-lateral 
aspect  and  many  of  its  cells  lie  among  the  fibers  of  the  posterior  longitudinal  bundle. 
The  nucleus  of  the  oculomotor  nerve  contains  several  distinct  groups  of  cells  which 
differ  in  size  and  appearance  from  each  other  and  are  supposed  to  send  their  axons 
each  to  a  separate  muscle.  Much  uncertainty  still  exists  as  to  which  group  supplies 
which  muscle.  There  are  seven  of  these  groups  or  nuclei  on  either  side  of  the  mid- 
line and  one  medial  nucleus.  The  cells  of  the  anterior  nuclei  are  smaller  and  are 
supposed  to  give  off  the  sympathetic  efferent  axons.  The  majority  of  fibers  arise 
from  the  nucleus  of  the  same  side  some,  however,  cross  from  the  opposite  side  and 
are  supposed  to  supply  the  Rectus  medialis  muscle.  Since  oculomotor  and  abducens 
nuclei  are  intimately  connected  by  the  posterior  longitudinal  bundle  this  decussa- 
tion of  fibers  to  the  Medial  rectus  may  facili- 
tate the  conjugate  movements  of  the  eyes  in 
which  the  Medial  and  Lateral  recti  are  espe- 
cially involved. 

Many  collaterals  and  terminals  are  given  off 
to  the  oculomotor  nucleus  from  the  posterior 
longitudinal  bundle  and  thus  connect  it  with 
the  vestibular  nucleus,  the  trochlear  and  ab- 
ducens nuclei  and  probably  with  other  cranial 
nuclei.  Fibers  from  the  visual  reflex  center  in 
the  superior  colliculus  pass  to  the  nucleus.  It 
is  also  connected  with  the  cortex  of  the  occip- 
ital lobe  of  the  cerebrum  by  fibers  which 
pass  through  the  optic  radiation.  The  path- 
way for  voluntary  motor  impulses  is  probably 
similar  to  that  for  the  abducent  nerve. 

The  Optic  Nerve  or  Nerve  of  Sight  (//  cranial) 
consists  chiefly  of  coarse  fibers  which  arise 
from  the  ganglionic  layer  of  the  retina.  They 
constitute  the  third  neuron  in  the  series  com- 
posing the  visual  path  and  are  supposed  to 
convey  only  visual  impressions.  A  number  of 
fine  fibers  also  pass  in  the  optic  nerve  from 
the  retina  to  the  primary  centers  and  are  sup- 
posed to  be  concerned  in  the  pupillary  re- 
flexes. There  are  in  addition  a  few  fibers  which 
pass  from  the  brain  to  the  retina ;  they  are  sup- 
posed to  control  chemical  changes  in  the  retina 
and  the  movements  of  the  pigment  cells  and  cones.  Each  optic  nerve  has,  accord- 
ing to  Salzer,  about  500,000  fibers. 

In  the  optic  chiasma  the  nerves  from  the  medial  half  of  each  retina  cross  to  enter 
the  opposite  optic  tract,  while  the  nerves  from  the  lateral  half  of  each  retina  pass 
into  the  optic  tract  of  the  same  side.  The  crossed  fibers  tend  to  occupy  the  medial 
side  of  each  optic  nerve,  but  in  the  chiasma  and  in  the  optic  tract  they  are  more 
intermingled.  The  optic  tract  is  attached  to  the  tuber  cinereum  and  lamina 
terminalis  and  also  to  the  cerebral  peduncle  as  it  crosses  obliquely  over  its  under 
surface.  These  are  not  functional  connections.  A  small  band  of  fibers  from  the 
medial  geniculate  body  joins  the  optic  tract  as  the  latter  passes  over  it  and  crosses 
to  the  opposite  tract  and  medial  geniculate  body  in  the  posterior  part  of  the  chiasma. 
This  is  the  commissure  of  Gudden  and  is  probably  connected  with  the  auditory 
system. 

Most  of  the  fibers  of  the  optic  tract  terminate  in  the  lateral  geniculate  body, 
some  pass  through  the  superior  brachium  to  the  superior  colliculus,  and  others 


Fig.  762. — Figure  showing  the  different  groups 
of  cells,  which  constitute,  according  to  Perha, 
the  nucleus  of  origin  of  the  oculomotor  nerve. 
1.  Posterior  dorsal  nucleus.  1'.  Posterior  ven- 
tral nucleus.  2.  Anterior  dorsal  nucleus.  2'.  Ante- 
rior ventral  nucleus.  3.  Central  nucleus.  4. 
Nucleus  of  Edinger  and  Weatphal.  5.  Antero- 
internal  nucleus.  6.  Antero-external  nucleus.  8. 
Crossed  fibers.  9.  Trochlear  nerve,  with  9',  its 
nucleus  of  origin,  and  9",  its  decussation.  10. 
Third  ventricle.    M,  M.  Median  line.    (Testut.) 


■ 
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Imposition  and  central  connections  of  cranial  nerves  865 

either  pass  over  or  through  the  lateral  geniculate  body  to  the  pulvinar  of  the 
thalamus.    These  end-stations  are  often  called  the  primaxy  visual  centers. 

The  lateral  geniculate  body  consists  of  medium-sized  pigme"nted  nerve  cells 
arranged  in  several  layers  by  the  penetrating  fibers  of  the  optic  tract.  Their  axons 
pass  upward  beneath  the  longer  fibers  of  the  optic  tract,  the  taenia  semicircularis, 
the  caudate  nucleus  and  the  posterior  horn  of  the  lateral  ventricle  where  they  join 
the  optic  radiation  of  Gratiolet.  They  pass  backward  and  medially  to  terminate 
in  the  visuo-sensorA*  cortex  in  the  immediate  neighborhood  of  the  calcarine  fissure 


Optic  nerve 
Crossed  fibers 
Uncrossed  fibers 

Optic  chiasma 

Optic  tract 
Commissure  of  Gudden 


Pvlvinar 

Latercd  geniculate  body 
Superior  collicvlus 
Medial  geniculate  body 


Nucleus  of  oculomotor  nerve 
Nucleus  of  trochlear  nerve 

J^ucleu^  of  abducent  nerve 


I 


Cortex  of  occipital  lobes 
Fig.  763. — Scheme  showing  central  connections  of  the  optic  nerves  and  optic  tracts. 

of  the  occipital  lobe.  This  center  is  connected  with  the  one  in  the  opposite  side  by 
commissural  fibers  which  course  in  the  optic  radiation  and  the  splenium  of  the  corpus 
callosum.  Association  fibers  connect  it  with  other  regions  of  the  cortex  of  the  same 
side. 

The  region  of  the  pulvinar  in  which  optic  tract  fibers  terminate  resembles  in 
structure  the  lateral  geniculate  body.  Its  axons  also  have  a  similar  course  though 
in  a  somewhat  more  dorsal  plane. 

The  superior  colliculus  receives  fibers  from  the  optic  tract  through  the  superior 
brachium.  Some  enter  by  the  superficial  white  layer  (stratum  zonale),  others 
appear  to  dip  down  into  the  gray  cap  (stratum  cinereum)  while  others  probably 


866  NEUROLOGY 


I 


decussate  across  the  midline  to  the  opposite  colliculus.  Other  fibers  from  the 
superior  brachium  pass  into  the  stratum  opticum  (upper  gray-white  la>'er).  Some 
of  these  turn  upward  into  the  gray  cap  while  others  terminate  among  the  cells 
of  this  layer.  Since  the  superior  coUiculi  appear  to  be  the  central  organs  con- 
cerned in  the  control  of  eye-muscle  movements  and  eye-muscle  reflexes  we  should 
expect  to  find  them  receiving  fibers  from  other  sensory  paths.  Many  fibers  pass  t:o 
the  superior  colliculus  from  the  medial  fillet  as  the  latter  passes  through  the  teg- 
mentum bringing  the  superior  colliculus  into  relation  with  the  sensory  fibers  of  the 
spinal  cord.  Fibers  from  the  central  sensory  path  of  the  trigeminal  probably  pass 
with  these.  Part  of  the  ventral  spinocerebellar  tract  (Gowers)  is  said  to  pass  up 
through  the  reticular  formation  of  the  pons  and  mid-brain  toward  the  superior 
colliculus  and  the  thalamus.  The  superior  colliculus  is  intimately  connected  with 
the  central  auditory  path  (the  lateral  lemniscus),  as  part  of  its  fibers  pass  the 
inferior  colliculus  and  terminate  in  the  superior  colliculus.  They  are  probably 
concerned  with  reflex  movements  of  the  eyes  depending  on  auditory  stimuli.  The 
superior  colliculus  is  said  to  receive  fibers  from  the  stria  medullaris  thalamis  of 
the  opposite  side  which  pass  through  the  commissura  habenulse  and  turn  back 
to  the  roof  of  the  mid-brain,  especially  to  the  superior  colliculus.  By  this  path 
both  the  primary  and  cortical  olfactory  centers  are  brought  into  relation  with  the 
eye-muscle  reflex  apparatus. 

The  fibers  which  pass  to  the  nuclei  of  the  eye  muscles  arise  from  large  cells  in 
the  stratum  opticum  and  stratum  lemnisci  and  pass  around  the  ventral  aspect 
of  the  central  gray  matter  where  most  of  them  cross  the  midline  in  the  fountain 
decussation  of  Meynert,  and  then  turn  downward  to  form  the  ventral  longitudinal 
bundle.  This  bundle  runs  down  partly  through  the  red  nucleus,  in  the  formatio 
reticularis,  ventral  to  the  posterior  longitudinal  bundle  of  the  mid-brain,  pons  and 
medulla  oblongata  into  the  ventral  funiculus  of  the  spinal  cord  where  it  is  known 
as  the  tectospinal  fasciculus.  Some  of  the  fibers  are  said  to  pass  down  with  the 
rubrospinal  tract  in  the  lateral  funiculus.  Some  fibers  do  not  decussate  but  pass 
down  in  the  ventral  longitudinal  bundle  of  the  same  side  on  which  they  arise  unless 
possibly  they  come  from  the  opposite  colliculus  over  the  aqueduct.  From  the 
ventral  longitudinal  bundle  collaterals  are  given  off  to  the  nuclei  of  the  eye  muscles, 
the  oculomotor,  the  trochlear  and  the  abducens.  Many  collaterals  pass  to  the  red 
nucleus,  and  are  probably  concerned  with  the  reflexes  of  the  rubrospinal  tract. 
The  fibers  of  the  tectospinal  tract  end  by  collaterals  and  terminals  either  directly 
or  indirectly  among  the  motor  cells  in  the  anterior  column  of  the  spinal  cord. 

The  superior  colliculus  receives  fibers  from  the  visual  sensory  area  of  the  occipital 
cortex;  they  pass  in  the  optic  radiation.  Probably  no  fibers  pass  from  the  superior 
colliculus  to  the  visual  sensory  cortex. 

The  Olfactory  Nerves  (/  cranial)  or  nerves  of  smell  arise  from  spindle-shaped 
bipolar  cells  in  the  surface  epithelium  of  the  olfactory  region  of  the  nasal  cavity. 
The  non-medullated  axons  pass  upward  in  groups  through  numerous  foramina  in 
the  cribriform  plate  to  the  olfactory  bulb ;  here  several  fibers,  each  ending  in  a  tuft 
of  terminal  filaments,  come  into  relation  with  the  brush-like  end  of  a  single  den- 
drite from  a  mitral  cell.  This  interlacing  gives  rise  to  the  olfactory  glomeruli  of  the 
bulb.  The  termination  of  several  or  many  olfactory  fibers  in  a  single  glomerulus 
where  they  form  synapses  with  the  dendrites  of  one  or  two  mitral  cells  provides  for 
the  summation  of  stimuli  in  the  mitral  cells  and  accounts  in  part  at  least  for  the 
detection  by  the  olfactory  organs  of  very  dilute  solutions.  Lateral  arborizations 
of  the  dendrites  of  the  mitral  cells  and  the  connection  of  neighboring  glomeruli  by 
the  axons  of  small  cells  of  the  glomeruli  and  the  return  of  impulses  of  the  mitral 
cells  by  collaterals  either  directly  or  through  the  interpolation  of  granule  cells  to  the 
dendrites  of  the  mitral  cells  reinforce  the  discharge  of  the  mitral  cells  along  their 
axons.    The  axons  turn  abruptly  backward  in  the  deep  fiber  layer  of  the  bulb  to 


{COMPOSITION  AND  CENTRAL  CONNECTIONS  OF  CRANIAL   NERVES    867 


t..,„„.. ...... .....„„ 

^^  trigone,  just  in  front  of  the  anterior  perforated  substance.  The  axons  of  the  mitral 
cells  on  reaching  the  olfactory  trigone  separate  into  three  bundles,  the  lateral 
olfactory  stria,  the  medial  olfactory  stria  and  the  less  marked  intermedial  olfactory 
stria. 

The  lateral  olfactory  striae  curve  lateralward,  a  few  of  the  fibers  end  in  the 
olfactory  trigone  and  the  antero-lateral  portion  of  the  anterior  perforated  substance. 
Most  of  the  fibers,  howe\'er,  pass  into  the  uncus,  the  anterior  end  of  the  hippo- 
campal  g>'rus,  and  there  end  in  the  complicated  cortex  of  the  hippocampal  gyri. 
The  lateral  strine  more  or  less  disappear  as  they  cross  the  antero-lateral  region  of 
the  anterior  perforated  substance. 

The  greater  mass  of  the  fibers  of  the  olfactory  tract  pass  into  the  lateral  stria. 

)  Numerous  collaterals  are  given  into  the  plexiform  layer  of  the  subfrontal  cortex, 
pver  which  the  striae  pass  on  their  way  to  the  uncus,  where  they  intermingle  with 
khe  apical  dendrons  of  the  medium-sized  and  small  p^Tamidal  cells  of  the  pyramidal 
flayer  of  this  subfrontal  or  frontal  olfactory  cortex.  The  axons  give  rise  to  projection 
fibers  which  take  an  antero-posterior  direction  to  the  subthalamic  region  sending 
collaterals  and  terminal  branches  to  the  stria  meduUaris  and  others  toward  the 
thalamus.  Some  of  the  fibers  extend  farther  back  and  are  believed  to  reach  the 
pons  and  medulla  oblongata. 

jNIost  of  the  fibers  of  the  lateral  olfactory  stria  pass  to  the  hippocampal  region 
of  the  cortex,  especially  to  the  gyrus  hippocampi,  which  may  be  regarded  as  the 
main  ending  place  of  the  secondary  olfactory  path  derived  from  axons  of  the  mitral 
cells. 

The  fibers  of  the  medial  olfactory  striae  terminate  for  the  most  part  in  the  par- 
olfactory area  (Broca's  area),  a  few  end  in  the  subcallosal  gyrus  and  a  few  in  the 
anterior  perforated  substance  and  the  adjoining  part  -of  the  septum  pellucidum. 

■  .Some  of  the  fibers  pass  into  the  anterior  commissure  (pars  olfactoria)  to  the  olfac- 
ptory  tract  of  the  opposite  side  where  they  end  partly  within  the  granular  layer 
and  partly  in  the  neighborhood  of  the  glomeruli  of  the  olfactory  bulb,  thus  con- 
necting the  bulbs  of  the  two  sides. 

The  intermediate  olfactory  striae  are  as  a  rule  scarcely  visible,  the  fibers  terminate 
in  the  anterior  perforated  substance,  a  few  are  said  to  continue  to  the  uncus. 

The  trigonum  olfactorium,  anterior  perforated  substance  and  the  adjoining 
part  of  the  septum  pellucidum  are  important  primary  olfactory  centers,  especially 
for  olfactory  reflexes;  in  these  centers  terminate  many  axons  from  the  mitral  cells 
of  the  olfactory  bulb.  In  addition  the  gray  substance  of  the  olfactory  tract  and  the 
g>Tus  subcallosus  receive  terminals  of  the  mitral  cells. 

The  pathways  from  these  centers  to  lower  centers  in  the  brain-stem  and  spinal 
cord  are  only  partially  knoA\-n.  The  most  direct  path,  the  tractus  olfactomesen- 
cephalicus  (basal  olfactory  bundle  of  Wallenbiirg) ,  is  supposed  to  arise  from  cells  in 
the  gray  substance  of  the  olfactory  tract,  the  olfactory  trigone,  the  anterior  per- 
forated substance  and  the  adjoining  part  of  the  septum  pellucidum.  The  fibers 
are  said  to  pass  direct  to  the  tuber  cinereum,  to  the  corpus  mammillare,  to  the  brain- 
stem and  the  spinal  cord.  The  fibers  which  enter  the  mammillary  body  probably 
come  into  relation  with  cells  whose  axons  give  rise  to  the  fasciculus  mammillo- 
tegmentalis  {mammillo-tegmental  bundle  of  Gudden)  which  is  supposed  to  end  in 
the  gray  substance  of  the  tegmentum  and  of  the  aqueduct;  some  of  its  fibers  are 
said  to  join  the  posterior  longitudinal  bundle  and  others  to  extend  as  far  as  the 
reticular  formation  of  the  pons. 

■_  Some  of  the  fibers  of  the  medial  olfactory  stria  came  into  relation  with  cells 
1^  the  parolfactory  area  of  Broca  and  in  the  anterior  perforated  substance,  whose 
axons  course  in  the  meaullary  stria  of  the  thalamus.  As  the  axons  pass  through 
the  lower  part  of  the  septum  pellucidum  they  are  joined  by  other  fibers  whose  cells 


I 


868  ^^^m  NEUROLOGY 


receive  impulses  from  the  mitral  cells.  Thes5  fibers  of  the  medullary  stria  end  for 
the  most  part  in  the  habenular  nucleus  of  the  same  side,  some,  however,  cross  in  the 
habenular  commissure  (dorsal  part  of  the  posterior  commissure)  to  the  habenular 
nucleus  of  the  opposite  side.  A  few  fibers  of  the  medullary  stria  are  said  to  pass 
by  the  habenular  nucleus  to  the  roof  of  the  mid-brain,  especially  the  superior  col- 
liculus,  while  a  few  others  come  into  relation  with  the  posterior  longitudinal  bundle 
and  association  tracts  of  the  mesencephalon. 

The  ganglion  of  the  habenulse  located  in  the  trigonum  habenular  just  in  front  of 
the  superior  coUiculus  contains  a  mesial  nucleus  with  small  cells  and  a  lateral 
nucleus  with  larger  cells.  The  axons  of  these  cells  are  grouped  together  in  a  bundle, 
the  fasciculus  retroflexus  of  Meynert,  which  passes  ventrally  medial  to  the  red 
nucleus  and  terminates  in  a  small  medial  ganglion  in  the  substantia  perforata 
posterior,  immediately  in  front  of  the  pons,  called  the  interpeduncular  ganglion. 

The  interpeduncular  ganglion  has  rather  large  nerve  cells  whose  axons  cur\e 
backward  and  downward  as  the  tegmental  bundle  of  Gudden,  to  end  partly  in  the 
dorsal  tegmental  nucleus  and  surrounding  gray  substance  where  they  come  into 
relation  with  association  neurons  and  the  dorsal  longitudinal  bundle  of  Schiitz. 

The  majority  of  the  axons  that  arise  from  the  mitral  cells  of  the  olfactory  bulb 
and  course  in  the  olfactory  tract  course  in  the  lateral  olfactory  stria  to  the  uncus 
and  hippocampal  gyrus,  and  terminate  in  the  cortex.  Other  fibers  probably  pass 
to  the  uncus  and  hippocampal  g\Tus  from  the  primary  olfactory  centers  in  the 
trigonum  and  anterior  perforated  substance.  The  gyrus  hippocampus  is  continued 
through  the  isthmus  into  the  gyrus  cinguli  which  passes  over  the  corpus  callosum  to 
the  area  parolfactoria.  The  cortical  portions  of  these  gyri  are  connected  together 
by  a  thick  association  bundle,  the  cingulum,  that  lies  buried  in  the  depth  of  the 
gyrus  cinguli  extending  forward  to  the  parolfactory  area  and  backward  into  the 
hippocampal  region.  The  axons  from  the  gyrus  cinguli  pass  into  the  cingulum, 
many  of  them  bifurcate,  the  anterior  branches  together  with  the  axons  which  run 
in  that  direction  are  traceable  as  far  forward  as  the  anterior  part  of  the  septum 
pellucidum  and  the  anterior  end  of  the  corpus  striatum,  where  some  of  them  are 
incorporated  with  projection  fibers  passing  toward  the  internal  capsule.  The 
branches  and  axons  which  pass  backward  terminate  partly  in  the  hippocampus, 
the  dentate  gyrus  and  hippocampal  gyrus.  Shorter  association  fibers  connect 
various  sections  of  the  gyrus  fornicatus  (cingulate  g>Tus,  isthmus,  and  hippocampal 
gyrus)  and  these  with  other  regions  of  the  cortex.  These  gyri  constitute  the  cortical 
center  for  smell. 

The  dentate  gyrus  which  may  be  considered  as  a  modified  part  of  the  hippo- 
campus is  partially  separated  from  the  gyrus  hippocampus  by  the  hippocampal  fis- 
sure and  from  the  fimbria  by  the  fimbrio-dentate  sulcus;  it  is  intimately  connected 
with  the  hippocampal  gjTus  and  the  hippocampus.  When  followed  backward  the 
dentate  gyrus  separates  from  the  fimbria  at  the  splenium,  loses  its  incisions  and 
knobs,  and  as  the  fasciola  cinerea  passes  over  the  splenium  onto  the  dorsal  surface 
of  the  corpus  callosum  and  spreads  out  into  a  thin  layer  of  gray  substance  knowii 
as  the  indusium,  which  can  be  traced  forward  around  the  genu  of  the  corpus 
callosum  into  the  gyrus  subcallosus.  The  white  matter  of  the  indusium  knowTi 
as  the  medial  longitudinal  striae  {nerves  of  Lancisi)  and  the  lateral  longitudinal  striae, 
are  related  to  the  indusium  somewhat  as  the  cingulum  is  to  the  gyrus  cinguli. 
Axons  from  the  indusium  pass  into  the  longitudinal  striae,  some  running  forward 
and  others  backward  while  some  after  entering  the  medial  longitudinal  stria,  pierce 
the  corpus  callosum  to  join  the  fornix.  Some  of  the  fibers  which  pass  forward 
extend  around  the  front  of  the  corpus  callosum  and  the  anterior  commissure,  then 
curve  downward,  according  to  Cajal,  to  enter  the  corpus  striatum  where  they  join 
the  olfactory  projection-path.  Other  fibers  are  said  to  arise  in  the  parolfactory- 
area,  the  gjmis  subcallosus  and  the  anterior  perforated  substance  {diagonal  hand  of 


COMPOSITION  AND  CENTRAL  CONNECTIONS  OF  CRANIAL  NERVES    869 


f 

^^^roca)  and  course  backward  in  the  longitudinal  striae  to  the  dentate  g\'rus  and 
the  hippocampal  region.     The  indusium  is  usually  considered  as  a  rudimentary 

^_part  of  the  rhinencephalon. 

^■^  The  olfactory  projection  fibers  which  arise  from  the  pjTamid  cells  of  the  uncus  and 

^Tiippocampus  and  from  the  polymorphic  cells  of  the  dentate  g>Tus  form  a  dense 
stratum  on  the  ventricular  surface,  especially  on  the  hippocampus,  called  the  alveus. 
These  fibers  pass  over  into  the  fimbria  and  are  continued  into  the  fornix.  About 
one-fourth  of  all  the  fibers  of  the  fimbria  are  large  projection  fibers,  the  other  three- 
fourths  consist  of  fine  commissural  fibers  which  pass  from  the  hippocampus  of  one 
side  through  the  fimbria  and  hippocampal  commissure  (ventral  psaltermm  or  lyre), 
to  the  fimbria  and  hippocampus  of  the  opposite  side  where  they  penetrate  the  pyram- 
idal layer  and  terminate  in  the  stratum  radiatum.  The  fibers  which  course  in  the 
fornLx  pass  forward  and  downward  into  the  corpora  mammillare  w^here  numerous 
collaterals  are  given  off  and  a  few  terminate.  ]\Iost  of  the  fibers  in  the  fornix, 
however,  pass  through  the  corpora,  cross  the  middle  line  and  turn  downward  in 
the  reticular  formation  in  which  they  are  said  to  be  traceable  as  far  as  the  pons  and 
possibly  farther.  As  the  fornix  passes  beneath  the  corpus  callosum  it  receives 
fibers  from  the  longitudinal  striae  of  the  indusium  and  from  the  cingulum ;  these  are 
the  perforating  fibers  of  the  fornix  which  pass  through  the  corpus  callosum  and 
course  in  the  fornix  toward  the  mammillary  body.  As  the  fornix  passes  the  anterior 
end  of  the  thalamus  a  few  fibers  are  given  off  to  the  stria  medullaris  of  the  thalamus 
and  turn  back  in  the  stria  to  the  habenular  ganglion  of  the  same  and  the  opposite 
side,  having  probably  the  same  relation  that  the  reflex  fibers  have  which  arise  from 
the  primary  centers  and  course  in  the  stria  medullaris  of  the  thalamus.  Aside  from 
the  fibers  of  the  fornix  which  pass  through  the  mammillary  body  to  decussate  and 
descend  (as  the  mammillo-mesencephalic  fasciculus),  many  fibers  are  said  to  pass 
into  the  bundle  of  Vicq  d'Azyr,  and  one  bundle  of  fibers  is  said  to  pass  from  the 
fornix  to  the  tuber  cinereiun. 

The  mammillary  bodies  receive  collaterals  and  terminals  then  from  the  cortical 
centers  via  the  fornix  and  probably  other  collaterals  and  terminals  are  received 
directly  from  the  primary  centers  through  the  tractus  olfactomesencephalicus. 
According  to  Cajal  fibers  also  reach  the  mammillarv^  body  through  the  peduncle 
of  the  corpus  mammillare  from  the  arcuate  fibers  of  the  tegmentum  and  from  the 
main  fillet.  The  fornix  probably  brings  the  cortical  centers  into  relation  with  the 
reflex  path  that  runs  from  the  primary  centers  to  the  mammillary  body  and  the 
tuber  cinereum. 

The  bundle  of  Vicq  d'Azyr  {mammillo-thalamicfascicidiis)  arises  from  cells  in  both 
the  medial  and  lateral  nuclei  of  the  mammillary  body  and  by  fibers  that  are  directly 
continued  from  the  fornix.  There  axons  divide  within  the  gray  matter;  the  coarser 
branches  pass  into  the  anterior  nucleus  of  the  thalamus  as  the  bundle  of  Vicq  d'Azyr, 
the  finer  branches  pass  do^^•nward  as  the  mammillo-tegmental  bundle  of  Gudden. 
The  bundle  of  ^'icq  d'Azyr  spreads  out  fan-like  as  it  terminates  in  the  anterior 
or  dorsal  nucleus  of  the  thalamus.  A  few  of  the  fibers  pass  through  the  dorsal 
nucleus  to  the  angular  nucleus  of  the  thalamus.  The  axons  from  these  nuclei  are 
supposed  to  form  part  of  the  thalamocortical  system. 

The  mammillo-tegmental  bundle  has  already  been  considered  under  the  olfactory 
reflex  paths. 

The  amygdaloid  nucleus  and  the  taenia  semicircularis  (stria  termiimlis)  probably 
belong  to  the  central  olfactory  apparatus.  The  taenia  semicircularis  extends  from 
the  region  of  the  anterior  perforated  substance  to  the  nucleus  amygdalae.  Its 
anterior  connections  are  not  clearly  understood.  Fibers  are  said  to  arise  from  cells 
in  the  anterior  perforated  substance;  some  of  the  fibers  pass  in  front  of  the  anterior 
commissure,  others  join  the  fornix  for  a  short  distance  as  they  pass  behind  the 
nterior  commissure.    The  two  strands  ultimately  join  to  form  the  taenia  and  pass 


I 


870  mK&KKKKm     neurology 


L 


backward  in  the  groove  between  the  caudate  nucleus  and  the  thalamus  to  the 
amygdaloid  nucleus.  Other  fibers  are  said  to  pass  in  the  opposite  direction  frc»m 
the  amygdaloid  nucleus  to  the  thalamus. 

PATHWAYS  FROM  THE  BRAIN  TO  THE  SPINAL  CORD. 

The  descending  fasciculi  which  convey  impulses  from  the  higher  centers  to  the 
spinal  cord  and  located  in  the  lateral  and  ventral  funiculi. 

The  Motor  Tract  (Fig.  764),  conveying  voluntary  impulses,  arises  from  the 
pyramid  cells  situated  in  the  motor  area  of  the  cortex,  the  anterior  central  and  the 
posterior  portions  of  the  frontal  gyri  and  the  paracentral  lobule.  The  fibers  are 
at  first  somewhat  widely  diffused,  but  as  they  descend  through  the  corona  radiata 
they  gradually  approach  each  other,  and  pass  between  the  lentiform  nucleus  and 
thalamus,  in  the  genu  and  anterior  two-thirds  of  the  occipital  part  of  the  inter- 
nal capsule;  those  in  the  genu  are  named  the  geniculate  fibers,  while  the  remainder 
constitute  the  cerebrospinal  fibers;  proceeding  downward  they  enter  the  middle 
three-fifths  of  the  base  of  the  cerebral  peduncle.  The  geniculate  fibers  cross  the 
middle  line,  and  end  by  arborizing  around  the  cells  of  the  motor  nuclei  of  the  cra- 
nial nerves.  The  cerebrospinal  fibers  are  continued  downward  into  the  pyramids 
of  the  medulla  oblongata,  and  the  transit  of  the  fibers  from  the  medulla  oblongata 
is  effected  by  two  paths.  The  fibers  nearest  to  the  anterior  median  fissure  cross 
the  middle  line,  forming  the  decussation  of  the  pyramids,  and  descend  in  the 
opposite  side  of  the  medulla  spinalis,  as  the  lateral  cerebrospinal  fasciculus  (crossed 
pyramidal  tract) .  Throughout  the  length  of  the  medulla  spinalis  fibers  from  this 
column  pass  into  the  gray  substance,  to  terminate  either  directly  or  indirectly 
around  the  motor  cells  of  the  anterior  column.  The  more  laterally  placed  portion  of 
the  tract  does  not  decussate  in  the  medulla  oblongata,  but  descends  as  the  anterior 
cerebrospinal  fasciculus  {direct  pyramidal  tract) ;  these  fibers,  however,  end  in  the  ante- 
rior gray  column  of  the  opposite  side  of  the  medulla  spinalis  by  passing  across  in  the 
anterior  white  commissure.  There  is  considerable  variation  in  the  extent  to  which 
decussation  takes  place  in  the  medulla  oblongata ;  about  two-thirds  or  three-fourths 
of  the  fibers  usually  decussate  in  the  medulla  oblongata  and  the  remainder  in  the 
medulla  spinalis. 

The  axons  of  the  motor  cells  in  the  anterior  column  pass  out  as  the  fibers  of  the 
anterior  roots  of  the  spinal  nerves,  along  which  the  impulses  are  conducted  to  the 
muscles  of  the  trunk  and  limbs. 

From  this  it  will  be  seen  that  all  the  fibers  of  the  motor  tract  pass  to  the  nuclei 
of  the  motor  nerves  on  the  opposite  side  of  the  brain  or  medulla  spinalis,  a  fact 
which  explains  why  a  lesion  involving  the  motor  area  of  one  side  causes  paralysis 
of  the  muscles  of  the  opposite  side  of  the  body.  Further,  it  will  be  seen  that  there 
is  a  break  in  the  continuity  of  the  motor  chain;  in  the  case  of  the  cranial  nerves 
this  break  occurs  in  the  nuclei  of  these  nerves;  and  in  the  case  of  the  spinal  nerves, 
in  the  anterior  gray  column  of  the  medulla  spinalis.  For  clinical  purposes  it  is 
convenient  to  emphasize  this  break  and  divide  the  motor  tract  into  two  portions : 
(1)  a  series  of  upper  motor  neurons  which  comprises  the  motor  cells  in  the  cortex 
and  their  descending  fibers  down  to  the  nuclei  of  the  motor  nerves;  (2)  a  series 
of  lower  motor  neurons  which  includes  the  cells  of  the  nuclei  of  the  motor  cerebral 
nerves  or  the  cells  of  the  anterior  columns  of  the  medulla  spinalis  and  their  axis- 
cylinder  processes  to  the  periphery. 

The  rubrospinal  fasciculus  arises  from  the  large  cells  of  the  red  nucleus.  The  fibers 
cross  the  raphe  of  the  mid-brain  in  the  decussation  of  Forel  and  descend  in  the 
formatio  reticularis  of  the  pons  and  medulla  dorsal  to  the  medial  lemniscus  and  as 
they  pass  into  the  spinal  cord  come  to  lie  in  a  position  ventral  to  the  crossed  pyram- 
idal tracts  in  the  lateral  funiculus.    The  rubrospinal  fibers  end  either  directly  or 


PATHWAYS  FROM  THE  BRAIN  TO  THE  SPINAL  CORD 


871 


I  Indirectly  by  terminals  and  collaterals  about  the  motor  cells  in  the  anterior  column 

on  the  side  opposite  from  their  origin  in  the  red  nucleus.    A  few  are  said  to  pass 

do\Mi  on  the  same  side.    Since  the  red  nucleus  is  intimately  related  to  the  cerebellum 

liby  terminals  and  collaterals  of  the  superior  peduncle  which  arises  in  the  dentate 

mucleus  of  the  cerebellum,  the  rubrospinal  fasciculus  is  supposed  to  be  concerned 


Geniculate  fibers 


Motor  area  of 
cortex 


Internal 
capsule 


Decussation  of  pyramids 

Anterior  cerebrospinal  fascicvltis 
Lateral  cerebrospinal  fasciculus 


I 


r-^m,  Anterior  nerve  roots 


Pio.  764. — The  motor  tract.     (Modified  from  Poirier.) 

ith  cerebellar  reflexes,  complex  motor  coordinations  necessary  in  locomotion  and 
equilibrium.  The  afferent  paths  concerned  in  these  reflexes  have  already  been 
partly  considered,  namely,  the  dorsal  and  ventral  spinocerebellar  fasciculi,  and 
probably  some  of  the  fibers  of  the  posterior  funiculi  which  reach  the  cerebellum  by 
the  inferior  peduncle. 

The  tectospinal  fasciculus  arises  from  the  superior  coUiculus  of  the  roof  (tectum) 


872  NEUROLOGY 


I 


of  the  mid-brain.  The  axons  come  from  large  cells  in  the  stratum  opticum  and 
stratum  lemnisci  and  sweep  ventrally  around  the  central  gray  matter  of  the  aque- 
duct, cross  the  raphe  in  the  fountain  decussation  of  Meynert  and  turn  downwai-d 
in  the  tegmentum  in  the  ventral  longitudinal  bundle.  Some  of  the  fibers  do  not 
cross  in  the  raphe  but  pass  down  on  the  same  side;  it  is  uncertain  whether  they  come 
from  the  superior  colliculus  of  the  same  side  or  arch  over  the  aqueduct  from  the 
colliculus  of  the  opposite  side.  The  tectospinal  fasciculus  which  comprises  the 
major  part  of  the  ventral  longitudinal  bundle  passes  down  through  the  tegmentum 
and  reticular  formation  of  the  pons  and  medulla  oblongata  ventral  to  the  medial 
longitudinal  bundle.  In  the  medulla  the  two  bundles  are  more  or  less  interminghd 
and  the  tectospinal  portion  is  continued  into  the  antero-lateral  funiculus  of  the 
spinal  cord  ventral  to  the  rubrospinal  fasciculus  with  which  some  of  its  fibers  are 
intermingled.  Some  of  the  fibers  of  the  tectospinal  fasciculus  pass  through  the  red 
nucleus  giving  off  collaterals  to  it,  others  are  given  off  to  the  motor  nuclei  of  the 
cranial  nerves  and  in  the  spinal  cord  they  terminate  either  directly  or  indirectly 
by  terminals  and  collaterals  among  the  nuclei  of  the  anterior  column.  Since  the 
superior  colliculus  is  an  important  optic  reflex  center,  this  tract  is  probably  con- 
cerned in  optic  reflexes;  and  possibly  also  with  auditory  reflexes  since  some  of  the 
fibers  of  the  central  auditory  path,  the  lateral  lemniscus,  terminate  in  the  superior 
colliculus. 

The  vestibulospinal  fasciculus  {jyart  of  the  anterior  marginal  fascicvliis  or  Loewen- 
thaVs  tract)  situated  chiefly  in  the  marginal  part  of  the  anterior  funiculus  is  mainly 
derived  from  the  cells  of  the  terminal  nuclei  of  the  vestibular  nerve,  probably 
Deiters's  and  Bechterew's,  and  some  of  its  fibers  are  supposed  to  come  from  the 
nucleus  fastigius  (roof  nucleus  of  the  cerebellum) .  The  latter  nucleus  is  intimately 
connected  with  Dieters's  and  Bechterew's  nuclei.  The  vestibulospinal  fasciculus 
is  concerned  with  equilibratory  reflexes.  Its  terminals  and  collaterals  end  about 
the  motor  cells  in  the  anterior  column.  It  extends  to  the  sacral  region  of  the  cord. 
Its  fibers  are  intermingled  with  the  ascending  spinothalamic  fasciculus,  with  the 
anterior  proper  fasciculus  and  laterally  with  the  tectospinal  fasciculus.  Its  fibers 
are  supposed  to  be  both  crossed  and  uncrossed.  In  the  brain-stem  it  is  associated 
with  the  dorsal  longitudinal  bundle. 

The  pontospinal  fasciculus  (Bechterew)  arises  from  the  cells  in  the  reticular  forma- 
tion of  the  pons  from  the  same  and  the  opposite  side  and  is  associated  in  the  brain- 
stem with  the  ventral  longitudinal  bundle.  In  the  cord  it  is  intermingled  with  the 
fibers  of  the  vestibulospinal  fasciculus  in  the  anterior  funiculus.  Not  much  is  knowni 
about  this  tract. 

There  are  probably  other  descending  fasciculi  such  as  the  thalamospinal  but  not 
much  is  known  about  them. 

MENINGES    OF   THE   BRAIN    AND   MEDULLA   SPINALIS. 

The  brain  and  medulla  spinalis  are  enclosed  within  three  membranes.  These 
are  named  from  without  inward :  the  dura  mater,  the  arachnoid,  and  the  pia  mater. 

The  Dura  Mater. 

The  dura  mater  is  a  thick  and  dense  inelastic  membrane.  The  portion  which 
encloses  the  brain  differs  in  several  essential  particulars  from  that  which  surrounds 
the  medulla  spinalis,  and  therefore  it  is  necessary  to  describe  them  separately; 
but  at  the  same  time  it  must  be  distinctly  understood  that  the  two  form  one  com- 
plete membrane,  and  are  continuous  with  each  other  at  the  foramen  magnum. 

The  Cranial  Dura  Mater  {dura  mater  enceyhali;  dura  of  the  brain)  lines  the 
interior  of  the  skull,  and  serves  the  twofold  purpose  of  an  internal  periosteum 


THE  DURA  MATER 


873 


I  to  the  bones,  and  a  membrane  for  the  protection  of  the  brain.    It  is  composed  of 
two  layers,  an  inner  or  meningeal  and  an  outer  or  endosteal,  closely  connected 
together,  except  in  certain  situations,  where,  as  already  described  (page  654), 
^       they  separate  to  form  sinuses  for  the  passage  of  venous  blood.    Its  outer  surface 
^^  is  rough  and  fibrillated,  and  adheres  closely  to  the  inner  surfaces  of  the  bones, 
^■the  adhesions  being  most  marked  opposite  the  sutures  and  at  the  base  of  the  skull 
^Bits  inner  surface  is  smooth  and  lined  by  a  layer  of  endothelium.    It  sends  inward 
^Bfour  processes  which  divide  the  cavity  of  the  skull  into  a  series  of  freely  communicat- 
ing compartments,  for  the  lodgement  and  protection  of  the  different  parts  of  the 
^^ brain;  and  it  is  prolonged  to  the  outer  surface  of  the  skull,  through  the  various 
^■foramina  which  exist  at  the  base,  and  thus  becomes  continuous  with  the  peri- 
^^cranium;  its  fibrous  layer  forms  sheaths  for  the  nerves  which  pass  through  these 
apertures.    Around  the  margin  of  the  foramen  magnum  it  is  closely  adherent  to 
the  bone,  and  is  continuous  with  the  spinal  dura  mater. 


Abducent  nerve    Trigeminal  nerve 
765. — Dura  mater  and  its  processes  exposed  by  removing  part  of  the  right  half  of  the  skull  and  the  brain. 

Processes. — The  processes  of  the  cranial  dura  mater,  which  projects  into  the 
cavity  of  the  skull,  are  formed  by  reduplications  of  the  inner  or  meningeal  layer 
of  the  membrane,  and  are  four  in  number:  the  falx  cerebri,  the  tentorium  cerebeUi, 
the  falx  cerebelli,  and  the  diaphragma  sellse. 

The  falx  cerebri  (Fig.  765),  so  named  from  its  sickle-like  form,  is  a  strong,  arched 
process  Avhich  descends  vertically  in  the  longitudinal  fissure  between  the  cerebral 
hemispheres.  It  is  narrow  in  front,  where  it  is  attached  to  the  crista  galli  of  the 
ethmoid;  and  broad  behind,  where  it  is  connected  with  the  upper  surface  of  the 


k 


874 


NEUROLOGY 


tentorium  cerebelli.  Its  upper  margin  is  convex,  and  attached  to  the  inner  surface 
of  the  skull  in  the  middle  line,  as  far  back  as  the  internal  occipital  protuberance; 
it  contains  the  superior  sagittal  sinus.  Its  lower  margin  is  free  and  concave,  and 
contains  the  inferior  sagittal  sinus. 

The  tentorium  cerebelli  (Fig,  766)  is  an  arched  lamina,  elevated  in  the  middle, 
and  inclining  downward  toward  the  circumference.  It  covers  the  superior  surface 
of  the  cerebellum,  and  supports  the  occipital  lobes  of  the  brain.  Its  anterior  border 
is  free  and  concave,  and  bounds  a  large  oval  opening,  the  incisura  tentorii,  for  the 
transmission  of  the  cerebral  peduncles.  It  is  attached,  behind,  by  its  convex  border, 
to  the  transverse  ridges  upon  the  inner  surface  of  the  occipital  bone,  and  there 
encloses  the  transverse  sinuses;  in  front,  to  the  superior  angle  of  the  petrous  part 


Optic  nerve 

Diaphragma  sellce       \ 

Free  margin  qf  tentorium  \ 


Internal  carotid  artery 
I      Oculomotor  nerve 
I        /         Attached  margin  of  tentorium' 


■9^V  B 


End  of  superior  sagittal  sinus 
Fia.  766. — Tentorium  cerebelli  seen  from  above. 

of  the  temporal  bone  on  either  side,  enclosing  the  superior  petrosal  sinuses.  At 
the  apex  of  the  petrous  part  of  the  temporal  bone  the  free  and  attached  borders 
meet,  and,  crossing  one  another,  are  continued  forward  to  be  fixed  to  the  anterior 
and  posterior  clinoid  processes  respectively.  To  the  middle  line  of  its  upper  surface 
the  posterior  border  of  the  falx  cerebri  is  attached,  the  straight  sinus  being  placed 
at  their  line  of  junction. 

The  falx  cerebelli  is  a  small  triangular  process  of  dura  mater,  received  into  the 
posterior  cerebellar  notch.  Its  base  is  attached,  above,  to  the  under  and  back  part 
of  the  tentorium;  its  posterior  margin,  to  the  lower  division  of  the  vertical  crest 
on  the  inner  surface  of  the  occipital  bone.  As  it  descends,  it  sometimes  divides 
into  two  smaller  folds,  which  are  lost  on  the  sides  of  the  foramen  magnum. 

The  diaphragma  sellae  is  a  small  circular  horizontal  fold,  which  roofs  in  the  sella 
turcica  and  almost  completely  covers  the  hypophysis;  a  small  central  opening 
transmits  the  infundibulum. 


I 


THE  DURA  MATER 


875 


Structure. — The  cranial  dura  mater  consists  of  white  fibrous  tissue  and  elastic  fibers  arranged 
in  flattened  laminae  which  are  imperfectly  separated  by  lacunar  spaces  and  bloodvessels  into 
two  layers,  endosteal  and  meningeal.  The  endosteal  layer  is  the  internal  periosteum  for  the 
cranial  bones,  and  contains  the  bloodvessels  for  their  supply.  At  the  margin  of  the  foramen 
magnum  it  is  continuous  with  the  periosteum  lining  the  vertebral  canal.  The  meningeal  or 
supporting  layer  is  lined  on  its  inner  surface  by  a  layer  of  nucleated  flattened  mesothelium, 
similar  to  that  found  on  serous  membranes. 

The  arteries  of  the  dura  mater  are  very  niunerous.  Those  in  the  anterior  fossa  are  the  anterior 
meningeal  branches  of  the  anterior  and  posterior  ethmoidal  and  internal  carotid,  and  a  branch 
from  the  middle  meningeal.  Those  in  the  middle  fossa  are  the  middle  and  accessory  meningeal 
of  the  internal  maxillary;  a  branch  from  the  ascending  phar>Tigeal,  which  enters  the  skull  through 
the  foramen  lacerum;  branches  from  the  internal  carotid,  and  a  recurrent  branch  from  the  lacrimal. 
Those  in  the  posterior  fossa  are  meningeal  branches  from  the  occipital,  one  entering  the  skull 
through  the  jugular  foramen,  and  another  through  the  mastoid  foramen;  the  posterior  meningeal 
from  the  vertebral;  occasional  meningeal  branches  from  the  ascending  pharyngeal,  entering  the 
skull  through  the  jugular  foramen  and  hypoglossal  canal;  and  a  branch  from  the  middle  meningeal. 

■L  The  veins  returning  the  blood  from  the  cranial  dura  mater  anastomose  with  the  diploic  veins 
rand  end  in  the  various  sinuses.  Many  of  the  meningeal  veins  do  not  open  directly  into  the  sinuses, 
but  indirectly  through  a  series  of  ampullae,  termed  venous  lacunse.  These  are  found  on  either 
side  of  the  superior  sagittal  sinus,  especially  near  its  middle  portion,  and  are  often  invaginated 
by  arachnoid  granulations;  they  also  exist  near  the  transverse  and  straight  sinuses.  They 
communicate  with  the  underlying  cerebral  veins,  and  also  with  the  diploic  and  emissary  veins. 
The  nerves  of  the  cranial  dura  mater  are  filaments  from  the  semilunar  ganglion,  from  the 
ophthalmic,  maxillary,  mandibular,  vagus,  and  hypoglossal  nerves,  and  from  the  sympathetic. 

The  Spinal  Dura  Mater  {dura  mater  spinalis;  spinal  dura)  (Fig.  767)  forms  a 
loose  sheath  around  the  medulla  spinalis,  ahd  represents  only  the  inner  or  meningeal 
layer  of  the  cranial  dura  mater;  the  outer  or  endosteal  layer  ceases  at  the  foramen 
magnum,  its  place  being  taken  by  the  periosteum  lining  the  vertebral  canal.  The 
spinal  dura  mater  is  separated  from  the  arachnoid  by  a  potential  cavity,  the  sub- 
dural cavity;  the  two  membranes  are,  in  fact,  in  contact  with  each  other,  except 
where  they  are  separated  by  a  minute  quantity  of 
fluid,  which  serves  to  moisten  the  apposed  surfaces. 
It  is  separated  from  the  wall  of  the  vertebral  canal 
by  a  space,  the  epidural  space,  which  contains  a  quan- 
tity of  loose  areolar  tissue  and  a  plexus  of  veins;  the 
situation  of  these  veins  between  the  dura  mater  and 
the  periosteum  of  the  vertebrae  corresponds  therefore 
o  that  of  the  cranial  sinuses  between  the  meningeal 
and  endosteal  layers  of  the  cranial  dura  mater.  The 
spinal  dura  mater  is  attached  to  the  circumference  of 
the  foramen  magnum,  and  to  the  second  and  third 
cervical  vertebrae;  it  is  also  connected  to  the  pos- 
terior longitudinal  ligament,  especially  near  the  lower 
end  of  the  vertebral  canal,  by  fibrous  slips.  The 
subdural  cavity  ends  at  the  lower  border  of  the  second 
sacral  vertebra;  below  this  level  the  dura  mater  closely 
invests  the  filum  terminale  and  descends  to  the  back  of 
the  coccyx,  where  it  blends  with  the  periosteum.  The 
sheath  of  dura  mater  is  much  larger  than  is  necessary 
for  the  accommodation  of  its  contents,  and  its  size  is 
greater  in  the  cervical  and  lumbar  regions  than  in 
the  thoracic.  On  each  side  may  be  seen  the  double 
openings  which  transmit  the  two  roots  of  the  corre- 
sponding spinal  nerve,  the  dura  mater  being  continued 

in  the  form  of  tubular  prolongations  on  them  as  they  pass  through  the  interverte- 
bral foramina.  These  prolongations  are  short  in  the  upper  part  of  the  vertebral 
column,  but  gradually  become  longer  below,  forming  a  number  of  tubes  of  fibrous 
membrane,  which  enclose  the  lower  spinal  nerves  and  are  contained  in  the  verte- 
bral canal. 


11^ 

» 

II 


Dura-Matem 


FlQ. 


767. — The  medulla  spinalis  and 
its  membranes. 


II 


S76  NEUROLOGY 


I 


Structure. — The  spinal  dura  mater  resembles  in  structure  the  meningeal  or  supporting  iay(;r 
of  the  cranial  dura  mater,  consisting  of  white  fibrous  and  elastic  tissue  arranged  in  bands  or 
lamellae  which,  for  the  most  part,  are  parallel  with  one  another  and  have  a  longitudinal  arrange- 
ment. Its  internal  surface  is  smooth  and  covered  by  a  layer  of  mesothelium.  It  is  sparingly 
supplied  with  bloodvessels,  and  a  few  nerves  have  been  traced  into  it. 

The  Arachnoid. 

The  arachnoid  is  a  delicate  membrane  enveloping  the  brain  and  medulla  spinahs 
and  lying  between  the  pia  mater  internally  and  the  dura  mater  externally;  it  is 
separated  from  the  pia  mater  by  the  subarachnoid  cavity,  which  is  filled  with 
cerebrospinal  fluid. 

The  Cranial  Part  (arachnoidea  encephali)  of  the  arachnoid  invests  the  brain 
loosely,  and  does  not  dip  into  the  sulci  between  the  gyri,  nor  into  the  fissures,  with 
the  exception  of  the  longitudinal.  On  the  upper  surface  of  the  brain  the  arachnoid 
is  thin  and  transparent;  at  the  base  it  is  thicker,  and  slightly  opaque  toward  the 
central  part,  where  it  extends  across  between  the  two  temporal  lobes  in  front 
of  the  pons,  so  as  to  leave  a  considerable  interval  betAveen  it  and  the  brain. 

The  Spinal  Part  {arachnoidea  spinalis)  of  the  arachnoid  is  a  thin,  delicate,  tubular 
membrane  loosely  investing  the  medulla  spinalis.  Above,  it  is  continuous  with 
the  cranial  arachnoid ;  below,  it  w  idens  out  and  invests  the  cauda  equina  and  the 
nerves  proceeding  from  it.  It  is  separated  from  the  dura  mater  by  the  subdural 
space,  but  here  and  there  this  space  i^  traversed  by  isolated  connective-tissue 
trabeculse,  which  are  most  numerous  on  the  posterior  surface  of  the  medulla  spinalis. 

The  arachnoid  surrounds  the  cranial  and  spinal  nerves,  and  encloses  them 
in  loose  sheaths  as  far  as  their  points  of  exit  from  the  skull  and  vertebral  canal. 

Stracture. — The  arachnoid  consists  of  bundles  of  white  fibrous  and  elastic  tissue  intimately 
blended  together.  Its  outer  surface  is  covered  with  a  layer  of  low  cuboidal  mesothelium.  The 
inner  surface  and  the  trabeculse  are  likewise  covered  by  a  somewhat  low  type  of  cuboidal  meso- 
thelium which  in  places  are  flattened  to  a  pavement  type.  Vessels  of  considerable  size,  but  few 
in  number,  and,  according  to  Bochdalek,  a  rich  plexus  of  nerves  derived  from  the  motor  root 
of  the  trigeminal,  the  facial,  and  the  accessory  nerves,  are  found  in  the  arachnoid. 

The  Subarachnoid  Cavity  (cavum  subarachnoideale;  subarachnoid  space)  is  the 
interval  between  the  arachnoid  and  pia  mater.  It  is  occupied  by  a  spongy  tissue 
consisting  of  trabeculse  of  delicate  connective  tissue,  and  intercommunicating 
channels  in  which  the  subarachnoid  fluid  is  contained.  This  cavity  is  small  on  the 
surface  of  the  hemispheres  of  the  brain;  on  the  summit  of  each  gyrus  the  pia  mater 
and  the  arachnoid  are  in  close  contact;  but  in  the  sulci  between  the  gyri,  triangular 
spaces  are  left,  in  which  the  subarachnoid  trabecular  tissue  is  found,  for  the  pia 
mater  dips  into  the  sulci,  whereas  the  arachnoid  bridges  across  them  from  gyrus  to 
gyrus.  At  certain  parts  of  the  base  of  the  brain,  the  arachnoid  is  separated  from  the 
pia  mater  by  wide  intervals,  which  communicate  freely  with  each  other  and  are 
named  subarachnoid  cistemsB;  in  these  the  subarachnoid  tissue  is  less  abundant. 

Subarachnoid  Cistern®  (cisternce  subarachnoidales)  (Fig.  768).  —  The  cisterna 
cerebellomedullaris  (cisterna  magna)  is  triangular  on  sagittal  section,  and  results 
from  the  arachnoid  bridging  over  the  interval  between  the  medulla  oblongata 
and  the  under  surfaces  of  the  hemispheres  of  the  cerebellum;  it  is  continuous 
with  the  subarachnoid  cavity  of  the  medulla  spinalis  at  the  level  of  the  foramen 
magnum.  The  cisterna  pontis  is  a  considerable  space  on  the  ventral  aspect  of  the 
pons.  It  contains  the  basilar  artery,  and  is  continuous  behind  with  the  subarach- 
noid cavity  of  the  medulla  spinalis,  and  with  the  cisterna  cerebellomedullaris;  and 
in  front  of  the  pons  with  the  cisterna  interpeduncularis.  The  cisterna  interpeduncu- 
laris  (cisterna  basalis)  is  a  wide  cavity  where  the  arachnoid  extends  across  between 
the  two  temporal  lobes.  It  encloses  the  cerebral  peduncles  and  the  structures 
contained  in  the  interpeduncular  fossa,  and  contains  the  arterial  circle  of  Willis. 


I 


THE  ARACHNOID 


877 


In  front,  the  cisterna  interpeduncularls  extends  forward  across  the  optic  chiasma, 
forming  the  cisterna  chiasmatis,  and  on  to  the  upper  surface  of  the  corpus  callosum, 
for  the  arachnoid  stretches  across  from  one  cerebral  hemisphere  to  the  other  immedi- 
ately beneath  the  free  border  of  the  falx  cerebri,  and  thus  leaves  a  space  in  which 
the  anterior  cerebral  arteries  are  contained.  The  cisterna  fossae  cerebri  lateralis  is 
formed  in  front  of  either  temporal  lobe  by  the  arachnoid  bridging  across  the  lateral 
fissure.  This  cavity  contains  the  middle  cerebral  artery.  The  cisterna  venae 
magnae  cerebri  occupies  the  interval  between  the  splenium  of  the  corpus  callosum 
and  the  superior  surface  of  the  cerebellum ;  it  extends  between  the  layers  of  the  tela 
chorioidea  of  the  third  ventricle  and  contains  the  great  cerebral  vein. 


Optic  chiasma 


Cisterna  interpeduncularis 

Fourth  ventricle 
Cisterna  pontis 


Cisterna 
cerebellomedullaris 
FiQ.  768. — Diagram  shOvv'ing  the  positions  of  the  three  principal  subarachnoid  cisternae. 


V 

^^  The  subarachnoid  cavity  communicates  with  the  general  ventricular  cavity 
of  the  brain  by  three  openings;  one,  the  foramen  of  Majendie,  is  in  the  middle  line 
at  the  inferior  part  of  the  roof  of  the  fourth  ventricle;  the  other  two  are  at  the 
extremities  of  the  lateral  recesses  of  that  ventricle,  behind  the  upper  roots  of  the 
glossopharjTigeal  nerves  and  are  known  as  the  foramina  of  Luschka.    It  is  still  some- 

P,  what  uncertain  whether  these  foramina  are  actual  openings  or  merely  modified  areas 
lof  the  inferior  velum  which  permit  the  passage  of  the  cerebrospinal  fluid  from  the 
ventricle  into  the  subarachnoid  spaces  as  through  a  permeable  membrane. 
[  The  spinal  part  of  the  subarachnoid  cavity  is  a  very  wide  interval,  and  is  the 

Bilargest  at  the  lower  part  of  the  vertebral  canal,  where  the  arachnoid  encloses 
^  'the  nerves  which  form  the  cauda  equina.  Above,  it  is  continuous  with  the  cranial 
subarachnoid  cavity;  below,  it  ends  at  the  level  of  the  lower  border  of  the  second 
sacral  vertebra.  It  is  partially  divided  by  a  longitudinal  septum,  the  subarachnoid 
septum,  which  connects  the  arachnoid  with  the  pia  mater  opposite  the  posterior 
median  sulcus  of  the  medulla  spinalis,  and  forms  a  partition,  incomplete  and  cribri- 
form above,  but  more  perfect  in  the  thoracic  region.  The  spinal  subarachnoid 
cavity  is  further  subdivided  by  the  ligamentum  denticulatum,  which  will  be  described 
with  the  pia  mater. 

The  cerebrospinal  fluid  is  a  clear  limpid  fluid,  having  a  saltish  taste,  and  a  slightly  alkaline 
reaction.  According  to  Lassaigne,  it  consists  of  98.5  parts  of  water,  the  remaining  1.5  per  cent, 
being  solid  matters,  animal  and  saline.  It  varies  in  quantity,  being  most  abundant  in  old  persons, 
and  is  quickly  secreted. 


878 


NEUROLOGY 


I 


The  Arachnoid  Villi  (granulationes  arachnoideales;  glandulcePacchioni;  PacchM- 
nian  bodies)  (Fig.  769)  are  small,  fleshy-looking  elevations,  usually  collected  into 
clusters  of  variable  size,  which  are  present  upon  the  outer  surface  of  the  dura 
mater,  in  the  vicinity  of  the  superior  sagittal  sinus,  and  in  some  other  situations. 
Upon  laying  open  the  sagittal  sinus  and  the  venous  lacunje  on  either  side  of  it 
villi  will  be  found  protruding  into  its  interior.  They  are  not  seen  in  infancy, 
and  very  rarely  until  the  third  year.  They  are  usually  found  after  the  seventh 
year;  and  from  this  period  they  increase  in  number  and  size  as  age  advancers. 
They  are  not  glandular  in  structure,  but  are  enlarged  normal  villi  of  the  arach- 
noid. As  they  grow  they  push  the  thinned  dura  mater  before  them,  and  cause 
absorption  of  the  bone  from  pressure,  and  so  produce  the  pits  or  depressions 
on  the  inner  wall  of  the  calvarium. 


Emissccry  vein 
Venous  lacuna 

Cerebral  vein 
Diploic  vein 


Meningeal  vein 


Sup.  sagittal  sinus 

J  Arachnoid  granulation 


Subdural  cavity 
Subarachnoid  cavity 


Pto  mater 


Dura  mater 
Arachnoid 

Cerebral  cortex 


Fia.  769. — Diagrammatic  representation  of  a  section  across  the  top  of  the  skull,  showing  the  membranes  of  the 

brain,  etc.     (Modified  from  Testut.) 

Structure. — An  arachnoidal  villus  represents  an  invasion  of  the  dura  by  the  arachnoid  mem- 
brane, the  latter  penetrates  the  dura  in  such  a  manner  that  the  arachnoid  mesothelial  cells  come 
to  lie  directly  beneath  the  vascular  endothelium  of  the  great  dural  sinuses.  It  consists  of  the 
following  parts:  (1)  In  the  interior  is  a  core  of  subarachnoid  tissue,  continuous  with  the  mesh- 
work  of  the  general  subarachnoid  tissue  through  a  narrow  pedicle,  by  which  the  villus  is  attached 
to  the  arachnoid.  (2)  Around  this  tissue  is  a  layer  of  arachnoid  membrane,  limiting  and  enclosing 
the  subarachnoid  tissue.  (3)  Outside  this  is  the  thinned  wall  of  the  lacuna,  which  is  separated 
from  the  arachnoid  by  a  potential  space  which  corresponds  to  and  is  continuous  with  the  subdural 
cavity.  (4)  And  finally,  if  the  villus  projects  into  the  sagittal  sinus,  it  will  be  covered  by  the 
greatly  thinned  wall  of  the  sinus  which  may  consist  merely  of  endothelium.  It  will  be  seen,  there- 
fore, that  fluid  injected  into  the  subarachnoid  cavity  will  find  its  way  into  these  villi,  and  it  has 
been  found  experimentally  that  it  passes  from  the  villi  into  the  venous  sinuses  into  which  they 
project. 

The  Pia  Mater. 

The  pia  mater  is  a  vascular  membrane,  consisting  of  a  minute  plexus  of  blood- 
vessels, held  together  by  an  extremely  fine  areolar  tissue  and  covered  by  a  reflexion 
of  the  mesotheUal  cells  from  the  arachnoid  trabecular.    It  is  an  incomplete  mem- 


THE  PI  A  MATER 


879 


brane,  absent  p^obabl^'  at  the  foramen  of  Majendie  and  the  two  foramina  of  Luschka 
and  perforated  in  a  peculiar  manner  by  all  the  bloodvessels  as  they  enter  or  leave 
the  nervous  system.     In  the  peri\'ascular  spaces,  the  pia  apparently  enters  as  a 

Iinesothelial  lining  of  the  outer  surface  of  the  space;  a  variable  distance  from  the 
exterior  these  cells  become  unrecognizable  and  are  apparently  lacking,  replaced  by 
neuroglia  elements.  The  inner  walls  of  these  perivascular  spaces  seem  likewise 
covered  for  a  certain  distance  by  the  mesothelial  cells,  reflected  with  the  vessels 
from  the  arachnoid  co\'ering  of  these  vascular  channels  as  they  traverse  the  sub- 
arachnoid spaces. 

The  Cranial  Pia  Mater  (pia  mater  encephali;  pia  of  the  brain)  invests  the  entire 
surface  of  the  brain,  dips  between  the  cerebral  gyri  and  cerebellar  laminae,  and  is 
invaginated  to  form  the  tela  chorioidea  of  the  third  ventricle,  and  the  choroid 
plexuses  of  the  lateral  and  third  ventricles  (pages  840  and  841) ;  as  it  passes  over 
the  roof  of  the  fourth  ventricle,  it  forms  the  tela  chorioidea  and  the  choroid 
)lexuses  of  this  ventricle.  On  the  cerebellum  the  membrane  is  more  delicate;  the 
ressels  from  its  deep  surface  are  shorter,  and  its  relations  to  the  cortex  are  not 
intimate. 


Subdural  cavity 


Pia  mater 
Arachnoid 
Dura  mater 


Subdural  cavity 


Fig.  770. — Diagrammatic  transverse  section  of  the  medulla  spinalis  and  its  membranes. 


■  I  The  Spinal  Pia  Mater  {pia  mater  spinalis;  pia  of  the  cord)  (Figs.  767,  770)  is 
thicker,  firmer,  and  less  vascular  than  the  cranial  pia  mater:  this  is  due  to  the  fact 
that  it  consists  of  two  layers,  the  outer  or  additional  one  being  composed  of  bundles 
of  connective-tissue  fibers,  arranged  for  the  most  part  longitudinally.  Between 
the  layers  are  cleft-like  spaces  which  communicate  with  the  subarachnoid  cavity, 
and  a  number  of  bloodvessels  which  are  enclosed  in  perivascular  lymphatic  sheaths. 
The  spinal  pia  mater  covers  the  entire  surface  of  the  medulla  spinalis,  and  is  very 
intimately  adherent  to  it;  in  front  it  sends  a  process  backward  into  the  anterior 
fissure.  A  longitudinal  fibrous  band,  called  the  linea  splendens,  extends  along  the 
middle  line  of  the  anterior  surface;  and  a  somewhat  similar  band,  the  ligamentum 
denticulatiun,  is  situated  on  either  side.  Below  the  conus  medullaris,  the  pia  mater 
is  continued  as  a  long,  slender  filament  (filum  terminale),  which  descends  through 
the  center  of  the  mass  of  nerves  forming  the  cauda  equina.  It  blends  with  the 
dura  mater  at  the  level  of  the  lower  border  of  the  second  sacral  vertebra,  and  extends 
downward  as  far  as  the  base  of  the  coccyx,  where  it  fuses  with  the  periosteum.  It 
assists  in  maintaining  the  medulla  spinalis  in  its  position  during  the  movements 
of  the  trunk,  and  is,  from  this  circumstance,  called  the  central  ligament  of  the 

^^ medulla  spinalis. 

^Pf  The  pia  mater  forms  sheaths  for  the  cranial  and  spinal  nerves;  these  sheaths 


I 


are  closely  connected  Avith  the  nerves,  and  blend  with  their  common  membranous 
investments. 


880  NEUROLOGY 


I 


The  ligamentum  denticulatum  {dentate  ligament)  (Fig.  767)  is  a  narrow  fibrous 
band  situated  on  either  side  of  the  medulla  spinalis  throughout  its  entire  length, 
and  separating  the  anterior  from  the  posterior  nerve  roots.  Its  medial  border  is 
continuous  with  the  pia  mater  at  the  side  of  the  medulla  spinalis.  Its  lateral 
border  presents  a  series  of  triangular  tooth-like  processes,  the  points  of  which  are 
fixed  at  intervals  to  the  dura  mater.  These  processes  are  twenty-one  in  number, 
on  either  side,  the  first  being  attached  to  the  dura  mater,  opposite  the  margin 
of  the  foramen  magnum,  between  the  vertebral  artery  and  the  hypoglossal  nerve; 
and  the  last  near  the  lower  end  of  the  medulla  spinalis. 

THE  CEREBROSPINAL  FLXnD.i 

The  cerebrospinal  fluid,  for  the  most  part  elaborated  by  the  choroid  plexuses,, 
is  poured  into  the  cerebral  ventricles  which  are  lined  by  smooth  ependyma.  That 
portion  of  the  fluid  formed  in  the  lateral  ventricles  escapes  by  the  foramen  of  Monro 
into  the  third  ventricle  and  thence  by  the  aqueduct  into  the  fourth  ventricle. 
Likewise  an  ascending  current  of  fluid  apparently  occurs  in  the  central  canal  of 
the  spinal  cord;  this,  representing  a  possible  product  of  the  ependyma,  may  be  added 
to  the  intraventricular  supply.  From  the  fourth  ventricle  the  fluid  is  poured  into 
the  subarachnoid  spaces  through  the  medial  foramen  of  Majendie  and  the  two 
lateral  foramina  of  Luschka.  There  is  no  evidence  that  functional  communications 
between  the  cerebral  ventricles  and  the  subarachnoid  spaces  exist  in  any  region 
except  from  the  fourth  ventricle. 

In  addition  to  the  elaboration  of  the  cerebrospinal  fluid  by  the  choroid  plexuses,, 
there  seems  fairly  well  established  a  second  source  of  the  fluid  from  the  nervous- 
system  itself.  The  bloodvessels  that  enter  and  leave  the  brain  are  surrounded  by 
perivascular  channels.  It  seems  most  likely  that  the  outer  wall  of  these  channels  is 
lined  by  a  continuation  inward  of  the  pial  mesothelium  while  the  inner  wall  is 
probably  derived  from  the  mesothelial  covering  of  the  vessels,  which  are  thus 
protected  throughout  the  subarachnoid  spaces.  These  mesothelial  cells  continue 
inward  only  a  short  distance,  neuroglia  cells  probably  replacing  on  the  outer  surface 
the  mesothelial  elements.  Through  these  perivascular  channels  there  is  probably 
a  small  amount  of  fluid  flowing  from  nerve-cell  to  subarachnoid  space.  The  chemical 
differences  between  the  subarachnoid  fluid  (product  of  choroid  plexuses  and  peri- 
vascular system)  and  the  ventricular  fluid  (product  of  choroid  plexuses  alone) 
indicate  that  the  products  of  nerve-metabolism  are  poured  into  the  subarachnoid 
space. 

The  absorption  of  the  cerebrospinal  fluid  is  a  dual  process,  being  chiefly  a  rapid 
drainage  through  the  arachnoid  villi  into  the  great  dural  sinuses,  and,  in  small  part, 
a  slow  escape  into  the  true  lymphatic  vessels,  by  way  of  an  abundant  but  indirect 
perineural  course. 

In  general  the  arachnoid  channels  are  equipped  as  fluid  retainers  with  unques- 
tionable powers  of  diffusion  or  absorption  in  regard  to  certain  elements  in  the 
normal  cerebrospinal  fluid,  deriving  in  this  way  a  cellular  nutrition. 

The  subdural  space  (between  arachnoid  and  dura)  is  usually  considered  to  be  a 
part  of  the  cerebrospinal  channels.  It  is  a  very  small  space,  the  two  limiting  sur- 
faces being  separated  by  merely  a  capillary  layer  of  fluid.  Whether  this  fluid  is 
exactly  similar  to  the  cerebrospinal  fluid  is  very  difficult  to  ascertain.  Likewise 
our  knowledge  of  the  connections  between  the  subdural  and  subarachnoid  spaces 
is  hardly  definite.  In  some  ways  the  subdural  space  may  be  likened  to  a  serous 
cavity.  The  inner  surface  of  the  dura  is  covered  by  flattened  polygonal  mesothelial 
cells  but  the  outer  surface  of  the  arachnoid  is  covered  by  somewhat  cuboidal  meso- 
thelium. The  fluid  of  the  subdural  space  has  probably  a  local  origin  from  the  cells 
lining  it. 

'  Weed.  L.  H  ,  Anat.  Record,  1917,  12. 


THE  OLFACTORY  NERVES 


881 


THE  CRANIAL  NERVES  (NERVI  CEREBRALES;  CEREBRAL  NERVES). 


There  are  twelve  pairs  of  cranial  nerves;  they  are  attached  to  the  brain  and 
are  transmitted  through  foramina  in  the  base  of  the  cranium.  The  different  pairs 
are  named  from  before  backward  as  follows: 

I           1st.    Olfactory.  7th.  Facial. 

2d.     Optic.  8th.  Acoustic. 

t          3d.     Oculomotor.  9th.  Glossopharyngeal. 

\         4th.   Trochlear.  10th.  Vagus. 

I          5th.   Trigeminal.  11th.  Accessory. 

6th.   Abducent.  12th.  Hypoglossal. 


The  area  of  attachment  of  a  cranial  nerve  to  the  surface  of  the  brain  is  termed 
its  superficial  or  apparent  origin.  The  fibers  of  the  nerve  can  be  traced  into  the  sub- 
stance of  the  brain  to  a  special  nucleus  of  gray  substance.  The  motor  or  efferent 
cranial  nerves  arise  within  the  brain  from  groups  of  nerve  cells  which  constitute 
their  nuclei  of  origin.  The  sensory  or  afferent  cranial  nerves  arise  from  groups 
of  nerve  cells  outside  the  brain;  these  nerve  cells  may  be  grouped  to  form  ganglia 
on  the  trunks  of  the  nerves  or  may  be  situated  in  peripheral  sensory  organs  such 
as  the  nose  and  eye.  The  central  processes  of  these  cells  run  into  the  brain,  and 
there  end  by  arborizing  around  nerve  cells,  which  are  grouped  to  form  nuclei  of 
termination.  The  nuclei  of  origin  of  the  motor  nerves  and  the  nuclei  of  termination 
of  the  sensory  nerves  are  brought  into  relationship  with  the  cerebral  cortex,  the 
former  through  the  geniculate  fibers  of  the  internal  capsule,  the  latter  through 
;he  lemniscus.  The  geniculate  fibers  arise  from  the  cells  of  the  motor  area  of  the 
cortex,  and,  after  crossing  the  middle  line,  end  by  arborizing  around  the  cells  of  the 
auclei  of  origin  of  the  motor  cranial  nerves.  On  the  other  hand,  fibers  arise  from 
che  cells  of  the  nuclei  of  termination  of  the  sensory  nerves,  and  after  crossing  to 
the  opposite  side,  join  the  lemniscus,  and  thus  connect  these  nuclei,  directly  or 
indirectly,  with  the  cerebral  cortex. 


THE  OLFACTORY  NERVES  (NN.  OLFACTORH;  nRST  NERVE)  (Fig.  771). 

The  olfactory  nerves  or  nerves  of  smell  are  distributed  to  the  mucous  membrane 
of  the  olfactory  region  of  the  nasal  cavity :  this  region  comprises  the  superior  nasal 


Fibers  of  olfactory 

tract 

Mitral  cells 


Glomeruli 


Olfactory  cell 


Olfactory 
epithelium 


FiQ.  771. — Nerves  of  septum  of  nose.     Right  side. 


Fig.  772. — Plan  of  olfactory  neurons. 


concha,  and  the  corresponding  part  of  the  nasal  septum.    The  nerves  originate 
from  the  central  or  deep  processes  of  the  olfactory  cells  of  the  nasal  mucous  mem- 


882 


NEUROLOGY 


I 


brane.  They  form  a  plexiform  net-work  in  the  mucous  membrane,  and  are  tl  en 
collected  into  about  twenty  branches,  which  pierce  the  cribriform  plate  of  the  eth- 
moid bone  in  two  groups,  a  lateral  and  a  medial  group,  and  end  in  the  glomeruli 
of  the  olfactory  bulb  (Fig.  772).  Each  branch  receives  tubular  sheaths  from  the 
dura  mater  and  pia  mater,  the  former  being  lost  in  the  periosteum  of  the  nose, 
the  latter  in  the  neurolemma  of  the  nerve. 

The  olfactory  nerves  are  non-medullated,  and  consist  of  axis-cylinders  surrounded 
by  nucleated  sheaths,  in  which,  however,  there  are  fewer  nuclei  than  are  found  in 
the  sheaths  of  ordinary  non-medullated  nerve  fibers. 

The  olfactory  center  in  the  cortex  is  generally  associated  with  the  rhinencephalon 
(page  826). 

The  olfactary  nerves  are  developed  from  the  cells  of  the  ectoderm  which  lines 
the  olfactory  pits ;  these  cells  undergo  proliferation  and  give  rise  to  what  are  termed 
the  olfactory  cells  of  the  nose.  The  axons  of  the  olfactory  cells  grow  into  the  over- 
lying olfactory  bulb  and  form  the  olfactory  nerves. 

THE  OPTIC  NERVE  (N.  OPTICUS;   SECOND  NERVE)   (Fig.  773). 

The  optic  nerve,  or  nerve  of  sight,  consists  mainly  of  fibers  derived  from  the  gan- 
glionic cells  of  the  retina.    These  axons  terminate  in  arborizations  around  the  cells 

in  the  lateral  geniculate  body,  puh'inar,  and 
superior  colliculus  which  constitute  the  lower 
or  primary  visual  centers.  From  the  cells  of 
the  lateral  geniculate  body  and  the  pulvinar 
fibers  pass  to  the  cortical  visual  center,  situated 
in  the  cuneus  and  in  the  neighborhood  of  the 
calcarine  fissure.  A  few  fibers  of  the  optic  nerve, 
of  small  caliber,  pass  from  the  primary  centers 
to  the  retina  and  are  supposed  to  go\'ern 
chemical  changes  in  the  retina  and  also  the 
movements  of  some  of  its  elements  (pigment 
cells  and  cones) .  There  are  also  a  few  fine  fibers, 
afferent  fibers,  extending  from  the  retina  to  the 
brain,  that  are  supposed  to  be  concerned  in 
pupillary  reflexes. 

The  optic  nerve  is  peculiar  in  that  its  fibers 
and  ganglion  cells  are  probably  third  in  the 
series  of  neurons  from  the  receptors  to  the 
brain.  Consequently  the  optic  nerve  corre- 
sponds rather  to  a  tract  of  fibers  within  the  brain  than  to  the  other  cranial 
nerves.  Its  fibers  pass  backward  and  medialward  through  the  orbit  and  optic 
foramen  to  the  optic  commissure  where  they  partially  decussate.  The  mixed  fibers 
from  the  two  nerves  are  continued  in  the  optic  tracts,  the  primary  visual  centers 
of  the  brain. 

The  orbital  portion  of  the  optic  nerve  is  from  20  mm.  to  30  mm.  in  length  and  has 
a  slightly  sinuous  course  to  allow  for  movements  of  the  eyeball.  It  is  invested  by 
an  outer  sheath  of  dura  mater  and  an  inner  sheath  from  the  arachnoid  which  are 
attached  to  the  sclera  around  the  area  where  the  nerve  fibers  pierce  the  choroid 
and  sclera  of  the  bulb.  A  little  behind  the  bulb  of  the  eye  the  central  artery  of  the 
retina  with  its  accompanying  vein  perforates  the  optic  nerve,  and  runs  within  it 
to  the  retina.  As  the  nerve  enters  the  optic  foramen  its  dural  sheath  becomes 
continuous  with  that  lining  the  orbit  and  the  optic  foramen.  In  the  optic  foramen 
the  ophthalmic  artery  lies  below  and  to  its  outer  side.  The  intercranial  portion 
of  the  optic  nerve  is  about  10  mm.  in  length. 


Fig.  773. — The  left  optic  nerve  and  the 
optic  tracts. 


THE  OPTIC  NERVE 


883 


I  The  Optic  Chiasma  {chiasma  opticum),  somewhat  quadrilateral  in  form,  rests 
upon  the  tuberculum  sellse  and  on  the  anterior  part  of  the  diaphragma  sellae. 
It  is  in  relation,  above,  with  the  lamina  terminalis;  behind,  with  the  tuber  cinereum; 
on  either  side,  with  the  anterior  perforated  substance.  Within  the  chiasma,  the 
optic  nerves  undergo  a  partial  decussation.  The  fibers  forming  the  medial  part  of 
each  tract  and  posterior  part  of  the  chiasma  have  no  connection  with  the  optic 
nerves.  They  simply  cross  in  the  chiasma,  and  connect  the  medial  geniculate 
bodies  of  the  two  sides;  they  form  the  commissure  of  Gudden.  The  remaining  and 
principal  part  of  the  chiasma  consists  of  two  sets  of  fibers,  crossed  and  uncrossed. 
The  crossed  fibers  which  are  the  more  numerous,  occupy  the  central  part  of  the 
chiasma,  and  pass  from  the  optic  nerve  of  one  side  to  the  optic  tract  of  the  other, 
decussating  in  the  chiasma  with  similar  fibers  of  the  opposite  optic  nerve.  The 
uncrossed  fibers  occupy  the  lateral  part  of  the  chiasma,  and  pass  from  the  nerve 
«of  one  side  into  the  tract  of  the  same  side.^ 


Optic  nerve 
Crossed  fibers 
*  Uncrossed  fibers 

Optic  chiasma 

^ Optic  tract 

■^ Commissure  of  Chidden 


Pvlvinar 

Lateral  geniculate  body 
Superior  coUiculus 
Medial  geniculate  body 

Nudetia  of  oculomotor  nerve 
Nucleus  of  trochlear  nerve 
Nucleus  of  abducent  nerve 


Cortex  of  occipital  lobes 
Fig.  774. — Scheme  showing  central  connections  of  the  optic  nerves  and  optic  tracts. 


The  crossed  fibers  of  the  optic  nerve  tend  to  occupy  the  medial  side  of  the  nerve 
and  the  uncrossed  fibers  the  lateral  side.  In  the  optic  tract,  however,  the  fibers 
are  much  more  intermingled. 

'  A  specimen  of  congenital  absence  of  the  optic  chiasma  is  to  be  found  in  the  Museum  of  the  Westminister  Hospital. 
See  also  Henle,  A'ervenlehre,  p   393,  ed.  2. 


k 


TEUROLOGY 


I 


The  Optic  Tract  (Fig,  774),  passes  backward  and  outward  from  the  optic  chiasnia 
over  the  tuber  cinereum  and  anterior  perforated  space  to  the  cerebral  peduncle 
and  winds  obliquely  across  its  under  surface.  Its  fibers  terminate  in  the  lateral 
geniculate  body,  the  pulvinar  and  the  superior  colliculus.  It  is  adherent  to  the 
tuber  cinereum  and  the  cerebral  peduncle  as  it  passes  over  them.  In  the  region  of 
the  lateral  geniculate  body  it  splits  into  two  bands.  The  medial  and  smaller  one  is 
a  part  of  the  commissure  of  Gudden  and  ends  in  the  medial  geniculate  body.* 

From  its  mode  of  development,  and  from  its  structure,  the  optic  nerve  must  be  regarded  as  a 
prolongation  of  the  brain  substance,  rather  than  as  an  ordinary  cerebrospinal  nerve.  As  it 
passes  from  the  brain  it  receives  sheaths  from  the  three  cerebral  membranes,  a  perineural 
sheath  from  the  pia  mater,  an  intermediate  sheath  from  the  arachnoid,  and  an  outer  sheath 
from  the  dura  mater,  which  is  also  connected  with  the  periosteum  as  it  passes  through  the 
optic  foramen.  These  sheaths  are  separated  from  each  other  by  cavities  which  communicate 
with  the  subdural  and  subarachnoid  cavities  respectively.  The  innermost  or  perineural  sheath 
sends  a  process  around  the  arteria  centralis  retina)  into  the  interior  of  the  nerve,  and  enters 
intimately  into  its  structure. 

THE  OCULOMOTOR  NERVE  (N.  OCULOMOTORIUS ;  THIRD  NERVE) 

(Figs.  775,  776,  777). 

The  oculomotor  nerve  supplies  somatic  motor  fibers  to  all  the  ocular  muscles, 
except  the  Obliquus  superior  and  Rectus  lateralis;  it  also  supplies  through  its 
connections  with  the  ciliary  ganglion,  sympathetic  motor  fibers  to  the  Sphincter 
pupillse  and  the  Ciliaris  muscles. 


LEVATOR  PALPEBR>e 


RECTUS  SUPERIOR 


Short  ciliary 

ECTUS  MEDIALIS 
RECTUS  INFERIOR 
OBLIQUUS  INFERIOR 


Fig.  775. — Plan  of  oculomotor  nerve. 


The  fibers  of  the  oculomotor  nerve  arise  from  a  nucleus  which  lies  in  the  gray 
substance  of  the  floor  of  the  cerebral  aqueduct  and  extends  in  front  of  the  aqueduct 
for  a  short  distance  into  the  floor  of  the  third  ventricle.  From  this  nucleus  the 
fibers  pass  forward  through  the  tegmentum,  the  red  nucleus,  and  the  medial  part 
of  the  substantia  nigra,  forming  a  series  of  curves  with  a  lateral  convexity,  and 
emerge  from  the  oculomotor  sulcus  on  the  medial  side  of  the  cerebral  peduncle. 

The  nucleus  of  the  oculomotor  nerve  does  not  consist  of  a  continuous  column 
of  cells,  but  is  broken  up  into  a  number  of  smaller  nuclei,  which  are  arranged  in 
two  groups,  anterior  and  posterior.  Those  of  the  posterior  group  are  six  in  number, 
five  of  which  are  symmetrical  on  the  two  sides  of  the  middle  line,  while  the  sixth 
is  centrally  placed  and  is  common  to  the  nerves  of  both  sides.  The  anterior  group 
consists  of  two  nuclei,  an  antero-medial  and  an  antero-lateral  (Fig.  762). 

The  nucleus  of  the  oculomotor  nerve,  considered  from  a  physiological  standpoint, 
can  be  subdivided  into  several  smaller  groups  of  cells,  each  group  controlling  a 
particular  muscle. 

On  emerging  from  the  brain,  the  nerve  is  invested  with  a  sheath  of  pia  mater, 
and  enclosed  in  a  prolongation  from  the  arachnoid.  It  passes  between  the  superior 
cerebellar  and  posterior  cerebral  arteries,  and  then  pierces  the  dura  mater  in  front 


THE  TROCHLEAR  NERVE 


885 


of  and  lateral  to  the  posterior  clinoid  process,  passing  between  the  free  and  attached 
borders  of  the  tentorium  cerebelli.  It  runs  along  the  lateral  wall  of  the  cavernous 
sinus,  above  the  other  orbital  nerves,  receiving  in  its  course  one  or  two  filaments 
from  the  cavernous  plexus  of  the  sympathetic,  and  a  communicating  branch  from 
the  ophthalmic  division  of  the  trigeminal.  It  then  divides  into  two  branches, 
which  enter  the  orbit  through  the  superior  orbital  fissure,  between  the  two  heads 
of  the  Rectus  lateralis.  Here  the  nerve  is  placed  below  the  trochlear  nerve  and 
the  frontal  and  lacrimal  branches  of  the  ophthalmic  nerve,  while  the  nasociliary 
nerve  is  placed  between  its  two  rami. 

The  superior  ramus,  the  smaller,  passes  medialward  over  the  optic  nerve,  and 
supplies  the  Rectus  superior  and  Levator  palpebrse  superioris.  The  inferior  ramus, 
the  larger,  divides  into  three  branches.  One  passes  beneath  the  optic  nerve  to  the 
Rectus  medialis;  another,  to  the  Rectus  inferior;  the  third  and  longest  runs  for- 
ward between  the. Recti  inferior  and  lateralis  to  the  Obliquus  inferior.  From 
the  last  a  short  thick  branch  is  given  off  to  the  lower  part  of  the  ciliary  ganglion, 
and  forms  its  short  root.  All  these  branches  enter  the  muscles  on  their  ocular 
surfaces,  with  the  exception  of  the  nerve  to  the  Obliquus  inferior,  which  enters 
the  muscle  at  its  posterior  border. 
I 

THE  TROCHLEAR  NERVE  (N.  TROCHLEARIS;  FOURTH  NERVE)  (Fig.  776). 

The  trochlear  nerve,  the  smallest  of  the  cranial  nerves,  supplies  the  Obliquus 
superior  oculi. 

I  It  arises  from  a  nucleus  situated  in  the 
floor  of  the  cerebral  aqueduct,  opposite 
the  upper  part  of  the  inferior  colliculus. 
From  its  origin  it  runs  downward  through 
the  tegmentum,  and  then  turns  backward 
into  the  upper  part  of  the  anterior  medul- 
lary velum.  Here  it  decussates  with  its 
fellow  of  the  opposite  side  and  emerges 
from  the  surface  of  the  velum  at  the  side 
of  the  frenulum  veli,  immediately  behind 
the  inferior  colliculus. 

The  nerve  is  directed  across  the  super- 
ior cerebellar  peduncle,  and  then  winds 
forward  around  the  cerebral  peduncle, 
immediately  above  the  pons,  pierces  the 
dura  mater  in  the  free  border  of  the  ten- 

orium  cerebelli,  just  behind,  and  lateral 

o,   the    posterior    clinoid    process,    and 

asses  forward  in  the  lateral  wall  of  the 

cavernous  sinus,  between  the  oculomotor 

nerve  and  the  ophthalmic  division  of  the 

trigeminal.      It  crosses    the    oculomotor 

nerve,  and  enters  the  orbit  through  the 

Isuperior  orbital  fissure.    It  now  becomes 

the  highest  of  all  the   nerves,    and   lies 

medial  to  the  frontal  nerve.    In  the  orbit 

lit  passes  medialward,  above  the  origin  of 

Hhe    Levator    palpebrie    superioris,    and 

finally  enters  the  orbital  surface  of  the 

Obliquus  superior. 

In  the  lateral  wall  of  the  cavernous  sinus  the  trochlear  nerve  forms  communica- 
tions with  the  ophthalmic  division  of  the  trigeminal  and  with  the  cavernous  plexus 


Motor  n 
Sensory  root' 


Recurrent 
filament  to 
dura  mater 


Fig.  776. — Nerves  of  the  orbit.     Seen  from  above. 


886  NEUROLOGY 


I 


of  the  sympathetic.  In  the  superior  orbital  fissure  it  occasionally  gives  off  a 
branch  to  the  lacrimal  nerve.  It  gives  off  a  recurrent  branch  which  passes  back- 
ward between  the  layers  of  the  tentorium  cerebelli  and  divides  into  two  or  three 
filaments  which  may  be  traced  as  far  as  the  wall  of  the  transverse  sinus. 


THE  TRIGEMINAL  NERVE  (N.  TRIGEMINUS;  FIFTH  OR  TRIFACIAL 

NERVE). 

The  trigeminal  nerve  is  the  largest  cranial  nerve  and  is  the  great  sensory  nerve 
of  the  head  and  face,  and  the  motor  nerve  of  the  muscles  of  mastication. 

It  emerges  from  the  side  of  the  pons,  near  its  upper  border,  by  a  small  motor 
and  a  large  sensory  root — the  former  being  situated  in  front  of  and  medial  to  the 
latter. 

Motor  Root. — The  fibers  of  the  motor  root  arise  from  two  nuclei,  a  superior  and 
an  inferior.  The  superior  nucleus  consists  of  a  strand  of  cells  occupying  the  whole 
length  of  the  lateral  portion  of  the  gray  substance  of  the  cerebral  aqueduct.  The 
inferior  or  chief  nucleus  is  situated  in  the  upper  part  of  the  pons,  close  to  its  dorsal 
surface,  and  along  the  line  of  the  lateral  margin  of  the  rhomboid  fossa.  The  fibers 
from  the  superior  nucleus  constitute  the  mesencephalic  root :  they  descend  through 
the  mid-brain,  and,  entering  the  pons,  join  with  the  fibers  from  the  lower 
nucleus,  and  the  motor  root,  thus  formed,  passes  forward  through  the  pons  to  its 
point  of  emergence.  It  is  uncertain  whether  the  mesencephalic  root  is  motor  or 
sensory. 

Sensory  Root. — The  fibers  of  the  sensory  root  arise  from  the  cells  of  the  semilunar 
ganglion  which  lies  in  a  cavity  of  the  dura  mater  near  the  apex  of  the  petrous  part 
of  the  temporal  bone.  They  pass  backward  below  the  superior  petrosal  sinus 
and  tentorium  cerebelli,  and,  entering  the  pons,  divide  into  upper  and  lower  roots. 
The  upper  root  ends  partly  in  a  nucleus  which  is  situated  in  the  pons  lateral  to  the 
lower  motor  nucleus,  and  partly  in  the  locus  cseruleus;  the  lower  root  descends 
through  the  pons  and  medulla  oblongata,  and  ends  in  the  upper  part  of  the  sub- 
stantia gelatinosa  of  Rolando.  This  lower  root  is  sometimes  named  the  spinal 
root  of  the  nerve.  Medullation  of  the  fibers  of  the  sensory  root  begins  about  the 
fifth  month  of  fetal  life,  but  the  whole  of  its  fibers  are  not  medullated  until  the 
third  month  after  birth. 

The  Semilunar  Ganglion  (ganglion semihinare[Gasseri];  Gasserian ganglion)  occu- 
pies a  cavity  (cavum  Meckelii)  in  the  dura  mater  covering  the  trigeminal  impression 
near  the  apex  of  the  petrous  part  of  the  temporal  bone.  It  is  somewhat  crescentic  in 
shape,  with  its  convexity  directed  forward :  medially,  it  is  in  relation  with  the  inter- 
nal carotid  artery  and  the  posterior  part  of  the  cavernous  sinus.  The  motor  root 
runs  in  front  of  and  medial  to  the  sensory  root,  and  passes  beneath  the  ganglion; 
it  leaves  the  skull  through  the  foramen  ovale,  and,  immediately  below  this 
foramen,  joins  the  mandibular  nerve.  The  greater  superficial  petrosal  nerve  lies 
also  underneath  the  ganglion. 

The  ganglion  receives,  on  its  medial  side,  filaments  from  the  carotid  plexus 
of  the  sympathetic.  It  give  off  minute  branches  to  the  tentorium  cerebelli,  and  to 
the  dura  mater  in  the  middle  fossa  of  the  cranium.  From  its  convex  border,  which 
is  directed  forward  and  lateralward,  three  large  nerves  proceed,  viz.,  the  ophthalmic, 
maxillary,  and  mandibular.  The  ophthalmic  and  maxillary  consist  exclusively 
of  sensory  fibers;  the  mandibular  is  joined  outside  the  cranium  by  the  motor  root. 

Associated  with  the  three  divisions  of  the  trigeminal  nerve  are  four  small  ganglia. 
The  ciliary  ganglion  is  connected  with  the  ophthalmic  nerve;  the  sphenopalatine 
ganglion  with  the  maxillary  nerve;  and  the  otic  and  submaxillary  ganglia  with  the 
mandibular  nerve.    All  four  receive  sensory  filaments  from  the  trigeminal,  and 


THE  TRIGEMINAL  NERVE 


887 


i motor  and  sympathetic  filaments  from  various  sources;  these  filaments  are  called 
the  roots  of  the  ganglia. 

The  Ophthalmic  Nerve  (n.  ophthalmicus)  (Figs.  776,  777),  or  first  division  of  the 
trigeminal,  is  a  sensory  nerve.  It  supplies  branches  to  the  cornea,  ciliary  body, 
and  iris;  to  the  lacrimal  gland  and  conjunctiva;  to  the  part  of  the  mucous  membrane 
of  the  nasal  cavity;  and  to  the  skin  of  the  eyelids,  eyebrow,  forehead,  and  nose. 
It  is  the  smallest  of  the  three  divisions  of  the  trigeminal,  and  arises  from  the  upper 
part  of  the  Semilunar  ganglion  as  a  short,  flattened  band,  about  2.5  cm.  long, 
which  passes  forward  along  the  lateral  wall  of  the  cavernous  sinus,  below  the 
oculomotor  and  trochlear  nerves;  just  before  entering  the  orbit,  through  the  supe- 
rior orbital  fissure,  it  divides  into  three  branches,  lacrimal,  frontal,  and  nasociliary. 

The  ophthalmic  nerve  is  joined  by  filaments  from  the  cavernous  plexus  of  the 
sympathetic,  and  communicates  with  the  oculomotor,  trochlear,  and  abducent 
nerves;  it  gives  off  a  recurrent  filament  which  passes  between  the  layers  of  the 
tentorium. 


Internal  carotid  artery 
and  carotid  plexus 


Upper  division  of 
oculomotor  nerve 


Sensory 
root 

Motor  root 


I 


Fig.  777. — Nerve3  of  the  orbit,   and  the  ciliary  ganglion.     Side  view. 

The  Lacrimal  Nerve  {n.  lacrimalis)  is  the  smallest  of  the  three  branches  of  the 
)phthalmic.    It  sometimes  receives  a  filament  from  the  trochlear  nerve,  but  this 
Bs  possibly  derived  from  the  branch  which  goes  from  the  ophthalmic  to  the  troch- 
lear nerve.    It  passes  forward  in  a  separate  tube  of  dura  mater,  and  enters  the  orbit 
through  the  narrowest  part  of  the  superior  orbital  fissure.     In  the  orbit  it  runs 
I  lalong  the  upper  border  of  the  Rectus  lateralis,  with  the  lacrimal  artery,  and  com- 
'municates  with  the  zygomatic  branch  of  the  maxillary  nerve.    It  enters  the  lacrimal 
gland  and  gives  oft'  several  filaments,  which  supply  the  gland  and  the  conjunctiva. 
Finally  it  pierces  the  orbital  septum,  and  ends  in  the  skin  of  the  upper  eyelid, 
joining  with  filaments  of  the  facial  nerve.    The  lacrimal  nerve  is  occasionally 
llabsent,  and  its  place  is  then  taken  by  the  zygomaticotemporal  branch  of  the  max- 
illary.   Sometimes  the  latter  branch  is  absent,  and  a  continuation  of  the  lacrimal 
is  substituted  for  it. 

The  Frontal  Nerve  (n.  frontalis)  is  the  largest  branch  of  the  ophthalmic,  and  may 
be  regarded,  both  from  its  size  and  direction,  as  the  continuation  of  the  nerve. 
It  enters  the  orbit  through  the  superior  orbital  fissure,  and  runs  forward  between 
the  Levator  palpebra?  superioris  and  the  periosteum.  Midway  between  the  apex 
and  base  of  the  orbit  it  divides  into  two  branches,  supratrochlear  and  supraorbital. 


888  NEUROLOGY 

The  supratrochlear  nerve  {n.  supratrochlearis) ,  the  smaller  of  the  two,  passes 
above  the  pulley  of  the  Obliquus  superior,  and  gives  off  a  descending  filament,  tc> 
join  the  infratrochlear  branch  of  the  nasociliary  nerve.  It  then  escapes  from  the; 
orbit  between  the  pulley  of  the  Obliquus  superior  and  the  supraorbital  foramen, 
curves  up  on  to  the  forehead  close  to  the  bone,  ascends  beneath  the  Corrugator 
and  Frontalis,  and  dividing  into  branches  which  pierce  these  muscles,  it  supplies 
the  skin  of  the  lower  part  of  the  forehead  close  to  the  middle  line  and  sends 
filaments  to  the  conjunctiva  and  skin  of  the  upper  eyelid. 

The  supraorbital  nerve  (n.  swpraorhitalis)  passes  through  the  supraorbital  foramen, 
and  gives  off,  in  this  situation,  palpebral  filaments  to  the  upper  eyelid.  It  then 
ascends  upon  the  forehead,  and  ends  in  tw^o  branches,  a  medial  and  a  lateral, 
which  supply  the  integument  of  the  scalp,  reaching  nearly  as  far  back  as  the  lamb- 
doidal  suture;  they  are  at  first  situated  beneath  the  Frontalis,  the  medial  branch 
perforating  the  muscle,  the  lateral  branch  the  galea  aponeurotica.  Both  branches 
supply  small  twigs  to  the  pericranium. 

The  Nasociliary  Nerve  {n.  nasociliaris;  nasal  nerve)  is  intermediate  in  size  between 
the  frontal  and  lacrimal,  and  is  more  deeply  placed.  It  enters  the  orbit  between 
the  two  heads  of  the  Rectus  lateralis,  and  between  the  superior  and  inferior  rami 
of  the  oculomotor  nerve.  It  passes  across  the  optic  nerve  and  runs  obliquely 
beneath  the  Rectus  superior  and  Obliquus  superior,  to  the  medial  wall  of  the  orbital 
cavity.  Here  it  passes  through  the  anterior  ethmoidal  foramen,  and,  entering 
the  cavity  of  the  cranium,  traverses  a  shallow  groove  on  the  lateral  margin  of  the 
front  part  of  the  cribriform  plate  of  the  ethmoid  bone,  and  runs  down,  through 
a  slit  at  the  side  of  the  crista  galli,  into  the  nasal  cavity.  It  supplies  internal 
nasal  branches  to  the  mucous  membrane  of  the  front  part  of  the  septum  and  lateral 
wall  of  the  nasal  cavity.  Finally,  it  emerges,  as  the  external  nasal  branch,  between 
the  lower  border  of  the  nasal  bone  and  the  lateral  nasal  cartilage,  and,  passing 
down  beneath  the  Nasalis  muscle,  supplies  the  skin  of  the  ala  and  apex  of  the  nose. 

The  nasociliary  nerve  gives  off  the  following  branches,  viz.:  the  long  root  of  the 
ciliary  ganglion,  the  long  ciliary,  and  the  ethmoidal  nerves. 

The  long  root  of  the  ciliary  ganglion  {radix  longa  ganglii  ciliaris)  usually  arises 
from  the  nasociliary  between  the  two  heads  of  the  Rectus  lateralis.  It  passes 
forward  on  the  lateral  side  of  the  optic  nerve,  and  enters  the  postero-superior  angle 
of  the  ciliary  ganglion;  it  is  sometimes  joined  by  a  filament  from  the  cavernous 
plexus  of  the  sympathetic,  or  from  the  superior  ramus  of  the  trochlear  nerve. 

The  long  ciliary  nerves  {nn.  ciliares  longi),  tw-o  or  three  in  number,  are  given  off 
from  the  nasociliary,  as  it  crosses  the  optic  nerve.  They  accompany  the  short 
ciliary  nerves  from  the  ciliary  ganglion,  pierce  the  posterior  part  of  the  sclera, 
and  running  forward  between  it  and  the  choroid,  are  distributed  to  the  iris  and 
cornea.  The  long  ciliary  nerves  are  supposed  to  contain  sympathetic  fibers  from 
the  superior  cervical  ganglion  to  the  Dilator  pupillse  muscle. 

The  infratrochlear  nerve  (n.  infratrochlearis)  is  given  off  from  the  nasociliary 
just  before  it  enters  the  anterior  ethmoidal  foramen.  It  runs  forward  along  the 
upper  border  of  the  Rectus  medialis,  and  is  joined,  near  the  pulley  of  the  Obliquus 
superior,  by  a  filament  JFrom  the  supratrochlear  nerve.  It  then  passes  to  the 
medial  angle  of  the  eye,  and  supplies  the  skin  of  the  eyelids  and  side  of  the  nose, 
the  conjunctiva,  lacrimal  sac,  and  caruncula  lacrimalis. 

The  ethmoidal  branches  {nn.  ethmoidales)  supply  the  ethmoidal  cells;  the  posterior 
branch  leaves  the  orbital  cavity  through  the  posterior  ethmoidal  foramen  and  gives 
some  filaments  to  the  sphenoidal  sinus. 

The  Ciliary  Ganglion  {ophthalmic  or  lentindar  ganglion)  (Figs.  775,  777). — The 
ciliary  ganglion  is  a  small,  sjinpathetic  ganglion,  of  a  reddish-gray  color,  and  about 
the  size  of  a  pin's  head;  it  is  situated  at  the  back  part  of  the  orbit,  in  some  loose 
fat  betw^een  the  optic  nerve  and  the  Rectus  lateralis  muscle,  lying  generally  on  thej 
lateral  side  of  the  ophthalmic  artery. 


I 


THE  TRIGEMINAL  NERVE 


889 


Its  roots  are  three  in  number,  and  enter  its  posterior  border.  One,  the  long 
or  sensory  root,  is  derived  from  the  nasociliary  nerve,  and  joins  its  postero-superior 
angle.  The  second,  the  short  or  motor  root,  is  a  thick  nerve  (occasionally  divided 
into  two  parts)  derived  from  the  branch  of  the  oculomotor  nerve  to  the  Obliquus 
inferior,  and  connected  with  the  postero-inferior  angle  of  the  ganglion.  The  motor 
root  is  supposed  to  contain  s>Tiipathetic  efferent  fibers  (preganglionic  fibers)  from 
the  nucleus  of  the  third  nerve  in  the  mid-brain  to  the  ciliary  ganglion  w^here  they 
form  synapses  with  neurons  w^hose  fibers  (postganglionic)  pass  to  the  Ciliary  muscle 
and  to  Sphincter  muscle  of  the  pupil.  The  third,  the  s^Tnpathetic  root,  is  a  slender 
filament  from  the  cavernous  plexus  of  the  sympathetic;  it  is  frequently  blended 
with  the  long  root.  According  to  Tiedemann,  the  ciliary  ganglion  receives  a  twig 
)f  communication  from  the  sphenopalatine  ganglion. 

Its  branches  are  the  short  ciliary  nerves.  These  are  delicate  filaments,  from  six 
to  ten  in  number,  which  arise  from  the  forepart  of  the  ganglion  in  two  bundles 
connected  with  its  superior  and  inferior  angles;  the  lower  bundle  is  the  larger. 
They  run  forward  with  the  ciliary  arteries  in  a  wavy  course,  one  set  above  and  the 
other  below  the  optic  nerve,  and  are  accompanied  by  the  long  ciliary  nerves  from 
the  nasociliary.  They  pierce  the  sclera  at  the  back  part  of  the  bulb  of  the  eye,  pass 
forward  in  delicate  grooves  on  the  inner  surface  of  the  sclera,  and  are  distributed 
to  the  Ciliaris  muscle,  iris,  and  cornea.  Tiedemann  has  described  a  small  branch 
as  penetrating  the  optic  nerve  with  the  arteria  centralis  retinae. 

The  Maxillary  Nerve  {n.  maxillaris;  superior  maxillary  nerve)  (Fig.  778),  or 
second  division  of  the  trigeminal,  is  a  sensory  nerve.  It  is  intermediate,  both  in 
position  and  size,  between  the  ophthalmic  and  mandibular.  It  begins  at  the  middle 
of  the  semilunar  ganglion  as  a  flattened  plexiform  band,  and,  passing  horizontally 
forward,  it  leaves  the  skull  through  the  foramen  rotundum,  where  it  becomes  more 
cylindrical  in  form,  and  firmer  in  texture.  It  then  crosses  the  pterygopalatine 
fossa,  inclines  lateralward  on  the  back  of  the  maxilla,  and  enters  the  orbit  through 
the  inferior  orbital  fissure;  it  traverses  the  infraorbital  groove  and  canal  in  the 
floor  of  the  orbit,  and  appears  upon  the  face  at  the  infraorbital  foramen.^  At 
its  termination,  the  nerve  lies  beneath  the  Quadratus  labii  superioris,  and  divides 
into  a  leash  of  branches  which  spread  out  upon  the  side  of  the  nose,  the  lower 
eyelid,  and  the  upper  lip,  joining  with  filaments  of  the  facial  nerve. 

Branches. — Its  branches  may  be  divided  into  four  groups,  according  as  they  are 
given  off  in  the  cranium,  in  the  pterygopalatine  fossa,  in  the  infraorbital  canal,  or 
on  the  face. 


In  the  Cranium 


In  the  Pterygopalatine  Fossa 


In  the  Infraorbital  Canal 


On  the  Face 


Middle  meningeal. 

(Zygomatic. 
Sphenopalatine. 
Posterior  superior  alveolar. 
(  Anterior  superior  alveolar. 
1  Middle  superior  alveolar. 

(Inferior  palpebral. 
External  nasal. 
Superior  labial. 


The  Middle  Meningeal  Nerve  (n.  meningeus  medius;  meningeal  or  dural  branch)  is 
given  off  from  the  maxillary  nerve  directly  after  its  origin  from  the  semilunar 
ganglion;  it  accompanies  the  middle  meningeal  artery  and  supplies  the  dura  mater. 

The  Zygomatic  Nerve  {n.  zygomaticus;  temporomalar  nerve;  orbital  nerve)  arises 
in  the  pterygopalatine  fossa,  enters  the  orbit  by  the  inferior  orbital  fissure, 
and  divides  at  the  back  of  that  cavity  into  two  branches,  zygomaticotemporal  and 
zygomaticofacial. 


i_ 


'  After  it  enters  the  infraorbital  canal,  the  nerve  ia  frequently  called  the  infraorbital. 


890 


NEUROLOGY 


The  zygomaticotemporal  branch  {ramus  zygomaticotemporalis;  temporal  branch) 
runs  along  the  lateral  wall  of  the  orbit  in  a  groove  in  the  zygomatic  bone,  receives 
a  branch  of  communication  from  the  lacrimal,  and,  passing  through  a  foramen 
in  the  zygomatic  bone,  enters  the  temporal  fossa.  It  ascends  between  the  bone, 
and  substance  of  the  Temporalis  muscle,  pierces  the  temporal  fascia  about  2.5  cm. 
above  the  zygomatic  arch,  and  is  distributed  to  the  skin  of  the  side  of  the  fore- 
head, and  communicates  with  the  facial  nerve  and  with  the  auriculotemporal 
branch  of  the  mandibular  nerve.  As  it  pierces  the  temporal  fascia,  it  gives  off  a 
slender  twig,  which  runs  between  the  two  layers  of  the  fascia  to  the  lateral  angle 
of  the  orbit. 


Sensory  root 
Motor  root 


Aurictdotemporcd 
nerve 


Fia.  778. — Distribution  of  the  maxillary  and  mandibular  nerves,  and  the  submaxillary  ganglion. 

The  zygomaticofacial  branch  (ramus  zygomaiicofacialis;  malar  branch)  passes 
along  the  infero-lateral  angle  of  the  orbit,  emerges  upon  the  face  through  a  foramen 
in  the  zygomatic  bone,  and,  perforating  the  Orbicularis  oculi,  supplies  the  skin  on 
the  prominence  of  the  cheek.  It  joins  with  the  facial  nerve  and  with  the  inferior 
palpebral  branches  of  the  maxillary. 

The  Sphenopalatine  Branches  {nn.  sphenopalatini) ,  two  in  number,  descend  to  the 
sphenopalatine  ganglion. 

The  Posterior  Superior  Alveolar  Branches  (rami  aheolares  superiores  posteriores; 
posterior  superior  dental  branches)  arise  from  the  trunk  of  the  nerve  just  before 
it  enters  the  infraorbital  groove;  they  are  generally  two  in  number,  but  sometimes 
arise  by  a  single  trunk.  They  descend  on  the  tuberosity  of  the  maxilla  and  give  off 
several  twigs  to  the  gums  and  neighboring  parts  of  the  mucous  membrane  of  the 
cheek.    They  then  enter  the  posterior  alveolar  canals  on  the  infratemporal  surface 


I 


THE  TRIGEMINAL  NERVE 


891 


^|of  the  maxilla,  and,  passing  from  behind  forward  in  the  substance  of  the  bone, 
'  communicate  with  the  middle  superior  alveolar  nerve,  and  give  off  branches  to  the 
lining  membrane  of  the  maxillary  sinus  and  three  twigs  to  each  molar  tooth;  these 
twigs  enter  the  foramina  at  the  apices  of  the  roots  of  the  teeth. 
.  The  Middle  Superior  Alveolar  Branch  (ramus  alveolaris  superior  medius;  viiddle 
superior  dental  hranch),  is  given  off  from  the  nerve  in  the  posterior  part  of  the  infra- 
orbital canal,  and  runs  downward  and  forward  in  a  canal  in  the  lateral  wall  of  the 
maxillary  sinus  to  supply  the  two  premolar  teeth.  It  forms  a  superior  dental  plexus 
with  the  anterior  and  posterior  superior  alveolar  branches. 

The  Anterior  Superior  Alveolar  Branch  {ramus  alveolaris  superior  anteriores;  ante- 
rior superior  dental  hranch),  of  considerable  size,  is  given  oft'  from  the  nerve  just 
before  its  exit  from  the  infraorbital  foramen;  it  descends  in  a  canal  in  the  anterior 
wall  of  the  maxillary  sinus,  and  divides  into  branches  which  supply  the  incisor 
and  canine  teeth.  It  communicates  with  the  middle  superior  alveolar  branch, 
and  gives  off  a  nasal  branch,  which  passes  through  a  minute  canal  in  the  lateral  wall 
of  the  inferior  meatus,  and  supplies  the  mucous  membrane  of  the  anterior  part  of 
the  inferior  meatus  and  the  floor  of  the  nasal  cavity,  communicating  with  the  nasal 
branches  from  the  sphenopalatine  ganglion. 


POSTERIOR 
DENTAL 

ORBITAL 

BRANCH CUT 

SPHENOPALATINE 
QANOLION 
!  OOULO- 

,  MOTOR 


SUPERIOR  CERVICAL 
GANGLION  OF  THE 


SYMPATHETIC 

?IG.  779. — Alveolar  branches  of  superior  maxillary  nerve  and  sphenopalatine  ganglion.     (Testut.) 

The  Inferior  Palpebral  Branches  {rami  palpebrales  inferiores;  palpebral  branches) 
ascend  behind  the  Orbicularis  oculi.  They  supply  the  skin  and  conjunctiva  of  the 
lower  eyelid,  joining  at  the  lateral  angle  of  the  orbit  with  the  facial  and  zygomatico- 
facial nerves. 

The  External  Nasal  Branches  {rami  nasales  externi)  supply  the  skin  of  the  side 
of  the  nose  and  of  the  septum  mobile  nasi,  and  join  with  the  terminal  twigs  of  the 
nasociliary  nerve. 

The  Superior  Labial  Branches  {rami  labiales  superior es;  labial  branches),  the  largest 
and  most  numerous,  descend  behind  the  Quadratus  labii  superioris,  and  are  dis- 
tributed to  the  skin  of  the  upper  lip,  the  mucous  membrane  of  the  mouth,  and  labial 
glands.  They  are  joined,  immediately  beneath  the  orbit,  by  filaments  from  the 
facial  nerve,  forming  with  them  the  infraorbital  plexus. 

Sphenopalatine  Ganglion  {ganglion  of  Meckel)  (Fig.  780). — ^The  sphenopalatine 
ganglion,  the  largest  of  the  sxinpathetic  ganglia  associated  with  the  branches  of  the 
trigeminal  nerve,  is  deeply  placed  in  the  pterygopalatine  fossa,  close  to  the  spheno- 


i_ 


8? 


NEUROLOGY 


L 


palatine  foramen.  It  is  triangular  or  heart-shaped,  of  a  reddish-gray  color,  and  is 
situated  just  below  the  maxillary  nerve  as  it  crosses  the  fossa.  It  receives  a  sensory, 
a  motor,  and  a  s^Tnpathetic  root. 

Its  sensory  root  is  derived  from  two  sphenopalatine  branches  of  the  maxillary 
nerve;  their  fibers,  for  the  most  part,  pass  directly  into  the  palatine  nerves;  a  fe\^■, 
however,  enter  the  ganglion,  constituting  its  sensory  root.  Its  motor  root  is  probably 
derived  from  the  nervus  intermedins  through  the  greater  superficial  petrosal  nerve 
and  is  supposed  to  consist  in  part  of  sympathetic  efferent  (preganglionic)  fibers 
from  the  medulla.  In  the  sphenopalatine  ganglion  they  form  synapses  with  neurons 
whose  postganglionic  axons,  vasodilator  and  secretory  fibers,  are  distributed  with 
the  deep  branches  of  the  trigeminal  to  the  mucous  membrane  of  the  nose,  soft 
palate,  tonsils,  uvula,  roof  of  the  mouth,  upper  lip  and  gums,  and  to  the  upper  part 
of  the  pharjTix.  Its  sympathetic  root  is  derived  from  the  carotid  plexus  through  the 
deep  petrosal  nerve.  These  two  nerves  join  to  form  the  nerve  of  the  pterygoid 
canal  before  their  entrance  into  the  ganglion. 


Termination  of      \  ' 
naao'palaiine 
nerve 


Fig.   780. — The  sphenopalatine  ganglion  and  its  branches. 

The  greater  superficial  petrosal  nerve  {n.  petrosus  superficialis  major;  large  super- 
ficial petrosal  nerve)  is  given  off  from  the  genicular  ganglion  of  the  facial  nerve;  it 
paSses  through  the  hiatus  of  the  facial  canal,  enters  the  cranial  cavity,  and  runs 
forward  beneath  the  dura  mater  in  a  groove  on  the  anterior  surface  of  the  petrous 
portion  of  the  temporal  bone.  It  then  enters  the  cartilaginous  substance  which 
fills  the  foramen  lacerum,  and  joining  with  the  deep  petrosal  branch  forms  the 
nerve  of  the  pterygoid  canal.  h 

The  deep  petrosal  nerve  (n.  petrosus  profundus;  large  deep  petrosal  nerve)  is  given  ^ 
off  from  the  carotid  plexus,  and  runs  through  the  carotid  canal  lateral  to  the  internal 
carotid  artery.    It  then  enters  the  cartilaginous  substance  which  fills  the  foramen  ^ 
lacerum,  and  joins  with  the  greater  superficial  petrosal  nerve  to  form  the  nerve  fl 
of  the  pterygoid  canal. 

The  nerve  of  the  pterygoid  canal  (n.  canalis  pterygoidei  [Vidii])  Vidian  nerve). 


I 


THE  TRIGEMINAL  NERVE  893 

formed  by  the  junction  of  the  two  preceding  nerves  in  the  cartilaginous  substance 
which  fills  the  foramen  lacerum,  passes  forward,  through  the  pterygoid  canal,  with 
the  corresponding  artery,  and  is  joined  by  a  small  ascending  sphenoidal  branch 
from  the  otic  ganglion.  Finally,  it  enters  the  pterygopalatine  fossa,  and  joins 
the  posterior  angle  of  the  sphenopalatine  ganglion. 

Branches  ^f  Distribution. — These  are  divisible  into  four  groups,  viz.,  orbital, 
palatine,  posterior  superior  nasal,  and  pharyngeal. 

The  orbital  branches  {rami  orhitales;  ascending  branches)  are  two  or  three  delicate 
filaments,  which  enter  the  orbit  by  the  inferior  orbital  fissure,  and  supply  the  peri- 
osteum. According  to  Luschka,  some  filaments  pass  through  foramina  in  the  fronto- 
ethmoidal  suture  to  supply  the  mucous  membrane  of  the  posterior  ethmoidal  and 
sphenoidal  sinuses. 

The  palatine  nerves  {nn.  'palatini;  descending  branches)  are  distributed  to  the  roof 
of  the  mouth,  soft  palate,  tonsil,  and  lining  membrane  of  the  nasal  cavity.  Most 
of  their  fibers  are  derived  from  the  sphenopalatine  branches  of  the  maxillary  nerve. 
They  are  three  in  number :  anterior,  middle,  and  posterior. 

The  anterior  palatine  nerve  {n.  palaiinus  anterior)  descends  through  the  pterygo- 
palatine canal,  emerges  upon  the  hard  palate  through  the  greater  palatine  foramen, 
and  passes  forward  in  a  groove  in  the  hard  palate,  nearly  as  far  as  the  incisor  teeth. 
It  supplies  the  gums,  the  mucous  membrane  and  glands  of  the  hard  palate,  and 
communicates  in  front  with  the  terminal  filaments  of  the  nasopalatine  nerve. 
While  in  the  pterygopalatine  canal,  it  gives  off  posterior  inferior  nasal  branches, 
which  enter  the  nasal  cavity  through  openings  in  the  palatine  bone,  and  ramify 
over  the  inferior  nasal  concha  and  middle  and  inferior  meatuses;  at  its  exit  from 
the  canal,  a  palatine  branch  is  distributed  to  both  surfaces  of  the  soft  palate. 

The  middle  palatine  nerve  (n.  palatimis  medius)  emerges  through  one  of  the  minor 
palatine  canals  and  distributes  branches  to  the  uvula,  tonsil,  and  soft  palate.  It  is 
occasionally  wanting. 

The  posterior  palatine  nerve  (w.  palatinus  posterior)  descends  through  the  pterygo- 
palatine canal,  and  emerges  by  a  separate  opening  behind  the  greater  palatine 
foramen;  it  supplies  the  soft  palate,  tonsil,  and  uvula.  The  middle  and  posterior 
palatine  join  with  the  tonsillar  branches  of  the  glossopharyngeal  to  form  a  plexus 
(circulus  tonsillaris)  around  the  tonsil. 

The  posterior  superior  nasal  branches  {rami  nasales  posteriores  superiores)  are  dis- 
tributed to  the  septum  and  lateral  wall  of  the  nasal  fossa.  They  enter  the  posterior 
part  of  the  nasal  cavity  by  the  sphenopalatine  foramen  and  supply  the  mucous 
membrane  covering  the  superior  and  middle  nasal  conchse,  the  lining  of  the  poste- 
rior ethmoidal  cells,  and  the  posterior  part  of  the  septum.  One  branch,  longer 
[and  larger  than  the  others,  is  named  the  nasopalatine  nerve.  It  enters  the  nasal 
cavity  through  the  sphenopalatine  foramen,  passes  across  the  roof  of  the  nasal 
cavity  below  the  orifice  of  the  sphenoidal  sinus  to  reach  the  septum,  and  then  runs 
obliquely  downward  and  forward  between  the  periosteum  and  mucous  membrane 
of  the  lower  part  of  the  septum.  It  descends  to  the  roof  of  the  mouth  through  the 
incisive  canal  and  communicates  with  the  corresponding  nerve  of  the  opposite 
side  and  with  the  anterior  palatine  nerve.  It  furnishes  a  few  filaments  to  the 
mucous  membrane  of  the  nasal  septum. 

[  The  pharyngeal  nerve  {pterygopalatine  nerve)  is  a  small  branch  arising  from  the 
posterior  part  of  the  ganglion.  It  passes  through  the  pharyngeal  canal  with  the 
pharyngeal  branch  of  the  internal  maxillary  artery,  and  is  distributed  to  the  mucous 
membrane  of  the  nasal  part  of  the  pharynx,  behind  the  auditory  tube. 

The  mandibular  nerve  (n.  mandibularis;  inferior  maxillary  nerve)  (Figs.  77S, 
;781)  supplies  the  teeth  and  gums  of  the  mandible,  the  skin  of  the  temporal  region, 
the  auricula,  the  lower  lip,  the  lower  part  of  the  face,  and  the  muscles  of  mastica- 
tion; it  also  supplies  the  mucous. membrane  of  the  anterior  two-thirds  of  the  tongue. 


894 


NEUROLOGY 


It  is  the  largest  of  the  three  divisions  of  the  fifth,  and  is  made  up  of  two  roots :  a 
large,  sensory  root  proceeding  from  the  inferior  angle  of  the  semilunar  ganglion, 
and  a  small  motor  root  (the  motor  part  of  the  trigeminal),  which  passes  beneath  the 
ganglion,  and  unites  with  the  sensory  root,  just  after  its  exit  through  the  foramen 
ovale.  Immediately  beneath  the  base  of  the  skull,  the  nerve  gives  off  from  its 
medial  side  a  recurrent  branch  (nervus  spinosus)  and  the  nerve  to  the  Pterygoideus 
internus,  and  then  divides  into  two  trunks,  an  anterior  and  a  posterior. 

The  Nervus  Spinosus  {recurrent  or  meningeal  branch)  enters  the  skull  through  the 
foramen  spinosum  with  the  middle  meningeal  artery.  It  divides  into  two  branches, 
anterior  and  posterior,  which  accompany  the  main  divisions  of  the  artery  and 
supply  the  dura  mater;  the  posterior  branch  also  supplies  the  mucous  lining  of 
the  mastoid  cells;  the  anterior  communicates  with  the  meningeal  branch  of  the 
maxillary  nerve. 


ANTERIOR 
AURICULAR 
BRANCHES  TO 
MEATUS 

PAROTID 
BRANCHES 
COMMUNICATINQ 
TO  FACIAL 


POSTERIOR  TEMPORAL 
ZYGOMATICOFACIAL 
TEMPORAL  BRANCH 
OF  BUCCAL 

INFRAORBITAL 

ARTICULAR 


MYLOHYOID       LINGUAL 

Fig.  781. — Mandibular  division  of  the  trifacial  nerve.     (Testut.) 

The  Internal  Pterygoid  Nerve  (n.  pterygoideus  internus) . — The  nerve  to  the  Ptery- 
goideus internus  is  a  slender  branch,  which  enters  the  deep  surface  of  the  muscle; 
it  gives  off  one  or  two  filaments  to  the  otic  ganglion. 

The  anterior  and  smaller  division  of  the  mandibular  nerve  receives  nearly  the 
whole  of  the  fibers  of  the  motor  root  of  the  nerve,  and  supplies  the  muscles  of 
mastication  and  the  skin  and  mucous  membrane  of  the  cheek.  Its  branches  are 
the  masseteric,  deep  temporal,  buccinator,  and  external  pterygoid. 

The  Masseteric  Nerve  (n.  massetericus)  passes  lateral  ward,  above  the  Pterygoideus 
externus,  in  front  of  the  temporomandibular  articulation,  and  behind  the  tendon 
of  the  Temporalis;  it  crosses  the  mandibular  notch  with  the  masseteric  artery, 
to  the  deep  surface  of  the  Masseter,  in  which  it  ramifies  nearly  as  far  as  its  anterior 
border.    It  gives  a  filament  to  the  temporomandibular  joint. 


THE  TRIGEMINAL  NERVE  895 

The  Deep  Temporal  Nerves  {nn.  temporales  profundi)  are  two  in  number,  anterior 
and  posterior.  They  pass  above  the  upper  border  of  the  Pterygoideus  externus 
and  enter  the  deep  surface  of  the  TemporaUs.  The  posterior  branch,  of  small  size, 
is  placed  at  the  back  of  the  temporal  fossa,  and  sometimes  arises  in  common  with 
the  masseteric  nerve.  The  anterior  branch  is  frequently  given  off  from  the  buccina- 
tor nerve,  and  then  turns  upward  over  the  upper  head  of  the  Pterygoideus  externus. 
Frequently  a  third  or  intermediate  branch  is  present. 

The  Buccinator  Nerve  (n.  buccinator  us;  long  buccal  nerve)  passes  forward  between 
the  two  heads  of  the  Pterygoideus  externus,  and  downward  beneath  or  through 
the  lower  part  of  the  Temporalis;  it  emerges  from  under  the  anterior  border  of  the 
Masseter,  ramifies  on  the  surface  of  the  Buccinator,  and  unites  with  the  buccal 
branches  of  the  facial  nerve.  It  supplies  a  branch  to  the  Pterygoideus  externus 
during  its  passage  through  that  muscle,  and  may  give  off  the  anterior  deep  temporal 
nerve.  The  buccinator  nerve  supplies  the  skin  over  the  Buccinator,  and  the  mucous 
membrane  lining  its  inner  surface. 

External  Pterygoid  Nerve  (n.  pterygoideus  externus). — ^The  nerve  to  the  Ptery- 
goideus externus  frequently  arises  in  conjunction  with  the  buccinator  nerve, 
but  it  may  be  given  off  separately  from  the  anterior  division  of  the  mandibular 
nerve.    It  enters  the  deep  surface  of  the  muscle. 

The  posterior  and  larger  division  of  the  mandibular  nerve  is  for  the  most  part 
sensory,  but  receives  a  few  filaments  from  the  motor  root.  It  divides  into  auriculo- 
temporal, lingual,  and  inferici'  alveolar  nerves. 

The  Auriculotemporal  Nerve  (n.  auriculotemporalis)  generally  arises  by  two  roots, 
between  which  the  middle  meningeal  artery  ascends.  It  runs  backward  beneath 
the  Pterygoideus  externus  to  the  medial  side  of  the  neck  of  the  mandible.  It  then 
turns  upward  with  the  superficial  temporal  artery,  between  the  auricula  and  con- 
dyle of  the  mandible,  under  cover  of  the  parotid  gland;  escaping  from  beneath 
the  gland,  it  ascends  over  the  zygomatic  arch,  and  divides  into  superficial  temporal 
branches. 

The  branches  of  communication  of  the  auriculotemporal  nerve  are  with  the  facial 
'  nerve  and  with  the  otic  ganglion.  The  branches  to  the  facial,  usually  two  in  number, 
pass  forward  from  behind  the  neck  of  the  mandible  and  join  the  facial  nerve  at 
the  posterior  border  of  the  Masseter.  The  filaments  to  the  otic  ganglion  are  derived 
from  the  roots  of  the  auriculotemporal  nerve  close  to  their  origin. 

Its  branches  of  distribution  are: 


I 


I 


Anterior  auricular.  Articular. 

Branches  to  the  external  acoustic  meatus.  Parotid. 

Superficial  temporal. 

The  anterior  auricular  branches  (nn.  auriculares  anteriores)  are  usually  two  in 
number;  they  supply  the  front  of  the  upper  part  of  the  auricula,  being  distributed 
principally  to  the  skin  covering  the  front  of  the  helix  and  tragus. 

The  branches  to  the  external  acoustic  meatus  {n.  meatus  auditorii  externi),  two  in 
number,  enter  the  meatus  between  its  bony  and  cartilaginous  portions  and  supply 
the  skin  lining  it;  the  upper  one  sends  a  filament  to  the  tympanic  membrane. 

The  articular  branches  consist  of  one  or  two  twigs  which  enter  the  posterior  part 
of  the  temporomandibular  joint. 

The  parotid  branches  (rami  parotidei)  supply  the  parotid  gland. 

The  superficial  temporal  branches  {rami  temporales  superfi dales)  accompany  the 
superficial  temporal  artery  to  the  vertex  of  the  skull;  they  supply  the  skin  of  the 
temporal  region  and  communicate  with  the  facial  and  zygomaticotemporal  nerves. 

The  Lingual  Nerve  (w.  lingualis)  supplies  the  mucous  membrane  of  the  anterior 
two-thirds  of  the  tongue.  It  lies  at  first  beneath  the  Pterygoideus  externus,  medial 
to  and  in  front  of  the  inferior  alveolar  nerve,  and  is  occasionally  joined  to  this 


896 


NEUROLOGY 


nerve  by  a  branch  which  may  cross  the  internal  maxillary  artery.  The  chorda 
tympani  also  joins  it  at  an  acute  angle  in  this  situation.  The  nerve  then.passtjs 
between  the  Pterygoideus  internus  and  the  ramus  of  the  mandible,  and  cross(3s 
obliquely  to  the  side  of  the  tongue  over  the  Constrictor  pharyngis  superior  and 
Styloglossus,  and  then  between  the  Hyoglossus  and  deep  part  of  the  submaxillary 
gland;  it  finally  runs  across  the  duct  of  the  submaxillary  gland,  and  along  the  tongue 
to  its  tip,  lying  immediately  beneath  the  mucous  membrane. 

Its  branches  of  communication  are  with  the  facial  (through  the  chorda  tympani), 
the  inferior  alveolar  and  hypoglossal  nerves,  and  the  submaxillary  ganglion.  The 
branches  to  the  submaxillary  ganglion  are  two  or  three  in  number;  those  connected 
with  the  hypoglossal  nerVe  form  a  plexus  at  the  anterior  margin  of  the  Hyoglossus. 


SMALL   PETROSALS 
OTIC   GANGLION 


BRANCH  TO  TEN 

SOR  PALATI 

NERVE  TO  IN 

TERNAL  PTERV- 

QOIO 


BRANCH  FROM 

QANQLION  TO 

SUBLINQUAL 

QLAND 


1 


BRANCH  TO  TEN- 
SOR TYMPANI 
BRANCH  TO  AURIC- 
LO-TEMPORAL 
CH  TO  TEN- 
SOR PALATI 
CHORDA  TYMPANI 
MIDDLE  MENINGEAL 
ART.   WITH    SYMPA- 
THETIC PLEXUS 
^URICULO-TEM- 
POHAL 


SMALL   PETROSAL 
BRANCH  TO  TEN- 
SOR TYMPANI 
iTIC  QANQLION 

TO  CHOR- 
TYMPANl 


LOOP  BETWEEN 
LINQUAL  AND 
HYPOQLOSSAL 


SYMPATHETIC 
ROOT  OF 
GANGLION 
SUBMAXILLARY 
QANQLION 


NERVE   TO 
TENSOR    PALATI 


Fig.  782. — Mandibular  division  of  trifacial  nerve,  seen  irom  the  middle  line. 

the  otic  ganglion.     (Testut.) 


The  small  figure  is  an  enlarged  view  of 


Its  branches  of  distribution  supply  the  sublingual  gland,  the  mucous  membrane 
of  the  mouth,  the  gums,  and  the  mucous  membrane  of  the  anterior  two-thirds  of 
the  tongue;  the  terminal  filaments  communicate,  at  the  tip  of  the  tongue,  with 
the  hypoglossal  nerve. 

The  Inferior  Alveolar  Nerve  (n.  alveolaris  inferior;  inferior  dental  nerve)  (Fig.  782)  is 
the  largest  branch  of  the  mandibular  nerve.  It  descends  with  the  inferior  alveolar 
artery,  at  first  beneath  the  Pterygoideus  externus,  and  then  between  the  spheno- 
mandibular  ligament  and  the  ramus  of  the  mandible  to  the  mandibular  foramen. 
It  then  passes  forward  in  the  mandibular  canal,  beneath  the  teeth,  as  far  as  the 
mental  foramen,  where  it  divides  into  two  terminal  branches,  incisive  and  mental. 

The  branches  of  the  inferior  alveolar  nerve  are  the  mylohyoid,  dental,  incisive, 
and  mental. 

The  mylohyoid  nerve  (w.  mylohyoideus)  is  derived  from  the  inferior  alveolar  just 


THE  TRIGEMINAL  NERVE 


897 


hbefore  it  enters  the  mandibular  foramen.      It  descends  in  a  groove  on  the  deep 
surface   of  the  ramus  of  the  mandible,  and  reaching  the  under  surface  of  the 

IMylohyoideus  supplies  this  muscle  and  the  anterior  belly  of  the  Digastricus. 
I    The  dental  branches  supply  the  molar  and  premolar  teeth.     They  correspond 
m  number  to  the  roots  of  those  teeth;  each  nerve  entering  the  orifice  at  the  point 
of  the  root,  and  supplying  the  pulp  of  the  tooth ;  above  the  alveolar  nerve  they  form 
an  inferior  dental  plexus. 

The  incisive  branch  is  continued  onward  within  the  bone,  and  supplies  the  canine 
and  incisor  teeth. 

I      The  mental  nerve  (?i.  mentalis)  emerges  at  the  mental  foramen,   and  divides 
beneath  the  Triangularis  muscle  into  three  branches;  one  descends  to  the  skin  of 
the  chin,  and  two  ascend  to  the  skin  and  mucous  membrane  of  the  lower  lip;  these 
branches  communicate  freely  with  the  facial  nerve. 
Il    Two  small  ganglia,  the  otic  and  the  submaxillary,  are  connected  with  the  man- 
Ipibular  nerve. 


Fia.   783. — The  otic  ganglioQ  and  its  branches. 


I 


Otic  Ganglion  (ganglion  oticmn)  (Fig.  783). — The  otic  ganglion  is  a  small,  oval- 
shaped,  flattened  ganglion  of  a  reddish-gray  color,  situated  immediately  below 
the  foramen  ovale;  it  lies  on  the  medial  surface  of  the  mandibular  nerve,  and 
surrounds  the  origin  of  the  nerve  to  the  Pterygoideus  internus.  It  is  in  relation, 
laterally,  with  the  trunk  of  the  mandibular  nerve  at  the  point  where  the  motor  and 
sensory  roots  join;  medially,  with  the  cartilaginous  part  of  the  auditory  tube, 
and  the  origin  of  the  Tensor  veli  palatini;  posteriorly,  with  the  middle  meningeal 
artery. 

Branches  of  Communication.^ — It  is  connected  by  two  or  three  short  filaments 
with  the  nerve  to  the  Pterygoideus  internus,  from  which  it  may  obtain  a  motor, 
and  possibly  a  sensory  root.  It  communicates  with  the  glossopharyngeal  and  facial 
nerves,  through  the  lesser  superficial  petrosal  nerve  continued  from  the  tympanic 
plexus,  and  through  this  nerve  it  probably  receives  a  root  from  the  glosso- 
pharyngeal and  a  motor  root  from  the  facial;  its  sympathetic  root  consists  of  a 
filament  from  the  plexus  surrounding  the  middle  meningeal  artery.  The  fibers 
from  the  glossopha^^^lgeal  which  pass  to  the  otic  ganglion  in  the  small  superficial 
petrosal  are  supposed  to  be  sympathetic  efferent  (preganglionic)  fibers  from  the 
57 


898 


NEUROLOGY 


I 


dorsal  nucleus  or  inferior  salivatory  nucleus  of  the  medulla.  Fibers  (postganglioni3) 
from  the  otic  ganglion  with  which  these  form  synapses  are  supposed  to  pass  wii:h 
the  auriculotemporal  nerve  to  the  parotid  gland.  A  slender  filament  (sphenoidal) 
ascends  froni  it  to  the  nerve  of  the  Pterygoid  canal,  and  a  small  branch  connects 
it  with  the  chorda  tATnpani. 

Its  branches  of  distribution  are:  a  filament  to  the  Tensor  tympani,  and  one  to 
the  Tensor  veli  palatini.  The  former  passes  backward,  lateral  to  the  auditory 
tube;  the  latter  arises  from  the  ganglion,  near  the  origin  of  the  nerve  to  the  Ptery- 
goideus  internus,  and  is  directed  forward.  The  fibers  of  these  nerves  are,  however, 
mainly  derived  from  the  nerve  to  the  Pterygoideus  internus. 


LACRIMAL  N 

L 

SUPRATROCHLEAR  U.            Ill 

SUPRAORBITAL  N.     f-gjr 

INFRATROCHLEAR  ^--7^^^    \ 

NASAL  NERVE-^g^          >dV 

INFRAORBITALh^I     ^-^^^S 
NERVE           'S^'''         '^^/7 

■  ■  I 

BUCCAL  NERvr 

MENTAL  NERVE // — -^ 

TEMPORAL  BR. 
OF  TEMPORO-MALAR 


MALAR  BR.   OF 
TEMPORO  -MALAR 


AURICULO-TEMPORAL 
NERVE 


Fig.  7S4. 


-Sensory  areas  of  the  head,  showing  the  general  distribution  of  the  three  divisions  of  the  fifth  nerve. 
(Modified  from  Testut.) 


Submaxillary  Ganglion  (ganglion  submaxillare)  (Fig.  778). — The  submaxillary 
ganglion  is  of  small  size  and  is  fusiform  in  shape.  It  is  situated  above  the  deep 
portion  of  the  submaxillary  gland,  on  the  hyoglossus,  near  the  posterior  border 
of  the  Mylohyoideus,  and  is  connected  by  filaments  with  the  lower  border  of  the 
lingual  nerve.  It  is  suspended  from  the  lingual  nerve  by  two  filaments  which  join 
the  anterior  and  posterior  parts  of  the  ganglion.  Through  the  posterior  of  these 
it  receives  a  branch  from  the  chorda  tympani  nerve  which  runs  in  the  sheath  of 
the  lingual;  these  are  s^inpathetic  efferent  (preganglionic)  fibers  from  the  facial 
nucleus  or  the  superior  salivatory  nucleus  of  the  medulla  oblongata  that  terminate 
in  the  submaxillary  ganglion.  The  postganglionic  fibers  pass  to  the  submaxillary 
gland,  it  communicates  with  the  sympathetic  by  filaments  from  the  sympathetic 
plexus  around  the  external  maxillary  artery. 

Its  branches  of  distribution  are  five  or  six  in  number;  the}'  arise  from  the  lower 
part  of  the  ganglion,  and  supply  the  mucous  membrane  of  the  mouth  and  the  duct 
of  the  submaxillary  gland,  some  being  lost  in  the  submaxillary  gland.  The  branch 
of  communication  from  the  lingual  to  the  forepart  of  the  ganglion  is  by  some 
regarded  as  a  branch  of  distribution,  through  which  filaments  pass  from  the  gan- 
glion to  the  lingual  nerve,  and  by  it  are  conveyed  to  the  sublingual  gland  and  the 
tongue. 


THE  ABDUCENT  NERVE 


899 


Trigemiaal  Nerve  Reflexes. — Pains  referred  to  various  branches  of  the  trigeminal  nerve  are  of 
very  frequent  occurrence,  and  should  always  lead  to  a  careful  examination  in  order  to  discover 
a  local  cause.  As  a  general  rule  the  diffusion  of  pain  over  the  various  branches  of  the  nerve  is 
at  first  confined  to  one  only  of  the  main  divisions,  and  the  search  for  the  causative  lesion  should 
always  commence  with  a  thorough  examination  of  all  those  parts  which  are  supphed  by  that 
division;  although  in  severe  cases  pain  may  radiate  over  the  branches  of  the  other  main  divisions. 
The  commonest  example  of  this  condition  is  the  neuralgia  which  is  so  often  associated  with 
dental  caries — here,  although  the  tooth  itself  may  not  appear  to  be  painful,  the  most  distressing 
referred  pains  may  be  experienced,  and  these  are  at  once  relieved  by  treatment  directed  to  the 
affected  tooth. 

Many  other  examples  of  trigeminal  reflexes  could  be  quoted,  but  it  will  be  sufficient  to  mention 
the  more  common  ones.  Dealing  with  the  ophthalmic  nerve,  severe  supraorbital  pain  is  com- 
monly associated  with  acute  glaucoma  or  with  disease  of  the  frontal  or  ethmoidal  air  cells.  Malig- 
nant growths  or  empyema  of  the  maxillary  antrum,  or  unhealthy  conditions  about  the  inferior 
conchse  or  the  septum  of  the  nose,  are  often  found  giving  rise  to  "second  division"  neuralgia, 
and  should  be  always  looked  for  in  the  absence  of  dental  disease  in  the  maxilla. 

It  is  on  the  mandibular  nerve,  however,  that  some  of  the  most  striking  reflexes  are  seen  It 
is  quite  common  to  meet  with  patients  who  complain  of  pain  in  the  ear,  in  whom  there  is  no  sign 
of  aural  disease,  and  the  cause  is  usually  to  be  found  in  a  carious  tooth  in  the  mandible.  More- 
over, with  an  ulcer  or  cancer  of  the  tongue,  often  the  first  pain  to  be  experienced  is  one  which 
radiates  to  the  ear  and  temporal  fossa,  over  the  distribution  of  the  auriculotemporal  nerve. 


Il 


THE  ABDUCENT  NERVE   (N.   ABDUCENS;  SIXTH  NERVE)   (Fig.  777). 


Rectus  lateralis' 


I 


The  abducent  nerve  supplies  the  Rectus  lateraUs  ocuH. 

Its  fibers  arise  from  a  small  nucleus  situated  in  the  upper  part  of  the  rhomboid 
fossa,  close  to  the  middle  line  and  beneath  the  coUiculus  facialis.  They  pass  down- 
ward and  forward  through  the  pons, 
and  emerge  in  the  furrow  between  the 
lower  border  of  the  pons  and  the  upper 
end  of  the  pyramid  of  the  medulla  ob- 
longata. 

From  the  nucleus  of  the  sixth  nerve, 
fibers  are  said  to  pass  through  the  medial 
longitudinal  fasciculus  to  the  oculomotor 
nerve  of  the  opposite  side,  along  which 
they  are  carried  to  the  Rectus  medialis. 
The  Rectus  lateralis  of  one  eye  and  the 
Rectus  medialis  of  the  other  may  there- 
fore be  said  to  receive  their  nerves  from 
the  same  nucleus  (Fig.  785). 

The  nerve  pierces  the  dura  mater  on 
the  dorsum  sellse  of  the  sphenoid,  runs 
through  a  notch  in  the  bone  below  the 
posterior  clinoid  process,  and  passes  for- 
ward through  the  cavernous  sinus,  on 
the  lateral  side  of  the  internal  carotid 
p  artery.  It  enters  the  orbit  through  the 
superior  orbital  fissure,  above  the  oph- 
thalmic vein,  from  which  it  is  separated 
|by  a  lamina  of  dura  mater.  It  then 
passes  between  the  two  heads  of  the 
Rectus  lateralis,  and  enters  the  ocular 
surface  of  that  muscle.  The  abducent 
nerve  is  joined  by  several  filaments  from 

the  carotid  and  cavernous  plexuses,  and  by  one  from  the  ophthalmic  nerve.    The 
oculomotor,  trochlear,  ophthalmic,  and  abducent  nerves  bear  certain  relations  to  each 


Nucleus  VI. 


III.  nerve— 


VI.  nerve- 
Nucleus  III. 


Rhomboid  fossa 


Fig.  785. — Figure  showing  the  mode  of  innervation 
of  the  Recti  medialis  and  lateralis  of  the  eye  (after  Duval 
and  Laborde). 


900 


NEUROLOGY 


I 


Internal  carotid  artery 
Cavernous  sinus 


other  in  the  cavernous  sinus,  at  the  superior  orbital  fissure,  and  in  the  cavity  of 
the  orbit,  as  follows: 

In  the  cavernous  sinus  (Fig.  786),  the  oculomotor,  trochlear,  and  ophthalmic 
nerves  are  placed  in  the  lateral  wall  of  the  sinus,  in  the  order  given,  from  above 
downward.  The  abducent  nerve  lies  at  the  lateral  side  of  the  internal  carotid 
artery.  As  these  nerves  pass  forward  to  the  superior  orbital  fissure,  the  oculo- 
motor and  .  ophthalmic  divide  into 
branches,  and  the  abducent  nerve 
approaches  the  others;  so  that  their 
relative  positions  are  considerably 
changed. 

In  the  superior  orbital  fissure  (Fig. 
787),    the   trochlear   nerve  and    the 
frontal  and  lacrimal  divisions  of  the 
ophthalmic   lie    in   this   order    from 
the  medial  to  the  lateral  side  upon 
the  same  plane;  they  enter  the  cavity 
of  the  orbit  above  the  muscles.    The 
remaining  nerves  enter  the  orbit  be- 
tween the  two  heads  of  the  Rectus 
lateralis.     The   superior    division   of 
the  oculomotor  is  the  highest  of   these;  beneath  this  lies  the  nasociliary  branch 
of  the  ophthalmic;  then  the  inferior  division  of  the  oculomotor;  and  the  abducent 
lowest  of  all. 


Oculomotor  nervt 
Trochlear  nerve. 

Ophthalmic  nerve 
Abducent  nerve 

Maxillary  nerve 


Fig. 


786. — Oblique  section  through  the  right  cavernous 
sinus. 


Frontal  nerve 
Sup.  ramus  of  oculomotor  nerve 
Sup.  orbital  fissure 
Lacrimal  nerve 


Levator  palpebroe 
Nasociliary  nerve 
I     Trochlear  nerve 
Trochlea 


Abducent  nerve 

Inf.  ramus  of  oculomotor    Inf.  orbital        Optic  foramen 
nerve  fissure 

Fig.  787. — Dissection  showing  origins  of  right  ocular  muscles,  and  nerves  entering  by  the  superior  orbital  fissure. 

In  the  orbit,  the  trochlear,  frontal,  and  lacrimal  nerves  lie  immediately  beneath 
the  periosteum,  the  trochlear  nerve  resting  on  the  Obliquus  superior,  the  frontal 
on  the  Levator  palpebrse  superioris,  and  the  lacrimal  on  the  Rectus  lateralis. 
The  superior  division  of  the  oculomotor  nerve  lies  immediately  beneath  the  Rectus 


THE  FACIAL  NERVE 


901 


superior,  while  the  nasociliary  nerve  crosses  the  optic  nerve  to  reach  the  medial 
wall  of  the  orbit.  Beneath  these  is  the  optic  nerve,  surrounded  in  front  by  the 
ciliary  nerves,  and  having  the  ciliary  ganglion  on  its  lateral  side,  between  it  and  the 
Rectus  lateralis.  Below  the  optic  nerve  are  the  inferior  division  of  the  oculomotor, 
and  the  abducent,  the  latter  lying  on  the  medial  surface  of  the  Rectus  lateralis. 


THE   FACIAL  NERVE   (N.  FACIALIS;  SEVENTH  NERVE)  (Figs.  788,  790). 

The  facial  nerve  consists  of  a  motor  and  a  sensory  part,  the  latter  being  frequently 
described  under  the  name  of  the  nervus  intermedins  {yars  intermedii  of  Wrisberg) 
(Fig.  788).  The  two  parts  emerge  at  the  lower  border  of  the  pons  in  the  recess 
between  the  olive  and  the  inferior  peduncle,  the  motor  part  being  the  more  medial, 
immediately  to  the  lateral  side  of  the  sensory  part  is  the  acoustic  nerve. 


Nucleus  Salivatorius 


Nucleus  of 
Facial  X. 


/Afferent  division 

of 
N.Intennedius 
ending  in 
Glossopharyngeal 
Nucletis 


To  Auricular 
Branch  of  Vagus  .V 


Post  ^ 

Auricular  Br.-''^^ 


To  Digastric '' 
To  Stylo-hyoid 


>m> 


I 


Efferent  iexcito-glandular) 

fibers  to  submaxillary  and 

sublingual  ganglia  and  glands 

Fig.  788. — Plan  of  the  facial  and  intermediate  nerves  and  their  communication  with  other  nerves. 


The  motor  part  supplies  somatic  motor  fibers  to  the  muscles  of  the  face,  scalp, 
and  auricle,  the  Buccinator  and  Platysma,  the  Stapedius,  the  Stylohyoideus, 
•and  posterior  belly  of  the  Digastricus;  it  also  contains  some  sjinpathetic  motor 
fibers  which  constitute  the  vasodilator  nerves  of  the  submaxillary  and  sublingual 
glands,  and  are  conveyed  through  the  chorda  tympani  nerve.  These  are  pregan- 
glionic fibers  of  the  sympathetic  system  and  terminate  in  the  submaxillary  ganglion 
and  small  ganglia  in  the  hilus  of  the  submaxillary  gland.  From  these  ganglia 
postganglionic  fibers  are  conveyed  to  these  glands.  The  sensory  part  contains 
the  fibers  of  taste  for  the  anterior  two-thirds  of  the  tongue  and  a  few  somatic 


902 


NEUROLOGY 


I 


sensory  fibers  from  the  middle  ear  region.  A  few  splanchnic  sensory  fibers  are  aho 
present. 

The  motor  root  arises  from  a  nucleus  which  lies  deeply  in  the  reticular  formation 
of  the  lower  part  of  the  pons.  This  nucleus  is  situated  above  the  nucleus  ambiguus, 
behind  the  superior  olivary  nucleus,  and  medial  to  the  spinal  tract  of  the  trigemi- 
nal nerve.  From  this  origin  the  fibers  pursue  a  curved  course  in  the  substance 
of  the  pons.  They  first  pass  backward  and  medialward  toward  the  rhomboid 
fossa,  and,  reaching  the  posterior  end  of  the  nucleus  of  the  abducent  nerve,  run 
upward  close  to  the  middle  line  beneath  the  colliculus  fasciculus.  At  the  anterior 
end  of  the  nucleus  of  the  abducent  nerve  they  make  a  second  bend,  and  run  down- 
ward and  forward  through  the  pons  to  their  point  of  emergence  between  the  oli^'^e 
and  the  inferior  peduncle. 

The  sensory  root  arises  from  the  genicular  ganglion,  which  is  situated  on  the  genic- 
ulum  of  the  facial  nerve  in  the  facial  canal,  behind  the  hiatus  of  the  canal.  The  cells 
of  this  ganglion  are  unipolar,  and  the  single  process  divides  in  a  T-shaped  manner 
into  central  and  peripheral  branches.  The  central  branches  leave  the  trunk  of 
the  facial  nerve  in  the  internal  acoustic  meatus,  and  form  the  sensory  root;  the 
peripheral  branches  are  continued  into  the  chorda  tympani  and  greater  super- 
ficial petrosal  nerves.  Entering  the  brain  at  the  lower  border  of  the  pons  between 
the  motor  root  and  the  acoustic  nerve,  the  fibers  of  the  sensory  root  pass  into  the 
substance  of  the  medulla  oblongata  and  end  in  the  upper  part  of  the  terminal 
nucleus  of  the  glossopharyngeal  nerve  and  in  the  fasciculus  solitarius. 


External  siiperficud  petrosal 

Branch  to  join  lesser  superficial  petrosal 

Greater  superficial  petrosal 

Genicular  ganglion 


Fig.  789. — The  course  and  connections  of  the  facial  nerve  in  the  temporal  bone. 

From  their  superficial  attachments  to  the  brain,  the  two  roots  of  the  facial  nerve 
pass  lateralward  and  forward  with  the  acoustic  nerve  to  the  internal  acoustic 
meatus.  In  the  meatus  the  motor  root  lies  in  a  groove  on  the  upper  and  anterior 
surface  of  the  acoustic  nerve,  the  sensory  root  being  placed  between  them. 

At  the  bottom  of  the  meatus,  the  facial  nerve  enters  the  facial  canal,  which  it 
traverses  to  its  termination  at  the  stylomastoid  foramen.  It  is  at  first  directed 
lateralward  between  the  cochlea  and  vestibule  toward  the  medial  wall  of  the 
tympanic  cavity;  it  then  bends  suddenly  backward  and  arches  downward  behind 
the  tympanic  cavity  to  the  stylomastoid  foramen.  The  point  where  it  changes 
its  direction  is  named  the  geniculum ;  it  presents  a  reddish  ganglif orm  swelling,  the 
genicular  ganglion  {ganglion  geniculi;  geniculate  ganglion;  nucleus  of  the  sensory  root 
of  the  nerve)  (Fig.  789).  On  emerging  from  the  stylomastoid  foramen,  the  facial 
nerve  runs  forward  in  the  substance  of  the  parotid  gland,  crosses  the  external 
carotid  artery,  and  divides  behind  the  ramus  of  the  mandible  into  branches,  from* 
which  numerous  offsets  are  distributed  over  the  side  of  the  head,  face,  and  upper 
part  of  the  neck,  supplying  the  superficial  muscles  in  these  regions.  The  branches 
and  their  offsets  unite  to  form  the  parotid  plexus. 

Branches  of  Communication. — The  branches  of  communication  of  the  facial  nerve 
may  be  arranged  as  follows: 


THE  FACIAL  NERVE 


903 


At  the  genicular  ganglion 


In  the  facial  canal    . 

At  its  exit  from  the  stylo- 
mastoid foramen  . 


I 


In  the  internal  acoustic 

meatus With  the  acoustic  nerve. 

'With  the  sphenopalatine  ganglion  by  the  greater 

superficial  petrosal  nerve. 
With  the  otic  ganglion  by  a  branch  which  joins 

the  lesser  superficial  petrosal  nerve. 
With  the  sympathetic  on  the  middle  meningeal 

artery. 
With  the  auricular  branch  of  the  vagus. 
With  the  glossopharyngeal. 
With  the  vagus. 
With  the  great  auricular. 
With  the  auriculotemporal. 
Behind  the  ear         .        .        .     With  the  lesser  occipital. 
On  the  face       ....     With  the  trigeminal. 
In  the  neck       ....     With  the  cutaneous  cervical. 

In  the  internal  acoustic  meatus  some  minute  filaments  pass  from  the  facial  to 
the  acoustic  nerve. 

The  greater  superficial  petrosal  nerve  {large  superficial  petrosal  nerve)  arises  from 
the  genicular  ganglion,  and  consists  chiefly  of  sensory  branches  which  are  dis- 
tributed to  the  mucous  membrane  of  the  soft  palate;  but  it  probably  contains  a  few 
motor  fibers  which  form  the  motor  root  of  the  sphenopalatine  ganglion.  It  passes 
forward  through  the  hiatus  of  the  facial  canal,  and  runs  in  a  sulcus  on  the  anterior 
surface  of  the  petrous  portion  of  the  temporal  bone  beneath  the  semilunar  ganglion, 
to  the  foramen  lacerum.  It  receives  a  twig  from  the  tympanic  plexus,  and  in  the 
foramen  is  joined  by  the  deep  petrosal,  from  the  sympathetic  plexus  on  the  internal 
carotid  artery,  to  form  the  nerve  of  the  pterygoid  canal  which  passes  forward 
through  the  pterygoid  canal  and  ends  in  the  sphenopalatine  ganglion.  The  genicular 
ganglion  is  connected  with  the  otic  ganglion  by  a  branch  which  joins  the  lesser 
superficial  petrosal  nerve,  and  also  with  the  sympathetic  filaments  accompanying 
the  middle  meningeal  artery.  According  to  Arnold,  a  twig  passes  back  from  the 
ganglion  to  the  acoustic  nerve.  Just  before  the  facial  nerve  emerges  from  the 
stylomastoid  foramen,  it  generally  receives  a  twig  from  the  auricular  branch  of 
the  vagus. 

After  its  exit  from  the  stylomastoid  foramen,  the  facial  nerve  sends  a  twig  to 
the  glossopharyngeal,  and  communicates  with  the  auricular  branch  of  the  vagus, 
with  the  great  auricular  nerve  of  the  cervical  plexus,  with  the  auriculotemporal 
nerve  in  the  parotid  gland,  and  with  the  lesser  occipital  behind  the  ear;  on  the  face 
with  the  terminal  branches  of  the  trigeminal,  and  in  the  neck  with  the  cutaneous 
cervical  nerve. 

Branches  of  Distribution. — The  branches  of  distribution  (Fig.  788)  of  the  facial 
nerve  may  be  thus  arranged: 


With  the  facial  canal 

At  its  exit  from  the 
mastoid  foramen 


On  the  face 


stylo- 


/  Nerve  to  the  Stapedius  muscle. 
\  Chorda  tympani. 
(  Posterior  auricular. 
<  Digastric. 
t  Stylohyoid. 

Temporal. 

Zygomatic. 

Buccal. 

Mandibular. 

Cervical. 


904 


NEUROLOGY 


The  Nerve  to  the  Stapedius  (n.  stapedius;  tympanic  branch)  arises  oppose  me 
pyramidal  eminence  (page  1042);  it  passes  through  a  small  canal  in  this  eminence 
to  reach  the  muscle. 

The  Chorda  Tympani  Nerve  is  given  off  from  the  facial  as  it  passes  downward 
behind  the  tympanic  cavity,  about  6  mm.  from  the  stylomastoid  foramen.  It 
runs  upward  and  forward  in  a  canal,  and  enters  the  tympanic  cavity,  through  an 
aperture  (iter  chordae  posterius)  on  its  posterior  wall,  close  to  the  medial  surface 
of  the  posterior  border  of  the  tympanic  membrane  and  on  a  level  with  the  upper 


I 


Termination 
of  supratrochlear 
of  infratrocfilear 
of  nasociliary 


FiQ.  790. — The  nerves  of  the  scalp,  face,  and  side  of  neck. 

end  of  the  manubrium  of  the  malleus.  It  traverses  the  tympanic  cavity,  between 
the  fibrous  and  mucous  layers  of  the  tympanic  membrane,  crosses  the  manubrium 
of  the  malleus,  and  emerges  from  the  cavity  through  a  foramen  situated  at  the  inner 
end  of  the  petrotympanic  fissure,  and  named  the  iter  chordae  anterius  {canal  of 
Huguier).  It  then  descends  between  the  Pterygoid eus  externus  and  internus  on 
the  medial  surface  of  the  spina  angularis  of  the  sphenoid,  which  it  sometimes 
grooves,  and  joins,  at  an  acute  angle,  the  posterior  border  of  the  lingual  nerve. 
It  receives  a  few  efferent  fibers  from  the  motor  root;  these  enter  the  submaxillary 
ganglion,  and  through  it  are  distributed  to  the  submaxillary  and  sublingual  glands; 


THE  ACOUSTIC  NERVE  905 

the  majorit\'  of  its  fibers  are  afferent,  and  are  continued  onward  through  the  mus- 
cular substance  of  the  tongue  to  the  mucous  membrane  covering  its  anterior 
two-thirds;  they  constitute  the  nerve  of  taste  for  this  portion  of  the  tongue.  Before 
uniting  with  the  lingual  nerve  the  chorda  tympani  is  joined  by  a  small  branch  from 
the  otic  ganglion. 

The  Posterior  Auricular  Nerve  (n.  auricularis  posterior)  arises  close  to  the  stylo- 
mastoid foramen,  and  runs  upward  in  front  of  the  mastoid  process;  here  it  is  joined 
by  a  filament  from  the  auricular  branch  of  the  vagus,  and  communicates  with  the 
posterior  branch  of  the  great  auricular,  and  with  the  lesser  occipital.  As  it  ascends 
between  the  external  acoustic  meatus  and  mastoid  process  it  divides  into  auricular 
and  occipital  branches.  The  auricular  branch  supplies  the  Auricularis  posterior 
and  the  intrinsic  muscles  on  the  cranial  surface  of  the  auricula.  The  occipital 
branch,  the  larger,  passes  backward  along  the  superior  nuchal  line  of  the  occipital 
bone,  and  supplies  the  Occipitalis. 

The  Digastric  Branch  (ramus  digastricus)  arises  close  to  the  stylomastoid  foramen, 
and  divides  into  several  filaments,  which  supply  the  posterior  belly  of  the  Digas- 
tricus; one  of  these  filaments  joins  the  glossopharyngeal  nerve. 

The  Stylohyoid  Branch  {ramus  stylohyoideus)  frequently  arises  in  conjunction 
with  the  digastric  branch;  it  is  lohg  and  slender,  and  enters  the  Stylohyoideus  about 
its  middle. 

The  Temporal  Branches  {rami  temporales)  cross  the  zygomatic  arch  to  the  temporal 
1 1  region,  supplying  the  Auriculares  anterior  and  superior,  and  joining  with  the  zygo- 
maticotemporal branch  of  the  maxillary,  and  with  the  auriculotemporal  branch 
of  the  mandibular.  The  more  anterior  branches  supply  the  Frontalis,  the  Orbicu- 
laris oculi,  and  the  Corrugator,  and  join  the  supraorbital  and  lacrimal  branches 
of  the  ophthalmic, 
j  The  Zygomatic  Branches  {rami  zygoviatici;  malar  branches)  run  across  the  zygo- 
matic bone  to  the  lateral  angle  of  the  orbit,  where  they  supply  the  Orbicularis  oculi, 
and  join  with  filaments  from  the  lacrimal  nerve  and  the  zygomaticofacial  branch 
of  the  maxillary  nerve. 

The  Buccal  Branches  {rami  buccales;  infraorbital  branches),  of  larger  size  than  the 
I  rest,  pass  horizontally  forward  to  be  distributed  below  the  orbit  and  around  the 
mouth.  The  superficial  branches  run  beneath  the  skin  and  above  the  superficial 
muscles  of  the  face,  which  they  supply:  some  are  distributed  to  the  Procerus, 
joining  at  the  medial  angle  of  the  orbit  with  the  infratrochlear  and  nasociliary 
branches  of  the  ophthalmic.  The  deep  branches  pass  beneath  the  Zygomaticus  and 
I  the  Quadratus  labii  superioris,  supplying  them  and  forming  an  infraorbital  plexus  with 
the  infraorbital  branch  of  the  maxillary  nerve.  These  branches  also  supply  the 
small  muscles  of  the  nose.  The  lower  deep  branches  supply  the  Buccinator  and 
Orbicularis  oris,  and  join  with  filaments  of  the  buccinator  branch  of  the  mandibular 
nerve. 

The  Mandibular  Branch  {ramus  marginalis  mandibulce)  passes  forward  beneath 
the  Platysma  and  Triangularis,  supplying  the  muscles  of  the  lower  lip  and  chin, 
and  communicating  with  the  mental  branch  of  the  inferior  alveolar  nerve. 

The  Cervical  Branch  {ramus  colli)  runs  forward  beneath  the  Platysma,  and  forms 
a  series  of  arches  across  the  side  of  the  neck  over  the  suprahyoid  region.  One 
branch  descends  to  join  the  cervical  cutaneous  nerve  from  the  cervical  plexus; 
others  supply  the  Platysma. 

THE  ACOUSTIC  NERVE  (EIGHTH  NERVE). 

The  acoustic  nerve  consists  of  two  distinct  sets  of  fibers  which  differ  in  their 
peripheral  endings,  central  connections,  functions,  and  time  of  meduUation.  It  is 
soft  in  texture  and  devoid  of  neurilemma. 


906  ^^^^^^^  NEUROLOGY 


I 


Cochlear  Nerve. — The  cochlear  nerve  or  root,  the  nerve  of  hearing,  arises  from 
bipolar  cells  in  the  spiral  ganglion  of  the  cochlea,  situated  near  the  inner  edge  of 
the  osseous  spiral  lamina.  The  peripheral  fibers  pass  to  the  organ  of  Corti.  Th(; 
central  ones  pass  dowTi  the  modiolus  and  then  through  the  foramina  of  the  tractus 
spiralis  foraminosus  or  through  the  foramen  centrale  into  the  lateral  or  outer  end 
of  the  internal  auditory  meatus.  The  nerve  passes  along  the  internal  auditor^' 
meatus  with  the  vestibular  nerve  and  across  the  subarachnoid  space,  just  above- 
the  flocculus,  almost  directly  medialward  toward  the  inferior  peduncle  to  terminate 
in  the  cochlear  nucleus. 

The  cochlear  nerve  is  placed  lateral  to  the  vestibular  root.  Its  fibers  end  in  two 
nuclei:  one,  the  accessory  nucleus,  lies  immediately  in  front  of  the  inferior  peduncle; 
the  other,  the  tuberculum  acusticum,  somewhat  lateral  to  it. 

The  striae  medullares  {strixB  acusticoe)  are  the  axons  of  the  cells  of  the  tuberculum 
acusticum.  They  pass  over  the  inferior  peduncle,  and  across  the  rhomboid  fossa 
to  the  median  sulcus.  Here  they  dip  into  the  substance  of  the  pons,  to  end  around 
the  cells  of  the  superior  olivary  nuclei  of  both  sides.  There  are,  however,  other 
fibers,  and  these  are  both  direct  and  crossed,  which  pass  into  the  lateral  lemniscus. 
The  cells  of  the  accessory  nucleus  give  origin  to  fibers  which  run  transversely  in  the 
pons  and  constitute  the  trapezium.  Of  the  trapezoid  fibers  some  end  around  the 
cells  of  the  superior  olivary  nucleus  or  of  the  trapezoid  nucleus  of  the  same  or 
opposite  side,  while  others,  crossed  or  uncrossed,  pass  directly  into  the  lateral 
lemniscus. 

If  the  further  connections  of  the  cochlear  nerve  of  one  side,  say  the  left,  be  con- 
sidered, it  is  found  that  they  lie  lateral  to  the  main  sensory  tract,  the  lemniscus, 
and  are  therefore  termed  the  lateral  lemniscus.  The  fibers  comprising  the  left 
lateral  lemniscus  arise  in  the  superior  olivary  and  trapezoid  nuclei  of  the  same  or 
opposite  side,  while  others  are  the  uninterrupted  fibers  already  alluded  to,  and  these 
are  either  crossed  or  uncrossed,  the  former  being  the  axons  of  the  cells  of  the  right 
accessory  nucleus  or  of  the  cells  of  the  right  tuberculum  acusticum,  while  the 
latter  are  derived  from  the  cells  of  the  left  nuclei.  In  the  upper  part  of  the  lateral 
lemniscus  there  is  a  collection  of  nerve  cells,  the  nucleus  of  the  lateral  lemniscus, 
around  the  cells  of  which  some  of  the  fibers  arborize  and  from  the  cells  of  which 
axons  originate  to  continue  upward  the  tract  of  the  lateral  lemniscus.  The  ultimate 
ending  of  the  left  lateral  lemniscus  is  partly  in  the  opposite  medial  geniculate 
body,  and  partly  in  the  inferior  colliculi.  From  the  cells  of  these  bodies  new  fibers 
arise  and  ascend  in  the  occipital  part  of  the  internal  capsule  to  reach  the  posterior 
three-fifths  of  the  left  superior  temporal  gyrus  and  the  transverse  temporal  gyri. 

Vestibular  Nerve. — ^The  vestibular  nerve  or  root,  the  nerve  of  equilibration, 
arises  from  bipolar  cells  in  the  vestibular  ganglion,  ganglion  of  Scarpa,  which  is 
situated  in  the  upper  part  of  the  outer  end  of  the  internal  auditory  meatus.  The 
peripheral  fibers  divide  into  three  branches:  the  superior  branch  passes  through 
the  foramina  in  the  area  vestibularis  superior  and  ends  in  the  utricle  and  in  the 
ampullae  of  the  superior  and  lateral  semicircular  ducts;  the  fibers  of  the  inferior 
branch  traverse  the  foramina  in  the  area  vestibularis  inferior  and  end  in  the  saccule; 
the  posterior  branch  runs  through  the  foramen  singulare  and  supplies  the  ampulla 
of  the  posterior  semicircular  duct. 

THE  GLOSSOPHARYNGEAL  NERVE  (N.  GLOSSOPHARYNGEUS;  NINTH 

NERVE)  (Figs.  791,  792,  793). 

The  glossopharyngeal  nerve  contains  both  motor  and  sensory  fibers,  and  is  dis- 
tributed, as  its  name  implies,  to  the  tongue  and  pharynx.  It  is  the  nerve  of  ordinary 
sensation  to  the  mucous  membrane  of  the  pharynx,  fauces,  and  palatine  tonsil,  and 
the  nerve  of  taste  to  the  posterior  part  of  the  tongue.     It  is  attached  by  three  or 


I 


THE  GLOSSOPHARYNGEAL  NERVE 


907 


Auricular 


Tympanic 


Pharyngeal 


N 


I 


I 


four  filaments  to  the  upper  part  of  the  medulla  oblongata,  in  the  groove  between 
the  olive  and  the  inferior  peduncle. 

The  sensory  fibers  arise  from  the  cells  of  the  superior  and  petrous  ganglia,  which 
are  situated  on  the  trunk  of  the  nerve,  and  will  be  presently  described.  When 
traced  into  the  medulla, 
some  of  the  sensory  fibers, 
probably  sympathetic  af- 
ferent, end  by  arborizing 
around  the  cells  of  the 
upper  part  of  a  nucleus 
which  lies  beneath  the  ala 
cinerea  in  the  lower  part  of 
the  rhomboid  fossa.  Many 
of  the  fibers,  probably  the 
taste  fibers,  contribute  to 
form  a  strand,  named  the 
fasciculus  solitarius,  which 
descends  in  the  medulla 
oblongata.  Associated  with 
this  strand  are  numerous 
nerve  cells,  and  around 
these  the  fibers  of  the 
fasciculus  end.  The  so- 
matic sensory  fibers,  few  in 
number,  are  said  to  join 
the  spinal  tract  of  the  tri- 
geminal nerve. 

The  somatic  motor  fibers 
spring  from  the  cells  of  the 
nucleus  ambiguus,  which  lies  some  distance  from  the  surface  of  the  rhomboid  fossa 
in  the  lateral  part  of  the  medulla  and  is  continuous  below  with  the  anterior  gray 
column  of  the  medulla  spinalis.  From  this  nucleus  the  fibers  are  first  directed 
backward,  and  then  they  bend  forward  and  lateralward  to  join  the  fibers  of  the 
sensory  root.  The  nucleus  ambiguus  gives  origin  to  the  motor  branches  of  the 
glossopharyngeal  and  vagus  nerves,  and  to  the  cranial  part  of  the  accessory  nerve. 

The  S3rmpathetic  efferent  fibers  from  the  nucleus  beneath  the  ala  cinerea,  the  dorsal 
nucleus,  are  probably  both  preganglionic  motor  fibers  and  preganglionic  secretory 
fibers  of  the  sympathetic  system.  The  secretory  fibers  pass  to  the  otic  ganglion 
and  from  it  secondary  neurons  are  distributed  to  the  parotid  gland.  Some  authors 
describe  these  fibers  as  arising  from  a  distinct  nucleus  the  inferior  salivatory 
nucleus,  which  lies  near  the  dorsal  nucleus. 

From  the  medulla  oblongata,  the  glossopharyngeal  nerve  passes  lateralward 
across  the  flocculus,  and  leaves  the  skull  through  the  central  part  of  the  jugular 
foramen,  in  a  separate  sheath  of  the  dura  mater,  lateral  to  and  in  front  of  the  vagus 
and  accessory  nerves  (Fig.  792).  In  its  passage  through  the  jugular  foramen, 
it  grooves  the  lower  border  of  the  petrous  part  of  the  temporal  bone;  and,  at  its 
exit  from  the  skull,  passes  forward  between  the  internal  jugular  vein  and  internal 
carotid  artery;  it  descends  in  front  of  the  latter  vessel,  and  beneath  the  styloid 
process  and  the  muscles  connected  with  it,  to  the  lower  border  of  the  Stylo- 
pharyngeus.  It  then  curves  forward,  forming  an  arch  on  the  side  of  the  neck 
and  lying  upon  the  Stylopharyngeus  and  Constrictor  pharyngis  medius.  Thence 
it  passes  under  cover  of  the  Hyoglossus,  and  is  finally  distributed  to  the  palatine 
tonsil,  the  mucous  membrane  of  the  fauces  and  base  of  the  tongue,  and  the 
mucous  glands  of  the  mouth. 


Laryngeal 


Fig.  791. — Plan  of  upper  portions  of  glossopharyngeal,  vagus,  and 
accessory  nerves. 


908 


NEUROLOGY 


I 


In  passing  through  the  jugular  foramen,  the  nerve  presents  two  ganglia,  the 
superior  and  the  petrous  (Fig.  791). 

The  Superior  Ganglion  {ganglion  superius;  jugular  ganglion)  is  situated  in  thcj 
upper  part  of  the  groove  in  which  the  nerve  is  lodged  during  its  passage  through 
the  jugular  foramen.  It  is  very  small,  and  is  usually  regarded  as  a  detached 
portion  of  the  petrous  ganglion. 

The  Petrous  Ganglion  {ganglion  petrosum;  inferior  ganglion)  is  larger  than  the; 
superior  and  is  situated  in  a  depression  in  the  lower  border  of  the  petrous  portion 
of  the  temporal  bone. 


Trochlear  rterve 

Trigeminal  Tierve 
Facial  tierve 
Acmistic  nerve 


Fasciculus  cuneatuB 
FaaciczUus  (/racilis 


Dura  mater 
(laid  open, 


Fia.  792. — Upper  part  of  medulla  spinalis  and  hind-  and  mid-brains;  posterior  aspect,  exposed  in  situ. 

Branches  of  Communication.  —  The  glossopharyngeal  nerve  communicates  with 
the  vagus,  ssrmpathetic,  and  facial. 

The  branches  to  the  vagus  are  two  filaments  which  arise  from  the  petrous  gan- 
glion, one  passing  to  the  auricular  branch,  and  the  other  to  the  jugular  ganglion, 
of  the  vagus.  The  petrous  ganglion  is  connected  by  a  filament  with  the  superior 
cervical  ganglion  of  the  sympathetic.  The  branch  of  communication  with  the  facial 
perforates  the  posterior  belly  of  the  Digastricus,  It  arises  from  the  trunk  of  the 
glossopharyngeal  below  the  petrous  ganglion,  and  joins  the  facial  just  after  the  exit 
of  that  nerve  from  the  stylomastoid  foramen. 

Branches  of  Distribution. — The  branches  of  distribution  of  the  glossopharyngeal 
are:  the  tjrmpanic,  carotid,  pharyngeal,  muscular,  tonsillar,  and  lingual. 


THE  GLOSSOPHARYNGEAL  NERVE 


909 


W 


Internal  branch  of 
sup.  laryngeal 

External  branch  of 
sup,  laryngeal 


I) 


fl 


k) 


k* 


The  Tympanic  Nerve  (?i.  tympanicus;  nerve  of  Jacobson)  arises  from  the  petrous 
gangUon,  and  ascends  to  the  tympanic  cavity  through  a  small  canal  on  the 
under    surface   of   the    petrous 

portion  of  the  temporal  bone  on  Glossopharyngeal 

the  ridge  which   separates  the  "^"* 

carotid  canal  from  the  jugular 

fossa.     In  the  tympanic  cavity 

it  divides  into  branches  which 

form  the  tjrmpanic   plexus  and 

are  contained  in  grooves  upon 

the  surface  of  the  promontory. 

This  plexus  gives  off:    (1)    the 

lesser  superficial  petrosal  nerve; 

(2)  a  branch  to  join  the  greater 

superficial  petrosal  nerve;  and (3) 

branches  to  the  tympanic  cavity, 

all  of  which  will  be  described  in 

connection  with  the  anatomy  of 

the  middle  ear. 

The  Carotid  Branches  (??.  car- 
oticotympanicus  superior  and  n. 
caroticotympanicus  inferior)  de- 
scend along  the  trunk  of  the 
internal  carotid  artery  as  far  as 
its  origin,  communicating  with 
the  pharyngeal  branch  of  the 
vagus,  and  with  branches  of 
the  sympathetic. 

The  Pharyngeal  Branches  (rami 
pharyngei)  are  three  or  four  fila- 
ments which  unite,  opposite  the 
Constrictor  pharyngis  medius, 
with  the  pharyngeal  branches  of 
the  vagus  and  sympathetic,  to 
form  the  pharyngeal  plexus; 
branches  from  this  plexus  per- 
forate the  muscular  coat  of  the 
pharynx  and  supply  its  muscles 
and  mucous  membrane. 

The  Muscular  Branch  {ramus 
stylopharyjigeus)  is  distributed 
to  the  Stylopharyngeus. 

The  Tonsillar  Branches  (rami 
tonsillares)  supply  the  palatine 
tonsil,  forming  around  it  a  plexus 
from  which  filaments  are  dis- 
tributed to  the  soft  palate  and 
fauces,  where  they  communicate 
with  the  palatine  nerves. 

The  Lingual  Branches  {rami 
linguales)  are  two  in  number;  one 

supplies  the  papillae  vallata?  and  the  mucous  membrane  covering  the  base  of  the 
tongue;  the  other  supplies  the  mucous  membrane  and  follicular  glands  of  the 
posterior  part  of  the  tongue,  and  communicates  with  the  lingual  nerve. 


Fig.  793. — Coiuse  and  distribution  of  the  glossopnaryngeai, 
vagus,  and  accessory  nerves. 


n 


910  ^^^^^  NEUROLOGY 

THE  VAGUS  NERVE  (N.  VAGUS;  TENTH  NERVE;  PNEUMOGASTRIC 
NERVE)   (Figs.  791,  792,  793). 

The  vagus  nerve  is  composed  of  both  motor  and  sensory  fibers,  and  has  a  mor<2 
extensive  course  and  distribution  than  any  of  the  other  cranial  nerves,  since  it 
.  passes  through  the  neck  and  thorax  to  the  abdomen. 

The  vagus  is  attached  by  eight  or  ten  filaments  to  the  medulla  oblongata  in  th(j 
groove  between  the  olive  and  the  inferior  peduncle,  below  the  glossopharyngeal. 
The  sensory  fibers  arise  from  the  cells  of  the  jugular  ganglion  and  ganglion  nodosum 
of  the  nerve,  and,  when  traced  into  the  medulla  oblongata  mostly  end  by  arborizing 
around  the  cells  of  the  inferior  part  of  a  nucleus  which  lies  beneath  the  ala  cinereti 
in  the  lower  part  of  the  rhomboid  fossa.  These  are  the  sympathetic  afferent  fibers. 
Some  of  the  sensory  fibers  of  the  glossopharyngeal  nerve  have  been  seen  to  end  in 
the  upper  part  of  this  nucleus.  A  few  of  the  sensory  fibers  of  the  vagus,  probably 
taste  fibers,  descend  in  the  fasciculus  solitarius  and  end  around  its  cells.  The  somatic 
sensory  fibers,  few  in  number,  from  the  posterior  part  of  the  external  auditory 
meatus  and  the  back  of  the  ear,  probably  join  the  spinal  tract  of  the  trigeminal  as 
it  descends  in  the  medulla.  The  somatic  motor  fibers  arise  from  the  cells  of  the 
nucleus  ambigims,  already  referred  to  in  connection  with  the  motor  root  of  the 
glossopharyngeal  nerve. 

The  sympathetic  efferent  fibers,  distributed  probably  as  preganglionic  fibers  to 
the  thoracic  and  abdominal  viscera,  i.  e.,  as  motor  fibers  to  the  bronchial  tree, 
inhibitory  fibers  to  the  heart,  motor  fibers  to  the  esophagus,  stomach,  small  intes- 
tine and  gall  passages,  and  as  secretory  fibers  to  the  stomach  and  pancreas,  arise 
from  the  dorsal  nucleus  of  the  vagus. 

The  filaments  of  the  nerve  unite,  and  form  a  flat  cord,  which  passes  beneath 
the  flocculus  to  the  jugular  foramen,  through  which  it  leaves  the  cranium.  In 
emerging  through  this  opening,  the  vagus  is  accompanied  by  and  contained  in 
the  same  sheath  of  dura  mater  with  the  accessory  nerve,  a  septum  separating 
them  from  the  glossopharyngeal  which  lies  in  front  (Fig.  792).  In  this  situation 
the  vagus  presents  a  well-marked  ganglionic  enlargement,  which  is  called  the  jugular 
ganglion  {ganglion  of  the  root);  to  it  the  accessory  nerve  is  connected  by  one  or 
two  filaments.  After  its  exit  from  the  jugular  foramen  the  vagus  is  joined  by  the 
cranial  portion  of  the  accessory  nerve,  and  enlarges  into  a  second  gangliform  swell- 
ing, called  the  ganglion  nodosum  {ganglion  of  the  trunk) ;  through  this  the  fibers  of  the 
cranial  portion  of  the  accessory  pass  without  interruption,  being  principally 
distributed  to  the  pharyngeal  and  superior  laryngeal  branches  of  the  vagus,  but 
some  of  its  fibers  descend  in  the  trunk  of  the  vagus,  to  be  distributed  with  the 
recurrent  nerve  and  probably  also  with  the  cardiac  nerves. 

The  vagus  nerve  passes  vertically  down  the  neck  within  the  carotid  sheath, 
lying  between  the  internal  jugular  vein  and  internal  carotid  artery  as  far  as  the 
upper  border  of  the  thyroid  cartilage,  and  then  between  the  same  vein  and  the 
common  carotid  artery  to  the  root  of  the  neck.  The  further  course  of  the  nerve 
differs  on  the  two  sides  of  the  body. 

On  the  right  side,  the  nerve  passes  across  the  subclavian  artery  between  it  and 
the  right  innominate  vein,  and  descends  by  the  side  of  the  trachea  to  the  back  of 
the  root  of  the  lung,  where  it  spreads  out  in  the  posterior  pulmonary  plexus.  From 
the  lower  part  of  this  plexus  two  cords  descend  on  the  esophagus,  and  divide  to 
form,  with  branches  from  the  opposite  nerve,  the  esophageal  plexus.  Below,  these 
branches  are  collected  into  a  single  cord,  which  runs  along  the  back  of  the  esophagus 
enters  the  abdomen,  and  is  distributed  to  the  postero-inferior  surface  of  the  stomach, 
joining  the  left  side  of  the  celiac  plexus,  and  sending  filaments  to  the  lienal  plexus. 

On  the  left  side,  the  vagus  enters  the  thorax  between  the  left  carotid  and  sub- 
clavian arteries,  behind  the  left  innominate  vein.    It  crosses  the  left  side  of  the 


I 


I 


THE  VAGUS  NERVE 


911 


I 


arch  of  the  aorta,  and  descends  behind  the  root  of  the  left  lung,  forming  there 
the  posterior  pulmonary  plexus.  From  this  it  runs  along  the  anterior  surface  of  the 
esophagus,  where  it  unites  with  the  nerve  of  the  right  side  in  the  esophageal 
plexus,  and  is  continued  to  the  stomach,  distributing  branches  over  its  antero- 
superior  surface;  some  of  these  extend  over  the  fundus,  and  others  along  the  lesser 
curvature.  Filaments  from  these  branches  enter  .the  lesser  omentum,  and  join  the 
hepatic  plexus. 

The  Jugular  Ganglion  (ganglion  jugulare;  ganglion  of  the  root)  is  of  a  grayish 
color,  spherical  in  form,  about  4  mm.  in  diameter. 

Branches  of  Communication. — This  ganglion  is  connected  by  several  delicate 
filaments  to  the  cranial  portion  of  the  accessory  nerve;  it  also  communicates  by 
a  twig  with  the  petrous  ganglion  of  the  glossopharyngeal,  with  the  facial  nerve 
by  means  of  its  auricular  branch,  and  with  the  sympathetic  by  means  of  an  ascend- 
ing filament  from  the  superior  cervical  ganglion. 

The  Ganglion  Nodosum  {ganglion  of  the  trunk;  inferior  ganglion)  is  cylindrical 
in  form,  of  a  reddish  color,  and  2.5  cm.  in  length.  Passing  through  it  is  the  cranial 
portion  of  the  accessory  nerve,  which  blends  with  the  vagus  below  the  ganglion. 

Branches  of  Communication.^ — This  ganglion  is  connected  with  the  hypoglossal, 
the  superior  cervical  ganglion  of  the  sympathetic,  and  the  loop  between  the  first 
and  second  cervical  nerves. 

Branches  of  Distribution. — The  branches  of  distribution  of  the  vagus  are: 


In  the  Jugular  Fossa 


In  the  Neck 


Meningeal. 
Auricular. 

■  Pharyngeal. 
Superior  laryngeal. 
Recurrent. 
Superior  cardiac. 

■  Inferior  cardiac. 

Anterior  bronchial. 

Posterior  bronchial. 
J^sophageal. 

(Gastric. 
Celiac. 
Hepatic. 


In  the  Thorax 


* 


I 


W    The  Meningeal  Branch  {ramus  meningeus;  dural  branch)  is  a  recurrent  filament 

*  given  off  from  the  jugular  ganglion;  it  is  distributed  to  the  dura  mater  in  the 
posterior  fossa  of  the  base  of  the  skull. 

The  Auricular  Branch  {ramus  auricnlaris;  nerve  of  Arnold)  arises  from  the  jugular 
ganglion,  and  is  joined  soon  after  its  origin  by  a  filament  from  the  petrous  ganglion 
of  the  glossopharyngeal;  it  passes  behind  the  internal  jugular  vein,  and  enters  the 
mastoid  canaliculus  on  the  lateral  w^all  of  the  jugular  fossa.    Traversing  the  sub- 

•  stance  of  the  temporal  bone,  it  crosses  the  facial  canal  about  4  mm.  above  the  stylo- 
mastoid foramen,  and  here  it  gives  off  an  ascending  branch  which  joins  the  facial 
nerve.  The  nerve  reaches  the  surface  by  passing  through  the  tympanomastoid 
fissure  between  the  mastoid  process  and  the  tympanic  part  of  the  temporal  bone, 
and  divides  into  two  branches:  one  joins  the  posterior  auricular  nerve,  the  other 
is  distributed  to  the  skin  of  the  back  of  the  auricula  and  to  the  posterior  part  of 
the  external  acoustic  meatus. 

The  Pharyngeal  Branch  {ramus  yharyngeus) ,  the  principal  motor  nerve  of  the 
■  pharynx,  arises  from  the  upper  part  of  the  ganglion  nodosum,  and  consists  prin- 
cipally of  filaments  from  the  cranial  portion  of  the  accessory  nerve.     It  passes 
across  the  internal  carotid  artery  to  the  upper  border  of  the  Constrictor  pharyngis 


912  ^^^  NEUROLOGY 


medius,  where  it  divides  into  numerous  filaments,  which  join  with  branches  from 
the  glossopharyngeal,  sympathetic,  and  external  laryngeal  to  form  the  pharyngeal 
plexus.  From  the  plexus,  branches  are  distributed  to  the  muscles  and  mucous 
membrane  of  the  pharynx  and  the  muscles  of  the  soft  palate,  except  the  Tensor 
veli  palatini.  A  minute  filament  descends  and  joins  the  hypoglossal  nerve  as  it 
winds  around  the  occipital  artery. 

The  Superior  Laryngeal  Nerve  {n.  laryngeus  superior)  larger  than  the  preceding, 
arises  from  the  middle  of  the  ganglion  nodosum  and  in  its  course  receives  a  branch 
from  the  superior  cervical  ganglion  of  the  sympathetic.  It  descends,  by  the  side  of 
the  pharynx,  behind  the  internal  carotid  artery,  and  divides  into  two  branches, 
external  and  internal. 

The  external  branch  (ramus  exlernus),  the  smaller,  descends  on  the  larj'nx,  beneath 
the  Sternothyreoideus,  to  supply  the  Cricothyreoideus.  It  gives  branches  to  the 
pharyngeal  plexus  and  the  Constrictor  pharyngis  inferior,  and  communicates  with 
the  superior  cardiac  nerve,  behind  the  common  carotid  artery. 

The  internal  branch  {ramus  internus)  descends  to  the  hyothyroid  membrane, 
pierces  it  in  company  with  the  superior  laryngeal  artery,  and  is  distributed  to  the 
mucous  membrane  of  the  larynx.  Of  these  branches  some  are  distributed  to  the 
epiglottis,  the  base  of  the  tongue,  and  the  epiglottic  glands;  others  pass  backward, 
in  the  ary epiglottic  fold,  to  supply  the  mucous  membrane  surrounding  the  entrance 
of  the  larynx,  and  that  lining  the  cavity  of  the  larynx  as  low  down  as  the  vocal 
folds.  A  filament  descends  beneath  the  mucous  membrane  on  the  inner  surface 
of  the  thyroid  cartilage  and  joins  the  recurrent  nerve. 

The  Recurrent  Nerve  {n.  recurrens;  inferior  or  recurrent  laryngeal  nerve)  arises, 
on  the  right  side,  in  front  of  the  subclavian  artery;  winds  from  before  back- 
ward around  that  vessel,  and  ascends  obliquely  to  the  side  of  the  trachea  behind 
the  common  carotid  artery,  and  either  in  front  of  or  behind  the  inferior  thyroid 
artery.  On  the  left  side,  it  arises  on  the  left  of  the  arch  of  the  aorta,  and  winds 
below  the  aorta  at  the  point  where  the  ligamentum  arteriosum  is  attached,  and  then 
ascends  to  the  side  of  the  trachea.  The  nerve  on  either  side  ascends  in  the  groove 
between  the  trachea  and  esophagus,  passes  under  the  lower  border  of  the  Con- 
strictor pharyngis  inferior,  and  enters  the  larynx  behind  the  articulation  of  the, 
inferior  cornu  of  the  thyroid  cartilage  with  the  cricoid;  it  is  distributed  to  all  the 
muscles  of  the  larynx,  excepting  the  Cricothyreoideus.  It  communicates  with  the 
internal  branch  of  the  superior  laryngeal  nerve,  and  gives  off  a  few  filaments  to 
the  mucous  membrane  of  the  lower  part  of  the  larynx. 

As  the  recurrent  nerve  hooks  around  the  subclavian  artery  or  aorta,  it  gives 
off  several  cardiac  filaments  to  the  deep  part  of  the  cardiac  plexus.  As  it  ascends 
in  the  neck  it  gives  off  branches,  more  numerous  on  the  left  than  on  the  right  side, 
to  the  mucous  membrane  and  muscular  coat  of  the  esophagus;  branches  to  the 
mucous  membrane  and  muscular  fibers  of  the  trachea;  and  some  pharyngeal 
filaments  to  the  Constrictor  pharyngis  inferior. 

The  Superior  Cardiac  Branches  {rami  cardiaci  superiores;  cervical  cardiac  branches), 
two  or  three  in  number,  arise  from  the  vagus,  at  the  upper  and  lower  parts  of  the 
neck. 

The  upper  branches  are  small,  and  communicate  with  the  cardiac  branches 
of  the  sympathetic.    They  can  be  traced  to  the  deep  part  of  the  cardiac  plexus. 

The  lower  branch  arises  at  the  root  of  the  neck,  just  above  the  first  rib.  That 
from  the  right  vagus  passes  in  front  or  by  the  side  of  the  innominate  artery,  and 
proceeds  to  the  deep  part  of  the  cardiac  plexus;  that  from  the  left  runs  down  across 
the  left  side  of  the  arch  of  the  aorta,  and  joins  the  superficial  part  of  the  cardiac 
plexus. 

The  Inferior  Cardiac  Branches  {rami  cardiaci  inferiores;  thoracic  cardiac  branches) ^ 
on  the  right  side,  arise  from  the  trunk  of  the  vagus  as  it  lies  by  the  side  of  the! 


I 


I 


I 


THE  ACCESSORY  NERVE  913 

trachea,  and  from  its  recurrent  nerve;  on  the  left  side  from  the  recurrent  nerve  only; 
passing  inward,  the}"  end  in  the  deep  part  of  the  cardiac  plexus. 
i  The  Anterior  Bronchial  Branches  {rami  bronchiales  anteriores;  anterior  or  ventral 
pulmonary  branches),  two  or  three  in  number,  and  of  small  size,  are  distributed 
on  the  anterior  surface  of  the  root  of  the  lung.  They  join  with  filaments  from  the 
sympathetic,  and  form  the  anterior  pulmonary  plexus. 

The  Posterior  Bronchial  Branches  {rami  bronchiales  posteriores;  posterior  or  dorsal 
puhnonary  branches),  more  numerous  and  larger  than  the  anterior,  are  distributed 
on  the  posterior  surface  of  the  root  of  the  lung;  they  are  joined  by  filaments  from 
the  third  and  fourth  (sometimes  also  from  the  first  and  second)  thoracic  ganglia 
of  the  sympathetic  trunk,  and  form  the  posterior  pulmonary  plexus.  Branches  from 
this  plexus  accompany  the  ramifications  of  the  bronchi  through  the  substance  of 
the  lung. 

The  Esophageal  Branches  {rami  oesophagei)  are  given  off  both  above  and  below 
the  bronchial  branches;  the  lower  are  numerous  and  larger  than  the  upper.  They 
form,  together  with  the  branches  from  the  opposite  nerve,  the  esophageal  plexus. 
From  this  plexus  filaments  are  distributed  to  the  back  of  the  pericardium. 

The  Gastric  Branches  {rami  gastrici)  are  distributed  to  the  stomach.  The  right 
vagus  forms  the  posterior  gastric  plexus  on  the  postero-inferior  surface  of  the  stomach 
and  the  left  the  anterior  gastric  plexus  on  the  antero-superior  surface. 

The  Celiac  Branches  {rami  coeliaci)  are  mainly  derived  from  the  right  vagus:  they 
join  the  celiac  plexus  and  through  it  supply  branches  to  the  pancreas,  spleen, 
kidneys,  suprarenal  bodies,  and  intestine. 

The  Hepatic  Branches  {rami  hepatici)  arise  from  the  left  vagus:  they  join  the  hepatic 
[plexus  and  through  it  are  conveyed  to  the  liver. 


THE  ACCESSORY  NERVE   (N.  ACCESSORroS;  ELEVENTH  NERVE; 
SPINAL  ACCESSORY  NERVE)    (Figs.  792,  793,  794). 

The  accessory  nerve  consists  of  two  parts:  a  cranial  and  a  spinal. 

The  Cranial  Part  {ramus  internus;  accessory  portion)  is  the  smaller  of  the  two. 
Its  fibers  ari^e  from  the  cells  of  the  nucleus  ambiguus  and  emerge  as  four  or  five 
delicate  rootlets  from  the  side  of  the  medulla  oblongata,  below  the  roots  of  the 
vagus.  It  runs  lateral  ward  to  the  jugular  foramen,  where  it  interchanges  fibers 
with  the  spinal  portion  or  becomes  united  to  it  for  a  short  distance;  here  it  is  also 
connected  by  one  or  two  filaments  with  the  jugular  ganglion  of  the  vagus.  It 
then  passes  through  the  jugular  foramen,  separates  from  the  spinal  portion  and 
is  continued  over  the  surface  of  the  ganglion  nodosum  of  the  vagus,  to  the  surface  of 
which  it  is  adherent,  and  is  distributed' principally  to  the  pharyngeal  and  superior 
laryngeal  branches  of  the  vagus.  Through  the  pharyngeal  branch  it  probably  sup- 
plies the  Musculus  uvulae  and  Levator  veli  palatini.  Some  few  filaments  from  it 
are  continued  into  the  trunk  of  the  vagus  below  the  ganglion,  to  be  distributed  with 
the  recurrent  nerve  and  probably  also  with  the  cardiac  nerves. 

The  Spinal  Part  {ramus  externus;  spinal  portion)  is  firm  in  texture,  and  its  fibers 
arise  from  the  motor  cells  in  the  lateral  part  of  the  anterior  column  of  the  gray  sub- 
stance of  the  medulla  spinalis  as  low  as  the  fifth  cervical  nerve.  Passing  through  the 
lateral  funiculus  of  the  medulla  spinalis,  they  emerge  on  its  surface  and  unite  to 
form  a  single  trunk,  which  ascends  between  the  ligamentum  denticulatum  and  the 
posterior  roots  of  the  spinal  nerves,  enters  the  skull  through  the  foramen  magnum, 
and  is  then  directed  to  the  jugular  foramen,  through  which  it  passes,  h'ing  in  the 
same  sheath  of  dura  mater  as  the  vagus,  but  separated  from  it  by  a  fold  of  the 
arachnoid.  In  the  jugular  foramen,  it  receives  one  or  two  filaments  from  the 
cranial  part  of  the  nerve,  or  else  joins  it  for  a  short  distance  and  then  separates  from 
58 


914 


NEUROLOGY 


it  again.  As  its  exit  from  the  jugular  foramen,  it  runs  backward  in  front  of  the 
internal  jugular  vein  in  66.6  per  cent,  of  cases,  and  behind  in  it  33.3  per  cenc. 
(Tandler).  The  nerve  then  descends  obliquely  behind  the  Digastricus  and  Stylo- 
hyoideus  to  the  upper  part  of  the  Sternocleidomastoideus;  it  pierces  this  musch;, 
and  courses  obliquely  across  the  posterior  triangle  of  the  neck,  to  end  in  the  deep 
surface  of  the  Trapezius.  As  it  traverses  the  Sternocleidomastoideus  it  gives  several 
filaments  to  the  muscle,  and  joins  with  branches  from  the  second  cervical  nerve. 
In  the  posterior  triangle  it  unites  with  the  second  and  third  cervical  nerves,  while 
beneath  the  Trapezius  it  forms  a  plexus  with  the  third  and  fourth  cervical  nerves, 
and  from  this  plexus  fibers  are  distributed  to  the  muscle. 


Fig.  794. — Hypoglossal  nerve,  cervical  plexus,  and  their  branches. 


THE  HYPOGLOSSAL  NERVE  (N.  HYPOGLOSSUS;  TWELFTH  NERVE) 

(Figs.  794,  795). 

The  hypoglossal  nerve  is  the  motor  nerve  of  the  tongue. 

Its  fibers  arise  from  the  cells  of  the  hypoglossal  nucleus,  which  is  an  upward 
prolongation  of  the  base  of  the  anterior  column  of  gray  substance  of  the  medulla 
spinalis.  This  nucleus  is  about  2  cm.  in  length,  and  its  upper  part  corresponds 
with  the  trigonum  hypoglossi,  or  lower  portion  of  the  medial  eminence  of  the  rhom- 
boid fossa  (page  779).  The  lower  part  of  the  nucleus  extends  downward  into  the 
closed  part  of  the  medulla  oblongata,  and  there  lies  in  relation  to  the  ventro-lateral 


THE  HYPOGLOSSAL  NERVE 


915 


"aspect  of  the  central  canal.  The  fibers  run  forward  through  the  medulla  oblongata, 
and  emerge  in  the  antero-lateral  sulcus  between  the  pyramid  and  the  olive. 
11  The  rootlets  of  this  nerve  are  collected  into  two  bundles,  which  perforate  the 
■  dura  mater  separately,  opposite  the  hypoglossal  canal  in  the  occipital  bone,  and 
unite  together  after  their  passage  through  it;  in  some  cases  the  canal  is  divided 
into  two  by  a  small  bony  spicule.  The  nerve  descends  almost  vertically  to  a  point 
corresponding  with  the  angle  of  the  mandible.  It  is  at  first  deeply  seated  beneath 
the  internal  carotid  artery  and  internal  jugular  vein,  and  intimately  connected  with 
the  vagus  nerve;  it  then  passes  forward  between  the  vein  and  artery,  and  lower 

To  Dura  mater 

To  Ganglion  nodosum  of  vagus 
-  Hypoglossal  nerve- 

-Branch  from  first  cervical 
to  hypoglossal 


To  Lingual  nerve 

TO  GENIOHYOIDEUS 


TO  SUPERIOR  BELLY  OF  OMOHYOIDE.US 


II 


STERNOHYOIDEUS 

TO  STERNOTHYREOIDEUS 
TO  INFERIOR  BELLY  OF  OMOrfYOIDEUS 

Fig.  795. — Plan  of  hypoglossal  nerve. 

down  in  the  neck  becomes  superficial  below  the  Digastricus.  The  nerve  then  loops 
around  the  occipital  artery,  and  crosses  the  external  carotid  and  lingual  arteries 
below  the  tendon  of  the  Digastricus.  It  passes  beneath  the  tendon  of  the  Digas- 
tricus, the  Stylohyoideus,  and  the  Mylohyoideus,  lying  between  the  last-named 
muscle  and  the  Hyoglossus,  and  communicates  at  the  anterior  border  of  the  Hyo- 
glossus  with  the  lingual  nerve;  it  is  then  continued  forward  in  the  fibers  of  the 
Genioglossus  as  far  as  the  tip  of  the  tongue,  distributing  branches  to  its  muscular 
substance. 

Branches  of  Communication. — Its  branches  of  communication  are,  with  the 

Vagus.  First  and  second  cervical  nerves. 

Sympathetic.  Lingual. 

The  communications  with  the  vagus  take  place  close  to  the  skull,  numerous 
filaments  passing  between  the  hypoglossal  and  the  ganglion  nodosum  of  the  vagus 


916  NEUROLOGY 


n 


through  the  mass  of  connective  tissue  which  unites  the  two  nerves.    As  the  nerv^o 
winds  around  the  occipital  artery  it  gives  off  a  filament  to  the  pharyngeal  plexus. 

The  communication  with  the  sympathetic  takes  place  opposite  the  atlas  b>' 
branches  derived  from  the  superior  cervical  ganglion,  and  in  the  same  situatioE 
the  nerve  is  joined  by  a  filament  derived  from  the  loop  connecting  the  first  and 
second  cervical  nerves. 

The  communications  with  the  lingual  take  place  near  the  anterior  border  of  the 
Hyoglossus  by  numerous  filaments  which  ascend  upon  the  muscle. 

Branches  of  Distribution. — The  branches  of  distribution  of  the  hypoglossal  ner^ 
are: 

Meningeal.  Thyrohyoid. 

Descending.  jNIuscular. 

Of  these  branches,  the  meningeal,  descending,  thyrohyoid,  and  the  muscular 
twig  to  the  Geniohyoideus,  are  probably  derived  mainly  from  the  branch  which 
passes  from  the  loop  between  the  first  and  second  cervical  to  join  the  hvpoglossal 
(Fig.  795). 

Meningeal  Branches  (dural  branches). — As  the  hypoglossal  nerve  passes  through 
the  hypoglossal  canal  it  gives  off,  according  to  Luschka,  several  filaments  to  the 
dura  mater  in  the  posterior  fossa  of  the  skull. 

The  Descending  Ramus  (ramus  descendens;  descendens  hypoglossi) ,  long  and  slender, 
quits  the  hypoglossal  where  it  turns  around  the  occipital  artery  and  descends  in 
front  of  or  in  the  sheath  of  the  carotid  vessels;  it  gives  a  branch  to  the  superior 
belly  of  the  Omohyoideus,  and  then  joins  the  communicantes  cervicales  from  the 
second  and  third  cervical  nerves;  just  below  the  middle  of  the  neck,  to  form  a  loop, 
the  ansa  hypoglossi.  From  the  convexity  of  this  loop  branches  pass  to  supply 
the  Sternohyoideus,  the  Sternothyreoideus,  and  the  inferior  belly  of  the  Omo- 
hyoideus. According  to  Arnold,  another  filament  descends  in  front  of  the  vessels 
into  the  thorax,  and  joins  the  cardiac  ^nd  phrenic  nerves. 

The  Thjrrohyoid  Branch  {ramus  thyreohyoideus)  arises  from  the  hypoglossal  near 
the  posterior  border  of  the  hyoglossus;  it  runs  obliquely  across  the  greater  cornu 
of  the  hyoid  bone,  and  supplies  the  Thyreohyoideus  muscle. 

The  Muscular  Branches  are  distributed  to  the  Styloglossus,  Hyoglossus,  Genio- 
hyoideus, and  Genioglossus.  At  the  under  surface  of  the  tongue  numerous  slender 
branches  pass  upward  into  the  substance  of  the  organ  to  supply  its  intrinsic  muscles. 

THE  SPINAL  NERVES  (NERVI  SPIN  ALES). 

The  spinal  nerves  spring  from  the  medulla  spinalis,  and  are  transmitted  through 
the  intervertebral  foramina.  They  number  thirty-one  pairs,  which  are  grouped 
as  follows:    Cervical,  8;  Thoracic,  12;  Lumbar,  5;  Sacral,  5;  Coccygeal,  1. 

The  first  cervical  nerve  emerges  from  the  vertebral  canal  between  the  occipital 
bone  and  the  atlas,  and  is  therefore  called  the  suboccipital  nerve ;  the  eighth  issues 
between  the  seventh  cervical  and  first  thoracic  vertebrae. 

Nerve  Roots. — Each  nerve  is  attached  to  the  medulla  spinalis  by  two  roots, 
an  anterior  or  ventral,  and  a  posterior  or  dorsal,  the  latter  being  characterized  by 
the  presence  of  a  ganglion,  the  spinal  ganglion. 

The  Anterior  Root  {radix  anterior;  ventral  root)  emerges  from  the  anterior  surface 
of  the  medulla  spinalis  as  a  number  of  rootlets  or  filaments  {fila  radicularia) , 
which  coalesce  to  form  two  bundles  near  the  intervertebral  foramen. 

The  Posterior  Root  {radix  posterior;  dorsal  root)  is  larger  than  the  anterior  owing 
to  the  greater  size  and  number  of  its  rootlets;  these  are  attached  along  the  postero- 
lateral furrow  of  the  medulla  spinalis  and  unite  to  form  two  bundles  which  join 
the  spinal  ganglion.  The  posterior  root  of  the  first  cervical  nerve  is  exceptional 
in  that  it  is  smaller  than  the  anterior;  it  is  occasionally  wanting. 


m 


THE  SPINAL  NERVES 


917 


i¥ 


It 


11^ 


The  Spinal  Ganglia  (ganglion  spinale)  are  collections  of  nerve  cells  on  the  posterior 
roots  of  the  spinal  nerves.  Each  ganglion  is  oval  in  shape,  reddish  in  color,  and 
its  size  bears  a  proportion  to  that  of  the  nerve  root  on  which  it  is  situated;  it  is 
bifid  medially  where  it  is  joined  by  the  two  bundles  of  the  posterior  nerve  root. 
The  ganglia  are  usually  placed  in  the  intervertebral  foramina,  immediately  outside 
the  points  where  the  nerve  roots  perforate  the  dura  mater,  but  there  are  exceptions 
to  this  rule;  thus  the  ganglia  of  the  first  and  second  cervical  nerves  lie  on  the  verte- 
bral arches  of  the  atlas  and  axis  respectively,  those  of  the  sacral  nerves  are  inside 
the  vertebral  canal,  while  that  on  the  posterior  root  of  the  coccygeal  nerve  is  placed 
within  the  sheath  of  dura  mater. 

Structure  (Fig.  638). — The  ganglia  consist  chiefly  of  unipolar  nerve  cells,  and  from  these  the 
fibers  of  the  posterior  root  take  origin — the  single  process  of  each  cell  dividing  after  a  short  course 
into  a  central  fiber  which  enters  the  meduUa  spinahs  and  a  peripheral  fiber  which  runs  into  the 
spinal  nerve.  Two  other  forms  of  cells  are,  however,  present,  viz.:  (a)  the  cells  of  Dogiel,  whose 
axons  ramify  close  to  the  cell  (type  II,  of  Golgi),  and  are  distributed  entirely  within  the  ganglion; 
and  (b)  multipolar  cells  similar  to  those  found  in  the  sympathetic  ganglia. 

The  ganglia  of  the  first  cervical  nerve  may  be  absent,  while  small  aberrant  ganglia  consisting 
of  groups  of  nerve  cells  are  sometimes  found  on  the  posterior  roots  between  the  spinal  ganglia 
and  the  medulla  spinalis. 

Each  nerve  root  receives  a  covering  from  the  pia  mater,  and  is  loosely  invested 
y  the  arachnoid,  the  latter  being  prolonged  as  far  as  the  points  where  the  roots 
pierce  the  dura  mater.  The  two  roots 
pierce  the  dura  mater  .separately,  each 
receiving  a  sheath  from  this  membrane; 
where  the  roots  join  to  form  the  spinal 
nerve  this  sheath  is  continuous  with  the 
epineurium  of  the  nerve. 

Size  and  Direction. — The  roots  of  the 
upper  four  cervical  nerves  are  small, 
those  of  the  lower  four  are  large.  The 
posterior  roots  of  the  cervical  nerves 
bear  a  proportion  to  the  anterior  of 
three  to  one,  which  is  greater  than  in 
he  other  regions;  their  individual  fila- 
ments are  also  larger  than  those  of  the 
anterior  roots.  The  posterior  root  of 
the  first  cervical  is  an  exception  to  this 
rule,  being  smaller  than  the  anterior 
root;  in  eight  per  cent,  of  cases  it  is 
wanting.  The  roots  of  the  first  and 
second  cervical  nerves  are  short,  and 
run  nearly  horizontally  to  their  points 
of  exit  from  the  vertebral  canal.  From 
he  second  to  the  eighth  cervical  they 
are  directed  obliquely  downward,  the 
obliquity  and  length  of  the  roots  succes- 
sively increasing ;  the  distance,  however, 
between  the  level  of  attachment  of  any 
of  these  roots  to  the  medulla  spinalis  and 
the  points  of  exit  of  the  corresponding 
nerves  never  exceeds  the  depth  of  one 
vertebra. 

The  roots  of  the  thoracic  nerves,  with  the  exception  of  the  first,  are  of  small 
size,  and  the  posterior  only  slightly  exceed  the  anterior  in  thickness.  They  increase 
successively  in  length,  from  above  downward,  and  in  the  lower  part  of  the  thoracic 


POSTERIOR 
NERVE  , 
ROOTS  ) 


POSTERIOR 
ROOTS  ^ 


POSTERIOR 
ROOTS 


ANTERIOR 
NERVE 
ROOTS 


LIGAMENTUM 
DENTICULATUM 
DURA 
'OPENED 

i.. ANTERIOR 
ROOTS 

SPINAL  NERVE 
IN  ITS  PIAL 
SHEATH 


ANTERIOR 
ROOTS 


POSTERIOR 
ROOTS ■ 


LIGAMENTUM 
DENTICULATUM 
ANTERIOR 
ROOTS 


SPINAL    NERVE 
IN   ITS   SHEATH 


Fig.  79G. — A  jjw.  Lj..a  of  the  spinal  cord,  showing  its 
right  lateral  surface.  The  dura  is  opened  and  arranged  to 
show  the  nerve  roots.     (Testut.) 


918 


NEUROLOGY 


I 


region  descend  in  contact  with  the  medulla  spinalis  for  a  distance  equal  to  the  height 
of  at  least  two  vertebrae  before  they  emerge  from  the  vertebral  canal. 


Fia.  797. — Distribution  of  cutaneous  nerves.     Ventral  aspect. 


The  roots  of  the  lower  lumbar  and  upper  sacral  nerves  are  the  largest,  and  their 
individual  filaments  the  most  numerous  of  all  the  spinal  nerves,  while  the  roots 
of  the  coccygeal  nerve  are  the  smallest. 


THE  SPINAL  NERVES 


919 


The  roots  of  the  lumbar,  sacral,  and  coccygeal  nerves  run  vertically  downward 
their  respective  exits,  and  as  the  medulla  spinalis  ends  near  the  lower  border 


K 


Fig.  798. — Distribution  of  cutaneous  nerves.     Dorsal  aspect. 


of  the  first  lumbar  vertebra  it  follows  that  the  length  of  the  successive  roots  must 
rapidly  increase.  As  already  mentioned  (page  750),  the  term  cauda  equina  is  applied 
to  this  collection  of  nerve  roots. 


920 


NEUROLOGY 


I 


From  the  description  given  it  will  be  seen  that  the  largest  nerve  roots,  and 
consequently  the  largest  spinal  nerves,  are  attached  to  the  cervical  and  lumbar 
swellings  of  the  medulla  spinalis;  these  nerves  are  distributed  to  the  upper  and 
lower  limbs. 

Connections  with  Sympathetic. — Immediately  beyond  the  spinal  ganglion,  the 
anterior  and  posterior  nerve  roots  unite  to  form  the  spinal  nerve  which  emerges 
througli  the  intervertebral  foramen.  Each  spinal  nerve  receives  a  branch  (gray 
ramus  communicans)  from  the  adjacent  ganglion  of  the  sympathetic  trunk,  while 
the  thoracic,  and  the  first  and  second  lumbar  nerves  each  contribute  a  branch 
(white  ramus  communicans)  to  the  adjoining  sympathetic  ganglion.  The  second, 
third,  and  fourth  sacral  nerves  also  supply  white  rami;  these,  however,  are  not 
connected  with  the  ganglia  of  the  sympathetic  trunk,  but  run  directly  into  the 
pelvic  plexuses  of  the  sympathetic. 


\  Sympathefie 
>Y-  ~\ — ganglion 


Spinal  nerve 


Sympathetic 
ganglion 


Fig.  799. — Scheme  showing  structure  of  a  typical  spinal  nerve.    1.  Somatic  eflerent.    2.  Somatic  afferent. 
Sympathetic  efferent.     6,  7.   Sympathetic  afferent. 


3.4,5. 


Structure. — Each  typical  spinal  nerve  contains  fibers  belonging  to  two  systems,  viz.,  the 
somatic,  and  the  sympathetic  or  splanchnic,  as  well  as  fibers  connecting  these  systems  with  each 
other  (Fig.  799). 

1.  The  somatic  fibers  are  efferent  and  afferent.  The  efferent  fibers  originate  in  the  cells  of  the 
anterior  column  of  the  medulla  spinahs,  and  run  outward  through  the  anterior  nerve  roots  to  the 
spinal  nerve.  They  convey  impulses  to  the  voluntary  muscles,  and  are  continuous  from  their 
origin  to  their  peripheral  distribution.  The  afferent  fibers  convey  impressions  inward  from  the 
skin,  etc.,  and  originate  in  the  unipolar  nerve  cells  of  the  spinal  ganglia.  The  single  processes 
of  these  cells  divide  into  peripheral  and  central  fibers,  and  the  latter  enter  the  medulla  spinahs 
through  the  posterior  nerve  roots. 

2.  The  sympathetic  fibers  are  also  efferent  and  afferent.  The  efferent  fibers,  preganglionic  fibers, 
originate  in  the  lateral  column  of  the  medulla  spinalis,  and  are  conveyed  through  the  anterior 
nerve  root  and  the  white  ramus  communicans  to  the  corresponding  ganglion  of  the  sympathetic 
trunk;  here  they  may  end  by  forming  synapses  aroilnd  its  cells,  or  may  run  through  the  ganglion 
to  end  in  another  of  the  ganglia  of  the  sympathetic  trunk,  or  in  a  more  distally  placed  ganglion 


I 


THE  CERVICAL  NERVES 


921 


H 


» 


in  one  of  the  sympathetic  plexuses.  In  all  cases  they  end  by  forming  synapses  around  other  nerve 
cells.  From  the  cells  of  the  gangha  of  the  sympathetic  trunk  other  fibers,  postgangUonic  fibers, 
take  origin;  some  of  these  run  through  the  gray  rami  commimicantes  to  join  the  spinal  nerves,  along 
which  they  are  carried  to  the  bloodvessels  of  the  trunk  and  limbs,  while  others  pass  to  the  viscera, 
either  directly  or  after  interruption  in  one  of  the  distal  ganglia.  The  afferent  fibers  are  derived 
partly  from  the  unipolar  cells  and  partly  from  the  multipolar  cells  of  the  spinal  ganglia.  Their  per- 
ipheral processes  are  carred  through  the  white  rami  communicantes,  and  after  passing  through  one 
or  more  sympathetic  ganglia  (but  always  without  interruption  in  them)  finally  end  in  the  tissues  of 
the  viscera.  The  central  processes  of  the  unipolar  cells  enter  the  medulla  spinalis  through  the 
posterior  nerve  root  and  form  synapses  around  either  somatic  or  sympathetic  efferent  neurons,  thus 
completing  reflex  arcs.  The  dendrites  of  the  multipolar  nerve  cells  form  synapses  around  the  cells 
of  type  II  (cells  cf  Dogiel)  in  the  spinal  ganglia,  and  by  this  path  the  original  impulse  is  transferred 
from  the  sympathetic  to  the  somatic  system,  through  which  it  is  conveyed  to  the  sensorium. 

Divisions. — After  emerging  from  the  intervertebral  foramen,  each  spinal  nerve 
gives  off  a  small  meningeal  branch  which  reenters  the  vertebral  canal  through  the 
intervertebral  foramen  and  supplies  the  vertebrae  and  their  ligaments,  and  the 
bloodvessels  of  the  medulla  spinalis  and  its  membranes.  The  spinal  nerve  then 
splits  into  a  posterior  or  dorsal,  and  an  anterior  or  ventral  division,  each  receiving 
fibres  from  both  nerve  roots. 


POSTERIOR  DIVISIONS   OF   THE   SPINAL   NERVES  (RAMI  POSTERIORES). 


The  posterior  divisions  are  as  a  rule  smaller  than  the  anterior.  They  are  directed 
backward,  and,  with  the  exceptions  of  those  of  the  first  cervical,  the  fourth  and 
fifth  sacral,  and  the  coccygeal,  divide  into  medial  and  lateral  branches  for  the  supply 
f  the  muscles  and  skin  (Figs.  800,  801,  802)  of  the  posterior  part  of  the  trunk. 


GREAT   OCCIPI. 
TAL    NERVE 


RECTUS    CAPITIS 
LATERALIS 

ANTERIOR  PRIMARY    DIVI 
6I0N  OF  FIRST  CERVICAL 


OBLIQUUS 
SUPERIOR 


BRANCH  TO  COMPLEXUS — OUl 
VERTEBRAL   ARTERY 

POSTERIOR   PRIMARY  DIVISION 
FIRST  CERVICAL 
ASTOMOTIC  BRANCH 


POSTERIOR   PRIMARY    DIVI 
8I0N  OF  FIRST  CERVICALl 


ANASTOMOTIC 
HIRD    CERVICAL 


OBLIQUUS 
INFFRIOR 


Fig.  800. — Posterior  primary  divisions  of  the  upper  three  cervical  nerves.     (Testut.) 


The  Cervical  Nerves  (Nn.  Cervicales). 


The  posterior  division  of  the  first  cervical  or  suboccipital  nerve  is  larger  than 
the  anterior  division,  and  emerges  above  the  posterior  arch  of  the  atlas  and  beneath 
the  vertebral  artery.  It  enters  the  suboccipital  triangle  and  supplies  the  muscles 
which  bound  this  triangle,  viz.,  the  Rectus  capitis  posterior  major,  and  the  Obliqui 
superior  and  inferior;  it  gives  branches  also  to  the  Rectus  capitis  posterior  minor 


922 


NEUROLOGY 


and  the  Semispinalis  capitis.    A  filament  from  the  branch  to  the  Obliquus  inferior 
joins  the  posterior  division  of  the  second  cervical  nerve. 

The  nerve  occasionally  gives  off  a  cutaneous  branch  which  accompanies  the  occipital  artery 
to  the  scalp,  and  communicates  with  the  greater  and  lesser  occipital  nerves. 


Fia.  801. — Diagram  of  the  distribution  of 
the_  cutaneous  branches  of  the  posterior 
divisions  of  the  spinal  nerves. 


Fia._  802. — Areas  of  distribution  of  the  cutaneous  branches  of  the 
posterior  divisions  of  the  spinal  nerves.  The  areas  of  the  medial 
branches  are  in  black,  those  of  the  lateral  in  red.   (H.  M.  Johnston.) 


The  posterior  division  of  the  second  cervical  nerve  is  much  larger  than  the 
anterior  division,  and  is  the  greatest  of  all  the  cervical  posterior  divisions.  It 
emerges  between  the  posterior  arch  of  the  atlas  and  the  lamina  of  the  axis,  below 
the  Obliquus  inferior.  It  supplies  a  twig  to  this  muscle,  receives  a  communicating 
filament  from  the  posterior  division  of  the  first  cervical,  and  then  divides  into  a 
large  medial  and  a  small  lateral  branch. 


THE  THORACIC  NERVES  923 

The  medial  branch  {ramus  medialis;  internal  branch),  called  from  its  size  and 
distribution  the  greater  occipital  nerve  (n.  occipitalis  major;  great  occipital  nerve), 
ascends  obliquely  between  the  Obliquus  inferior  and  the  Semispinalis  capitis,  and 
pierces  the  latter  muscle  and  the  Trapezius  near  their  attachments  to  the  occipital 

11  bone  (Fig.  801).  It  is  then  joined  by  a  filament  from  the  medial  branch  of  the 
P  posterior  division  of  the  third  cervical,  and,  ascending  on  the  back  of  the  head 
with  the  occipital  artery,  divides  into  branches  which  communicate  with  the  lesser 
occipital  nerve  and  supply  the  skin  of  the  scalp  as  far  forward  as  the  vertex  of  the 
skull.  It  gives  off  muscular  branches  to  the  Semispinalis  capitis,  and  occasionally 
a  twig  to  the  back  of  the  auricula.  The  lateral  branch  {ramus  lateralis;  external 
branch)  supplies  filaments  to  the  Splenius,  Longus  capitis,  and  Semispinalis  capitis, 
and  is  often  joined  by  the  corresponding  branch  of  the  third  cervical. 

The  posterior  division  of  the  third  cervical  is  intermediate  in  size  between  those 
of  the  second  and  fourth.  Its  medial  branch  runs  between  the  Semispinalis  capitis 
and  cervicis,  and,  piercing  the  Splenius  and  Trapezius,  ends  in  the  skin.  While 
under  the  Trapezius  it  gives  off  a  branch  called  the  third  occipital  nerve,  which  pierces 
the  Trapezius  and  ends  in  the  skin  of  the  lower  part  of  the  back  of  the  head  (Fig. 
801).  It  lies  medial  to  the  greater  occipital  and  communicates  with  it.  The 
lateral  branch  often  joins  that  of  the  second  cervical. 

The  posterior  division  of  the  suboccipital,  and  the  medial  branches  of  the  posterior  division 
of  the  second  and  third  cervical  nerves  are  sometimes  joined  by  communicating  loops  to  form 
the  posterior  cervical  plexus  (Cruveilhier). 


I 


The  posterior  divisions  of  the  lower  five  cervical  nerves  divide  into  medial 
and  lateral  branches.  The  medial  branches  of  the  fourth  and  fifth  run  between  the 
Semispinales  cervicis  and  capitis,  and,  having  reached  the  spinous  processes, 
pierce  the  Splenius  and  Trapezius  to  end  in  the  skin  (Fig.  801).  Sometimes  the 
branch  of  the  fifth  fails  to  reach  the  skin.  Those  of  the  lower  three  nerves  are 
small,  and  end  in  the  Semispinales  cervicis  and  capitis,  Multifidus,  and  Inter- 
spinales.  The  lateral  branches  of  the  lower  five  nerves  supply  the  Iliocostalis 
cervicis,  Longissimus  cervicis,  and  Longissimus  capitis. 

I  The  Thoracic  Nerves  (Nn.  Thoracales). 

The  medial  branches  {ramus  medialis;  internal  branch)  of  the  posterior  divisions  of 
the  upper  six  thoracic  nerves  run  between  the  Semispinalis  dorsi  and  Multifidus, 
which  they  supply;  they  then  pierce  the  Rhomboidei  and  Trapezius,  and  reach 

tthe  skin  by  the  sides  of  the  spinous  processes  (Fig.  801).  The  medial  branches 
of  the  lower  six  are  distributed  chiefly  to  the  Multifidus  and  Longissimus  dorsi, 
occasionally  they  give  off  filaments  to  the  skin  near  the  middle  line. 
The  lateral  branches  {ramus  lateralis;  external  branch)  increase  in  size  from  above 
downward.  They  run  through  or  beneath  the  Longissimus  dorsi  to  the  interval 
betw^een  it  and  the  Iliocostales,  and  supply  these  muscles;  the  lower  five  or  six 
also  give  off  cutaneous  branches  which  pierce  the  Serratus  posterior  inferior  and 
Latissimus  dorsi  in  a  line  with  the  angles  of  the  ribs  (Fig.  801).  The  lateral 
branches  of  a  variable  number  of  the  upper  thoracic  nerves  also  give  filaments 
to  the  skin.  The  lateral  branch  of  the  twelfth  thoracic,  after  sending  a  filament 
medialward  along  the  iliac  crest,  passes  downward  to  the  skin  of  the  buttock. 

The  medial  cutaneous  branches  of  the  posterior  divisions  of  the  thoracic  nerves  descend  for 
some  distance  close  to  the  spinous  processes  before  reaching  the  skin,  while  the  lateral  branches 
travel  downward  for  a  considerable  distance — it  may  be  as  much  as  the  breadth  of  four  ribs — 
before  they  become  superficial;  the  branch  from  the  twelfth  thoracic,  for  instance,  reaches  the 
akin  only  a  little  way  above  the  iliac  crest.^ 

See  article  by  H.  M.  Johnston,  Journal  of  Anatomy  and  Physiology,  vol.  xliii. 


924 


NEUROLOGY 


The  Lumbar  Nerves  (Nn.  Lumbales). 

The  medial  branches  of  the  posterior  divisions  of  the  lumbar  nerves  run  close  to  the 
articular  processes  of  the  vertebrae  and  end  in  the  Multifidus. 

The  lateral  branches  supply  the  Sacrospinalis.  The  upper  three  give  off  cutaneous 
nerves  which  pierce  the  aponeurosis  of  the  Latissimus  dorsi  at  the  lateral  border  of 
the  Sacrospinalis  and  descend  across  the  posterior  part  of  the  iliac  crest  to  the  skin 
of  the  buttock  (Fig.  801),  some  of  their  twigs  running  as  far  as  the  level  of  the 
greater  trochanter. 


■'^ 


ANTERrOft^BRANCHt-s, 

OF    LOWEtt     SACRAL    NERVES 

Fig.  803.— The- posterior  divisions  of  the  sacral  nervea. 


The  Sacral  Nerves  (Nn.  Sacrales). 

The  posterior  divisions  of  the  sacral  nerves  {rami  posteriores)  (Fig.  803)  are 
small,  and  diminish  in  size  from  above  downward;  they  emerge,  except  the  last, 
through  the  posterior  sacral  foramina.  The  ujjper  three  are  covered  at  their  points 
of  exit  by  the  Multifidus,  and  divide  into  medial  and  lateral  branches. 

The  medial  branches  are  small,  and  end  in  the  Multifidus. 

The  lateral  branches  join  with  one  another  and  with  the  lateral  branches  of  the 
posterior  divisions  of  the  last  lumbar  and  fourth  sacral  to  form  loops  on  the  dorsal 
surface  of  the  sacrum.  From  these  loops  branches  run  to  the  dorsal  surface  of  the 
sacrotuberous  ligament  and  form  a  second  series  of  loops  under  the  Glutseus  maxi- 
mus.  •  From  this  second  series  cutaneous  branches,  two  or  three  in  number,  pierce 
the  Glutseus  maximus  along  a  line  drawn  from  the  posterior  superior  iliac  spine  to 
the  tip  of  the  cocc\Ti;  they  supply  the  skin  over  the  posterior  part  of  the  buttock. 

The  posterior  divisions  of  the  loiver  two  sacral  nerves  are  small  and  lie  below  the 
Multifidus.    They  do  not  divide  into  medial  and  lateral  branches,  but  unite  with  fl 
each  other  and  with  the  posterior  division  of  the  coccygeal  nerve  to  form  loops  on 
the  back  of  the  sacrum ;  filaments  from  these  loops  supply  the  skin  over  the  coccyx. 


THE  CERVICAL  NERVES 


925 


I 


The  Coccygeal  Nerve  (N.  Coccygeus). 

The  posterior  division  of  the  coccygeal  nerve  {ramus  posterior)  does  not  divide 
into  a  medial  and  a  lateral  branch,  but  receives,  as  already  stated,  a  communicating 
branch  from  the  last  sacral ;  it  is  distributed  to  the  skin  over  the  back  of  the  coccyx. 

ANTERIOR  DIVISIONS  OF   THE   SPINAL   NERVES    (RAMI  ANTERIORES). 

The  anterior  divisions  of  the  spinal  nerves  supply  the  antero-lateral  parts  of  the 
trunk,  and  the  limbs ;  they  are  for  the  most  part  larger  than  the  posterior  divisions. 
In  the  thoracic  region  they  run  independently  of  one  another,  but  in  the  cervical, 
umbar,  and  sacral  regions  they  unite  near  their  origins  to  form  plexuses. 


The  Cervical  Nerves  (Nn.  Cervicales). 

The  anterior  divisions  of  the  cervical  nerves  {rami  anteriores),  with  the  exception 
of  the  first,  pass  outward  between  the  Intertransversarii  anterior  and  posterior, 
lying  on  the  grooved  upper  surfaces  of  the  transverse  processes  of  the  vertebrae. 
The  anterior  division  of  the  first  or  suboccipital  nerve  issues  from  the  vertebral  canal 
above  the  posterior  arch  of  the  atlas  and  runs  forward  around  the  lateral  aspect 
of  its  superior  articular  process,  medial  to  the  vertebral  artery.  In  most  cases  it 
descends  medial  to  and  in  front  of  the  Rectus  capitis  lateralis,  but  occasionally  it 
pierces  the  muscle. 

The  anterior  divisions  of  the  upper  four  cervical  nerves  unite  to  form  the  cervical 
plexus,  and  each  receives  a  gray  ramus  communicans  from  the  superior  cervical 
ganglion  of  the  sympathetic  trunk.  Those  of  the  lower  four  cervical,  together  with 
the  greater  part  of  the  first  thoracic,  form  the  brachial  plexus.  They  each  receive 
a  gray  ramus  communicans,  those  for  the  fifth  and  sixth  being  derived  from  the 
middle,  and  those  for  the  seventh  and  eighth  from  the  lowest,  cervical  ganglion 
of  the  sympathetic  trunk. 

The  Cervical  Plexus  {plexus  cervicalis)  (Fig.  804). — The  cervical  plexus  is  formed 
by  the  anterior  divisions  of  the  upper  four  cervical  nerves;  each  nerve,  except 
the  first,  divides  into  an  upper  and  a  lower  branch,  and  the  branches  unite  to  form 
three  loops.  The  plexus  is  situated  opposite  the  upper  four  cervical  vertebrae,  in 
front  of  the  Levator  scapuhe  and  Scalenus  medius,  and  covered  by  the  Sterno- 
cleidomastoideus. 

Its  branches  are  divided  into  two  groups,  superficial  and  deep,  and  are  here 
given  in  tabular  form;  the  figures  following  the  names  indicate  the  nerves  from 
hich  the  different  branches  take  origin: 

Smaller  occipital 

Great  auricular  . 
[Cutaneous  cervical 
iSupraclavicular 


Superficial 


Deep 


Internal 


Communicating 


Muscular 


External 


With  hypoglossal 
"    vagus   . 
"    sympathetic 
Rectus  capitis  lateralis 
Rectus  capitis  anterior 
Longus  capitis 
Communicantes  cervi- 
cales 
Phrenic 
Communicating  with  accessory 

Sternocleidomastoideus 


Muscular 


Trapezius 
(Levator  scapulae 
(Scalenus  medius 


2, 

C 

2, 

3, 

C. 

2, 

3, 

C. 

3,' 

4, 

C. 

9 

"'J 

C. 

2 

C. 

2,3,4,C. 

C. 

2 

C. 

2 

3,  C. 

2, 

3, 

C. 

3,' 

4, 

5,  C. 

2, 

3, 

4,0. 

2, 

C 

3, 

4, 

C. 

3, 

4, 

C. 

3, 

4, 

c. 

926 


NEUROLOGY 


Superficial  Branches  of  the  Cervical  Plexus  (Fig.  805). — The  Smaller  Occipital 
Nerve  {n.  occipitalis  minor;  small  occipital  nerve)  arises  from  the  second  cervical 
nerve,  sometimes  also  from  the  third;  it  curves  around  and  ascends  along  th(} 
posterior  border  of  the  Sternocleidomastoideus.  Near  the  cranium  it  perforates 
the  deep  fascia,  and  is  continued  upward  along  the  side  of  the  head  behind  the 
auricula,  supphdng  the  skin  and  communicating  with  the  greater  occipital,  th(3 
great  auriciilar,  and  the  posterior  auricular  branch  of  the  facial.  The  smaller 
occipital  varies  in  size,  and  is  sometimes  duplicated. 


.R.C.A.    MIN. 


-\     f^R.A.   MA 


11^ 


COMMUNICATING  TO 
HYPOGLOSSAL 


SYMPATHETIC 


LONGUS  COLL.  A 
RECTUS  ANT.  MAJOR 


III 


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Fig.  804. — Plan  of  the  cervical  plexus.     (Gerrish.) 


It  gives  off  an  auricular  branch,  which  supplies  the  skin  of  the  upper  and  back 
part  of  the  auricula,  communicating  with  the  mastoid  branch  of  the  great  auricular. 
This  branch  is  occasionally  derived  from  the  greater  occipital  nerve. 

The  Great  Auricular  Nerve  {n.  auricularis  magnus)  is  the  largest  of  the  ascending 
branches.  It  arises  from  the  second  and  third  cervical  nerves,  winds  around  the 
posterior  border  of  the  Sternocleidomastoideus,  and,  after  perforating  the  deep 


THE  CERVICAL  NERVES 


927 


fascia,  ascends  upon  that  muscle  beneath  the  Platysma  to  the  parotid  gland,  where 
it  divides  into  an  anterior  and  a  posterior  branch. 

The  anterior  branch  {ramus  anterior;  facial  branch)  is  distributed  to  the  skin  of 
the  face  over  the  parotid  gland,  and  communicates  in  the  substance  of  the  gland 
with  the  facial  nerve. 


Termination 
»/  supratrochlear 
)/  infratrochlear 
?/  nasociliary 


U 


Fia.  805. — The  nerves  of  the  scalp,  face,  and  side  of  neck. 

The  posterior  branch  (ramus  posterior;  mastoid  branch)  supplies  the  skin  over  the 
mastoid  process  and  on  the  back  of  the  auricula,  except  at  its  upper  part;  a  filament 
pierces  the  auricula  to  reach  its  lateral  surface,  where  it  is  distributed  to  the  lobule 
and  lower  part  of  the  concha.  The  posterior  branch  communicates  with  the  smaller 
occipital,  the  auricular  branch  of  the  vagus,  and  the  posterior  auricular  branch 
of  the  facial. 

The  Cutaneous  Cervical  (n.  cutaneus  colli;  superficial  or  transverse  cervical  nerve) 
arises  from  the  second  and  third  cervical  nerves,  turns  around  the  posterior  border 
of  the  Sternocleidomastoideus  about  its  middle,  and,  passing  obliquely  forward 
beneath  the  external  jugular  vein  to  the  anterior  border  of  the  muscle,  it  perforates 
the  deep  cervical  fascia,  and  divides  beneath  the  Platysma  into  ascending  and 
descending  branches,  which  are  distributed  to  the  antero-lateral  parts  of  the  neck. 


928  ^^^^^^^       NEUROLOGY 


and  form  a  plexus  with  the  cervical  branch  of  the  facial  nerve  beneath  the  Platysma; 
others  pierce  that  muscle,  and  are  distributed  to  the  skin  of  the  upper  and  fron- 
part  of  the  neck. 

The  descending  branches  {rami  injeriores)  pierce  the  Platysma,  and  are  distributed 
to  the  skin  of  the  side  and  front  of  the  neck,  as  low  as  the  sternum. 

The  Supraclavicular  Nerves  {mi.  supraclavicvlares;  descending  branches)  arise  from 
the  third  and  fourth  cervical  nerves;  they  emerge  beneath  the  posterior  border 
of  the  Sternocleidomastoideus,  and  descend  in  the  posterior  triangle  of  the  neck 
beneath  the  Platysma  and  deep  cervical  fascia.  Near  the  clavicle  they  perforate 
the  fascia  and  Platysma  to  become  cutaneous,  and  are  arranged,  according  to 
their  position,  into  three  groups — anterior,  middle  and  posterior. 

The  anterior  supraclavicular  nerves  {jin.  svpraclaviculares  anteriores;  suprasternal 
nerves)  cross  obliquely  over  the  external  jugular  vein  and  the  clavicular  and  sternal 
heads  of  the  Sternocleidomastoideus,  and  supply  the  skin  as  far  as  the  middle  line. 
They  furnish  one  or  two  filaments  to  the  sternoclavicular  joint. 

The  middle  supraclavicular  nerves  {nn.  supraclamculares  medii;  supraclavicular 
nerves)  cross  the  clavicle,  and  supply  the  skin  over  the  Pectoralis  major  and  Del- 
toideus,  communicating  with  the  cutaneous  branches  of  the  upper  intercostal  nerves. 

The  posterior  supraclavicular  nerves  {nn.  supraclaviculares  posteriores;  supra-acromial 
nerves)  pass  obliquely  across  the  outer  surface  of  the  Trapezius  and  the  acromion, 
and  supply  the  skin  of  the  upper  and  posterior  parts  of  the  shoulder. 

Deep  Branches  of  the  Cervical  Plexus,  Internal  Series. — The  Communicating: 
Branches  consist  of  several  filaments,  which  pass  from  the  loop  between  the  first 
and  second  cervical  nerves  to  the  vagus,  hypoglossal,  and  sympathetic.  The  branch 
to  the  hypoglossal  ultimately  leaves  that  nerve  as  a  series  of  branches,  viz.,  the 
descending  ramus,  the  nerve  to  the  Thyreohyoideus  and  the  nerve,  to  the  Genio- 
hyoideus  (see  page  916).  A  communicating  branch  also  passes  from  the  fourth 
to  the  fifth  cervical,  while  each  of  the  first  four  cervical  nerves  receives  a  gray 
ramus  communicans  from  the  superior  cervical  ganglion  of  the  sympathetic. 

Muscular  Branches  supply  the  Longus  capitis,  Rectus  capitis  anterior,  and  Rectus 
capitis  lateralis. 

The  Communicantes  Cervicales  {communicanies  hypoglossi)  (Fig.  804)  consist 
usually  of  two  filaments,  one  derived  from  the  second,  and  the  other  from  the  third 
cervical.  These  filaments  join  to  form  the  descendens  cervicalis,  which  passes 
downward  on  the  lateral  side  of  the  internal  jugular  vein,  crosses  in  front  of  the 
vein  a  little  below  the  middle  of  the  neck,  and  forms  a  loop  (ansa  hypoglossi)  with 
the  descending  ramus  of  the  hypoglossal  in  front  of  the  sheath  of  the  carotid 
vessels  (see  page  916).    Occasionally,  the  loop  is  formed  within  the  sheath. 

The  Phrenic  Nerve  {n.  phrenicus;  internal  respiratory  nerve  of  Belt)  contains  motor 
and  sensory  fibers  in  the  proportion  of  about  two  to  one.  It  arises  chiefly  from  the 
fourth  cervical  nerve,  but  receives  a  branch  from  the  third  and  another  from  the 
fifth;  the  fibers  from  the  fifth  occasionally  come  through  the  nerve  to  the  Sub- 
clavius.  It  descends  to  the  root  of  the  neck,  running  obliquely  across  the  front 
of  the  Scalenus  anterior,  and  beneath  the  Sternocleidomastoideus,  the  inferior 
belly  of  the  Omohyoideus,  and  the  transverse  cervical  and  transverse  scapular 
vessels.  It  next  passes  in  front  of  the  first  part  of  the  subclavian  artery,  between 
it  and  the  subclavian  vein,  and,  as  it  enters  the  thorax,  crosses  the  internal  mam- 
mary artery  near  its  origin.  Within  the  thorax,  it  descends  nearly  vertically  in 
front  of  the  root  of  the  lung,  and  then  between  the  pericardium  and  the  medias- 
tinal pleura,  to  the  diaphragm,  where  it  divides  into  branches,  which  pierce 
that  muscle,  and  are  distributed  to  its  under  surface.  In  the  thorax  it  is  accom- 
panied by  the  pericardiacophrenic  branch  of  the  internal  mammary  artery. 

The  two  phrenic  nerves  differ  in  their  length,  and  also  in  their  relations  at  the 
upper  part  of  the  thorax. 


I 


THE  CERVICAL  NERVES 


929 


The  right  nerve  is  situated  more  deeply,  and  is  shorter  and  more  vertical  in 
direction  than  the  left;  it  lies  lateral  to  the  right  innominate  vein  and  superior 
vena  cava. 

The  left  nerve  is  rather  longer  than  the  right,  from  the  inclination  of  the  heart 
to  the  left  side,  and  from  the  diaphragm  being  lower  on  this  than  on  the  right  side. 
At  the  root  of  the  neck  it  is  crossed  by  the  thoracic  duct ;  in  the  superior  mediastinal 
cavity  it  lies  between  the  left  common  carotid  and  left  subclavian  arteries,  and 
crosses  superficial  to  the  vagus  on  the  left  side  of  the  arch  of  the  aorta. 


ANTERIOR    PRIMARY 

DIVISION  OF. 

FOURTH    CERVICAL 


BRACHIAL 
PLCXUS 


PERICARDIAL 
BRANC 


PHRENIC 

INFERIOR 
CERVICAL 
GANGLION 
NFERIOR 
LARYNGEAL 

NERVETO 

SUBCLAVIUS 

MUSCLE 

COMMUNICATING 
^RANCH   FROM 
BRACHIAL  PLEXUS 

THORACIC  CARDIAC 
BRANCH  OF 
VAGUS 

FERIOR 
RYNGEAL 
ANTERIOR 
PULMONARY 

ANTERIOR 

PULMONARY 

PLEXUS 


RAMIFICATIONS 
OF  PHRENIC 


Fig.  806. — The  phrenic  nerve  and  its  relations  with  the  vagus  nerve. 


Each  nerve  supplies  filaments  to  the  pericardium  and  pleura,  and  at  the  root 
of  the  neck  is  joined  by  a  filament  from  the  sympathetic,  and,  occasionally,  by 
one  from  the  ansa  hypoglossi.  Branches  have  been  described  as  passing  to  the 
peritoneum. 

From  the  right  nerve,  one  or  two  filaments  pass  to  join  in  a  small  phrenic  ganglion 
with  phrenic  branches  of  the  celiac  plexus;  and  branches  from  this  ganglion  are 
59 


930 


NEUROLOGY 


i 


distributed  to  the  falciform  and  coronary  ligaments  of  the  liver,  the  suprarenal 
gland,  inferior  vena  cava,  and  right  atrium.  From  the  left  nerve,  filaments  pass  to 
join  the  phrenic  branches  of  the  celiac  plexus,  but  without  any  ganglionic  enlarge- 
ment; and  a  twig  is  distributed  to  the  left  suprarenal  gland. 

Deep  Branches  of  the  Cervical  Plexus.  External  Series. — Communicating 
Branches. — ^The  external  series  of  deep  branches  of  the  cervical  plexus  communi- 
cates with  the  accessory  nerve,  in  the  substance  of  the  Sternocleidomastoideus, 
in  the  posterior  triangle,  and  beneath  the  Trapezius. 

Muscular  Branches  are  distributed  to  the  Sternocleidomastoideus,  Trapezius, 
Levator  scapultF,  and  Scalenus  medius. 

The  branch  for  the  Sternocleidomastoideus  is  derived -from  the  second  cervdcal; 
the  Trapezius  and  Levator  scapulae  receive  branches  from  the  third  and  fourth. 
The  Scalenus  medius  receives  twigs  either  from  the  third  or  fourth,  or  occasionally 
from  both. 

From.  FC, 


To  Bhomboidei- 
Tojoin  the  phrenic  ■ 

Suprascapular  — ^--- 


Lateral  anterior 
thoracic  ■ 


_  To  Longus  colli 
and  Scaleni 


To  Lonrjus  colli 
and  Scaleni 


To  Longus  colli 
and  Scaleni 

Long  thoracic 


To  Longus  colli 
and  Scaleni 


Median 


Ulnar       J  Medial  brachial 

Medial  antibrachial      cutaneous 
cutaneous 


^ 


Fig.  807. — ^Plan  of  brachial  plexus. 

The  Brachial  Plexus  {plexus  brachialis)  (Fig.  807). — The  brachial  plexus  is 
formed  by  the  union  of  the  anterior  divisions  of  the  lower  four  cervical  nerves  and 
the  greater  part  of  the  anterior  division  of  the  first  thoracic  nerve;  the  fourth  cer- 
vical usually  gives  a  branch  to  the  fifth  cervical,  and  the  first  thoracic  frequently 
receives  one  from  the  second  thoracic.  The  plexus  extends  'from  the  lower  part 
of  the  side  of  the  neck  to  the  axilla.  The  nerves  which  form  it  are  nearly  equal  in 
size,  but  their  mode  of  communication  is  subject  to  some  variation.  The  following 
is,  however,  the  most  constant  arrangement.  The  fifth  and  sixth  cervical  unite 
soon  after  their  exit  from  the  intervertebral  foramina  to  form  a  trunk.  The  eighth 
cervical  and  first  thoracic  also  unite  to  form  one  trunk,  while  the  seventh  cervical 


THE  CERVICAL  NERVES 


runs  out  alone.  Three  trunks — upper,  middle,  and  lower — are  thus  formed,  and, 
as  they  pass  beneath  the  clavicle,  each  splits  into  an  anterior  and  a  posterior  divi- 
sion.^ The  anterior  divisions  of  the  upper  and  middle  trunks  unite  to  form  a  cord, 
which  is  situated  on  the  lateral  side  of  the  second  part  of  the  axillary  artery,  and 
is  called  the  lateral  cord  or  fasciculus  of  the  plexus.  The  anterior  division  of  the 
lower  trunk  passes  down  on  the  medial  side  of  the  axillary  artery,  and  forms  the 
medial  cord  or  fasciculus  of  the  brachial  plexus.  The  posterior  divisions  of  all  three 
trunks  unite  to  form  the  posterior  cord  or  fasciculus  of  the  plexus,  which  is  situated 
behind  the  second  portion  of  the  axillary  artery. 

Relations. — In  the  neck,  the  brachial  plexus  lies  in  the  posterior  triangle,  being  covered  by  the 
skin,  Platysma,  and  deep  fascia;  it  is  crossed  by  the  supraclavicular  nerves,  the  inferior  belly 
of  the  Omohyoideus,  the  external  jugular  vein,  and  the  transverse  cervical  artery.  It  emerges 
between  the  Scaleni  anterior  and  medius;  its  upper  part  lies  above  the  third  part  of  the  sub- 
clavian artery,  while  the  trunk  formed  by  the  union  of  the  eighth  cervical  and  first  thoracic  is 
placed  behind  the  artery;  the  plexus  next  passes  behind  the  clavicle,  the  Subclavius,  and  the  trans- 
verse scapular  vessels,  and  lies  upon  the  first  digitation  of  the  Serratus  anterior,  and  the  Sub- 
scapularis.  hi  the  axilla  it  is  placed  lateral  to  the  first  portion  of  the  axillary  artery;  it  surrounds 
the  second  part  of  the  artery,  one  cord  lying  medial  to  it,  one  lateral  to  it,  and  one  behind  it; 
at  the  lower  part  of  the  axilla  it  gives  off  its  terminal  branches  to  the  upper  limb. 


ANTERIOR 
DIVISION   OF 
FOURTH   CERVICAL" 


DESCENDING 
BRANCH    OF 
HYPOGLOSSA-. 

ANSA 
HYPOGLOSSI 


INTERNAL 
MAMMARY 
ARTERY 

SUBCLAVIAN 


BRANCH  TO 
PHRENIC 


ANTERIOR 
THORACIC 


II 


Fig.  808. — The  right  brachial  plexus  with  its  short  branches,  viewed  from  in  front.  The  Sternomastoid  and  Trajiezius 
muscles  have  been  completely,  the  Omohyoid  and  Subclavius  have  been  partially,  removed;  a  piece  has  been  sawed  out 
of  the  clavicle;  the  Pectoralis  muscles  have  been  incised  and  reflected.     (Spalteholz.) 

Branches  of  Communication.- — Close  to  their  exit  from  the  intervertebral  foramina 
the  lifth  and  sixth  cervical  nerves  each  receive  a  gray  ramus  communicans  from 
the  middle  cervical  ganglion  of  the  sympathetic  trunk,  and  the  seventh  and  eighth 
cervical  similar  twigs  from  the  inferior  ganglion.  The  first  thoracic  nerve  receives 
a  gray  ramus  from,  and  contributes  a  white  ramus  to,  the  first  thoracic  ganglion. 

'  The  posterior  division  of  the  lower  trunk  is  very  much  smaller  than  the  others,  and  is  frequently  derived  entirely 
from  the  eighth  cervical  nerve. 


k 


932 


NEUROLOGY 


On  the  Scalenus  anterior  the  phrenic  nerve  is  joined  by  a  branch  from  the  fifth 
cervical. 

Branches  of  Distribution. — The  branches  of  distribution  of  the  brachial  plexus 
may  be  arranged  into  two  groups,  viz.,  those  given  off  above  and  those  below  the 
clavicle. 

SUPRACLAVICULAK  BRANCHES. 

Dorsal  scapular 5  C. 

Suprascapular 5,  6  C. 

Nerve  to  Subclavius 5,  6  C. 

Long  thoracic 5,  6,  7  C. 

To  Longus  colli  and  Scaleni 5, 6,  7, 8  C. 


MUSCULOCUTANEOUS 
NERVC 


INTERCOSTO-HUMERAL 
NERVES 


LONG  SUBSCAPULAR 
NERVE 


SUBSCAPUL4R 
NERVES 


LATERAL  CUTA- 
NEOUS BRANCH 
OF  FOURTH 
INTERCOSTAL 


LATERAL  CUTANEOUS 

BRANCH  OF 

THIRD   INTERCOSTAL 


LONG  THORACIC 
NERVE 

Fig.  809. — The  right  brachial  plexus  (infraclavicular  portion)  in  the  axillary  fossa;  viewed  from  below  and  in 
front.  The  Peetoralis  major  and  minor  muscles  have  been  in  large  part  removed;  their  attachhients  have  been 
reflected.     (Spalteholz.) 


The  Dorsal  Scapular  Nerve  {n.  dorsalis  scapulce;  nerve  to  the  Rhomhoidei;  'posterior 
scapular  nerve)  arises  from  the  fifth  cervical,  pierces  the  Scalenus  medius,  passes 
beneath  the  Levator  scapulae,  to  which  it  occasionally  gives  a  {wig,  and  ends  in 
the  Rhomboidei. 

The  Suprascapular  (w.  suprascapularis)  (Fig.  818)  arises  from  the  trunk  formed 
by  the  union  of  the  fifth  and  sixth  cervical  nerves.  It  runs  lateralward  beneath 
the  Trapezius  and  the  Omohyoideus,  and  enters  the  supraspinatous  fossa  through 
the  suprascapular  notch,  below,  the  superior  transverse  scapular  ligament;  it  then 
passes  beneath  the  Supraspinatus,  and  curves  around  the  lateral  border  of  the 
spine  of  the  scapula  to  the  infraspinatous  fossa.  In  the  supraspinatous  fossa  it 
gives  off  two  branches  to  the  Supraspinatus  muscle,  and  an  articular  filament 
to  the  shoulder-joint;  and  in  the  infraspinatous  fossa  it  gives  off  tMo  branches 


THE  CERVl 


mvi 


to  the  Infraspinatous  muscle,  besides  some  filaments  to  the  shoulder-joint  and 
scapula. 

The  Nerve  to  the  Subclavius  {n.  suhclavius)  is  a  small  filament,  which  arises  from 
the  point  of  junction  of  the  fifth  and  sixth  cervical  nerves;  it  descends  to  the  muscle 
in  front  of  the  third  part  of  the  subclavian  artery  and  the  lower  trunk  of  the  plexus, 
and  is  usually  connected  by  a  filament  with  the  phrenic  nerve. 

^H        The  Long  Thoracic  Nerve  {n.  thoracalis  longus;  external  respiratory  nerve  of  Bell; 

^|i  posterior  thoracic  nerve)  (Fig.  816)  supplies  the  Serratus  anterior.  It  usually  arises 
by  three  roots  from  the  fifth,  sixth,  and  seventh  cervical  nerves;  but  the  root  from 
the  seventh  nerve  may  be  absent.  The  roots  from  the  fifth  and  sixth  nerves  pierce 
the  Scalenus  medius,  while  that  from  the  seventh  passes  in  front  of  the  muscle. 
The  nerve  descends  behind  the  brachial  plexus  and  the  axillary  vessels,  resting 
on  the  outer  surface  of  the  Serratus  anterior.  It  extends  along  the  side  of  the  thorax 
to  the  lower  border  of  that  muscle,  supplying  filaments  to  each  of  its  digitations. 

»The  branches  for  the  Longus  colli  and  Scaleni  arise  from  the  lower  four  cervical 
nerves  at  their  exit  from  the  intervertebral  foramina. 


Infraclavicular  Branches. 


The  infraclavicular  branches  are  derived  from  the  three  cords  of  the  brachial 
plexus,  but  the  fasciculi  of  the  nerves  may  be  traced  through  the  plexus  to  the  spinal 
nerves  from  which  they  originate.    They  are  as  follows: 


Musculocutaneous 

5,  6,  7  C. 

Lateral  anterior  thoracic 

5,  6,  7  C. 

Lateral  head  of  median  . 

6,  7C. 

Medial  anterior  thoracic 

Medial  antibrachial  cutaneous 

ISIedial  brachial  cutaneous 

8  C,  1  T. 

Ulnar         

Medial  head  of  median  . 

Upper  subscapular  .... 

5,  6C. 

Lower  subscapular  .... 

5,  6C. 

Thoracodorsal 

5,  6,  7  C. 

Axillary 

5,  6C. 

Radial 

6,  7,8  C,  IT 

Lateral  cord 


Medial  cord 


Posterior  cord 


The  Anterior  Thoracic  Nerves  {nn.  thoracales  anteriores)  (Fig.  816)  supply  the 
Pectorales  major  and  minor. 

The  lateral  anterior  thoracic  (fasciculus  lateralis)  the  larger  of  the  two,  arises 
from  the  lateral  cord  of  the  brachial  plexus,  and  through  it  from  the  fifth,  sixth, 
and  seventh  cervical  nerves.  It  passes  across  the  axillary  artery  and  vein,  pierces  the 
coracoclavicular  fascia,  and  is  distributed  to  the  deep  surface  of  the  Pectoralis 
major.  It  sends  a  filament  to  join  the  medial  anterior  thoracic  and  form  with  it 
a  loop  in  front  of  the  first  part  of  the  axillary  artery. 

The  medial  anterior  thoracic  (fasciculus  medialis)  arises  from  the  medial  cord  of 
the  plexus  and  through  it  from  the  eighth  cervical  and  first  thoracic.  It  passes 
behind  the  first  part  of  the  axillary  artery,  curves  forward  between  the  axillary 
artery  and  vein,  and  unites  in  front  of  the  artery  with  a  filament  from  the  lateral 
nerve.  It  then  enters  the  deep  surface  of  the  Pectoralis  minor,  where  it  divides 
into  a  number  of  branches,  which  supply  the  muscle.  Two  or  three  branches  pierce 
the  muscle  and  end  in  the  Pectoralis  major. 

The  Subscapular  Nerves  (iin.  suhscapidares) ,  two  in  number,  spring  from  the 
posterior  cord  of  the  plexus  and  through  it  from  the  fifth  and  sixth  cervical  nerves. 


934 


NEUROLOGY 


I 


The  upper  subscapular  {short  subscapular),  the  smaller  enters  the  upper  part  ol' 
the  Subscapularis,  and  is  frequently  represented  by  two  branches. 

The  lower  subscapular  supplies  the  lower  part  of  the  Subscapularis,  and  ends  in 
the  Teres  major;  the  latter  muscle  is  sometimes  supplied  by  a  separate  branch. 

The  Thoracodorsal  Nerve  (n.  thoracodorsalis;  middle  or  long  subscapular  nerve), 
a  branch  of  the  posterior  cord  of  the  plexus,  derives  its  fibers  from  the  fifth,  sixth, 
and  seventh  cervical  nerves;  it  follows  the  course  of  the  subscapular  artery,  along 
the  posterior  wall  of  the  axilla  to  the  Latissimus  dorsi,  in  which  it  may  be  traced 
as  far  as  the  lower  border  of  the  muscle. 


UPERIOH    BRANCH 
OF   AXILLARY 


NFERIOR     BRANCH 
OF  AXILLARY 


CUTANEOUS 
BRANCHES 


Fig.  810. — Suprascapular  and  axillary  nerves  of  right  side,  seen  from  behind.     (Testut.) 

The  Axillary  Nerve  (n.  axillaris;  circumflex  nerve)  (Fig.  818)  arises  from  the  pos- 
terior cord  of  the  brachial  plexus,  and  its  fibers  are  derived  from  the  fifth  and  sixth 
cervical  nerves.  It  lies  at  first  behind  the  axillary  artery,  and  in  front  of  the 
Subscapularis,  and  passes  downward  to  the  lower  border  of  that  muscle.  It  then 
winds  backward,  in  company  with  the  posterior  humeral  circumflex  artery,  through 
a  quadrilateral  space  bounded  above  by  the  Subscapularis,  below  by  the  Teres 
major,  medially  by  the  long  head  of  the  Triceps  brachii,  and  laterally  by  the 
surgical  neck  of  the  humerus,  and  divides  into  an  anterior  and  a  posterior  branch. 

The  anterior  branch  {upper  branch)  winds  around  the  surgical  neck  of  the  humerus, 
beneath  the  Deltoideus,  with  the  posterior  humeral  circumflex  vessels,  as  far  as 
the  anterior  border  of  that  muscle,  supplying  it,  and  giving  off  a  few  small  cuta- 
neous branches,  which  pierce  the  muscle  and  ramify  in  the  skin  covering  its  lower 
part. 

The  posterior  branch  (lower  branch)  supplies  the  Teres  minor  and  the  j)osterior 
part  of  the  Deltoideus;  upon  the  branch  to  the  Teres  minor  an  oval  enlargement 
(pseudoganglion)  usually  exists.  The  posterior  branch  then  pierces  the  deep  fascia 
and  is  continued  as  the  lateral  brachial  cutaneous  nerve,  which  sweeps  around  the 
posterior  border  of  the  Deltoideus  and  supplies  the  skin  over  the  lower  two-thirds 
of  the  posterior  part  of  this  muscle,  as  well  as  that  covering  the  long  head  of  the 
Triceps  brachii  (Figs  811,  813). 


I 


THE  CERVICAL  NERVES 


935 


The  trunk  of  the  axillary  nerve  gives  off  an  articular  filament  which  enters 
[the  shoulder- joint  below  the  Subscapularis. 

The  Musculocutaneous  Nerve  (n.  musculocutaneus)  (Fig.  816)  arises  from  the 
lateral  cord  of  the  brachial  plexus,  opposite  the  lower  border  of  the  Pectoralis 


Fio.  811. — Cutaneous  nerves  of  right  upper 
extremity.    Anterior  view. 


Fig.  812. — Diagram  of  segmental  distribution  of  the  cutaneous 
nerves  of  the  right  upper  extremity.    Anterior  view. 


1 

I 


minor,  its  fibers  being  derived  from  the  fifth,  sixth,  and  seventh  cervical  nerves. 
It  pierces  the  Coracobrachialis  muscle  arid  passes  obliquely  between  the  Biceps 
brachii  and  the  Brachialis,  to  the  lateral  side  of  the  arm;  a  little  above  the  elbow 
it  pierces  the  deep  fascia  lateral  to  the  tendon  of  the  Biceps  brachii  and  is  continued 
into  the  forearm  as  the  lateral  antibracjiial  cutaneous  nerve.    In  its  course  through 


936 


NEUROLOGY 


the  arm  it  supplies  the  CoracobrachiaHs,  Biceps  brachii,  and  the  greater  part  of  the 
Brachialis.  The  branch  to  the  CoracobrachiaHs  is  given  off  from  the  nerve  close 
to  its  origin,  and  in  some  instances  as  a  separate  filament  from  the  lateral  cord 
of  the  plexus;  it  is  derived  from  the  seventh  cervical  nerve.  The  branches  to  the 
Biceps  brachii  and  Brachialis  are  given  off  after  the  musculocutaneous  has  pierced 


Intercosto 


Fta.  813. — Cutaneous  nerves  of  right  upper 
extremity.    Posterior  view. 


Fig.  814. — Diagram  of  segmental  distribution  of  the  cuta- 
neous nerves  of  the  right  upper  extremity.    Posterior  view. 


the  CoracobrachiaHs;  that  supplying  the  Brachialis  gives  a  filament  to  the  elbow- 
joint.  The  nerve  also  sends  a  small  branch  to  the  bone,  which  enters  the  nutrient 
foramen  with  the  accompanying  artery. 

The  lateral  antibrachial  cutaneous  nerve  {n.  cuianeus  antibrachii  cutaneous  lateralis; 
branch  of  musculocutaneous  nerve)  passes  behind  the  cephalic  vein,  and  divides, 
opposite  the  elbow-joint,  into  a  volar  and  a  dorsal  branch  (Figs.  811,  813). 


THE  CERVICAL  NERVES 


If  The  volar  branch  {ramus  volaris;  anterior  branch)  descends  along  the  radial  border 
of  the  forearm  to  the  wrist,  and  supplies  the  skin  over  the  lateral  half  of  its  volar 
surface.  At  the  wrist-joint  it  is  placed  in  front  of  the  radial  artery,  and  some 
filaments,  piercing  the  deep  fascia,  accompany  that  vessel  to  the -dorsal  surface  of 
the  carpus.  The  nerve  then  passes  downward  to  the  ball  of  the  thumb,  where  it 
ends  in  cutaneous  filaments.  It  communicates  with  the  superficial  branch  of  the 
radial  nerve,  and  with  the  palmar  cutaneous  branch  of  the  median  nerve. 

The  dorsal  branch  {ramus  dorsalis;  posterior  branch)  descends,  along  the  dorsal 
surface  of  the  radial  side  of  the  forearm  to  the  wrist.  It  supplies  the  skin  of  the 
lower  two-thirds  of  the  dorso-lateral  surface  of  the  forearm,  communicating  with 
the  superficial  branch  of  the  radial  nerve  and  the  dorsal  antibrachial  cutaneous 
branch  of  the  radial. 

The  musculocutaneous  nerve  presents  frequent  irregularities.  It  may  adhere 
for  some  distance  to  the  median  and  then  pass  outward,  beneath  the  Biceps  brachii, 

■  instead  of  through  the  Coracobrachialis.  Some  of  the  fibers  of  the  median  may 
prun  for  some  distance  in  the  musculocutaneous  and  then  leave  it  to  join  their 
proper  trunk;  less  frequently  the  reverse  is  the  case,  and  the  median  sends  a  branch 
to  join  the  musculocutaneous.  The  nerve  may  pass  under  the  Coracobrachialis 
or  through  the  Biceps  brachii.  Occasionally  it  gives  a  filament  to  the  Pronator 
teres,  and  it  supplies  the  dorsal  surface  of  the  thumb  when  the  superficial  branch 
of  the  radial  nerve  is  absent. 

The  Medial  Antibrachial  Cutaneous  Nerve  {n.  cutaneus  antibrachii  medialis;  internal 
cutaneous  nerve)  (Fig.  816)  arises  from  the  medial  cord  of  the  brachial  plexus.  It 
derives  its  fibers  from  the  eighth  cervical  and  first  thoracic  nerves,  and  at  its  com- 
mencement is  placed  medial  to  the  axillary  artery.  It  gives  off,  near  the  axilla,  a 
filament,  which  pierces  the  fascia  and  supplies  the  integument  covering  the  Biceps 
brachii,  nearly  as  far  as  the  elbow.  The  nerve  then  runs  down  the  ulnar  side  of  the 
arm  medial  to  the  brachial  artery,  pierces  the  deep  fascia  with  the  basilic  vein, 
about  the  middle  of  the  arm,  and  divides  into  a  volar  and  an  ulnar  branch. 

The  volar  branch  {ramus  tolaris;  anterior  branch),  ihe  larger,  passes  usually  in  front 
of,  but  occasionally  behind,  the  vena  mediana  cubiti  {median  basilic  vein).  It  then 
descends  on  the  front  of  the  ulnar  side  of  the  forearm,  distributing  filaments  to  the 
skin  as  far  as  the  wrist,  and  communicating  with  the  palmar  cutaneous  branch  of 
the  ulnar  nerve  (Fig.  811). 

The  ulnar  branch  {ramus  ulnaris;  posterior  branch)  passes  obliquely  downward  on 
the  medial  side  of  the  basilic  vein,  in  front  of  the  medial  epicondyle  of  the  humerus, 
to  the  back  of  the  forearm,  and  descends  on  its  ulnar  side  as  far  as  the  wrist,  dis- 

»tributing  filaments  to  the  skin.  It  communicates  with  the  medial  brachial  cutaneous, 
the  dorsal  antibrachial  cutaneous  branch  of  the  radial,  and  the  dorsal  branch  of 
the  ulnar  (Fig.  813). 

The  Medial  Brachial  Cutaneous  Nerve  (n.  cutaneus  brachii  medialis;  lesser 'internal 
cutarieous  yierve;  nerve  of  Wrisberg)  is  distributed  to  the  skin  on  the  ulnar  side  of  the 
arm  (Figs.  811,  813).  It  is  the  smallest  branch  of  the  brachial  plexus,  and  arising 
from  the  medial  cord  receives  its  fibers  from  the  eighth  cervical  and  first  thoracic 
nerves.  It  passes  through  the  axilla,  at  first  lying  behind,  and  then  medial  to  the 
axillary  vein,  and  communicates  with  the  intercostobrachial  nerve.  It  descends 
along  the  medial  side  of  the  brachial  artery  to  the  middle  of  the  arm,  where  it  pierces 
the  deep  fascia,  and  is  distributed  to  the  skin  of  the  back  of  the  lower  third  of  the 
arm,  extending  as  far  as  the  elbow,  where  some  filaments  are  lost  in  the  skin  in 
front  of  the  medial  epicondyle,  and  others  over  the  olecranon.  It  communicates 
with  the  ulnar  branch  of  the  medial  antibrachial  cutaneous  nerve. 

In  some  cases  the  medial  brachial  cutaneous  and  intercostobrachial  are  connected  by  two  or 

three  filaments,  which  form  a  plexus  in  the  axilla.      In  other  cases  the  intercostobrachial  is  of 

large  size,  and  takes  the  place  of  the  medial  brachial  cutaneous,  receiving  merely  a  filament  of 

——commimication  from  the  brachial  plexus,  which  represents  the  latter  nerve;  in  a  few  cases,  this 


938  ^^^^"^  NEUROLOGY 


The  Median  Nerve  (n.  medianus)  (Fig.  816)  extends  along  the  middle  of  the  ana 
and  forearm  to  the  hand.  It  arises  by  two  roots,  one  from  the  lateral  and  one  frora 
the  medial  cord  of  the  brachial  plexus;  these  embrace  the  lower  part  of  the  axillary 
artery,  uniting  either  in  front  of  or  lateral  to  that  vessel.  Its  fibers  are  derived 
from  the  sixth,  seventh,  and  eighth  cervical  and  first  thoracic  nerves.  As  it  descends 
through  the  arm,  it  lies  at  first  lateral  to  the  brachial  artery;  about  the  level  of  the 
insertion  of  the  Coracobrachialis  it  crosses  the  artery,  usually  in  front  of,  but  occasion- 
ally behind  it,  and  lies  on  its  medial  side  at  the  bend  of  the  elbow,  where  it  is  situated 
behind  the  lacertus  fibrosus  (bicipital  fascia) ,  and  is  separated  from  the  elbow-joint 
by  the  Brachialis.  In  the  forearm  it  passes  between  the  two  heads  of  the  Pronator 
teres  and  crosses  the  ulnar  artery,  but  is  separated  from  this  vessel  by  the  deep 
head  of  the  Pronator  teres.  It  descends  beneath  the  Flexor  digitorum  sublimis, 
lying  on  the  Flexor  digitOrum  profundus,  to  within  5  cm.  of  the  transverse  carpal 
ligament;  here  it  becomes  more  superficial,  and  is  situated  between  the  tendons  of 
the  Flexor  digitorum  sublimis  and  Flexor  carpi  radialis.  In  this  situation  it  lies 
behind,  and  rather  to  the  radial  side  of,  the  tendon  of  the  Palmaris  longus,  and  is 
covered  by  the  skin  and  fascia.  It  then  passes  behind  the  transverse  carpal  liga- 
ment into  the  palm  of  the  hand.  In  its  course  through  the  forearm  it  is  accompanied 
by  the  median  artery,  a  branch  of  the  volar  interroseous  artery. 

Branches. — With  the  exception  of  the  nerve  to  the  Pronator  teres,  which  some- 
times arises  above  the  elbow-joint,  the  median  nerve  gives  off  no  branches  in 
the  arm.  As  it  passes  in  front  of  the  elbow,  it  supplies  one  or  two  twigs  to  the 
joint. 

In  the  forearm  its  branches  are :  muscular,  volar  interosseous,  and  palmar. 

The  muscular  branches  (rami  viusculares)  are  derived  from  the  nerve  near  the 
elbow  and  supply  all  the  superficial  muscles  on  the  front  of  the  forearm,  except 
the  Flexor  carpi  ulnaris. 

The  volar  interosseous  nerve  (n.  interosseus  [antibrachii]  volaris;  anterior  inter- 
osseous nerve)  supplies  the  deep  muscles  on  the  front  of  the  forearm,  except  the  ulnar 
half  of  the  Flexor  digitorum  profundus.  It  accompanies  the  volar  interosseous 
artery  along  the  front  of  the  interosseous  membrane,  in  the  interval  between  the 
Flexor  pollicis  longus  and  Flexor  digitorum  profundus,  supplying  the  whole  of  the 
former  and  the  radial  half  of  the  latter,  and  ending  below  in  the  Pronator  quadratus 
and  wrist-joint. 

The  palmar  branch  {ramus  cutaneus  palmaris  n.  mediani)  of  the  median  nerve  arises 
at  the  lower  part  of  the  forearm.  It  pierces  the  volar  carpal  ligament,  and  divides  into 
a  lateral  and  a  medial  branch;  the  lateral  branch  supplies  the  skin  over  the  ball  of 
the  thumb,  and  communicates  with  the  volar  branch  of  the  lateral  antibrachial 
cutaneous  nerve;  the  medial  branch  supplies  the  skin  of  the  palm  and  communi- 
cates with  the  palmar  cutaneous  branch  of  the  ulnar. 

In  the  palm  of  the  hand  the  median  nerve  is  covered  by  the  skin  and  the  palmar 
aponeurosis,  and  rests  on  the  tendons  of  the  Flexor  muscles.  Immediately  after 
emerging  from  under  the  transverse  carpal  ligament  the  nerve  becomes  enlarged 
and  flattened  and  splits  into  a  smaller,  lateral,  and  a  larger,  medial  portion.  The 
lateral  portion  supplies  a  short,  stout  branch  to  certain  of  the  muscles  of  the  ball  of 
the  thumb,  viz.,  the  Abductor  brevis,  the  Opponens,  and  the  superficial  head  of  the 
Flexor  brevis,  and  then  divides  into  three  proper  volar  digital  nerves;  two  of  these 
supply  the  sides  of  the  thumb,  while  the  third  gives  a  twig  to  the  first  Lumbricalis 
and  is  distributed  to  the  radial  side  of  the  index  finger.  The  medial  portion  of  the 
nerve  divides  into  two  common  volar  digital  nerves.  The  first  of  these  gives  a  twig 
to  the  second  Lumbricalis  and  runs  toward  the  cleft  between  the  index  and  middle 
fingers,  where  it  divides  into  two  proper  digital  nerves  for  the  adjoining  sides  of 
these  digits;  the  second  runs  toward  the  cleft  between  the  middle  and  ring  fingers, 
and  splits  into  two  proper  digital  nerves  for  the  adjoining  sides  of  these  digits; 


I 


I 


THE  CERVICAL  NERVES 


939 


communicates  with  a  branch  from  the  ulnar  nerve  and  sometimes  sends  a  twig 
to  the  third  LumbricaHs. 

Each  proper  digital  nerve,  opposite  the  base  of  the  first  phalanx,  gives  off  a 
dorsal  branch  which  joins  the  dorsal  digital  nerve  from  the  superficial  branch  of 
the  radial  nerve,  and  supplies  the  integument  on  the  dorsal  aspect  of  the  last 
phalanx.  At  the  end  of  the  digit,  the  proper  digital  nerve  divides  into  two 
branches,  one  of  which  supplies  the  pulp  of  the  finger,  the  other  ramifies  around 
and  beneath  the  nail.  The  proper  digital  nerves,  as  they  run  along  the  fingers,  are 
)laced  superficial  to  the  corresponding  arteries. 


SUPERFICIAL   BRANCH 
OF  ULNAR 


COMMUNICATING 
TO   MEDIAN 


Fig.  815. — Superficial  palmar  nerves.     (Testut.) 


The  Ulnar  Nerve  (n.  ulnaris)  (Fig.  816)  is  placed  along  the  medial  side  of  the  limb, 
and  is  distributed  to  the  muscles  and  skin  of  the  forearm  and  hand.  It  arises 
from  the  medial  cord  of  the  brachial  plexus,  and  derives  its  fibers  from  the  eighth 
cervical  and  first  thoracic  nerves.  It  is  smaller  than  the  median,  and  lies  at  first 
behind  it,  but  diverges  from  it  in  its  course  down  the  arm.    At  its  origin  it  lies 


I 


940 


NEUROLOGY 


medial  to  the  axillary  artery,  and  bears  the  same  relation  to  the  brachial  artery 
as  far  as  the  middle  of  the  arm.    Here  it  pierces  the  medial  intermuscular  septum. 

Lateral  anterior  thoracic 

^^  Medial  anterior  thoracic 

\ 

■'  \ 

*  \  ^  Uusculocutaneous 


Median 


Radial 

Deep  br,  of  radial 


Swperfic.  br.  of  radial 
Volar  interosseoua 


Fia.  816. — Nerves  of  the  left  upper  extremity. 


THE  CERVICAL  NERVES 


941 


runs  obliquely  across  the  medial  head  of  the  Triceps  brachii,  and  descends  to  the 
groove  between  the  medial  epicondyle  and  the  olecranon,  accompanied  by  the 
superior  ulnar  collateral  artery.  At  the  elbow,  it  rests  upon  the  back  of  the  medial 
epicondyle,  and  enters  the  forearm  between  the  two  heads  of  the  Flexor  carpi 
ulnaris.  In  the  forearm,  it  descends  along  the  ulnar  side,  lying  upon  the  Flexor 
digitorum  profundus;  its  upper  half  is  covered  by  the  Flexor  carpi  ulnaris,  its  lower 


VOLAR 
INTEROSSEOUS 


RADIAL' 


LNAR  NERVE 


INTERNAL  BRANCH 
OF  RADIAL 


EXTERNAL  BRANCJi 
OF  RADIAL 


BRANCH  OP  ANTERIOn 
INTEROSSEOUS  TO 
WRIST  JOINT 


SUPERFICIAL  BRANCH 

OF  ULNAR 
DEEP  BRANCH 
OF  ULNAR 


ERVE  TO  PALMA- 
RI8  BREVIS 


EEP  BRANCH 
OF  ULNAR 


TERMINATION  OF  1 

ULNAR  IN  THUMB  >- 

MUSCLES  J. 


(nerve  to 

-<       AND   FOL 
(.       LUMBRK 


THIRD 
FOURTH 
CALS 


DIGITAL  COL* 

LATERAL 

BRANCHES 


Pro.  817. — Deep  palmar  nerves.     (Testut.) 


I 


half  lies  on  the  lateral  side  of  the  muscle,  covered  by  the  integument  and  fascia.  In 
the  upper  third  of  the  forearm,  it  is  separated  from  the  ulnar  artery  by  a  consider- 
able interval,  but  in  the  rest  of  its  extent  lies  close  to  the  medial  side  of  the  artery. 
About  5  cm.  above  the  wrist  it  ends  by  dividing  into  a  dorsal  and  a  volar  branch. 
The  branches  of  the  ulnar  nerve  are:  articular  to  the  elbow-joint,  muscular, 
palmar  cutaneous,  dorsal,  and  volar. 


942 


NEUROLOGY 


The  articular  branches  to  the  elbow-joint  are  several  small  filaments  which  arise 

from  the  nerve  as  it  lies  in  the  groove  between  the  medial  epicondyle  and  olecranon. 

The  muscular  branches  {rami 

Suprascapular  ^55^  musculares)  two  in  number,  arise 

near  the  elbow :  one  supplies  the 
Flexor  carpi  ulnaris;  the  other, 
the  ulnar  half  of  the  Flexor 
digitorum  profundus. 

The  palmar  cutaneous  branch 
{ramus  cutaneus  jJalmaris)  arises 
about  the  middle  of  the  forearm, 
and  descends  on  the  ulnar  artery, 
giving  off  some  filaments  to  the 
vessel.  It  perforates  the  volar 
carpal  ligament  and  ends  in  the 
skin  of  the  palm,  communicating 
with  the  palmar  branch  of  the 
median  nerve. 

The  dorsal  branch  {ramus  dor- 
salis  manus)  arises  about  5  cm. 
above  the  wrist;  it  passes  back- 
ward beneath  the  Flexor  carpi 
ulnaris,  perforates  the  deep  fas- 
cia, and,  running  along  the  ulnar 
side  of  the  back  of  the  wrist 
and  hand,  divides  into  two  dor- 
sal digital  branches;  one  supplies 
the  ulnar  side  of  the  little  finger; 
the  other,  the  adjacent  sides  of 
the  little  and  ring  fingers.  It 
also  sends  a  twig  to  join  that 
given  by  the  superficial  branch 
of  the  radial  nerve  for  the  ad- 
joining sides  of  the  middle  and 
ring  fingers,  and  assists  in  sup- 
plying them.  A  branch  is  dis- 
tributed to  the  metacarpal  region 
of  the  hand,  communicating 
with  a  twig  of  the  superficial 
branch  of  the  radial  nerve  (Fig. 
813). 

On  the  little  finger  the  dor- 
sal digital  branches  extend  only 
as  far  as  the  base  of  the  ter- 
minal phalanx,  and  on  the  ring 
finger  as  far  as  the  base  of  the 
second  phalanx;  the  more  distal 

parts  of  these  digits  are  supplied  by  dorsal  branches  derived  from  the  proper  volar 

digital  branches  of  the  ulnar  nerve. 

The  volar  branch  {ramv^  volaris  manus)  crosses  the  transverse  carpal  ligament 

on  the  lateral  side  of  the  pisiform  bone,  medial  to  and  a  little  behind  the  ulnar 

artery.    It  ends  by  dividing  into  a  superficial  and  a  deep  branch. 
The  superficial  branch  {ramus  superficialis  [n.  ulnaris]  (supplies  the  Palmaris 

brevis,  and  the  skin  on  the  ulnar  side  of  the  hand,  and  divides  into  a  proper  volar 


Fig.  818. — The  suprascapular,  axillary,  and  radial  nerves. 


THE  CERVICAL  NERVES  943 

digital  branch  for  the  ulnar  side  of  the  little  finger,  and  a  common  volar  digital 
branch  which  gives  a  communicating  twig  to  the  median  nerve  and  divides  into 
two  proper  digital  nerves  for  the  adjoining  sides  of  the  little  and  ring  fingers  (Fig. 
811).  The  proper  digital  branches  are  distributed  to  the  fingers  in  the  same 
manner  as  those  of  the  median. 

The  deep  branch  {ramus  profundus)  accompanied  by  the  deep  branch  of  the  ulnar 

artery,  passes  between  the  Abductor  digiti  quinti  and  Flexor  digiti  quinti  brevis; 

it  then  perforates  the  Opponens  digiti  quinti  and  follows  the  course  of  the  deep 

volar  arch  beneath  the  Flexor  tendons.    At  its  origin  it  supplies  the  three  short 

muscles  of  the  little  finger.    As  it  crosses  the  deep  part  of  the  hand,  it  supplies  all 

the  Interossei  and  the  third  and  fourth  Lumbricales;  it  ends  by  supplying  the  Ad- 

ductores  pollicis  and  the  medial  head  of  the  Flexor  poUicis  brevis.     It  also  sends 

articular  filaments  to  the  wrist-joint. 

H      It  has  been  pointed  out  that  the  ulnar  part  of  the  Flexor  digitorum  profundus 

^B  is  supplied  by  the  ulnar  nerve ;  the  third  and  fourth  Lumbricales,  which  are  con- 

f  nected  with  the  tendons  of  this  part  of  the   muscle,  are  supplied  by  the  same 

nerve.     In  like  manner  the  lateral  part  of  the  Flexor  digitorum  profundus  and 

the  first  and  second  Lumbricales  are  supplied  by  the  median  nerve;  the  third 

Lumbricalis  frequently  receives  an  additional  twig  from  the  median  nerve. 

The  Radial  Nerve  (?i.  radialis;  musctilospiral  nerve)  (Fig.  818),  the  largest  branch 
of  the  brachial  plexus,  is  the  continuation  of  the  posterior  cord  of  the  plexus.  Its 
fibres  are  derived  from  the  fifth,  sixth,  seventh,  and  eighth  cervical  and  first  thoracic 
nerves.  It  descends  behind  the  first  part  of  the  axillary  artery  and  the  upper  part 
of  the  brachial  artery,  and  in  front  of  the  tendons  of  the  Latissimus  dorsi  and  Teres 
major.  It  then  w  inds  around  from  the  medial  to  the  lateral  side  of  the  humerus  in 
a  groove  with  the  a.  profunda  brachii,  between  the  medial  and  lateral  heads  of  the 
Triceps  brachii.  It  pierces  the  lateral  intermuscular  septum,  and  passes  between 
the  Brachialis  and  Brachioradialis  to  the  front  of  the  lateral  epicondyle,  where 
it  divides  into  a  superficial  and  a  deep  branch. 

»The  branches  of  the  musculospiral  nerve  are: 
Muscular.  Superficial. 

Cutaneous.  Deep. 

The  muscular  branches  (rami  musculares)  supply  the  Triceps  brachii,  Anconseus, 
Brachioradialis,  Extensor  carpi  radialis  longus,  and  Brachialis,  and  are  grouped  as 
medial,  posterior,  and  lateral. 

The  medial  muscular  branches  supply  the  medial  and  long  heads  of  the  Triceps 
brachii.  That  to  the  medial  head  is  a  long,  slender  filament,  which  lies  close  to  the 
ulnar  nerve  as  far  as  the  lower  third  of  the  arm,  and  is  therefore  frequently  spoken 
of  as  the  ulnar  collateral  nerve. 

The  posterior  muscular  branch,  of  large  size,  arises  from  the  nerve  in  the  groove 
between  the  Triceps  brachii  and  the  humerus.  It  divides  into  filaments,  which 
supply  the  medial  and  lateral  heads  of  the  Triceps  brachii  and  the  Anconseus 
muscles.  The  branch  for  the  latter  muscle  is  a  long,  slender  filament,  which  descends 
in  the  substance  of  the  medial  head  of  the  Triceps  brachii. 

I^_     The  lateral  muscular  branches  supply  the  Brachioradialis,  Extensor  carpi  radialis 
^■longus,  and  the  lateral  part  of  the  Brachialis. 

The  cutaneous  branches  are  two  in  number,  the  posterior  brachial  cutaneous 
and  the  dorsal  antibrachial  cutaneous. 

The  posterior  brachial  cutaneous  nerve  (?i.  cutaneus  brachii  posterior;  internal 
cutaneous  branch  of  musculospiral)  arises  in  the  axilla,  with  the  medial  muscular 
branch.  It  is  of  small  size,  and  passes  through  the  axilla  to  the  medial  side  of 
the  area  supplying  the  skin  on  its  dorsal  surface  nearly  as  far  as  the  olecranon. 
In  its  course  it  crosses  behind,  and  communicates  with,  the  intercostobrachial. 


II 


I 


944  NEUROLOGY 

The  dorsal  antibrachial  cutaneous  nerve  {n.  cutaneus  antihrachii  dorsalis;  external 
cutaneous  branch  of  musculosjnral)  perforates  the  lateral  head  of  the  Triceps  brachii  at 
its  attachment  to  the  humerus.  The  upper  and  smaller  branch  of  the  nerve  passes 
to  the  front  of  the  elbow,  lying  close  to  the  cephalic  vein,  and  supplies  the  skia 
of  the  lower  half  of  the  arm  (Fig.  811).  The  lower  branch  pierces  the  deep  fasciaj 
below  the  insertion  of  the  Deltoideus,  and  descends  along  the  lateral  side  of  the 
arm  and  elbow,  and  then  along  the  back  of  the  forearm  to  the  wrist,  supplying 
the  skin  in  its  course,  and  joining,  near  its  termination,  with  the  dorsal  branch 
of  the  lateral  antibrachial  cutaneous  nerve  (Fig.  813). 

The  Superficial  Branch  of  the  Radial  Nerve  (ramus  superficialis  radial  nerve) 
passes  along  the  front  of  the  radial  side  of  the  forearm  to  the  commencement  of 
its  lower  third.  It  lies  at  first  slightly  lateral  to  the  radial  artery,  concealed 
beneath  the  Brachioradialis.  In  the  middle  third  of  the  forearm,  it  lies  behind  the 
same  muscle,  close  to  the  lateral  side  of  the  artery.  It  quits  the  artery  about  7  cm. 
above  the  wrist,  passes  beneath  the  tendon  of  the  Brachioradialis,  and,  piercing 
the  deep  fascia,  divides  into  two  branches  (Fig.  813). 

The  lateral  branch,  the  smaller,  supplies  the  skin  of  the  radial  side  and  ball 
of  the  thumb,  joining  with  the  volar  branch  of  the  lateral  antibrachial  cutaneous 
nerve. 

The  medial  branch  communicates,  above  the  wrist,  with  the  dorsal  branch  of  the 
lateral  antibrachial  cutaneous,  and,  on  the  back  of  the  hand,  with  the  dorsal 
branch  of  the  ulnar  nerve.  It  then  divides  into  four  digital  nerves,  which  are 
distributed  as  follows:  the  first  supplies  the  ulnar  side  of  the  thumb;  the  second, 
the  radial  side  of  the  index  finger;  the  third,  the  adjoining  sides  of  the  index  and 
middle  fingers;  the  fourth  communicates  with  a  filament  from  the  dorsal  branch 
of  the  ulnar  nerve,  and  supplies  the  adjacent  sides  of  the  middle  and  ring  _ 
fingers.^  ■ 

The  Deep  Branch  of  the  Radial  Nerve  (n.  interosseus  dorsalis;  dorsal  or  posterior 
interosseous  nerve)  winds  to  the  back  of  the  forearm  around  the  lateral  side  of  the 
radius  between  the  two  planes  of  fibers  of  the  Supinator,  and  is  prolonged  down- 
ward between  the  superficial  and  deep  layers  of  muscles,  to  the  middle  of  the 
forearm.  Considerably  diminished  in  size,  it  descends,  as  the  dorsal  interosseous 
nerve,  on  the  interosseous  membrane,  in  front  of  the  Extensor  pollicis  longus,  to  the. 
back  of  the  carpus,  where  it  presents  a  gangliform  enlargement  from  which  filaments 
are  distributed  to  the  ligaments  and  articulations  of  the  carpus.  It  supplies  all 
the  muscles  on  the  radial  side  and  dorsal  surface  of  the  forearm,  excepting  the 
Anconseus,  Brachioradialis,  and  Extenosr  carpi  radialis  longus. 

The  Thoracic  Nerves  (Nn.  Thoracales). 

The  anterior  divisions  of  the  thoracic  nerves  {rami  anteriores;  ventral  divisions) 
are  twelve  in  number  on  either  side.  Eleven  of  them  are  situated  between  the  ribs, 
and  are  therefore  termed  intercostal;  the  twelfth  lies  below  the  last  rib.  Each  nerve 
is  connected  with  the  adjoining  ganglion  of  the  sympathetic  trunk  by  a  gray  and  a 
white  ramus  communicans.  The  intercostal  nerves  are  distributed  chiefly  to  the 
parietes  of  the  thorax  and  abdomen,  and  differ  from  the  anterior  divisions  of  the 
other  spinal  nerves,  in  that  each  pursues  an  independent  course,  i.  e.,  there  is  no 
plexus  formation.  The  first  two  nerves  supply  fibers  to  the  upper  limb  in  addition 
to  their  thoracic  branches;  the  next  four  are  limited  in  their  distribution  to  the 
parietes  of  the  thorax;  the  lower  five  supply  the  parietes  of  the  thorax  and  abdomen. 
The  twelfth  thoracic  is  distributed  to  the  abdominal  wall  and  the  skin  of  the  buttock. 

'  According  to  Hutchison,  the  digital  nerve  to  the  thumb  reaches  only  as  high  as  the  root  of  the  nail;  the  one  to  the 
forefinger  as  high  as  the  middle  of  the  second  phalanx;  and  the  one  to  the  middle  and  ring  fingers  not  higher  than  the 
first  phalangeal  joint. — London  Hosp.  Gaz.,  iii,  319. 


THE  THORACIC  NERVES 


945 


II 


The  First  Thoracic  Nerve. — ^The  anterior  division  of  the  first  thoracic  nerve  divides 
into  two  branches :  one,  the  larger,  leaves  the  thorax  in  front  of  the  neck  of  the  first 
rib,  and  enters  the  brachial  plexus;  the  other  and  smaller  branch,  the  first  intercostal 
nerve,  runs  along  the  first  intercostal  space,  and  ends  on  the  front  of  the  chest  as 
the  first  anterior  cutaneous  branch  of  the  thorax.  Occasionally  this  anterior  cuta- 
neous branch  is  wanting.  The  first  intercostal  nerve  as  a  rule  gives  off  no  lateral 
cutaneous  branch;  but  sometimes  it  sends  a  small  branch  to  communicate  with 
the  intercostobrachial.  From  the  second  thoracic  nerve  it  frequently  receives  a 
connecting  twig,  which  ascends  over  the  neck  of  the  second  rib. 


Posterior  division  ^/ 


Lateral  cutatieous 


Anterior  cutanecms 
Fig.  819. — Diagram  of  the  course  and  branches  of  a  typica  intercostal  nerve. 

The  Upper  Thoracic  Nerves  {mi.  intercostales) . — The  anterior  divisions  of  the 
second,  third,  fourth,  fifth,  and  sixth  thoracic  nerves,  and  the  small  branch  from  the 
first  thoracic,  are  confined  to  the  parietes  of  the  thorax,  and  are  named  thoracic 
intercostal  nerves.  They  pass  forward  (Fig.  819)  in  the  intercostal  spaces  below  the 
intercostal  vessels.  At  the  back  of  the  chest  they  lie  between  the  pleura  and  the 
posterior  intercostal  membranes,  but  soon  pierce  the  latter  and  run  between  the 
two  planes  of  Intercostal  muscles  as  far  as  the  middle  of  the  rib.  They  then  enter 
the  substance  of  the  Intercostales  interni,  and,  running  amidst  their  fibers  as  far  as 
the  costal  cartilages,  they  gain  the  inner  surfaces  of  the  muscles  and  lie  between 
them  and  the  pleura.  Near  the  sternum,  they  cross  in  front  of  the  internal  mammary 
artery  and  Transversus  thoracis  muscle,  pierce  the  Intercostales  interni,  the  anterior 
intercostal  membranes,  and  Pectoralis  major,  and  supply  the  integument  of  the 
front  of  the  thorax  and  over  the  mamma,  forming  the  anterior  cutaneous  branches 
of  the  thorax;  the  branch  from  the  second  nerve  unites  with  the  anterior  supra- 
clavicular nerves  of  the  cervical  plexus. 

Branches. — Numerous  slender  muscular  filaments  supply  the  Intercostales,  the 
Subcostales,  the  Levatores  costarum,  the  Serratus  posterior  superior,  and  the  Trans- 
versus thoracis.  At  the  front  of  the  thorax  some  of  these  branches  cross  the  costal 
cartilages  from  one  intercostal  space  to  another. 

Lateral  cutaneous  branches  (rami  cutanei  laterales)  are  derived  from  the  intercostal 
nerves,  about  midway  between  the  vertebrae  and  sternum;  they  pierce  the  Inter- 
60 


946 


NEUROLOGY 


costales  externi  and  Serratiis  anterior,  and  divide  into  anterior  and  posterior 
branches.  The  anterior  branches  run  forward  to  the  side  and  the  forepart  of  the 
chest,  supplying  the  skin  and  the  mamma;  those  of  the  fifth  and  sixth  nerves 


INTERCOSTCj 
BRACHIAL 


)    ANTERIOR  OUTAN 
'/      NERVES  OF  THOI 


LATERAL  CUTA- 
NEOUS OF   III  TO 
XI  THORACIC 


E0U8 
ORAX 


II 


LATERAL  CUTA 
NEOUS  OF  XII      , ^^VT'       77 

THORACIC        (       //fjr      Jj 


ANT.   CUTANEOUS 
OF  X,  XI,   ANO 
XII  THORACIO 


Fig.  820. — Cutaneous  distribution  of   thoracic  nerves.     (Testut.) 

supply  the  upper  digitations  of  the  Obliquus  externus  abdominis.     The  posterior 

branches  run  backward,  and  supply  the  skin  over  the  scapula  and  Latissimus  dorsi. 

The  lateral  cutaneous  branch  of  the  second  intercostal  nerve  does  not  divide, 

like  the  others,  into  an  anterior  and  a  posterior  branch;  it  is  named  the  intercosto- 


THE  THORACIC  NERVES 


947 


brachial  nerve  (Fig.  816).  It  pierces  the  Intercostalis  externus  and  the  Serratus 
anterior,  crosses  the  axilla  to  the  medial  side  of  the  arm,  and  joins  with  a  filament 
from  the  medial  brachial  cutaneous  nerve.  It  then  pierces  the  fascia,  and  supplies 
the  skin  of  the  upper  half  of  the  medial  and  posterior  part  of  the  arm,  communicat- 


INTERCOSTO- 
BRACHIAL 


LATERAL  CUTANEOUS  | 
BRANCHES  or  III  -< 
TO  XI  THORACIC       ) 


LATERAL  OUT 

NEOUS  OF   X. 

THORACIC 


ILIOHYPOGASTRIC- i- 


PiG.  821. — Intercostal  nerves,  the  superficial  muscles  having  been  removed.     (Testut). 

ing  with  the  posterior  brachial  cutaneous  branch  of  the  radial  nerve.  The  size 
of  the  intercostobrachial  nerve  is  in  inverse  proportion  to  that  of  the  medial  brachial 
cutaneous  nerve.  A  second  intercostobrachial  nerve  is  frequently  gi\en  off  from 
the  lateral  cutaneous  branch  of  the  third  intercostal;  it  supplies  filaments  to  the 
axilla  and  medial  side  of  the  arm. 


948  NEUROLOGY 

The  Iiower  Thoracic  Nerves. — ^The  anterior  divisions  of  the  seventh,  eighth,  ninth, 
tenth,  and  eleventh  thoracic  nerves  are  continued  anteriorly  from  the  intercostal 
spaces  into  the  abdominal  wall;  hence  they  are  named  thoracicoabdominal  inter- 
costal nerves.  They  have  the  same  arrangement  as  the  upper  ones  as  far  as  the 
anterior  ends  of  the  intercostal  spaces,  where  they  pass  behind  the  costal  cartilages, 
and  between  the  Obliquus  internus  and  Transversus  abdominis,  to  the  sheath  of 
the  Rectus  abdominis,  which  they  perforate.  They  supply  the  Rectus  abdominis 
and  end  as  the  anterior  cutaneous  branches  of  the  abdomen;  they  supply  the  skin 
of  the  front  of  the  abdomen.  The  lower  intercostal  nerves  supply  the  Intercostales 
and  abdominal  muscles;  the  last  three  send  branches  to  the  Serratus  posterior 
inferior.  About  the  middle  of  their  course  they  give  off  lateral  cutaneous  branches. 
These  pierce  the  Intercostales  externi  and  the  Obliquus  externus  abdominis,  in  the 
same  line  as  the  lateral  cutaneous  branches  of  the  upper  thoracic  nerves,  and  divide 
into  anterior  and  posterior  branches,  which  are  distributed  to  the  skin  of  the  abdo- 
men and  back;  the  anterior  branches  supply  the  digitations  of  the  Obliquus  externus 
abdominis,  and  extend  downward  and  forward  nearly  as  far  as  the  margin  of  the 
Rectus  abdominis;  the  posterior  branches  pass  backward  to  supply  the  skin  over 
the  Latissimus  dorsi. 

The  anterior  division  of  the  twelfth  thoracic  nerve  is  larger  than  the  others;  it 
runs  along  the  lower  border  of  the  twelfth  rib,  often  gives  a  communicating  branch 
to  the  first  lumbar  nerve,  and  passes  under  the  lateral  lumbocostal  arch.  It  then 
runs  in  front  of  the  Quadratus  lumborum,  perforates  the  Transversus,  and  passes 
forward  between  it  and  the  Obliquus  internus  to  be  distributed  in  the  same  manner 
as  the  lower  intercostal  nerves.  It  communicates  with  the  iliohypogastric  nerve 
of  the  lumbar  plexus,  and  gives  a  branch  to  the  Pyramidalis.  The  lateral  cutaneous 
branch  of  the  last  thoracic  nerve  is  large,  and  does  not  divide  into  an  anterior  and 
a  posterior  branch.  It  perforates  the  Obliqui  internus  and  externus,  descends  over 
the  iliac  crest  in  front  of  the  lateral  cutaneous  branch  of  the  iliohypogastric  (Fig. 
819),  and  is  distributed  to  the  skin  of  the  front  part  of  the  gluteal  region,  some  of 
its  filaments  extending  as  low  as  the  greater  trochanter. 

The  Lumbosacral  Plexus  (Plexus  Lumbosacralis). 

The  anterior  divisions  of  the  lumbar,  sacral,  and  coccygeal  nerves  form  the 
lumbosacral  plexus,  the  first  lumbar  nerve  being  frequently  joined  by  a  branch 
from  the  twelfth  thoracic.  For  descriptive  purposes  this  plexus  is  usually  divided 
into  three  parts — the  lumbar,  sacral,  and  pudendal  plexuses. 

The  Lumbar  Nerves  (Nn.  Lumbales). 

The  anterior  divisions  of  the  lumbar  nerves  {rami  anteriores)  increase  in  size 
from  above  downward.  They  are  joined,  near  their  origins,  by  gray  rami  com- 
municantes  from  the  lumbar  ganglia  of  the  sympathetic  trunk.  These  rami  consist 
of  long,  slender  branches  which  accompany  the  lumbar  arteries  around  the  sides  of 
the  vertebral  bodies,  beneath  the  Psoas  major.  Their  arrangement  is  somewhat 
irregular:  one  ganglion  may  give  rami  to  two  lumbar  nerves,  or  one  lumbar  nerve 
may  receive  rami  from  two  ganglia.  The  first  and  second,  and  sometimes  the 
third  and  fourth  lumbar  nerves  are  each  connected  with  the  lumbar  part  of  the 
sympathetic  trunk  by  a  white  ramus  communicans. 

The  nerves  pass  obliquely  outward  behind  the  Psoas  major,  or  between  its 
fasciculi,  distributing  filaments  to  it  and  the  Quadratus  lumborum.  The  first 
three  and  the  greater  part  of  the  fourth  are  connected  together  in  this  situation 
by  anastomotic  loops,  and  form  the  lumbar  plexus.  The  smaller  part  of  the  fourth 
joins  with  the  fifth  to  form  the  lumbosacral  trunk,  which  assists  in  the  formation 


THE  LUMBAR  NERVES 


949 


of  the  sacral  plexus.    The  fourth  nerve  is  named  the  nervus  furcalis,  from  the  fact 
that  it  is  subdivided  between  the  two  plexuses.^ 

The  Lumbar  Plexus^  (plexm  lumhalis)  (Figs.  822, 823, 824). — ^The  lumbar  plexus»is 
formed  by  the  loops  of  communication  between  the  anterior  divisions  of  the  first 
three  and  the  greater  part  of  the  fourth  lumbar  nerves;  the  first  lumbar  often 
receives  a  branch  from  the  last  thoracic  nerve.  It  is  situated  in  the  posterior  part 
of  the  Psoas  major,  in  front  of  the  transverse  processes  of  the  lumbar  vertebrae. 


— From  \2lh  thoracic 


—\st  lumbar 


Iliohypogastric 
Ilioinguinal 


Lot.  femoral  cutaneous 


To  Psoas  and 
lliacus 


2nd  lumbar 


rd  lumbar 


ith  lumbar 


,5th  lumbar 


Femoral 
Accessory  obturator 

Obturator 

Lumbosacral  trunk  ■ 

Fig.  822. — Plan  of  lumbar  plexus. 


The  mode  in  which  the  plexus  is  arranged  varies  in  different  subjects.  It  differs 
from  the  brachial  plexus  in  not  forming  an  intricate  interlacement,  but  the  several 
nerves  of  distribution  arise  from  one  or  more  of  the  spinal  nerves,  in  the  following 
manner:  the  first  lumbar  nerve,  frequently  supplemented  by  a  twig  from  the  last 
thoracic,  splits  into  an  upper  and  lower  branch;  the  upper  and  larger  branch  divides 
into  the  iliohypogastric  and  ilioinguinal  nerves;  the  lower  and  smaller  branch 
unites  with  a  branch  of  the  second  lumbar  to  form  the  genitofemoral  nerve.  The 
remainder  of  the  second  nerve,  and  the  third  and  fourth  nerves,  divide  into  ventral 
and  dorsal  divisions.  The  ventral  division  of  the  second  unites  with  the  ventral 
divisions  of  the  third  and  fourth  nerves  to  form  the  obturator  ner^^e.  The  dorsal 
divisions  of  the  second  and  third  nerves  divide  into  two  branches,  a  smaller  branch 
from  each  uniting  to  form  the  lateral  femoral  cutaneous  nerve,  and  a  larger  branch 
from  each  joining  with  the  dorsal  division  of  the  fourth  nerve  to  form  the  femoral 

1  In  most  cases  the  fourth  lumbar  is  the  nervus  furcalis;  but  this  arrangement  is  frequently  departed  from.  The 
third  is  occasionally  the  lowest  nerve  which  enters  the  lumbar  plexus,  giving  at  the  same  time  some  fibers  to  the  sacral 
plexus,  and  thus  forming  the  nervus  furcalis;  or  both  the  third  and  fourth  may  be  furcal  nerves.  When  this  occurs, 
the  plexus  is  termed  Atff/i  or  prefixed.  More  frequently  the  fifth  nerve  is  divided  between  the  lumbar  and  sacral  plexuses, 
and  constitutes  the  nervus  furcalis;  and  when  this  takes  place,  the  plexus  is  distinguished  as  a  low  or  postfixed  plexus. 
These  variations  necessarily  produce  corresponding  modifications  in  the  sacral  plexus. 

2  Bardeen,  Amer.  Jour.  Anat.,  1907,  vol.  vi: 


)50 


NEUROLOGY 


nerve.    The  accessory  obturator,  when  it  exists,  is  formed  by  the  union  of  two  small 
branches  given  off  from  the  third  and  fourth  nerves. 


I 


Fig.  823. — The  lumbar  plexus  and  its  branches. 

M 

The  branches  of  the  lumbar  plexus  may  therefore  be  arranged  as  follows:        ^* 

Iliohypogastric 1  L.  ^^k 

Ilioinguinal 1  L.  f^H 

Genitofemoral  1,  2  L.  ^H 

Dorsal  divisions. 

Lateral  femoral  cutaneous 2,  3  L. 

Femoral .       2,  3,  4  L. 

Ventral  divisions. 

Obturator 2,  3,  4  L. 

Accessory  obturator 3,  4  L. 

The  Iliohypogastric  Nerve  {n.  iliohypogastricus)  arises  from  the  first  lumbar  nerve. 
It  emerges  from  the  upper  part  of  the  lateral  border  of  the  Psoas  major,  and  crosses 
obliquely  in  front  of  the  Quadratus  lumborum  to  the  iliac  crest.  It  then  perforates 
the  posterior  part  of  the  Transversus  abdominis,  near  the  crest  of  the  ilium,  and 


THE  LUMBAR  NERVES 


951 


divides  between  that  muscle  and  the  Obhquus  internus  abdominis  into  a  lateral 
and  an  anterior  cutaneous  branch. 

The  lateral  cutaneous  branch  {ramvs  cutaneus  lateralis;  iliac  branch)  pierces  the 
Obliqiii  internus  and  externus  immediately  above  the  iliac  crest,  and  is  distributed 
to  the  skin  of  the  gluteal  region,  behind  the  lateral  cutaneous  branch  of  the  last 
thoracic  nerve  (Fig.  830) ;  the  size  of  this  branch  bears  an  inverse  proportion  to  that 
of  the  lateral  cutaneous  branch  of  the  last  thoracic  nerve. 


TWELFTH  THORACIC 


LUMBAR  PORTION 
,'OF  SYMPATHETIC 


FIRST  LUMBAR 


TWELFTH  THORACIC 


NERVE  TO  QUADRA 
TUS  LUMBORUM 


TRANSVERSALIS 

OBLIQUUS    INTERNUS 

OBLIQUUS    EXTERNUS 

SECOND    LUMBAR 


ILIOHYPOGASTRIC 

THIRD   LUMBAR 

ILIAC  BRANCH  OF 

ILIOHYPOGASTRIC 

ABDOMINAL  BRANCH 

OF  ILIOHYPO. 

FOURTH    LUMBAR' 


FIFTH    LUMBAR 
ILIOINGUINAL 


LATERAL  FEMORAL 

CUTANEOUS^ 

OBTURATOR    NERVE 


EXTERNAL    SPERMATIC 
bRANCH  OF  GENITO- 
FEMORAL 
lUMBO.NGUINAL    BRANCH 

OF  GENITOFEMORAL""!*^ 
POSTERIOR  BRANCH  OF"      j  W 
lATERAL  FEMORAL         I  R 
CUTANEOUS         j^ 
ANTERIOR  BRANCH  OF  !^       1 

LATERAL  FEMORAL 
CUTANEOUS 


IIIOHYPOQA8TRIC 

ILIOINGUINAL 


GENITOFEMORAI 
RAMUS  COMMU- 
NICAN8 


LAT.    FEMORAL 
CUTANEOUS 


GENITOFEMORAL 


;         EXTERNAL  SPERMATIC 
BRANCH 


LUMBOINSUINAL    BRANCH 


APONEUROSIS  OF   EX- 
TERNAL OBLIQUE 


DORSAL   NERVE 
OF  PENIS 


Fig.  824. — Deep  and  superficial  dissection  of  the  lumbar  plexus.     (Testut.J 


The  anterior  cutaneous  branch  {ramus  cutaneus  anterior;  hypogastric  branch) 
(Fig.  825)  continues  onward  between  the  Obliquus  internus  and  Transversus.  It 
then  pierces  the  Obliquus  internus,  becomes  cutaneous  by  perforating  the  aponeu- 
rosis of  the  Obliquus  externus  about  2.5  cm.  aboAe  the  subcutaneous  inguinal  ring, 
and  is  distributed  to  the  skin  of  the  hypogastric  region. 

The  iliohypogastric  nerve  communicates  with  the  last  thoracic  and  ilioinguinal 
nerves. 


952 


NEUROLOGY 


The  nioinguinal  Nerve  {n.  ilioinguinalis) ,  smaller  than  the  preceding,  arises  with! 
it  from  the  first  lumbar  nerve.     It  emerges  from  the  lateral  border  of  the  Psoas 


Suralr 


m 


Deep  peronceal 


Fio.  825. — Cutaneous  nerves  of  right  lower  extremity. 
Front  view. 


Fia.  826. — Diagram  of  segoiental  distribution  _  of 
the  cutaneous  nerves  of  the  right  lower  extremity. 
Front  view. 


THE  LUMBAR  NERVES  953 

major  just  below  the  iliohypogastric,  and,  passing  obliquely  across  the  Quadratus 
lumborum  and  Iliacus,  perforates  the  Transversus  abdominis,  near  the  anterior 
part  of  the  iliac  crest,  and  communicates  with  the  iliohypogastric  nerve  between  the 
Transversus  and  the  Obliquus  internus.  The  nerve  then  pierces  the  Obliquus 
internus,  distributing  filaments  to  it,  and,  accompanying  the  spermatic  cord  through 
the  subcutaneous  inguinal  ring,  is  distributed  to  the  skin  of  the'  upper  and  medial 
part  of  the  thigh,  to  the  skin  over  the  root  of  the  penis  and  upper  part  of  the  scrotum 
in  the  male,  and  to  the  skin  covering  the  mons  pubis  and  labium  majus  in  the  femak. 
The  size  of  this  nerve  is  in  inverse  proportion  to  that  of  the  iliohypogastric.  Occa- 
sionally it  is  very  small,  and  ends  by  joining  the  iliohypogastric;  in  such  cases,  a 
branch  from  the  iliohypogastric  takes  the  place  of  the  ilioinguinal,  or  the  latter 
nerve  may  be  altogether  absent. 

The  Genitofemoral  Nerve  (n.  genitofemoralis;  genitocrural  nerve)  arises  from  the 
first  and  second  lumbar  nerves.  It  passes  obliquely  through  the  substance  of  the 
Psoas  major,  and  emerges  from  its  medial  border,  close  to  the  vertebral  column, 
opposite  the  fibrocartilage  between  the  third  and  fourth  lumbar  vertebrae;  it 
then  descends  on  the  surface  of  the  Psoas  major,  under  cover  of  the  peritoneum, 
and  divides  into  the  external  spermatic  and  lumboinguinal  nerves.  Occasionally 
these  two  nerves  emerge  separately  through  the  substance  of  the  Psoas. 

The  external  spermatic  nerve  (n.  spermaiicus  externus;  genital  branch  of  genito- 
femoral) passes  outward  on  the  Psoas  major,  and  pierces  the  fascia  transversalis,  or 
passes  through  the  abdominal  inguinal  ring;  it  then  descends  behind  the  spermatic 
cord  to  the  scrotum,  supplies  the  Cremaster,  and  gives  a  few  filaments  to  the  skin 
of  the  scrotum.  In  the  female,  it  accompanies  the  round  ligament  of  the  uterus, 
and  is  lost  upon  it. 

The  lumboinguinal  nerve  (n.  lumhoinguinalis;  femoral  or  crural  branch  of  genito- 
femoral) descends  on  the  external  iliac  artery,  sending  a  few  filaments  around  it, 
and,  passing  beneath  the  inguinal  ligament,  enters  the  sheath  of  the  femoral  vessels, 
lying  superficial  and  lateral  to  the  femoral  artery.  It  pierces  the  anterior  layer  of 
the  sheath  of  the  vessels  and  the  fascia  lata,  and  supplies  the  skin  of  the  anterior 
surface  of  the  upper  part  of  the  thigh  (Fig.  825).  On  the  front  of  the  thigh  it 
communicates  with  the  anterior  cutaneous  branches  of  the  femoral  nerve.  A  few 
filaments  from  the  lumboinguinal  nerve  may  be  traced  to  the  femoral  artery. 

The  Lateral  Femoral  Cutaneous  Nerve  {n.  cutaneus  femoralis  lateralis;  external 
cutaneous  nerve)  arises  from  the  dorsal  divisions  of  the  second  and  third  lumbar 
nerves.  It  emerges  from  the  lateral  border  of  the  Psoas  major  about  its  middle, 
and  crosses  the  Iliacus  obliquely,  toward  the  anterior  superior  iliac  spine.  It  then 
passes  under  the  inguinal  ligament  and  over  the  Sartorius  muscle  into  the  thigh, 
where  it  divides  into  two  branches,  an  anterior  and  a  posterior  (Fig.  825). 

The  anterior  branch  becomes  superficial  about  10  cm.  below  the  inguinal  ligament, 
and  divides  into  branches  which  are  distributed  to  the  skin  of  the  anterior  and 
lateral  parts  of  the  thigh,  as  far  as  the  knee.  The  terminal  filaments  of  this  nerve 
frequently  communicate  with  the  anterior  cutaneous  branches  of  the  femoral  nerve, 
and  with  the  infrapatellar  branch  of  the  saphenous  nerve,  forming  with  them  the 
patellar  plexus. 

The  posterior  branch  pierces  the  fascia  lata,  and  subdivides  into  filaments  which 
pass  backward  across  the  lateral  and  posterior  surfaces  of  the  thigh,  supplying 
the  skin  from  the  level  of  the  greater  trochanter  to  the  middle  of  the  thigh. 

The  Obturator  Nerve  {n.  obturatorius)  arises  from  the  ventral  divisions  of  the 
second,  third,  and  fourth  lumbar  nerves;  the  branch  from  the  third  is  the  largest, 
while  that  from  the  second  is  often  very  small.  It  descends  through  the  fibers 
of  the  Psoas  major,  and  emerges  from  its  medial  border  near  the  brim  of  the  pelvis; 
it  then  passes  behind  the  common  iliac  vessels,  and  on  the  lateral  side  of  the  hypo- 
gastric vessels  and  ureter,  which  separate  it  from  the  ureter,  and  runs  along  the 


954 


NEUROLOGY 


lateral  wall  of  the  lesser  pelvis,  above  and  in  front  of  the  obturator  vessels,  to 
the  upper  part  of  the  obturator  foramen.     Here  it  enters  the  thigh,  and  divides 

into  an  anterior  and  a  posterior 
branch,  which  are  separated  at 
first  by  some  of  the  fibers  of  the 


Lateral 
femoral 
cutaneous 


Iliacus 
Femoral 


Psoas  major 


Anterior  division 
of  obturator 

Med.  br,  of  ant. 
cutaneous 


Saphenous 


Fia.  827. — Nerves  of  the  right  lower  extremity.     Front  view. 


Obturator  externus,  and  lower 
down  by  the  Adductor  brevis. 

The  anterior  branch  {ramus 
anterior)  (Fig.  827)  leaves  the 
pelvis  in  front  of  the  Obturator 
externus  and  descends  in  front  of 
the  Adductor  brevis,  and  behind 
the  Pectineus  and  Adductor 
longus;  at  the  lower  border  of 
the  latter  muscle  it  communi- 
cates with  the  anterior  cutaneous 
and  saphenous  branches  of  the 
femoral  nerve,  forming  a  kind  of 
plexus.  It  then  descends  upon 
the  femoral  artery,  to  which  it 
is  finally  distributed.  Near  the 
obturator  foramen  the  nerve  gives 
off  an  articular  branch  to  the  hip- 
joint.  Behind  the  Pectineus,  it 
distributes  branches  to  the  Ad- 
ductor longus  and  Gracilis,  and 
usually  to  the  Adductor  brevis, 
and  in  rare  cases  to  the  Pecti- 
neus; it  receives  a  communicating 
branch  from  the  accessory  ob- 
turator nerve  when  that  nerve  is 
present. 

Occasionally  the  communicat- 
ing branch  to  the  anterior  cuta- 
neous and  saphenous  branches  of 
the  femoral  is  continued  down, 
as  a  cutaneous  branch,  to  the 
thigh  and  leg.  When  this  is  so,  it 
emerges  from  beneath  the  lower 
border  of  the  Adductor  longus, 
descends  along  the  posterior 
margin  of  the  Sartorius  to  the 
medial  side  of  the  knee,  where  it 
pierces  the  deep  fascia,  communi- 
cates with  the  saphenous  nerve, 
and  is  distributed  to  the  skin  of 
the  tibial  side  of  the  leg  as  low 
down  as  its  middle. 

The  posterior  branch  (ramus 
posterior)  pierces  the  anterior 
part  of  the  Obturator  externus, 
and  supplies  this  muscle;  it  then 
passes  behind  the  Adductor  brevis 
on   the   front   of    the    Adductor 


11 


THE  LUMBAR  NERVES  955 

magnus,  where  it  divides  into  numerous  muscular  branches  which  are  distributed 
to  the  Adductor  magnus  and  the  Adductor  brevis  when  the  latter  does  not  receive 
a  branch  from  the  anterior  division  of  the  nerve.  It  usually  gives  off  an  articular 
filament  to  the  knee-joint. 

The  articular  branch  for  the  knee-joint  is  sometimes  absent;  it  either  perforates 
the  Tower  part  of  the  Adductor  magnus,  or  passes  through  the  opening  which  trans- 
mits the  femoral  artery,  and  enters  the  popliteal  fossa;  it  then  descends  upon  the 
popliteal  artery,  as  far  as  the  back  part  of  the  knee-joint,  where  it  perforates  the 
oblique  popliteal  ligament,  and  is  distributed  to  the  synovial  membrane.  It  gives 
filaments  to  the  popliteal  artery. 

The  Accessory  Obturator  Nerve  (n.  obturatorius  accessorius)  (Fig.  823)  is  present 
in  about  29  per  cent,  of  cases.  It  is  of  small  size,  and  arises  from  the  ventral  divi- 
sions of  the  third  and  fourth  lumbar  nerves.  It  descends  along  the  medial  border 
of  the  Psoas  major,  crosses  the  superior  ramus  of  the  pubis,  and  passes  under  the 
Pectineus,  where  it  divides  into  numerous  branches.  One  of  these  supplies  the 
Pectineus,  penetrating  its  deep  surface,  another  is  distributed  to  the  hip-joint; 
while  a  third  communicates  with  the  anterior  branch  of  the  obturator  nerve. 
Occasionally  the  accessory  obturator  nerve  is  very  small  and  is  lost  in  the  capsule 
of  the  hip-joint.  When  it  is  absent,  the  hip-joint  receives  two  branches  from  the 
obturator  nerve. 

The  Femoral  Nerve  {n.  femoralis;  anterior  crural  nerve)  (Fig.  827),  the  largest 
branch  of  the  lumbar  plexus,  arises  from  the  dorsal  divisions  of  the  second,  third, 
and  fourth  lumbar  nerves.  It  descends  through  the  fibers  of  the  Psoas  major, 
emerging  from  the  muscle  at  the  lower  part  of  its  lateral  border,  and  passes  down 
between  it  and  the  Iliacus,  behind  the  iliac  fascia;  it  then  runs  beneath  the  inguinal 
ligament,  into  the  thigh,  and  splits  into  an  anterior  and  a  posterior  division.  Under 
the  inguinal  ligament,  it  is  separated  from  the  femoral  artery  by  a  portion  of  the 
Psoas  major. 

Within  the  abdomen  the  femoral  nerve  gives  off  small  branches  to  the  Iliacus, 
and  a  branch  which  is  distributed  upon  the  upper  part  of  the  femoral  artery;  the 
latter  branch  may  arise  in  the  thigh. 

In  the  thigh  the  anterior  division  of  the  femoral  nerve  gives  off  anterior  cuta- 
neous and  muscular  branches.  The  anterior  cutaneous  branches  comprise  the 
intermediate  and  medial  cutaneous  nerves  (Fig.  825). 

The  intermediate  cutaneous  nerve  (ramus  cutaneus  anterior;  middle  cutaneous 
nerve)  pierces  the  fascia  lata  (and  generally  the  Sartorius)  about  7.5  cm.  below 
the  inguinal  ligament,  and  divides  into  two  branches  which  descend  in  immediate 
proximity  along  the  forepart  of  the  thigh,  to  supply  the  skin  as  low  as  the  front 
of  the  knee.  Here  they  communicate  with  the  medial  cutaneous  nerve  and  the 
infrapatellar  branch  of  the  saphenous,  to  form  the  patellar  plexus.  In  the  upper 
part  of  the  thigh  the  lateral  branch  of  the  intermediate  cutaneous  communicates 
with  the  lumboinguinal  branch  of  the  genitofemoral  nerve. 

The  medial  cutaneous  nerve  {ramus  cutaneus  anterior;  internal  cutaneous  nerve) 
passes  obliquely  across  the  upper  part  of  the  sheath  of  the  femoral  artery,  and  divides 
in  front,  or  at  the  medial  side  of  that  vessd,  into  two  branches,  an  anterior  and  a 
posterior.  The  anterior  branch  runs  downward  on  the  Sartorius,  perforates  the 
fascia  lata  at  the  lower  third  of  the  thigh,  and  divides  into  two  branches:  one 
supplies  the  integument  as  low  down  as  the  medial  side  of  the  knee;  the  other 
crosses  to  the  lateral  side  of  the  patella,  communicating  in  its  course  with  the  infra- 
patellar branch  of  the  saphenous  nerve.  The  posterior  branch  descends  along  the 
medial  border  of  the  Sartorius  muscle  to  the  knee,  where  it  pierces  the  fascia  lata, 
communicates  with  the  saphenous  nerve,  and  gives  off  several  cutaneous  branches. 
It  then  passes  down  to  supply  the  integument  of  the  medial  side  of  the  leg.  Beneath 
the  fascia  lata,  at  the  lower  border  of  the  Adductor  longus,  it  joins  to  form  a  plexi- 


956  NEUROLOGY 

form  net-work  (subsartorial  plexus)  with  branches  of  the  saphenous  and  obturator 
nerves.  When  the  communicating  branch  from  the  obturator  nerve  is  large  and 
continued  to  the  integument  of  the  leg,  the  posterior  branch  of  the  medial  cutaneous 
is  small,  and  terminates  in  the  plexus,  occasionally  giving  off  a  few  cutaneous 
filaments.  The  medial  cutaneous  nerve,  before  dividing,  gives  off  a  few  filaments, 
which  pierce  the  fascia  lata,  to  supply  the  integument  of  the  medial  side  of  the 
thigh,  accompanying  the  long  saphenous  vein.  One  of  these  filaments  passes 
through  the  saphenous  opening;  a  second  becomes  subcutaneous  about  the  middle 
of  the  thigh;  a  third  pierces  the  fascia  at  its  lower  third. 

Muscular  Branches  {rami  musculares). — The  nerve  to  the  Pectineus  arises 
immediately  below  the  inguinal  ligament,  and  passes  behind  the  femoral  sheath  to 
enter  the  anterior  surface  of  the  muscle;  it  is  often  duplicated.  The  nerve  to  the 
Sartorius  arises  in  common  with  the  intermediate  cutaneous. 

The  posterior  division  of  the  femoral  nerve  gives  off  the  saphenous  nerve,  and 
muscular  and  articular  branches. 

The  Saphenous  Nerve  {n.  saphenus;  long  or  internal  saphenous  nerve)  (Fig.  827) 
is  the  largest  cutaneous  branch  of  the  femoral  nerve.  It  approaches  the  femoral 
artery  where  this  vessel  passes  beneath  the  Sartorius,  and  lies  in  front  of  it,  behind 
the  aponeurotic  covering  of  the  adductor  canal,  as  far  as  the  opening  in  the  lower 
part  of  the  Adductor  magnus.  Here  it  quits  the  artery,  and  emerges  from  behind 
the  lower  edge  of  the  aponeurotic  covering  of  the  canal;  it  descends  vertically 
along  the  medial  side  of  the  knee  behind  the  Sartorius,  pierces  the  fascia  lata,, 
between  the  tendons  of  the  Sartorius  and  Gracilis,  and  becomes  subcutaneous. 
The  nerve  then  passes  along  the  tibial  side  of  the  leg,  accompanied  by  the  great 
saphenous  vein,  descends  behind  the  medial  border  of  the  tibia,  and,  at  the  lower 
third  of  the  leg,  divides  into  two  branches :  one  continues  its  course  along  the  margin 
of  the  tibia,  and  ends  at  the  ankle;  the  other  passes  in  front  of  the  ankle,  and  is 
distributed  to  the  skin  on  the  medial  side  of  the  foot,  as  far  as  the  ball  of  the  great 
toe,  communicating  with  the  medial  branch  of  the  superficial  peroneal  nerve. 

Branches. — The  saphenous  nerve,  about  the  middle  of  the  thigh,  gives  off  a 
branch  which  joins  the  subsartorial  plexus. 

At  the  medial  side  of  the  knee  it  gives  off  a  large  infrapatellar  branch,  which 
pierces  the  Sartorius  and  fascia  lata,  and  is  distributed  to  the  skin  in  front  of  the 
patella.  This  nerve  communicates  above  the  knee  with  the  anterior  cutaneous 
branches  of  the  femoral  nerve;  below  the  knee,  with  other  branches  of  the  saphenous; 
and,  on  the  lateral  side  of  the  joint,  with  branches  of  tHe  lateral  femoral  cutaneous 
nerve,  forming  a  plexiform  net-work,  the  plexus  patellsB.  The  infrapatellar  branch 
is  occasionally  small,  and  ends  by  joining  the  anterior  cutaneous  branches  of  the 
femoral,  which  supply  its  place  in  front  of  the  knee. 

Below  the  knee,  the  branches  of  the  saphenous  nerve  are  distributed  to  the  skin 
of  the  front  and  medial  side  of  the  leg,  communicating  with  the  cutaneous  branches 
of  the  femoral,  or  with  filaments  from  the  obturator  nerve. 

The  muscular  branches  supply  the  four  parts  of  the  Quadriceps  femoris.  The 
branch  to  the  Rectus  femoris  enters  the  upper  part  of  the  deep  surface  of  the  muscle, 
and  supplies  a  filament  to  the  hip-joint.  The  branch  to  the  Vastus  lateraHs,  of 
large  size,  accompanies  the  descending  branch  of  the  lateral  femoral  circumflex 
artery  to  the  lower  part  of  the  muscle.  It  gives  off  an  articular  filament  to  the 
knee-joint.  The  branch  to  the  Vastus  medialis  descends  lateral  to  the  femoral 
vessels  in  company  with  the  saphenous  nerve.  It  enters  the  muscle  about  its  middle, 
and  gives  off  a  filament,  which  can  usually  be  traced  downward,  on  the  surface  of 
the  muscle,  to  the  knee-joint.  The  branches  to  the  Vastus  intermedins,  two  or 
three  in  number,  enter  the  anterior  surface  of  the  muscle  about  the  middle  of  the 
thigh;  a  filament  from  one  of  these  descends  through  the  muscle  to  the  Articularis 
genu  and  the  knee-joint.  The  articular  branch  to  the  hip-joint  is  derived  from  the 
nerve  to  the  Rectus  femoris. 


I 


THE  SACRAL  AND  COCCYGEAL  NERVES  957 

The  articular  branches  to  the  knee-joint  are  three  in  number.  One,  a  long  slender 
filament,  is  derived  from  the  nerve  to  the  Vastus  lateralis;  it  penetrates  the  capsule 
of  the  joint  on  its  anterior  aspect.  Another,  derived  from  the  nerve  to  the  Vastus 
medialis,  can  usually  be  traced  downward  on  the  surface  of  this  muscle  to  near  the 
joint;  it  then  penetrates  the  muscular  fibers,  and  accompanies  the  articular  branch 
of  the  highest  genicular  artery,  pierces  the  medial  side  of  the  articular  capsule, 
and  supplies  the  synovial  membrane.  The  third  branch  is  derived  from  the  nerve 
to  the  Vastus  intermedius. 

The  Sacral  and  Coccygeal  Nerves  (Nn.  Sacrales  et  Coccygeus). 

The  anterior  divisions  of  the  sacral  and  coccygeal  nerves  (rami  anteriores)  form 
the  sacral  and  pudendal  plexuses.  The  anterior  divisions  of  the  upper  four  sacral 
nerves  enter  the  pelvis  through  the  anterior  sacral  foramina,  that  of  the  fifth 
between  the  sacrum  and  coccyx,  while  that  of  the  coccygeal  nerve  curves  forward 
below  the  rudimentary  transverse  process  of  the  first  piece  of  the  coccyx.  The 
first  and  second  sacral  nerves  are  large;  the  third,  fourth,  and  fifth  diminish  pro- 
gressively from  above  downward.  Each  receives  a  gray  ramus  communicans 
from  the  corresponding  ganglion  of  the  sympathetic  trunk,  while  from  the  third 
and  frequently  from  the  second  and  the  fourth  sacral  nerves,  a  white  ramus  com- 
municans is  given  to  the  pelvic  plexuses  of  the  sympathetic. 

The  Sacral  Plexus  (plexus  sacralis)  (Fig.  828), — The  sacral  plexus  is  formed  by 
the  lumbosacral  trunk,  the  anterior  division  of  the  first,  and  portions  of  the  anterior 
divisions  of  the  second  and  third  sacral  nerves. 

The  lumbosacral  trunk  comprises  the  whole  of  the  anterior  division  of  the  fifth 
and  a  part  of  that  of  the  fourth  lumbar  nerve ;  it  appears  at  the  medial  margin  of 
the  Psoas  major  and  runs  downward  over  the  pelvic  brim  to  join  the  first  sacral 
nerve.  The  anterior  division  of  the  third  sacral  nerve  divides  into  an  upper  and  a 
lower  branch,  the  former  entering  the  sacral  and  the  latter  the  pudendal  plexus. 

The  nerves  forming  the  sacral  plexus  converge  toward  the  lower  part  of  the  greater 
sciatic  foramen,  and  unite  to  form  a  flattened  band,  from  the  anterior  and  posterior 
surfaces  of  which  several  branches  arise.  The  band  itself  is  continued  as  the  sciatic 
nerve,  which  splits  on  the  back  of  the  thigh  into  the  tibial  and  common  peroneal 
nerves;  these  two  nerves  sometimes  arise  separately  from  the  plexus,  and  in  all 
cases  their  independence  can  be  shown  by  dissection. 

Relations. — The  sacral  plexus  lies  on  the  back  of  the  pelvis  .between  the  Piriformis  and  the 
pelvic  fascia  (Fig.  829) ;  in  front  of  it  are  the  hypogastric  vessels,  the  ureter  and  the  sigmoid  colon. 
The  superior  gluteal  vessels  run  between  the  lumbosacral  trunk  and  the  first  sacral  lierve,  and  the 
inferior  gluteal  vessels  between  the  second  and  third  sacral  nerves. 

All  the  nerves  entering  the  plexus)  with  the  exception  of  the  third  sacral,  split  into  ventral 
and  dorsal  divisions,  and  the  nerves  arising  from  these  are  as  follows: 

Ventral  divisions.  Dorsal  divisions. 

Nerve  to  Quadratus  femoris       I  ^   r  t    i  q 

and  Gemellus  inferior  j"  4,  5  L,  1  b. 

Nerve  to  Obturator  internus      1     -j.        ^  ^ 

and  Gemellus  superior  1 5  L,  1,  2  b. 

Nerve  to  Piriformis (1)  2  S. 

Superior  gluteal 4,  5  L,  1  S. 

Inferior  gluteal 5  L,  1,  2  S. 

Posterior  femoral  cutaneous  2,  3  S     .        .        .         1,  2  S. 

Sciatic    1™^^^     •       •       •         4,  5  L,  1,2,3  8. 

\  Common  peroneal 4,  5  L,  1,  2  S. 

The  Nerve  to  the  Quadratus  Femoris  and  Gemellus  Inferior  arises  from  the  ventral 
divisions  of  the  fourth  and  fifth  lumbar  and  first  sacral  nerves:  it  leaves  the  pelvis 


958 


NEUROLOGY 


through  the  greater  sciatic  foramen,  below  the  Piriformis,  and  runs  down  in  front  of 
the  sciatic  nerve,  the  Gemelli,  and  the  tendon  of  the  Obturator  internus,  and  enters 
the  anterior  surfaces  of  the  muscles;  it  gives  an  articular  branch  to  the  hip-joint. 


Superior  gluteal 

Inferior  gluteal 
To  Piriformis 


Common 


Sciatic 


j    peroneal'      ///, 
I        Tibial-^i 


To  Quadratiis  femoris  and 
Inferior  gemellus 
To  Obturator  internus  and 
Superior  gemellus 

Post.  fern.  cuta7ieous 
Perforating  cutaneous 


Coccygeal 


Pudendal 

To  Levator  ani,  Coccygeus  and 
Sphincter  ani  ezternus 

FiQ.  828. — ^Plan  of  sacral  and  pudendal  plexuses. 

The  Nerve  to  the  Obturator  Internus  and  Gemellus  Superior  arises  from  the  ventral 
divisions  of  the  fifth  lumbar  and  first  and  second  sacral  nerves.  It  leaves  the  pelvis 
through  the  greater  sciatic  foramen  below  the  Piriformis,  and  gives  off  the  branch 
to  the  Gemellus  superior,  which  enters  the  upper  part  of  the  posterior  surface  of 
the  muscle.  It  then  crosses  the  ischial  spine,  reenters  the  pelvis  through  the 
lesser  sciatic  foramen,  and  pierces  the  pelvic  surface  of  the  Obturator  internus. 


THE  SACRAL  AND  COCCYGEAL  NERVES 


959 


The  Nerve  to  the  Piriformis  arises  from  the  dorsal  division  of  the  second  sacral 
nerve,  or  the  dorsal  divisions  of  the  first  and  second  sacral  nerves,  and  enters 
the  anterior  surface  of  the  muscle;  this  nerve  may  be  double. 


Sympathetic 
trunk 


Fig.  829. — Dissection  of  side  wall  of  pelvis  showing  sacral  and  pudendal  plexuses.     (Testut.) 


The  Superior  Gluteal  Nerve  (n.  glutceus  superior)  arises  from  the  dorsal  divisions 
of  the  fourth  and  fifth  lumbar  and  first  sacral  nerves:  it  leaves  the  pelvis  through 
the  greater  sciatic  foramen  above  the  Piriformis,  accompanied  by  the  superior 
gluteal  vessels,  and  divides  into  a  superior  and  an  inferior  branch.  The  superior 
branch  accompanies  the  upper  branch  of  the  deep  division  of  the  superior  gluteal 
artery  and  ends  in  the  Glutseus  minimus.  The  inferior  branch  runs  with  the  lower 
branch  of  the  deep  division  of  the  superior  gluteal  artery  across  the  Glutseus 
minimus;  it  gives  filaments  to  the  Glutsei  medius  and  minimus,  and  ends  in  the 
Tensor  fasciae  latie. 

The  Inferior  Gluteal  Nerve  {n.  gluiceus  inferior)  arises  from  the  dorsal  divisions 
of  the  fifth  lumbar  and  first  and  second  sacral  nerves :  it  leaves  the  pelvis  through 
the  greater  sciatic  foramen,  below  the  Piriformis,  and  divides  into  branches  which 
enter  the  deep  surface  of  the  Glutseus  maximus. 

The  Posterior  Femoral  Cutaneous  Nerve  (n.  cutaneus  femoralis  posterior;  small 
sciatic  nerve)  is  distributed  to  the  skin  of  the  perineum  and  posterior  surface  of 
the  thigh  and  leg.  It  arises  partly  from  the  dorsal  divisions  of  the  first  and  second, 
and  from  the  ventral  divisions  of  the  second  and  third  sacral  nerves,  and  issues  from 


960  ^^^^^^"^  NEUROLOGY 

the  pelvis  through  the  greater  sciatic  foramen  bel  o w  th  e  Piriformis .  It  then  descends 
beneath  the  Glutseus  maximus  with  the  inferior  gluteal  artery,  and  runs  down  the 
back  of  the  thigh  beneath  the  fascia  lata,  and  over  the  long  head  of  the  Biceps 
femoris  to  the  back  of  the  knee;  here  it  pierces  the  deep  fascia  and  accompanies 
the  small  saphenous  vein  to  about  the  middle  of  the  back  of  the  leg,  its  terminal 
twigs  communicating  with  the  sural  nerve. 

Its  branches  are  all  cutaneous,  and  are  distributed  to  the  gluteal  region,  the  peri- 
neum, and  the  back  of  the  thigh  and  leg. 

The  gluteal  branches  {nn.  cluniuminferiores),  three  or  four  in  number,  turn  upward 
around  the  lower  border  of  the  Glutseus  maximus,  and  supply  the  skin  covering 
the  lower  and  lateral  part  of  that  muscle. 

The  perineal  branches  {rami  perineales)  are  distributed  to  the  skin  at  the  upper 
and  medial  side  of  the  thigh.  One  long  perineal  branch,  inferior  pudendal  (long 
scrotal  nerve) ,  curves  forward  below  and  in  front  of  the  ischial  tuberosity,  pierces 
the  fascia  lata,  and  runs  forward  beneath  the  superficial  fascia  of  the  perineum  to 
the  skin  of  the  scrotum  in  the  male,  and  of  the  labium  majus  in  the  female.  It 
communicates  with  the  inferior  hemorrhoidal  and  posterior  scrotal  nerves. 

The  branches  to  the  back  of  the  thigh  and  leg  consist  of  numerous  filaments  derived 
from  both  sides  of  the  nerve,  and  distributed  to  the  skin  covering  the  back  and 
medial  side  of  the  thigh,  the  popliteal  fossa,  and  the  upper  part  of  the  back  of  the 
leg  (Fig.  830). 

The  Sciatic  (n.  ischiadicus;  great  sciatic  nerve)  (Fig.  832)  supplies  nearly  the  whole 
of  the  skin  of  the  leg,  the  muscles  of  the  back  of  the  thigh,  and  those  of  the  leg 
and  foot.  It  is  the  largest  nerve  in  the  body,  measuring  2  cm.  in  breadth,  and  is 
the  continuation  of  the  flattened  band  of  the  sacral  plexus.  It  passes  out  of  the 
pelvis  through  the  greater  sciatic  foramen,  below  the  Piriformis  muscle.  It  descends 
between  the  greater  trochanter  of  the  femur  and  the  tuberosity  of  the  ischium,  and 
along  the  back  of  the  thigh  to  about  its  lower  third,  where  it  divides  into  two  large 
branches,  the  tibial  and  common  peroneal  nerves.  This  division  may  take  place 
at  any  point  between  the  sacral  plexus  and  the  lower  third  of  the  thigh.  When  it 
occurs  at  the  plexus,  the  common  peroneal  nerve  usually  pierces  the  Piriformis. 

In  the  upper  part  of  its  course  the  nerve  rests  upon  the  posterior  surface  of  the 
ischium,  the  nerve  to  the  Quadratus  femoris,  the  Obturator  internus  and  Gemelli, 
and  the  Quadratus  femoris;  it  is  accompanied  by  the  posterior  femoral  cutaneous 
nerve  and  the  inferior  gluteal  artery,  and  is  covered  by  the  Glutaeus  maximus. 
Lower  down,  it  lies  upon  the  Adductor  magnus,  and  is  crossed  obliquely  by  the 
long  head  of  the  Biceps  femoris. 

The  nerve  gives  off  articular  and  muscular  branches. 

The  articular  branches  (rami  articulares)  arise  from  the  upper  part  of  the  nerve 
and  supply  the  hip-joint,  perforating  the  posterior  part  of  its  capsule;  they  are 
sometimes  derived  from  the  sacral  plexus. 

The  muscular  branches  (rami  musculares)  are  distributed  to  the  Biceps  femoris, 
Semitendinosus,  Semimembranosus,  and  Adductor  magnus.  The  nerve  to  the  short 
head  of  the  Biceps  femoris  comes  from  the  common  peroneal  part  of  the  sciatic, 
while  the  other  muscular  branches  arise  from  the  tibial  portion,  as  may  be  seen  in 
those  cases  where  there  is  a  high  division  of  the  sciatic  nerve. 

The  Tibial  Nerve  (n.  tibialis;  internal  popliteal  nerve)  (Fig.  832)  the  larger  of  the 
two  terminal  branches  of  the  sciatic,  arises  from  the  anterior  branches  of  the 
fourth  and  fifth  lumbar  and  first,  second,  and  third  sacral  nerves.  It  descends 
along  the  back  of  the  thigh  and  through  the  middle  of  the  popliteal  fossa,  to  the  lower 
part  of  the  Popliteus  muscle,  where  it  passes  with  the  popliteal  artery  beneath  the 
arch  of  the  Soleus.  It  then  runs  along  the  back  of  the  leg  with  the  posterior 
tibial  vessels  to  the  interval  between  the  medial  malleolus  and  the  heel,  where  it 
divides  beneath  the  laciniate  ligament  into  the  medial  and  lateral  plantar  nerves. 


THE  SACRAL  AND  COCCYGEAL  NERVES 


961 


In  the  thigh  it  is  overlapped  by  the  hamstring  muscles  above,  and  then  becomes 
more  superficial,  and  lies  lateral  to,  and  some  distance  from,  the  popliteal  vessels; 


Fig.  830. — Cutaneous  nerves  of  right  lower 
extremity.    Posterior  view. 

61 


Fia.  831. — Diagram  of  the  eegmental  distribution  of  the 
cutaneous  ner\'es  of  the  right  lower  extremity.  Posterior 
view. 


962 


NEUROLOGY 


Superior 
gluteal 

Pudendal 
Nerve  to 
obturator  intemus    ^ 

Post.  fern, 
cutaneous 
Perineal 
branch 


Medial      '-^^ 
calcaneal 


Fig.  832. — Nerves  of  the  right  lower  extremity 
Posterior  view. 


opposite  the  knee-joint,  it  is  in  close 
relation  with  these  vessels,  and  crosses 
to  the  medial  side  of  the  artery.  In  the 
leg  it  is  covered  in  the  upper  part  of 
its  course  by  the  muscles  of  the  calf; 
lower  down  by  the  skin,  the  superficial 
and  deep  fasciae.  It  is  placed  on  the 
deep  muscles,  and  lies  at  first  to  the 
medial  side  of  the  posterior  tibial 
artery,  but  soon  crosses  that  vessel  and 
descends  on  its  lateral  side  as  far  as 
the  ankle.  In  the  lower  third  of  the 
leg  it  runs  parallel  with  the  medial 
margin  of  the  tendo  calcaneus. 

The  branches  of  this  nerve  are :  artic- 
ular, muscular,  medial  sural  cutaneous, 
medial  calcaneal,  medial  and  lateral 
plantar. 

Articular  branches  (rami  articulares) , 
usually  three  in  number,  supply  the 
knee-joint;  two  of  these  accompany 
the  superior  and  inferior  medial  genic- 
ular arteries;  and  a  third,  the  middle 
genicular  artery.  Just  above  the  bi- 
furcation of  the  nerve  an  articular 
branch  is  given  off  to  the  ankle-joint. 

Muscular  branches  {rami  musculares), 
four  or  five  in  number,  arise  from  the 
nerve  as  it  lies  between  the  two  heads 
of  the  Gastrocnemius  muscle;  they 
supply  that  muscle,  and  the  Plantaris, 
Soleus,  and  Popliteus.  The  branch 
for  the  Popliteus  turns  around  the  lower 
border  and  is  distributed  to  the  deep 
surface  of  the  muscle.  Lower  down, 
muscular  branches  arise  separately  or 
by  a  common  trunk  and  supply  the 
Soleus,  Tibialis  posterior.  Flexor  digi- 
torum  longus,  and  Flexor  hallucis 
longus;  the  branch  to  the  last  muscle 
accompanies  the  peroneal  artery;  that 
to  the  Soleus  enters  the  deep  surface 
of  the  muscle. 

The  medial  sural  cutaneous  nerve  {n. 
cutaneus  surce  medialis;  n.  communi- 
cans  tibialis)  descends  between  the 
two  heads  of  the  Gastrocnemius,  and, 
about  the  middle  of  the  back  of  the 
leg,  pierces  the  deep  fascia,  and  unites 
with  the  anastomotic  ramus  of  the 
common  peroneal  to  form  the  sural 
nerve  (Fig.  830). 


•  N.  B. — In  this  diagram  the  medial  sura     cutaneous  and  peroneal  anastomotic  are  not  in  their  normal  position. 
They  have  been  displaced  by  the  removal  of  the  superficial  muscles. 


V 


I 


THE  SACRAL  AND  COCCYGEAL  NERVES  963 

The  sural  nerve  (n.  suralis;  short  saphenous  nerve),  formed  by  the  junction  of  the 
medial  sural  cutaneous  with  the  peroneal  anastomotic  branch,  passes  downward 
near  the  lateral  margin  of  the  tendo  calcaneus,  lying  close  to  the  small  saphenous 
vein,  to  the  interval  between  the  lateral  malleolus  and  the  calcaneus.  It  runs 
forward  below  the  lateral  malleolus,  and  is  continued  as  the  lateral  dorsal  cutaneous 
nerve  along  the  lateral  side  of  the  foot  and  little  toe,  communicating  on  the  dorsum 
of  the  foot  with  the  intermediate  dorsal  cutaneous  nerve,  a  branch  of  the  superficial 
peroneal.  In  the  leg,  its  branches  communicate  with  those  of  the  posterior  femoral 
cutaneous. 

The  medial  calcaneal  branches  {rami  calcanei  mediales;  internal  calcaneal  branches) 
perforate  the  laciniate  ligament,  and  supply  the  skin  of  the  heel  and  medial  side 
of  the  sole  of  the  foot. 

The  medial  plantar  nerve  {n.  planiaris  medialis;  internal  plantar  nerve)  (Fig.  833), 
the  larger  of  the  two  terminal  divisions  of  the  tibial  nerve,  accompanies  the  medial 
plantar  artery.  From  its  origin  under  the  laciniate  ligament  it  passes  under  cover 
of  the  Abductor  hallucis,  and,  appearing  between  this  muscle  and  the  Flexor  digi- 
torum  brevis,  gives  off  a  proper  digital  plantar  nerve  and  finally  divides  opposite 
the  bases  of  the  metatarsal  bones  into  three  common  digital  plantar  nerves. 

Braxches. — The  branches  of  the  medial  plantar  nerve  are:  (1)  cutaneous, 
(2)  muscular,  (3)  articular,  (4)  a  proper  digital  nerve  to  the  medial  side  of  the  great 
toe,  and  (5)  three  common  digital  nerves. 

The  cutaneous  branches  pierce  the  plantar  aponeurosis  between  the  Abductor 
hallucis  and  the  Flexor  digitorum  brevis  and  are  distributed  to  the  skin  of  the  sole 
of  the  foot. 

The  muscular  branches  supply  the  Abductor  hallucis,  the  Flexor  digitorum  brevis, 
the  Flexor  hallucis  brevis,  and  the  first  Lumbricalis ;  those  for  the  Abductor  hallucis 
and  Flexor  digitorum  brevis  arise  from  the  trunk  of  the  nerve  near  its  origin  and 
enter  the  deep  surfaces  of  the  muscles;  the  branch  of  the  Flexor  hallucis  brevis 
springs  from  the  proper  digital  nerve  to  the  medial  side  of  the  great  toe,  and  that 
for  the  first  Lumbricalis  from  the  first  common  digital  nerve. 

The  articular  branches  supply  the  articulations  of  the  tarsus  and  metatarsus. 

The  proper  digital  nerve  of  the  great  toe  {nn.  digitales  plantares  proprii;  plantar 
digital  branches)  supplies  the  Flexor  hallucis  brevis  and  the  skin  on  the  medial  side 
of  the  great  toe. 

The  three  common  digital  nerves  {nn.  digitales  plantares  communes)  pass  between 
the  divisions  of  the  plantar  aponeurosis,  and  each  splits  into  two  proper  digital 
nerves — those  of  the  first  common  digital  nerve  supply  the  adjacent  sides  of  the 
great  and  second  toes;  those  of  the  second,  the  adjacent  sides  of  the  second  and 
third  toes;  and  those  of  the  third,  the  adjacent  sides  of  the  third  and  fourth  toes. 
The  third  common  digital  nerve  receives  a  communicating  branch  from  the  lateral 
plantar  nerve ;  the  first  gives  a  twig  to  the  first  Lumbricalis.  Each  proper  digital 
nerve  gives  off  cutaneous  and  articular  filaments;  and  opposite  the  last  phalanx 
sends  upward  a  dorsal  branch,  which  supplies  the  structures  around  the  nail, 
the  continuation  of  the  nerve  being  distributed  to  the  ball  of  the  toe.  It  will  be 
observed  that  these  digital  nerves  are  similar  in  their  distribution  to  those  of  the 
median  nerve  in  the  hand. 

The  Lateral  Plantar  Nerve  {n.  plantaris  lateralis;  external  plantar  nerve)  (Fig. 
833)  supplies  the  skin  of  the  fifth  toe  and  lateral  half  of  the  fourth,  as  well  as  most 
of  the  deep  muscles,  its  distribution  being  similar  to  that  of  the  ulnar  nerve  in  the 
hand.  It  passes  obliquely  forward  with  the  lateral  plantar  artery  to  the  lateral 
side  of  the  foot,  lying  between  the  Flexor  digitorum  brevis  and  Quadratus  plantse; 
and,  in  the  interval  between  the  former  muscle  and  the  Abductor  digiti  quinti, 
divides  into  a  superficial  and  a  deep  branch.  Before  its  division,  it  supplies  the 
Quadratus  plantse  and  Abductor  digiti  quinti. 


964 


NEUROLOGY 


The  superficial  branch  {ramus  swperficialis)  splits  into  a  proper  and  a  common 
digital  nerve;  the  proper  digital  nerve  supplies  the  lateral  side  of  the  little  toe, 

the  Flexor  digiti  quinti  brevis,  and  the  two 
Interossei  of  the  fourth  intermetatarsal  space; 
the  common  digital  nerve  communicates  with 
the  third  common  digital  branch  of  the  medial 
plantar  nerve  and  divides  into  two  proper 
digital  nerves  which  supply  the  adjoining 
sides  of  the  fourth  and  fifth  toes. 


Medial 
'plantar 


Lateral 
'plantar 


Deep 

branch 


Fig.  833. — The  plantar  nerves. 


Fig.  834. — Diagram  of  the  segmental  distribution  of  the 
cutaneous  nerves  of  the  sole  of  the  foot. 


The  deep  branch  (ramus  profundus;  muscular  branch)  accompanies  the  lateral 
plantar  artery  on  the  deep  surface  of  the  tendons  of  the  Flexor  muscles  and  the " 
Adductor  hallucis,  and  supplies  all  the  Interossei  (except  those  in  the  fourth 
metatarsal  space),  the  second,  third,  and  fourth  Lumbricales,  and  the  Adductor 
hallucis. 

The  Common  Peroneal  Nerve  (n.  peronoeus  communis;  external  popliteal  nerve; 
peroneal  nerve)  (Fig,  832),  about  one-half  the  size  of  the  tibial,  is  derived  from  the 
dorsal  branches  of  the  fourth  and  fifth  lumbar  and  the  first  and  second  sacral 
nerves.  It  descends  obliquely  along  the  lateral  side  of  the  popliteal  fossa  to  the  head 
of  the  fibula,  close  to  the  medial  margin  of  the  Biceps  femoris  muscle.  It  lies 
between  the  tendon  of  the  Biceps  femoris  and  lateral  head  of  the  Gastrocnemius 
muscle,  winds  around  the  neck  of  the  fibula,  between  the  Peronaeus  longus  and  the 
bone,  and  divides  beneath  the  muscle  into  the  superficial  and  deep  peroneal  nerves. 
Previous  to  its  division  it  gives  off  articular  and  lateral  sural  cutaneous  nerves. 

The  articular  branches  (rami  articulares)  are  three  in  number;  two  of  these  accom- 
pany the  superior  and  inferior  lateral  genicular  arteries  to  the  knee;  the  upper  one 
occasionally  arises  from  the  trunk  of  the  sciatic  nerve.  The  third  {recurrent) 
articular  nerve  is  given  off  at  the  point  of  division  of  the  common  peroneal  nerve; 
it  ascends  with  the  anterior  recurrent  tibial  artery  through  the  Tibialis  anterior  to 
the  front  of  the  knee. 

The  lateral  sural  cutaneous  nerve  {n.  cutaneus  suroe  lateralis;  lateral  cutaneous 
branch)  supplies  the  skin  on  the  posterior  and  lateral  surfaces  of  the  leg;  one 
branch,  the  peroneal  anastomotic  {n.  communicans  fibularis) ,  arises  near  the  head 
of  the  fibula,  crosses  the  lateral  head  of  the  Gastrocnemius  to  the  middle  of  the 


THE  SACRAL  AND  COCCYGEAL  NERVES 


965 


J  PATELLAR  BRANCH  OF 
IsAPHENOUS  NERVE 


COMMON    PERC 
NCAL    NERVE 


SUPERFICIAL 
PERONEAL    NERVE 


-SAPHENOUS    NERVE 


PERONEAL 
NERVE 


CUTANEOUS    BRANCH] 
OF   SUPERFICIAL 

PERONEAL       I 


leg,  and  joins  with  the  medial  sural  cutaneous  to  form  the  sural  nerve.  The 
peroneal  anastomotic  is  occasionally  continued  down  as  a  separate  branch  as  far 
as  the  heel. 

The  Deep  Peroneal  Nerve  (w.  peroncBus  profundus;  anterior  tibial  nerve)  (Fig. 
827)  begins  at  the  bifurcation  of  the  common  peroneal  nerve,  between  the  fibula 
and  upper  part  of  the  Peronseus 
longus,  passes  obliquely  forward 
beneath  the  Extensor  digitorum 
longus  to  the  front  of  the  inter- 
osseous membrane,  and  comes 
into  relation  with  the  anterior 
tibial  artery  above  the  middle 
of  the  leg;  it  then  descends  with 
the  artery  to  the  front  of  the 
ankle-joint,  where  it  divides  into 
a  lateral  and  a  medial  terminal 
branch.  It  lies  at  first  on  the 
lateral  side  of  the  anterior  tibial 
artery,  then  in  front  of  it,  and 
again  on  its  lateral  side  at  the 
ankle-joint. 

In  the  leg,  the  deep  peroneal 
nerve  supplies  muscular  branches 
to  the  Tibialis  anterior,  Extensor 
digitorum  longus,  Peronfeus  ter- 
tius,  and  Extensor  hallucis  pro- 
p  ius,  and  an  articular  branch  to 
the  ankle-joint. 

The  lateral  terminal  branch 
{external  or  tarsal  branch)  passes 
across  the  tarsus,  beneath  the 
>1xtensor  digitorum  brevis,  and, 
having  become  enlarged  like  the 
dorsal  interosseous  nerve  at  the 
wrist,  supplies  the  Extensor  digi- 
torumbrevis.  From  the  enlarge- 
ment three  minute  interosseous 
branches  are  given  off,  which  sup- 
ply the  tarsal  joints  and  the 
metatarsophalangeal  joints  of 
the  second,  third,  and  fourth 
toes.  The  first  of  these  sends  a 
filament  to  the  second  Inter- 
osseus  dorsalis  muscle. 

The  medial  terminal  branch 
{internal  branch)  accompanies 
the  dorsalis  pedis  artery  along 
the  dorsum  of  the  foot,  and,  at 
the  first  interosseous  space,  di- 
vides into  two  dorsal  digital 
nerves  {nn.  digitales  dorsales  hallucis  lateralis  et  digiti  secimdi  medialis)  which  supply 
the  adjacent  sides  of  the  great  and  second  toes,  communicating  with  the  medial 
dorsal  cutaneous  branch  of  the  superficial  peroneal  nerve.  Before  it  divides  it 
gives  off  to  the  first  space  an  interosseous  branch  which  supplies  the  metatarso- 


W 


.LATERAL  BRANCH  OF 
DEEP  PERONEAL 

.MEDIAL   TERMINAL 
BRANCH 

-DIGITORUM 


SURAL  NCRVE- 


FiG.  835. 


BRANCHES   OF 
SUPERFICIAL    PERONEAL 

-Deep  nerves  of  the  front  of  the  leg. 


(Testut. 


966 


NEUROLOGY 


MEDIAL  DORSAL  CUTA- 
NEOUS BFiANChI 
OF  SUPERFICIAL  DEEP 

PERONEAL         PERONEAL 
INTERMEDIAL  DORSAL 
CUTANEOUS    BRANCH 
OF   SUPERFICIAL 
PERONEAL 


SAPHENOUS  VEIN 


SAPHCNOUS 
NERVE 


LATERAL    BRANCH 
OF    DEEP  PERONEAL 


phalangeal  joint  of  the  great  toe  and  sends  a  filament  to  the  first  Interosseous 
dorsalis  muscle. 

The  Superficial  Peroneal  Nerve  {n.  yeronceus  swperfidalis;  musculocutaneous  nerve) 
(Figs.  827,  835)  supplies  the  Peronei  longus  and  brevis  and  the  skin  over  the  greater 
part  of  the  dorsum  of  the  foot.  It  passes  forward  between  the  Peronaii  and  the 
Extensor  digitorum  longus,  pierces  the  deep  fascia  at  the  lower  third  of  the  leg,  and 

divides  into  a  medial  and  an  inter- 
mediate dorsal  cutaneous  nerve.  In 
its  course  between  the  muscles,  the 
nerve  gives  off  muscular  branches 
to  the  Perouffii  longus  and  brevis, 
and  cutaneous  filaments  to  the 
integument  of  the  lower  part  of 
the  leg. 

The  medial  dorsal  cutaneous 
nerve  {n.  cutaneiis  dorsalis medialis; 
internal  dorsal  cutaneous  branch) 
passes  in  front  of  the  ankle-joint, 
and  divides  into  two  dorsal  digital 
branches,  one  of  which  supplies 
the  medial  side  of  the  great  toe, 
the  other,  the  adjacent  side  of  the 
second  and  third  toes.  It  also 
supplies  the  integument  of  the 
medial  side  of  the  foot  and  ankle, 
and  communicates  with  the  saphe- 
nous nerve,  and  with  the  deep 
peroneal  nerve  (Fig.  825). 

The  intermediate  dorsal  cuta- 
neous nerve  (n.  cutaneus  dorsalis 
intermedins;  external  dorsal  cuta- 
neous branch),  the  smaller,  passes 
along  the  lateral  part  of  the  dor- 
sum of  the  foot,  and  divides  into 
dorsal  digital  branches,  which  sup- 
ply the  contiguous  sides  of  the 
third  and  fourth,  and  of  the 
fourth  and  fifth  toes.  It  also 
supplies  the  skin  of  the  lateral 
side  of  the  foot  and  ankle,  and  communicates  with  the  sural  nerve  (Fig.  825). 
The  branches  of  the  superficial  peroneal  nerve  supply  the  skin  of  the  dorsal 
surfaces  of  all  the  toes  excepting  the  lateral  side  of  the  little  toe,  and  the  adjoining 
sides  of  the  great  and  second  toes,  the  former  being  supplied  by  the  lateral  dorsal 
cutaneous  nerve  from  the  sural  nerve,  and  the  latter  by  the  medial  branch  of  the 
deep  peroneal  nerve.  Frequently  some  of  the  lateral  branches  of  the  superficial 
peroneal  are  absent,  and  their  places  are  then  taken  by  branches  of  the  sural 
nerve. 

The  Pudendal  Plexus  {plexus  pudendum)  (Fig.  828).— The  pudendal  plexus  is 
not  sharply  marked  off  from  the  sacral  plexus,  and  as  a  consequence  some  of  the 
branches  which  spring  from  it  may  arise  in  conjunction  with  those  of  the  sacral 
plexus.  It  lies  on  the  posterior  wall  of  the  pelvis,  and  is  usually  formed  by  branches 
from  the  anterior  divisions  of  the  second  and  third  sacral  nerves,  the  whole  of  the 
anterior  divisions  of  the  fourth  and  fifth  sacral  nerves,  and  the  coccygeal  nerve. 


BRANCHES   OF 

EXTERNAL    PLAN 

TAR    NERVE 


BRANCHES    OF    INTERNAL 
PLANTAR    NERVE 


Fig.  836. — Nerves  of  the  dorsum  of  the  foot.     (Testut.) 


THE  SACRAL  AND  COCCYGEAL  NERVES 


967 


It  gives  off  the  following  branches: 

Perforating  cutaneous 
Pudendal       .        .        .        . 
Visceral  .        .        .        . 

Muscular       .        .        .        . 
Anococcygeal 


2,  3S. 

2,  3,  4  S. 

3,  4S. 
4S. 

4,  5  S.  and  Cocc. 


LATERAL    FEMORAL 


FIFTH 
LUMBAR 


EXTERNAL    SPER- 
MATIC   BRANCH    OF 
GENITO-CRURAU 
LUMBO-INGUINAL 

BRANCH    OF-- 
GENITO-CRURAL 


SYMPATHETIC 

TRUNK 

LUMBO-SACRAL 

CORD 

SUPERIOR 
GLUTEAL 

RAMUS 

COMMUNICANS 


VISCERAL 
BRANCHES 
NERVE    TO 
-LEVATOR  AN  I 

EMORRHOIDAL  BRANCH 
OF  PUOIO 


PUDENDAL 
PERINEAL 

POST.    FEMORAL 


EXTERNAL  SUPER- 
FICIAL  PERINEAL 

INTERNAL  SUPER- 
FICIAL PERINEAL 


NERVE   TO    BULB 


INFERIOR 
PUDENDAL 


Fig.  837. — Sacral  plexus  of  the  right  side.     (Testut). 

The  Perforating  Cutaneous  Nerve  (/i,  clunium  inferior  medialis)  usually  arises  from 
the  posterior  surface  of  the  second  and  third  sacral  nerves.  It  pierces  the  lower 
part  of  the  sacrotuberous  ligament,  and  winding  around  the  inferior  border  of  the 
Glutseus  maximus  supplies  the  skin  covering  the  medial  and  lower  parts  of  that 
muscle. 

The  perforating  cutaneous  nerve  may  arise  from  the  pudendal  or  it  may  be  absent;  in  the 
latter  case  its  place  may  be  taken  by  a  branch  from  the  posterior  femoral  cutaneous  nerve  or  by 
a  branch  from  the  third  and  fourth,  or  fourth  and  fifth,  sacral  nerves. 

The  Pudendal  Nerve  (n.  pudendus;  internal  pudic  nerve)  derives  its  fibers  from  the 
ventral  branches  of  the  second,  third,  and  fourth  sacral  nerves.  It  passes  between 
the  Piriformis  and  Coccygeus  muscles  and  leaves  the  pelvis  through  the  lower  part 
of  the  greater  sciatic  foramen.  It  then  crosses  the  spine  of  the  ischium,  and 
reenters  the  pelvis  through  the  lesser  sciatic  foramen.  It  accompanies  the  internal 
pudendal  vessels  upward  and  forward  along  the  lateral  wall  of  the  ischiorectal 


968  NEUROLOGY 

fossa,  being  contained  in  a  sheath  of  the  obturator  fascia  termed  Alcock's  canial, 
and  divides  into  two  terminal  branches,  viz.,  the  perineal  nerve,  and  the  dorsal  nerve 
of  the  penis  or  clitoris.     Before  its  division  it  gives  off  the  inferior  hemorrhoidal  nerve. 

The  inferior  hemorrhoidal  nerve  {n.  hcemorrhoidalis  inferior)  occasionally  arises 
directly  from  the  sacral  plexus;  it  crosses  the  ischiorectal  fossa,  with  the  inferior 
hemorrhoidal  vessels,  toward  the  anal  canal  and  the  lower  end  of  the  rectum, 
and  is  distributed  to  the  Sphincter  ani  externus  and  to  the  integument  around  the 
anus.  Branches  of  this  nerve  communicate  with  the  perineal  branch  of  the  posterior 
femoral  cutaneous  and  with  the  posterior  scrotal  nerves  at  the  forepart  of 
the  perineum. 

The  perineal  nerve  {n.  perinei),  the  inferior  and  larger  of  the  two  terminal  branches 
of  the  pudendal,  is  situated  below  the  internal  pudendal  artery.  It  accpmpanies 
the  perineal  artery  and  divides  into  posterior  scrotal  (or  labial)  and  muscular  branches. 

The  posterior  scrotal  (or  labial)  branches  (nn.  scrotales  (or  labiates)  posteriores; 
superficial  peroneal  nerves)  are  two  in  number,  medial  and  lateral.  They  pierce 
the  fascia  of  the  urogenital  diaphragm,  and  run  forward  along  the  lateral  part  of 
the  urethral  triangle  in  company  with  the  posterior  scrotal  branches  of  the  perineal 
artery;  they  are  distributed  to  the  skin  of  the  scrotum  and  communicate  with  the 
perineal  branch  of  the  posterior  femoral  cutaneous  nerve.  These  nerves  supply  the 
labium  majus  in  the  female. 

The  muscular  branches  are  distributed  to  the  Transversus  perinsei  superficialis. 
Bulbocavernous,  Ischiocavernosus,  and  Constrictor  urethrse.  A  branch,  the 
nerve  to  the  bulb,  given  off  from  the  nerve  to  the  Bulbocavernosus,  pierces  this 
muscle,  and  supplies  the  corpus  cavernosum  urethrse,  ending  in  the  mucous 
membrane  of  the  urethra. 

The  dorsal  nerve  of  the  penis  (n.  dorsalis  penis)  is  the  deepest  division  of  the  puden- 
dal nerve;  it  accompanies  the  internal  pudendal  artery  along  the  ramus  of  the 
ischium;  it  then  runs  forward  along  the  margin  of  the  inferior  ramus  of  the  pubis, 
between  the  superior  and  inferior  layers  of  the  fascia  of  the  urogenital  diaphragm. 
Piercing  the  inferior  layer  it  gives  a  branch  to  the  corpus  cavernosum  penis,  and 
passes  forward,  in  company  with  the  dorsal  artery  of  the  penis,  between  the  layers 
of  the  suspensory  ligament,  on  to  the  dorsum  of  the  penis,  and  ends  on  the  glans 
penis.  In  the  female  this  nerve  is  very  small,  and  supplies  the  clitoris  (w.  dorsalis 
clitoridis). 

The  Visceral  Branches  arise  from  the  third  and  fourth,  and  sometimes  from  the 
second,  sacral  nerves,  and  are  distributed  to  the  bladder  and  rectum  and,  in  the 
female,  to  the  vagina;  they  communicate  with  the  pelvic  plexuses  of  the  sympathetic. 

The  Muscular  Branches  are  derived  from  the  fourth  sacral,  and  supply  the  Levator 
ani,  Coccygeus,  and  Sphincter  ani  externus.  The  branches  to  the  Levator  ani 
and  Coccygeus  enter  their  pelvic  surfaces;  that  to  the  Sphincter  ani  externus 
(perineal  branch)  reaches  the  ischiorectal  fossa  by  piercing  the  Coccygeus  or  by 
passing  between  it  and  the  Levator  ani.  Cutaneous  filaments  from  this  branch 
supply  the  skin  between  the  anus  and  the  coccyx. 

Anococcygeal  Nerves  (nn.  anococcygei). — The  fifth  sacral  nerve  receives  a  com- 
municating filament  from  the  fourth,  and  unites  with  the  coccygeal  nerve  to  form 
the  coccygeal  plexus.  From  this  plexus  the  anococcygeal  nerves  take  origin;  they 
consist  of  a  few  fine  filaments  which  pierce  the  sacrotuberous  ligament  to  supply 
the  skin  in  the  region  of  the  coccyx. 

THE   SYMPATHETIC   NERVOUS   SYSTEM. 

The  sympathetic  nervous  system  (Fig.  838)  innervates  all  the  smooth  muscles  and 
the  various  glands  of  the  body,  and  the  striated  muscle  of  the  heart.  The  efferent 
sympathetic  fibers  which  leave  the  central  nervous  system  in  connection   with 


THE  SYMPATHl 


m 


969 


certain  of  the  cranial  and  spinal  nerves  all  end  in  sympathetic  ganglia  and  are 
kno\^Ti  as  preganglionic  fibers.     From  these  ganglia  postganglionic  fibers  arise  and 


Maxillary  nerve 
Ciliary  ganglion 
Sphenopalatine  ganglion 
Superior  cervicai  ganglion  of  sympathetic 


Cervical  pleams  ■ 


Brachial  jHextts 


Cheater  splanchnic 
nerve 

Lesser  splaivchnic 
nerve 


Lumbar  plexus 


Sacral  plexus 


Pharyngeal  plexus 

Middle  cervical  ganglion  of 

sympathetic 
Inferior  cervical  ganglion  of 

sympathetic 
Recurrent  nerve 

Bronchial  plexus 


Cardiac  plexus 


(Esophageal  plexus 
Coronary  plexuses 


Left  vagus  nerve 

Gastric  plexus 
Ccdiac  plexus 

Superior  mesenteric 
plexus 


Aortic  plexus 

Inferior  mesenteric 
plexus 

Hypogastric  plexus 


Pelvic  plexus 

Bladder 
Vesical  plexus 


Fig    838. — The  right  sympathetic  chain  and  its  connections  with  the  thoracic,  abdominal,  and  pelvic  plezusea. 

(After  Schwalbe.) 

conduct  impulses  to  the  different  organs.    In  addition,  afferent  or  sensory  fibers 
connect  many  of  these  structures  with  the  central  nervous  system. 


970 


NEUROLOGY 


The  peripheral  portion  of  the  sympathetic  nervous  system  is  characterized  by 
the  presence  of  numerous  ganglia  and  complicated  plexuses.  These  ganglia  are 
connected  with  the  central  nervous  system  by  three  groups  of  sympathetic  efferent 
or  preganglionic  fibers,  i,  e.,  the  cranial,  the  thoracolumbar,  and  the  sacral.  These 
outflows  of  sympathetic  fibers  are  separated  by  intervals  where  no  connections 
exist.  The  cranial  and  sacral  sympathetics  are  often  grouped  together  owing  to 
the  resemblance  between  the  reactions  produced  by  stimulating  them  and  by  the 
effects  of  certain  drugs.  Acetyl-choline,  for  example,  when  injected  intravenously 
in  very  small  doses,  produces  the  same  effect  as  the  stimulation  of  the  cranial  or 
sacral  sympathetics,  while  the  introduction  of  adrenalin  produces  the  same  effect 
as  the  stimulation  of  the  thoracolumbar  sympathetics.  Much  of  our  present 
knowledge  of  the  sjTTipathetic  nervous  system  has  been  acquired  through  the  appli- 
cation of  various  drugs,  especially  nicotine  which  paral;s'zes  the  connections  or 
synapses  between  the  preganglionic  and  postganglionic  fibers  of  the  sympathetic 
nerves.  When  it  is  injected  into  the  general  circulation  all  such  synapses  are 
paralyzed;  when  it  is  applied  locally  on  a  ganglion  only  the  sjmapses  occurring  in 
that  particular  ganglion  are  paralyzed. 

Langley,^  who  has  contributed  greatly  to  our  knowledge,  adopted  a  terminology 
somewhat  different  from  that  used  here  and  still  different  from  that  used  by  the 
pharmacologists.  This  has  led  to  considerable  confusion,  as  shown  by  the  arrange- 
ment of  the  terms  in  the  following  colmnns.  Gaskell  has  used  the  term  involuntary 
nervous  svstem.^ 


Gray. 

Sympathetic  nervous  system. 
Cranio-sacral  sympathetics. 

Oculomotor  sympathetics. 

Facial  sympathetics. 

Glossopharyngeal  sympathetics. 

Vagal  sympathetics. 

Sacral  sympathetics. 
Thoracolumbar  sympathetics. 

Enteric. 


Langley. 
Autonomic  nervous  system. 
Parasympathetics. 
Tectal  autonomics. 

Bulbar  autonomics. 

Sacral  autonomics. 
Sympathetic. 

Thoracic  autonomic. 
Enteric. 


Meyer  and  Gottlieb.' 

Vegetative  nervous  system. 
Autonomic. 

Cranial  autonomics. 


Sacral  autonomics. 
Sympathetic. 


Enteric. 


THE  CRANIAL  SYMPATHETICS. 

The  cranial  sympathetics  include  sympathetic  efferent  fibers  in  the  oculomotor, 
facial,  glossopharyngeal  and  vagus  nerves,  as  well  as  sympathetic  afferent  in  the 
last  three  nerves. 

The  Sympathetic  Efferent  Fibers  of  the  Oculomotor  Nerve  probably  arise  from  cells 
in  the  anterior  part  of  the  oculomotor  nucleus  which  is  located  in  the  tegmentum 
of  the  mid-brain.  These  preganglionic  fibers  run  with  the  third  nerve  into  the  orbit 
and  pass  to  the  ciliar/  ganglion  where  they  terminate  by  forming  synapses  with 
sympathetic  motor  neurons  whose  axons,  postganglionic  fibers,  proceed  as  the  short 
ciliary  nerves  to  the  eyeball.  Here  they  supply  motor  fibers  to  the  Ciliaris  muscle 
and  the  Sphincter  pupillse  muscle.  So  far  as  known  there  are  no  sympathetic 
afferent  fibers  connected  with  the  nerve. 

The  Sympathetic  Efferent  Fibers  of  the  Facial  Nerve  are  supposed  to  arise  from  the 
small  cells  of  the  facial  nucleus.  According  to  some  authors  the  fibers  to  the  sali- 
vary glands  arise  from  a  special  nucleus,  the  superior  salivatory  nucleus,  consisting 
of  cells  scattered  in  the  reticular  formation,  dorso-medial  to  the  facial  nucleus. 
These  preganglionic  fibers  are  distributed  partly  through  the  chorda  tympani  and 


1  Schafer.     Textbook  of  Physiology,  1900. 

2  Gaskell,  W.  H.,  The  Involuntary  Nervous  System,  London,  1916. 
•  Die  Experimentelle  Pharmakologie,  1910. 


THE  CRANl 

lingual  nerves  to  the  submaxillary  ganglion  where  they  terminate  about  the  cell 
bodies  of  neurons  whose  axons  as  postganglionic  fibers  conduct  secretory  and  vaso- 


Lacrimal  gland 

Mucous  mem, 
nose  and  palate 

Submaxillary  gland 

Sublingual  gland 

Mucous  mem,  mouth 
Parotid  gland 


Bladder 


Sexual  organs 


External  genitalia, 


Fig.  839. — Diagram  of  efferent  sympathetic  nervous  system.     Blue,  cranial  and  sacral  outflow.     Red,  thoraco- 

humeral  outflow.     ,  Postganglionic  fibers  to  spinal  and  cranial  nerves  to  supply  vasomotors  to  head,  trunk  and 

limbs,  motor  fibers  to  smooth  muscles  of  skin  and  fibers  to  sweat  glands.     (Modifiecf  after  Meyer  and  Gottlieb.) 


972 


NEUROLOGY 


dilator  impulses  to  the  submaxillary  and  sublingual  glands.  Other  preganglionic 
fibers  of  the  facial  nerve  pass  via  the  great  superficial  petrosal  nerve  to  the  spheno- 
palatine ganglion  where  they  form  synapses  with  neurons  whose  postganglionic 
fibers  are  distributed  with  the  superior  maxillary  nerve  as  vasodilator  and  secretory 
fibers  to  the  mucous  membrane  of  the  nose,  soft  palate,  tonsils,  uvula,  roof  of  the 
mouth,  upper  lips  and  gums,  parotid  and  orbital  glands. 

There  are  supposed  to  be  a  few  s^Tnpathetic  afferent  fibers  connected  with  the 
facial  nerve,  whose  cell  bodies  lie  in  the  geniculate  ganglion,  but  very  little  is  known 
about  them. 


Sympathetic 
efferent  fibers , 


Midbrain 


Medulla 


Short  ciliary  nerve  to  ciliary  muscle 
Ciliary  ganglion 


I 
I 


Long  ciliary  nerve  to  p 
Dilator  pupillce 


Carotid  plexus 
Postganglionie  fibers 

Superior  cervical  ganglion 


Short  ciliary  nerve  to 
Sphincter  pupillce 


I.  Thoracic  ganglion 


Sympathetic  efferent  {preganglionic)  fibers 

Fio.  840. — Sympathetic  connections  of  the  ciliary  and  superior  cervical  ganglia. 

The  Sympathetic  Afferent  Fibers  of  the  Glossopharyngeal  Nerve  are  supposed  to  arise 
either  in  the  dorsal  nucleus  (nucleus  ala  cinerea)  or  in  a  distinct  nucleus,  the  inferior 
salivatory  nucleus,  situated  near  the  dorsal  nucleus.  These  preganglionic  fibers 
pass  into  the  tympanic  branch  of  the  glossopharyngeal  and  then  with  the  small 
superficial  petrosal  nerve  to  the  otic  ganglion.  Postganglionic  fibers,  vasodilator 
and  secretory  fibers,  are  distributed  to  the  parotid  gland,  to  the  mucous  membrane 
and  its  glands  on  the  tongue,  the  floor  of  the  mouth,  and  the  lower  gums. 

Sympathetic  Afferent  Fibers,  whose  cells  of  origin  lie  in  the  superior  or  inferior 
ganglion  of  the  trunk,  are  supposed  to  terminate  in  the  dorsal  nucleus.  Very  little 
is  known  of  the  peripheral  distribution  of  these  fibers. 

The  Sympathetic  Efferent  Fibers  of  the  Vagus  Nerve  are  supposed  to  arise  in  the 
dorsal  nucleus  (nucleus  ala  cinerea) .  These  preganglionic  fibers  are  all  supposed  to 
end  in  sympathetic  ganglia  situated  in  or  near  the  organs  supplied  by  the  vagus  sym- 


THE  SACRAL  SYMPATHETICS 


973 


pathetics.  The  inhibitory  fibers  to  the  heart  probably  terminate  in  the  small  ganglia 
of  the  heart  wall  especially  the  atrium,  from  which  inhibitory  postganglionic  fibers 
are  distributed  to  the  musculature.  The  preganglionic  motor  fibers  to  the  esophagus, 
the  stomach,  the  small  intestine,  and  the  greater  part  of  the  large  intestine  are 
supposed  to  terminate  in  the  plexuses  of  Auerbach,  from  which  postganglionic 
fibers  are  distributed  to  the  smooth  muscles  of  these  organs.  Other  fibers  pass  to 
the  smooth  muscles  of  the  bronchial  tree  and  to  the  gall-bladder  and  its  ducts. 
In  addition  the  vagus  is  believed  to  contain  secretor\'  fibers  to  the  stomach  and 
pancreas.  It  probably  contains  many  other  efferent  fibers  than  those  enumerated 
above. 


Greater  superior  petrosal 
I 

Sphenopalatine  ganglion 


Lacrimal 
gland 


I 


Fig.  841. — Sympathetic  connections  of  the  sphenopalatine  and  superior  cervical  gangha. 

Sympathetic  Afferent  Fibers  of  the  Vagus,  whose  cells  of  origin  lie  in  the  jugular 
ganglion  or  the  ganglion  nodosum,  probably  terminate  in  the  dorsal  nucleus  of  the 
medulla  oblongata  or  according  to  some  authors  in  the  nucleus  of  the  tractus 
solitarius.  Peripherally  the  fibers  are  supposed  to  be  distributed  to  the  various 
organs  supplied  by  the  s\Tnpathetic  efferent  fibers. 

THE  SACRAL  SYMPATHETICS. 

The  Sacral  Sympathetic  Efferent  Fibers  leave  the  spinal  cord  with  the  anterior  roots 
of  the  second,  third  and  fourth  sacral  nerves.  These  small  medullated  preganglionic 
fibers  are  collected  together  in  the  pelvis  into  the  nervus  erigentes  or  pelvic  nerve 


974 


NEUROLOGY 


I 


which  proceeds  to  the  hypogastric  or  pelvic  plexuses  from  which  postganglionic 
fibers  are  distributed  to  the  pelvic  viscera.  Motor  fibers  pass  to  the  smooth  muscle 
of  the  descending  colon,  rectum,  anus  and  bladder.  Vasodilators  are  distributed 
to  these  organs  and  to  the  external  genitalia,  while  inhibitory  fibers  probably  pass 
to  the  smooth  muscles  of  the  external  genitalia.  Afferent  sympathetic  fibers  conduct 
impulses  from  the  pelvic  viscera  to  the  second,  third  and  fourth  sacral  nerves. 
Their  cells  of  origin  lie  in  the  spinal  ganglia. 


—  Submaxillary  ganglion 

-Sublingual  gland 
Submaxillary  gland 


I.Th. 


Fig.  842. — Sympathetic  connections  of  the  submaxillary  and  superior  cervical  ganglia. 

THE  THORACOLUMBAR  SYMPATHETICS. 

The  thoracolumbar  sympathetic  fibers  arise  from  the  dorso-lateral  region  of  the 
anterior  column  of  the  gray  matter  of  the  spinal  cord  and  pass  with  the  anterior 
roots  of  all  the  thoracic  and  the  upper  two  or  three  lumbar  spinal  nerves.  These 
preganglionic  fibers  enter  the  white  rami  communicantes  and  proceed  to  the 
sympathetic  trunk  where  many  of  them  end  in  its  ganglia,  others  pass  to  the  pre- 
vertebral plexuses  and  terminate  in  its  collateral  ganglia.  The  postganglionic 
fibers  have  a  wide  distribution.  The  vasoconstrictor  fibers  to  the  bloodvessels  of  the 
skin  of  the  trunk  and  limbs,  for  example,  leave  the  spinal  cord  as  preganglionic 
fibers  in  all  the  thoracic  and  the  upper  two  or  three  lumbar  spinal  nerves  and 
terminate  in  the  ganglia  of  the  sympathetic  trunk,  either  in  the  ganglion  directly 
connected  with  its  ramus  or  in  neighboring  ganglia.     Postganglionic  fibers  arise 


THE  THORACOLUMBAR  SYMPATHETICS 


975 


in  these  ganglia,  pass  through  gray  rami  communicantes  to  all  the  spinal  nerves, 
and  are  distributed  with  their  cutaneous  branches,  ultimately  leaving  these  branches 
to  join  the  small  arteries.  The  postganglionic  fibers  do  not  necessarily  return  to 
the  same  spinal  nerves  which  contain  the  corresponding  preganglionic  fibers.  The 
vasoconstrictor  fibers  to  the  head  come  from  the  upper  thoracic  nerves,  the  pre- 
ganglionic fibers  end  in  the  superior  cervical  ganglion.  The  postganglionic  fibers 
pass  through  the  internal  carotid  nerve  and  branch  from  it  to  join  the  sensory 
branches  of  the  various  cranial  nerves,  especially  the  trigeminal  nerve;  other  fibers 
to  the  deep  structiu*es  and  the  salivary  glands  probably  accompany  the  arteries. 


,  I  -—Auriculotemporal 
Parotid  gland, 

Tympanic  nerve 


Fig.  843. — Sympathetic  connections  of  the  otic  and  superior  cervical  ganglia. 

The  postganglionic  vasoconstrictor  fibers  to  the  bloodvessels  of  the  abdominal 
viscera  arise  in  the  prevertebral  or  collateral  ganglia  in  which  terminate  many 
preganglionic  fibers.  Vasoconstrictor  fibers  to  the  pelvic  viscera  arise  from  the 
inferior  mesenteric  ganglia. 

The  pilomotor  fibers  to  the  hairs  and  the  motor  fibers  to  the  sweat  glands  appar- 
ently have  a  distribution  similar  to  that  of  the  vasoconstrictors  of  the  skin. 

A  vasoconstrictor  center  has  been  located  by  the  physiologists  in  the  neighbor- 
hood of  the  facial  nucleus.  Axons  from  its  cells  are  supposed  to  descend  in  the  spinal 
cord  to  terminate  about  cell  bodies  of  the  preganglionic  fibers  located  in  the  dorso- 
lateral portion  of  the  anterior  column  of  the  thoracic  and  upper  lumbar  region. 

The  motor  supply  to  the  dilator  pupillse  muscle  of  the  eye  comes  from  pregan- 


H 


NEUROLOGY 

glionic  s\Tnpathetic  fibers  which  leave  the  spinal  cord  with  the  anterior  roots  of  the 
upper  thoracic  nerves.  These  fibers  pass  to  the  sympathetic  trunk  through  the  im 
white  rami  communicantes  and  terminate  in  the  superior  cervical  ganglion.  Post-  ^| 
ganglionic  fibers  from  the  superior  cervical  ganglion  pass  through  tlae  internal 
carotid  nerve  and  the  ophthalmic  division  of  the  trigeminal  nerve  to  the  orbit 
where  the  long  ciliary  nerves  conduct  the  impulses  to  the  eyeball  and  the  dilator 
pupillse  muscle.  The  cell  bodies  of  these  preganglionic  fibers  are  connected  with 
fibers  which  descend  from  the  mid-brain. 

Other  postganglionic  fibers  from  the  superior  cervical  ganglion  are  distributed  as 
secretory  fibers  to  the  salivary  glands,  the  lacrimal  glands  and  to  the  small  glands  j_ 
of  the  mucous  membrane  of  the  nose,  mouth  and  pharynx.  II 

The  thoracic  sympathetics  supply  accelerator  nerves  to  the  heart.  They  are 
supposed  to  emerge  from  the  spinal  cord  in  the  anterior  roots  of  the  upper  four  or 
five  thoracic  nerves  and  pass  with  the  white  rami  to  the  first  thoracic  ganglion, 
here  some  terminate,  others  pass  in  the  ansa  subclavia  to  the  inferior  cervical 
ganglion.  The  postganglionic  fibers  pass  from  these  ganglia  partly  through  the 
ansa  subclavia  to  the  heart,  on  their  way  they  intermingle  with  sympathetic  fibers 
from  the  vagus  to  form  the  cardiac  plexus. 

Inhibitory  fibers  to  the  smooth  musculature  of  the  stomach,  the  small  intestine 
and  most  of  the  large  intestine  are  supposed  to  emerge  in  the  anterior  roots  of  the 
lower  thoracic  and  upper  lumbar  nerves.  These  fibers  pass  through  the  white  rami 
and  sympathetic  trunk  and  are  conveyed  by  the  splanchnic  nerves  to  the  pre- 
vertebral plexus  where  they  terminate  in  the  collateral  ganglia.  From  the  celiac  and 
superior  mesenteric  ganglia  postganglionic  fibers  (inhibitory)  are  distributed  to  the 
stomach,  the  small  intestine  and  most  of  the  large  intestine.  Inhibitory  fibers  to 
the  descending  colon,  the  rectum  and  Internal  sphincter  ani  are  probably  post- 
ganglionic fibers  from  the  inferior  mesenteric  ganglion. 

The  thoracolumbar  sympathetics  are  characterized  by  the  presence  of  numerous 
ganglia  which  may  be  divided  into  two  groups,  central  and  collateral. 

The  central  ganglia  are  arranged  in  two  vertical  rows,  one  on  either  side  of  the 
middle  line,  situated  partly  in  front  and  partly  at  the  sides  of  the  vertebral  column. 
Each  ganglion  is  joined  by  intervening  nervous  cords  to  adjacent  ganglia  so  that 
two  chains,  the  sympathetic  trunks,  are  formed.  The  collateral  ganglia  are  found 
in  connection  with  three  great  prevertebral  plexuses,  placed  within  the  thorax, 
abdomen,  and  pelvis  respectively. 

The  sympathetic  trunks  {truncus  sympathicus;  gangliated  cord)  extend  from  the 
base  of  the  skull  to  the  coccyx.  The  cephalic  end  of  each  is  continued  upward 
through  the  carotid  canal  into  the  skull,  and  forms  a  plexus  on  the  internal  carotid 
artery;  the  caudal  ends  of  the  trunks  converge  and  end  in  a  single  ganglion,  the 
ganglion  impar,  placed  in  front  of  the  coccyx.  The  ganglia  of  each  trunk  are  dis- 
tinguished as  cervical,  thoracic,  lumbar,  and  sacral  and,  except  in  the  neck,  they 
closely  correspond  in  number  to  the  vertebrae.    They  are  arranged  thus: 


Cervical  portion  ....         ...  3  ganglia 

Thoracic      "         . 12 

Lumbar       " 4 

Sacral  " 4  or  5  " 


m 


In  the  neck  the  ganglia  lie  in  front  of  the  transverse  processes  of  the  vertebrae; 
in  the  thoracic  region  in  front  of  the  heads  of  the  ribs;  in  the  lumbar  region  on  the 
sides  of  the  vertebral  bodies ;  and  in  the  sacral  region  in  front  of  the  sacrum. 

Connections  with  the  Spinal  Nerves. — Communications  are  established  between 
the  sympathetic  and  spinal  nerves  through  what  are  known  as  the  gray  and  white 
rami  communicantes  (Fig.  799) ;  the  gray  rami  convey  sympathetic  fibers  into  the 
spinal  nerves  and  the  white  rami  transmit  spinal  fibers  into  the  sympathetic. 


11^' 


ll!: 


THE  CEPHALIC  PORTION  OF  THE  SYMPATHETIC  SYSTEM        977 

ach  spinal  nerve  receives  a  gray  ramus  communicans  from  the  sympathetic 
trunk,  but  white  rami  are  not  supplied  by  all  the  spinal  nerves.  White  rami  are 
derived  from  the  first  thoracic  to  the  first  lumbar  nerves  inclusive,  while  the 
isceral  branches  which  run  from  the  second,  third,  and  fourth  sacral  nerves  directly 
to  the  pelvic  plexuses  of  the  sympathetic  belong  to  this  category.  The  fibers  which 
reach  the  sympathetic  through  the  white  rami  communicantes  are  medullated; 
those  which  spring  from  the  cells  of  the  sympathetic  ganglia  are  almost  entirely 
non-medullated.  The  sympathetic  nerves  consist  of  efferent  and  afferent  fibers,  the 
origin  and  course  of  which  are  described  on  page  920) . 

The  three  great  gangliated  plexuses  {collateral  ganglia)  are  situated  in  front  of 
the  vertebral  column  in  the  thoracic,  abdominal,  and  pelvic  regions,  and  are  named, 
respectively,  the  cardiac,  the  solar  or  epigastric,  and  the  hypogastric  plexuses. 
The}'  consist  of  collections  of  nerves  and  ganglia;  the  nerves  being  derived  from 
the  sympathetic  trunks  and  from  the  cerebrospinal  nerves.  They  distribute 
branches  to  the  viscera. 

Development. — The  ganglion  cells  of  the  sympathetic  system  are  derived  from 
;he  cells  of  the  neural  crests.  As  these  crests  move  forward  along  the  sides  of  the 
neural  tube  and  become  segmented  off  to  form  the  spinal  ganglia,  certain  cells 
detach  themselves  from  the  ventral  margins  of  the  crests  and  migrate  toward  the 
sides  of  the  aorta,  where  some  of  them  are  grouped  to  form  the  ganglia  of  the 
s^TTipathetic  trunks,  while  others  undergo  a  further  migration  and  form  the  ganglia 
of  the  prevertebral  and  visceral  plexuses.  The  ciliary,  sphenopalatine,  otic,  and 
submaxillary  ganglia  which  are  found  on  the  branches  of  the  trigeminal  nerve  are 
formed  by  groups  of  cells  which  have  migrated  from  the  part  of  the  neural  crest 
which  gives  rise  to  the  semilunar  ganglion.  Some  of  the  cells  of  the  ciliary  ganglion 
are  said  to  migrate  from  the  neural  tube  along  the  oculomotor  nerve. 


THE    CEPHALIC   PORTION    OF    THE    SYMPATHETIC    SYSTEM    (PARS 
CEPHALIC  A   S.    SYMPATHICI). 


The  cephaUc  portion  of  the  sympathetic  system  begins  as  the  internal  carotid 
nerve,  which  appears  to  be  a  direct  prolongation  of  the  superior  cervical  ganglion. 
It  is  soft  in  texture,  and  of  a  reddish  color.  It  ascends  by  the  side  of  the  internal 
carotid  artery,  and,  entering  the  carotid  canal  in  the  temporal  bone,  divides  into 
two  branches,  which  lie  one  on  the  lateral  and  the  other  on  the  medial  side  of  that 
vessel. 

I   The  lateral  hranch,  the  larger  of  the  two,  distributes  filaments  to  the  internal 
carotid  artery,  and  forms  the  internal  carotid  plexus. 

The  medial  branch  also  distributes  filaments  to  the  internal  carotid  artery,  and, 
continuing  onward,  forms  the  cavernous  plexus. 

The  internal  carotid  plexus  (plexus  caroticus  internus;  carotid  plexus)  is  situated 
on  the  lateral  side  of  the  internal  carotid  artery,  and  in  the  plexus  there  occasionally 
exists  a  small  gangliform  swelling,  the  carotid  ganglion,  on  the  under  surface  of 
the  artery.  The  internal  carotid  plexus  communicates  with  the  semilunar  gan- 
glion, the  abducent  nerve,  and  the  sphenopalatine  ganglion;  it  distributes  filaments 
to  the  wall  of  the  carotid  artery,  and  also  communicates  with  the  tympanic  branch 
of  the  glossopharyngeal  nerve. 

The  communicating  branches  with  the  abducent  nerve  consist  of  one  or  two 
filaments  which  join  that  nerve  as  it  lies  upon  the  lateral  side  of  the  internal  carotid 
artery.  The  communication  with  the  sphenopalatine  ganglion  is  effected  by  a 
branch,  the  deep  petrosal,  given  oft'  from  the  plexus  on  the  lateral  side  of  the  artery; 
this  branch  passes  through  the  cartilage  filling  up  the  foramen  lacerum,  and  joins 
the  greater  superficial  petrosal  to  form  the  nerve  of  the  pterygoid  canal  (Vidian 
nerve),  which  passes  through  the  pterygoid  canal  to  the  sphenopalatine  ganglion. 
62 


978  NEUROLOGY 

The  communication  with  the  tympanic  branch  of  the  glossopharyngeal  nerve  is 
effected  by  the  caroticotympanic,  which  may  consist  of  two  or  three  delicate 
filaments. 

The  cavernous  plexus  {plexus  cavernosus)  is  situated  below  and  medial  to  that 
part  of  the  internal  carotid  artery  which  is  placed  by  the  side  of  the  sella  turcica 
in  the  cavernous  sinus,  and  is  formed  chiefly  by  the  medial  division  of  the  internal 
carotid  nerve.  It  communicates  with  the  oculomotor,  the  trochlear,  the  ophthalmic 
and  the  abducent  nerves,  and  with  the  ciliary  ganglion,  and  distributes  filaments  to 
the  wall  of  the  internal  carotid  artery.  The  branch  of  communication  with  the 
oculomotor  nerve  joins  that  nerve  at  its  point  of  division;  the  branch  to  the  troch- 
lear nerve  joins  it  as  it  lies  on  the  lateral  wall  of  the  cavernous  sinus;  other  filaments 
are  connected  with  the  under  surface  of  the  ophthalmic  nerve;  and  a  second  fila- 
ment joins  the  abducent  nerve. 

The  filaments  of  connection  with  the  ciliary  ganglion  arise  from  the  anterior  part 
of  the  cavernous  plexus  and  enter  the  orbit  through  the  superior  orbital  fissure; 
they  may  join  the  nasociliary  branch  of  the  ophthalmic  nerve,  or  be  continued  for- 
ward as  a  separate  branch. 

The  terminal  filaments  from  the  internal  carotid  and  cavernous  plexuses  are 
prolonged  as  plexuses  around  the  anterior  and  middle  cerebral  arteries  and  the 
ophthalmic  artery;  along  the  former  vessels,  they  may  be  traced  to  the  pia  mater; 
along  the  latter,  into  the  orbit,  where  they  accompany  each  of  the  branches  of  the 
vessel.  The  filaments  prolonged  on  to  the  anterior  communicating  artery  connect 
the  sympathetic  nerves  of  the  right  and  left  sides. 


THE   CERVICAL   PORTION   OF   THE   SYMPATHETIC   SYSTEM    (PARS 
CERVICALIS    S.    SYMPATHICI). 

The  cervical  portion  of  the  sympathetic  trunk  consists  of  three  ganglia,  distin- 
guished, according  to  their  positions,  as  the  superior,  middle,  and  inferior  ganglia, 
connected  by  intervening  cords.  This  portion  receives  no  white  rami  communi- 
cantes  from  the  cervical  spinal  nerves;  its  spinal  fibers  are  derived  from  the  white 
rami  of  the  upper  thoracic  nerves,  and  enter  the  corresponding  thoracic  ganglia 
of  the  sympathetic  trunk,  through  which  they  ascend  into  the  neck. 

The  superior  cervical  ganglion  (ganglion  cervicale  superius),  the  largest  of  the 
three,  is  placed  opposite  the  second  and  third  cervical  vertebrae.  It  is  of  a  reddish- 
gray  color,  and  usually  fusiform  in  shape;  sometimes  broad  and  flattened,  and  occa- 
sionally constricted  at  intervals;  it  is  believed  to  be  formed  by  the  coalescence 
of  four  ganglia,  corresponding  to  the  upper  four  cervical  nerves.  It  is  in  relation, 
m  front,  with  the  sheath  of  the  internal  carotid  artery  and  internal  jugular  vein; 
behind,  with  the  Longus  capitis  muscle. 

Its  branches  may  be  divided  into  inferior,  lateral,  medial,  and  anterior. 

The  Inferior  Branch  communicates  with  the  middle  cervical  ganglion. 

The  Lateral  Branches  (external  branches)  consist  of  gray  rami  communicantes  to 
the  upper  four  cervical  nerves  and  to  certain  of  the  cranial  nerves.  Sometimes  the 
branch  to  the  fourth  cervical  nerve  may  come  from  the  trunk  connecting  the 
upper  and  middle  cervical  ganglia.  The  branches  to  the  cranial  nerves  consist 
of  delicate  filaments,  which  run  to  the  ganglion  nodosum  of  the  vagus,  and  to  the 
hypoglossal  nerve.  A  filament,  the  jugular  nerve,  passes  upward  to  the  base  of 
the  skull,  and  divides  to  join  the  petrous  ganglion  of  the  glossopharyngeal,  and  the 
jugular  ganglion  of  the  vagus. 

The  Medial  Branches  (internal  branches)  are  peripheral,  and  are  the  lamygo- 
pharyngeal  branches  and  the  superior  cardiac  nerve. 

The  larjmgopharyngeal  branches  (rami  laryngopharyngei)  pass  to  the  side  of  the 


THE  CERVICAL  PORTION  OF  Ti 


^ATRETIC  SYSTEM 


979 


pharynx,  where  they  join  with  branches  from  the  glossopharyngeal,  vagus,  and 
external  laryngeal  nerves  to  form  the  pharjmgeal  plexus. 

The  superior  cardiac  nerve  (n.  cardiacus  superior)  arises  by  two  or  more  branches 
from  the  superior  cervical  ganglion,  and  occasionally  receives  a  filament  from  the 
trunk  between  the  first  and  second  cervical  ganglia.  It  runs  down  the  neck  behind 
the  common  carotid  artery,  and  in  front  of  the  Longus  colli  muscle;  and  crosses 
in  front  of  the  inferior  thyroid 


CAVERNOUS    PLEXUS 


MAXILLARY  NERVE 


SPHENOPALATINE 
GANGLION 


FIRST 

CERVICAL 

NERVE 


artery,  and  recurrent  nerve. 
The  course  of  the  nerves  on  the 
two  sides  then  differ.  The  right 
nerve,  at  the  root  of  the  neck, 
passes  either  in  front  of  or  behind 
the  subclavian  artery,  and  along 
the  innominate  artery  to  the 
back  of  the  arch  of  the  aorta, 
where  it  joins  the  deep  part  of 
the  cardiac  plexus.  It  is  con- 
nected with  other  branches  of 
the  sympathetic;  about  the 
middle  of  the  neck  it  receives 
filaments  from  the  external 
laryngeal  nerve;  lower  down, 
one  or  two  twigs  from  the 
vagus;  and  as  it  enters  the 
thorax  it  is  joined  by  a  fila- 
ment from  the  recurrent  nerve. 
Filaments  from  the  nerve  com- 
municate with  the  thyroid 
branches  from  the  middle  cer- 
vical ganglion.  The  left  nerve, 
in  the  thorax,  runs  in  front  of 
the  left  common  carotid  artery 
and  across  the  left  side  of  the 
arch  of  the  aorta,  to  the  super- 
ficial part  of  the  cardiac  plexus. 

The  Anterior  Branches  {nn. 
carotid  exierni)  ramify  upon 
the  common  carotid  artery  and 
upon  the  external  carotid  artery 

and  its  branches,  forming  around  each  a  delicate  plexus,  on  the  nerves  composing 
which  small  ganglia  are  occasionally  found.  The  plexuses  accompanying  some 
of  these  arteries  have  important  communications  with  other  nerves.  That  sur- 
rounding the  external  maxillary  artery  communicates  with  the  submaxillary  gan- 
glion by  a  filament;  and  that  accompanying  the  middle  meningeal  artery  sends  an 
offset  to  the  otic  ganglion,  and  a  second,  the  external  petrosal  nerve,  to  the  genicular 
ganglion  of  the  facial  nerve. 

The  middle  cervical  ganglion  {ganglion  cervicale  medium)  is  the  smallest  of  the 
three  cervical  ganglia,  and  is  occasionally  wanting.  It  is  placed  opposite  the  sixth 
cervical  vertebra,  usually  in  front  of,  or  close  to,  the  inferior  thyroid  artery.  It 
is  probably  formed  by  the  coalescence  of  two  ganglia  corresponding  to  the  fifth 
and  sixth  cervical  nerves. 

It  sends  gray  rami  communicantes  to  the  fifth  and  ^ixth  cervical  nerves,  and 
gives  off  the  middle  cardiac  nerve. 

The  Middle  Cardiac  Nerve  {n.  cardiacus  medius;  great  cardiac  nerve),  the  largest 


CERVICAL 
NERVE 


FIRST 

THORACIC 

NERVE 


MIDDLE   CARDIAC 
NERVE 


^  LOWER    CERVICAL 
I  A  GANGLION 

INFERIOR  CARDIAC 
NERVE 


Fig.  844. — Diagram  of  the  cervical  sympathetic.     (Testut.) 


9S0 


NEUROLOGY 


I 


of  the  three  cardiac  nerves,  arises  from  the  middle  cervical  ganglion,  or  from  the 
trunk  between  the  middle  and  inferior  ganglia.  On  the  right  side  it  descends  behind 
the  common  carotid  artery,  and  at  the  root  of  the  neck  runs  either  in  front  of  or 
behind  the  subclavian  artery;  it  then  descends  on  the  trachea,  receives  a  few 
filaments  from  the  recurrent  nerve,  and  joins  the  right  half  of  the  deep  part  of  the 
cardiac  plexus.  In  the  neck,  it  communicates  with  the  superior  cardiac  and  recur- 
rent nerves.  On  the  left  side,  the  middle  cardiac  nerve  enters  the  chest  between 
the  left  carotid  and  subclavian  arteries,  and  joins  the  left  half  of  the  deep  par, 
of  the  cardiac  plexus. 


THORACIC    NERVES 
RAMI   COMMUNICANTES' 


INFERIOR    CER- 
VICAL   GANGLION 


VISCERAL 
BRANCHES 


SPLANCHNI 
GANGLION 
GREATER 

SPLANCHNI 


LESSER 
SPLANCHNIC 


RIGHT  VAGUS 


LOWEST 
SPLANCHNIC 


BRANCH  OF  VAGUS 
TO  CELIAC  GANGLION 
CELIAC   AXIS 


SEMILUNAR  GANGLION 
SUPERIOR  MESENTERIC 
ARTERY  AND   PLEXUS 

CELIAC  PLEXUS 


QUADRATUS 
LUMBORUM 


RENAL   PLEXUS 

Fig.  845. — ^Plan  of  right  sympathetic  cord  and  splanchnic  nerves. 


(Testut.) 


#1 


The  inferior  cervical  ganglion  {ganglion  cervicale  inferius)  is  situated  between 
the  base  of  the  transverse  process  of  the  last  cervical  vertebra  and  the  neck  of  the 
first  rib,  on  the  medial  side  of  the  costocer vical  artery.  Its  form  is  irregular ;  it  is 
larger  in  size  than  the  preceding,  and  is  frequently  fused  with  the  first  thoracic 
ganglion.  It  is  probably  formed  by  the  coalescence  of  two  ganglia  which  corre- 
spond to  the  seventh  and  eighth  cervical  nerves.    It  is  connected  to  the  middle 


I 


THE  THORACIC  PORTION  OF  THE  SYMPATHETIC  SYSTEM         981 

cervical  ganglion  by  two  or  more  cords,  one  of  which  forms  a  loop  around  the  sub- 
clavian artery  and  supplies  offsets  to  it.  This  loop  is  named  the  ansa  subclavia 
(Vieussenii). 

The  ganglion  sends  gray  rami  communicantes  to  the  seventh  and  eighth  cervical 
nerves. 

It  gives  oft'  the  inferior  cardiac  nerve,  and  offsets  to  bloodvessels. 

The  inferior  cardiac  nerve  (?i.  cardiacus  inferior)  arises  from  either  the  inferior 
cervical  or  the  first  thoracic  ganglion.  It  descends  behind  the  subclavian  artery 
and  along  the  front  of  the  trachea,  to  join  the  deep  part  of  the  cardiac  plexus.  It 
communicates  freely  behind  the  subclavian  artery  with  the  recurrent  nerve  and 
the  middle  cardiac  nerve. 

The  offsets  to  bloodvessels  form  plexuses  on  the  subclavian  artery  and  its  branches. 
The  plexus  on  the  vertebral  artery  is  continued  on  to  the  basilar,  posterior  cerebral, 
and  cerebellar  arteries.  The  plexus  on  the  inferior  thyroid  artery  accompanies 
the  artery  to  the  thyroid  gland,  and  communicates  with  the  recurrent  and  external 
laryngeal  nerves,  with  the  superior  cardiac  nerve,  and  with  the  plexus  on  the 
common  carotid  artery. 

THE   THORACIC  PORTION   OF   THE   SYMPATHETIC   SYSTEM    (PARS 
THORACALIS   S.  SMYPATHICI)   (Fig.  846). 

The  thoracic  portion  of  the  sympathetic  trunk  consists  of  a  series  of  ganglia, 
which  usually  correspond  in  number  to  that  of  the  vertebrae;  but,  on  account 
of  the  occasional  coalescence  of  two  ganglia,  their  number  is  uncertain.  The 
thoracic  ganglia  rest  against  the  heads  of  the  ribs,  and  are  covered  by  the  costal 
pleura;  the  last  two,  however,  are  more  anterior  than  the  rest,  and  are  placed  on 
the  sides  of  the  bodies  of  the  eleventh  and  twelfth  thoracic  vertebrae.  The  ganglia 
are  small  in  size,  and  of  a  grayish  color.  The  first,  larger  than  the  others,  is  of 
an  elongated  form,  and  frequently  blended  with  the  inferior  cervical  ganglion. 
They  are  connected  together  by  the  intervening  portions  of  the  trunk. 

Two  rami  communicantes,  a  white  and  a  gray,  connect  each  ganglion  with  its 
corresponding  spinal  nerve. 

The  branches  from  the  upper  five  ganglia  are  very  small;  they  supply  filaments 
to  the  thoracic  aorta  and  its  branches.  Twigs  from  the  second,  third,  and  fourth 
ganglia  enter  the  posterior  pulmonary  plexus. 

The  branches  from  the  lower  seven  ganglia  are  large,  and  white  in  color;  they 
distribute  filaments  to  the  aorta,  and  unite  to  form  the  greater,  the  lesser,  and  the 
lowest  splanchnic  nerves. 

The  greater  splanchnic  nerve  (n.  splanchnicus  major;  great  splanchnic  nerve)  is 
white  in  color,  firm  in  texture,  and  of  a  considerable  size;  it  is  formed  by  branches 
from  the  fifth  to  the  ninth  or  tenth  thoracic  ganglia,  but  the  fibers  in  the  higher 
roots  may  be  traced  upward  in  the  sympathetic  trunk  as  far  as  the  first  or  second 
thoracic  ganglion.  It  descends  obliquely  on  the  bodies  of  the  vertebrae,  perforates 
the  crus  of  the  diaphragm,  and  ends  in  the  celiac  ganglion.  A  ganglion  (ganglion 
splanchnicum)  exists  on  this  nerve  opposite  the  eleventh  or  twelfth  thoracic  vertebra. 

The  lesser  splanchnic  nerve  {n.  splanchnicus  minor)  is  formed  by  filaments  from 
the  ninth  and  tenth,  and  sometimes  the  eleventh  thoracic  ganglia,  and  from  the 
cord  between  them.  It  pierces  the  diaphragm  with  the  preceding  nerve,  and 
joins  the  aorticorenal  ganglion. 

The  lowest  splanchnic  nerve  {n.  splanchnicus  imvs;  least  splanchnic  nerve)  arises 
from  the  last  thoracic  ganglion,  and,  piercing  the  diaphragm,  ends  in  the  renal 
plexus. 

A  striking  analogy  exists  between  the  splanchnic  and  the  cardiac  nerves.  The 
cardiac  nerves  are  three  in  number;  they  arise  from  all  three  cervical  ganglia, 


582 


NEUROLOGY 


I 


and  are  distributed  to  a  large  and  important  organ  in  the  thoracic  cavity.  The 
splanchnic  nerves,  also  three  in  number,  are  connected  probably  with  all  the  thoracic 
ganglia,  and  are  distributed  to  important  organs  in  the  abdominal  cavity. 

ghest  intercostal  artery 

Highest  intercostal  vein 

Rami  comniunicantes 
Lig.  arteriosum. 


Fio.  846. — Thoracic  portion  of  the  sympathetic  trunk. 


THE    ABDOMINAL   PORTION    OF    THE    SYMPATHETIC    SYSTEM    (PARS 

ABDOMINALIS    S.   SYMPATHICI;  LUMBAR  PORTION   OF 

GANGLIATED  CORD)  (Fig.  847). 

The  abdominal  portion  of  the  sympathetic  trunk  is  situated  in  front  of  the  ver- 
tebral column,  along  the  medial  margin  of  the  Psoas  major.  It  consists  usually  of 
four  lumbar  ganglia,  connected  together  by  interganglionic  cords.  It  is  continuous 
above  with  the  thoracic  portion  beneath  the  medial  lumbocostal  arch,  and 
below  with  the  pelvic  portion  behind  the  common  iliac  artery.  The  ganglia  are 
of  small  size,  and  placed  much  nearer  the  median  line  than  are  the  thoracic  ganglia. 


THE  ABDOMINAL  PORTION  OF  THE  SYMPATHETIC  SYSTEM      983 

Gray  rami  communicantes  pass  from  all  the  ganglia  to  the  lumbar  spinal  nerves. 
The  first  and  second,  and  sometimes  the  third,  lumbar  nerves  send  white  rami 


Diaphragmatic 
ganglion 

Swprarenal  gland 


Greater 

splanchnic 

nerve 

Right 

celiac 

ganglion 


Aorticorenal  ganglion 
Lowest  splanchnic 


Hepatic 
artery 


Benal  artery 


Communicating  branch 


eft  celiac  ganglion 
Superior  mesenteric 
artery 
Greater  splatichnic  nerve 
^       ^  Lesser  splanchnic 

Aorticorenal 
ganglion 


Renal  artery 


Superior  mesenteric 
ganglion 


Branch  to  aortic  plexus 


Branch  to  aortic  plexus 


Sympaihetic  trunk 


Inferior  mesenteric  artery 


Inferior  mesenteric 
ganglion 


Sacrovertebral  angle 

Common  iliac  vein 
Common  iliac  artery 


<'io.  847. — Abdominal  portion  of  the  sympathetic   truuk,  with  the  celiac  and  hypogastric  plezusea.     (Henle.) 


984  1^^^^  NEUROLOGY 

communicantes  to  the  corresponding  ganglia.  The  rami  communicantes  ar^oi 
considerable  length,  and  accompany  the  lumbar  arteries  around  the  sides  of  the 
bodies  of  the  vertebrae,  passing  beneath  the  fibrous  arches  from  which  some  of  the 
fibers  of  the  Psoas  major  arise. 

Of  the  branches  of  distribution,  some  pass  in  front  of  the  aorta,  and  join  the  aortic 
plexus;  others  descend  in  front  of  the  common  iliac  arteries,  and  assist  in  forming 
the  hypogastric  plexus. 

THE   PELVIC   PORTION   OF   THE   SYMPATHETIC   SYSTEM   (PARS  ! 

PELVINA   S.    SYMPATHICI).  ' 

The  pelvic  portion  of  each  sympathetic  trunk  is  situated  in  front  of  the  sacrum, 
medial  to  the  anterior  sacral  foramina.  It  consists  of  four  or  five  small  sacral 
ganglia,  connected  together  by  interganglionic  cords,  and  continuous  above  with 
the  abdominal  portion.  Below,  the  two  pelvic  sympathetic  trunks  converge,  and 
end  on  the  front  of  the  coccyx  in  a  small  ganglion,  the  ganglion  impar. 

Gray  rami  communicantes  pass  from  the  ganglia  to  the  sacral  and  coccygeal 
nerves.  No  white  rami  communicantes  are  given  to  this  part  of  the  gangliated 
cord,  but  the  visceral  branches  which  arise  from  the  third  and  fourth,  and  sometimes 
from  the  second,  sacral,  and  run  directly  to  the  pelvic  plexuses,  are  regarded  as 
white  rami  communicantes. 

The  branches  of  distribution  communicate  on  the  front  of  the  sacrum  with  the 
corresponding  branches  from  the  opposite  side;  some,  from  the  first  two  ganglia, 
pass  to  join  the  pelvic  plexus,  and  others  form  a  plexus,  which  accompanies  the 
middle  sacral  artery  and  sends  filaments  to  the  glomus  coccygeum  {coccygeal  body). 

THE   GREAT   PLEXUSES    OF   THE   SYMPATHETIC   SYSTEM. 

The  great  plexuses  of  the  sympathetic  are  aggregations  of  nerves  and  ganglia, 
situated  in  the  thoracic,  abdominal,  and  pelvic  cavities,  and  named  the  cardiac, 
celiac,  and  hypogastric  plexuses.  They  consist  not  only  of  sympathetic  fibers 
derived  from  the  ganglia,  but  of  fibers  from  the  naedulla  spinalis,  which  are  con- 
veyed through  the  white  rami  communicantes.  From  the  plexuses  branches  are 
given  to  the  thoracic,  abdominal,  and  pelvic  viscera. 

The  Cardiac  Plexus  (Plexus  Cardiacus)  (Fig.  838). 

The  cardiac  plexus  is  situated  at  the  base  of  the  heart,  and  is  divided  into  a  super- 
ficial part,  which  lies  in  the  concavity  of  the  aortic  arch,  and  a  deep  part,  between 
the  aortic  arch  and  the  trachea.    The  two  parts  are,  however,  closely  connected. 

The  superficial  part  of  the  cardiac  plexus  lies  beneath  the  arch  of  the  aorta, 
in  front  of  the  right  pulmonary  artery.  It  is  formed  by  the  superior  cardiac  branch 
of  the  left  sympathetic  and  the  lower  superior  cervical  cardiac  branch  of  the  left 
vagus.  A  small  ganglion,  the  cardiac  ganglion  of  Wrisberg,  is  occasionally  found 
connected  with  these  nerves  at  their  point  of  junction.  This  ganglion,  when 
present,  is  situated  immediately  beneath  the  arch  of  the  aorta,  on  the  right  side 
of  the  ligamentum  arteriosum.  The  superficial  part  of  the  cardiac  plexus  gives 
branches  (a)  to  the  deep  part  of  the  plexus;  (6)  to  the  anterior  coronary  plexus; 
and  (c)  to  the  left  anterior  pulmonarj^  plexus. 

The  deep  part  of  the  cardiac  plexus  is  situated  in  front  of  the  bifurcation  of 
the  trachea,  above  the  point  of  division  of  the  pulmonary  artery,  and  behind  the 
aortic  arch.  It  is  formed  by  the  cardiac  nerves  derived  from  the  cervical  ganglia 
of  the  sympathetic,  and  the  cardiac  branches  of  the  vagus  and  recurrent  nerves. 
The  only  cardiac  nerves  which  do  not  enter  into  the  formation  of  the  deep  part 


I 


I 


THE  CELIAC  PLEXUS  ^^^  985 

of  the  cardiac  plexus  are  the  superior  cardiac  nerve  of  the  left  sympathetic,  and  the 
lower  of  the  two  superior  cervical  cardiac  branches  from  the  left  vagus,  which  pass 
to  the  superficial  part  of  the  plexus. 

The  branches  from  the  right  half  of  the  deep  part  of  the  cardiac  plexus  pass, 
some  in  front  of,  and  others  behind,  the  right  pulmonary  artery;  the  former,  the 
more  numerous,  transmit  a  few  filaments  to  the  anterior  pulmonary  plexus,  and 
are  then  continued  onward  to  form  part  of  the  anterior  coronary  plexus;  those 
behind  the  pulmonary  artery  distribute  a  few  filaments  to  the  right  atrium,  and  are 
then  continued  onward  to  form  part  of  the  posterior  coronary  plexus. 

The  left  half  of  the  deep  part  of  the  plexus  is  connected  with  the  superficial  part 
of  the  cardiac  plexus,  and  gives  filaments  to  the  left  atrium,  and  to  the  anterior 
pulmonary  plexus,  and  is  then  continued  to  form  the  greater  part  of  the  posterior 
coronary  plexus. 

The  Posterior  Coronary  Plexus  (plexus  coronarius  posterior;  left  coronary  plexus) 
is  larger  than  the  anterior,  and  accompanies  the  left  coronary  artery;  it  is  chiefly 
formed  by  filaments  prolonged  from  the  left  half  of  the  deep  part  of  the  cardiac 
plexus,  and  by  a  few  from  the  right  half.  It  gives  branches  to  the  left  atrium  and 
ventricle. 

The  Anterior  Coronary  Plexus  (plexus  coronarius  anterior;  right  coronary  plexus) 
is  formed  partly  from  the  superficial  and  partly  from  the  deep  parts  of  the  cardiac 
plexus.  It  accompanies  the  right  coronary  artery,  and  gives  branches  to  the  right 
atrium  and  ventricle. 

The  Celiac  Plexus  (Plexus  Coeliacus;  Solar  Plexus)  (Figs.  838,  848). 

The  celiac  plexus,  the  largest  of  the  three  sympathetic  plexuses,  is  situated  at 
the  level  of  the  upper  part  of  the  first  lumbar  vertebra  and  is  composed  of  two 
large  ganglia,  the  celiac  ganglia,  and  a  dense  net-work  of  nerve  fibers  uniting  them 
together.  It  surrounds  the  celiac  artery  and  the  root  of  the  superior  mesenteric 
artery.  It  lies  behind  the  stomach  and  the  omental  bursa,  in  front  of  the  crura 
of  the  diaphragm  and  the  commencement  of  the  abdominal  aorta,  and  between 
the  suprarenal  glands.  The  plexus  and  the  ganglia  receive  the  greater  and  lesser 
splanchnic  nerves  of  both  sides  and  some  filaments  from  the  right  vagus,  and  give 
off  numerous  secondary  plexuses  along  the  neighboring  arteries. 

The  Celiac  Ganglia  (ganglia  coeliaca;  semilunar  ganglia)  are  two  large  irregularly- 
shaped  masses  having  the  appearance  of  lymph  glands  and  placed  one  on  either 
side  of  the  middle  line  in  front  of  the  crura  of  the  diaphragm  close  to  the  supra- 
renal glands,  that  on  the  right  side  being  placed  behind  the  inferior  vena  cava.  The 
upper  part  of  each  ganglion  is  joined  by  the  greater  splanchnic. nerve,  while  the 
lower  part,  which  is  segmented  off  and  named  the  aorticorenal  ganglion,  receives 
the  lesser  splanchnic  nerve  and  gives  oft'  the  greater  part  of  the  renal  plexus. 

The  secondary  plexuses  springing  from  or  connected  with  the  celiac  plexus  are 
the 

Phrenic.  •  Renal. 

Hepatic.  Spermatic. 

Lienal.  Superior  mesenteric. 

Superior  gastric.  Abdominal  aortic. 

Suprarenal.  Inferior  mesenteric. 

The  phrenic  plexus  {plexus  phrenicus)  accompanies  the  inferior  phrenic  artery 
to  the  diaphragm,  some  filaments  passing  to  the  suprarenal  gland.  It  ari.ses 
from  the  upper  part  of  the  celiac  ganglion,  and  is  larger  on  the  right  than  on  the 
left  side.  It  receives  one  or  two  branches  from  the  phrenic  nerve.  At  the  point 
of  junction  of  the  right  phrenic  plexus  with  the  phrenic  nerve  is  a  small  ganglion 


986 


NEUROLOGY 


(ganglion  phrenicum).     This  plexus  distributes  branches  to  the  inferior  vena  cava, 
and  to  the  suprarenal  and  hepatic  plexuses. 

The  hepatic  plexus  {plexvs  hepaticus),  the  largest  offset  from  the  celiac  plexus, 
receives  filaments  from  the  left  vagus  and  right  phrenic  nerves.  It  accompanies 
the  hepatic  artery,  ramifying  upon  its  branches,  and  upon  those  of  the  portal  vein 
in  the  substance  of  the  liver.  Branches  from  this  plexus  accompany  all  the  divisions 
of  the  hepatic  artery.  A  considerable  plexus  accompanies  the  gastroduodenal 
arterj'^  and  is  continued  as  the  inferior  gastric  plexus  on  the  right  gastroepiploic 
artery  along  the  greater  curvature  of  the  stomach,  where  it  unites  with  offshoots 
from  the  lienal  plexus. 


Phrenic 
plexus 


Celiac    Left 
plexris  vagus 


ight  vagus 


Hepatic 
plexus 

Common 
hile-duct 


Superior 

mesenteric 

plexus 

Aortic 

plexus 


Gastric  plexus 

Phrenic 
plexus 

Suprarenal 
plexus 


Lienal 
plexus 

Phrenic 
ganglion 

Greater 
splanchnic 

Celiac 
ganglion 


Renal  plexus 

Superior 
mesenteric 
ganglion 

Spermatic 
plexus 

Lumbar 
ganglia 

Inferior 

mesenteric 

plexus 


Fia.  848. — The  celiac  ganglia  with  the  sympathetic  plexuses  of  the  abdominal  viscera  radiating  from  the  ganglia. 

(Toldt.) 


The  lienal  plexus  {plexus  lienalis;  splenic  plexus)  is  formed  by  branches  from  the 
celiac  plexus,  the  left  celiac  ganglion,  and  from  the  right  vagus  nerve.  It  accom- 
panies the  lienal  artery  to  the  spleen,  giving  off,  in  its  course,  subsidiary  plexuses 
along  the  various  branches  of  the  artery. 


I 


I 


THE  HYPOGASTRIC  PLEXUS  '  987 

The  superior  gastric  plexus  {-plexus  gastricus  superior;  gastric  or  coronary  plexus) 
accompanies  the  left  gastric  artery  along  the  lesser  curvature  of  the  stomach,  and 
joins  with  branches  from  the  left  vagus. 

The  suprarenal  plexus  {plexus  suprarenalis)  is  formed  by  branches  from  the 
celiac  plexus,  from  the  celiac  ganglion,  and  from  the  phrenic  and  greater  splanchnic 
nerves,  a  ganglion  being  formed  at  the  point  of  junction  with  the  latter  nerve. 
The  plexus  supplies  the  suprarenal  gland,  being  distributed  chiefly  to  its  medullary 
portion;  its  branches  are  remarkable  for  their  large  size  in  comparison  with  that 
of  the  organ  they  supply. 

The  renal  plexus  {plexus  renalis)  is  formed  by  filaments  from  the  celiac  plexus, 
the  aorticorenal  ganglion,  and  the  aortic  plexus.  It  is  joined  also  by  the  smallest 
splanchnic  nerve.  The  nerves  from  these  sources,  fifteen  or  twenty  in  number, 
have  a  few  ganglia  developed  upon  them.  They  accompany  the  branches  of  the 
renal  artery  into  the  kidney;  some  filaments  are  distributed  to  the  spermatic 
plexus  and,  on  the  right  side,  to  the  inferior  vena  cava. 

The  spermatic  plexus  {plexus  spermaticus)  is  derived  from  the  renal  plexus, 
receiving  branches  from  the  aortic  plexus.  It  accompanies  the  internal  spermatic 
artery  to  the  testis.  In  the  female,  the  ovarian  plexus  {plexus  arterioe  ovaricce) 
arises  from  the  renal  plexus,  and  is  distributed  to  the  ovary,  and  fundus  of  the 
uterus. 

The  superior  mesenteric  plexus  {plexus  mesentericus  superior)  is  a  continuation 
of  the  lower  part  of  the  celiac  plexus,  receiving  a  branch  from  the  junction  of  the 
right  vagus  nerve  with  the  plexus.  It  surrounds  the  superior  mesenteric  artery, 
accompanies  it  into  the  mesentery,  and  divides  into  a  number  of  secondary  plexuses, 
which  are  distributed  to  all  the  parts  supplied  by  the  artery,  viz.,  pancreatic  branches 
to  the  pancreas;  intestinal  branches  to  the  small  intestine;  and  ileocolic,  right 
colic,  and  middle  colic  branches,  which  supply  the  corresponding  parts  of  the  great 
intestine.  The  nerves  composing  this  plexus  are  white  in  color  and  firm  in  texture; 
in  the  upper  part  of  the  plexus  close  to  the  origin  of  the  superior  mesenteric  artery 
is  a  ganglion  (ganglion  mesentericum  superius) . 

The  abdominal  aortic  plexus  {plexus  aorticus  ahdominalis;  aortic  plexus)  is  formed 
by  branches  derived,  on  either  side,  from  the  celiac  plexus  and  ganglia,  and  receives 
filaments  from  some  of  the  lumbar  ganglia.  It  is  situated  upon  the  sides  and  front  of 
the  aorta,  between  the  origins  of  the  superior  and  inferior  mesenteric  arteries.  From 
this  plexus  arise  part  of  the  spermatic,  the  inferior  mesenteric,  and  the  hypogastric 
plexuses;  it  also  distributes  filaments  to  the  inferior  vena  cava. 

The  inferior  mesenteric  plexus  {plexus  mesentericum  inferior)  is  derived  chiefly 
from  the  aortic  plexus.  It  surrounds  the  inferior  mesenteric  artery,  and  divides 
into  a  number  of  secondary  plexuses,  which  are  distributed  to  all  the  parts  supplied 
by  the  artery,  viz.,  the  left  colic  and  sigmoid  plexuses,  which  supply  the  descending 
and  sigmoid  parts  of  the  colon;  and  the  superior  hemorrhoidal  plexus,  w^hich  supplies 
the  rectum  and  joins  in  the  pelvis  wath  branches  from  the  pelvic  plexuses. 

The  Hypogastric  Plexus  (Plexus  Hypogastricus)  (Fig.  838). 

The  hypogastric  plexus  is  situated  in  front  of  the  last  lumbar  vertebra  and  the 
promontory  of  the  sacrum,  between  the  two  common  iliac  arteries,  and  is  formed 
by  the  union  of  numerous  filaments,  which  descend  on  either  side  from  the  aortic 
plexus,  and  from  the  lumbar  ganglia;  it  divides,  below,  into  two  lateral  portions 
which  are  named  the  pelvic  plexuses. 

The  Pelvic  Plexuses  (Fig.  838).— The  pelvic  plexuses  supply  the  viscera  of  the 
pelvic  cavity,  and  are  situated  at  the  sides  of  the  rectum  in  the  male,  and  at  the 
sides  of  the  rectum  and  vagina  in  the  female.  They  are  formed  on  either  side  by 
a  continuation  of  the  hypogastric  plexus,  by  the  sacral  sympathetic  efferent  fibers 


988 


NEUROLOGY 


from  the  second,  third,  and  fourth  sacral  nerves,  and  by  a  few  filaments  from  the 
first  two  sacral  ganglia.  At  the  points  of  junction  of  these  nerves  small  ganglia  are 
found.  From  these  plexuses  numerous  branches  are  distributed  to  the  viscera  of 
the  pelvis.    They  accompany  the  branches  of  the  hypogastric  artery. 

The  Middle  Hemorrhoidal  Plexus  {plexus  hccmorrhoidalis  medius)  arises  from  the 
upper  part  of  the  pelvic  plexus.  It  supplies  the  rectum,  and  joins  with  branches 
of  the  superior  hemorrhoidal  plexus. 


GREATER    SPLANCHNIC,      .CELIAC    GANGLION 


LOWEST  THORACIC 
GANGLION 

UPPER     LUMBAR 
GANGLION 

RENAL    PLEXUS 

ABDOMINAL    AORTA 

AORTIC    PLEXUS 


LUMBAR  SYMPATHETIC 
VENA  CAVA  INFERIOR 
COMMISSURE  BETWEEN 
AORTIC  AND  HYPOGAS- 
TRIC PLEXUSES 

COMMON    ILIAC 
ARTERY 
UPPER    SACRAL 
GANGLION 


RECTUM 
HYPOGASTRIC 
PLEXUS 


.-CELIAC  PLEXUS 

SUPERIOR    MESEN- 
TERIC   PLEXUS 


SMALL   IN- 
TESTINE 


INFERIOR    MESEN- 
TERIC   PLEXUS 


VESICAL 
PLEXUS 
BLADDER 
■URETER 
VESICULA 
SEMINALIS 
SPERMATIC 

PLEXUS 
PROSTATE 


Fig.  849. — Lower  half  of  right  sympathetic  cord.     (Testut  after  Hirschfeld.) 


The  Vesical  Plexus  (jjlexus  vesicalis)  arises  from  the  forepart  of  the  pelvic  plexus. 
The  nerves  composing  it  are  numerous,  and  contain  a  large  proportion  of  spinal 
nerve  fibers.  They  accompany  the  vesical  arteries,  and  are  distributed  to  the  sides 
and  fundus  of  the  bladder.  Numerous  filaments  also  pass  to  the  vesiculse  seminales 
and  ductus  deferentes;  those  accompanying  the  ductus  deferens  join,  on  the  sper- 
matic cord,  with  branches  from  the  spermatic  plexus. 

The  Prostatic  Plexus  {plexus  prostaticus)  is  continued  from  the  lower  part  of  the 
pelvic  plexus.  The  nerves  composing  it  are  of  large  size.  They  are  distributed 
to  the  prostate  vesiculse  seminales  and  the  corpora  cavernosa  of  the  penis  and 
urethra.     The  nerves  supplying  the  corpora  cavernosa  consist  of  two  sets,  the 


PLEXUS 


"989 


lesser  and  greater  cavernous  nerves,  which  arise  from  the  forepart  of  the  prostatic 
plexus,  and,  after  joining  with  branches  from  the  pudendal  nerve,  pas?  forward 
beneath  the  pubic  arch. 

The  lesser  cavernous  nerves  (7in.  cavernosi  yenis  ininores;  small  cavernous  nerves) 
perforate  the  fibrous  covering  of  the  penis,  near  its  root. 

The  greater  cavernous  nerve  (w.  cavernosus  penis  major;  large  cavernous  plexus) 
passes  forward  along  the  dorsum  of  the  penis,  joins  with  the  dorsal  nerve  of  the 
penis,  and  is  distributed  to  the  corpora  cavernosa. 

The  Vaginal  Plexus  arises  from  the  lower  part  of  the  pelvic  plexus.  It  is  distributed 
to  the  walls  of  the  vagina,  to  the  erectile  tissue  of  the  vestibule,  and  to  the  clitoris. 
The  nerves  composing  this  plexus  contain,  like  the  vesical,  a  large  proportion  of 
spinal  nerve  fibers. 

The  Uterine  Plexus  accompanies  the  uterine  artery  to  the  side  of  the  uterus, 
between  the  layers  of  the  broad  ligament ;  it  communicates  with  the  ovarian  plexus. 


»    Barker,  L.  F.  : 
Herrick,  C.  J. 
HuBER,  G.  C: 
73-145. 
L     Ramon  y  Cajal,  S.:     Histologie  du  Syst^me  Nerveux,  Paris,  1909. 
P     Sherrington,  C.  S.:     The  Integrative  Action  of  the  Nervous  System,  1906. 

Streeter,  G.  L.  :    The  Development  of  the  Nervous  System,  Keibel  and  Mall,  Manual  of 
Human  Embryology,  1912. 


BIBLIOGRAPHY. 

The  Nervous  System  and  its  Constituent  Neurons,  1901. 

An  Introduction  to  Neurology,  1915. 
Lectures  on  the  Sympathetic  Nervous  System,  Jour.  Comp.  Neur.,  1897,  vii. 


THE  ORGANS  OF  THE  SENSES  AND 
THE  COMMON  INTEGUMENT. 


I^H^^^P 


THE  organs  of  the  senses  may  be  divided  into  (a)  those  of  the  special  senses  of 
taste,  smell,  sight,  and  hearing,  and  (6)  those  associated  with  the  general  sensa- 
tions of  heat,  cold,  pain,  pressure,  etc. 


THE  PERIPHERAL   ORGANS   OF   THE    SPECIAL  SENSES. 


THE   ORGAN    OF   TASTE    (ORGANON   GUSTUS). 


\^^  The  peripheral  gustatory  or  taste  organs  consist  of  certain  modified  epithelial 
IH  cells  arranged  in  flask-shaped  groups  termed  gustatory  calyculi  (taste-buds),  which 
are  found  on  the  tongue  and  adjacent  parts.  They  occupy  nests  in  the  stratified 
epithelium,  and  are  present  in  large  numbers  on  the  sides  of  the  papillae  vallatae 
(Fig.  850),  and  to  a  less  extent  on  their  opposed  walls.    They  are  also  found  on  the 


Central  lamina  of 
corium. 

Lateral  lamina 
Gustatory  calycuhts^. 

Section  across  a  sinus- 
like vein,  traversing 
whole  length  of  folium 


Serous  aland  Q^ 


Serous  gland 


^  JiiatiUMd^  at' 


Nerve  bundles  .'     ''***■* 

Fig.  850. — Vertical  section  of  papilla  foliata  of  the  rabbit,  crossing  the  folia.     (Ranvier.) 

fungiform  papillae  over  the  back  part  and  sides  of  the  tongue,  and  in  the  general 
epithelial  covering  of  the  same  areas.  They  are  very  plentiful  over  the  fimbriae 
linguae,  and  are  also  present  on  the  under  surface  of  the  soft  palate,  and  on  the 
posterior  surface  of  the  epiglottis. 

Structure. — Each  taste  bud  is  flask-like  in  shape  (Fig.  851),  its  broad  base  resting  on  the  corium, 
and  its  neck  opening  by  an  orifice,  the  gustatory  pore,  between  the  cells  of  the  epithelium.  The 
bud  is  formed  by  two  kinds  of  cells:  supporting  cells  and  gustatory  cells.  The  supportiiig  cells 
are  mostly  arranged  like  the  staves  of  a  cask,  and  form  an  outer  envelope  for  the  bud.  Some, 
however,  are  found  in  the  interior  of  the  bud  between  the  gustatory  cells.  The  gustatory  cells 
occupy  the  central  portion  of  the  bud;  they  are  spindle-shaped,  and  each  possesses  a  large  spherical 

(  991 ) 


992        ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

nucleus  near  the  middle  of  the  cell.  The  peripheral  end  of  the  cell  terminates  at  the  gustatory 
pore  in  a  fine  hair-like  filament,  the  gustatory  hair.  The  central  process  passes  toward  the  deep 
extremity  of  the  bud,  and  there  ends  in  single  or  bifurcated  varicosities.  The  nerve  fibrils  after 
losing  their  medullary  sheaths  enter  the  taste  bud,  and  end  in  fine  extremities  between  the  gusta- 
tory cells;  other  nerve  fibrils  ramify  between  the  supporting  cells  and  terminate  in  fine  extremities; 
these,  however,  are  believed  to  be  nerves  of  ordinary  sensation  and  not  gustatory. 

Gustatory  pore  and 
gzistatory  hairs 


Fia.  851. — Taste-bud,  highly  magnified. 


Nerves  of  Taste. — -The  chorda  tjmapani  nerve,  derived  from  the  sensory  root  of  the  facial,  is 
the  nerve  of  taste  for  the  anterior  two-thirds  of  the  tongue;  the  nerve  for  the  posterior  third 
is  the  glossopharyngeal. 


THE  ORGAN  OF  SMELL   (ORGANON  OLFACTORIUS;    THE  NOSE). 

The  peripheral  olfactory  organ  or  organ  of  smell  consists  of  two  parts :  an  outer, 
the  external  nose,  which  projects  from  the  center  of  the  face;  and  an  internal,  the 
nasal  cavity,  which  is  divided  by  a  septum  into  right  and  left  nasal  chambers. 


The  External  Nose  (Nasus  Extemus;  Outer  Nose). 

The  external  nose  is  pyramidal  in  form,  and  its  upper  angle  or  root  is  connected 
directly  ^dth  the  forehead ;  its  free  angle  is  termed  the  apex.  Its  base  is  perforated 
by  two  elliptical  orifices,  the  nares,  separated  from  each  other  by  an  antero-posterior 
septum,  the  columna.  The  margins  of  the  nares  are  provided  with  a  number  of 
stiff  hairs,  or  vibrissas,  which  arrest  the  passage  of  foreign  substances  carried  with 
the  current  of  air  intended  for  respiration.  The  lateral  surfaces  of  the  nose  form, 
by  their  union  in  the  middle  line,  the  dorsum  nasi,  the  direction  of  which  varies 
considerably  in  different  individuals;  the  upper  part  of  the  dorsum  is  supported 
by  the  nasal  bones,  and  is  named  the  bridge.  The  lateral  surface  ends  below  in 
a  rounded  eminence,  the  ala  nasi. 

Structvire. — The  frame-work  of  the  external  nose  is  composed  of  bones  and  cartilages;  it  is 
covered  by  the  integument,  and  lined  by  mucous  membrane. 

The  bony  frame-work  occupies  the  upper  part  of  the  organ ;  it  consists  of  the  nasal  bones,  and 
the  frontal  processes  of  the  maxillae. 

The  cartilaginous  frame-work  (cartilagines  nasi)  consists  of  five  large  pieces,  viz.,  the  cartilage 
of  the  septum,  the  two  lateral  and  the  two  greater  alar  cartilages,  and  several  smaller  pieces, 
the  lesser  alar  cartilages  (Figs.  852,  853,  854).  The  various  cartilages  are  connected  to  each  other 
and  to  the  bones  by  a  tough  fibrous  membrane. 

The  cartilage  of  the  septum  (cartilago  septi  nasi)  is  somewhat  quadrilateral  in  form,  thicker  at 
its  margins  than  at  its  center,  and  completes  the  separation  between  the  nasal  cavities  in  front. 
Its  anterior  margin,  thickest  above,  is  connected  with  the  nasal  bones,  and  is  continuous  with 
the  anterior  margins  of  the  lateral  cartilages;  below,  it  is  connected  to  the  medial  crura  of  the 
greater  alar  cartilages  by  fibrous  tissue.  Its  posterior  margin  is  connected  with  the  perpendicular 
plate  of  the  ethmoid;  its  inferior  margin  with  the  vomer  and  the  palatine  processes  of  the  maxillae. 


THE  EXTERNAL  NOSE 


993 


H 


It  may  be  prolonged  backward  (especially  in  children)  as  a  narrow  process,  the  sphenoidal  pro- 
cess, for  some  distance  between  the  vomer  and  perpendicular  plate  of  the  ethmoid.  The  septal 
cartilage  does  not  reach  as  far  as  the  lowest  part  of  the  nasal  septum.  This  is  formed  by  the 
medial  crura  of  the  greater  alar  cartilages  and  by  the 
skin;  it  is  freely  movable,  and  hence  is  termed  the 
septum  mobile  nasi. 

The  lateral  cartilage  {cartilago  nasi  lateralis;  upper 
lateral  cartilage)  is  situated  below  the  inferior  margin 
of  the  nasal  bone,  and  is  flattened,  and  triangular  in 
shape.  Its  anterior  margin  is  thicker  than  the  pos- 
terior, and  is  continuous  above  with  the  cartilage  of 
the  septum,  but  separated  from  it  below  by  a 
narrow  fissure;  its  superior  margin  is  attached  to 
the  nasal  bone  and  the  frontal  process  of  the  max- 
illa; its  inferior  margin  is  connected  by  fibrous 
tissue  with  the  greater  alar  cartilage. 

The  greater  alar  cartilage  (cartilago  alaris  major; 
lower  lateral  cartilage)  is  a  thin,  flexible  plate,  sit- 
uated immediately  below  the  preceding,  and  bent 
upon  itself  in  such  a  manner  as  to  form  the  medial 
and  lateral  walls  of  the  naris  of  its  own  side.  The 
portion  which  forms  the  medial  wall  (cms  mediaUy 
is  loosely  connected  with  the  corresponding  portion 
of  the  opposite  cartilage,  the  two  forming,  together 
with  the  thickened  integument  and  subjacent  tis- 
sue, the  septum  mobile  nasi.  The  part  which 
forms  the  lateral  wall  (cms  laterale)  is  curved  to 
correspond  with  the  ala  of  the  nose;  it  is  oval  and 

flattened,  narrow  behind,  where  it  is  connected  with  the  frontal  process  of  the  maxilla  by  a  tough 
fibrous  membrane,  in  which  are  found  three  or  four  small  cartilaginous  plates,  the  lesser  alar 
cartilages  (cartilagines  alares  minores;  sesamoid  cartilages).  Above,  it  is  connected  by  fibrous 
tissue  to  the  lateral  cartilage  and  front  part  of  the  cartilage  of  the  septimi;  below,  it  falls  short 
of  the  margin  of  the  naris,  the  ala  being  completed  by  fatty  and  fibrous  tissue  covered  by  skin. 
In  front,  the  greater  alar  cartilages  are  separated  by  a  notch  which  corresponds  with  the  apex 
,  of  the  nose. 


r  alar 
cartilage 


Fig.  852. — Cartilages  of  the  nose.     Side  view. 


Lesser  alar 
cartilages 


Fio.  85.3. — Cartilages  of  the  nose,  seen  from  below. 


FiQ.  854. — Bones  and  cartilages  of  septum  of  nose. 
Right  side. 


The  muscles  acting  on  the  external  nose  have  been  described  in  the  section  on  Myology. 

The  integument  of  the  dorsum  and  sides  of  the  nose  is  thin,  and  loosely  connected  with  the 
subjacent  parts;  but  over  the  tip  and  alae  it  is  thicker  and  more  firmly  adherent,  and  is  furnished 
with  a  large  number  of  sebaceous  folUcles,  the  orifices  of  which  are  usually  very  distinct. 

The  arteries  of  the  external  nose  are  the  alar  and  septal  branches  of  the  external  maxillary, 
which  supply  the  ate  and  septum;  the  dorsum  and  sides  being  suppHed  from  the  dorsal  nasal 
branch  of  the  ophthalmic  and  the  infraorbital  branch  of  the  internal  maxillary.  The  veins  end  in 
the  anterior  facial  and  ophthalmic  veins. 

The  nerves  for  the  muscles  of  the  nose  are  derived  from  the  facial,  while  the  skin  receives 
branches  from  the  infratrochlear  and  nasociliary  branches  of  the  ophthalmic,  and  from  the  infra- 
orbital of  the  maxillary. 
63 


994 


ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


The  Nasal  Cavity  (Cavum  Nasi;  Nasal  Fossa). 

The  nasal  chambers  are  situated  one  on  either  side  of  the  median  plane.  They' 
open  in  front  through  the  nares,  and  communicate  behind  through  the  choanae 
with  the  nasal  part  of  the  pharynx.  The  nares  are  somewhat  pear-shaped  apertures, 
each  measuring  about  2.5  cm.  antero-posteriorly  and  1.25  cm.  transversely  at  its 
widest  part.  The  choanse  are  two  oval  openings  each  measuring  2.5  cm.  in  the 
vertical,  and  1.25  cm.  in  the  transverse  direction  in  a  well-developed  adult  skull. 

For  the  description  of  the  bony  boundaries  of  the  nasal  cavities,  see  pages  194 
and  195. 

Inside  the  aperture  of  the  nostril  is  a  slight  dilatation,  the  vestibule,  bounded 
laterally  by  the  ala  and  lateral  crus  of  the  greater  alar  cartilage,  and  medially  by 
the  medial  crus  of  the  same  cartilage.  It  is  lined  by  skin  containing  hairs  and 
sebaceous  glands,  and  extends  as  a  small  recess  toward  the  apex  of  the  nose.  Each 
nasal  cavity,  above  and  behind  the  vestibule,  is  divided  into  two  parts :  an  olfactory 
region,  consisting  of  the  superior  nasal  concha  and  the  opposed  part  of  the  septum, 
and  a  respiratory  region,  which  comprises  the  rest  of  the  cavity. 


I 


SpJieno-ethmoidal  recess 


Pharyngecd  orifice  of  avdilory  tube, 

Fig.  855. — Lateral  wall  of  nasal  cavity. 


Pharyngeal  recess 


I 


Lateral  Wall  (Figs.  855,  856). — On  the  lateral  wall  are  the  superior,  middle,  and 
inferior  nasal  conchae,  and  below  and  lateral  to  each  concha  is  the  correspond- 
ing nasal  passage  or  meatus.  Above  the  superior  concha  is  a  narrow  recess, 
the  sphenoethmoidal  recess,  into  which  the  sphenoidal  sinus  opens.  The  superior 
meatus  is  a  short  oblique  passage  extending  about  half-way  along  the  upper  border 
of  the  middle  concha;  the  posterior  ethmoidal  cells  open  into  the  front  part  of  this 
meatus.  The  middle  meatus  is  below  and  lateral  to  the  middle  concha,  and  is 
continued  anteriorly  into  a  shallow  depression,  situated  above  the  vestibule  and 
named  the  atrium  of  the  middle  meatus.    On  raising  or  removing  the  middle  concha 


THE  NASAL  CAVITY 


995 


the  lateral  wall  of  this  meatus  is  fully  displayed.  On  it  is  a  rounded  elevation, 
the  bulla  ethmoidalis,  and  below  and  in  front  of  this  is  a  curved  cleft,  the  hiatus 
semilunaris. 

The  bulla  ethmoidalis  is  caused  by  the  bulging  of  the  middle  ethmoidal  cells 
which  open  on  or  immediately  above  it,  and  the  size  of  the  bulla  varies  with  that 
of  its  contained  cells. 

Bristle  in  infundibulum 
Cut  edge  of  middle  concha 
Hiatus  semilunaris 
'  Bulla  ethmoidalis 

Opening  of  middle  ethmoidal  cells 
Cut  edge,  of  superior  concha 
Openings  of  posterior  ethynoidal  cells 
Bristle  in  opening  of  sjihenoidal  sintit 


Bristle  in  nasolacrimal  canal         \        ^  .    ,       . 
T,  ■  ^7    •  .        e       Cut  edge  ot 

Bristle  in  opening  of  ^^^^^-^  ^^j^ 

maxillary  sinus  '' 


Orifice  of 

auditory 

tube 


Pharyngeal  recess 


FiQ.  856. — Lateral  wall  of  naaal  cavity;  the  three  nasal  concha  have  been  removed. 


I 


The  hiatus  semilunaris  is  bounded  inferiorly  by  the  sharp  concave  margin  of  the 
uncinate  process  of  the  ethmoid  bone,  and  leads  into  a  curved  channel,  the  infundib- 
ulum, bounded  above  by  the  bulla  ethmoidalis  and  below  by  the  lateral  surface 
of  the  uncinate  process  of  the  ethmoid.  The  anterior  ethmoidal  cells  open  into  the 
front  part  of  the  infundibulum,  and  this  in  slightly  over  50  per  cent,  of  subjects 
is  directly  continuous  with  the  frontonasal  duct  or  passage  leading  from  the  frontal 
air  sinus;  but  when  the  anterior  end  of  the  uncinate  process  fuses  with  the  front 
part  of  the  bulla,  this  continuity  is  interrupted  and  the  frontonasal  duct  then  opens 
directly  into  the  anterior  end  of  the  middle  meatus. 

Below  the  bulla  ethmoidalis,  and  partly  hidden  by  the  inferior  end  of  the  uncinate 
process,  is  the  ostium  maxillare,  or  opening  from  the  maxillary  sinus;  in  a  frontal 
section  this  opening  is  seen  to  be  placed  near  the  roof  of  the  sinus.  An  accessory 
opening  from  the  sinus  is  frequently  present  below  the  posterior  end  of  the  middle 
nasal  concha.  The  inferior  meatus  is  below  and  lateral  to  the  inferior  nasal  concha; 
the  nasolacrimal  duct  opens  into  this  meatus  under  cover  of  the  anterior  part  of 
the  inferior  concha. 

Medial  Wall  (Fig.  854). — The  medial  wall  or  septum  is  frequently  more  or 
less  deflected  from  the  median  plane,  thus  lessening  the  size  of  one  nasal  cavity 


996        ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

and  increasing  that  of  the  other;  ridges  or  spurs  of  bone  growing  into  one  or  other 
cavity  from  the  septum  are  also  sometimes  present.  Immediately  over  the  incisive 
canal  at  the  lower  edge  of  the  cartilage  of  the  septum  a  depression,  the  nasopalatine 
recess,  is  seen.  In  the  septum  close  to  this  recess  a  minute  orifice  may  be  discerned; 
it  leads  backward  into  a  blind  pouch,  the  rudimentary  vomeronasal  organ  of  Jacobson, 
which  is  supported  by  a  strip  of  cartilage,  the  vomeronasal  cartilage.  This  organ 
is  well-developed  in  many  of  the  lower  animals,  where  it  apparently  plays  a  part 
in  the  sense  of  smell,  since  it  is  supplied  by  twigs  of  the  olfactory  nerve  and  lined 
by  epithelium  similar  to  that  in  the  olfactory  region  of  the  nose. 

The  roof  of  the  nasal  cavity  is  narrow  from  side  to  side,  except  at  its  posterior 
part,  and  may  be  divided,  from  behind  forward,  into  sphenoidal,  ethmoidal,  and 
frontonasal  parts,  after  the  bones  which  form  it. 

The  floor  is  concave  from  side  to  side  and  almost  horizontal  antero-posteriorly; 
its  anterior  three-fourths  are  formed  by  the  palatine  process  of  the  maxilla,  its 
posterior  fourth  by  the  horizontal  process  of  the  palatine  bone.  In  its  antero- 
medial  part,  directly  over  the  incisive  foramen,  a  small  depression,  the  nasopalatine 
recess,  is  sometimes  seen;  it  points  downward  and  forward  and  occupies  the 
position  of  a  canal  which  connected  the  nasal  with  the  buccal  cavity  in  early 
fetal  life. 

The  Mucous  Membrane  (membrana  mucosa  nasi). — ^The  nasal  mucous  membrane 
lines  the  nasal  cavities,  and  is  intimately  adherent  to  the  periosteum  or  perichon- 
drium. It  is  continuous  with  the  skin  through  the  nares,  and  with  the  mucous 
membrane  of  the  nasal  part  of  the  pharynx  through  the  choanse.  From  the  nasal 
cavity  its  continuity  with  the  conjunctiva  may  be  traced,  through  the  nasolacrimal 
and  lacrimal  ducts;  and  with  the  frontal,  ethmoidal,  sphenoidal,  and  maxillary 
sinuses,  through  the  several  openings  in  the  meatuses.  The  mucous  membrane 
is  thickest,  and  most  vascular,  over  the  nasal  conchse.  It  is  also  thick  over  the 
septum;  but  it  is  very  thin  in  the  meatuses  on  the  floor  of  the  nasal  cavities,  and  in 
the  various  sinuses. 

Owing  to  the  thickness  of  the  greater  part  of  this  membrane,  the  nasal  cavities 
are  much  narrower,  and  the  middle  and  inferior  nasal  conchse  appear  larger  and 
more  prominent  than  in  the  skeleton;  also  the  various  apertures  communicating 
with  the  meatuses  are  considerably  narrowed. 

Structure  of  the  Mucous  Membrane  (Fig.  857). — The  epithelium  covering  the  mucous  mem- 
brane differs  in  its  character  according  to  the  functions  of  the  part  of  the  nose  in  which  it  is  found. 
In  the  respiratory  region  it  is  columnar  and  ciliated.  Interspersed  among  the  columnar  cells 
are  goblet  or  mucin  cells,  while  between  their  bases  are  found  smaller  pyramidal  cells.  Beneath 
the  epithelium  and  its  basement  membrane  is  a  fibrous  layer  infiltrated  with  lymph  corpuscles, 
so  as  to  form  in  many  parts  a  diffuse  adenoid  tissue,  and  under  this  a  nearly  continuous  layer 
of  small  and  larger  glands,  some  mucous  and  some  serous,  the  ducts  of  which  open  upon  the 
surface.  In  the  olfactory  region  the  mucous  membrane  is  yellowish  in  color  and  the  epithelial 
cells  are  columnar  and  non-ciliated;  they  are  of  two  kinds,  supporting  cells  and  olfactory  cells. 
The  supporting  cells  contain  oval  nuclei,  which  are  situated  in  the  deeper  parts  of  the  cells  and 
constitute  the  zone  of  oval  nuclei;  the  superficial  part  of  each  cell  is  columnar,  and  contains 
granules  of  yellow  pigment,  while  its  deep  part  is  prolonged  as  a  delicate  process  which  ramifies 
and  communicates  with  similar  processes  from  neighboring  cells,  so  as  to  form  a  net-work  in  the 
mucous  membrane.  Lying  between  the  deep  processes  of  the  supporting  cells  are  a  number  of 
bipolar  nerve  cells,  the  olfactory  cells,  each  consisting  of  a  small  amount  of  granular  protoplasm 
with  a  large  spherical  nucleus,  and  possessing  two  processes — a  superficial  one  which  runs  between 
the  columnar  epithelial  cells,  and  projects  on  the  surface  of  the  mucous  membrane  as  a  fine, 
hair-hke  process,  the  olfactory  hair ;  the  other  or  deep  process  runs  inward,  is  frequently  beaded, 
and  is  continued  as  the  axon  of  an  olfactory  nerve  fiber.  Beneath  the  epithehum,  and  extending 
through  the  thickness  of  the  mucous  membrane,  is  a  layer  of  tubular,  often  branched,  glands, 
the  glands  of  Bowman,  identical  in  structure  with  serous  glands.  The  epithelial  cells  of  the  nose, 
fauces  and  respiratory  passages  play  an  important  role  in  the  maintenance  of  an  equable  tempera- 
ture, by  the  moisture  with  which  they  keep  the  surface  always  slightly  lubricated. 

Vessels  and  Nerves. — The  arteries  of  the  nasal  cavities  are  the  anterior  and  posterior  eth- 
moidal branches  of  the  ophthalmic,  which  supply  the  ethmoidal  cells,  frontal  sinuses,  and  roof 


THE  NASAL  CAVITY 


997 


of  the  nose;  the  sphenopalatine  branch  of  the  internal  maxillary,  which  supplies  the  mucous 
membrane  covering  the  conchse,  the  meatuses  and  septum;  the  septal  branch  of  the  superior  labial 
of  the  external  maxillary;  the  infraorbital  and  alveolar  branches  of  the  internal  maxillary,  which 
supply  the  Uning  membrane  of  the  maxillary  sinus;  and  the  pharyngeal  branch  of  the  same  artery, 
distributed  to  the  sphenoidal  sinus.  The  ramifications  of  these  vessels  form  a  close  plexiform 
net-work,  beneath  and  in  the  substance  of  the  mucous  membrane. 


Epitheliu. 


Nerve  bundles 


Glands  of  Bow 
man 


Nerve  bundles 


Fia.  857. — Section  of  the  olfactory  mucoua  membrane.    (Cadiat.) 


The  veins  form  a  close  cavernous  plexus  beneath  the  mucous  membrane.    This  plexus  is  especi- 
ally well-marked  over  the  lower  part  of  the  septum  and  over  the  middle  and  inferior  conchae.    Some 
of  the  veins  open  into  the  sphenopalatine  vein;  others  join  the  anterior  facial  vein;  some  accom- 
pany the  ethmoidal  arteries,  and  end  in  the 
ophthalmic  veins;  and,  lastly,  a  few  communi- 
cate with  the  veins  on  the  orbital  surface  of  the 
frontal  lobe  of  the  brain,  through  the  foramina 
in  the  cribriform  plate  of  the  ethmoid  bone; 
when  the  foramen  cecum  is  patent  it  transmits 
a  vein  to  the  superior  sagittal  sinus. 
I     The  lymphatics  have  already  been  described 
'  (p.  695). 

The  nerves  of  ordinary  sensation  are:  the 
nasociliary  branch  of  the  ophthalmic,  filaments 
from  the  anterior  alveolar  branch  of  the  max- 
illary, the  nerve  of  the  pterygoid  canal,  the 
nasopalatine,  the  anterior  palatine,  and  nasal 
branches  of  the  sphenopalatine  ganghon. 

The  nasociliary  branch  of  the  ophthalmic 
distributes  filaments  to  the  forepart  of  the 
septum  and  lateral  wall  of  the  nasal  cavity. 
Filaments  from  the  anterior  alveolar  nerve 
supply  the  inferior  meatus  and  inferior  concha. 
The  nerve  of  the  pterygoid  canal  supphes  the 
upper  and  back  part  of  the  septum,  and  superior 

concha;  and  the  upper  nasal  branches  from  the  sphenopalatine  ganglion  have  a  similar  distri- 
bution. The  nasopalatine  nerve  supphes  the  middle  of  the  septum.  The  anterior  palatine 
nerve  supplies  the  lower  nasal  branches  to  the  middle  and  inferior  conchae. 

The  olfactory,  the  special  nerve  of  the  sense  of  smell,  is  distributed  to  the  olfactory  region. 
Its  fibers  arise  from  the  bipolar  olfactory  cells  and  are  destitute  of  meduUaxy  sheaths.  They 
imite  in  fasciculi  which  form  a  plexus  beneath  the  mucous  membrane  and  then  ascend  in  grooves 
or  canals  in  the  ethmoid  bone;  they  pass  into  the  skull  through  the  foramina  in  the  cribriform 
plate  of  the  ethmoid  and  enter  the  under  surface  of  the  olfactory  bulb,  in  which  they  ramify 
and  form  synapses  with  the  dendrites  of  the  mitral  cells  (Fig.  772). 


Fig.  858. — Nerves  of  septum  of  nose.     Right  side 


998 


ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


The  Accessory  Sinuses  of  the  Nose  (Sinus  Paranasales)  (Figs.  855,  856,  859). 

The  accessory  sinuses  or  air  cells  of  the  nose  are  the  frontal,  ethmoidal,  sphe- 
noidal, and  maxillary;  they  vary  in  size  and  form  in  different  individuals,  and 
are  lined  by  ciliated  mucous  membrane  directly  continuous  with  that  of  the  nasgl, 
cavities.  ^ 

The  Frontal  Sinuses  {sinus  frontales),  situated  behind  the  superciliary  archeS, 
are  rarely  symmetrical,  and  the  septum  between  them  frequently  deviates  to  one 
or  other  side  of  the  middle  line.  Their  average  measurements  are  as  folfows: 
height,  3  cm.;  breadth,  2.5  cm.;  depth  from  before  backward,  2.5  cm.  Each  opens 
into  the  anterior  part  of  the  corresponding  middle  meatus  of  the  nose  through  the 
frontonasal  duct  which  traverses  the  anterior  part  of  the  labyrinth  of  the  ethmoid. 
Absent  at  birth,  they  are  generally  fairly  well  developed  between  the  seventh  and 
eighth  years,  but  only  reach  their  full  size  after  puberty. 


il 


Superior  conclia 

Ethmoidal  air  cell 


Superior 
■meatus 

Middle 
concha 

Middle 
meatus 

Septum 

nasi 
Inferior 
concha 
Maxillary 

sinus 
Inferior 
meatus 


Fig.  859. — Coronal  section  of  na.sal  cavities. 


The  Ethmoidal  Air  Cells  {cellulce  ethmoidales)  consist  of  numerous  thin-walled 
cavities  situated  in  the  ethmoidal  labyrinth  and  completed  by  the  frontal,  maxilla, 
lacrimal,  sphenoidal,  and  palatine.  They  lie  between  the  upper  parts  of  the  nasal 
cavities  and  the  orbits,  and  are  separated  from  these  cavities  by  thin  bony 
laminae.  On  either  side  they  are  arranged  in  three  groups,  anterior,  middle,  and 
posterior.  The  anterior  and  middle  groups  open  into  the  middle  meatus  of  the 
nose,  the  former  by  way  of  the  infundibulum,  the  latter  on  or  above  the  bulla 
ethmoidalis.  The  posterior  cells  open  into  the  superior  meatus  under  cover  of 
the  superior  nasal  concha;  sometimes  one  or  more  opens  into  the  sphenoidal  sinus. 
The  ethmoidal  cells  begin  to  develop  during  fetal  life. 

The  Sphenoidal  Sinuses  {sinus  sphenoidales)  contained  within  the  body  of  the 
sphenoid  vary  in  size  and  shape;  owing  to  the  lateral  displacement  of  the  inter- 


THE  ACCESSORY  SINUSES  OF  THE  NOSE 


999 


rening  septum  they  are  rarely  symmetrical.  The  following  are  their  average 
measurements:  vertical  height,  2.2  cm. ;  transverse  breadth,  2  cm.;  antero-posterior 
depth,  2.2  cm.    When  exceptionally  large  they  may  extend  into  the  roots  of  the 


Ethmoidal  infundihulum 
Ant.  ethmoidal  air  cells  % 


Post,  ethmoidal  air  cells, 


Primitive  frontal  sinus 
^  N asolacrim.al  duct 


Maxillary  sinus 


Fig.  860.' — Specimen  from  a  child  eight  days  old.     By  sagittal  sections  removing  the  lateral  portion  of  frontal  bone, 
lamina  papyracea  of  ethmoid,  and  lateral  portion  of  maxilla — the  sinus  maxillaris,  cellute  ethmoidales,  anterior  and  po8- 
,  terior,  infundibulum  ethmoidale,  and  the  primitive  sinus  frontalis  are  brought  into  view.     (Davis.) 

pterygoid  processes  or  great  wings,  and  may  invade  the  basilar  part  of  the  occipital 
bone.  Each  sinus  communicates  with  the  sphenoethmoidal  recess  by  means  of 
an  aperture  in  the  upper  part  of  its  anterior  wall.  They  are  present  as  minute 
,  cavities  at  birth,  but  their  main  development  takes  place  after  puberty. 


Ant.  ethmoidal  air  cells ^ 
Post,  ethmoidal  air  ceZZ*. 


Kiasserian  ganglion 


Optic  foramen 
Int.  carotid  art. 
Oculomotor  nerve 
Trochlear  nerve 


Frontul  sinws  developing 
from  a  frontal  cell 

ihmoidal  infundihulum 
ijssa  of  lacrimul  sac 


[axillary  ostium 


Abduc 
Int.  carotid  art. 

Fig.  861. — Specimen  from  a  child  one  year,  four  months,  and  seven  days  old.    Lateral  view  of  frontal, 
ethmoidal,  and  maxillary  sinus  areas.     (Davis.) 


The  Maxillary  Sinus  {sinus  maxillaris;  antrum  of  Highmore),  the  largest  of  the 
accessory  sinuses  of  the  nose,  is  a  pyramidal  cavity  in  the  body  of  the  maxilla. 
Its  base  is  formed  by  the  lateral  wall  of  the  nasal  cavity,  and  its  apex  extends  into 
the  zygomatic  process.    Its  roof  or  orbital  wall  is  frequently  ridged  by  the  infra- 


1  Davis,  W.  B.    Nasal  Accessory  Sinuses  in  Man,  1914. 


1000       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

orbital  canal,  while  its  floor  is  formed  by  the  alveolar  process  and  is  usually  ^  to  10 
mm.  below  the  level  of  the  floor  of  the  nose;  projecting  into  the  floor  are  several 
conical  elevations  corresponding  with  the  roots  of  the  first  and  second  molar  teeth, 
and  in  some  cases  the  floor  is  perforated  by  one  or  more  of  these  roots.  The  size 
of  the  sinus  varies  in  difl^erent  skulls,  and  even  on  the  two  sides  of  the  same  skull. 
The  adult  capacity  varies  from  9.5  c.c.  to  20  c.c,  average  about  14.75  c.c.  The  fol- 
lowing measurements  are  those  of  an  average-sized  sinus:  vertical  height  opposite 
the  first  molar  tooth,  3.75  cm.;  transverse  breadth,  2.5  cm.;  antero-posterior  depth, 
3  cm.  In  the  antero-superior  part  of  its  base  is  an  opening  through  which  it  com- 
municates with  the  lower  part  of  the  hiatus  semilunaris ;  a  second  orifice  is  frequently 
seen  in,  or  immediately  behind,  the  hiatus.  The  maxillary  sinus  appears  as  a  shal- 
low groove  on  the  medial  surface  of  the  bone  about  the  fourth  month  of  fetal  life, 
but  does  not  reach  its  full  size  until  after  the  second  dentition.^  At  birth  it  measures 
about  7  mm.  in  the  dorso-ventral  direction  and  at  twenty  months  about  20  mm.^ 


Frontal  sinus 

Frontal  ostium 
Infundibulum  cells 

Fossa  of  lacrimul  sac 


Maxillary  ostium      v 


Maxillary  septum 


Ant.  ethmoidal  air  cells 


Post,  ethmoidal  air  cells 
ic  nerve 


Fig.  862. — Specimen  from  a  child  eight  years,  eight  months,  and  one  day  old.  Lateral  view  of  frontal,  ethmoidal  and 
maxillary  sinus  areas,  the  lateral  portion  of  each  having  been  removed  by  sagittal  cuts.  Note  that  the  sinus  frontalis 
developed  directly  from  the  infundibulum  ethmoidale.    Note  also  the  incomplete  septa  in  the  sinus  maxillaris.     (Davis.) 


THE    ORGAN   OF   SIGHT    (ORG ANON  VISUS;   THE  EYE). 

The  bulb  of  the  eye  {hulhus  oculi;  eyeball),  or  organ  of  sight,  is  contained  in  the 
cavity  of  the  orbit,  where  it  is  protected  from  injury  and  moved  by  the  ocular 
muscles.  Associated  with  it  are  certain  accessory  structures,  viz.,  the  muscles, 
fasciae,  eyebrows,  eyelids,  conjunctiva,  and  lacrimal  apparatus. 

The  bulb  of  the  eye  is  imbedded  in  the  fat  of  the  orbit,  but  is  separated  from  it 
by  a  thin  membranous  sac,  the  fascia  bulbi  (page  1024) .  It  is  composed  of  segments 
of  two  spheres  of  different  sizes.    The  anterior  segment  is  one  of  a  small  sphere; 


1  The  various  measurements  of  the  accessory  sinuses  of  the  nose  are  based  on  those  given  by  Aldren  Turner  in  hi» 
Accessory  Sinuses  of  the  Nose. 

2  Schaeffer,  J.  P.,   Am.  Jour.  Anat.,  1910,  x. 


THE  ORGAN  OF  SIGHT 


1001 


it  is  transparent,  and  forms  about  one-sixth  of  the  bulb.  It  is  more  prominent 
than  the  posterior  segment,  which  is  one  of  a  larger  sphere,  and  is  opaque,  and  forms 
about  five-sixths  of  the  bulb.  The  term  anterior  pole  is  applied  to  the  central  point 
of  the  anterior  curvature  of  the  bulb,  and  that  of  posterior  pole  to  the  central  point 
of  its  posterior  curvature;  a  line  joining  the  two  poles  forms  the  optic  axis.  The 
axes  of  the  two  bulbs  are  nearly  parallel,  and  therefore  do  not  correspond  to  the 


Cavity  of  fore-brain 


Invagination  of 

ectoderm  to  form 

lens  rvdiment 


Pigmented  layer  of  retina 


Margin  of  optic  cup 


Nervous  layer  of  retina 
Optic  vesicle 


Fig.  863. — Transverse  section  of  head  of  chick  embryo  of  forty-eight  hours'  incubation.     (Duval.) 


axes  of  the  orbits,  which  are  directed  forward  and  lateral  ward.  The  optic  nerves 
follow  the  direction  of  the  axes  of  the  orbits,  and  are  therefore  not  parallel;  each 
enters  its  eyeball  3  mm.  to  the  nasal  side  and  a  little  below  the  level  of  the  posterior 
pole.  The  bulb  measures  rather  more  in  its  transverse  and  antero-posterior  diame- 
ters than  in  its  vertical  diameter,  the  former  amounting  to  about  24  mm.,  the  latter 
to  about  23.5  mm. ;  in  the  female  all  three  diameters  are  rather  less  than  in  the  male; 
its    antero-posterior    diameter    at 


Cavity  of  fore-brain 


Pigmented  layer 
of  retina 

Ectoderm 


Lens 

Nervous  layer  of 
retina 


birth  is  about  17.5  mm.,  and  at 
puberty  from  20  to  21  mm. 

Development.— The  eyes  begin 
to  develop  as  a  pair  of  diverticula 
from  the  lateral  aspects  of  the  fore- 
brain.  These  diverticula  make  their 
appearance  before  the  closure  of  the 
anterior  end  of  the  neural  tube; 
after  the  closure  of  the  tube  they  are 
known  as  the  optic  vesicles.  They 
project  toward  the  sides  of  the 
head,  and  the  peripheral  part  of 
each  expands  to  form  a  hollow 
bulb,  while  the  proximal  part  re- 
mains narrow  and  constitutes  the 
optic  stalk  (Figs.  863,  864).  The 
ectoderm  overlying  the  bulb  be- 
comes thickened,  invaginated,  and  finally  severed  from  the  ectodermal  covering 
of  the  head  as  a  vesicle  of  cells,  the  lens  vesicle,  which  constitutes  the  rudi- 
ment of  the  crystalline  lens.  The  outer  wall  of  the  bulb  becomes  thickened  and 
invaginated,  and  the  bulb  is  thus  converted  into  a  cup,  the  optic  cup,  consisting 
of  two  strata  of  cells  (Fig.  864).  These  two  strata  are  continuous  with  each 
other  at  the  cup  margin,  which  ultimately  overlaps  the  front  of  the  lens  and 
reaches  as  far  forward  as  the  future  aperture  of  the  pupil.  The  invagination  is  not 
limited  to  the  outer  wall  of  the  bulb,  but  involves  also  its  postero-inferior  surface 


Optic  stalk 


Fig.  864. — Transverse  section  of  head  of  chick  embryo  of 
fifty-two  hours'  incubation.     (Duval.) 


ORGANS  OF  THEWnSESAND  THE  COMMON  INTEGUMENT 

and  extends  in  the  form  of  a  groove  for  some  distance  along  the  optic  stalk,  so  that, 
for  a  time,  a  gap  or  fissure,  the  choroidal  fissure,  exists  in  the  lower  part  of  the 
cup  (Fig.  865).  Through  the  groove  and  fissure  the  mesoderm  extends  into  the 
optic  stalk  and  cup,  and  in  this  mesoderm  a  bloodvessel  is  developed;  during  the 
seventh  week  the  groove  and  fissure  are  closed  and  the  vessel  forms  the  central 
artery  of  the  retina.  Sometimes  the  choroidal  fissure  persists,  and  when  this 
occurs  the  choroid  and  iris  in  the  region  of  the  fissure  remain  undeveloped,  giving 
rise  to  the  condition  known  as  coloboma  of  the  choroid  or  iris. 


Telencephalon 

Edge  of  optic  cup 


I 


Thalamencephalon 
Optic  stalk 


Choroidal  fissure 


Arteria  centralis 
retinae 


Fig.  865. — Optic  cup  and  choroidal  fissure  seen  from  below,  from  a  human  embryo  of  about  four  weeks. 

(Kollmann.) 

The  retina  is  developed  from  the  optic  cup.  The  outer  stratum  of  the  cup 
persists  as  a  single  layer  of  cells  which  assume  a  columnar  shape,  acquire  pigment, 
and  form  the  pigmented  layer  of  the  retina;  the  pigment  first  appears  in  the  cells 
near  the  edge  of  the  cup.  The  cells  of  the  inner  stratum  proliferate  and  form  a 
layer  of  considerable  thickness  from  which  the  nervous  elements  and  the  susten- 
tacular  fibers  of  the  retina,  together  with  a  portion  of  the  vitreous  body,  are 
developed.  In  that  portion  of  the  cup  which  overlaps  the  lens  the  inner  stratum  is 
not  differentiated  into  nervous  elements,  but  forms  a  layer  of  columnar  cells  which 
is  applied  to  the  pigmented  layer,  and  these  two  strata  form  the  pars  ciliaris  and 
pars  iridica  retinae. 

The  cells  of  the  inner  or  retinal  layer  of  the  optic  cup  become  differentiated  into  spongioblasts 
and  germinal  cells,  and  the  latter  by  their  subdivisions  give  rise  to  neuroblasts.  From  the  spongio- 
blasts the  sustentacular  fibers  of  Miiller,  the  outer  and  inner  limiting  membranes,  together  with 
the  groimdwork  of  the  molecular  layers  of  the  retina  are  formed.  The  neuroblasts  become 
arranged  to  form  the  ganglionic  and  nuclear  layers.  The  layer  of  rods  and  cones  is  first  developed 
in  the  central  part  of  the  optio  cup,  and  from  there  gradually  extends  toward  the  cup  margin. 
All  the  layers  of  the  retina  are  completed  by  the  eighth  month  of  fetal  life. 

The  optic  stalk  is  converted  into  the  optic  nerve  by  the  obliteration  of  its  cavity 
and  the  growth  of  nerve  fibers  into  it.  Most  of  these  fibers  are  centripetal,  and 
grow  backward  into  the  optic  stalk  from  the  nerve  cells  of  the  retina,  but  a  few 
extend  in  the  opposite  direction  and  are  derived  from  nerve  cells  in  the  brain.  The 
fibers  of  the  optic  nerve  receive  their  medullary  sheaths  about  the  tenth  week  after 
birth.  The  optic  chiasma  is  formed  by  the  meeting  and  partial  decussation  of  the 
fibers  of  the  two  optic  nerves.  Behind  the  chiasma  the  fibers  grow  backward  as 
the  optic  tracts  to  the  thalami  and  mid-brain. 

The  crystalline  lens  is  developed  from  the  lens  vesicle,  which  recedes  within  the 


THE  ORGAN  OF  SIGHT 


1003 


margin  of  the  cup,  and  becomes  separated  from  the  overlying  ectoderm  by  mes- 
oderm. The  cells  forming  the  posterior  wall  of  the  vesicle  lengthen  and  are  con- 
verted into  the  lens  fibers,  which  grow  forward  and  fill  up  the  cavity  of  the  vesicle 
(Fig.  866) .  The  cells  forming  the  anterior  wall  retain  their  cellular  character,  and 
form  the  epithelium  on  the  anterior  surface  of  the  adult  lens.  By  the  second  month 
the  lens  is  invested  by  a  vascular  mesodermal  capsule,  the  capsula  vasculosa  lentis; 
the  bloodvessels  supplying  the  posterior  part  of  this  capsule  are  derived  from  the 
hyaloid  artery;  those  for  the  anterior  part  from  the  anterior  ciliary  arteries;  the 
portion  of  the  capsule  which  covers  the  front  of  the  lens  is  named  the  pupillary 
membrane.  By  the  sixth  month  all  the  vessels  of  the  capsule  are  atrophied  except 
the  hyaloid  artery,  which  disappears  during  the  ninth  month;  the  position  of  this 
artery  is  indicated  in  the  adult  by  the  hyaloid  canal,  which  reaches  from  the  optic 
disk  to  the  posterior  surface  of  the  lens.  With  the  loss  of  its  bloodvessels  the  cap- 
sula vasculosa  lentis  disappears,  but  sometimes  the  pupillary  membrane  persists 
at  birth,  giving  rise  to  the  condition  termed  congenital  atresia  of  the  pupil. 


Rudiment  of  chotmd 
Rectus  muscle 


Optic  nerve 


Retina 
Pigmented  layer 
Vitreous  body 
(shrunken) 


Cornea 
Membrana  pupillarta 


Pars  ciliaris  and  fare  iridica  retince 
Fia.  866. — Horizontal  section  through  the  eye  of  an  eighteen  days'  embryo  rabbit.      X  30. 


(KoUiker.) 


The  vitreous  body  is  developed  between  the  lens  and  the  optic  cup.  The  lens 
rudiment  and  the  optic  vesicle  are  at  first  in  contact  with  each  other,  but  after  the 
closure  of  the  lens  vesicle  and  the  formation  of  the  optic  cup  the  former  withdraws 
itself  from  the  retinal  layer  of  the  cup;  the  two,  however,  remain  connected  by  a  net- 
work of  delicate  protoplasmic  processes.  This  network,  derived  partly  from  the  cells 
of  the  lens  and  partly  from  those  of  the  retinal  layer  of  the  cup,  constitutes  the 
primitive  vitreous  body  (Figs.  867,  868).  At  first  these  protoplasmic  processes 
spring  from  the  whole  of  the  retinal  layer  of  the  cup,  but  later  are  limited  to  the 
ciliary  region,  where  by  a  process  of  condensation  they  appear  to  form  the  zonula 
ciliaris.  The  mesoderm  which  enters  the  cup  through  the  choroidal  fissure  and 
around  the  equator  of  the  lens  becomes  intimately  united  with  this  reticular  tissue, 
and  contributes  to  form  the  vitreous  body,  which  is  therefore  derived  partly  from 
the  ectoderm  and  partly  from  the  mesoderm. 


1004     ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


Pigmented     Mesodermal 

layer  of        part  of  Rudiment 

Upper  eyelid        retina    vitreous  body       of  sclera 


f&S'a^  ^V  ^S  '^  9ZAP  c»    «»    -«» 


Mesoderm  Ectodermal    Nervous  layer 

part  of  of  retina 

vitreous  body 
Fig.  867. — Sagittal  section  of  eye  of  human  embryo  of  six  weeks.      (KoUmann.) 


Lens 


Ehod-vesad 


Primitive 

vitreous 

body 


Retina 


Outer  layer  of 
optic  cup 


Fia.  868. — Section  of  developing  eye  of  trout.     (Swly.) 


THE  TUNICS  OF  THE  EYE  1005 

The  anterior  chamber  of  the  eye  appears  as  a  cleft  in  the  mesoderm  separating 
the  lens  from  the  overlying  ectoderm.  The  layer  of  mesoderm  in  front  of  the  cleft 
forms  the  substantia  propria  of  the  cornea,  that  behind  the  cleft  the  stroma  of  the 
iris  and  the  pupillary  membrane.  The  fibers  of  the  ciliary  muscle  are  derived  from 
the  mesoderm,  but  those  of  the  Sphincter  and  Dilatator  pupillse  are  of  ectodermal 
origin,  being  developed  from  the  cells  of  the  pupillary  part  of  the  optic  cup. 

The  sclera  and  choroid  are  derived  from  the  mesoderm  surrounding  the  optic  cup. 

The  eyelids  are  formed  as  small  cutaneous  folds  (Figs.  866,  867),  which  about 
the  middle  of  the  third  month  come  together  and  unite  in  front  of  the  cornea. 
They  remain  united  until  about  the  end  of  the  sixth  month. 

The  lacrimal  sac  and  nasolacrimal  duct  result  from  a  thickening  of  the  ectoderm 
in  the  groove,  nasooptic  furrow,  between  the  lateral  nasal  and  maxillary  processes. 
This  thickening  forms  a  solid  cord  of  cells  which  sinks  into  the  mesoderm ;  during 
the  third  month  the  central  cells  of  the  cord  break  down,  and  a  lumen,  the  naso- 
lacrimal duct,  is  established.  The  lacrimal  ducts  arise  as  buds  from  the  upper  part 
of  the  cord  of  cells  and  secondarily  establish  openings  (punda  lacrimalia)  on  the 
margins  of  the  lids.  The  epithelium  of  the  cornea  and  conjunctiva,  and  that  which 
lines  the  ducts  and  alveoli  of  the  lacrimal  gland,  are  of  ectodermal  origin,  as  are 
also  the  eyelashes  and  the  lining  cells  of  the  glands  which  open  on  the  lid-margins. 


The  Tunics  of  the  Eye  (Fig.  869). 


I ...^... 

F  sclera  behind  and  the  cornea  in  front;  (2)  a  vascular  pigmented  tunic,  comprising, 
from  behind  forward,  the  choroid,  ciliary  body,  and  iris;  and  (3)  a  nervous  tunic, 
the  retina. 

»The  Fibrous  Tunic  {tunica  fibrosa  oculi). — The  sclera  and  cornea  (Fig.  869) 
form  the  fibrous  tunic  of  the  bulb  of  the  eye;  the  sclera  is  opaque,  and  constitutes 
the  posterior  five-sixths  of  the  tunic;  the  cornea  is  transparent,  and  forms  the 
anterior  sixth. 
Ih  The  Sclera. — The  sclera  has  received  its  name  from  its  extreme  density  and  hard- 
■™  ness;  it  is  a  firm,  unyielding  membrane,  serving  to  maintain  the  form  of  the  bulb. 
It  is  much  thicker  behind  than  in  front;  the  thickness  of  its  posterior  part  is  1  mm. 
Its  external  surface  is  of  white  color,  and  is  in  contact  with  the  inner  surface  of  the 
fascia  of  the  bulb ;  it  is  quite  smooth,  except  at  the  points  where  the  Recti  and 
Obliqui  are  inserted  into  it;  its  anterior  part  is  covered  by  the  conjunctival  mem- 
brane. Its  inner  surface  is  brown  in  color  and  marked  by  grooves,  in  which  the 
ciliarj^  nerves  and  vessels  are  lodged ;  it  is  separated  from  the  outer  surface  of  the 
choroid  by  an  extensive  lymph  space  (spatiuni  perichorioideale)  which  is  traversed 

I  by  an  exceedingly  fine  cellular  tissue,  the  lamina  suprachorioidea.  Behind  it  is 
■  pierced  by  the  optic  nerve,  and  is  continuous  through  the  fibrous  sheath  of  this 
nerve  with  the  dura  mater.  Where  the  optic  nerve  passes  through  the  sclera,  the 
latter  forms  a  thin  cribriform  lamina,  the  lamina  cribrosa  sclerae;  the  minute  orifices 
in  this  lamina  serve  for  the  transmission  of  the  nervous  filaments,  and  the  fibrous 

1^  septa  dividing  them  from  one  another  are  continuous  with  the  membranous  pro- 
H  cesses  which  separate  the  bundles  of  nerve  fibers.  One  of  these  openings,  larger 
than  the  rest,  occupies  the  center  of  the  lamina;  it  transmits  the  central  artery 
and  vein  of  the  retina.  Around  the  entrance  of  the  optic  nerve  are  numerous 
small  apertures  for  the  transmission  of  the  ciliary  vessels  and  nerves,  and  about 
midway  between  this  entrance  and  the  sclerocorneal  junction  are  four  or  five 
large  apertures  for  the  transmission  of  veins  (venae  vorticosae) .  In  front,  the  sclera 
is  directly  continuous  with  the  cornea,  the  line  of  union  being  termed  the  sclero- 
corneal junction.  In  the  inner  part  of  the  sclera  close  to  this  junction  is  a  circular 
canal,  the  sinus  venosus  sclerae  {canal  of  Schlemm) .    In  a  meridional  section  of  this 


OF  THE  SENSES  AND  THE'COMWoN  INTEGUMENT 

region  this  sinus  presents  the  appearance  of  a  cleft,  the  outer  wall  of  which  consists 
of  the  firm  tissue  of  the  sclera,  while  its  inner  wall  is  formed  by  a  triangular  mass 
of  trabecular  tissue  (Fig.  870);  the  apex  of  the  mass  is  directed  forward  and  is  con- 
tinuous with  the  posterior  elastic  lamina  of  the  cornea.  The  sinus  is  lined  by 
endothelium  and  communicates  externally  with  the  anterior  ciliary  veins. 

The  aqueous  humor  drains  into  the  scleral  sinuses  by  passage  through  the 
"pectinate  villi"  which  are  analogous  in  structure  and  function  to  the  arachnoid 
villi  of  the  cerebral  meninges.^ 


StUcus  cirevlaris  comece 
Posterior  cTiarnber 


Sulcus  drcularis  cornece 
Ciliary  body 


Zonular  spaces 


Rectus 
lateralis 


Hyaloid  canal 

Rectus 
medialis 


Sclera 

Choroid 

Retina 


A.  centralis  retince 

y\\m\\\\\\\"m-  Optic  nerve 

Fovea  centralis  /\\m\vu-'Jii» 

Nerve  sheath 

Via.  869. — Horizontal  section  of  the  eyeball. 

Structure. — The  sclera  is  formed  of  white  fibrous  tissue  intermixed  with  fine  elastic  fibers; 
flattened  connective-tissue  corpuscles,  some  of  which  ai"e  pigmented,  are  contained  in  cell  spaces 
between  the  fibers.  The  fibers  are  aggregated  into  bundles,  which  are  arranged  chiefly  in  a 
longitudinal  direction.  Its  vessels  are  not  numerous,  the  capillaries  being  of  small  size,  uniting 
at  long  and  wide  intervals.  Its  nerves  are  derived  from  the  ciliary  nerves,  but  their  exact  mode 
of  ending  is  not  known. 

The  Cornea. — The  cornea  is  the  projecting  transparent  part  of  the  external  tunic^ 
and  forms  the  anterior  sixth  of  the  surface  of  the  bulb.^  It  is  almost  circular  in 
outline,  occasionally  a  little  broader  in  the  transverse  than  in  the  vertical  direction. 
It  is  convex  anteriorly  and  projects  like  a  dome  in  front  of  the  sclera.  Its  degree 
of  curvature  varies  in  different  individuals,  and  in  the  same  individual  at  different 
periods  of  life,  being  more  pronounced  in  youth  than  in  advanced  life.  The  cornea 
is  dense  and  of  uniform  thickness  throughout;  its  posterior  surface  is  perfectly 
circular  in  outline,  and  exceeds  the  anterior  surface  slightly  in  diameter.  Imme- 
diately in  front  of  the  sclero-corneal  junction  the  cornea  bulges  inward  as  a  thickened 
rim,  and  behind  this  there  is  a  distinct  furrow  between  the  attachment  of  the  iris 
and  the  sclero-corneal  junction.     This  furrow  has  been  named  by  Arthur  Thomson^ 


1  Wegefarth,  Jour.  Med.  Research,  September,  1914. 

2  Atlas  of  the  Eye,  Clarendon  Press,  Oxford,  1912. 


THE  TUNICS  OF  THE  EYE 


1007 


le  "sulcus  circularis  comeae;  it  is  bounded  externally  by  the  trabecular  tissue 
already  described  as  forming  the  inner  wall  of  the  sinus  venosus  sclerse.  Between 
this  tissue  and  the  anterior  surface  of  the  attached  margin  of  the  iris  is  an  angular 
recess,  named  the  iridial  angle  or  filtration  angle  of  the  eye  (Fig.  870) .  Immediately 
outside  the  filtration  angle  is  a  projecting  rim  of  scleral  tissue  which  appears  in  a 
meridional  section  as  a  small  triangular  area,  termed  the  scleral  spur.  Its  base 
is  continuous  with  the  inner  surface  of  the  sclera  immediately  to  the  outer  side  of  the 
filtration  angle  and  its  apex  is  directed  forward  and  inward.  To  the  anterior  sloping 
margin  of  this  spur  are  attached  the  bundles  of  trabecular  tissue  just  referred  to; 
from  its  posterior  margin  the  meridional  fibers  of  the  Ciliaris  muscle  arise. 


Cornea 


Sirnis  venous  sclerce 
Trabecular  tissue  \ 


Sclera 


Scleral  vein 


Radial  muscular  fibers  t  \  i  nr  -j-       7  ^t         t  r^-i-     ■ 

of  iris  /  I  I         Meridional  fibers  of  Ciliarts 

Circular  fibers  of  Ciliaris  I  Scleral  spur 

Iridial  angle 

Fig.  870. — Enlarged  general  view  of  the  iridial  angle.      (Arthur  Thomson.) 


Structure  (Fig.  871). — The  cornea  consists  from  before  backward  of  four  layers,  viz.:  (IJ 
the  corneal  epithelium,  continuous  with  that  of  the  conjunctiva;  (2)  the  substantia  propria 
(3)  the  posterior  elastic  lamina;  and  (4)  the  endothelium  of  the  anterior  chamber. 

The  corneal  epithelium  {epithelium  corneoe;  anterior  layer)  covers  the  front  of  the  cornea  and 
consists  of  several  layers  of  cells.  The  cells  of  the  deepest  layer  are  columnar;  then  follow  two  or 
three  layers  of  polyhedral  cells,  the  majority  of  which  are  prickle  cells  similar  to  those  found  in 
the  stratum  mucosum  of  the  cuticle.  Lastly,  there  are  three  or  four  layers  of  squamous  cells, 
with  flattened  nuclei. 

The  substantia  propria  is  fibrous,  tough,  imyielding,  and  perfectly  transparent.  It  is  com- 
posed of  about  sixty  flattened  lamellae,  superimposed  one  on  another.  These  lamellae  are  made 
up  of  bundles  of  modified  connective  tissue,  the  fibers  of  which  are  directly  continuous  with  those 
of  the  sclera.  The  fibers  of  each  lamella  are  for  the  most  part  parallel  with  one  another,  but  at 
right  angles  to  those  of  adjacent  lamellae.  Fibers',  however,  frequently  pass  from  one  !amella 
to  the  next.  '^ 


)8      ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

The  lamelte  are  connected  with  each  other  by  an  interstitial  cement  substance,  in  which  are 
spaces,  the  corneal  spaces.  These  are  stellate  in  shape  and  communicate  with  one  another  by 
numerous  offsets.  Each  contains  a  cell,  the  corneal  corpuscle,  resembling  in  form  the  space  in 
which  it  is  lodged,  but  not  entirely  filling  it. 


^iiaf^v,'Jv^.Jaaj^.rii-l«i'UXV^WJ.tl:-lial..n.i-aj'j^.,|.:f^^,.,o.V6,Xiaig:a 


Fig.  871. — Vertical  section  of  human  cornea  from  near  the  margin.  (Waldcyer.)  Magnified.  1.  Epithelium. 
2.  Anterior  elastic  lamina.  3.  substantia  propria.  4.  Posterior  elastic  lamina.  5.  Endothelium  of  the  anterior 
chamber,  a.  Oblique  fibers  in  the  anterior  layer  of  the  substantia  propria,  b.  Lamellse  the  fibers  of  which  are  cut 
across,  producing  a  dotted  appearance,  c.  Corneal  corpuscles  appearing  fusiform  in  section,  d.  Lamellse  the  fibers 
of  which  are  cut  longitudinally,  e.  Transition  to  the  sclera,  with  more  distinct  fibrillation,  and  surmounted  by  a 
thicker  epithelium.    /.  Small  bloodvessels  cut  across  near  the  margin  of  the  cornea. 

The  layer  immediately  beneath  the  corneal  epithelium  presents  certain  characteristics  which 
have  led  some  anatomists  to  regard  it  as  a  distinct  membrane,  and  it  has  been  named  the  anterior 
elastic  lamina  {lamina  elastica  anterior;  anterior  limiting  layer;  Bowman's  membrane).  It  differs, 
however,  from  the  posterior  elastic  lamina,  in  presenting  evidence  of  fibrillar  structure,  and  in 
not  having  the  same  tendency  to  curl  inward,  or  to  undergo  fracture,  when  detached  from  the 
other  layers  of  the  cornea.  It  consists  of  extremely  closely  interwoven  fibrils,  similar  to  those 
found  in  the  substantia  propria,  but  contains  no  corneal  corpuscles.  It  may  be  regarded  as  a 
condensed  part  of  the  substantia  propria. 

The  posterior  elastic  lamina  (lamina  elastica  posterior;  membrane  of  Descemet;  membrane  of 
Demours)  covers  the  posterior  surface  of  the  substantia  propria,  and  is  an  elastic,  transparent 
homogeneous  membrane,  of  extreme  thinness,  which  is  not  rendered  opaque  by  either  water, 
alcohol,  or  acids.  When  stripped  from  the  substantia  propria  it  curls  up,  or  rolls  upon  itself 
with  the  attached  surface  innermost. 

At  the  margin  of  the  cornea  the  posterior  elastic  lamina  breaks  up  into  fibers  which  form 
the  trabecular   tissue   already  described;   the  spaces  between   the  trabeculae  are  termed  the 


THE  TUNICS  OF  THE  EYE 


1009 


spaces  of  the  angle  of  the  iris  (spaces  of  Fontana);  they  communicate  with  the  sinus  venosus 
sclerge  and  with  the  anterior  chamber  at  the  filtration  angle.  Some  of  the  fibers  of  this  trabecular 
tissue  are  continued  into  the  substance  of  the  iris,  forming  the  pectinate  ligament  of  the  iris; 
while  others  are  connected  with  the  forepart  of  the  sclera  and  choroid. 

The  endothelium  of  the  anterior  chamber  {endothelium  cameroe  anterioris;  posterior  layer; 
corneal  endothelium)  covers  the  posterior  surface  of  the  elastic  lamina,  is  reflected  on  to  the 
front  of  the  iris,  and  also  lines  the  spaces  of  the  angle  of  the  iris;  it  consists  of  a  single  stratum 
of  polygonal,  flattened,  nucleated  cells. 

Vessels  and  Nerves. — The  cornea  is  a  non-vascular  structure;  the  capillary  vessels  ending  in 
loops  at  its  circumference  are  derived  from  the  anterior  ciliary  arteries.  Lymphatic  vessels  have 
not  yet  been  demonstrated  in  it,  but  are 
represented  by  the  channels  in  which  the 
bundles  of  nerves  run;  these  channels  are 
lined  by  an  endothehum.  The  nerves  are 
numerous  and  are  derived  from  the  ciliary 
nerves.  Around  the  periphery  of  the  cor- 
nea they  form  an  annular  plexus,  from 
which  fibers  enter  the  substantia  propria. 
They  lose  their  medullary  sheaths  and 
ramify  throughout  its  substance  in  a  deli- 
cate net-work,  and  their  terminal  filaments 
form  a  firm  and  closer  plexus  on  the  sur- 
face of  the  cornea  proper,  beneath  the 
epithelium.  This  is  termed  the  subepithe- 
lial plexus,  and  from  it  fibrils  are  given  off 
which  ramify  between  the  epithelial  cells, 
forming  an  intraepithelial  plexus. 

The  Vascular  Tunic  {tunica  vascu- 
losa  ocidi)  (Figs.  872,  873,  874).— 
The  vascular  tunic  of  the  eye  is 
formed  from  behind  forward  by  the 
choroid,  the  ciHary  body ,  and  the  iris. 

The  choroid  invests  the  posterior 
five-sixths  of  the  bulb,  and  extends 
as  far  forward  as  the  ora  serrata  of 
the  retina.  The  ciliary  body  connects 
the  choroid  to  the  circumference  of 

the  iris.  The  iris  is  a  circular  diaphragm  behind  the  cornea,  and  presents  near 
its  center  a  rounded  aperture,  the  pupil. 

Anlericyr  ciliary  artery 


Fig.  872. — The  choroid  and  iris.     (Enlarged.) 


Short  ciliary  arteries 


Anterior  ciliary  artery 


Fia.  873. — The  arteries  of  the  choroid  and  ins.     i  ue  greater  part  of  the  sclera  has  been  removed.     (Enlarged.) 


The  Choroid  (chorioidea) . — The  choroid  is  a  thin,  highl}^  vascular  membrane,  of 
a  dark  brown  or  chocolate  color,  investing  the  posterior  five-sixths  of  the  globe; 
64 


1010       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


it  is  pierced  behind  by  the  optic  nerve,  and  in  this  situation  is  firmly  adherent  to 
the  sclera.  It  is  thicker  behind  than  in  front.  Its  outer  surface  is  loosely  connected 
by  the  lamina  suprachorioidea  with  the  sclera;  its  inner  surface  is  attached  to  the 
pigmented  layer  of  the  retina. 

Structure. — The  choroid  consists  mainly  of  a  dense  capillary  plexus,  and  of  small  arteri(!8 
and  veins  carrying  blood  to  and  returning  it  from  this  plexus.  On  its  external  surface  is  a  thin 
membrane,  the  lamina  suprachorioidea,  composed  of  deUcate  non-vascular  lamellae — each  lamella 
consisting  of  a  net-work  of  fine  elastic  fibers  among  which  are  branched  pigment  cells.  The  spaces 
between  the  lamellae  are  lined  by  endothelium,  and  open  freely  into  the  perichoroidal  lymph 
space,  which,  in  its  turn,  communicates  with  the  periscleral  space  by  the  perforations  in  the 
sclera  through  which  the  vessels  and  nerves  are  transmitted. 

Internal  to  this  lamina  is  the  choroid  proper,  consisting  of  two  layers:  an  outer,  composed 
of  small  arteries  and  veins,  with  pigment  cells  interspersed  between  them;  and  an  inner,  consist- 
ing of  a  capillary  plexus.  The  outer  layer  {lamina  vasculosa)  consists,  in  part,  of  the  larger  branches 
of  the  short  ciliary  arteries  which  run  forward  between  the  veins,  before  they  bend  inward  to  end 
in  the  capillaries,  but  is  formed  principally  of  veins,  named,  from  their  arrangement,  the  ven8B 

vorticosse.  They  converge  to  four  or 
five  equidistant  trunks,  which  pierce  the 
sclera  about  midway  between  the  sclero- 
corneal  junction  and  the  entrance  of  the 
optic  nerve.  Interspersed  between  the 
vessels  are  dark  star-shaped  pigment 
cells,  the  processes  of  which,  communicat- 
ing with  those  of  neighboring  cells,  form 
a  delicate  net-work  or  stroma,  which 
toward  the  inner  surface  of  the  choroid 
loses  its  pigmentary  character.  The 
inner  layer  {lamina  choriocapillaris)  con- 
sists of  an  exceedingly  fine  capillary 
plexus,  formed  by  the  short  ciliary  vessels; 
the  net-work  is  closer  and  finer  in  the  pos- 
terior than  in  the  anterior  part  of  the 
choroid.  About  1.25  cm.  behind  the 
cornea  its  meshes  become  larger,  and  are 
continuous  with  those  of  the  ciliary 
processes.  These  two  laminae  are  con- 
nected by  a  stratum  intermedivmi  con- 
sisting of  fine  elastic  fibers.  On  the  inner 
surface  of  the  lamina  choriocapillaris  is 
a  very  thin,  structureless,  or  faintly 
fibrous  membrane,  called  the  lamina  basalis;  it  is  closely  connected  with  the  stroma  of  the 
choroid,  and  separates  it  from  the  pigmentary  layer  of  the  retina. 

One  of  the  functions  of  the  choroid  is  to  provide  nutrition  for  the  retina,  and  to  convey  vessels 
and  nerves  to  the  ciliary  body  and  iris. 

Tapetum. — This  name  is  apphed  to  the  outer  and  posterior  part  of  the  choroid,  which  in  many 
animals  presents  an  iridescent  appearance. 

The  Ciliary  Body  {corpus  ciliare). — ^The  ciliary  body  comprises  the  orbiculus 
ciliaris,  the  ciliary  processes,  and  the  Ciliaris  muscle. 

The  orbiculus  ciliaris  is  a  zone  of  about  4  mm.  in  width,  directly  continuous 
with  the  anterior  part  of  the  choroid;  it  presents  numerous  ridges  arranged  in  a 
radial  manner  (Fig.  875). 

The  ciliary  processes  {processus  ciliares)  are  formed  by  the  inward  folding  of  the 
various  layers  of  the  choroid,  i.  e.,  the  choroid  proper  and  the  lamina  basalis,  and 
are  received  between  corresponding  foldings  of  the  suspensory  ligament  of  the  lens. 
They  are  arranged  in  a  circle,  and  form  a  sort  of  frill  behind  the  iris,  around  the 
margin  of  the  lens  (Fig.  875) .  They  vary  from  sixty  to  eighty  in  number,  lie  side 
by  side,  and  may  be  divided  into  large  and  small;  the  former  are  about  2.5  mm. 
in  length,  and  the  latter,  consisting  of  about  one-third  of  the  entire  number,  are 
situated  in  spaces  between  them,  but  without  regular  arrangement.  They  are 
attached  by  their  periphery  to  three  or  four  of  the  ridges  of  the  orbiculus  ciliaris, 
and  are  continuous  with  the  layers  of  the  choroid:  their  opposite  extremities  are 
free  and  rounded,  and  are  directed  toward  the  posterior  chamber  of  the  eyeball  and 


I 


FiQ.  874. — The  veins  of  the  choroid.      (Enlarged.) 


THE  TUNICS  OF  THE  EYE 


1011 


circumterence  ot  the  lens.    In  front,  they  are  continuous  with  the  periphery  of  the 
iris.    Their  posterior  surfaces  are  connected  with  the  suspensory  Hgament  of  the 


lens. 


Ora  serrata 
_____^  /        Pars  ciliaris  retinas 
~"~~  Ciliary  -process 


Orhicvlus 
ciliaris 


Retina 

Choroid 

Sclera 


ki 


FiQ.  875. — Interior  of  anterior  half  of  bulb  of  eye. 

Structure. — The  ciliary  processes  (Figs.  876,  877)  are  similar  in  structure  to  the  choroid,  but 
the  vessels  are  larger,  and  have  chiefly  a  longitudinal  direction.  Their  posterior  surfaces  are 
covered  by  a  bilaminar  layer  of  black  pigment  cells, 
which  is  continued  forward  from  the  retina,  and  is 
named  the  pars  ciliaris  retinae.  In  the  stroma  of  the 
ciliary  processes  there  are  also  stellate  pigment  cells, 
but  these  are  not  so  numerous  as  in  the  choroid  itself. 

According  to  Henderson  the  aqueous  humor  is  a 
secretion  formed  by  the  active  intervention  of  the 
epithelial  cells  lining  the  apices  of  the  ciliary  processes.^ 


The  Ciliaris  muscle  (m.  ciliaris;  Bowman's 
muscle)  consists  of  unstriped  fibers:  it  forms  a 
grayish,  semitransparent,  circular  band,  about 
3  mm.  broad,  on  the  outer  surface  of  the  fore- 
part of  the  choroid.  It  is  thickest  in  front,  and 
consists  of  two  sets  of  fibers,  meridional  and 
circular.  The  meridional  fibers,  much  the  more 
numerous,  arise  from  the  posterior  margin  of 
the  scleral  spur  (page  1007);  they  run  back- 
ward, and  are  attached  to  the  ciliary  processes 
and  orbiculus  ciliaris.  One  bundle,  according 
to  Waldeyer,  is  inserted  into  the  sclera.  The 
circular  fibers  are  internal  to  the  meridional 
ones,  and  in  a  meridional  section  appear  as  a 
triangular  zone  behind  the  filtration  angle  and 
close  to  the  circumference  of  the  iris.  They 
are  well-developed  in  hypermetropic,  but  are 
rudimentary  or  absent  in  myopic  eyes.  The 
Ciliaris  muscle  is  the  chief  agent  in  accom- 
modation, i.  e.,  in  adjusting  the  eye  to  the  vision  of  near  objects.  When  it  con- 
tracts it  drawls  forward  the  ciliary  processes,  relaxes  the  suspensory  ligament  of 

„._. 


Fig.  876. — Vessels  of  the  choroid,  ciliary  pro* 
cesses,  and  iris  of  a  child.  (Arnold.)  Magnified 
10  times,  a.  Capillary  net-work  of  the  posterior 
part  of  the  choroid,  ending  at  b,  the  ora  serrata. 
c.  Arteries  of  the  corona  ciliaris.  supplying  the 
ciliary  processes,  (I,  and  passing  into  the  iris  e. 
f.  The  capillary-  net-work  close  to  the  pupillary 
margin  of  the  iris. 


>  Henderson.  T.,   Glaucoma,  London,  1910. 


1012       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


I 


The  Iris. — The  iris  has  received  its  name  from  its  various  colors  in  different 
individuals.  It  is  a  thin,  circular,  contractile  disk,  suspended  in  the  aqueous 
humor  between  the  cornea  and  lens,  and  perforated  a  little  to  the  nasal  side  of  its 
center  by  a  circular  aperture,  the  pupil.  By  its  periphery  it  is  continuous  with 
the  ciliary  body,  and  is  also  connected  with   the  posterior  elastic  lamina  of 


h.ff, 


Corned 


Lens. 


Fig.  877. — Diagram  of  the  bloodvessels  of  the  eye,  as  seen  in  a  horizontal  section.     (Leber,  after  Stohr.) 

Course  of  vasa  centralia  retinse:  a.  Arteria.  a.'  Vera  centralis  retinae,  b.  Anastomosis -with  vessels  of  outer  coatjs. 
C.  Anastomosis  with  branches  of  short  posterior  ciliary  arttrifs.     D.  Ansstcn  csis  with  chorioideal  vessels. 

Course  of  vasa  ciliar.  postic.  brev. :  I.  Arterise,  and  Ii.  Venae  ciliar.  postic.  brev.  II.  Episcleral  artery.  IIi.  Episcleral 
vein.     III.  Capillaries  of  lamina  choriocapillaris. 

Course  of  vasa  ciliar.  postic.  long.:  1.  a.  ciliar.  post,  longa.  2.  Circulus  iridis  major  cut  across.  3.  Branches  to  ciliary 
body.     4.  Branches  to  iris. 

Course  of  vasa  ciliar.  ant.:  a.  Arteria.  ai.  Vena  ciliar.  ant.  h.  Junction  -with  the  circulus  iridis  major.  ('.Junction 
with  lamina  choriocapill.  d.  Arterial,  and  rfi.  Venous  episcleral  branches,  e.  Arterial,  and  n.  Venous  branches  to 
conjunctiva  sclerse.  /.  Arterial,  and/i.  Venous  branches  to  corneal  border.  T'.  Vena  vorticosa.  S.  Transveree section 
of  sinus  venosus  scleree. 

cornea  by  means  of  the  pectinate  ligament;  its  surfaces  are  flattened,  and  look 
forward  and  backward,  the  anterior  toward  the  cornea,  the  posterior  toward  the 
ciliary  processes  and  lens.  The  iris  divides  the  space  between  the  lens  and  the 
cornea  into  an  anterior  and  a  posterior  chamber.  The  anterior  chamber  of  the  eye 
is  bounded  in  front  by  the  posterior  surface  of  the  cornea;  behind  by  the  front  of 
the  iris  and  the  central  part  of  the  lens.    The  posterior  chamber  is  a  narrow  chink 


I 


THE  TUNICS  OF  THE  EYE 


1013 


behind  the  peripheral  part  of  the  iris,  and  in  front  of  the  suspensory  ligament 

■  of  the  lens  and  the  ciliary  processes.     In  the  adult  the  two  chambers  communi- 
i  cate  through  the  pupil,  but  in  the  fetus  up  to  the  seventh  month  they  are  separ- 
ated by  the  membrana  pupillaris. 

■        Structure. — The  iris  is  composed  of  the  following  structures: 
(      1.  In  front  is  a  layer  of  flattened  endothelial  cells  placed  on  a  delicate  hyaline  basement  mem- 
brane.   This  layer  is  continuous  with  the  endothelium  covering  the  posterior  elastic  lamina  of 
the  cornea,  and  in  individuals  with  dark-colored  irides  the  cells  contain  pigment  granules. 

2.  The  stroma  (stroma  iridis)  of  the  iris  consists  of  fibers  and  cells.    The  former  are  made  up 

of  delicate  bundles  of  fibrous  tissue;  a  few  fibers  at  the  circumference  of  the  iris  have  a  circular 

direction;  but  the  majority  radiate  toward  the  pupil,  forming  by  their  interlacement,  deUcate 

meshes,  in  which  the  vessels  and  nerves  are  contained.     Interspersed  between  the  bundles  of 

^B>  connective  tissue  are  numerous  branched  cells  with  fine  processes.    In  dark  eyes  many  of  them 

^■1  contain  pigment  granules,  but  in  blue  eyes  and  the  eyes  of  albinos  they  are  unpigmented. 

^■"      3.  The  muscular  fibers  are  involuntary,  and  consist  of  circular  and  radiating  fibers.     The 

circular  fibers  form  the  Sphincter  pupillae;   they  are  arranged  in  a  narrow  band  about  1  mm.  in 

width  which  surrounds  the  margin  of  the  pupil  toward  the  posterior  surface  of  the  iris;  those 

near  the  free  margin  are  closely  aggregated;  those  near  the  periphery  of  the  band  are  somewhat 

separated  and  form  incomplete  circle^.    The  radiatinif  fibers  form  the  Dilatator  pupillae;  they 

converge  from  the  circumference  toward  the  center,  and  blend  with  the  circular  fibers  near  the 

margin  of  the  pupil. 

ANTERIOR    CILIARY    ARTERIES 


LONG   CILIARY 
ARTERY 


ANTERIOR  CILIARY  ARTERIES 

Fig.  878. — Iris,  front  view. 

4.  The  posterior  surface  of  the  iris  is  of  a  deep  purple  tint,  being  covered  by  two  layers  of 
pigmented  columnar  epithehum,  continuous  at  the  periphery  of  the  iris  with  the  pars  ciliaris 
retinae.  This  pigmented  epithehum  is  named  the  pars  iridica  retrnae,  or,  from  the  resemblance 
of  its  color  to  that  of  a  ripe  grape,  the  uvea. 

The  color  of  the  iris  is  produced  by  the  reflection  of  light  from  dark  pigment  cells  underlying 
a  translucent  tissue,  and  is  therefore  determined  by  the  amount  of  the  pigment  and  its  distribu- 
tion throughout  the  texture  of  the  iris.  The  number  and  the  situation  of  the  pigment  cells  differ 
in  different  irides.  In  the  albino  pigment  is  absent;  in  the  various  shades  of  blue  eyes  the  pigment 
cells  are  confined  to  the  posterior  surface  of  the  iris,  whereas  in  gray,  brown,  and  black  eyes 
pigment  is  found  also  in  the  cells  of  the  stroma  and  in  those  of  the  endothelium  on  the  front  of 
the  iris. 

The  iris  may  be  absent,  either  in  part  or  altogether  as  a  congenital  condition,  and  in  some 
instances  the  pupillary  membrane  may  remain  persistent,  though  it  is  rarely  complete.  Again, 
the  iris  may  be  the  seat  of  a  maKormation,  termed  coloboma,  which  consists  in  a  deficiency  or 


1014       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


I 


cleft,  clearly  due  in  a  great  number  of  cases  to  an  arrest  in  development.  In  these  cases  th(! 
cleft  is  found  at  the  lower  aspect,  extending  directly  downward  from  the  pupil,  and  the  gap 
frequently  extends  through  the  choroid  to  the  porus  opticus.  In  some  rarer  cases  the  gap  i.s 
found  in  other  parts  of  the  iris,  and  is  not  then  associated  with  any  deficiency  of  the  choroid. 

Vessels  and  Nerves. — ^The  arteries  of  the  iris  are  derived  from  the  long  and  anterior  cilian' 
arteries,  and  from  the  vessels  of  the  ciliary  processes  (see  p.  571).  Each  of  the  two  long  ciliarj' 
arteries,  having  reached  the  attached  margin  of  the  iris,  divides  into  an  upper  and  lower  branch ; 
these  anastomose  with  corresponding  branches  from  the  opposite  side  and  thus  encircle  the  iris; 
into  this  vascular  circle  {circulus  arteriosus  major)  the  anterior  ciliary  arteries  pour  their  blood, 
and  from  it  vessels  converge  to  the  free  margin  of  the  iris,  and  there  communicate  and  form  a, 
second  circle  (circulus  arteriosus  minor)  (Figs.  877  and  878). 

The  nerves  of  the  choroid  and  iris  are  the  long  and  short  ciliary;  the  former  being  branches 
of  the  nasociliary  nerve,  the  latter  of  the  ciliary  ganglion.  They  pierce  the  sclera  around  the 
entrance  of  the  optic  nerve,  run  forward  in  the  perichoroidal  space,  and  supply  the  bloodvessels 
of  the  choroid.  After  reaching  the  iris  they  form  a  plexus  around  its  attached  margin;  from  this 
are  derived  non-meduUated  fibers  which  end  in  the  Sphincter  and  Dilatator  pupilla?;  their  exact 
mode  of  termination  has  not  been  ascertained.  Other  fibers  from  the  plexus  end  in  a  net-work 
on  the  anterior  surface  of  the  iris.  The  fibers  derived  through  the  motor  root  of  the  ciliary  ganglion 
from  the  oculomotor  nerve,  supply  the  Sphincter,  while  those  derived  from  the  sympathetic  supply 
the  Dilatator. 

Membrana  Pupillaris. — In  the  fetus,  the  pupil  is  closed  by  a  delicate  vascular 
membrane,  the  membrana  pupillaris,  which  divides  the  space  in  which  the  iris  is 
suspended  into  two  distinct  chambers.  The  vessels  of  this  membrane  are  partly 
derived  from  those  of  the  margin  of  the  iris  and  partly  from  those  of  the  capsule 
of  the  lens;  they  have  a  looped  arrangement,  and  converge  toward  each  other  with- 
out anastomosing.  About  the  sixth  month  the  membrane  begins  to  disappear 
by  absorption  from  the  center  toward  the  circumference,  and  at  birth  only  a  few 
fragments  are  present;  in  exceptional  cases  it  persists. 


Optic  disc 


Mactda  liitea 


Sclera 
Choroid 

Retina 
Fig.  879.-Iiiterior  of  posterior  half  of  bulb  of  left  eye.    The  veins  are  darker  in  appearance  than  the  arteries. 

The  Retina  (tunica  interna)  .—The  retina  is  a  delicate  nervous  membrane,  upon 
which  the  images  of  external  objects  are  received.  Its  outer  surface  is  m  contact 
with  the  choroid;  its  inner  with  the  hyaloid  membrane  of  the  vitreous  body.  Be- 
hind it  is  continuous  with  the  optic  nerve;  it  gradually  diminishes  m  thickness 
from' behind  forward,  and  extends  nearly  as  far  as  the  ciliary  body,  where  it  appears 
to  end  in  a  jagged  margin,  the  ora  serrata.  Here  the  nervous  tissues  of  the  retina 
end   but  a  thin  prolongation  of  the  membrane  extends  fonvard  over  the  back  of 


THE  TUNICS  OF  THE  EYl 


1015 


I 


the  ciliary  processes  and  iris,  forming  the  pars  ciliaris  retin89  and  pars  iridica  retinae 
already  referred  to.  This  forward  prolongation  consists  of  the  pigmentary  layer 
of  the  retina  together  with  a  stratum  of  columnar  epithelium.  The  retina  is  soft, 
semitransparent,  and  of  a  purple  tint  in  the  fresh  state,  owing  to  the  presence  of  a 
coloring  material  named  rhodopsin  or  visual  purple;  but  it  soon  becomes  clouded, 
opaque,  and  bleached  when  exposed  to  sunlight.  Exactly  in  the  center  of  the 
posterior  part  of  the  retina,  corresponding  to  the  axis  of  the  eye,  and  at  a  point 
in  which  the  sense  of  vision  is  most  perfect,  is  an  oval  yellowish  area,  the  macula 
lutea;  in  the  macula  is  a  central  depression,  the  fovea  centralis  (Fig.  879).  At  the 
fovea  centralis  the  retina  is  exceedingly  thin,  and  the  dark  color  of  the  choroid  is 
distinctly  seen  through  it.  About  3  mm.  to  the  nasal  side  of  the  macula  lutse 
is  the  entrance  of  the  optic  nerve  (optic  disk),  the  circumference  of  which  is  slightly 
raised  to  form  an  eminence  (colliculus  nervi  optici)  (Fig.  880) ;  the  arteria  centralis 
retinae  pierces  the  center  of  the  disk.  This  is  the  only  part  of  the  surface  of  the 
retina  which  is  insensitive  to  light,  and  it  is  termed  the  blind  spot. 


La  }iihia  eribrom      Colliculus  nervi  optici 
Porus  opticus 


Retina 
Choroid 

Sclera 


Posterior     , 
short  ciliary  J^^^. 
arterii  arid  ^^te 
vein  ^^ 

Pial  sheath "-% 

Arachnoid 
sheath 

Dural  sheath 
Intervaginal  spaces 


Bundles  of 
optic  nerve 


Central  artery  and 
vein  of  retina 


'  Fig.  8S0. — The  terminal  portion  of  the  optic  nerve  and  its  entrance  into  the  eyeball,  in  horizontal  section.    (Toldt.) 


Structure  (Figs.  8S1,  882). — The  retina  consists  of  an  outer  pigmented  layer  and  an  inner 
nervous  stratum  or  retina  proper. 

The  pigmented  layer  consists  of  a  single  stratum  of  cells.  When  viewed  from  the  outer  surface 
these  cells  are  smooth  and  hexagonal  in  shape;  when  seen  in  section  each  cell  consists  of  an  outer 
non-pigmented  part  containing  a  large  oval  nucleus  and  an  inner  pigmented  portion  which  extends 
as  a  series  of  straight  thread-like  processes  between  the  rods,  this  being  especially  the  case  when 
the  eye  is  exposed  to  light.      In  the  eyes  of  albinos  the  cells  of  this  layer  are  destitute  of  pigment. 

Retina  Proper. — The  nervous  structures  of  the  retina  proper  are  supported  by  a  series  of  non- 
nervous  or  sustentacular  fibers,  and,  when  examined  microscopically  by  means  of  sections  made 
perpendicularly  to  the  surface  of  the  retina,  are  found  to  consist  of  seven  layers,  named  from 
within  outward  as  follows : 

1.  Stratum  opticum. 

2.  GangUonic  layer. 

3.  Inner  plexiform  layer. 

4.  Inner  nuclear  layer,  or  layer  of  inner  granules. 

5.  Outer  plexiform  layer. 

6.  Outer  nuclear  layer,  or  layer  of  outer  granules. 

7.  Layer  of  rods  and  cones. 
1.  The  stratum  opticum  or  layer  of  nerve  fibers  is  formed  by  the  expansion  of  the  fibers  of  the 

.optic  nerve;  it  is  thickest  near  the  porus  opticus,  gradually  diminishing  toward  the  ora  serrata. 


1016      ORi 


[ND  THE  COMMON  INTEGUMENT 


I 


As  the  nerve  fibers  pass  through  the  lamina  cribrosa  sclera?  they  lose  their  medullary  sheaths 
and  are  continued  onward  through  the  choroid  and  retina  as  simple  axis-cyUnders.  When  they 
reach  the  internal  surface  of  the  retina  they  radiate  from  their  point  of  entrance  over  this  sur- 
face grouped  in  bundles,  and  in  many  places  arranged  in  plexuses.  Most  of  the  fibers  are 
centripetal,  and  are  the  direct  continuations  of  the  axis-cylinder  processes  of  the  cells  of  the 

ganglionic  layer,  but  a  few  of  them 
Memhrana  limitans 

interna 
-Straturn  opticum 
.Ganglionic  layer 


Fibers  of  Muller- 


Fig.  881. — Section  of  retina. 


Inner  plexiform  layer 

Inner  nuclear  layer 

Outer  plexiform  layei 

Outer  nuclear  layer 
Memhrana  limitans 

externa 
Layer  of  rods  and 

cones 
Pigmented  layer 
(Magnified.) 


are  centrifugal  and  ramify  in  the 
inner  plexiform  and  inner  nuclear 
layers,  where  they  end  in  enlarged 
extremities. 

2.  The  ganglionic  layer  consists 
of  a  single  layer  of  large  ganglion 
cells,  except  in  the  macula  lutea, 
where  there  are  several  strata.  The 
cells  are  somewhat  flask-shaped;  the 
rounded  internal  surface  of  each 
resting  on  the  stratum  opticum,  and 
sending  off  an  axon  which  is  pro- 
longed into  it.  From  the  opposite 
end  numerous  dendrites  extend  into 
the  inner  plexiform  layer,  where 
they  branch  and  form  flattened 
arborizations  at  different  levels. 
The  gangUon  cells  vary  much  in 
size,  and  the  dendrites  of  the  smaller  ones  as  a  rule  arborize  in  the  inner  plexiform  layer  as  soon 
as  they  enter  it;  while  those  of  the  larger  cells  ramify  close  to  the  inner  nuclear  layer. 

3.  The  inner  plexiform  layer  is  made  up  of  a  dense  reticulum  of  minute  fibrils  formed  by  the 
interlacement  of  the  dendrites  of  the  ganghon  cells  with  those  of  the  cells  of  the  inner  nuclear 
layer;  within  this  reticulum  a  few  branched  spongioblasts  are  sometimes  imbedded. 

Memhrana 
lim,itans  interna  ■- 
Stratum  opticum"\  ~-=^ 

Ganglionic  layer-- 


Inner  'plexiform  .. 
layer 

Centrifugal  fibre  '' 


Inner  nuclear 
layer 

Fibre  of  Midler  - 

Outer  plexiform .. 

layer 

Outer  nuclear  _ 
layer 

Memhrana 
limitans  externa 

Layer  of  rods 
and  cones 


Diffuse  amMcrine 

cell 

••AmMcrine  cells 
'—.  Horizontal  cell 


r-yBod  granules 


>■«  Cone  granules 


j'  Pigmented  layer 


Fig.  882. — Plan  of  retinal  neurons.     (After  Cajal.) 


4.  The  inner  nuclear  layer  or  layer  of  inner  granules  is  made  up  of  a  number  of  closely  packed 
cells,  of  which  there  are  three  varieties,  viz.:    bipolar  cells,  horizontal  cells,  and  amacrine  cells. 

The  bipolar  cells,  by  far  the  most  numerous,  are  round  or  oval  in  shape,  and  each  is  prolonged 
into  an  inner  and  an  outer  process.    They  are  divisible  into  rod  bipolars  and  cone  bipolars.    The 


THE  TUNICS  OF  THE  EYE  1017 

inner  processes  of  the  rod  bipolars  run  through  the  inner  plexiform  layer  and  arborize  around 
the  bodies  of  the  cells  of  the  ganglionic  layer;  their  outer  processes  end  in  the  outer  plexiform 
layer  in  tufts  of  fibrils  around  the  button-like  ends  of  the  inner  processes  of  the  rod  granules. 
The  inner  processes  of  the  cone  bipolars  ramify  in  the  inner  plexiform  layer  in  contact  with  the 
dendrites  of  the  ganghonic  cells. 

The  horizontal  cells  lie  in  the  outer  part  of  the  inner  nuclear  layer  and  possess  somewhat 
flattened  cell  bodies.  Their  dendrites  divide  into  numerous  branches  in  the  outer  plexiform 
layer,  while  their  axons  run  horizontally  for  some  distance  and  finally  ramify  in  the  same  layer. 

The  amacrine  cells  are  placed  in  the  inner  part  of  the  inner  nuclear  layer,  and  are  so  named 
becai-oe  they  have  not  yet  been  shown  to  possess  axis-cylinder  processes.  Their  dendrites  undergo 
extensive  ramification  in  the  inner  plexiform  layer. 

5.  The  outer  plexiform  layer  is  much  thinner  than  the  inner;  but,  like  it,  consists  of  a  dense 
net-work  of  minute  fibrils  derived  from  the  processes  of  the  horizontal  cells  of  the  preceding  layer, 
and  the  outer  processes  of  the  rod  and  cone  bipolar  granules,  which  ramify  in  it,  forming  arboriza- 
tions aroimd  the  enlarged  ends  of  the  rod  fibers  and  with  the  branched  foot  plates  of  the  cone 
fibers. 

6.  The  outer  nuclear  layer  or  layer  of  outer  granules,  Uke  the  inner  nuclear  layer,  contains 
several  strata  of  oval  nuclear  bodies;  they  are  of  two  kinds,  viz.:  rod  and  cone  granules,  so 
named  on  account  of  their  being  respectively  connected  with  the  rods  and  cones  of  the  next  layer. 
The  rod  granules  are  much  the  more  numerous,  and  are  placed  at  different  levels  throughout 
the  layer.  Their  nuclei  present  a  pecuhar  cross-striped  appearance,  and  prolonged  from  either 
extremity  of  each  cell  is  a  fine  process;  the  outer  process  is  continuous  with  a  single  rod  of  the 
layer  of  rods  and  cones;  the  inner  ends  in  the  outer  plexiform  layer  in  an  enlarged  extremity,  and 
is  imbedded  in  the  tuft  into  which  the  outer  processes  of  the  rod  bipolar  cells  break  up.  In  its 
course  it  presents  numerous  varicosities.  The  cone  granules,  fewer  in  number  than  the  rod 
granules,  are  placed  close  to  the  membrana  limitans  externa,  through  which  they  are  continuous 
with  the  cones  of  the  layer  of  rods  and  cones.  They  do  not  present  any  cross-striation,  but  con- 
tain a  pyriform  nucleus,  which  almost  completely  fills  the  cell.  F^om  the  inner  extremity  of  the 
granule  a  thick  process  passes  into  the  outer  plexiform  layer,  and  there  expands  into  a  pyramidal 
enlargement  or  foot  plate,  from  which  are  given  off  numerous  fine  fibrils,  that  come  in  contact 
with  the  outer  processes  of  the  cone  bipolars. 

7.  The  Layer  of  Rods  and  Cones  {Jacob's  membrane). — The  elements  composing  this  layer  are 
of  two  kinds,  rods  and  cones,  the  former  being  much  more  numerous  than  the  latter  except  in 
the  macula  lutea.  The  rods  are  cyUndrical,  of  nearly  uniform  thickness,  and  are  arranged  per- 
pendicularly to  the  surface.  Each  rod  consists  of  two  segments,  an  outer  and  inner,  of  about 
equal  lengths.  The  segments  differ  from  each  other  as  regards  refraction  and  in  their  behavior 
toward  coloring  reagents;  the  inner  segment  is  stained  by  carmine,  iodine,  etc.;  the  outer  segment 
is  not  stained  by  these  reagents,  but  is  colored  yellowish  brown  by  osmic  acid.  The  outer  segment 
is  marked  by  transverse  strise,  and  tends  to  break  up  into  a  number  of  thin  disks  superimposed 
on  one  another;  it  also  exhibits  faint  longitudinal  markings.  The  deeper  part  of  the  inner  seg- 
ment is  indistinctly  granular;  its  more  superficial  part  presents  a  longitudinal  striation,  being 
composed  of  fine,  bright,  highly  refracting  fibrils.  The  visual  purple  or  rhodopsin  is  found  only 
in  the  outer  segments. 

The  cones  are  conical  or  flask-shaped,  their  broad  ends  resting  upon  the  membrana  limitane 
externa,  the  narrow-pointed  extremity  being  turned  to  the  choroid.  Like  the  rods,  each  is  made 
up  of  two  segments,  outer  and  inner;  tha  outer  segment  is  a  short  conical  process,  which,  like 
the  outer  segment  of  the  rod,  exhibits  transverse  strise.  The  inner  segment  resembles  the  inner 
segment  of  the  rods  in  structure,  presenting  a  superficial  striated  and  deep  granular  part,  but 
differs  from  it  in  size  and  shape,  being  bulged  out  laterally  and  flask-shaped.  The  chemical 
and  optical  characters  of  the  two  portions  are  identical  with  those  of  the  rods. 

Supporting  Frame-work  of  the  Retina. — The  nervous  layers  of  the  retina  are  connected  together 
by  a  supporting  frame-work,  formed  by  the  sustentacular  fibers  of  Miiller;  these  fibers  pass 
through  all  the  nervous  layers,  except  that  of  the  rods  and  cones.  Each  begins  on  the  inner  surface 
of  the  retina  by  an  expanded,  often  forked  base,  which  sometimes  contains  a  spheroidal  body 
staining  deeply  with  hematoxylin,  the  edges  of  the  bases  of  adjoining  fibers  being  imited  to  form 
the  membriCna  limitans  interna.  As  the  fibers  pass  through  the  nerve  fiber  and  ganglionic  layers 
they  give  off  a  few  lateral  branches;  in  the  inner  nuclear  layer  they  give  off  numerous  lateral 
processes  for  the  support  of  the  bipolar  cells,  while  in  the  outer  nuclear  layer  they  form  a  net- 
work around  the  rod-  and  cone-fibrils,  and  unite  to  form  the  membrana  limitans  externa  at  the 
bases  of  the  rods  and  cones.  At  the  level  of  the  inner  nuclear  layer  each  sustentacular  fiber 
contains  a  clear  oval  nucleus. 

Macula  Lutea  and  Fovea  Centralis. — In  the  macula  lutea  the  nerve  fibers  are  wanting  as  a 
continuous  layer,  the  ganglionic  layer  consists  of  several  strata  of  cells,  there  are  no  rods,  but 
only  cones,  which  are  longer  and  narrower  than  in  other  parts,  and  in  the  outer  nuclear  layer 
there  are  only  cone-granules,  the  processes  of  which  are  very  long  and  arranged  in  curved  lines. 
In  the  fovea  centraUs  the  only  parts  present  are  (1)  the  cones;  (2)  the  outer  nuclear  layer,  the 


1018       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

cone-fibers  of  which  are  ahnost  horizontal  in  direction;  (3)  an  exceedingly  thin  inner  plexiform  '| 
layer.    The  pigmented  layer  is  thicker  and  its  pigment  more  pronounced  than  elsewhere.    The 
color  of  the  macula  seems  to  imbue  all  the  layers  except  that  of  the  rods  and  cones;  it  is  of  a  rich 
yellow,  deepest  toward  the  center  of  the  macula,  and  does  not  appear  to  be  due  to  pigment  cells, 
but  simply  to  a  staining  of  the  constituent  parts. 

At  the  era  serrata  the  nervous  layers  of  the  retina  end  abruptly,  and  the  retina  is  continued 
onward  as  a  single  layer  of  columnar  cells  covered  by  the  pigmented  layer.  This  double  layer  is 
known  as  the  pars  ciliaris  retinse,  and  can  be  traced  forward  from  the  ciliary  processes  on  to  the 
back  of  the  iris,  where  it  is  termed  the  pars  iridica  retinse  or  uvea. 

The  arteria  centralis  retinae  (Fig.  879)  and  its  accompanying  vein  pierce  the  optic  nerve,  and 
enter  the  bulb  of  the  eye  through  the  porus  opticus.  The  artery  immediately  bifurcates  into 
an  upper  and  a  lower  branch,  and  each  of  these  again  divides  into  a  medial  or  nasal  and  a  lateral 
or  temporal  branch,  which  at  first  run  between  the  hyaloid  membrane  and  the  nervous  layer; 
but  they  soon  enter  the  latter,  and  pass  forward,  dividing  dichotomously.  From  these  branches 
a  minute  capillary  plexus  is  given  off,  which  does  not  extend  beyond  the  inner  nuclear  layer. 
The  macula  receives  two  small  branches  (superior  and  inferior  macular  arteries)  from  the  tem- 
poral branches  and  small  twigs  directly  from  the  central  artery;  these  do  not,  however,  reach 
as  far  as  the  fovea  centralis,  which  has  no  bloodvessels.  The  branches  of  the  arteria  centralis 
retinae  do  not  anastomose  with  each  other — in  other  words  they  are  terminal  arteries.  In  the 
fetus,  a  small  vessel,  the  arteria  hyaloidea,  passes  forward  as  a  continuation  of  the  arteria  centralis 
retinae  through  the  vitreous  hiunor  to  the  posterior  surface  of  the  capsule  of  the  lens. 

The  Refracting  Media. 

The  refracting  media  are  three,  viz. : 

Aqueous  humor.  Vitreous  body.  Crystalline  lens. 

The  Aqueous  Humor  {humor  aqiieus). — The  aqueous  humor  fills  the  anterior 
and  posterior  chambers  of  the  eyeball.  It  is  small  in  quantity,  has  an  alkaline 
reaction,  and  consists  mainly  of  water,  less  than  one-fiftieth  of  its  weight  being 
solid  matter,  chiefly  chloride  of  sodium. 

The  Vitreous  Body  {corpus  vitreum). — The  vitreous  body  forms  about  four- 
fifths  of  the  bulb  of  the  eye.  It  fills  the  concavity  of  the  retina,  and  is  hollowed 
in  front,  forming  a  deep  concavity,  the  hyaloid  fossa,  for  the  reception  of  the  lens. 
It  is  transparent,  of  the  consistence  of  thin  jelly,  and  is  composed  of  an  albuminous 
fluid  enclosed  in  a  delicate  transparent  membrane,  the  hyaloid  membrane.  It  has 
been  supposed,  by  Hannover,  that  from  its  surface  numerous  thin  lamellae  are 
prolonged  inward  in  a  radiating  manner,  forming  spaces  in  which  the  fluid  is  con- 
tained. In  the  adult,  these  lamellae  cannot.be  detected  even  after  careful  micro- 
scopic examination  in  the  fresh  state,  but  in  preparations  hardened  in  weak  chromic 
acid  it  is  possible  to  make  out  a  distinct  lamellation  at  the  periphery  of  the  body. 
In  the  center  of  the  vitreous  body,  running  from  the  entrance  of  the  optic  nerve 
to  the  posterior  surface  of  the  lens,  is  a  canal,  the  hyaloid  canal,  filled  with  lymph 
and  lined  by  a  prolongation  of  the  hyaloid  membrane.  This  canal,  in  the  embryonic 
vitreous  body,  conveyed  the  arteria  hyaloidea  from  the  central  artery  of  the  retina 
to  the  back  of  the  lens.  The  fluid  from  the  vitreous  body  is  nearly  pure  water;  it 
contains,  however,  some  salts,  and  a  little  albumin. 

The  hyaloid  membrane  envelopes  the  vitreous  body.  The  portion  in  front  of  the 
ora  serrata  is  thickened  by  the  accession  of  radial  fibers  and  is  termed  the  zonula 
ciliaris  {zonule  of  Zinn).  Here  it  presents  a  series  of  radially  arranged  furrows, 
in  which  the  ciliary  processes  are  accommodated  and  to  which  they  adhere,  as  is 
shown  by  the  fact  that  when  they  are  removed  some  of  their  pigment  remains 
attached  to  the  zonula.  The  zonula  ciliaris  splits  into  two  layers,  one  of  which 
is  thin  and  lines  the  hyaloid  fossa;  the  other  is  named  the  suspensory  ligament 
of  the  lens :  it  is  thicker,  and  passes  over  the  ciliary  body  to  be  attached  to  the  cap- 
sule of  the  lens  a  short  distance  in  front  of  its  equator.  Scattered  and  delicate 
fibers  are  also  attached  to  the  region  of  the  equator  itself.  This  ligament  retains 
the  lens  in  position,  and  is  relaxed  by  the  contraction  of  the  meridional  fibers  of 
the  Ciliaris  muscle,  so  that  the  lens  is  allowed  to  become  more  convex.    Behind 


THE  REFRACTING  MEDIA 


1019 


the  suspensory  ligament  there  is  a  sacculated  canal,  the  spatia  zonularis  {canal 
of  Petit),  which  encircles  the  equator  of  the  lens;  it  can  be  easily  inflated  through 
a  fine  blowpipe  inserted  under  the  suspensory  ligament. 

No  bloodvessels  penetrate  the  vitreous  body,  so  that  its  nutrition  must  be  carried 
on  by  vessels  of  the  retina  and  ciliary  processes,  situated  upon  its  exterior. 


INSE 

TENDON  OF  S 

RECTUS 


SCLERA 

ANTERIOR  CILIARY 

ARTERIES  AND 

VEINS 

CIRCULAR 
MAJOR 

ANGLE  OF 

ANTERIOR 

CHAMBER 
CANAL   OF. 
SCHLEMM 


CONJUNCTIVA 
EPISCLERAL 
CONNECTIVE- 
TISSUE 
LIGAMENTUM 
PECTINATUM 


POSTERIOR 

SURFACE 

OF  CORNEA 

EPITHELIUM 

OF  CORNEA 

ANTERIOR 

ELASTIC 

LAMINA 


CORTICAL  SUBSTANCE 
OF  LENS 


NUCLEUS 
OF  LENS 


POSTERIOR  ELASTIC 
LAMINA 


SPHINCTER 
OF  PUPIL 


STROMA   OF  IRIS 
PIGMENTARY 
LAYERS  OF  IRIS 


I 


Fig.  883. — The  upper  half  of  a  sagittal  section  through  the  front  of  the  eyeball. 

The  Crystalline  Lens  {lens  crystallina) . — The  crystalline  lens,  enclosed  in  .its 
capsule,  is  situated  immediately  behind  the  iris,  in  front  of  the  vitreous  body, 
and  encircled  by  the  ciliary  processes,  which  slightly  overlap  its  margin. 

The  capsule  of  the  lens  {capsula  lentis)  is  a  transparent,  structureless  membrane 
which  closely  surrounds  the  lens,  and  is  thicker  in  front  than  behind.  It  is  brittle 
but  highly  elastic,  and  when  ruptured  the  edges  roll  up  with  the  outer  surface 
innermost.  It  rests,  behind,  in  the  hyaloid  fossa  in  the  forepart  of  the  vitreous 
body;  in  front,  it  is  in  contact  with  the  free  border  of  the  iris,  but  recedes  from  it 
at  the  circumference,  thus  forming  the  posterior  chamber  of  the  eye;  it  is  retained 
in  its  position  chiefly  by  the  suspensory  ligament  of  the  lens,  already  described. 

The  lens  is  a  transparent,  biconvex  body,  the  convexity  of  its  anterior  being 
less  than  that  of  its  posterior  surface.  The  central  points  of  these  surfaces  are 
termed  respectively  the  anterior  and  posterior  poles;  a  line  connecting  the  poles 
constitutes  the  axis  of  the  lens,  while  the  marginal  circumference  is  termed  the 
equator. 


1020       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


Structure. — The  lens  is  made  up  of  soft  cortical  substance  and  a  firm,  central  part,  the  nucleus 
(Fig.  884).  Faint  lines  {radii  lentis)  radiate  from  the  poles  to  the  equator.  In  the  adult  there 
may  be  six  or  more  of  these  lines,  but  in  the  fetus  they  are  only 
three  in  number  and  diverge  from  each  other  at  angles  of  120° 
(Fig.  885) ;  on  the  anterior  surface  one  line  ascends  vertically 
and  the  other  two  diverge  downward;  on  the  posterior  sur- 
face one  ray  descends  vertically  and  the  other  two  diverge 
upward.  They  correspond  with  the  free  edges  of  an  equal 
number  of  septa  composed  of  an  amorphous  substance,  which 
dip  into  the  substance  of  the  lens.  When  the  lens  has  been 
hardened  it  is  seen  to  consist  of  a  series  of  concentrically 
arranged  laminae,  each  of  which  is  interrupted  at  the  septa 
referred  to.  Each  lamina  is  built  up  of  a  number  of  hexagonal, 
ribbon-like  lens  fibers,  the  edges  of  which  are  more  or  less  ser- 
rated— the  serrations  fitting  between  those  of  neighboring 
fibers,  while  the  ends  of  the  fibers  come  into  apposition  at 
the  septa.  The  fibers  run  in  a  curved  manner  from  the  septa 
on  the  anterior  surface  to  those  on  the  posterior  surface. 
No  fibers  pass  from  pole  to  pole;  they  are  arranged  in  such 
a  way  that  those  which  begin  near  the  pole  on  one  surface 


Fig.  884. — The  crystalline  lens,   hardened  and  divided.     (Enlarged.) 


Fig.  885. — Diagram  to  show  the  direction  and  arrangement  of  the 
radiating  lines  on  the  front  and  back  of  the  fetal  lens.  A.  From  the 
front.     B.  From  the  back. 


Fia.  886. — Profile  views  of  the  lens  at  different  periods  of  life 
1.   In  the  fetus.     2.   In  adult  life.     3    In  old  age. 


Fig.  887. — Section  through  the  margin 
of  the  lens,  showing  the  transition  of 
the  epithelium  into  the  lens  fibers. 
(Babuchin.) 


of  the  lens  end  near  the  peripheral  extremity  of  the  plane  on  the  other,  and  vice  versa.  The 
fibers  of  the  outer  layers  of  the  lens  are  nucleated,  and  together  form  a  nuclear  layer,  most 
distinct  toward  the  equator.  The  anterior  surface  of  the  lens  is  covered  by  a  layer  of  transparent, 
columnar,  nucleated  epithelium.  At  the  equator  the  cells  become  elongated,  and  their  gradual 
transition  into  lens  fibers  can  be  traced  (Fig.  887). 


THE  ACCESSORY  ORGANS  OF  THE  EYE 


1021 


In  the  fetus,  the  lens  is  nearly  spherical,  and  has  a  slightly  reddish  tint;  it  is  soft  and  breaks 
down  readily  on  the  slightest  pressure.  A  small  branch  from  the  arteria  centralis  retina?  runs 
forward,  as  already  mentioned,  through  the  vitreous  body  to  the  posterior  part  of  the  capsule 
of  the  lens,  where  its  branches  radiate  and  form  a  plexiform  network,  which  covers  the  posterior 
surface  of  the  capsule,  and  they  are  continuous  around  the  margin  of  the  capsule  with  the  vessels 
of  the  pupillary  membrane,  and  with  those  of  the  iris.  In  the  adult,  the  lens  is  colorless,  trans- 
parent, firm  in  texture,  and  devoid  of  vessels.  In  old  age  it  becomes  flattened  on  both  surfaces, 
sUghtly  opaque,  of  an  amber  tint,  and  increased  in  density  (Fig.  886). 

Vessels  and  Nerves. — The  arteries  of  the  bulb  of  the  eye  are  the  long,  short,  and  anterior 
ciliary  arteries,  and  the  arteria  centrahs  retina;.    They  have  already  been  described  (see  p.  571). 

The  ciliary  veins  are  seen  on  the  outer  surface  of  the  choroid,  and  are  named,  from  their  arrange- 
ment, the  vence  vorticosce;  they  converge  to  four  or  five  equidistant  trunks  which  pierce  the 
sclera  midway  between  the  sclero-comeal  j unction  and  the  porus  opticus.  Another  set  of  veins 
accompanies  the  anterior  cihary  arteries.    All  of  these  veins  open  into  the  ophthalmic  veins. 

The  ciliary  nerves  are  derived  from  the  nasociUary  nerve  and  from  the  ciUary  gangUon. 

The  Accessory  Organs  of  the  Eye  (Organa  Oculi  Accessoria). 

The  accessory  organs  of  the  eye  include  the  ocular  muscles,  the  fasciae,  the  eye- 
brows, the  eyelids,  the  conjunctiva,  and  the  lacrimal  apparatus. 

The  Ocular  Muscles  (musculi  oculi). — The  ocular  muscles  are  the: 
Levator  palpebrse  superioris.  Rectus  medialis. 

Rectus  superior.  Rectus  lateralis. 

Rectus  inferior.  Obliquus  superior. 

Obliquus  inferior. 

Tendon  of  Obliquus  superior 
Orbital  plate  of  frontal  bone 
Levator  palpebrcB  superioris 
Rectus  superior 


L  OrbicvZans  ocvli 
Superior  taraus 
Upper  eyelid 


r\  .-  I  I  ~\->^::!W«^^MKIE«*^au    \    ^'v^e.r  eyelid 

Optic  nerve  1       C^7«^S^^^Wi\    \  7    -.    ■  \ 

r>  -<       ■  t    ■  '>?2*,r-I---...  V  >J£r^      inferior  tarsus 

Rectus  inferior  /^^y^^^T  /^-  I     v^ n\ 

Roof  of  maxillary  sinus     /     V^l^'^^-^^      VA      Orbicularis  ocvli 
Obliquus  inferior 

Fig.  888. — Sagittal  section  of  rigiit  orbital  cavity. 

The  Levator  palpebrae  superioris  (Fig.  888)  is  thin,  flat,  and  triangular  in  shape. 
It  arises  from  the  under  surface  of  the  small  wing  of  the  sphenoid,  above  and  in 
front  of  the  optic  foramen,  from  which  it  is  separated  by  the  origin  of  the  Rectus 
superior.  At  its  origin,  it  is  narrow  and  tendinous,  but  soon  becomes  broad  arid 
fleshy,  and  ends  anteriorly  in  a  wide  aponeurosis  which  splits  into  three  lamellae. 
The  superficial  lamella  blends  with  the  upper  part  of  the  orbital  septum,  and  is  pro- 
longed forward  above  the  superior  tarsus  to  the  palpebral  part  of  the  Orbicularis 
oculi,  and  to  the  deep  surface  of  the  skin  of  the  upper  eyelid.  The  middle  lamella, 
largely  made  up  of  non-striped  muscular  fibers,  is  inserted  into  the  upper  margin 
of  the  superior  tarsus,  while  the  deepest  lamella  blends  with  an  expansion  from 
the  sheath  of  the  Rectus  superior  and  with  it  is  attached  to  the  superior  fornix 
of  the  conjunctiva. 


1022       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


Whitnall^  has  pointed  out  that  the  upper  part  of  the  sheath  of  the  Levator  palpebrse  becomes 
thickened  in  front  and  forms,  above  the  anterior  part  of  the  muscle,  a  transverse  hgamentous 
band  which  is  attached  to  the  sides  of  the  orbital  cavity.  On  the  medial  side  it  is  mainly  fixed 
to  the  pulley  of  the  ObUquus  superior,  but  some  fibers  are  attached  to  the  bone  behind  the  pulley 
and  a  slip  passes  forward  and  bridges  over  the  supraorbital  notch;  on  the  lateral  side  it  is  fixed 
to  the  capsule  of  the  lacrimal  gland  and  to  the  frontal  bone.  In  front  of  the  transverse  ligament- 
ous band  the  sheath  is  continued  over  the  aponeurosis  of  the  Levator  palpebrse,  as  a  thin  con- 
nective-tissue layer  which  is  fixed  to  the  upper  orbital  margin  immediatly  behind  the  attach- 
ment of  the  orbital  septum.  When  the  Levator  palpebral  contracts,  the  lateral  and  medial  parts 
of  the  ligamentous  band  are  stretched  and  check  the  action  of  the  muscle;  the  retraction  of  the 
upper  eyelid  is  checked  also  by  the  orbital  septum  coming  into  contact  with  the  transverse  part 
of  the  ligamentous  band. 


•I 


Fig.  889. — Muscles  of  the  right  orbit. 


The  four  Recti  (Fig.  889)  arise  from  a  fibrous  ring  {annulus  tendineiis  communis) 
which  surrounds  the  upper,  medial,  and  lower  margins  of  the  optic  foramen  and 
encircles  the  optic  nerve  (Fig.  890) .  The  ring  is  completed  by  a  tendinous  bridge 
prolonged  over  the  lower  and  medial  part  of  the  superior  orbital  fissure  and  attached 
to  a  tubercle  on  the  margin  of  the  great  wing  of  the  sphenoid,  bounding  the  fissure. 
Two  specialized  parts  of  this  fibrous  ring  may  be  made  out:  a  lower,  the  ligament 
or  tendon  of  Zinn,  which  gives  origin  to  the  Rectus  inferior,  part  of  the  Rectus  in- 
ternus,  and  the  lower  head  of  origin  of  the  Rectus  lateralis;  and  an  upper,  which 
gives  origin  to  the  Rectus  superior,  the  rest  of  the  Rectus  medialis,  and  the  upper 
head  of  the  Rectus  lateralis.  This  upper  band  is  sometimes  termed  the  superior 
tendon  of  Lockwood.  Each  muscle  passes  forward  in  the  position  implied  by  its 
name,  to  be  inserted  by  a  tendinous  expansion  into  the  sclera,  about  6  mm.  from  the 
margin  of  the  cornea.  Between  the  two  heads  of  the  Rectus  lateralis  is  a  narrow 
interval,  through  which  pass  the  two  divisions  of  the  oculomotor  nerve,  the  naso- 
ciliary nerve,  the  abducent  nerve,  and  the  ophthalmic  vein.  Although  these 
muscles  present  a  common  origin  and  are  inserted  in  a  similar  manner  into  the 
sclera,  there  are  certain  differences  to  be  observed  in  them  as  regards  their  length 
and  breadth.  The  Rectus  medialis  is  the  broadest,  the  Rectus  lateralis  the  longest, 
and  the  Rectus  superior  the  thinnest  and  narrowest. 

The  Obliquus  ocuU  superior  (superior  oblique)  is  a  fusiform  muscle,  placed  at  the 
upper  and  medial  side  of  the  orbit.  It  arises  immediately  above  the  margin  of  the 
optic  foramen,  above  and  medial  to  the  origin  of  the  Rectus  superior,  and,  passing 
forward,  ends  in  a  rounded  tendon,  which  plays  in  a  fibrocartilaginous  ring  or  pulley 
attached  to  the  trochlear  fovea  of  the  frontal  bone.  The  contiguous  surfaces  of 
the  tendon  and  ring  are  lined  by  a  delicate  mucous  sheath,  and  enclosed  in  a  thin 


11 


'  Journal  of  Anatomy  and  Physiology,  vol.  xlv. 


THE  ACCESSORY  ORGANS  OF  THE  EYE 


1023 


fibrous  investment.  The  tendon  is  reflected  backward,  lateralward,  and  downward 
beneath  the  Rectus  superior  to  the  lateral  part  of  the  bulb  of  the  eye,  and  is  inserted 
into  the  sclera,  behind  the  equator  of  the  eyeball,  the  insertion  of  the  muscle  lying 
between  the  Rectus  superior  and  Rectus  lateralis. 

The  Obliquus  oculi  inferior  (inferior  oblique)  is  a  thin,  narrow  muscle,  placed  near 
the  anterior  margin  of  the  floor  of  the  orbit.  It  arises  from  the  orbital  surface  of 
the  maxilla,  lateral  to  the  lacrimal  groove.  Passing  lateralward,  backward,  and 
upward,  at  first  between  the  Rectus  inferior  and  the  floor  of  the  orbit,  and  then 
between  the  bulb  of  the  eye  and  the  Rectus  lateralis,  it  is  inserted  into  the  lateral 
part  of  the  sclera  between  the  Rectus  superior  and  Rectus  lateralis,  near  to,  but 
somewhat  behind  the  insertion  of  the  Obliquus  superior. 


Frontal  nerve 
Sup.  rarmis  of  oculomotor  nerve 
Sup.  orbital  fissure 
Lacrimal  nerve 


Levator  palpebrcB  super. 
Nasociliary  nerve 
Trochlear  nerve 
Trochlea 


/ 

Abducent  nerve 

Jnf.  ramus  of  oculomotor     Inf.  orbital         Optic  foramen 
nerve  -fissure 

Fig.  890. — Dissection  showing  origins  of  right  ocular  muscles,  and  nerves  entering  by  the  superior  orbital  fissure. 


Nerves. — The  Levator  palpebrse  superioris,  Obliquus  inferior,  and  the  Recti  superior,  inferior, 
and  medialis  are  supplied  by  the  oculomotor  nerve;  the  Obliquus  superior,  by  the  trochleai 
nerve;  the  Rectus  lateraUs,  by  the  abducent  nerve. 

Actions. — The  Levator  palpebral  raises  the  upper  eyelid,  and  is  the  direct  antagonist  of  the 
Orbicularis  oculi.  The  four  Recti  are  attached  to  the  bulb  of  the  eye  in  such  a  manner  that, 
acting  singly,  they  wiU  turn  its  corneal  surface  either  upward,  downward,  medialward,  or  lateral- 
ward,  as  expressed  by  their  names.  The  movement  produced  by  the  Rectus  superior  or  Rectus 
inferior  is  not  quite  a  simple  one,  for  inasmuch  as  each  passes  obhquely  lateralward  and  forward 
to  the  bulb  of  the  eye,  the  elevation  or  depression  of  the  cornea  is  accompanied  by  a  certain 
deviation  medialward,  with  a  slight  amount  of  rotation.  These  latter  movements  are  corrected 
by  the  Obliqui,  the  Obliquus  inferior  correcting  the  medial  deviation  caused  by  the  Rectus  superior 
and  the  ObUquus  superior  that  caused  by  the  Rectus  inferior.  The  contraction  of  the  Rectus 
lateralis  or  Rectus  medialis,  on  the  other  hand,  produces  a  piu-ely  horizontal  movement.  If  any 
two  neighboring  Recti  of  one  eye  act  together  they  carry  the  globe  of  the  eye  in  the  diagonal  of 
these  directions,  viz.,  upward  and  medialward,  upward  and  lateralward,  downward  and  medial- 
ward,  or  downward  and  lateralward.  Sometimes  the  corresponding  Recti  of  the  two  eyes  act 
in  unison,  and  at  other  times  the  opposite  Recti  act  together.  Thus,  in  turning  the  eyes  to  the 
right,  the  Rectus  lateralis  of  the  right  eye  will  act  in  unison  with  the  Rectus  mediaUs  of  the  left 
eye;  but  if  both  eyes  are  directed  to  an  object  in  the  middle  Une  at  a  short  distance,  the  two  Recti 
mediales  wiU  act  in  unison.  The  movement  of  circumduction,  as  in  looking  around  a  room,  is 
performed  by  the  successive  actions  of  the  four  Recti.     The  ObUqui  rotate  the  eyeball  on  its 


1024      ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

inferior  directing  it  upward  and  lateralward;  these  movements  are  required  for  the  correct  viewing 
of  an  object  when  the  head  is  moved  laterally,  as  from  shoulder  to  shoulder,  in  order  that  the 
picture  may  fall  in  all  respects  on  the  same  part  of  the  retina  of  either  eye. 

A  layer  of  non-striped  muscle,  the  Orbitalis  muscle  of  H.  Miiller,  may  be  seen 
bridging  across  the  inferior  orbital  fissure. 


■"  Superior  tarsus 


Inferior  tarsus 


Fig.  891. — The  right  eye  in  sagittal  section,  showing  the  fascia  bulbi  (semidiagrammatic) .      (Testut.) 

The  Fascia  Bulb  (capsule  of  Tenon)  (Fig.  891)  is  a  thin  membrane  which  envelops 
the  bulb  of  the  eye  from  the  optic  nerve  to  the  ciliary  region,  separating  it  from 
the  orbital  fat  and  forming  a  socket  in  which  it  plays.  Its  inner  surface  is  smooth, 
and  is  separated  from  the  outer  surface  of  the  sclera  by  the  periscleral  Isrmph  space. 
This  lymph  space  is  continuous  with  the  subdural  and  subarachnoid  cavities, 
and  is  traversed  by  delicate  bands  of  connective  tissue  which  extend  between  the 
fascia  and  the  sclera.  The  fascia  is  perforated  behind  by  the  ciliary  vessels  and 
nerves,  and  fuses  with  the  sheath  of  the  optic  nerve  and  with  the  sclera  around  the 
entrance  of  the  optic  nerve.  In  front  it  blends  with  the  ocular  conjunctiva,  and 
with  it  is  attached  to  the  ciliary  region  of  the  eyeball.  It  is  perforated  by  the 
tendons  of  the  ocular  muscles,  and  is  reflected  backward  on  each  as  a  tubular 
sheath.  The  sheath  of  the  Obliquus  superior  is  carried  as  far  as  the  fibrous  pulley 
of  that  muscle;  that  on  the  Obliquus  inferior  reaches  as  far  as  the  floor  of  the 
orbit,  to  which  it  gives  off  a  slip.  The  sheaths  on  the  Recti  are  gradually  lost  in 
the  perimysium,  but  they  give  off  important  expansions.  The  expansion  from  the 
Rectus  superior  blends  with  the  tendon  of  the  Levator  palpebrse;  that  of  the 
Rectus  inferior  is  attached  to  the  inferior  tarsus.  The  expansions  from  the  sheaths 
of  the  Recti  lateralis  and  medialis  are  strong,  especially  that  from  the  latter  muscle, 
and  are  attached  to  the  lacrimal  and  zygomatic  bones  respectively.  As  they  prob- 
ably check  the  actions  of  these  two  Recti  they  have  been  named  the  medial  and 
lateral  check  ligaments.    Lockwood  has  described  a  thickening  of  the  lower  part 


I 


THE  ACCESSORY  ORGANS  OF  THE  EYE  1025 


n 


of  the  facia  bulbi,  which  he  has  named  the  suspensory  ligament  of  the  eye.  It  is 
slung  like  a  hammock  below  the  eyeball,  being  expanded  in  the  center,  and  narrow 
at  its   extremities   which    are   attached   to   the   zygomatic   and   lacrimal  bones 

I  J  respectively.^ 
[  The  Orbital  Fascia  forms  the  periosteum  of  the  orbit.  It  is  loosely  connected 
I  to  the  bones  and  can  be  readily  separated  from  them.  Behind,  it  is  united  with 
the  dura  mater  by  processes  which  pass  through  the  optic  foramen  and  superior 
orbital  fissure,  and  with  the  sheath  of  the  optic  nerve.  In  front,  it  is  connected 
with  the  periosteum  at  the  margin  of  the  orbit,  and  sends  off  a  process  which 
assists  in  forming  the  orbital  septum.  From  it  two  processes  are  given  off;  one  to 
enclose  the  lacrimal  gland,  the  other  to  hold  the  pulley  of  the  Obliquus  superior  in 
position . 

The  Eyebrows  (supercilia)  are  two  arched  eminences  of  integument,  which  sur- 
mount the  upper  circumference  of  the  orbits,  and  support  numerous  short,  thick 
■    hairs,  directed  obliquely  on  the  surface.    The  eyebrows  consist  of  thickened  integu- 
■  ment,  connected  beneath  with  the  Orbicularis  oculi,  Corrugator,  and  Frontalis 
muscles. 

The  Eyelids  (palpebrce)  are  two  thin,  movable  folds,  placed  in  front  of  the  eye, 
protecting  it  from  injury  by  their  closure.  The  upper  eyelid  is  the  larger,  and  the 
more  movable  of  the  two,  and  is  furnished  with  an  elevator  muscle,  the  Levator 
palpebrse  superioris.  When  the  eyelids  are  open,  an  elliptical  space,  the  palpebral 
fissure  (rima  'palpebrarum),  is  left  between  their  margins,  the  angles  of  which  corre- 
spond to  the  junctions  of  the  upper  and  lower  eyelids,  and  are  called  the  palpebral 
commissures  or  canthi. 

The  lateral  palpebral  commissure  {commissura  palpebrarum  lateralis;  external 

canthiis)  is  more  acute  than  the  medial,  and  the  eyelids  here  lie  in  close  contact 

with  the   bulb  of  the  eye:  but  the  medial  palpebral  commissure  {commissura 

,        palpebrarum  medialis;  internal  canthus)  is  prolonged  for  a  short  distance  toward  the 

B  ^  nose,  and  the  two  eyelids  are  separated  by  a  triangular  space,  the  lacus  lacrimalis 

P"  (Fig.  892).    At  the  basal  angles  of  the  lacus  lacrimalis,  on  the  margin  of  each 

eyelid,  is  a  small  conical  elevation,  the  lacrimal  papilla,  the  apex  of  which  is  pierced 

by  a  small  orifice,  the  punctum  lacrimale,  the  commencement  of  the  lacrimal  duct. 

The  eyelashes  (cilia)  are  attached  to  the  free  edges  of  the  eyelids ;  they  are  short, 

thick,  curved  hairs,  arranged  in  a  double  or  triple  row:  those  of  the  upper  eyelid, 

more  numerous  and  longer  than  those  of  the  lower,  curve  upward;  those  of  the  lower 

eyelid  curve  downward,  so  that  they  do  not  interlace  in  closing  the  lids.    Near 

the  attachment  of  the  eyelashes  are  the  openings  of  a  number  of  glands,  the  ciliary 

glands,  arranged  in  several  rows  close  to  the  free  margin  of  the  lid;  they  are  regarded 

■  Kas  enlarged  and  modified  sudoriferous  glands. 

Structure  of  the  Eyelids. — The  eyelids  are  composed  of  the  following  structures  taken  in  their 
order  from  without  inward:  integument,  areolar  tissue,  fibers  of  the •  Orbicularis  oculi,  tarsus, 
orbital  septum,  tarsal  glands  and  conjunctiva.  The  upper  eyehd  has,  in  addition,  the  aponeu- 
rosis of  the  Levator  palpebra?  superioris  (Fig.  893). 

The  integument  is  extremely  thin,  and  continuous  at  the  margins  of  the  eyelids  with  the  con- 
junctiva. 

The  subcutaneous  areolar  tissue  is  very  lax  and  delicate,  and  seldom  contains  any  fat. 

The  palpebral  fibers  of  the  Orbicularis  oculi  are  thin,  pale  in  color,  and  possess  an  involuntary 
action. 

The  tarsi  {tarsal  plates)  (Fig.  894)  are  two  thin,  elongated  plates  of  dense  connective  tissue, 
about  2.5  cm.  in  length;  one  is  placed  in  each  eyelid,  and  contributes  to  its  form  and  support. 
The  superior  tarsus  {tarsus  superior;  superior  tarsal  plate),  the  larger,  is  of  a  semilunar  form,  about 
10  mm.  in  breadth  at  the  center,  and  gradually  narrowing  toward  its  extremities.  To  the 
anterior  surface  of  this  plate  the  aponeurosis  of  the  Levator  palpebrae  superioris  is  attached.  The 
inferior  tarsus  {tarsus  inferior;  inferior  tarsal  plate),  the  smaller,  is  thin,  elliptical  in  form,  and 

^  C.  B.  Lockwood,  Journal  of  Anatomy  and  Physiology,  vol.  xx. 


II 


1026       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


I 


has  a  vertical  diameter  of  about  5  mm.  The  free  or  ciliary  margins  of  these  plates  are  thick  and 
straight.  The  attached  or  orbital  margins  are  connected  to  the  circumference  of  the  orbit  by 
the  orbital  septum.  The  lateral  angles  are  attached  to  the  zygomatic  bone  by  the  lateral  palpe- 
bral raph6.  The  medial  angles  of  the  two  plates  end  at  the  lacus  lacrimalis,  and  are  attached  to 
the  frontal  process  of  the  maxilla  by  the  medial  palpebral  ligament  (page  381). 

The  orbital  septum  (septum  orbitale;   palpebral  ligament)  is  a  membranous  sheet,  attached  to 
the  edge  of  the  orbit,  where  it  is  continuous  with  the  periosteum.    In  the  upper  eyeUd  it  blends 


Pwnetum  lacrimdle 

Plica  semilunaris 

Canincida 

Punctum  laerimale 

Openings  of  tarsal 

glands 


FiQ.  892.- 


-Front  of  left  eye  with  eyelids  separated  to  show 
medial  eanthus. 


by  its  peripheral  circumference  with  the  tendon 
of  the  Levator  palpebrae  superioris  and  the 
superior  tarsus,  in  the  lower  eyeUd  with  the  infe- 
rior tarsus.  Medially  it  is  thin,  and,  beconiing 
separated  from  the  medial  palpebral  ligament,  is 
fixed  to  the  lacrimal  bone  immediately  behind 
the  lacrimal  sac.  The  septum  is  perforated  by 
the  vessels  and  nerves  which  pass  from  the  orbital 
cavity  to  the  face  and  scalp.  The  eyeUds  are 
richly  supphed  with  blood. 

The  Tarsal  Glands  (glanduloB  tarsales 
[Meibomi];  Meibomian  glands)  (Fig.  895). 
— The  tarsal  glands  are  situated  upon  the 
inner  surfaces  of  the  eyelids,  between  the 
tarsi  and  conjunctiva,  and  may  be  dis- 
tinctly seen  through  the  latter  on  everting 
the  eyelids,  presenting  an  appearance  like 
parallel  strings  of  pearls.  There  are  about 
thirty  in  the  upper  eyelid,  and  somewhat 
fewer  in  the  lower.  They  are  imbedded  in  grooves  in  the  inner  surfaces  of  the 
tarsi,  and  correspond  in  length  with  the  breadth  of  these  plates;  they  are,  con- 
sequently, longer  in  the  upper  than  in  the  lower  eyelid.  Their  ducts  open  on  the 
free  magins  of  the  lids  by  minute  foramina. 

Structiire. — The  tarsal  glands  are  modified  sebaceous  glands,  each  consisting  of  a  single  straight 
tube  or  follicle,  with  numerous  small  lateral  diverticula.  The  tubes  are  supported  by  a  basement 
membrane,  and  are  lined  at  their  mouths  by  stratified  epithehum;  the  deeper  parts  of  the  tubes 
and  the  lateral  offshoots  are  lined  by  a  layer  of  polyhedral  cells. 

The  conjunctiva  is  the  mucous  membrane  of  the  eye.  It  lines  the  inner  surfaces 
of  the  eyelids  or  palpebrae,  and  is  reflected  over  the  forepart  of  the  sclera  and  cornea. 


Fig.  893. — Sagittal  section  through  the  upper 
eyelid.  (After  Waldeyer.)  a.  Skin.  b.  Orbicularis 
oculi.  b'.  Marginal  fasciculus  of  Orbicularis  (ciliarjj 
bundle),  c.  Levator  palpebrse.  d.  Conjunctiva. 
e.  Tarsus.  /.  Tarsal  gland,  g.  Sebaceous  gland. 
h.  Eyelashes,    t.  Small   hairs   of    skin.  Sweat 

glands,    k.  Posterior  tarsal  glands. 


THE  ACCESSORY  ORGANS  OF  THE  EYE 


1027 


The  Palpebral  Portion  (tunica  conjunctiva  palpebrarum)  is  thick,  opaque,  highly 
vascular,  and  covered  with  numerous  papillae,  its  deeper  part  presenting  a 
considerable  amount  of  lymphoid  tissue.  At  the  margins  of  the  lids  it  becomes 
continuous  with  the  lining  membrane  of  the  ducts  of  the  tarsal  glands,  and,  through 
the  lacrimal  ducts,  with  the  lining  membrane  of  the  lacrimal  sac  and  nasolacrimal 


1 


Lacrimal  artery 
and  nerve 


Lateral  pal- 
pebral raphe 


]_  Supraorbital  vessels 
and  nerve 


f  Lacrimal  sac 
Medial  palpebral 
ligament 


Fig.  894. — The  tarsi  and  their  ligaments.     Right  eye;  front  view. 

met.  At  the  lateral  angle  of  the  upper  eyelid  the  ducts  of  the  lacrimal  gland  open 
on  its  free  surface;  and  at  the  medial  angle  it  forms  a  semilunar  fold,  the  plica 
semilunaris.  The  line  of  reflection  of  the  conjunctiva  from  the  upper  eyelid  on 
to  the  bulb  of  the  eye  is  named  the  superior  fornix,  and  that  from  the  lower  lid  the 
inferior  fornix. 


Puncta  lacrinudia  - 


Fig.  895. — The  tarsal  glands,  etc.,  seen  from  the  inner  surface  of  the  eyelids. 


The  Bulbar  Portion  (tunica  conjunctiva  hulhi). — Upon  the  sclera  the  conjunctiva 
is  loosely  connected  to  the  bulb  of  the  eye;  it  is  thin,  transparent,  destitute  of 
papillae,  and  only  slightly  vascular.  Upon  the  cornea,  the  conjunctiva  consists 
only  of  epithelium,  constituting  the  epithelium  of  the  cornea,  already  described 
(see  page  1007).  Lymphatics  arise  in  the  conjunctiva  in  a  delicate  zone  around 
the  cornea,  and  run  to  the  ocular  conjunctiva. 


1028       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

In  and  near  the  fornices,  but  more  plentiful  in  the  upper  than  in  the  lower  eyelid, 
a  number  of  convoluted  tubular  glands  open  on  the  surface  of  the  conjunctiva. 
Other  glands,  analogous  to  lymphoid  follicles,  and  called  by  Henle  trachoma  glands, 
are  found  in  the  conjunctiva,  and,  according  to  Strohmeyer,  are  chiefly  situated 
near  the  medial  palpebral  commissure.  They  were  first  described  by  Brush,  in 
his  description  of  Peyer's  patches  of  the  small  intestine,  as  "identical  structures 
existing  in  the  under  eyelid  of  the  ox." 

The  caruncula  lacrimalis  is  a  small,  reddish,  conical-shaped  body,  situated  at 
the  medial  palpebral  commissure,  and  filling  up  the  lacus  lacrimalis.  It  consists 
of  a  small  island  of  skin  containing  sebaceous  and  sudoriferous  glands,  and  is  the 
source  of  the  whitish  secretion  which  constantly  collects  in  this  region.  A  few 
slender  hairs  are  attached  to  its  surface.  Lateral  to  the  caruncula  is  a  slight  semi- 
lunar fold  of  conjunctiva,  the  concavity  of  which  is  directed  toward  the  cornea; 
it  is  called  the  plica  semilunaris.  Muller  found  smooth  muscular  fibers  in  this  fold; 
in  some  of  the  domesticated  animals  it  contains  a  thin  plate  of  cartilage. 

The  nerves  in  the  conjunctiva  are  numerous  and  form  rich  plexuses.  According 
to  Krause  they  terminate  in  a  peculiar  form  of  tactile  corpuscle,  which  he  terms 
"terminal  bulb." 

The  Lacrimal  Apparatus  (apparatus  lacrimalis)  (Fig.  896)  consists  of  (a)  the 
lacrimal  gland,  which  secretes  the  tears,  and  its  excretory  ducts,  which  convey  the 
fluid  to  the  surface  of  the  eye;  (6)  the  lacrimal  ducts,  the  lacrimal  sac,  and  the  naso- 
lacrimal duct,  by  which  the  fluid  is  conveyed  into  the  cavity  of  the  nose. 

The  Lacrimal  Gland  {glandula  lacrimalis). — The  lacrimal  gland  is  lodged  in  the 
lacrimal  fossa,  on  the  medial  side  of  the  zygomatic  process  of  the  frontal  bone. 
It  is  of  an  oval  form,  about  the  size  and  shape  of  an  almond,  and  consists  of  two 
portions,  described  as  the  superior  and  inferior  lacrimal  glands.  The  superior 
lacrimal  gland  is  connected  to  the  periosteum  of  the  orbit  by  a  few  fibrous  bands, 
and  rests  upon  the  tendons  of  the  Recti  superioris  and  lateralis,  which  separate  it 
from  the  bulb  of  the  eye.  The  inferior  lacrimal  gland  is  separated  from  the  superior 
by  a  fibrous  septum,  and  projects  into  the  back  part  of  the  upper  eyelid,  where 
its  deep  surface  is  related  to  the  conjunctiva.  The  ducts  of  the  glands,  from  six 
to  twelve  in  number,  run  obliquely  beneath  the  conjunctiva  for  a  short  distance, 
and  open  along  the  upper  and  lateral  half  of  the  superior  conjunctival  fornix. 

Structures  of  the  Lacrimal  Gland  (Fig.  897). — In  structure  and  general  appearance  the  lacrimal 
resembles  the  serous  salivary  glands  (p.  1136).  In  the  recent  state  the  cells  are  so  crowded  with 
granules  that  their  limits  can  hardly  be  defined.  They  contain  oval  nuclei,  and  the  cell  proto- 
plasm is  finely  fibrillated. 

The  Lacrimal  Ducts  {ductus  lacrimalis;  lacrimal  canals). — ^The  lacrimal  ducts,  one 
in  each  eyelid,  commence  at  minute  orifices,  termed  puncta  lacrimalia,  on  the 
summits  of  the  papillae  lacrimales,  seen  on  the  margins  of  the  lids  at  the  lateral 
extremity  of  the  lacus  lacrimalis.  The  superior  duct,  the  smaller  and  shorter  of  the 
two,  at  first  ascends,  and  then  bends  at  an  acute  angle,  and  passes  medialward 
and  downward  to  the  lacrimal  sac.  The  inferior  duct  at  first  descends,  and  then 
runs  almost  horizontally  to  the  lacrimal  sac.  At  the  angles  they  are  dilated  into 
ampullae ;  their  walls  are  dense  in  structure  and  their  mucous  lining  is  covered  by 
stratified  squamous  epithelium,  placed  on  a  basement  membrane.  Outside  the 
latter  is  a  layer  of  striped  muscle,  continuous  with  the  lacrimal  part  of  the  Orbic- 
ularis oculi;  at  the  base  of  each  lacrimal  papilla  the  muscular  fibers  are  circu- 
larly arranged  and  form  a  kind  of  sphincter. 

The  Lacrimal  Sac  {saccv^  lacrimalis). — ^The  lacrimal  sac  is  the  upper  dilated  end 
of  the  nasolacrimal  duct,  and  is  lodged  in  a  deep  groove  formed  hy  the  lacrimal  bone 
and  frontal  process  of  the  maxilla.  It  is  oval  in  form  and  measures  from  12  to  15 
mm.  in  length;  its  upper  end  is  closed  and  rounded;  its  lower  is  continued  into  the 
nasolacrimal  duct.    Its  superficial  surface  is  covered  by  a  fibrous  expansion  derived 


THE  ORGAN  OF  HEARING 


1029 


from  the  medial  palpebral  ligament,  and  its  deep  surface  is  crossed  by  the  lacrimal 
part  of  the  Orbicularis  oculi  (page  380),  which  is  attached  to  the  crest  on  the 
lacrimal  bone. 

Structure. — The  lacrimal  sac  consists  of  a  fibrous  elastic  coat,  lined  internally  by  mucous 
membrane:  the  latter  is  continuous,  through  the  lacrimal  ducts,  with  the  conjunctiva,  and 
through  the  nasolacrimal  duct  with  the  mucous  membrane  of  the  nasal  cavity. 

The  Nasolacrimal  Duct  {ductus  nasolacrimalis;  nasal  duct). — The  nasolacrimal 
duct  is  a  membranous  canal,  about  18  mm.  in  length,  which  extends  from  the  lower 

part  of  the  lacrimal  sac  to  the  inferior 
meatus  of  the  nose,  where  it  ends  by  a 
somewhat  expanded  orifice,  provided 
with  an  imperfect  valve,  the  plica 
lacrimalis  (/Ta^nen),  formed  by  a  fold 
of  the  mucous  membrane.  It  is  con- 
tained  in  an  osseous  canal,  formed  by 

Punctalacrimalia.     ^" 


Fig.  896. — The  lacrimal  apparatus.      Right  side. 


Fig.  897. — Alveoli  of  lacrimal  gland. 


w 


the  maxilla,  the  lacrimal  bone,  and  the  inferior  nasal  concha;  it  is  narrower  in 
the  middle  than  at  either  end,  and  is  directed  downward,  backward,  and  a  little 
lateralward.  The  mucous  lining  of  the  lacrimal  sac  and  nasolacrimal  duct  is 
covered  with  columnar  epithelium,  which  in  places  is  ciliated. 

THE  ORGAN  OF  HEARING  (ORG ANON  AUDITUS;  THE  EAR). 

The  ear,  or  organ  of  hearing,  is  divisible  into  three  parts:  the  external  ear,  the 
middle  ear  or  tympanic  cavity,  and  the  internal  ear  or  labyrinth. 


Cavity  of  hind-brain 


Hind-bratn 


PI 


Auditory  pit 


Ectoderm 


Notochord 

FiQ.  898. — Section  through  the  head  of  a  human 
embryo,  about  twelve  days  old,  in  the  region  of  the 
hind-btain.     (Kollmann.) 


Auditory 

vesicle 


Fig.  899. — Section  through  hind-brain  and  audi- 
tory ve.sicles  of  an  embryo  more  advanced  than  that 
of  Fig.  898.     (After  His.) 


The  Development  of  the  Ear. — The  first  rudiment  of  the  internal  ear  appears 
shortly  after  that  of  the  eye,  in  the  form  of  a  patch  of  thickened  ectoderm,  the 
auditory  plate,  over  the  region  of  the  hind-brain.  The  auditory  plate  becomes 
depressed  and  converted  into  the  auditory  pit  (Fig.  898).     The  mouth  of  the  pit  is 


i_ 


1030     ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

then  closed,  and  thus  a  shut  sac,  the  auditory  vesicle,  is  formed  (Fig.  899) ;  from  it 
the  epithelial  lining  of  the  membranous  labyrinth  is  derived.  The  vesicle  becomes 
pear-shaped,  and  the  neck  of  the  flask  is  obliterated  (Fig.  900).    From  the  vesicle 


Neural  tube 


Endolymph    L<aeralgro<m 


Endolymph 

Veatib. 

Vestib.  P'^'^^ 
r''  pouch 


d.  8c.  sup 


4-3  mm.  front 


absorpt.  focu. 


f—Coch.  pouch 
6.6  mm.  lateral 


d.  sc.  post. 

Lateral  groove 

d.  sc.  lat. 


mM 


''CocIUea 
9  mm.  lateral 


^K-  CO*-'  ,a 
IS  mm.  lateral 


20  mm.  lateral 


SO  mm.  lateral 


Fig.  900. — Lateral  views  of  membranous  labyrinth  and  acoustic  complex.  X  25  dia.  (Streeter.)  absorpt.  focu, 
area  of  wall  where  absorption  is  complete;  amp.,  ampulla  membranacea;  cms,  crus  commune;  d.  sc.  lat.,  ductus  semi- 
circularis  lateralis;  d.  sc.  post.,  ductus  semicircularis  posterior;  d.  sc.  sup.,  ductus  semicircular  superior;  cock,  or  cochlea, 
ductus  cochlearis;  duct,  endolymph,  ductus  endolymphaticus;  d.  rewiie^is,  ductus  reuniens  Henseni;  endol.  or  endolympha 
appendix  endolymphaticus;  rec.  utr.,  recessus  utriculi;  sacc,  sacculus;  sac.  endol.,  saccus  endolymphaticus;  sinus  utr.  Iqt., 
sinus  utriculi  lateralis;  utric,  utriculus;  xcstib.  p.,  vestibular  pouch. 

certain  diverticula  are  given  off  which  form  the  various  parts  of  the  membranous 
labyrinth.  One  from  the  middle  part  forms  the  ductus  and  saccus  endolymphaticus, 
another  from  the  anterior  end  gradually  elongates,  and,  forming  a  tube  coiled  on 


THE  ORGAN  OF  HEARING 


1031 


itself,  becomes  the  cochlear  duct,  the  vestibular  extremity  of  which  is  subsequently 
constricted  to  form  the  canalis  reuniens.  Three  others  appear  as  disk-like  evagi- 
nations  on  the  surface  of  the  vesicle;  the  central  parts  of  the  walls  of  the  disks 
ll  coalesce  and  disappear,  while  the  peripheral  portions  persist  to  form  the  semi- 

Endolymph 


Veatih.  pouch 


Endolymph 


Veatib.  pouch. 


Cochlea^ 


Utric.-sacc 


9  mm.  median 


11  mm.  median 


Reuniens' 

IB       Fig.  901. — Median  views  of  membranous  labyrinth  and  acotistic  complex  in  human  embryos.     X  25  dia.    (Streeter.) 


SO  mm.  median 


I 


circular  ducts;  of  these  the  superior  is  the  first  and  the  lateral  the  last  to  be  com- 
pleted (Fig.  902) .  The  central  part  of  the  vesicle  represents  the  membranous 
vestibule,  and  is  subdivided  by  a  constriction  into  a  smaller  ventral  part,  the 
saccule,  and  a  larger  dorsal  and  posterior  part,  the  utricle.    This  subdivision  is 


1032    ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

effected  by  a  fold  which  extends  deeply  into  the  proximal  part  of  the  ductus 
endolymphaticus,  with  the  result  that  the  utricle  and  saccule  ultimately  com- 
municate with  each  other  by  means  of  a  Y-shaped  canal.  The  saccule  opens 
into  the  cochlear  duct,  through  the  canalis  reuniens,  and  the  semicircular  ducts 
communicate  with  the  utricle. 


Ductv^  endolymphaticus 


Superior  semi- 
circular duct 


Utricle 

^       1-  \i  y/jm         I  _i  _  ..III     I'lui..,',!.  Saccule 

Ganqtion  ^  AdW        Mr  ^       ^ r  .      ? 

cx^chleare-— — _.::#^     ^1    f  ^W^ I^i^ral  semi- 

^„ry.m^  .n»k=.        a  _  CirCUUir  ttUCt 

■/Ductus  cocJdearis 


Fig.  902. — Transverse  section  through  head  of  fetal  sheep,  in  the  region  of  the  labyrinth.      X  30.    (After  Boettcher.) 


The  mesodermal  tissue  surrounding  the  various  parts  of  the  epithelial  labyrinth 
is  converted  into  a  cartilaginous  ear-capsule,  and  this  is  finally  ossified  to  form  the 
bony  labyrinth.  Between  the  cartilaginous  capsule  and  the  epithelial  structures 
is  a  stratum  of  mesodermal  tissue  which  is  differentiated  into  three  layers,  viz., 


Embryonic 
connective  tissue 
\ 


Cochlear  duct 


Fig. 


Epithelium  of  the  spiral 
organ  of  Corti 

903. — Transverse  section  of  the  cochlear  duct  of  a  fetal  cat. 


Ligamentum-  spirale 
Scala  tyrnpani 


(After  Boettcher  and  Ayres.) 


an  outer,  forming  the  periosteal  lining  of  the  bony  labyrinth;  an  inner,  in  direct 
contact  with  the  epithelial  structures;  and  an  intermediate,  consisting  of  gelatinous 
tissue:  by  the  absorption  of  this  latter  tissue  the  perilymphatic  spaces  are  developed. 
The  modiolus  and  osseous  spiral  lamina  of  the  cochlea  are  not  preformed  in  cartil- 
age but  are  ossified  directly  from  connective  tissue. 


THE  EXTERNAL  EAR  ^^^  1033 


The  middle  ear  and  auditory  tube  are  developed  from  the  first  pharyngeal  pouch. 

KThe  entodermal  lining  of  the  dorsal  end  of  this  pouch  is  in  contact  with  the  ecto- 
derm of  the  corresponding  pharyngeal  groove;  by  the  extension  of  the  mesoderm 
between  these  two  layers  the  tympanic  membrane  is  formed.  During  the  sixth  or 
seventh  month  the  tympanic  antrum  appears  as  an  upward  and  backward  expan- 
sion of  the  tympanic  cavity.  With  regard  to  the  exact  mode  of  development 
of  the  ossicles  of  the  middle  ear  there  is  some  difference  of  opinion.  The  view 
generally  held  is  that  the  malleus  is  developed  from  the  proximal  end  of  the 
mandibular  (Meckel's)  cartilage  (Fig.  43),  the  incus  in  the  proximal  end  of  the 
mandibular  arch,  and  that  the  stapes  is  formed  from  the  proximal  end  of  the  hyoid 
arch.  The  malleus,  with  the  exception  of  its  anterior  process  is  ossified  from  a  single 
center  which  appears  near  the  neck  of  the  bone;  the  anterior  process  is  ossified 
separately  in  membrane  and  joins  the  main  part  of  the  bone  about  the  sixth  month 
of  fetal  life.  The  incus  is  ossified  from  one  center  which  appears  in  the  upper 
part  of  its  long  crus  and  ultimately  extends  into  its  lenticular  process.  The 
stapes  first  appears  as  a  ring  {annuhis  stapedius)  encircling  a  small  vessel,  the  stape- 
dial artery,  which  subsequently  undergoes  atrophy;  it  is  ossified  from  a  single 
center  which  appears  in  its  base. 

The  external  acoustic  meatus  is  developed  from  the  first  branchial  groove.  The 
lower  part  of  this  groove  extends  inward  as  a  funnel-shaped  tube  (primary  meatus) 
from  which  the  cartilaginous  portion  and  a  small  part  of  the  roof  of  the  osseous 
portion  of  the  meatus  are  developed.  From  the  lower  part  of  the  funnel-shaped 
tube  an  epithelial  lamina  extends  downward  and  inward  along  the  inferior  wall  of 
the  primitive  tympanic  cavity;  by  the  splitting  of  this  lamina  the  inner  part  of 
the  meatus  (secondary  meatus)  is  produced,  while  the  inner  portion  of  the  lamina 
forms  the  cutaneous  stratum  of  the  tympanic  membrane.  The  auricula  or  pinna 
is  developed  by  the  gradual  differentiation  of  tubercles  which  appear  around  the 
margin  of  the  first  branchial  groove.  The  rudiment  of  the  acoustic  nerve  appears 
about  the  end  of  the  third  week  as  a  group  of  ganglion  cells  closely  applied  to  the 

(^cephalic  edge  of  the  auditory  vesicle.  Whether  these  cells  are  derived  from  the 
■ectoderm  adjoining  the  auditory  vesicle,  or  have  migrated  from  the  wall  of  the 
neural  tube,  is  as  yet  uncertain.  The  ganglion  gradually  splits  into  two  parts, 
the  vestibular  ganglion  and  the  spiral  ganglion.  The  peripheral  branches  of  the 
vestibular  ganglion  pass  in  two  divisions,  the  pars  superior  giving  rami  to  the 
superior  ampulla  of  the  superior  semicircular  duct,  to  the  lateral  ampulla  and  to 
the  utricle;  and  the  pars  inferior  giving  rami  to  the  saccule  and  the  posterior 
ampulla.  The  proximal  fibers  of  the  vestibular  ganglion  form  the  vestibular  nerve; 
the  proximal  fibers  of  the  spiral  ganglion  form  the  cochlear  nerve. 


I 


The  External  Ear. 


The  external  ear  consists  of  the  expanded  portion  named  the  auricula  or  pinna, 
and  the  external  acoustic  meatus.  The  former  projects  from  the  side  of  the  head 
and  serves  to  collect  the  vibrations  of  the  air  by  which  sound  is  produced ;  the  latter 
leads  inward  from  the  bottom  of  the  auricula  and  conducts  the  vibrations  to  the 
tympanic  cavity. 

The  Auricula  or  Pinna  (Fig.  904)  is  of  an  ovoid  form,  with  its  larger  end  directed 
upward.  Its  lateral  surface  is  irregularly  concave,  directed  slightly  forward,  and 
presents  numerous  eminences  and  depressions  to  which  names  have  been  assigned. 
The  prominent  rim  of  the  auricula  is  called  the  helix ;  where  the  helix  turns  down- 
ward behind,  a  small  tubercle,  the  auricular  tubercle  of  Darwin,  is  frequently  seen ;  this 
tubercle  is  very  evident  about  the  sixth  month  of  fetal  life  when  the  whole  auric- 
ula has  a  close  resemblance  to  that  of  some  of  the  adult  monkeys.  Another 
curved  prominence,  parallel  with  and  in  front  of  the  helix,  is  called  theantihelix; 


1034    ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

this  divides  above  into  two  crura,  between  which  is  a  triangular  depression,  the 
fossa  triangularis.    The  narrow-curved  depression  between  the  helix  and  the  antihelix 

is  called  the  scapha;  the  antihelix  describes  a  curve 
around  a  deep,  capacious  cavity,  the  concha,  which  is 
partially  divided  into  two  parts  by  the  cms  or  com- 
mencement of  the  helix;  the  upper  part  is  termed  the 
C3nnba  conchse,  the  lower  part  the  cavum  conchse. 
In  front  of  the  concha,  and  projecting  backward  over 
the  meatus,  is  a  small  pointed  eminence,  the  tragus, 
so  called  from  its  being  generally  covered  on  its  under 
surface  with  a  tuft  of  hair,  resembling  a  goat's  beard. 
Opposite  the  tragus,  and  separated  from  it  by  the 
intertragic  notch,  is  a  small  tubercle,  the  antitragus. 
Below  this  is  the  lobule,  composed  of  tough  areolar 
and  adipose  tissues,  and  wanting  the  firmness  and 
elasticity  of  the  rest  of  the  auricula. 

The  cranial  surface  of  the  auricula  presents  ele- 
vations which  correspond  to  the  depressions  on  its 
lateral  surface  and  after  which  they  are  named, 
e,    q.,     eminentia     conchse,      eminentia      triangularis, 

Fig.  904.— The  auricula.     Lateral  ,  &  » 

surface.  CtC. 


Structure. — The  auricula  is  composed  of  a  thin  plate  of  yellow  fibrocartilage,  covered  with 
integument,  and  connected  to  the  surrounding  parts  by  ligaments  and  muscles;  and  to  the  com- 
mencement of  the  external  acoustic  meatus  by  fibrous  tissue. 

The  skin  is  thin,  closely  adherent  to  the  cartilage,  and  covered  with  fine  hairs  furnished  with 
sebaceous  glands,  which  are  most  numerous  in  the  concha  and  scaphoid  fossa.  On  the  tragus 
and  antitragus  the  hairs  are  strong  and  numerous.  The  skin  of  the  auricula  is  continuous  with 
that  lining  the  external  acoustic  meatus. 


Spina  helicis ^ 


Sulcus  antihelicis  transversua 


Eminentia  conchce 


Ponticulus 
Cauda  helicis 


Cartilage  of 
meatus 

Fia.  905. — Cranial  surface  of  cartilage  of  right  auricula. 

The  cartilage  of  the  auricula  (cartilago  auricula';  cartilage  of  the  -pinna)  (Figs.  905,  906)  con- 
sists of  a  single  piece;  it  gives  form  to  this  part  of  the  ear,  and  upon  its  surface  are  found  the 
eminences  and  depressions  above  described.  It  is  absent  from  the  lobule;  it  is  deficient,  also, 
between  the  tragus  and  beginning  of  the  helix,  the  gap  being  filled  up  by  dense  fibrous  tissue. 
At  the  front  part  of  the  auricula,  where  the  hehx  bends  upward,  is  a  small  projection  of  cartilage, 
called  the  spina  helicis,  while  in  the  lower  part  of  the  helix  the  cartilage  is  prolonged  downward 
as  a  tail-hke  process,  the  Cauda  helicis;  this  is  separated  from  the  antihelix  by  a  fissure,  the 
fissura  antitragohelicina.  The  cranial  aspect  of  the  cartilage  exhibits  a  transverse  furrow,  the 
sulcus  antihelicis  transversus,  which  corresponds  with  the  inferior  crus  of  the  antihelix  and 
separates  the  eminentia  conchaj  from  the  eminentia  triangularis.  The  emitientia  conchae  is 
crossed  by  a  vertical  ridge  {ponticulus),  which   gives  attachment  to  the  Auricularis  posterior 


THE  EXTERNAL  EAR 


1035 


muscle.    In  the  cartilage  of  the  auricula  are  two  fissures,  one  behind  the  crus  helicis  and  another 
in  the  tragus. 

The  ligaments  of  {he  auricula  (ligamenii  auricularia  [  Valsalva] ;  ligaments  of  the  pinria)  consist 
of  two  sets:  (1)  extrinsic,  connecting  it  to  the  side  of  the  head;  (2)  intrinsic,  connecting  various 
parts  of  its  cartilage  together. 

The  extrinsic  ligaments  are  two  in  number,  anterior  and  posterior.  The  anterior  ligament 
extends  from  the  tragus  and  spina  helicis  to  the  root  of  the  zygomatic  process  of  the  temporal 
bone.  The  posterior  ligament  passes  from  the  posterior  surface  of  the  concha  to  the  outer  surface 
of  the  mastoid  process. 

The  chief  intrinsic  ligaments  are:  (a)  a  strong  fibrous  band,  stretching  from  the  tragus  to  the 
commencement  of  the  helix,  completing  the  meatus  in  front,  and  partly  encircling  the  boundary 
of  the  concha;  and  (h)  a  band  between  the  antihelix  and  the  cauda  hehcis.  Other  less  important 
bands  are  found  on  the  cranial  surface  of  the  pinna. 

The  muscles  of  the  auricula  (Fig.  906)  consist  of  two  sets:  (1)  the  extrinsic,  which  connect  it 
with  the  skull  and  scalp  and  move  the  auricula  as  a  whole;  and  (2)  the  intrinsic,  which  extend 
from  one  part  of  the  auricle  to  another. 

The  extrinsic  muscles  are  the  Auriculares  anterior,  superior,  and  posterior. 

The  Auricularis  anterior  (Attrahens 
aurem),  the  smallest  of  the  three,  is  thin, 
fan-shaped,  and  its  fibers  are  pale  and  in- 
distinct. It  arises  from  the  lateral  edge 
of  the  galea  aponeurotica,  and  its  fibers 
converge  to  be  inserted  into  a  projection 
on  the  front  of  the  helix. 

The  Auricularis  superior  (Atlolens 
aurem),  the  largest  of  the  three,  is  thin 
and  fan-shaped.  Its  fibers  arise  from  the 
galea  aponeurotica,  and  converge  to  be 
inserted  by  a  thin,  flattened  tendon  into 
the  upper  part  of  the  cranial  surface  of  the 
auricula. 

The  Auricularis  posterior  {Retrahens 
aurem)  consists  of  two  or  three  fleshy 
fasciculi,  which  arise  from  the  mastoid 
portion  of  the  temporal  bone  by  short 
aponeurotic  fibers.  They  are  inserted  into 
the  lower  part  of  the  cranial  surface  of 
the  concha. 

Actions. — In  man,  these  muscles  possess 
very  little  action :  the  Auricularis  anterior 
draws  the  auricula  forward  and  upward; 
the  Auricularis  superior  slightly  raises  it; 
and  the  Auricularis  posterior  draws  it 
backward. 

The  intrinsic  muscles  are  the: 


Hehcis  major. 
Helicis  minor. 
I  Tragicus. 


Antitragicus. 
Transversus  auriculae. 
Obliquus  auriculae. 


Fig.  906. — The  muscles  of  the  auricula. 


The  Helicis  major  is  a  narrow  vertical  band  situated  upon  the  anterior  margin  of  the  heUx. 

It  arises  below,  from  the  spina  helicis,  and  is  inserted  into  the  anterior  border  of  the  heUx, 
just  where  it  is  about  to  curve  backward. 

The  Helicis  minor  is  an  oblique  fasciculus,  covering  the  crus  helicis. 

The  Tragicus  is  a  short,  flattened  vertical  band  on  the  lateral  surface  of  the  tragus. 

The  Antitragicus  arises  from  the  outer  part  of  the  antitragus,  and  is  inserted  into  the  cauda 
hehcis  and  antihehx. 

The  Transveisus  auriculoe  is  placed  on  the  cranial  surface  of  the  pinna.  It  consists  of  scattered 
fibers,  partly  tendinous  and  partly  muscular,  extending  from  the  eminentia  conchae  to  the  promi- 
nence corresponding  with  the  scapha. 

The  Obliquus  auriculae,  also  on  the  cranial  surface,  consists  of  a  few  fibers  extending  from 
the  upper  and  back  part  of  the  concha  to  the  convexity  immediately  above  it. 

Nerves. — The  Auriculares  anterior  and  superior  and  the  intrinsic  muscles  on  the  lateral  surface 
are  supphed  by  the  temporal  branch  of  the  facial  nerve,  the  Auricularis  posterior  and  the  intrinsic 
muscles  on  the  cranial  surface  by  the  posterior  auricular  branch  of  the  same  nerve. 


1036      ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


I 


The  arteries  of  the  auricula  are  the  posterior  auricular  from  the  external  carotid,  the  anterior 
auricular  from  the  superficial  temporal,  and  a  branch  from  the  occipital  artery.  ^fib^H 

The  veins  accompany  the  corresponding  arteries.  '^^^1 

The  sensory  nerves  are:  the  great  auricular,  from  the  cervical  plexus;  the  auricular  branch 
of  the  vagus;  the  auriculotemporal  branch  of  the  mandibular  nerve;  and  the  lesser  occipital 
from  the  cervical  plexus. 

Cartilage  of  auricvJa 
Attic 
Incus 

Malleus 

Tympanic  cavity 

Tensor  tympani 


Tympanic  membrane 


Cartilaginous 

part  of  ext. 

acoustic  meatus 


Bony  part  of 

ext.  acoustic 

meatU:S 


Fig.  907. — External  and  middle  ear,  opened  from  the  front.     Right  side. 

The  External  Acoustic  Meatus  (meatus  acusticus  extermis;  external  auditory  canal 
.or  meatus)  extends  from  the  bottom  of  the  concha  to  the  tympanic  membrane  (Figs. 
907,  908).  It  is  about  4  cm.  in  length  if  measured  from  the  tragus;  from  the  bottom 
of  the  concha  its  length  is  about  2.5  cm.  It  forms  an  S-shaped  curve,  and  is  directed 
at  first  inward,  forward,  and  slightly  upward  (pars  externa) ;  it  then  passes  inward 
and  backward  (pars  media),  and  lastly  is  carried  inward,  forward,  and  slightly 
downward  (pars  interna).  It  is  an  oval  cylindrical  canal,  the  greatest  diameter 
being  directed  downward  and  backward  at  the  external  orifice,  but  nearl}^  hori- 
zontally at  the  inner  end.  It  presents  two  constrictions,  one  near  the  inner  end 
of  the  cartilaginous  portion,  and  another,  the  isthmus,  in  the  osseous  portion,  about 
2  cm.  from  the  bottom  of  the  concha.  The  tympanic  membrane,  which  closes  the 
inner  end  of  the  meatus,  is  obliquely  directed ;  in  consequence  of  this  the  floor  and 
anterior  wall  of  the  meatus  are  longer  than  the  roof  and  posterior  wall. 

The  external  acoustic  meatus  is  formed  partly  by  cartilage  and  membrane, 
and  partly  by  bone,  and  is  lined  by  skin. 

The  cartilaginous  portion  (meatus  acusticus  externus  cartilagineus)  is  about  8  mm. 
in  length;  it  is  continuous  with  the  cartilage  of  the  auricula,  and  firmly  attached 
to  the  circumference  of  the  auditory  process  of  the  temporal  bone.  The  cartilage 
is  deficient  at  the  upper  and  back  part  of  the  meatus,  its  place  being  supplied  by 
fibrous  membrane;  two  or  three  deep  fissures  are  present  in  the  anterior  part  of  the 
cartilage. 

The  osseous  portion  (meatus  acusticus  externus  osseus)  is  about  16  mm.  in  length, 
and  is  narrower  than  the  cartilaginous  portion.    It  is  directed  inward  and  a  little 


THE  MIDDLE  EAR  OR  TYMPANIC  CAVITY 


1037 


forward,  forming  in  its  course  a  slight  curve  the  convexity  of  which  is  upward  and 
backward.  Its  inner  end  is  smaller  than  the  outer,  and  sloped,  the  anterior  wall 
projecting  beyond  the  posterior  for  about  4  mm. ;  it  is  marked,  except  at  its  upper 
part,  by  a  narrow  groove,  the  tympanic  sulcus,  in  which  the  circumference  of  the 
tympanic  membrane  is  attached.  Its  outer  end  is  dilated  and  rough  in  the  greater 
part  of  its  circumference,  for  the  attachment  of  the  cartilage  of  the  auricula.  The 
front  and  lower  parts  of  the  osseous  portion  are  formed  by  a  curved  plate  of  bone, 
the  tympanic  part  of  the  temporal,  which,  in  the  fetus,  exists  as  a  separate  ring 
(annulus  tympanicus,)  incomplete  at  its  upper  part  (page  146). 

Auditory  tube 

Condyle  of  mandible 


Internal  carotid 
artery 


Internal  acoustic 
meattis 


Part  of  parotid  gland 
Tragus 


External  acoustic 
meatus 


Tympanic  cavity 
Tympanic  membrane  / 

Mastoid  air-ceUs 

Transverse  sinus 


Helix 


Fig.  90S. — Horizontal  section  through  left  ear;  upper  half  of  section. 

The  skin  lining  the  meatus  is  very  thin;  adheres  closely  to  the  cartilaginous 
and  osseous  portions  of  the  tube,  and  covers  the  outer  surface  of  the  tympanic 
membrane.  After  maceration,  the  thin  pouch  of  epidermis,  when  withdrawn, 
preserves  the  form  of  the  meatus.  In  the  thick  subcutaneous  tissue  of  the  cartil- 
aginous part  of  the  meatus  are  numerous  ceruminous  glands,  which  secrete  the 
1 K  ear-wax ;  their  structure  resembles  that  of  the  sudoriferous  glands. 

Relations  of  the  Meatus. — In  front  of  the  osseous  part  is  the  condyle  of  the  mandible,  which 
however,  is  frequently  separated  from  the  cartilaginous  part  by  a  portion  of  the  parotid  gland. 
The  movements  of  the  jaw  influence  to  some  extent  the  lumen  of  this  latter  portion.  Behind  the 
osseous  part  are  the  mastoid  air  cells,  separated  from  the  meatus  by  a  thin  layer  of  bone. 

The  arteries  supplying  the  meatus  are  branches  from  the  posterior  auricular,  internal  maxillary, 
and  temporal. 

The  nerves  are  chiefly  derived  from  the  auriculotemporal  branch  of  the  mandibular  nerve 
And  the  auricular  branch  of  the  vagus. 

^^^^^      The  Middle  Ear  or  Tympanic  Cavity  (Cavum  Tympani;  Drum; 
^^HV  Tympanum). 

V  The  middle  ear  or  tympanic  cavity  is  an  irregular,  laterally  compressed  space 
'■^  within  the  temporal  bone.  It  is  filled  with  air,  which  is  conveyed  to  it  from  the 
nasal  part  of  the  pharynx  through  the  auditory  tube.  It  contains  a  chain  of  mov- 
able bones,  which  connect  its  lateral  to  its  medial  wall,  and  serve  to  convey  the 
vibrations  communicated  to  the  tympanic  membrane  across  the  cavity  to  the 
internal  ear. 


1038        ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

The  tympanic  cavity  consists  of  two  parts:  the  tsrmpanic  cavity  proper,  opposite 
the  tympanic  membrane,  and  the  attic  or  epitsrmpanic  recess,  above  the  level  of 
the  membrane;  the  latter  contains  the  upper  half  of  the  malleus  and  the  greater 
part  of  the  incus.  Including  the  attic,  the  vertical  and  antero-posterior  diameters 
of  the  cavity  are  each  about  15  mm.  The  transverse  diameter  measures  about 
6  mm.  above  and  4  mm.  below;  opposite  the  center  of  the  tympanic  membrane 
it  is  only  about  2  mm.  The  tympanic  cavity  is  bounded  laterally  by  the  tympanic 
membrane;  medially,  by  the  lateral  wall  of  the  internal  ear;  it  communicates, 
behind,  with  the  tympanic  antrum  and  through  it  with  the  mastoid  air  cells,  and 
in  front  with  the  auditory  tube  (Fig.  907) . 

The  Tegmental  Wall  or  Roof  (paries  tegmentalis)  is  formed  by  a  thin  plate  of  bone, 
the  tegmen  tjnnpani,  which  separates  the  cranial  and  tympanic  cavities.  It  is 
situated  on  the  anterior  surface  of  the  petrous  portion  of  the  temporal  bone  close 
to  its  angle  of  junction  with  the  squama  temporalis;  it  is  prolonged  backward  so 
as  to  roof  in  the  tympanic  antrum,  and  forw^ard  to  cover  in  the  semicanal  for  the 
Tensor  tympani  muscle.  Its  lateral  edge  corresponds  with  the  remains  of  the 
petrosquamous  suture. 

The  Jugular  Wall  or  Floor  (paries  jugvlaris)  is  narrow,  and  consists  of  a  thin  plate 
of  bone  (fundus  tympani)  which  separates  the  tympanic  cavity  from  the  jugular 
fossa.  It  presents,  near  the  labyrinthic  wall,  a  small  aperture  for  the  passage  of 
the  tympanic  branch  of  the  glossopharyngeal  nerve. 

Post,  malleolar  fold 
Long  crus  of  incus  p^^g  flaccida 

\  \        I  Lai.  'proc.  of  Ttialleus 

Ant.  malleolar  fold 

Manijibriwm, 
of  malleus 
Postero-swperior 
quadrant 


I 


Postero-inferior 
guadravi 


Antero-superior 

quadrant 
Urnbo 


Cone  of  light 


Antero-inferior  quadrant 
Fig.  909. — Right  tympanic  membrane  as  seen  through  a  speculum. 

The  Membranous  or  Lateral  Wall  (paries  memhranacea;  outer  wall)  is  formed 
mainly  by  the  tympanic  membrane,  partly  by  the  ring  of  bone  into  which  this 
membrane  is  inserted.  This  ring  of  bone  is  incomplete  at  its  upper  part,  forming 
a  notch  (notch  of  Rivinus),  close  to  which  are  three  small  apertures:  the  iter  chordae 
posterius,  the  petrotympanic  fissure,  and  the  iter  chordae  anterius. 

The  iter  chordae  posterius  (apertura  tympanica  canalicidi  chordoe)  is  situated  in 
the  angle  of  junction  between  the  mastoid  and  membranous  wall  of  the  tympanic 
cavity  immediately  behind  the  tympanic  membrane  and  on  a  level  with  the  upper 
end  of  the  manubrium  of  the  malleus;  it  leads  into  a  minute  canal,  which  descends 
in  front  of  the  canal  for  the  facial  nerve,  and  ends  in  that  canal  near  the  stylo- 
mastoid foramen.  Through  it  the  chorda  tympani  nerve  enters  the  tympanic 
cavity. 

The  petrotympanic  fissure  (fissnra  petrotympanica;  Glaserian  fissure)  opens  just 
above  and  in  front  of  the  ring  of  bone  into  which  the  tympanic  membrane  is 
inserted;  in  this  situation  it  is  a  mere  slit  about  2  mm.  in  length.  It  lodges 
the  anterior  process  and  anterior  ligament  of  the  malleus,  and  gives  passage  to  the 
anterior  tympanic  branch  of  the  internal  maxillary  artery. 


THE  MIDDLE  EAR  OR  TYMPANIC  CAVITY 


1039 


"The  iter  chordae  anterius  (canal  of  Hugider)  is  placed  at  the  medial  end  of  the 
petrotympanic  fissure;  through  it  the  chorda  tympani  nerve  leaves  the  tympanic 
cavity. 

The  Tympanic  Membrane  {membrana  tympani)  (Figs.  909,  910)  separates  the 
tympanic  cavity  from  the  bottom  of  the  external  acoustic  meatus.  It  is  a  thin, 
semitransparent  membrane,  nearly  oval 
in  form,  somewhat  broader  above  than 
below,  and  directed  very  obliquely  down- 
ward and  inward  so  as  to  form  an  angle 
of  about  fifty-five  degrees  with  the  floor 
of  the  meatus.  Its  longest  diameter  is 
downward  and  forward,  and  measures 
from  9  to  10  mm.;  its  shortest  diameter 
measures  from  8  to  9  mm.  The  greater 
part  of  its  circumference  is  thickened, 
and  forms  a  fibrocartilaginous  ring  which  is 
fixed  in  the  tympanic  sulcus  at  the  inner 
end  of  the  meatus.  This  sulcus  is  defi- 
cient superiorly  at  the  notch  of  Rivinus, 
and  from  the  ends  of  this  notch  two  bands, 
the  anterior  and  posterior  malleolar  folds, 
are  prolonged  to  the  lateral  process  of  the 
malleus.  The  small,  somewhat  triangular 
part  of  the  membrane  situated  above  these 
folds  is  lax  and  thin,  and  is  named  the 
pars  flaccida ;  in  it  a  small  orifice  is  some- 
times seen.  The  manubrium  of  the  malleus 
is  firmly  attached  to  the  medial  surface  of 
the  membrane  as  far  as  its  center,  which 
it  draws  toward  the  tympanic  cavity;  the 
lateral  surface  of  the  membrane  is  thus 
concave,  and  the  most  depressed  part  of 
this  concavity  is  named  the  irnibo. 

Structure. — The  tjrmpanic  membrane  is  com- 
posed of  three  strata:    a  lateral  (cutaneous),  an 

intermediate  (fibrous),  and  a  medial  (mucous).     The  cutaneous  stratum  is  derived  from  the 
integument  lining  the  meatus.     The  fibrous  stratum  consists  of  two  layers:    a  radiate  stratum, 


Fig.  910.- 


-The  tympanic  membrane  viewed  Irom 
within.  (Testut.)  The  malleus  has  been  resected 
immediately  beyond  it^  lateral  process,  in  order  to 
show  the  tympanomalleolar  folds  and  the  membrana 
flaccida.  1.  Tympanic  membrane.  2.  IJmbo.  3. 
Handle  of  the  malleus.  4.  Lateral  process.  5.  Anterior 
tympanomalleolar  fold.  6.  Posterior  tympanomalleolar 
fold.  7.  Pars  flaccida.  8.  Anterior  pouch  of  Troltsch. 
9.  Posterior  pouch  of  Troltsch.  10.  Fibrocartilaginous 
ring.  11.  Petrotympanic  fissure.  12.  Auditory  tube. 
13.  Iter  chordae^  posterius.  14.  Iter  chordae  anterius. 
15  Fossa  incudis  for  short  cms  of  the  incus.  16.  Pro- 
minentia styloidea. 


Chorda  tympani. 


Fig.  911. — ^View  of  the  inner  wall  of  the  tympanum  (enlarged.) 

the  fibers  of  which  diverge  from  the  manubrium  of  the  malleus,  and  a  circular  stratum,  the 
fibers  of  which  are  plentiful  around  the  circmnference  but  sparse  and  scattered  near  the  center 


J040      ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

of  the  membrane.     Branched  or  dendritic  fibers,  as  pointed  out  by  Grtiber,  are  also  present, 
especially  in  the  posterior  half  of  the  membrane. 

Vessels  and  Nerves. — The  arteries  of  the  tympanic  membrane  are  derived  from  the  deep 
auricular  branch  of  the  internal  maxillary,  which  ramifies  beneath  the  cutaneous  stratum;  and 
from  the  stylomastoid  branch  of  the  posterior  auricular,  and  tympanic  branch  of  the  internal 
maxillary,  which  are  distributed  on  the  mucous  surface.  The  superficial  veins  open  into  the 
external  jugular;  those  on  the  deep  surface  drain  partly  into  the  transverse  sinus  and  veins  of 
the  dura  mater,  and  partly  into  a  plexus  on  the  auditory  tube.  The  membrane  receives  its 
chief  nerve  supply  from  the  auriculotemporal  branch  of  the  mandibular;  the  auricular  branch  of 
the  vagus,  and  the  tympanic  branch  of  the  glossopharyngeal  also  supply  it.i 


GUPERlon  LIGAMENT 
OF    MALLEOLUS 


EPITYMPANIC 
RECESS 


m 


ARTICULAR   SURFACE 
FOR  BODY  OF  INCUS 


FLACCID  PORTION  OF 
MEMBRANA  TYMPANI 


POSTERIOR 

TYMPANIC 

SPINE 


TYMPANIC 
ORIFICE 
OF  CANAL 
FOR  CHORDA 
TYMPANi 
NERVe 


EUSTACHIAN 
TUBE 


TENSE  PORTION   OF 
MEMBRANA  TYMPANI 


Fig.  912. — The  right  membrana  tympani  with  the  hammer  and  the  chorda  tympani,  viewed  from  within,  from  behind, 

and  from  above.     (Spalteholz.) 

The  Labyrinthic  or  Medial  Wall  {yaries  labyrinthica;  inner  wall)  (Fig.  913)  is 
vertical  in  direction,  and  presents  for  examination  the  fenestrae  vestibuli  and 
cochleae,  the  promontory,  and  the  prominence  of  the  facial  canal. 

The  fenestra  vestibuli  {fenestra  ovalis)  is  a  reniform  opening  leading  from  the 
tympanic  cavity  into  the  vestibule  of  the  internal  ear;  its  long  diameter  is  horizontal, 
and  its  convex  border  is  upward.  In  the  recent  state  it  is  occupied  by  the  base  of 
the  stapes,  the  circumference  of  which  is  fixed  by  the  annular  ligament  to  the  margin 
of  the  foramen. 

The  fenestra  cochleae  (fenestra  rotunda)  is  situated  below  and  a  little  behind  the 
fenestra  vestibuli,  from  which  it  is  separated  by  a  rounded  elevation,  the  promontory. 
It  is  placed  at  the  bottom  of  a  funnel-shaped  depression  and,  in  the  macerated  bone, 
leads  into  the  cochlea  of  the  internal  ear;  in  the  fresh  state  it  is  closed  by  a  mem- 
brane, the  secondary  tympanic  membrane,  which  is  concave  toward  the  tympanic 
cavity,  convex  toward  the  cochlea.    This  membrane  consists  of  three  layers;  an 

'  Wilson,  J.  G..  American  Journal  of  Anatomy,  1911,  xi. 


THE  MIDDLE  EAR  OR  TYMPANIC  CAVITY 


1041 


external,  or  mucous,  derived  from  the  mucous  lining  of  the  tympanic  cavity;  an 
internal,  from  the  lining  membrane  of  the  cochlea;  and  an  intermediate,  or  fibrous 
laver. 


Tympanic  antrum 

Tegmen  tympani 

Prominence  of  lateral  semicircvlar  canal 
Prominence  of  facial  canal 
Fenestra  vestibuli 
Bristle  in  semicanal  for  Tensor  tympani 
Septum  canalis  muscvlotubarii 

Bristle  in  hiatus  of  facial  canal 


Carotid  canal 
Boriy  part  of  auditory  tube 
Promontory 
Bristle  in  pyramid 
Fenestra  cochlece 

Sulcus  tympanicus 
Mastoid  cells    "^"'^'^^  *^  stylomastoid  foramen 
Fig.  913. — Coronal  section  of  right  temporal  bone. 


JUNCTION   BETWEEN   MAS- 
TOID ANTRUM   AND 
EPITYMPANIC  RECESS 
TEGMEN 
TYMPANI 

EPITYMPANIC 
RECESS 

PROMINENCE  OF  EXTERNAL 
SEMICIRCULAR  CANAL 

PROMINENCE  OF  AQUEDUCT 
OF  F.ALLOPIUS 

TENDON  OF 
STAP.EDIUS  MUSCLE 
PLICA 


RMIS 
R  TYMPANI        ,  . 

U8CLE  (cut  through) 

WALL  OF 
LABYRINTH 


TYMPANIC     '^ 
SINUS 


/ 

-  \:/ 

^^ 

P***r^ 

FOSSULA  OF 

JUGULAR 

TYMPANIC 

FENESTRA  ROTUNDA 

Wi 

kLL 

PLEXUS 

Fig.  914. — The  medial  wall  and  part  of  the  posterior  and  anterior  -walls  of  the  right  tympanic  ca-idty,  lateral  view. 

(Spalteholz.) 


1042      ORGANS  OF  THE  SENSES  AND  THE   COMMON  INTEGUMENT 


I 


The  promontory  {promontorium)  is  a  rounded  hollow  prominence,  formed  by  the 
projection  outward  of  the  first  turn  of  the  cochlea ;  it  is  placed  between  the  f enestrse, 
and  is  furrowed  on  its  surface  by  small  grooves,  for  the  lodgement  of  branches  of  the 
tympanic  plexus.  A  minute  spicule  of  bone  frequently  connects  the  promontory 
to  the  pyramidal  eminence. 

The  prominence  of  the  facial  canal  (prominentia  canalis  facialis;  prominence  of 
aqueduct  of  Fallopiu^)  indicates  the  position  of  the  bony  canal  in  which  the 
facial  nerve  is  contained;  this  canal  traverses  the  labyrinthic  wall  of  the  tympanic 
cavity  above  the  fenestra  vestibuli,  and  behind  that  opening  curves  nearly 
vertically  downward  along  the  mastoid  wall. 

The  mastoid  or  posterior  wall  (paries  mastoidea)  is  wider  above  than  below,  and 
presents  for  examination  the  entrance  to  the  tympanic  antrmn,  the  pyramidal  eminence, 
and  the  fossa  incudis. 

The  entrance  to  the  antrum  is  a  large  irregular  aperture,  which  leads  backward 
from  the  epitympanic  recess  into  a  considerable  air  space,  named  the  t3rmpanic 
or  mastoid  antrum  (see  page  142).  The  antrum  communicates  behind  and  below 
with  the  mastoid  air  cells,  which  vary  considerably  in  number,  size,  and  form; 
the  antrum  and  mastoid  air  cells  are  lined  by  mucous  membrane,  continuous  with 
that  lining  the  tympanic  cavity.  On  the  medial  wall  of  the  entrance  to  the  antrum 
is  a  rounded  eminence,  situated  above  and  behind  the  prominence  of  the  facial 
canal;  it  corresponds  with  the  position  of  the  ampullated  ends  of  the  superior  and 
lateral  semicircular  canals. 

The  P3rramidal  eminence  (eminentia  pyramidalis;  pyramid)  is  situated  immedi- 
ately behind  the  fenestra  vestibuli,  and  in  front  of  the  vertical  portion  of  the  facial 
canal;  it  is  hollow,  and  contains  the  Stapedius  muscle;  its  summit  projects  forward 
toward  the  fenestra  vestibuli,  and  is  pierced  by  a  small  aperture  which  transmits 
the  tendon  of  the  muscle.  The  cavity  in  the  pyramidal  eminence  is  prolonged 
downward  and  backward  in  front  of  the  facial  canal,  and  communicates  with  it 
by  a  minute  aperture  which  transmits  a  twig  from  the  facial  nerve  to  the  Stapedius 
muscle. 

The  fossa  incudis  is  a  small  depression  in  the  lower  and  back  part  of  the  epi- 
tympanic recess;  it  lodges  the  short  crus  of  the  incus. 

The  Carotid  or  Anterior  Wall  (paries  carotica)  is  wider  above  than  below;  it  corre- 
sponds with  the  carotid  canal,  from  which  it  is  separated  by  a  thin  plate  of  bone 
perforated  by  the  tympanic  branch  of  the  internal  carotid  artery,  and  by  the  deep 
petrosal  nerve  which  connects  the  sympathetic  plexus  on  the  internal  carotid 
artery  with  the  tympanic  plexus  on  the  promontory.  At  the  upper  part  of  the 
anterior  wall  are  the  orifice  of  the  semicanal  for  the  Tensor  tympani  muscle  and 
the  tympanic  orifice  of  the  auditory  tube,  separated  from  each  other  by  a  thin 
horizontal  plate  of  bone,  the  septum  canalis  musculotubarii.  These  canals  run  from 
the  tympanic  cavity  forward  and  downward  to  the  retiring  angle  between  the 
squama  and  the  petrous  portion  of  the  temporal  bone. 

The  semicanal  for  the  Tensor  'tympani  (semicanalis  m.  tensoris  tympani)  is  the 
superior  and  the  smaller  of  the  two;  it  is  cylindrical  and  lies  beneath  the  tegmen 
tympani.  It  extends  on  to  the  labyrinthic  wall  of  the  tympanic  cavity  and  ends 
immediately  above  the  fenestra  vestibuli. 

The  septum  canalis  musculotubarii  (processus  cochleariformis)  passes  backward 
below  this  semicanal,  forming  its  lateral  wall  and  floor;  it  expands  above  the  ante- 
rior end  of  the  fenestra  vestibuli  and  terminates  there  by  curving  laterally  so  as 
to  form  a  pulley  over  which  the  tendon  of  the  muscle  passes. 

The  auditory  tube  (tuba  auditiva;  Eustachian  tube)  is  the  channel  through  which 
the  tympanic  cavity  communicates  with  the  nasal  part  of  the  pharynx.  Its  length 
is  about  36  mm.,  and  its  direction  is  downward,  forward,  and  medialward,  forming 
an  angle  of  about  45  degrees  with  the  sagittal  plane  and  one  of  from  30  to  40  degrees 


THE  MIDDLE  EAR  OR  TYMPANIC  CAVITY 


1043 


with  the  horizontal  plane.    It  is  formed  partly  of  bone,  partly  of  cartilage  and  fibrous 
tissue  (Figs.  819,  915). 

The  osseous  portion  (pars  osseo  tubes  miditivce)  is  about  12  mm.  in  length.  It 
begins  in  the  carotid  wall  of  the  tympanic  cavity,  below  the  septum  canalis  musculo- 
tubarii,  and,  gradually  narrowing,  ends  at  the  angle  of  junction  of  the  squama  and 
the  petrous  portion  of  the  temporal  bone,  its  extremity  presenting  a  jagged  margin 
which  serves  for  the  attachment  of  the  cartilaginous  portion. 


MEMBRANA 
TYMPANI 


ARYNGEAL   OPEN 
INC    OF  TUBE 


Fig.  915. — Auditory  tube,  laid  open  by  a  cut  in  its  long  axis.     (Testut.) 

The  cartilaginous  portion  (pars  cartilaginea  tubes  auditivce),  about  24  mm.  in  length, 
is  formed  of  a  triangular  plate  of  elastic  fibrocartilage,  the  apex  of  which  is  attached 
to  the  margin  of  the  medial  end  of  the  osseous  portion  of  the  tube,  while  its  base 
lies  directly  under  the  mucous  membrane  of  the  nasal  part  of  the  pharynx,  where 
it  forms  an  elevation,  the  torus  tubarius  or  cushion,  behind  the  pharyngeal  orifice  of 
the  tube.  The  upper  edge  of  the  cartilage  is  curled  upon  itself,  being  bent  laterally 
IK  so  as  to  present  on  transverse  section  the  appearance  of  a  hook;  a  groove  or  furrow 
■  ^  is  thus  produced,  which  is  open  below  and  laterally,  and  this  part  of  the  canal  is 
completed  by  fibrous  membrane.  The  cartilage  lies  in  a  groove  between  the  petrous 
part  of  the  temporal  and  the  great  wing  of  the  sphenoid;  this  groove  ends  opposite 
the  middle  of  the  medial  pterygoid  plate.  The  cartilaginous  and  bony  portions  of 
the  tube  are  not  in  the  same  plane,  the  former  inclining  downward  a  little  more 
than  the  latter.  The  diameter  of  the  tube  is  not  uniform  throughout,  being  greatest 
at  the  pharyngeal  orifice,  least  at  the  junction  of  the  bony  and  cartilaginous  por- 
tions, and  again  increased  toward  the  tympanic  cavity;  the  narrowest  part  of  the 
tube  is  termed  the  isthmus.  The  position  and  relations  of  the  pharyngeal  orifice 
are  described  with  the  nasal  part  of  the  pharynx.  The  mucous  membrane  of  the 
tube  is  continuous  in  front  with  that  of  the  nasal  part  of  the  pharynx,  and  behind 
with  that  of  the  tympanic  cavity;  it  is  covered  with  ciliated  epithelium  and  is  thin 
in  the  osseous  portion,  while  in  the  cartilaginous  portion  it  contains  many  mucous 
glands  and  near  the  pharyngeal  orifice  a  considerable  amount  of  adenoid  tissue, 
which  has  been  named  by  Gerlach  the  tube  tonsil.    The  tube  is  opened  during  deglu- 


1044      ORGANS  OF  THE  SENSES  AND  THE   COMMON  INTEGUMENT 

tition  by  the  Salpingopharyngeus  and  Dilatator  tubse.  The  latter  arises  from  the 
hook  of  the  cartilage  and  from  the  membranous  part  of  the  tube,  and  blends  below 
with  the  Tensor  veli  palatini. 


I 


The  Auditory  Ossicles  (Ossicula  Auditus). 


nalleus. 


Head 


Lateral 
process 


Anterior 
process 


Fig.  916. — Left  malleus.    A.  From  behind.     B.  From  within. 


The  tympanic  cavity  contains  a  chain  of  three  movable  ossicles,  the  mal 
incus,  and  stapes.  The  first  is  attached  to  the  tympanic  membrane,  the  last  to 
the  circumference  of  the  fenestra  vestibuli,  the  incus  being  placed  between  and 
connected  to  both  by  delicate  articulations. 

The  Malleus  (Fig.  916),  so  named  from  its  fancied  resemblance  to  a  hammer, 
consists  of  a  head,  neck,  and  three  processes,  viz.,  the  manubrium,  the  anterior  and 
lateral  processes. 

The  head  (capitulum  mallei)  is  the  large  upper  extremity  of  the  bone;  it  is  oval 
in  shape,  and  articulates  posteriorly  with  the  incus,  being  free  in  the  rest  of  its 

extent.  The  facet  for  articu- 
lation with  the  incus  is  con- 
stricted near  the  middle,  and 
consists  of  an  upper  larger  and 
lower  smaller  part,  which  form 
nearly  a  right  angle  with  each 
other.  Opposite  the  constric- 
tion the  lower  margin  of  the 
facet  projects  in  the  form  of  a 
process,  the  cog-tooth  or  spur  oi 
the  malleus. 

The  neck  (collum  mallei)  is 
the  narrow  contracted  part  just 
beneath  the  head ;  below  it,  is  a 
a  prominence,  to  which  the 
various  processes  are  attached. 
The  manubrium  mallei  (handle)  is  connected  by  its  lateral  margin  with  the  tym- 
panic membrane.  It  is  directed  downward,  medialward,  and  backward ;  it  decreases 
in  size  toward  its  free  end,  which  is  curved  slightly  forward,  and  flattened  trans- 
versely. On  its  medial  side,  near  its  upper  end,  is  a  slight  projection,  into  which 
the  tendon  of  the  Tensor  tympani  is  inserted. 

The  anterior  process  (processus  anterior  [Folii];  processus  gracilis)  is  a  delicate 
spicule,  which  springs  from  the  eminence  below  the  neck  and  is  directed  forward 
to  the  petrotympanic  fissure,  to  which  it  is  connected  by  ligamentous  fibers.  In 
the  fetus  this  is  the  longest  process  of  the  malleus,  and  is  in  direct  continuity  with 
the  cartilage  of  Meckel. 

The  lateral  process  (processus  lateralis;  processus  brevis)  is  a  slight  conical  projec- 
tion, which  springs  from  the  root  of  the  manubrium;  it  is  directed  laterally,  and  is 
attached  to  the  upper  part  of  the  tympanic  membrane  and,  by  means  of  the  ante- 
rior and  posterior  malleolar  folds,  to  the  extremities  of  the  notch  of  Rivinus. 

The  Incus  (Fig.  917)  has  received  its  name  from  its  supposed  resemblance  to 
an  anvil,  but  it  is  more  like  a  premolar  tooth,  with  two  roots,  which  difi'er  in 
length,  and  are  widely  separated  from  each  other.  It  consists  of  a  body  and  two 
crura. 

The  body  (corpus  incudis)  is  somewhat  cubical  but  compressed   transversely. 
On  its  anterior  surface  is  a  deeply  concavo-convex  facet,  which  articulates  with 
the  head  of  the  malleus. 
The  two  crura  diverge  from  one  another  nearly  at  right  angles. 
The  short  cms  (crus  breve;   short  process),  somewhat  conical  in  shape,  projects 


THE  AUDITORY  OSSICLES 


1045 


almost  horizontally  backward,  and  is  attached  to  the  fossa  incudis,  in  the  lower 
and  back  part  of  the  epitympanic  recess. 

The  long  eras  {cms  longum;  long  process)  descends  nearly  vertically  behind  and 
parallel  to  the  manubrium  of  the  malleus,  and,  bending  medialward,  ends  in  a 
rounded  projection,  the  lenticular  process,  which  is  tipped  with  cartilage,  and 
articulates  with  the  head  of  the  stapes. 

The  Stapes  (Fig.  918),  so  called  from  its  resemblance  to  a  stirrup,  consists  of  a 
head,  neck,  two  crura,  and  a  base. 

The  head  (capitulum  stapedis)  presents  a  depression,  which  is  covered  by  cartilage, 
and  articulates  with  the  lenticular  process  of  the  incus. 

The  neck,  the  constricted  part  of  the  bone  succeeding  the  head,  gives  insertion 
to  the  tendon  of  the  Stapedius  muscle. 

The  two  crura  {cms  anterius  and  cms  posterius)  diverge  from  the  neck  and  are 
connected  at  their  ends  by  a  flattened  oval  plate,  the  base  {basis  stapedis),  which 
forms  the  foot-plate  of  the  stirrup  and  is  fixed  to  the  margin  of  the  fenestra  vestibuli 
by  a  ring  of  ligamentous  fibers.    Of  the  two  crura  the  anterior  is  shorter  and  less 

turved  than  the  posterior. 


Facet  for 
malleus 


Short  crus 


Long  crus 

Lenticular 
process 


Bead 


Neck, 


Anterior  crus 
Posterior  crtis 
Base 


£ 


-Left  incus.     A.  From  within, 
the  front. 


B.  From 


Fig.  918. — A.  Left  stapes.    B.  Base  of  stapes,  medial 
surface. 


m 


IB.*' 

I 


Articulations  of  the  Auditory  Ossicles  {articulationes  ossicuhrum  auditus). — 
he  incudomalleolar  joint  is  a  saddle-shaped  diarthrosis;  it  is  surrounded  by  an 
articular  capsule,  and  the  joint  cavity  is  incompletely  divided  into  two  by  a  wedge- 
shaped  articular  disk  or  meniscus.  The  incudostapedial  joint  is  an  enarthrosis, 
surrounded  by  an  articular  capsule;  some  observers  have  described  an  articular 
disk  or  meniscus  in  this  joint;  others  regard  the  joint  as  a  syndesmosis. 

Ligaments  of  the  Ossicles  {ligamenta  ossicuhrum  auditus). — The  ossicles  are 
connected  with  the  walls  of  the  tympanic  cavity  by  ligaments:  three  for  the 
malleus,  and  one  each  for  the  incus  and  stapes. 

The  anterior  ligament  of  the  malleus  {lig.  mallei  anterius)  is  attached  by  one  end 

to  the  neck  of  the  malleus,  just  above  the  anterior  process,  and  by  the  other  to 

he  anterior  wall  of  the  tympanic  cavity,  close  to  the  petrotympanic  fissure,  some 

of  its  fibers  being  prolonged  through  the  fissure  to  reach  the  spina  angularis  of  the 

sphenoid. 

The  superior  ligament  of  the  malleus  {lig.  mallei  superiu^)  is  a  delicate,  round 
bundle  which  descends  from  the  roof  of  the  epitympanic  recess  to  the  head  of  the 
malleus. 

The  lateral  ligament  of  the  malleus  {lig.  mallei  later  ale;  external  ligament  of  the 
malleus)  is  a  triangular  band  passing  from  the  posterior  part  of  the  notch  of  Rivinus 
to  the  head  of  the  malleus.  Helmholtz  described  the  anterior  ligament  and  the 
posterior  part  of  the  lateral  ligament  as  forming  together  the  axis  ligament  around 
which  the  malleus  rotates. 

The  posterior  ligament  of  the  incus  {lig.  incudis  posterius)  is  a  short,  thick  band 
connecting  the  end  of  the  short  crus  of  the  incus  to  the  fossa  incudis. 


1046      ORGANS  OF  THE  SENSES  AND  THE   COMMON  INTEGUMENT 

A  superior  ligament  of  the  incus  (lig.  incudis  suyerius)  has  been  described,  but  it 

is  little  more  than  a  fold  of  mucous  membrane. 
The  vestibular  surface  and  the  circumference  of  the  base  of  the  stapes  are  covered 

with  hyaline  cartilage;  that  encircling  the  base  is  attached  to  the  margin  of  the 

fenestra  vestibuli  by  a  fibrous  ring,  the  annular 
ligament  of  the  base  of  the  stapes  {lig.  cmnulare 
baseos  stapedis) . 

The  Muscles  of  the  Tympanic  Cavity  {musculi 
ossicidorum  andihis)  are  the  Tensor  tympani 
and  Stapedius. 

The  Tensor  tympani,  the  larger,  is  contained 
in  the  bony  canal  above  the  osseous  portion  of 
the  auditory  tube,  from  which  it  is  separated 
by  the  septum  canalis  musculotubarii.  It 
arises  from  the  cartilaginous  portion  of  the 
auditory  tube  and  the  adjoining  part  of  the 
great  wing  of  the  sphenoid,  as  well  as  from  the 
osseous  canal  in  which  it  is  contained.  Passing 
backward  through  the  canal,  it  ends  in  a  slen- 
der tendon  which  enters  the  tympanic  cavity, 
makes  a  sharp  bend  around  the  extremity  of 
the  septum,  and  is  inserted  into  the  manubrium 
of  the  malleus,  near  its  root.  It  is  supplied 
by  a  branch  of  the  mandibular  nerve  through 
the  otic  ganglion. 

The  Stapedius  arises  from  the  wall  of  a  con- 
ical cavity,  hollowed  out  of  the  interior  of  the 
pyramidal  eminence;  its  tendon  emerges  from 

the  orifice  at  the  apex  of  the  eminence,  and,  passing  forward,  is  inserted  into  the 

posterior  surface  of  the  neck  of  the  stapes.    It  is  supplied  by  a  branch  of  the  facial 

nerve. 

Actions. — The  Tensor  tympani  draws  the  tympanic  membrane  medialward,  and  thus  increases 
its  tension.  The  Stapedius  pulls  the  head  of  the  stapes  backward  and  thus  causes  the  base  of 
the  bone  to  rotate  on  a  vertical  axis  drawn  through  its  own  center;  the  back  part  of  the  base  is 
pressed  inward  toward  the  vestibule,  while  the  forepart  is  withdrawn  from  it.  By  the  action  of 
the  muscle  the  tension  of  the  fluid  within  the  Internal  ear  is  probably  increased. 

The  Mucous  Membrane  of  the  Tsrmpanic  Cavity  is  continuous  with  that  of  the  pharynx,  through 
the  auditory  tube.  It  invests  the  auditory  ossicles,  and  the  muscles  and  nerves  contained  in 
the  tympanic  cavity;  forms  the  medial  layer  of  the  tympanic  membrane,  and  the  lateral  layer 
of  the  secondary  tympanic  membrane,  and  is  reflected  into  the  tympanic  antrum  and  mastoid 
cells,  which  it  lines  throughout.  It  forms  several  vascular  folds,  which  extend  from  the  walla 
of  the  tympanic  cavity  of  the  ossicles;  of  these,  one  descends  from  the  roof  of  the 
cavity  to  the  head  of  the  malleus  and  upper  margin  of  the  body  of  the  incus,  a  second 
invests  the  Stapedius  muscle:  other  folds  invest  the  chorda  tympani  nerve  and  the  Tensor 
tympani  muscle.  These  folds  separate  off  pouch-Uke  cavities,  and  give  the  interior  of  the  tym- 
panum a  somewhat  honey-combed  appearance.  One  of  these  pouches,  the  pouch  of  Prussak, 
is  well-marked  and  lies  between  the  neck  of  the  malleus  and  the  membrana  flaccida.  Two  other 
recesses  may  be  mentioned:  they  are  formed  by  the  mucous  membrane  which  envelops  the 
chorda  tympani  nerve  and  are  situated,  one  in  front  of,  and  the  other  behind  the  manubrium  of 
the  malleus;  they  are  named  the  anterior  and  posterior  recesses  of  Troltsch.  In  the  tympanic 
cavity  this  membrane  is  pale,  thin,  slightly  vascular,  and  covered  for  the  most  part  with  colum- 
nar ciliated  epithehum,  but  over  the  pyramidal  eminence,  ossicles,  and  tympanic  membrane 
it  possesses  a  flattened  non-ciliated  epithelium.  In  the  tympanic  antrum  and  mastoid  cells 
its  epithelium  is  also  non-ciliated.  In  the  osseous  portion  of  the  auditory  tube  the  membrane  is 
thin;  but  in  the  cartilaginous  portion  it  is  very  thick,  highly  vascular,  and  provided  with  numerous 
mucous  glands;  the  epithehum  which  lines  the  tube  is  columnar  and  cihated. 

Vessels  and  Nerves. — The  arteries  are  six  in  number.  Two  of  them  are  larger  than  the  others, 
viz.,  the  tympanic  branch  of  the  internal  maxillary,  which  supplies  the  tympanic  membrane; 


Fig.  919. — Chain  of  ossicles  and  their  liga- 
ments, seen  from  the  front  in  a  vertical,  trans- 
verse section  of  the  tympanum.    (Testut.) 


I 

I 


I 


THE  INTERNAL  EAR  OR  LABYRINTH  1047 

and  the  stylomastoid  branch  of  the  posterior  auricular,  which  supphes  the  back  part  of  l^e 
tympanic  cavity  and  mastoid  cells.  The  smaller  arteries  are — the  petrosal  branch  of  the  midale 
meningeal,  which  enters  through  the  hiatus  of  the  facial  canal;  a  branch  from  the  ascending 
pharyngeal,  and  another  from  the  artery  of  the  pterygoid  canal,  which  accompany  the  auditory 
tube;  and  the  tympanic  branch  from  the  internal  carotid,  given  off  in  the  carotid  canal  and 
perforating  the  thin  anterior  wall  of  the  tympanic  cavity.  The  veins  terminate  in  the  pterygoid 
plexus  and  the  superior  petrosal  sinus.  The  nerves  constitute  the  tympanic  plexus,  which 
ramifies  upon  the  surface  of  the  promontory.  The  plexus  is  formed  by  (1)  the  tympanic  branch 
of  the  glossopharyngeal;  (2)  the  caroticotympanic  nerves;  (3)  the  smaller  superficial  petrosal 
nerve;  and  (4)  a  branch  which  joins  the  greater  superficial  petrosal. 

The  tympanic  branch  of  the  glossopharyngeal  (Jacobson's  nerve)  enters  the  tympanic  cavity 
by  an  aperture  in  its  floor  close  to  the  labyrinthic  wall,  and  divides  into  branches  which 
ramify  on  the  promontory  and  enter  into  the  formation  of  the  tympanic  plexus.  The  superior 
and  inferior  caroticot]rmpanic  nerves  from  the  carotid  plexus  of  the  sympathetic  pass  through 
the  wall  of  the  carotid  canal,  and  join  the  branches  of  the  tympanic  branch  of  the  glossopharyn- 
geal. The  branch  to  the  greater  superficial  petrosal  passes  through  an  opening  on  the  laby- 
rinthic wall,  in  front  of  the  fenestra  vestibuli.  The  smaller  superficial  petrosal  nerve,  from 
the  otic  ganglion,  passes  backward  through  a  foramen  in  the  middle  fossa  of  the  base  of  the 
skull  (sometimes  through  the  foramen  ovale),  and  enters  the  anterior  surface  of  the  petrous 
part  of  the  temporal  bone  through  a  small  aperture,  situated  lateral  to  the  hiatus  of  the  facial 
canal;  it  courses  downward  through  the  bone,  past  the  genicular  gangUon  of  the  facial  nerve, 
receiving  a  connecting  filament  from  it,  and  enters  the  tympanic  cavity,  where  it  communicates 
with  the  tympanic  branch  of  the  glossopharyngeal,  and  assists  in  forming  the  tympanic  plexus. 

The  branches  of  distribution  of  the  tympanic  plexus  are  suppUed  to  the  mucous  membrane 
of  the  tympanic  cavity;  a  branch  passes  to  the  fenestra  vestibuli,  another  to  the  fenestra  cochleae, 
and  a  third  to  the  auditory  tube.  The  smaller  superficial  petrosal  may  be  looked  upon  as  the 
continuation  of  the  tympanic  branch  of  the  glossopharjTigeal  through  the  plexus  to  the  otic 
ganglion. 

In  addition  to  the  tympanic  plexus  there  are  the  nerves  supplying  the  muscles.  The  Tensor 
tympani  is  supphed  by  a  branch  from  the  mandibular  through  the  otic  ganghon,  and  the  Stapedius 
by  a  branch  from  the  facial. 

The  chorda  tympani  nerve  crosses  the  tympanic  davity.  It  is  given  off  from  the  sensory  part 
of  the  facial,  about  6  mm.  before  the  nerve  emerges  from  the  stylomastoid  foramen.  It  runs 
from  below  upward  and  forward  in  a  canal,  and  enters  the  tympanic  cavity  through  the  iter 
chordae  posterius,  and  becomes  invested  with  mucous  membrane.  It  traverses  the  tympanic 
cavity,  crossing  medial  to  the  tympanic  membrane  and  over  the  upper  part  of  the  manubrium 
of  the  malleus  to  the  carotid  wall,  where  it  emerges  through  the  iter  chordae  anterius  {canal 
of  Huguier). 


The  Internal  Ear  or  Labjrrinth  (Auris  Interna). 


I 


The  internal  ear  is  the  essential  part  of  the  organ  of  hearing,  receiving  the  ultimate 
distribution  of  the  auditory  nerve.  It  is  called  the  labyrinth,  from  the  complexity 
of  its  shape,  and  consists  of  two  parts:  the  osseous  labyrinth,  a  series  of  cavities 
within  the  petrous  part  of  the  temporal  bone,  and  the  membranous  labyrinth,  a 
series  of  communicating  membranous  sacs  and  ducts,  contained  within  the  bony 
cavities. 

The  Osseous  Labyrinth  (labyrinthus  osseus)  (Figs.  920,  921). — The  osseous 
labyrinth  consists  of  three  parts:  the  vestibule,  semicircular  canals,  and  cochlea. 
These  are  cavities  hollowed  out  of  the  substance  of  the  bone,  and  lined  by 
periosteum;  they  contain  a  clear  fluid,  the  perilymph,  in  which  the  membranous 
labyrinth  is  situated. 

The  Vestibule  {vestihulum) . — The  vestibule  is  the  central  part  of  the  osseous 
labyrinth,  and  is  situated  medial  to  the  tympanic  cavity,  behind  the  cochlea,  and 
in  front  of  the  semicircular  canals.  It  is  somewhat  ovoid  in  shape,  but  flattened 
transversely;  it  measures  about  5  mm.  from  before  backward,  the  same  from  above 
downward,  and  about  3  mm.  across.  In  its  lateral  or  tympanic  wall  is  the  fenestra 
vestibuli,  closed,  in  the  fresh  state,  by  the  base  of  the  stapes  and  annular  ligament. 
On  its  medial  wall,  at  the  forepart,  is  a  small  circular  depression,  the  recessus 
sphaericus,  which  is  perforated,  at  its  anterior  and  inferior  part,  by  several  minute 
holes  (macula  cribrosa  media)  for  the  passage  of  filaments  of  the'  acoustic  nerve 
to  the  saccule;  and  behind  this  depression  is  an  oblique  ridge,  the  crista  vestibuli, 


1048      ORGANS  OF  THE  SENSES  AND   THE   COMMON  INTEGUMENT 

the  anterior  end  of  which  is  named  the  pyramid  of  the  vestibule.  This  ridge  bifur- 
cates below  to  enclose  a  small  depression,  the  fossa  cochlearis,  which  is  perforated 
by  a  number  of  holes  for  the  passage  of  filaments  of  the  acoustic  nerve  which  supply 
the  vestibular  end  of  the  ductus  cochlearis.  As  the  hinder  part  of  the  medial  wall 
is  the  orifice  of  the  aquaeductus  vestibuli,  which  extends  to  the  posterior  surface  of 


Fig.  920. — Right  osseous  labyrinth.     Lateral  view. 

the  petrous  portion  of  the  temporal  bone.  It  transmits  a  small  vein,  and  contains 
a  tubular  prolongation  of  the  membranous  labyrinth,  the  ductus  endolymphaticus, 
which  ends  in  a  cul-de-sac  between  the  layers  of  the  dura  mater  within  the  cranial 
cavity.  On  the  upper  wall  or  roof  is  a  transversely  oval  depression,  the  recessus 
ellipticus,  separated  from  the  recessus  sphsericus  by  the  crista  vestibuli  already 
mentioned.   The  pyramid  and  adjoining  part  of  the  recessus  ellipticus  are  perforated 


Bece88U8  ellipticus 
Recessus  sphcericus 


Orifice  oj  aquoeductus  vestibuli 

Ti  TT      '    /       Orifice  of  aquceductus  cochleae 

i  ossa  cocMeans  /  ^       j    i 

Cochlear  fenestra 
Fig.  921. — Interior  of  right  osseous  labyrinth. 

by  a  number  of  holes  (macula  cribrosa  superior).  The  apertures  in  the  pyramid 
transmit  the  nerves  to  the  utricle ;  those  in  the  recessus  ellipticus  the  nerves  to  the 
ampullae  of  the  superior  and  lateral  semicircular  ducts.  Behind  are  the  five  orifices 
of  the  semicircular  canals.  In  fi'ont  is  an  elliptical  opening,  which  communicates 
with  the  scala  vestibuli  of  the  cochlea. 


THE  INTERNAL  EAR  OR  LABYRINTH 


1049 


The  Bony  Semicircular  Canals  (canales  semicirculares  ossei). — The  bony  semi- 
circular canals  are  three  in  number,  superior,  posterior,  and  lateral,  and  are  situated 
above  and  behind  the  vestibule.  They  are  unequal  in  length,  compressed  from  side 
to  side,  and  each  describes  the  greater  part  of  a  circle.  Each  measures  about 
0.8  mm.  in  diameter,  and  presents  a  dilatation  at  one  end,  called  the  ampulla,  which 
measures  more  than  twice  the  diameter  of  the  tube.  They  open  into  the  vestibule 
by  five  orifices,  one  of  the  apertures  being  common  to  two  of  the  canals. 


Plane  of  superior 
/      semicircular  canal 


\y-\— -Facial 


Fig.  922. — Position  of  the  right  bony  labyrinth  of  the  ear  in  the  skull,  viewed  from  above.    The  temporal  bone  is  con- 
sidered transparent  and  the  labyrinth  drawn  in  from  a  corrosion  preparation.      (Spalteholz.) 

The  superior  semicircular  canal  (canalis  semicircularis  superior),  15  to  20  mm. 
in  length,  is  vertical  in  direction,  and  is  placed  transversely  to  the  long  axis  of  the 
petrous  portion  of  the  temporal  bone,  on  the  anterior  surface  of  which  its  arch 
forms  a  round  projection.  It  describes  about  two-thirds  of  a  circle.  Its  lateral 
extremity  is  ampullated,  and  opens  into  the  upper  part  of  the  vestibule;  the  oppo- 
site end  joins  with  the  upper  part  of  the  posterior  canal  to  form  the  cms  commune, 
which  opens  into  the  upper    nd  medial  part  of  the  vestibule. 

The  posterior  semicircular  canal  {canalis  semicircularis  posterior),  also  vertical,  is 
directed  backward,  nearly  parallel  to  the  posterior  surface  of  the  petrous  bone; 
it  is  the  longest  of  the  three,  measuring  from  18  to  22  mm.;  its  lower  or  ampullated 
end  opens  into  the  lower  and  back  part  of  the  vestibule,  its  upper  into  the  crus 
commune  already  mentioned. 

The  lateral  or  horizontal  canal  (canalis  semicircularis  lateralis;  external  semicircular 
canal)  is  the  shortest  of  the  three.  It  measures  from  12  to  15  mm.,  and  its  arch 
is  directed  horizontally  backward  and  lateralward;  thus  each  semicircular  canal 
stands  at  right  angles  to  the  other  two.    Its  ampullated  end  corresponds  to  the 


1050      ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

upper  and  lateral  angle  of  the  vestibule,  just  above  the  fenestra  vestibuli,  where 
it  opens  close  to  the  ampullated  end  of  the  superior  canal ;  its  opposite  end  opens 
at  the  upper  and  back  part  of  the  vestibule.  The  lateral  canal  of  one  ear  is  very 
nearly  in  the  same  plane  as  that  of  the  other;  while  the  superior  canal  of  one  ear 
is  nearly  parallel  to  the  posterior  canal  of  the  other. 


I 


Helicotrema 


Lamina  spiralis 
/  '     ossea 


Cupula^ 


Tympanic  cavity 


Cochlea 
Scala  vestihuli 
Scala  tympani 


'-^■Vestibular  fenestra 
^Fissura  vestibuli 

■  Recessus 
sphoericus 
~  Fossa  cochlearis 

-Lat.  semicircular 
canal 


Vestibule 


Post,  semicircular 
canal 


Aqv/Bductua 
vestibuli 


Reces  suscepticua 


Fio.  923. — The  cochlea  and  vestibule,  viewed  from  above.    All  the  hard  parts  which  form  the  roof  of  the  internal 

ear  have  been  removed  with  the  saw. 

The  Cochlea  (Figs.  922,  923) . — ^The  cochlea  bears  some  resemblance  to  a  common 
snail-shell;  it  forms  the  anterior  part  of  the  labyrinth,  is  conical  in  form,  and  placed 
almost  horizontally  in  front  of  the  vestibule;  its  apex  (cupula)  is  directed  forward 
and  lateralward,  with  a  slight  inclination  downward,  toward  the  upper  and  front 
part  of  the  labyrinthic  wall  of  the  tympanic  cavity;  its  base  corresponds  with  the 
bottom  of  the  internal  acoustic  meatus,  and  is  perforated  by  numerous  apertures 
for  the  passage  of  the  cochlear  division  of  the  acoustic  nerve.  It  measures  about 
5  mm.  from  base  to  apex,  and  its  breadth  across  the  base  is  about  9  mm.  It  con- 
sists of  a  conical  shaped  central  axis,  the  modiolus;  of  a  canal,  the  inner  wall  of  which 
is  formed  by  the  central  axis,  wound  spirally  around  it  for  two  turns  and  three- 
quarters,  from  the  base  to  the  apex;  and  of  a  delicate  lamina,  the  osseous  spiral 
lamina,  which  projects  from  the  modiolus,  and,  following  the  windings  of  the  canal, 
partially  subdivides  it  into  two.  In  the  recent  state  a  membrane,  the  basilar 
membrane,  stretches  from  the  free  border  of  this  lamina  to  the  outer  wall  of  the  bony 
cochlea  and  completely  separates  the  canal  into  two  passages,  which,  however, 
communicate  with  each  other  at  the  apex  of  the  modiolus  by  a  small  opening 
named  the  helicotrema. 

The  modiolus  is  the  conical  central  axis  or  pillar  of  the  cochlea.  Its  base  is  broad, 
and  appears  at  the  bottom  of  the  internal  acoustic  meatus,  where  it  corresponds 
with  the  area  cochleae;  it  is  perforated  by  numerous  orifices,  which  transmit  fila- 
ments of  the  cochlear  division  of  the  acoustic  nerve;  the  nerves  for  the  first  turn 
and  a  half  pass  through  the  foramina  of  the  tractus  spiralis  foraminosus;  those 
for  the  apical  turn,  through  the  foramen  centrale.  The  canals  of  the  tractus 
spiralis  foraminosus  pass  up  through  the  modiolus  and  successively  bend  outward 


THE  INTERNAL  EAR  OR  LABYRINTH  1051 

to  reach  the  attached  margin  of  the  lamina  spiraHs  ossea.  Here  they  become 
enlarged,  and  by  their  apposition  form  the  spiral  canal  of  the  modiolus,  which 
folloAvs  the  course  of  the  attached  margin  of  the  osseous  spiral  lamina  and  lodges 
the  spiral  ganglion  (ganglion  of  Corti).  The  foramen  centrale  is  continued  into 
a  canal  which  runs  up  the  middle  of  the  modiolus  to  its  apex.  The  modiolus 
diminishes  rapidly  in  size  in  the  second  and  succeeding  coil. 

The  bony  canal  of  the  cochlea  takes  two  turns  and  three-quarters  around  the 
modiolus.  It  is  about  30  mm.  in  length,  and  diminishes  gradually  in  diameter 
from  the  base  to  the  summit,  where  it  terminates  in  the  cupula,  which  forms  the 
apex  of  the  cochlea.  The  beginning  of  this  canal  is  about  3  mm.  in  diameter; 
it  diverges  from  the  modiolus  toward  the  tympanic  cavity  and  vestibule,  and 
presents  three  openings.  One,  the  fenestra  cochleae,  communicates  with  the  tym- 
panic cavity — in  the  fresh  state  this  aperture  is  closed  by  the  secondary  tympanic 
membrane ;  another,  of  an  elliptical  form,  opens  into  the  vestibule.  The  third  is  the 
aperture  of  the  aquseductus  cochleie,  leading  to  a  minute  funnel-shaped  canal, 
which  opens  on  the  inferior  surface  of  the  petrous  part  of  the  temporal  bone 
and  transmits  a  small  vein,  and  also  forms  a  communication  between  the 
subarachnoid  cavity  and  the  scala  tympani. 

The  osseous  spiral  lamina  {lamina  spiralis  ossea)  is  a  bony  shelf  or  ledge  which  pro- 
jects from  the  modiolus  into  the  interior  of  the  canal,  and,  like  the  canal,  takes  two- 
and  three-quarter  turns  around  the  modiolus.  It  reaches  about  half-way  toward 
the  outer  wall  of  the  tube,  and  partially  divides  its  cavity  into  two  passages  or 
scalse,  of  which  the  upper  is  named  the  scala  vestibuli,  while  the  lower  is  termed 
the  scala  tympani.  Near  the  summit  of  the  cochlea  the  lamina  ends  in  a  hook- 
shaped  process,  the  hamulus  laminae  spiralis;  this  assists  in  forming  the  boundary 
of  a  small  opening,  the  helicotrema,  through  which  the  two  scalae  communicate 
with  each  other.  From  the  spiral  canal  of  the  modiolus  numerous  canals  pass  out- 
ward through  the  osseous  spiral  lamina  as  far  as  its  free  edge.  In  the  lower  part 
of  the  first  turn  a  second  bony  lamina,  the  secondary  spiral  lamina,  projects  inward 
from  the  outer  wall  of  the  bony  tube;  it  does  not,  however,  reach  the  primary 
osseous  spiral  lamina,  so  that  if  viewed  from  the  vestibule  a  narrow  fissure,  the 
vestibule  fissure,  is  seen  between  them. 

The  osseous  labyrinth  is  lined  by  an  exceedingly  thin  fibro-serous  membrane; 
its  attached  surface  is  rough  and  fibrous,  and  closely  adherent  to  the  bone;  its 
free  surface  is  smooth  and  pale,  covered  with  a  layer  of  epithelium,  and  secretes 
a  thin,  limpid  fluid,  the  perilymph.  A  delicate  tubular  process  of  this  membrane 
is  prolonged  along  the  aqueduct  of  the  cochlea  to  the  inner  surface  of  the  dura 
mater. 

The  Membranous  Labyrinth  {labyrinthus  membranaceus)  (Figs.  924,  925,  926). — 
The  membranous  labyrinth  is  lodged  within  the  bony  cavities  just  described, 
and  has  the  same  general  form  as  these;  it  is,  however,  considerably  smaller,  and 
is  partly  separated  from  the  bony  walls  by  a  quantity  of  fluid,  the  perilymph.  In 
certain  places  it  is  fixed  to  the  walls  of  the  cavity.  The  membranous  labyrinth 
contains  fluid,  the  endolymph,  and  on  its  walls  the  ramifications  of  the  acoustic 
nerve  are  distributed. 

Within  the  osseous  vestibule  the  membranous  labyrinth  does  not  quite  preserve 
the  form  of  the  bony  cavity,  but  consists  of  two  membranous  sacs,  the  utricle, 
and  the  saccule. 

The  Utricle  {utriculus) . — The  utricle,  the  larger  of  the  two,  is  of  an  oblong  form, 
compressed  transversely,  and  occupies  the  upper  and  back  part  of  the  vestibule, 
lying  in  contact  with  the  recessus  ellipticus  and  the  part  below  it.  That  portion 
which  is  lodged  in  the  recess  forms  a  sort  of  pouch  or  cul-de-sac,  the  floor  and  ante- 
rior wall  of  which  are  thickened,  and  form  the  macula  acustica  utriculi,  which  receives 
the  utricular  filaments  of  the  acoustic  nerve.    The  cavity  of  the  utricle  communi- 


1052      ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

cates  behind  with  the  semicircular  ducts  by  five  orifices.  From  its  anterior  wall  is 
given  off  the  ductus  utriculosaccularis,  which  opens  into  the  ductus  endolymphaticus. 
The  Saccule  {saccuhis). — The  saccule  is  the  smaller  of  the  two  vestibular  sacs; 
it  is  globular  in  form,  and  lies  in  the  recessus  sphsericus  near  the  opening  of  the 
scala  vestibuli  of  the  cochlea.  Its  anterior  part  exhibits  an  oval  thickening,  the 
macula  acustica  sacculi,  to  which  are  distributed  the  saccular  filaments  of  the 
acoustic  nerve.  Its  cavity  does  not  directly  communicate  with  that  of  the  utricle. 
From  the  posterior  wall  a  canal,  the  ductus  endolymphaticus,  is  given  off;  this  duct 
is  joined  by  the  ductus  utriculosaccularis,  and  then  passes  along  the  aquaeductus 
vestibuli  and  ends  in  a  blind  pouch  (saccus  endolsrmphatlcus)  on  the  posterior  sur- 
face of  the  petrous  portion  of  the  temporal  bone,  where  it  is  in  contact  with  the 
dura  mater.  From  the  lower  part  of  the  saccule  a  short  tube,  the  canalis  reuniens 
of  Hensen,  passes  downward  and  opens  into  the  ductus  cochlearis  near  its  vestibular 
extremity  (Fig.  924). 


I 


_    'DUCTUS 
ENDOLYMPHATICUS 

Fig.  924. — The  membranous  labyrinth.     (Enlarged.) 

The  Semicircular  Ducts  {ductus  semicircular es;  membranous  semicircular  canals), 
(Figs.  925,  926). — The  semicircular  ducts  are  about  one-fourth  of  the  diameter 
of  the  osseous  canals,  but  in  number,  shape,  and  general  form  they  are  precisely 
similar,  and  each  presents  at  one  end  an  ampulla.  They  open  by  five  orifices  into 
the  utricle,  one  opening  being  common  to  the  medial  end  of  the  superior  and  the 
upper  end  of  the  posterior  duct.  In  the  ampullae  the  wall  is  thickened,  and  projects 
into  the  cavity  as  a  fiddle-shaped,  transversely  placed  elevation,  the  septum  trans- 
versum,  in  which  the  nerves  end. 

The  utricle,  saccule,  and  semicircular  ducts  are  held  in  position  by  numerous 
fibrous  bands  which  stretch  across  the  space  between  them  and  the  bony  walls. 

Structure  (Fig.  927). — The  walls  of  the  utricle,  saccule,  and  semicircular  ducts  consist  of 
three  layers.  The  outer  layer  is  a  loose  and  fiocculent  structure,  apparently  composed  of  ordinary 
fibrous  tissue  containing  bloodvessels  and  some  pigment-cells.  The  middle  layer,  thicker  and 
more  transparent,  forms  a  homogeneous  membrana  propria,  and  presents  on  its  internal  surface, 
especially  in  the  semicircular  ducts,  numerous  papilliform  projections,  which,  on  the  addition 
of  acetic  acid,  exhibit  an  appearance  of  longitudinal  fibrillation.  The  inner  layer  is  formed  of 
polygonal  nucleated  epithelial  cells.  In  the  maculae  of  the  utricle  and  saccule,  and  in  the  trans- 
verse septa  of  the  ampullae  of  the  semicircular  ducts,  the  middle  coat  is  thickened  and  the  epi- 
thehum  is  columnar,  and  consists  of  supporting  cells  and  hair  cells.  The  former  are  fusiform, 
and  their  deep  ends  are  attached  to  the  membrana  propria,  while  their  free  extremities  are 
united  to  form  a  thin  cuticle.  The  hair  cells  are  flask-shaped,  and  their  deep,  rounded  ends  do 
not  reach  the  membrana  propria,  but  lie  between  the  supporting  cells.  The  deep  part  of  each 
contains  a  large  nucleus,  while  its  more  superficial  part  is  granular  and  pigmented .  The  free  end 
is  surmounted  by  a  long,  tapering,   hair-like   filament,   which  projects  into  the  cavity.     The 


filaments  of  the  acoustic  nerve  enter  these  parts,  and  having  pierced  the  outer  and  middle  layers, 
they  lose  their  medullary  sheaths,  and  their  axis-cylinders  ramify  between  the  hair  cells. 


7  8    9    1110 
I   I 


_  Fig.  926. — The  same  from  the  postero-medial  aspect.  1.  Lateral  semicircular  canal;  1',  its  ampulla;  2.  Poste- 
rior canal;  2',  its  ampulla.  3.  Superior  canal;  3',  its  ampulla.  4.  Conjoined  limb  of  superior  and  posterior 
canals  (sinus  utricuti  superior).  6.  Utricle.  5'.  Recessus  utriculi.  5".  Sinus  utriculi  posterior.  6.  Ductus  endo- 
lymp_haticus._  7.  Canalis  utriculosaccularis.  8.  Nerve  to  ampulla  of  superior  canal.  9.  Nerve  to  ampulla  of  lateral 
canal.  10.  Nerve  to  recessus  utriculi  (in  Fig.  925,  the  three  branches  appear  conjoined).  10'.  Ending  of  nerve  in 
recessus  utriculi.  11.  Facial  nerve.  12.  Lagena  cochleae.  13.  Nerve  of  cochlea  within  spiral  lamina.  14.  Basilar 
membrane.  15.  Nerve  fibers  to  macula  of  saccule.  16.  Nerve  to  ampulla  of  posterior  canal.  17.  Saccule.  18. 
Secondary  membrane  of  tympanum.  19.  Canalis  reunions.  20.  Vestibular  end  of  ductus  cochlearis.  23.  Section 
of  the  facial  and  acoustic  nerves  within  internal  acoustic  meatus  (the  separation  between  them  is  not  apparent  in  the 
section).    (G.  RetziusJ 


1054      ORGANS  OF  THE  SENSES  AND  THE   COMMON  INTEGUMENT 


Two  small  rounded  bodies  termed  otoconia,  each  consisting  of  a  mass  of  minute  crystalline 
grains  of  carbonate  of  lime,  held  together  in  a  mesh  of  gelatinous  tissue,   are  suspended  in  [ 
the  endolymph  in  contact  wish  the  free  ends  of  the  hairs  projecting  from  the  maculae.    Accord- 
ing to  Bowman,  a  calcareoutmaterial  is  also  sparingly  scattered  in  the  cells  lining  the  ampullae  I 
of  the  semicircular  ducts. 


Connective  tissue  binding 
duct  to  periosteum 


•Semicircular  dv/A 

—Fibrous  band  uniting 
free  surface  of  du^ 
to  periosteum 


Semicircular 
canal 


Periosteum 
Fia.  927. — Transverse  section  of  a  human  semicircular  canal  and  duct  (after  RUdinger) . 


The  Ductus  Cochlearis  (membranous  cochlea;  scala  media) . — The  ductus  cochlearis 
consists  of  a  spirally  arranged  tube  enclosed  in  the  bony  canal  of  the  cochlea  and 
lying  along  its  outer  wall. 

As  already  stated,  the  osseous  spiral  lamina  extends  only  part  of  the  distance 
between  the  modiolus  and  the  outer  wall  of  the  cochlea,  while  the  basilar  membrane 
stretches  from  its  free  edge  to  the  outer  wall  of  the  cochlea,  and  completes  the  roof 
of  the  scala  tympani.  A  second  and  more  delicate  membrane,  the  vestibular  mem- 
brane (Reissneri)  extends  from  the  thickened  periosteum  covering  the  osseous 
spiral  lamina  to  the  outer  wall  of  the  cochlea,  where  it  is  attached  at  some  little 
distance  above  the  outer  edge  of  the  basilar  membrane.  A  canal  is  thus  shut  off 
between  the  scala  tympani  below  and  the  scala  vestibuli  above;  this  is  the  ductus 
cochlearis  or  scala  media  (Fig.  928).  It  is  triangular  on  transverse  section,  its  roof 
being  formed  by  the  vestibular  membrane,  its  outer  wall  by  the  periosteum  lining 
the  bony  canal,  and  its  floor  by  the  membrana  basilaris  and  the  outer  part  of  the 
lamina  spiralis  ossea.  Its  extremities  are  closed;  the  upper  is  termed  the  lagena 
and  is  attached  to  the  cupula  at  the  upper  part  of  the  helicotrema;  the  lower  is 
lodged  in  the  recessus  cochlearis  of  the  vestibule.  Near  the  lower  end  the  ductus 
cochlearis  is  brought  into  continuity  with  the  saccule  by  a  narrow,  short  canal, 
the  canalis  reuniens  of  Hensen  (Fig.  924).  On  the  membrana  basilaris  is  situated 
the  spiral  organ  of  Corti.  The  vestibular  membrane  is  thin  and  homogeneous, 
and  is  covered  on  its  upper  and  under  surfaces  by  a  layer  of  epithelium.  The 
periosteum,  forming  the  outer  wall  of  the  ductus  cochlearis,  is  greatly  thickened 
and  altered  in  character,  and  is  called  the  spiral  ligament.  It  projects  inward  below 
as  a  triangular  prominence,  the  basilar  crest,  which  gives  attachment  to  the  outer 
edge  of  the  basilar  membrane;  immediately  above  the  crest  is  a  concavity,  the 


THE  INTERNAL  EAR  OR  LABYRINTH 


1055 


sulcus  spiralis  extemus.    The  upper  portion  of  the  spiral  Hgament  contains  numerous 
capillary  loops  and  small  bloodvessels,  and  is  termed  the  stria  vascularis. 

The  osseous  spiral  lamina  consists  of  two  plates  of  bone,  and  between  these  are 
the  canals  for  the  transmission  of  the  filaments  of  the  acoustic  nerve.  On  the  upper 
plate  of  that  part  of  the  lamina  which  is  outside  the  vestibular  membrane,  the  perios- 
teum is  thickened  to  form  the  limbus  laminae  spiralis  (Fig.  929),  this  ends  externally 


Fig.  928. — Diagrammatic  longitudinal  section  of  the  cochlea. 

in  a  concavity,  the  sulcus  spiralis  intemus,  which  represents,  on  section,  the  form 
of  the  letter  C;  the  upper  part,  formed  by  the  overhanging  extremity  of  the  limbus, 
is  named  the  vestibular  lip;  the  lower  part,  prolonged  and  tapering,  is  called  the 
tjrmpanic  lip,  and  is  perforated  by  numerous  foramina  for  the  passage  of  the  cochlear 
nerves.  The  upper  surface  of  the  vestibular  lip  is  intersected  at  right  angles  by  a 
number  of  furrows,  between  which  are  numerous  elevations;  these  present  the 
appearance  of  teeth  along  the  free  surface  and  margin  of  the  lip,  and  have  been 


Crista  BasUaris 


Fig.  929. — Floor  of  ductus  cochlearis. 


named  by  Huschke  the  auditory  teeth  (Fig.  930).  The  limbus  is  covered  by  a  layer 
of  what  appears  to  be  squamous  epithelium,  but  the  deeper  parts  of  the  cells  with 
their  contained  nuclei  occupy  the  intervals  between  the  elevations  and  between  the 
auditory  teeth.  This  layer  of  epithelium  is  continuous  on  the  one  hand  with  that 
lining  the  sulcus  spiralis  internus,  and  on  the  other  with  that  covering  the  under 
surface  of  the  vestibular  membrane. 


I 


1056      ORGANS  OF  THE  SENSES  AND  THE   COMMON  INTEGUMENT 

Basilar  Membrane. — The  basilar  membrane  stretches  from  the  tympanic  lip  of] 
the  osseous  spiral  lamina  to  the  basilar  crest  and  consists  of  two  parts,  an  inner 
and  an  outer.  The  inner  is  thin,  and  is  named  the  zona  arcuata :  it  supports  the  spiral 
organ  of  Corti.  The  outer  is  thicker  and  striated,  and  is  termed  the  zona  pectinata. 
The  under  surface  of  the  membrane  is  covered  by  a  layer  of  vascular  connective 
tissue;  one  of  the  vessels  in  this  tissue  is  somewhat  larger  than  the  rest,  and  is 
named  the  vas  spirals;  it  lies  below  Corti's  tunnel. 


Fia.  930. — Limbus  laminse  spiralis  and  membrana  basilaris.  (Schematic.)  1,  1'.  Upper  and  lower  lamellae 
of  the  lamina  spiralis  ossea.  2.  Limbua  laminae  spiralis,  with  a,  the  teeth  of  the  first  row;  b,  b',  the  auditory  teeth 
of  the  other  rows;  c,  c',  the  interdental  grooves  and  the  cells  which  are  lodged  in  them.  3.  Sulcus  spiralis  internua, 
with  3',  its  labium  vestibulare,  and  3",  its  labium  tympanicum.  4.  Foramina  nervosa,  giving  passage  to  the  nerves 
from  the  ganglion  spirale  or  ganglion  of  Corti.  6.  Vas  spirale.  6.  Zona  arcuata,  and  6',  zona  pectinata  of  the  basilar 
membrane,  with  a,  its  hyaline  layer,  B,  its  connective-tissue  layer.  7.  Arch  of  spiral  organ,  with  7',  its  inner  rod,  and 
7",  its  outer  rod.  8.  Feet  of  the  internal  rods,  from  which  the  cells  are  removed.  9.  Feet  of  the  external  rods.  10. 
Vestibular  membrane,  at  its  origin.     (Testut.) 


Membrana  tectoria 


Older  hair  cells 


Limbus 


Nerve  fibers 


Outer  rod 
Basilar  membrane 


■-  "^'"'"^    ®<?opS}  "o'cPoV 

Cells  of  Deiters 


Fig.  931. — Section  through  the  spiral  organ  of  Corti.     Magnified.     (G.  Retzius.) 


The  spiral  organ  of  Corti  {organon  spirale  [Corti];  organ  of  Corti)  (Figs.  931,  932) 
is  composed  of  a  series  of  epithelial  structures  placed  upon  the  inner  part  of  the 
basilar  membrane.  The  more  central  of  these  structures  are  two  rows  of  rod-like 
bodies,  the  inner  and  outer  rods  or  pillars  of  Corti.  The  bases  of  the  rods  are  supported 
on  the  basilar  membrane,  those  of  the  inner  row  at  some  distance  from  those  of  the 


THE  INTERNAL  EAR  OR  LABYRINTH 


iWi 


outer;  the  two  rows  incline  toward  each  other  and,  coming  into  contact  above, 
enclose  between  them  and  the  basilar  membrane  a  triangular  tunnel,  the  tunnel 
of  Corti.  On  the  inner  side  of  the  inner  rods  is  a  single  row  of  hair  cells,  and  on  the 
outer  side  of  the  outer  rods  three  or  four  rows  of  similar  cells,  together  with  certain 
supporting  cells  termed  the  cells  of  Deiters  and  Hensen.  The  free  ends  of  the  outer 
hair  cells  occupy  a  series  of  apertures  in  a  net-like  membrane,  the  reticular  membrane, 
and  the  entire  organ  is  covered  by  the  tectorial  membrane. 

Rods  of  Corti. — Each  of  these  consists  of  a  base  or  foot-plate,  and  elongated 
part  or  body,  and  an  upper  end  or  head;  the  body  of  each  rod  is  finely  striated,  but 
in  the  head  there  is  an  oval  non-striated  portion  which  stains  deeply  Avith  carmine. 
Occupying  the  angles  between  the  rods  and  the  basilar  membrane  are  nucleated 
cells  which  partly  envelop  the  rods  and  extend  on  to  the  floor  of  Corti's  tunnel; 
these  may  be  looked  upon  as  the  undifferentiated  parts  of  the  cells  from  which  the 
rods  have  been  formed. 


Fig.  932. — The  lamina  reticularis  and  subjacent  structures.  (Schematic.)  A.  Internal  rod  of  Corti,  with  o,  its 
plate,  fi.  External  rod  (in  yellow).  C.  Tunnel  of  Corti.  D.  Membrana  basilaris.  £^.  Inner  hair  cells.  1,1'.  Internal 
and  external  borders  of  the  membrana  reticularis.  2,  2',  2".  The  three  rows  of  circular  holes  (in  blue).  3.  First  row 
of  phalanges  (in  yellow).  4,  4',  4".  Second,  third,  and  fourth  rows  of  phalanges  (in  red).  6,  6',  6".  The  three  rows 
of  outer  hair  cells  (in  blue}.    7,  7'.  7".  Cells  of  Deiters.    8.  Cells  of  Hensen  and  Claudius.     (Teatut.) 

I V  The  inner  rods  number  nearly  6000,  and  their  bases  rest  on  the  basilar  membrane 
close  to  the  tympanic  lip  of  the  sulcus  spiralis  internus.  The  shaft  or  body  of  each 
is  sinously  curved  and  forms  an  angle  of  about  60  degrees  with  the  basilar  mem- 
brane. The  head  resembles  the  proximal  end  of  the  ulna  and  presents  a  deep 
concavity  which  accommodates  a  convexity  on  the  head  of  the  outer  rod.  The 
head-plate,  or  portion  overhanging  the  concavity,  overlaps  the  head-plate  of  the  ' 
outer  rod. 

The  outer  rods,  nearly  4000  in  number,  are  longer  and  more  obliquely  set  than  the 
inner,  forming  with  the  basilar  membrane  an  angle  of  about  40  degrees.  Their 
heads  are  convex  internally;  they  fit  into  the  concavities  on  the  heads  of  the  inner 
rods  and  are  continued  outward  as  thin  flattened  plates,  termed  phalangeal  processes, 
which  unite  with  the  phalangeal  processes  of  Deiters'  cells  to  form  the  reticular 
membrane. 

Hair  Cells. — The  hair  cells  are  short  columnar  cells;  their  free  ends  are  on  a  level 
with  the  heads  of  Corti's  rods,  and  each  is  surmounted  by  about  twenty  hair-like 
processes  arranged  in  the  form  of  a  crescent  with  its  concavity  directed  inward. 
The  deep  ends  of  the  cells  reach  about  half-way  along  Corti's  rods,  and  each  con- 
67 


1058      ORGANS  OF  THE  SENSES  AND  THE   COMMON  INTEGUMENT 

tains  a  large  nucleus;  in  contact  with  the  deep  ends  of  the  hair  cells  are  the  terminal 
filaments  of  the  cochlear  division  of  the  acoustic  nerve.  The  inner  hair  cells  are 
arranged  in  a  single  row  on  the  medial  side  of  the  inner  rods,  and  their  diameters 
being  greater  than  those  of  the  rods  it  follows  that  each  hair  cell  is  supported  by 
more  than  one  rod.  The  free  ends  of  the  inner  hair  cells  are  encircled  by  a  cuticular 
membrane  which  is  fixed  to  the  heads  of  the  inner  rods.  Adjoining  the  inner 
hair  cells  are  one  or  two  rows  of  columnar  supporting  cells,  which,  in  turn,  are  con- 
tinuous with  the  cubical  cells  lining  the  sulcus  spiralis  internus.  The  ovter  hair  cells 
number  about  12,000,  and  are  nearly  twice  as  long  as  the  inner.  In  the  basal  coil 
of  the  cochlea  they  are  arranged  in  three  regular  rows;  in  the  apical  coil,  in  four, 
somewhat  irregular,  rows. 

Between  the  rows  of  the  outer  hair  cells  are  rows  of  supporting  cells,  called  the 
cells  of  Deiters;  their  expanded  bases  are  planted  on  the  basilar  membrane,  while 
the  opposite  end  of  each  presents  a  clubbed  extremity  or  phalangeal  process.  Imme- 
diately to  the  outer  side  of  Deiters'  cells  are  five  or  six  rows  of  columnar  cells,  the 
supporting  cells  of  Hensen.  Their  bases  are  narrow,  while  their  upper  parts  are 
expanded  and  form  a  rounded  elevation  on  the  floor  of  the  ductus  cochlearis. 
The  columnar  cells  lying  outside  Hensen's  cells  are  termed  the  cells  of  Claudius. 
A  space  exists  between  the  outer  rods  of  Corti  and  the  adjacent  hair  cells;  this  is 
called  the  space  of  Nuel. 

The  reticular  lamina  (Fig.  932)  is  a  delicate  frame-work  perforated  by  rounded 
holes  which  are  occupied  by  the  free  ends  of  the  outer  hair  cells.  It  extends  from 
the  heads  of  the  outer  rods  of  Corti  to  the  external  row  of  the  outer  hair  cells,  and 
is  formed  by  several  rows  of  "  minute  fiddle-shaped  cuticular  structures,"  called  pha- 
langes, between  which  are  circular  apertures  containing  the  free  ends  of  the  hair  cells. 
The  inner  most  row  of  phalanges  consists  of  the  phalangeal  processes  of  the  outer 
rods  of  Corti;  the  outer  rows  are  formed  by  the  modified  free  ends  of  Deiters'  cells. 

Covering  the  sulcus  spiralis  internus  and  the  spiral  organ  of  Corti  is  the  tectorial 
membrane,  which  is  attached  to  the  limbus  laminae  spiralis  close  to  the  inner  edge 
of  the  vestibular  membrane.  Its  inner  part  is  thin  and  overlies  the  auditory  teeth 
of  Huschke ;  its  outer  part  is  thick,  and  along  its  lower  surface,  opposite  the  inner 
hair  cells,  is  a  clear  band,  named  Hensen's  stripe,  due  to  the  intercrossing  of  its  fibers. 
The  lateral  margin  of  the  membrane  is  much  thinner.  Hardesty^  considers  the 
tectorial  membrane  as  the  vibrating  mechanism  in  the  cochlea.  It  is  inconceivable- 
delicate  and  flexible;  far  more  sensitively  flexible  in  the  transverse  than  in  the 
longitudinal  direction  and  the  readiness  with  which  it  bends  when  touched  is  beyond 
description.  It  is  ectodermal  in  origin.  It  consists  of  fine  colorless  fibers  embedded 
in  a  transparent  matrix  (the  matrix  may  be  a  variety  of  soft  keratin),  of  a  soft 
collagenous,  semisolid  character  with  marked  adhesiveness.  The  general  transverse 
direction  of  the  fibers  inclines  from  the  radius  of  the  cochlea  toward  the  apex. 

The  acoustic  nerve  (n.  acusticus;  auditory  nerve  or  nerve  of  hearing)  divides  near 
the  bottom  of  the  internal  acoustic  meatus  into  an  anterior  or  cochlear  and  a 
posterior  or  vestibular  branch. 

The  vestibular  nerve  {n.  vestibularis)  supplies  the  utricle,  the  saccule,  and  the 
ampullae  of  the  semicircular  ducts.  On  the  trunk  of  the  nerve,  within  the  internal 
acoustic  meatus,  is  a  ganglion,  the  vestibular  ganglion  {ganglion  of  Scarpa);  the 
fibers  of  the  nerve  arise  from  the  cells  of  this  ganglion.  On  the  distal  side  of  the 
ganglion  the  nerve  splits  into  a  superior,  an  inferior,  and  a  posterior  branch.^  The 
filaments  of  the  superior  branch  are  transmitted  through  the  foramina  in  the  area 
vestibularis  superior,  and  end  in  the  macula  of  the  utricle  and,  in  the  ampullae 
of  the  superior  and  lateral  semicircular  ducts;  those  of  the  inferior  branch  traverse 

•  American  Journal  of  Anatomy,  1908,  viii. 

^  The  nerve  sometimes  splits  on  the  proximal  side  of  the  ganglion,  and  the  latter  is  then  divided  into  three  parts, 
one  on  each  branch  of  the  nerve. 


PERIPHERAL  TERMINATIONS  OF  NERVES  OF  GENERAL  SENSATIONS   1059 

the  foramina  in  the  area  vestibularis  inferior,  and  end  in  the  macula  of  the  saccule. 
The  posterior  branch  runs  through  the  foramen  singulare  at  the  postero-inferior 
part  of  the  bottom  of  the  meatus  and  divides  into  filaments  for  the  supply  of  the 
ampulla  of  the  posterior  semicircular  duct. 

The  cochlearnerve  (?i.  cochlearis)  divides  into  numerous  filaments  at  the  base  of  the 
modiolus;  those  for  the  basal  and  middle  coils  pass  through  the  foramina  in  the 
tractus  spiralis  foraminosis,  those  for 


Ganglion 


Nerve  fibers  passing  out 
Spiral  between  the  two  layers  of 
;  fibers     the  lamina  spiralis  ossea 


Fia.  933. — Part  of  the  cochlear  division  of  the  acoustic 
nerve,  highly  magnified.     (Henle.) 


I 


the  apical  coil  through  the  canalis  cen- 
tralis, and  the  nerves  bend  outward  to 
pass  between  the  lamellae  of  the  osseous 
spiral  lamina.  Occupying  the  spiral 
canal  of  the  modiolus  is  the  spiral 
ganglion  of  the  cochlea  (ganglion  of 
Corti)  (Fig.  933),  consisting  of  bipolar 
nerve  cells,  which  constitute  the  cells 
of  origin  of  this  nerve.  Reaching  the 
outer  edge  of  the  osseous  spiral  lamina, 
the  fibers  of  the  nerve  pass  through 
the  foramina  in  the  tympanic  lip;  some 
end  by  arborizing  around  the  bases  of 
the  inner  hair  cells,  while  others  pass 

between  Corti's  rods  and  across  the  tunnel,  to  end  in  a  similar  manner  in  relation 
to  the  outer  hair  cells.  The  cochlear  nerve  gives  oflF  a  vestibular  branch  to 
supply  the  vestibular  end  of  the  ductus  cochlearis;  the  filaments  of  this  branch  pass 
through  the  foramina  in  the  fossa  cochlearis  (page  1048). 

Vessels. — The  arteries  of  the  labyrinth  are  the  internal  auditory,  from  the  basilar,  and  the 
stylomastoid,  from  the  posterior  auricular.  The  internal  auditory  artery  divides  at  the  bottom 
of  the  internal  acoustic  meatus  into  two  branches:  cochlear  and  vestibular.  The  cochlear 
branch  subdivides  into  twelve  or  fourteen  twigs,  which  traverse  the  canals  in  the  modiolus, 
and  are  distributed,  in  the  form  of  a  capillary  net-work,  in  the  lamina  spiralis  and  basilar  mem- 
brane.   The  vestibular  branches  are  distributed  to  the  utricle,  saccule,  and  semicircular  ducts. 

The  veiQS  of  the  vestibule  and  semicircular  canals  accompany  the  arteries,  and,  receiving 
those  of  the  cochlea  at  the  base  of  the  modiolus,  unite  to  form  the  internal  auditory  veins  which 
end  in  the  posterior  part  of  the  superior  petrosal  sinus  or  in  the  transverse  sinus. 


PERIPHERAL  TERMINATIONS  OF  NERVES  OF  GENERAL  SENSATIONS. 

The  peripheral  terminations  of  the  nerves  associated  with  general  sensations,  i.  e.,  the  mus- 
cular sense  and  the  senses  of  heat,  cold,  pain,  and  pressure,  are  widely  distributed  throughout 
the  body.  These  nerves  may  end  free  among  the  tissue  elements,  or  in  special  end-organs  where 
the  terminal  nerve  filaments  are  enclosed  in  capsules. 

Free  nerve-endings  occur  chiefly  in  the  epidermis  and  in  the  epithehimi  covering  certain 
mucous  membranes;  they  are  well  seen  also  in  the  stratified  squamous  epithelium  of  the  cornea, 
and  are  also  found  in  the  root-sheaths  and  papillae  of  the  hairs,  and  around  the  bodies  of  the 
sudoriferous  glands.     When  the  nerve  fiber  approaches  its  termination,  the  medullary  sheath 

I^L  suddenly  disappears,  leaving  only  the  axis-cylinder  surrounded  by  the  neurolemma.  After  a  time 
f  the  fiber  loses  its  neurolemma,  and  consists  only  of  an  axis-cylinder,  which  can  be  seen,  in 
preparations  stained  with  chloride  of  gold,  to  be  made  up  of  fine  varicose  fibrillae.  Finally,  the 
axis-cylinder  breaks  up  into  its  constituent  fibrillae  which  often  present  regular  varicosities  and 
anastomose  with  one  another,  and  end  in  small  knobs  or  disks  between  the  epithelial  cells. 

Under  this  heading  may  be  classed  the  tactile  disks  described  by  Merkel  as  occurring  in  the 
epidermis  of  the  pig's  snout,  where  the  fibrillae  of  the  axis-cylinder  end  in  cup-shaped  disks  in 
apposition  with  large  epithelial  cells. 

The  special  end-organs  exhibit  great  variety  in  size  and  shape,  but  have  one  feature  in  common, 
viz.,  the  terminal  nerve  fibrillae  are  enveloped  by  a  capsule.  Included  in  this  group  are  the  end- 
bulbs  of  Krause,  the  corpuscles  of  Grandry,  of  Pacini,  of  Golgi  and  Mazzoni,  of  Wagner  and 
Meissner,  and  the  neurotendinous  and  neuromuscular  spindles. 


Capsule  of  corpuscle 


t060       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

The  end-bulbs  of  Krause   (Fig.  934)  are  minute  cylindrical  or  oval  bodies,  consisting  of  a 
capsule  formed  by  the  expansion  of  the  connective-tissue  sheath  of  a  medullated  fiber,  and 

containing  a  soft  semifluid  core  in  which  the  axis-cylinder 
terminates  either  in  a  bulbous  extremity  or  in  a  coiled-up 
plexiform  mass.  End-bulbs  are  found  in  the  conjunctiva 
of  the  eye  (where  they  are  spheroidal  in  shape  in  man,  but 
cylindrical  in  most  other  animals),  in  the  mucous  mem- 
brane of  the  lips  and  tongue,  and  in  the  epineurium  of 
nerve  trunks.  They  are  also  found  in  the  penis  and  the 
clitoris,  and  have  received  the  name  of  genital  corpuscles ; 
in  these  situations  they  have  a  mulberry-like  appearance, 
being  constricted  by  connective-tissue  septa  into  from  two 
to  six  knob-like  masses.  In  the  synovial  membranes  of 
certain  joints,  e.  g.,  those  of  the  fingers,  rounded  or  oval 
end-bulbs  occur,  and  are  designated  articular  end-bulbs. 

The  tactile  corpuscles  of  Grandry  occur  in  the  papillae  of 
the  beak  and  tongue  of  birds.    Each  consists  of  a  capsule 
composed  of  a   very  delicate,  nucleated    membrane,  and 
contains  two  or  more  granular,  somewhat  flattened  cells; 
between  these  cells  the  axis-cylinder  ends  in  flattened  disks. 
The  Pacinian  corpuscles    (Fig.  935)    are   found  in  the 
subcutaneous  tissue  on  the  nerves  of  the  palm  of  the  hand 
and  sole  of  the  foot  and  in  the  genital  organs  of  both  sexes; 
they  also  occur  in  connection  with  the  nerves  of  the  joints,  and  in  some  other  situations,  as  in 
the  mesentery  and  pancreas  of  the  cat  and  along  the  tibia  of  the  rabbit.     Each  of  these  cor- 
puscles is  attached  to  and  encloses  the  termi- 
nation of  a  single  nerve  fiber.    The  corpuscle, 
which  is  perfectly   visible  to  the  naked  eye 
(and  which  can  be  most  easily  demonstrated 
in  the  mesentery  of  a  cat),  consists  of  a  num- 
ber of  lamellae  or  capsules  arranged  more  or 
less  concentrically  around  a  central  clear  space, 
in  which  the  nerve  fiber  is  contained.     Each 
lamella  is  composed  of  bundles  of  fine  connec- 
tive-tissue fibers,  and  is  lined  on  its  inner  sur- 
face by  a  single  layer  of  flattened  epithelioid 
cells.     The  central  clear  space,  which  is  elon- 


I 


Medullated 
nerve  fiber 

Fig.   934.— End-bulb  of  Krau.se.      (Klein.) 


Fio.  935. — Pacinian  corpuscle,  with  its  system  of 
capsules  and  central  cavity,  a.  Arterial  twig,  end- 
ing in  capillaries,  which  form  loops  in  some  of  the 
intercapsular  spaces,  and  one  penetrates  to  the  cen- 
tral capsule,  b.  The  fibrous  tissue  of  the  stalk,  n. 
Nerve  tube  advancing  to  the  central  capsule,  there 
losing  its  white  matter,  and  stretching  along  the 
axis  to  the  opposite  end,  where  it  ends  by  a  tubercu- 
lated  enlargement. 


Fig.  936. — Papilla  of  the  hand,  treated  with  acetic 
acid.  Magnified  350  times.  A.  Side  view  of  a  papilla 
of  the  hand.  a.  Cortical  layer,  b.  Tactile  corpuscle,  c. 
Small  nerve  of  the  papilla,  with  neurolemma.  5.  Its  two 
nervous  fibers  running  with  spiral  coils  around  the  tactile 
corpuscle,  e.  Apparent  termination  of  one  of  these  fibers. 
B.  A  tactile  papilla  seen  from  above  so  as  to  show  its 
transverse  section,  a.  Cortical  layer.  6.  Nerve  fiber,  c. 
Outer  layer  of  the  tactile  body,  with  nuclei,  d.  Clear 
interior  substance. 


gated  or  cylindrical  in  shape,  is  filled  with  a  transparent  core,  in  the  middle  of  which  the  axis- 
cylinder  traverses  the  space  to  near  its  distal  extremity,  where  it  ends  in  one  or  more  small 
knobs.  Todd  and  Bowman  have  described  minute  arteries  as  entering  by  the  sides  of  the 
nerves  and  forming  capillary  loops  in  the  intercapsular  spaces,  and  even  penetrating  into  the 
central  space. 


IPERIPHERAL  TERMINATIONS  OF  NERVES  OF  GENERAL  SENSATIONS   1061 


Herbst  has  described  a  nerve-ending  somewhat  similar  to  the  Pacinian  corpuscle,  in  the  mucous 
membrane  of  the  tongue  of  the  duck,  and  in  some  other  situations.  It  differs,  however,  from 
the  Pacinian  corpuscle,  in  being  smaller,  in  its  capsules  being  more  closely  approximated,  and 
especiall}'  in  the  act  that  the  axis-cylinder  in  the  central  clear  space  is  coated  with  a  continuous 
row  of  nuclei.     These  bodies  are  known  as  the  corpuscles  of  Herbst. 

The  corpuscles  of  Golgi  and  Mazzoni  are  found  in  the  subcutaneous  tissue  of  the  pulp  of 
the  fingers.  They  differ  from  Pacinian  corpuscles  in  that  their  capsules  are  thinner,  their  con- 
tained cores  thicker,  and  in  the  latter  the  axis-cylinders  ramify  more  extensively  and  end  in 
flat  expansions. 

The  tactile  corpuscles  of  Wagner  and  Meissner  (Fig.  936)  are  oval-shaped  bodies.  Each 
is  enveloped  by  a  connective-tissue  capsule,  and  imperfect  membranous  septa  derived  from  this 
penetrate  the  interior.  The  axis-cylinder  passes  through  the  capsule,  and  after  making  several 
spiral  turns  around  the  body  of  the  corpuscle  ends  in  small  globular  or  pyriform  enlargements. 
These  tactile  corpuscles  occur  in  the  papillae  of  the  corium  of  the  hand  and  foot,  the  front  of 
the  forearm,  the  skin  of  the  lips,  the  mucous  membrane  of  the  tip  of  the  tongue,  the  palpebral 
conjunctiva,  and  the  skin  of  the  mammary  papilla. 


Nerve  fibers 


Terminal  ramifications 
of  axis  cylinders 


Connective  tissiie  sheath 


■     Corpuscles  of  Ruffini. — Ruffini  described  a  special  variety  of  nerve-ending  in  the  subcuta- 
"  neous  tissue  of  the  human  finger  (Fig.  937);  they  are  principally  situated  at  the  junction  of  the 
corium  with  the  subcutaneous  tissue.    They  are  oval  in  shape,  and  consist  of  strong  connective- 
tissue  sheaths,  inside  which  the  nerve  fibers  divide  into  numerous  branches,  which  show  vari- 
cosities and  end  in  small  free  knobs. 

The  neurotendinous  spindles  (organs  of  Golgi)  are  chiefly  found  near  the  junctions  of  tendons 
and  muscles.  Each  is  enclosed  in  a  capsule  which  contains  a  number  of  enlarged  tendon  fasciculi 
{intrafusal  fasciculi).  One  or  more  nerve  fibers  perforate  the  side  of  the  capsule  and  lose  their 
medullary  sheaths;  the  axis-cylinders  subdivide  and  end  between  the  tendon  fibers  in  irregular 
disks  or  varicosities  (Fig.  938). 


— Nerve  ending  of  Ruffini.      (After  A.  Ruffini.) 


Tendon 
bundles 


Fig. 


Organ  of  Golgi,  showing 
ramification  of  nerve-fibrils 

Miiscular  fibers 
938. — Organ  of  Golgi   (neurotendinous  spindle)   from  the  human  tendo  calcaneus.     (After  Ciaccio.) 


The  neuromuscular  spindles  are  present  in  the  majority  of  voluntary  muscles,  and  consist 
of  small  bundles  of  peculiar  muscular  fibers  (intrafusal  fibers),  embryonic  in  type,  invested  by 
capsules,  within  which  nerve  fibers,  experimentally  shown  to  be  sensory  in  origin,  terminate. 
These  neuromuscular  spindles  vary  in  length  from  0.8  mm.  to  5  mm.,  and  have  a  distinctly 
fusiform  appearance.     The  large  medullated  nerve  fibers  passing  to  the  end-organ  are  from 


1062       ORGANS  OF  THE  SENSES  AND  THE   COMMON  INTEGUMENT 


one  to  three  or  four  in  number;  entering  the  fibrous  capsule,  they  divide  several  times,  and, 
losing  their  medullary  sheaths,  ultimately  end  in  naked  axis-cyhnders  encircling  the  intrafusal 
fibers  by  flattened  expansions,  or  irregular  ovoid  or  rounded  disks  (Fig.  939).  Neuromusculai* 
spindles  have  not  yet  been  demonstrated  in  the  tongue  muscles,  and  only  a  few  exist  in  th« 
ocular  muscles. 


■''■'"' "  "'  *'''''"w;it. .i^^j .^..ii.mT.j.M^j.mic^'--''-'^-"' 


Fig.  939. — Middle  third  of  a  terminal  plaque  in  the  muscle  spindle  of  an  adult  oat.     (After  RuflBni.) 

THE  COMMON  INTEGUMENT  (INTEGUMENTUM  COMMUNE;   SKIN). 

The  integument  (Fig.  940)  covers  the  body  and  protects  the  deeper  tissues  from 
injury,  from  drying  and  from  invasion  by  foreign  organisms;  it  contains  the  per- 
ipheral endings  of  many  of  the  sensory  nerves;  it  plays  an  important  part  in  the 
regulation  of  the  body  temperature,  and  has  also  limited  excretory  and  absorbing 
powers.  It  consists  principally  of  a  layer  of  vascular  connective  tissue,  named  the 
corium  or  cutis  vera,  and  an  external  covering  of  epithelium,  termed  the  epidermis 
or  cuticle.  On  the  surface  of  the  former  layer  are  sensitive  and  vascular  papillae* 
within,  or  beneath  it,  are  certain  organs  with  special  functions :  namely,  the  sudorif' 
erous  and  sebaceous  glands,  and  the  hair  follicles. 

The  epidermis,  cuticle,  or  scarf  skin  is  non-vascular,  and  consists  of  stratified 
epithelium  (Fig.  941),  and  is  accurately  moulded  on  the  papillary  layer  of  the  corium' 
It  varies  in  thickness  in  different  parts.  In  some  situations,  as  in  the  palms  of  the 
hands  and  soles  of  the  feet,  it  is  thick,  hard,  and  horny  in  texture.  This  may  be  in 
a  measure  due  to  the  fact  that  these  parts  are  exposed  to  intermittent  pressure, 
but  that  this  is  not  the  only  cause  is  proved  by  the  fact  that  the  condition  exists 
to  a  very  considerable  extent  at  birth.  The  more  superficial  layers  of  cells,  called 
the  homy  layer  (stratum  corneum),  may  be  separated  by  maceration  from  a  deeper 
stratum,  which  is  called  the  stratum  mucosum,  and  which  consists  of  several  layers 
of  differently  shaped  cells.  The  free  surface  of  the  epidermis  is  marked  by  a 
net-work  of  linear  furrows  of  variable  size,  dividing  the  surface  into  a  number  of 
polygonal  or  lozenge-shaped  areas.  Some  of  these  furrows  are  large,  as  opposite  the 
flexures  of  the  joints,  and  correspond  to  the  folds  in  the  corium  produced  by  move- 
ments. In  other  situations,  as  upon  the  back  of  the  hand,  they  are  exceedingly 
fine,  and  intersect  one  another  at  various  angles.  Upon  the  palmar  surfaces  of  the 
hand'3  and  fingers,  and  upon  the  soles  of  the  feet,  the  epidermal  ridges  are  very  dis- 
tinct, and  are  disposed  in  curves;  they  depend  upon  the  large  size  and  peculiar 
arrangements  of  the  papillae  upon  which  the  epidermis  is  placed.  The  function 
of  these  ridges  is  primarily  to  increase  resistance  between  contact  surfaces  for  the 
purpose  of  preventing  slipping  whether  in  walking  or  prehension.  The  direction 
of  the  ridges  is  at  right  angles  with  the  force  that  tends  to  produce  slipping  or  to 
the  resultant  of  such  forces  when  these  forces  vary  in  direction.^    In  each  individual 

1  Whipple,  Inez  L.,  The  Ventral  Surface  of  the  Mammalian  Chiridium,  etc.,  Zeit.  f.  Morph.  u.  Anthropol.- 
1904,  vol.  vii. 


THE  COMMON  INTEGUMENT 


1063 


the  lines  on  the  tips  of  the  fingers  and  thumbs  form  distinct  patterns  unlike  those  of 
any  other  person.  A  method  of  determining  the  identity  of  a  criminal  is  based  on 
this  fact,  impressions  ("finger-prints")  of  these  lines  being  made  on  paper  covered 
with  soot,  or  on  white  paper  after  first  covering  the  fingers  with  ink.  The  deep 
surface  of  the  epidermis  is  accurately  moulded  upon  the  papillary  layer  of  the 
corium,  the  papillae  being  covered  by  a  basement  membrane;  so  that  when  the 
epidermis  is  removed  by  maceration,  it  presents  on  its  under  surface  a  number  of 
pits  or  depressions  corresponding  to  the  papillae,  and  ridges  corresponding  to  the 
intervals  between  them.  Fine  tubular  prolongations  are  continued  from  this 
layer  into  the  ducts  of  the  sudoriferous  and  sebaceous  glands. 


Diict  of 

svdorijerous' 

gland 


Tactile 
corpuscle 

Duct  of 

sudoriferous. 

gland 


Adipose  tissue  -.  ^■ 
Artery  — 


Pacinian 
corpuscle' 


Stratum 
corneum 


Stratum 

lucidum 
Stratitm 

granxdosum 
'Stratum 

mucosum 

Stratum 
germirwiivuTn 


f^^i*~  -Dermis 


8udoriferofU9 
gland 


^ -Nerve 


Fig.  940. — A  ciiagrammatic  sectional  view  of  the  skin  (magnified). 


The  epidermis  consists  of  stratified  epithelium  which  is  arranged  in  four  layers 
from  within  outward  as  follows:  (a)  stratum  mucosum,  (6)  stratum  granulosum,  (c) 
stratum  lucidum,  and  (d)  stratum  corneum. 

The  stratum  mucosum  {mucous  layer)  is  composed  of  several  layers  of  cells;  those 
of  the  deepest  layer  are  columnar  in  shape  and  placed  perpendicularly  on  the 
surface  of  the  basement  membrane,  to  which  they  are  attached  by  toothed  extrem- 
ities; this  deepest  layer  is  sometimes  termed  the  stratimi  germinativum ;  the  succeed- 
ing strata  consist  of  cells  of  a  more  rounded  or  polyhedral  form,  the  contents  of 


)64       ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

which  are  soft,  opaque,  granular,  and  soluble  in  acetic  acid.  These  are  known  as 
prickle  cells  because  of  the  bridges  by  which  they  are  connected  to  one  another. 
They  contain  fine  fibrils  which  are  continuous  across  the  connecting  processes 
with  corresponding  fibrils  in  adjacent  cells.  Between  the  bridges  are  fine  inter- 
cellular clefts  serving  for  the  passage  of  lymph,  and  in  these  lymph  corpuscles  or 
pigment  granules  may  be  found. 

The  stratum  granulosum  comprises  two  or  three  layers  of  flattened  cells  which 
contain  granules  of  eleidin,  a  substance  readily  stained  by  hematoxylin  or  carmine, 
and  probably  an  intermediate  substance  in  the  formation  of  keratin.  They  are 
supposed  to  be  cells  in  a  transitional  stage  between  the  protoplasmic  cells  of  the 
stratum  mucosum  and  the  horny  cells  of  the  superficial  layers. 

The  stratum  lucidum  appears  in  section  as  a  homogeneous  or  dimly  striated  mem- 
brane, composed  of  closely  packed  cells  in  which  traces  of  flattened  nuclei  may  be 
found,  and  in  which  minute  granules  of  a  substance  named  keratohyalin  are  present. 


Stratum  comeum  - 


I 


Stratum  Iticidum 
Stratum  granulosum 


■Stratum  mvcoaum 


'  —  Nerve  jQmls 


Stratum  germinativum 


Fig.  941. — Section  of  epidermis.     (Ranvier.) 

The  stratum  comeum  (homy  layer)  consists  of  several  layers  of  horny  epithelial 
scales  in  which  no  nuclei  are  discernible,  and  which  are  unaffected  by  acetic  acid,  the 
protoplasm  having  become  changed  into  horny  material  or  keratin.  According  to 
Ranvier  they  contain  granules  of  a  material  which  has  the  characteristics  of  beeswax. 

The  black  color  of  the  skin  in  the  negro,  and  the  tawny  color  among  some  of 
the  white  races,  is  due  to  the  presence  of  pigment  in  the  cells  of  the  epidermis. 
This  pigment  is  more  especially  distinct  in  the  cells  of  the  stratum  mucosum,  and 
is  similar  to  that  found  in  the  cells  of  the  pigmentary  layer  of  the  retina.  As  the 
cells  approach  the  surface  and  desiccate,  the  color  becomes  partially  lost;  the 
disappearance  of  the  pigment  from  the  superficial  layers  of  the  epidermis  is, 
however,  difficult  to  explain. 

The  pigment  (melanin)  consists  of  dark  brown  or  black  granules  of  very  small 
size,  closely  packed  together  within  the  cells,  but  not  involving  the  nucleus. 

The  main  purpose  served  by  the  epidermis  is  that  of  protection,  as  the  surface 
is  worn  away  new  cells  are  supplied  and  thus  the  true  skin,  the  vessels  and  nerves 
which  it  contains  are  defended  from  damage. 


THE  COMMON  INTEGUMENT 


1065 


The  Corium,  Cutis  Vera,  Dennis,  or  True  Skin  is  tough,  flexible,  and  highly 
elastic.  It  varies  in  thickness  in  different  parts  of  the  body.  Thus  it  is  very 
thick  in  the  palms  of  the  hands  and  soles  of  the  feet;  thicker  on  the  posterior  aspect 
of  the  body  than  on  the  front,  and  on  the  lateral  than  on  the  medial  sides  of  the 
limbs.    In  the  eyelids,  scrotum,  and  penis  it  is  exceedingly  thin  and  delicate. 

It  consists  of  felted  connective  tissue,  with  a  varying  amount  of  elastic  fibers 
and  numerous  bloodvessels,  lymphatics,  and  nerves.  The  connective  tissue  is 
arranged  in  two  layers:  a  deeper  or  reticular,  and  a  superficial  or  papillary.  Un- 
striped  muscular  fibers  are  found  in  the  superficial  layers  of  the  corium,  wherever 
hairs  are  present,  and  in  the  subcutaneous  areolar  tissue  of  the  scrotum,  penis, 
labia  majora,  and  nipples.  In  the  nipples  the  fibers  are  disposed  in  bands,  closely 
reticulated  and  arranged  in  superimposed  laminae. 


EPIDERMIS 

PAPILLARY  layer- 


Fig.  912. 


SUBCUTANEOUS 

TISSUE  _ 

\ 
BETE 
VENOSUM 

-The  distribution  of  the  bloodvessels  in  the  skin  of  the  sole  of  the  foot. 


(Spalteholz.) 


The  reticular  layer  {stratum  reticulare;  deep  layer)  consists  of  strong  interlacing 
bands,  composed  chiefly  of  white  fibrous  tissue,  but  containing  some  fibers  of  yellow 
elastic  tissue,  which  vary  in  number  in  different  parts;  and  connective-tissue  cor- 
puscles, which  are  often  to  be  found  flattened  against  the  white  fibrous  tissue  bundles. 
Toward  the  attached  surface  the  fasciculi  are  large  and  coarse,  and  the  areolae 
left  by  their  interlacement  are  large,  and  occupied  by  adipose  tissue  and  sweat 
glands.    Below  the  reticular  layer  is  the  subcutaneous  areolar  tissue,  which,  except 

I  Bin  a  few  situations,  contains  fat. 

■^  The  papillary  layer  (stratum  papillare;  superficial  layer;  corpus  pap'dlare  of  the 
corium)  consists  of  numerous  small,  highly  sensitive,  and  vascular  eminences, 
the  papillae,  which  rise  perpendicularly  from  its  surface.  The  papillae  are  minute 
conical  eminences,  having  rounded  or  blunted  extremities,  occasionally  divided 

I  ft  into  two  or  more  parts,  and  are  received  into  corresponding  pits  on  the  under 
surface  of  the  cuticle.  On  the  general  surface  of  the  body,  more  especially  in  parts 
endowed  with  slight  sensibility,  they  are  few  in  number,  and  exceedingly  minute;  but 
in  some  situations,  as  upon  the  palmar  surfaces  of  the  hands  and  fingers,  and  upon 
the  plantar  surfaces  of  the  feet  and  toes,  they  are  long,  of  large  size,  closely  aggre- 
gated together,  and  arranged  in  parallel  curved  lines,  forming  the  elevated  ridges 


1066     ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 


seen  on  the  free  surface  of  the  epidermis.  Each  ridge  contains  two  rows  of  papillse, 
between  which  the  ducts  of  the  sudoriferous  glands  pass  outward  to  open  on  the 
summit  of  the  ridge.  Each  papilla  consists  of  very  small  and  closely  interlacing 
bundles  of  finely  fibrillated  tissue,  with  a  few  elastic  fibers;  within  this  tissue  is  a 
capillary  loop,  and  in  some  papillae,  especially  in  the  palms  of  the  hands  and  the 
fingers,  there  are  tactile  corpuscles. 

Development. — The  epidermis  and  its  appendages,  consisting  of  the  hairs,  nails, 
sebaceous  and  sweat  glands,  are  developed  from  the  ectoderm,  while  the  corium  or 
true  skin  is  of  mesodermal  origin.  About  the  fifth  week  the  epidermis  consists  of 
two  layers  of  cells,  the  deeper  one  corresponding  to  the  rete  mucosum.  The  subcuta- 
neous fat  appears  about  the  fourth  month,  and  the  papillae  of  the  true  skin  about  the 
sixth.  A  considerable  desquamation  of  epidermis  takes  place  during  fetal  life,  and 
this  desquamated  epidermis,  mixed  with  sebaceous  secretion,  constitutes  the  vemix 
caseosa,  with  which  the  skin  is  smeared  during  the  last  three  months  of  fetal  life.  The 
nails  are  formed  at  the  third  month,  and  begin  to  project  from  the  epidermis  about 
the  sixth.  The  hairs  appear  between  the  third  and  fourth  months  in  the  form  of 
solid  downgrowths  of  the  deeper  layer  of  the  epidermis,  the  growing  extremities 
of  which  become  inverted  by  papillary  projections  from  the  corium.  The  central 
cells  of  the  solid  downgrowths  undergo  alteration  to  form  the  hair,  while  the 
peripheral  cells  are  retained  to  form  the  lining  cells  of  the  hair-follicle.  About  the 
fifth  month  the  fetal  hairs  (lanugo)  appear,  first  on  the  head  and  then  on  the  other 
parts;  they  drop  off  after  birth,  and  give  place  to  the  permanent  hairs.  The  cellular 
structures  of  the  sudoriferous  and  sebaceous  glands  are  formed  from  the  ectoderm, 
while  the  connective  tissue  and  bloodvessels  are  derived  from  the  mesoderm.  All 
the  sweat-glands  are  fully  formed  at  birth;  they  begin  to  develop  as  early  as  the 
fourth  month. 

The  arteries  supplying  the  skin  form  a  net-work  in  the  subcutaneous  tissue,  and  from  this 
net-work  branches  are  given  off  to  supply  the  sudoriferous  glands,  the  hair  folUcles,  and  the 
fat.  Other  branches  unite  in  a  plexus  immediately  beneath  the  corium;  from  this  plexus,  fine 
capillary  vessels  pass  into  the  papillae,  forming,  in  the  smaller  ones,  a  single  capillary  loop,  but 
in  the  larger,  a  more  or  less  convoluted  vessel.  The  lymphatic  vessels  of  the  skin  form  two 
net-works,  Guperficial  and  deep,  which  commimicate  with  each  other  and  with  those  of  the  sub- 
cutaneous tissue  by  oblique  branches. 

The  nerves  of  the  skin  terminate  partly  in  the  epidermis  and  partly  in  the  corium;  their  different 
modes  of  ending  are  described  on  pages  1059  to  i061. 

THE  APPENDAGES  OF  THE  SKIN. 

The  appendages  of  the  skin  are  the  nails,  the  hairs,  and  the  sudoriferous  and 
sebaceous  glands  with  their  ducts. 

The  Nails  (ungues)  (Fig.  943)  are  flattened,  elastic  structures  of  a  horny  texture, 
placed  upon  the  dorsal  surfaces  of  the  terminal  phalanges  of  the  fingers  and  toes. 
Each  nail  is  convex  on  its  outer  surface,  concave  within,  and  is  implanted  by  a 
portion,  called  the  root,  into  a  groove  in  the  skin ;  the  exposed  portion  is  called  the 
body,  and  the  distal  extremity  the  free  edge.  The  nail  is  firmly  adherent  to  the 
corium,  being  accurately  moulded  upon  its  surface;  the  part  beneath  the  body  and 
root  of  the  nail  is  called  the  nail  matrix,  because  from  it  the  nail  is  produced.  Under 
the  greater  part  of  the  body  of  the  nail,  the  matrix  is  thick,  and  raised  into  a  series 
of  longitudinal  ridges  which  are  very  vascular,  and  the  color  is  seen  through  the 
transparent  tissue.  Near  the  root  of  the  nail,  the  papillae  ^re  smaller,  less  vascular, 
and  have  no  regular  arrangement,  and  here  the  tissue  of  the  nail  is  not  firmly 
adherent  to  the  connective-tissue  stratum  but  only  in  contact  with  it;  hence  this 
portion  is  of  a  whiter  color,  and  is  called  the  lunula  on  account  of  its  shape. 

The  cuticle  as  it  passes  forward  on  the  dorsal  surface  of  the  finger  or  toe  is 
attached  to  the  surface  of  the  nail  a  little  in  advance  of  its  root;  at  the  extremity  of 


7ES  OF  THE  SKIN 


1067 


the  finger  it  is  connected  with  the  under  surface  of  the  nail  a  little  behind  its  free 
edge.  The  cuticle  and  the  horny  substance  of  the  nail  (both  epidermic  structures) 
are  thus  directly  continuous  with  each  other.  The  superficial,  horny  part  of  the 
nail  consists  of  a  greatly  thickened  stratum  lucidum,  the  stratum  corneum  forming 
merely  the  thin  cuticular  fold  (eponychium)  w4iich  overlaps  the  lunula;  the  deeper 
part  consists  of  the  stratum  mucosum.  The  cells  in  contact  with  the  papillae  of  the 
matrix  are  columnar  in  form  and  arranged  perpendicularly  to  the  surface;  those 
which  succeed  them  are  of  a  rounded  or  polygonal  form,  the  more  superficial  ones 
becoming  broad,  thin,  and  flattened,  and  so  closely  packed  as  to  make  the  limits 
of  the  cells  very  indistinct.  The  nails  grow  in  length  by  the  proliferation  of  the 
cells  of  the  stratum  mucosum  at  the  root  of  the  nail,  and  in  thickness  from  that 
part  of  the  stratum  mucosum  which  underlies  the  lunula. 


Eponychium.  »^ 

If  ail  „rir~~  ^.^ 

stratum   ^S^^i^^fe, 

Stratum  cor- 
neum, of  the 
nail  groove 


'  fh']  r^\'^'"r\   )J     "  ",  -  A'^'O"*    Stratum 
v/  lyjy^\^^^J^^      V  >^  V.    J-      granulosum 


Stratum 
corneum 


—  Corium 


-7—  Blood-vessel 


Fig.  94.3. — Longitudinal  section  through  nail  and  its  nail  groove  (sulcus). 

Hairs  {pili)  are  found  on  nearly  every  part  of  the  surface  of  the  body,  but  are 
absent  from  the  palms  of  the  hands,  the  soles  of  the  feet,  the  dorsal  surfaces  of  the 
terminal  phalanges,  the  glans  penis,  the  inner  surface  of  the  prepuce,  and  the 
inner  surfaces  of  the  labia.  They  vary  much  in  length,  thickness,  and  color  in 
different  parts  of  the  body  and  in  different  races  of  mankind.  In  some  parts,  as 
in  the  skin  of  the  eyelids,  they  are  so  short  as  not  to  project  beyond  the  follicles 
containing  them;  in  others,  as  upon  the  scalp,  they  are  of  considerable  length; 
again,  in  other  parts,  as  the  eyelashes,  the  hairs  of  the  pubic  region,  and  the  whiskers 
and  beard,  they  are  remarkable  for  their  thickness.  Straight  hairs  are  stronger 
than  curly  hairs,  and  present  on  transverse  section  a  cylindrical  or  oval  outline; 
curly  hairs,  on  the  other  hand,  are  flattened.  A  hair  consists  of  a  root,  the  part  im- 
planted in  the  skin ;  and  a  shaft  or  scapus,  the  portion  projecting  from  the  surface. 

The  root  of  the  hair  (radix  pili)  ends  in  an  enlargement,  the  hair  bulb,  which  is 
whiter  in  color  and  softer  in  texture  than  the  shaft,  and  is  lodged  in  a  follicular 
involution  of  the  epidermis  called  the  hair  follicle  (Fig.  944).  When  the  hair  is  of 
considerable  length  the  follicle  extends  into  the  subcutaneous  cellular  tissue.  The 
hair  follicle  commences  on  the  surface  of  the  skin  with  a  funnel-shaped  opening, 
and  passes  inward  in  an  oblique  or  curved  direction — the  latter  in  curly  hairs — to 
become  dilated  at  its  deep  extremity,  where  it  corresponds  with  the  hair  bulb. 
Opening  into  the  follicle,  near  its  free  extremity,  are  the  ducts  of  one  or  more 
sebaceous  glands.  At  the  bottom  of  each  hair  follicle  is  a  small  conical,  vascular 
eminence  or  papilla,  similar  in  every  respect  to  those  found  upon  the  surface  of  the 
skin;  it  is  continuous  with  the  dermic  layer  of  the  follicle,  and  is  supplied  with 
nerve  fibrils.  The  hair  follicle  consists  of  two  coats — an  outer  or  dermic,  and  an 
inner  or  epidermic. 

The  outer  or  dermic  coat  is  formed  mainly  of  fibrous  tissue;  it  is  continuous 
with  the  corium,  is  highly  vascular,  and  supplied  by*  numerous  minute  nervous 
filaments.  It  consists  of  three  layers  (Fig.  945).  The  most  internal  is  a  hyaline 
basement  membrane,  which  is  well-marked  in  the  larger  hair  follicles,  but  is  not 


1068     ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

very  distinct  in  the  follicles  of  minute  hairs ;  it  is  limited  to  the  deeper  part  of  the 
follicle.  Outside  this  is  a  compact  layer  of  fibers  and  spindle-shaped  cells  arranged 
circularly  around  the  follicle;  this  layer  extends  from  the  bottom  of  the  follicle 
as  high  as  the  entrance  of  the  ducts  of  the  sebaceous  glands.  Externally  is  a  thick 
layer  of  connective  tissue,  arranged  in  longitudinal  bundles,  forming  a  more 
open  texture  and  corresponding  to  the  reticular  part  of  the  corium;  in  this  are 
contained  the  bloodvessels  and  nerves. 


I 


d 


'  Stratum  comeum 

S^"  Stratum  lucidum 

Stratum  granulosum 
Stratum,  mucosum 
Stratum 

germinativum 


Arrector  pili 
muscle 


Bidb  of  hair  - 


Papilla  of  hair  ^"^^^f^^^^: 


^. ..__... 


Dermic  coat 
Medulla  of  hair 


Fig.  944. — Section  of  skin,  showing  the  epidermis  and  dermis;  a  hair  in  its  follicle;  the  Arrector  pili  muscle; 

sebaceous  glands. 

The  inner  or  epidermic  coat  is  closely  adherent  to  the  root  of  the  hair,  and  con- 
sists of  two  strata  named  respectively  the  outer  and  inner  root  sheaths ;  the  former 
of  these  corresponds  with  the  stratum  mucosum  of  the  epidermis,  and  resembles 
it  in  the  rounded  form  and  soft  character  of  its  cells;  at  the  bottom  of  the  hair 
follicle  these  cells  become  continuous  with  those  of  the  root  of  the  hair.  The  inner 
root  sheath  consists  of  (1)  a  delicate  cuticle  next  the  hair,  composed  of  a  single 
layer  of  imbricated  scales  with  atrophied  nuclei;  (2)  one  or  two  layers  of  horny, 
flattened,  nucleated  cells,  known  as  Huxley's  layer;  and  (3)  a  single  layer  of  cubical 
cells  with  clear  flattened  nuclei,  called  Henle's  layer. 

The  hair  bulb  is  moulded  over  the  papilla  and  composed  of  polyhedral  epithelial 
cells,  which  as  they  pass  upward  into  the  root  of  the  hair  become  elongated  and 
spindle-shaped,  except  some  in  the  center  which  remain  polyhedral.  Some  of 
these  latter  cells  contain  pigment  granules  which  give  rise  to  the  color  of  the  hair. 
It  occasionally  happens  that  these  pigment  granules  completely  fill  the  cells  in 


THE  APPENDAGES  OF  THE  SKIN 


Hyaline  layer  —•'»*' 

Cortex  _ 
of  hair 


Outer  or 
dermic  coat 


the  center  of  the  bulb;  this  gives  rise  to  the  dark  tract  of  pigment  often  found, 
of  greater  or  less  length,  in  the  axis  of  the  hair. 

The  shaft  of  the  hair  (scapus  pill)  consists,  from  within  outward,  of  three  parts, 
the  medulla,  the  cortex,  and  the  cuticle.  The  medulla  is  usually  wanting  in  the 
fine  hairs  covering  the  surface  of 
the  body,  and  commonly  in  those 
of  the  head.  It  is  more  opaque 
and  deeper  colored  than  the  cor- 
tex when  viewed  by  transmitted 
light;  but  when  viewed  by  re- 
flected light  it  is  white.  It  is 
composed  of  rows  of  polyhedral 
cells,  containing  granules  of  elei- 
din  and  frequently  air  spaces. 
The  cortex  constitutes  the  chief 
part  of  the  shaft;  its  cells  are 
elongated  and  united  to  form 
flattened  fusiform  fibers  which 
contain  pigment  granules  in  dark 
hair,  and  air  in  white  hair.  The 
cuticle  consists  of  a  single  layer 
of  flat  scales  which  overlap  one 
another  from  below  upward. 

Connected  with  the  hair  fol- 
licles are  minute  bundles  of  in- 
voluntary muscular  fibers,  termed 
the  Arrectores  pilorum.  They 
arise  from  the  superficial  layer 
of  the  corium,  and  are  inserted 
into  the  hair  follicle,  below  the 
entrance  of  the  duct  of  the  seba- 
ceous gland.  They  are  placed  on 
the  side  toward  which  the  hair 

slopes,  and  by  their  action  diminish  the  obliquity  of  the  follicle  and  elevate  the 
hair  (Fig.  944).^  The  sebaceous  gland  is  situated  in  the  angle  which  the  Arrector 
muscle  forms  with  the  superficial  portion  of  the  hair  follicle,  and  contraction  of  the 
muscle  thus  tends  to  squeeze  the  sebaceous  secretion  out  from  the  duct  of  the  gland. 

The  Sebaceous  Glajids  (glandidoB  sehaceoe)  are  small,  sacculated,  glandular 
organs,  lodged  in  the  substance  of  the  corium.  They  are  found  in  most  parts  of 
the  skin,  but  are  especially  abundant  in  the  scalp  and  face;  they  are  also  very 
numerous  around  the  apertures  of  the  anus,  nose,  mouth,  and  external  ear,  but  are 
wanting  in  the  palms  of  the  hands  and  soles  of  the  feet.  Each  gland  consists  of  a 
single  duct,  more  or  less  capacious,  which  emerges  from  a  cluster  of  oval  or  flask- 
shaped  alveoli  which  vary  from  two  to  five  in  number,  but  in  some  instances  there 
may  be  as  many  as  twenty.  Each  alveolus  is  composed  of  a  transparent  basement 
membrane,  enclosing  a  number  of  epithelial  cells.  The  outer  or  marginal  cells 
are  small  and  polyhedral,  and  are  continuous  with  the  cells  lining  the  duct.  The 
remainder  of  the  alveolus  is  filled  with  larger  cells,  containing  fat,  except  in  the 
center,  where  the  cells  have  become  broken  up,  leaving  a  cavity  filled  with  their 
debris  and  a  mass  of  fatty  matter,  which  constitutes  the  sebum  cutaneum.  The 
ducts  open  most  frequently  into  the  hair  follicles,  but  occasionally  upon  the  general 
surface,  as  in  the  labia  minora  and  the  free  margin  of  the  lips.    On  the  nose  and  face 


Fia.  945. — Transverse  section  of  hair  follicle. 


'  Professor  Arthur  Thomson,  of  Oxford,  suggests  that  the  contraction  of  these  muscles  on  follicles  which  contain 
weak,  flat  hairs  will  tend  to  produce  a  permanent  curve  in  the  follicle,  and  this  curve  will  be  impressed  on  the  hair 
which  is  moulded  within  it,  so  that  the  nair,  on  emerging  through  the  skin,  will  be  curled.  Curved  hair  follicles  are 
characteristic  of  the  scalp  of  the  Bushman. 


1070     ORGANS  OF  THE  SENSES  AND  THE  COMMON  INTEGUMENT 

the  glands  are  of  large  size,  distinctly  lobulated,  and  often  become  much  enlarged 
from  the  accumulation  of  pent-up  secretion.  The  tarsal  glands  of  the  eyelids  are 
elongated  sebaceous  glands  with  numerous  lateral  diverticula. 

The  Sudoriferous  or  Sweat  Glands  (glandulcB  sudoriferoe)  are  found  in  almost 
every  part  of  the  skin,  and  are  situated  in  small  pits  on  the  under  surface  of  the 
corium,  or,  more  frequently,  in  the  subcutaneous  areolar  tissue,  surrounded  by  a 
quantity  of  adipose  tissue.  Each  consists  of  a  single  tube,  the  deep  part  of  which 
is  rolled  into  an  oval  or  spherical  ball,  named  the  body  of  the  gland,  while  the  super- 
ficial part,  or  duct,  traverses  the  corium 
and  cuticle  and  opens  on  the  surface  of 
^  the  skin  by  a  funnel-shaped  aperture. 

1^         In  the  superficial  layers  of  the  corium 
the  duct  is  straight,  but  in  the  deeper 
??^>g^g=<\iBKaf  V      layers  it  is  convoluted  or  even  twisted; 
'^X^^^tlK/^^$^i^^^^^^^^^     where  the  epidermis  is  thick,  as  in  the 
\^y/^->{\_^y^      palms  of  the  hands  and  soles  of  the  feet, 
/'//^^'LJZ  the  part  of  the  duct  which  passes  through 

^i^^^'^'^^^^^^^^J^^         it   is  spirally  coiled.    The  size  of   the 

glands  varies.     They  are  especially  large 

^^^    ^■Mirfliw^^^^^/  ^^  those  regions   w^here   the  amount  of 

P^^BJ^*^  perspiration  is  great,  as  in  the  axillae, 

'^'*^^  where  they  form  a  thin,   mammillated 

Fig.  946.— Body  of  a  sudoriferous-gland  cut  in  various     layer  of  a  rcddisli  color,  which  corre- 

SXTofiedUe.'^H'.^Ss'^^^^^^^^^^^^  sponds  cxactly  to  the  situation  of  the 

'^n^!'^T%'ifnr4^''^.^l  otthifame.°^Krein^tn1     1^^^^  ^^  this  rcgiou;  they  are  large  also 

Noble  Smith.)  {ji  the    groiu.     Their   number    varies. 

They  are  very  plentiful  on  the  palms 
of  the  hands,  and  on  the  soles  of  the  feet,  where  the  orifices  of  the  ducts  are  exceed- 
ingly regular,  and  open  on  the  curved  ridges;  they  are  least  numerous  in  the  neck 
and  back.  On  the  palm  there  are  about  370  per  square  centimeter;  on  the  back  of 
the  hand  about  200;  forehead  175,  breast,  abdomen  and  forearm  155,  and  on  the 
leg  and  back  from  60  to  80  per  square  centimeter.  Krause  estimates  the  total 
number  at  about  2,000,000.  The  average  number  of  sweat  glands  per  square 
centimeter  of  skin  area  in  various  races  as  shown  by  the  fingers  is  as  follows  ■} 

American  (white) 558.2 

American  (negro) 597.2 

Filipino 653.6 

Moro 684.4 

Negrito  (adult) 709.2 

Hindu 738.2 

Negrito  (youth) 950.0 

They  are  absent  in  the  deeper  portion  of  the  external  auditory  meatus,  the  pre- 
puce and  the  glans  penis.  The  tube,  both  in  the  body  of  the  gland  and  in  the  duct 
consists  of  two  layers — ^an  outer,  of  fine  areolar  tissue,  and  an  inner  of  epithelium 
(Fig.  946).  The  outer  layer  is  thin  and  is  continuous  with  the  superficial  stratum  of 
the  corium.  In  body  of  the  gland  the  epithelium  consists  of  a  single  layer  of  cubical 
cells,  between  the  deep  ends  of  which  and  the  basement  membrane  is  a  layer 
of  longitudinally  or  obliquely  arranged  non-striped  muscular  fibers.  The  ducts  are 
destitute  of  muscular  fibers  and  are  composed  of  a  basement  membrane  lined  by  two 
or  three  layers  of  polyhedral  cells;  the  lumen  of  the  duct  is  coated  by  a  thin  cuticle. 
When  the  cuticle  is  carefully  removed  from  the  surface  of  the  corium,  the  ducts 
may  be  drawn  out  in  the  form  of  short,  thread-like  processes  on  its  under  surface. 
The  ceruminous  glands  of  the  external  acoustic  meatus  and  the  ciliary  glands  at 
the  margins  of  the  eyelids  are  modified  sudoriferous  glands. 

'  Clark  and  Lhamon,  Anatomical  Record,  1917,  xii. 


SPLANCHNOLOGY. 


I 


TTNDER  this  heading  are  included  the  respiratory,   digestive,   and  urogenital 
^    organs,  and  the  ductless  glands. 

THE  RESPIRATORY  APPARATUS  (APPARATUS  RESPIRATORIUS ; 
RESPIRATORY  SYSTEM). 


The  respiratory  apparatus  consists  of  the  larynx,  trachea,  bronchi,  lungs,  and 
pleurae. 

Development. — The  rudiment  of  the  respiratory  organs  appears  as  a  median 

longitudinal  groove  in  the  ventral  wall  of  the  pharynx.    The  groove  deepens 

and  its  lips  fuse  to  form  a  septum  which  grows  from  below  upward  and  con- 

i^erts  the  groove  into  a  tube,  the  larsmgo-tracheal  tube  (Fig.  947),  the  cephalic 


Mouth  of  olfactory  pit 

Median  part  of  fronto- 
nasal process 


Eye 

Maxillary  process 

Mandibular  arch 

Future  tympanic 
membrane 

Hyoid  arch 

Third  arch 


Processus  glohulari 

Hypophysis 
1st  branchial  pouch 

Sinus  cervicalis 
Laryngo-tracheal  tube 


Fourth  arch 


[FlQ.  947. — The  head  and  neck  of  a  human  embryo  thirt.\'-t\vo  days  old,  seen  from  the  ventral  surface. 
the  mouth  and  pharynx  have  been  removed.     (His.) 


The  floor  of 


end  of  which  opens  into  the  pharynx  by  a  slit-like  aperture  formed  by  the  persistent 
anterior  part  of  the  groove.  The  tube  is  lined  by  entoderm  from  which  the  epithe- 
lial lining  of  the  respiratory  tract  is  developed.  The  cephalic  part  of  the  tube 
becomes  the  larynx,  and  its  next  succeeding  part  the  trachea,  while  from  its  caudal 
end  two  lateral  outgrowths,  the  right  and  left  lung  buds,  arise,  and  from  them  the 
bronchi  and  lungs  are  developed.  The  first  rudiment  of  the  larynx  consists  of  two 
arytenoid  swellings,  which  appear,  one  on  either  side  of  the  cephalic  end  of  the  laryngo- 
tracheal groove,  and  are  continuous  in  front  of  the  groove  with  a  transverse  ridge 
(furcula  of  His)  which  lies  between  the  ventral  ends  of  the  third  branchial  arches 
and  from  which  the  epiglottis  is  subsequently  developed  (Figs.  980,  981).  After 
the  separation  of  the  trachea  from  the  esophagus  the  arytenoid  swellings  come 

( 1071 ) 


1072 


SPLANCHNOLOGY 


into  contact  with  one  another  and  with  the  back  of  the  epiglottis,  and  the  entrance 
to  the  larynx  assumes  the  form  of  a  T-shaped  cleft,  the  margins  of  the  cleft  adhere 
to  one  another  and  the  laryngeal  entrance  is  for  a  time  occluded.  The  mesodermal 
wall  of  the  tube  becomes  condensed  to  form  the  cartilages  of  the  larynx  and  trachea. 
The  arytenoid  swellings  are  differentiated  into  the  arytenoid  and  corniculate  car- 
tilages, and  the  folds  joining  them  to  the  epiglottis  form  the  aryepiglottic  folds 
in  which  the  cuneiform  cartilages  are  developed  as  derivatives  of  the  epiglottis. 
The  thyroid  cartilage  appears  as  two  lateral  plates,  each  chondrified  from  two 
centers  and  united  in  the  mid-ventral  line  by  membrane  in  which  an  additional 
center  of  chondrification  develops.  The  cricoid  cartilage  arises  from  two  cartil- 
aginous centers,  which  soon  unite  ventrally  and  gradually  extend  and  ultimately 
fuse  on  the  dorsal  aspect  of  the  tube. 

J.  Ernest  Frazer^  has  made  an  important  investigation  on  the  development  of  the  larynx 
and  the  following  are  his  main  conclusions: 

The  opening  of  the  pulmonary  diverticulum  lies  between  the  two  fifth  arch  masses  and  behind 
a  "central  mass"  in  the  middle  hne — -the  proximal  end  of  the  diverticulum  is  compressed  between 
the  fifth  arch  masses.  The  fifth  arch  is  joined  by  the  fourth  to  form  a  "lateral  mass"  on  each 
side  of  the  opening,  and  these  "lateral  masses"  grow  forward  and  overlap  the  central  mass  and 
so  form  a  secondary  transverse  cavity,  which  is  really  a  part  of  the  cavity  of  the  phaiynx.  The 
two  parts  of  the  cavity  of  the  larynx  are  separated  in  the  adult  by  a  line  drawn  back  along  the 
vocal  fold  and  then  upward  along  the  border  of  the  arytenoid  eminence  to  the  interarytenoid 
notch.  The  arytenoid  and  cricoid  are  developed  in  the  fifth  arch  mass.  The  thyroid  is  primarily 
a  fourth  arch  derivative,  and  if  it  has  a  fifth  arch  element  this  is  a  later  addition.  The  epiglottis 
is  derived  from  the  "central  mass,"  and  has  a  third  arch  element  in  its  oral  and  upper  aspect; 
the  arch  value  of  the  "central  mass"  is  doubtful. 


^^^■xAw^ 


Fio.  948. — Lung  buds  from  a  human  embryo  of 
about  four  weeks,  showing  commencing  lobulations. 
(His.) 


Fig.  949. — Lungs  of  a  human  embryo  more 
advanced  in  development.     (His.) 


The  right  and  left  lung  buds  grow  out  behind  the  ducts  of  Cuvier,  and  are  at 
first  symmetrical,  but  their  ends  soon  become  lobulated,  three  lobules  appearing 
on  the  right,  and  two  on  the  left;  these  subdivisions  are  the  early  indications  of  the 
corresponding  lobes  of  the  lungs  (Figs.  948,  949).  The  buds  undergo  further  sub- 
division and  ramification,  and  ultimately  end  in  minute  expanded  extremities — 
the  infundibula  of  the  lung.  After  the  sixth  month  the  air-sacs  begin  to  make  their 
appearance  on  the  infundibula  in  the  form  of  minute  pouches.  The  pulmonary 
arteries  are  derived  from  the  sixth  aortic  arches.  During  the  course  of  their 
development  the  lungs  migrate  in  a  caudal  direction,  so  that  by  the  time  of  birth 
the  bifurcation  of  the  trachea  is  opposite  the  fourth  thoracic  vertebra.  As  the 
lungs  grow  they  project  into  that  part  of  the  celom  which  will  ultimately  form  the 
pleural  cavities,  and  the  superficial  layer  of  the  mesoderm  enveloping  the  lung 
rudiment  expands  on  the  growing  lung  and  is  converted  into  the  pulmonary  pleura. 


THE   LARYNX. 


The  larynx  or  organ  of  voice  is  placed  at  the  upper  part  of  the  air  passage. 
It  is  situated  between  the  trachea  and  the  root  of  the  tongue,  at  the  upper  and 


'  .Journal  of  Anatomy  and  Physiology,  vol.  xliv. 


I 


THE  LARYNX  "^^^^K"  1073 

orepart  of  the  neck,  where  It  presents  a  considerable  projection  in  the  middle 
line.  It  forms  the  lower  part  of  the  anterior  wall  of  the  pharynx,  and  is  covered 
behind  by  the  mucous  lining  of  that  cavity;  on  either  side  of  it  lie  the  great  vessels 
of  the  neck.  Its  vertical  extent  corresponds  to  the  fourth,  fifth,  and  sixth  cervical 
vertebrae,  but  it  is  placed  somewhat  higher  in  the  female  and  also  during  childhood. 
Symington  found  that  in  infants  between  six  and  twelve  months  of  age  the  tip 
of  the  epiglottis  was  a  little  above  the  level  of  the  fibrocartilage  between  the 
odontoid  process  and  body  of  the  axis,  and  that  between  infancy  and  adult  life 
the  larynx  descends  for  a  distance  equal  to  two  vertebral  bodies  and  two  inter- 
vertebral fibrocartilages.  According  to  Sappey  the  average  measurements  of  the 
adult  larynx  are  as  follows: 

In  males.  In  females. 

Length 44  mm.  36  mm. 

Transverse  diameter          ....  43  "  41     " 

Antero-posterior  diameter        ...  36  "  26     " 

Circumference 136  "  112 

Until  puberty  the  larynx  of  the  male  differs  little  in  size  from  that  of  the  female.  In  the 
female  its  increase  after  puberty  is  only  slight;  in  the  male  it  undergoes  considerable  increase; 
all  the  cartilages  are  enlarged  and  the  thyroid  cartilage  becomes  prominent  in  the  middle  line  of 
the  neck,  while  the  length  of  the  rima  glottidis  is  nearly  doubled. 

The  larj-nx  is  broad  above,  where  it  presents  the  form  of  a  triangular  box  flattened 
behind  and  at  the  sides,  and  bounded  in  front  by  a  prominent  vertical  ridge. 
Below,  it  is  narrow  and  cylindrical.  It  is  composed  of  cartilages,  which  are  con- 
nected together  by  ligaments  and  moved  by  numerous  muscles.  It  is  lined  by 
mucous  membrane  continuous  above  with  that  of  the  pharynx  and  below  with 
that  of  the  trachea. 

The  Cartilages  of  the  Lar3mx  (cartilagines  laryngis)  (Fig.  950)  are  nine  in  number, 
three  single  and  three  paired,  as  follows: 

^  Thyroid.  Two  Corniculate. 

^  Cricoid.  Two  Cuneiform. 

m  Two  Arjrtenoid.  Epiglottis. 

The  Th3rroid  Cartilage  (cartilago  thyreoidea)  is  the  largest  cartilage  of  the  larynx. 
II  consists  of  two  laminae  the  anterior  borders  of  which  are  fused  with  each  other 
at  an  acute  angle  in  the  middle  line  of  the  neck,  and  form  a  subcutaneous  projec- 
tion named  the  larjmgeal  prominence  (pomum  Adami).    This  prominence  is  most 
distinct  at  its  upper  part,  and  is  larger  in  the  male  than  in  the  female.    Immediately 
above  it  the  laminae  are  separated  by  a  V-shaped  notch,  the  superior  th3rroid  notch. 
The  laminae  are  irregularly  quadrilateral  in  shape,  and  their  posterior  angles  are 
prolonged  into  processes  termed  the  superior  and  inferior  comua. 
^B     The  outer  surface  of  each  lamina  presents  an  oblique  line  which  runs  downward 
^M  and  forward  from  the  superior  thyroid  tubercle  situated  near  the  root  of  the 
^  superior  cornu,  to  the  inferior  thyroid  tubercle  on  the  lower  border.    This  line 
gives  attachment  to  the  SternOthyreoideus,    Thyreohyoideus,   and  Constrictor 
pharyngis  inferior. 
H      The  inner  surface  is  smooth;  above  and  behind,  it  is  slightly  concave  and  covered 
^  by  mucous  membrane.    In  front,  in  the  angle  formed  by  the  junction  of  the  laminae, 
are  attached  the  stem  of  the  epiglottis,  the  ventricular  and  vocal  ligaments,  the 
Thyreoarytaenoidei,  Thyreoepiglottici  and  Vocales  muscles,  and  the  thyroepiglottic 

■  ligament. 
The  upper  border  is  concave  behind  and  convex  in  front;  it  gives  attachment  to 
the  corresponding  half  of  the  hyothyroid  membrane. 

The  lower  border  is  concave  behind,  and  nearly  straight  in  front,  the  two  parts 
being  separated  by  the  inferior  thyroid  tubercle.    A  small  part  of  it  in  and  near 
68 


1074 


SPLANCHNOLOGY 


EPIGLOTTIS 


the  middle  line  is  connected  to  the  cricoid  cartilage  by  the  middle  cricothyroid 

ligament. 
The  posterior  border,  thick  and  rounded,  receives  the  insertions  of  the  Stylo- 

pharyngeus  and  Pharyngopalatinus.     It  ends  above,  in  the  superior  cornu,  and 

below,  in  the  inferior  cornu.  The 
superior  cornu  is  long  and  narrow, 
directed  upward,  backward,  and 
medialward,  and  ends  in  a  conical 
extremity,  which  gives  attachment 
to  the  lateral  hyothyroid  ligament. 
The  inferior  cornu  is  short  and  thick; 
it  is  directed  downward,  with  a  slight 
inclination  forward  and  medialward, 
and  presents,  on  the  medial  side  of 
its  tip,  a  small  oval  articular  facet 
for  articulation  with  the  side  of  the 
cricoid  cartilage. 

During  infancy  the  laminae  of  the 
thyroid  cartilage  are  joined  to  each 
other  by  a  narrow,  lozenge-shaped 
strip,  named  the  intrathyroid  cartil- 
age. This  strip  extends  from  the 
upper  to  the  lower  border  of  the 
cartilage  in  the  middle  line,  and  is 
distinguished  from  the  laminae  by 
being  more  transparent  and  more 
flexible. 

The  Cricoid  Cartilage  (cartilago 
cricoidea)  is  smaller,  but  thicker  and 
stronger  than  the  thyroid,  and  forms 
the  lower  and  posterior  parts  of  the 
wall  of  the  larynx.  It  consists  of  two 
parts:  a  posterior  quadrate  lamina, 
and  a  narrow  anterior  arch,  one- 
fourth  or  one-fifth  of  the  depth  of 
the  lamina. 

The  lamina  (lamina  cartilaginis 
cricoidea;;  posterior  ''portion)  is  deep 
and  broad,  and  measures  from  above 
downward  about  2  or  3  cm.;  on  its 
posterior  surface,  in  the  middle  line, 
is  a  vertical  ridge  to  the  lower  part 
of  which  are  attached  the  longitu- 
dinal fibers  of  the  esophagus;  and  on  either  side  of  this  a  broad  depression  for  the 

Cricoarytaenoideus  posterior. 

The  arch  {arcus  cartilaginis  cricoideos;  anterior  portimi)  is  narrow  and  convex, 

and  measures  vertically  from  5  to  7  mm.;  it  affords  attachment  externally  in  front 

and  at  the  sides  to  the  Cricothyreiodei,  and  behind,  to  part  of  the  Constrictor 

pharyngis  inferior. 

On  either  side,  at  the  junction  of  the  lamina  with  the  arch,  is  a  small  round 

articular  surface,  for  articulation  with  the  inferior  cornu  of  the  thyroid  cartilage. 
The  lower  border  of  the  cricoid  cartilage  is  horizontal,  and  connected  to  the 

highest  ring  of  the  trachea  by  the  cricotracheal  ligament. 
The  upper  border  runs  obliquely  upward  and  backward,  owing  to  the  great 


Cuneiform  cartilage 


AKYTENOID 


Insertion  of 

CricoarytcenoidetLs 

posterior 


Posterior 
surface 


Arytenoid  cartilages^  base 


ArticvUar  facet  for 
arytenoid  cartilage 

Articular  facet  for 
inferior  cornu  of 
thyroid  cartilage 


Fio.  950. — The  cartilages  of  the  larj'nx.     Posterior  view. 


THE 

depth  of  the  lamina.  It  gives  attachment,  in  front,  to  the  middle  cricothyroid 
ligament;  at  the  side,  to  the  conus  elasticus  and  the  Gricoarytsenoidei  laterales; 
behind,  it  presents,  in  the  middle,  a  shallow  notch,  and  on  either  side  of  this  is  a 
smooth,  oval,  convex  surface,  directed  upward  and  lateralward,  for  articulation 
with  the  base  of  an  arytenoid  cartilage. 

The  inner  surface  of  the  cricoid  cartilage  is  smooth,  and  lined  by  mucous 
membrane. 

The  Arytenoid  Cartilages  {cartilagines  arytosnoideoB)  are  two  in  number,  and  sit- 
uated at  the  upper  border  of  the  lamina  of  the  cricoid  cartilage,  at  the  back  of 
the  larynx.  Each  is  pyramidal  in  forcft,  and  has  three  surfaces,  a  base,  and  an 
apex. 

The  posterior  surface  is  a  triangular,  smooth,  concave,  and  gives  attachment 
to  the  Arytpenoidei  obliquus  and  transversus. 

The  antero-lateral  surface  is  somewhat  convex  and  rough.  On  it,  near  the  apex 
of  the  cartilage,  is  a  rounded  elevation  (colliculus)  from  which  a  ridge  (crista  arcuata) 
curves  at  ifirst  backward  and  then  downward  and  forward  to  the  vocal  process. 
The  lower  part  of  this  crest  intervenes  between  two  depressions  or  foveas,  an 
upper,  triangular,  and  a  lower  oblong  in  shape;  the  latter  gives  attachment  to  the 
Vocalis  muscle. 

The  medial  surface  is  narrow,  smooth,  and  flattened,  covered  by  mucous  mem- 
brane, and  forms  the  lateral  boundary  of  the  intercartilaginous  part  of  the  rima 
glottidis. 

The  base  of  each  cartilage  is  broad,  and  on  it  is  a  concave  smooth  surface, 
for  articulation  with  the  cricoid  cartilage.  Its  lateral  angle  is  short,  rounded, 
and  prominent;  it  projects  backward  and  lateralward,  and  is  termed  the  muscular 
process;  it  gives  insertion  to  the  Cricoarytsenoideus  posterior  behind,  and  to  the 
Cricoarytsenoideus  lateralis  in  front.  Its  anterior  angle,  also  prominent,  but  more 
pointed,  projects  horizontally  forward;  it  gives  attachment  to  the  vocal  ligament, 
and  is  called  the  vocal  process. 

The  apex  of  each  cartilage  is  pointed,  curved  backward  and  medialward,  and 
surmounted  by  a  small  conical,  cartilaginous  nodule,  the  comiculate  cartilage. 

The  Corniculate  Cartilages  {cartilagines  corniculatoe;  cartilages  of  Santorini)  are 
two  small  conical  nodules ,  consisting  of  yellow  elastic  cartilage,  which  articulate 
with  the  summits  of  the  arytenoid  cartilages  and  serve  to  prolong  them  backward 
and  medialward.  They  are  situated  in  the  posterior  parts  of  the  aryepiglottic 
folds  of  mucous  membrane,  and  are  sometimes  fused  with  the  arytenoid  cartilages. 

The  Cuneiform  Cartilages  {cartilagines  cuneijormes;  cartilages  of  Wrisberg)  are  two 
small,  elongated  pieces  of  yellow  elastic  cartilage,  placed  one  on  either  side,  in  the 
aryepiglottic  fold,  where  they  give  rise  to  small  whitish  elevations  on  the  surface 
of  the  mucous  membrane,  just  in  front  of  the  arytenoid  cartilages. 

The  Epiglottis  {cartilago  epiglottica)  is  a  thin  lamella  of  fibrocartilage  of  a  yel- 
lowish color,  shaped  like  a  leaf,  and  projecting  obliquely  upward  behind  the  root 
of  the  tongue,  in  front  of  the  entrance  to  the  larynx.  The  free  extremity  is  broad 
and  rounded;  the  attached  part  or  stem  is  long,  narrow,  and  connected  by  the 
thyroepiglottic  ligament  to  the  angle  formed  by  the  two  laminae  of  the  thyroid 
cartilage,  a  short  distance  below  the  superior  thyroid  notch.  The  lower  part  of 
its  anterior  surface  is  connected  to  the  upper  border  of  the  body  of  the  hyoid 
bone  by  an  elastic  ligamentous  band,  the  hyoepiglottic  ligament. 

The  anterior  or  lingual  surface  is  curved  forward,  and  covered  on  its  upper,  free 
part  by  mucous  membrane  which  is  reflected  on  to  the  sides  and  root  of  the  tongue, 
forming  a  median  and  two  lateral  glossoepiglottic  folds;  the  lateral  folds  are  partly 
attached  to  the  wall  of  the  pharynx.  The  depressions  between  the  epiglottis  and 
the  root  of  the  tongue,  on  either  side  of  the  median  fold,  are  named  the  valleculae. 
The  lower  part  of  the  anterior  surface  lies  behind  the  hyoid  bone,  the  hyothyroid 


1076 


SPLANCHNOLOGY 


I 


membrane,  and  upper  part  of  the  thyroid  cartilage,  but  is  separated  from  these 
structures  by  a  mass  of  fatty  tissue. 

The  posterior  or  larsmgeal  surface  is  smooth,  concave  from  side  to  side,  concavo- 
convex  from  above  downward;  its  lower  part  projects  backward  as  an  elevation, 
the  tubercle  or  cushion.  When  the  mucous  membrane  is  removed,  the  surface  of 
the  cartilage  is  seen  to  be  indented  by  a  number  of  small  pits,  in  which  mucous 
glands  are  lodged.    To  its  sides  the  ary epiglottic  folds  are  attached. 

Structure. — The  corniculate  and  cuneiform  cartilages,  the  epiglottis,  and  the  apices  of  the 
arytenoids  at  first  consist  of  hyaline  cartilage,  but  later  elastic  fibers  are  deposited  in  the  matrix, 
converting  them  into  yellow  fibrocartilage,  which  shows  httle  tendency  to  calcification.  The 
thyroid,  cricoid,  and  the  greater  part  of  the  arytenoids  consist  of  hyaline  cartilage,  and  become 
more  or  less  ossified  as  age  advances.  Ossification  commences  about  the  twenty-fifth  year  in 
the  thyroid  cartilage,  and  somewhat  later  in  the  cricoid  and  arytenoids;  by  the  sixty-fifth  year 
these  cartilages  may  be  completely  converted  into  bone. 


Lateral  hyothyroid  ligament 
Internal  laryngeal  nerve 
Cartilago  tnttcea 

Superior  laryngeal  artery 

Superior  comu 
Thyroid  notch 


Oblique  line 

Conug  elastieu&  (lateral  parts) 

Middle  cricothyroid  ligament 
Inferior  comu 


Fia.  951. — The  ligaments  of  the  larynx.     Anterolateral  view. 


Ligaments. — The  ligaments  of  the  larynx  (Figs.  951, 952)  are  extrinsic,  i.  e.,  those 
connecting  the  thyroid  cartilage  and  epiglottis  with  the  hyoid  bone,  and  the  cricoid 
cartilage  with  the  trachea;  and  intrinsic,  those  which  connect  the  several  cartilages 
of  the  larynx  to  each  other. 

Extrinsic  Ligaments. — The  ligaments  connecting  the  thyroid  cartilage  with  the 
hyoid  bone  are  the  hyothyroid  membrane,  and  a  middle  and  two  lateral  hyo- 
thyroid ligaments. 

The  Hyothyroid  Membrane  (membrana  hyothyreoidea;  thyrohyoid  membrane)  is 
a  broad,  fibro-elastic  layer,  attached  below  to  the  upper  border  of  the  thyroid 
cartilage  and  to  the  front  of  its  superior  comu,  and  above  to  the  upper  margin  of 
the  posterior  surface  of  the  body  and  greater  cornua  of  the  hyoid  bone,  thus  passing 
behind  the  posterior  surface  of  the  body  of  the  hyoid,  and  being  separated  from  it 


THE  LARYNX 


1077 


by  a  mucous  bursa,  which  facilitates  the  upward  movement  of  the  larynx  during 
deglutition.  Its  middle  thicker  part  is  termed  the  middle  hyothyroid  ligament 
\ligamentum  hyothyreoideum  medium;  middle  thyrohyoid  ligament) ,  its  lateral  thinner 
portions  are  pierced  by  the  superior  laryngeal  vessels  and  the  internal  branch  of 
the  superior  laryngeal  nerve.  Its  anterior  surface  is  in  relation  with  the  Thyreo- 
hyoideus,  Sternohyoideus,  and  Omohyoideus,  and  with  the  body  of  the  hyoid 
bone. 

The  Lateral  Hyothsnroid  Ligament  (ligamentum  hyothyreoideum  laterale;  lateral 
thyrohyoid  ligament)  is  a  round  elastic  cord,  which  forms  the  posterior  border 
of  the  hyothyroid  membrane  and  passes  between  the  tip  of  the  superior  cornu  of 
the  thyroid  cartilage  and  the  extremit}'  of  the  greater  cornu  of  the  hyoid  bone. 
A  small  cartilaginous  nodule  (cartilago  triticea),  sometimes  bony,  is  frequently 
found  in  it. 


Hyoid  bone 


Cartilago  triticea 


—  Hyothyroid  membrane, 


Comictdate  cartilage 


,1      ■  Arytenoid 


Posterior  crico-arytenoid 
ligament 


Cricothyroid 
articulation 


Fia.  952. — Ligaments  of  the  larynx.     Posterior  view. 

The  Epiglottis  is  connected  with  the  hyoid  bone  by  an  elastic  band,  the  hyo- 
epiglottic  ligament  {ligamentum  hyoepiglotticum) ,  which  extends  from  the  anterior 
surface  of  the  epiglottis  to  the  upper  border  of  the  body  of  the  hyoid  bone.  The 
glossoepiglottic  folds  of  mucous  membrane  (page  1075)  may  also  be  considered 
as  extrinsic  ligaments  of  the  epiglottis. 

The  Cricotracheal  Ligament  (ligamentum  cricotracheale)  connects  the  cricoid  car- 
tilage with  the  first  ring  of  the  trachea.  It  resembles  the  fibrous  membrane  which 
connects  the  cartilaginous  rings  of  the  trachea  to  each  other. 

Intrinsic  Ligaments. — Beneath  the  mucous  membrane  of  the  larynx  is  a  broad 
sheet  of  fibrous  tissue  containing  many  elastic  fibers,  and  termed  the  elastic  membrane 
of  the  larynx.    It  is  subdivided  on  either  side  by  the  interval  between  the  ven- 


1078  SPLANCHNOLOGY 

tricular  and  vocal  ligaments,  the  upper  portion  extends  between  the  arytenoid 
cartilage  and  the  epiglottis  and  is  often  poorly  defined;  the  lower  part  is  a  well- 
marked  membrane  forming,  with  its  fellow  of  the  opposite  side,  the  conus  elasticus 
which  connects  the  thyroid,  cricoid,  and  arytenoid  cartilages  to  one  another. 
In  addition  the  joints  between  the  individual  cartilages  are  provided  with  ligaments. 

The  Conus  Elasticus  {cricothyroid  membrane)  is  composed  mainly  of  yellow  elastic 
tissue.  It  consists  of  an  anterior  and  two  lateral  portions.  The  anterior  part  or 
middle  cricothyroid  ligament  (ligamentvm  cricothyreoideum  medium;  central  part  of 
cricothyroid  membrane)  is  thick  and  strong,  narrow  above  and  broad  below.  It 
connects  together  the  front  parts  of  the  contiguous  margins  of  the  thyroid  and 
cricoid  cartilages.  It  is  overlapped  on  either  side  by  the  Cricothyreoideus,  but 
between  these  is  subcutaneous;  it  is  crossed  horizontally  by  a  small  anastomoticjB 
arterial  arch,  formed  by  the  junction  of  the  two  cricothyroid  arteries,  branches 
of  which  pierce  it.  The  lateral  portions  are  thinner  and  lie  close  under  the  mucous 
membrane  of  the  larynx;  they  extend  from  the  superior  border  of  the  cricoid  cartil- 
age to  the  inferior  margin  of  the  vocal  ligaments,  with  which  they  are  continuous. 
These  ligaments  may  therefore  be  regarded  as  the  free  borders  of  the  lateral  por- 
tions of  the  conus  elasticus,  and  extend  from  the  vocal  processes  of  the  arytenoid 
cartilages  to  the  angle  of  the  thyroid  cartilage  about  midway  between  its  upper 
and  lower  borders. 

An  articular  capsule,  strengthened  posteriorly  by  a  well-marked  fibrous  band^ 
encloses  the  articulation  of  the  inferior  cornu  of  the  thyroid  with  the  cricoid  car- 
tilage on  either  side. 

Each  arytenoid  cartilage  is  connected  to  the  cricoid  by  a  capsule  and  a  posterior 
cricoarytenoid  ligament.  The  capsule  (capsula  articularis  cricoarytenoidea)  is  thin 
and  loose,  and  is  attached  to  the  margins  of  the  articular  surfaces.  The  posterior 
cricoarytenoid  ligament  {ligamentum  cricoarytenoideum  ■posterius)  extends  from  the 
cricoid  to  the  medial  and  back  part  of  the  base  of  the  arytenoid. 

The  thjrroepiglottic  ligament  (ligamentum  thyreoepiglotticum)  is  a  long,  slender, 
elastic  cord  which  connects  the  stem  of  the  epiglottis  with  the  angle  of  tlie  thyroid 
cartilage,  immediately  beneath  the  superior  thyroid  notch,  above  the  attachment 
of  the  ventricular  ligaments. 

Movements. — The  articulation  between  the  inferior  cornu  of  the  thyroid  cartilage  and  the 
cricoid  cartilage  on  either  side  is  a  diarthrodial  one,  and  permits  of  rotatory  and  gliding  move- 
ments. The  rotatory  movement  is  one  in  which  the  cricoid  cartilage  rotates  upon  the  inferior 
cornua  of  the  thyroid  cartilage  around  an  axis  passing  transversely  through  both  joints. 
The  gliding  movement  consists  in  a  limited  shifting  of  the  cricoid  on  the  thyroid  in  different- 
directions. 

The  articulation  between  the  arytenoid  cartilages  and  the  cricoid  is  also  a  diarthrodial  one,, 
and  permits  of  two  varieties  of  movement :  one  is  a  rotation  of  the  arytenoid  on  a  vertical  axis,, 
whereby  the  vocal  process  is  moved  lateralward  or  medialward,  and  the  rima  glottidis  increased 
or  diminished;  the  other  is  a  gliding  movement,  and  allows  the  ar3rtenoid  cartilages  to  approach 
or  recede  from  each  other;  from  the  direction  and  slope  of  the  articular  surfaces  lateral  gliding 
is  accompanied  by  a  forward  and  downward  movement.  The  two  movements  of  gliding  and 
rotation  are  associated,  the  medial  gliding  being  connected  with  medialward  rotation,  and  the 
lateral  gliding  with  lateralward  rotation.  The  posterior  cricoarytenoid  ligaments  limit  the 
forward  movement  of  the  arytenoid  cartilages  on  the  cricoid. 

Interior  of  the  Larynx  (Figs.  953,  954). — The  cavity  of  the  larynx  (cavum 
laryngis)  extends  from  the  laryngeal  entrance  to  the  lower  border  of  the  cricoid 
cartilage  where  it  is  continuous  with  that  of  the  trachea.  It  is  divided  into  twa 
parts  by  the  projection  of  the  vocal  folds,  between  which  is  a  narrow  triangular 
fissure  or  chink,  the  rima  glottidis.  The  portion  of  the  cavity  of  the  larynx  above 
the  vocal  folds  is  called  the  vestibule ;  it  is  wide  and  triangular  in  shape,  its  base 
or  anterior  wall  presenting,  however,  about  its  center  the  backward  projection 
of  the  tubercle  of  the  epiglottis.  It  contains  the  ventricular  folds,  and  between 
these  and  the  vocal  folds  are  the  ventricles  of  the  larynx.    The  portion  below  the 


THE  LARYNX 


1079 


Glossoepiglottid 
fold 


If'pirjlottic 


Ventricular 
and  vocal 
folds  bound- 
ing ventricle 


Middle 

cricothyroid 

ligament 


rytenoid 
irtilage 


ytoBnoideua 
mvscle 


Fia.  953. — Sagittal  section  of  the  larynx  and  upper  part  of  the 
trachea. 


vocal  folds  is  at  first  of  an  elliptical 
form,  but  lower  down  it  widens  out, 
assumes  a  circular  form,  and  is  con- 
tinuous with  the  tube  of  the  trachea. 
The  entrance  of  the  larynx  (Fig. 
955)  is  a  triangular  opening,  wide 
in  front,  narrow  behind,  and  sloping 
obliquely  downward  and  backward. 
It  is  bounded,  in  front,  by  the  epi- 
glottis; behind,  by  the  apices  of  the 
arytenoid  cartilages,  the  corniculate 
cartilages,  and  the  interarytenoid 
notch;  and  on  either  side,  by  a  fold 
of  mucous  membrane,  enclosing 
ligamentous  and  muscular  fibers, 
stretched  between  the  side  of  the 
epiglottis  and  the  apex  of  the  aryte- 
noid cartilage;  this  is  the  aryepi- 
glottic  fold,  on  the  posterior  part  of 
the  margin  of  which  the  cuneiform 
cartilage  forms  a  more  or  less  dis- 
tinct whitish  prominence,  the  cunei- 
form tubercle. 

The  Ventricular  Folds  (plicoe  ventric- 
ulares;  superior  or  false  vocal  cords) 
are  two  thick  folds  of  mucous  membrane,  each  enclosing  a  narrow  band  of  fibrous 
tissue,  the  ventricular  ligament  which  is  attached  in  front  to  the  angle  of  the  thyroid 

cartilage  immediately  below  the  attach- 
ment of  the  epiglottis,  and  behind  to  the 
antero-lateral  surface  of  the  arytenoid 
cartilage,  a  short  distance  above  the  vocal 
process.  The  lower  border  of  this  ligament, 
enclosed  in  mucous  membrane,  forms  a 
free  crescentic  margin,  which  constitutes 
the  upper  boundary  of  the  ventricle  of  the 
larynx. 

The  Vocal  Folds  {plicoe  vocales;  inferior 
or  true  vocal  cords)  are  concerned  in  the 
production  of  sound,  and  enclose  two 
strong  bands,  named  the  vocal  ligaments 
{ligamenta  vocales;  inferior  thyroarytenoid). 
Each  ligament  consists  of  a  band  of  yellow 
elastic  tissue,  attached  in  front  to  the 
angle  of  the  thyroid  cartilage,  and  behind 
to  the  vocal  process  of  the  arytenoid.  Its 
lower  border  is  continuous  with  the  thin 
lateral  part  of  the  conus  elasticus.  Its 
upper  border  forms  the  lower  boundary 
of  the  ventricle  of  the  larynx.  Laterally, 
the  Vocalis  muscle  lies  parallel  with  it. 
It  is  covered  medially  by  mucous  mem- 
brane, which  is  extremely  thin  and  closely 

F,o.  954.-Corona!  section^o^^larynx  and  upper  part       adherent  tO   itS  SUrf  aCC. 


1080 


SPLANCHNOLOGY 


The  Ventricle  of  the  Larynx  {ventriculus  laryiigis  [Morgagnii];  laryngeal  sinus) 
is  a  fusiform  fossa,  situated  between  the  ventricular  and  vocal  folds  on  either  side, 
and  extending  nearly  their  entire  length.  The  fossa  is  bounded,  above,  by  the  free 
crescentic  edge  of  the  ventricular  fold;  below,  by  the  straight  margin  of  the  vocal 
fold;  laterally,  by  the  mucous  membrane  covering  the  corresponding  Thyreoary- 
tsenoideus.  The  anterior  part  of  the  ventricle  leads  up  by  a  narrow  opening 
into  a  cecal  pouch  of  mucous  membrane  of  variable  size  called  the  appendix. 

The  appendix  of  the  laryngeal  ventricle  {appendix  ventriculi  laryngis;  laryngeal 
saccule)  is  a  membranous  sac,  placed  between  the  ventricular  fold  and  the  inner 
surface  of  the  thyroid  cartilage,  occasionally  extending  as  far  as  its  upper  border 
or  even  higher;  it  is  conical  in  form,  and  curved  slightly  backward.  On  the  surface 
of  its  mucous  membrane  are  the  openings  of  sixty  or  seventy  mucous  glands,  which 

Svlcus  termincdis 


Foramen  cecum 


Vallecula 

Jjaieral  gloaso- 
epigloUic  fold 


-  Tvberde 

I 

^  Aryepiglottic  fold 

Glottis 
H    il  '   f' — '  C'tt»«*/o'"w  cartilagt 

nf 
'lart/pr' 


Comiculate  cartilage 


I 


Median  glosso- 
epiglottic  fold 


Greater  cornu  of 
Jiyoid  bone 

Sup.  cornu  of 
thyroid  cart. 

Ventribular  fold 
Ventricle 

Vocal  fold 
Pyriform  airvua 


Fig.  955. — The  entrance  to  the  larynx,  viewed  from  behind. 

are  lodged  in  the  submucous  areolar  tissue.  This  sac  is  enclosed  in  a  fibrous 
capsule,  continuous  below  with  the  ventricular  ligament.  Its  medial  surface  is 
covered  by  a  few  delicate  muscular  fasciculi,  which  arise  from  the  apex  of  the 
arytenoid  cartilage  and  become  lost  in  the  aryepiglottic  fold  of  mucous  membrane; 
laterally  it  is  separated  from  the  thyroid  cartilage  by  the  Thyreoepiglotticus. 
These  muscles  compress  the  sac,  and  express  the  secretion  it  contains  upon  the 
vocal  folds  to  lubricate  their  surfaces. 

The  Rima  Glottidis  (Fig.  956)  is  the  elongated  fissure  or  chink  between  the 
vocal  folds  in  front,  and  the  bases  and  vocal  processes  of  the  arytenoid  cartilages 
behind.  It  is  therefore  subdivided  into  a  larger  anterior  intramembranous 
part  (glottis  vocalis),  which  measures  about  three-fifths  of  the  length  of  the 
entire    aperture,   and    a  posterior  intercartilaginous  part   {glottis   respiratoria). 


THE  LARYNX 


1081 


Posteriorly  it  is  limited  by  the  mucous  membrane  passing  between  the  arytenoid 
cartilages.  The  rima  glottidis  is  the  jiarrowest  part  of  the  cavity  of  the  lan^nx, 
and  its  level  corresponds  with  the  bases  of  the  arytenoid  cartilages.  Its  length, 
in  the  male,  is  about  23  mm.;  in  the  female  from  17  to  18  mm.  The  width 
and  shape  of  the  rima  glottidis  vary  with  the  movements  of  the  vocal  folds 
and  arytenoid  cartilages  during  respiration  and  phonation.  In  the  condition 
of  rest,  i.  e.,  when  these  structures  are  uninfluenced  by  muscular  action,  as  in 
quiet  respiration,  the  intramembranous  part  is  triangular,  with  its  apex  in  front 
and  its  base  behind — the  latter  being  represented  by  a  line,  about  8  mm.  long, 
connecting  the  anterior  ends  of  the  vocal  processes,  while  the  medial  surfaces  of 
the  arytenoids  are  parallel  to  each  other,  and  hence  the  intercartilaginous  part 
is  rectangular.  During  extreme  adduction  of  the  vocal  folds,  as  in  the  emission 
of  a  high  note,  the  intramembranous  part  is  reduced  to  a  linear  slit  by  the  ap- 
position of  the  vocal  folds,  while  the  intercartilaginous  part  is  triangular,  its  apex 
corresponding  to  the  anterior  ends  of  the  vocal  processes  of  the  arytenoids,  which 
are  approximated  by  the  medial  rotation  of  the  cartilages.  Conversely  in  extreme 
abduction  of  the  vocal  folds,  as  in  forced  inspiration,  the  arytenoids  and  their 


Median  glosso-epiglottic  fold 
Vallecula  j         Epiglottis 

\  /  /     y  Tubercle  ofepiglottig 

Vocal  fold 


Ventricular  /aid 


/         — ■  Aryepiglottic  fold 


I 


Cuneiform  cartilage 


Comiculate  cartilage 

Trachea 
Fia.  956. — Laryagoscopic  view  of  interior  of  larynx. 

vocal  processes  are  rotated  lateralward,  and  the  intercartilaginous  part  is  trian- 
gular in  shape  but  with  its  apex  directed  backward.  In  this  condition  the  entire 
glottis  is  somewhat  lozenge-shaped,  the  sides  of  the  intramembranous  part 
diverging  from  before  backward,  those  of  the  intercartilaginous  part  diverging 
from  behind  forward — the  widest  part  of  the  aperture  corresponding  with  the 
attachments  of  the  vocal  folds  to  the  vocal  processes. 

Muscles. — The  muscles  of  the  larynx  are  extrinsic,  passing  between  the  larynx 
and  parts  around — these  have  been  described  in  the  section  on  Myology;  and 
intrinsic,  confined  entirely  to  the  larynx. 
The  intrinsic  muscles  are: 

Cricothyreoideus.  Cricoarytsenoideus  lateralis. 

Cricoarytfenoideus  posterior.  Arytsenoideus. 

Thy  roary  tsenoideus . 

The  Cricothyreoideus  {Cricothyroid)  (Fig.  957),  triangular  in  form,  arises  from  the 
front  and  lateral  part  of  the  cricoid  cartilage ;  its  fibers  diverge,  and  are  arranged 
in  two  groups.  The  lower  fibers  constitute  a  pars  obliqua  and  slant  backward 
and  lateralward  to  the  anterior  border  of  the  inferior  cornu;  the  anterior  fibers, 
forming  a  pars  recta,  run  upward,  backward,  and  lateralward  to  the  posterior  part 
of  the  lower  border  of  the  lamina  of  the  thyroid  cartilage. 


1082 


SPLANCHNOLOGY 


The  medial  borders  of  the  two  muscles  are  separated  by  a  triangular  interval, 
occupied  by  the  middle  cricothyroid  ligament. 

The  Cricoarytsenoideus  posterior  (posterior 
cricoarytenoid)  (Fig.  958)  arises  from  the  broad 
depression  on  the  corresponding  half  of  the  pos- 
terior surface  of  the  lamina  of  the  cricoid  cartil- 
age; its  fibers  run  upward  and  lateralward, 
and  converge  to  be  inserted  into  the  back  of 
the  muscular  process  of  the  arytenoid  cartil- 
age. The  uppermost  fibers  are  nearly  hori- 
zontal, the  middle  oblique,  and  the  lowest 
almost  vertical. 

The  Cricoarytaenoideus  lateralis  (lateral 
cricoarytenoid)  (Fig.  959)  is  smaller  than  the 
preceding,  and  of  an  oblong  form.  It  arises 
from  the  upper  border  of  the  arch  of  the 
cricoid  cartilage,  and,  passing  obliquely  up- 
ward and  backward,  is  inserted  into  the  front 
of  the  muscular  process  of  the  arytenoid  cartil- 
age. 

The  Arytaenoideus  (Fig.  958)  is  a  single  muscle, 
filling  up  the  posterior  concave  surfaces  of  the 
arytenoid  cartilages.  It  arises  from  the  pos- 
terior surface  and  lateral  border  of  one  ary- 
Fxo.  ^'^--^^^IJ^^^^^l^'^^Z^;-  «^--«      tenoid  cartilage,  and  is  inserted  into  the  corre- 


Tubercle  q/ 
epiglottis 

Cuneiform 
cartilage 

Corniculate 
cartilage 

}  Arytae- 
noideus 


Crycoarytae- 

noideus 
posterior 


Corniculate 
cartilages 


Articular  jacet  joi 
inferior  cornu  of 
thyroid  cartilage 


Fig.  958. — Muscles  of  larynx.     Posterior  view. 


Fig.  959. — Muscles  of  larynx.    Side  view.    Right  lamina 
of  thyroid  cartilage  removed. 


spending  parts  of  the  opposite  cartilage.    It  consists  of  oblique  and  transverse  parts. 
The  Arytaenoideus  obliquus,  the  more  superficial,  forms  two  fasciculi,  which  pass 


~ARYNX 


1083 


Fia.  960. 


-Muscles  of  the  larynx,  seen  from  above. 
(Enlarged.) 


from  the  base  of  one  cartilage  to  the  apex  of  the  opposite  one,  and  therefore 
cross  each  other  like  the  limbs  of  the  letter  X;  a  few  fibers  are  continued  around 
the  lateral  margin  of  the  cartilage,  and 
are  prolonged  into  the  aryepiglottic  fold; 
they  are  sometimes  described  as  a  sepa- 
rate muscle,  the  Aryepiglotticus.  The 
Arytaenoideus  transversus  crosses  trans- 
versely between  the  two  cartilages. 

The  Thyreoarytaenoideus  (Thyroary- 
tenoid) (Figs.  959,  960)  is  a  broad,  thin, 
muscle  which  lies  parallel  with  and  lateral 
to  the  vocal  fold,  and  supports  the  wall  of 
the  ventricle  and  its  appendix.  It  arises 
in  front  from  the  lower  half  of  the  angle 
of  the  thyroid  cartilage,  and  from  the 
middle  cricothyroid  ligament.  Its  fibers 
pass  backward  and  lateralward,  to  be  in- 
serted into  the  base  and  anterior  surface 
of  the  arytenoid  cartilage.  The  lower  and 
deeper  fibers  of  the  muscle  can  be  differ- 
entiated as  a  triangular  band  which  is 
inserted  into  the  vocal  process  of  the 
arytenoid  cartilage,  and  into  the  adjacent 
portion    of    its    anterior   surface;    it    is 

termed  the  Vocalis,  and  lies  parallel  with  the  vocal  ligament,  to  which  it  is  ad- 
herent. 

A  considerable  number  of  the  fibers  of  the  Thyreoarytsenoideus  are  prolonged 
into  the  arj'epiglottic  fold,  where  some  of  them  become  lost,  while  others  are  con- 
tinued to  the  margin  of  the  epiglottis.  They  have  received  a  distinctive  name, 
Thyreoepiglotticus,  and  are  sometimes  described  as  a  separate  muscle.  A  few  fibers 
extend  along  the  wall  of  the  ventricle  from  the  lateral  wall  of  the  arytenoid  cartilage 
to  the  side  of  the  epiglottis  and  constitute  the  Ventricularis  muscle. 

Actions. — In  considering  the  actions  of  the  muscles  of  the  larynx,  they  may  be  conveniently 
divided  into  two  groups,  vix.:  1.  Those  which  open  and  close  the  glottis.  2.  Those  which  regu- 
late the  degree  of  tension  of  the  vocal  folds. 

The  Cricoarytanoidei  posteriores  separate  the  vocal  folds,  and,  consequently,  open  the  glottis, 
by  rotating  the  arytenoid  cartilages  outward  around  a  vertical  axis  passing  through  the  crico- 
arytenoid joints;  so  that  their  vocal  processes  and  the  vocal  folds  attached  to  them  become 
widely  separated. 

The  Cricoarytoenoidei  laterales  close  the  glottis  by  rotating  the  arytenoid  cartilages  mward, 
BO  as  to  approximate  their  vocal  processes. 

The  ArytcBnoideus  approximates  the  arytenoid  cartilages,  and  thus  closes  the  opening  of 
the  glottis,  especially  at  its  back  part. 

The  Cricothyreoidei  produce  tension  and  elongation  of  the  vocal  folds  by  drawing  up  the  arch 
of  the  cricoid  cartilage  and  tilting  back  the  upper  border  of  its  lamina;  the  distance  between  the 
vocal  processes  and  the  angle  of  the  thyroid  is  thus  increased,  and  the  folds  are  consequently 
elongated. 

The  Thyreoarytcenoidei,  consisting  of  two  parts  having  different  attachments  and  different 
directions,  are  rather  comphcated  as  regards  their  action.  Their  main  use  is  to  draw  the  aryte- 
noid cartilages  forward  toward  the  thyroid,  and  thus  shorten  and  relax  the  vocal  folds.  But, 
owing  to  the  connection  of  the  deeper  portion  with  the  vocal  fold,  this  part,  if  acting  separately, 
is  supposed  to  modify  its  elasticity  and  tension,  while  the  lateral  portion  rotates  the  arytenoid 
cartilage  inward,  and  thus  narrows  the  rima  glottidis  by  bringing  the  two  vocal  folds  together. 

The  manner  in  which  the  entrance  of  the  larynx  is  closed  during  deglutition  is  referred  to 
on  page  1140. 

Mucous  Membrane. — The  mucous  membrane  of  the  larynx  is  continuous  above  with  that 
lining  the  mouth  and  pharynx,  and  is  prolonged  through  the  trachea  and  bronchi  into  the  lungs. 
It  lines  the  posterior  surface  and  the  upper  part  of  the  anterior  surface  of  the  epiglottis,  to  which 


1084  SPLANCHNOLOGY 

it  is  closely  adherent,  and  forms  the  aryepiglottic  folds  which  bound  the  entrance  of  the  larynx. 
It  lines  the  whole  of  the  cavity  of  the  larynx;  forms,  by  its  reduplication,  the  chief  part  of  the 
ventricular  fold,  and,  from  the  ventricle,  is  continued  into  the  ventricular  appendix.  It  is  then 
reflected  over  the  vocal  ligament,  where  it  is  thin,  and  very  intimately  adherent;  covers  the 
inner  surface  of  the  conus  elasticus  and  cricoid  cartilage;  and  is  ultimately  continuous  with  the 
lining  membrane  of  the  trachea.  The  anterior  surface  and  the  upper  half  of  the  posterior  surface 
of  the  epiglottis,  the  upper  part  of  the  aryepiglottic  folds  and  the  vocal  folds  are  covered  by 
stratified  squamous  epithelium;  all  the  rest  of  the  laryngeal  mucous  membrane  is  covered  by 
columnar  ciliated  cells,  but  patches  of  stratified  squamous  epithelium  are  found  in  the  mucous 
membrane  above  the  glottis. 

Glands. — The  mucous  membrane  of  the  larynx  is  fm^ished  with  numerous  mucous  secreting 
glands,  the  orifices  of  which  are  found  in  nearly  every  part;  they  are  very  plentiful  upon  the 
epiglottis,  being  lodged  in  little  pits  in  its  substance;  they  are  also  found  in  large  numbers  along 
the  margin  of  the  aryepiglottic  fold,  in  front  of  the  arytenoid  cartilages,  where  they  are  termed 
the  arytenoid  glands.  They  exist  also  in  large  numbers  in  the  ventricular  appendages.  None 
are  found  on  the  free  edges  of  the  vocal  folds. 

Vessels  and  Nerves. — The  chief  arteries  of  the  larynx  are  the  laryngeal  branches  derived 
from  the  superior  and  inferior  thyroid.  The  veins  accompany  the  arteries;  those  accompanying 
the  superior  laryngeal  artery  join  the  superior  thyroid  vein  which  opens  into  the  internal  jugular 
vein;  while  those  accompanying  the  inferior  laryngeal  artery  join  the  inferior  thyroid  vein 
which  opens  into  the  innominate  vein.  The  lymphatic  vessels  consist  of  two  sets,  superior 
and  inferior.  The  former  accompany  the  superior  laryngeal  artery  and  pierce  the  hyothyroid 
membrane,  to  end  in  the  glands  situated  near  the  bifurcation  of  the  common  carotid  artery.  Of 
the  latter,  some  pass  through  the  middle  cricothyroid  ligament  and  open  into  a  gland  lying  in 
front  of  that  ligament  or  in  front  of  the  upper  part  of  the  trachea,  while  others  pass  to  the  deep 
cervical  glands  and  to  the  glands  accompanying  the  inferior  thyroid  artery.  The  nerves  are 
derived  from  the  internal  and  external  branches  of  the  superior  laryngeal  nerve,  from  the 
recurrent  nerve,  and  from  the  sympathetic.  The  internal  laryngeal  branch  is  almost  entirely 
sensory,  but  some  motor  filaments  are  said  to  be  carried  by  it  to  the  Arytajnoideus.  It  enters 
the  larynx  by  piercing  the  posterior  part  of  the  hyothyroid  membrane  above  the  superior 
laryngeal  vessels,  and  divides  into  a  branch  which  is  distributed  to  both  surfaces  of  the  epi- 
glottis, a  second  to  the  aryepiglottic  fold,  and  a  third,  the  largest,  which  suppUes  the  mucous 
membrane  over  the  back  of  the  larynx  and  communicates  with  the  recurrent  nerve.  The  external 
laryngeal  branch  supplies  the  Cricothyreoideus.  The  recurrent  nerve  passes  upward  beneath 
the  lower  border  of  the  Constrictor  pharyngis  inferior  immediately  behind  the  cricothyroid  joint. 
It  supphes  all  the  muscles  of  the  larynx  except  the  Cricothyreoideus,  and  perhaps  a  part  of  the 
Arytsenoideus.  The  sensory  branches  of  the  laryngeal  nerves  form  subepithelial  plexuses,  from 
which  fibers  pass  to  end  between  the  cells  covering  the  mucous  membrane. 

Over  the  posterior  surface  of  the  epiglottis,  in  the  aryepiglottic  folds,  and  less  regularly 
some  other  parts,  taste-buds,  similar  to  those  in  the  tongue,  are  found. 


I 


y  in  fl 

mi 


THE  TRACHEA  AND  BRONCHI  (Fig.  961). 

The  trachea  or  windpipe  is  a  cartilaginous  and  membranous  tube,  extending 
from  the  lower  part  of  the  larynx,  on  a  level  with  the  sixth  cervical  vertebra,  to  the 
upper  border  of  the  fifth  thoracic  vertebra,  where  it  divides  into  the  two  bronchi, 
one  for  each  lung.  The  trachea  is  nearly  but  not  quite  cylindrical,  being  flattened 
posteriorly;  it  measures  about  11  cm.  in  length;  its  diameter,  from  side  to  side, 
is  from  2  to  2.5  cm.,  being  always  greater  in  the  male  than  in  the  female.  In 
the  child  the  trachea  is  smaller,  more  deeply  placed,  and  more  movable  than 
in  the  adult. 

Relations. — The  anterior  surface  of  the  trachea  is  convex,  and  covered,  in  the  neck,  from 
above  downward,  by  the  isthmus  of  the  thyroid  gland,  the  inferior  thyroid  veins,  the  arteria 
thyroidea  ima  (when  that  vessel  exists),  the  Sternothyreoideus  and  Sternohyoideus  muscles, 
the  cervical  fascia,  and,  more  superficially,  by  the  anastomosing  branches  between  the  anterior 
jugular  veins;  in  the  tihorax,  it  is  covered  from  before  backward  by  the  manubrium  sterni, 
the  remains  of  the  thymus,  the  left  innominate  vein,  the  aortic  arch,  the  innominate  and  left 
common  carotid  arteries,  and  the  deep  cardiac  plexus.  Posteriorly  it  is  in  contact  with  the 
esophagus.  Laterally,  in  the  neck,  it  is  in  relation  with  the  common  carotid  arteries,  the  right 
and  left  lobes  of  the  thyroid  gland,  the  inferior  thyroid  arteries,  and  the  recurrent  nerves;  in 
the  thorax,  it  lies  in  the  superior  mediastinum,  and  is  in  relation  on  the  right  side  with  the 
pleura  and  right  vagus,  and  near  the  root  of  the  neck  with  the  innominate  artery;  on  its  left  side 
are  the  left  recurrent  nerve,  the  aortic  arch,  and  the  left  common  carotid  and  subclavian  arteries. 


THE  TRACHEA  AND  BRONCHI 


1085 


The  Right  Bronchus  (bronchus  dexter),  wider,  shorter,  and  more  vertical  in  direc- 
tion than  the  left,  is  about  2.5  cm.  long,  and  enters  the  right  lung  nearly  opposite 
the  fifth  thoracic  vertebra.  The  azygos  vein  arches  over  it  from  behind;  and  the 
right  pulmonary  artery  lies  at  first  below  and  then  in  front  of  it.  About  2  cm. 
from  its  commencement  it  gives  off  a  branch  to  the  upper  lobe  of  the  right  lung. 
This  is  termed  the  eparterial  branch  of  the  bronchus,  because  it  arises  above  the  right 
pulmonary  artery.  The  bronchus  now  passes  below  the  artery,  and  is  known  as  the 
hyparterial  branch;  it  divides  into  two  branches  for  the  middle  and  lower  lobes. 


Superior 
Comu. 


Inferior 
Qnmu. 


Fig.  961. — Front  view  of  cartilages  of  larynx,  trachea,  and  bronchi. 


The  Left  Bronchus  (bronchus  sinister)  is  smaller  in  caliber  but  longer  than  the 
right,  being  nearly  5  cm.  long.  It  enters  the  root  of  the  left  lung  opposite  the  sixth 
thoracic  vertebra.  It  passes  beneath  the  aortic  arch,  crosses  in  front  of  the  esoph- 
agus, the  thoracic  duct,  and  the  descending  aorta,  and  has  the  left  pulmonary 
artery  lying  at  first  above,  and  then  in  front  of  it.  The  left  bronchus  has  no 
eparterial  branch,  and  therefore  it  has  been  supposed  by  some  that  there  is  no 
upper  lobe  to  the  left  lung,  but  that  the  so-called  upper  lobe  corresponds  to  the 
middle  lobe  of  the  right  lung. 


1086 


SPLANCHNOLOGY 


The  further  subdivisions  of  the  bronchi  will  be  considered  with  the  anatomy  of 
the  lung.  Jl 

If  a  transverse  section  be  made  across  the  trachea  a  short  distance  above  itsiB 
point  of  bifurcation,  and  a  bird's-eye  view  taken  of  its  interior  (Fig.  963),  the  septum 


Fig.  962. — Bronchi  and  bronchioles.    The  lungs  have  been  widely  separated  and  tissue  cut  away  to  expose  the  air-tubes. 

(Testut.) 

placed  at  the  bottom  of  the  trachea  and  separating  the  two  bronchi  will  be  seen  | 
to  occupy  the  left  of  the  median  line,  and  the  right  bronchus  appears  to  be  a  more 
direct  continuation  of  the  trachea  than  the  left,  so  that  any  solid  body  dropping 
into  the  trachea  would  naturally  be  directed  toward  the  right  bronchus.    This 

tendency  is  aided  by  the  larger  diameter 
of  the  right  tube  as  compared  with  its 
fellow.    This  fact  serves  to  explain  why 
a  foreign  body  in  the  trachea  more  fre-  ^ 
quently  falls  into  the  right  bronchus.^        I 

Structure  (Fig.  984) — The  trachea  and  extra- 
pulmonary bronchi  are  composed  of  imperfect 
rings  of  hyaline  cartilage,  fibrous  tissue,  mus- 
cular fibers,  mucous  membrane,  and  glands. 

The  cartilages  of  the  trachea  vary  from  sixteen 
to  twenty  in  number:  each  forms  an  imperfect 
ring,  which  occupies  the  anterior  two-thirds  or 
so  of  the  circumference  of  the  trachea,  being 
deficient  behind,  where  the  tube  is  completed  by  fibrous  tissue  and  unstriped  muscular  fibers. 
The  cartilages  are  placed  horizontally  above  each  other,  separated  by  narrow  intervals.  They 
measure  about  4  mm.  in  depth  and  1  mm.  in  thickness.  Their  outer  surfaces  are  flattened  in 
a  vertical  direction,  but  the  internal  are  convex,  the  cartilages  being  thicker  in  the  middle  than 

'  Reigel  asserts  that  the  entry  of  a  foreign  body  into  the  le/t  bronchus  is  by  no  means  so  infrequent  as  is  generally 
supposed.     See  also  Med.-Chi.  Trans.,  Ixxi,  121. 


Fia._  963.— Transverse  section  of  the  trachea,  just 
above  its  bifurcation,  with  a  bird's-eye  view  of  the 
interior. 


THE  PLEURA 


1087 


Stratified 
ciliated 
epitheliuTn 
■Longitudinal 
elastic  fibers 


Submucous 
layer 

.  ^  Mucous 


at  the  margins.  Two  or  more  of  the  cartilages  often  unite,  partially  or  completely,  and  they 
are  sometimes  bifurcated  at  their  extremities.  They  are  highly  elastic,  but  may  become  calcified 
in  advanced  life.  In  the  right  bronchus  the  cartilages  vary  in  number  from  six  to  eight;  in  the 
left,  from  nine  to  twelve.  They  are  shorter  and  narrower  than  those  of  the  trachea,  but  have 
the  same  shape  and  arrangement.  The  peculiar  tracheal  cartilages  are  the  first  and  the  last 
(Fig.  961). 

The  first  cartilage  is  broader  than  the  rest,  and  often  divided  at  one  end;  it  is  connected  by 
the  cricotracheal  ligament  with  the  lower  border  of  the  cricoid  cartilage,  with  which,  or  with 
the  succeeding  cartilage,  it  is  sometimes  blended. 

The  last  cartilage  is  thick  and  broad  in  the  middle,  in  consequence  of  its  lower  border  being 
prolonged  into  a  triangular  hook-shaped  process,  which  curves  downward  and  backward  between 
the  two  bronchi.  It  ends  on  each  side  in 
an  imperfect  ring,  which  encloses  the  com- 
mencement of  the  bronchus.  The  cartilage 
above  the  last  is  somewhat  broader  than 
the  others  at  its  center. 

The  Fibrous  Membrane. — The  cartilages 
are  enclosed  in  an  elastic  fibrous  mem- 
brane, which  consists  of  two  layers;  one, 
the  thicker,  passing  over  the  outer  surface 
of  the  ring,  the  other  over  the  inner  sur- 
face: at  the  upper  and  lower  margins  of 
the  cartilages  the  two  layers  blend  together 
to  form  a  single  membrane,  which  connects 
the  rings  one  with  another.  They  are  thus 
invested  by  the  membrane.  In  the  space 
behind,  between  the  ends  of  the  rings,  the 
membrane  forms  a  single  layer. 

The  muscular  tissue  consists  of  two 
layers  of  non-striated  muscle,  longitudinal 
and  transverse.  The  longitudinal  fibers 
are  external,  and  consist  of  a  few  scattered 
bundles.  The  transverse  fibers  (TracheaUs 
muscle)  are  internal,  and  form  a  thin  layer 
which  extends  transversely  between  the 
ends  of  the  cartilages. 

Mucous  Membrane. — The  mucous  mem- 
brane is  continuous  above  with  that  of  the 
larynx,  and  below  with  that  of  the  bron- 
chi. It  consists  of  areolar  and  lymphoid 
tissue,  and  presents  a  well-marked  base- 
ment membrane,  supporting  a  stratified 
epithehum,  the  surface  layer  of  which  is 
columnar  and  ciliated,  while  the  deeper 
layers  are  composed  of  oval  or  rounded 
cells.  Beneath  the  basement  membrane 
there   is   a  distinct   layer  of  longitudinal 

elastic  fibers  with  a  small  amount  of  intervening  areolar  tissue.  The  submucous  layer  is  com- 
posed of  a  loose  mesh-work  of  connective  tissue,  containing  large  bloodvessels,  nerves,  and 
mucous  glands;  the  ducts  of  the  latter  pierce  the  overlying  layers  and  open  on  the  surface 
(Fig.  964). 

Vessels  and  Nerves. — The  trachea  is  supplied  with  blood  by  the  inferior  thyroid  arteries. 
The  veins  end  in  the  thyroid  venous  plexus.  The  nerves  are  derived  from  the  vagvis  and  the 
recurrent  nerves,  and  from  the  sjnnpathetic;  they  are  distributed  to  the  Trachealis  muscles  and 
between  the  epithelial  cells. 


Fibrous 
membrane 


Hyaline 
cartilage 


Fibrous 
membrane 


Fig.  964. — ^Transverse  section  of  trachea. 


II 


THE   PLEURA. 

Each  lung  is  invested  by  an  exceedingly  delicate  serous  membrane,  the  pleura, 
which  is  arranged  in  the  form  of  a  closed  invaginated  sac.  A  portion  of  the  serous 
membrane  covers  the  surface  of  the  lung  and  dips  into  the  fissures  between  its 
lobes;  it  is  called  the  pulmonary  pleura.  The  rest  of  the  membrane  lines  the  inner 
surface  of  the  chest  wall,  covers  the  diaphragm,  and  is  reflected  over  the  structures 
occupying  the  middle  of  the  thorax;  this  portion  is  termed  the  parietal  pleura.  The 
two  layers  are  continuous  with  one  another  around  and  below  the  root  of  the  lung; 


fCHNOLOGY 

in  health  they  are  in  actual  contact  with  one  another,  but  the  potential  space] 
between  them  is  known  as  the  pleural  cavity.  When  the  lung  collapses  or  when 
air  or  fluid  collects  between  the  two  layers  the  cavity  becomes  apparent.  The  right 
and  left  pleural  sacs  are  entirely  separate  from  one  another;  between  them  are  all 
the  thoracic  viscera  except  the  lungs,  and  they  only  touch  each  other  for  a  short 
distance  in  front;  opposite  the  second  and  third  pieces  of  the  sternum  the  interval 
between  the  two  sacs  is  termed  the  mediastinum. 

Different  portions  of  the  parietal  pleura  have  received  special  names  which 
indicate  their  position:  thus,  that  portion  which  lines  the  inner  surfaces  of  the 
ribs  and  Intercostales  is  the  costal  pleura;  that  clothing  the  convex  surface  of  the 
diaphragm  is  the  diaphragmatic  pleura;  that  which  rises  into  the  neck,  over  the 
summit  of  the  lung,  is  the  cupula  of  the  pleura  (cervical  fleura) ;  and  that  which  is 
applied  to  the  other  thoracic  viscera  is  the  mediastinal  pleura. 


I 


Lower  margin  of  pleura 


Fig.  965. — Front  view  of  thorax,  showing  the  relations  of  the  pleurse  and  lungs  to  the  chest  wall. 

Pletira  in  blue ;  lungs  in  purple.  ^ 

Reflections  of  the  Pleura  (Figs.  965,  966). — Commencing  at  the  sternum,  tfie 
pleura  passes  lateralward,  lines  the  inner  surfaces  of  the  costal  cartilages,  ribs, 
and  Intercostales,  and  at  the  back  part  of  the  thorax  passes  over  the  sympathetic 
trunk  and  its  branches,  and  is  reflected  upon  the  sides  of  the  bodies  of  the  verte- 
brae, where  it  is  separated  by  a  narrow  interval,  the  posterior  mediastinum,  from 
the  opposite  pleura.  From  the  vertebral  column  the  pleura  passes  to  the  side  of  the 
pericardium,  which  it  covers  to  a  slight  extent;  it  then  covers  the  back  part  of  the 
root  of  the  lung,  from  the  lower  border  of  which  a  triangular  sheet  descends  verti- 
cally toward  the  diaphragm.  This  sheet  is  the  posterior  layer  of  a  wide  fold, 
known  as  the  pulmonary  ligament.    From  the  back  of  the  lung  root,  the  pleura 


THE  PLEURM 


1089 


Trachea 

R.  subclavian  art. 
R.  innominate  vein 


may  be  traced  over  the  costal  surface  of  the  lung,  the  apex  and  Fase,  and  also  over 
the  sides  of  the  fissures  between  the  lobes,  on  to  its  mediastinal  surface  and  the  front 
part  of  its  root.  It  is  continued  from  the  lower  margin  of  the  root  as  the  anterior 
layer  of  the  pulmonary  ligament,  and  from  this  it  is  reflected  on  to  the  pericardium 
(pericardial  pleura),  and  from  it  to  the  back  of  the  sternum.  Above  the  level  of 
the  root  of  the  lung,  however,  the  mediastinal  pleura  passes  uninterruptedly  from 
the  vertebral  column  to  the  sternum  over  the  structures  in  the  superior  medias- 
tinum. Below,  it  covers  the  upper  surface  of  the  diaphragm  and  extends,  in 
front,- as  low  as  the  costal  cartilage  of  the  seventh  rib;  at  the  side  of  the  chest, 
to  the  lower  border  of  the  tenth  rib  on  the  left  side  and  to  the  upper  border  of  the 
same  rib  on  the  right  side;  and  behind,  it  reaches  as  low  as  the  twelfth  rib,  and  some- 
times even  to  the  transverse  process 
of  the  first  lumbar  vertebra.  Above, 
its  cupula  projects  through  the 
superior  opening  of  the  thorax  into 
the  neck,  extending  from  2.5  to  5 
cm.  above  the  sternal  end  of  the 
first  rib;  this  portion  of  the  sac  is 
strengthened  by  a  dome-like  expan- 
sion of  fascia  (Sibson's  fascia),  at- 
tached in  front  to  the  inner  border 
of  the  first  rib,  and  behind  to  the 
anterior  border  of  the  transverse 
process  of  the  seventh  cervical 
vertebra.  This  is  covered  and 
strengthened  by  a  few  spreading 
muscular  fibers  derived  from  the 
Scaleni. 

In  the  front  of  the  chest,  where 
the  parietal  pleura  is  reflected  back- 
ward to  the  pericardium,  the  two 
pleural  sacs  are  in  contact  for  a 
short  distance.  At  the  upper  part 
of  the  chest,  behind  the  manubrium, 
they  are  separated  by  an  angular 
interval ;  the  line  of  reflection  being 
represented  by  a  line  drawn  from 
the  sternoclavicular  articulation  to 
the  mid-point  of  the  junction  of 
the  manubrium  with  the  body  of  the 
sternum.  From  this  point  the  two 
pleurae  descend  in  close  contact  to 

the  level  of  the  fourth  costal  cartilages,  and  the  line  of  reflection  on  the  right  side 
is  continued  downward  in  nearly  a  straight  line  to  the  xiphoid  process,  and  then 
turns  lateralward,  while  on  the  left  side  the  line  of  reflection  diverges  lateralward 
and  is  continued  downward,  close  to  the  left  border  of  the  sternum,  as  far  as  the 
sixth  costal  cartilage.  The  inferior  limit  of  the  pleura  is  on  a  considerably  lower 
level  than  the  corresponding  limit  of  the  lung,  but  does  not  extend  to  the  attach- 
ment of  the  diaphragm,  so  that  below  the  line  of  reflection  of  the  pleura  from  the 
chest  wall  on  to  the  diaphragm  the  latter  is  in  direct  contact  with  the  rib  cartilages 
and  the  Intercostales  interni.  Moreover,  in  ordinary  inspiration  the  thin  inferior 
margin  of  the  lung  does  not  extend  as  low  as  the  line  of  the  pleural  reflection,  with 

I        the  result  that  the  costal  and  diaphragmatic  pleurae  are  here  in  contact,  the  inter- 
■    vening  narrow  slit  being  termed  the  phrenicocostal  sinus.     A  similar  condition 


Lower  margin 

of  pleura 

Lower  margin  of  lung 


Fig.  966. — Lateral  view  of  thorax,  showing  the  relations  of 
the  pleurae  and  lungs  to  the  chest  wall.  Pleura  in  blue;  lungs  in 
purple. 


1090  SPLANCHNOLOGY 

exists  behind  the  sternum  and  rib  cartilages,  where  the  anterior  thin  margin  of 
the  lung  falls  short  of  the  line  of  pleural  reflection,  and  where  the  slit-like  cavity'' 
between  the  two  layers  of  pleura  forms  what  is  called  the  costomediastinal  sinus. 

The  line  along  which  the  right  pleura  is  reflected  from  the  chest-wall  to  the 
diaphragm  starts  in  front,  immediately  below  the  seventh  sternocostal  joint,  and  i^ 
runs  downward  and  backward  behind  the  seventh  costal  cartilage  so  as  to  cfosmB 
the  tenth  rib  in  the  mid-axillary  line,  from  which  it  is  prolonged  to  the  spinous 
process  of  the  twelfth  thoracic  vertebra.  The  reflection  of  the  left  pleura  follows 
at  first  the  ascending  part  of  the  sixth  costal  cartilage,  and  in  the  rest  of  its  course 
is  slightly  lower  than  that  of  the  right  side.  ■_ 

The  free  surface  of  the  pleura  is  smooth,  polished,  and  moistened  by  a  serous^J 
fluid;  its  attached  surface  is  intimately  adherent  to  the  lung,  and  to  the  pulmonary 
vessels  as  they  emerge  from  the  pericardium;   it  is  also  adherent  to  the  upper  sur- 
face of  the  diaphragm :  throughout  the  rest  of  its  extent  it  is  easily  separable  from 
the  adjacent  parts. 

The  right  pleural  sac  is  shorter,  wider,  and  reaches  higher  in  the  neck  than  the 
left. 

Pulmonary  Ligament  (ligamentum  pulmonale;  ligamentum  latum  pulmonis). — 
From  the  above  description  it  will  be  seen  that  the  root  of  the  lung  is  covered  in 
front,  above,  and  behind  by  pleura,  and  that  at  its  lower  border  the  investing 
layers  come  into  contact.  Here  they  form  a  sort  of  mesenteric  fold,  the  pulmonary 
ligament,  which  extends  between  the  lower  part  of  the  mediastinal  surface  of  the 
lung  and  the  pericardium.  Just  above  the  diaphragm  the  ligament  ends  in  a  free 
falciform  border.    It  serves  to  retain  the  lower  part  of  the  lung  in  position. 

Structure  of  Pleura. — Like  other  serous  membranes,  the  pleura  is  covered  by  a  single  layer 
of  flattened,  nucleated  cells,  united  at  their  edges  by  cement  substance.  These  cells  are  modified 
connective-tissue  corpuscles,  and  rest  on  a  basement  membrane.  Beneath  the  basement  mem- 
brane there  are  net-works  of  yellow  elastic  and  white  fibers,  imbedded  in  ground  substance  which 
also  contains  connective-tissue  cells.  Bloodvessels,  lymphatics,  and  nerves  are  distributed  in 
the  substance  of  the  pleura. 

Vessels  and  Nerves. — The  arteries  of  the  pleura  are  derived  from  the  intercostal,  internal 
mammary,  musculophrenic,  thymic,  pericardiac,  and  bronchial  vessels.  The  veins  correspond 
to  the  arteries.  The  Ijrmphatics  are  described  on  page  719.  The  nerves  are  derived  from  the 
phrenic  and  s3Tnpathetic  (Luschka).  Kolliker  states  that  nerves  accompany  the  ramifications 
of  the  bronchial  arteries  in  the  pulmonary  pleura. 

THE  MEDIASTINUM    (INTERPLEURAL   SPACE).  " 

The  mediastinum  lies  between  the  right  and  left  pleurae  in  and  near  the  median 
sagittal  plane  of  the  chest.  It  extends  from  the  sternum  in  front  to  the  vertebral 
column  behind,  and  contains  all  the  thoracic  viscera  excepting  the  lungs.  It  may 
be  divided  for  purposes  of  description  into  two  parts:  an  upper  portion,  above  the 
upper  level  of  the  pericardium,  which  is  named  the  superior  mediastinum;  and  a 
lower  portion,  below  the  upper  level  of  the  pericardium.  This  lower  portion  is 
again  subdivided  into  three  parts,  viz.,  that  in  front  of  the  pericardium,  the 
anterior  mediastinum;  that  containing  the  pericardium  and  its  contents,  the  middle  ' 
mediastinum;  and  that  behind  the  pericardium,  the  posterior  mediastinum. 

The  Superior  Mediastinum  (P^ig.  967)  is  that  portion  of  the  interpleural  space 
which  lies  between  the  manubrium  sterni  in  front,  and  the  upper  thoracic  verte- 
brae behind.  It  is  bounded  below  by  a  slightly  oblique  plane  passing  backward 
from  the  junction  of  the  manubrium  and  body  of  the  sternum  to  the  lower  part 
of  the  body  of  the  fourth  thoracic  vertebra,  and  laterally  by  the  pleurae.  It  con- 
tains the  origins  of  the  Sternohyoidei  and  Sternothyreoidei  and  the  lower  ends  of 
the  Longi  colli;  the  aortic  arch;  the  innominate  artery  and  the  thoracic  portions 
of  the  left  common  carotid  and  the  left  subclavian  arteries;  the  innominate  veins 


THE  LUNGS 


1093 


I 


into  its  two  branches,  the  right  and  left  pulmonary  veins,  the  phrenic  nerves, 
and  some  bronchial  lymph  glands. 

The  Posterior  Mediastinum  (Figs.  968,  969)  is  an  irregular  triangular  space 
running  parallel  with  the  vertebral  column;  it  is  bounded  in  front  by  the  peri- 
cardium above,  and  by  the  posterior  surface  of  the  diaphragm  below,  behind  by 
the  vertebral  column  from  the  lower  border  of  the  fourth  to  the  twelfth  thoracic 
vertebra,  and  on  either  side  by  the  mediastinal  pleura.  It  contains  the  thoracic 
part  of  the  descending  aorta,  the  azygos  and  the  two  hemiazygos  veins,  the  vagus 
and  splanchnic  nerves,  the  esophagus,  the  thoracic  duct,  and  some  lymph  glands. 

THE   LUNGS    (PULMONES) . 


The  lungs  are  the  essential  organs  of  respiration;  they  are  two  in  number,  placed 
one  on  either  side  within  the  thorax,  and  separated  from  each  other  by  the  heart 
and  other  contents  of  the  mediastinum  (Fig.  970).  The  substance  of  the  lung  is 
of  a  light,  porous,  spongy  texture;  it  floats  in  water,  and  crepitates  when  handled, 
owing  to  the  presence  of  air  in  the  alveoli ;  it  is  also  highly  elastic ;  hence  the  retracted 
state  of  these  organs  when  they  are  removed  from  the  closed  cavity  of  the  thorax. 
,  The  surface  is  smooth,  shining,  and  marked  out  into  numerous  polyhedral  areas, 
indicating  the  lobules  of  the  organ:  each  of  these  areas  is  crossed  by  numerous 
lighter  lines. 


Cut  edge  of  pericardium 


Front  view  of  heart  and  lungs. 


I 


At  birth  the  lungs  are  pinkish  white  in  color;  in  adult  life  the  color  is  a  dark 
slaty  gray,  mottled  in  patches;  and  as  age  advances,  this  mottling  assumes  a  black 
color.  The  coloring  matter  consists  of  granules  of  a  carbonaceous  substance 
deposited  in  the  areolar  tissue  near  the  surface  of  the  organ.    It  increases  in  quan- 


1094 


SPLANCHNOLOGY 


tity  as  age  advances,  and  is  more  abundant  in  males  than  in  females.    As  a  rule, 
the  posterior  border  of  the  lung  is  darker  than  the  anterior. 

The  right  lung  usually  weighs  about  625  gm.,  the  left  567  gm.,  but  much  varia- 
tion is  met  with  according  to  the  amount  of  blood  or  serous  fluid  they  may  contain. 
The  lungs  are  heavier  in  the  male  than  in  the  female,  their  proportion  to  the  body 
being,  in  the  former,  as  1  to  37,  in  the  latter  as  1  to  43. 

Each  lung  is  conical  in  shape,  and  presents  for  examination  an  apex,  a  base, 
three  borders,  and  two  surfaces. 

The  apex  (apex  pulmonis)  is  rounded,  and  extends  into  the  root  of  the  neck, 
reaching  from  2.5  to  4  cm.  above  the  level  of  the  sternal  end  of  the  first  rib.  A 
sulcus  produced  by  the  subclavian  artery  as  it  curves  in  front  of  the  pleura  runs 
upward  and  lateralward  immediately  below  the  apex. 

The  base  (basis  pulmonis)  is  broad,  concave,  and  rests  upon  the  convex  surface 
of  the  diaphragm,  which  separates  the  right  lung  from  the  right  lobe  of  the  liver, 
and  the  left  lung  from  the  left  lobe  of  the  liver,  the  stomach,  and  the  spleen.  Since 
the  diaphragm  extends  higher  on  the  right  than  on  the  left  side,  the  concavity 
on  the  base  of  the  right  lung  is  deeper  than  that  on  the  left.  Laterally  and  behind, 
the  base  is  bounded  by  a  thin,  sharp  margin  which  projects  for  some  distance 
into  the  phrenicocostal  sinus  of  the  pleura,  between  the  lower  ribs  and  the  costal  ( 
attachment  of  the  diaphragm.  The  base  of  the  lung  descends  during  inspiration 
and  ascends  during  expiration. 


I 
I 


entrance  of 
vena  azygos 
branch  of  pul- 
'monary  artery 


Fig.  971. — Pulmonary  vessels,  seen  in  a  dorsal  view  of  the  heart  and  lungs.  The  lunga  have  been  pulled  away 
from  the  median  line,  and  a  part  of  the  right  lung  has  been  cut  away  to  display  the  air-ducts  and  bloodvessela. 
(Testut.) 

Surfaces. — The  costal  surface  (fades  costalis;  external  or  thoracic  surface)  is 
smooth,  convex,  of  considerable  extent,  and  corresponds  to  the  form  of  the  cavity 
of  the  chest,  being  deeper  behind  than  in  front.  It  is  in  contact  with  the  costal 
pleura,  and  presents,  in  specimens  which  have  been  hardened  in  situ,  slight  grooves 
corresponding  with  the  overlying  ribs. 


THE  LUNGS 


"1095 


The  mediastinal  surface  (fades  mediastinalis ;  inner  surface)  is  in  contact  with 
the  mediastinal  pleura.  It  presents  a  deep  concavity,  the  cardiac  impression, 
which  accommodates  the  pericardium;  this  is  larger  and  deeper  on  the  left  than 
on  the  right  lung,  on  account  of  the  heart  projecting  farther  to  the  left  than  to  the 
right  side  of  the  median  plane.  Above  and  behind  this  concavity  is  a  triangular 
depression  named  the  hilum,  where  the  structures  which  form  the  root  of  the  lung 
enter  and  leave  the  viscus.  These  structures  are  invested  by  pleura,  which,  below 
the  hilus  and  behind  the  pericardial  impression,  forms  the  pulmonary  ligament. 
On  the  right  lung  (Fig.  972),  immediately  above  the  hilus,  is  an  arched  furrow 
which  accommodates  the  azygos  vein;  while  running  upward,  and  then  arching 
lateralward  some  little  distance  below  the  apex,  is  a  wide  groove  for  the  superior 
vena  cava  and  right  innominate  vein ;  behind  this,  and  nearer  the  apex,  is  a  furrow 


Groove  j or 
innonuTutte  artery 


Groove  for 
sup,  vena  cava 


Groove  for  azygos 
vein 


Pulmonary         /  ,)* , 
artery 


Eparterial 
bronchus 


Hyparterial 

bronchus 
Pulmonary 


Groove  for 
esophagus 


Pulmonary 
ligament 


Fia.  972. — Mediastinal  surface  of  right  lung. 


I 


for  the  innominate  artery.  Behind  the  hilus  and  the  attachment  of  the  pulmonary 
ligament  is  a  vertical  groove  for  the  esophagus;  this  groove  becomes  less  distinct 
below,  owing  to  the  inclination  of  the  lower  part  of  the  esophagus  to  the  left  of 
the  middle  line.  In  front  and  to  the  right  of  the  lower  part  of  the  esophageal 
groove  is  a  deep  concavity  for  the  extrapericardiac  portion  of  the  thoracic  part 
of  the  inferior  vena  cava.  On  the  left  lung  (Fig.  973),  immediately  above  the  hilus, 
is  a  well-marked  curved  furrow  produced  by  the  aortic  arch,  and  running  upward 
from  this  toward  the  apex  is  a  groove  accommodating  the  left  subclavian  artery; 
a  slight  impression  in  front  of  the  latter  and  close  to  the  margin  of  the  lung  lodges 
the  left  innominate  vein.  Behind  the  hilus  and  pulmonary  ligament  is  a  vertical 
furrow  produced  by  the  descending  aorta,  and  in  front  of  this,  near  the  base  of 
the  lung,  the  lower  part  of  the  esophagus  causes  a  shallow  impression. 


1096 


SPLANCHNOLOGY 


Borders. — The  inferior  border  {margo  inferior)  is  thin  and  sharp  where  it  sepa- 
rates the  base  from  the  costal  surface  and  extends  into  the  phrenicocostal  sinus; 
medially  where  it  divides  the  base  from  the  mediastinal  surface  it  is  blunt  and 
rounded. 

The  posterior  border  {margo  posterior)  is  broad  and  rounded,  and  is  received  into 
the  deep  concavity  on  either  side  of  the  vertebral  column.  It  is  much  longer 
than  the  anterior  border,  and  projects,  below,  into  the  phrenicocostal  sinus. 

The  anterior  border  {margo  anterior)  is  thin  and  sharp,  and  overlaps  the  front 
of  the  pericardium.  The  anterior  border  of  the  right  lung  is  almost  vertical,  and 
projects  into  the  costomediastinal  sinus;  that  of  the  left  presents,  below,  an  angular 
notch,  the  cardiac  notch,  in  which  the  pericardium  is  exposed.  Opposite  this 
notch  the  anterior  margin  of  the  left  lung  is  situated  some  little  distance  lateral 
to  the  line  of  reflection  of  the  corresponding  part  of  the  pleura. 

Groove  for  left  subclavian  artery 
Groove  for  left  innominate  vein 


Bronchris 


Posterior 
border 


Ptdmonary 
ligament 


Pulmonary 
artery 

Pulmonary 
veins 


Cardiac  notch 


Fig.  973. — Mediastinal  surface  of  left  lung. 

Fissures  and  Lobes  of  the  Lungs. — The  left  lung  is  divided  into  two  lobes, 
an  upper  and  a  lower,  by  an  interlobular  fissure,  which  extends  from  the  costal 
to  the  mediastinal  surface  of  the  lung  both  above  and  below  the  hilus.  As  seen 
on  the  surface,  this  fissure  begins  on  the  mediastinal  surface  of  the  lung  at  the 
upper  and  posterior  part  of  the  hilus,  and  runs  backward  and  upward  to  the  pos- 
terior border,  which  it  crosses  at  a  point  about  6  cm.  below  the  apex.  It  then 
extends  downward  and  forward  over  the  costal  surface,  and  reaches  the  lower 
border  a  little  behind  its  anterior  extremity,  and  its  further  course  can  be  followed 
upward  and  backward  across  the  mediastinal  surface  as  far  as  the  lower  part  of 
the  hilus.  The  superior  lobe  lies  above  and  in  front  of  this  fissure,  and  includes  the 
apex,  the  anterior  border,  and  a  considerable  part  of  the  costal  surface  and  the 
greater  part  of  the  mediastinal  surface  of  the  lung.    The  inferior  lobe,  the  larger 


THE  LUNGS  1097 

of  the  two,  is  situated  below  and  behind  the  fissure,  and  comprises  almost  the 
whole  of  the  base,  a  large  portion  of  the  costal  surface,  and  the  greater  part  of 
the  posterior  border. 

The  right  lung  is  divided  into  three  lobes,  superior,  middle,  and  inferior,  by 
two  interlobular  fissures.  One  of  these  separates  the  inferior  from  the  middle 
and  superior  lobes,  and  corresponds  closely  with  the  fissure  in  the  left  lung.  Its 
direction  is,  however,  more  vertical,  and  it  cuts  the  lower  border  about  7.5  cm. 
behind  its  anterior  extremity.  The  other  fissure  separates  the  superior  from  the 
middle  lobe.  It  begins  in  the  previous  fissure  near  the  posterior  border  of  the  lung, 
and,  running  horizontally  forward,  cuts  the  anterior  border  on  a  level  with  the 
sternal  end  of  the  fourth  costal  cartilage;  on  the  mediastinal  surface  it  may  be 
traced  backward  to  the  hilus.  The  middle  lobe,  the  smallest  lobe  of  the  right 
lung,  is  wedge-shaped,  and  includes  the  lower  part  of  the  anterior  border  and  the 
anterior  part  of  the  base  of  the  lung. 

The  right  lung,  although  shorter  by  2.5  cm.  than  the  left,  in  consequence  of  the 
diaphragm  rising  higher  on  the  right  side  to  accommodate  the  liver,  is  broader, 
owing  to  the  inclination  of  the  heart  to  the  left  side;  its  total  capacity  is  greater 
and  it  weighs  more  than  the  left  lung. 

The  Root  of  the  Lung  {radix  pulmonis) . — A  little  above  the  middle  of  the  medias- 
tinal surface  of  each  lung,  and  nearer  its  posterior  than  its  anterior  border,  is  its 
root,  by  which  the  lung  is  connected  to  the  heart  and  the  trachea.  The  root  is 
formed  by  the  bronchus,  the  pulmonary  artery,  the  pulmonary  veins,  the  bronchial 
arteries  and  veins,  the  pulmonary  plexuses  of  nerves,  lymphatic  vessels,  bronchial 
lymph  glands,  and  areolar  tissue,  all  of  which  are  enclosed  by  a  reflection  of  the 
pleura.  The  root  of  the  right  lung  lies  behind  the  superior  vena  cava  and  part 
of  the  right  atrium,  and  below  the  azygos  vein.  That  of  the  left  lung  passes 
beneath  the  aortic  arch  and  in  front  of  the  descending  aorta;  the  phrenic  nerve, 
the  pericardiacophrenic  artery  and  vein,  and  the  anterior  pulmonary  plexus,  lie 
in  front  of  each,  and  the  vagus  and  posterior  pulmonary  plexus  behind  each; 
below  each  is  the  pulmonary  ligament. 

The  chief  structures  composing  the  root  of  each  lung  are  arranged  in  a  similar 
manner  from  before  backward  on  both  sides,  viz.,  the  upper  of  the  two  pulmonary 
veins  in  front;  the  pulmonary  artery  in  the  middle;  and  the  bronchus,  together 
with  the  bronchial  vessels,  behind.  From  above  downward,  on  the  two  sides, 
their  arrangement  differs,  thus: 

On  the  right  side  their  position  is — eparterial  bronchus,  pulmonary  artery, 
hyparterial  bronchus,  pulmonary  veins,  but  on  the  left  side  their  position  is — 
pulmonary  artery,  bronchus,  pulmonary  veins.  The  lower  of  the  two  pulmonary 
veins,  is  situated  below  the  bronchus,  at  the  apex  or  lowest  part  of  the  hilus 
(Figs.  972,  973). 

Divisions  of  the  Bronchi. — Just  as  the  lungs  differ  from  each  other  in  the  number 
of  their  lobes,  so  the  bronchi  differ  in  their  mode  of  subdivision. 

The  right  bronchus  gives  off,  about  2.5  cm.  from  the  bifurcation  of  the  trachea, 
a  branch  for  the  superior  lobe.  This  branch  arises  above  the  level  of  the  pulmonary 
artery,  and  is  therefore  named  the  eparterial  bronchus.  All  the  other  divisions 
of  the  main  stem  come  off  below  the  pulmonary  artery,  and  consequently  are 
termed  hyparterial  bronchi.  The  first  of  these  is  distributed  to  the  middle  lobe, 
and  the  main  tube  then  passes  downward  and  backward  into  the  inferior  lobe, 
giving  off  in  its  course  a  series  of  large  ventral  and  small  dorsal  branches.  The 
ventral  and  dorsal  branches  arise  alternately,  and  are  usually  eight  in  number — 
four  of  each  kind.  The  branch  to  the  middle  lobe  is  regarded  as  the  first  of  the 
ventral  series. 

The  left  bronchus  passes  below  the  level  of  the  pulmonary  artery  before  it  divides, 
and  hence  all  its  branches  are  hyparterial;  it  may  therefore  be  looked  upon  as 


1098 


SPLANCHNOLOGY 


equivalent  to  that  portion  of  the  right  bronchus  which  lies  on  the  distal  side  of  its 
eparterial  branch.  The  first  branch  of  the  left  bronchus  arises  about  5  cm.  from 
the  bifurcation  of  the  trachea,  and  is  distributed  to  the  superior  lobe.  The  main 
stem  then  enters  the  inferior  lobe,  where  it  divides  into  ventral  and  dorsal  branches 
similar  to  those  in  the  right  lung.  The  branch  to  the  superior  lobe  of  the  left  lung 
is  regarded  as  the  first  of  the  ventral  seiies. 

Structure. — The  lungs  are  composed  of  an  external  serous  coat,  a  subserous  areolar  tissue 
and  the  pulmonary  substance  or  parenchyma. 

The  serous  coat  is  the  pulmonary  pleura  (page  1090) ;  it  is  thin,  transparent,  and  invests  the 
entire  organ  as  far  as  the  root. 

The  subserous  areolar  tissue  contains  a  large  proportion  of  elastic  fibers;  it  invests  the  entire 
surface  of  the  lung,  and  extends  inward  between  the  lobules. 

The  parenchyma  is  composed  of  secondary  lobules  which,  although  closely  connected  together 
by  an  interlobular  areolar  tissue,  are  quite  distinct  from  one  another,  and  may  be  teased 
asunder  without  much  difficulty  in  the  fetus.  The  secondary  lobules  vary  in  size;  those  on 
the  surface  are  large,  of  pyramidal  form,  the  base  turned  toward  the  surface;  those  in  the 
interior  smaller,  and  of  various  forms.  Each  secondary  lobule  is  composed  of  several  primary 
lobules,  the  anatomical  units  of  the  lung.  The  primary  lobule  consists  of  an  alveolar  duct, 
the  air  spaces  connected  with  it  and  their  bloodvessels,  lymphatics  and  nerves. 

The  intrapulmonary  bronchi  divide  and  subdivide  throughout  the  entire  organ,  the  smallest 
subdivisions  constituting  the  lobular  bronchioles.  The  larger  divisions  consist  of:  (1)  an  outer 
coat  of  fibrous  tissue  in  which  are  found  at  intervals  irregular  plates  of  hyaline  cartilage,  most 
developed  at  the  points  of  division;  (2)  internal  to  the  fibrous  coat,  a  layer  of  circularly  disposed 
smooth  muscle  fibers,  the  bronchial  muscle;  and  (3)  most  internally,  the  mucous  membrane, 
lined  by  columnar  ciliated  epithelium  resting  on  a  basement  membrane.  The  corium  of  the 
mucous  membrane  contains  numerous  elastic  fibers  running  longitudinally,  and  a  certain  amount 
of  lymphoid  tissue;  it  also  contains  the  ducta  of  mucous  glands,  the  acini  of  which  lie  in  the 
fibrous  coat.  The  lobular  bronchioles  differ  from  the  larger  tubes  in  containing  no  cartilage 
and  in  the  fact  that  the  ciliated  epithelial  cells  are  cubical  in  shape.  The  lobular  bronchioles 
are  about  0.2  mm.  in  diameter. 


Fig.  974. — Part  of  a  secondary  lobule  from  the  depth  of  a  human  lung,  showing  parts  of  several  primary  lobules. 
1,  bronchiole;  2,  respiratory  bronchiole;  3,  alveolar  duct;  4,  atria;  5,  alveolar  sac;  6,  alveolus  or  air  cell;  m,  smooth 
muscle;  a,  branch  pulmonary  artery;  v,  branch  pulmonary  vein;  s,  septum  between  secondary  lobules.  Camera 
•drawing  of  one  50  M  section.      X  20  diameters.     (Miller.) 

Each  bronchiole  divides  into  two  or  more  respiratory  bronchioles,  with  scattered  alveoli,  and 
each  of  these  again  divides  into  several  alveolar  ducts,  with  a  greater  number  of  alveoli  con- 
nected with  them.  Each  alveolar  duct  is  connected  with  a  variable  number  of  irregularly 
spherical  spaces,  which  also  possess  alveoli,  the  atria.  With  each  atrium  a  variable  number 
(2-5)  of  alveolar  sacs  are  connected  which  bear  on  all  parts  of  their  circumference  alveoli  or  air 
sacs.     (Miller.) 


THE  LUNGS 


1099 


The  alveoli  are  lined  by  a  delicate  layer  of  simple  squamous  epithelium,  the  cells  of  which 
are  imited  at  their  edges  by  cement  substance.    Between  the  squames  are  here  and  there  smaller, 


Fig.  975. — Schematic  longitudinal  section  of  a  primary  lobule  of  the  lung  (anatomical  unit);  r.  6.,  respiratory 
bronchiole,  al.  d..  alveolar  duct;  at.,  atria;  a.  s..  alveolar  sac;  a.  alveolus  or  air  cell;  p.  a...  pulmonary  artery:  p.  v., 
pulmonary  vein;  i.,  lymphatic;  i.  n.,  lymph  node.     (Miller.) 

polygonal,  nucleated  cells.  Outside  the  epithelial  hning  is  a  little  delicate  connective  tissue 
containing  numerous  elastic  fibers  and  a  close  net-work  of  blood  capillaries,  and  forming  a  common 
wall  to  adjacent  alveoli  (Fig.  975). 

c 
?  • 

c  ■ 


Pig.  976. — Section  of  lung  of  pig  embryo,  13  cm.  long,  showing  the  glandular  character  of  the  developing  alveoli 
(J.  M.  Flint.)  X  70.  a.  Interstitial  connective  tissue,  b.  A  bronchial  tube.  c.  An  Alveolus.  I.  lymphatic  clefts. 
q.  Pleura. 

The  f  ?tal  lung  resembles  a  gland  in  that  the  alveoU  have  a  small  lumen  and  are  lined  by 
cubical  epithelium  (Fig.  976).  After  the  first  respiration  the  alveoli  become  distended,  and  the 
epithelium  takes  on  the  characters  described  above. 


1 1 00  SPLANCHNOLOGY 

Vessels  and  Nerves. — The  pulmonary  artery  conveys  the  venous  blood  to  the  lungs;  it  divides 
into  branches  which  accompany  the  bronchial  tubes  and  end  in  a  dense  capillary  net-work  in 
the  walls  of  the  alveoli.  In  the  lung  the  branches  of  the  pulmonary  artery  are  usually  above 
and  in  front  of  a  bronchial  tube,  the  vein  below. 

The  pulmonary  capillaries  form  plexuses  which  lie  immediately  beneath  the  lining  epithe- 
lium, in  the  walls  and  septa  of  the  alveoli  and  of  the  infundibula.  In  the  septa  between  the 
alveoli  the  capillary  net-work  forms  a  single  layer.  The  capillaries  form  a  very  minute  net-work, 
the  meshes  of  which  are  smaller  than  the  vessels  themselves;  their  walls  are  also  exceedingly 
thin.  The  arteries  of  neighboring  lobules  are  independent  of  each  other,  but  the  veins  freely 
anastonK)se. 

The  pulmonary  veins  commence  in  the  pulmonary  capillaries,  the  radicles  coalescing  into 
larger  branches  which  run  through  the  substance  of  the  lung,  independently  of  the  pulmonary 
arteries  and  bronchi.  After  freely  communicating  with  other  branches  they  form  large  vessels, 
which  ultimately  come  into  relation  with  the  arteries  and  bronchial  tubes,  and  accompany 
them  to  the  hilus  of  the  organ.  Finally  they  open  into  the  left  atrium  of  the  heart,  conveying 
oxygenated  blood  to  be  distributed  to  all  parts  of  the  body  by  the  aorta. 

The  bronchial  arteries  supply  blood  for  the  nutrition  of  the  lung;  they  are  derived  from  the 
thoracic  aorta  or  from  the  upper  aortic  intercostal  arteries,  and,  accompanying  the  bronchial 
tubes,  are  distributed  to  the  bronchial  glands  and  upon  the  walls  of  the  larger  bronchial  tubes 
and  pulmonary  vessels.  Those  supplying  the  bronchial  tubes  form  a  capillary  plexus  in  the 
muscular  coat,  from  which  branches  are  given  off  to  form  a  second  plexus  in  the  mucous  coat; 
this  plexus  communicates  with  small  venous  trunks  that  empty  into  the  pulmonary  veins. 
Others  are  distributed  in  the  interlobular  areolar  tissue,  and  end  partly  in  the  deep,  partly 
in  the  superficial,  bronchial  veins.  Lastly,  some  ramify  upon  the  surface  of  the  lung,  beneath 
the  pleura,  where  they  form  a  capillary  network. 

The  bronchial  vein  is  formed  at  the  root  of  the  lung,  receiving  superficial  and  deep  veins  corre- 
sponding to  branches  of  the  bronchial  artery.  It  does  not,  however,  receive  all  the  blood  suppUed 
by  the  artery,  as  some  of  it  passes  into  the  pulmonary  veins.  It  ends  on  the  right  side  in  the 
azygos  vein,  and  on  the  left  side  in  the  highest  intercostal  or  in  the  accessory  hemiazygos  vein. 

The  lymphatics  are  described  on  page  718. 

Nerves. — The  lungs  are  supplied  from  the  anterior  and  posterior  pulmonary  plexuses,  formed 
chiefly  by  branches  from  the  sympathetic  and  vagus.  The  filaments  from  these  plexuses  accom- 
pany the  bronchial  tubes,  supplying  efferent  fibers  to  the  bronchial  muscle  and  afferent  fibers 
to  the  bronchial  mucous  membrane  and  probably  to  the  alveoh  of  the  limg.  Small  ganglia 
are  foimd  upon  these  nerves. 

THE  DIGESTIVE  APPARATUS   (APPARATUS  DIGESTORIUS;  ORGANS 

OF  DIGESTION). 

The  apparatus  for  the  digestion  of  the  food  consists  of  the  digestive  tube  and  of 
certain  accessory  organs. 

The  Digestive  Tube  (alimentary  canal)  is  a  musculomembranous  tube,  about 
9  metres  long,  extending  from  the  mouth  to  the  anus,  and  lined  throughout  its 
entire  extent  by  mucous  membrane.  It  has  received  different  names  in  the  various 
parts  of  its  course:  at  its  commencement  is  the  mouth,  where  provision  is  made 
for  the  mechanical  division  of  the  food  {mastication),  and  for  its  admixture  with 
a  fluid  secreted  by  the  salivary  glands  (insalivation) ;  beyond  this  are  the  organs 
of  deglutition,  the  pharjmx  and  the  esophagus,  which  convey  the  food  into  the 
stomach,  in  which  it  is  stored  for  a  time  and  in  which  also  the  first  stages  of  the 
digestive  process  take  place;  the  stomach  is  followed  by  the  small  intestine,  which 
is  divided  for  purposes  of  description  into  three  parts,  the  duodenum,  the  jejunum, 
and  ilemn.  In  the  small  intestine  the  process  of  digestion  is  completed  and  the 
resulting  products  are  absorbed  into  the  blood  and  lacteal  vessels.  Finally  the 
small  intestine  ends  in  the  large  intestine,  which  is  made  up  of  cecum,  colon,  rectum, 
and  anal  canal,  the  last  terminating  on  the  surface  of  the  body  at  the  anus. 

The  accessory  organs  are  the  teeth,  for  purposes  of  mastication;  the  three  pairs 
of  salivary  glands — the  parotid,  submaxillary,  and  sublingual — the  secretion  from 
which  mixes  with  the  food  in  the  mouth  and  converts  it  into  a  bolus  and  acts 
chemically  on  one  of  its  constituents;  the  liver  and  pancreas,  two  large  glands 
in  the  abdomen,  the  secretions  of  which,  in  addition  to  that  of  numerous,  minute 
glands  in  the  walls  of  the  alimentary  canal,  assist  in  the  process  of  digestion. 


THE  DIGESTIVE  APPARATUS 


1101 


The  Development  of  the  Digestive  Tube. — The  primitive  digestive  tube  con- 
sists of  two  parts,  viz.:  (1)  the  fore-gut,  within  the  cephaHc  flexure,  and  dorsal 
to  the  heart;  and  (2)  the  hind-gut,  within  the  caudal  flexure  (Fig.  977).  Between 
these  is  the  wide  opening  of  the  yolk-sac,  which  is  gradually  narrowed  and  reduced 
to  a  small  foramen  leading  into  the  vitelline  duct.  At  first  the  fore-gut  and  hind- 
gut  end  blindly.  The  anterior  end  of  the  fore-gut  is  separated  from  the  stomo- 
deum  by  the  buccopharyngeal  membrane  (Fig.  977);  the  hind-gut  ends  in  the 
cloaca,  which  is  closed  by  the  cloacal  membrane. 


ThcUamencephalon 


Optic  vesicle 


Mid-hrain 


Buccopharyngeal 

membrane 

Pharynx 
Auditory  pit 

BvXbvs  cordis 
Stomach 


Stomodeum 
Ventricle 


Cloaca 


Body-stalk 
Umbilical  vein 


Yolk-sac 


Hind-gut 


AUarUois 
Umbilical  artery 


II 


[Fia.  977. — Human  embryo  about  fifteen  days  old.   Brain  and  heart  represented  from  right  side.    Digestive  tube  and 

yolk  sac  in  median  section.     (After  His.) 

The  Mouth. — The  mouth  is  developed  partly  from  the  stomodeum,  and  partly 
from  the  floor  of  the  anterior  portion  of  the  fore-gut.  By  the  growth  of  the  head 
end  of  the  embryo,  and  the  formation  of  the  cephalic  flexure,  the  pericardial  area 
and  the  buccopharyngeal  membrane  come  to  lie  on  the  ventral  surface  of  the 
embryo.  With  the  further  expansion  of  the  brain,  and  the  forward  bulging  of  the 
pericardium,  the  buccopharyngeal  membrane  is  depressed  between  these  two 
prominences.  This  depression  constitutes  the  stomodeum  (Fig.  977).  It  is  lined 
by  ectoderm,  and  is  separated  from  the  anterior  end  of  the  fore-gut  by  the  bucco- 
pharyngeal membrane.  This  membrane  is  devoid  of  mesoderm,  being  formed 
by  the  apposition  of  the  stomodeal  ectoderm  with  the  fore-gut  entoderm;  at  the 
end  of  the  third  week  it  disappears,  and  thus  a  communication  is  established 
between  the  mouth  and  the  future  pharynx.  No  trace  of'  the  membrane  is  found 
in  the  adult ;  and  the  communication  just  mentioned  must  not  be  confused  with  the 
permanent  isthmus  faucium.  The  lips,  teeth,  and  gums  are  formed  from  the  walls 
of  the  stomodeum,  but  the  tongue  is  developed  in  the  floor  of  the  pharynx. 

The  visceral  arches  extend  in  a  ventral  direction  between  the  stomodeum  and 
the  pericardium;  and  with  the  completion  of  the  mandibular  arch  and  the  formation 
of  the  maxillary  processes,  the  mouth  assumes  the  appearance  of  a  pentagonal 
orifice.    The  orifice  is  bounded  in  front  by  the  fronto-nasal  process,  behind  by  the 


1102 


SPLANCHNOLOGY 


mandibular  arch,  and  laterally  by  the  maxillary  processes  (Fig.  978) .  With  the 
inward  growth  and  fusion  of  the  palatine  processes  (Figs.  50,  51),  the  stomodeum 
is  divided  into  an  upper  nasal,  and  a  lower  buccal  part.  Along  the  free  margins 
of  the  processes  bounding  the  mouth  cavity  a  shallow  groove  appears;  this  is 
termed  the  primary  labial  groove,  and  from  the  bottom  of  it  a  downgrowth  of 
ectoderm  takes  place  into  the  underlying  mesoderm.  The  central  cells  of  the 
ectodermal  downgrowth  degenerate  and  a  secondary  labial  groove  is  formed;  by 
the  deepening  of  this,  the  lips  and  cheeks  are  separated  from  the  alveolar  processes 
of  the  maxillae  and  mandible. 

The  Salivary  Glands. — The  salivary  glands  arise  as  buds  from  the  epithelial 
lining  of  the  mouth;  the  parotid  appears  during  the  fourth  week  in  the  angle 

between  the  maxillary  process  and  the 
mandibular  arch;  the  submaxillary  ap- 
pears in  the  sixth  week,  and  the  sublin- 
gual during  the  ninth  week  in  the  hollow 
between  the  tongue  and  the  mandibular 
arch. 

The  Tongue  (Figs.  979  to  981).— The 
tongue  is  developed  in  the  floor  of  the 
pharynx,  and  consists  of  an  anterior  or 
buccal  and  a  posterior  or  pharyngeal  part 
which  are  separated  in  the  adult  by  the 
V-shaped  sulcus  terminalis.  During  the 
third  week  there  appears,  immediately 
behind  the  ventral  ends  of  the  two  halves 
of  the  mandibular  arch,  a  rounded 
swelling  named  the  tuberculum  impar, 
which  was  described  by  His  as  un- 
dergoing enlargement  to  form  the 
buccal  part  of  the  tongue.  More  re- 
cent researches,  how^ever,  show  that 
this  part  of  the  tongue  is  mainly,  if 
not  entirely,  developed  from  a  pair 
of  lateral  swellings  which  rise  from 
the  inner  surface  of  the  mandibular  arch  and  meet  in  the  middle  line.  The  tuber- 
culum impar  is  said  to  form  the  central  part  of  the  tongue  immediately  in  front 


i 

II 


Future  apex  of  nose 

Medial  nasal  process 

Olfactory  pit 
Lateral  nasal  process 
Globular  process 
Maxillary  process 
Stomodeum 

Mandibular  arch 


Fig.  978. — Head  end  of  human  embryo  of  about  thirty 
to  thirty-one  days.     (From  model  by  Peters.) 


Lateral  t-ongue      Thyroid 
swellings      diverticvium 


Lateral  tongue 


Fig.  979.— Floor  of  i)!iar,.  i 
about  twenty-six  dajs  old. 
Peters.) 


Entrance  to 
larynx 


of  human  embryo 
(From    model   by 


Entrance  to 

larynx 
Arytenoid 
swellings 


Fig.  980. — Floor  of  pharynx  of  human  embryo 
of  a^out  the  end  of  the  fourth  week.  (From 
model  by  Peters.) 


of  the  foramen  cecum,  but  Hammar  insists  that  it  is  purely  a  transitory  structure 
and  forms  no  part  of  the  adult  tongue.    From  the  ventral  ends  of  the  fourth  arch 


THE  DIGESTIVE 


(From  model  by  Peter.) 


I 


there  arises  a  second  and  larger  elevation,  in  the  center  of  which  is  a  median  groove 

or  furrow.    This  elevation  was  named  by  His  the  furcula,  and  is  at  first  separated 

from  the  tuberculum  impar  by  a  depression,  but  later  by  a  ridge,  the  copula, 

formed  by  the  forward  growth  and  fusion  of  the  ventral  ends  of  the  second  and 

third  arches.    The  posterior  or  pharyngeal  part  of  the  tongue  is  developed  from 

the  copula,  which  extends  forward  in  the  form  of  a  V,  so  as  to  embrace  between  its 

two  limbs  the  buccal  part  of  the  tongue.  At  the  apex  of  the  V  a  pit-like  invagination 

occurs,  to   form  the  thyroid  gland, 

and  this  depression  is  represented  in 

the  adult  by  the  foramen  cecum  of 

the  tongue.    In  the  adult  the  union 

of  the  anterior  and  posterior  parts 

of  the  tongue  is  marked  by  the  V- 

shaped  sulcus  terminalis,  the  apex  of 

which  is  at  the  foramen  cecum,  while 

the  two  limbs  run  lateralward  and 

forward,  parallel  to,  but  a  little  be-        ^  \    f  'S~^  r^  Arytenoid 

hind,  the  vallate  papillae.  //  \iM^  \      sweUings 

The  Palatine  Tonsils. — The  palatine 
tonsils  are  developed  from  the  dorsal  ''"'■  ^^^"'^feVoif 
angles  of  the  secondbranchial pouches. 
The  entoderm  which  lines  these  pouches  grows  in  the  form  of  a  number  of  solid 
buds  into  the  surrounding  mesoderm.  These  buds  become  hollowed  out  by  the 
degeneration  and  casting  off  of  their  central  cells,  and  by  this  means  the  tonsillar 
crypts  are  formed.  Lymphoid  cells  accumulate  around  the  crypts,  and  become 
grouped  to  form  the  lymphoid  follicles;  the  latter,  however,  are  not  well-defined 
until  after  birth. 

The  Further  Development  of  the  Digestive  Tube. — ^The  upper  part  of  the  fore-gut 
becomes  dilated  to  form  the  pharynx  (Fig.  977),  in  relation  to  which  the  branchial 
arches  are  developed  (see  page  65) ;  the  succeeding  part  remains  tubular,  and  with 
the  descent  of  the  stomach  is  elongated  to  form  the  esophagus.  About  the  fourth 
week  a  fusiform  dilatation,  the  future  stomach,  makes  its  appearance,  and  beyond 
this  the  gut  opens  freely  into  the  yolk-sac  (Fig.  982,  A  and  B).  The  opening  is  at 
first  wide,  but  is  gradually  narrow  ed  into  a  tubular  stalk,  the  yolk-stalk  or  vitelline 
duct.  Between  the  stomach  and  the  mouth  of  the  yolk-sac  the  liver  diverticulum 
appears.  From  the  stomach  to  the  rectum  the  alimentary  canal  is  attached  to  the 
notochord  by  a  band  of  mesoderm,  from  which  the  common  mesentery  of  the  gut 
is  subsequently  developed.  The  stomach  has  an  additional  attachment,  viz.,  to 
the  ventral  abdominal  wall  as  far  as  the  umbilicus  by  the  septum  trans versum. 
The  cephalic  portion  of  the  septum  takes  part  in  the  formation  of  the  diaphragm, 
while  the  caudal  portion  into  which  the  liver  grows  forms  the  ventral  mesogastrium 
(Fig.  984).  The  stomach  undergoes  a  further  dilatation,  and  its  two  curvatures 
can  be  recognized  (Figs.  983,  B,  and  984),  the  greater  directed  toward  the  vertebral 
column  and  the  lesser  toward  the  anterior  wall  of  the  abdomen,  while  its  two 
surfaces  look  to  the  right  and  left  respectively.  Behind  the  stomach  the  gut 
undergoes  great  elongation,  and  forms  a  V-shaped  loop  which  projects  downward 
and  forward;  from  the  bend  or  angle  of  the  loop  the  vitelline  duct  passes  to  the 
umbilicus  (Fig.  984).  For  a  time  a  considerable  part  of  the  loop  extends  beyond 
the  abdominal  cavity  into  the  umbilical  cord,  but  by  the  end  of  the  third  month 
it  is  withdrawn  within  the  cavity.  With  the  lengthening  of  the  tube,  the  mesoderm, 
which  attaches  it  to  the  future  vertebral  column  and  carries  the  bloodvessels  for 
the  supply  of  the  gut,  is  thinned  and  drawn  out  to  form  the  posterior  common 
mesentery.  The  portion  of  this  mesentery  attached  to  the  greater  curvature  of 
the  stomach  is  named  the  dorsal  mesogastrium,  and  the  part  which  suspends  the 


1104 


SPLANCHNOLOGY 


colon  is  termed  the  mesocolon  (Fig.  985).    About  the  sixth  week  a  diverticulum! 
of  the  gut  appears  just  behind  the  opening  of  the  vitelline  duct,  and  indicates! 


Notochcrd         Rathlce's  •pouch 


Lang  diverticvlwm — 

Stomach - 
Liver--\ 


Opening  into  _ 
yolk-sac 


AllarUoisX — 


,  Mandibular 
arch 


—  Postallantoic  part 
of  hind-gut 

Wolffian  duct 


Lung  diverticulum 
Esophagus  ^      ^^ 


Vitelline  duct 
Allantois  — 


Thyroid  gland 

Mandibular  arch 

I         I    Notochord 

I     I 
I     I 
I 


—  Eathke's  pouch 


Postallantoic  part 
of  hind-gut 


Wolffian  duct 


Fia.  982. — Sketches  in  profile  of  two  stages  in  the  development  of  the  human  digestive  tube.    (His.) 

A  X  30.     B  X  20. 

the  future  cecum  and  vermiform  process.   The  part  of  the  loop  on  the  distal  side 
of  the  cecal  diverticulum  increases  in  diameter  and  forms  the  future  ascending 


THE  DIGESTIVE  APPARATUS 


1105 


and  transverse  portions  of  the  large  intestine.  Until  the  fifth  month  the  cecal 
diverticulum  has  a  uniform  caliber,  but  from  this  time  onward  its  distal  part 
remains  rudimentary  and  forms  the  vermiform  process,  while  its  proximal  part 
expands  to  form  the  cecum.  Changes  also  take  place  in  the  shape  and  position 
of  the  stomach.    Its  dorsal  part  or  greater  curvature,  to  which  the  dorsal  meso- 


Trachea-— 


Esophagus 


Stomach 


Bile-dtict  — 


•■""  Lung 


—  Trachea 


y/-shaped  loop  of 
small  intestine  - 

Vitelline  dttct  - 
Cloaca  ' 


>• —  Pancreas 


Bile-duct 
Pancreas 


—   Lung 
'•"  -Esophagus 


Stomach 


Fig.  083. — Front  view  of  two  successive  stages  in  the  development  of  the  digestive  tube.     (His.) 

gastrium  is  attached,  grows  much  more  rapidly  than  its  ventral  part  or  lesser 
curvature  to  which  the  ventral  mesogastrium  is  fixed.  Further,  the  greater  curva- 
ture is  carried  downward  and  to  the  left,  so  that  the  right  surface  of  the  stomach  is 
now  directed  backward  and  the  left  surface  forward  (Fig.  986),  a  change  in  position 


Septum  trarisversum 


Liver 


Falciform  ligament  of  liver 
Lesser  omentum 

Umbilical  vein 
Umbilical  cord 


Aorta 

Dorsal  mesogastrium 

Stomach 


Intestinal  W-shaped  loop 
Mesentery 


Colon 


FiQ.  984. — The  primitive  mesentery  of  a  six  weeks'  human  embryo,  half  schematic.     (Kollmann.) 

which  explains  why  the  left  vagus  nerve  is  found  on  the  front,  and  the  right  vagus 
on  the  back  of  the  stomach.  The  dorsal  mesogastrium  being  attached  to  the  greater 
curvature  must  necessarily  follow  its  movements,  and  hence  it  becomes  greatly 
elongated  and  drawn  lateralward  and  ventralward  from  the  vertebral  column, 
and,  as  in  the  case  of  the  stomach,  the  right  surfaces  of  both  the  dorsal  and  ventral 
70 


1106 


SPLANCHNOLOGY 


mesogastria  are  now  directed  backward,  and  the  left  forward.  In  this  way  a  pouch, 
the  bursa  omentalis,  is  formed  behind  the  stomach,  and  this  increases  in  size  as 
the  digestive  tube  undergoes  further  development;  the  entrance  to  the  pouch 
constitutes  the  future  foramen  epiploicum  or  foramen  of  Winslow.  The  duodenum 
is  developed  from  that  part  of  the  tube  which  immediately  succeeds  the  stomach; 
it  undergoes  little  elongation,  being  more  or  less  fixed  in  position  by  the  liver  and 
pancreas,  which  arise  as  diverticula  from  it.  The  duodenum  is  at  first  suspended 
by  a  mesentery,  and  projects  forward  in  the  form  of  a  loop.  The  loop  and  its  mes- 
entery are  subsequently  displaced  by  the  transverse  colon,  so  that  the  right  surface 
of  the  duodenal  mesentery  is  directed  backward,  and,  adhering  to  the  parietal 
peritoneum,  is  lost.  The  remainder  of  the  digestive  tube  becomes  greatly  elongated, 
and  as  a  consequence  the  tube  is  coiled  on  itself,  and  this  elongation  demands  a 
corresponding  increase  in  the  width  of  the  intestinal  attachment  of  the  mesentery, 
which  becomes  folded. 


Ventral  mesogastrium 


I 


Aorta 


S'pleen 

Dorsal 
mesogastrium 

Celiac  artery 


Pancreas 


Superior  mesenteric 
artery 


Mesentery 


Inferior  mesenteric  artery 


Hind-gut 


FiQ.  985. — Abdominal  part  of  digestive  tube  and  its  attachment  to  the  primitive  or  common  mesentery. 

embryo  of  six  weeks.     (After  Toldt.) 


Human 


At  this  stage  the  small  and  large  intestines  are  attached  to  the  vertebral  column 
by  a  common  mesentery,  the  coils  of  the  small  intestine  falling  to  the  right  of  the 
middle  line,  while  the  large  intestine  lies  on  the  left  side.^ 

The  gut  is  now  rotated  upon  itself,  so  that  the  large  intestine  is  carried  over  in 
front  of  the  small  intestine,  and  the  cecum  is  placed  immediately  below  the  liver; 
about  the  sixth  month  the  cecum  descends  into  the  right  iliac  fossa,  and  the  large 
intestine  forms  an  arch  consisting  of  the  ascending,  transverse,  and  descending 
portions  of  the  colon — the  transverse  portion  crossing  in  front  of  the  duodenum 
and  lying  just  below  the  greater  curvature  of  the  stomach;  within  this  arch  the 
coils  of  the  small  intestine  are  disposed  (Fig.  988).     Sometimes  the  downward 


'  Sometimes  this  condition  persists  throughout  life,  and  it  is  then  found  that  the  duodenum  does  not  cross  from  the 
right  to  the  left  side  of  the  vertebral  column,  but  lies  entirely  on  the  right  side  of  the  median  plane,  where  it  is  continued 
into  the  jejunum;  the  arteries  to  the  small  intestine  (ao.  intestinales)  also  arise  from  the  right  instead  of  the  left  side 
of  the  superior  mesenteric  artery. 


THE  DIGESTIVE  APPARATUS 


1107 


progress  of  the  cecum  is  arrested,  so  that  in  the  adult  it  may  be  found  lying  imme- 
diatel}'  below  the  liver  instead  of  in  the  right  iliac  region. 

Further  changes  take  place  in  the  bursa  omental  is  and  in  the  common  mesentery, 
and  give  rise  to  the  peritoneal  relations  seen  in  the  adult.  The  bursa  omentalis, 
which  at  first  reaches  only  as  far  as  the  greater  curvature  of  the  stomach,  grows 
downward  to  form  the  greater  omentum,  and  this  downward  extension  lies  in  front 
of  the  transverse  colon  and  the  coils  of  the  small  intestine  (Fig.  989) .  Above,  before 
the  pleuro-peritoneal  opening  is  closed,  the  bursa  omentalis  sends  up  a  diverticulum 


Sth  cervical  nerve 

1st  thoracic 
vertebra 


Suprarenal 
gland 

Stomach 
I2th  thoracic 

nerve 
Mesonephros 


Great 
Cecum         intestine        Wolffian  dvct 

Fig.  986. — Reconstruction  of  a  human  embryo  of  17  mm. 


(After  MaU.) 


I 


on  either  side  of  the  esophagus;  the  left  diverticulum  soon  disappears,  but  the  right 
is  constricted  off  and  persists  in  most  adults  as  a  small  sac  lying  within  the  thorax 
on  the  right  side  of  the  lower  end  of  the  esophagus.  The  anterior  layer  of  the 
transverse  mesocolon  is  at  first  distinct  from  the  posterior  layer  of  the  greater 
omentum,  but  ultimately  the  two  blend,  and  hence  the  greater  omentum  appears  as 
if  attached  to  the  transverse  colon  (Fig.  990).  The  mesenteries  of  the  ascending  and 
descending  parts  of  the  colon  disappear  in  the  majority  of  cases,  while  that  of  the 
small  intestine  assumes  the  oblique  attachment  characteristic  of  its  adult  condition. 
The  lesser  omentum  is  formed,  as  indicated  above,  by  a  thinning  of  the  meso- 
derm or  ventral  mesogastrium,  which  attaches  the  stomach  and  duodenum  to  the 
anterior  abdominal  wall.  By  the  subsequent  growth  of  the  liver  this  leaf  of 
mesoderm  is  divided  into  two  parts,  viz.,  the  lesser  omentum  between  the  stomach 


IIOS 


SPLANCHNOLOGY 


and  liver,  and  the  falciform  and  coronary  ligaments  between  the  liver  and  the 
abdoiniiiiil  wall  and  diapliragni  (Fig.  980). 

The  Rectum  and  Anal  Canal. — Tlie  liiiid-gut  is  at  first  prolonged  backward  into 
the  body-stalk  aa  the  tube  of  the  allantois;  but,  with  the  growth  arid  flexure  of  the 


Mttogaatriuni 


Stnall 
inteatiiif. 


yUelline  duct 


Greater 

curmture 

o/ntomach 


Greater 
omentum 


Point  where 
intestinal 
toopx  eroxg 
each  other 


MfHO- 

nnKtrinw 


Duodentim 


Mesocolon 


Ceoum 

Larije  Vermiform 

inte'gline  prooets 

Mesenteiy 


llectwn 


yitelline  duct 


Greater  omentum 


Large  intentine 
Smallintestine 


lieotum 


A  b 

Fia.  987. — Diagramfi  to  illuatrato  two  stages  in  the  riovelopmont  of  the  digestive  tube  and  its  mesentery. 
The  (vrrow  indicates  the  ontranco  to  the  bursa  oment.ilis. 


Fia.  988. — Final  disposition  of  the 
intestines  and  thoir  vascular  relations. 
(Jonnesco.)  A.  Aorta.  //.  Hepatic 
artery.  Ai,  Col.  Branches  of  superior 
meseaterio  artery,  wi,  m'.  Branches 
of  inferior  roesenterio  artery.  S. 
Splenic  artery. 


Ventral 
mesogastrium 


Vmbilicai  vein. 


Border  of 
ventral 
me8oga8tr%um>^ 


Bursa 
omenialia 


Pancreas 

Dorsal 
mesogastrium 

Duodenum 


Greater 
omentum 
Transverse 

mesocolon 

Transverse 
colon 


Fio.  989. — Sohematio  figure  of  the  bursa  omontalis,  etc.      Human 
embryo  of  eight  weeks.     (Kollmann.) 


Stomach 


tail-end  of  the  embryo,  the  body-stalk,  with  its  contained  allantoic  tube,  is  carried 
forward  to  the  ventral  aspect  of  the  body,  and  consequently  a  bend  is  formed  at  the 


THE  DIGESTIVE  APPARATUS 


1109 


junction  of  the  hind-gut  and  allantois.  This  bend  beajnies  dilated  into  a  pouch, 
which  constitutes  the  entodermal  cloaca;  into  its  dorsal  part  the  hind-gut  opens, 
and  from  its  ventral  part  tlie  allantois  passes  forward.  At  a  later  stage  the  Wolffian 
and  Miillerian  ducts  open  into  its  ventral  portion.    The  cloaca  is,  for  a  time,  shut 


Diaphragm 


Liu&r 


Lesger  omenttiw 

linriia  oinentalin 
Stouuich 
I'aiierea  ti 

Greater  omentum    . 

t  Triiiuti'er»e  menocolon  - 
Transverse  colim   - 


fjcsucr  otncHtum 
--  liiima  omcntalis 
>Stiimach 

—  Pancreas 

■  Olililrrated  part  of  mesogastrium 

-  DiiodcnvDi 

-  Transverse  colon 

Mesentery 


- -SniaU  intestine 

c,      „  .        '         !    l>uodenuin 
Small  intestine    j 

Mesentery 
Fio.  900. — Diagrams  to  illustrato  the  dovolopmont  of  the  greater  omontutn  and  tranaverae  niMOCoIon. 

off  from  the  anterior  by  a  membrane,  the  cloacal  membrane,  formed  by  the  apposi- 
tion of  the  ectoderm  and  entoderm,  and  reaching,  at  first,  as  far  forward  as  the 
future  umbilicus.  Behind  the  umbilicus,  however,  the  mesoderm  subsequently 
extends  to  form  the  lower  part  of  the  abdominal  wall  and  symphysis  pubis.  By 
the  growth  of  the  surrounding  tissues  the  cloacal  membrane  comes  to  lie  at  the 
bottom  of  a  depression,  which  is  lined  by  ectoderm  and  named  the  ectodermal 
cloaca  (Fig.  991). 

t'he  entodermal  cloaca  is  divided  into  a  dorsal  and  a  ventral  part  by  means  of  a 
tition,  the  urorectal  septum  (Fig.  992),  which  grows  downward  from  the  ridge 

i^ctodermal  clcxun 
Cloacal  membraiK 


Woljfian  dvct 


Wolffian  duel 


Notochord 


[Fia.  991. — Tail  end  of  iniiiinn  oinl)ryo  from  fifteen  to 
eighteen  days  old.     (From  model  by  Keibol.) 


Fio.  992.^<;;ioaca  of  human  embryo  from 
twenty-five  to  twonty-soven  days  old.  (From 
model  by  Keibel.) 


(separating  the  allantoic  from  the  cloacal  opening  of  the  intestine  and  ultimately 
{fuses  with  the  cloacal  membrane  and  divides  it  into  an  anal  and  a  urogenital  part. 
The  dorsal  part  of  the  cloaca  forms  the  rectum,  and  the  anterior  part  of  the  uro- 
genital sinus  and  bladder.    For  a  time  a  communication  named  the  cloacal  duct 


1110 


SPLANCHNOLOGY 


exists  between  the  two  parts  of  the  cloaca  below  the  urorectal  septum;  this  duct 
occasionally  persists  as  a  passage  between  the  rectum  and  urethra.  The  anal 
canal  is  formed  by  an  invagination  of  the  ectoderm  behind  the  urorectal  septum. 
This  invagination  is  termed  the  proctodeum,  and  it  meets  with  the  entoderm  of  the 
hind-gut  and  forms  with  it  the  anal  membrane.  By  the  absorption  of  this  membrane 
the  anal  canal  becomes  continuous  with  the  rectum  (Fig.  993).  A  small  part  of  the 
hind-gut  projects  backward  beyond  the  anal  membrane;  it  is  named  the  post-anal 
gut  (Fig.  991),  and  usually  becomes  obliterated  and  disappears.^ 


Vertebral  column 
FiQ.  993. — Tail  end  of  human  embryo,  from  eight  and  a  half  to  nine  weeks  old.     (From  model  by  Keibel J 


THE  MOUTH   (CAVUM   ORIS;   ORAL   OR  BUCCAL  CAVITY). 

The  cavity  of  the  mouth  is  placed  at  the  commencement  of  the  digestive  tube 
(Fig.  994);  it  is  a  nearly  oval-shaped  cavity  which  consists  of  two  parts:  an 
outer,  smaller  portion,  the  vestibule,  and  an  inner,  larger  part,  the  mouth  cavity 
proper. 

The  Vestibule  (vestibulum  oris)  is  a  slit-like  space,  bounded  externally  by  the 
lips  and  cheeks;  internally  by  the  gums  and  teeth.  It  communicates  with  the 
surface  of  the  body  by  the  rima  or  orifice  of  the  mouth.  Above  and  below,  it  is 
limited  by  the  reflection  of  the  mucous  membrane  from  the  lips  and  cheeks  to 
the  gum  covering  the  upper  and  lower  alveolar  arch  respectively.  It  receives  the 
secretion  from  the  parotid  salivary  glands,  and  communicates,  when  the  jaws  are 
closed,  with  the  mouth  cavity  proper  by  an  aperture  on  either  side  behind  the 
wisdom  teeth,  and  by  narrow  clefts  between  opposing  teeth. 

The  Mouth  Cavity  Proper  {cavum  oris  proprium)  (Fig.  1014)  is  bounded  laterally 
and  in  front  by  the  alveolar  arches  with  their  contained  teeth;  behind,  it  communi- 
cates with  the  pharynx  by  a  constricted  aperture  termed  the  isthmus  faucium. 
It  is  roofed  in  by  the  hard  and  soft  palates,  while  the  greater  part  of  the  floor  is 
formed  by  the  tongue,  the  remainder  by  the  reflection  of  the  mucous  membrane 
from  the  sides  and  under  surface  of  the  tongue  to  the  gum  lining  the  inner  aspect 
of  the  mandible.  It  receives  the  secretion  from  the  submaxillary  and  sublingual 
salivary  glands. 

Structure. — The  mucous  membrane  lining  the  mouth  is  continuous  with  the  integument  at  S 
the  free  margin  of  the  lips,  and  with  the  mucous  lining  of  the  pharynx  behind;  it  is  of  a  rose-  fl 
pink  tinge  during  hfe,  and  very  thick  where  it  overlies  the  hard  parts  boimding  the  cavity.    It 
is  covered  by  stratified  squamous  epithelium. 

>  Consult,  in  this  connection,  the  following  article:  "A  Contribution  to  the  Morphology  of  the  Human  Urino- 
genital  Tract,"  by  D.  Berry  Hart,  M.D.,  F.R.C.P.E.,  Journal  of  Anatomy  and  Physiology,  April,  1901,  vol.  xxxv. 


THE  MOUTH 


1111 


The  Lips  {labia  oris),  the  two  fleshy  folds  which  surround  the  rima  or  orifice  of 
the  mouth,  are  formed  externally  of  integument  and  internally  of  mucous  mem- 
)rane,  between  which  are  found  the  Orbicularis  oris  muscle,  the  labial  vessels, 
some  nerves,  areolar  tissue,  and  fat,  and  numerous  small  labial  glands.  The  inner 
surface  of  each  lip  is  connected  in  the  middle  line  to  the  corresponding  gum  by  a 
fold  of  mucous  membrane,  the  frenulum — the  upper  being  the  larger. 


Bypophysis 


Pharyngeal 
tonsil 

Orifice  of  /V^  /  ^~, 

auditory  tube  If^y^^^ 
Nasal  part  of tf  V^    -     \ 

pharynx 

Anterior  arch  of 
atlas 

Odontoid  process 
of  axis 


Oral  part  of 

pharynx 

Body  of  axis 


Epiglottis 

Laryngeal  part 
of  pharynx 
I  Aryepiglottic  fold 


Frenulum  linguce 
Mylohyoideus  mv^de 
Hyoid  hone 
Thyroid  cartilage 

Ventricular  fold 

Vocal  fold 

Cricoid  cartilage 


Isthmus  of  thyroid  gland 
Fia.  994. — Sagittal  section  of  nose    mouth,  pharynx,  and  larynx. 


The  Labial  Glands  (glandulcB  lahiales)  are  situated  between  the  mucous  membrane 
and  the  Orbicularis  oris,  around  the  orifice  of  the  mouth.  They  are  circular  in  form, 
and  about  the  size  of  small  peas;  their  ducts  open  by  minute  orifices  upon  the 
mucous  membrane.     In  structure  they  resemble  the  salivary  glands. 


1112  SPLANCHNOLOGY 

The  Cheeks  (bucccB)  form  the  sides  of  the  face,  and  are  continuous  in  front  with 
the  lips.  They  are  composed  externally  of  integument;  internally  of  mucous 
membrane;  and  between  the  two  of  a  muscular  stratum,  besides  a  large  quantity 
of  fat,  areolar  tissue,  vessels,  nerves,  and  buccal  glands. 

Structure. — The  mucous  membrane  lining  the  cheek  is  reflected  above  and  below  upon  the 
gums,  and  is  continuous  behind  with  the  lining  membrane  of  the  soft  palate.     Opposite  the 
second  molar  tooth  of  the  maxilla  is  a  papilla,  on  the  summit  of  which  is  the  aperture  of  the 
parotid  duct.    The  principal  muscle  of  the  cheek  is  the  Buccinator;  but  other  muscles  enter  intai 
its  formation,  viz.,  the  Zvgomaticus,  Risorius,  and  Platysma.  ' 

The  buccal  glands  are  placed  between  the  mucous  membrane  and  Buccinator  muscle:  they 
are  similar  in  structure  to  the  labial  glands,  but  smaller.  About  five,  of  a  larger  size  than  the 
rest,  are  placed  between  the  Masseter  and  Buccinator  muscles  around  the  distal  extremity  of 
the  parotid  duct;  their  ducts  opeji  in  the  mouth  opposite  the  last  molar  tooth.  They  are  called 
molar  glands. 

The  Gums  (gingivcB)  are  composed  of  dense  fibrous  tissue,  closely  connected  to 
the  periosteum  of  the  alveolar  processes,  and  surrounding  the  necks  of  the  teeth. 
They  are  covered  by  smooth  and  vascular  mucous  membrane,  which  is  remark- 
able for  its  limited  sensibility.  Around  the  necks  of  the  teeth  this  membrane 
presents  numerous  fine  papillae,  and  is  reflected  into  the  alveoli,  where  it  is  con- 
tinuous with  the  periosteal  membrane  lining  these  cavities. 

The  Palate  (palatum)  forms  the  roof  of  the  mouth;  it  consists  of  two  portions, 
the  hard  palate  in  front,  the  soft  palate  behind. 

The  Hard  Palate  (palatum  durum)  (Fig.  1014)  is  bounded  in  front  and  at  the  sides 
by  the  alveolar  arches  and  gums;  behind,  it  is  continuous  with  the  soft  palate. 
It  is  covered  by  a  dense  structure,  formed  by  the  periosteum  and  mucous  mem- 
brane of  the  mouth,  which  are  intimately  adherent.  Along  the  middle  line  is  a 
linear  raphe,  which  ends  anteriorly  in  a  small  papilla  corresponding  with  the 
incisive  canal.  On  either  side  and  in  front  of  the  raphe  the  mucous  membrane 
is  thick,  pale  in  color,  and  corrugated;  behind,  it  is  thin,  smooth,  and  of  a  deeper 
color;  it  is  covered  with  stratified  squamous  epithelium,  and  furnished  with 
numerous  palatal  glands,  which  lie  between  the  mucous  membrane  and  the  surface 
of  the  bone. 

The  Soft  Palate  (palatum  molle)  (Fig.  1014)  is  a  movable  fold,  suspended  from  the 
posterior  border  of  the  hard  palate,  and  forming  an  incomplete  septum  between 
the  mouth  and  pharynx.  It  consists  of  a  fold  of  mucous  membrane  enclosing 
muscular  fibers,  an  aponeurosis,  vessels,  nerves,  adenoid  tissue,  and  mucous  glands. 
When  occupying  its  usual  position,  i.  e.,  relaxed  and  pendent,  its  anterior  surface 
is  concave,  continuous  with  the  roof  of  the  mouth,  and  marked  by  a  median  raphe. 
Its  posterior  surface  is  convex,  and  continuous  with  the  mucous  membrane  covering 
the  floor  of  the  nasal  cavities.  Its  upper  border  is  attached  to  the  posterior  margin 
of  the  hard  palate,  and  its  sides  are  blended  with  the  pharynx.  Its  lower  border 
is  free.  Its  lower  portion,  which  hangs  like  a  curtain  between  the  mouth  and 
pharynx  is  termed  the  palatine  velum. 

Hanging  from  the  middle  of  its  lower  border  is  a  small,  conical,  pendulous 
process,  the  palatine  uvula;  and  arching  lateralward  and  downward  from  the  base 
of  the  uvula  on  either  side  are  two  curved  folds  of  mucous  membrane,  containing 
muscular  fibers,  called  the  arches  or  pillars  of  the  fauces. 

The  Teeth  (dentes)  (Figs.  995  to  997).— Man  is  provided  with  two  sets  of  teeth, 
which  make  their  appearance  at  different  periods  of  life.  Those  of  the  first  set 
appear  in  childhood,  and  are  called  the  deciduous  or  milk  teeth.  Those  of  the  second 
set,  which  also  appear  at  an  early  period,  may  continue  until  old  age,  and  are 
named  permanent. 

The  deciduous  teeth  are  twenty  in  number:  four  incisors,  two  canines,  and  four 
molars,  in  each  jaw. 


I 


THE  MOUTH 


1113 


The  permanent  teeth  are  thirty-two  in  number:  four  incisors,  two  canines,  four 
premolars,  and  six  molars,  in  each  jaw. 


Premolars 


Molar 


'f 


'alatine  process  of  maxilla 
Horizontal  part  of  palatine  hone 


Greater  palatine  foramen 
Lesser  palati)ie  foramina 


Fig.  996. — Permanent  teeth  of  upper  dental  arch, 
seen  from  below. 


Fig.  997. — Permanent  teeth  of  right  half  of 
lower  dental  arch,  seen  from  above. 


1114 


SPLANCHNOLOGY 


The  dental  formulae  may  be  represented  as  follows: 

Deciduous  Teeth. 


Upper  jaw 


mol. 

2 


can. 
1 


Lower  jaw 
Upper  jaw 


can. 
1 


mol. 

2 


1 
-  }  Total  20 

J 


Permanent  Teeth. 

mol. 

3 

pr.  mol.      can.          in.    i  in. 

2         1        2     2 

can. 
1 

pr.  mcl. 

2 

mol. 

3^ 

Lower  jaw 


2      2 


Total  32 


3j 


General  Characteristics.  —  Each  tooth  consists  of  three  portions:  the  crown, 
projecting  above  the  gum;  the  root,  imbedded  in  the  alveolus;  and  the  neck,  the 
constricted  portion  between  the  crown  and  root. 


Fig.  998. — Maxillte  at  about  one  year.     (Noyes.) 

The  roots  of  the  teeth  are  firmly  implanted  in  depressions  within  the  alveoli; 
these  depressions  are  lined  with  periosteum  which  invests  the  tooth  as  far  as  the 
neck.  At  the  margins  of  the  alveoli,  the  periosteum  is  continuous  with  the  fibrous 
structure  of  the  gums. 

In  consequence  of  the  curve  of  the  dental  arch,  terms  such  as  anterior  and 
posterior,  as  applied  to  the  teeth,  are  misleading  and  confusing.  Special  terms 
are  therefore  used  to  indicate  the  different  surfaces  of  a  tooth :  the  surface  directed 
toward  the  lips  or  cheek  is  known  as  the  labial  or  buccal  surface;  that  directed 
toward  the  tongue  is  described  as  the  lingual  surface;  those  surfaces  which  touch 
neighboring  teeth  are  termed  surfaces  of  contact.  In  the  case  of  the  incisor  and 
canine  teeth  the  surfaces  of  contact  are  medial  and  lateral;  in  the  premolar  and 
molar  teeth  they  are  anterior  and  posterior. 

The  superior  dental  arch  is  larger  than  the  inferior,  so  that  in  the  normal  condi- 
tion the  teeth  in  the  maxillae  slightly  overlap  those  of  the  mandible  both  in  front 
and  at  the  sides.  Since  the  upper  central  incisors  are  wider  than  the  lower,  the 
other  teeth  in  the  upper  arch  are  thrown  somewhat  distally,  and  the  two  sets  do 


THE  MOUTH 


1115 


not  quite  correspond  to  each  other  when  the  mouth  is  closed:  thus  the  upper 
canine  tooth  rests  partly  on  the  lower  canine  and  partly  on  the  first  premolar, 
and  the  cusps  of  the  upper  molar  teeth  lie  behind  the  corresponding  cusps  of  the 
lower  molar  teeth.  The  two  series,  however,  end  at  nearly  the  same  point  behind; 
this  is  mainly  because  the  molars  in  the  upper  arch  are  the  smaller. 


Fig.  999.—' 


•The  complete  temporary  dentition  (about  three  years),  showing  the  relation  of  the  developing  permanent 

teeth.     (Noyes.) 


Fig.  1000 


. — The  complete  temporary  dentition  and  the  first  permanent  molar.     Note  the  relation  of  the  bicuspids  to 
the  temporary  molars.     (In  the  seventh  year.)     (Noyes.) 

The  Permanent  Teeth  {denies  permanenies)  (Figs.  1002, 1003). — The  Incisors  (denies 
incisivi;  incisive  or  cutting  teeth)  are  so  named  from  their  presenting  a  sharp  cutting 
edge,  adapted  for  biting  the  food.  They  are  eight  in  number,  and  form  the  four 
front  teeth  in  each  dental  arch. 


1116 


SPLANCHNOLOGY 


The  crown  is  directed  vertically,  and  is  chisel-shaped,  being  bevelled  at  the  expense 
of  its  lingual  surface,  so  as  to  present  a  sharp  horizontal  cutting  edge,  which, 
before  being  subjected  to  attrition,  presents  three  small  prominent  points  separated 
by  two  slight  notches.  It  is  convex,  smooth,  and  highly  polished  on  its  labial 
surface;  concave  on  its  lingual  surface,  where,  in  the  teeth  of  the  upper  arch,  it  is 
frequently  marked  by  an  inverted  V-shaped  eminence,  situated  near  the  gum. 
This  is  known  as  the  basal  ridge  or  cingulum.  The  neck  is  constricted.  The  root 
is  long,  single,  conical,  transversely  flattened,  thicker  in  front  than  behind,  and 
slightly  grooved  on  either  side  in  the  longitudinal  direction. 


Fig.  1001. 


-Front  view  of  the  skull  shown  in  Fig.  1000.    Note  the  relation  of  the  permanent  incisors  and  cuspids  to  each 
other  and  the  roots  of  the  temporary  teeth.      (Noyes.) 


The  upper  incisors  are  larger  and  stronger  than  the  lower,  and  are  directed 
obliquely  downward  and  forward.  The  central  ones  are  larger  than  the  lateral, 
and  their  roots  are  more  rounded. 

The  lower  incisors  are  smaller  than  the  upper:  the  central  ones  are  smaller  than 
the  lateral,  and  are  the  smallest  of  all  the  incisors.  They  are  placed  vertically 
and  are  somewhat  bevelled  in  front,  where  they  have  been  worn  down  by  contact 
with  the  overlapping  edge  of  the  upper  teeth.    The  cingulum  is  absent. 

The  Canine  Teeth  {denies  canini)  are  four  in  number,  two  in  the  upper,  and  two 
in  the  lower  arch,  one  being  placed  laterally  to  each  lateral  incisor.  They  are  larger 
and  stronger  than  the  incisors,  and  their  roots  sink  deeply  into  the  bones,  and 
cause  well-marked  prominences  upon  the  surface. 


THE  MOUTH 


1117 


The  crown  is  large  and  conical,  very  convex  on  its  labial  surface,  a  little  hollowed 
and  uneven  on  its  lingual  surface,  and  tapering  to  a  blunted  point  or  cusp,  which 
projects  beyond  the  level  of  the  other  teeth.  The  root  is  single,  but  longer  and 
thicker  than  that  of  the  incisors,  conical  in  form,  compressed  laterally,  and  marked 
by  a  slight  groove  on  each  side. 


First  and  sec- 
ond inferior 
premolars 


-^  Mental  fora- 
men 


[  Pig.  1003. — The  permanent  teeth,  viewed  from  the  right.    The  external  layer  of  bone  has  been  partly  removed  and  the 

maxillary  sinus  has  been  opened.     (Spalteholz.) 

The  upper  canine  teeth  (popularly  called  eye  teeth)  are  larger  and  longer  than 
[the  lower,  and  usually  present  a  distinct  basal  ridge. 

The  lower  canine  teeth  (popularly  called  stomach  teeth)  are  placed  nearer  the 
middle  line  than  the  upper,  so  that  their  summits  correspond  to  the  intervals 
between  the  upper  canines  and  the  lateral  incisors. 


1118 


SPLANCHNOLOGY 


I 


The  Premolars  or  Bicuspid  teeth  {denies  jpraemolares)  are  eight  in  number,  four 
in  each  arch.  They  are  situated  lateral  to  and  behind  the  canine  teeth,  and  are 
smaller  and  shorter  than  they. 

The  crown  is  compressed  antero-posteriorly,  and  surmounted  by  two  pyramidal 
eminences  or  cusps,  a  labial  and  a  lingual,  separated  by  a  groove;  hence  their  name 
bicuspid.  Of  the  two  cusps  the  labial  is  the  larger  and  more  prominent.  The 
neck  is  oval.  The  root  is  generall}'  single,  compressed,  and  presents  in  front  and 
behind  a  deep  groove,  which  indicates  a  tendency  in  the  root  to  become  double. 
The  apex  is  generally  bifid. 

The  upper  premolars  are  larger,  and  present  a  greater  tendency  to  the  division 
of  their  roots  than  the  lower;  this  is  especially  the  case  in  the  first  upper  pre- 
molar. 

The  Molar  Teeth  {denies  molares)  are  the  largest  of  the  permanent  set,  and  their 
broad  crowns  are  adapted  for  grinding  and  pounding  the  food.  They  are  twelve 
in  number;  six  in  each  arch,  three  being  placed  posterior  to  each  of  the  second 
premolars. 

The  crown  of  each  is  nearly  cubical  in  form,  convex  on  its  buccal  and  lingual 
surfaces,  flattened  on  its  surfaces  of  contact;  it  is  surmounted  by  four  or  five  tuber- 
cles, or  cusps,  separated  from  each  other  by  a  crucial  depression;  hence  the  molars 
are  sometimes  termed  multicuspids.    The  neck  is  distinct,  large,  and  rounded. 

Upper  Molars. — As  a  rule  the  first  is  the  largest,  and  the  third  the  smallest  of 
the  upper  molars.  The  crow^n  of  the  first  has  usually  four  tubercles;  that  of  the 
second,  three  or  four;  that  of  the  third,  three.  Each  upper  molar  has  three  roots, 
and  of  these  two  are  buccal  and  nearly  parallel  to  one  another;  the  third  is  lingual 
and  diverges  from  the  others  as  it  runs  upward.  The  roots  of  the  third  molar 
{dens  serotinus  or  wisdom-tooih)  are  more  or  less  fused  together. 

Lower  Molars. — ^The  lower  molars  are  larger  than  the  upper.  On  the  crown 
of  the  first  there  are  usually  five  tubercles;  on  those  of  the  second  and  third,  four 

or  five.  Each  lower  molar  has  two  roots,  an 
anterior,  nearly  vertical,  and  a  posterior, 
directed  obliquely  backward;  both  roots  are 
grooved  longitudinally,  indicating  a  tendency 
to  division.  The  two  roots  of  the  third  molar 
{dens  serotinus  or  wisdom  tooth)  are  more  or 
less  united. 

The  Deciduous  Teeth  {denies  decidui;  tem- 
porary or  milk  teeth)  (Fig.  1004). — The  decid- 
uous are  smaller  than,  but,  generally  speak- 
ing, resemble  in  form,  the  teeth  which  bear 
the  same  names  in  the  permanent  set.  The 
hinder  of  the  two  molars  is  the  largest  of  all 
the  deciduous  teeth,  and  is  succeeded  by  the 
second  premolar.  The  first  upper  molar  has  only  three  cusps — two  labial,  one 
lingual;  the  second  upper  molar  has  four  cusps.  The  first  lower  molar  has  four 
cusps;  the  second  lower  molar  has  five.  The  roots  of  the  deciduous  molars  are 
smaller  and  more  divergent  than  those  of  the  permanent  molars,  but  in  other 
respects  bear  a  strong  resemblance  to  them. 

Structure  of  the  Teeth. — On  making  a  vertical  section  of  a  tooth  (Fig.  1005),  a  cavity  will  be 
found  in  the  interior  of  the  crown  and  the  center  of  each  root;  it  opens  by  a  minute  orifice  at 
the  extremity  of  the  latter.  This  is  called  the  pulp  cavity,  and  contains  the  dental  pulp,  a  loose 
connective  tissue  richly  supplied  with  vessels  and  nerves,  which  enter  the  cavity  through  the 
small  aperture  at  the  point  of  each  root.  Some  of  the  cells  of  the  pulp  are  arranged  as  a  layer 
on  the  wall  of  the  pulp  cavity;  they  are  named  the  odontoblasts  of  Waldeyer,  and  during  the 
development  of  the  tooth,  are  columnar  in  shape,  but  later  on,  after  the  dentin  is  fully  formed, 
they  become  flattened  and  resemble  osteoblasts.     Each  has  two  fine  processes,  the  outer  one 


Fig.  1004. — Deciduous  teeth.     Left  side. 


THE  MOUTH 


1119 


passing  into  a  dental  canaliculus,  the  inner  being  continuous  with  the  processes  of  the  connective- 
tissue  cells  of  the  pulp  matrix. 

The  solid  portion  of  the  tooth  consists  of  (1)  the  ivory  or  dentin,  which  forms  the  bulk  of  the 
tooth;  (2)  the  enamel,  which  covers  the  exposed  part  of  the  crown;  and  (3)  a  thin  layer  of  bone, 
the  cement  or  crusta  petrosa,  which  is  disposed  on  the  surface  of  the  root. 

The  dentin  (substantia  eburnea;  ivory)  (Fig.  1007)  forms  the  principal  mass  of  a  tooth.  It  is 
a  modification  of  osseous  tissue,  from  which  it  differs,  however,  in  structure.  On  microscopic 
examination  it  is  seen  to  consist  of  a  number  of  minute  wavy  and  branching  tubes,  the  dental 
canaliculi,  imbedded  in  a  dense  homogeneous  substance,  the  matrix. 


Fig.   1006. — Vertical  section  of  a  molar  tooth. 


Crown 


Fig.  1005. — Vertical  section  of  a  tooth  in  situ.  X  15. 
c  is  placed  in  the  pulp  cavity,  opposite  the  neck  of  the 
tootn;  the  part  above  it  is  the  crown,  that  below  is  the 
root.  1.  Enamel  with  radial  and  concentric  markings. 
2.  Dentin  with  tubules  and  incremental  lines.  3.  Cement 
or  crusta  petrosa,  with  bone  corpuscles.  4.  Dental 
periosteum.    5.  Mandible. 


Fig.  1007. — Vertical  section  of  a  premolar  tooth. 
(Magnified.) 


I 


The  dental  canaliculi  (dentinal  tubules)  (Fig.  1008)  are  placed  parallel  with  one  another,  and 
open  at  their  inner  ends  into  the  pulp  cavity.  In  their  course  to  the  periphery  they  present  two 
or  three  curves,  and  are  twisted  on  themselves  in  a  spiral  direction.  These  canaliculi  vary  in 
direction:  thus  in  a  togth  of  the  mandible  they  are  vertical  in  the  upper  portion  of  the  crown, 
becoming  oblique  and  then  horizontal  in  the  neck  and  upper  part  of  the  root,  while  toward  the 
lower  part  of  the  root  they  are  inclined  downward.  In  their  course  they  divide  and  subdivide 
dichotomously,  and,  especially  in  the  root,  give  off  minute  branches,  which  join  together  in 
loops  in  the  matrix,  or  end  bUndly.  Near  the  periphery  of  the  dentin,  the  finer  ramifications 
of  the  canalicuh  terminate  imperceptibly  by  free  ends.  The  dental  canahculi  have  definite  walls, 
consisting  of  an  elastic  homogeneous  membrane,  the  dentinal  sheath  of  Neumann,  which  resists 
the  action  of  acids;  they  contain  slender  cylindrical  prolongations  of  the  odontoblasts,  first 
described  by  Tomes,  and  named  Tomes'  fibers  or  dentinal  fibers. 


1120 


SPLANCHNOLOGY 


s  Cement 


Interglobular 
s'paces 


Dentin 


The  matrix  (intertubular  dentin)  is  translucent,  and  contains  the  chief  part  of  the  earth 
matter  of  the  dentin.     In  it  are  a  number  of  fine  fibrils,  which  are  continuous  with  the  fibrils 

of  the  dental  pulp.     After   the  earthy  matter  has 

■ ■■_"^-£^.  been  removed  by  steeping   a  tooth  in  weak  acid, 

the  animal  basis  remaining  may  be  torn  into  laminae 
which  run  parallel  with  the  pulp  cavity,  across  the 
direction  of  the  tubes.  A  section  of  dry  dentin  often 
displays  a  series  of  somewhat  parallel  lines — th 
incremental  lines  of  Salter.  These  lines  are  com- 
posed  of  imperfectly  calcified  dentin  arranged  in 
layers.  In  consequence  of  the  imperfection  in  the 
calcifying  process,  little  irregular  cavities  are  left, 
termed  interglobular  spaces  (Fig.  1008).  Normally 
a  series  of  these  spaces  is  found  toward  the  outer 
surface  of  the  dentin,  where  they  form  a  layer  which 
is  sometimes  known  as  the  granular  layer.  They 
have  received  their  name  from  the  fact  that  they 
are  surrounded  by  minute  nodules  or  globules  of 
dentin.  Other  curved  lines  may  be  seen  parallel  to 
the  surface.  These  are  the  lines  of  Schreger,  and 
are  due  to  the  optical  effect  of  simultaneous  curva- 
tm-e  of  the  dentinal  fibers. 

Chemical  Composition.  —  According  to  Berzelius 
and  von  Bibra,  dentin  consists  of  28  parts  of  animal 
and  72  parts  of  earthy  matter.  The  animal  matter 
is  converted  by  boihng  into  gelatin.  The  earthy 
matter  consists  of  phosphate  of  lime,  carbonate  of 
lime,  a  trace  of  fluoride  of  calcium,  phosphate  of 
magnesium,  and  other  salts. 

The  enamel  {substantia  adaniantina)  is  the  hardest 
and  most  compact  part  of  the  tooth,  and  forms  a 
thin  crust  over  the  exposed  part  of  the  crown,  as  far 
as  the  commencement  of  the  root.  It  is  thickest  on 
the  grinding  surface  of  the  crown,  until  worn  away 
by  attrition,  and  becomes  thinner  toward  the  neck. 
It  consists  of  minute  hexagonal  rods  or  columns 
termed  enamel  fibers  or  enamel  prisms  {prismata  adamantina).  They  lie  parallel  with  one 
another,  resting  by  one  extremity  upon  the  dentin,  which  presents  a  number  of  minute  depres- 
sions for  their  reception;  and  forAiing  the  free  surface  of  the  crown  by  the  other  extremity. 
The  columns  are  directed  vertically  on  the  summit  of  the  crown,  horizontally  at  the  sides;  they 
are  about  4m  in  diameter,  and  pursue  a  more  or  less  wavy  course.  Each  column  is  a  six-sided 
prism  and  presents  numerous  dark  transverse  shadings;  these  shadings  are  probably  due  to  the 
manner  in  which  the  columns  are  developed  in  successive  stages,  producing  shallow  constric- 
tions, as  will  be  subsequently  explained.  Another  series  of  lines,  having  a  brown  appearance, 
the  parallel  striae  or  colored  lines  of  Retzius,  is  seen  on  section.  According  to  Ebner,  they  are 
produced  by  air  in  the  interprismatic  spaces;  others  believe  that  they  are  the  result  of  true 
pigmentation. 

Numerous  minute  interstices  intervene  between  the  enamel  fibers  near  their  dentinal  ends, 
a  provision  calculated  to  allow  of  the  permeation  of  fluids  from  the  dental  canaliculi  into  the 
substance  of  the  enamel. 

Chemical  Composition. — According  to  von  Bibra,  enamel  consists  of  96.5  per  cent,  of  earthy 
matter,  and  3.5  per  cent,  of  animal  matter.  The  earthy  matter  consists  of  phosphate  of  lime, 
with  traces  of  fluoride  of  calcium,  carbonate  of  lime,  phosphate  of  magnesium,  and  other  salts. 
According  to  Tomes,  the  enamel  contains  the  merest  trace  of  organic  matter. 

The  crusta  petrosa  or  cement  {substantia  ossea)  is  disposed  as  a  thin  layer  on  the  roots  of  the 
teeth,  from  the  termination  of  the  enamel  to  the  apex  of  each  root,  where  it  is  usually  very  thick. 
In  structure  and  chemical  composition  it  resembles  bone.  It  contains,  sparingly,  the  lacunae 
and  canahculi  which  characterize  true  bone;  the  lacuna?  placed  near  ,the  surface  receive  the 
canaliculi  radiating  from  the  side  of  the  lacunae  toward  the  periodontal  membrane;  and  those 
more  deeply  placed  join  with  the  adjacent  dental  canahculi.  In  the  thicker  portions  of  the 
crusta  petrosa,  the  lamellae  and  Haversian  canals  peculiar  to  bone  are  also  found. 

As  age  advances,  the  cement  increases  in  thickness,  and  gives  rise  to  those  bony  growths  or 
exostoses  so  common  in  the  teeth  of  the  aged;  the  pulp  cavity  also  becomes  partially  filled  up  by 
a  hard  substance,  intermediate  in  structure  between  dentin  and  bone  {osteodentin,  Owen;  second- 
ary dentin,  Tomes).  It  appears  to  be  formed  by  a  slow  conversion  of  the  dental  pulp,  which 
shrinks,  or  even  disappears. 


Fia. 


1008. — Transverse  section  of  a  portion  of  the 
root  of  a  canine  tooth.     X  300. 


Development  of  the  Teeth  (Figs.  1009  to  1012).^ — In  describing  the  development  of  the  teeth, 
the  mode  of  formation  of  the  deciduous  teeth  must  first  be  considered,  and  then  that  of  the 
permanent  series. 


Fia.  1009. — Sagittal  section  through  the  first  lower  deciduous  molar  of  a  human  embryo  30  mm.  long.  (Rose.) 
X  100.  L.E.L.  Labiodental  lamina,  here  separated  from  the  dental  lamina.  Z.L.  Placed  over  the  shallow  dental 
furrow,  points  to  the  dental  lamina,  which  is  spread  out  below  to  form  the  enamel  germ  of  the  future  tooth.  P.p. 
Bicuspicfate  papilla,  capped  by  the  enamel  germ.     Z.S.  Condensed  tissue  forming  dental  sac.     M.E.  Mouth  epithelium 


Fia.   1010. — Similar  section  through  the  canine  tooth  of  an  embryo  40  mm.  long 
dental  furrow.     The  other  lettering  as  in  Fig.  1009. 


Dental  furroio 
Hemains  of  enamel  germ. 

Secondary  enamel  germ 


(Rose.)      X  100.     L.F.  Labio 


MeckcVs  cartilage 


Enamel  organ 
Dental  papilla 


Mandible 


Fia.  1011. — Verticai  section  of  the  mandible  of  an  early  human  fetus.      X  25. 


1122 


SPLANCHNOLOGY 


I 


d.  0(1. 


Development  of  the  Deciduous  Teeth. — The  development  of  the  deciduous  teeth  begins 
about  the  sixth  week  of  fetal  life  as  a  thickening  of  the  epithehum  along  the  line  of  the  future 
jaw,  the  thickening  being  due  to  a  rapid  multiplication  of  the  more  deeply  situated  epithelial 
cells.  As  the  cells  multiply  they  extend  into  the  subjacent  mesoderm,  and  thus  form  a  ridge 
or  strand  of  cells  imbedded  in  mesoderm.  About  the  seventh  week  a  longitudinal  spUtting  or 
cleavage  of  this  strand  of  cells  takes  place,  and  it  becomes  divided  into  two  strands;  the  separa- 
tion begins  in  front  and  extends  laterally,  the  process  occupying  four  or  five  weeks.  Of  the  two 
strands  thus  formed,  the  labial  forms  the  labiodental  lamina;  while  the  other,  the  lingual, 
is  the  ridge  of  cells  in  connection  with  which  the  teeth,  both  deciduous  and  permanent,  are 
developed.  Hence  it  is  known  as  the  dental  lamina  or  common  dental  germ.  It  forms  a  flat 
band  of  cells,  which  grows. into  the  substance  of  the  embryonic  jaw,  at  first  horizontally 
inward,  and  then,  as  the  teeth  develop,  vertically,  i.  e.,  upward  in  the  upper  jaw,  and 
downward  in  the  lower  jaw.  While  still  maintaining  a  horizontal  direction  it  has  two  edges 
— an  attached  edge,  continuous  with  the  epithelium  hning  the  mouth,  and  a  free  edge,  projecting 
inward,  and  imbedded  in  the  mesodermal  tissue  of  the  embryonic  jaw.  Along  its  line  of 
attachment  to  the  buccal  epithelium  is  a  shallow  groove,  the  dental  furrow. 

About  the  ninth  week  the  dental  lamina  begins 
to  develop  enlargements  along  its  free  border. 
These  are  ten  in  number  in  each  jaw,  and  each 
corresponds  to  a  future  deciduous  tooth.  They 
consist  of  masses  of  epithelial  cells;  and  the  cells 
of  the  deeper  part — that  is,  the  part  farthest  from 
the  margin  of  the  jaw — increase  rapidly  and  spread 
out  in  all  directions.  Each  mass  thus  comes  to 
assume  a  club  shape,  connected  with  the  general 
epithelial  lining  of  the  mouth  by  a  narrow  neck, 
embraced  by  mesoderm.  They  are  now  known  as 
special  dental  germs.  After  a  time  the  lower  ex- 
panded portion  inclines  outward,  so  as  to  form  an 
angle  with  the  superficial  constricted  portion,  which 
is  sometimes  known  as  the  neck  of  the  special 
dental  germ.  About  the  tenth  week  the  meso- 
dermal tissue  beneath  these  special  dental  germs 
becomes  differentiated  into  papillae;  these  grow 
upward,  and  come  in  contact  with  the  epithelial 
cells  of  the  special  dental  germs,  which  become 
folded  over  them  like  a  hood  or  cap.  There  is, 
then,  at  this  stage  a  papilla  (or  papillae)  which 
has  already  begun  to  assume  somewhat  the  shape 
of  the  crown  of  the  future  tooth,  and  from  which 
the  dentin  and  pulp  of  the  tooth  are  formed,  sur- 
mounted by  a  dome  or  cap  of  epithelial  cells  from 
which  the  enamel  is  derived. 

In  the  meantime,  while  these  changes  have  been 
going  on,  the  dental  lamina  has  been  extending 
backward  behind  the  special  dental  germ  corre- 
sponding to  the  second  deciduous  molar  tooth, 
and  at  about  the  seventeenth  week  it  presents  an 
enlargement,  the  special  dental  germ,  for  the  first 
permanent  molar,  soon  followed  by  the  formation 
of  a  papilla  in  the  mesodermal  tissue  for  the  same  tooth.  This  is  followed,  about  the  sixth 
month  after  birth,  by  a  further  extension  backward  of  the  dental  lamina,  with  the  formation 
of  another  enlargement  and  its  corresponding  papilla  for  the  second  molar.  And  finally  the  pro- 
cess is  repeated  for  the  third  molar,  its  papilla  appearing  about  the  fifth  year  of  life. 

After  the  formation  of  the  special  dental  germs,  the  dental  lamina  undergoes  atrophic  changes 
and  becomes  cribriform,  except  on  the  Ungual  and  lateral  aspects  of  each  of  the  special  germs 
of  the  temporary  teeth,  where  it  undergoes  a  local  thickening  forming  the  special  dental  germ 
of  each  of  the  successional  permanent  teeth — i.  e.,  the  ten  anterior  ones  in  each  jaw.  Here  the 
same  process  goes  on  as  has  been  described  in  connection  with  those  of  the  deciduous  teeth: 
that  is,  they  recede  into  the  substance  of  the  gum  behind  the  germs  of  the  deciduous  teeth.  As 
they  recede  they  become  club-shaped,  form  expansions  at  their  distal  extremities,  and  finally 
meet  papillae,  which  have  been  formed  in  the  mesoderm,  just  in  the  same  manner  as  was  the 
case  in  the  deciduous  teeth.  The  apex  of  each  papilla  indents  the  dental  germ,  which  encloses 
it,  and,  forming  a  cap  for  it,  becomes  converted  into  the  enamel,  while  the  papilla  forms  the 
dentin  and  pulp  of  the  permanent  tooth. 

The  special  dental  germs  consist  at  first  of  rounded  or  polyhedral  epithelial  cells;  after  the 


^•v  •  1  •■<?-.v:-'?>;.';'5W 


PtG.  1012. — Longitudinal  section  of  the  lower  part 
of  a  growing  tooth,  showing  the  extension  of  the  layer 
of  adamantoblasts  beyond  the  crown  to  mark  off 
the  limit  of  formation  of  the  dentin  .of  the  root. 
(Rose.)  ad.  Adamantoblasts,  continuous  below  with 
ep.ach.,  the  epithelial  sheath  of  Hertwig.  d.  Dentin. 
en.  Enamel,    od.  Odontoblasts,    p.  Pulp. 


THE  MOUTH  1123 

formation  of  the  papillae,  these  cells  undergo  a  differentiation  into  three  layers.  Those  which 
are  in  immediate  contact  with  the  papilla  become  elongated,  and  form  a  layer  of  well-marked 
columnar  epithelium  coating  the  papilla.  They  are  the  cells  which  form  the  enamel  fibers, 
and  are  therefore  termed  enamel  cells  or  adamantoblasts.  The  cells  of  the  outer  layer  of  the 
special  dental  germ,  which  are  in  contact  with  the  inner  surface  of  the  dental  sac,  presently  to 
be  described,  are  much  shorter,  cubical  in  form,  and  are  named  the  external  enamel  epitheUiun. 
All  the  intermediate  round  cells  of  the  dental  germ  between  these  two  layers  imdergo  a  peculiar 
change.  They  become  stellate  in  shape  and  develop  processes,  which  unite  to  form  a  net-work 
into  which  fluid  is  secreted;  this  has  the  appearance  of  a  jelly,  and  to  it  the  name  of  enamel  pulp 
is  given.  This  transformed  special  dental  germ  is  now  known  under  the  name  of  enamel  organ 
(Fig.  1011). 

While  these  changes  are  going  on,  d  sac  is  formed  around  each  enamel  organ  from  the  sur- 
rounding mesodermal  tissue.  This  is  known  as  the  dental  sac,  and  is  a  vascular  membrane 
of  connective  tissue.  It  grows  up  from  below,  and  thus  encloses  the  whole  tooth  germ;  as  it 
grows  it  causes  the  neck  of  the  enamel  organ  to  atrophy  and  disappear;  so  that  all  communi- 
cation between  the  enamel  organ  and  the  superficial  epithelium  is  cut  off.  At  this  stage  there 
are  vascular  papillae  surmounted  by  caps  of  epithelial  cells,  the  whole  being  surrounded  by 
by  membranous  sacs. 

Formation  of  the  Enamel. — The  enamel  is  formed  exclusively  from  the  enamel  cells  or  adaman- 
toblasts of  the  special  dental  germ,  either  by  direct  calcification  of  the  columnar  cells,  which 
become  elongated  into  the  hexagonal  rods  of  the  enamel;  or,  as  is  more  generally  beUeved,  as 
a  secretion  from  the  adamantoblasts,  within  which  calcareous  matter  is  subsequently  deposited. 

The  process  begins  at  the  apex  of  each  cusp,  at  the  ends  of  the  enamel  cells  in  contact  with 
the  dental  papilla.  Here  a  fine  globular  deposit  takes  place,  being  apparently  shed  from  the  end 
of  the  adamantoblasts.  It  is  known  by  the  name  of  the  enamel  droplet,  and  resembles  keratin 
in  its  resistance  to  the  action  of  mineral  acids.  This  droplet  then  becomes  fibrous  and  calcifies 
and  forms  the  first  layer  of  the  enamel;  a  second  droplet  now  appears  and  calcifies,  and  so  on; 
successive  droplets  of  keratin-Uke  material  are  shed  from  the  adamantoblasts  and  form  successive 
layers  of  enamel,  the  adamantoblasts  gradually  receding  as  each  layer  is  produced,  imtil  at  the 
termination  of  the  process  they  have  almost  disappeared.  The  intermediate  cells  of  the  enamel 
pulp  atrophy  and  disappear,  so  that  the  newly  formed  calcified  material  and  the  external  enamel 
epithehum  come  into  apposition.  This  latter  layer,  however,  soon  disappears  on  the  emergence 
of  the  tooth  beyond  the  gum.  After  its  disappearance  the  crown  of  the  tooth  is  still  covered 
by  a  distinct  membrane,  which  persists  for  some  time.  This  is  known  as  the  cuticula  dentis,  or 
Nasmyth's  membrane,  and  is  beheved  to  be  the  last-formed  layer  of  enamel  derived  from  the 
adamantoblasts,  which  has  not  become  calcified.  It  forms  a  horny  layer,  which  may  be  sepa- 
rated from  the  subjacent  calcified  mass  by  the  action  of  strong  agids.  It  is  marked  by  the  hexagonal 
impressions  of  the  enamel  prisms,  and,  when  stained  by  nitrate  of  silver,  shows  the  characteristic 
appearance  of  epithelium. 

Formation  of  the  Dentin. — While  these  changes  are  taking  place  in  the  epithelium  to  form 
the  enamel,  contemporaneous  changes  occurring  in  the  differentiated  mesoderm  of  the  dental 
papillae  result  in  the  formation  of  the  dentin.  As  before  stated,  the  first  germs  of  the  dentin  are 
the  papillae,  corresponding  in  nmnber  to  the  teeth,  formed  from  the  soft  mesodermal  tissue 
which  bounds  the  depressions  containing  the  special  enamel  germs.  The  papillae  grow  upward 
into  the  enamel  germs  and  become  covered  by  them,  both  being  enclosed  in  a  vascular  connective 
tissue,  the  dental  sac,  in  the  manner  above  described.  Each  papiUa  then  constitutes  the  forma- 
tive pulp  from  which  the  dentin  and  permanent  pulp  are  developed;  it  consists  of  rounded  cells 
and  is  very  vascular,  and  soon  begins  to  assimie  the  shape  of  the  future  tooth.  The  next  step 
is  the  appearance  of  the  odontoblasts,  which  have  a  relation  to  the  development  of  the  teeth 
similar  to  that  of  the  osteoblasts  to  the  formation  of  bone.  They  are  formed  from  the  cells 
of  the  periphery  of  the  papilla — that  is  to  say,  from  the  cells  in  immediate  contact  with  the 
adamantoblasts  of  the  special  dental  germ.  These  cells  become  elongated,  one  end  of  the 
elongated  cell  resting  against  the  epithelium  of  the  special  dental  germs,  the  other  being  tapered 
and  oftened  branched.  By  the  direct  transformation  of  the  peripheral  ends  of  these  cells,  or 
by  a  secretion  from  them,  a  layer  of  uncalcified  matrix  (prodentin)  is  formed  which  caps  the 
cusp  or  cusps,  if  there  are  more  than  one,  of  the  papillae.  This  matrix  becomes  fibrillated,  and 
in  it  islets  of  calcification  make  their  appearance,  and  coalescing  give  rise  to  a  continuous  layer 
of  calcified  material  which  covers  each  cusp  and  constitutes  the  first  layer  of  dentin.  The  odon- 
toblasts, having  thus  formed  the  first  layer,  retire  toward  the  center  of  the  papilla,  and,  as  they 
do  so,  produce  successive  layers  of  dentin  from  their  peripheral  extremities — that  is  to  say, 
they  form  the  dentinal  matrix  in  which  calcification  subsequently  takes  place.  As  they  thus 
recede  from  the  periphery  of  the  papiUa,  they  leave  behind  them  filamentous  processes  of  cell 
protoplasm,  provided  with  finer  side  processes;  these  are  surrounded  by  calcified  material,  and 
thus  form  the  dental  canaUcuh,  and,  by  their  side  branches,  the  anastomosing  canalicuh:  the 
processes  of  protoplasm  contained  within  them  constitute  the  dentinal  fibers  {Tomes'  fibers). 
In  this  way  the  entire  thickness  of  the  dentin  is  developed,  each  canaliculus  being  completed 


l_ 


1124  SPLANCHNOLOGY 

throughout  its  whole  length  by  a  single  odontoblast.  The  central  part  of  the  papilla  does  not 
undergo  calcification,  but  persists  as  the  pulp  of  the  tooth.  In  this  process  of  formation  of  dentin 
it  has  been  shown  that  an  uncalcified  matrix  is  first  developed,  and  that  in  this  matrix  islets  of 
calcification  appear  which  subsequently  blend  together  to  form  a  cap  to  each  cusp :  in  like  manner 
successive  layers  are  produced,  which  ultimately  become  blended  with  each  other.  In  certain 
places  this  blending  is  not  complete,  portions  of  the  matrix  remaining  uncalcified  between  the 
successive  layers;  this  gives  rise  to  little  spaces,  which  are  the  interglobular  spaces  alluded  to 
above. 

Formation  of  the  Cement. — The  root  of  the  tooth  begins  to  be  formed  shortly  before  the  crown 
emerges  through  the  gum,  but  is  not  completed  until  some  time  afterward.  It  is  produced  by  a 
downgrowth  of  the  epithehum  of  the  dental  germ,  which  extends  almost  as  far  as  the  situation 
of  the  apex  of  the  future  root,  and  determines  the  form  of  this  portion  of  the  tooth.  This  fold 
of  epithelium  is  known  as  the  epithelial  sheath,  and  on  its  papillary  surface  odontoblasts  appear, 
which  in  turn  form  dentin,  so  that  the  dentin  formation  is  identical  in  the  crown  and  root  of  the 
tooth.  After  the  dentin  of  the  root  has  been  developed,  the  vascular  tissues  of  the  dental  sac 
begin  to  break  through  the  epithehal  sheath,  and  spread  over  the  surface  of  the  root  as  a  layer 
of  bone-forming  material.  In  this  osteoblasts  make  their  appearance,  and  the  process  of  ossi- 
fication goes  on  in  identically  the  same  manner  as  in  the  ordinary  intramembranous  ossification 
of  bone.  In  this  way  the  cement  is  formed,  and  consists  of  ordinary  bone  containing  canaliculi 
and  lacunae. 

Formation  of  the  Alveoli. — About  the  fourteenth  week  of  embryonic  hfe  the  dental  lamina 
becomes  enclosed  in  a  trough  or  groove  of  mesodermal  tissue,  which  at  first  is  common  to  all  the 
dental  germs,  but  subsequently  becomes  divided  by  bony  septa  into  locuh,  each  loculus  con- 
taining the  special  dental  germ  of  a  deciduous  tooth  and  its  corresponding  permanent  tooth. 
After  birth  each  cavity  becomes  subdivided,  so  as  to  form  separate  loculi  (the  future  alveoli) 
for  the  deciduous  tooth  and  its  corresponding  permanent  tooth.  Although  at  one  time  the  whole 
of  the  growing  tooth  is  contained  in  the  cavity  of  the  alveolus,  the  latter  never  completely  encloses 
it,  since  there  is  always  an  aperture  over  the  top  of  the  crown  filled  by  soft  tissue,  by  which  the 
dental  sac  is  connected  with  the  surface  of  the  gum,  and  which  in  the  permanent  teeth  is  called 
the  gubemaculum  dentis. 

Development  of  the  Permanent  Teeth. — The  permanent  teeth  as  regards  their  development 
may  be  divided  into  two  sets:  (1)  those  which  replace  the  deciduous  teeth,  and  which,  like  them, 
are  ten  in  number  in  each  jaw:  these  are  the  successional  permanent  teeth;  and  (2)  those  which 
have  no  deciduous  predecessors,  but  are  superadded  distal  to  the  temporary  dental  series.  These 
are  three  in  number  on  either  side  in  each  jaw,  and  are  termed  superadded  permanent  teeth. 
They  are  the  three  molars  of  the  permanent  set,  the  molars  of  the  deciduous  set  being  replaced 
by  the  premolars  of  the  permanent  set.  The  development  of  the  successional  permanent  teeth — 
the  ten  anterior  ones  in  either  jaw — has  already  been  indicated.  During  their  development  the 
permanent  teeth,  enclosed  in  their  sacs,  come  to  be  placed  on  the  lingual  side  of  the  deciduous 
teeth  and  more  distant  from  the  margin  of  the  future  gum,  and,  as  already  stated,  are  separated 
from  them  by  bony  partitions.  As  the  crown  of  the  permanent  tooth  grows,  absorption  of  these 
bony  partitions  and  of  the  root  of  the  deciduous  tooth  takes  place,  through  the  agency  of  osteo- 
clasts, which  appear  at  this  time,  and  finally  nothing  but  the  crown  of  the  deciduous  tooth  remains. 
This  is  shed  or  removed,  and  the  permanent  tooth  takes  its  place. 

The  superadded  permanent  teeth  are  developed  in  the  manner  aheady  described,  by  extensions 
backward  of  the  posterior  part  of  the  dental  lamina  in  each  jaw. 

Eruption  of  the  Teeth. — When  the  calcification  of  the  different  tissues  of  the  tooth 
is  sufficiently  advanced  to  enable  it  to  bear  the  pressure  to  which  it  will  be  afterward 
subjected,  eruption  takes  place,  the  tooth  making  its  way  through  the  gum.  The 
gum  is  absorbed  by  the  pressure  of  the  crown  of  the  tooth  against  it,  which  is 
itself  pressed  up  by  the  increasing  size  of  the  root.  At  the  same  time  the  septa 
between  the  dental  sacs  ossify,  and  constitute  the  alveoli;  these  firmly  embrace 
the  necks  of  the  teeth,  and  afford  them  a  solid  basis  of  support. 

The  eruption  of  the  deciduous  teeth  commences  about  the  seventh  month  after 
birth,  and  is  completed  about  the  end  of  the  second  year,  the  teeth  of  the  lower 
jaw  preceding  those  of  the  upper. 
The  following,  according  to  C.  S.  Tomes,  are  the  most  usual  times  of  eruption; 

Lower  central  incisors 6  to    9  months. 

Upper  incisors 8  to  10  months. 

Lower  lateral  incisors  and  first  molars         .       .     15  to  21  months. 

Canines 16  to  20  months. 

Second  molars 20  to  24  months. 


I 


I 


THE  MOUTH  ^^^^^M         1125 


There  are,  however,  considerable  variations  in  these  times;  thus,  according 
to  Holt: 

At  the  age  of  1    vear  a  child  should  have    6  teeth. 
"     1|  years        "  "  12      " 

((  i(       91  a  i(  K  9A  (f 

Calcification  of  the  permanent  teeth  proceeds  in  the  following  order  in  the 
lower  jaw  (in  the  upper  jaw  it  takes  place  a  little  later) :  the  first  molar,  soon 
after  birth;  the  central  and  lateral  incisors,  and  the  canine,  about  six  months 
after  birth;  the  premolars,  at  the  second  year,  or  a  little  later;  the  second  molar, 
about  the  end  of  the  second  year;  the  third  molar,  about  the  twelfth  year. 

The  eruption  of  the  permanent  teeth  takes  place  at  the  following  periods,  the 
teeth  of  the  lower  jaw  preceding  those  of  the  upper  by  short  intervals : 

First  molars 6th  year. 

Two  central  incisors 7th  year. 

Two  lateral  incisors 8th  year. 

First  premolars      ...  9th  year. 

Second  premolars 10th  year. 

Canines 11th  to  12th  yean 

Second  molars 12th  to  13th  year. 

Third  molars 17th  to  25th  year. 

Toward  the  sixth  year,  before  the  shedding  of  the  deciduous  teeth  begins,  there 
are  twenty-four  teeth  in  each  jaw,  viz.,  the  ten  deciduous  teeth  and  the  crowns 
of  all  the  permanent  teeth  except  the  third  molars. 

The  Tongue  {Ungua). — The  tongue  is  the  principal  organ  of  the  sense  of  taste, 
and  an  important  organ  of  speech ;  it  also  assists  in  the  mastication  and  deglutition 
of  the  food.  It  is  situated  in  the  floor  of  the  mouth,  within  the  curve  of  the 
body  of  the  mandible. 

Its  Root  {radix  linguce;  hose)  (Fig.  954)  is  directed  backward,  and  connected 
with  the  hyoid  bone  by  the  Hyoglossi  and  Genioglossi  muscles  and  the  hyoglossal 
membrane;  with  the  epiglottis  by  three  folds  (glossoepiglottic)  of  mucous  membrane; 
wdth  the  soft  palate  by  the  glossopalatine  arches;  and  with  the  pharynx  by  the 
Constrictores  pharyngis  superiores  and  the  mucous  membrane. 

Its  Apex  (apex  linguae;  tip),  thin  and  narrow,  is  directed  forward  against  the 
lingual  surfaces  of  the  lower  incisor  teeth. 

Its  Inferior  Surface  (fades  inferior  lingnas;  under  surface)  (Fig.  1013)  is  connected 
with  the  mandible  by  the  Genioglossi;  the  mucous  membrane  is  reflected  from  it 
to  the  lingual  surface  of  the  gum  and  on  to  the  floor  of  the  mouth,  where,  in  the 
middle  line,  it  is  elevated  into  a  distinct  vertical  fold,  the  frenulum  linguae.  On 
either  side  lateral  to  the  frenulum  is  a  slight  fold  of  the  mucous  membrane,  the 
plica  fimbriata,  the  free  edge  of  which  occasionally  exhibits  a  series  of  fringe-like 
processes. 

The  apex  of  the  tongue,  part  of  the  inferior  surface,  the  sides,  and  dorsum  are 
free. 

The  Dorsum  of  the  Tongue  (dorsum  lingu(p)  (Fig.  1014)  is  convex  and  marked  by 
a  median  sulcus,  which  divides  it  into  symmetrical  halves;  this  sulcus  ends  behind, 
about  2.5  cm.  from  the  root  of  the  organ,  in  a  depression,  the  foramen  cecum, 
from  which  a  shallow  groove,  the  sulcus  terminalis,  runs  lateralward  and  forward 
on  either  side  to  the  margin  of  the  tongue.  The  part  of  the  dorsum  of  the  tongue 
in  front  of  this  groove,  forming  about  two-thirds  of  its  surface,  looks  upward,  and 
is  rough  and  covered  with  papillse;  the  posterior  third  looks  backward,  and  is 


1126 


SPLANCHNOLOGY 


smoother,  and  contains  numerous  muciparous  glands  and  lymph  follicles  (lingual 
tonsil).  The  foramen  cecum  is  the  remains  of  the  upper  part  of  the  thyroglossal 
duct  or  diverticulum  from  which  the  thyroid  gland  is  developed;  the  pyramidal 
lobe  of  the  thyroid  gland  indicates  the  position  of  the  lower  part  of  the  duct. 

The  Papillae  of  the  Tongue  (Fig.  1014)  are  projections  of  the  corium.  They  are 
thickly  distributed  over  the  anterior  two-thirds  of  its  dorsum,  giving  to  this  surface 
its  characteristic  roughness.  The  varieties  of  papillae  met  with  are  the  papillae 
vallatae,  papillae  fungiformes,  papillae  filiformes,  and  papillae  simplices. 


Anterior  Unguud  gland 

Lingual  nerve 

Art.  profunda  linguoe 

Vena  com,  n.  Tiypoglossi 

Lojujttitdinalis  inferior 


Plica  fimbriata 


Vena  com,  n  hypogloaai 


Orifice  of  submax.  duct 
Plica  sublingualis 


Fig. 


1013. — The  mouth  cavity.    The  apex  of  the  tongue  ia  turned  upward,  and  on  the  right  side  a  superficial 
dissection  of  its  under  surface  has  been  made. 


The  papillae  vallatae  {circumvallate  papilloB)  (Fig.  1015)  are  of  large  size,  and  vary 
from  eight  to  twelve  in  number.  They  are  situated  on  the  dorsum  of  the  tongue 
immediately  in  front  of  the  foramen  cecum  and  sulcus  terminalis,  forming  a  row 
on  either  side;  the  two  rows  run  backward  and  medial  ward,  and  meet  in  the  middle 
line,  like  the  limbs  of  the  letter  V  inverted.  Each  papilla  consists  of  a  projection 
of  mucous  membrane  from  1  to  2  mm.  wide,  attached  to  the  bottom  of  a  circular 
depression  of  the  mucous  membrane;  the  margin  of  the  depression  is  elevated  to 
form  a  wall  {valluvi),  and  between  this  and  the  papilla  is  a  circular  sulcus  termed 
the  fossa.  The  papilla  is  shaped  like  a  truncated  cone,  the  smaller  end  being 
directed  downward  and  attached  to  the  tongue,  the  broader  part  or  base  projecting 
a  little  above  the  surface  of  the  tongue  and  being  studded  with  numerous  small 
secondary  papillae  and  covered  by  stratified  squamous  epithelium. 

The  papillae  fungiformes  {fungiform  papillae)  (Fig.  1017),  more  numerous  than  the 
preceding,  are  found  chiefly  at  the  sides  and  apex,  but  are  scattered  irregularly 
and  sparingly  over  the  dorsum.     They  are  easily  recognized,  among  the  other 


THE  MOUTH 


1127 


papillae,  by  their  large  size,  rounded  eminences,  and  deep  red  color.  They  are 
narrow  at  their  attachment  to  the  tongue,  but  broad  and  rounded  at  their  free 
extremities,  and  covered  with  secondary  papillae. 

Pliaryngo'palatine  arch 

Palatine  tonsil 

Glossopalaiine  arch 
Bticcinator 


Idhmua 
faucium 


'Fungiform  pajriXUs 


I 


Fig.   1015. — Circumvallate  papilla  in  vertical  section,  shearing  arrangement  of  liif  uiMf-uuds  and  nerves. 

The  papillse  filiformes  {filiform  or  conical  papilloB)  (Fig.  1016)  cover  the  anterior 
two-thirds  of  the  dorsum.    They  are  very  minute,  filiform  in  shape,  and  arranged 


1128 


SPLANCHNOLOGY 


in  lines  parallel  with  the  two  rows  of  the  papillae  vallatse,  excepting  at  the  apex  j 
of  the  organ,  where  their  direction  is   transverse.     Projecting  from  their  apices 
are  numerous  filamentous  processes,  or  secondary  papillae;  these  are  of  a  whitish 
tint,  owing  to  the  thickness  and  density  of  the  epithelium  of  which  they  are 
composed,  which  has  here  undergone  a  peculiar  modification,  the  cells  having  be- 1 


Secondary 
papillae 


Vein 


Fig.  1016. — A  filiform  papiUa.    Magnified 


Artery 
Vein 


Fig.  1017. — Section  of  a  fungiform  papilla.     Magnified. 


come  cornified  and  elongated  into  dense,  imbricated,  brush-like  processes.  They 
contain  also  a  number  of  elastic  fibers,  which  render  them  firmer  and  more  elastic 
than  the  papillae  of  mucous  membrane  generally.  The  larger  and  longer  papillae 
of  this  group  are  sometimes  termed  papillas  conicae. 


Fig.  1018. — Semidiagrammatic  view  of  a  portion  of  the  mucoiia  membrane  of  the  tongue.  Two  fungiform  papillffi 
are  shown.  On  some  of  the  filiform  papillae  the  epithelial  prolongations  stand  erect,  in  one  they  are  spread  out,  and  in 
three  they  are  folded  in. 


The  papillae  simplices  are  similar  to  those  of  the  skin,  and  cover  the  whole  of 
the  mucous  membrane  of  the  tongue,  as  well  as  the  larger  papillae.  They  consist 
of  closely  set  microscopic  elevations  of  the  corium,  each  containing  a  capillary 
loop,  covered  by  a  layer  of  epithelium. 

Muscles  of  the  Tongue. — The  tongue  is  divided  into  lateral  halves  by  a  median 
fibrous  septum  which  extends  throughout  its  entire  length  and  is  fixed  below  to  the 


THE  MOUTH 


hyoid  bone.    In  either  half  there  are  two- sets  of  muscles,  extrinsic  and  intrinsic; 
the  former  have  their  origins  outside  the  tongue,  the  latter  are  contained  entirely 
within  it. 
The  extrinsic  muscles  (Fig.  1019)  are: 

Genioglossus.  Chondroglossus. 

Hyoglossus.  Styloglossus. 

Glossopalatinus.^ 


Fig.   1019. — Extrinsic  muscles  of  the  tongue.     Left  side. 

The  Genioglossus  {Geniohyoglossus)  is  a  flat  triangular  muscle  close  to  and  par- 
allel with  the  median  plane,  its  apex  corresponding  with  its  point  of  origin  from  the 
mandible,  its  base  with  its  insertion  into  the  tongue  and  hyoid  bone.  It  arises 
by  a  short  tendon  from  the  superior  mental  spine  on  the  inner  surface  of  the  sym- 
physis menti,  immediately  above  the  Geniohyoideus,  and  from  this  point  spreads 
out  in  a  fan-like  form.  The  inferior  jBbers  extend  downward,  to  be  attached  by  a 
thin  aponeurosis  to  the  upper  part  of  the  body  of  the  hyoid  bone,  a  few  passing 
between  the  Hyoglossus  and  Chondroglossus  to  blend  with  the  Constrictores 
pharyngis;  the  middle  fibers  pass  backward,  and  the  superior  ones  upward  and  for- 
ward, to  enter  the  whole  length  of  the  under  surface  of  the  tongue,  from  the  root 
to  the  apex.  The  muscles  of  opposite  sides  are  separated  at  their  insertions  by  the 
median  fibrous  septum  of  the  tongue;  in  front,  they  are  more  or  less  blended  owing 
to  the  decussation  of  fasciculi  in  the  median  plane. 

The  Hyoglossus,  thin  and  quadrilateral,  arises  from  the  side  of  the  body  and 
from  the  whole  length  of  the  greater  cornu  of  the  hyoid  bone,  and  passes  almost 
vertically  upward  to  enter  the  side  of  the  tongue,  between  the  Styloglossus  and 
Longitudinalis  inferior.  The  fibers  arising  from  the  body  of  the  hyoid  bone  overlap 
those  from  the  greater  cornu. 

1  The  Glossopalatinua  (Palatoglossus) ,  although  one  of  the  muscles  of  the  tongue,  is  mc~e  closely  associated  with  the 
soft  palate  both  in  situation  and  function;  it  has  consequently  been  described  with  the  muscles  of  that  structure 
(p.  1139). 


1130 


SPLANCHNOLOGY 


The  Chondroglossus  is  sometimes  described  as  a  part  of  the  Hyoglossus,  but  is 
separated  from  it  by  fibers  of  the  Genioglossus,  which  pass  to  the  side  of  the 
pharynx.  It  is  about  2  cm.  long,  and  arises  from  the  medial  side  and  base  of  the 
lesser  cornu  and  contiguous  portion  of  the  body  of  the  hyoid  bone,  and  passes 
directly  upward  to  blend  with  the  intrinsic  muscular  fibers  of  the  tongue,  betwee^ji^ 
the  Hyoglossus  and  Genioglossus. 

A  small  slip  of  muscular  fibers  is  occasionally  found,  arising  from  the  cartilage 
triticea  in  the  lateral  hyothyroid  ligament  and  entering  the  tongue  with  the  hinder- 
most  fibers  of  the  Hyoglossus. 

The  Styloglossus,  the  shortest  and  smallest  of  the  three  styloid  muscles,  arises 
from  the  anterior  and  lateral  surfaces  of  the  styloid  process,  near  its  apex,  and 
from  the  stylomandibular  ligament.  Passing  downward  and  forward  between  the 
internal  and  external  carotid  arteries,  it  divides  upon  the  side  of  the  tongue 
into  two  portions:  one,  longitudinal,  enters  the  side  of  the  tongue  near  its 
dorsal  surface,  blending  with  the  fibers  of  the  Longitudinalis  inferior  in  front  of 
the  Hyoglossus;  the  other,  oblique,  overlaps  the  Hyoglossus  and  decussates  with 
its  fibers. 

The  intrinsic  muscles  (Fig.  1020)  are: 


Longitudinalis  superior. 
Longitudinalis  inferior. 


Transversus. 
Verticalis. 


The  Longitudinalis  linguae  superior  {Superior  lingualis)  is  a  thin  stratum  of  oblique 
and  longitudinal  fibers  immediately  underlying  the  mucous  membrane  on  the 
dorsum  of  the  tongue.  It  arises  from  the  submucous  fibrous  layer  close  to  the 
epiglottis  and  from  the  median  fibrous  septujm,  and  runs  forward  to  the  edges 
of  the  tongue. 


Longitudina- 
lis superior 


Papillce 
of  tongue 


Vertical  fibers  of  Genio- 
glossus intersecting 
Transversus 

Septum 


Insertion  of  Transversusi 

Styloglossus 
Hyoglossus 
Longitudinalis  inferior 

Lingual  artery 


Fig.   1020. — Coronal  section  of  tongue,   showing  intrinsic  muscles.     (Altered  from  Krause.) 


The  Longitudinalis  linguae  inferior  {Inferior  lingualis)  is  a  narrow  band  situated 
on  the  under  surface  of  the  tongue  between  the  Genioglossus  and  Hyoglossus. 
It  extends  from  the  root  to  the  apex  of  the  tongue:  behind,  some  of  its  fibers  are 
connected  with  the  body  of  the  hyoid  bone ;  in  front  it  blends  with  the  fibers  of 
the  Styloglossus. 

The  Transversus  linguae  {Transverse  lingualis)  consists  of  fibers  which  arise  from 
the  median  fibrous  septum  and  pass  lateralward  to  be  inserted  into  the  submucous 
fibrous  ti§sue  at  the  sides  of  the  tongue. 


THE  MOUTH 

The  Verticalis  linguae  (Vertical  lingualis)  is  found  only  at  the  borders  of  the  fore- 
part of  the  tongue.  Its  fibers  extend  from  the  upper  to  the  under  surface  of  the 
organ. 

^Hi  The  median  fibrous  septum  of  the  tongue  is  very  complete,  so  that  the  anastomosis  between 
^^^  the  two  Ungual  arteries  is  not  very  free. 

Nerves.— The  muscles  of  the  tongue  described  above  are  suppUed  by  the  hypoglossal  nerve. 

Actions. — The  movements  of  the  tongue,  although  numerous  and  compUcated,  may  be  under- 
stood by  carefully  considering  the  direction  of  the  fibers  of  its  muscles.  The  Genioglossi,  by  means 
of  their  posterior  fibers,  draw  the  root  of  the  tongue  forward,  and  protrude  the  apex  from  the 
mouth.  The  anterior  fibers  draw  the  tongue  back  into  the  mouth.  The  two  muscles  acting  in 
their  entirety  draw  the  tongue  downward,  so  as  to  make  its  superior  surface  concave  from  side 
to  side,  forming  a  channel  along  which  fluids  may  pass  toward  the  pharynx,  as  in  sucking.  The 
Hyoglossi  depress  the  tongue,  and  draw  down  its  sides.  The  Styloglossi  draw  the  tongue  upward 
and  backward.  The  Glossopalatini  draw  the  root  of  the  tongue  upward.  The  intrinsic  muscles 
are  mainly  concerned  in  altering  the  shape  of  the  tongue,  whereby  it  becomes  shortened,  nar- 
rowed, or  curved  in  different  directions;  thus,  the  Longitudinalis  superior  and  inferior  tend  to 
shorten  the  tongue,  but  the  former,  in  addition,  turn  the  tip  and  sides  upward  so  as  to  render 
the  dorsiun  concave,  while  the  latter  pull  the  tip  downward  and  render  the  dorsum  convex. 
The  Transversus  narrows  and  elongates  the  tongue,  and  the  Verticalis  flattens  and  broadens  it. 
The  complex  arrangement  of  the  muscular  fibers  of  the  tongue,  and  the  various  directions  in 
which  they  run,  give  to  this  organ  the  power  of  assuming  the  forms  necessary  for  the  enuncia- 
tion of  the  different  consonantal  sounds;  and  Macahster  states  "there  is  reason  to  believe  that 
the  musculature  of  the  tongue  varies  in  different  races  owing  to  the  hereditary  practice  and 
habitual  use  of  certain  motions  required  for  enunciating  the  several  vernacular  languages." 

Structure  of  the  Tongue. — The  tongue  is  partly  invested  by  mucous  membrane  and  a  sub- 
mucous fibrous  layer. 

The  mucous  membrane  {tunica  mucosa  lingms)  differs  in  different  parts.  That  covering  the 
under  surface  of  the  organ  is  thin,  smooth,  and  identical  in  structure  with  that  lining'  the  rest 
of  the  oral  cavity.  The  mucous  membrane  of  the  dorsum  of  the  tongue  behind  the  foramen 
cecum  and  sulcus  terminaUs  is  thick  and  freely  movable  over  the  subjacent  parts.  It  contains 
a  large  number  of  lymphoid  follicles,  which  together  constitute  what  is  sometimes  termed  the 
lingual  tonsil.  Each  folHcle  forms  a  rounded  eminence,  the  center  of  which  is  perforated  by  a 
minute  orifice  leading  into  a  funnel-shaped  cavity  or  recess;  around  this  recess  are  grouped 
numerous  oval  or  rounded  nodules  of  lymphoid  tissue,  each  enveloped  by  a  capsule  derived  from 
the  submucosa,  while  opening  into  the  bottom  of  the  recesses  are  also  seen  the  ducts  of  mucous 
glands.  The  mucous  membrane  on  the  anterior  part  of  the  dorsum  of  the  tongue  is  thin,  inti- 
mately adherent  to  the  muscular  tissue,  and  presents  nmnerous  minute  surface  eminences,  the 
papillae  of  the  tongue.  It  consists  of  a  layer  of  connective  tissue,  the  corium  or  mucosa,  covered 
with  epithelium. 

The  epithelium  is  of  the  stratified  squamous  variety,  similar  to  but  much  thinner  than  that 
of  the  skin :  and  each  papilla  has  a  separate  investment  from  root  to  summit.  The  deepest  cells 
may  sometimes  be  detached  as  a  separate  layer,  corresponding  to  the  rete  mucosum,  but  they 
never  contain  coloring  matter. 

The  corium  consists  of  a  dense  felt-work  of  fibrous  connective  tissue,  with  numerous  elastic 
fibers,  firmly  connected  with  the  fibrous  tissue  forming  the  septa  between  the  muscular  bundles 
of  the  tongue.  It  contains  the  ramifications  of  the  numerous  vessels  and  nerves  from  which 
the  papillae  are  supplied,  large  plexuses  of  lymphatic  vessels,  and  the  glands  of  the  tongue. 

Structure  of  the  Papillce.— The  papillae  apparently  resemble  in  structure  those  of  the  cutis, 
consisting  of  cone-shaped  projections  of  connective  tissue,  covered  with  a  thick  layer  of  stratified 
squamous  epithelium,  and  containing  one  or  more  capillary  loops  among  which  nerves  are  dis- 
tributed in  great  abundance.  If  the  epithelium  be  removed,  it  will  be  found  that  they  are  not 
simple  elevations  hke  the  papillae  of  the  skin,  for  the  surface  of  each  is  studded  with  minute 
^  conical  processes  which  form  secondary  papillae.  In  the  papillae  vallatae,  the  nerves  are  numer- 
Bfc.ous  and  of  large  size;  in  the  papillae  fungiformes  they  are  also  nmnerous,  and  end  in  a  plexiform 
■  ■  net-work,  from  which  brush-like  branches  proceed;  in  the  papillae  fihformes,  their  mode  of 
termination  is  uncertain. 

Glands  of  the  Tongue. — The  tongue  is  provided  with  mucous  and  serous  glands. 

The  mucous  glands  are  similar  in  structure  to  the  labial  and  buccal  glands.  They  are  found 
especially  at  the  back  part  behind  the  vallate  papillae,  but  are  also  present  at  the  apex  and  mar- 
ginal parts.  In  this  connection  the  anterior  lingual  glands  (Blandin  or  Nuhn)  require  special 
»  notice.  They  are  situated  on  the  under  surface  of  the  apex  of  the  tongue  (Fig.  1013),  one  on  either 
side  of  the  frenulum,  where  they  are  covered  by  a  fasciculus  of  muscular  fibers  derived  from  the 
Styloglossus  and  Longitudinalis  inferior.  They  are  from  12  to  25  mm.  long,  and  about  8  mm. 
broad,  and  each  opens  by  three  or  four  ducts  on  the  under  surface  of  the  apex. 

The  serous  glands  occur  only  at  the  back  of  the  tongue  in  the  neighborhood  of  the  taste-buds, 


SPLANCHNOLOGY 

their  ducts  opening  for  the  most  part  into  the  fossae  of  the  vallate  papillae.  These  glands  are 
racemose,  the  duct  of  each  branching  into  several  minute  ducts,  which  end  in  alveoU,  lined  by 
a  single  layer  of  more  or  less  columnar  epithelium.  Their  secretion  is  of  a  watery  nature,  and 
probably  assists  in  the  distribution  of  the  substance  to  be  tasted  over  the  taste  area.     (Ebner.) 

The  septum  consists  of  a  vertical  layer  of  fibrous  tissue,  extending  throughout  the  entire 
length  of  the  median  plane  of  the  tongue,  though  not  quite  reaching  the  dorsum.  It  is  thicker 
behind  than  in  fron,t,  and  occasionally  contains  a  small  fibrocartilage,  about  6  mm.  in  length. 
It  is  well  displayed  by  making  a  vertical  section  across  the  organ. 

The  hyoglossal  membrane  is  a  strong  fibrous  lamina,  which  connects  the  under  surface  of 
the  root  of  the  tongue  to  the  body  of  the  hyoid  bone.  This  membrane  receives,  in  front,  some 
of  the  fibers  of  the  Genioglossi. 

Taste-buds,  the  end-organs  of  the  gustatory  sense,  are  scattered  over  the  mucous  membrane 
of  the  mouth  and  tongue  at  irregular  intervals.  They  occur  especially  in  the  sides  of  the  vallate 
papillae.  In  the  rabbit  there  is  a  localized  area  at  the  side  of  the  base  of  the  tongue,  the  papilla 
foUata,  in  which  they  are  especially  abundant  (Fig.  1021).  They  are  described  imder  the  organs 
of  the  senses  (page  991). 


I 


Central  lamina  of 
corium 
Lateral  lamina  in  which 
nerve  fibers  run 
Gustatory  calyculus 

Sinus-like  vein  travers-. 
ing  whole  length  of 
folium 


Nerve  bundles 


Serous  gland 


4;sii««^«      -  -  ^g^g  bundles  -^-^c^^ 

Fig.   1021. — ^Vertical  section  of  papilla  foliata  of  the  rabbit,  passing  across  the  folia.     (Ranvier.) 

Vessels  and  Nerves. — The  main  artery  of  the  tongue  is  the  lingual  branch  of  the  external 
carotid,  but  the  external  maxillary  and  ascending  pharyngeal  also  give  branches  to  it.  The 
veins  open  into  the  internal  jugular. 

The  lymphatics  of  the  tongue  have  been  described  on  page  696. 

The  sensory  nerves  of  the  tongue  are:  (1)  the  lingual  branch  of  the  mandibular,  which  is 
distributed  to  the  papillae  at  the  forepart  and  sides  of  the  tongue,  and  forms  the  nerve  of  ordinary 
sensibility  for  its  anterior  two-thirds;  (2)  the  chorda  tympani  branch  of  the  facial,  which  runs 
in  the  sheath  of  the  lingual,  and  is  generally  regarded  as  the  nerve  of  taste  for  the  anterior  two- 
thirds;  this  nerve  is  a  continuation  of  the  sensory  root  of  the  facial  {nervus  intermedius) ;  (3)  the 
lingual  branch  of  the  glossopharyngeal,  which  is  distributed  to  the  mucous  membrane  at  the 
base  and  sides  of  the  tongue,  and  to  the  papiUae  vallatae,  and  which  supplies  both  gustatory 
filaments  and  fibers  of  general  sensation  to  this  region;  (4)  the  superior  laryngeal,  which  sends 
some  fine  branches  to  the  root  near  the  epiglottis. 

The  Salivary  Glands  (Fig.  1024). — Three  large  pairs  of  salivary  glands  communi- 
cate with  the  mouth,  and  pour  their  secretion  into  its  cavity;  they  are  the  parotid, 
submaxillary,  and  sublingual. 

Parotid  Gland  (glandula  parotis). — The  parotid  gland  (Figs.  1022, 1023),  the  largest 
of  the  three,  varies  in  weight  from  14  to  28  gm.  It  lies  upon  the  side  of  the  face, 
immediately  below  and  in  front  of  the  external  ear.  The  main  portion  of  the  gland 
is  superficial,  somewhat  flattened  and  quadrilateral  in  form,  and  is  placed  between 
the  ramus  of  the  mandible  in  front  and  the  mastoid  process  and  Sternocleidor 
mastoideus  behind,  overlapping,  however,  both  boundaries.  Above,  it  is  broad 
and  reaches  nearly  to  .the  zygomatic  arch;  below,  it  tapers  somewhat  to  about 


THE  MOUTH 


1133 


the  level  of  a  line  joining  the  tip  of  the  mastoid  process  to  the  angle  of  the  mandible. 
The  remainder  of  the  gland  is  irregularly  wedge-shaped,  and  extends  deeply 
inward  toward  the  pharyngeal  wall. 


Superficial  temporal  an. 


Parotid  duct 


Portion  in  front  of  styloid  pr<  i 


Impression  for  styloid  process 

Ext.  carotid  art 


Posterior  facial  vein 


Impression  for  ext.  acoustic 

meatus 

Portion  behind  styloid  process 


Impression  for  mastoid  pro- 
cess and  Sternocleidomas- 
toideus 


Impression  for  Digastricus 


Fio.   1022. — Right  parotid  gland.     Posterior  and  deep  aspects. 


The  gland  is  enclosed  within  a  capsule  continuous  with  the  deep  cervical  fascia; 

'the  layer  covering  the  superficial  surface  is  dense  and  closely  adherent  to  the 

gland;  a  portion  of  the  fascia,  attached  to  the  styloid  process  and  the  angle  of  the 

mandible,  is  thickened  to  form  the  stylomandibular  ligament  which  intervenes 

between  the  parotid  and  submaxillary  glands. 


Buperfic.  temp,  artery 
Int.  max.  artery 

Portion  in  front  of  styloid, 
process 
Portion  behind  styloid 
process 

Impression  for  styloid 
process 


External  carotid  artery 


Posterior  facial  vein 


i 


Fio    1023. — Right  parotid  gland.     Deep  and  anterior  aspects. 

The  anterior  surface  of  the  gland  is  moulded  on  the  posterior  border  of  the 
ramus  of  the  mandible,  clothed  by  the  Pterygoideus  internus  and  Masseter.  The 
inner  lip  of  the  groove  dips,  for  a  short  distance,  between  the  two  Pterygoid  muscles, 


1134  SPLANCHNOLOGY 

while  the  outer  lip  extends  for  some  distance  over  the  superficial  surface  of  the 
Masseter;  a  small  portion  of  this  lip  immediately  below  the  zygomatic  arch  is 
usually  detached,  and  is  named  the  accessory  part  {socia  yarotidis)  of  the  gland. 

The  posterior  surface  is  grooved  longitudinally  and  abuts  against  the  external 
acoustic  meatus,  the  mastoid  process,  and  the  anterior  border  of  the  Sterno- 
cleidomastoideus. 

The  superficial  surface,  slightly  lobulated,  is  covered  by  the  integument,  the 
superficial  fascia  containing  the  facial  branches  of  the  great  auricular  nerve  and 
some  small  lymph  glands,  and  the  fascia  which  forms  the  capsule  of  the  gland. 

The  deep  surface  extends  inward  by  means  of  two  processes,  one  of  which  lies 
on  the  Digastricus,  styloid  process,  and  the  styloid  group  of  muscles,  and  projects 
under  the  mastoid  process  and  Sternocleidomastoideus;  the  other  is  situated  in 
front  of  the  styloid  process,  and  sometimes  passes  into  the  posterior  part  of  the 
mandibular  fossa  behind  the  temporomandibular  joint.  The  deep  surface  is  in 
contact  with  the  internal  and  external  carotid  arteries,  the  internal  jugular  vein, 
and  the  vagus  and  glossopharyngeal  nerves. 

The  gland  is  separated  from  the  pharyngeal  wall  by  some  loose  connective 
tissue. 

Structures  within  the  Gland. — ^The  external  carotid  artery  lies  at  first  on  the  deep 
surface,  and  then  in  the  substance  of  the  gland.  The  artery  gives  off  its  'posterior 
auricular  branch  which  emerges  from  the  gland  behind;  it  then  divides  into  its 
terminal  branches,  the  internal  maxillary  and  superficial  temporal;  the  former  runs 
forward  deep  to  the  neck  of  the  mandible;  the  latter  runs  upward  across  the  zygo- 
matic arch  and  gives  off  its  transverse  facial  branch  which  emerges  from  the  front 
of  the  gland.  Superficial  to  the  arteries  are  the  superficial  temporal  and  internal 
maxillary  veins,  uniting  to  form  the  posterior  facial  vein ;  in  the  low^er  part  of  the 
gland  this  vein  splits  into  anterior  and  posterior  divisions.  The  anterior  division 
emerges  from  the  gland  and  unites  with  the  anterior  facial  to  form  the  common 
facial  vein;  the  posterior  unites  in  the  gland  with  the  posterior  auricular  to  form 
the  external  jugular  vein.  On  a  still  more  superficial  plane  is  the  facial  nerve,  the 
branches  of  which  emerge  from  the  borders  of  the  gland.  Branches  of  the  great 
auricular  nerve  pierce  the  gland  to  join  the  facial,  while  the  auriculotemporal  nerve 
issues  from  the  upper  part  of  the  gland. 

The  parotid  duct  (ductus  parotideus;  Stensen's  duct)  is  about  7  cm.  long.  It 
begins  by  numerous  branches  from  the  anterior  part  of  the  gland,  crosses  the  Masse- 
ter, and  at  the  anterior  border  of  this  muscle  turns  inward  nearly  at  a  right  angle, 
passes  through  the  corpus  adiposum  of  the  cheek  and  pierces  the  Buccinator;  it 
then  runs  for  a  short  distance  obliquely  forward  between  the  Buccinator  and  mucous 
membrane  of  the  mouth,  and  opens  upon  the  oral  surface  of  the  cheek  by  a  small 
orifice,  opposite  the  second  upper  molar  tooth.  While  crossing  the  Masseter, 
it  receives  the  duct  of  the  accessory  portion;  in  this  position  it  lies  between  the 
branches  of  the  facial  nerve;  the  accessory  part  of  the  gland  and  the  transverse 
facial  artery  are  above  it. 

Structure. — The  parotid  duct  is  dense,  its  wall  being  of  considerable  thickness;  its  canal  is 
about  the  size  of  a  crow-quill,  but  at  its  orifice  on  the  oral  surface  of  the  cheek  its  lumen  is 
greatly  reduced  in  size.  It  consists  of  a  thick  external  fibrous  coat  which  contains  contractile 
fibers,  and  of  an  internal  or  mucous  coat  lined  with  short  columnar  epithelium. 

Vessels  and  Nerves. — The  arteries  supplying  the  parotid  gland  are  derived  from  the  external 
carotid,  and  from  the  branches  given  off  by  that  vessel  in  or  near  its  substance.  The  veins 
empty  themselves  into  the  external  jugular,  through  some  of  its  tributaries.  The  Ijrmphatics 
end  in  the  superficial  and  deep  cervical  Ijonph  glands,  passing  in  their  course  through  two  or 
three  glands,  placed  on  the  surface  and  in  the  substance  of  the  parotid.  The  nerves  are  derived 
from  the  plexus  of  the  sympathetic  on  the  external  carotid  artery,  the  facial,  the  auriculotem- 
poral, and  the  great  auricular  nerves.  It  is  probable  that  the  branch  from  the  auriculotemporal 
nerve  is  derived  from  the  glossopharyngeal  through  the  otic  ganglion.  At  all  events,  in  some  of 
the  lower  animals  this  has  been  proved  experimentally  to  be  the  case. 


THE  MOUTH 


1135 


Submaxillary  Gland  (glanduJa  suhmaxillaris) . —  The  submaxillary  gland  (Fig. 
1024)  is  irregular  in  form  and  about  the  size  of  a  walnut.  A  considerable  part  of 
it  is  situated  in  the  submaxillary  triangle,  reaching  forward  to  the  anterior  belly 
of  the  Digastricus  and  backward  to  the  stylomandibular  ligament,  which  inter- 
venes between  it  and  the  parotid  gland.  Above,  it  extends  under  cover  of  the 
body  of  the  mandible;  below,  it  usually  overlaps  the  intermediate  tendon  of 
the  Digastricus  and  the  insertion  of  the  Stylohyoideus,  while  from  its  deep  surface 
a  tongue-like  deep  process  extends  forward  above  the  Mylohyoideus  muscle. 

Its  superficial  surface  consists  of  an  upper  and  a  lower  part.  The  upper  part 
is  directed  outward,  and  lies  partly  against  the' submaxillary  depression  on  the 
inner  surface  of  the  body  of  the  mandible,  and  partly  on  the  Pterygoideus  internus. 
The  lower  part  is  directed  downward  and  outward,  and  is  covered  by  the  skin, 
superficial  fascia,  Platysma,  and  deep  cervical  fascia;  it  is  crossed  by  the  anterior 
facial  vein  and  by  filaments  of  the  facial  nerve;  in  contact  with  it,  near  the  mandible, 
are  the  submaxillary  lymph  glands. 


Opening  of  parotid 

duct 
Submaxillary  duct 


I 


/         Anterior  facial  vein   ' 

Fig.   1024. — Dissection,  showing  salivary  glands  of  right  side. 

The  deep  surface  is  in  relation  with  the  Mylohyoideus,  Hyoglossus,  Styloglossus, 
Stylohyoideus,  and  posterior  belly  of  the  Digastricus;  in  contact  with  it  are  the 
mylohyoid  nerve  and  the  mylohyoid  and  submental  vessels. 

The  external  maxillary  artery  is  imbedded  in  a  groove  in  the  posterior  border 
of  the  gland. 

The  deep  process  of  the  gland  extends  forward  between  the  Mylohyoideus 
below  and  externally,  and  the  Hyoglossus  and  Styloglossus  internally;  above 
it  is  the  lingual  nerve  and  submaxillary  ganglion;  below  it  the  hypoglossal  nerve 
and  its  accompanying  vein. 

The  submaxillary  duct  (ductus  suhmaxillaris;  Wharton's  duct)  is  about  5  cm.  long, 
and  its  wall  is  much  thinner  than  that  of  the  parotid  duct.    It  begins  by  numerous 


1136  SPLANCHNOLOGY 


I 


branches  from  the  deep  surface  of  the  gland,  and  runs  forward  between  the  Mylo- 
hyoideus  and  the  Hyoglossus  and  Genioglossus,  then  between  the  subHngual 
gland  and  the  Genioglossus,  and  opens  by  a  narrow  orifice  on  the  summit  of  a  small 
papilla,  at  the  side  of  the  frenulum  linguae.  On  the  Hyoglossus  it  lies  between  the 
lingual  and  hypoglossal  nerves,  but  at  the  anterior  border  of  the  muscle  it  is  crossed 
laterally  by  the  lingual  nerve;  the  terminal  branches  of  the  lingual  nerve  ascend 
on  its  medial  side.  ^B^l 

Vessels  and  Nerves.— The  arteries  supplying  the  submaxillary  gland  are  branches  of  tW^ 
external  maxillary  and  lingual.     Its  veins  follow  the  course  of  the  arteries.     The  nerves  are 
derived  from  the  submaxillary  ganglion,  through  which  it  receives  filaments  from  the  chorda 
tympani  of  the  facial  nerve  and  the  lingual  branch  of  the  mandibular,  sometimes  from  the 
mylohyoid  branch  of  the  inferior  alveolar,  and  from  the  sympathetic. 

Sublingual  Gland  (glandula  ^wfe/mg^wa/i*)  .—The  sublingual  gland  (Fig.  1024)  is  the 
smallest  of  the  three  glands.  It  is  situated  beneath'  the  mucous  membrane  of 
the  floor  of  the  mouth,  at  the  side  of  the  frenulum  linguae,  in  contact  with  the 
sublingual  depression  on  the  inner  surface  of  the  mandible,  close  to  the  symphysis. 
It  is  narrow,  flattened,  shaped  somewhat  like  an  almond,  and  weighs  nearly  2  gm. 
It  is  in  relation,  above,  with  the  mucous  membrane;  below,  with  the  Mylohyoideus; 
behind,  with  the  deep  part  of  the  submaxillary  gland;  laterally,  with  the  mandible; 
and  medially,  with  the  Genioglossus,  from  which  it  is  separated  by  the  lingual  nerve 
and  the  submaxillary  duct.  Its  excretory  ducts  are  from  eight  to  twenty  in 
number.  Of  the  smaller  sublingual  ducts  {duds  of  Rivinus),  some  join  the  sub- 
maxillary duct;  others  open  separately  into  the  mouth,  on  the  elevated  crest  of 
mucous  membrane  (plica  sublingualis),  caused  by  the  projection  of  the  gland,  on 
either  side  of  the  frenulum  linguae.  One  or  more  join  to  form  the  larger  sublingual 
duct  (duct  of  Bartholin),  which  opens  into  the  submaxillary  duct. 

Vessels  and  Nerves. — The  sublingual  gland  is  suppUed  with  blood  from  the  sublingual  and 
submental  arteries.  Its  nerves  are  derived  from  the  lingual,  the  chorda  tympani,  and  the 
sympathetic. 

Structure  of  the  Salivary  Glands. — The  salivary  glands  are  compound  racemose  glands, 
consisting  of  numerous  lobes,  which  are  made  up  of  smaller  lobules,  connected  together  by 
dense  areolar  tissue,  vessels,  and  ducts.  Each  lobule  consists  of  the  ramifications  of  a  single 
duct,  the  branches  ending  in  dilated  ends  or  alveoU  on  which  the  capillaries  are  distributed. 
The  alveoli  are  enclosed  by  a  basement  membrane,  which  is  continuous  with  the  membrana 
propria  of  the  duct  and  consists  of  a  net-work  of  branched  and  flattened  nucleated  cells. 

The  alveoli  of  the  saUvary  glands  are  of  two  kinds,  which  differ  in  the  appearance  of  their 
secreting  cells,  in  their  size,  and  in  the  nature  of  their  secretion.  (1)  The  milcous  variety  secretes 
a  viscid  fluid,  which  contains  mucin;  (2)  the  serous  variety  secretes  a  thinner  and  more  watery 
fluid.  The  sublingual  gland  consists  of  mucous,  the  parotid  of  serous  alveoli.  The  submaxillary 
contains  both  mucous  and  serous  alveoli,  the  latter,  however,  preponderating. 

The  cells  in  the  mucous  alveoli  are  columnar  in  shape.  In  the  fresh  condition  they  contain 
large  granules  of  mucinogen.  In  hardened  preparations  a  deUcate  protoplasmic  net-work  is  seen, 
and  the  cells  are  clear  and  transparent.  The  nucleus  is  usually  situated  near  the  basement 
membrane,  and  is  flattened. 

In  some  alveoli  are  seen  pecuUar  crescentic  bodies,  lying  between  the  cells  and  the  mem- 
brana propria.  They  are  termed  the  crescents  of  Gianuzzi,  or  the  demilunes  of  Heidenhain 
(Fig.  1025),  and  are  composed  of  polyhedral  granular  ceUs,  which  Heidenhain  regards  as  young 
epithelial  cells  destined  to  supply  the  place  of  those  salivary  cells  which  have  undergone 
disintegration.  This  view,  however,  is  not  accepted  by  Klein.  Fine  canaUculi  pass  between 
the  mucus-secreting  cells  to  .reach  the  demilunes  and  even  penetrate  the  cells  forming  these 
structures. 

In  the  serous  alveoli  the  cells  almost  completely  fill  the  cavity,  so  that  there  is  hardly  any 
lumen  perceptible;  they  contain  secretory  granules  imbedded  in  a  closely  reticulated  protoplasm 
(Fig.  1026).  The  cells  are  more  cubical  than  those  of  the  mucous  type;  the  nucleus  of  each  is 
spherical  and  placed  near  the  center  of  the  cell,  and  the  granules  are  smaller. 

Both  mucous  and  serous  cells  vary  in  appearance  according  to  whether  the  gland  is  in  a  resting 
condition  or  has  been  recently  active.  In  the  former  case  the  cells  are  large  and  contain  many 
secretory  granules ;  in  the  latter  case  they  are  shrunken  and  contain  few  granules,  chiefly  collected 
at  the  inner  ends  of  the  cells.    The  granules  are  best  seen  in  fresh  preparations. 


THE  FAUCES 


1137 


The  ducts  are  lined  at  their  origins  by  epithelium  which  differs  little  from  the  pavement  form. 
As  the  ducts  enlarge,  the  epithehal  cells  change  to  the  columnar  type,  and  the  part  of  the  cell 
next  the  basement  membrane  is  finely  striated. 

The  lobules  of  the  sahvary  glands  are  richly  supplied  with  bloodvessels  which  form  a  dense 
net-work  in  the  interalveolar  spaces.  Fine  plexuses  of  nerves  are  also  found  in  the  interlobular 
tissue.  The  nerve  fibrils  pierce  the  basement  membrane  of  the  alveoh,  and  end  in  branched 
varicose  filaments  between  the  secreting  cells.  In  the  hilus  of  the  submaxillary  gland  there  is 
a  collection  of  nerve  cells  termed  Langley's  ganglion. 


x^S^^0k<0: 


I 

^^V   Fia.   1025. — Section  of  submaxillary  gland  of  kitten.     Duct 
^^H  semidiagrammatic.     X  200. 

H 


Dvct 


Demilune 


Fig.  1026. — Human  submaxillary  gland.  (R.  Hei- 
denhain.)  At  the  right  is  a  group  of  mucous  alveoli, 
at  the  left  a  group  of  serous  alveoli. 


I 


Accessory  Glands. — Besides  the  sahvary  glands  proper,  nvunerous  other  glands  are  found 
in  the  mouth.  Many  of  these  glands  are  found  at  the  posterior  part  of  the  dorsum  of  the  tongue 
behind  the  vallate  papillae,  and  also  along  its  margins  as  far  forward  as  the  apex.  Others  lie 
around  and  in  the  palatine  tonsil  between  its  crypts,  and  large  numbers  are  present  in  the  soft 
palate,  the  lips,  and  cheeks.  These  glands  are  of  the  same  structure  as  the  larger  salivary  glands, 
and  are  of  the  mucous  or  mixed  type. 


THE  FAUCES. 


The  aperture  by  which  the  mouth  communicates  with  the  pharynx  is  called 
the  isthmus  faucium.  It  is  bounded,  above,  by  the  soft  palate;  below,  by  the  dorsum 
of  the  tongue;  and  on  either  side,  by  the  glossopalatine  arch. 

The  glossopalatine  arch  {arcus  glossopalatinus;  anterior  pillar  of  fauces)  on  either 
side  runs  downward,  lateralward,  and  forward  to  the  side  of  the  base  of  the  tongue, 
and  is  formed  by  the  projection  of  the  Glossopalatinus  with  its  covering  mucous 
membrane. 

The  pharsmgopalatine  arch  (arcus  pharyngopalatinus;  posterior  pillar  of  fauces)  is 
larger  and  projects  farther  toward  the  middle  line  than  the  anterior;  it  runs  down- 
ward, lateralward,  and  backwartl  to  the  side  of  the  pharynx,  and  is  formed  by  the 
projection  of  the  Pharyngopalatinus,  covered  by  mucous  membrane.  On  either  side 
the  two  arches  are  separated  below  by  a  triangular  interval,  in  which  the  palatine 
tonsil  is  lodged. 

The  Palatine  Tonsils  {tonsillce  palatince;  tonsil)  are  two  prominent  masses  situated 

one  on  either  side  between  the  glossopalatine  and  pharj-ngopalatine  arches.    Each 

tonsil  consists  fundamentally  of  an  aggregation  of  lymphoid  tissue  underlying 

the  mucous  membrane  between  the  palatine  arches.    The  lymphoid  mass,  however, 

72  . 


1138 


SPLANCHNOLOGY 


does  not  completely  fill  the  interval  between  the  two  arches,  so  that  a  small  depres- 
sion, the  supratonsillar  fossa,  exists  at  the  upper  part  of  the  interval.  Further, 
the  tonsil  extends  for  a  variable  distance  under  cover  of  the  glossopalatine  arch, 
and  is  here  covered  by  a  reduplication  of  mucous  membrane;  the  upper  part  of  this 
fold  reaches  across  the  supratonsillar  fossa,  between  the  two  arches,  as  a  thin 
fold  sometimes  termed  the  plica  semilunaris ;  the  remainder  of  the  fold  is  called  the 
plica  triangularis.  Between  the  plica  triangularis  and  the  surface  of  the  tonsil  is 
a  space  knowTi  as  the  tonsillar  sinus ;  in  many  cases,  however,  this  sinus  is  obliterated 
by  its  walls  becoming  adherent.  From  this  description  it  wdll  be  apparent  that  a 
portion  of  the  tonsil  is  below  the  level  of  the  surrounding  mucous  membrane,  i.  e.,  is 
imbedded,  while  the  remainder  projects  as  the  visible  tonsil.  In  the  child  the 
tonsils  are  relatively  (and  frequently  absolutely)  larger  than  in  the  adult,  and  about 
one-third  of  the  tonsil  is  imbedded.  After  puberty  the  imbedded  portion  diminishes 
considerably  in  size  and  the  tonsil  assumes  a  disk-like  form,  flattened  from  side 
to  side;  the  shape  and  size  of  the  tonsil,  however,  vary  considerably  in  different 
individuals. 


Fig.  1027.-;— Section  through  one  of  the  crypts  of  the  tonsil.  (Stohr.)  Magnified,  e.  Stratified  epithelium  of  general 
surface,  continued  into  crypt.  /,  /.  Nodules  of  lymphoid  tissue — opposite  each  nodule  numbers  of  lymph  cells  are 
passing  into  or  through  the  epithelium,    s,  s.  Cells  which  have  thus  escaped  to  mix  with  the  saliva  as  salivary  corpuscles. 

The  medial  surface  of  the  tonsil  is  free  except  anteriorly,  where  it  is  covered  by 
the  plica  triangularis;  it  presents  from  twelve  to  fifteen  orifices  leading  into  small 
crypts  or  recesses  from  which  numerous  follicles  branch  out  into  the  tonsillar 
substance. 

The  lateral  or  deep  surface  is  adherent  to  a  fibrous  capsule  which  is  continued 
into  the  plica  triangularis.  It  is  separated  from  the  inner  surface  of  the  Constrictor 
pharyngis  superior  usually  by  some  loose  connective  tissue;  this  muscle  intervenes 
between  the  tonsil  and  the  external  maxillary  artery  with  its  tonsillar  and  ascend- 
ing palatine  branches.  The  internal  carotid  artery  lies  behind  and  lateral  to  the 
tonsil  at  a  distance  of  20  to  25  mm.  from  it. 

The  tonsils  form  part  of  a  circular  band  of  adenoid  tissue  which  guards  the 
opening  into  the  digestive  and  respiratory  tubes.  The  anterior  part  of  the  ring 
is  formed  by  the  submucous  adenoid  collections  (lingual  tonsil)  on  the  posterior 
part  of  the  tongue;  the  lateral  portions  consist  of  the  palatine  tonsils  and  the  ade- 


THE  PHARYNX  W^^^^M        1141 

3t  the  epiglottis — a  movement  produced  by  the  contraction  of  the  Thyreoarytsenoidei,  the 
Arytsenoidei,  and  the  Arytacnoepiglottidei. 

After  leaving  the  tongue  the  bolus  passes  on  to  the  posterior  or  laryngeal  surface  of  the  epi- 
glottis, and  glides  along  this  for  a  certain  distance;  then  the  Glossopalatini,  the  constrictors  of 
the  fauces,  contract  behind  it;  the  palatine  velum  is  slightly  raised  by  the  Levator  veli  palatini, 
and  made  tense  by  the  Tensor  veli  palatini;  and  the  Pharyngopalatini,  by  their  contraction, 
pull  the  pharynx  upward  over  the  bolus,  and  come  nearly  together,  the  uvula  filling  up  the 
slight  interval  between  them.  By  these  means  the  food  is  prevented  from  passing  into  the  nasal 
part  of  the  pharynx;  at  the  same  time,  the  Pharyngopalatini  form  an  incUned  plane,  directed 
obliquely  downward  and  backward  along  the  under  surface  of  which  the  bolus  descends  into 
the  lower  part  of  the  pharynx.  The  Salpingopharyngei  raise  the  upper  and  lateral  parts  of  the 
pharynx — i.  e.,  those  parts  which  are  above  the  points  where  the  Stylopharyngei  are  attached 
to  the  pharynx. 

Mucous  Membrane. — The  mucous  membrane  of  the  soft  palate  is  thin,  and  covered  with  strati- 
fied squamous  epithelium  on  both  surfaces,  excepting  near  the  pharyngeal  ostium  of  the  auditory 
tube,  where  it  is  columnar  and  ciMated.  According  to  Klein,  the  mucous  membrane  on  the 
nasal  surface  of  the  soft  palate  in  the  fetus  is  covered  throughout  by  columnar  cihated  epithehum, 
which  subsequently  becomes  squamous;  some  anatomists  state  that  it  is  covered  with  columnar 
ciliated  epithelium,  except  at  its  free  margin,  throughout  life.  Beneath  the  mucous  membrane 
on  the  oral  surface  of  the  soft  palate  is  a  considerable  amount  of  adenoid  tissue.  The  palatine 
glands  form  a  continuous  layer  on  its  posterior  surface  and  around  the  uvula. 

Vessels  and  Nerves. — The  arteries  sjapplying  the  palate  are  the  descending  palatine  branch 
of  the  internal  maxillary,  the  ascending  palatine  branch  of  the  external  maxillary,  and  the  pala- 
tine branch  of  the  ascending  pharyngeal.  The  veins  end  chiefly  in  the  pterygoid  and  tonsillar 
plexuses.  The  Ijmaphatic  vessels  pass  to  the  deep  cervical  glands.  The  sensory  nerves  are 
derived  from  the  palatine  and  nasopalatine  nerves  and  from  the  glossopharyngeal. 

THE   PHARYNX. 

The  pharynx  is  that  part  of  the  digestive  tube  which  is  placed  behind  the  nasal 
cavities,  mouth,  and  larynx.  It  is  a  musculomembranous  tube,  somewhat  conical 
in  form,  with  the  base  upward,  and  the  apex  downward,  extending  from  the  under 
surface  of  the  skull  to  the  level  of  the  cricoid  cartilage  in  front,  and  that  of  the 
sixth  cervical  vertebra  behind. 

The  cavity  of  the  pharynx  is  about  12.5  cm.  long,  and  broader  in  the  transverse 

than  in  the  antero-posterior  diameter.    Its  greatest  breadth  is  immediately  below 

the  base  of  the  skull,  where  it  projects  on  either  side,  behind  the  pharyngeal  ostium 

of  the  auditory  tube,  as  the  pharjrageal  recess  (fossa  of  Rosenmiiller) ;  its  narrowest 

point  is  at  its  termination  in  the  esophagus.    It  is  limited,  above,  by  the  body 

of  the  sphenoid  and  basilar  part  of  the  occipital  bone;  below,  it  is  continuous  with 

the  esophagus;  posteriorly,  it  is  connected  by  loose  areolar  tissue  with  the  cervical 

portion  of  the  vertebral  column,  and  the  prevertebral  fascia  covering  the  Longus 

colli  and  Longus  capitis  muscles;  anteriorly,  it  is  incomplete,  and  is  attached  in 

succession  to  the  medial  pterygoid  plate,  pterygomandibular  raphe,  mandible, 

ongue,  hyoid  bone,  and  thyroid  and  cricoid  cartilages;  laterally,  it  is  connected  to 

he  styloid  processes  and  their  muscles,  and  is  in  contact  with  the  common  and 

iternal  carotid  arteries,  the  internal  jugular  veins,  the  glossopharyngeal,  vagus, 

nd  hypoglossal  nerves,  and  the  sympathetic  trunks,  and  above  with  small  parts 

"the  Pterygoidei  interni.     Seven  cavities  communicate  with  it,  viz.,  the  two 

al  cavities,  the  two  tympanic  caviti.es,  the  mouth,  the  larynx,  and  the  esophagus. 

^^~^  cavity  of  the  pharynx  may  be  subdivided  from  above  downward  into  three 
"^  s:  nasal,  oral,  and  laryngeal  (Fig.  994). 

^  °  Nasal  Part  of  the  Pharynx  (pars  nasalis  pharyngis;  nasopharyrix)  lies  behind 
aowLgg  g^j^^  above  the  level  of  the  soft  palate:  it  differs  from  the  oral  and  laryn- 
m  o  ^^g  q£  ^j^g  pharynx  in  that  its  cavity  always  remains  patent.  In  front  (Fig. 
otners  communicates  through  the  choanse  with  the  nasal  cavities.  On  its  lateral 
iransv«^g  pharyngeal  ostium  of  the  auditory  tube,  somewhat  triangular  in  shape, 
.  r^^  ded  behind  by  a  firm  prominence,  the  torus  or  cushion,  caused  by  the 
m  the  mu  ^^  ^^^  cartilage  of  the  tube  which  elevates  the  mucous  membrane. 


1138 


SPLANCHNOLOGY 


does  not  completely  fill  the  interval  between  the  two  arches,  so  that  a  small  depreS' 
sion,  the  supratonsillar  fossa,  exists  at  the  upper  part  of  the  interval.  Further, 
the  tonsil  extends  for  a  variable  distance  under  cover  of  the  glossopalatine  arch, 
and  is  here  covered  by  a  reduplication  of  mucous  membrane;  the  upper  part  of  this 
fold  reaches  across  the  supratonsillar  fossa,  between  the  two  arches,  as  a  thin 
fold  sometimes  termed  the  plica  semilunaris ;  the  remainder  of  the  fold  is  called  the 
plica  triangularis.  Between  the  plica  triangularis  and  the  surface  of  the  tonsil  is 
a  space  known  as  the  tonsillar  sinus ;  in  many  cases,  however,  this  sinus  is  obliterated 
by  its  walls  becoming  adherent.  From  this  description  it  will  be  apparent  that  a 
portion  of  the  tonsil  is  below  the  level  of  the  surrounding  mucous  membrane,  i.  e.,  is 
imbedded,  while  the  remainder  projects  as  the  visible  tonsil.  In  the  child  the 
tonsils  are  relatively  (and  frequently  absolutely)  larger  than  in  the  adult,  and  about 
one-third  of  the  tonsil  is  imbedded.  After  puberty  the  imbedded  portion  diminishes 
considerably  in  size  and  the  tonsil  assumes  a  disk-like  form,  flattened  from  side 
to  side;  the  shape  and  size  of  the  tonsil,  however,  vary  considerably  in  different 
individuals. 


I 
I 


Fio.  1027.— Section  through  one  of  the  crypts  of  the  tonsil.  (Stohr.)  Magnified,  e.  Stratified  epithelium  of  general 
surface,  continued  into  crypt.  /,  /.  Nodules  of  lymphoid  tissue — opposite  each  nodule  numbers  of  lymph  cells  are 
passing  into  or  through  the  epithelium.    «,  s.  Cells  which  have  thus  escaped  to  mix  with  the  saliva  as  salivary  corpuscles. 

The  medial  surface  of  the  tonsil  is  free  except  anteriorly,  where  it  is  covered  by 
the  plica  triangularis;  it  presents  from  twelve  to  fifteen  orifices  leading  into  smaU 
crypts  or  recesses  from  which  numerous  follicles  branch  out  into  the  tonsillar 
substance. 

The  lateral  or  deep  surface  is  adherent  to  a  fibrous  capsule  which  is  continue 
into  the  plica  triangularis.    It  is  separated  from  the  inner  surface  of  the  Constrict 
pharyngis  superior  usually  by  some  loose  connective  tissue;  this  muscle  interver 
between  the  tonsil  and  the  external  maxillary  artery  with  its  tonsillar  and  asceaain- 
ing  palatine  branches.    The  internal  carotid  artery  lies  behind  and  lateral  to-h  the 
tonsil  at  a  distance  of  20  to  25  mm.  from  it. 

The  tonsils  form  part  of  a  circular  band  of  adenoid  tissue  which  guarfjjg  ^^^^ 
opening  into  the  digestive  and  respiratory  tubes.  The  anterior  part  of  t' entrance 
is  formed  by  the  submucous  adenoid  collections  (lingual  tonsil)  on  the  pe  cushion 
part  of  the  tongue;  the  lateral  portions  consist  of  the  palatine  tonsils  and 

xiii,  523. 


I 


THE  PHARYNX 


1141 


ot  the  epiglottis — a  movement  produced  by  the  contraction  of  the  Thyreoaryttenoidei,  the 
Arjrtaenoidei,  and  the  Arytajnoepiglottidei. 

After  leaving  the  tongue  the  bolus  passes  on  to  the  posterior  or  laryngeal  surface  of  the  epi- 
glottis, and  gUdes  along  this  for  a  certain  distance;  then  the  Glossopalatini,  the  constrictors  of 
the  fauces,  contract  behind  it;  the  palatine  velum  is  slightly  raised  by  the  Levator  veU  palatini, 
and  made  tense  by  the  Tensor  veh  palatini;  and  the  Pharyngopalatini,  by  their  contraction, 
pull  the  pharynx  upward  over  the  bolus,  and  come  nearly  together,  the  uvula  filling  up  the 
slight  interval  between  them.  By  these  means  the  food  is  prevented  from  passing  into  the  nasal 
part  of  the  pharynx;  at  the  same  time,  the  Pharyngopalatini  form  an  incUned  plane,  directed 
obhquely  downward  and  backward  along  the  under  surface  of  which  the  bolus  descends  into 
the  lower  part  of  the  phar3nix.  The  Salpingopharyngei  raise  the  upper  and  lateral  parts  of  the 
pharynx — i.  e.,  those  parts  which  are  above  the  points  where  the  Stylopharyngei  are  attached 
to  the  pharynx. 

Mucous  Membrane. — The  mucous  membrane  of  the  soft  palate  is  thin,  and  covered  with  strati- 
fied squamous  epithelium  on  both  surfaces,  excepting  near  the  pharyngeal  ostiima  of  the  auditory 
tube,  where  it  is  columnar  and  ciliated.  According  to  Klein,  the  mucous  membrane  on  the 
nasal  surface  of  the  soft  palate  in  the  fetus  is  covered  throughout  by  columnar  ciliated  epithehum, 
which  subsequently  becomes  squamous;  some  anatomists  state  that  it  is  covered  with  columnar 
ciliated  epithelium,  except  at  its  free  margin,  throughout  life.  Beneath  the  mucous  membrane 
on  the  oral  surface  of  the  soft  palate  is  a  considerable  amount  of  adenoid  tissue.  The  palatine 
glands  form  a  continuous  layer  on  its  posterior  surface  and  around  the  uvula. 

Vessels  and  Nerves. — The  arteries  s^upplying  the  palate  are  the  descending  palatine  branch 
of  the  internal  maxillary,  the  ascending  palatine  branch  of  the  external  maxillary,  and  the  pala- 
tine branch  of  the  ascending  pharyngeal.  The  veins  end  chiefly  in  the  pterygoid  and  tonsillar 
plexuses.  The  lymphatic  vessels  pass  to  the  deep  cervical  glands.  The  sensory  nerves  are 
derived  from  the  palatine  and  nasopalatine  nerves  and  from  the  glossopharyngeal. 


I 


THE   PHARYNX. 

The  pharynx  is  that  part  of  the  digestive  tube  which  is  placed  behind  the  nasal 
cavities,  mouth,  and  larynx.  It  is  a  musculomembranous  tube,  somewhat  conical 
in  form,  with  the  base  upward,  and  the  apex  downward,  extending  from  the  under 
surface  of  the  skull  to  the  level  of  the  cricoid  cartilage  in  front,  and  that  of  the 
sixth  cervical  vertebra  behind. 

The  cavity  of  the  pharynx  is  about  12.5  cm.  long,  and  broader  in  the  transverse 
than  in  the  antero-posterior  diameter.  Its  greatest  breadth  is  immediately  below 
the  base  of  the  skull,  where  it  projects  on  either  side,  behind  the  pharyngeal  ostium 
of  the  auditory  tube,  as  the  pharjmgeal  recess  (fossa  of  Rosenmilller) ;  its  narrowest 
point  is  at  its  termination  in  the  esophagus.  It  is  limited,  above,  by  the  body 
of  the  sphenoid  and  basilar  part  of  the  occipital  bone;  below,  it  is  continuous  with 
the  esophagus;  posteriorly,  it  is  connected  by  loose  areolar  tissue  with  the  cervical 
portion  of  the  vertebral  column,  and  the  prevertebral  fascia  covering  the  Longus 
colli  and  Longus  capitis  muscles;  anteriorly,  it  is  incomplete,  and  is  attached  in 
succession  to  the  medial  pterygoid  plate,  pterygomandibular  raphe,  mandible, 
tongue,  hyoid  bone,  and  thyroid  and  cricoid  cartilages;  laterally,  it  is  connected  to 
the  styloid  processes  and  their  muscles,  and  is  in  contact  with  the  common  and 
internal  carotid  arteries,  the  internal  jugular  veins,  the  glossopharyngeal,  vagus, 
a.nd  hypoglossal  nerves,  and  the  sympathetic  trunks,  and  above  with  small  parts 
of  the  Pterygoidei  interni.  Seven  cavities  communicate  with  it,  viz.,  the  two 
nasal  cavities,  the  two  tympanic  cavities,  the  mouth,  the  larynx,  and  the  esophagus. 
The  cavity  of  the  pharynx  may  be  subdivided  from  above  downward  into  three 
parts:  nasal,  oral,  and  laryngeal  (Fig.  994). 

The  Nasal  Part  of  the  Pharynx  (pars  nasalis  pharyngis;  nasopharynx)  lies  behind 
the  nose  and  above  the  level  of  the  soft  palate :  it  differs  from  the  oral  and  laryn- 
geal parts  of  the  pharynx  in  that  its  cavity  always  remains  patent.  In  front  (Fig. 
1029)  it  communicates  through  the  choanse  with  the  nasal  cavities.  On  its  lateral 
wall  is  the  pharyngeal  ostium  of  the  auditory  tube,  somewhat  triangular  in  shape, 
and  bounded  behind  by  a  firm  prominence,  the  torus  or  cushion,  caused  by  the 
medial  end  of  the  cartilage  of  the  tube  which  elevates  the  mucous  membrane. 


1142 


SPLANCHNOLOGY 


A  vertical  fold  of  mucous  membrane,  the  salpingopharyngeal  fold,  stretches  from 
the  lower  part  of  the  torus;  it  contains  the  Salpingopharyngeus  muscle.  A  second 
and  smaller  fold,  the  salpingopalatine  fold,  stretches  from  the  upper  part  of  the  torus 
to  the  palate.  Behind  the  ostium  of  the  auditory  tube  is  a  deep  recess,  the  pharsm- 
geal  recess  (fossa  of  Rosenmuller) .  On  the  posterior  wall  is  a  prominence,  best 
marked  in  childhood,  produced  by  a  mass  of  lymphoid  tissue,  which  is  known  as  the 
pharyngeal  tonsil.  Above  the  pharyngeal  tonsil,  in  the  middle  line,  an  irregular 
flask-shaped  depression  of  the  mucous  membrane  sometimes  extends  up  as  far 
as  the  basilar  process  of  the  occipital  bone;  it  is  known  as  the  pharyngeal  bursa. 

Nasal  septum 

/ 


/  Nasal  conckce 


Pharyngeal  recese 


Torus  of  auditory 
tube 


Pharyngeal  ostium  0/ 
auditory  tube 

Fig.   1029. — Front  of  nasa   part  of  pharynx,  as  seen  with  the  laryngoscope. 

The  Oral  Part  of  the  Pharynx  {yars  oralis  pharyngis)  reaches  from  the  soft  palate 
to  the  level  of  the  hyoid  bone.  It  opens  anteriorly,  through  the  isthmus  faucium, 
into  the  mouth,  while  in  its  lateral  wall,  between  the  two  palatine  arches,  is  the 
palatine  tonsil. 

The  Laryngeal  Part  of  the  Pharynx  (pars  laryngea  pharyngis)  reaches  from  the 
hyoid  bone  to  the  lower  border  of  the  cricoid  cartilage,  where  it  is  continuous  with 
the  esophagus.  In  front  it  presents  the  triangular  entrance  of  the  larynx,  the  base 
of  which  is  directed  forward  and  is  formed  by  the  epiglottis,  while  its  lateral  boun- 
daries are  constituted  by  the  aryepiglottic  folds.  On  either  side  of  the  laryngeal 
orifice  is  a  recess,  termed  the  sinus  piriformis,  which  is  bounded  medially  by  the 
aryepiglottic  fold,  laterally  by  the  thyroid  cartilage  and  hyothyroid  membrane. 

Muscles  of  the  Pharynx. — ^The  muscles  of  the  pharynx  (Fig.  1030)  are: 
Constrictor  inferior.  Stylopharyngeus. 

Constrictor  medius.  Salpingopharyngeus. 

Constrictor  superior.  Pharyngopalatinus.^ 

The  Constrictor  pharyngis  inferior  {Inferior  constrictor)  (Figs.  1030, 1031),  the  thickest 
of  the  three  constrictors,  arises  from  the  sides  of  the  cricoid  and  thyroid  cartilage. 
From  the  cricoid  cartilage  it  arises  in  the  interval  between  the  Cricothyreoideus 
in  front,  and  the  articular  facet  for  the  inferior  cornu  of  the  thyroid  cartilage 
behind.  On  the  thyroid  cartilage  it  arises  from  the  oblique  line  on  the  side  of  the 
lamina,  from  the  surface  behind  this  nearly  as  far  as  the  posterior  border  and  from 
the  inferior  cornu.  From  these  origins  the  fibers  spread  backward  and  medialward 
to  be  inserted  with  the  muscle  of  the  opposite  side  into  the  fibrous  raphe  in  the 
posterior  median  line  of  the  pharynx.  The  inferior  fibers  are  horizontal  and  con- 
tinuous with  the  circular  fibers  of  the  esophagus;  the  rest  ascend,  increasing  in. 
obliquity,  and  overlap  the  Constrictor  medius. 

'  The  Pharyngopa]atinu8  is  described  with  the  muscles  of  the  palate  (p.  1139). 


THE  ESOPHAGUS 


1145 


orifice  of  the  stomach,  opposite  the  eleventh  thoracic  vertebra.  The  general  direc- 
tion of  the  esophagus  is  vertical;  but  it  presents  two  slight  curves  in  its  course. 
At  its  commencement  it  is  placed  in  the  middle  line;  but  it  inclines  to  the  left  side 
as  far  as  the  root  of  the  neck,  gradually  passes  to  the  middle  line  again  at  the  level 
of  the  fifth  thoracic  vertebra,  and  finally  deviates  to  the  left  as  it  passes  forward 
to  the  esophageal  hiatus  in  the  diaphragm.  The  esophagus  also  presents 
antero-posterior  flexures  corresponding  to  the  curvatures  of  the  cervical  and 
thoracic  portions  of  th,e  vertebral  column.  It  is  the  narrowest  part  of  the  diges- 
tive tube,  and  is  most  contracted  at  its  commencement,  and  at  the  point  where 
it  passes  through  the  diaphragm. 


SUPERIOR   LARYN° 
GEAL  NERVE 


THYROID  ARTERY 


LEFT 

PULMONARY 

ARTERY 

LEFT  LUNG 

LEFT  BRONCHUS 

THORACIC    DUCT 
PLEURA 

VAGUS  NERVE 


Ai:ycos  VEIN 


RECURRENT 
NERVE 

.SUBCLAVICULAR 
ARTERY 
RIGHT  CEPHALIC 

RUNK 

"ESOPHAGUS 

VAGUS  NERVE 


AZYGOS  VEIN 


-  RONCHIAL 
ARTERY 


RIGHT  PUL- 
MONARY VEIN 


RIGHT  LUNG 


NF     VENA    CAVA 


DIAPHRAGM 


II 


Fig.  1032. — ^The  position  and  relation  of  the  esophagus  in  the  cervical  region  and  in  the  posterior  mediastinum. 

from  behmd.      (Poirier  and  Charpy.) 


Seen 


I 


Relations.— The  cervical  portion  of  the  esophagus  is  in  relation,  in  front,  with  the  trachea; 
and  at  the  lower  part  of  the  neck,  where  it  projects  to  the  left  side,  with  the  thyroid  gland;  behind, 
it  rests  upon  the  vertebral  column  and  Longus  colli  muscles;  on  either  side  it  is  in  relation  with 
the  common  carotid  artery  (especially  the  left,  as  it  inclines  to  that  side),  and  parts  of  the  lobes 
of  the  thyroid  gland;  the  recurrent  nerves  ascend  between  it  and  the  trachea;  to  its  left  side  is 
the  thoracic  duct. 

The  thoracic  portion  of  the  esophagus  is  at  first  situated  in  the  superior  mediastinum  be- 
tween the  trachea  and  the  vertebral  column,  a  little  to  the  left  of  the  median  Une.  It  then 
passes  behind  and  to  the  right  of  the  aortic  arch,  and  descends  in  the  posterior  mediastinum 
along  the  right  side  of  the  descending  aorta,  then  runs  in  front  and  a  little  to  the  left  of 
the  aorta,  and  enters  the  abdomen  through  the  diaphragm  at  the  level  of  the  tenth  thoracic 
vertebra.    Just  before  it  perforates  the  diaphragm  it  presents  a  distinct  dilatation.    It  is  in 


1146 


SPLANCHNOLOGY 


^^^^^m 


relation,  in  front,  with  the  trachea,  the  left  bronchus,  the  pericardium,  and  the  diaphragm;] 
behind,  it  rests  upon  the  vertebral  column,  the  Longus  colli  muscles,  the  right  aortic  intercostal 
arteries,  the  thoracic  duct,  and  the  hemiazygos  veins;  and  below,  near  the  diaphragm,  upon 
the  front  of  the  aorta.  On  its  left  side,  in  the  superior  mediastinum,  are  the  terminal  part 
of  the  aortic  arch,  the  left  subclavian  artery,  the  thoracic  duct,  and  left  pleura,  while  running 
upward  in  the  angle  between  it  and  the  trachea  is  the  left  recurrent  nerve;  below,  it  is  in  relation 
with  the  descending  thoracic  aorta.  On  its  right  side  are  the  right  pleura,  and  the  azygos  vein 
which  it  overlaps.  Below  the  roots  of  the  lungs  the  vagi  descend  in  close  contact  with  it,  thejB 
right  nerve  passing  down  behind,  and  the  left  nerve  in  front  of  it;  the  two  nerves  uniting  toll 
form  a  plexus  around  the  tube.  '" 

In  the  lower  part  of  the  posterior  mediastinum  the  thoracic  duct  lies  to  the  right  side 
of  the  esophagus;  higher  up,  it  is  placed  behind  it,  and,  crossing  about  the  level  of  the  fourth 
thoracic  vertebra,  is  continued  upward  on  its  left  side. 

The  abdominal  portion  of  the  esophagus  lies  in  the 
esophageal  groove  on  the  posterior  surface  of  the  left 
lobe  of  the  liver.  It  measures  about  1.25  cm.  in  length, 
and  only  its  front  and  left  aspects  are  covered  by 
peritoneum.  It  is  somewhat  conical  with  its  base 
applied  to  the  upper  orifice  of  the  stomach,  and  is 
known  as  the  antrum  cardiacum. 

Structure  (Fig.  1033). — The  esophagus  has  four 
coats:  an  external  or  fibrous,  a  muscular,  a  sub- 
mucous or  areolar,  and  an  internal  or  mucous  coat. 

The  muscular  coat  {tunica  muscularis)  is  composed 
of  two  planes  of  considerable  thickness:  an  external 
of  longitudinal  and  an  internal  of  circular  fibers. 

The  longitudinal  fibers  are  arranged,  at  the  com- 
mencement of  the  tube,  in  three  fasciculi:  one  in  front, 
which  is  attached  to  the  vertical  ridge  on  the  posterior 
surface  of  the  lamina  of  the  cricoid  cartilage;  and 
one  at  either  side,  which  is  continuous  with  the  mus- 
cular fibers  of  the  pharynx :  as  they  descend  they  blend 
together,  and  form  a  uniform  layer,  which  covers  the 
outer  surface  of  the  tube. 

Accessory  slips  of  muscular  fibers  pass  between  the 
esophagus  and  the  left  pleura,  where  the  latter  covers 
the  thoracic  aorta,  or  the  root  of  the  left  bronchus, 
or  the  back  of  the  pericardium. 

The  circular  fibers  are  continuous  above  with  the 
Constrictor  pharyngis  inferior;  their  direction  is  trans- 
verse at  the  upper  and  lower  parts  of  the  tube,  but 
obUque  in  the  intermediate  part. 

The  muscular  fibers  in  the  upper  part  of  the  esoph- 
agus are  of  a  red  color,  and  consist  chiefly  of  the  striped 
variety;  but  below  they  consist  for  the  most  part  of 
involuntary  fibers. 

The  areolar  or  submucous  coat  {tela  submucosa) 
connects  loosely  the  mucous  and  muscular  coats.  It 
contains  bloodvessels,  nerves,  and  mucous  glands. 
The  mucous  coat  {tunica  mucosa)  is  thick,  of  a  reddish  color  above,  and  pale  below.  It  is 
disposed  in  longitudinal  folds,  which  disappear  on  distension  of  the  tube.  Its  surface  is  studded 
with  minute  papillae,  and  it  is  covered  throughout  with  a  thick  layer  of  stratified  squamous 
epithelium.  Beneath  the  mucous  membrane,  between  it  and  the  areolar  coat,  is  a  layer  of  longi- 
tudinally arranged  non-striped  muscular  fibers.  This  is  the  muscularis  mucosae.  At  the  com- 
mencement of  the  esophagus  it  is  absent,  or  only  represented  by  a  few  scattered  bundles;  lower 
down  it  forms  a  considerable  stratum. 

The  esophageal  glands  {glandulce  oesophageoe)  are  small  compound  racemose  glands  of  the 
mucous  type:  they  are  lodged  in  the  submucous  tissue,  and  each  opens  upon  the  surface  by  a 
long  excretory  duct. 

Vessels  and  Nerves. — The  arteries  supplying  the  esophagus  are  derived  from  the  inferior 
thyroid  branch  of  the  thyrocervical  trunk,  from  the  descending  thoracic  aorta,  from  the  left 
gastric  branch  of  the  celiac  artery,  and  from  the  left  inferior  phrenic  of  the  abdominal  aorta. 
They  have  for  the  most  part  a  longitudinal  direction. 

The  nerves  are  derived  from  the  vagi  and  from  the  sympathetic  trunks;  they  form  a  plexus, 
in  which  are  groups  of  ganglion  cells,  between  the  two  layers  of  the  muscular  coats,  and  also  a 
second  plexus  in  the  submucous  tissue. 


Fig.  1033. — Section  of  the  human  esophagus. 
(From  a  drawing  by  V.  Horsley.)  Moderately 
magnified.  The  section  is  transverse  and  from 
near  the  middle  of  the  gullet,  a.  Fibrous  cover- 
ing, b.  Divided  fibers  of  longitudinal  muscular 
coat.  c.  Transverse  m.uscular  fibers,  d.  Sub- 
mucous or  areolar  layer,  e.  Muscularis  mucosae. 
/.  Mucous  membrane,  with  vessels  and  part  of  a 
lymphoid  nodule,  g.  Stratified  epithelial  lining. 
h.  Mucous  gland,  i.  Gland  duct.  m'.  Striated 
muscular  fibers  cut  across. 


THE  ABDOMEN 


1147 


THE  ABDOMEN. 

The  abdomen  is  the  largest  cavity  in  the  body.  It  is  of  an  oval  shape,  the  extrem- 
ities of  the  oval  being  directed  upward  and  downward.  The  upper  extremity  is 
formed  by  the  diaphragm  which  extends  as  a  dome  over  the  abdomen,  so  that  the 
cavity  extends  high  into  the  bony  thorax,  reaching  on  the  right  side,  in  the  mammary 
line,  to  the  upper  border  of  the  fifth  rib ;  on  the  left  side  it  falls  below  this  level  by 
about  2.5  cm.  The  lower  extremity  is  formed  by  the  structures  which  clothe  the 
inner  surface  of  the  bony  pelvis,  principally  the  Levator  ani  and  Coccygeus  on 
either  side.  These  muscles  are  sometimes  termed  the  diaphragm  of  the  pelvis. 
The  cavity  is  wider  above  than  below,  and  measures  more  in  the  vertical  than  in 
the  transverse  diameter.  In  order  to  facilitate  description,  it  is  artificially  divided 
into  two  parts :  an  upper  and  larger  part,  the  abdomen  proper ;  and  a  lower  and  smaller 
part,  the  pelvis.  These  two  cavities  are  not  separated  from  each  other,  but  the 
limit  between  them  is  marked  by  the  superior  aperture  of  the  lesser  pelvis. 

The  abdomen  proper  differs  from  the  other  great  cavities  of  the  body  in  being 
bounded  for  the  most  part  by  muscles  and  fasciae,  so  that  it  can  vary  in  capacity 
and  shape  according  to  the  condition  of  the  viscera  which  it  contains;  but,  in  addi- 
tion to  this,  the  abdomen  varies  in  form  and  extent  with  age  and  sex.  In  the  adult 
male,  with  moderate  distension  of  the  viscera,  it  is  oval  in  shape,  but  at  the  same 
time  flattened  from  before  backward.  In  the  adult  female,  with  a  fully  developed 
pelvis,  it  is  ovoid  with  the  narrower  pole  upward,  and  in  young  children  it  is  also 
ovoid  but  with  the  narrower  pole  downward. 

Boundaries. — It  is  bounded  in  front  and  at  the  sides  by  the  abdominal  muscles 
and  the  Iliacus  muscles;  behind  by  the  vertebral  column  and  the  Psoas  and 
Quadratus  lumborum  muscles;  above  by  the  diaphragm;  below  by  the  plane  of 
the  superior  aperture  of  the  lesser  pelvis.  The  muscles  forming  the  boundaries 
of  the  cavity  are  lined  upon  their  inner  surfaces  by  a  layer  of  fascia. 

The  abdomen  contains  the  greater  part  of  the  digestive  tube;  some  of  the 
accessory  organs  to  digestion,  viz.,  the  liver  and  pancreas;  the  spleen,  the  kidneys, 
and  the  suprarenal  glands.  Most  of  these  structures,  as  well  as  the  wall  of  the 
cavity  in  which  they  are  contained,  are  more  or  less  covered  by  an  extensive  and 
complicated  serous  membrane,  the  peritoneum. 

The  Apertures  in  the  Walls  of  the  Abdomen. — ^The  apertures  in  the  walls  of  the 
abdomen,  for  the  transmission  of  structures  to  or  from  it,  are,  in  front,  the  umbilical 
(in  the  fetus),  for  the  transmission  of  the  umbilical  vessels,  the  allantois,  and  vitel- 
line duct;  above,  the  vena  caval  opening,  for  the  transmission  of  the  inferior  vena 
cava,  the  aortic  hiatus,  for  the  passage  of  the  aorta,  azygos  vein,  and  thoracic  duct, 
and  the  esophageal  hiatus,  for  the  esophagus  and  vagi.  Below,  there  are  two 
apertures  on  either  side:  one  for  the  passage  of  the  femoral  vessels  and  lumbo- 
inguinal  nerve,  and  the  other  for  the  transmission  of  the  spermatic  cord  in  the  male, 
and  the  round  ligament  of  the  uterus  in  the  female. 

Regions. — For  convenience  of  description  of  the  viscera,  as  well  as  of  reference 
to  the  morbid  conditions  of  the  contained  parts,  the  abdomen  is  artificially  divided 
into  nine  regions  by  imaginary  planes,  two  horizontal  and  two  sagittal,  passing 
through  the  cavity,  the  edges  of  the  planes  being  indicated  by  lines  drawn  on  the 
surface  of  the  body.  Of  the  horizontal  planes  the  upper  or  transpyloric  is  indicated 
by  a  line  encircling  the  body  at  the  level  of  a  point  midway  between  the  jugular 
notch  and  the  symphysis  pubis,  the  lower  by  a  line  carried  around  the  trunk  at  the 
level  of  a  point  midway  between  the  transpyloric  and  the  symphysis  pubis.  The 
latter  is  practically  the  interfcubercular  plane  of  Cunningham,  who  pointed  out^ 
that  its  level  corresponds  with  the  prominent  and  easily  defined  tubercle  on  the 
iliac  crest  about  5  cm.  behind  the  anterior  superior  iliac  spine.    By  means  of  these 

^  Journal  of  Anatomy  and  Physiology,  vol.  xxvii. 


SPLANCHNOLOGY 

imaginary  planes  the  abdomen  is  divided  into  three  zones,  which  are  named  from 
above  downward  the  subcostal,  umbilical,  and  hypogastric  zones.    Each  of  these  is 


FlQ.   1034. — Front  view  of  the  thoracic  and  abdominal  viscera,     a.    Median  plane.     6  5.  Lateral  planes,     c  c.  Tranf  , 
tubercular  plane,     d  d.  Subcostal  plane,     e  e.  Transpyloric  plane. 


THE  PERITONEUM  ^^^  1149 

further  subdivided  into  three  regions  by  the  two  sagittal  planes,  which  are  indi- 
cated on  the  surface  by  lines  drawn  vertically  through  points  half-way  between 
the  anterior  superior  iliac  spines  and  the  symphysis  pubis. ^ 

The  middle  region  of  the  upper  zone  is  called  the  epigastric ;  and  the  two  lateral 
regions,  the  right  and  left  hypochondriac.  The  central  region  of  the  middle  zone 
is  the  umbilical;  and  the  two  lateral  regions,  the  right  and  left  lumbar.  The  middle 
region  of  the  lower  zone  is  the  hypogastric  or  pubic  region;  and  the  lateral  regions 
are  the  right  and  left  iliac  or  inguinal  (Fig.  1034). 

The  pelvis  is  that  portion  of  the  abdominal  cavity  which  lies  below  and  behind 
a  plane  passing  through  the  promontory  of  the  sacrum,  linese  terminales  of  the 
hip  bones,  and  the  pubic  crests.  It  is  bounded  behind  by  the  sacrum,  coccyx, 
Piriformes,  and  the  sacrospinous  and  sacrotuberous  ligaments;  in  front  and 
laterally  by  the  pubes  and  ischia  and  Obturatores  interni;  above  it  communicates 
with  the  abdomen  proper;  below  it  is  closed  by  the  Levatores  ani  and  Coccygei  and 
the  urogenital  diaphragm.  The  pelvis  contains  the  urinary  bladder,  the  sigmoid 
colon  and  rectum,  a  few  coils  of  the  small  intestine,  and  some  of  the  generative 
organs. 

When  the  anterior  abdominal  wall  is  removed,  the  viscera  are  partly  exposed 
as  follows:  above  and  to  the  right  side  is  the  liver,  situated  chiefly  under  the  shelter 
of  the  right  ribs  and  their  cartilages,  but  extending  across  the  middle  line  and  reach- 
ing for  some  distance  below  the  level  of  the  xiphoid  process.  To  the  left  of  the  liver 
is  the  stomach,  from  the  lower  border  of  which  an  apron-like  fold  of  peritoneum, 
the  greater  omentum,  descends  for  a  varying  distance,  and  obscures,  to  a  greater 
or  lesser  extent,  the  other  viscera.  Below  it,  however,  some  of  the  coils  of  the  small 
intestine  can  generally  be  seen,  while  in  the  right  and  left  iliac  regions  respectively 
the  cecum  and  the  iliac  colon  are  partly  exposed.  The  bladder  occupies  the  ante- 
rior part  of  the  pelvis,  and,  if  distended,  will  project  above  the  symphysis  pubis; 
the  rectum  lies  in  the  concavity  of  the  sacrum,  but  is  usually  obscured  by  the  coils 
of  the  small  intestine.    The  sigmoid  colon  lies  between  the  rectum  and  the  bladder. 

When  the  stomach  is  followed  from  left  to  right  it  is  seen  to  be  continuous  with 
the  first  part  of  the  small  intestine,  or  duodenum,  the  point  of  continuity  being 
marked  by  a  thickened  ring  which  indicates  the  position  of  the  pyloric  valve. 
The  duodenum  passes  toward  the  under  surface  of  the  liver,  and  then,  curving 
downward,  is  lost  to  sight.  If,  however,  the  greater  omentum  be  thrown  upward 
over  the  chest,  the  inferior  part  of  the  duodenum  will  be  observed  passing  across 
the  vertebral  column  toward  the  left  side,  where  it  becomes  continuous  with  the 
coils  of  the  jejunum  and  ileum.  These  measure  some  6  meters  in  length,  and  if 
followed  downward  the  ileum  will  be  seen  to  end  in  the  right  iliac  fossa  by  opening 
into  the  cecum,  the  commencement  of  the  large  intestine.  From  the  cecum  the 
large  intestine  takes  an  arched  course,  passing  at  first  upward  on  the  right  side, 
then  across  the  middle  line  and  downward  on  the  left  side,  and  forming  respectively 
the  ascending  transverse,  and  descending  parts  of  the  colon.  In  the  pelvis  it 
assumes  the  form  of  a  loop,  the  sigmoid  colon,  and  ends  in  the  rectum. 

The  spleen  lies  behind  the  stomach  in  the  left  hypochondriac  region,  and  may 
be  in  part  exposed  by  pulling  the  stomach  over  toward  the  right  side. 

The  ghstening  appearance  of  the  deep  surface  of  the  abdominal  wall  and  of  the 
surfaces  of  the  exposed  viscera  is  due  to  the  fact  that  the  former  is  lined,  and  the 
latter  are  more  or  less  completely  covered,  by  a  serous  membrane,  the  peritoneum. 

The  Peritoneum  (Tunica  Serosa). 

The  peritoneum  is  the  largest  serous  membrane  in  the  body,  and  consists,  in  the 
male,  of  a  closed  sac,  a  part  of  which  is  applied  against  the  abdominal  parietes, 

'Journal  of  Anatomj-  and  Physiology,  vols,  xxxiii,  xxxiv,  xxxv. 


1150  ^       SPLANCHNOLOGY 

while  the  remainder  is  reflected  over  the  contained  viscera.  In  the  female  the 
peritoneum  is  not  a  closed  sac,  since  the  free  ends  of  the  uterine  tubes  open  directly 
into  the  peritoneal  cavity.  The  part  which  lines  the  parietes  is  named  the  parietal 
portion  of  the  peritoneum;  that  which  is  reflected  over  the  contained  viscera  con- 
stitutes the  visceral  portion  of  the  peritoneum.  The  free  surface  of  the  membrane 
is  smooth,  covered  by  a  layer  of  flattened  mesothelium,  and  lubricated  by  a  small 
quantity  of  serous  fluid.  Hence  the  viscera  can  glide  freely  against  the  wall  of  the 
cavity  or  upon  one  another  with  the  least  possible  amount  of  friction.  The  attached 
surface  is  rough,  being  connected  to  the  viscera  and  inner  surface  of  the  parietes  by 
means  of  areolar  tissue,  termed  the  subserous  areolar  tissue.  The  parietal  portion 
is  loosely  connected  with  the  fascial  lining  of  the  abdomen  and  pelvis,  but  is  more 
closely  adherent  to  the  under  surface  of  the  diaphragm,  and  also  in  the  middle 
line  of  the  abdomen. 

The  space  between  the  parietal  and  visceral  layers  of  the  peritoneum  is  named 
the  peritoneal  cavity ;  but  under  normal  conditions  this  cavity  is  merely  a  potential 
one,  since  the  parietal  and  visceral  layers  are  in  contact.  The  peritoneal  cavity 
gives  off  a  large  diverticulum,  the  omental  bursa,  which  is  situated  behind  the 
stomach  and  adjoining  structures;  the  neck  of  communication  between  the  cavity 
and  the  bursa  is  termed  the  epiploic  foramen  {foramen  of  Winslow).  Formerly  the 
main  portion  of  the  cavity  was  described  as  the  greater,  and  the  omental  bursa 
as  the  lesser  sac. 

The  peritoneum  differs  from  the  other  serous  membranes  of  the  body  in  pre- 
senting a  much  more  complex  arrangement,  and  one  that  can  be  clearly  understood 
only  by  following  the  changes  which  take  place  in  the  digestive  tube  during  its 
development. 

To  trace  the  membrane  from  one  viscus  to  another,  and  from  the  viscera  to  the 
parietes,  it  is  necessary  to  follow  its  continuity  in  the  vertical  and  horizontal 
directions,  and  it  will  be  found  simpler  to  describe  the  main  portion  of  the  cavity 
and  the  omental  bursa  separately. 

Vertical  Disposition  of  the  Main  Peritoneal  Cavity  {greater  sac)  (Fig.  1035). — It 
is  convenient  to  trace  this  from  the  back  of  the  abdominal  wall  at  the  level  of  the 
umbilicus.  On  following  the  peritoneum  upward  from  this  level  it  is  seen  to  be 
reflected  around  a  fibrous  cord,  the  ligamentum  teres  {obliterated  umbilical  vein), 
which  reaches  from  the  umbilicus  to  the  under  surface  of  the  liver.  This  reflection 
forms  a  somewhat  triangular  fold,  the  falciform  ligament  of  the  liver,  attaching  the 
upper  and  anterior  surfaces  of  the  liver  to  the  diaphragm  and  abdominal  wall. 
With  the  exception  of  the  line  of  attachment  of  this  ligament  the  peritoneum 
covers  the  whole  of  the  under  surface  of  the  anterior  part  of  the  diaphragm, 
and  is  continued  from  it  on  to  the  upper  surface  of  the  right  lobe  of  the  liver  as 
the  superior  layer  of  the  coronary  ligament,  and  on  to  the  upper  surface  of  the  left 
lobe  as  the  superior  layer  of  the  left  triangular  ligament  of  the  liver.  Covering  the 
upper  and  anterior  surfaces  of  the  liver,  it  is  continued  around  its  sharp  margin 
on  to  the  under  surface,  where  it  presents  the  following  relations :  (a)  It  covers  the 
under  surface  of  the  right  lobe  and  is  reflected  from  t!ie  back  part  of  this  on  to  the 
right  suprarenal  gland  and  upper  extremity  of  the  right  kidney,  forming  in  this 
situation  the  inferior  layer  of  the  coronary  ligament;  a  special  fold,  the  hepatorenal 
ligament,  is  frequently  present  between  the  inferior  surface  of  the  liver  and  the 
front  of  the  kidney.  From  the  kidney  it  is  carried  downward  to  the  duodenum 
and  right  colic  flexure  and  medialward  in  front  of  the  inferior  vena  cava,  where  it 
is  continuous  with  the  posterior  wall  of  the  omental  bursa.  Between  the  two  layers 
of  the  coronary  ligament  there  is  a  large  triangular  surface  of  the  liver  devoid  of 
peritoneal  covering;  this  is  named  the  bare  area  of  the  liver,  and  is  attached  to  the 
diaphragm  by  areolar  tissue.  Toward  the  right  margin  of  the  liver  the  two 
layers  of  the  coronary  ligament  gradually  approach  each  other,  and  ultimately 


THE  PERITONEUM 


1151 


fuse  to  form  a  small  triangular  fold  connecting  the  right  lobe  of  the  liver  to  the 
diaphragm,  and  named  the  right  triangular  ligament  of  the  liver.  The  apex  of 
the  triangular  bare  area  corresponds  with  the  point  of  meeting  of  the  two  layers 
of  the  coronary  ligament,  its  base  with  the  fossa  for  the  inferior  vena  cava.  (6) 
It  covers  the  lower  surface  of  the  quadrate  lobe,  the  under  and  lateral  surfaces 
of  the  gall-bladder,  and  the  under  surface  and  posterior  border  of  the  left  lobe;  it  is 
then  reflected  from  the  upper  surface  of  the  left  lobe  to  the  diaphragm  as  the 
inferior  layer  of  the  left  triangular  ligament,  and  from  the  porta  of  the  liver  and  the 
fossa  for  the  ductus  venosus  to  the  lesser  curvature  of  the  stomach  and  the  first 
2.5  cm.  of  the  duodenum  as  the  anterior  layer  of  the  hepatogastric  and  hepatoduodenal 
ligaments,  which  together  constitute  the  lesser  omentum.  If  this  layer  of  the  lesser 
omentum  be  followed  to  the  right  it  will  be  found  to  turn  around  the  hepatic  artery, 
bile  duct,  and  portal  vein,  and  become  continuous  with  the  anterior  wall  of  the 


Superior  layer  oj 
coronary  ligament 

Bare  area  of  liver 

Inferior  layer  of 
coronary  ligament 


Bristle  in  epiploic 
foramen 

Stomach 


Transverse  colon 

Greater  omentum 

Small  intestine 


Uterovesical 
excavation 

Bladder 


Vagina 


Uterus 
Rectovaginal 
excavation 
Rectum 


Fig.   1035. — Vertical  dispositioa  of  the  peritoneum.     Main  cavity,  red;  omental  bursa,  blue. 


omental  bursa,  forming  a  free  folded  edge  of  peritoneum.     Traced  downward,  it 

covers  the  antero-superior  surface  of  the  stomach  and  the  commencement  of  the 

Bfcduodenum,  and  is  carried  down  into  a  large  free  fold,  known  as  the  gastrocolic 

■■ligament  or  greater  omentum.    Reaching  the  free  margin  of  this  fold,  it  is  reflected 

upward  to  cover  the  under  and  posterior  surfaces  of  the  transverse  colon,  and  thence 

^to  the  posterior  abdominal  wall  as  the  inferior  layer  of  the  transverse  mesocolon. 
It  reaches  the  abdominal  wall  at  the  head  and  anterior  border  of  the  pancreas, 
is  then  carried  down  over  the  lower  part  of  the  head  and  over  the  inferior  surface 
■^.of  the  pancreas  on  the  superior  mesenteric  vessels,  and  thence  to  the  small  intestine 
Hpas  the  anterior  layer  of  the  mesentery.    It  encircles  the  intestine,  and  subsequently 
^    may  be  traced,  as  the  posterior  layer  of  the  mesentery,  upward  and  backward 
to  the  abdominal  wall.    From  this  it  sweeps  down  over  the  aorta  into  the  pelvis, 
where  it  invests  the  sigmoid  colon,  its  reduplication  forming  the  sigmoid  mesocolon. 


k 


1152 


SPLANCHNOLOGY 


Leaving  first  the  sides  and  then  the  front  of  the  rectum,  it  is  reflected  on  to  the  semi 
nal  vesicles  and  fundus  of  the  urinary  bladder  and,  after  covering  the  upper  surface 
of  that  viscus,  is  carried  along  the  medial  and  lateral  umbilical  ligaments  (Fig. 
1036)  on  to  the  back  of  the  abdominal  wall  to  the  level  from  which  a  start  was  made. 


M.  iliac'is 


Femoral 


External 

iliac 

artery 


Internal 

iliac 

artery 


Femoral 
fovea 

Superior 
vesical 
artery 
Medial 
inguinal 
fovea 

Fig.  1036. — Posterior  view  of  the  anterior  abdominal  wall  in  its  lower  half.     The  peritoneum  is  in  place,  and  the  various 

cords  are  shining  through.      (After  Joessel.) 


Between  the  rectum  and  the  bladder  it  forms,  in  the  male,  a  pouch,  the  recto- 
vesical excavation,  the  bottom  of  which  is  slightly  below  the  level  of  the  upper 
ends  of  the  vesiculse  seminales — i.  e.,  about  7.5  cm.  from  the  orifice  of  the  anus. 
When  the  bladder  is  distended,  the  peritoneum  is  carried  up  with  the  expanded 
viscus  so  that  a  considerable  part  of  the  anterior  surface  of  the  latter  lies  directly 
against  the  abdominal  wall  without  the  intervention  of  peritoneal  membrane  {yre- 
vesical  space  of  Retzins) .  In  the  female  the  peritoneum  is  reflected  from  the  rectum 
over  the  posterior  vaginal  fornix  to  the  cervix  and  body  of  the  uterus,  forming 
the  rectouterine  excavation  {youch  of  Douglas) .  It  is  continued  over  the  intestinal 
surface  and  fundus  of  the  uterus  on  to  its  vesical  surface,  which  it  covers  as  far  as 
the  junction  of  the  body  and  cervix  uteri,  and  then  to  the  bladder,  forming  here 
a  second,  but  shallower,  pouch,  the  vesicouterine  excavation.  It  is  also  reflected 
from  the  sides  of  the  uterus  to  the  lateral  walls  of  the  pelvis  as  two  expanded 
folds,  the  broad  ligaments  of  the  uterus,  in  the  free  margin  of  each  of  which  is  the 
uterine  tube. 

Vertical  Disposition  of  the  Omental  Bursa  {lesser  peritoneal  sac)  (Fig.  1035). — A 
start  may  be  made  in  this  case  on  the  posterior  abdominal  wall  at  the  anterior 
border  of  the  pancreas.    From  this  region  the  peritoneum  may  be  followed  upward 


THE  PERITONEUM 


1153 


over  the  pancreas  on  to  the  inferior  surface  of  the  diaphragm,  and  thence  on  to  the 
caudate  lobe  and  caudate  process  of  the  liver  to  the  fossa  from  the  ductus  venosus 
and  the  porta  of  the  liver.  Traced  to  the  right,  it  is  continuous  over  the  inferior 
vena  cava  with  the  posterior  wall  of  the  main  cavity.  From  the  liver  it  is  carried 
downward  to  the  lesser  curvature  of  the  stomach  and  the  commencement  of  the 
duodenum  as  the  posterior  layer  of  the  lesser  omentum,  and  is  continuous  on  the 
right,  around  the  hepatic  artery,  bile  duct,  and  portal  vein,  with  the  anterior  layer 
of  this  omentum.  The  posterior  layer  of  the  lesser  omentum  is  carried  down  as  a 
covering  for  the  postero-inferior  surfaces  of  the  stomach  and  commencement  of  the 
duodenum,  and  is  continued  downward  as  the  deep  layer  of  the  gastrocolic  ligament 
or  greater  omentum.  From  the  free  margin  of  this  fold  it  is  reflected  upward  on 
itself  to  the  anterior  and  superior  surfaces  of  the  transverse  colon,  and  thence  as 
the  superior  layer  of  the  transverse  mesocolon  to  the  anterior  border  of  the  pancreas, 
the  level  from  which  a  start  was  made.  It  will  be  seen  that  the  loop  formed  by 
the  wall  of  the  omental  bursa  below  the  transverse  colon  follows,  and  is  closely 
applied  to,  the  deep  surface  of  that  formed  by  the  peritoneum  of  the  main  cavity, 
and  that  the  greater  omentum  or  large  fold  of  peritoneum  which  hangs  in  front 
of  the  small  intestine  therefore  consists  of  four  layers,  two  anterior  and  two  posterior 
separated  by  the  potential  cavity  of  the  omental  bursa. 

Horizontal  Disposition  of  the  Peritoneum. — Below  the  transverse  colon  the 
arrangement  is  simple,  as  it  includes  only  the  main  cavity;  above  the  level  of  the 
transverse  colon  it  is  more  complicated  on  account  of  the  existence  of  the  omental 
bursa.  Below  the  transverse  colon  it  may  be  considered  in  the  two  regions,  viz., 
in  the  pelvis  and  in  the  abdomen  proper. 


Fig.    1037. — The  peritoneum  of  the  male  pelvis.     (Dixon  and  Birmingham.) 

(1)  In  the  Pelvis. — The  peritoneum  here  follows  closely  the  surfaces  of  the 
pelvic  viscera  and  the  inequalities  of  the  pelvic  walls,  and  presents  important 
differences  in  the  two  sexes,  (a)  In  the  male  (Fig.  1037)  it  encircles  the  sigmoid 
colon,  from  which  it  is  reflected  to  the  posterior  wall  of  the  pelvis  as  a  fold,  the 
sigmoid  mesocolon.    It  then  leaves  the  sides  and,  finally,  the  front  of  the  rectum, 


I 


73 


)HNOLOG\ 

and  is  continued  on  to  the  upper  ends  of  the  seminal  vesicles  and  the  bladder; 
on  either  side  of  the  rectum  it  forms  a  fossa,  the  pararectal  fossa,  which  varies  in 
size  with  the  distension  of  the  rectum.  In  front  of  the  rectum  the  peritoneum  forms 
the  rectovesical  excavation,  which  is  limited  laterally  by  peritoneal  folds  extending 
from  the  sides  of  the  bladder  to  the  rectum  and  sacrum.  These  folds  are  known 
from  their  position  as  the  rectovesical  or  sacrogenital  folds.  The  peritoneum  of 
the  anterior  pelvic  wall  covers  the  superior  surface  of  the  bladder,  and  on  either 
side  of  this  viscus  forms  a  depression,  termed  the  paravesical  fossa,  which  is  limited 
laterally  by  the  fold  of  peritoneum  covering  the  ductus  deferens.  The  size  of  this 
fossa  is  dependent  on  the  state  of  distension  of  the  bladder;  when  the  bladder  is 
empty,  a  variable  fold  of  peritoneum,  the  plica  vesicalis  transversa,  divides  the  fossa 
into  two  portions.  On  the  peritoneum  between  the  paravesical  and  pararectal 
fossae  the  only  elevations  are  those  produced  by  the  ureters  and  the  hypogastric 
vessels.  (6)  la.  the  female,  pararectal  and  paravesical  fossae  similar  to  those  in  the 
male  are  present :  the  lateral  limit  of  the  paravesical  fossa  is  the  peritoneum  invest- 
ing the  round  ligament  of  the  uterus.  The  rectovesical  excavation  is,  however, 
divided  by  the  uterus  and  vagina  into  a  small  anterior  vesicouterine  and  a  large, 
deep,  posterior  rectouterine  excavation.  The  sacrogenital  folds  form  the  margins 
of  the  latter,  and  are  continued  on  to  the  back  of  the  uterus  to  form  a  transverse 
fold,  the  torus  uterinus.  The  broad  ligaments  extend  from  the  sides  of  the  uterus 
to  the  lateral  walls  of  the  pelvis;  they  contain  in  their  free  margins  the  uterine 
tubes,  and  in  their  posterior  laj-ers  the  ovaries.  Below,  the  broad  ligaments  are 
continuous  with  the  peritoneum  on  the  lateral  walls  of  the  pelvis.  On.  the  lateral 
pelvic  wall  behind  the  attachment  of  the  broad  ligament,  in  the  angle  between 
the  elevations  produced  by  the  diverging  hypogastric  and  external  iliac  vessels  is 
a  slight  fossa,  the  ovarian  fossa,  in  which  the  ovary  normally  lies. 


Recitis 


Small  intestine 

Mesentery 


Inferior  vena  cava 


Ascending  colon 


Descending  colon 
Quadratus  lumborum 

Psoas  major     L  ... 

•'        isacrosjnnali 

Fig.   1038. — Horizontal  disposition  of  the  peritoneum  in  the  lower  part  of  the  abdomen. 


(2)  In  the  Lower  Abdomen  (Fig.  1038). — Starting  from  the  linea  alba,  below  the 
level  of  the  transverse  colon,  and  tracing  the  continuity  of  the  peritoneum  in  a 
horizontal  direction  to  the  right,  the  membrane  covers  the  inner  surface  of  the 
abdominal  wall  almost  as  far  as  the  lateral  border  of  the  Quadratus  lumborum; 


THE  PERITONEUM 


1155 


it  encloses  the  cecum  and  vermiform  process,  and  is  reflected  over  the  sides  and  front 
of  the  ascending  colon;  it  may  then  be  traced  over  the  duodenum,  Psoas  major, 
and  inferior  vena  cava  toward  the  middle  line,  whence  it  passes  along  the  mesen- 
teric vessels  to  invest  the  small  intestine,  and  back  again  to  the  large  vessels  in 
front  of  the  vertebral  column,  forming  the  mesentery,  between  the  layers  of  which 
are  contained  the  mesenteric  bloodvessels,  lacteals,  and  glands.  It  is  then  con- 
tinued over  the  left  Psoas;  it  covers  the  sides  and  front  of  the  descending  colon, 
and,  reaching  the  abdominal  wall,  is  carried  on  it  to  the  middle  line. 

Lesser  cmentum 

Falciform  ligament  of  liver 


Gastrolienal 
ligament 


Hepatic  artery 
bile  duct,  and 
portal  vein 


Epiploic 
foramen 

Inferior 
vena  cava 


Phrenicolienal  ligament 

Aorta 
Fig.    1039. — Horizontal  disposition  of  the  peritoneum  in  the  upper  part  of  the  abdomen. 

(3)  In  the  Upper  Abdomen  (Fig.  1039). — Above  the  transverse  colon  the  omental 
bursa  is  superadded  to  the  general  sac,  and  the  communication  of  the  two  cavities 
with  one  another  through  the  epiploic  foramen  can  be  demonstrated. 

(a)  Main  Cavity. — Commencing  on  the  posterior  abdominal  w  all  at  the  inferior 
vena  cava,  the  peritoneum  may  be  followed  to  the  right  over  the  front  of  the 
suprarenal  gland  and  upper  part  of  the  right  kidney  on  to  the  antero-Iateral 
abdominal  wall.  From  the  middle  line  of  the  anterior  wall  a  backwardly  directed 
fold  encircles  the  obliterated  umbilical  vein  and  forms  the  falciform  ligament 
of  the  liver.  Continuing  to  the  left,  the  peritoneum  lines  the  antero-Iateral 
abdominal  wall  and  covers  the  lateral  part  of  the  front  of  the  left  kidney,  and  is 
reflected  to  the  posterior  border  of  the  hilus  of  the  spleen  as  the  posterior  layer 
of  the  phrenicolienal  ligament.  It  can  then  be  traced  around  the  surface  of  the  spleen 
to  the  front  of  the  hilus,  and  thence  to  the  cardiac  end  of  the  greater  curvature 
of  the  stomach  as  the  anterior  layer  of  the  gastrolienal  ligament.  It  covers  the 
antero-superior  surfaces  of  the  stomach  and  commencement  of  the  duodenum, 
and  extends  up  from  the  lesser  curvature  of  the  stomach  to  the  liver  as  the  anterior 
layer  of  the  lesser  omentum. 

(6)  Omental  Bursa  (bursa  omentalis;  lesser  peritoneal  sac). — On  the  posterior 
abdominal  wall  the  peritoneum  of  the  general  cavity  is  continuous  with  that  of 
the  omental  bursa  in  front  of  the  inferior  vena  cava.  Starting  from  here,  the 
bursa  may  be  traced  across  the  aorta  and  over  the  medial  part  of  the  front  of 
the  left  kidney  and  diaphragm  to  the  hilus  of  the  spleen  as  the  anterior  layer 
of  the  phrenicolienal  ligament.    From  the  spleen  it  is  reflected  to  the  stomach  as 


1156  ^Ktm  SPLANCHNOLOGY 

the  posterior  layer  of  the  gastrosplenic  ligament.  It  covers  the  postero-inferior 
surfaces  of  the  stomach  and  commencement  of  the  duodenum,  and  extends 
upward  to  the  liver  as  the  posterior  layer  of  the  lesser  omentum;  the  right  margin 
of  this  layer  is  continuous  around  the  hepatic  artery,  bile  duct,  and  portal  vein, 
with  the  wall  of  the  general  cavity. 

The  epiploic  foramen  (foramen  epiploicum;  foramen  of  Winslow)  is  the  passage  of 
communication  between  the  general  cavity  and  the  omental  bursa.  It  is  bounded 
in  front  by  the  free  border  of  the  lesser  omentum,  with  the  common  bile  duct, 
hepatic  artery,  and  portal  vein  between  its  two  layers;  behind  by  the  peritoneum 
covering  the  inferior  vena  cava;  above  by  the  peritoneum  on  the  caudate  process 
of  the  liver,  and  beloiv  by  the  peritoneum  covering  the  commencement  of  the 
duodenum  and  the  hepatic  artery,  the  latter  passing  forward  below  the  foramen 
before  ascending  between  the  two  layers  of  the  lesser  omentum. 

The  boundaries  of  the  omental  bursa  will  now  be  evident.  It  is  bounded  in  front, 
from  above  downw^ard,  by  the  caudate  lobe  of  the  liver,  the  lesser  omentum,  the 
stomach,  and  the  anterior  two  layers  of  the  greater  omentum.  Behind,  it  is  limited, 
from  below  upward,  by  the  two  posterior  layers  of  the  greater  omentum,  the  trans- 
verse colon,  and  the  ascending  layer  of  the  transverse  mesocolon,  the  upper  surface 
of  the  pancreas,  the  left  suprarenal  gland,  and  the  upper  end  of  the  left  kidney. 
To  the  right  of  the  esophageal  opening  of  the  stomach  it  is  formed  by  that  part 
of  the  diaphragm  which  supports  the  caudate  lobe  of  the  liver.  Laterally,  the 
bursa  extends  from  the  epiploic  foramen  to  the  spleen,  where  it  is  limited  by 
the  phrenicolienal  and  gastrolienal  ligaments. 

The  omental  bursa,  therefore,  consists  of  a  series  of  pouches  or  recesses  to  which 
the  following  terms  are  applied:  (1)  the  vestibule,  a  narrow  channel  continued 
from  the  epiploic  foramen,  over  the  head  of  the  pancreas  to  the  gastropancreatic 
fold;  this  fold  extends  from  the  omental  tuberosity  of  the  pancre'as  to  the  right 
side  of  the  fundus  of  the  stomach,  and  contains  the  left  gastric  artery  and  coronary 
vein ;  (2)  the  superior  omental  recess,  between  the  caudate  lobe  of  the  liver  and  the 
diaphragm;  (3)  the  lienal  recess,  between  the  spleen  and  the  stomach;  (4)  the  J 
inferior  omental  recess,  which  comprises  the  remainder  of  the  bursa.  I 

In  the  fetus  the  bursa  reaches  as  low  as  the  free  margin  of  the  greater  omentum, 
but  in  the  adult  its  vertical  extent  is  usually  more  limited  owing  to  adhesions 
between  the  layers  of  the  omentum.  During  a  considerable  part  of  fetal  life  the 
transverse  colon  is  suspended  from  the  posterior  abdominal  wall  by  a  mesentery 
of  its  own,  the  two  posterior  layers  of  the  greater  omentum  passing  at  this  stage 
in  front  of  the  colon.  This  condition  occasionally  persists  throughout  life,  but  as 
a  rule  adhesion  occurs  between  the  mesentery  of  the  transverse  colon  and  the  pos- 
terior layer  of  the  greater  omentum,  wuth  the  result  that  the  colon  appears  to  receive 
its  peritoneal  covering  by  the  splitting  of  the  two  posterior  layers  of  the  latter  fold. 
In  the  adult  the  omental  bursa  intervenes  betw^een  the  stomach  and  the  structures 
on  which  that  viscus  lies,  and  performs  therefore  the  functions  of  a  serous  bursa 
for  the  stomach. 

Numerous  peritoneal  folds  extend  between  the  various  organs  or  connect  them 
to  the  parietes;  they  serve  to  hold  the  viscera  in  position,  and,  at  the  same  time, 
enclose  the  vessels  and  nerves  proceeding  to  them.  They  are  grouped  under  the 
three  headings  of  ligaments,  omenta,  and  mesenteries. 

The  ligaments  will  be  described  with  their  respective  organs. 

There  are  two  omenta,  the  lesser  and  the  greater. 

The  lesser  omentum  {omentum  minus;  small  omentum;  gastrohepatic  omentum)  is  the 
duplicature  which  extends  to  the  liver  from  the  lesser  curvature  of  the  stomach  and 
the  commencement  of  the  duodenum.  It  is  extremely  thin,  and  is  continuous  with  the 
two  layers  of  peritoneum  which  cover  respectively  the  antero-superior  and  postero- 
inferior  surfaces  of  the  stomach  and  first  part  of  the  duodenum.  When  these 
two  layers  reach  the  lesser  curvature  of  the  stomach  and  the  upper  border  of  the 


1157 

duodenum,  they  join  together  and  ascend  as  a  double  fold  to  the  porta  of  the  liver; 
to  the  left  of  the  porta  the  fold  is  attached  to  the  bottom  of  the  fossa  for  the  ductus 
venosus,  along  which  it  is  carried  to  the  diaphragm,  where  the  two  layers  separate 
to  embrace  the  end  of  the  esophagus.  At  the  right  border  of  the  omentum  the 
two  layers  are  continuous,  and  form  a  free  margin  which  constitutes  the  anterior 
boundary  of  the  epiploic  foramen.  The  portion  of  the  lesser  omentum  extending 
between  the  liver  and  stomach  is  termed  the  hepatogastric  ligament,  while  that 
between  the  liver  and  duodenum  is  the  hepatoduodenal  ligament.  Between  the  two 
la^'ers  of  the  lesser  omentum,  close  to  the  right  free  margin,  are  the  hepatic 
artery,  the  common  bile  duct,  the  portal  vein,  lymphatics,  and  the  hepatic  plexus  of 
nerves — all  these  structures  being  enclosed  in  a  fibrous  capsule  (Glisson's  capsule). 
Between  the  layers  of  the  lesser  omentum,  where  they  are  attached  to  the 
stomach,  run  the  right  and  left  gastric  vessels. 

The  greater  omentum  (omentum  majus;  great  omentum;  gastrocolic  omentum)  is  the 
largest  peritoneal  fold.  It  consists  of  a  double  sheet  of  peritoneum,  folded  on  itself 
so  that  it  is  made  up  of  four  layers.  The  two  layers  which  descend  from  the  stomach 
and  commencement  of  the  duodenum  pass  in  front  of  the  small  intestines,  sometimes 
as  low  down  as  the  pelvis;  they  then  turn  upon  themselves,  and  ascend  again  as 
far  as  the  transverse  colon,  where  they  separate  and  enclose  that  part  of  the  intes- 
tine. These  individual  layers  may  be  easily  demonstrated  in  the  young  subject, 
but  in  the  adult  they  are  more  or  less  inseparably  blended.  The  left  border  of  the 
greater  omentum  is  continuous  with  the  gastrolienal  ligament;  its  right  border 
extends  as  far  as  the  commencement  of  the  duodenum.  The  greater  omentum  is 
usually  thin,  presents  a  cribriform  appearance,  and  always  contains  some  adipose 
tissue,  which  in  fat  people  accumulates  in  considerable  quantity.  Between  its 
two  anterior  layers,  a  short  distance  from  the  greater  curvature  of  the  stomach, 
is  the  anastomosis  between  the  right  and  left  gastroepiploic  vessels. 

The  mesenteries  are:  the  mesentery  proper,  the  transverse  mesocolon,  and  the 
sigmoid  mesocolon.  In  addition  to  these  there  are  sometimes  present  an  ascending 
and  a  descending  mesocolon. 

The  mesentery  proper  (mesenterium)  is  the  broad,  fan-shaped  fold  of  peritoneum 
which  connects  the  convolutions  of  the  jejunum  and  ileum  W'ith  the  posterior  wall 
of  the  abdomen.  Its  root — the  part  connected  with  the  structures  in  front  of  the 
vertebral  column — is  narrow,  about  15  cm.  long,  and  is  directed  obliquely  from  the 
duodenojejunal  flexure  at  the  left  side  of  the  second  lumbar  vertebra  to  the  right 
sacroiliac  articulation  (Fig.  1040).  Its  intestinal  border  is  about  6  metres  long;  and 
here  the  two  layers  separate  to  enclose  the  intestine,  and  form  its  peritoneal  coat. 
It  is  narrow  above,  but  widens  rapidly  to  about  20  cm.,  and  is  thrown  into  numerous 
plaits  or  folds.  It  suspends  the  small  intestine,  and  contains  between  its  layers 
the  intestinal  branches  of  the  superior  mesenteric  artery,  with  their  accompanying 
veins  and  plexuses  of  nerves,  the  lacteal  vessels,  and  mesenteric  lymph  glands. 

The  transverse  mesocolon  (mesocolon  transversum)  is  a  broad  fold,  which  connects 
the  transverse  colon  to  the  posterior  wall  of  the  abdomen.  It  is  continuous  with 
the  two  posterior  layers  of  the  greater  omentum,  which,  after  separating  to  surround 
the  transverse  colon,  join  behind  it,  and  are  continued  backward  to  the  vertebral 
column,  where  they  diverge  in  front  of  the  anterior  border  of  the  pancreas.  This 
fold  contains  between  its  layers  the  vessels  which  supply  the  transverse  colon. 

The  sigmoid  mesocolon  (mesocolon  sigmoideum)  is  the  fold  of  peritoneum  which 
retains  the  sigmoid  colon  in  connection  with  the  pelvic  wall.  Its  line  of  attachment 
forms  a  V-shaped  curve,  the  apex  of  the  curve  being  placed  about  the  point  of 
division  of  the  left  common  iliac  artery.  The  curve  begins  on  the  medial  side  of 
the  left  Psoas  major,  and  runs  upward  and  backw^ard  to  the  apex,  from  which  it 
bends  sharply  downward,  and  ends  in  the  median  plane  at  the  level  of  the  third 
sacral  vertebra.  The  sigmoid  and  superior  hemorrhoidal  vessels  run  between  the 
two  layers  of  this  fold. 


■&  two  lay 

ft— 


1158 


SPLANCHNOLOGY 


In  most  cases  the  peritoneum  covers  only  the  front  and  sides  of  the  ascending 
and  descending  parts  of  the  colon.  Sometimes,  however,  these  are  surrounded 
by  the  serous  membrane  and  attached  to  the  posterior  abdominal  wall  by  an 
ascending  and  a  descending  mesocolon  respectively.  A  fold  of  peritoneum,  the 
phrenicocolic  ligament,  is  continued  from  the  left  colic  flexure  to  the  diaphragm 
opposite  the  tenth  and  eleventh  ribs;  it  passes  below  and  serves  to  support  the 
spleen,  and  therefore  has  received  the  name  of  sustentaculum  lienis. 


Sight  triangular  Falei/orm  ligament 
ligament  0/ liver  of  liver 


Left  triangular 
ligament  of  liver 


Inferior  vena  cai  11  ——- 


^sophagu 
Bight  phrenic  artery 


Left  gastric  artery  - 
Hepatic  artery  . 

Lienal  artery  - 
Fanct  eas 

Inf.  pancduo.  artery  . 

Middle  colic - 

Superior  mesenteric 

Duodenum  (horiz.  part)  - 

Aorta  - 

Duodenum  (desc.  part}  - 

Right  and  left  kidneys 
Superior  inesenteric 
Aorta  - 

Left  colic  - 

Bight  colic 

Intestinal  arteries  <  ~ 

Sigmoid  artery 
Sap.  hemorrhoidal  artery 

Common  iliac  artery 


Hypogastric  artery 

External  iliac  artery  — — 

Inf.  epija.-itric  arterij 

Bladder tm 


Fitraperitoneal  tissue 


^   (  Diaphragmatic  end  of 
\    ^      Itsser  omentum 
7~  Gastrophrenic  ligameni 


Phrenicolienal  ligament 
1 1  iploic  foramen 
Duodenum  {sup,  part) 


J  hremcocohc  ligament 
(  Dot  betvxen  two  anterior 
\  layers  of  greater  omentum 

Transverse  mesocolon 


(  Bare  surface  for  descend- 
I,  ing  colon 


(  The  two  layers  of  the 
(.    mesentery  proper 


(Bare  surface  for  ascend- 
1  ing  colon 


—  Iliac  mesocolon 


Sigmoid  mesocolon 

—  Bare  surface  for  rectum 

(  Cut  edge  of  peritoneum 
\  on  bladder 


Fig.   1040. — Diagram  devised  by  DeI6pine  to  show  the  lines  along  which  the  peritoneum  leaves  the  wail  of  the  abdomen 

to  invest  the  viscera. 

The  appendices  epiploicse  are  small  pouches  of  the  peritoneum  filled  with  fat 
and  situated  along  the  colon  and  upper  part  of  the  rectum.  They  are  chiefly 
appended  to  the  transverse  and  sigmoid  parts  of  the  colon. 

Peritoneal  Recesses  or  Fossae  (retroperitoneal  fosscp). — In  certain  parts  of  the 
abdominal  cavity  there  are  recesses  of  peritoneum  forming  culs-de-sac  or  pouches, 
which  are  of  surgical  interest  in  connection  with  the  possibility  of  the  occurrence 
of  "retroperitoneal"  hernise.  The  largest  of  these  is  the  omental  bursa  (already 
described),  but  several  others,  of  smaller  size,  require  mention,  and  may  be  divided 
into  three  groups,  viz. :  duodenal,  cecal,  and  intersigmoid. 


THE  PERITONEUM 


1159 


1.  Duodenal  Fossae  (Figs.  1041,  1042). — Three  are  fairly  constant,  viz. :  (a)  The 
inferior  duodenal  fossa,  present  in  from  70  to  75  per  cent,  of  cases,  is  situated 
opposite  the  third  lumbar  vertebra  on  the  left  side  of  the  ascending  portion  of 
the  duodenum.    Its  opening  is  directed  upward,  and  is  bounded  by  a  thin  sharp 


f    ((  4:1! miu 


Fig.   1(H1. — Superior  and  inferior  duodenal  fossse. 


Inferior 

Tnesenteric 

vein 


Duode  nojejuTuil 
fold 


Superior 
duodenal  fossa 


Inferior 
d/uodenal  fossa 

Duodenomesocol  ic 
fold 

Left  colic  artery 

(Poirier  and  Charpy.) 


fold  of  peritoneum  with  a  concave  margin,  called  the  duodenomesocolic  fold.  The 
tip  of  the  index  finger  introduced  into  the  fossa  under  the  fold  passes  some 
little  distance  behind  the  ascending  portion  of  the  duodenum,  (b)  The  superior 
duodenal  fossa,  present  in  from  40  to  50  per  cent,  of  cases,  often  coexists  with  the 
inferior  one,  and  its  orifice  looks  downward.    It  lies  on  the  left  of  the  ascending 


Duodenum 


Right 
duode7io- 
mesocdic 

fold 


Inferior 
mesenteric  vein 

Left 

dvAjdenomesocolic 

fold 

Left  colic  artery 


Inferior  mesenteric  artery 
Fig.   1042. — Duodenojejunal  fossa.     (Poirier  and  Charpy.) 

portion  of  the  duodenum,  in  front  of  the  second  lumbar  vertebra,  and  behind  a 
sickle-shaped  fold  of  peritoneum,  the  duodenojejunal  fold,  and  has  a  depth  of  about 
2  cm.  (c)  The  duodenojejunal  fossa  exists  in  from  15  to  20  per  cent,  of  cases, 
but  has  never  yet  been  found  in  conjunction  with  the  other  forms  of  duodenal 


1160 


SPLANCHNOLOGY 


fossae;  it  can  be  seen  by  pulling  the  jejunum  downward  and  to  the  right,  after  thd| 
transverse  colon  has  been  pulled  upward.    It  is  bounded  above  by  the  pancreas, 
to  the  right  by  the  aorta,  and  to  the  left  by  the  kidney;  beneath  is  the  left  renal 
vein.    It  has  a  depth  of  from  2  to  3  cm.,  and  its  orifice,  directed  downward  and  to 
the  right,  is  nearly  circular  and  will  admit  the  tip  of  the  little  finger. 

2.  Cecal  Fossae  (pericecal  folds  or  fosses). — There  are  three  principal  pouches 
or  recesses  in  the  neighborhood  of  the  cecum  (Figs.  1043  to  1045) :  (a)  The  superior 
ileocecal  fossa  is  formed  by  a  fold  of  peritoneum,  arching  over  the  branch  of  the 
ileocolic  artery  which  supplies  the  ileocolic  junction.  The  fossa  is  a  narrow  chink 
situated  between  the  mesentery  of  the  small  intestine,  the  ileum,  and  the  small 
portion  of  the  cecum  behind.  (6)  The  inferior  ileocecal  fossa  is  situated  behind  the 
angle  of  junction  of  the  ileum  and  cecum.  It  is  formed  by  the  ileocecal  fold  of 
peritoneum  (bloodless  fold  of  Treves),  the  upper  border  of  which  is  fixed  to  the  ileum, 

opposite    its  mesenteric   attach- 


Anterior 
Superior  ileocecal 
ileocecal     ar 


Mesentery 


Superior 

ileocecal 

fossa 


ment,  while  the  lower  border, 
passing  over  the  ileocecal  junc- 
tion, joins  the  mesenteriole  of  the 
vermiform  process,  and  some- 
times the  process  itself.  Between 
this  fold  and  the  mesenteriole 
of  the  vermiform  process  is  the 
inferior  ileocecal  fossa.  It  is 
bounded  above  by  the  posterior 
surface  of  the  ileum  and  the  me- 
sentery; in  front  and  below  by  the 
ileocecal  fold,  and  behind  by  the 
upper  part  of  the  mesenteriole 
of  the  vermiform  process,  (c) 
The  cecal  fossa  is  situated  im- 
mediately behind  the  cecum, 
which  has  to  be  raised  to  bring 

Fig.   1043.— Superior  ileocecal  fossa.     (Poirier  and  Charpy.)  it  iuto  vicW.      It  VaricS    mUch  iu 

size  and  extent.  In  some  cases 
it  is  suflBciently  large  to  admit  the  index  finger,  and  extends  upward  behind  the 
ascending  colon  in  the  direction  of  the  kidney;  in  others  it  is  merelv  a  shallow 


Inferior 
ileocecal 

fold 
Ileum 


Inferior 
ileocecal  fossa 


Mesentery 

\         Artery  to 

J  vermiform  process 


Mesenteriole  of 
term,iform  process 


Fig.  1044. — Inferior  ileocecal  fossa.     The  cecum  and  ascending  colon  have  been  drawn  lateralward  and  downward, 
the  ileum  upward  and  backward,  and  the  vermiform  process  downward.     (Poirier  and  Charpy.) 

depression.    It  is  bounded  on  the  right  by  the  cecal  fold,  which  is  attached  by 
one  edge  to  the  abdominal  wall  from  the  lower  border  of  the  kidney  to  the  iliac 


THE  STOMACH 


1161 


fossa  and  by  the  other  to  the  postero-lateral    aspect   of  the   colon.    In  some 
instances  additional  fossae,  the  retrocecal  fossae,  are  present. 

3.  The  intersigmoid  fossa  (recessus  intersigmoideus)  is  constant  in  the  fetus  and 
during  infancy,  but  disappears  in  a  certain  percentage  of  cases  as  age  advances. 
Upon  drawing  the  sigmoid  colon  upward,  the  left  surface  of  the  sigmoid  mesocolon 
is  exposed,  and  on  it  will  be  seen  a  funnel-shaped  recess  of  the  peritoneum,  lying 
on  the  external  iliac  vessels,  in  the  interspace  between  the  Psoas  and  Iliacus  muscles. 
This  is  the  orifice  leading  to  the  intersigmoid  fossa,  which  lies  behind  the  sigmoid 
mesocolon,  and  in  front  of  the  parietal  peritoneum.  The  fossa  varies  in  size;  in 
some  instances  it  is  a  mere  dimple,  whereas  in  others  it  will  admit  the  whole  of  the 
index  finger.' 

Inferior  ileocecal  •«> 

fold 


Inferior  ileocecal  fossa 

Mesenteriole  of 
vermiform  process 


Mesentericoparietal 
fold 


Cecal  fossa 
Fig.   1045. — The  cecal  fossa.      The  ileum  and  cecum  are  drawn  backward  and  upward.     (Souligoux.) 


I» 


li 


The  Stomach  (Ventriculus ;  Gaster). 

The  stomach  is  the  most  dilated  part  of  the  digestive  tube,  and  is  situated  between 
the  end  of  the  esophagus  and  the  beginning  of  the  small  intestine.  It  lies  in  the 
epigastric,  umbilical,  and  left  hypochondriac  regions  of  the  abdomen,  and  occupies 
a  recess  bounded  by  the  upper  abdominal  viscera,  and  completed  in  front  and  on 
the  left  side  by  the  anterior  abdominal  wall  and  the  diaphragm. 

The  shape  and  position  of  the  stomach  are  so  greatly  modified  by  changes  within 
itself  and  in  the  surrounding  viscera  that  no  one  form  can  be  described  as  typical. 
The  chief  modifications  are  determined  by  (1)  the  amount  of  the  stomach  contents, 
(2)  the  stage  which  the  digestive  process  has  reached,  (3)  the  degree  of  develop- 
ment of  the  gastric  musculature,  and  (4)  the  condition  of  the  adjacent  intestines. 
It  is,  however,  possible  by  comparing  a  series  of  stomachs  to  determine  certain 
markings  more  or  less  common  to  all  (Figs.  1046,  1047,  1048,  1049). 

The  stomach  presents  two  openings,  two  borders  or  curvatures,  and  two  surfaces. 

Openings. — The  opening  by  which  the  esophagus  communicates  with  the 
stomach  is  known  as  the  cardiac  orifice,  and  is  situated  on  the  left  of  the  middle 
line  at  the  level  of  the  tenth  thoracic  vertebra.  The  short  abdominal  portion  of  the 
esophagus  (antrum  cardiacum)  is  conical  in  shape  and  curved  sharply  to  the  left, 


I 


>  On  the  anatomy  of  these  fossse,  see  the  Arris  and  Gale  Lectures  by  Moynihan,  1899. 


1162  V^^^P         SPLANCHNOLOGY 

the  base  of  the  cone  being  continuous  with  the  cardiac  orifice  of  the  stomachJ 
The  riglit  margin  of  the  esophagus  is  continuous  with  the  lesser  curvature  of  the 
stomach,  while  the  left  margin  joins  the  greater  curvature  at  an  acute  angle,  termed 
the  incisura  cardiaca. 

The  pyloric  orifice  communicates  with  the  duodenum,  and  its  position  is  usually 
indicated  on  the  surface  of  the  stomach  by  a  circular  groove,  the  duodenopyloric 
constriction.  This  orifice  lies  to  the  right  of  the  middle  line  at  the  level  of  the  upper 
border  of  the  first  lumbar  vertebra. 

Curvatures. — The  lesser  curvature  {curvatura  ventriculi  minor),  extending  between 
the  cardiac  and  pyloric  orifices,  forms  the  right  or  posterior  border  of  the  stomach. 
It  descends  as  a  continuation  of  the  right  margin  of  the  esophagus  in  front  of  the 
fibej*  of  the  right  crus  of  the  diaphragm,  and  then,  turning  to  the  right,  it  crosses 
the  first  lumbar  vertebra  and  ends  at  the  pylorus.  Nearer  its  pyloric  than  its 
cardiac  end  is  a  well-marked  notch,  the  incisura  annularis,  which  varies  somewhat 
in  position  with  the  state  of  distension  of  the  viscus;  it  serves  to  separate  the 
stomach  into  a  right  and  a  left  portion.  The  lesser  curvature  gives  attachment 
to  the  two  layers  of  the  hepatogastric  ligament,  and  between  these  two  layers  are 
the  left  gastric  artery  and  the  right  gastric  branch  of  the  hepatic  artery. 

The  greater  curvature  {curvatura  ventriculi  major)  is  directed  mainly  forward, 
and  is  four  or  five  times  as  long  as  the  lesser  curvature.  Starting  from  the  cardiac 
orifice  at  the  incisura  cardiaca,  it  forms  an  arch  backward,  upward,  and  to  the  left; 
the  highest  point  of  the  convexity  is  on  a  level  with  the  sixth  left  costal  cartilage. 
From  this  level  it  may  be  followed  downward  and  forward,  with  a  slight  convexity 
to  the  left  as  low  as  the  cartilage  of  the  ninth  rib;  it  then  turns  to  the  right,  to  the 
end  of  the  pylorus.  Directly  opposite  the  incisura  angularis  of  the  lesser  curva- 
ture the  greater  curvature  presents  a  dilatation,  w^hich  is  the  left  extremity  of  the 
pyloric  part;  this  dilatation  is  limited  on  the  right,  by  a  slight  groove,  the  sulcus 
intermedins,  which  is  about  2.5  cm,  from  the  duodenopyloric  constriction.  The 
portion  between  the  sulcus  intermedins  and  the  duodenopyloric  constriction  is 
termed  the  pyloric  antrum.  At  its  commencement  the  greater  curvature  is  covered 
by  peritoneum  continuous  with  that  covering  the  front  of  the  organ.  The  left 
part  of  the  curvature  gives  attachment  to  the  gastrolienal  ligament,  while  to  its 
anterior  portion  are  attached  the  two  layers  of  the  greater  omentum,  separated 
from  each  other  by  the  gastroepiploic  vessels. 

Surfaces. — When  the  stomach  is  in  the  contracted  condition,  its  surfaces  are 
directed  upward  and  downward  respectively,  but  when  the  viscus  is  distended  they 
are  directed  forward,  and  backward.  They  may  therefore  be  described  as  antero- 
superior  and  postero-inferior. 

Antero-superior  Surface. — The  left  half  of  this  surface  is  in  contact  with  the 
diaphragm,  which  separates  it  from  the  base  of  the  left  lung,  the  pericardium, 
and  the  seventh,  eighth,  and  ninth  ribs,  and  intercostal  spaces  of  the  left  side.  The 
right  half  is  in  relation  with  the  left  and  quadrate  lobes  of  the  liver  and  with  the 
anterior  abdominal  wall.  When  the  stomach  is  empty,  the  transverse  colon  may 
lie  on  the  front  part  of  this  surface.    The  whole  surface  is  covered  by  peritoneum. 

The  Postero-inferior  Surface  is  in  relation  with  the  diaphragm,  the  spleen, 
the  left  suprarenal  gland,  the  upper  part  of  the  front  of  the  left  kidney,  the  anterior 
surface  of  the  pancreas,  the  left  colic  flexure,  and  the  upper  layer  of  the  transverse 
mesocolon.  These  structures  form  a  shallow  bed,  the  stomach  bed,  on  which  the 
viscus  rests.  The  transverse  mesocolon  separates  the  stomach  from  the  duodeno- 
jejunal flexure  and  small  intestine.  The  postero-inferior  surface  is  covered  by 
peritoneum,  except  over  a  small  area  close  to  the  cardiac  orifice;  this  area  is  limited 
by  the  lines  of  attachment  of  the  gastrophrenic  ligament,  and  lies  in  apposition 
with  the  diaphragm,  and  frequently  with  the  upper  portion  of  the  left  supra- 
renal gland. 


m 


Y)MACH 


m 


Component  Parts  oZ  the  Stomach. ^A  plane  passing  through  the  incisura  angularis  on  the  lesser 
curvature  and  the  left  limit  of  the  opposed  dilatation  on  the  greater  curvature  divides  the  stomach 
into  a  left  portion  or  body  and  a  right  or  pyloric  portion.  The  left  portion  of  the  body  is  known 
as  the  fundus,  and  is  marked  off  from  the  remainder  of  the  body  by  a  plane  passing  horizon- 
tally through  the  cardiac  orifice.  The  pyloric  portion  is  divided  by  a  plane  through  the  sulcus 
intermedins  at  right  angles  to  the  long  axis  of  this  portion;  the  part  to  the  right  of  this  plane 
[is  the  pyloric  antr\un  (Fig.  1046). 


Antruvi  cardiactim 


Incisura  angularis     % 


Pyloroduodenal       /V,-''    V 
openiwj  /  /\ 

Pijloric  antrum 
I  Sulcus  intermedius 


Pllloric  part 


Fig.   1046. — Outline  of  stomach,  showing  its  anatomical 
landmarks. 


Fig.  1047. — Diagram  showing  shape  and  position 
of  empty  stomach.     Erect  posture.     (Hertz.) 


If  the  stomach  be  examined  during  the  process  of  digestion  it  will  be  found  divided  by  a 

'rnuscular  constriction  into  a  large  dilated  left  portion,  and  a  narrow  contracted  tubular  right 

portion.     The  constriction  is  in   the  body  of   the  stomach,  and   does   not  follow  any  of  the 

anatomical  landmarks;  indeed,  it  shifts  gradually  toward  the  left  as  digestion  progresses,  i.  e., 

lore  of  the  body  is  gradually  absorbed  into  the  tubular  part  (Figs.  1047,  1048,  1049). 


Tia.  104S. — Diagram  showing   shape   and   position   of 
moderately  filled  stomach.    Erect  posture.    (Hertz.) 


Fig.    1049. — Diagram  showing  shape  and  position  of 
distended  stomach.     Erect  posture.      (Hertz.) 


Position  of  the  Stomach. — The  position  of  the  stomach  varies  with  the  posture,  with  the 

amount  of  the  stomach  contents  and  with  the  condition  of  the  intestines  on  which  it  rests.     In 

the  erect  posture  the  empty  stomach  is  somewhat  J-shaped;  the  part  above  the  cardiac  orifice 

is  usually  distended  with  gas;  the  pylorus  descends  to  the  level  of  the  second  lumbar  vertebra 

and  the  most  dependent  part  of  the  stomach  is  at  the  level  of  the  umbilicus.    Variation  in  the 

amount  of  its  contents  affects  mainly  the  cardiac  portion,  the  pyloric  portion  remaining  in  a  more 

or  less  contracted  condition  during  the  process  of  digestion.     As  the  stomach  fills  it  tends  to 

expand  forward  and  downward  in  the  direction  of  least  resistance,  but  when  this  is  interfered 

with  by  a  distended  condition  of  the  colon  or  intestines  the  fundus  presses  upward  on  the  liver 

and  diaphragm  and  gives  rise  to  the  feelings  of  oppression  and  palpitation  complained  of  in 

i.-«uch  cases.     His^  and  Cunningham'  have  shown  by  hardening  the  viscera  in  situ  that  the  con- 

Jiracted  stomach  has  a  sickle  shape,  the  fundus  looking  directly  backward.     The  surfaces  are 

irected  upward  and  downward,  the  upper  surface  having,  however,  a  gradual  downward  slope 

to  the  right.    The  greater  curvature  is  in  front  and  at  a  slightly  higher  level  than  the  lesser. 

1  Archiv  fiir  .Vnatomie  und  Physiologic,  anat.  Abth.,  1903. 

'  Traasactioa-3  of  the  Royal  Society  of  Edinburgh,  vol.  xlv,  part  i. 


1164 


SPLANCHNOLOGY 


The  position  of  the  full  stomach  depends,  as  abeady  indicated,  on  the  state  of  the  intestines;  i 
when  these  are  empty  the  fundus  expands  vertically  and  also  forward,  the  pylorus  is  displaced 
toward  the  right  and  the  whole  organ  assumes  an  oblique  position,  so  that  its  surfaces  are  directed 
more  forward  and  backward.  The  lowest  part  of  the  stomach  is  at  the  pyloric  vestibule,  which 
reaches  to  the  region  of  the  umbilicus.  Where  the  intestines  interfere  with  the  downward 
expansion  of  the  fundus  the  stomach  retains  the  horizontal  position  which  is  characteristic  of 
the  contracted  viscus. 

Examination  of  the  stomach  during  life  by  x-rays  has  confirmed  these  findings,  and  has 
demonstrated  that,  in  the  erect  posture,  the  full  stomach  usually  presents  a  hook-like  appear- 
ance, the  long  axis  of  the  clinical  fundus  being  directed  downward,  medialward,  and  forward 
toward  the  umbilicus,  while  the  pyloric  portion  curves  upward  to  the  duodenopyloric  junction. 

Interior  of  the  Stomach. — When  examined  after  death,  the  stomach  is  usually  fixed  at  some 
temporary  stage  of  the  digestive  process.  A  common  form  is  that  shown  in  Fig.  1050.  If  the 
viscus  be  laid  open  by  a  section  through  the  plane  of  its  two  curvatures,  it  is  seen  to  consist  of 
two  segments:  (a)  a  large  globular  portion  on  the  left  and  (6)  a  narrow  tubular  part  on  the 
right.  These  correspond  to  the  clinical  subdivisions  of  fundus  and  pyloric  portions  already 
described,  and  are  separated  by  a  constriction  which  indents  the  body  and  greater  curvature, 
but  does  not  involve  the  lesser  curvature.  To  the  left  of  the  cardiac  orifice  is  the  incisura 
cardiaca:  the  projection  of  this  notch  into  the  cavity  of  the  stomach  increases  as  the  organ 
distends,  and  has  been  supposed  to  act  as  a  valve  preventing  regurgitation  into  the  esophagus. 
In  the  pyloric  portion  are  seen:  (a)  the  elevation  corresponding  to  the  incisura  angularis,  and 
(b)  the  circular  projection  from  the  duodenopyloric  constriction  which  forms  the  pyloric  valve; 
the  separation  of  the  pyloric  antrum  from  the  rest  of  the  pyloric  part  is  scarcely  indicated. 


Antrum  cardiacum 
Pyloric  valve 


Pylorus 
Pyloric  antrum 


FiQ.   1050. — Interior  of  the  stomach. 


The  pyloric  valve  (valvula  pylori)  is  formed  by  a  reduplication  of  the  mucous 
membrane  of  the  stomach,  covering  a  muscular  ring  composed  of  a  thickened  por- 
tion of  the  circular  layer  of  the  muscular  coat.  Some  of  the  deeper  longitudinal 
fibers  turn  in  and  interlace  with  the  circular  fibers  of  the  valve. 

Structure. — The  wall  of  the  stomach  consists  of  four  coats:  serous,  muscular,  areolar,  and 
mucous,  together  with  vessels  and  nerves. 

The  serous  coat  (tunica  serosa)  is  derived  from  the  peritoneum,  and  covers  the  entire  surface 
of  the  organ,  excepting  along  the  greater  and  lesser  curvatures  at  the  points  of  attachment  of 
the  greater  and  lesser  omenta;  here  the  two  layers  of  peritoneum  leave  a  small  triangular  space, 
along  which  the  nutrient  vessels  and  nerves  pass.  On  the  posterior  surface  of  the  stomach, 
close  to  the  cardiac  orifice,  there  is  also  a  small  area  uncovered  by  peritoneum,  where  the  organ 
is  in  contact  with  the  under  surface  of  the  diaphragm. 

The  muscular  coat  (tunica  muscularis)  (Figs.  1051,  1052)  is  situated  immediately  beneath  the 
serous  covering,  with  which  it  is  closely  connected.  It  consists  of  three  sets  of  smooth  muscle 
fibers:  longitudinal,  circular  and  oblique. 

The  longitudinal  fibers  (stratum  longitudinale)  are  the  most  superficial,  and  are  arranged  in 


THE 

two  sets.  The  first  set  consists  of  fibers  continuous  with  the  longitudinal  fibers  of  the  esophagus; 
they  radiate  in  a  stellate  manner  from  the  cardiac  orifice  and  are  practically  all  lost  before  the 
pyloric  portion  is  reached.    The  second  set  commences  on  the  body  of  the  stomach  and  passes 


he  stomach,  viewed  from  above  and  in  front.  (Spalteholz.) 


to  the  right,  its  fibers  becoming  more  thickly  distributed  as  they  approach  the  pylorus.  Some 
of  the  more  superficial  fibers  of  this  set  pass  on  to  the  duodenum,  but  the  deeper  fibers  dip  inward 
and  interlace  with  the  circular  fibers  of  the  pyloric  valve. 


Esophagus 


Fia.   1052. — The  oblique  muscular  fibers  of  the  stomach,  viewed  from  above  and  in  front.      (Spalteholz.) 

The  circular  fibers  {stratum  circulare)  form  a  uniform  layer  over  the  whole  extent  of  the  stomach 
^eneath  the  longitudinal  fibers.    At  the  pylorus  they  are  most  abundant,  and  are  aggregated  into 


1166 


SPLANCHNOLOGY 


4 


a  circular  ring,  which  projects  into  the  lumen,  and  forms,  with  the  fold  of  mucous  membrane 
covering  its  surface,  the  pyloric  valve.  They  are  continuous  with  the  circular  fibers  of  the 
esophagus,  but  are  sharply  marked  ofT  from  the  circular  fibers  of  the  duodenum. 

The  oblique  fibers  (fibrcp  obliguce)  internal  to  the  circular  layer,  are  limited  chiefly  to  the 
cardiac  end  of  the  stomach,  where  they  are  disposed  as  a  thick  uniform  layer,  covering  both 
surfaces,  some  passing  obliquely  from  left  to  right,  others  from  right  to  left,  around  the  cardiac 
end. 

The  areolar  or  submucous  coat  {tela  submucosa)  consists  of  a  loose,  areolar  tissue,  connectin] 
the  mucous  and  muscular  layers. 

The  mucous  membrane  {tunica  mucosa)  is  thick  and  its  surface  is  smooth,  soft,  and  velvety^ 
In  the  fresh  state  it  is  of  a  pinkish  tinge  at  the  pyloric  end,  and  of  a  red  or  reddish-brown  color 
over  the  rest  of  its  surface.  In  infancy  it  is  of  a  brighter  hue,  the  vascular  redness  being  more 
marked.  It  is  thin  at  the  cardiac  extremity,  but  thicker  toward  the  pylorus.  During  the  con- 
tracted state  of  the  organ  it  is  thrown  into  numerous  plaits  or  rugae,  which,  for  the  most  part, 
have  a  longitudinal  direction,  and  are  most  marked  toward  the  pyloric  end  of  the  stomach, 
and  along  the  greater  curvature  (Fig.  1050).  These  folds  are  entirely  obliterated  when  the  organ 
becomes  distended. 


Fio.  1053. — Section  of  mucous  membrane  of  human  stomach,  near  the  cardiac  orifice,  (v.  Ebner,  after  J.  Schaffer.) 
X  45.  c.  Cardiac  glands,  d.  Their  ducts,  cr.  Gland  similar  to  the  intestinal  glands,  with  goblet  cells,  mjn.  Mucous 
membrane,    m.  Muscularis  mucosae,    m'.  Muscular  tissue  within  the  mucous  membrane. 

Structure  of  the  Mucous  Membrane. — When  examined  with  a  lens,  the  inner  surface  of  the 
mucous  membrane  presents  a  peculiar  honeycomb  appearance  from  being  covered  with  small 
shallow  depressions  or  alveoli,  of  a  polygonal  or  hexagonal  form,  which  vary  from  0.12  to  0.25 
mm.  in  diameter.  These  are  the  ducts  of  the  gastric  glands,  and  at  the  bottom  of  each  may  be 
seen  one  or  more  minute  orifices,  the  openings  of  the  gland  tubes.  The  surface  of  the  mucous 
membrane  is  covered  bv  a  single  layer  of  columnar  epithelium  with  occasional  goblet  cells.  This 
epithelium  commences  very  abruptly  at  the  cardiac  orifice,  where  there  is  a  sudden  transition 
from  the  stratified  epitheUum  of  the  esophagus.  The  epithelial  lining  of  the  gland  ducts  is  of 
the  same  character  and  is  continuous  with  the  general  epithelial  lining  of  the  stomach  (Fig.  1055). 

The  Gastric  Glands. — The  gastric  glands  are  of  three  kinds:  (a)  pyloric,  (b)  cardiac,  and  (c) 
fundus  or  oxyntic  glands.  They  are  tubular  in  character,  and  are  formed  of  a  delicate  basement 
membrane,  consisting  of  flattened  transparent  endothelial  cells  lined  by  epithehum.  The  pyloric 
glands  (Fig,  1054)  are  found  in  the  pyloric  portion  of  the  stomach.  They  consist  of  two  or 
three  short  closed  tubes  opening  into  a  common  duct  or  mouth.  These  tubes  are  wavy,  and 
are  about  one-half  the  length  of  the  duct.  The  duct  is  lined  by'  columnar  cells,  continuous 
with  the  epithelium  lining  the  surface  of  the  mucous  membrane  of  the  stomach,  the  tubes 
by  shorter  and  more  cubical  cell  which  are  finely  granular.  The  cardiac  glands  (Fig.  1053), 
few  in  nvunber,  occur  close  to  the  cardiac  orifice.  They  are  of  two  kinds:  (1)  simple  tubular 
glands  resembling  those  of  the  pyloric  end  of  the  stomach,  but  with  short  ducts;  (2)  com- 
pound racemose  glands  resembling  the  duodenal  glands.  The  fxmdus  glands  (Fig.  1055)  are 
found  in  the  body  and  fundus  of  the  stomach;  they  are  simple  tubes,  two  or  more  of  which 


THE  STOMACH 


1167 


"open  into  a  single  duct.  The  duct,  however,  in  these  glands  is  shorter  than  in  the  pyloric 
variety,  sometimes  not  amounting  to  more  than  one-sixth  of  the  whole  length  of  the  gland; 
it  is  lined  throughout  by  columnar  epithelium.  The  gland  tubes  are  straight  and  parallel  to  each 
other.  At  the  point  where  they  open  into  the  duct,  which  is  termed  the  neck,  the  epithelium 
alters,  and  consists  of  short  columnar  or  polyhedral,  granular  cells,  which  almost  fill  the  tube, 
so  that  the  lumen  becomes  suddenly  constricted  and  is  continued  down  as  a  verj-  fine  channel. 
They  are  known  as  the  chief  or  central  cells  of  the  glands.  Between  these  cells  and  the  basement 
membrane,  larger  oval  cells,  which  stain  deeply  with  eosin,  are  found;  these  cells  are  studded 
throughout  the  tube  at  intervals,  giving  it  a  beaded  or  varicose  appearance.  These  are  known 
as  the  parietal  or  oxyntlc  cells,  and  they  are  connected  with  the  lumen  by  fine  channels  which  run 
into  their  substance.  Between  the  glands  the  mucous  membrane  consists  of  a  connective-tissue 
frame-work,  with  lymphoid  tissue.  In  places,  this  latter  tissue,  especially  in  early  life,  is  collected 
into  little  masses,  which  to  a  certain  extent  resemble  the  solitary  nodules  of  the  intestine,  and  are 
termed  the  lenticular  glands  of  the  stomach.  They  are  not,  however,  so  distinctly  circumscribed 
as  the  solitary  nodules.  Beneath  the  mucous  membrane,  and  between  it  and  the  submucous 
coat,  is  a  thin  stratum  of  involuntary  muscular  fiber  (muscularis  mucosw),  which  in  some  parts 
consists  only  of  a  single  longitudinal  layer;  in  others  of  two  layers,  an  inner  circular  and  an  outer 
longitudinal. 


II 


Fig.  1054. — A  pyloric  gland,  from  a  section  of  the 
dog's  stomach.  (Ebstein.)  m.  Mouth,  n.  Neck.  tr. 
A  deep  portion  of  a  tubule  cut  transversely. 


Fig.  1055.- 


-X  fundus  gland, 
of  gland. 


A.  Transverse  section 


Vessels  and  Nerves. — The  arteries  supplying  the  stomach  are:  the  left  gastric,  the  right 
gastric  and  right  gastroepiploic  branches  of  the  hepatic,  and  the  left  gastroepiploic  and  short 
gastric  branches  of  the  lienal.  They  supply  the  muscular  coat,  ramify  in  the  submucous  coat,  and 
are  finally  distributed  to  the  mucous  membrane.  The  arrangement  of  the  vessels  in  the  mucous 
membrane  is  somewhat  pecuhar.  The  arteries  break  up  at  the  base  of  the  gastric  tubules  into 
a  plexus  of  fine  capillaries  which  run  upward  between  the  tubules,  anastomosing  with  each  other, 
and  ending  in  a  plexus  of  larger  capillaries,  which  surround  the  mouths  of  the  tubes,  and  also 
form  hexagonal  meshes  around  the  ducts.  From  these  the  veins  arise,  and  pursue  a  straight 
coui'se  downward,  between  the  tubules,  to  the  submucous  tissue;  they  end  cither  in  the  lienal 
and  superior  mesenteric  veins,  or  directly  in  the  portal  vein.  The  Isrmphatics  are  numerous: 
they  consist  of  a  superficial  and  a  deep  set,  and  pass  to  the  lymph  glands  found  along  the  two 
curvatures  of  the  organ  (page  706).     The  nerves  are  the  terminal  branches  of  the  right  and  left 


II 


1168 


SPLANCHNOLOGY 


vagi,  the  former  being  distributed  upon  the  back,  and  the  latter  upon  the  front  part  of  the  organ 
A  great  number  of  branches  from  the  celiac  plexus  of  the  sympathetic  are  also  distributed  to 
it.  Nerve  plexuses  are  found  in  the  submucous  coat  and  between  the  layers  of  the  muscular  coat 
as  in  the  intestine.  From  these  plexuses  fibrils  are  distributed  to  the  muscular  tissue  and  the 
mucous  membrane. 


The  Small  Intestine  (Intestinum  Tenue). 


m 


The  small  intestine  is  a  convoluted  tube,  extending  from  the  pylorus  to  the  colic 
valve,  where  it  ends  in  the  large  intestine.  It  is  about  7  metres  long,^  and  gradually 
diminishes  in  size  from  its  commencement  to  its  termination.  It  is  coritained  in 
the  central  and  lower  part  of  the  abdominal  cavity,  and  is  surrounded  above  and 
at  the  sides  by  the  large  intestine;  a  portion  of  it  extends  below  the  superior 
aperture  of  the  pelvis  and  lies  in  front  of  the  rectum.  It  is  in  relation,  in  front,  with 
the  greater  omentum  and  abdominal  parietes,  and  is  connected  to  the  vertebral 
column  by  a  fold  of  peritoneum,  the  mesentery.  The  small  intestine  is  divisible 
into  three  portions:  the  duodenum,  the  jejunum,  and  the  ileum. 


Fig.   105C. — The  duodenum  and  pancreas. 


The  Duodenum  (Fig.  1056)  has  received  its  name  from  being  about  equal  in 
length  to  the  breadth  of  twelve  fingers  (25  cm.).  It  is  the  shortest,  the  widest, 
and  the  most  fixed  part  of  the  small  intestine,  and  has  no  mesentery,  being  only 
partially  covered  by  peritoneum.  Its  course  presents  a  remarkable  curve,  some- 
what of  the  shape  of  an  imperfect  circle,  so  that  its  termination  is  not  far  removed 
from  its  starting-point. 

In  the  adult  the  course  of  the  duodenum  is  as  follows :  commencing  at  the  pylorus 
it  passes  backward,  upward,  and  to  the  right,  beneath  the  quadrate  lobe  of  the 
liver  to  the  neck  of  the  gall-bladder,  varying  slightly  in  direction  according  to  the 
degree  of  distension  of  the  stomach:  it  then  takes  a  sharp  curve  and  descends 
along  the  right  margin  of  the  head  of  the  pancreas,  for  a  variable  distance,  generally 
to  the  level  of  the  upper  border  of  the  body  of  the  fourth  lumbar  vertebra.    It 


1  Treves  states  that,  in  one  hundred  cases,  the  average  length  of  the  small  intestine  in  the  adult  male  was  22  feet 
6  inches,  and  in  the  adult  female  23  feet  4  inches:  but  that  it  varies  very  much,  the  extremes  in  the  male  being  31  feet 
10  inches,  and  15  feet  6  inches.  He  states  that  in  the  adult  the  length  of  the  bowel  is  independent  of  age,  height,  and 
weight. 


THE  SMALL  INTESTINE 


1169 


^  takes  a  second  bend,  and  passes  from  right  to  left  across  the  vertebral  column, 
having  a  slight  inclination  upward;  and  on  the  left  side  of  the  vertebral  column 
it  ascends  for  about' 2.5  cm.,  and  then  ends  opposite  the  second  lumbar  vertebra 
in  the  jejunum.  As  it  unites  with  the  jejunum  it  turns  abruptly  forward,  forming 
the  duodendojejunal  flexure.  From  the  above  description  it  will  be  seen  that  the 
duodenum  may  be  divided  into  four  portions:  superior,  descending,  horizontal, 
and  ascending. 

Relations. — The  superior  portion  {pars  superior;  first  portion)  is  about  5  cm.  long. 
Beginning  at  the  pylorus,  it  ends  at  the  neck  of  the  gall-bladder.  It  is  the  most 
movable  of  the  four  portions.  It  is  almost  completely  covered  by  peritoneum,  but  a 
small  part  of  its  posterior  surface  near  the  neck  of  the  gall-bladder  and  the  inferior 


Fig.  1057, 


Probe  in  'pancreatic  duct 

Probe  in  common  bile-duct 
— Interior  of  the  descending  portion  of  the  duodenum,  showing  bile  papilla. 


vena  cava  is  uncovered;  the  upper  border  of  its  first  half  has  the  hepatoduodenal 
ligament  attached  to  it,  while  to  the  lower  border  of  the  same  segment  the  greater 
omentum  is  connected.  It  is  in  such  close  relation  with  the  gall-bladder  that  it 
is  usually  found  to  be  stained  by  bile  after  death,  especially  on  its  anterior  surface. 
It  is  in  relation  above  and  in  front  with  the  quadrate  lobe  of  the  liver  and  the  gall- 
bladder; behind  with  the  gastroduodenal  artery,  the  common  bile  duct,  and  the 
portal  vein;  and  below  and  behind  with  the  head  and  neck  of  the  pancreas. 

The  descending  portion  {pars  descendens;  second  portion)  is  from  7  to  10  cm.  long,  and 
extends  from  the  neck  of  the  gall-bladder,  on  a  level  with  the  first  lumbar  vertebra, 
along  the  right  side  of  the  vertebral  column  as  low  as  the  upper  border  of  the  body 
of  the  fourth  lumbar  vertebra.  It  is  crossed  in  its  middle  third  by  the  transverse 
colon,  the  posterior  surface  of  which  is  uncovered  by  peritoneum  and  is  connected 
to  the  duodenum  by  a  small  quantity  of  connective  tissue.  The  supra-  and  infra- 
colic  portions  are  covered  in  front  by  peritoneum,  the  infracolic  part  by  the  right 
leaf  of  the  mesentery.  Posteriorly  the  descending  portion  of  the  duodenum  is  not 
covered  by  peritoneum.  The  descending  portion  is  in  relation,  in  front,  from  above 
downward,  with  the  duodenal  impression  on  the  right  lobe  of  the  liver,  the  trans- 
verse colon,  and  the  small  intestine;  behind,  it  has  a  variable  relation  to  the  front 
[  of  the  right  kidney  in  the  neighborhood  of  the  hilum,  and  is  connected  to  it  by 
Ift loose  areolar  tissue;  the  renal  vessels,  the  inferior  vena  cava,  and  the  Psoas  below, 

L 


Vr 


1 170  SPLANCHNOLOG  Y 

are  also  behind  it.  At  its  medial  side  is  the  head  of  the  pancreas,  and  the  commf 
bile  duct;  to  its  lateral  side  is  the  right  colic  flexure.  The  common  bile  duct  and 
the  pancreatic  duct  together  perforate  the  medial  side  of  this  poKion  of  the  intestine 
obliquely  (Figs.  1057  and  1100),  some  7  to  10  cm.  below  the  pylorus;  the  accessory 
pancreatic  duct  sometimes  pierces  it  about  2  cm.  above  and  slightly  fti  front  of  these. 

The  horizontal  portion  {pars  horizontalis;  third  or  preaortic  or  transverse  portion)  is 
from  5  to  7.5  cm.  long.  It  begins  at  the  right  side  of  the  upper  border  of  the  fourth 
lumbar  vertebra  and  passes  from  right  to  left,  with  a  slight  inclination  upward, 
in  front  of  the  great  vessels  and  crura  of  the  diaphragm,  and  ends  in  the  ascending 
portion  in  front  of  the  abdominal  aorta.  It  is  crossed  by  the  superior  mesenteric 
vessels  and  the  mesentery.  Its  front  surface  is  covered  by  peritoneum,  except 
near  the  middle  line,  where  it  is  crossed  by  the  superior  mesenteric  vessels.  Its 
posterior  surface  is  uncovered  by  peritoneum,  except  toward  its  left  extremity, 
where  the  posterior  layer  of  the  mesentery  may  sometimes  be  found  covering  it 
to  a  variable  extent.  This  surface  rests  upon  the  right  crus  of  the  diaphragm, 
the  inferior  vena  cava,  and  the  aorta.  The  upper  surface  is  in  relation  with  the 
head  of  the  pancreas. 

The  ascending  portion  (pars  ascendens;  fourth  portion)  of  the  duodenum  is  about 
2.5  cm  long.  It  ascends  on  the  left  side  of  the  aorta,  as  far  as  the  level  of  the  upper 
border  of  the  second  lumbar  vertebra,  where  it  turns  abruptly  forward  to  become 
the  jejunum,  forming  the  duodenojejunal  flexure.  It  lies  in  front  of  the  left  Psoas 
major  and  left  renal  vessels,  and  is  covered  in  front,  and  partly  at  the  sides,  by 
peritoneum  continuous  with  the  left  portion  of  the  mesentery. 

The  superior  part  of  the  duodenum,  as  stated  above,  is  somewhat  movable, 
but  the  rest  is  practically  fixed,  and  is  bound  down  to  neighboring  viscera  and  the 
posterior  abdominal  wall  by  the  peritoneum.  In  addition  to  this,  the  ascending 
part  of  the  duodenum  and  the  duodenojejunal  flexure  are  fixed  by  a  structure 
to  which  the  name  of  Musculus  siispensoriiis  duodeni  has  been  given.  This  structure 
commences  in  the  connective  tissue  around  the  celiac  artery  and  left  crus  of  the 
diaphragm,  and  passes  downward  to  be  inserted  into  the  superior  border  of  the 
duodenojejunal  curve  and  a  part  of  the  ascending  duodenum,  and  from  this  it  is 
continued  into  the  mesentery.  It  possesses,  according  to  Treitz,  plain  muscular 
fibers  mixed  with  the  fibrous  tissue  of  which  it  is  principally  made  up.  It  is  of 
little  importance  as  a  muscle,  but  acts  as  a  suspensory  ligament. 

Vessels  and  Nerves. — The  arteries  supplying  the  duodenum  are  the  right  gastric  and  superior 
pancreaticoduodenal  branches  of  the  hepatic,  and  the  inferior  pancreaticoduodenal  branch  of 
the  superior  mesenteric.  The  veins  end  in  the  lienal  and  superior  mesenteric.  The  nerves  are 
derived  from  the  ccehac  plexus. 

Jejunum  and  Ileum. — ^The  remainder  of  the  small  intestine  from  the  end  of  the 
duodenum  is  named  jejunum  and  ileum;  the  former  term  being  given  to  the  upper 
two-fifths  and  the  latter  to  the  lower  three-fifths.  There  is  no  morphological  line 
of  distinction  between  the  two,  and  the  division  is  arbitrary;  but  at  the  same  time 
the  character  of  the  intestine  gradually  undergoes  a  change  from  the  commence- 
ment of  the  jejunum  to  the  end  of  the  ileum,  so  that  a  portion  of  the  bowel  taken 
from  these  two  situations  would  present  characteristic  and  marked  differences. 
These  are  briefly  as  follows: 

The  Jejunum  {intestinum  jejunum)  is  wider,  its  diameter  being  about  4  cm., 
and  is  thicker,  more  vascular,  and  of  a  deeper  color  than  the  ileum,  so  that  a  given 
length  weighs  more.  The  circular  folds  {valvulcB  conniventes)  of  its  mucous  mem- 
brane are  large  and  thickly  set,  and  its  villi  are  larger  than  in  the  ileum.  The  aggre- 
gated lymph  nodules  are  almost  absent  in  the  upper  part  of  the  jejunum,  and  in 
the  lower  part  are  less  frequently  found  than  in  the  ileum,  and  are  smaller  and  tend 
to  assume  a  circular  form.  By  grasping  the  jejunum  between  the  finger  and  thumb 
the  circular  folds  can  be  felt  through  the  walls  of  the  gut;  these  being  absent  in 


THE  SMALL  INTESTINE 


1171 


TEe  lower  part  of  the  ileum,  it  is  possible  in  this  way  to  distinguish  the  upper 
from  the  lower  part  of  the  small  intestine. 

The  neum  {intestinum  ileum)  is  narrow,  its  diameter  being  3.75  cm.,  and  its 
coats  thinner  and  less  vascular  than  those  of  the  jejunum.  It  possesses  but  few 
circular  folds,  and  they  are  small  and  disappear  entirely  toward  its  lower  end, 
but  aggregated  lymph  nodules  (Peyer's  patches)  are  larger  and  more  numerous. 
The  jejunum  for  the  most  part  occupies  the  umbilical  and  left  iliac  regions,  while 


Villi 


Intestinal  glands 


Mvscvlans  mucoscB 


Duodenal  glands  in 
svbmvcosa 


Fig.  1058. — Section  of  duodenum  of  cat.     (After  Schafer.) 


Circular  muscular  layer 


Longitudinal  muscular 
layer 

Serous  coat 
X  60. 


the  ileum  occupies  chiefly  the  umbilical,  hypogastric,  right  iliac,  and  pelvic  regions. 
The  terminal  part  of  the  ileum  usually  lies  in  the  pelvis,  from  which  it  ascends  over 
the  right  Psoas  and  right  iliac  vessels;  it  ends  in  the  right  iliac  fossa  by  opening 
into  the  medial  side  of  the  commencement  of  the  large  intestine.  The  jejunum 
and  ileum  are  attached  to  the  posterior  abdominal  wall  by  an  extensive  fold  of 
peritoneum,  the  mesentery,  which  allows  the  freest  motion,  so  that  each  coil  can 
accommodate  itself  to  changes  in  form  and  position.    The  mesentery  is  fan-shaped; 


1172 


SPLANCHNOLOGY 


its  posterior  border  or  root,  about  15  cm.  long,  is  attached  to  the  posterior  abdominai 
wall  from  the  left  side  of  the  body  of  the  second  lumbar  vertebra  to  the  right  sacro- 
iliac articulation,  crossing  successively  the  horizontal  part  of  the  duodenum,  the 
aorta,  the  inferior  vena  cava,  the  ureter,  and  right  Psoas  muscle  (Fig.  1040).  Its 
breadth  between  its  vertebral  and  intestinal  borders  averages  about  20  cm.,  and  is 
greater  in  the  middle  than  at  its  upper  and  lower  ends.  According  to  Lockwood  it 
tends  to  increase  in  breadth  as  age  advances.  Between  the  two  layers  of  which  it  is 
composed  are  contained  bloodvessels,  nerves,  lacteals,  and  lymph  glands,  together 
with  a  variable  amount  of  fat. 


Central  lacteal 
Smooth  muscle  fibers 

Reticular  tissue 
Columnar  epithelium, 


Fig.  1059. — Vertical  section  of  a  villus  from  the 
dog's  small  intestine.      X  80. 


FiQ.  1060. — Transverse  section  of  a  villus,  from  the  human  intes- 
tine, (v.  Ebner.)  X  350.  a.  Basement  membrane,  here  some- 
what shrunken  away  from  the  epithelium.  6.  Lacteal,  c. 
Columnar  epithelium,  d.  Its  striated  border,  e.  Goblet  cells. 
/.  Leucocytes  in  epithelium.  /'.  Leucocytes  below  epithelium. 
g.  Bloodvessels,    h.  Muscle  cells  cut  across. 


Meckel's  Diverticulum  {diverticulum  ilei). — This  consists  of  a  pouch  which  projects  from  the 
lower  part  of  the  ileum  in  about  2  per  cent,  of  subjects.  Its  average  position  is  about  1  meter 
above  the  colic  valve,  and  its  average  length  about  5  cm.  Its  caHber  is  generally  similar  to  that 
of  the  ileum,  and  its  blind  extremity  may  be  free  or  may  be  coimected  with  the  abdominal  wall 
or  with  some  other  portion  of  the  intestine  by  a  fibrous  band.  It  represents  the  remains  of 
the  proximal  part  of  the  viteUine  duct,  the  duct  of  communication  between  the  yolk-sac  and  the 
primitive  digestive  tube  in  early  fetal  life. 

Structure.— The  wall  of  the  small  intestine  (Fig.  1058)  is  composed  of  four  coats :  serous, 
muscular,  areolar,  and  mucous. 

The  serous  coat  {tunica  serosa)  is  derived  from  the  peritoneum.  The  superior  portion  of  the 
duodenum  is  almost  completely  surrounded  by  this  membrane  near  its  pyloric  end,  but  is  only 
covered  in  front  at  the  other  extremity;  the  descending  portion  is  covered  by  it  in  front,  except 
where  it  is  carried  off  by  the  transverse  colon;  and  the  inferior  portion  lies  behind  the  peritoneum 
which  passes  over  it  without  being  closely  incorporated  with  the  other  coats  of  this  part  of  the 
intestine,  and  is  separated  from  it  in  and  near  the  middle  line  by  the  superior  mesenteric  vessels. 
The  rest  of  the  small  intestine  is  surrounded  by  the  peritoneum,  excepting  along  its  attached 
or  mesenteric  border;  here  a  space  is  left  for  the  vessels  and  nerves  to  pass  to  the  gut. 

The  muscular  coat  {tunica  muscularis)  consists  of  two  layers  of  unstriped  fibers:  an  external, 
longitudinal,  and  an  internal,  circular  layer.  The  longitudinal  fibers  are  thinly  scattered  over  the 
surface  of  the  intestine,  and  are  more  distinct  along  its  free  border.  The  circular  fibers  form  a 
thick,  uniform  layer,  and  are  composed  of  plain  muscle  cells  of  considerable  length.  The  mus- 
cular coat  is  thicker  at  the  upper  than  at  the  lower  part  of  the  small  intestine. 

The  areolar  or  submucous  coat  {tela  submucosa)  connects  together  the  mucous  and  muscular 
layers.  It  consists  of  loose,  filamentous  areolar  tissue  containing  bloodvessels,  lymphatics,  and 
nerves.    It  is  the  strongest  layer  of  the  intestine. 


THE  SMALL  INTESTINE 


1173 


The  mucous  membrane  {tunica  mucosa)  is  thick  and  highly  vascular  at  the  upper  part  of 
the  small  intestine,  but  somewhat  paler  and  thinner  below.    It  consists  of  the  following  structures: 


Capillaries 
Lymphatic  vessel 


Capillaries 


Lymphatic  vessel 


Small  artery        Lymphatic  plexus 
FiQ.   1061  — Villi  of  small  intestine,  showing  bloodvessels  and  lymphatic  vessels.      (Cadiat.) 


II 


tiext  the  areolar  or  submucous  coat  is  a  double  layer  of  unstriped  muscular  fibers,  outer  longi- 
tudinal and  inner  circular,  the  muscularis  mucosae;  internal  to  this  is  a  quantity  of  retiform 
tissue,  enclosing  in  its  meshes  lymph  corpuscles,  and  in  this  the 
bloodvessels  and  nerves  ramify;  lastly,  a  basement  membrane, 
supporting  a  single  layer  of  epithelial  cells,  which  throughout  the 
intestine  are  columnar  in  character.  The  cells  are  granular  in 
appearance,  and  each  possesses  a  clear  oval  nucleus.  At  their 
superficial  or  unattached  ends  they  present  a  distinct  layer  of 
highly  refracting  material,  marked  by  vertical  -striae,  the  striated 
border. 

The  mucous  membrane  presents  for  examination  the  following 
structures,  contained  within  it  or  belonging  to  it: 

Circular  folds.  Duodenal  glands. 

Villi.  SoMtary  lymphatic  nodules. 

Intestinal  glands.  Aggregated  lymphatic  nodules. 


I 


The  circular  folds  (plicre  circular es  {Kerkringi];  valvuloe  conni' 
ventes;  valves  of  Kerkring)  are  large  valvular  flaps  projecting  into 
the  lumen  of  the  bowel.  They  are  composed  of  reduphcations  of  the 
mucous  membrane,  the  two  layers  of  the  fold  being  bound  together 
by  submucous  tissue;  unlike  the  folds  in  the  stomach,  they  are  per- 
manent, and  are  not  obliterated  when  the  intestine  is  distended. 
The  majority  extend  transversely  around  the  cylinder  of  the  intes- 
tine for  about  one-half  or  two-thirds  of  its  circumference,  but  some 
form  complete  circles,  and  others  have  a  spiral  direction;  the  latter 
usually  extend  a  little  more  than  once  around  the  bowel,  but  occa- 
sionally two  or  three  times.  The  larger  folds  are  about  8  mm.  in 
depth  at  their  broadest  part;  but  the  greater  number  are  of  smaller 
size.  The  larger  and  smaller  folds  alternate  with  each  other.  They 
are  not  found  at  the  commencement  of  the  duodenum,  bui  begin 
to  appear  about  2.5  or  5  cm.  beyond  the  pylorus.    In  the  lower 

part  of  the  descending  portion,  below  the  point  where  the  bile  and  pancreatic  ducts  enter  the 
intestine,  they  are  very  large  and  closely  approximated.  In  the  horizontal  and  ascending 
portions  of  the  duodenum  and  uooer  half  of  the  jejunum  they  are  large  and  numerous,  but 


Fig.  1062. — An  intestinal  gland 
from  the  human  intestine.  (Flem- 
ming.) 


1174 


SPLANCHNOLOGY 


from  this  point,  down  to  the  middle  of  the  ileum,  they  diminish  considerably  in  size.  In  the 
lower  part  of  the  ileum  they  almost  entirely  disappear;  hence  the  comparative  thinness  of  this 
portion  of  the  intestine,  as  compared  with  the  duodenum  and  jejunum.  The  circular  folds 
retard  the  passage  of  the  food  along  the  intestines,  and  afford  an  increased  surface  for  absorption. 


Fig.  1063. — Vertical  section  of  a  human  aggregated  lymphatic  nodule,  injected  through  its  lymphatic  canals,  a. 
Villi  with  their  chyle  passages.  6.  Intestinal  glands,  c.  Muscularis  mucosa;,  d.  Cupola  or  apex  of  solitary  nodule. 
e.  Mesial  zone  of  nodule.  /.  Base  of  nodule,  o-  Points  of  exit  of  the  lacteals  from  the  villi,  and  entrance  into  the  true 
mucous  membrane,  h.  Retiform  arrangement  of  the  lymphatics  in  the  mesial  zone.  i.  Course  of  the  latter  at  the 
base  of  the  nodule,  k.  Confluence  of  the  lymphatics  opening  into  the  vessels  of  the  submucous  tissue.  I.  Follicular 
tissue  of  the  latter. 


Capillary  network 


The  intestinal  villi  {villi  intestinales)  are  highly  vascular  processes,  projecting  from  the  mucous 
membrane  of  the  small  intestine  throughout  its  whole  extent,  and  giving  to  its  surface  a  velvety 

appearance.  They  are  largest  and  most  numer- 
ous in  the  duodenum  and  jejunum,  and  become 
fewer  and  smaller  in  the  ileum. 

Structure  of  the  villi  (Figs.  1059,  1060).— The 
essential  parts  of  a  villus  are :  the  lacteal  vessel, 
the  bloodvessels,  the  epithelium,  the  basement 
•membrane,  and  the  muscular  tissue  of  the  mu- 
cosa, all  being  supported  and  held  together  by 
retiform  lymphoid  tissue. 

The  lacteals  are  in  some  cases  double,  and  in 
some  animals  multiple,  but  usually  there  is  a 
single  vessel.  Situated  in  the  axis  of  the  viUus, 
each  commences  by  dilated  cecal  extremities 
near  to,  but  not  quite  at,  the  summit  of  the 
villus.  The  walls  are  composed  of  a  single  layer 
of  endothelial  cells. 

The  muscular  fibers  are  derived  from  the  mus- 
cularis mucosa;,  and  are  arranged  in  longitudinal 
bundles  around  the  lacteal  vessel,  extending  from 
the  base  to  the  summit  of  the  villus,  and  giving 
off,  laterally,  individual  muscle  cells,  which  are 
enclosed  by  the  reticulum,  and  by  it  are  attached 
to  the  basement-membrane  and  to  the  lacteal. 

The  bloodvessels  (Fig.  1C61)  form  a  plexus 
under  the  basement  membrane,  and  are  enclosed 
in  the  reticular  tissue. 

These  structures  are  surroimded  by  the  base- 

,  inent  viembrane,  which  is  made  up  of  a  stratiun 

of  endothelial  cells,  and  upon  this  is  placed  a  layer  of  columnar  epithelium,  the  characteristics  of 

which  have  been  described.    The  retiform  tissue  forms  a  net-work    (Fig.  lOoO)  in  the  meshes 

of  which  a  number  of  leucocytes  are  found. 

The  intestinal  glands  {glandulee  intestinales  [Lieberkuhni] ;  crypts  of  Lieberkuhn)  (Fig.  1062)  are 


Fig.  1064. — Transverse  section  through  the  equatorial 
plane  of  three  aggregated  lymphatic  nodules  from  the 
rabbit. 


THE  SMALL  INTESTINE 


1175 


found  in  considerable  numbers  over  every  part  of  the  mucous  membrane  of  the  small  intestine. 
They  consist  of  minute  tubular  depressions  of  the  mucous  membrane,  arranged  perpendicularly  to 
the  surface,  upon  which  they  open  by  small  circular  apertures.    They  may  be  seen  with  the  aid 


Fig.  1066 


Six  feet. 


Fig.  1068 


Twelve  feet. 


Fig.  1070 


Seventeen  feet. 


Twenty  feet. 


FiGH.  1065,  1066,  1067,  1068,  1069,  1070. — Diagrams  showing  the  arrangement  and  variations  of  the  loops  of  the 
mesenteric  vessels  for  various  segments  of  the  small  intestine  of  average  length.  Nearest  the  duodenum  the  mesenteric 
loops  are  primary,  the  vasa  recta  are  long  and  regular  in  distribution,  and  the  translucent  spaces  (lunettes)  are  extensive. 
Toward  the  ileocolic  junction,  secondary  and  tertiary  loops  are  observed,  the  vessels  are  smaller  and  become  obscured 
by  numerous  fat-tabs,     (.\fter  Monks.) 


1176 


SPLANCHNOLOGY 


of  a  lens,  their  orifices  appearing  as  minute  dots  scattered  between  the  vilh.     Their  walls  are 
thin,  consisting  of  a  basement  membrane  lined  by  columnar  epithelium,  and  covered  on  theia|H 
exterior  by  capillary  vessels.  ^| 

The  duodenal  glands  (glandulcc  duodenales  [Brunneri];  Brunner's  glands)  are  limited  to  the 
duodenum  (Fig.  1058),  and  are  found  in  the  submucous  areolar  tissue.  They  are  largest  and  most 
numerous  near  the  pylorus,  forming  an  almost  complete  layer  in  the  superior  portion  and 
upper  half  of  the  descending  portions  of  the  duodenum.  They  then  begin  to  diminish  in 
number,  and  practically  disappear  at  the  junction  of  the  duodenum  and  jejunum.  They  are 
small  compound  acinotubular  glands  consisting  of  a  number  of  alveoli  lined  by  short  columnar 
epithelium  and  opening  by  a  single  duct  on  the  inner  surface  of  the  intestine. 

The  solitary  lymphatic  nodules  (noduli  lymphatici  solitarii;  solitary  glands)  are  found  scattered 
throughout  the  mucous  membrane  of  the  small  intestine,  but  are  most  numerous  in  the  lower 
part  of  the  ileum.  Their  free  surfaces  are  covered  with  rudimentary  villi,  except  at  the  sum- 
mits, and  each  gland  is  surrounded  by  the  openings  of  the  intestinal  glands.  Each  consists  of  a 
dense  interlacing  retiform  tissue  closely  packed  with  lymph-corpuscles,  and  permeated  with  an 
abundant  capillary  network.  The  interspaces  of  the  retiform  tissue  are  continuous  with  larger 
lymph  spaces  which  surround  the  gland,  through  which  they  communicate  with  the  lacteal 
system.  They  are  situated  partly  in  the  submucous  tissue,  partly  in  the  mucous  membrane, 
where  they  form  slight  projections  of  its  epithelial  layer  (see  Fig.  1082). 

The  aggregated  lymphatic  nodules  {noduli  lymphatici  aggregati;  Peyer's  patches;  Peyer's  glands; 
agminated  follicles;  tonsillae  inteslinales)  (Fig.  1063)  form  circular  or  oval  patches,  from  twenty 
to  thirty  in  number,  and  varying  in  length  from  2  to  10  cm.  They  are  largest  and  most  numerous 
in  the  ileum.  In  the  lower  part  of  the  jejunum  they  are  small,  circular,  and  few  in  number. 
They  are  occasionally  seen  in  the  duodenum.  They  are  placed  lengthwise  in  the  intestine,  and 
are  situated  in  the  portion  of  the  tube  most  distant  from  the  attachment  of  the  mesentery.  Each 
patch  is  formed  of  a  group  of  sohtary  lymphatic  nodules  covered  with  mucous  membrane,  but 
the  patches  do  not,  as  a  rule,  possess  villi  on  their  free  surfaces.  They  are  best  marked  in  the 
young  subject,  become  indistinct  in  middle  age,  and  sometimes  disappear  altogether  in 
advanced  life.  They  are  freely  supplied  with  bloodvessels  (Fig.  1064),  which  form  an  abundant 
plexus  around  each  foUicle  and  give  off  fine  branches  permeating  the  lymphoid  tissue  in  the 
interior  of  the  follicle.    The  lymphatic  plexuses  are  especially  abundant  around  these  patches. 

Vessels  and  Nerves. — The  jejunum  and  ileum  are  supplied  by  the  superior  mesenteric  artery, 
the  intestinal  branches  of  which,  having  reached  the  attached  border  of  the  bowel,  run  between 

the  serous  and  muscular  coats,  with  frequent  in- 
osculations to  the  free  border,  where  they  also 
anastomose  with  other  branches  running  around 
the  opposite  surface  of  the  gut.  From  these 
vessels  numerous  branches  are  given  off,  which 
pierce  the  muscular  coat,  supplying  it  and  forming 
an  intricate  plexus  in  the  submucous  tissue. 
From  this  plexus  minute  vessels  pass  to  the  glands 
and  villi  of  the  mucous  membrane.  The  veins 
have  a  similar  course   and   arrangement  to  the 


Fig.   1071. — The  myenteric  plexus  from  the  rabbit. 
X  50. 


Fig.   1072. — The  plexus  of  the  submucosa  from  the 
rabbit       XoO. 


arteries.  The  lymphatics  of  the  small  intestine  (lacteals)  are  arranged  in  two  sets,  those  of  the 
mucous  membrane  and  those  of  the  muscular  coat.  The  lymphatics  of  the  villi  commence  in 
these  structures  in  the  manner  described  above.  They  form  an  intricate  plexus  in  the  mucous 
and  submucous  tissue,  being  joined  by  the  lymphatics  from  the  lymph  spaces  at  the  bases  of 
the  solitary  nodules,  and  from  this  pass  to  larger  vessels  at  the  mesenteric  border  of  the  gut.  The 
lymphatics  of  the  muscular  coat  are  situated  to  a  great  extent  between  the  two  layers  of  muscular 
fibers,  where  they  form  a  close  plexus;  throughout  their  course  they  communicate  freely  with 


I 


THE  LARGE  INTESTINE  1177 

the  lymphatics  from  the  mucous  membrane,  and  empty  themselves  in  the  same  manner  as 
these  into  the  origins  of  the  lacteal  vessels  at  the  attached  border  of  the  gut. 

The  nerves  of  the  small  intestines  are  derived  from  the  plexuses  of  sympathetic  nerves  around 
the  superior  mesenteric  artery.  From  this  source  they  run  to  the  myenteric  plexus  {Auerbach's 
plexus)  (Fig.  1071)  of  nerves  and  ganglia  situated  between  the  circular  and  longitudinal  mus- 
cular fibers  from  which  the  nervous  branches  are  distributed  to  the  muscular  coats  of  the 
intestine.  From  this  a  secondary  plexus,  the  plexus  of  the  submucosa  (Meissner's  -plexus) 
(Fig.  1072)  is  derived,  and  is  formed  by  branches  which  have  perforated  the  circular  muscular 
fibers.  This  plexus  lies  in  the  submucous  coat  of  the  intestine;  it  also  contains  ganglia  from 
which  nerve  fibers  pass  to  the  muscularis  mucosa;  and  to  the  mucous  membrane.  The  nerve 
bundles  of  the  submucous  plexus  are  finer  than  those  of  the  myenteric  plexus. 

The  Large  Intestine  (Intestinum  Crassmn). 

The  large  intestine  extends  from  the  end  of  the  ileum  to  the  anus.  It  is  about 
1.5  meters  long,  being  one-fifth  of  the  whole  extent  of  the  intestinal  canal.  Its 
caliber  is  largest  at  its  commencement  at  the  cecum,  and  gradually  diminishes 
as  far  as  the  rectum,  where  there  is  a  dilatation  of  considerable  size  just  above 
the  anal  canal.  It  differs  from  the  small  intestine  in  its  greater  caliber,  its  more 
fixed  position,  its  sacculated  form,  and  in  possessing  certain  appendages  to  its 
external  coat,  the  appendices  epiploicse.  Further,  its  longitudinal  muscular  fibers 
do  not  form  a  continuous  layer  around  the  gut,  but  are  arranged  in  three  longitudinal 
bands  or  taeniae.  The  large  intestine,  in  its  course,  describes  an  arch  which  sur- 
rounds the  convolutions  of  the  small  intestine.  It  commences  in  the  right  iliac 
region,  in  a  dilated  part,  the  cecum.  It  ascends  through  the  right  lumbar  and  hypo- 
chondriac regions  to  the  under  surface  of  the  liver;  it  here  takes  a  bend,  the  right 
colic  flexure,  to  the  left  and  passes  transversely  across  the  abdomen  on  the  confines 
of  the  epigastric  and  umbilical  regions,  to  the  left  hypochondriac  region;  it  then 
bends  again,  the  left  colic  flexure,  and  descends  through  the  left  lumbar  and  iliac 
regions  to  the  pelvis,  where  it  forms  a  bend  called  the  sigmoid  flexure;  from  this  it 
is  continued  along  the  posterior  wall  of  the  pelvis  to  the  anus.  The  large  intestine 
is  divided  into  the  cecum,  colon,  rectum,  and  anal  canal. 

The  Cecum  {intestinum  ccecum)  (Fig.  1073),  the  commencement  of  the  large 
intestine,  is  the  large  blind  pouch  situated  below  the  colic  valve.  Its  blind  end 
is  directed  downward,  and  its  open  end  upward,  communicating  directly  with  the 
colon,  of  which  this  blind  pouch  appears  to  be  the  beginning  or  head,  and  hence  the 
old  name  of  caput  caecum  coli  was  applied  to  it.  Its  size  is  variously  estimated  by 
different  authors,  but  on  an  average  it  may  be  said  to  be  6.25  cm.  in  length  and  7.5  in 
breadth.  It  is  situated  in  the  right  iliac  fossa,  above  the  lateral  half  of  the  inguinal 
ligament :  it  rests  on  the  Iliacus  and  Psoas  major,  and  usually  lies  in  contact  with  the 
anterior  abdominal  wall,  but  the  greater  omentum  and,  if  the  cecum  be  empty, 
some  coils  of  small  intestine  may  lie  in  front  of  it.  As  a  rule,  it  is  entirely  enveloped 
by  peritoneum,  but  in  a  certain  number  of  cases  (5  per  cent..  Berry)  the  peritoneal 
covering  is  not  complete,  so  that  the  upper  part  of  the  posterior  surface  is  uncovered 
and  connected  to  the  iliac  fascia  b}'  connective  tissue.  The  cecum  lies  quite  free 
in  the  abdominal  cavity  and  enjoys  a  considerable  amount  of  movement,  so  that 
it  may  become  herniated  down  the  right  inguinal  canal,  and  has  occasionally 
been  found  in  an  inguinal  hernia  on  the  left  side.  The  cecum  varies  in  shape,  but, 
according  to  Treves,  in  man  it  may  be  classified  under  one  of  four  types.  In  early 
fetal  life  it  is  short,  conical,  and  broad  at  the  base,  with  its  apex  turned  upward 
and  medialward  toward  the  ileocolic  junction.  It  then  resembles  the  cecum  of  some 
monkeys,  e.  g.,  mangabey  monkey.  As  the  fetus  grows  the  cecum  increases  in 
length  more  than  in  breadth,  so  that  it  forms  a  longer  tube  than  in  the  primitive 
form  and  without  the  broad  base,  but  with  the  same  inclination  of  the  apex  toward 
the  ileocolic  junction.  This  form  is  seen  in  other  monkeys,  e.  g.,  the  spider  monkey. 
As  development  goes  on,  the  lower  part  of  the  tube  ceases  to  grow  and  the  upper 


1178 


SPLANCHNOLOGY 


part  becomes  greatly  increased,  so  that  at  birth  there  is  a  narrow  tube,  the  vermi- 
form process,  hanging  from  a  conical  projection,  the  cecum.  This  is  the  infantile 
form,  and  as  it  persists  throughout  life  in  about  2  per  cent,  of  cases,  it  is  regarded 
by  Treves  as  the  first  of  his  four  types  of  human  ceca.  The  cecum  is  conical  and 
the  appendix  rises  from  its  apex.  The  three  longitudinal  bands  start  from  the 
appendix  and  are  equidistant  from  each  other.  In  the  second  type,  the  conical 
cecum  has  become  quadrate  by  the  growing  out  of  a  saccule  on  either  side  of  the 
anterior  longitudinal  band.  These  saccules  are  of  equal  size,  and  the  appendix 
arises  from  between  them,  instead  of  from  the  apex  of  a  cone.  This  type  is  found 
in  about  3  per  cent,  of  cases.  The  third  type  is  the  normal  tj-pe  of  man.  Here 
the  two  saccules,  which  in  the  second  type  were  uniform,  have  grown  at  unequal 
rates:  the  right  with  greater  rapidity  than  the  left.  In  consequence  of  this  9,niH 
apparently  new  apex  has  been  formed  by  the  growing  downward  of  the  right  sac-  ™ 
cule,  and  the  original  apex,  with  the  appendix  attached,  is  pushed  over  to  the  left 


Terminal  part  of  ileocolic  artery 

Cecal  branches 

Ileal  branches 


Appendicular 
artery 


^-^o^rn  process 

Fig.   1073. — The  cecum  and  vermiform  process,  with  their  arteries. 

toward  the  ileocolic  junction.  The  three  longitudinal  bands  still  start  from  the 
base  of  the  vermiform  process,  but  they  are  now  no  longer  equidistant  from  each 
other,  because  the  right  saccule  has  grown  between  the  anterior  and  postero- 
lateral bands,  pushing  them  over  to  the  left.  This  type  occurs  in  about  90  per 
cent,  of  cases.  The  fourth  type  is  merely  an  exaggerated  condition  of  the  third; 
the  right  saccule  is  still  larger,  and  at  the  same  time  the  left  saccule  has  become 
atrophied,  so  that  the  original  apex  of  the  cecum,  with  the  vermiform  process,  is 
close  to  the  ileocolic  junction,  and  the  anterior  band  courses  medialward  to  the 
same  situation.    This  type  is  present  in  about  4  per  cent,  of  cases. 

The  Vermiform  Process  or  Appendix  (processus  vermiformis)  (Fig.  1073)  is  a  long, 
narrow,  worm-shaped  tube,  which  starts  from  what  was  originally  the  apex  of  the 
cecum,  and  may  pass  in  one  of  several  directions:  upward  behind  the  cecum;  to 
the  left  behind  the  ileum  and  mesentery;  or  downward  into  the  lesser  pelvis.  It 
varies  from  2  to  20  cm.  in  length,  its  average  being  about  8.3  cm.  It  is  retained 
in  position  by  a  fold  of  peritoneum  (mesenteriole),  derived  from  the  left  leaf  of 


THE  LARGE  INTESTINE 


1179 


the  mesentery.  This  fold,  in  the  majority  of  cases,  is  more  or  less  triangular  in 
shape,  and  as  a  rule  extends  along  the  entire  length  of  the  tube.  Between  its  two 
layers  and  close  to  its  free  margin  lies  the  appendicular  arten'  (Fig.  1073).  The  canal 
of  the  vermiform  process  is  small,  extends  throughout  the  whole  length  of  the  tube, 
and  communicates  with  the  cecum  by  an  orifice  which  is  placed  below  and  behind 
the  ileocecal  opening.  It  is  sometimes  guarded  by  a  semilunar  valve  formed  by  a 
fold  of  mucous  membrane,  but  this  is  by  no  means  constant. 

Structure. — The  coats  of  the  vermiform  process  are  the  same  as  those  of  the  intestine:  serous, 
muscular,  submucous,  and  mucous.  The  serous  coat  forms  a  complete  investment  for  the  tube, 
except  along  the  narrow  line  of  attachment  of  its  mesenteriole  in  its  proximal  two-thirds.  The 
longitudinal  muscular  fibers  do  not  form  three  bands  as  in  the  greater  part  of  the  large  intestine, 
but  invest  the  whole  organ,  except  at  one  or  two  points  where  both  the  longitudinal  and  circular 
fibers  are  deficient  so  that  the  peritoneal  and  submucous  coats  are  contiguous  over  small  areas. 

The  circular  muscle  fibers  form  a  much  thicker  layer  than  the  longitudinal  fibers,  and  are 
Beparated  from  them  by  a  small  amount  of  connective  tissue.  The  submucous  coat  is  well 
marked,  and  contains  a  large  number  of  masses  of  lymphoid  tissue  which  cause  the  mucous 
membrane  to  bulge  into  the  lumen  and  so  render  the  latter  of  small  size  and  irregular  shape. 
The  mucous  membrane  is  lined  by  columnar  epithelium  and  resembles  that  of  the  rest  of  the 
large  intestine,  but  the  intestinal  glands  are  fewer  in  number  (Fig.  1074). 


Muscular  coat 

Columnar 
epithelium 


-    Glands 


Lymph  nodule 


Fia.   1074. — Transverse  section  of  human  vermiform  process.      X  20. 


The  Colic  Valve  {valvulacoli;  ileocecal  valve)  (Fig.  1075). — ^Thelowerend  of  the  ileum 
ends  by  opening  into  the  medial  and  back  part  of  the  large  intestine,  at  the  point 
of  junction  of  the  cecum  with  the  colon.  The  opening  is  guarded  by  a  valve, 
consisting  of  two  segments  or  lips,  which  project  into  the  lumen  of  the  large  intes- 
tine. If  the  intestine  has  been  inflated  and  dried,  the  lips  are  of  a  semilunar  shape. 
The  upper  one,  nearly  horizontal  in  direction,  is  attached  by  its  convex  border 
to  the  line  of  junction  of  the  ileum  with  the  colon;  the  lower  lip,  which  is  longer 
and  more  concave,  is  attached  to  the  line  of  junction  of  the  ileum  with  the  cecum. 
At  the  ends  of  the  aperture  the  two  segments  of  the  valve  coalesce,  and  are  continued 
as  narrow  membranous  ridges  around  the  canal  for  a  short  distance,  forming  the 
frenula  of  the  valve.  The  left  or  anterior  end  of  the  aperture  is  rounded;  the  right 
or  posterior  is  narrow  and  pointed.  In  the  fresh  condition,  or  in  specimens  which 
have  been  hardened  in  situ,  the  lips  project  as  thick  cushion-like  folds  into  the  lumen 
of  the  large  gut,  while  the  opening  betw^een  them  may  present  the  appearance  of  a 
L  slit  or  may  be  somewhat  oval  in  shape. 


1180 


SPLANCHNOLOGY 


Each  lip  of  the  valve  is  formed  by  a  reduplication  of  the  mucous  membrane 
and  of  the  circular  muscular  fibers  of  the  intestine,  the  longitudinal  fibers  and 
peritoneum  being  continued  uninterruptedly  from  the  small  to  the  large  intestine. 

The  surfaces  of  the  valve  directed  toward  the  ileum  are  covered  with  villi,  and 
present  the  characteristic  structure  of  the  mucous  membrane  of  the  small  intestine; 
while  those  turned  toward  the  large  intestine  are  destitute  of  villi,  and  marked 
with  the  orifices  of  the  numerous  tubular  glands  peculiar  to  the  mucous  membrane 
of  the  large  intestine.  These  differences  in  structure  continue  as  far  as  the  free 
margins  of  the  valve.  It  is  generally  maintained  that  this  valve  prevents  reflux 
from  the  cecum  into  the  ileum,  but  in  all  probability  it  acts  as  a  sphincter  around 
the  end  of  the  ileum  and  prevents  the  contents  of  the  ileum  from  passing  too 
quickly  into  the  cecum.  |H 

The  Colon  is  divided  into  four  parts:  the  ascending,  transverse,  descending,  and 
sigmoid. 


Upper  segmeyit 
of  colic  valve 


Opening  of  ileum 


Lower  segment 
qf  colic  valve 


Probe  in  vermiform 
process 


Fig.   1075. — Interior  of  the  cecum  and  lower  end  of  ascending  colon,  sliowing  colic  valve. 


The  Ascending  Colon  {colon  ascendens)  is  smaller  in  caliber  than  the  cecum,  with 
which  it  is  continuous.  It  passes  upward,  from  its  commencement  at  the  cecum, 
opposite  the  colic  valve,  to  the  under  surface  of  the  right  lobe  of  the  liver,  on  the 
right  of  the  gall-bladder,  where  it  is  lodged  in  a  shallow  depression,  the  colic  impres- 
sion; here  it  bends  abruptly  forward  and  to  the  left,  forming  the  right  colic  {hepatic) 
flexure  (Fig.  1056).  It  is  retained  in  contact  with  the  posterior  wall  of  the  abdomen 
by  the  peritoneum,  which  covers  its  anterior  surface  and  sides,  its  posterior  surface 
being  connected  by  loose  areolar  tissue  with  the  Iliacus,  Quadratus  lumborum, 
aponeurotic  origin  of  Transversus  abdominis,  and  with  the  front  of  the  lower  and 
lateral  part  of  the  right  kidney.  Sometimes  the  peritoneum  completely  invests 
it,  and  forms  a  distinct  but  narrow  mesocolon.^  It  is  in  relation,  in  front,  with  the 
convolutions  of  the  ileum  and  the  abdominal  parietes. 

The  Transverse  Colon  {colon  transversum)  the  longest  and  most  movable  part  of 
the  colon,  passes  with  a  downward  convexity  from  the  right  hypochondriac  region 
across  the  abdomen,  opposite  the  confines  of  the  epigastric  and  umbilical  zones, 
into  the  left  hypochondriac  region,  where  it  curves  sharply  on  itself  beneath  the 
lower  end  of  the  spleen,  forming  the  left  colic  {splenic)  flexure.  In  its  course  it 
describes  an  arch,  the  concavity  of  which  is  directed  backward  and  a  little  upward; 
toward  its  splenic  end  there  is  often  an  abrupt  U-shaped  curve  which  may  descend 

'  Treves  states  that,  after  a  careful  examination  of  one  hundred  subjects,  he  found  that  in  fifty-two  there  was  neither 
an  ascending  nor  a  descending  mesocolon.  In  twenty-two  there  was  a  descending  mesocolon,  but  no  trace  of  a  corre- 
sponding fold  on  the  other  side.  In  fourteen  subjects  there  was  a  mesocolon  to  both  the  ascending  and  the  descending 
segments  of  the  bowel;  while  in  the  remaining  twelve  there  was  an  ascending  mesocolon,  but  no  corresponding  fold 
on  the  left  side.  It  follows,  therefore,  that  in  performing  lumbar  colotomy  a  mesocolon  may  be  expected  upon  the  left 
side  in  36  per  cent,  of  all  cases,  and  on  the  right  in  26  per  cent. — The  Anatomy  of  the  Intestinal  Canal  and  Peritoneum 
in  Man,  1885,  p.  55. 


THE  LARGE  INTESTINE 


1181 


lower  than  tlie  main  curve.  It  is  almost  completely  invested  by  peritoneum,  and 
is  connected  to  the  inferior  border  of  the  pancreas  by  a  large  and  wide  duplicature 
of  that  membrane,  the  transverse  mesocolon.  It  is  in  relation,  by  its  upper  surface, 
with  the  liver  and  gall-bladder,  the  greater  curvature  of  the  stomach,  and  the 
lower  end  of  the  spleen;  by  its  under  surface,  with  the  small  intestine;  by  its  ante- 
rior surface,  with  the  anterior  layers  of  the  greater  omentum  and  the  abdominal 
parietes;  its  posterior  surface  is  in  relation  from  right  to  left  with  the  descending 
portion  of  the  duodenum,  the  head  of  the  pancreas,  and  some  of  the  convolutions 
of  the  jejunum  and  ileum. 

The  left  colic  or  splenic  flexure  (Fig.  1056)  is  situated  at  the  junction  of  the  trans- 
verse and  descending  parts  of  the  colon,  and  is  in  relation  with  the  lower  end  of  the 
spleen  and  the  tail  of  the  pancreas ;  the  flexure  is  so  acute  that  the  end  of  the  trans- 
verse colon  usually  lies  in  contact  with  the  front  of  the  descending  colon.  It  lies 
at  a  higher  level  than,  and  on  a  plane  posterior  to,  the  right  colic  flexure,  and  is 
attached  to  the  diaphragm,  opposite  the  tenth  and  eleventh  ribs,  by  a  peritoneal 
fold,  named  the  phrenicocolic  ligament,  which  assists  in  supporting  the  lower  end 
,of  the  spleen  (see  page  1158). 


Femoral  nerve 
Femoral  vessels 
Peritoneum 

Levator  ant  muscle 


1076. — Iliac  colon,  sigmoid  or  pelvic  colon,  and  rectum  seen  from  the  front,  after  removal  of  pubic  bones 

and  bladder. 

The  Descending  Colon^  (colon  descendens)  passes  downward  through  the  left 
hypochondriac  and  lumbar  regions  along  the  lateral  border  of  the  left  kidney. 
At  the  lower  end  of  the  kidney  it  turns  medialward  toward  the  lateral  border  of 
the  Psoas,  and  then  descends,  in  the  angle  between  Psoas  and  Quadratus  lumborum, 
to  the  crest  of  the  ilium,  where  it  ends  in  the  iliac  colon.  The  peritoneum  covers 
its  anterior  surface  and  sides,  while  its  posterior  surface  is  connected  by  areolar 
tissue  with  the  lower  and  lateral  part  of  the  left  kidney,  the  aponeurotic  origin  of 

1  In  the  Basle  nomenclature  the  descending  colon  is  the  portion  between  the  left  colic  flexure  and  the  superior  aper- 
ture of  the  lesser  pelvis;  it  is,  however,  convenient  to  describe  its  lowest  part  as  the  iliac  colon. 


1182 


SPLANCHNOLOGY 


the  Transversiis  abdominis,  andtheQuadratuslumborum  (Fig.  1056).  It  is  smaller 
in  caliber  and  more  deeply  placed  than  the  ascending  colon,  and  is  more  frequently 
covered  with  peritoneum  on  its  posterior  surface  than  the  ascending  colon  (Treves). 
In  front  of  it  are  some  coils  of  small  intestine.  jh 

The  Iliac  Colon  (Fig.  1076)  is  situated  in  the  left  iliac  fossa,  and  is  about  12  to|| 
15  cm.  long.    It  begins  at  the  level  of  the  iliac  crest,  where  it  is  continuous  with 
the  descending  colon,  and  ends  in  the  sigmoid  colon  at  the  superior  aperture  of  the 
lesser  pelvis.    It  curves  downward  and  medialward  in  front  of  the  Iliacus  and  Psoas, 
and,  as  a  rule,  is  covered  by  peritoneum  on  its  sides  and  anterior  surface  only. 


FiQ.   1077. — The  posterior  aspect  of  the  rectum  exposed  by  removing  the  lower  part  of  the  sacrum  and  the  coccyx. 

The  Sigmoid  Colon  (colon  sigmoideum;  yehic  colon;  sigmoid  flexure)  (Fig.  1076) 
forms  a  loop  which  averages  about  40  cm.  in  length,  and  normally  lies  within  the 
pelvis,  but  on  account  of  its  freedom  of  movement  it  is  liable  to  be  displaced  into 
the  abdominal  cavity.  It  begins  at  the  superior  aperture  of  the  lesser  pelvis, 
where  it  is  continuous  with  the  iliac  colon,  and  passes  transversely  across  the  front 
of  the  sacrum  to  the  right  side  of  the  pelvis;  it  then  curves  on  itself  and  turns 
toward  the  left  to  reach  the  middle  line  at  the  level  of  the  third  piece  of  the  sacrum, 
where  it  bends  downward  and  ends  in  the  rectum.  It  is  completely  surrounded  by 
peritoneum,  which  forms  a  mesentery  (sigmoid  mesocolon),  which  diminishes  in 


THE  LARGE  INTESTINE 


1183 


length  from  the  center  toward  the  ends  of  the  loop,  where  it  disappears,  so  that  the 
loop  is  fixed  at  its  junctions  with  the  iliac  colon  and  rectum,  but  enjoys  a  consider- 
able range  of  movement  in  its  central  portion.  Behind  the  sigmoid  colon  are  the 
external  iliac  vessels,  the  left  Piriformis,  and  left  sacral  plexus  of  nerves;  m  front, 
it  is  separated  from  the  bladder  in  the  male,  and  the  uterus  in  the  female,  by  some 
coils  of  the  small  intestine. 

The  Rectum  {intestinum  rectum)  (Fig.  1077)  is  continuous  above  with  the  sigmoid 
colon,  while  below  it  ends  in  the  anal  canal.  From  its  origin  at  the  level  of  the 
third  sacral  vertebra  it  passes  downward,  lying  in  the  sacrococcygeal  curve,  and 
extends  for  about  2.5  cm.  in  front  of,  and  a  little  below,  the  tip  of  the  coccyx, 
as  far  as  the  apex  of  the  prostate.  It  then  bends  sharply  backward  into  the  anal 
canal.  It  therefore  presents  two  antero-posterior  curves:  an  upper,  with  its  con- 
vexity backward,  and  a  lower,  with  its  convexity  forward.  Two  lateral  curves  are 
also  described,  one  to  the  right  opposite  the  junction  of  the  third  and  fourth  sacral 
vertebrae,  and  the  other  to  the  left,  opposite  the  left  sacrococcygeal  articulation; 
they  are,  however,  of  little  importance.  The  rectum  is  about  12  cm.  long,  and  at 
its  commencement  its  caliber  is  similar  to  that  of  the  sigmoid  colon,  but  near  its 
termination  it  is  dilated  to  form  the  rectal  ampulla.  The  rectum  has  no  sacculations 
comparable  to  those  of  the  colon,  but  when  the  lower  part  of  the  rectum  is  con- 
tracted, its  mucous  membrane  is  thrown  into  a  number  of  folds,  which  are  longitudi- 
nal in  direction  and  are  effaced  by  the  distension  of  the  gut.  Besides  these  there 
are  certain  permanent  transverse  folds,  of  a  semilunar  shape,  known  as  Houston's 
valves  (Fig.  1078).  They  are  usually  three  in  number;  sometimes  a  fourth  is  found, 
and  occasionally  only  two  are  present.  One  is 
situated  near  the  commencement  of  the  rectum, 
on  the  right  side;  a  second  extends  inward  from 
the  left  side  of  the  tube,  opposite  the  middle  of 
the  sacrum;  a  third,  the  largest  and  most  con- 
stant, projects  backward  from  the  forepart  of 
the  rectum,  opposite  the  fundus  of  the  urinary 
bladder.  When  a  fourth  is  present,  it  is  situated 
nearly  2.5  cm.  above  the  anus  on  the  left  and 
posterior  wall  of  the  tube.  These  folds  are  about 
12  mm.  in  width,  and  contain  some  of  the 
circular  fibers  of  the  gut.  In  the  empty  state  of 
the  intestine  they  overlap  each  other,  as  Houston 
remarks,  so  effectually  as  to  require  considerable 
maneuvering  to  conduct  a  bougie  or  the  finger 
along  the  canal.  Their  use  seems  to  be,  "to 
support  the  weight  of  fecal  matter,  and  prevent 
its  urging  toward  the  anus,  where  its  presence 
always  excites  a  sensation  demanding  its  dis- 
charge.^ 

The  peritoneum  is  related  to  the  upper  two- 
thirds  of  the  rectum,  covering  at  first  its  front 
and  sides,  but  lower  down  its  front  only;  from 
the  latter  it  is  reflected  on  to  the  seminal  vesicles 
in  the  male  and  the  posterior  vaginal  wall  in  the 
female. 

The  level  at  which  the  peritoneum  leaves  the  anterior  wall  of  the  rectum  to  be 
reflected  oji  to  the  viscus  in  front  of  it  is  of  considerable  importance  from  a  surgical 


Rectal  columns 

Sphincter  ani 

intemus 
Sphiticter  ani 

externus 


FiQ.   1078. — Coronal  section  of  rectum  and 
anal  canal. 


'  Paterson  ("The  Form  of  the  Rectum,"  Journal  of  Anatomy  and  Physiology,  vol.  xliii)  utilizes  the  third  fold  for 
the  purpose  of  dividing  the  rectum  into  an  upper  and  a  lower  portion;  he  considers  the  latter  "to  be  just  as  much  a 
duct  as  the  narrower  anal  canal  below,"  and  maintains  that,  under  normal  conditions,  it  does  not  contain  feces  except 
during  the  act  of  defecation. 


I 


1184 


SPLANCHNOLOGY 


point  of  view,  in  connection  with  the  removal  of  the  lower  part  of  the  rectum.  It 
is  higher  in  the  male  than  in  the  female.  In  the  former  the  height  of  the  recto- 
vesical excavation  is  about  7.5  cm.,  i.  e.,  the  height  to  which  an  ordinary  index 
finger  can  reach  from  the  anus.  In  the  female  the  height  of  the  rectouterine 
excavation  is  about  5.5  cm.  from  the  anal  orifice.    The  rectum  is  surrounded  by 

a  dense  tube  of  fascia  derived  from  the 
fascia  endopelvina,  but  fused  behind 
with  the  fascia  covering  the  sacrum 
and  coccyx.  The  facial  tube  is  loosely 
attached  to  the  rectal  wall  by  areolar 
tissue  in  order  to  allow  of  distension  of 
the  viscus. 


Relations  of  the  Rectum. — The  upper  part 
of  the  rectum  is  in  relation,  behind,  with  the 
superior  hemorrhoidal  vessels,  the  left  Piri- 
formis, and  left  sacral  plexus  of  nerves,  which 
separate  it  from  the  pelvic  surfaces  of  the 
sacral  vertebrse ;  in  its  lower  part  it  lies  directly 
on  the  sacrum,  coccyx,  and  Levatores  ani,  a 
dense  fascia  alone  intervening;  in  front,  it  is 
separated  above,  in  the  male,  from  the  fundus 
of  the  bladder;  in  the  female,  from  the  intes- 
tinal surface  of  the  uterus  and  its  appendages, 
by  some  convolutions  of  the  small  intestine, 
and  frequently  by  the  sigmoid  colon ;  below,  it 
is  in  relation  in  the  male  wi  th  the  triangular 
portion  of  the  fundus  of  the  bladder,  the  vesic- 
ute  seminales,  and  ductus  deferentes,  and 
more  anteriorly  with  the  posterior  surface  of 
the  prostate;,  in  the  female,  with  the  poste- 
rior wall  of  the  vagina. 

The  Anal  Caiial  (pars  analis  recti)  (Figs.  1079, 1080, 1081),  or  terminal  portion  of  the 
large  intestine,  begins  at  the  level  of  the  apex  of  the  prostate,  is  directed  downward 
and  backward,  and  ends  at  the  anus.    It  forms  an  angle  with  the  lower  part  of 


>l 


Fig.  1079. — Coronal  section  tbrough  the  anal  canal. 
(Symington.)  B.  Cavity  of  urinary  bladder.  F.D.  Ductus 
deferens.  S.V.  Seminal  vesicle.  R.  Second  part  of 
rectum.  A.C.  Anal  canal.  L.A.  Levator  am.  I.S. 
Sphincter  ani  internus.    E.S.  Sphincter  ani  externus. 


LONGITUDINAL 

MUSCLE   FIBRES 

OF  RECTUM 


PART  OF 

LEVATOR  ANI 

INTERNAL 

SPHINCTER 


ANAL  CANAL 


RUG>E  OF 

/JJjil,— MUCOUS 


MEMBRANE 


COLUMNS  OF 
MORGAQNI 


ANAL  VALVES 


Fig.  1080. — The  interior  of  the  anal  canal  and  lower  part  of  the  rectum,  showing  the  columns  of  Morgagni  and  the  anal 
valves  between  their  lower  ends.    The  columns  were  more  numerous  in  the  specimen  than  usual.     (Cunningham.) 

the  rectum,  and  measures  from  2.5  to  4  cm.  in  length.  It  has  no  peritoneal  cov- 
ering, but  is  invested  by  the  Sphincter  ani  internus,  supported  by  the  Levatores 
ani,  and  surrounded  at  its  termination  by  the  Sphincter  ani  externus.    In  the 


THE  LARGE  INTESTINE 


1185 


"empty  condition  it  presents  the  appearance  of  an  antero-posterior  longitudinal 
slit.  Behind  it  is  a  mass  of  muscular  and  fibrous  tissue,  the  anococcygeal  body 
(Symington) ;  in  front  of  it,  in  the  male,  but  separated  by  connective  tissue  from 
it,  are  the  membranous  portion  and  bulb  of  the  urethra,  and  the  fascia  of  the 
urogenital  diaphragm;  and  in  the  female  it  is  separated  from  the  lower  end  of 
the  vagina  by  a  mass  of  muscular  and  fibrous  tissue,  named  the  perineal  body. 


MUCOUS 
MEMBRANE 

DILATATION 

OF   VEINS 

COLUMNS  OF. 

MORGAGNI 

VALVE    OF 

MORGAGNI 


HILTON'S 
WHITE  LINE 


MUSCULAR  WALL 
OF  RECTUM 


INTERNAL  HEMOR- 
RHOIDAL  PLEXUS 


SKIN 


COMMUNICATION   BE- 
TWEEN    INTERNALAND 
EXTERNAL  HEMOR- 
RHOIDAL   PLEXUS 
INTERNAL 
SPHINCTER 


I- 

■  ^■'  Fig.  1081. — Inner  wall  of  the  lower  end  of  the  rectum  and  anus.  On  the  riglit  the  mucous  membrane  has  been 
H^l  removed  to  show  the  dilatation  of  the  veins  and  how  they  pass  through  the  muscular  wall  to  anastomose  with  the 
B^B     external  hemorrhoidal  plexus.      (Luschka.) 

II      ^ 


'  jj^  LONGITUDINAL 

TENDINOUS  FIBRES 


SUBCUTANEOUS 
CELLULAR  TISSUE 


The  lumen  of  the  anal  canal  presents,  in  its  upper  half,  a  number  of  vertical 
folds,  produced  by  an  infolding  of  the  mucous  membrane  and  some  of  the  mus- 
cular tissue.    They  are  known  as  the  rectal  columns  [Morgagni]  (Fig.  1078),  and  are 


Leucocytes  in 
epithelium 


Gland 


Muscularia 
rmicosce 


Solitary  lymphatic  nodule 
Fia.   1082. — Section  of  mucous  membrane  of  human  rectum.      (Sobotta.)      X  60. 

separated  from  one  another  by  furrows  (rectal  sinuses),  which  end  below  in  small 
valve-like  folds,  termed  anal  valves,  which  join  together  the  lower  ends  of  the 
rectal  columns. 


Structure  of  the  Colon. — The  large  intestine  has  four  coats:    serous,  muscular,  areolar,  and 
mucous. 
75 


IL_ 


1186 


SPLANCHNOLOGY 


The  serous  coat  (tunica  serosa)  is  derived  from  the  peritoneum,  and  invests  the  different 
portions  of  the  large  intestine  to  a  variable  extent.  The  cecum  is  completely  covered  by  the 
serous  membrane,  except  in  about  5  per  cent,  of  cases  where  the  upper  part  of  the  posterior 
surface  is  uncovered.  The  ascending,  descending,  and  iliac  parts  of  the  colon  are  usually  covered 
only  in  front  and  at  the  sides;  a  variable  amount  of  the  posterior  surface  is  uncovered.^  The 
transverse  colon  is  almost  completely  invested,  the  parts  corresponding  to  the  attachment  of 
the  greater  omentum  and  transverse  mesocolon  being  alone  excepted.  The  sigmoid  colon  is 
entirely  surrounded.  The  rectum  is  covered  above  on  its  anterior  surface  and  sides;  below, 
on  its  anterior  aspect  only;  the  anal  canal  is  entirely  devoid  of  any  serous  covering.     In  the 

course  of  the  colon  the  peritoneal 
coat  is  thrown  into  a  number  of 
small  pouches  filled  with  fat,  called 
appendices  epiploicse.  They  are 
most  numerous  on  the  transverse 
colon. 

The  muscular  coat  {tunica  mus- 
cularis)  consists  of  an  external  longi- 
tudinal, and  an  internal  circular, 
layer  of  non-striped  muscular  fibers. 
The  longitudinal  fibers  do  not 
form  a  continuous  layer  over  the 
whole  surface  of  the  large  intestine. 
In  the  cecmn  and  colon  they  are 
especially  collected  into  three  flat 
longitudinal  bands  {ta;n(Fi  coli), 
each  of  about  12  mm.  in  width; 
one,  the  posterior,  is  placed  along 
the  attached  border  of  the  intestine; 
the  anterior,  the  largest,  corre- 
sponds along  the  arch  of  the  colon 
to  the  attachment  of  the  greater 
omentum,  but  is  in  front  in  the 
ascending,  descending,  and  iliac 
parts  of  the  colon,  and  in  the  sig- 
moid colon;  the  third,  or  lateral 
band,  is  found  on  the  medial  side 
of  the  ascending  and  descending 
parts  of  the  colon,  and  on  the  under 
aspect  of  the  transverse  colon. 
These  bands  are  shorter  than  the 
other  coats  of  the  intestine,  and 
serve  to  produce  the  sacculi  which 
are  characteristic  of  the  cecum  and 
colon;  accordingly,  when  they  are 
dissected  off,  the  tube  can  be  length- 
ened, and  its  sacculated  character 
disappears.  In  the  sigmoid  colon 
the  longitudinal  fibers  become  more 
scattered;  and  around  the  rectum 
they  spread  out  and  form  a  layer, 
which  completely  encircles  this  por- 
tion of  the  gut,  but  is  thicker  on 
the  anterior  and  posterior  surfaces, 
where  it  forms  two  bands,  than  on 
the  lateral  surfaces.  In  addition, 
two  bands  of  plain  muscular  tissue  arise  from  the  second  and  third  coccygeal  vertebrae,  and 
pass  downward  and  forward  to  blend  with  the  longitudinal  muscular  fibers  on  the  posterior 
wall  of  the  anal  canal.    These  are  known  as  the  Rectococcygeal  muscles. 

The  circular  fibers  form  a  thin  layer  over  the  cecum  and  colon,  being  especially  accumulated 
in  the  intervals  between  the  sacculi;  in  the  rectum  they  form  a  thick  layer,  and  in  the  anal  canal 
they  become  numerous,  and  constitute  the  Sphincter  ani  internus. 

The  areolar  coat  (tela  submucosa;  submucous  coat)  connects  the  muscular  and  mucous  layers 
closely  together. 

The  mucous  membrane  {tunica  mucosa)  in  the  cecum  and  colon,  is  pale,  smooth,  destitute 
of  viUi,  and  raised  into  numerous  crescentic  folds  which  correspond  to  the  intervals  between 

I  See  footnote,  p.  1183. 


MIOOLC 

HEMORRHOIDAL 

ARTERY 


RIOR 

ORRHOIDAL 
RY 


Fig.  1083.^The  bloodvessels  of  the  rectum  and  anus,  showing  the  dis- 
tribution and  anastomosis  on  the  posterior  surface  near  the  termination 
of  the  gut.     (Poirier  and  Charpy) 


THE  LARGE  INTESTINE 


1187 


tt 


the  sacculi.    In  the  rectuni  it  is  thicker,  of  a  darker  color,  more  vascular,  and  connected  loosely 
to  the  muscular  coat,  as  in  the  esophagus. 

As  in  the  small  intestine,  the  mucous  membrane  (Fig.  1082)  consists  of  a  muscular  layer,  the 
muscularis  mucosae;  a  quantity  of  retiform  tissue  in  which  the  vessels  ramify;  a  basement  mem- 
brane and  epithelium  which  is  of  the  columnar  variety,  and  resembles  the  epithelium  found  in 
the  small  intestine.  The  mucous  membrane  of  the  large  intestine  presents  for  examination  glands 
and  solitary  lymphatic  nodules. 

The  glands  of  the  great  intestine  are  minute  tubular  prolongations  of  the  mucous  membrane 
arranged  perpendicularly,  side  by  side,  over  its  entire  surface;  they  are  longer,  more  numerous, 
and  placed  in  much  closer  apposition  than  those  of  the  small  intestine;  and  they  open  by  minute 
rounded  orifices  upon  the  surface,  giving  it  a  cribriform  appearance.  Each  gland  is  lined  by 
short  columnar  epithelium  and  contains  numerous  goblet  cells. 

The  solitary  lymphatic  nodules  {noduli  lymphatic  solitarii)  (Fig.  1082)  of  the  large  intestine 
are  most  abundant  in  the  cecum  and  vermiform  process,  but  are  irregularly  scattered  also  over 
the  rest  of  the  intestine.    They  are  similar  to  tliose  of  the  smaU  intestine. 

Vessels  and  Nerves. — The  arteries  supplying  the  colon  are  derived  from  the  colic  and  sigmoid 
branches  of  the  mesenteric  arteries.  They  give  off  large  branches,  which  ramify  between  and 
supply  the  muscular  coats,  and  after  dividing  into  small  vessels  in  the  submucous  tissue,  pass 
to  the  mucous  membrane.  The  rectum  is  supplied  by  the  superior  hemorrhoidal  branch  of  the 
inferior  mesenteric,  and  the  anal  canal  by  the  middle  hemorrhoidal  from  the  hypogastric,  and 
the  inferior  hemorrhoidal  from  the  internal  pudendal  artery.  The  superior  hemorrhoidal,  the 
continuation  of  the  inferior  mesenteric,  divides  into  two  branches,  which  run  down  either  side 
of  the  rectum  to  within  about  12.5  cm.  of  the  anus;  they  here  spht  up  into  about  six  branches 
which  pierce  the  muscular  coat  and  descend  between  it  and  the  mucous  membrane  in  a  longi- 
tudinal direction,  parallel  with  each  other  as  far  as  the  Sphincter  ani  internus,  where  they  anas- 
tomose with  the  other  hemorrhoidal  arteries  and  form  a  series  of  loops  around  the  anus.  The 
veins  of  the  rectum  commence  in  a  plexus  of  vessels  which  surrounds  the  anal  canal.  In  the 
vessels  forming  this  plexus  are  smaller  saccular  dilatations  just  within  the  margin  of  the  anus; 
from  the  plexus  about  six  vessels  of  considerable  size  are  given  off.  These  ascend  between  the 
muscular  and  mucous  coats  for  about  12.5  cm.,  running  parallel  to  each  other;  they  then 
pierce  the  muscular  coat,  and,  by  their  union,  form  a  single  trunk,  the  superior  hemorrhoidal 
vein.  This  arrangement  is  termed  the  hemorrhoidal  plexus;  it  communicates  with  the  tribu- 
taries of  the  middle  and  inferior  hemor- 
rhoidal veins,  at  its  commencement, 
and  thus  a  communication  is  estab- 
hshed  between  the  systemic  and  portal 
circulations.  The  lymphatics  of  the  large 
intestine  are  described  on  page  711. 
The  nerves  are  derived  from  the  sym- 
pathetic plexuses  around  the  branches 
of  the  superior  and  inferior  mesenteric 
arteries.  They  are  distributed  in  a 
similar  way  to  those  found  in  the  small 
intestine. 

Congenital  Hernia. — There  are  some 
varieties  of  obhque  inguinal  hernia 
(Fig.  1084)  depending  upon  congenital 
defects  in  the  saccus  vaginalis,  the  pouch 
of  peritoneum  which  precedes  the 
descent  of  the  testis.  Normally  this 
pouch  is  closed  before  birth,  closure 
commencing  at  two  points,  viz.,  at  the 
abdominal  inguinal  ring  and  at  the  top 
of  the  epididymis,  and  gradually  ex- 
tending until  the  whole  of  the  inter- 
vening portion  is  converted  into  a 
fibrous  cord.  From  failure  in  the  com- 
pletion of  this  process,  variations  in  the 
relation  of  the  hernial  protrusion  to  the 
testis  and  tunica  vaginalis  are  pro- 
duced; these  constitute  distinct  varieties  of  inguinal  hernia,  viz.,  the  hernia  of  the  funicular 
process  and  the  complete  congenital  variety. 

Where  the  saccus  vaginalis  remains  patent  throughout,  the  cavity  of  the  timica  vaginahs 
communicates  directly  with  that  of  the  peritoneum.  The  intestine  descends  along  this  pouch 
into  the  cavity  of  the  tunica  vaginahs  which  constitutes  the  sac  of  the  hernia,  and  the  gut  hes 
in  contact  with  the  testis.     Though  this  form  of  hernia  is  termed  complete  congenital,  the  term 


Complete  oblique  inguinal 


Complete  congenital 


Incomplete  congenital 
Fig.   1084. — Varieties  of  oblique  inguinal  hernia. 


IISS  ^^^^V       SPLANCHNOLOGY 

does  not  imply  that  the  hernia  existed  at  birth,  but  merely  that  a  condition  is  present  which 
may  allow  of  the  descent  of  the  hernia  at  any  moment.  As  a  matter  of  fact,  congenital  herniae 
frequently  do  not  appear  until  adult  life. 

Where  the  processus  vaginalis  is  occluded  at  the  lower  point  only,  i.  e.,  just  above  the  testis, 
the  intestine  descends  into  the  pouch  of  peritoneum  as  far  as  the  testis,  but  is  prevented 
from  entering  the  sac  of  the  tunica  vaginalis  by  the  septum  which  has  formed  between  it  and  the 
pouch.  This  is  known  as  hernia  into  the  funicular  process  or  incomplete  congenital  hernia;  it 
differs  from  the  former  in  that  instead  of  enveloping  the  testis  it  lies  above  it. 


The  Liver  (Hepar). 

The  liver,  the  largest  gland  in  the  body,  has  both  external  and  internal  secretions, 
which  are  formed  in  the  hepatic  cells.  Itp  external  secretion,  the  bile,  is  collected 
after  passing  through  the  bile  capillaries  by  the  bile  ducts,  which  join  like  the  twigs 
and  branches  of  a  tree  to  form  two  large  ducts  that  imite  to  form  the  hepatic  duct. 
The  bile  is  either  carried  to  the  gall-bladder  by  the  cystic  duct  or  poured  directly 
into  the  duodenum  by  the  common  bile  duct  where  it  aids  in  digestion.  The  internal 
secretions  are  concerned  with  the  metabolism  of  both  nitrogenous  and  carbohydrate 
materials  absorbed  from  the  intestine  and  carried  to  the  liver  by  the  portal  vein. 
The  carbohydrates  are  stored  in  the  hepatic  cells  in  the  form  of  glycogen  which  is 
secreted  in  the  form  of  sugar  directly  into  the  blood  stream.  Some  of  the  cells 
lining  the  blood  capillaries  of  the  liver  are  concerned  in  the  destruction  of  red  blood 
corpuscles.  It  is  situated  in  the  upper  and  right  parts  of  the  abdominal  cavity, 
occupying  almost  the  whole  of  the  right  hypochondrium,  the  greater  part  of  the 
epigastrium,  and  not  uncommonly  extending  into  the  left  hypochondrium  as  far 
as  the  mammillary  line.  In  the  male  it  weighs  from  1 .4  to  1 .6  kilogm.,  in  the  female 
from  1.2  to  1.4  kilogm.  It  is  relatively  much  larger  in  the  fetus  than  in  the  adult, 
constituting,  in  the  former,  about  one-eighteenth,  and  in  the  latter  about  one 
thirty-sixth  of  the  entire  body  weight.  Its  greatest  transverse  measurement  is 
from  20  to  22.5  cm.  Vertically,  near  its  lateral  or  right  surface,  it  measures  about 
15  to  17.5  cm.,  while  its  greatest  antero-posterior  diameter  is  on  a  level  with  the 
upper  end  of  the  right  kidney,  and  is  from  10  to  12.5  cm.  Opposite  the  vertebral 
column  its  measurement  from  before  backward  is  reduced  to  about  7.5  cm.  Its 
consistence  is  that  of  a  soft  solid;  it  is  friable,  easily  lacerated  and  highly  vascular; 
its  color  is  a  dark  reddish  brown,  and  its  specific  gravity  is  1.05. 

To  obtain  a  correct  idea  of  its  shape  it  must  be  hardened  in  situ,  and  it  will 
then  be  seen  to  present  the  appearance  of  a  wedge,  the  base  of  which  is  directed 
to  the  right  and  the  thin  edge  toward  the  left.  Symington  describes  its  shape 
as  that  "of  a  right-angled  triangular  prism  with  the  right  angle  rounded  off." 

Surfaces. — The  liver  possesses  three  surfaces,  viz.,  superior,  inferior  and  posterior. 
A  sharp,  well-defined  margin  divides  the  inferior  from  the  superior  in  front;  the  other 
margins  are  rounded.  The  superior  surface  is  attached  to  the  diaphragm  and 
anterior  abdominal  wall  by  a  triangular  or  falciform  fold  of  peritoneum,  the  falci- 
form ligament,  in  the  free  margin  of  which  is  a  rounded  cord,  the  ligamentum  teres 
(obliterated  umbilical  vein).  The  line  of  attachment  of  the  falciform  ligament 
divides  the  liver  into  two  parts,  termed  the  right  and  left  lobes,  the  right  being  much 
the  larger.  The  inferior  and  posterior  surfaces  are  divided  into  four  lobes  by  five 
fossae,  which  are  arranged  in  the  form  of  the  letter  H.  The  left  limb  of  the  H  marks 
on  these  surfaces  the  division  of  the  liver  into  right  and  left  lobes;  it  is  known  as  the 
left  sagittal  fossa,  and  consists  of  two  parts,  viz.,  the  fossa  for  the  umbilical  vein  in 
front  and  the  fossa  for  the  ductus  venosus  behind.  The  right  limb  of  the  H  is  formed 
in  front  by  the  fossa  for  the  gall-bladder,  and  behind  by  the  fossa  for  the  inferior  vena 
cava  I  these  two  f osste  are  separated  from  one  another  by  a  band  of  liver  substance, 
termed  the  caudate  process.  The  bar  connecting  the  two  limbs  of  the  H  is  the 
porta  (transverse  fissure) ;  in  front  of  it  is  the  quadrate  lobe,  behind  it  the  caudate  lobe. 


THE  LIVER 


1189 


The  superior  surface  {fades  superior)  (Fig.  1085)  comprises  a  part  of  both  lobes, 
and,  as  a  whole,  is  convex,  and  fits  under  the  vault  of  the  diaphragm  which  in  front 
separates  it  on  the  right  from  the  sixth  to  the  tenth  ribs  and  their  cartilages,  and 
on  the  left  from  the  seventh  and  eighth  costal  cartilages.  Its  middle  part  lies 
behind  the  xiphoid  process,  and,  in  the  angle  between  the  diverging  rib  cartilage 
of  opposite  sides,  is  in  contact  with  the  abdominal  wall.  Behind  this  the  diapliragm 
separates  the  li^'er  from  the  lower  part  of  the  lung§  and  pleurse,  the  heart  and  peri- 
cardium and  the  right  costal  arches  from  the  seventh  to  the  eleventh  inclusive.  It 
is  completely  covered  by  peritoneum  except  along  the  line  of  attachment  of  the 
falciform  ligament. 

Oall-bladder 


Left  triangular  ligament 


Bight  triangvlar 
Ugcument 


Fia.   1085. — The  superior  surface  of  the  liver.     (From  model  by  His.) 

The  inferior  surf  ace  (fades  inferior;  visceral  surface)  (Figs.  1086, 1087),  is  uneven, 
concave,  directed  downward,  backward,  and  to  the  left,  and  is  in  relation  with 
the  stomach  and  duodenum,  the  right  colic  flexure,  and  the  right  kidney  and  supra- 
renal gland.  The  surface  is  almost  completely  invested  by  peritoneum;  the  only 
parts  devoid  of  this  covering  are  w^here  the  gall-bladder  is  attached  to  the  liver, 
and  at  the  porta  hepatis  where  the  two  layers  of  the  lesser  omentum  are  separated 
from  each  other  by  the  bloodvessels  and  ducts  of  the  liver.  The  inferior  surface 
of  the  left  lobe  presents  behind  and  to  the  left  the  gastric  impression,  moulded 
over  the  antero-superior  surface  of  the  stomach,  and  to  the  right  of  this  a  rounded 
eminence,  the  tuber  omentale,  which  fits  into  the  concavity  of  the  lesser  curvature 
of  the  stomach  and  lies  in  front  of  the  anterior  layer  of  the  lesser  omentum.  The 
under  surface  of  the  right  lobe  is  divided  into  two  unequal  portions  by  the  fossa 
for  the  gall-bladder;  the  portion  to  the  left,  the  smaller  of  the  two,  is  the  quadrate 
lobe,  and  is  in  relation  with  the  pyloric  end  of  the  stomach,  the  superior  portion 
of  the  duodenum,  and  the  transverse  colon.  The  portion  of  the  under  surface  of 
the  right  lobe  to  the  right  of  the  fossa  for  the  gall-bladder  presents  two  impressions, 
one  situated  behind  the  other,  and  separated  by  a  ridge.  The  anterior  of  these 
two  impressions,  the  colic  impression,  is  shallow  and  is  produced  by  the  right  colic 
flexure;  the  posterior,  the  renal  impression,  is  deeper  and  is  occupied  by  the  upper 
part  of  the  right  kidney  and  lower  part  of  the  right  suprarenal  gland.  Medial 
to  the  renal  impression  is  a  third  and  slightly  marked  impression,  lying  between  it 
and  the  neck  of  the  gall-bladder.    This  is  caused  by  the  descending  portion  of  the 


b^ 


1190 


SPLANCHNOLOGY 


duodenum,  and  is  known  as  the  duodenal  impression.  Just  in  front  of  the  inferior 
vena  cava  is  a  narrow  strip  of  liver  tissue,  the  caudate  process,  which  connects 
the  right  inferior  angle  of  the  caudate  lobe  to  the  under  surface  of  the  right  lobe. 
It  forms  the  upper  boundary  of  the  epiploic  foramen  of  the  peritoneum. 


Fossa  for  ductus  venosus 
Hsofihageal  groove 


Papillary 
process 

Hepatic  artery 

Portal  vein    /  ^  Bound  ligament 

Common  bile  duct 
Fig.  1086. — Inferior  surface  of  the  liver.     (From  model  by  His.) 

The  posterior  surface  (fades  posterior)  (Fig.  1087)  is  rounded  and  broad  behind 
the  right  lobe,  but  narrow  on  the  left.    Over  a  large  part  of  its  extent  it  is  not 


Esophageal  groove 


Fossa  for 

ductus  venosus  „      •„  t^         j.  t  •,  •    ,      • 

Papillary      Fossa  for  umbilical  vein 

process 
Fig.  ,1087. — Posterior  and  inferior  surfaces  of  the  liver.      (From  model  by  His. 

covered  by  peritoneum;  this  uncovered  portion  is  about  7.5  cm.  broad  at  its  widest 
part,  and  is  in  direct  contact  with  the  diaphragm.  It  is  marked  off  from  the  upper 
surface  by  the  line  of  reflection  of  the  upper  layer  of  the  coronary  ligament,  and 


I 


THE  LIVER  ^^^^^P  ^^^^ 

from  the  under  surface  by  the  line  of  reflection  of  the  lower  layer  of  the  coronary 
ligament.  The  central  part  of  the  posterior  surface  presents  a  deep  concavity 
which  is  moulded  on  the  vertebral  column  and  crura  of  the  diaphragm.  To  the 
right  of  this  the  inferior  vena  cava  is  lodged  in  its  fossa  between  the  uncovered 
area  and  the  caudate  lobe.  Close  to  the  right  of  this  fossa  and  immediately  above 
the  renal  impression  is  a  small  triangular  depressed  area,  the  suprarenal  impression, 
the  greater  part  of  which  is  devoid  of  peritoneum;  it  lodges  the  right  suprarenal 
gland.  To  the  left  of  the  inferior  vena  cava  is  the  caudate  lobe,  which  lies  between 
the  fossa  for  the  vena  cava  and  the  fossa  for  the  ductus  venosus.  Its  lower  end 
projects  and  forms  part  of  the  posterior  boundary  of  the  porta;  on  the  right,  it 
is  connected  with  the  under  surface  of  the  right  lobe  of  the  liver  by  the  caudate 
process,  and  on  the  left  it  presents  an  elevation,  the  papillary  process.  Its  posterior 
surface  rests  upon  the  diaphragm,  being  separated  from  it  merely  by  the  upper 
part  of  the  omental  bursa.  To  the  left  of  the  fossa  for  the  ductus  venosus  is  a 
groove  in  which  lies  the  antrum  cardiacum  of  the  esophagus. 

The  anterior  border  {iriargo  anterior)  is  thin  and  sharp,  and  marked  opposite 
the  attachment  of  the  falciform  ligament  by  a  deep  notch,  the  umbilical  notch, 
and  opposite  the  cartilage  of  the  ninth  rib  by  a  second  notch  for  the  fundus  of  the 
gall-bladder.  In  adult  males  this  border  generally  corresponds  with  the  lower 
margin  of  the  thorax  in  the  right  mammillary  line;  but  in  women  and  children  it 
usually  projects  below  the  ribs. 

The  left  extremity  of  the  liver  is  thin  and  flattened  from  above  downward. 

Fossae. — The  left  sagittal  fossa  (fossa  sagittalis  sinistra;  longitudinal  fissure) 
is  a  deep  groove,  which  extends  from  the  notch  on  the  anterior  margin  of  the  liver 
to  the  upper  border  of  the  posterior  surface  of  the  organ ;  it  separates  the  right  and 
left  lobes.  The  porta  joins  it,  at  right  angles,  and  divides  it  into  two  parts.  The 
anterior  part,  or  fossa  for  the  umbilical  vein,  lodges  the  umbilical  vein  in  the  fetus, 
and  its  remains  (the  ligamentum  teres)  in  the  adult;  it  lies  between  the  quadrate 
lobe  and  the  left  lobe  of  the  liver,  and  is  often  partially  bridged  over  by  a  pro- 
longation of  the  hepatic  substance,  the  pons  hepatis.  The  posterior  part,  or  fossa 
for  the  ductus  venosus,  lies  between  the  left  lobe  and  the  caudate  lobe;  it  lodges  in 
the  fetus,  the  ductus  venosus,  and  in  the  adult  a  slender  fibrous  cord,  the  ligamentum 
venosum,  the  obliterated  remains  of  that  vessel. 

The  porta  or  transverse  fissure  {porta  hepatis)  is  a  short  but  deep  fissure,  about 
5  cm.  long,  extending  transversely  across  the  under  surface  of  the  left  portion  of  the 
right  lobe,  nearer  its  posterior  surface  than  its  anterior  border.  It  joins  nearly 
at  right  angles  with  the  left  sagittal  fossa,  and  separates  the  quadrate  lobe  in 
front  from  the  caudate  lobe  and  process  behind.  It  transmits  the  portal  vein, 
the  hepatic  artery  and  nerves,  and  the  hepatic  duct  and  lymphatics.  The  hepatic 
duct  lies  in  front  and  to  the  right,  the  hepatic  artery  to  the  left,  and  the  portal 
vein  behind  and  between  the  duct  and  artery. 

The  fossa  for  the  gall-bladder  (fossa  vesicae  felleas)  is  a  shallow,  oblong  fossa, 
placed  on  the  under  surface  of  the  right  lobe,  parallel  with  the  left  sagittal  fossa. 
It  extends  from  the  anterior  free  margin  of  the  liver,  which  is  notched  by  it,  to  the 
right  extremity  of  the  porta. 

The  fossa  for  the  inferior  vena  cava  (fossa  vence  cavce)  is  a  short  deep  depression, 
occasionally  a  complete  canal  in  consequence  of  the  substance  of  the  liver  surround- 
ing the  vena  cava.  It  extends  obliquely  upward  on  the  posterior  surface  between 
the  caudate  lobe  and  the  bare  area  of  the  liver,  and  is  separated  from  the  porta 
by  the  caudate  process.  On  slitting  open  the  inferior  vena  cava  the  orifices  of 
the  hepatic  veins  will  be  seen  opening  into  this  vessel  at  its  upper  part,  after 
perforating  the  floor  of  this  fossa. 

Lobes. — The  right  lobe  (lohiis  hepatis  dexter)  is  much  larger  than  the  left;  the 
proportion  between  them  being  as  six  to  one.      It  occupies  the  right  hypo- 


II 


1192  ^im^        SPLANCHNOLOGY 

chondrium,  and  is  separated  from  the  left  lobe  on  its  upper  surface  by  the 
falciform  ligament;  on  its  under  and  posterior  surfaces  by  the  left  sagittal 
fossa;  and  in  front  by  the  umbilical  notch.  It  is  of  a  somewhat  quadrilateral  form, 
its  under  and  posterior  surfaces  being  marked  by  three  fossae:  the  porta  and  the 
fossae  for  the  gall-bladder  and  inferior  vena  cava,  which  separate  its  left  part 
into  two  smaller  lobes;  the  quadrate  and  caudate  lobes.  The  impressions  on  the 
right  lobe  have  already  been  described.  ll 

The  quadrate  lobe  {lobus  quadratus)  is  situated  on  the  under  surface  of  the  right 
lobe,  bounded  in  front  by  the  anterior  margin  of  the  liver;  behind  by  the  porta; 
on  the  right,  by  the  fossa  for  the  gall-bladder;  and  on  the  left,  by  the  fossa  for  the 
umbilical  vein.  It  is  oblong  in  shape,  its  antero-posterior  diameter  being  greater 
than  its  transverse. 

The  caudate  lobe  (lobii^  caudatus;  Spigelian  lobe)  is  situated  upon  the  posterior 
surface  of  the  right  lobe  of  the  liver,  opposite  the  tenth  and  eleventh  thoracic 
vertebrae.  It  is  bounded,  below,  by  the  porta;  on  the  right,  by  the  fossa  for  the 
inferior  vena  cava;  and,  on  the  left,  by  the  fossa  for  the  ductus  venosus.  It  looks 
backward,  being  nearly  vertical  in  position;  it  is  longer  from  above  downward 
than  from  side  to  side,  and  is  somewhat  concave  in  the  transverse  direction.  The 
caudate  process  is  a  small  elevation  of  the  hepatic  substance  extending  obliquely 
lateralward,  from  the  lower  extremity  of  the  caudate  lobe  to  the  under  surface  of 
the  right  lobe.  It  is  situated  behind  the  porta,  and  separates  the  fossa  for  the  gall- 
bladder from  the  commencement  of  the  fossa  for  the  inferior  vena  cava. 

The  left  lobe  {lobus  hepatis  sinister)  is  smaller  and  more  flattened  than  the  right. 
It  is  situated  in  the  epigastric  and  left  hypochondriac  regions.  Its  upper  surface 
is  slightly  convex  and  is  moulded  on  to  the  diaphragm;  its  under  surface  presents 
the  gastric  impression  and  omental  tuberosity,  already  referred  to  page  1189. 

Ligaments. — The  liver  is  connected  to  the  under  surface  of  the  diaphragm 
and  to  the  anterior  wall  of  the  abdomen  by  five  ligaments;  four  of  these — the 
falciform,  the  coronary,  and  the  two  lateral — are  peritoneal  folds;  the  fifth,  the 
round  ligament,  is  a  fibrous  cord,  the  obliterated  umbilical  vein.  The  liver  is  also 
attached  to  the  lesser  curvature  of  the  stomach  by  the  hepatogastric  and  to  the 
duodenum  by  the  hepatoduodenal  ligament  (see  page  1157). 

The  falciform  ligament  (ligamentum  falciforme  hepatis)  is  a  broad  and  thin  antero- 
posterior peritoneal  fold,  falciform  in  shape,  its  base  being  directed  downward 
and  backward,  its  apex  upward  and  backward.  It  is  situated  in  an  antero-posterior 
plane,  but  lies  obliquely  so  that  one  surface  faces  forward  and  is  in  contact  with 
the  peritoneum  behind  the  right  Rectus  and  the  diaphragm,  while  the  other  is 
directed  backward  and  is  in  contact  with  the  left  lobe  of  the  liver.  It  is  attached 
by  its  left  margin  to  the  under  surface  of  the  diaphragm,  and  the  posterior  surface 
of  the  sheath  of  the  right  Rectus  as  low  down  as  the  umbilicus;  by  its  right  margin 
it  extends  from  the  notch  on  the  anterior  margin  of  the  liver,  as  far  back  as  the 
posterior  surface.  It  is  composed  of  two  layers  of  peritoneum  closely  united 
together.  Its  base  or  free  edge  contains  between  its  layers  the  round  ligament 
and  the  parumbilical  veins. 

The  coronary  ligament  (ligamentum  coronarium  hepatis)  consists  of  an  upper 
and  a  lower  layer.  The  upper  layer  is  formed  by  the  reflection  of  the  peritoneum 
from  the  upper  margin  of  the  bare  area  of  the  liver  to  the  under  surface  of  the  dia- 
phragm, and  is  continuous  with  the  right  layer  of  the  falciform  ligament.  The 
lower  layer  is  reflected  from  the  lower  margin  of  the  bare  area  on  to  the  right  kidney 
and  suprarenal  gland,  and  is  termed  the  hepatorenal  ligament. 

The  triangular  ligaments  {lateral  ligaments)  are  two  in  number,  right  and  left. 
The  right  triangular  ligament  {ligamentum  triangulare  dextrum)  is  situated  at  the 
right  extremity  of  the  bare  area,  and  is  a  small  fold  which  passes  to  the  diaphragm, 
being  formed  by  the  apposition  of  the  upper  and  lower  layers  of  the  coronary 


THE  LIVER 


1193 


II 


ligament.  The  left  triangular  ligament  (ligamentum  triangulare  sinistrum)  is  a  fold 
of  some  considerable  size,  which  connects  the  posterior  part  of  the  upper  surface 
of  the  left  lobe  to  the  diaphragm;  its  anterior  layer  is  continuous  with  the  left 
layer  of  the  falciform  ligament. 

The  round  ligament  (ligamentum  teres  hepatis)  is  a  fibrous  cord  resulting  from  the 
obliteration  of  the  umbilical  vein.  It  ascends  from  the  umbilicus,  in  the  free  margin 
of  the  falciform  ligament,  to  the  umbilical  notch  of  the  liver,  from  which  it  may  be 
traced  in  its  proper  fossa  on  the  inferior  surface  of  the  liver  to  the  porta,  where 
it  becomes  continuous  with  the  ligamentum  venosum. 

Fixation  of  the  Liver.— Several  factors  contribute  to  maintain  the  liver  in 
place.  The  attachments  of  the  liver  to  the  diaphragm  by  the  coronary  and  tri- 
angular ligaments  and  the  intervening  connective  tissue  of  the  uncovered  area, 
together  with  the  intimate  connection  of  the  inferior  vena  cava  by  the  connective 
tissue  and  hepatic  veins  would  hold  up  the  posterior  part  of  the  liver.  Some  sup- 
port is  derived  from  the  pressure  of  the  abdominal  viscera  which  completely  fill 
the  abdomen  whose  muscular  walls  are  always  in  a  state  of  tonic  contraction.  The 
superior  surface  of  the  liver  is  perfectly  fitted  to  the  under  surface  of  the  diaphragm 
so  that  atmospheric  pressure  alone  would  be  enough  to  hold  it  against  the  dia- 
phragm. The  latter  in  turn  is  held  up  by  the  negative  pressure  in  the  thorax.  The 
lax  falciform  ligament  certainly  gives  no  support  though  it  probably  limits  lateral 
displacement. 


Pericardial  cavity 


Anterior  wail  of 
pericardium 


Lower  wall  of 
pericardium 


Truncus  arteriostis 

Dorsal  mesocardium 

Atrium 

Cuvierian  duct 

Umbilical  vein 
Vitelline  vein 

Communication 
between  pericardial 
and  peritoneal  cavities 


Vitelline  duct  __v,^__ 

Peritoneal  cavity 

FiQ.   1088. — Liver  with  the  septum  transversum.     Humaa  embryo  3  mm.  long.    (After  model  and  figure  by  His.) 

Development. — ^The  liver  arises  in  the  form  of  a  diverticulum  or  hollow  outgrowth 
from  the  ventral  surface  of  that  portion  of  the  gut  which  afterward  becomes 
the  descending  part  of  the  duodenum  (Fig.  1088).  This  diverticulum  is  lined  by 
entoderm,  and  grows  upward  and  forward  into  the  septum  transversum,  a  mass 
of  mesoderm  between  the  vitelline  duct  and  the  pericardial  cavit}',  and  there  gives 
off  two  solid  buds  of  cells  which  represent  the  right  and  the  left  lobes  of  the  liver. 
The  solid  buds  of  cells  grow  into  columns  or  cylinders,  termed  the  hepatic  cylinders, 
which  branch  and  anastomose  to  form  a  close  meshwork.  This  network  invades 
the  vitelline  and  umbilical  veins,  and  breaks  up  these  vessels  into  a  series  of  capil- 
lary-like vessels  termed  sinusoids  (Minot),  which  ramify  in  the  meshes  of  the  cellular 


1194 


SPLANCHNOLOGY 


network  and  ultimately  form  the  venous  capillaries  of  the  liver.  By  the  continued 
growth  and  ramification  of  the  hepatic  cylinders  the  mass  of  the  liver  is  gradually 
formed.  The  original  diverticulum  from  the  duodenum  forms  the  common  bile- 
duct,  and  from  this  the  cystic  duct  and  gall-bladder  arise  as  a  solid  outgrowth  which 
later  acquires  a  lumen.  The  opening  of  the  common  duct  is  at  first  in  the  ventral 
.  wall  of  the  duodenum;  later,  owing  to  the  rotation  of  the  gut,  the  opening  is  carried 
to  the  left  and  then  dorsalward  to  the  position  it  occupies  in  the  adult. 

As  the  liver  undergoes  enlargement,  both  it  and  the  ventral  mesogastrium  of 
the  fore-gut  are  gradually  differentiated  from  the  septum  transversum;  and  from 
the  under  surface  of  the  latter  the  liver  projects  downward  into  the  abdominal 
cavity.  By  the  growth  of  the  liver  the  ventral  mesogastrium  is  divided  into  two 
parts,  of  which  the  anterior  forms  the  falciform  and  coronary  ligaments,  and  the 
posterior  the  lesser  omentum.  About  the  third  month  the  liver  almost  fills  the 
abdominal  cavity,  and  its  left  lobe  is  nearly  as  large  as  its  right.  From  this  period 
the  relative  development  of  the  liver  is  less  active,  more  especially  that  of  the  left 
lobe,  which  actually  undergoes  some  degeneration  and  becomes  smaller  than  the 
right;  but  up  to  the  end  of  fetal  life  the  liver  remains  relatively  larger  than  in 
the  adult. 


Hepatic 


Orifices  of  intralobular  veins 


Fig.  1089. — Longitudinal  section  of  a  hepatic  vein. 
(After  Kiernan.) 


Portal 


"^dncta^:; 


Portion  of  canal 

from  which 

vein  has  been 

removed. 


Fio.  1090. — Longitudinal  section  of  a  small  portal  vein 
and  canal.     (After  Kiernan.) 


Vessels  and  Nerves. — The  vessels  connected  with  the  liver  are:  the  hepatic  artery,  the  portal 
vein,  and  the  hepatic  veins. 

The  hepatic  artery  and  portal  vein,  accompanied  by  numerous  nerves,  ascend  to  the  porta, 
between  the  layers  of  the  lesser  omentum.  The  bile  duct  and  the  lymphatic  vessels  descend 
from  the  porta  between  the  layers  of  the  same  omentum.  The  relative  positions  of  the  three 
structures  are  as  follows:  the  bile  duct  lies  to  the  right,  the  hepatic  artery  to  the  left,  and  the 
portal  vein  behind  and  between  the  other  two.  They  are  enveloped  in  a  loose  areolar  tissue,  the 
fibrous  capsule  of  Glisson,  which  accompanies  the  vessels  in  their  course  through  the  portal 
canals  in  the  interior  of  the  organ  (Fig.  1090). 

The  hepatic  veins  (Fig.  1089)  convey  the  blood  from  the  liver,  and  are  described  on  page  680. 
They  have  very  little  cellular  investment,  and  what  there  is  binds  their  parietes  closely  to  the 
walls  of  the  canals  through  which  they  run;  so  that,  on  section  of  the  organ,  they  remain  widely 
open  and  are  solitary,  and  may  be  easily  distinguished  from  the  branches  of  the  portal  vein, 
which  are  more  or  less  collapsed,  and  always  accompanied  by  an  artery  and  duct. 

The  lymphatic  vessels  of  the  liver  are  described  on  page  711. 

The  nerves  of  the  liver,  derived  from  the  left  vagus  and  sympathetic,  enter  at  the  porta  and 
accompany  the  vessels  and  ducts  to  the  interlobular  spaces.    Here,  according  to  Korolkow.  the 


THE  LIVER 


1195 


medullated  fibers  are  distributed  almost  exclusively  to  the  coats  of  the  bloodvessels;  while  the 
non-medullated  enter  the  lobules  and  ramify  between  the  cells  and  even  within  them.' 


Intralobular  vein 


Intralobular  vein  — -. 


Fio.   1091. — Section  of  injected  liver  (dog). 


Sinusoid 


Column  of  liver- 
cells 
Interlobular  vein 


Intralobular  vein 


Structure  of  the  Liver. — The  substance  of  the  liver  is  composed  of  lobules,  held  together  by 
an  extremely  fine  areolar  tissue,  in  which  ramify  the  portal  vein,  hepatic  ducts,  hepatic  artery, 
hepatic  veins,  lymphatics,  and  nerves;  the  whole  being  invested  by  a  serous  and  a  fibrous  coat. 

The  serous  coat  {tunica  serosa)  is  derived  from  the  peritoneum,  and  invests  the  greater  part 
of  the  surface  of  the  organ.    It  is  intimately  adherent  to  the  fibrous  coat. 

The  fibrous  coat  (capsula  fibrosa 
[Glissoni];  areolar  coat)  lies  beneath 
the  serous  investment,  and  covers 
the  entire  surface  of  the  organ.  It 
is  difficult  of  demonstration,  except- 
ing where  the  serous  coat  is  defi- 
cient. At  the  porta  it  is  continuous 
with  the  fibrous  capsule  of  GUsson, 
and  on  the  surface  of  the  organ  with 
the  areolar  tissue  separating  the 
lobules. 

The  lobules  {lohuli  hepaiis)  form 
the  chief  niass  of  the  hepatic  sub- 
stance; they  may  be  seen  either  on 
the  surface  of  the  organ,  or  by  mak- 
ing a  section  through  the  gland,  as 
small  granular  bodies,  about  the  size 
of  a  miUet-seed,  measuring  from  1  to 
2.5  mm.  in  diameter.  In  the  human 
subject  their  outlines  are  very  irreg- 
ular; but  in  some  of  the  lower  ani- 
mals (for  example,  the  pig)  they  are 
well-defined,  and,  when  divided 
transversely,  have  polygonal  out- 
lines. The  bases  of  the  lobules  are  clustered  around  the  smallest  radicles  (sublobular)  of  the 
hepatic  veins,  to  which  each  is  connected  (Fig.  10S9)  by  means  of  a  small  branch  which  issues 
from  the  center  of  the  lobule  {intralobular).  The  remaining  part  of  the  surface  of  each  lobule 
is  imperfectly  isolated  from  the  surrounding  lobules  by  a  thin  stratum  of  areolar  tissue,  in 
which  is  contained  a  plexus  of  vessels,  the  interlobular  plexus,  and  ducts.  In  some  animals,  as 
the  pig,  the  lobules  are  completely  isolated  from  one  another  by  the  interlobular  areolar  tissue 
(Fig.  1092). 

If  one  of  the  sublobular  veins  be  laid  open,  the  bases  of  the  lobules  may  be  seen  through  the 
thin  wall  of  the  vein  on  which  they  rest,  arranged  in  a  form  resembling  a  tesselated  pavement, 

»  Berkeley,  Anat.,  .\ug.,  8,  1893;  MacCalluni,  A.  B..  Quart.  Jour.  Micr.  Sci.,  1887,  27;  Allegra,  Anat.,  Aug.  25,  1904. 


Sublobular  vein 


Fig.   1092. — A  single  lobule  of  the  liver  of  a  pig.      X  60. 


rCHNOl 


the  center  of  each  polygonal  space  presenting  a  minute  aperture,  the  mouth  of  an  intralobular  I 
vein  (Fig.  1089).  I 

Microscopic  Appearance  (Fig.  1092). — Each  lobule  consists  of  a  mass  of  cells,  hepatic  cells, 
arranged  in  irregular  radiating  columns  between  which  are  the  blood  channels  (sinusoids) .  These 
convey  the  blood  from  the  circumference  to  the  center  of  the  lobule,  and  end  in  the  intralobular 
vein,  which  runs  through  its  center,  to  open  at  its  base  into  one  of  the  sublobular  veins.  Between 
the  cells  are  also  the  minute  bile  capillaries.  Therefore,  in  the  lobule  there  are  all  the  essentials 
of  a  secreting  gland;  that  is  to  say:  (1)  cells,  by  which  the  secretion  is  formed;  (2)  bloodvessels, 
in  close  relation  with  the  cells,  containing  the  blood  from  which  the  secretion  is  derived;  (3)3 1 
ducts,  by  which  the  secretion,  when  formed,  is  carried  away.  I 

1.  The  hepatic  cells  are  polyhedral  in  form.  They  vary  in  size  from  12  to  25/^  in  diameter. 
They  contain  one  or  sometimes  two  distinct  nuclei.  The  nucleus  exhibits  an  intranuclear  net- 
work and  one  or  two  refractile  nucleoli.  The  cells  usually  contain  granules;  some  of  which  are 
protoplasmic,  while  others  consist  of  glycogen,  fat,  or  an  iron  compound.  In  the  lower  vertebrates, 
e.  g.,  frog,  the  cells  are  arranged  in  tubes  with  the  bile  duct  forming  the  lumen  and  bloodvessels 
externally.  According  to  Delepine,  evidences  of  this  arrangement  can  be  found  in  the  human 
liver. 

2.  The  Bloodvessels. — The  blood  in  the  capillary  plexus  around  the  hver  cells  is  brought  to 
the  liver  principally  by  the  portal  vein,  but  also  to  a  certain  extent  by  the  hepatic  artery. 

The  hepatic  artery,  entering  the  liver  at  the  porta  with  the  portal  vein  and  hepatic  duct, 
ramifies  with  these  vessels  through  the  portal  canals.  It  gives  off  vaginal  branches,  which  ramify 
in  the  fibrous  capsule  of  Glisson,  and  appear  to  be  destined  chiefly  for  the  nutrition  of  the  coats 
of  the  vessels  and  ducts.  It  also  gives  off  capsular  branches,  which  reach  the  surface  of  the 
organ,  ending  in  its  fibrous  coat  in  stellate  plexuses.  Finally,  it  gives  off  interlobular  branches, 
which  form  a  plexus  outside  each  lobule,  to  supply  the  walls  of  the  interlobular  veins  and  the 
accompanying  bile  ducts.  From  this  plexus  lobular  branches  enter  the  lobule  and  end  in  the 
net-work  of  sinusoids  between  the  cells. 

The  portal  vein  also  enters  at  the  porta,  and  runs  through  the  portal  canals  (Fig.  1093), 
enclosed  in  Glisson's  capsule,  dividing  in  its  course  into  branches,  which  finally  break  up  into  a 
plexus,  the  interlobular  plexus,  in  the  interlobular  spaces.    These  branches  receive  the  vaginal 

and  capsular  veins,  correspond- 
Hepatic  artery 


Bile-duct 


Lymphatic 
vessel 


ing  to  the  vaginal  and  capsular 
branches  of  the  hepatic  artery. 
Thus  it  will  be  seen  that  all  the 
blood  carried  to  the  liver  by  the 
portal  vein  and  hepatic  artery 
finds  its  way  into  the  interlob- 
ular plexus.  From  this  plexus 
the  blood  is  carried  into  the  lobule 
by  fine  branches  which  converge 
from   the  circumference   to  the 


Fig.  1093. — Section  across  portal  canal  of  pig.     X  250. 


Fig.   1094.^ — Bile   capillaries  of  rabbit, 
shown  by  Golgi's  method.     X  450. 


center  of  the  lobule,  and  are  connected  by  transverse  branches  (Fig.  1091).  The  wall3  of  these 
small  vessels  are  incomplete  so  that  the  blood  is  brought  into  direct  relationship  with  the  liver 
cells.  The  lining  endothelium  consists  of  irregularly  branched,  disconnected  cells  (stellale  cells  of 
Kupffer).  Moreover,  according  to  Herring  and  Simpson,  minute  channels  penetrate  the  liver  cells 
themselves,  conveying  the  constituents  of  the  blood  into  their  substance.  It  will  be  seen  that  the 
blood  capillaries  of  the  liver  lobule  differ  structurally  from  capillaries  elsewhere.  Developmentally 
they  are  formed  by  the  growth  of  the  columns  of  liver  cells  into  large  blood  spaces  or  sinuses, 
and  hence  they  have  received  the  name  of  "sinusoids."     Arrived  at  the  center  of  the  lobule, 


THE  LIVER 


il97 


Gall, 
bladder 


II 

II 


:the  sinusoids  empty  themselves  into  one  vein,  of  considerable  size,  which  runs  down  the 
center  of  the  lobule  from  apex  to  base,  and  is  called  the  intralobular  vein.  At  the  base  of 
the  lobule  this  vein  opens  directly  into  the  sublobular  vein,  with  which  the  lobule  is  con- 
nected. The  sublobular  veins  unite  to  form  larger  and  larger  trunks,  and  end  at  last  in  the 
hepatic  veins,  these  converge  to  form  three  large  trunks  which  open  into  the  inferior  vena  cava 
while  that  vessel  is  situated  in  its  fossa  on  the  posterior  surface  of  the  Uver. 

3.  The  bile  ducts  commence  by  little  passages  in  the  Uver  cells  which  communicate  with 
canahculi  termed  intercellular  biliary  passages  (bile  capillaries).  These  passages  are  merely 
little  channels  or  spaces  left  between  the  contiguous  surfaces  of  two  cells,  or  in  the  angle  where 
three  or  more  hver  cells  meet  (Fig.  1094),  and  they  are  always  separated  from  the  blood  capil- 
laries by  at  least  half  the  width  of  a  liver  cell.  The  channels  thus  formed  radiate  to  the  circum- 
ference of  the  lobule,  and  open  into  the  interlobular  bile  ducts  which  run  in  Glisson's  capsule, 
accompanying  the  portal  vein  and  hepatic  artery  (Fig.  1093).  These  join  with  other  ducts  to 
form  two  main  trunks,  which  leave  the  liver  at  the  transverse  fissure,  and  by  their  union  form 
the  hepatic  duct. 

Structure  of  the  Ducts. — The  walls  of  the  biUary  ducts  consist  of  a  connective-tissue  coat,  in 
which  ai'e  muscle  cells,  arranged  both  circularly  and  longitudinally,  and  an  epithelial  layer, 
consisting  of  short  columnar  cells  resting  on  a  distinct  basement  membrane. 

Excretory  Apparatus  of  the  Liver.— The  excretory  apparatus  of  the  Hver  con- 
sists of  (1)  the  hepatic  duct,  formed  by  the  junction  of  tlie  two  main  ducts,  which 
pass  out  of  the  liver  at  the  porta;  (2)  the  gall- 
bladder, which  serves  as  a  reservoir  for  the  bile; 
(3)  the  cystic  duct,  or  the  duct  of  the  gall-blad- 
der; and  (4)  the  common  bile  duct,  formed  b}^ 
the  junction  of  the  hepatic  and  cystic  ducts 

The  Hepatic  Duct  {ductus  hepaticus). — Two 
main  trunks  of  nearly  equal  size  issue  from 
the  liver  at  the  porta,  one  from  the  right,  the 
other  from  the  left  lobe;  these  unite  to  form 
the  hepatic  duct,  which  passes  downward  and 
to  the  right  for  about  4  cm.,  between  the  layers 
of  the  lesser  omentum,  where  it  is  joined  at 
an  acute  angle  by  the  cystic  duct,  and  so  forms 
the  common  bile  duct.  The  hepatic  duct  is 
accompanied  by  the  hepatic  artery  and  portal 
vein. 

The  GaU-bladder  {vesica  fellea)  (Fig.  1095). 
— The  gall-bladder  is  a  conical  or  pear-shaped 
musculomembranoiis  sac,  lodged  in  a  fossa  on 
the  under  surface  of  the  right  lobe  of  the  liver, 
and  extending  from  near  the  right  extremity  of 
the  porta  to  the  anterior  border  of  the  organ.  It 
is  from  7  to  10  cm.  in  length,  2.5  cm.  in  breadth  at 
its  widest  part,  and  holds  from  30  to  35  c.c.  It  is 
divided  into  a  fundus,  body,  and  neck.  The 
fimdus,  or  broad  extremity,  is  directed  down- 
ward, forward,  and  to  the  right,  and  projects 
beyond  the  anterior  border  of  the  liver;  the 
body  and  neck  are  directed  upward  and  back- 
ward to  the  left.  The  upper  surface  of  the  gall- 
bladder is  attached  to  the  liver  by  connective 
tissue  and  vessels.  The  under  surface  is  covered  by  peritoneum,  which  is  reflected 
on  to  it  from  the  surface  of  the  liver.  Occasionally  the  whole  of  the  organ  is 
invested  by  the  serous  membrane,  and  is  then  connected  to  the  liver  by  a  kind 
of  mesentery. 

Relations. — The  body  is  in  relation,  by  its  upper  surface,  with  the  liver;  by  its  under  surface, 
with  the  commencement  of  the  transverse  colon;  and  farther  back  usually  with  the  upper  end 


Hepatic 
duct 


Common  bile- 
dvjct 


Fig.   1095. — The  gall-bladder  and  bile  ducts 
laid  open.      (Spalteholz.) 


B^ 


1198 


SPLANCHNOLOGY 


of  the  descending  portion  of  the  duodenum,  but  sometimes  with  the  superior  portion  of  the 
duodenum  or  pyloric  end  of  the  stomach.  The  fundus  is  completely  invested  by  peritoneum; 
it  is  in  relation,  in  front,  with  the  abdominal  parietes,  immediately  below  the  ninth  costal  car- 
tilage; behind  with  the  transverse  colon.  The  neck  is  narrow,  and  curves  upon  itself  like  the 
letter  S;  at  its  point  of  connection  with  the  cystic  duct  it  presents  a  well-marked  constriction. 


Columnar  epithelium 


-^ Fihro-muscvlar 

coat 


Liver-cells 


Fig.  1096. — Transverse  section  of  gall-bladder. 

Structure (  Fig.  10;)6). — The  gall-bladder  consists  of  three  coats:  serous,  fibromuscular,  and 
mucous. 

The  external  or  serous  coat  (tunica  serosa  vesicee  felleoe)  is  derived  from  the  peritoneum;  it 
completely  invests  the  fundus,  but  covers  the  body  and  neck  only  on  their  under  surfaces. 

The  fibromuscular  coat  (tunica  muscularis  vesicae  fellece),  a  thin  but  strong  layer  forming  the 
frame-work  of  the  sac,  consists  of  dense  fibrous  tissue,  which  interlaces  in  all  directions,  and  is 
mixed  with  plain  muscular  fibers,  disposed  chiefly  in  a  longitudinal  direction,  a  few  running 
transversely. 

The  internal  or  mucous  coat  (tunica  mucosa  vesicae  fellece)  is  loosely  connected  with  the  fibrous 
layer.  It  is  generally  of  a  yellowish-brown  color,  and  is  elevated  into  minute  rugae.  Opposite 
the  neck  of  the  gall-bladder  the  mucous  membrane  projects  inward  in  the  form  of  oblique  ridges 
or  folds,  forming  a  sort  of  spiral  valve. 

The  mucous  membrane  is  continuous  through  the  hepatic  duct  with  the  mucous  membrane 
lining  the  ducts  of  the  Mver,  and  through  the  common  bile  duct  with  the  mucous  membrane  of 
the  duodenum.  It  is  covered  with  columnar  epithelium,  and  secretes  mucin;  in  some  animals 
it  secretes  a  nucleoprotein  instead  of  mucin. 

The  Cystic  Duct  (ductus  cysticus). — The  cystic  duct  about  4  cm.  long,  runs  back- 
ward, downward,  and  to  the  left  from  the  neck  of  the  gall-bladder,  and  joins  the 
hepatic  duct  to  form  the  common  bile  duct.  The  mucous  membrane  lining  its 
interior  is  thrown  into  a  series  of  crescentic  folds,  from  five  to  twelve  in  number, 
similar  to  those  found  in  the  neck  of  the  gall-bladder.  They  project  into  the  duct 
in  regular  succession,  and  are  directed  obliquely  around  the  tube,  presenting 
much  the  appearance  of  a  continuous  spiral  valve.  When  the  duct  is  distended, 
the  spaces  between  the  folds  are  dilated,  so  as  to  give  to  its  exterior  a  twisted 
appearance. 

The  Common  Bile  Duct  (ductus  choledochu^) . — The  common  bile  duct  is  formed 
by  the  junction  of  the  cystic  and  hepatic  ducts;  it  is  about  7.5  cm.  long,  and  of  the 
diameter  of  a  goose-quill. 

It  descends  along  the  right  border  of  the  lesser  omentum  behind  the  superior 
portion  of  the  duodenum,  in  front  of  the  portal  vein,  and  to  the  right  of  the  hepatic 
artery;  it  then  runs  in  a  groove  near  the  right  border  of  the  posterior  surface  of  the 
head  of  the  pancreas;  here  it  is  situated  in  front  of  the  inferior  vena  cava,  and  is 
occasionally  completely  imbedded  in  the  pancreatic  substance.  At  its  termination 
it  lies  for  a  short  distance  along  the  right  side  of  the  terminal  part  of  the  pancreatic 
duct  and  passes  with  it  obliquely  between  the  mucous  and  muscular  coats.    The 


THl 


1199 


li 


wo  ducts  unite  and  open  by  a  common  orifice  upon  the  summit  of  the  duodenal 
papilla,  situated  at  the  medial  side  of  the  descending  portion  of  the  duodenum,  a 
little  below  its  middle  and  about  7  to  10  cm.  from  the  pylorus  (Fig.  1100).  The 
short  tube  formed  by  the  union  of  the  two  ducts  is  dilated  into  an  ampulla,  the 
ampulla  of  Vater. 


Structure. — The  coats  of  the  large  biliary  ducts  are  an  external  or  fibrous,  and  an  internal  or 
mucous.  The  fibrous  coat  is  composed  of  strong  fibroareolar  tissue,  with  a  certain  amount  of 
muscular  tissue,  arranged,  for  the  most  part,  in  a  circular  manner  aroimd  the  duct.  The  mucous 
coat  is  continuous  with  the  lining  membrane  of  the  hepatic  ducts  and  gall-bladder,  and  also  with 
that  of  the  duodenum;  and,  hke  the  mucous  membrane  of  these  structures,  its  epithelium  is  of  • 
the  columnar  variety.  It  is  provided  with  numerous  mucous  glands,  which  are  lobulated  and 
open  by  minute  orifices  scattered  irregularly  in  the  larger  ducts. 


h. 


The  Pancreas  (Figs.  1097,  1098). 


e  pancreas  is  a  compound  racemose  gland,  analogous  in  its  structures  to  the 
salivary  glands,  though  softer  and  less  compactly  arranged  than  those  organs. 
Its  secretion,  the  pancreatic  juice,  carried  by  the  pancreatic  duct  to  the  duodenum, 
is  an  important  digestive  fluid.  In  addition  the  pancreas  has  an  important  internal 
secretion,  proba'bly  elaborated  by  the  cells  of  Langerhans,  which  is  taken  up  by 
the  blood  stream  and  is  concerned  with  sugar  metabolism.    It  is  long  and  irregularly 

Eighth  costal  Cartilage 

Seventh  costal,  cartilage 


Seventh  rib 


Eighth 
rib 


Ninth 
rib 


Tenth  rib 


Diaphragm 


Abdominal  aorta 


Twelfth  rib 


Eleventh  rib 


Fig.  1097. 


1^ 


-Transverse  section  through  the  middle  of  the  first  lumbar  vertebra,  showing  the  relations  of  the  pancreas. 

(Braune.) 


prismatic  in  shape;  its  right  extremity,  being  broad,  is  called  the  head,  and  is  con- 
nected to  the  main  portion  of  the  organ,  or  body,  by  a  slight  constriction,  the  neck; 
while  its  left  extremity  gradually  tapers  to  form  the  tail.  It  is  situated  transversely 
across  the  posterior  wall  of  the  abdomen,  at  the  back  of  the  epigastric  and  left 
hypochondriac  regions.  Its  length  varies  from  12.5  to  15  cm.,  and  its  weight  from 
60  to  100  gm. 


B 


1200 


SPLANCHNOLOGY 


Relations. — The  Head  {caput  iiancreatis)  is  flattened  from  before  backward,  and 
is  lodged  within  the  curve  of  the  duodenum.  Its  upper  border  is  overlapped  by  the 


Fig.  1098. — The  duodenum  and  pancreas. 


superior  part  of  the  duodenum  and  its  lower  overlaps  the  horizontal  part;  its  right 
and  left  borders  overlap  in  front,  and  insinuate  themselves  behind,  the  descending 


Celiac  artery 


Superior  mesenteric  artery 


Area  for  Diaphragm 

Fig.   1099. — The  pancreas  and  duodenum  from  behind.     (From  model  by  His.) 

and  ascending  parts  of  the  duodenum  respectively.    The  angle  of  junction  of  the 
lower  and  left  lateral  borders  forms  a  prolongation,  termed  the  uncinate  process.    In 


Ik 


THE  PANCREAS  — ^^^— f  j201 

the  groove  between  the  duodenum  and  the  right  lateral  and  lower  borders  in  front 
are  the  anastomosing  superior  and  inferior  pancreaticoduodenal  arteries;  the  com- 
mon bile  duct  descends  behind,  close  to  the  right  border,  to  its  termination  in  the 
descending  part  of  the  duodenum. 

Anterior  Surface. — The  greater  part  of  the  right  half  of  this  surface  is  in  contact 
with  the  transverse  colon,  only  areolar  tissue  intervening.  From  its  upper  part 
the  neck  springs,  its  right  limit  being  marked  by  a  groove  for  the  gastroduodenal 
artery.  The  lower  part  of  the  right  half,  below  the  transverse  colon,  is  covered 
by  peritoneum  continuous  with  the  inferior  layer  of  the  transverse  mesocolon, 
and  is  in  contact  with  the  coils  of  the  small  intestine.  The  superior  mesenteric 
artery  passes  down  in  front  of  the  left  half  across  the  uncinate  process;  the  superior 
mesenteric  vein  runs  upward  on  the  right  side  of  the  artery  and,  behind  the  neck, 
joins  with  the  lienal  vein  to  form  the  portal  vein. 

Posterior  Surface. — The  posterior  surface  is  in  relation  with  the  inferior  vena 
cava,  the  common  bile  duct,  the  renal  veins,  the  right  cms  of  the  diaphragm,  and 
the  aorta. 

The  Neck  springs  from  the  right  upper  portion  of  the  front  of  the  head.  It  is 
about  2.5  cm.  long,  and  is  directed  at  first  upward  and  forward,  and  then  upward 
and  to  the  left  to  join  the  body;  it  is  somewhat  flattened  from  above  downward 
and  backward.  Its  antero-superior  surface  supports  the  pylorus;  its  postero- 
inferior  surface  is  in  relation  with  the  commencement  of  the  portal  vein;  on  the 
right  it  is  grooved  by  the  gastroduodenal  artery. 

The  Body  (corpus  yancreatw)  is  somewhat  prismatic  in  shape,  and  has  three 
surfaces:  anterior,  posterior,  and  inferior. 

The  anterior  surface  (fades  anterior)  is  somewhat  concave;  and  is  directed  for- 
ward and  upward:  it  is  covered  by  the  postero-inferior  surface  of  the  stomach 
which  rests  upon  it,  the  two  organs  being  separated  by  the  omental  bursa.  Where 
it  joins  the  neck  there  is  a  well-marked  prominence,  the  tuber  omentale,  which 
abuts  against  the  posterior  surface  of  the  lesser  omentum. 

The  posterior  surface  (fades  posterior)  is  devoid  of  peritoneum,  and  is  in  contact 
with  the  aorta,  the  lienal  vein,  the  left  kidney  and  its  vessels,  the  left  suprarenal 
gland,  the  origin  of  the  superior  mesenteric  artery,  and  the  crura  of  the  diaphragm. 

The  inferior  surface  (fades  inferior)  is  narrow  on  the  right  but  broader  on  the  left, 
and  is  covered  by  peritoneum;  it  lies  upon  the  duodenojejunal  flexure  and  on  some 
coils  of  the  jejunum;  its  left  extremity  rests  on  the  left  colic  flexure. 

The  superior  border  (mar go  superior)  is  blunt  and  flat  to  the  right;  narrow  and 
sharp  to  the  left,  near  the  tail.  It  commences  on  the  right  in  the  omental  tuber- 
osity, and  is  in  relation  with  the  celiac  artery,  from  which  the  hepatic  artery 
courses  to  the  right  just  above  the  gland,  while  the  lienal  artery  runs  toward  the 
left  in  a  groove  along  this  border. 

The  anterior  border  (mar go  anterior)  separates  the  anterior  from  the  inferior 
surface,  and  along  this  border  the  two  layers  of  the  transverse  mesocolon  diverge 
from  one  another;  one  passing  upward  over  the  anterior  surface,  the  other 
backward  over  the  inferior  surface. 

The  inferior  border  (margo  inferior)  separates  the  posterior  from  the  inferior 
surface ;  the  superior  mesenteric  vessels  emerge  under  its  right  extremity. 

The  Tail  (cauda  pancreaiis)  is  narrow;  it  extends  to  the  left  as  far  as  the  lower 
part  of  the  gastric  surface  of  the  spleen,  lying  in  the  phrenicolienal  ligament, 
and  it  is  in  contact  with  the  left  colic  flexure.    . 

Birmingham  described  the  body  of  the  pancreas  as  projecting  forward  as  a  promi- 
nent ridge  into  the  abdominal  cavity  and  forming  part  of  a  shelf  on  which  the 
stomach  lies.  "The  portion  of  the  pancreas  to  the  left  of  the  middle  line  has  a 
very  considerable  antero-posterior  thickness;  as  a  result  the  anterior  surface  is  of 
considerable  extent;  it  looks  strongly  upward,  and  forms  a  large  and  important 
76 


1202 


SPLANCHNOLOGY 


part  of  the  sl>elf .  As  the  pancreas  extends  to  the  left  toward  the  spleen  it  crosses 
the  upper  part  of  the  kidney,  and  is  so  moulded  on  to  it  that  the  top  of  the  kidney 
forms  an  extension  inward  and  backward  of  the  upper  surface  of  the  pancreas 
and  extends  the  bed  in  this  direction.  On  the  other  hand,  the  extremity  of  the 
pancreas  comes  in  contact  with  the  spleen  in  such  a  way  that  the  plane  of  its 
upper  surface  runs  with  little  interruption  upward  and  backward  into  the  concave 
gastric  surface  of  the  spleen,  which  completes  the  bed  behind  and  to  the  left,  and, 
running  upward,  forms  a  partial  cap  for  the  wide  end  of  the  stomach.^ 

Hepatic  artery 
Portal  vein 
Common  hile-diict 
Orifice    of    common 
bile-dvct  ana  pan-  P-II^B     Accessory  pancreatic  duct 

creattc  duct  ...m/iwmm'K'T^WBM  ,    „  .■    j    _. 

Pancreatic  duct 


The  Pancreatic  Duct  {ductus  pancreaticus  [Wirsungi];  dv^t  of  Wirsung)  extends 
transversely  from  left  to  right  through  the  substance  of  the  pancreas  (Fig.  1 100) .  It 
commences  by  the  junction  of  the  small  ducts  of  the  lobules  situated  in  the  tail  of  the 
pancreas,  and,  running  from  left  to  right  through  the  body,  it  receives  the  ducts  of  the 
various  lobules  composing  the  gland.  Considerably  augmented  in  size,  it  reaches  the 
neck,  and  turning  downward,  backward,  and  to  the  right,  it  comes  into  relation  with 
the  common  bile  duct,  which  lies  to  its  right  side;  leaving  the  head  of  the  gland, 
it  passes  very  obliquely  through  the  mucous  and  muscular  coats  of  the  duodenum, 
and  ends  by  an  orifice  common  to  it  and  the  common  bile  duct  upon  the  summit 
of  the  duodenal  papilla,  situated  at  the  medial  side  of  the  descending  portion 
of  the  duodenum,  7.5  to  10  cm.  below  the  pylorus.  The  pancreatic  duct,  near  the 
duodenum,  is  about  the  size  of  an  ordinary  quill.  Sometimes  the  pancreatic  duct 
and  the  common  bile  duct  open  separately  into  the  duodenum.  Frequently  there 
is  an  additional  duct,  which  is  given  off  from  the  pancreatic  duct  in  the  neck  of 
the  pancreas  and  opens  into  the  duodenum  about  2.5  cm.  above  the  duodenal 
papilla.  It  receives  the  ducts  from  the  lower  part  of  the  head,  and  is  known  as 
the  accessory  pancreatic  duct  (duct  of  Santorini). 

Development  (Figs.  1101,  1102).— The  pancreas  is  developed  in  two  parts,  a 
dorsal  and  a  ventral.    The  former  arises  as  a  diverticulum  from  the  dorsal  aspect 


'  Journal  of  Anatomy  and  Physiology,  pt.  1,  xxxi,  102. 


THE  PANCREAS 


1203 


of  the  duodenum  a  short  distance  above  the  hepatic  diverticulum,  and,  growing 
upward  and  backward  into  the  dorsal  mesogastrium,  forms  a  part  of  the  head  and 
uncinate  process  and  the  whole  of  the  body  and  tail  of  the  pancreas.  The  ventral 
part  appears  in  the  form  of  a  diverticulum  from  the  primitive  bile-duct  and  forms 
the  remainder  of  -the  head  and  uncinate  process  of  the  pancreas.  The  duct  of 
the  dorsal  part  (accessory  pancreatic  duct)  therefore  opens  independently  into  the 
duodenum,  while  that  of  the  ventral  part  (pancreatic  duct)  opens  with  the  common 
bile-duct.     About  the  si^th  week  the  two  parts  of  the  pancreas  meet  and  fuse 


Accessory  pancreatic  duel 
Dorsal  pancreas 


Ventral  jjancreas 
Pancreatic  duct 
Bile  duct 

Fig.   1101. — Pancreas  of  a  human  embryo  of  five 
weeks.     (KoUmann.) 


Accessory  pancreatic  duct 
Dorsal  pancreas 


Fig.  1102. 


Ventral  pancreas 
Pancreatic  duct 

-Pancreas  of  a  human  embryo  at  end  of 
sixth  week.     (KoUmann.) 


and  a  communication  is  established  between  their  ducts.  After  this  has  occurred 
the  terminal  part  of  the  accessory  duct,  i.  e.,  the  part  between  the  duodenum  and 
the  point  of  meeting  of  the  two  ducts,  undergoes  little  or  no  enlargement,  while 
the  pancreatic  duct  increases  in  size  and  forms  the  main  duct  of  the  gland.  The 
opening  of  the  accessory  duct  into  the  duodenum  is  sometimes  obliterated,  and 
even  when  it  remains  patent  it  is  probable  that  the  whole  of  the  pancreatic  secretion 
is  conveyed  through  the  pancreatic  duct. 


Liver      Stomach 


Lesser 
omentum  Liver 


Left  suprarenal 
gland 


Eight  suprarerwl 
gland 


k 


Fig.  1103. — Schematic  and  enlarged  cross-section  through  the  body  of  a  human  embryo  in  the  region  of  the 
mesogastrium.     Beginning  of  third  month.     (Toldt.) 

At  first  the  pancreas  is  directed  upward  and  backward  between  the  two  layers 
of  the  dorsal  mesogastrium,  which  give  to  it  a  complete  peritoneal  investment, 
and  its  surfaces  look  to  the  right  and  left.  With  the  change  in  the  position  of  the 
stomach  the  dorsal  mesogastrium  is  drawn  downward  and  to  the  left,  and  the  right 
side  of  the  pancreas  is  directed  backward  and  the  left  forward  (Fig.  1103).  The 
right  surface  becomes  applied  to  the  posterior  abdominal  wall,  and  the  peritoneum 
which  covered  it  undergoes  absorption  (Fig.  1104);  and  thus,  in  the  adult,  the  gland 
appears  to  lie  behind  the  peritoneal  cavity. 

Structure  (Fig.  1105). — In  structure,  the  pancreas  resembles  the  saHvary  glands.  It  differs 
from  them,  however,  in  certain  particulars,  and  is  looser  and  softer  in  its  texture.  It  is  not 
enclosed  in  a  distinct  capsule,  but  is  surrounded  by  areolar  tissue,  which  dips  into  its  interior, 


1204 


SPLANCHNOLOGY 


and  connects  together  the  various  lobules  of  which  it  is  composed.  Each  lobule,  like  the  lobules 
of  the  sahvary  glands,  consists  of  one  of  the  ultimate  ramifications  of  the  main  duct,  ending  in  a 
number  of  cecal  pouches  or  alveoli,  which  are  tubular  and  somewhat  convoluted.  The  minute 
ducts  connected  with  the  alveoli  are  narrow  and  lined  with  flattened  cells.     The  alveoli  are 


Liver 


Liver 


Bight  suprarenal  gland 


Left  suprarenal  gland 


Cell-islet 


Fig.   1104. — Section  through  same  region  as  in  Fig.  1103,  at  end  of  third  month.     (Toldt.) 

almost  completely  filled  with  secreting  cells,  so  that  scarcely  any  lumen  is  visible.  In  some 
animals  spindle-shaped  cells  occupy  the  center  of  the  alveolus  and  are  known  as  the  centro- 
acinar  cells  of  Langerhans.  These  are  prolongations  of  the  terminal  ducts.  The  true  secreting 
cells  which  lire  the  wall  of  the  alveolus  are  very  characteristic.     They  are  columnar  in  shape 

and  present  two  zones :   an  outer  one,  clear 
Alveolus  and  finely  striated  next  the  basement  mem- 

brane, and  an  inner  granular  one  next  the 
liunen.  In  hardened  specimens  the  outer 
zone  stains  deeply  with  various  dyes,  where- 
as the  inner  zone  stains  slightly.  During 
activity  the  granular  zone  gradually  dimin- 
ishes in  size,  and  when  exhausted  is  only 
seen  as  a  smaU  area  next  to  the  lumen. 
During  the  resting  stages  it  gradually  in- 
creases until  it  forms  nearly  three-fourths 
of  the  ceU.  In  some  of  the  secreting  cells 
of  the  pancreas  is  a  spherical  mass,  stain- 
ing more  easily  than  the  rest  of  the  cell; 
this  is  termed  the  paranucleus,  and  is  be- 
lieved to  be  an  extension  from  the  nucleus. 
The  connective  tissue  between  the  alveoli 
presents  in  certain  parts  collections  of  cells, 
which  are  termed  interalveolar  cell  islets 
(islands  of  Langerhans).  The  cells  of  these 
stain  lightly  with  hematoxylin  or  carmine, 
and  are  more  or  less  polyhedral  in  shape, 
forming  a  net-work  in  which  ramify  many 
capillaries.  There  are  two  main  types  of  cell  in  the  islets,  distinguished  as  A-cells  and  B-cells 
according  to  the  special  staining  reactions  of  the  granules  they  contain.  The  cell  islets  have 
been  supposed  to  produce  the  internal  secretion  of  the  pancreas  which  is  necessarj'  for  carbo- 
hydrate metabolism,  but  numerous  researches  have  so  far  failed  to  elucidate  their  real  function. 
The  walls  of  the  pancreatic  duct  are  thin,  consisting  of  two  coats,  an  external  fibrous  and  an 
internal  mucous;  the  latter  is  smooth,  and  furnished  near  its  termination  with  a  few  scattered 
foUicles. 

Vessels  and  Nerves.  —  The  arteries  of  the  pancreas  are  derived  from  the  lienal,  and  the 
pancreaticoduodenal  branches  of  the  hepatic  and  superior  mesenteric.  Its  veins  open  into  the 
lienal  and  superior  mesenteric  veins.  Its  lymphatics  are  described  on  page  711.  Its  nerves  are 
filaments  from  the  lienal  plexus. 


Fig.  1105. — Section  of  pancreas  of  dog.      X  250. 


THE  UROGENITAL  APPARATUS   (APPARATUS  UROGENITALIS ; 
UROGENITAL   ORGANS). 

The  urogenital  apparatus  consists  of  (a)  the  urinary  organs  for  the  secretion 
and  discharge  of  the  urine,  and  (6)  the  genital  organs,  which  are  concerned  with 
the  process  of  reproduction. 


I 


DEVELOPMENT  OF  THE  URINARY  AND  GENERATIVE  ORGANS     1205 


I 
I 


DEVELOPMENT  OF  THE  URINARY  AND  GENERATIVE  ORGANS. 

The  urinary  and  generative  organs  are  developed  from  the  intermediate  cell- 
mass  which  is  situated  between  the  primitive  segments  and  the  lateral  plates  of 
mesoderm.  The  permanent  organs  of  the  adult  are  preceded  by  a  set  of  structures 
which  are  purely  embryonic,  and  which  with  the  exception  of  the  ducts  disappear 
almost  entirely  before  the  end  of  fetal  life.  These  embryonic  structures  are  on 
either  side ;  the  pronephros,  the  mesonephros,  the  metanephros,  and  the  Wolffian  and 
Mullerian  ducts.  The  pronephros  disappears  very  early;  the  structural  elements 
of  the  mesonephros  mostly  degenerate,  but  in  their  place  is  developed  the  genital 
gland  in  association  with  which  the  Wolffian  duct  remains  as  the  duct  of  the  male 
genital  gland,  the  Mullerian  as  that  of  the  female;  some  of  the  tubules  of  the 
metanephros  form  part  of  the  permanent  kidney. 

The  Pronephros  and  Wolffian  Duct. — In  the  outer  part  of  the  intermediate 
cell-mass,  immediately  under  the  ectoderm,  in  the  region  from  the  fifth  cervical  to 
the  third  thoracic  segments,  a  series  of  short  evaginations  from  each  segment  grows 
dorsalward  and  extends  caudalward,  fusing  successively  from  before  backward  to 
form  the  pronephric  duct.  This  continues  to  grow  caudalward  until  it  opens  into 
the  ventral  part  of  the  cloaca;  beyond  the  pronephros  it  is  termed  the  Wolffian  duct. 

The  original  evaginations  form  a  series  of  transverse  tubules  each  of  which  com- 
municates by  means  of  a  funnel-shaped  ciliated  opening  with  the  celomic  cavity, 
and  in  the  course  of  each  duct  a  glomerulus  also  is  developed.  A  secondary 
glomerulus  is  formed  ventral  to  each  of  these,  and  the  complete  group  constitutes 
the  pronephros.    The  pronephros  undergoes  rapid  atrophy  and  disappears. 


Wolffian  duct 

_,  Mullerian  duct 


"~~i»  Wolffian  tubides 


fStroma 
G€7iitalJ      of  ovary— - 
ridge    j  Primitive 

t      ova 


Body-wall 

\  \11\\|H  ^'^S^'^  f/ll 

Mesentery-—"— 

Fig.   1106. — Section  of  the  urogenital  fold  of  a  chick  embryo  of  the  fourth  day.     (Waldeyer.) 


B 


The  Mesonephros,  Mullerian  Duct,  and  Genital  Gland. — On  the  medial  side  of 
the  Wolffian  duct,  from  the  sixth  cervical  to  the  third  lumbar  segments,  a  series 
of  tubules,  the  Wolffian  tubules  (Fig.  1106),  is  developed;  at  a  later  stage  in  develop- 
ment they  increase  in  number  by  outgrowths  from  the  original  tubules.  These 
tubules  first  appear  as  solid  masses  of  cells,  which  later  become  hollowed  in  the 
center;  one  end  grows  toward  and  finally  opens  into  the  Wolffian  duct,  the  other 
dilates  and  is  invaginated  by  a  tuft  of  capillary  bloodvessels  to  form  a  glomerulus. 
The  tubules  collectively  constitute  the  mesonephros  or  Wolffian  body  (Figs.  986, 


1206 


SPLANCHNOLOGY 


1107).  By  the  fifth  or  sixth  week  this  body  forms  an  elongated  spindle-shaped 
structure,  termed  the  urogenital  fold  (Fig.  1106),  which  projects  into  the  celomic 
cavity  at  the  side  of  the  dorsal  mesentery,  reaching  from  the  septum  transversum 
in  front  to  the  fifth  lumbar  segment  behind;  in  this  fold  the  reproductive  glands  are  ]H 
developed.  The  Wolffian  bodies  persist  and  form  the  permanent  kidneys  in  fishes  ™ 
and  amphibians,  but  in  reptiles,  birds,  and  mammals,  they  atrophy  and  for  the 
most  part  disappear  coincidently  with  the  development  of  the  permanent  kidneys. 
The  atrophy  begins  during  the  sixth  or  seventh  week  and  rapidly  proceeds,  so  that 
by  the  beginning  of  the  fifth  month  only  the  ducts  and  a  few  of  the  tubules  remain.  iH 

In  the  male  the  Wolffian  duct  persists, 
and  forms  the  tube  of  the  epididymis,  the 
ductus  deferens  and  the  ejaculatory  duct, 
while  the  seminal  vesicle  arises  during  the 
third  month  as  a  lateral  diverticulum  from 
its  hinder  end.  A  large  part  of  the  head 
end  of  the  mesonephros  atrophies  and  dis- 
appears; of  the  remainder  the  anterior 
tubules  form  the  efferent  ducts  of  the 
testis;  while  the  posterior  tubules  are 
represented  by  the  ductuli  aberrantes, 
and  by  the  paradidymis,  which  is  some- 
times found  in  front  of  the  spermatic 
cord  above  the  head  of  the  epididymis 
(Fig.  1110-,  C). 
In  the  female  the  Wolffian  bodies  and  ducts  atrophy.  The  remains  of  the 
Wolffian  tubules  are  represented  by  the  epoophoron  or  organ  of  RosenmuUer,  and 
the  paroophoron,  two  small  collections  of  rudimentary  blind  tubules  which  are 
situated  in  the  mesosalpinx  (Fig.  1108).  The  lower  part  of  the  Wolffian  duct 
disappears,  while  the  upper  part  persists  as  the  longitudinal  duct  of  the  epoophoron 
or  duct  of  Gartner^  (Fig.  1110,  B). 


Fig.  1107. — Enlarged  view  from  the  front  of  the 
left  Wolffian  body  before  the  establishment  of  the 
distinction  of  sex.  (From  Farre,  after  Kobelt.)  a, 
a,  b,  c,  d.  Tubular  structure  of  the  Wolffian  body. 
e.  Wolffian  duct.  /.  Its  upper  extremity,  g.  Its 
termination  in  x,  the  urogenital  sinus,  h.  The  duct 
of  Miiller.  i.  Its  upper,  funnel-shaped  extremity. 
k.  Its  lower  end,  terminating  in  the  urogenital  sinus. 
I.  The  genital  gland. 


FiQ.  1108. — Broad  ligament  of  adult,  showing  epoophoron.  (From  Farre,  after  Kobelt.)  a,  a.  Epoophoron  formed 
from  the  upper  part  of  the  Wolffian  body.  b.  Remains  of  the  uppermost  tubes  sometimes  forming  appendices,  c.  Middle 
set  of  tubes,  d.  Some  lower  atrophied  tubes,  e.  Atrophied  remains  of  the  Wolffian  duct.  /.  The  terminal  bulb  or 
hydatid,    h.  The  uterine  tube,  originally  the  duct  of  Miiller:    t.  Appendix  attached  to  the  extremity.    /.  The  ovary. 

The  MuUerian  Ducts. — Shortly  after  the  formation  of  the  Wolffian  ducts  a 
second  pair  of  ducts  is  developed;  these  are  named  the  Miillerian  ducts.  Each 
arises  on  the  lateral  aspect  of  the  corresponding  Wolffian  duct  as  a  tubular  invag- 

>  Berry  Hart  {op.  cit.)  has  described  the  Wolffian  ducts  as  ending  at  the  site  of  the  future  hymen  in  bulbous  enlarge- 
ments, which  he  has  named  the  Wolffian  bulbs;  and  states  that  the  hymen  is  formed  by  these  bulbs,  "aided  by  a  special 
involution  from  below  of  the  cells  lining  the  urogenital  sinus.  "  He  further  believes  that  "the  lower  third  of  the  vagina 
is  due  to  the  coalescence  of  the  upper  portion  of  the  urogenital  sinus  and  the  lower  ends  of  the  Wolffian  ducts, '  and 
that  "the  epithelial  lining  of  the  vagina  is  derived  from  the  Wolffian  bulbs. "  He  also  regards  the  colUculus  seminaus- 
of  the  male  urethra  as  being  formed  from  the  lower  part  of  the  Wolffian  ducts. 


DEVELOPMENT  OF  THE  URINARY  AND  GENERATIVE  ORGANS    1207 

ination  of  the  cells  lining  the  celom  (Fig.  1106).  The  orifice  of  the  invagination 
remains  patent,  and  undergoes  enlargement  and  modification  to  form  the  abdomi- 
nal ostium  of  the  uterine  tube.  The  ducts  pass  backward  lateral  to  the  Wolffian 
ducts,  but  toward  the  posterior  end  of  the  embryo  they  cross  to  the  medial  side 
of  these  ducts,  and  thus  come  to  lie  side  by  side  between  and  behind  the  latter — 
the  four  ducts  forming  what  is  termed  the  genital  cord  (Fig.  1109).  The  Miillerian 
ducts  end  in  an  epithelial  elevation,  the  Miillerian  eminence,  on  the  ventral  part  of 
the  cloaca  between  the  orifices  of  the  Wolfiian 

ducts;  at  a  later  date  they  open  into  the  cloaca  Mulhrian  dvcts 

in  this  situation. 

In  the  male  the  Miillerian  ducts  atrophy, 
but  traces  of  their  anterior  ends  are  repre- 
sented by  the  appendices  testis  {hydatids  of 
Morgagni),  while  their  terminal  fused  portions 
form  the  utriculus  in  the  floor  of  the  prostatic 
portion  of  the  urethra  (Fig.  1110,  C). 

In  the  female  the  Miillerian  ducts  persist 
and  undergo  further  development.  The  por- 
tions which  lie  in  the  genital  core  fuse  to  form 
the  uterus  and  vagina;  the  parts  in  front  of 
this  cord  remain  separate,  and  each  forms 
the  corresponding  uterine  tube — the  abdomi- 
nal   ostium    of    which     is    developed    from    the  Fig.  1109.— Urogenital  sinus  of  female  human 

anterior  extremity  of  the  original  tubular  in-  (From  m°^1i  by  Keibeo^"  *°  '''°'  "''^'  °''^- 
vagination  from  the  celom  (Fig.  1110,  5).    The 

fusion  of  the  Miillerian  ducts  begins  in  the  third  month,  and  the  septum  formed 
by  their  fused  medial  walls  disappears  from  below  upward,  and  thus  the  cavities 
of  the  vagina  and  uterus  are  produced.  About  the  fifth  month  an  annular  con- 
striction marks  the  position  of  the  neck  of  the  uterus,  and  after  the  sixth  month 
the  walls  of  the  uterus  begin  to  thicken.  For  a  time  the  vagina  is  represented  by  a 
solid  rod  of  epithelial  cells.  A  ring-like  outgrowth  of  this  epithelium  occurs  at 
[the  lower  end  of  the  uterus  and  marks  the  future  vaginal  fornices;  about  the  fifth 
or  sixth  month  the  lumen  of  the  vagina  is  produced  by  the  breaking  down  of  the 
central  cells  of  the  epithelium.  The  hymen  represents  the  remains  of  the  Miillerian 
eminence. 

Genital  Glands. — The  first  appearance  of  the  genital  gland  is  essentially  the 
same  in  the  two  sexes,  and  consists  in  a  thickening  of  the  epithelial  layer  which 
lines  the  peritoneal  cavity  on  the  medial  side  of  the  urogenital  fold  (Fig.  1106). 
The  thick  plate  of  epithelium  extends  deeply,  pushing  before  it  the  mesoderm  and 
forming  a  distinct  projection.  This  is  termed  the  genital  ridge  (Fig.  1106),  and  from 
it  the  testis  in  the  male  and  the  ovary  in  the  female  are  developed.  At  first  the 
mesonephros  and  genital  ridge  are  suspended  by  a  common  mesentery,  but  as  the 
embryo  grows  the  genital  ridge  gradually  becomes  pinched  off  from  the  meso- 
nephros, with  which  it  is  at  first  continuous,  though  it  still  remains  connected  to 
the  remnant  of  this  body  by  a  fold  of  peritoneum,  the  mesorchium  or  mesovarium 
(Fig.  1111).  About  the  seventh  week  the  distinction  of  sex  in  the  genital  ridge 
begins  to  be  perceptible. 

The  Ovary. — ^The  ovary,  thus  formed  from  the  genital  ridge,  is  at  first  a  mass 
of  cells  derived  from  the  celomic  epithelium;  later  the  mass  is  differentiated 
into  a  central  part  or  medulla  (Fig.  1112)  covered  by  a  surface  layer,  the  germinal 
epithelium.  Between  the  cells  of  the  germinal  epithelium  a  number  of  larger 
cells,  the  primitive  ova,  are  found,  and  these  are  carried  into  the  subjacent  stroma 
by  bud-like  ingrowths  (genital  cords)  of  the  germinal  epithelium  (Fig.  1113). 
The  surface  epithelium  ultimately  forms  the  permanent  epithelial  covering  of  this 


1208 


SPLANCHNOLOGY 


Fig.  Ill  0. — Diagrams  to  show  the  develop- 
ment of  male  and  female  generative  organs 
from  a  common  type.     (Allen  Thomson.) 


A. — Diagram  of  the  primitive  urogenital 
organs  in  the  embryo  previous  to  sexual  dis- 
tinction. 3.  Ureter.  4.  Urinary  bladder.  5. 
Urachus.  c^  Cloaca,  cp.  Elevation  which  be- 
comes clitoris  or  penis,  i.  Lower  part  of  the 
intestine.  Is.  Fold  of  integument  froni  which 
the  labia  majora  or  scrotum  are  formed, 
m,  m.  Right  and  left  MuUerian  ducts  uniting 
together  and  running  with  the  Wolffian  ducts 
in  gc,  the  genital  cord.  ot.  The  genital  ridge 
from  which  either  the  ovary  or  testis  is 
formed,  ug.  Sinus  urogenitalis.  W.  Left 
Wolffian  bodj'.  w,  w.  Right  and  left  WolflSan 
ducts. 


B. — Diagram  of  the  female  type  of  sexual 
organs.  C.  Greater  vestibular  gland,  and 
immediately  above  it  the  urethra,  cc.  Corpus 
cavernosum  clitoridis.  dG.  Remains  of  the 
left  Wolffian  duct,  such  as  give  rise  to  the 
duct  of  Gartner,  represented  by  dotted  lines; 
that  of  the  right  side  is  marked  w.  f.  The 
abdominal  opening  of  the  left  uterine  tube. 
g.  Round  ligament,  corresponding  to  guber- 
naculum.  h.  Situation  of  the  hymen,  i.  Lower 
part  of  the  intestine.  I.  Labium  major,  n. 
Labium  minus,  o.  The  left  ovary,  po.  Epo- 
ophoron.  sc.  Corpus  cavernosum  urethrae.  «. 
Uterus.  The  uterine  tube  of  the  right  side 
is  marked  m.  v.  Vulva,  va.  Vagina.  W. 
Scattered  remains  of  Wolffian  tubes  near  it 
(paroophoron  of  Waldeyer). 


C. — Diagram  of  the  male  type  of  sexual 
organs.  C.  Bulbo-urethral  gland  of  one  side. 
cp.  Corpora  cavernosa  penis  cut  short,  e. 
Caput  epididymis,  g.  The  gubernaculum. 
i.  Lower  part  of  the  intestine,  m.  Miillerian 
duct,  the  upper  part  of  which  remains  as 
the  hydatid  of  IVIorgagni;  the  lower  part, 
represented  by  a  dotted  line  descending  to 
the  prostatic  utricle,  constitutes  the  occa- 
sionally existing  cornu  and  tube  of  the  uterus 
masculinus.  pr.  The  prostate,  s.  Scrotuni, 
sp.  Corpus  cavernosum  urethrae.  t.  Testis 
in  the  place  of  its  original  formation,  t', 
together  with  the  dotted  lines  above,  indi- 
cates the  direction  in  which  the  testis  and 
epididymis  descend  from  the  abdomen  into 
the  scrotum,  vd.  Ductus  deferens,  yh.  Ductus 
aberrans.  vs.  The  vesicula  seminalis.  W. 
Scattered  remains  of  the  Wolffian  body,  con- 
stituting the  organ  of  Giraldds,  or  the  para- 
didymis of  Waldeyer. 


DEVELOPMENT  OF  THE  URINARY  AND  GENERATIVE  ORGANS     1209 


organ;  it  soon  loses  its  connection  with  the  central  mass,  and  a  tunica  albuginea 
develops  between  them.  The  ova  are  chiefly  derived  from  the  cells  of  the  central 
mass;  these  are  separated  from  one 
another  by  the  growth  of  connective 
tissue  in  an  irregular  manner;  each  ovum 
assumes  a  covering  of  connective  tissue 
(follicle)  cells,  and  in  this  way  the  rudi- 
ments of  the  ovarian  follicles  are  formed 
(Fig.  1113).  According  to  Beard  the 
primitive  ova  are  early  set  apart  during 
the  segmentation  of  the  ovum  and  migrate 
into  the  germinal  ridge. 


Wolffian  body 
MuUerian  duet 

Wolffian  duct 


Intestine 


Bladder 


Waldeyer  taught  that  the  primitive  germ 
cells  are  derived  from  the  "germinal  epithe- 
lium," covering  the  genital  ridge.  Beard/  on 
the  other  hand,  maintains  that  in  the  skate  they 
are  not  derived  from  this  epithelium,  but  are 
probably  formed  during  the  later  stages  of  cell 
cleavage,  before  there  is  any  trace  of  an  embryo; 
and  a  similar  view  was  advanced  by  Nussbaum 
as  to  their  origin  in  amphibia.  Beard  says:  "At 
the  close  of  segmentation  many  of  the  future 
germ  cells  he  in  the  segmentation  cavity  just 
beneath  the  site  of  the  future  embryo,  and  there 
is  no  doubt  they  subsequently  wander  into  it." 
The  germ   cells,  "after  they   enter  the  resting 

phase,  are  sharply  marked  off  from  the  cells  of  the  embryo  by  entire  absence  of  mitoses  among 
them."    They  can  be  further  recognized  by  their  irregular  form  and  ameboid  processes,  and  by 


Medulla  sjnnalis 

Spinal  ganglion 

Notoehord 

Sympathetic  ganglion 
Inferior  vena  cava 
Common  iliac  artery 
Ureter 
Mesovarium, 


Wmbilical  artery 


Fio.  1111. — Transverse  section  of  human  embryo  eight 
and  a  half  to  nine  weeks  old.    (From  model  by  Keibel.) 


Uterine  tube 


Germinal  epithelium -. 


Medvila  — 


Reie 


EpoSphoron 


Mesonephros 


Plica  peritonalis 
tuboe 


Uterine  tube 

Fia.  1112. — Longitudinal  section  of  ovary  of  cat  embryo  of  9.4  cm.  long.     Schematic.     (After  Coert.) 
'Journal  of  Anatomy  and  Phys  ology,  vol.  xxxviii. 


1210 


SPLANCHNOLOGY 


the  fact  that  their  cj^toplasm  has  no  affinity  for  ordinary  stains,  but  assumes  a  brownish  tinge 
when  treated  by  osmic  acid.  The  path  along  which  they  travel  into  the  embryo  is  a  very  definite 
one,  viz.,  "from  the  yolk  sac  upward  between  the  splanchnopleure  and  gut  in  the  hinder  portion 
of  the  embryo."  This  pathway,  named  by  Beard  the  germinal  path,  "leads  them  directly  to  the 
position  which  they  ought  finally  to  take  up  in  the  'germinal  ridge' or  nidus."  A  considerable 
number  apparently  never  reach  their  proper  destination,  since  "vagrant  germ  cells  are  found  in 
all  sorts  of  places,  but  more  particularly  on  the  mesentery."  Some  of  these  may  possibly  find 
their  way  into  the  germinal  ridge;  some  probably  undergo  atrophy,  while  others  may  persist 
and  become  the  seat  of  dermoid  tumors. 

Genital  cord 
I 


Germinal 
epithelium 

Primitive  ova 
Cell-nest 


Blood-vessel  - 
Ovarian  follicle  ■- 


Fia.  1113. — Section  of  the  ovary  of  a  newly  born  child.     (Waldeyer.) 


Tunica 
alhuginea 


.Interstitial 
cell 


The  Testis. — The  testis  is  developed  in  much  the  same  way  as  the  ovary.  Like 
the  ovary,  in  its  earhest  stages  it  consists  of  a  central  mass  of  epithelium  covered 
by  a  surface  epithelium.    In  the  central  mass  a  series  of  cords  appear  (Fig.  1114), 

and  the  periphery  of  the  mass  is  con- 
Epithelium  -"Tg-Tt-*r^,  _  _„  mrf^  verted  into  the  tunica  albuginea,  thus 

excluding  the  surface  epithelium  from 
any  part  in  the  formation  of  the 
tissue  of  the  testis.  The  cords  of 
the  central  mass  run  together  toward 
the  future  hilus  and  form  a  network 
which  ultimately  becomes  the  rete 
testis.  From  the  cords  the  seminifer- 
ous tubules  are  developed,  and  be- 
tween them  connective-tissue  septa 
extend.  The  seminiferous  tubules 
become  connected  with  outgrowths 
from  the  Wolffian  body,  which,  as 
before  mentioned,  form  the  efferent 
ducts  of  the  testis. 

Descent  of  the  Testes. — The  testes, 
at  an  early  period  of  fetal  life,  are 
placed  at  the  back  part  of  the  ab- 
dominal cavity,  behind  the  perito- 
neum, and  each  is  attached  by  a 
peritoneal  fold,  the  mesorchium,  to  the  mesonephros.  From  the  front  of  the  meso- 
nephros  a  fold  of  peritoneum  termed  the  inguinal  fold  grows  forward  to  meet  and 
fuse  with  a  peritoneal  fold,  the  inguinal  crest,  which  grows  backward  from  the 


Supporting 
cell 


^  Genital 
cell 


Fig 


1114. — Section  of  a  genital  cord  of  the  testis  of  a  human 
embryo  3.5  cm.  long.     (Felix  and  Biihler.) 


I 


DEVELOPMENT  OF  THE  URINARY  AND  GENERATIVE  ORGANS     1211 

antero-lateral  abdominal  wall.  The  testis  thus  acquires  an  indirect  connection 
with  the  anterior  abdominal  wall;  and  at  the  same  time  a  portion  of  the  peri- 
toneal cavity  lateral  to  these  fused  folds  is  marked  off  as  the  future  saccus  vagi- 
nalis. In  the  inguinal  crest  a  peculiar  structure,  the  gubemaculum  testis,  makes 
its  appearance.  This  is  at  first  a  slender  band,  extending  from  that  part  of  the 
skin  of  the  groin  which  afterward  forms  the  scrotum  through  the  inguinal 
canal  to  the  body  and  epididymis  of  the  testis.  As  development  advances,  the 
peritoneum  enclosing  the  gubernaculum  forms  tw^o  folds,  one  above  the  testis 
and  the  other  below  it.  The  one  above  the  testis  is  the  plica  vascularis,  and  con- 
tains ultimately  the  internal  spermatic  vessels;  the  one  below,  the  plica  guber- 
natrix,  contains  the  lower  part  of  the  gubernaculum,  which  has  now  grown  into 
a  thick  cord;  it  ends  below  at  the  abdominal  inguinal  ring  in  a  tube  of  peritoneum, 
the  saccus  vaginalis,  which  protrudes  itself  down  the  inguinal  canal.  By  the  fifth 
month  the  lower  part  of  the  gubernaculum  has  become  a  thick  cord,  while  the 
upper  part  has  disappeared.  The  lower  part  now  consists  of  a  central  core  of 
unstriped  muscle  fiber,  and  outside  this  of  a  firm  layer  of  striped  elements,  con- 
nected, behind  the  peritoneum,  with  the  abdominal  wall.  As  the  scrotum  develops, 
the  main  portion  of  the  lower  end  of  the  gubernaculum  is  carried,  with  the  skin 
to  which  it  is  attached,  to  the  bottom  of  this  pouch;  other  bands  are  carried  to 
the  medial  side  of  the  thigh  and  to  the  perineum.  The  tube  of  peritoneum  con- 
stituting the  saccus  vaginalis  projects  itself  downward  into  the  inguinal  canal, 
and  emerges  at  the  cutaneous  inguinal  ring,  pushing  before  it  a  part  of  the  Obliquus 
internus  and  the  aponeurosis  of  the  Obliquus  externus,  which  form  respectively 
the  Cremaster  muscle  and  the  intercrural  fascia.  It  forms  a  gradually  elongating 
pouch,  which  eventually  reaches  the  bottom  of  the  scrotum,  and  behind  this  pouch 
the  testis  is  drawn  by  the  growth  of  the  body  of  the  fetus,  for  the  gubernaculum 
does  not  grow  commensurately  with  the  growth  of  other  parts,  and  therefore 
the  testis,  being  attached  by  the  gubernaculum  to  the  bottom  of  the  scrotum, 
is  prevented  from  rising  as  the  body  grows,  and  is  drawn  first  into  the  inguinal 
canal  and  eventually  into  the  scrotum.  It  seems  certain  also  that  the  guber- 
nacular  cord  becomes  shortened  as  development  proceeds,  and  this  assists  in  caus- 
ing the  testis  to  reach  the  bottom  of  the  scrotum.  By  the  end  of  the  eighth  month 
the  testis  has  reached  the  scrotum,  preceded  by  the  saccus  vaginalis,  which  com- 
municates by  its  upper  extremity  with  the  peritoneal  cavity.  Just  before  birth 
the  upper  part  of  the  saccus  vaginalis  usually  becomes  closed,  and  this  obliteration 
extends  gradually  downward  to  within  a  short  distance  of  the  testis.  The  process 
of  peritoneum  surrounding  the  testis  is  now  entirely  cut  off  from  the  general  peri- 
toneal cavity  and  constitutes  the  tunica  vaginalis. 

Descent  of  the  Ovaries.— In  the  female  there  is  also  a  gubernaculum,'  which 
effects  a  considerable  change  in  the  position  of  the  ovary,  though  not  so  extensive 
a  change  as  in  that  of  the  testis.  The  gubernaculum  in  the  female  lies  in  contact 
with  the  fundus  of  the  uterus  and  contracts  adhesions  to  this  organ,  and  thus 
the  ovary  is  prevented  from  descending  below  this  level.  The  part  of  the  guber- 
naculum between  the  ovary  and  the  uterus  becomes  ultimately  the  proper  ligament 
of  the  ovary,  while  the  part  between  the  uterus  and  the  labium  majus  forms  the 
round  ligament  of  the  uterus.  A  pouch  of  peritoneum  analogous  to  the  saccus 
vaginalis  in  the  male  accompanies  it  along  the  inguinal  canal :  it  is  called  the  canal 
of  Nuck.  In  rare  cases  the  gubernaculum  may  fail  to  contract  adhesions  to  the 
uterus,  and  then  the  ovary  descends  through  the  inguinal  canal  into  the  labium 
majus,  and  under  these  circumstances  its  position  resembles  that  of  the  testis. 

The  Metanephros  and  the  Permanent  Kidney.— The  rudiments  of  the  perma- 
nent kidneys  make  their  appearance  about  the  end  of  the  first  or  the  beginning 
of  the  second  month.  Each  kidney  has  a  two-fold  origin,  part  arising  from  the 
metanephros,  and  part  as  a  diverticulum  from  the  hind-end  of  the  Wolffian  duct. 


1212 


SPLANCHNOLOGY 


close  to  where  the  latter  opens  into  the  cloaca  (Figs.  1115, 1116).  The  metanephros 
arises  in  the  intermediate  cell  mass,  caudal  to  the  mesonephros,  which  it  resembles 
in  structure.  The  diverticulum  from  the  WolflBan  duct  grows  dorsalward  and 
forward  along  the  posterior  abdominal  wall,  where  its  blind  extremity  expands 
and  subsequently  divides  into  several  buds,  which  form  the  rudiments  of  the 
pelvis  and  calyces  of  the  kidney;  by  continued  growth  and  subdivision  it  giveaj 


Wolffian  duct 
Allantots  \  Kidney  diverticulum 
Umbilical  cord    I      I    Rectum 


Un^ilical  vessels 
Hind-gut 


yotoehord 


Fig.  1115. — Tail  end  of  human   embryo  twenty- 
five  to  twenty-nine  days  old.    (From  model  by  Keibel.) 


Fig.   1110. — Tail  end  of  human  embryo  thirty-two 
to  thirty-three  days  old.     (From  model  by  Keibel.) 


Wolffian  duct 
MiVlerian  duct 

Bladder 
Symphysis  pubis  ^  ^^^ 


rise  to  the  collecting  tubules  of  the  kidney.  The  proximal  portion  of  the  diver- 
ticulum becomes  the  ureter.  The  secretory  tubules  are  developed  from  the 
metanephros,  which  is  moulded  over  the  growing  end  of  the  diverticulum  from  the 
Wolffian  duct.  The  tubules  of  the  metanephros,  unlike  those  of  the  pronephros 
and  mesonephros,  do  not  open  into  the  Wolffian  duct.  One  end  expands  to  form 
a  glomerulus,  while  the  rest  of  the  tubule  rapidly  elongates  to  form  the  convoluted 
and  straight  tubules,  the  loops  of  Henle,  and  the  connecting  tubules;  these  last 

join    and    establish    communications 
Ureter  with   the    collecting    tubules   derived 

from  the  ultimate  ramifications  of  the 
diverticulum  from  the  Wolffian  duct. 
The  mesoderm  around  the  tubules  be- 
comes condensed  to  form  the  connec- 
tive tissue  of  the  kidney.  The  ureter 
opens  at  first  into  the  hind-end  of  the 
Wolffian  duct;  after  the  sixth  week  it 
separates  from  the  Wolffian  duct,  and 
opens  independently  into  the  part  of 
the  cloaca  which  ultimately  becomes 
the  bladder  (Figs.  1117,  1118). 

The  secretory  tubules  of  the  kid- 
ney become  arranged  into  pyramidal 
masses  or  lobules,  and  the  lobulated 
condition  of  the  kidneys  exists  for 
some  time  after  birth,  while  traces  of 
The  kidney  of  the  ox  and  many  other  animals 


Glans  penis 

Urethra 


Vertebral  column 


Fia.  1117. — Tail  end  of  human  embryo;  from  eight  and  a 
half  to  nine  weeks  old.     (From  model  by  Keibel.) 


it  may  be  found  even  in  the  adult, 
remains  lobulated  throughout  life 

The  Urinary  Bladder.^ — The  bladder  is  formed  partly  from  the  entodermal 
cloaca  and  partly  from  the  ends  of  the  Wolffian  ducts;  the  allantois  takes  no  share 
in  its  formation.  After  the  separation  of  the  rectum  from  the  dorsal  paH  of  the 
cloaca  (p.  1109),  the  ventral  part  becomes  subdivided  into  three  portions:  (1)  an 
anterior  vesico-urethral  portion,  continuous  with  the  allantois — into  this  portion  the 
Wolffian  ducts  open;  (2)  an  intermediate  narrow  channel,  the  pelvic  portion;  and 


DEVELOPMENT  OF  THE  URINARY  AND  GENERATIVE  ORGANS     1213 


(3)  a  posterior  phallic  portion,  closed  externally  by  the  urogenital  membrane  (Fig. 
1118).  The  second  and  third  parts  together  constitute  the  urogenital  sinus.  The 
vesico-urethral  portion  absorbs  the  ends  of  the  Wolffian  ducts  and  the  associated 
ends  of  the  renal  diverticula,  and  these  give  rise  to  the  trigone  of  the  bladder  and 
part  of  the  prostatic  urethra.  The  remainder  of  the  vesico-urethral  portion  forms 
the  body  of  the  bladder  and  part  of  the  prostatic  urethra;  its  apex  is  prolonged  to 
the  umbilicus  as  a  narrow  canal,  which  later  is  obliterated  and  becomes  the  medial 
umbilical  ligament  (urachus). 


Wolffian  duct  - 


Hind-gut 


Bladder 


OtUer  zone\ 

,  )of  kidney 

inner  zone) 

Pelvis  oj  kidney 


Urogenital 
membrane 


Fia.   1118. — Primitive  kidney  and  bladder,  from  a  reconstruction.      (After  Schreiner.) 

The  Prostate. — The  prostate  originally  consists  of  two  separate  portions,  each 
of  which  arises  as  a  series  of  diverticular  buds  from  the  epithelial  lining  of  the  uro- 
genital sinus  and  vesico-urethral  part  of  the  cloaca,  between  the  third  and  fourth 
months.  These  buds  become  tubular,  and  form  the  glandular  substance  of  the  two 
lobes,  which  ultimately  meet  and  fuse  behind  the  urethra  and  also  extend  on  to  its 
ventral  aspect.  The  isthmus  or  middle  lobe  is  formed  as  an  extension  of  the  lateral 
lobes  between  the  common  ejaculatory  ducts  and  the  bladder.  Skene's  ducts  in  the 
female  urethra  are  regarded  as  the  homologues  of  the  prostatic  glands. 

The  bulbo-urethral  glands  of  Cowper  in  the  male,  and  greater  vestibular  glands 
of  Bartholin  in  the  female,  also  arise  as  diverticula  from  the  epithelial  lining  of  the 
urogenital  sinus. 

The  External  Organs  of  Generation  (Fig.  1119).— As  already  stated  (page  1109), 
the  cloacal  membrane,  composed  of  ectoderm  and  entoderm,  originally  reaches  from 
the  umbilicus  to  the  tail.  The  mesoderm  extends  to  the  midventral  line  for  some 
distance  behind  the  umbilicus,  and  forms  the  lower  part  of  the  abdominal  wall; 
it  ends  below  in  a  prominent  swelling,  the  cloacal  tubercle.  Behind  this  tubercle 
the  urogenital  part  of  the  cloacal  membrane  separates  the  ingrowing  sheets  of 
mesoderm. 

I  The  first  rudiment  of  the  penis  (or  clitoris)  is  a  structure  termed  the  phallus;  it 

B  is  derived  from  the  phallic  portion  of  the  cloaca  which  has  extended  on  to  the 
end  and  sides  of  the  under  surface  of  the  cloacal  tubercle.    The  terminal  part  of 
the  phallus  representing  the  future  glans  becomes  solid;   the  remainder,  which 
is  hollow,  is   converted  into  a  longitudinal  groove  by  the   absorption   of  the 
_^  urogenital  membrane. 
IB      In  the  female  a  deep  groove  forms  around  the  phallus  and  separates  it  from  the 


1214 


SPLANCHNOLOGY 


the  genital  tubercle  grow  backward  as  the  genital  swellings,  which  ultimately  form 
the  labia  majora;  the  tubercle  itself  becomes  the  mons  pubis.  The  labia  minora 
arise  by  the  continued  growth  of  the  lips  of  the  groove  on  the  under  surface  of  the 
phallus;  the  remainder  of  the  phallus  forms  the  clitoris. 


Umbilical  cord 
Genital  tubercle 


Genital  tiibercle 
hahium  majus 
iMbium  miiiuH 
Urogenital 
membrane 


K 


—  Qla,ns  penig- 


Scrotal  swelling 

Edge  of  groove  on  phallus 

Opening  of  urogenital  sinu>: 

Perineum 

Anus 


Glans  clitoridit 
Labium  majus 
Labium  minus 
Opening  of 
urogenital  sinvt 


— ■  Perineum, 


Anua 


i 


Glans  penis 
Cavernous  urethra 

Scrotum, 
Raphe 

Anus 


Prepuce 
Glans  clitoridit 

Labium  majus 
Labium  ininus 

Vestibule 

Vaginal  orifice 


-    Amis 


Yia.  1119.- 


-Stages  in  the  development  of  the  external  sexual  organs  in  the  male  and  female.     (Drawn  from  the 
Ecker-Ziegler  models.) 


1 


In  the  male  the  early  changes  are  similar,  but  the  pelvic  portion  of  the  cloaca 
undergoes  much  greater  development,  pushing  before  it  the  phallic  portion.  The 
genital  swellings  extend  around  between  the  pelvic  portion  and  the  anus,  and  form  a 
scrotal  area;  during  the  changes  associated  with  the  descent  of  the  testes  this  area 
is  drawn  out  to  form  the  scrotal  sacs.  The  penis  is  developed  from  the  phallus. 
As  in  the  female,  the  urogenital  membrane  undergoes  absorption,  forming  a  channel 
on  the  under  surface  of  the  phallus;  this  channel  extends  only  as  far  forward  as  the 
corona  glandis. 

The  corpora  cavernosa  of  the  penis  (or  clitoris)  and  of  the  urethra  arise  from  the 


THE  KIDNEYS  1215 

mesodermal  tissue  in  the  phallus;  they  are  at  first  dense  structures,  but  later 
vascular  spaces  appear  in  them,  and  they  gradually  become  cavernous. 

The  prepuce  in  both  sexes  is  formed  by  the  growth  of  a  solid  plate  of  ectoderm 
into  the  superficial  part  of  the  phallus;  on  coronal  section  this  plate  presents  the 
shape  of  a  horseshoe.  By  the  breaking  down  of  its  more  centrally  situated  cells 
the  plate  is  split  into  two  lamellse,  and  a  cutaneous  fold,  the  prepuce,  is  liberated 
and  forms  a  hood  over  the  glans.  "Adherent  prepuce  is  not  an  adhesion  really, 
but  a  hindered  central  desquamation"  (Berry  Hart,  op.  cit.). 

The  Urethra.' — As  already'  described,  in  both  sexes  the  phallic  portion  of  the 
cloaca  extends  on  to  the  under  surface  of  the  cloacal  tubercle  as  far  forward  as  the 
apex.  At  the  apex  the  walls  of  the  phallic  portion  come  together  and  fuse,  the 
lumen  is  obliterated,  and  a  solid  plate,  the  urethral  plate,  is  formed.  The  remainder 
of  the  phallic  portion  is  for  a  time  tubular,  and  then,  by  the  absorption  of  the 
urogenital  membrane,  it  establishes  a  communication  with  the  exterior;  this  open- 
ing is  the  primitive  urogenital  ostium,  and  it  extends  forward  to  the  corona  glandis. 

In  the  female  this  condition  is  largely  retained;  the  portion  of  the  groove  on  the 
clitoris  broadens  out  while  the  body  of  the  clitoris  enlarges,  and  thus  the  adult 
urethral  opening  is  situated  behind  the  base  of  the  clitoris. 

In  the  male,  by  the  greater  growth  of  the  pelvic  portion  of  the  cloaca  a  longer 
urethra  is  formed,  and  the  primitive  ostium  is  carried  forward  with  the  phallus, 
but  it  still  ends  at  the  corona  glandis.  Later  it  closes  from  behind  forward.  Mean- 
while the  urethral  plate  of  the  glans  breaks  down  centrally  to  form  a  median 
groove  continuous  with  the  primitive  ostium.  This  groove  also  closes  from  behind 
forward,  so  that  the  external  urethral  opening  is  shifted  forward  to  the  end  of 
fthe  glans. 

*  THE   URINARY   ORGANS. 

The  urinary  organs  comprise  the  kidneys,  which  secrete  the  urine,  the  ureters, 
or  ducts,  which  convey  urine  to  the  urinary  bladder,  where  it  is  for  a  time  retained ; 
and  the  urethra,  through  which  it  is  discharged  from  the  body. 


I 


The  Kidneys  (Renes). 

The  kidneys  are  situated  in  the  posterior  part  of  the  abdomen,  one  on  either  side 
of  the  vertebral  column,  behind  the  peritoneum,  and  surrounded  by  a  mass  of  fat 
and  loose  areolar  tissue.  Their  upper  extremities  are  on  a  level  with  the  upper 
border  of  the  twelfth  thoracic  vertebra,  their  lower  extremities  on  a  level  with  the 
third  lumbar.  The  right  kidney  is  usually  slightly  lower  than  the  left,  probably 
on  account  of  the  vicinity  of  the  liver.  The  long  axis  of  each  kidney  is  directed 
downward  and  lateralward;  the  transverse  axis  backward  and  lateralward. 

Each  kidney  is  about  11.25  cm.  in  length,  5  to  7.5  cm.  in  breadth,  and  rather 
more  than  2.5  cm.  in  thickness.  The  left  is  somewhat  longer,  and  narrower,  than 
the  right.  The  weight  of  the  kidney  in  the  adult  male  varies  from  125  to  170  gm., 
in  the  adult  female  from  115  to  155  gm.  The  combined  weight  of  the  two 
kidneys  in  proportion  to  that  of  the  body  is  about  1  to  240. 

The  kidney  has  a  characteristic  form,  and  presents  for  examination  two  surfaces, 
two  borders,  and  an  upper  and  lower  extremity. 

Relations. — The  anterior  surface  (fades  anterior)  (Figs.  1120  and  1122)  of 
each  kidney  is  convex,  and  looks  forward  and  lateralward.  Its  relations  to 
adjacent  viscera  differ  so  completely  on  the  two  sides  that  separate  descriptions 
are  necessary. 

Anterior  Surface  of  Right  Kidney. — A  narrow  portion  at  the  upper  extremity  is  in 
relation  with  the  right  suprarenal  gland.  A  large  area  just  below  this  and  involv- 
ing about  three-fourths  of  the  surface,  lies  in  the  renal  impression  on  the  inferior 


1216 


SPLANCHNOLOGY 


surface  of  the  liver,  and  a  narrow  but  somewhat  variable  area  near  the  medial 
border  is  in  contact  with  the  descending  part  of  the  duodenum.   The  lower  part  of- 


Great  splanchnic 
nerve  piercing 


Receptaculum 
chyli. 


Semilunar 
gangh 


Great  splanchnic 

nerve  piercing 

crus. 

Semilunar 


I 


Fia.  1120. — The  relations  of  the  viscera  and  large  vessels  of  the  abdomen.     (Seen  from  behind,  the  last  thoracic 

vertebra  being  well  raised.) 


the  anterior  surface  is  in  contact  laterally  with  the  right  colic  flexure,  and  medially, 
as  a  rule,  with  the  small  intestine.    The  areas  in  relation  with  the  liver  and  small 


THE  KIDNEYS 


1217 


intestine  are  covered  by  peritoneum;  the  suprarenal,  duodenal,  and  colic  areas 
are  devoid  of  peritoneum. 

Anterior  Surface  of  Left  Kidney. — A  small  area  along  the  upper  part  of  the  medial 
border  is  in  relation  with  the  left  suprarenal  gland,  and  close  to  the  lateral 
border  is  a  long  strip  in  contact  with  the  renal  impression  on  the  spleen.  A 
somewhat  quadrilateral  field,  about  the  middle  of  the  anterior  surface,  marks  the 
site  of  contact  with  the  body  of  the  pancreas,  on  the  deep  surface  of  which  are  the 
lienal  vessels.  Above  this  is  a  small  triangular  portion,  between  the  suprarenal 
and  splenic  areas,  in  contact  with  the  postero-inferior  surface  of  the  stomach. 
Below  the  pancreatic  area  the  lateral  part  is  in  relation  with  the  left  colic  flexure. 


INFERIOR    PHRENIC 
ARTERIES 


SUPER 
MESENTE 
ARTE 


INFER 
MESENTT 
ARTE 


COMM 
ILIAC  ARTE 
AND  V 


CCZLIAO 
ARTERY 


INTERNAL 
SPERMATIC 
ARTERY 
AND  VEIN 
INTERNAL 
ILIAC  ARTERY 
AND  URETER 


?IG.    1121. 


-Posterior  abdominal  wall,  after  removal  of  the  peritoneum,  showing  kidneys,  suprarenal  capsules,  and 
great  vesseb.     (Corning). 


'the  medial  with  the  small  intestine.  The  areas  in  contact  with  the  stomach  and 
spleen  are  covered  by  the  peritoneum  of  the  omental  bursa,  while  that  in  relation 
to  the  small  intestine  is  covered  by  the  peritoneum  of  the  general  cavity;  behind 
the  latter  are  some  branches  of  the  left  colic  ves.sels.  The  suprarenal,  pancreatic, 
and  colic  areas  are  devoid  of  peritoneum. 

The  Posterior  Surface  (fades  posterior)  (Figs.  1123,  1124). — The  posterior  surface 
of  each  kidney  is  directed  backward  and  medialward.  It  is  imbedded  in  areolar 
and  fatty  tissue  and  entirely  devoid  of  peritoneal  covering.  It  lies  upon  the  dia- 
phragm, the  medial  and  lateral  lumbocostal  arches,  the  Psoas  major,  the  Quadratus 
77 


1218 


SPLANCHNOLOGY 


lumborum,  and  the  tendon  of  the  Transversus  abdominis,  the  subcostal,  and  one 
or  two  of  the  upper  lumbar  arteries,  and  the  last  thoracic,  iliohypogastric,  and 
ilioinguinal  nerves.  The  right  kidney  rests  upon  the  twelfth  rib,  the  left  usually 
on  the  eleventh  and  twelfth.     The  diaphragm  separates  the  kidney  from  the. 


SUPRARENAL  AREA 


SUPRARENAL  AREA 


Fig.  1122. — The  anterior  surfaces  of  the  kidneys,  showing  the  areas  of  contact  of  neighboring  viscera. 

pleura,  which  dips  down  to  form  the  phrenicocostal  sinus,  but  frequently  the 
muscular  fibers  of  the  diaphragm  are  defective  or  absent  over  a  triangular  area 
immediately  above  the  lateral  lumbocostal  arch,  and  when  this  is  the  case  the 
perinephric  areolar  tissue  is  in  contact  with  the  diaphragmatic  pleura. 


ELEVENTH   RIB 


TWELFTH   RIB 


TRANSVERSE   PROCESSES 
OF  FIRST  LUMBAR  VERTEBRA 


TWELFTH    RIB 


TRANSVERSE  PROCESS 
OF  SECOND  LUMBAR 
VERTEBRA 


Fig.   1123. — The  posterior  surfaces  of  the  kidneys,  showing  areas  of  relation  to  the  parietes. 

Borders. — The  lateral  border  {margo  lateralis;  external  border)  is  convex,  and  is 
directed  toward  the  postero-lateral  wall  of  the  abdomen.  On  the  left  side  it  is  in 
contact  at  its  upper  part,  with  the  spleen. 


THE  KIDNEYS 


1219 


The  medial  border  (margo  medialis;  internal  border)  is  concave  in  the  center  and 
convex  toward  either  extremity;  it  is  directed  forward  and  a  little  downward. 


I 


Fig.   1124. — The  relations  of  the  kidneys  from  behind. 


Its  central  part  presents  a  deep  longitudinal  fissure,  bounded  by  prominent  over- 


hanging anterior  and  posterior  lips, 
the  vessels,  nerves,  and  ureter. 
Above  the  hilum  the  medial 
border  is  in  relation  with  the 
suprarenal  gland ;  below  the  hilum, 
with  the  ureter. 

Extremities. — ^The  superior  ex- 
tremity {extremitas  superior)  is 
thick  and  rounded,  and  is  nearer 
the  median  line  than  the  lower;  it 
is  surmounted  by  the  suprarenal 
gland,  which  covers  also  a  small 
portion  of  the  anterior  surface. 

The  inferior  extremity  {extrem- 
itas inferior)  is  smaller  and  thin- 
ner than  the  superior  and  farther 
from  the  median  line.  It  extends 
to  within  5  cm.  of  the  iliac  crest. 

The  relative  position  of  the 
main  structures  in  the  hilum  is  as 
follows:  the  vein  is  in  front,  the 
artery  in  the  middle,  and  the 
ureter  behind  and  directed  down- 
ward. Frequently,  however, 
branches  of  both  artery  and 
vein  are  placed  behind  the  ureter. 


This  fissure  is  named  the  hilum,  and  transmits 


Eleventh 


Twelfth 


Posterior 

lamella  of 

renal  fascia 


Paranephr 
body 


Peritoneum 

Vessels  of  hilum 
of  kidney 

Section  of 

right  colic 

flexure 


Fig.  1125. — Sagittal  section  through  posterior  abdominal  wall, 
showing  the  relations  of  the  capsule  of  the  kidney.   (After  Gerota). 


1220 


SPLANCHNOLOGY 


Fixation  of  the  Kidney  (Figs.  1125,  1126).— The  kidney  and  its  vessels  are  im-j 
bedded  in  a  mass  of  fatty  tissue,  termed  the  adipose  capsule,  which  is  thickest  at 
the  margins  of  the  kidney  and  is  prolonged  through  the  hilum  into  the  renal  sinus. 
The  kidney  and  the  adipose  capsule  are  enclosed  in  a  sheath  of  fibrous  tissue  con- 
tinuous with  the  subperitoneal  fascia,  and  named  the  renal  fascia.  At  the  lateral 
border  of  the  kidney  the  renal  fascia  splits  into  an  anterior  and  a  posterior  layer. 
The  anterior  layer  is  carried  medialward  in  front  of  the  kidney  and  its  vessels, 
and  is  continuous  over  the  aorta  with  the  corresponding  layer  of  the  opposite 
side.  The  posterior  layer  extends  medialward  behind  the  kidney  and  blends  w^ith 
the  fascia  on  the  Quadratus  lumborum  and  Psoas  major,  and  through  this  fascia 
is  attached  to  the  vertebral  column.  Above  the  suprarenal  gland  the  two  layers 
of  the  renal  fascia  fuse,  and  unite  with  the  fascia  of  the  diaphragm ;  below  they 
remain  separate,  and  are  gradually  lost  in  the  subperitoneal  fascia  of  the  iliac 
fossa.  The  renal  fascia  is  connected  to  the  fibrous  tunic  of  the  kidney  by  numerous 
trabeculse,  which  traverse  the  adipose  capsule,  and  are  strongest  near  the  lower 
end  of  the  organ.  Behind  the  fascia  renalis  is  a  considerable  quantity  of  fat,  which 
constitutes  the  paranephric  body.  The  kidney  is  held  in  position  partly  through 
the  attachment  of  the  renal  fascia  and  partly  by  the  apposition  of  the  neighboring 
viscera. 


SKhperitoneal  fascia 


Anterior  lamella  of 
renal  fascia 


Fig.   1126 


Peritoneum 
^7^- —  Adipose  capsvle 


Paranephric  body 
Quadratus  lumborum. 
Sacrospinalis 
-Transverse  section,  showing  the  relations  of  the  capsule  of  the  kidney.     (After  Gerota.) 


General  Structure  of  the  Kidney. — The  kidney  is  invested  by  a  fibrous  tunic, 
which  forms  a  firm,  smooth  covering  to  the  organ.  The  tunic  can  be  easily  stripped 
off,  but  in  doing  so  numerous  fine  processes  of  connective  tissue  and  small  bloodvessels 
are  torn  through.  Beneath  this  coat  a  thin,  wide-meshed  net-work  of  unstriped 
muscular  fiber  forms  an  incomplete  covering  to  the  organ.  When  the  capsule  is 
stripped  off,  the  surface  of  the  kidney  is  found  to  be  smooth  and  even  and  of  a  deep 
red  color.  In  infants  fissures  extending  for  some  depth  may  be  seen  on  the  surface 
of  the  organ,  a  remnant  of  the  lobular  construction  of  the  gland.  The  kidney  is 
dense  in  texture,  but  is  easily  lacerable  by  mechanical  force.    If  a  vertical  section 


THE  KIDNEYS 


1221 


I 


of  the  kidney  be  made  from  its  convex  to  its  concave  border,  it  will  be  seen  that  the 
hilum  expands  into  a  central  cavity,  the  renal  sinus,  this  contains  the  upper  part  of 
the  renal  pelvis  and  the  calyces,  surrounded  by  some  fat  in  which  are  imbedded  the 
branches  of  the  renal  vessels  and  nerves.  The  renal  sinus  is  lined  by  a  prolongation 
of  the  fibrous  tunic,  which  is  continued  around  the  lips  of  the  hilum.  The  renal 
calyces,  from  seven  to  thirteen  in  number,  are  cup-shaped  tubes,  each  of  which 
embraces  one  or  more  of  the  renal  papilhe;  they  unite  to  form  two  or  three  short 
tubes,  and  these  in  turn  join  to  form  a  funnel-shaped  sac,  the  renal  pelvis.  The 
renal  pelvis,  wide  above  and  narrow  below  where  it  joins  the  ureter,  is  partly  out- 
side the  renal  sinus.  The  renal  calyces  and  pelvis  form  the  upper  expanded  end  of 
the  excretory  duct  of  the  kidney. 

The  kidney  is  composed  of  an  internal  medullary  and  an  external  cortical  substance. 

The  medullary  substance  (substantia  medullaris)  consists  of  a  series  of  red-colored 
striated  conical  masses,  termed  the  renal  pyramids,  the  bases  of  which  are  directed 
toward  the  circumference  of  the  kidney,  while  their  apices  converge  toward  the 
renal  sinus,  where  they  form  prominent  papillae  projecting  into  the  interior  of  the 
calyces. 

The  cortical  substance  (substantia  corticalis)  is  reddish  brown  in  color  and  soft  and 
granular  in  consistence.  It  lies  immediately  beneath  the  fibrous  tunic,  arches  over 
the  bases  of  the  pyramids,  and  dips  in  between 
adjacent  pyramids  toward  the  renal  sinus.  The 
parts  dipping  in  between  the  pyramids  are 
named  the  renal  columns  (Bertini),  while  the 
portions  which  connect  the  renal  columns  to 
each  other  and  intervene  between  the  bases  of 
the  pyramids  and  the  fibrous  tunic  are  called 
the  cortical  arches  (indicated  between  A  and  A' 
in  Fig.  1127).  If  the  cortex  be  examined  with  a 
lens,  it  will  be  seen  to  consist  of  a  series  of 
lighter-colored,  conical  areas,  termed  the  radiate 
part,  and  a  darker-colored  intervening  substance, 
which  from  the  complexity  of  its  structure  is 
named  the  convoluted  part.  The  rays  gradually 
taper  toward  the  circumference  of  the  kidney, 
and  consist  of  a  series  of  outward  prolongations 
from  the  base  of  each  renal  pyramid. 

Minute  Anatomy.— The  renal  tubules  (Fig.  1028), 
of  which  the  kidney  ia  for  the  most  part  made  up, 
commence  in  the  cortical  substance,  and  after  pursuing 
a  very  circuitous  course  through  the  cortical  and  medul- 
lary substances,  finally  end  at  the  apices  of  the  renal 
pyramids  by  open  mouths,  so  that  the  fluid  which 
they  contain  is  emptied,  through  the  calyces,  into  the 
pelvis  of  the  kidney.  If  the  surface  of  one  of  the 
papiUse  be  examined  with  a  lens,  it  will  be  seen  to  be 
studded  over  with  minute  openings,  the  orifices  of  the  renal  tubules,  from  sixteen  to  twenty 
in  number,  and  if  pressure  be  made  on  a  fresh  kidney,  urine  will  be  seen  to  exude  from  these 
orifices.  The  tubules  commence  in  the  convoluted  part  and  renal  columns  as  the  renal  cor- 
puscles, which  are  small  rounded  masses  of  a  deep  red  color,  varying  in  size,  but  of  an  average 
of  about  0.2  mm.  in  diameter.  Each  of  these  little  bodies  is  composed  of  two  parts:  a  central 
glomerulus  of  vessels,  and  a  membranous  envelope,  the  glomerular  capsule  (capsule  of  Bowman), 
which  is  the  small  pouch-like  commencement  of  a  renal  tubule. 

The  glomerulus  is  a  lobulated  net-work  of  convoluted  capillary  bloodvessels,  held  together 
by  scanty  connective  tissue.  This  capillary  net-work  is  derived  from  a  small  arterial  twig, 
the  afferent  vessel,  which  enters  the  capsule,  generally  at  a  point  opposite  to  that  at  which 
the  latter  is  connected  with  the  tubule;  and  the  resulting  vein,  the  efferent  vessel,  emerges 
from   the  capsule  at   the  same  point.     The  afferent  vessel  is  usually  the  larger  of  the  two 


Fig.  1127. — \  ertical  section  of  kidney. 


1222 


SPLANCHNOLOGY 


(Fig.  1129).     The    glomerular  or  Bowman's   capsule,  which    surrounds  the  glomerulus,   con- 
sists of  a  basement  membrane,  lined  on  its  inner  surface  by  a  layer  of  flattened  epithelial  cells. 


Glomerular  capsule     Neck        1st  convoluted  tvhule 


Afferent  vessel 
Efferent  vessel 

Interlubular  capillaries 
Interlobular  vein 

Interlobular  artery 
Spiral  tubule 


Henle'sf  Ascending  limb 
loop  \Descending  Unib 


Arterial  arch 
Yevmis  arch 


Cortical  substance 


Boundary  zone 


Medullary 
substance 


Duct  of  Bellini 


Fia.  1128. — Scheme  of  renal  tubule  and  its  vascular  supply. 

which  are  reflected  from  the  lining  membrane  on  to  the  glomerulus,  at  the  point  of  entrance  or 
exit  of  the  afferent  and  efferent  vessels.  The  whole  surface  of  the  glomerulus  is  covered  with  a 
continuous  layer  of  the  same  cells,  on  a  delicate  supporting  membrane  (Fig.  1130).  Thus  between 
the  glomerulus  and  the  capsule  a  space  is  left,  forming  a  cavity  lined  by  a  continuous  layer  of 


,,v6rtt^!<^, 


Fig.  1129. — Distribution  of  bloodvessels  in  cortex  of  kidney. 


FiQ.  1130. — Glomerulus. 


squamous  cells;  this  cavity  varies  in  size  according  to  the  state  of  secretion  and  the  amount  of 
fluid  present  in  it.  In  the  fetus  and  young  subject  the  lining  epithelial  cells  are  polyhedral  or  even 
columnar. 


THE  KIDNEYS 


1223 


The  renal  tubules,  commencing  in  the  renal  corpuscles,  present,  during  their  course,  many 
changes  in  shape  and  direction,  and  are  contained  partly  in  the  medullary  and  partly  in  the 
cortical  substance.  At  their  junction  with  the  glomerular  capsule  they  exhibit  a  somewhat 
constricted  portion,  which  is  termed  the  neck.  Beyond  this  the  tubule  becomes  convoluted, 
and  pursues  a  considerable  course  in  the  cortical  substance  constituting  the  proximal  convoluted 
tube.  After  a  time  the  convolutions  disappear,  and  the  tube  approaches  the  medullary  sub- 
stance in  a  pore  or  less  spiral  manner;  this  section  of  the  tubule  has  beea  called  the  spiral  tube. 
Throughout  this  portion  of  their  course  the  renal  tubules  are  contained  entirely  in  the  cortical 
substance,  and  present  a  fairly  uniform  caliber.  They  now  enter  the  medullary  substance, 
suddenly  become  much  smaller,  quite  straight  in  direction,  and  dip  down  for  a  variable  depth 
into  the  pyramids,  constituting  the  descending  limb  of  Henle's  loop.  Bending  on  themselves, 
they  form  what  is  termed  the  loop  of  Henle,  and  reascending,  they  become  suddenly  enlarged, 
forming  the  ascending  limb  of  Henle's  loop,  and  reenter  the  cortical  substance.  This  portion 
of  the  tubule  ascends  for  a  short  distance,  when  it  again  becomes  dilated,  irregular,  and  angular. 
This  section  is  termed  the  zigzag  tubule;  it  ends  in  a  convoluted  tube,  which  resembles  the 
proximal  convoluted  tubule,  and  is  called  the  distal  convoluted  tubule.  This  again  terminates 
in  a  narrow  junctional  tube,  which  enters  the  straight  or  collecting  tube. 

The  straight  or  collecting  tubes  commence  in  the  radiate  part  of  the  cortex,  where  they  receive 
the  curved  ends  of  the  distal  convoluted  tubules.  They  unite  at  short  intervals  with  one  another, 
the  resulting  tubes  presenting  a  considerable  increase  in  caliber,  so  that  a  series  of  comparatively 
large  tubes  passes  from  the  bases  of  the  rays  into  the  renal  pyramids.  In  the  medulla  the  tubes 
of  each  pyramid  converge  to  join  a  central  tube  {duct  of  Bellini)  which  finally  opens  on  the  summit 
of  one  of  the  papillae;  the  contents  of  the  tube  are  therefore  discharged  into  one  of  the  calyces. 

Structure  of  the  Renal  Tubules. — The  renal  tubules  consist  of  a  basement  membrane  lined  with 
epithelium.  The  epithelium  varies  considerably  in  different  sections  of  the  tubule.  In  the  neck 
the  epithelium  is  continuous  with  that  lining  the  glomerular  capsule,  and  like  it  consists  of 
flattened  cells  each  containing  an  oval  nucleus  (Fig.  1132).  The  two  convoluted  tubules,  the 
spiral  and  zigzag  tubules  and  the  ascending  limb  of  Henle's  loop,  are  lined  by  a  type  of  epithehum 
which  is  histologically  the  same  in  all.  The  cells  are  somewhat  columnar  in  shape  and  dovetail 
into  one  another  of  their  lateral  aspect.  Each  has  a  striated  border  next  the  lumen  of  the  tube, 
its  inner  part  is  granular  and  its  outer  portion  vertically  striated,  The  nucleus  is  spherical  and 
situated  about  the  center  of  the  cell.  In  the  descend- 
ing limb  of  Henle's  loop  the  epithelium  resembles  that 
found  in  the  glomerular  capsule  and  the  commence- 
ment of  the  tube,  consisting  of  flat,  clear  epithelial 
plates,  each  with  an  oval  nucleus  (Fig.  1131).  The 
nuclei  alternate  on  opposite  surfaces  of  the  tubule  so 
that  the  lumen  remains  fairly  constant. 

In  the  straight  tube  the  epithelium  is  clear  and 
cubical:  in  its  papillary  portion  the  cells  are  distinctly 
columnar  and  transparent  (Fig.  1132). 

The  Renal  Bloodvessels.— The  kidney  is  plentifully 
euppUed  with  blood  (Fig.  1133)  by  the  renal  artery,  a 
large  branch  of  the  abdominal  aorta.  Before  it  enters 
the  kidney,  each  artery  divides  into  four  or  five 
branches  which  at  the  hilum  lie  mainly  between  the 
renal  vein  and  ureter,  the  vein  being  in  front,  the 
ureter  behind;  one  branch  usually  lies  behind  the 
ureter.  Each  vessel  gives  off  some  small  branches  to 
the  suprarenal  glands,  to  the  ureter,  land  to  the  sur- 
rounding cellular  tissue  and  muscles.  Frequently  a 
second  renal  artery,  termed  the  inferior  renal,  is  given 
off  from  the  abdominal  aorta  at  a  lower  level,  and  suppUes  the  lower  portion  of  the  kidney, 
while  occasionally  an  additional  artery  enters  the  upper  part  of  the  kidney.  The  branches 
of  the  renal  artery,  while  in  the  sinus,  give  off  a  few  twigs  for  the  nutrition  of  the  surround- 
ing tissues,  and  end  in  the  arteriae  proprise  renales,  which  enter  the  kidney  proper  in  the 
renal  columns.  Two  of  these  pass  to  each  renal  pyramid,  and  run  along  its  sides  for  its 
entire  length,  giving  off  in  their  course  the  afferent  vessels  of  the  renal  corpuscles  in  the  renal 
columns.  Having  arrived  at  the  bases  of  the  pyramids,  they  form  arterial  arches  or  arcades 
which  lie  in  the  boundary  zone  between  the  bases  of  the  pyramids  and  the  cortical  arches,  and 
break  up  into  two  distinct  sets  of  branches  devoted  to  the  supply  of  the  remaining  portions 
of  the  kidney. 

The  first  set,  the  interlobular  arteries  (Fig.  1128),  are  given  off  at  right  angles  from  the  side 
of  the  arterial  arcade  looking  toward  the  cortical  substance,  and  pass  directly  outward  between 
the  medullary  rays  to  reach  the  fibrous  tunic,  where  they  end  in  the  capillary  net-work  of  this 
part.    These  vessels  do  not  anastomose  with  each  other,  but  form  what  are  called  end-arteries. 


FiQ.  1131.  —  Longitudinal  section  of  de- 
scending limb  of  Henle's  loop.  a.  Membrana 
propria.    6.  Epithelium. 


1224 

In  their  outward  course  they  give  off  lateral  branches;  these  are  the  afferent  vessels  for  the 
renal  corpuscles  (see  page  1221);  they  enter  the  capsule,  and  end  in  the  glomerulus.  From 
each  tuft  the  corresponding  efferent  vessel  arises,  and,  having  made  its  egress  from  the  capsule 
near  to  the  point  where  the  afferent  vessel  enters,  breaks  up  into  a  number  of  branches,  which 
form  a  dense  plexus  around  the  adjacent  urinary  tubes. 


I 


Convoluted  tvhvXe 


Glomerulus 


Neck  of  tubule 


Fia.  1132. — Section  of  cortex  of  human  kidney. 

The  second  set  of  branches  from  the  arterial  arcades  supply  the  renal  pyramids,  which  they 
enter  at  their  bases;  and,  passing  straight  through  their  substance  to  their  apices,  terminate 
in  the  venous  plexuses  found  in  that  situation.  They  are  called  the  arteriae  rectse.  The  efferent 
vessels  from  the  glomeruU  nearest  the  medulla  break  up  into  leashes  of  straight  vessels  (falsi 
arterice  recta)  which  pass  down  into  the  medulla  and  join  the  plexus  of  vessels  there  (Fig.  1128). 


FlQ.  1133. — Transverse  section  of  pyramidal  substance  of  kidney  of  pig,  the  bloodvessels  of  which  are  injected. 
o._  Large  collecting  tube,  cut  across,  Imed  with  cylindrical  epitheUum.  6.  Branch  of  collecting  tube,  cut  across,  lined 
with  cubical  epithelium,  c,  d.  Henle's  loops  cut  across,  e.  Bloodvessels  cut  across.  D  Connective  tissue  ground 
substance. 

The  renal  veins  arise  from  three  sources,  viz.,  the  veins  beneath  the  fibrous  tunic,  the  plexuses 
around  the  convoluted  tubules  in  the  cortex,  and  the  plexuses  situated  at  the  apices  of 
the  renal  pyramids.  The  veins  beneath  the  fibrous  tunic  (venae  stellatae)  are  stellate  in 
arrangement,  and  are  derived  from  the  capillary  net-work,  into  which  the  terminal  branches  of 
the  interlobular  arteries  break  up.  These  join  to  form  the  interlobular  veins,  which  pass  inward 
between  the  rays,  receive  branches  from  the  plexuses  around  the  convoluted  tubules,  and,  having 
arrived  at  the  bases  of  the  renal  pyramids,  join  with  the  venae  rectsD,  next  to  be  described. 


I 


THE  URETERS  ^^^^^  1225 

The  venae  rectse  are  branches  from  the  plexuses  at  the  apices  of  the  medullary  pyramids, 
formed  by  the  terminations  of  the  arterise  rectse.  They  run  outward  in  a  straight  course  between 
the  tubes  of  the  medullary  substance,  and  joining,  as  above  stated,  the  interlobular  veins,  form 
venous  arcades;  these  in  turn  unite  and  form  veins  which  pass  along  the  sides  of  the  pyramids 
(Fig.  1128). 

These  vessels,  venae  propriae  renales,  accompany  the  arteries  of  the  same  name,  running 
along  the  entire  length  of  the  sides  of  the  pyramids,  and  quit  the  kidney  substance  to  enter  the 
sinus.  In  this  cavity  they  join  the  corresponding  veins  from  the  other  pyramids  to  form  the 
renal  vein,  which  emerges  from  the  kidney  at  the  hilum  and  opens  into  the  inferior  vena  cava; 
the  left  vein  is  longer  than  the  right,  and  crosses  in  front  of  the  abdominal  aorta. 

The  Ijrmphatics  of  the  kidney  are  described  on  page  712. 

Nerves  of  the  Kidney. — The  nerves  of  the  kidney,  although  small,  are  about  fifteen  in  number. 
They  have  small  ganglia  developed  upon  them,  and  are  derived  from  the  renal  plexus,  which  is 
formed  by  branches  from  the  cehac  plexus,  the  lower  and  outer  part  of  the  celiac  gangHon  and 
aortic  plexus,  and  from  the  lesser  and  lowest  splanchnic  nerves.  They  commimicate  with  the 
spermatic  plexus,  a  circumstance  which  may  explain  the  occurrence  of  pain  in  the  testis  in  affec- 
tions of  the  kidney.  They  accompany  the  renal  artery  and  its  branches,  and  are  distributed  to 
the  bloodvessels  and  to  the  cells  of  the  urinary  tubules. 

Connective  Tissue  (intertubular  stroma).  —  Although  the  tubules  and  vessels  are  closely 
packed,  a  small  amount  of  connective  tissue,  continuous  with  the  fibrous  tunic,  binds  them 
firmly  together  and  supports  the  bloodvessels,  lymphatics,  and  nerves. 

Variations. — Malformations  of  the  kidney  are  not  uncommon.  There  may  be  an  entire 
absence  of  one  kidney,  but,  according  to  Morris,  the  number  of  these  cases  is  "excessively 
small":  or  there  may  be  congenital  atrophy  of  one  kidney,  when  the  kidney  is  very  small,  but 
usually  healthy  in  structure.  These  cases  are  of  great  importance,  and  must  be  duly  taken  into 
account  when  nephrectomy  is  contemplated.  A  more  common  malformation  is  where  the  two 
kidneys  are  fused  together.  They  may  be  joined  together  only  at  their  lower  ends  by  means 
of  a  thick  mass  of  renal  tissue,  so  as  to  form  a  horseshoe-shaped  body,  or  they  may  be  completely 
united,  forming  a  disk-like  kidney,  from  which  two  ureters  descend  into  the  bladder.  These  fused 
kidneys  are  generally  situated  in  the  middle  line  of  the  abdomen,  but  may  be  misplaced  as  well. 
In  some  mammals,  e.  g.,  ox  and  bear,  the  kidney  consists  of  a  number  of  distinct  lobules;  this 
lobulated  condition  is  characteristic  of  the  kidney  of  the  human  fetus,  and  traces  of  it  may  persist 
in  the  adult.  Sometimes  the  pelvis  is  duphcated,  while  a  double  ureter  is  not  very  imcommon. 
In  some  rare  instances  a  third  kidney  may  be  present. 

One  or  both  kidneys  may  be  misplaced  as  a  congenital  condition,  and  remain  fixed  in  this 
abnormal  position.  They  are  then  very  often  misshapen.  They  may  be  situated  higher,  though 
this  is  very  uncommon,  or  lower  than  normal  or  removed  farther  from  the  vertebral  column 
than  usual;  or  they  may  be  displaced  into  the  iUac  fossa,  over  the  sacroihac  joint,  on  to  the 
promontory  of  the  sacrum,  or  into  the  pelvis  between  the  rectima  and  bladder  or  by  the  side  of 
the  uterus.  In  these  latter  cases  they  may  give  rise  to  very  serious  trouble.  The  kidney  may  also 
be  misplaced  as  a  congenital  condition,  but  may  not  be  fixed;  it  is  then  known  as  a,  floating  kidney. 
It  is  believed  to  be  due  to  the  fact  that  the  kidney  is  completely  enveloped  by  peritoneum  which 
then  passes  backward  to  the  vertebral  column  as  a  double  layer,  forming  a  mesonephron  which 
permits  movement.  The  kidney  may  also  be  misplaced  as  an  acquired  condition;  in  these  cases 
the  kidney  is  mobile  in  the  tissues  by  which  it  is  surrounded,  moving  with  the  capsule  in  the 
perinephric  tissues.  This  condition  is  known  as  movable  kidney,  and  is  more  common  in  the  female 
than  in  the  male.  It  occurs  in  badly  nourished  people,  or  in  those  who  have  become  emaciated 
from  any  cause.  It  must  not  be  confounded  with  the  floating  kidney,  which  is  a  congenital 
condition  due  to  the  development  of  a  mesonephron.  The  two  conditions  cannot,  however, 
be  distinguished  until  the  abdomen  is  opened  or  the  kidney  explored  from  the  loin. 

The  Ureters. 


The  ureters  are  the  two  tubes  which  convey  the  urine  from  the  kidneys  to  the 
urinary  bladder.    Each  commences  within  the  sinus  of  the  corresponding  kidney 

IB  as  a  number  of  short  cup-shaped  tubes,  termed  calyces,  which  encircle  the  renal 
"  papillae.  Since  a  single  calyx  may  enclose  more  than  one  papilla  the  calyces  are 
generally  fewer  in  number  than  the  pyramids — the  former  varying  from  seven  to 
thirteen,  the  latter  from  eight  to  eighteen.  The  calyces  join  to  form  two  or  three 
short  tubes,  and  these  unite  to  form  a  funnel-shaped  dilatation,  wide  above  and 
narrow  below,  named  the  renal  pelvis,  which  is  situated  partly  inside  and  partly 
outside  the  renal  sinus.  It  is  usually  placed  on  a  level  with  the  spinous  process  of 
the  first  lumbar  vertebra. 


1226 


SPLANCHNOLOGY 


I 


The  Ureter  Proper  measures  from  25  to  30  cm.  in  length,  and  is  a  thick-walled 
narrow  cylindrical  tube  which  is  directly  continuous  near  the  lower  end  of  the 
kidney  with  the  tapering  extremity  of  the  renal  pelvis.  It  runs  downward  and 
medialward  in  front  of  the  Psoas  major  and,  entering  the  pelvic  cavity,  finally 
opens  into  the  fundus  of  the  bladder. 

The  abdominal  part  (pars  ahdominalis)  lies  behind  the  peritoneum  on  the  medial 
part  of  the  Psoas  major,  and  is  crossed  obliquely  by  the  internal  spermatic  vessels. 
It  enters  the  pelvic  cavity  by  crossing  either  the  termination  of  the  common,  or 
the  commencement  of  the  external,  iliac  vessels. 

At  its  origin  the  right  ureter  is  usually  covered  by  the  descending  part  of  the 
duodenum,  and  in  its  course  downward  lies  to  the  right  of  the  inferior  vena  cava, 
and  is  crossed  by  the  right  colic  and  ileocolic  vessels,  while  near  the  superior  aperture 
of  the  pelvis  it  passes  behind  the  lower  part  of  the  mesentery  and  the  terminal 
part  of  the  ileum.  The  left  ureter  is  crossed  by  the  left  colic  vessels,  and  near  the 
superior  aperture  of  the  pelvis  passes  behind  the  sigmoid  colon  and  its  mesentery. 
The  pelvic  part  {yars  pelvina)  runs  at  first  downward  on  the  lateral  wall  of  the 
pelvic  cavity,  along  the  anterior  border  of  the  greater  sciatic  notch  and  under 
cover  of  the  peritoneum.  It  lies  in  front  of  the  hypogastric  artery  medial  to  the 
obturator  nerve  and  the  umbilical,  obturator,  inferior  vesical,  and  middle  hemor- 
rhoidal arteries.  Opposite  the  lower  part  of  the  greater  sciatic  foramen  it  inclines 
medialward,  and  reaches  the  lateral  angle  of  the  bladder,  where  it  is  situated  in 
front  of  the  upper  end  of  the  seminal  vesicle  and  at  a  distance  of  about  5  cm. 
from  the  opposite  ureter;  here  the  ductus  deferens  crosses  to  its  medial  side,  and 
the  vesical  veins  surround  it.  Finally,  the  ureters  run  obliquely  for  about  2  cm. 
through  the  wall  of  the  bladder  and  open  by  slit-like  apertures  into  the  cavity 
of  the  viscus  at  the  lateral  angles  of  the  trigone.  When  the  bladder  is  distended 
the  openings  of  the  ureters  are  about  5  cm.  apart,  but  w^hen  it  is  empty  and  con- 
tracted the  distance  between  them  is  diminished  by  one-half.     Owing  to  their 

oblique  course  through  the  coats 
of  the  bladder,  the  upper  and 
lower  walls  of  the  terminal  por- 
tions of  the  ureters  become  closely 
applied  to  each  other  when  the 
viscus  is  distended,  and,  acting  as 
valves,  prevent  regurgitation  of 
urine  from  the  bladder. 

In  the  female,  the  ureter  forms, 
as  it  lies  in  relation  to  the  wall 
of  the  pelvis,  the  posterior  bound- 
ary of  a  shallow  depression  named 
the  ovarian  fossa,  in  which  the 
ovary  is  situated.  It  then  runs 
medialward  and  forward  on  the 
lateral  aspect  of  the  cervix  uteri 
and  upper  part  of  the  vagina  to 
reach  the  fundus  of  the  bladder. 
In  this  part  of  its  course  it  is  ac- 
companied for  about  2.5  cm.  by 
the  uterine  artery,  which  then 
crosses  in  front  of  the  ureter  and 
ascends  between  the  two  layers  of 
the  broad  ligament.  The  ureter 
is  distant  about  2  cm.  from  the  side  of  the  cervix  of  the  uterus.  The  ureter  is 
sometimes  duplicated  on  one  or  both  sides,   and  the  two  tubes  may  remam 


Fibrov^  tisstie 

Longitudinal 
muscvlar  fibers 

Circular  muscvlaT 
fibers 

Svbepithelial 
connective  tissini 

Transitional 
epitheliur/h 


Fig.  1134. — ^Transverse  section  of  ureter. 


I 


THE  URINARY  BLADDER 

distinct  as  far  as  the  fundus  of  the   bladder.     On   rare   occasions  they    open 
separately  into  the  bladder  cavity. 

Structure  (Fig.  1134). — The  ureter  is  composed  of  three  coats:  fibrous,  muscular,  and  mucous 
coats. 

The  fibrous  coat  {tunica  adventitia)  is  continuous  at  one  end  with  the  fibrous  timic  of  the  kidney 
on  the  floor  of  the  sinus;  while  at  the  other  it  is  lost  in  the  fibrous  structure  of  the  bladder. 

In  the  renal  pelvis  the  muscular  coat  {tunica  mitscularis)  consists  of  two  layers,  longitudinal 
and  circular:  the  longitudinal  fibers  become  lost  upon  the  sides  of  the  papillae  at  the  extremities 
of  the  calyces;  the  circular  fibers  may  be  traced  surrounding  the  medullary  substance  in  the 
same  situation.  In  the  ureter  proper  the  muscular  fibers  are  very  distinct,  and  are  arranged 
in  three  layers:  an  external  longitudinal,  a  middle  circular,  and  an  internal,  less  distinct  than 
the  other  two,  but  having  a  general  longitudinal  direction.  According  to  KoUiker  this  internal 
layer  is  found  only  in  the  neighborhood  of  the  bladder. 

The  mucous  coat  {tunica  mucosa)  is  smooth,  and  presents  a  few  longitudinal  folds  which 
become  effaced  by  distension.  It  is  continuous  with  the  mucous  membrane  of  the  bladder 
below,  while  it  is  prolonged  over  the  papillae  of  the  kidney  above.  Its  epithelitun  is  of  a  tran- 
sitional character,  and  resembles  that  found  in  the  bladder  (see  Fig.  1141).  It  consists  of  sev- 
eral layers  of  cells,  of  which  the  innermost — that  is  to  say,  the  cells  in  contact  with  the  urine — 
are  somewhat  fiattened,  with  concavities  on  their  deep  surfaces  into  which  the  rounded  ends 
of  the  cells  of  the  second  layer  fit.  These,  the  intermediate  cells,  more  or  less  resemble  columnar 
epithehum,  and  are  pear-shaped,  with  rounded  internal  extremities  which  fit  into  the  concavities 
of  the  cells  of  the  first  layer,  and  narrow  external  extremities  which  are  wedged  in  between  the 
cells  of  the  third  layer.  The  external  or  third  layer  consists  of  conical  or  oval  cells  varying  in 
number  in  different  parts,  and  presenting  processes  which  extend  down  into  the  basement 
membrane.  Beneath  the  epithehum,  and  separating  it  from  the  muscular  coats,  is  a  dense  layer 
of  fibrous  tissue  containing  many  elastic  fibers. 

Vessels  and  Nerves. — The  arteries  supplying  the  ureter  are  branches  from  the  renal,  internal 
spermatic,  hypogastric,  and  inferior  vesical. 

The  nerves  are  derived  from  the  inferior  mesenteric,  spermatic,  and  pelvic  plexuses. 

Variations. — The  upper  portion  of  the  ureter  is  sometimes  double;  more  rarely  it  is  double  the 
greater  part  of  its  extent,  or  even  completely  so.  In  such  cases  there  are  two  openings  into  the 
bladder.    Asynunetry  in  these  variations  is  common. 

The  Urinary  Bladder  (Vesica  Urinaria;  Bladder)  (Fig.  1135). 

The  urinary  bladder  is  a  musculomembranous  sac  which  acts  as  a  reservoir 
for  the  urine;  and  as  its  size,  position,  and  relations  vary  according  to  the  amount 
of  fluid  it  contains,  it  is  necessary  to  study  it  as  it  appears  (a)  when  empty,  and  (6) 
when  distended.  In  both  conditions  the  position  of  the  bladder  varies  with  the 
condition  of  the  rectum,  being  pushed  upward  and  forward  when  the  rectum  is 
distended. 

The  Empty  Bladder. — When  hardened  in  situ,  the  empty  bladder  has  the 
form  of  a  flattened  tetrahedron,  with  its  vertex  tilted  forward.  It  presents  a  fundus, 
a  vertex,  a  superior  and  an  inferior  surface.  The  fundus  (Fig.  1152)  is  triangular 
in  shape,  and  is  directed  downward  and  backward  toward  the  rectum,  from  which 
it  is  separated  by  the  rectovesical  fascia,  the  vesiculse  seminales,  and  the  terminal 
portions  of  the  ductus  deferentes.  The  vertex  is  directed  forward  toward  the  upper 
part  of  the  symphysis  pubis,  and  from  it  the  middle  umbilical  ligament  is  continued 
upward  on  the  back  of  the  anterior  abdominal  wall  to  the  umbilicus.  The  peri- 
toneum is  carried  by  it  from  the  vertex  of  the  bladder  on  to  the  abdominal  wall 
to  form  the  middle  umbilical  fold.  The  superior  surface  is  triangular,  bounded 
on  either  side  by  a  lateral  border  which  separates  it  from  the  inferior  surface,  and 
behind  by  a  posterior  border,  represented  by  a  line  joining  the  two  ureters,  which 
intervenes  between  it  and  the  fundus.  The  lateral  borders  extend  from  the  ureters 
to  the  vertex,  and  from  them  the  peritoneum  is  carried  to  the  walls  of  the  pelvis. 
On  either  side  of  the  bladder  the  peritoneum  shows  a  depression,  named  the  para- 
vesical fossa  (Fig.  1037) .  The  superior  surface  is  directed  upward,  is  covered  by  peri- 
toneum, and  is  in  relation  with  the  sigmoid  colon  and  some  of  the  coils  of  the  small 
intestine.    When  the  bladder  is  empty  and  firmly  contracted,  this  surface  is  convex 


!_ 


1228 


SPLANCHNOLOGY 


and  the  lateral  and  posterior  borders  are  rounded;  whereas  if  the  bladder  be  relaxed 
it  is  concave,  and  the  interior  of  the  viscus,  as  seen  in  a  median  sagittal  section, 
presents  the  appearance  of  a  V-shaped  slit  with  a  shorter  posterior  and  a  longer 
anterior  limb — the  apex  of  the  V  corresponding  with  the  internal  orifice  of  the 
urethra.  The  inferior  surface  is  directed  downward  and  is  uncovered  by  peritoneum. 
It  may  be  divided  into  a  posterior  or  prostatic  area  and  two  infero-lateral  surfaces. 
The  prostatic  area  is  somewhat  triangular :  it  rests  upon  and  is  in  direct  continuity 
with  the  base  of  the  prostate;  and  from  it  the  urethra  emerges.  The  infero-lateral 
portions  of  the  inferior  surface  are  directed  downward  and  lateralward:  in  front, 
they  are  separated  from  the  symphysis  pubis  by  a  mass  of  fatty  tissue  which  is 
named  the  retropubic  pad ;  behind,  they  are  in  contact  with  the  fascia  which  covers 
the  Levatores  ani  and  Obturatores  interni. 


Ureter 


Ductus  deferens       ^)s^ 


Urethra 


External  urethral 
orifice 


a 


Ejaculatory  duct 
—  Anal  canal 


Fig.  1135. — Median  sagitta  section  of  male  pelvis. 


When  the  bladder  is  empty  it  is  placed  entirely  within  the  pelvis,  below  the  level 
of  the  obliterated  hypogastric  arteries,  and  below  the  level  of  those  portions  of  the 
ductus  deferentes  which  are  in  contact  with  the  lateral  wall  of  the  pelvis;  after 
they  cross  the  ureters  the  ductus  deferentes  come  into  contact  with  the  fundus 
of  the  bladder.  As  the  viscus  fills,  its  fundus,  being  more  or  less  fixed,  is  only 
slightly  depressed;  while  its  superior  surface  gradually  rises  into  the  abdominal 
cavity,  carrying  with  it  its  peritoneal  covering,  and  at  the  same  time  rounding 
off  the  posterior  and  lateral  borders. 

The  Distended  Bladder. — When  the  bladder  is  moderately  full  it  contains 
about  0.5  liter  and  assumes  an  oval  form;  the  long  diameter  of  the  oval  measures 
about  12  cm.  and  is  directed  upward  and  forward.  In  this  condition  it  presents 
a  postero-superior,  an  antero-inferior,  and  two  lateral  surfaces,  a  fundus  and  a 


THE  URINARY  BLADDER 


1229 


summit.  The  postero-superior  surface  is  directed  upward  and  backward,  and  is  cov- 
ered by  peritoneum:  behind,  it  is  separated  from  the  rectum  by  the  rectovesical 
excavation,  while  its  anterior  part  is  in  contact  with  the  coils  of  the  small  intestine. 
The  antero-inferior  surface  is  devoid  of  peritoneum,  and  rests,  below,  against  the 
pubic  bones,  above  which  it  is  in  contact  with  the  back  of  the  anterior  abdominal 
wall.  The  lower  parts  of  the  lateral  surfaces  are  destitute  of  peritoneum,  and  are 
in  contact  with  the  lateral  walls  of  the  pelvis.  The  line  of  peritoneal  reflection 
from  the  lateral  surface  is  raised  to  the  level  of  the  obliterated  hypogastric  artery. 
The  fundus  undergoes  little  alteration  in  position,  being  only  slightly  lowered. 
It  exhibits,  however,  a  narrow  triangular  area,  which  is  separated  from  the  rectum 
merely  by  the  rectovesical  fascia.  This  area  is  bounded  below  by  the  prostate, 
above  by  the  rectovesical  fold  of  peritoneum,  and  laterally  by  the  ductus  deferentes. 


I'^^$^i  i 


CORPUS 
CAVERNOSUM 


COWPER'S' 
GLA^D 

BULBO- 

CAVERNOSUS 

MUSCLE 


Fig.  1136.- 


-Male  pelvic  organs  seen  from  right  side.     Bladder  and  rectum  distended;  relations  of  peritoneum  to  the 
bladder  and  rectum  shown  in  blue.    The  arrow  points  to  the  rectovesical  pouch. 


The  ductus  deferentes  frequently  come  in  contact  with  each  other  above  the  pros- 
tate, and  under  such  circumstances  the  lower  part  of  the  triangular  area  is  obliter- 
ated. The  line  of  reflection  of  the  peritoneum  from  the  rectum  to  the  bladder 
appears  to  undergo  little  or  no  change  when  the  latter  is  distended;  it  is  situated 
about  10  cm.  from  the  anus.  The  summit  is  directed  upward  and  forward  above 
the  point  of  attachment  of  the  middle  umbilical  ligament,  and  hence  the  peritoneum 
which  follows  the  ligament,  forms  a  pouch  of  varying  depth  between  the  summit 
of  the  bladder,  and  the  anterior  abdominal  wall. 

The  Bladder  in  the  Child  (Figs.  1137, 1138).— In  the  newborn  child  the  internal 
urethral  orifice  is  at  the  level  of  the  upper  border  of  the  symphysis  pubis;  the 
bladder  therefore  lies  relatively  at  a  much  higher  level  in  the  infant  than  in  the 
adult.    Its  anterior  surface  "  is  in  contact  with  about  the  lower  two-thirds  of  that 


1^ 


1230 


SPLANCHNOLOGY 


part  of  the  abdominal  wall  which  lies  between  the  symphysis  pubis  and  the  umbili- 
cus" (Symington^).  Its  fundus  is  clothed  with  peritoneum  as  far  as  the  level 
of  the  internal  orifice  of  the  urethra.  Although  the  bladder  of  the  infant  is  usually 
described  as  an  abdominal  organ,  Symington  has  pointed  out  that  only  about 


Sacrum 


Rectum 
Coccyx 


Anal  canal 


Symphysis  pubis 
Urethra 


FiQ.   1137. — Sagittal  section  through  the  pelvis  of  a  newly  born  male  child. 

one-half  of  it  lies  above  the  plane  of  the  superior  aperture  of  the  pelvis.  Disse 
maintains  that  the  internal  urethral  orifice  sinks  rapidly  during  the  first  three 
years,  and  then  more  slowly  until  the  ninth  year,  after  which  it  remains  stationary 
until  puberty,  when  it  again  slowly  descends  and  reaches  its  adult  position. 


Uterine  tube 


Cavity  of  uterus 
Sigmoid  colon 

Rectum 


Anal  canal  ~T 


Round  ligament  of 

uterus 
Bladder 

Symphysis  pubis 

~  Urethra 
Vagina 


FiQ.   1138. — Sagittal  section  through  the  pelvis  of  a  newly  born  female  child. 

The  Female  Bladder  (Fig.  1139). — In  the  female,  the  bladder  is  in  relatioit 
behind  with  the  uterus  and  the  upper  part  of  the  vagina.  It  is  separated  from  the 
anterior  surface  of  the  body  of  the  uterus  by  the  vesicouterine  excavation,  but 


'  The  Anatomy  of  the  Child. 


THE  URINARY  BLADDER 


1231 


hbelow  the  level  of  this  excavation  it  is  connected  to  the  front  of  the  cervix  uteri 
and  the  upper  part  of  the  anterior  wall  of  the  vagina  by  areolar  tissue.  When 
the  bladder  is  empty  the  uterus  rests  upon  its  superior  surface.  The  female  bladder 
is  said  by  some  to  be  more  capacious  than  that  of  the  male,  but  probably  the 
opposite  is  the  case. 


Sacrum 


Coccyx 

Rectovaginal 
excavation 
External  uterine 
orifice 


AnaL  canal 


Uterovesical 
excavation 


Urethra 


Fia.   1139. — Median  sagittal  section  of  female  pelvis. 

Ligaments. — The  bladder  is  connected  to  the  pelvic  wall  by  the  fascia  endo- 
pelvina.  In  front  this  fascial  attachment  is  strengthened  by  a  few  muscular  fibers, 
the  Pubovesicales,  which  extend  from  the  back  of  the  pubic  bones  to  the  front 
of  the  bladder;  behind,  other  muscular  fibers  run  from  the  fundus  of  the  bladder 
to  the  sides  of  the  rectum,  in  the  sacrogenital  folds,  and  constitute  the  Rectovesicales. 

The  vertex  of  the  bladder  is  joined  to  the  umbilicus  by  the  remains  of  the  urachus 
which  forms  the  middle  umbilical  ligament,  a  fibromuscular  cord,  broad  at  its 
attachment  to  the  bladder  but  narrowing  as  it  ascends. 

From  the  superior  surface  of  the  bladder  the  peritoneum  is  carried  off  in  a  series 
of  folds  which  are  sometimes  termed  the  false  ligaments  of  the  bladder.  Anteriorly 
there  are  three  folds:  the  middle  mnbilical  fold  on  the  middle  umbilical  ligament, 
and  two  lateral  umbilical  folds  on  the  obliterated  hypogastric  arteries.  The  reflec- 
tions of  the  peritoneum  on  to  the  side  walls  of  the  pelvis  form  the  lateral  false 
ligaments,  while  the  sacrogenital  folds  constitute  posterior  false  ligaments. 

Interior  of  the  Bladder  (Fig.  1140). — The  mucous  membrane  lining  the  bladder 
is,  over  the  greater  part  of  the  viscus,  loosely  attached  to  the  muscular  coat,  and 
%ppears  wrinkled  or  folded  when  the  bladder  is  contracted :  in  the  distended  condi- 
tion of  the  bladder  the  folds  are  effaced.  Over  a  small  triangular  area,  termed  the 
trigonum  vesicae,  immediately  above  and  behind  the  internal  orifice  of  the  urethra, 
the  mucous  membrane  is  firmly  bound  to  the  muscular  coat,  and  is  always  smooth. 


SPLANCHNOLOGY 

The  anterior  angle  of  the  trigonum  vesicae  is  formed  by  the  Internal  orifice  of  the 
urethra:  its  postero-lateral  angles  by  the  orifices  of  the  ureters.  Stretching  behind 
the  latter  openings  is  a  slightly  curved  ridge,  the  torus  uretericus,  forming  the  base 
of  the  trigone  and  produced  by  an  underlying  bundle  of  non-striped  muscular 
fibers.  The  lateral  parts  of  this  ridge  extend  beyond  the  openings  of  the  ureters, 
and  are  named  the  plicae  uretericae ;  they  are  produced  by  the  terminal  portions  of 
the  ureters  as  they  traverse  obliquely  the  bladder  wall.  When  the  bladder  is 
illuminated  the  torus  uretericus  appears  as  a  pale  band  and  forms  an  important 
guide  during  the  operation  of  introducing  a  catheter  into  the  ureter. 

Vertex 


.  urethral 
orifice 

UvulcB  vesicae 
Trigonum 


Torus 
uretericus 

Orifice  of 
ureter 


Fig.  1140. — The  interior  of  bladder. 


The  orifices  of  the  ureters  are  placed  at  the  postero-lateral  angles  of  the  trigonum 
vesicae,  and  are  usually  slit-like  in  form.  In  the  contracted  bladder  they  are  about 
2.5  cm.  apart  and  about  the  same  distance  from  the  internal  urethral  orifice;  in 
the  distended  viscus  these  measurements  may  be  increased  to  about  5  cm. 

The  internal  urethral  orifice  is  placed  at  the  apex  of  the  trigonum  vesicae,  in  the 
most  dependent  part  of  the  bladder,  and  is  usually  somewhat  crescentic  in  form ; 
the  mucous  membrane  immediately  behind  it  presents  a  slight  elevation,  the 
uvula  vesicae,  caused  by  the  middle  lobe  of  the  prostate. 

Structure  (Fig.  1141). — The  bladder  is  composed  of  the  four  coats:  serous,  muscular,  sub- 
mucous, and  mucous  coats. 

The  serous  coat  (tunica  serosa)  is  a  partial  one,  and  is  derived  from  the  peritoneimi.  It  invests 
the  superior  surface  and  the  upper  parts  of  the  lateral  surfaces,  and  is  reflected  from  these  on 
to  the  abdominal  and  pelvic  walls. 

The  muscular  coat  {tunica  muscularis)  consists  of  three  layers  of  unstriped  muscular  fibers: 
an  external  layer,  composed  of  fibers  having  for  the  most  part  a  longitudinal  arrangement;  a 
middle  layer,  in  which  the  fibers  are  arranged,  more  or  less,  in  a  circular  manner;  and  an  internal 
layer,  in  which  the  fibers  have  a  general  longitudinal  arrangement. 

The  fibers  of  the  external  layer  arise  from  the  posterior  surface  of  the  body  of  the  pubis  in  both 
sexes  {musculi  pubovesicales),  and  in  the  male  from  the  adjacent  part  of  the  prostate  and  its 


THE  URINARY  BLADDER 


1233 


Transitional 
epithelium 

Submucous  coat 


Inner  layer  of 
longitudinal 
muscle  fibers 


Circular  muscle 

fibers 


Outer  layer  of 
longitudincu, 
rauscle  fibers 


Fio.   1141. — Vertical  section  of  bladder  wall. 


capsule.  They  pass,  in  a  more  or  less  longitudinal  manner,  up  the  inferior  surface  of  the  bladder, 
over  its  vertex,  and  then  descend  along  its  fundus  to  become  attached  to  the  prostate  in  the 
male,  and  to  the  front  of  the  vagina  in  the  female.  At  the  sides  of  the  bladder  the  fibers  are 
arranged  obliquely  and  intersect  one  another.  This 
layer  has  been  named  the  Detrusor  urinse  muscle. 

The  fibers  of  the  middle  circular  layer  are  verj- 
thinly  and  irregularly  scattered  on  the  body  of  the 
organ,  and,  although  to  some  extent  placed  trans- 
versely to  the  long  axis  of  the  bladder,  are  for  the 
most  part  arranged  obUquely.  Toward  the  lower 
part  of  the  bladder,  around  the  internal  urethral 
orifice,  they  are  disposed  in  a  thick  circular  layer, 
forming  the  Sphincter  vesicae,  which  is  continuous 
with  the  muscular  fibers  of  the  prostate. 

The  internal  longitudinal  layer  is  thin,  and  its 
fasciculi  have  a  reticular  arrangement,  but  with  a 
tendency  to  assume  for  the  most  part  a  longitudinal 
direction.  Two  bands  of  oblique  fibers,  originating 
behind  the  orifices  of  the  ureters,  converge  to  the 
back  part  of  the  prostate,  and  are  inserted  by  means 
of  a  fibrous  process,  into  the  middle  lobe  of  that 
organ.  They  are  the  muscles  of  the  ureters,  de- 
scribed by  Sir  C.  Bell,  who  supposed  that  during 
the  contraction  of  the  bladder  they  serve  to  retain 
the  oblique  direction  of  the  ureters,  and  so  prevent 
the  reflux  of  the  urine  into  them. 

The  submucous  coat  (tela  submucosa)  consists  of 
a  laj^er  of  areolar  tissue,  connecting  together  the 
muscular  and  mucous  coats,  and  intimately  united 
to  the  latter. 

The  mucous  coat  {tunica  mucosa)  is  thin,  smooth,  and  of  a  pale  rose  color.  It  is  continuous 
above  through  the  ureters  with  the  lining  membrane  of  the  renal  tubules,  and  below  with  that 
of  the  urethra.  The  loose  texture  of  the  submucous  layer  allows  the  mucous  coat  to  be  thrown 
into  folds  or  rugce  when  the  bladder  is  empty.  Over  the  trigonum  vesicae  the  mucous  mem- 
brane is  closely  attached  to  the  muscular  coat,  and  is  not  thrown  into  folds,  but  is  smooth  and 
flat.  The  epithelium  covering  it  is  of  the  transitional  variety,  consisting  of  a  superficial  layer 
of  polyhedral  flattened  cells,  each  with  one,  two,  or  three  nuclei;  beneath  these  is  a  stratum 
of  large  club-shaped  cells,  with  their  narrow  extremities  directed  downward  and  wedged  in 
between  smaller  spindle-shaped  cells,  containing  oval  nuclei  (Fig.  1141).  The  epithelium  varies 
according  as  the  bladder  is  distended  or  contracted.  In  the  former  condition  the  superficial  cells 
are  flattened  and  those  of  the  other  layers  are  shortened;  in  the  latter  they  present  the  appear- 
ance described  above.  There  are  no  true  glands  in  the  mucous  membrane  of  the  bladder,  though 
certain  mucous  follicles  which  exist,  especially  near  the  neck  of  the  bladder,  have  been  regarded 
as  such. 

Vessels  and  Nerves. — The  arteries  supplying  the  bladder  are  the  superior,  middle,  and  inferior 
vesical,  derived  from  the  anterior  trimk  of  the  hypogastric.  The  obturator  and  inferior  gluteal 
arteries  also  supply  small  visceral  branches  to  the  bladder,  and  in  the  female  additional  branches 
are  derived  from  the  uterine  and  vaginal  arteries. 

The  veins  form  a  compUcated  plexus  on  the  inferior  surface,  and  fundus  near  the  prostate,  and 
end  in  the  hypogastric  veins. 

The  lymphatics  are  described  on  page  712. 

The  nerves  of  the  bladder  are  (1)  fine  medullated  fibers  from  the  third  and  fourth  sacral  nerves, 
and  (2)  non-medullated  fibers  from  the  hypogastric  plexus.  They  are  connected  with  gangUa 
in  the  outer  and  submucous  coats  and  are  finally  distributed,  all  as  non-medullated  fibers,  to  the 
muscular  layer  and  epithehal  lining  of  the  viscus. 

Abnormalities. — A  defect  of  development,  in  which  the  bladder  is  impUcated,  is  known 
under  the  name  of  extroversion  of  the  bladder.  In  this  condition  the  lower  part  of  the  abdominal 
wall  and  the  anterior  wall  of  the  bladder  are  wanting,  so  that  the  fundus  of  the  bladder  presents 
on  the  abdominal  surface,  and  is  pushed  forward  by  the  pressure  of  the  viscera  within  the  abdomen, 
forming  a  red  vascular  tumor  on  which  the  openings  of  the  ureters  are  visible.  The  penis,  except 
the  glans,  is  rudimentary  and  is  cleft  on  its  dorsal  surface,  exposing  the  floor  of  the  urethra,  a 
condition  known  as  epispadias.    The  pelvic  bones  are  also  arrested  in  development. 


1234 


SPLANCHNOLOGY 


The  Male  Urethra  (Urethra  Virilis)  (Fig.  1142). 


Urethral  crest 

Openings  of  'prostatic  utricle 

and  ejaculatory  ducts 
Prostatic  part  of  urethra 

Membranous  part  of  urethra 


The  male  urethra  extends  from  the  internal  urethral  orifice  in  the  urin/iry  bladOer" 
to  the  external  urethral  orifice  at  the  end  of  the  penis.  It  presents  a  double  curve 
in  the  ordinary  relaxed  state  of  the  penis  (Fig.  1137).  Its  length  varies  from  17.5 
to  20  cm.;  and  it  is  divided  into  three  portions,  the  prostatic,  membranous,  and 

cavernous,  the  structure  and  rela- 
tions of  which  are  essentially 
different.  Except  during  the 
passage  of  the  urine  or  semen, 
the  greater  part  of  the  urethral 
canal  is  a  mere  transverse  cleft 
or  slit,  with  its  upper  and  under 
surfaces  in  contact;  at  the  external 
orifice  the  slit  is  vertical,  in  the 
membranous  portion  irregular  or 
stellate,  and  in  the  prostatic  por- 
tion somewhat  arched. 

The  prostatic  portion  {pars  pros- 
tatica),  the  widest  and  most  dila- 
table part  of  the  canal,  is  about 
3  cm.  long.  It  runs  almost  ver- 
tically thro.ugh  the  prostate  from 
its  base  to  its  apex,  lying  nearer 
its  anterior  than  its  posterior 
surface;  the  form  of  the  canal 
is  spindle-shaped,  being  wider  in 
the  middle  than  at  either  extrem- 
ity, and  narrowest  below,  where 
it  joins  the  membranous  portion. 
A  transverse  section  of  the  canal 
as  it  lies  in  the  prostate  is  horse- 
shoe-shaped, with  the  convexity 
directed  forward. 

Upon  the  posterior  wall  or 
floor  is  a  narrow  longitudinal 
ridge,  the  urethral  crest  (veru- 
montanum),  formed  by  an  eleva- 
tion of  the  mucous  membrane 
and  its  subjacent  tissue.  It  is 
from  15  to  17  mm.  'in  length, 
and  about  3  mm.  in  height,  and 
contains,  according  to  Kobelt,  muscular  and  erectile  tissue.  When  distended, 
it  may  serve  to  prevent  the  passage  of  the  semen  backward  into  the  bladder. 
On  either  side  of  the  crest  is  a  slightly  depressed  fossa,  the  prostatic  sinus,  the  floor 
of  which  is  perforated  by  numerous  apertures,  the  orifices  of  the  prostatic  ducts 
from  the  lateral  lobes  of  the  prostate;  the  ducts  of  the  middle  lobe  open  behind 
the  crest.  At  the  forepart  of  the  urethral  crest,  below  its  summit,  is  a  median 
elevation,  the  colliculus  seminalis,  upon  or  within  the  margins  of  which  are  the 
orifices  of  the  prostatic  utricle  and  the  slit-like  openings  of  the  ejaculatory  ducts. 
The  prostatic  utricle  {sinus  pocularis)  forms  a  cul-de-sac  about  6  mm.  long,  which 
runs  upward  and  backward  in  the  substance  of  the  prostate  behind  the  middle 
lobe.    Its  walls  are  composed  of  fibrous  tissue,  muscular  fibers,   and    mucous 


Small  lacuna 


Lacuna  magna 


Ext.  urethral  orifice 


Fig.   1142. — ^The  male  urethra  laid  open  on  its  anterior  (upper) 
surface. 


THE  MALE  URETHRA  ^^^^^  1235 

membrane,  and  numerous  small  glands  open  on  its  inner  surface.  It  was  called 
by  Weber  the  uterus  masculinus,  from  its  being  developed  from  the  united 
lower  ends  of  the  atrophied  Miillerian  ducts,  and  therefore  homologous  with  the 
uterus  and  vagina  in  the  female. 

The  membranous  portion  {yars  membranacea)  is  the  shortest,  least  dilatable, 
and,  with  the  exception  of  the  external  orifice,  the  narrowest  part  of  the  canal. 
It  extends  downward  and  forward,  with  a  slight  anterior  concavity,  between  the 
apex  of  the  prostate  and  the  bulb  of  the  urethra,  perforating  the  urogenital  dia- 
phragm about  2.5  cm.  below  and  behind  the  pubic  symphysis.  The  hinder  part 
of  the  urethral  bulb  lies  in  apposition  with  the  inferior  fascia  of  the  urogenital 
diaphragm,  but  its  upper  portion  diverges  somewhat  from  this  fascia :  the  anterior 
wall  of  the  membranous  urethra  is  thus  prolonged  for  a  short  distance  in  front 
of  the  urogenital  diaphragm;  it  measures  about  2  cm.  in  length,  while  the  posterior 
wall  which  is  between  the  two  fasciae  of  the  diaphragm  is  only  1.25  cm.  long. 

The  membranous  portion  of  the  urethra  is  completely  surrounded  by  the  fibers 
of  the  Sphincter  urethrse  membranacese.  In  front  of  it  the  deep  dorsal  vein  of 
the  penis  enters  the  pelvis  between  the  transverse  ligament  of  the  pelvis  and  the 
arcuate  pubic  ligament ;  on  either  side  near  its  termination  are  the  bulbourethral 
glands. 

The  cavernous  portion  {pars  cavernosa;  penile  or  spongy  portion)  is  the  longest 
part  of  the  urethra,  and  is  contained  in  the  corpus  cavernosum  urethrse.  It  is 
about  15  cm.  long,  and  extends  from  the  termination  of  the  membranous  portion 
to  the  external  urethral  orifice.  Commencing  below  the  inferior  fascia  of  the 
urogenital  diaphragm  it  passes  forward  and  upward  to  the  front  of  the  symphysis 
pubis;  and  then,  in  the  flaccid  condition  of  the  penis,  it  bends  downward  and 
forward.  It  is  narrow,  and  of  uniform  size  in  the  body  of  the  penis,  measur- 
ing about  6  mm.  in  diameter;  it  is  dilated  behind,  within  the  bulb,  and  again 
anteriorly  within  the  glans  penis,  where  it  forms  the  fossa  navicularis  urethrae. 

The  external  urethral  orifice  (orificium  urethrae  externum;  meatus  urinarius)  is 
the  most  contracted  part  of  the  urethra;  it  is  a  vertical  slit,  about  6  mm.  long, 
bounded  on  either  side  by  two  small  labia. 

The  lining  membrane  of  the  urethra,  especially  on  the  floor  of  the  cavernous 
portion,  presents  the  orifices  of  numerous  mucous  glands  and  follicles  situated 
in  the  submucous  tissue,  and  named  the  urethral  glands  (Liitre).  Besides  these 
there  are  a  number  of  small  pit-like  recesses,  or  lacunse,  of  varying  sizes.  Their 
orifices  are  directed  forward,  so  that  they  may  easily  intercept  the  point  of  a 
catheter  in  its  passage  along  the  canal.  One  of  these  lacunae,  larger  than  the  rest, 
is  situated  on  the  upper  surface  of  the  fossa  navicularis;  it  is  called  the  lacuna 
magna.  The  bulbo-urethral  glands  open  into  the  cavernous  portion  about  2.5  cm. 
in  front  of  the  inferior  fascia  of  the  urogenital  diaphragm. 

Structurd. — The  urethra  is  composed  of  mucous  membrane,  supported  by  a  submucous  tissue 
which  connects  it  with  the  various  structures  through  which  it  passes. 

The  mucous  coat  forms  part  of  the  genito-urinary  mucous  membrane.  It  is  continuous  with 
the  mucous  membrane  of  the  bladder,  ureters,  and  kidneys;  externally,  with  the  integument 
covering  the  glans  penis;  and  is  prolonged  into  the  ducts  of  the  glands  which  open  into  the  urethra, 
viz.,  the  bulbo-urethral  glands  ar.d  the  prostate;  and  into  the  ductus  deferentes  and  vesiculae 
seminales,  through  the  ejaculatory  ducts.  In  the  cavernous  and  membranous  portions  the  mucous 
membrane  is  arranged  in  longitudinal  folds  when  the  tube  is  empty.  Small  papillae  are  found 
upon  it,  near  the  external  urethral  orifice;  its  epithehal  lining  is  of  the  coliminar  variety  except 
near  the  external  orifice,  where  it  is  squamous  and  stratified. 

The  submucous  tissue  consists  of  a  vascular  erectile  layer;  outside  this  is  a  layer  of  unstriped 
muscular  fibers,  arranged  in  a  circular  direction,  which  separates  the  mucous  membrane  and 
submucous  tissue  from  the  tissue  of  the  corpus  cavernosum  urethra;. 

Congenital  defects  of  the  urethra  occur  occasionally.  The  one  most  frequently  met  with  is 
where  there  is  a  cleft  on  the  floor  of  the  urethra  owing  to  an  arrest  of  union  in  the  middle  line. 
This  is  known  as  hypospadias,  and  the  cleft  may  vary  in  extent.    The  simplest  and  by  far  the 


1236  SPLANCHNOLOGY 


most  common  form  is  where  the  deficiency  is  confined  to  the  glans  penis.  The  urethra  ends  at 
the  point  where  the  extremity  of  the  prepuce  joins  the  body  of  the  penis,  in  a  small  valve-like 
opening.  The  prepuce  is  also  cleft  on  its  under  surface  and  forms  a  sort  of  hood  over  the  glans 
There  is  a  depression  on  the  glans  in  the  position  of  the  normal  meatus.  This  condition  produces 
no  disability  and  requires  no  treatment.  In  more  severe  cases  the  cavernous  portion  of  the 
urethra  is  cleft  throughout  its  entire  length,  and  the  opening  of  the  urethra  is  at  the  point  of 
junction  of  the  penis  and  scrotum.  The  under  surface  of  the  penis  in  the  middle  line  presents  a 
furrow  lined  by  a  moist  mucous  membrane,  on  either  side  of  which  is  often  more  or  less  dense 
fibrous  tissue  stretching  from  the  glans  to  the  opening  of  the  urethra,  which  prevents  complete 
erection  taking  place.  Great  discomfort  is  induced  during  micturition,  and  sexual  connection  is 
impossible.  The  condition  may  be  remedied  by  a  series  of  plastic  operations.  The  worst  form 
of  this  condition  is  where  the  urethra  is  deficient  as  far  back  as  the  perineum,  and  the  scrotum 
is  cleft.  The  penis  is  small  and  bound  down  between  the  two  halves  of  the  scrotum,  so  as  to 
resemble  an  hypertrophied  chtoris.  The  testes  are  often  retained.  The  condition  of  parts, 
therefore,  very  much  resembles  the  external  organs  of  generation  of  the  female,  and  many  chil- 
dren the  victims  of  this  malformation  have  been  brought  up  as  girls.  The  halves  of  the  scrotum, 
deficient  of  testes,  resemble  the  labia,  the  cleft  between  them  looks  like  the  orifice  of  the  vagina, 
and  the  diminutive  penis  is  taken  for  an  enlarged  cUtoris.  There  is  no  remedy  for  this  condition. 
A  much  more  uncommon  form  of  malformation  is  where  there  is  an  apparent  deficiency  of  the 
upper  wall  of  the  urethra;  this  is  named  epispadias.  The  deficiency  may  vary  in  extent;  when 
it  is  complete  the  condition  is  associated  with  extroversion  of  the  bladder.  In  less  extensive  cases, 
where  there  is  no  extroversion,  there  is  an  infundibuUform  opening  into  the  bladder.  The 
penis  is  usually  dwarfed  and  turned  upward,  so  that  the  glans  lies  over  the  opening.  Con- 
genital stricture  is  also  occasionally  met  with,  and  in  such  cases  multiple  strictures  may  be 
present  throughout  the  whole  length  of  the  cavernous  portion. 

The  Female  Urethra  (Urethra  Muliebris)  (Fig.  1139). 

The  female  urethra  is  a  narrow  membranous  canal,  about  4  cm.  long,  extending 
from  the  internal  to  the  external  urethral  orifice.  It  is  placed  behind  the  sym- 
physis pubis,  imbedded  in  the  anterior  wall  of  the  vagina,  and  its  direction  is  ob- 
liquely downward  and  forward;  it  is  slightly  curved  with  the  concavity  directed 
forward.  Its  diameter  when  undilated  is  about  6  mm.  It  perforates  the  fasciae 
of  the  urogenital  diaphragm,  and  its  external  orifice  is  situated  directly  in  front 
of  the  vaginal  opening  and  about  2.5  cm.  behind  the  glans  clitoridis.  The  lining 
membrane  is  thrown  into  longitudinal  folds,  one  of  which,  placed  along  the  floor 
of  the  canal,  is  termed  the  urethral  crest.  Many  small  urethral  glands  open  into 
the  urethra. 

Structure. — The  urethra  consists  of  three'coats:  musctilar,  erectile,  and  mucous. 

The  muscular  coat  is  continuous  with  that  of  the  bladder;  it  extends  the  whole  length  of  the 
tube,  and  consists  of  circular  fibers.  In  addition  to  this,  between  the  superior  and  inferior  fasciae 
of  the  urogenital  diaphragm,  the  female  urethra  is  surrounded  by  the  Sphincter  urethrse  mem- 
branaceae,  as  in  the  male. 

A  thin  layer  of  spongy  erectile  tissue,  containing  a  plexus  of  large  veins,  intermixed  with 
bundles  of  unstriped  muscular  fibers,  lies  immediately  beneath  the  mucous  coat. 

The  mucous  coat  is  pale;  it  is  continuous  externally  with  that  of  the  vulva,  and  internally  with 
that  of  the  bladder.  It  is  lined  by  stratified  squamous  epithehum,  which  becomes  transitional 
near  the  bladder.    Its  external  orifice  is  surrounded  by  a  few  mucous  folUcles. 

THE   MALE    GENITAL   ORGANS  (ORGANA  GENITALIA  VIRILIA).        j^ 

The  male  genitals  include  the  testes,  the  ductus  deferentes,  the  vesiculae  semi- 
nales,  the  ejaculatory  ducts,  and  the  penis,  together  with  the  following  accessory 
structures,  viz.,  the  prostate  and  the  bulbourethral  glands. 

The  Testes  and  Their  Coverings.  (Figs.  1143,  1144,  1145). 

The  testes  are  two  glandular  organs,  which  secrete  the  semen;  they  are  suspended 
in  the  scrotum  by  the  spermatic  cords.  At  an  early  period  of  fetal  life  the  testes 
are  contained  in  the  abdominal  cavity,  behind  the  peritoneum.    Before  birth  they 


n 


THE  TESTES  AND  THEIR  COVERINGS 


1237 


lescend  to  the  inguinal  canal,  along  which  they  pass  with  the  spermatic  cord, 
and,  emerging  at  the  subcutaneous  inguinal  ring,  they  descend  into  the  scrotum, 
becoming  invested  in  their  course  by  coverings  derived  from  the  serous,  muscular, 
and  fibrous  layers  of  the  abdominal  parietes,  as  well  as  by  the  scrotum. 
The  coverings  of  the  testes  are,  the 


Skm  1  o      , 

T-k    4.     4.     •     /  bcrotum. 
Dartos  tunic  j 

Intercrural  fascia. 


Cremaster. 

Infundibuliform  fascia. 
Tunica  vaginalis. 


RIGHT   INGUINAL  CANAL 

(opened) 


CREMASTERIC  MUSCLE-—^ 
AND   FASCIA 
INTERCOLUMNAR 
FASCIA 


PERSISTENT  SEROUS 

CAVITY  AROUND 
CORD EXCEPTIONAL 


TUNICA  VAQINALIS- 
PARIETAL  LAYER 

INFUNDIBULIFORM 

FASCIA 
SESSILE 
HYDATID 


RIGHT    HALF   OF   SCROTUM     SKIN 


LEFT    HALF   OF   SCROTUM 


Fig.  1143. — The  scrotum.    On  the  left  side  the  cavity  of  the  tunica  vaginalis  has  been  opened;  on  the  right  side 
only  the  layers  superficial  to  the  Cremaster  have  been  removed.     (Testut.) 


The  Scrotum  is  a  cutaneous  pouch  which  contains  the  testes  and  parts  of  the 
spermatic  cords.  It  is  divided  on  its  surface  into  two  lateral  portions  by  a  ridge 
or  raphe,  which  is  continued  forward  to  the  under  surface  of  the  penis,  and  backward, 
_  _  along  the  middle  line  of  the  perineum  to  the  anus.  Of  these  two  lateral  portions 
IB  the  left  hangs  lower  than  the  right,  to  correspond  with  the  greater  length  of  the 
left  spermatic  cord.  Its  external  aspect  varies  under  different  circumstances: 
thus,  under  the  influence  of  warmth,  and  in  old  and  debilitated  persons,  it  becomes 
elongated  and  flaccid;  but,  under  the  influence  of  cold,  and  in  the  young  and 
robust,  it  is  short,  corrugated,  and  closely  applied  to  the  testes. 

The  scrotum  consists  of  two  layers,  the  integument  and  the  dartos  tunic. 
The  Integimient  is  very  thin,  of  a  brownish  color,  and  generally  thrown  into 
folds  or  rugae.    It  is  provided  with  sebaceous  follicles,  the  secretion  of  which  has  a 


1238 


SPLANCHNOLOGY 


peculiar  odor,  and  is  beset  with  thinly  scattered,  crisp  hairs,  the  roots  of  which 
are  seen  through  the  skin. 

The  Dartos  Tunic  {tunica  clartos)  is  a  thin  layer  of  non-striped  muscular  fibers, 
continuous,  around  the  base  of  the  scrotum,  with  the  two  layers  of  the  superficial 
fascia  of  the  groin  and  the  perineum;  it  sends  inward  a  septum,  which  divides 
thfe  scrotal  pouch  into  two  cavities  for  the  testes,  and  extends  between  the  raphe 
and  the  under  surface  of  the  penis,  as  far  as  its  root. 


EXTERNAL 

RING 

ACCESSORY 
SLIP  OF 

ORIGIN  OF^ 

CREMASTER 
MUSCLE 

"^ 

8PEBMATIC 

CORD 

•  ^ 

CREMASTER 
MUSCLE 


SEPTUM    OF 
SCROTUM 


VAS 
DEFERENS 


SPERMATIC 
ARTERY 


NERVE  FILAMENTS 
OF  SPERMATIC 
PLEXUS 
DEFERENTIAL 
ARTERY 


INFUNDIBULIFORM 
FASCIA 


SPERMATIC 
PLEXUS 

EPIDIDYMIS 
PARIETAL 
LAYER   OF 
TUNICA 
VAGINALIS 


Fig.  1 144. — ;The  scrotum.  The  penis  has  been  turned  upward,  and  the-anterior  wall  of  the  scrotum  has  been  removed. 
On  the  right  side,  the  spermatic  cord,  the  infundibuliform  fascia,  and  the  Cremaster  muscle  are  displayed;  on  the  left 
side,  the  inf undibidiform  fascia  has  been  divided  by  a  longitudinal  incision  passing  along  the  front  of  the  cord  and  the 
testicle,  and  a  portion  of  the  parietal  layer  of  the  tunica  vaginalis  has  been  removed  to  display  the  testicle  and  d  portion 
of  the  head  of  the  epididymis,  which  are  covered  by  the  visceral  layer  of  the  tunica  vaginalis.       (Toldt.) 

The  dartos  tunic  is  closely  united  to  the  skin  externally,  but  connected  with 
the  subjacent  parts  by  delicate  areolar  tissue,  upon  which  it  glides  with  the 
greatest  facility. 

The  Intercrural  Fascia  {intercolumnar  or  external  spermatic  fascia)  is  a  thin 
membrane,  prolonged  downward  around  the  surface  of  the  cord  and  testis  ^ee 
page  411).    It  is  separated  from  the  dartos  tunic  by  loose  areolar  tissue. 

The  Cremaster  consists  of  scattered  bundles  of  muscular  fibers  connected 
together  into  a  continuous  covering  by  intermediate  areplar. tissue  (see  page  414). 


TESTES  AND  THEIR  COVERINGS 


1239 


The  Infundibuliform  Fascia  (tunica  vaginalis  communis  [testis  et  funiculi  sper- 
matici])  is  a  thin  layer,  which  loosely  invests  the  cord;  it  is  a  continuation 
downward  of  the  transversalis  fascia  (see  page  418). 

The  Tunica  Vaginalis  is  described  with  the  testes. 


Skin 

Dartos  tunic 

Intercrural  fOiScia 

Crem  asterio  fascia 

Infundibuliform  fascia 

Parietal  tunica  vaginalis 

Visceral  tunica  vaginalis 

Tunica  albuginea 
A  lobule  of  the  testis 


A  septum 

Mediastinum  testis 

Sinus  of  epididymis 

Spermatic  vein 

Epididymis 

Ductus  deferens 

Artery  to  ductus 

Internal  spermatic  artery 

Internal  muscular  tunic 


FiQ.   1 145. — Transverse  section  through  the  left  side  of  the  scrotum  and  the  left  testis.     Tiio  sac  of  the  tunica 
vaginalis  is  represented  in  a  distended  condition.     (Diagrammatic.)     (Del6pine.) 

Vessels  and  Nerves. — The  arteries  supplying  the  coverings  of  the  testes  are:  the  superficial 
and  deep  external  pudendal  branches  of  the  femoral,  the  superficial  perineal  branch  of  the 
internal  pudendal,  and  the  cremasteric  branch  from  the  inferior  epigastric.  The  veins  follow 
the  course  of  the  corresponding  arteries.  The  Ijrmphatics  end  in  the  inguinal  lymph  glands. 
The  nerves  are  the  ilioinguinal  and  lumboinguinal  branches  of  the  lumbar  plexus,  the  two 
superficial  perineal  branches  of  the  internal  pudendal  nerve,  and  the  pudendal  branch  of  the 
posterior  femoral  cutaneous  nerve. 

The  Inguinal  Canal  (canalis  inguinalis)  is  described  on  page  418. 

The  Spermatic  Coid  (funiculus  siJermaticus)  (Fig.  1146)  extends  from  the  abdom- 

'  inal  inguinal  ring",  where  the  structures  of  w^hich  it  is  composed  converge,  to  the  back 
part  of  the  testis.  In  the  abdominal  wall  the  cord  passes  obliquely  along  the 
inguinal  canal,  lying  at  first  beneath  the  Obliquus  internus,  and  upon  the  fascia 
transversalis;  but  nearer  the  pubis,  it  rests  upon  the  inguinal  and  lacunar  liga- 
ments, having  the  aponeurosis  of  the  Obliquus  externus  in  front  of  it,  and  the 

^  inguinal  falx  behind  it.  It  then  escapes  at  the  subcutaneous  ring,  and  descends 
nearly  vertically  into  the  scrotum.  The  left  cord  is  rather  longer  than  the  right, 
consequently  the  left  testis  hangs  somewhat  lower  than  its  fellow. 

Structure  of  the  Spermatic  Cord. — The  spermatic  cord  is  composed  of  arteries,  veins,  lymphatics, 
nerves,  and  the  excretory  duct  of  the  testis.  These  structures  are  connected  together  by  areolar 
tissue,  and  invested  by  the  layers  brought  down  by  the  testis  in  its  descent. 

The  arteries  of  the  cord  are;  the  internal  and  external  spermatics;  and  the  artery  to  the  ductus 
deferens. 

The  irdernal  spermatic  artery,  a  branch  of  the  abdominal  aorta,  escapes  from  the  abdomen 
at  the  abdominal  inguinal  ring,  and  accompanies  the  other  constituents  of  the  spermatic  cord 
along  the  inguinal  canal  and  through  the  subcutaneous  inguinal  ring  into  the  scrotum.  It  then 
>  descends,  to  the  testis,  and,  becoming  tortuous)  divides  into  several  branches,  two  or  three  of 
which  accompany  the  ductus  deferens  and  supply  the  epididymis,  anastomosing  with  the  artery 
of  the  ductus  deferens:  the  others  supply  the  substance  of  the  testis. 


SPLANCHNOLOGY 

The  external  spermatic  artery  is  a  branch  of  the  inferior  epigastric  artery.  It  accompanies  the 
spermatic  cord  and  supphes  the  coverings  of  the  cord,  anastomosing  with  the  internal  spermatic 
artery. 

The  artery  of  the  ductus  deferens,  a  branch  of  the  superior  vesical,  is  a  long,  slender  vessel,  which 
accompanies  the  ductus  deferens,  ramifying  upon  its  coats,  and  anastomosing  with  the  internal 
spermatic  artery  near  the  testis. 


I 


VAS 
DEFERENS 


SPERMATIC 
CORD 


Fia.  1146. — The  spermatic  cord  in  the  inguinal  canal.     (Poirier  and  Charpy.) 

The  Spermatic  veins  (Fig.  1 147)  emerge  from  the  back  of  the  testis,  and  receive  tributaries  from 
the  epididymis:  they  unite  and  form  a  convoluted  plexus,  the  plexus  pampiniformis,  which  forms 
the  chief  mass  of  the  cord ;  the  vessels  composing  this  plexus  are  very  numerous,  and  ascend  along 
the  cord  in  front  of  the  ductus  deferens;  below  the  subcutaneous  inguinal  ring  they  unite  to  form 
three  or  four  veins,  which  pass  along  the  inguinal  canal,  and,  entering  the  abdomen  through  the 
abdominal  inguinal  ring,  coalesce  to  form  two  veins.  These  again  unite  to  form  a  single  vein, 
which  opens  on  the  right  side  into  the  inferior  vena  cava,  at  an  acute  angle,  and  on  the  left  side 
into  the  left  renal  vein,  at  a  right  angle. 

The  lymphatic  vessels  are  described  on  page  713, 

The  nerves  are  the  spermatic  plexus  from  the  sympathetic,  joined  by  filaments  from  the  pelvic 
plexus  which  accompany  the  artery  of  the  ductus  deferens. 

The  scrotum  forms  an  admirable  covering  for  the  protection  of  the  testes.  These  bodies,  lying 
suspended  and  loose  in  the  cavity  of  the  scrotum  and  surrounded  by  serous  membrane,  are 
capable  of  great  mobihty,  and  can  therefore  easily  slip  about  within  the  scrotum  and  thus 
avoid  injuries  from  blows  or  squeezes.  The  skin  of  the  scrotum  is  very  elastic  and  capable 
of  great  distension,  and  on  accoimt  of  the  looseness  and  amount  of  subcutaneous  tissue,  the 
scrotum  becomes  greatly  enlarged  in  cases  of  edema,  to  which  this  part  is  especially  liable  as 
a  result  of  its  dependent  position. 

The  Testes  are  suspended  in  the  scrotum  by  the  spermatic  cords,  the  left  testis 
hanging  somewhat  lower  than  its  fellow.  The  average  dimensions  of  the  testis 
are  from  4  to  5  cm.  in  length,  2.5  cm.  in  breadth,  and  3  cm.  in  the  antero-posterior 
diameter;  its  weight  varies  from  10.5  to  14  gm.  Each  testis  is  of  an  oval  form 
(Fig.  1148),  compressed  laterally,  and  having  an  oblique  position  in  the  scrotum; 
the  upper  extremity  i^  directed  forward  and  a  little  lateralward;  the  lower, 
backward  and  a  little  medialward;  the  anterior  convex  border  looks  forward  and 
downward,  the  posterior  or  straight  border,  to  which  the  cord  is  attached, 
backward  and  upward. 


THE  TEt 


AND  THEIR  COVERINGS 


The  anterior  border  and  lateral  surfaces,  as  well  as  both  extremities  of  the  organ, 
are  convex,  free,  smooth,  and  invested  by  the  visceral  layer  of  the  tunica  vaginalis. 


Fia.  1147. — Spermatic  veins.     (Testut.) 


Tail  of 
epididymis 


Cremaster 

Tunica  vaginalis 

Appendix  of  epididymis 
Head  of  epididymis 


Appendix  of  testis 


Fig.  1148. — The  right  testis,  exposed  by  laying  open  the  tunica  vaginalis. 


1242  SPLANCHNOLOGY 

The  posterior  border,  to  which  the  cord  is  attached,  receives  only  a  partial  invest- 
ment from  that  membrane.  Lying  upon  the  lateral  edge  of  this  posterior  border 
is  a  long,  narrow,  flattened  body,  named  the  epididymis. 

The  epididymis  consists  of  a  central  portion  or  body ;  an  upper  enlarged  extremity, 
the  head  {globus  major)',  and  a  lower  pointed  extremity,  the  tail  {glohns  minor), 
which  is  continuous  with  the  ductus  deferens,  the  duct  of  the  testis.  The  head 
is  intimately  connected  with  the  upper  end  of  the  testis  by  means  of  the  efferent 
ductules  of  the  gland;  the  tail  is  connected  with  the  lower  end  by  cellular  tissue, 
and  a  reflection  of  the  tunica  vaginalis.  The  lateral  surface,  head  and  tail  of  the 
epididymis  are  free  and  covered  by  the  serous  membrane;  the  body  is  also  com- 
pletely invested  by  it,  excepting  along  its  posterior  border;  while  between  the 
body  and  the  testis  is  a  pouch,  named  the  sinus  of  the  epididymis  {digital  fossa). 
The  epididymis  is  connected  to  the  back  of  the  testis  by  a  fold  of  the  serous 
membrane. 

Appendages  of  the  Testis  and  Epididymis. — On  the  upper  extremity  of  the  testis, 
just  beneath  the  head  of  the  epididymis,  is  a  minute  oval,  sessile  body,  the  appendix 
of  the  testis  {hydatid  of  Morgagni) ;  it  is  the  remnant  of  the  upper  end  of  the  Miillerian 
duct.  On  the  head  of  the  epididymis  is  a  second  small  stalked  appendage  (some- 
times duplicated) ;  it  is  named  the  appendix  of  the  epididymis  {pedunculated  hydatid), 
and  is  usually  regarded  as  a  detached  efferent  duct. 

The  testis  is  invested  by  three  tunics:  the  tunica  vaginalis,  tunica  albuginea, 
and  tunica  vasculosa. 

The  Tunica  Vaginalis  {tunica  vaginalis  propria  testis)  is  the  serous  covering  of 
the  testis.  It  is  a  pouch  of  serous  membrane,  derived  from  the  saccus  vaginalis 
of  the  peritoneum,  which  in  the  fetus  preceded  the  descent  of  the  testis  from  the 
abdomen  into  the  scrotum.  After  its  descent,  that  portion  of  the  pouch  which 
extends  from  the  abdominal  inguinal  ring  to  near  the  upper  part  of  the  gland 
becomes  obliterated;  the  lower  portion  remains  as  a  shut  sac,  which  invests  the 
surface  of  the  testis,  and  is  reflected  on  to  the  internal  surface  of  the  scrotum; 
hence  it  may  be  described  as  consisting  of  a  visceral  and  a  parietal  lamina. 

The  visceral  lamina  {lamina  visceralis)  covers  the  greater  part  of  the  testis  and 
epididymis,  connecting  the  latter  to  the  testis  by  means  of  a  distinct  fold.  From 
the  posterior  border  of  the  gland  it  is  reflected  on  to  the  internal  surface  of  the 
scrotum. 

The  parietal  lamina  {lamina  parietalis)  is  far  more  extensive  than  the  visceral, 
extending  upward  for  some  distance  in  front  and  on  the  medial  side  of  the  cord, 
and  reaching  below  the  testis.  The  inner  surface  of  the  tunica  vaginalis  is 
smooth,  and  covered  by  a  layer  of  endothelial  cells.  The  interval  between  the 
visceral  and  parietal  laminae  constitutes  the  cavity  of  the  tunica  vaginalis. 

The  obliterated  portion  of  the  saccus  vaginalis  may  generally  be  seen  as  a  flbro- 
cellular  thread  lying  in  the  loose  areolar  tissue  around  the  spermatic  cord;  some- 
times this  may  be  traced  as  a  distinct  band  from  the  upper  end  of  the  inguinal 
canal,  where  it  is  connected  with  the  peritoneum,  dow^n  to  the  tunica  vaginalis; 
sometimes  it  gradually  becomes  lost  on  the  spermatic  cord.  Occasionally  no  trace 
of  it  can  be  detected.  In  some  cases  it  happens  that  the  pouch  of  peritoneum  does 
not  become  obliterated,  but  the  sac  of  the  peritoneum  communicates  with  the 
tunica  vaginalis.  This  may  give  rise  to  one  of  the  varieties  of  oblique  inguinal 
hernia  (page  1187).  In  other  cases  the  pouch  may  contract,  but  not  become 
entirely  obliterated;  it  then  forms  a  minute  canal  leading  from  the  peritoneum  to 
the  tunica  vaginalis. 

The  Tunica  Albuginea  is  the  fibrous  covering  of  the  testis.  It  is  a  dense  membrane, 
of  a  bluish-white  color,  composed  of  bundles  of  white  fibrous  tissue  which  interlace 
in  every  direction.  It  is  covered  by  the  tunica  vaginalis,  except  at  the  points  of 
attachment  of  the  epididymis  to  the  testis,  and  along  its  posterior  border,  where 


THE  TESTES  AND  THEIR  COVERINGS 


1243 


the  spermatic  vessels  enter  the  gland.  It  is  applied  to  the  tunica  vasculosa  over 
the  glandular  substance  of  the  testis,  and,  at  its  posterior  border,  is  reflected 
into  the  interior  of  the  gland,  forming  an  incomplete  vertical  septum,  called  the 
mediastinum  testis  (corpus  Highmori) . 

The  mediastinum  testis  extends  from  the  upper  to  near  the  lower  extremity 
of  the  gland,  and  is  wider  above  than  below.  From  its  front  and  sides  numerous 
imperfect  septa  (trabeciiIcB)  are  given  off,  which  radiate  toward  the  surface  of  the 
organ,  and  are  attached  to  the  tunica  albuginea.  They  divide  the  interior  of  the 
organ  into  a  number  of  incomplete  spaces  which  are  somewhat  cone-shaped,  being 
broad  at  their  bases  at  the  surface  of  the  gland,  and  becoming  narrower  as  they 
converge  to  the  mediastinum.  The  mediastinum  supports  the  vessels  and  duct 
of  the  testis  in  their  passage  to  and  from  the  substance  of  the  gland. 

The  Tunica  Vasculosa  is  the  vascular  layer  of  the  testis,  consisting  of  a  plexus 
of  bloodvessels,  held  together  by  delicate  areolar  tissue.  It  clothes  the  inner  sur- 
face of  the  tunica  albuginea  and  the  different  septa  in  the  interior  of  the  gland, 
and  therefore  forms  an  internal  investment  to  all  the  spaces  of  which  the  gland  is 
composed. 

Structure. — The  glandular  structxire  of  the  testis  consists  of  numerous  lobules.  Their  number, 
in  a  single  testis,  is  estimated  by  Berres  at  250,  and  by  Krause  at  400.  They  differ  in  size 
according  to  their  position,  those  in  the  middle  of  the  gland  being  larger  and  longer.  The 
lobules  (Fig.  1149)  are  conical  in  shape,  the  base  being  directed  toward  the  circumference  of  the 
organ,  the  apex  toward  the  mediastinum.  Each  lobule 
is  contained  in  one  of  the  intervals  between  the  fibrous 
septa  which  extend  between  the  mediastinum  testis 
and  the  tunica  albuginea,  and  consists  of  from  one  to 
three,  or  more,  minute  convoluted  tubes,  the  tubuli 
seminiferi.  The  tubules  may  be  separately  unravelled, 
by  careful  dissection  under  water,  and  may  be  seen  to 
commence  either  by  free  cecal  ends  or  by  anastomotic 
loops.  They  are  supported  by  loose  connective  tissue 
which  contains  here  and  there  groups  of  "interstitial 
cells"  containing  yellow  pigment  granules.  The  total 
number  of  tubules  is  estimated  by  Lauth  at  840,  and 
the  average  length  of  each  is  70  to  80  cm.  Their  diam- 
eter varies  from  0.12  to  0.3  mm.  The  tubules  are  pale 
in  color  in  early  life,  but  in  old  age  they  acquire  a  deep 
yellow  tinge  from  containing  much  fatty  matter.  Each 
tubule  consists  of  a  basement  layer  formed  of  lamin- 
ated connective  tissue  containing  numerous  elastic  fibers 
with  flattened  cells  between  the  layers  and  covered  ex- 
ternally by  a  layer  of  flattened  epithelioid  cells.  Within 
the  basement  membrane  are  epitheUal  cells  arranged 
in  several  irregular  layers,  which  are  not  always  clearly 
separated,  but  which  may  be  arranged  in  three  different 
groups  (Fig.  1150).  Among  these  cells  may  be  seen  the 
spermatozoa  in  different  stages  of  development.  (1) 
Lining  the  basement  membrane  and  forming  the  outer 
zone  is  a  layer  of  cubical  ceUs,  with  small  nuclei; 
some  of  these  enlarge  to  become  spermatogonia.  The 
nuclei  of  some  of  the  spermatogonia  may  be  seen  to  be  in  process  of  indirect  division  {karyo- 
kineses,  page  37) ,  and  in  consequence  of  this  daughter  cells  are  formed,  which  constitute  the  second 
zone.  (2)  Within  this  first  layer  is  to  be  seen  a  number  of  larger  polyhedral  cells,  with  clear 
nuclei,  arranged  in  two  or  three  layers;  these  are  the  intermediate  cells  or  spermatocytes.  Most 
of  these  cells  are  in  a  condition  of  karyokinetic  division,  and  the  cells  which  result  from  this 
division  form  those  of  the  next  layer,  the  spermatoblasts  or  spermatids.  (3)  The  third  layer  of 
cells  consists  of  the  spermatoblasts  or  spermatids,  and  each  of  these,  without  further  subdivision, 
becomes  a  spermatozoon.  The  spermatids  are  small  polyhedral  cells,  the  nucleus  of  each  of 
which  contains  half  the  usual  number  of  chromosomes.  In  addition  to  these  three  layers  of  cells 
others  are  seen,  which  are  termed  the  supporting  cells  {cells  of  Sertoli).  They  are  elongated 
and  columnar,  and  project  inward  from  the  basement  membrane  toward  the  lumen  of  the  tube. 
As  development  of  the  spermatozoa  proceeds  the  latter  group  themselves  around  the  inner 
extremities  of  the  supporting  cells.    The  nuclear  portion  of  the  spermatid,  which  is  partly 


Tunica  vagiruilis 
Tunica  albuginea 
Its  septa 


Fig.   1149. — Vertical  section  of  the  testis,  to 
show  the  arrangement  of  the  ducts. 


ANCHNOLOGY 


imbedded  in  the  supporting  cell,  is  differentiated  to  form  the  head  of  the  spermatozoon,  while 
part  of  the  cell  protoplasm  forms  the  middle  piece  and  the  tail  is  produced  by  an  outgrowth 
from  the  double  centriole  of  the  cell.    Ultimately  the  heads  are  liberated  and  the  spermatozoa  iH 
are  set  free.    The  structure  of  the  spermatozoa  is  described  on  pages  42,  43.  lH 

In  the  apices  of  the  lobules,  the  tuboiles  become  less  convoluted,  assume  a  nearly  straight 
course,  and  unite  together  to  form  from  twenty  to  thirty  larger  ducts,  of  about  0.5  mm.  in 
diameter,  and  these,  from  their  straight  course,  are  called  tubuli  recti  (Fig.  1149). 


Spermatocyte 


Spermatid 


Cell  of  Sertoli 
Spermatogonium 


Spermatozoon 
Fig.   1150. — Transverse  section  of  a  tubule  of  the  testis  of  a  rat.     X  250. 

The  tubuli  recti  enter  the  fibrous  tissue  of  the  mediastinum,  and  pass  upward  and  backward, 
forming,  in  their  ascent,  a  close  net-work  of  anastomosing  tubes  which  are  merely  channels  in 
the  fibrous  stroma,  lined  by  flattened  epithelium,  and  having  no  proper  walls;  this  constitutes  the 
rete  testis.  At  the  upper  end  of  the  mediastinum,  the  vessels  of  the  rete  testis  terminate  in  from 
twelve  to  fifteen  or  twenty  ducts,  the  ductuli  eSerentes;  they  perforate  the  tunica  albuginea, 
and  carry  the  seminal  fluid  from  the  testis  to  the  epididymis.  Their  course  is  at  first  straight; 
they  then  become  enlarged,  and  exceedingly  convoluted,  and  form  a  series  of  conical  masses, 
the  coni  vasculosi,  which  together  constitute  the  head  of  the  epididymis.  Each  cone  consists 
of  a  single  convoluted  duct,  from  15  to  20  cm.  in  length,  the  diameter  of  which  gradually  decreases 
from  the  testis  to  the  epididymis.  Opposite  the  bases  of  the  cones  the  efferent  vessels  open  at 
narrow  intervals  into  a  single  duct,  which  constitutes,  by  its  complex  convolutions,  the  body 
and  taU  of  the  epididymis.  When  the  convolutions  of  this  tube  are  unravelled,  it  measures 
upward  of  6  meters  in  length;  it  increases  in  diameter  and  thickness  as  it  approaches  the  ductus 
deferens.  The  convolutions  are  held  together  by  fine  areolar  tissue,  and  by  bauds  of  fibrous 
tissue. 


Ciliated 
epithelium 

Spermatozoa 
in  lumen 


Fig.   1151. — Section  of  epididymis  of  guinea-pig.     X  255. 

The  tubuli  recti  have  very  thin  walls;  like  the  channels  of  the  rete  testis  they  are  lined  by  a 
single  layer  of  flattened  epithelium.  The  ductuli  efferentes  and  the  tube  of  the  epididymis  have 
walls  of  considerable  thickness,  on  account  of  the  presence  in  them  of  muscular  tissue,  which  is 
principally  arranged  in  a  circular  manner.  These  tubes  are  lined  by  columnar  ciliated  epithe- 
lium (Fig.  1151). 


DEFEREI 

Peculiarities. — The  testis,  developed  in  the  lumbar  region,  may  be  arrested  or  delayed  in  its 
transit  to  the  scrotum  {cryptorchism).  It  may  be  retained  in  the  abdomen;  or  it  may  be  arrested  at 
the  abdominal  inguinal  ring,  or  in  the  inguinal  canal;  or  it  may  just  pass  out  of  the  subcutaneous 
inguinal  ring  without  finding  its  way  to  the  bottom  of  the  scrotum.  When  retained  in  the  abdo- 
men it  gives  rise  to  no  symptoms,  other  than  the  absence  of  the  testis  from  the  scrotum;  but 
when  it  is  retained  in  the  inguinal  canal  it  is  subjected  to  pressure  and  may  become  inflamed 
and  painful.  The  retained  testis  is  probably  functionally  useless;  so  that  a  man  in  whom  both 
testes  are  retained  {anorckism)  is  sterile,  though  he  may  not  be  impotent.  The  absence  of  one 
testis  is  termed  monorchism.  When  a  testis  is  retained  in  the  inguinal  canal  it  is  often  compli- 
cated with  a  congenital  hernia,  the  funicular  process  of  the  peritoneum  not  being  obhterated. 
In  addition  to  the  cases  above  described,  where  there  is  some  arrest  in  the  descent  of  the  testis, 
this  organ  may  descend  through  the  inguinal  canal,  but  may  miss  the  scrotum  and  assume  some 
abnormal  position.  The  most  common  form  is  where  the  testis,  emerging  at  the  subcutaneous 
inguinal  ring,  slips  down  between  the  scrotum  and  thigh  and  comes  to  rest  in  the  perineum. 
This  is  known  as  perineal  ectopia  testis.  With  ea^'h  variety  of  abnormality  in  the  position  of  the 
testis,  it  is  very  common  to  find  concurrently  a  congenital  hernia,  or,  if  a  hernia  be  not  actually 
present,  the  funicular  process  is  usually  patent,  and  almost  invariably  so  if  the  testis  is  in  the 
inguinal  canal. 

The  testis,  finally  reaching  the  scrotum,  may  occupy  an  abnormal  position  in  it.  It  may  be 
inverted,  so  that  its  posterior  or  attached  border  is  directed  forward  and  the  tunica  vaginalis  is 
situated  behind. 

Fluid  collections  of  a  serous  character  are  very  frequently  found  in  the  scrotum.  To  these  the 
term  hydrocele  is  applied.  The  most  common  form  is  the  ordinary  vaginal  hydrocele,  in  which 
the  fluid  is  contained  in  the  sac  of  the  tunica  vaginalis,  which  is  separated,  in  its  normal  condition, 
from  the  peritoneal  cavity  by  the  whole  extent  of  the  inguinal  canal.  In  another  form,  the 
congenital  hydrocele,  the  fluid  is  in  the  sac  of  the  tunica  vaginalis,  but  this  cavity  communicates 
with  the  general  peritoneal  cavity,  its  tubular  process  remaining  pervious.  A  third  variety, 
known  as  an  infantile  hydrocele,  occurs  in  those  cases  where  the  tubular  process  becomes  obliter- 
ated only  at  its  upper  part,  at  or  near  the  abdominal  inguinal  ring.  It  resembles  the  vaginal 
hydrocele,  except  as  regards  its  shape,  the  collection  of  fluid  extending  up  the  cord  into  the  inguinal 
canal.  Fourthly,  the  funicular  process  may  become  obliterated  both  at  the  abdominal  inguinal 
ring  and  above  the  epididymis,  leaving  a  central  unobliterated  portion,  which  may  become 
distended  with  fluid,  giving  rise  to  a  condition  known  aa  the  encysted  hydrocele  of  the  cord. 


» 


The  Ductus  Deferens  (Vas  Deferens;  Seminal  Duct). 


I 


The  ductus  deferens,  the  excretory  duct  of  the  testis,  is  the  continuation  of  the 
canal  of  the  epididymis.  Commencing  at  the  lower  part  of  the  tail  of  the  epididymis 
it  is  at  first  very  tortuous,  but  gradually  becoming  less  twisted  it  ascends  along 
the  posterior  border  of  the  testis  and  medial  side  of  the  epididymis,  and,  as  a  con- 
stituent of  the  spermatic  cord,  traverses  the  inguinal  canal  to  the  abdominal 
inguinal  ring.  Here  it  separates  from  the  other  structures  of  the  cord,  curves 
around  the  lateral  side  of  the  inferior  epigastric  artery,  and  ascends  for  about 
2.5  cm.  in  front  of  the  external  iliac  artery.  It  is  next  directed  backward  and  slightly 
downward,  and,  crossing  the  external  iliac  vessels  obliquely,  enters  the  pelvic 
cavity,  where  it  lies  between  the  peritoneal  membrane  and  the  lateral  wall  of  the 
pelvis,  and  descends  on  the  medial  side  of  the  obliterated  umbilical  artery  and  the 
obturator  nerve  and  vessels.  It  then  crosses  in  front  of  the  ureter,  and,  reaching 
the  medial  side  of  this  tube,  bends  to  form  an  acute  angle,  and  runs  medialward 
and  slightly  forward  between  the  fundus  of  the  bladder  and  the  upper  end  of 
the  seminal  vesicle.  Reaching  the  medial  side  of  the  seminal  vesicle,  it  is  directed 
downward  and  medialward  in  contact  with  it,  gradually  approaching  the  opposite 
ductus.  Here  it  lies  between  the  fundus  of  the  bladder  and  the  rectum,  where  it 
is  enclosed,  together  with  the  seminal  vesicle,  in  a  sheath  derived  from  the  recto- 
vesical portion  of  the  fascia  endopelvina.  Lastly,  it  is  directed  downward  to  the 
base  of  the  prostate,  where  it  becomes  greatly  narrowed,  and  is  joined  at  an  acute 
angle  by  the  duct  of  the  seminal  vesicle  to  form  the  ejaculatory  duct,  which  tra- 
verses the  prostate  behind  its  middle  lobe  and  opens  into  the  prostatic  portion 
of  the  urethra,  close  to  the  orifice  of  the  prostatic  utricle.  The  ductus  deferens 
presents  a  hard  and  cord-like  sensation  to  the  fingers,  and  is  of  cylindrical  form ;  its 


1246 


SPLANCHNOLOGY 


walls  are  dense,  and  its  canal  is  extremely  small.  At  the  fundus  of  the  bladder 
it  becomes  enlarged  and  tortuous,  and  this  portion  is  termed  the  ampulla.  A  small 
triangular  area  of  the  fundus  of  the  bladder,  between  the  ductus  deferentes  laterally 
and  the  bottom  of  the  rectovesical  excavation  of  peritoneum  above,  is  in  contact 
with  the  rectum. 

Ductuli  Aberrantes. — A  long  narrow  tube,  the  ductulus  aberrans  inferior  {vas  aberrans  of 
H alter),  is  occasionally  found  connected  with  the  lower  part  of  the  canal  of  the  epididymis,  or 
with  the  commencement  of  the  ductus  deferens.  Its  length  varies  from  3.5  to  35  cm.,  and  it 
may  become  dilated  toward  its  extremity;  more  commonly  it  retains  the  same  diameter  through- 
out. Its  structure  is  similar  to  that  of  the  ductus  deferens.  Occasionally  it  is  found  unconnected 
with  the  epididymis.  A  second  tube,  the  ductulus  aberrans  superior,  occurs  in  the  head  of  the 
epididymis;  it  is  connected  with  the  rete  testis. 

Paradid3rmi3  (organ  of  Giraldes). — This  term  is  applied  to  a  small  collection  of  convoluted 
tubules,  situated  in  front  of  the  lower  part  of  the  cord  above  the  head  of  the  epididymis.  These 
tubes  are  lined  with  columnar  ciliated  epithelium,  and  probably  represent  the  remains  of  a  part 
of  the  Wolffian  body. 

Structure. — The  ductus  deferens  consists  of  three  coats:  (1)  an  external  or  areolar  coat;  (2)  a 
muscular  coat  which  in  the  greater  part  of  the  tube  consists  of  two  layers  of  unstriped  muscular 
fiber:  an  outer,  longitudinal  in  direction,  and  an  inner,  circular;  but  in  addition  to  these,  at  the 
commencement  of  the  ductus,  there  is  a  third  layer,  consisting  of  longitudinal  fibers,  placed 
internal  to  the  circular  stratum,  between  it  and  the  mucous  membrane;  (3)  an  internal  or  mucous 
coat,  which  is  pale,  and  arranged  in  longitudinal  folds.  The  mucous  coat  is  lined  by  columnar 
epithelium  which  is  non-ciliated  throughout  the  greater  part  of  the  tube;  a  variable  portion  of 
the  testicular  end  of  the  tube  is  lined  by  two  strata  of  columnar  cells  and  the  cells  of  the 
superficial  layer  are  ciliated. 


'  -■^*.-*^ 


T^ro  s  b  cot  c 


FiQ.  1152. — Fundus  of  the  bladder  with  the  vesiculse  seminales. 

The  Vesiculae  Seminales  (Seminal  Vesicales)  (Fig.  1152). 

The  vesiculse  seminales  are  two  lobulated  membranous  pouches,  placed  between 
the  fundus  of  the  bladder  and  the  rectum,  serving  as  reservoirs  for  the  semen, 
and  secreting  a  fluid  to  be  added  to  the  secretion  of  the  testes.  Each  sac  is  somewhat 
pyramidal  in  form,  the  broad  end  being  directed  backward,  upward  and  lateralward. 
It  is  usually  about  7.5  cm.  long,  but  varies  in  size,  not  only  in  different  individuals, 
but  also  in  the  same  individual  on  the  two  sides.  The  anterior  surface  is  in  contact 
with  the  fundus  of  the  bladder,  extending  from  near  the  termination  of  the  ureter 


THE  PENIS 


II 


to  the  base  of  the  prostate.  The  posterior  surface  rests  upon  the  rectum,  from  which 
it  is  separated  by  the  rectovesical  fascia.  The  upper  extremities  of  the  two  vesicles 
diverge  from  each  other,  and  are  in  relation  with  the  ductus  deferentes  and  the 
terminations  of  the  ureters,  and  are  partly  covered  by  peritoneum.  The  lower 
extremities  are  pointed,  and  converge  toward  the  base  of  the  prostate,  w^here  each 
joins  w^ith  the  corresponding  ductus  deferens  to  form  the  ejaculatory  duct.  Along 
the  medial  margin  of  each  vesicle  runs  the  ampulla  of  the  ductus  deferens. 

Each  vesicle  consists  of  a  single  tube,  coiled  upon  itself,  and  giving  off  several 
irregular  cecal  diverticula ;  the  separate  coils,  as  well  as  the  diverticula,  are  connected 
together  by  fibrous  tissue.  When  uncoiled,  the  tube  is  about  the  diameter  of  a 
quill,  and  varies  in  length  from  10  to  15  cm.;  it  ends  posteriorly  in  a  cul-de-sac; 
its  anterior  extremity  becomes  constricted  into  a  narrow  straight  duct,  which 
joins  with  the  corresponding  ductus  deferens  to  form  the  ejaculatory  duct. 

Structure. — The  vesiculae  seminales  are  composed  of  three  coats:  an  external  or  areolar  coat; 
a  middle  or  muscular  coat  thinner  than  in  the  ductus  deferens  and  arranged  in  two  layers,  an 
outer  longitudinal  and  inner  circular;  an  internal  or  mucous  coat,  which  is  pale,  of  a  whitish 
brown  color,  and  presents  a  delicate  reticular  structure.  The  epithelium  is  columnar,  and  in 
the  diverticula  goblet  cells  are  present,  the  secretion  of  which  increases  the  bulk  of  the  seminal 
fluid. 

Vessels  and  Nerves. — The  arteries  supplying  the  vesiculse  seminales  are  derived  from  the 
middle  and  inferior  vesical  and  middle  hemorrhoidal.  The  veins  and  lymphatics  accompany 
the  arteries.    The  nerves  are  derived  from  the  pelvic  plexuses. 

The  Ejaculatory  Ducts  (Ductus  Ejaculatorii)  (Fig.  1153). 

The  ejaculatory  ducts  are  two  in  number,  one  on  either  side  of  the  middle  line. 
Each  is  formed  by  the  union  of  the  duct  from  the  vesicula  seminalis  with  the  ductus 
deferens,  and  is  about  2  cm.  long. 
They  commence  at  the  base  of 
the  prostate,  and  run  forward 
and  downward  between  its  mid- 
dle and  lateral  lobes,  and  along 
the  sides  of  the  prostatic  utricle, 
to  end  by  separate  slit-like  ori- 
fices close  to  or  just  within  the 
margins  of  the  utricle.  The  ducts 
diminish  in  size,  and  also  converge, 
toward  their  terminations. 

Structure. — The  coats  of  the  ejacula- 
tory ducts  are  extremely  thin.  They 
are:  an  outer  fibrous  layer,  which  is 
almost  entirely  lost  after  the  entrance 
of  the  ducts  into  the  prostate;  a  layer 
of  muscular  fibers  consisting  of  a  thin 
outer  circular,  and  an  inner  longitu- 
dinal, layer;  and  mucous  membrane. 


Ejctcvlatary  dtict 

Prostatic  utricle 
Urethral  crest 
Prostatic  urethra 


Fig.  1153. — VeBiculse  seminales  and  ampullae  of  ductus  defer- 
entes, seen  from  the  front.  The  anterior  walls  of  the  left  ampulla, 
left  seminal  vesicle,  and  prostatic  urethra  have  been  cut  away. 


I 


The  Penis. 

The  penis  is  a  pendulous  organ  suspended  from  the  front  and  sides  of  the  pubic 
arch  and  containing  the  greater  part  of  the  urethra.  In  the  flaccid  condition  it  is 
cylindrical  in  shape,  but  when  erect  assumes  the  form  of  a  triangular  prism  with 
rounded  angles,  one  side  of  the  prism  forming  the  dorsum.  It  is  composed  of 
three  cylindrical  masses  of  cavernous  tissue  bound  together  by  fibrous  tissue  and 
covered  with  skin.  Two  of  the  masses  are  lateral,  and  are  known  as  the  corpora 
cavernosa  penis;  the  third  is  median,  and  is  termed  the  corpus  cavemosum  urethrse 
(Figs.  1154,  1155). 


1248 


SPLANCHNOLOGY 


The  Corpora  Cavernosa  Penis  form  the  greater  part  of  the  substance  of  the 
penis.  For  their  anterior  three-fourths  they  lie  in  intimate  apposition  with  one 
another,  but  behind  they  diverge  in  the  form  of  two  tapering  processes,  known 
as  the  crura,  which  are  firmly  connected  to  the  rami  of  the  pubic  arch.  Traced 
from  behind  forward,  each  crus  begins  by  a  blunt-pointed  process  in  front  of  the 
tuberosity  of  the  ischium.  Just  before  it  meets  its  fellow  it  presents  a  slight  enlarge- 
ment, named  by  Kobelt  the  bulb  of  the  corpus  cavernosum  penis.  Beyond  this  point 
the  crus  undergoes  a  constriction  and  merges  into  the  corpus  cavernosum  proper, 

which  retains  a  uniform  diameter  to  its 
anterior  end.  Each  corpus  cavernosum 
penis  ends  abruptly  in  a  rounded  ex- 
tremity some  distance  from  the  point  of 
the  penis. 

The  corpora  cavernosa  penis  are  sur- 
rounded by  a  strong  fibrous  envelope 
consisting  of  superficial  and  deep  fibers. 
The  superficial  fibers  are  longitudinal  in 
direction,  and  form  a  single  tube  which 
encloses  both  corpora;  the  deep  fibers  are 
arranged  circularly  around  each  corpus, 
and  form  by  their  junction  in  the  median 
plane  the  septum  of  the  penis.  This  is 
thick  and  complete  behind,  but  is  imper- 
fect in  front,  where  it  consists  of  a  series 
of  vertical  bands  arranged  like  the  teeth 
of  a  comb ;  it  is  therefore  named  the  sep- 
tum pectiniforme. 

The  Corpus  Cavernosum  Urethrse 
{corpus  spongiosumy  contains  the  urethra. 


i 


Dorsal  veins 


Dorsal  artery  and  nerve 
Integument 


Fig.  1154. — The  constituent  cavernous  cylinders  of 
the  penis.  The  glans  and  anterior  part  of  the  corpus 
cavernosum  urethrse  are  detached  from  the  corpora 
cavernosa  penis  and  turned  to  one  side. 


Fibrous  envelope 

Corpora  cavernosa  penia 
Septum  pectiniforme 

Urethra 


Corpus  cavernosum  urethrce 

Fig.   1155. — Transverse  section  of  the  penis. 


Behind,  it  is  expanded  to  form  the  urethral  bulb,  and  lies  in  apposition  with  the 
inferior  fascia  of  the  urogenital  diaphragm,  from  which  it  receives  a  fibrous  invest- 
ment. The  urethra  enters  the  bulb  nearer  to  the  upper  than  to  the  lower  surface. 
On  the  latter  there  is  a  median  sulcus,  from  which  a  thin  fibrous  septum  projects 
into  the  substance  of  the  bulb  and  divides  it  imperfectly  into  two  lateral  lobes  or 

hemispheres.  u  lu  r  *   • 

The  portion  of  the  corpus  cavernosum  urethrse  in  front  of  the  bulb  lies  in  a 
groove  on  the  under  surface  of  the  conjoined  corpora  cavernosa  penis.  It  is  cylin- 
drical in  form  and  tapers  slightly  from  behind  forward.  Its  anterior  end  is  expanded 
in  the  form  of  an  obtuse  cone,  flattened  from  above  downward.  This  expansion, 
termed  the  glans  penis,  is  moulded  on  the  rounded  ends  of  the  corpora  cavernosa 


THE  PENIS 


1249 


penis,  extending  farther  on  their  upper  than  on  their  lower  surfaces.  At  the  summit 
of  the  glans  is  the  sht-like  vertical  external  urethral  orifice.  The  circumference 
of  the  base  of  the  glans  forms  a  rounded  projecting  border,  the  corona  glandis, 
overhanging  a  deep  retroglandular  sulcus,  behind  which  is  the  neck  of  the  penis. 

For  descriptive  purposes  it  is  convenient  to  divide  the  penis  into  three  regions : 
the  root,  the  body,  and  the  extremity. 


Prostatic  portion 
of  urethra. 
EJaeulatory  duct. 


SPHINCTER    ANI 

Prostatic  plexus* 
qf  veins. 


'iiavicularis. 


Prepuce.-- 
FiG.   1156. — Vertical  section  of  bladder,  penis,  and  urethra. 


The 


root  {radix  penis)  of  the  penis  is  triradiate  in  form,  consisting  of  the 
diverging  crura,  one  on  either  side,  and  the  median  urethral  bulb.  Each  crus 
is  covered  by  the  Ischiocavernosus,  while  the  bulb  is  surrounded  by  the  Bulbo- 
cavernosus.  The  root  of  the  penis  lies  in  the  perineum  between  the  inferior  fascia 
of  the  urogenital  diaphragm  and  the  fascia  of  Colles.  In  addition  to  being  attached 
to  the  fasciae  and  the  pubic  rami,  it  is  bound  to  the  front  of  the  symphysis  pubis 
by  the  fundiform  and  suspensory  ligaments.  The  fundiform  ligament  springs  from 
the  front  of  the  sheath  of  the  Rectus  abdominis  and  the  linea  alba;  it  splits  into  two 
fasciculi  which  encircle  the  root  of  the  penis.  The  upper  fibers  of  the  suspensory 
ligament  pass  downward  from  the  lower  end  of  the  linea  alba,  and  the  lower  fibers 
from  the  symphysis  pubis;  together  they  form  a  strong  fibrous  band,  which  extends 
to  the  upper  surface  of  the  root,  where  it  blends  with  the  fascial  sheath  of  the  organ. 
The  body  {corpus  penis)  extends  from  the  root  to  the  ends  of  the  corpora  caver- 
nosa penis,  and  in  it  these  corpora  cavernosa  are  intimately  bound  to  one  another. 
A  shallow  groove  which  marks  their  junction  on  the  upper  surface  lodges  the 
deep  dorsal  vein  of  the  penis,  while  a  deeper  and  wider  groove  between  them 
on  the  under  surface  contains  the  corpus  cavernosum  urethrse.  The  body  is 
ensheathed  by  fascia,  which  is  continuous  above  with  the  fascia  of  Scarpa,  and 
below  with  the  dartos  tunic  of  the  scrotum  and  the  fascia  of  Colles. 


1250 


SPLANCHNOLOGY 


•I 


The  extremity  is  formed  by  the  glans  penis,  the  expanded  anterior  end  of  the 
corpus  cavernosum  urethrse.  It  is  separated  from  the  body  by  the  constricted 
neck,  which  is  overhung  by  the  corona  glandis. 

The  integument  covering  the  penis  is  remarkable  for  its  thinness,  its  dark  color, 
its  looseness  of  connection  with  the  deeper  parts  of  the  organ,  and  its  absence  of 
adipose  tissue.  At  the  root  of  the  penis  it  is  continuous  with  that  over  the  pubes, 
scrotum,  and  perineum.  At  the  neck  it  leaves  the  surface  and  becomes  folded  ,^ 
upon  itself  to  form  the  prepuce  or  foreskin.  The  internal  layer  of  the  prepuce  is  iH 
directly  continuous,  along  the  line  of  the  neck,  with  the  integument  over  the  glans. 
Immediately  behind  the  external  urethral  orifice  it  forms  a  small  secondary  redu- 
plication, attached  along  the  bottom  of  a  depressed  median  raphe,  which  extends 
from  the  meatus  to  the  neck;  this  fold  is  termed  the  frenulum  of  the  prepuce.  The 
integument  covering  the  glans  is  continuous  with  the  urethral  mucous  membrane 
at  the  orifice;  it  is  devoid  of  hairs,  but  projecting  from  its  free  surface  are  a  number 
of  small,  highly  sensitive  papillae.  Scattered  glands  on  the  corona,  neck,  glans  and 
inner  layer  of  the  prepuce,  the  preputial  glands,  have  been  described.^  They  secrete 
a  sebaceous  material  of  very  peculiar  odor,  which  probably  contains  casein,  and 
readily  undergoes  decomposition;  when  mixed  with  discarded  epithelial  cells  it  is 
called  smegma. 

The  prepuce  covers  a  variable  amount  of  the  glans,  and  is  separated  from  it 
by  a  potential  sac — the  preputial  sac — which  presents  two  shallow  fossae,  one  on 
either  side  of  the  frenulum. 

Structure  of  the  Penis. — From  the  internal  surface  of  the  fibrous  envelope  of  the  corpora 
cavernosa  penis,  as  well  as  from  the  sides  of  the  septum,  numerous  bands  or  cords  are  given  oflF, 

which  cross  the  interior  of  these  cor- 
pora cavernosa  in  all  directions,  sub- 
dividing them  into  a  number  of  sepa- 
rate compartments,  and  giving  the 
entire  structure  a  spongy  appearance 
(Fig.  1157).  These  bands  and  cords 
are  called  trabeculse,  and  consist  of 
white  fibrous  tissue,  elastic  fibers,  and 
■>^>xS  ^l^^^fv  "      fc{\^W!l^^^'^^^(^  plain    muscular  fibers.     In    them    are 

).l,}y]i   ^SSSSk.       »in«ok       rjllli^F^^^^^^  contained  numerous  arteries  and  nerves. 

The  component  fibers  which  form  the 
trabeculse  are  larger  and  stronger 
around  the  circumference  than  at  the 
centers  of  the  corpora  cavernosa;  they 
are  also  thicker  behind  than  in  front. 
The  interspaces  (cavernous  spaces),  on 
the  contrary,  are  larger  at  the  center 
than  at  the  circumference,  their  long 
diameters  being  directed  transversely. 
They  are  filled  with  blood,  and  are 
lined  by  a  layer  of  flattened  cells  sim- 
ilar to  the  endothelial  lining  of  veins. 
The  fibrous  envelope  of  the  corpus 
cavernosum  urethrje  is  thinner,  whiter 
in  color,  and  more  elastic  than  that  of 
the  corpora  cavernosa  penis.  The  trabec- 
ulse are  more  delicate,  nearly  uniform  in  size,  and  the  meshes  between  them  smaller  than  in  the 
corpora  cavernosa  penis:  their  long  diameters,  for  the  most  part,  corresponding  with  that  of 
the  penis.  The  external  envelope  or  outer  coat  of  the  corpus  cavernosum  urethrae  is  formed 
partly  of  unstriped  muscular  fibers,  and  a  layer  of  the  same  tissue  immediately  surrounds  the 
canal  of  the  urethra. 

Vessels  and  Nerves. — The  arteries  bringing  the  blood  to  the  cavernous  spaces  are  the  deep 
arteries  of  the  penis  and  branches  from  the  dorsal  arteries  of  the  penis,  which  perforate  the  fibrous 
capsule,  along  the  upper  surface,  especially  near  the  forepart   of  the  organ.     On  entering  the 

1  Stieda  (Comptes-rendus  du  XII  Congr6s  International  de  M6decine,  Moscow,  1897)  asserts  that  glands  are  never 
found  on  the  corona  glandia,  and  that  what  have  hitherto  been  mistaken  for  glands  are  really  large  papilla. 


'— ^ 


Fig.  1157.— Section  of  corpus  cavernosum  penis  in  a  non-dis- 
tended condition.  (Cadiat.)  a.  Trabecula;  of  connective  tissue, 
with  many  _  elastic  fibers  and  bundles  of  plain  muscular  tissue, 
some  of  which  are  cut  across  (c).     b.  Blood  sinuses. 


PROSTATE 


cavernous  structure  the  arteries  divide  into  branches,  which  are  supported  and  enclosed  by  the 
trabeculse.  Some  of  these  arteries  end  in  a  capillary  net-work,  the  branches  of  which  open  directly 
into  the  cavernous  spaces;  others  assume  a  tendril-like  appearance,  and  form  convoluted  and 
somewhat  dilated  vessels,  which  were  named  by  Miiller  heUcine  arteries.    They  open  into  the 


CAVERNOUS 
BRANCH 


INTERNAL  PUDIC       ''    ^^ 


Fia.  1158. — Diagram  of  the  arteries  of  the  penis.     (Testut) 

spaces,  and  from  them  are  also  given  off  small  capillary  branches  to  supply  the  trabecular  struc- 
ture. They  are  bound  down  in  the  spaces  by  fine  fibrous  processes,  and  are  most  abundant 
in  the  back  part  of  the  corpora  cavernosa  (Fig.  1157). 

The  blood  from  the  cavernous  spaces  is 
returned  by  a  series  of  vessels,  some  of 
which  emerge  in  considerable  numbers 
from  the  base  of  the  glans  penis  and 
converge  on  the  dorsum  of  the  organ  to 
form  the  deep  dorsal  vein;  others  pass  out 
on  the  upper  surface  of  the  corpora  caver- 
nosa and  join  the  same  vein;  some  emerge 
from  the  under  surface  of  the  corpora 
cavernosa  penis  and  receiving  branches 
from  the  corpus  cavernosum  urethra?,  wind 
around  the  sides  of  the  penis  to  end  in  the 
deep  dorsal  vein ;  but  th  ;  greater  number 
pass  out  at  the  root  of  the  penis  and 
join  the  prostatic  plexus. 

The  lymphatic  vessels  of  the  penis  are 
described  on  page  713. 

The  nerves  are  derived  from  the  puden- 
dal nerve  and  the  pelvic  plexuses.  On  the 
glans  and  bulb  some  filaments  of  the 
cutaneous  nerves  have  Pacinian  bodies 
connected  with  them,  and,  according  to 
Ejause,  many  of  them  end  in  peculiar  end- 
bulbs  (see  page  1060). 


The  Prostate  (Prostata;  Prostate 
Gland).    (Fig.  1160.) 


SUPERFICIAL   DORSAL  VEIN 
-EXTERNAL   PUDIC   VEIN 


"OBTURATOR   VEIN 


Fig.  1159. — Veins  of  the  penis.     (Testut.) 


The  prostate  is  a  firm,  partly 
glandular  and  partly  muscular  body, 
which  is  placed  immediately  below 
the  internal  urethral  orifice  and 
around  the  commencement  of  the 
urethra.  It  is  situated  in  the  pelvic  cavity,  below  the  lower  part  of  the  symphysis 
pubis,  above  the  superior  fascia  of  the  urogenital  diaphragm,  and  in  front  of 
the  rectum,  through  which  it  may  be  distinctly  felt,  especially  when  enlarged. 
It  is  about  the  size  of  a  chestnut  and  somewhat  conical  in  shape,  and  presents  for 
examination  a  base,  an  apex,  an  anterior,  a  posterior,  and  two  lateral  surfaces. 


WHNOLO&Y 

The  base  {basis  prostata)  is  directed  upward,  and  is  applied  to  the  inferior 
surface  of  the  bladder,  The  greater  part  of  this  surface  is  directly  continuous 
with  the  bladder  wall;  the  urethra  penetrates  it  nearer  its  anterior  than  its 
posterior  border. 

The  apex  {apex  prostatas)  is   directed   downward,  and  is  in  contact  with  the^ 
superior  fascia  of  the  urogenital  diaphragm. 


VAS 

DEFERENS 


AC-JLATORY 
DUCT 


PROSTATE 

Fia.  1160. — Prostate  with  seminal  vesicles  and  seminal  ducts,  viewed  from  in  front  and  above.     (Spalteholz.) 

Surfaces. — The  posterior  surface  {fades  posterior)  is  flattened  from  side  to  side 
and  slightly  convex  from  above  downward ;  it  is  separated  from  the  rectum  by  its 
sheath  and  some  loose  connective  tissue,  and  is  distant  about  4  cm.  from  the  anus. 
Near  its  upper  border  there  is  a  depression  through  which  the  two  ejaculatory 
ducts  enter  the  prostate.  This  depression  serves  to  divide  the  posterior  surface 
into  a  lower  larger  and  an  upper  smaller  part.  The  upper  smaller  part  constitutes 
the  middle  lobe  of  the  prostate  and  intervenes  between  the  ejaculatory  ducts  and 
the  urethra;  it  varies  greatly  in  size,  and  in  some  cases  is  destitute  of  glandular  tissue. 
The  lower  larger  portion  sometimes  presents  a  shallow  median  furrow,  which 
imperfectly  separates  it  into  a  right  and  a  left  lateral  lobe:  these  form  the  main 
mass  of  the  gland  and  are  directly  continuous  with  each  other  behind  the  urethra. 
In  front  of  the  urethra  they  are  connected  by  a  band  which  is  named  the  isthmus: 
this  consists  of  the  same  tissues  as  the  capsule  and  is  devoid  of  glandular  substance. 

The  anterior  surface  {fades  anterior)  measures  about  2.5  cm.  from  above  downward 
but  is  narrow  and  convex  from  side  to  side.  It  is  placed  about  2  cm.  behind  the 
pubic  symphysis,  from  which  it  is  separated  by  a  plexus  of  veins  and  a  quantity 
of  loose  fat.  It  is  connected  to  the  pubic  bone  on  either  side  by  the  puboprostatic 
ligaments.  The  urethra  emerges  from  this  surface  a  little  above  and  in  front  of  the 
apex  of  the  gland. 

The  lateral  surfaces  are  prominent,  and  are  covered  by  the  anterior  portions  of 
the  Levatores  ani,  which  are,  however,  separated  from  the  gland  by  a  plexus 
of  veins. 

The  prostate  measures  about  4  cm.  transversely  at  the  base,  2  cm.  in  its  antero- 
posterior diameter,  and  3  cm.  in  its  vertical  diameter.  Its  weight  is  about  8  gm. 
It  is  held  in  its  position  by  the  puboprostatic  ligaments;  by  the  superior  fascia  of 


THE  BULBOURETHRAL  GLANDS  1253 

the  urogenital  diaphragm,  which  invests  the  prostate  and  the  commencement 
of  the  membranous  portion  of  the  urethra;  and  by  the  anterior  portions  of  the 
Levatores  ani,  which  pass  backward  from  the  pubis  and  embrace  the  sides  of 
the  prostate.  These  portions  of  the  Levatores  ani,  from  the  support  they  afford 
to  the  prostate,  are  named  the  Levatores  prostatse. 

The  prostate  is  perforated  by  the  urethra  and  the  ejaculatory  ducts.  The 
urethra  usually  lies  along  the  junction  of  its  anterior  with  its  middle  third.  The 
ejaculatory  ducts  pass  obliquely  downward  and  forward  through  the  posterior 
part  of  the  prostate,  and  open  into  the  prostatic  portion  of  the  urethra. 

Structure. — ^The  prostate  is  immediately  enveloped  by  a  thin  but  firm  fibrous  capsule, 
distinct  from  that  derived  from  the  fascia  endopelvina,  and  separated  from  it  by  a  plexus 
of  veins.  This  capsule  is  firmly  adherent  to  the  prostate  and  is  structurally  continuous  with 
the  stroma  of  the  gland,  being  composed  of  the  same  tissues,  viz. :  non-striped  muscle  and  fibrous 
tissue.  The  substance  of  the  prostate  is  of  a  pale  reddish-gray  color,  of  great  density,  and  not 
easily  torn.     It  consists  of  glandular  substance  and  muscular  tissue. 

The  muscular  tissue  according  to  Kolliker,  constitutes  the  proper  stroma  of  the  prostate; 
the  connective  tissue  being  very  scanty,  and  simply  forming  between  the  muscular  fibers,  thin 
trabeculse,  in  which  the  vessels  and  nerves  of  the  gland  ramify.  The  muscular  tissue  is  arranged 
as  follows:  immediately  beneath  the  fibrous  capsule  is  a  dense  laj'er,  which  forms  an  investing 
sheath  for  the  gland;  secondly,  around  the  urethra,  as  it  lies  in  the  prostate,  is  another  dense 
layer  of  circular  fibers,  continuous  above  with  the  internal  layer  of  the  muscular  coat  of  the 
bladder,  and  blending  below  with  the  fibers  surrounding  the  membranous  portion  of  the  urethra. 
Between  these  two  layers  strong  bands  of  muscular  tissue,  which  decussate  freely,  form  meshes 
in  which  the  glandular  structure  of  the  organ  is  imbedded.  In  that  part  of  the  gland  which  is 
situated  in  front  of  the  urethra  the  muscular  tissue  is  especially  dense,  and  there  is  here  little  or 
no  gland  tissue;  while  in  that  part  which  is  behind  the  urethra  the  muscular  tissue  presents  a 
wide-meshed  structure,  which  is  densest  at  the  base  of  the  gland — that  is,  near  the  bladder — 
becoming  looser  and  more  sponge-like  toward  the  apex  of  the  organ. 

The  glandular  substance  is  composed  of  numerous  follicular  pouches  the  lining  of  which  fre- 
quently shows  papillary  elevations.  The  follicles  open  into  elongated  canals,  which  join  to  form 
from  twelve  to  twenty  small  excretory  ducts.  They  are  connected  together  by  areolar  tissue, 
supported  by  prolongations  from  the  fibrous  capsule  and  muscular  stroma,  and  enclosed  in  a 
delicate  capillary  plexus.  The  epithelium  which  lines  the  canals  and  the  terminal  vesicles  is  of 
the  columnar  variety.  The  prostatic  ducts  open  into  the  floor  of  the  prostatic  portion  of  the 
urethra,  and  are  lined  by  two  layers  of  epithelium,  the  inner  layer  consisting  of  columnar  and 
the  outer  of  small  cubical  cells.  Small  colloid  masses,  known  as  amyloid  bodies  are  often  found 
in  the  gland  tubes. 

Vessels  and  Nerves. — The  arteries  supplying  the  prostate  are  derived  from  the  internal 
pudendal,  inferior  vesical,  and  middle  hemorrhoidal.  Its  veins  form  a  plexus  around  the  sides 
and  base  of  the  gland;  they  receive  in  front  the  dorsal  vein  of  the  penis,  and  end  in  the  hypogastric 
veins.     The  nerves  are  derived  from  the  pelvic  plexus. 


The  Bulbourethral  Glands  (Glandulse  Bulbourethrales ;  Cowper's  Glands). 


The  bulbourethral  glands  are  two  small,  rounded,  and  somewhat  lobulated  bodies, 
of  a  yellow  color,  about  the  size  of  peas,  placed  behind  and  lateral  to  the  membran- 
ous portion  of  the  urethra,  between  the  two  layers  of  the  fascia  of  the  urogenital 
diaphragm.  They  lie  close  above  the  bulb,  and  are  enclosed  by  the  transverse  fibers 
of  the  Sphincter  urethrse  membranacese.  Their  existence  is  said  to  be  constant: 
they  gradually  diminish  in  size  as  age  advances. 

The  excretory  duct  of  each  gland,  nearly  2.5  cm.  long,  passes  obliquely  forward 
beneath  the  mucous  membrane,  and  opens  by  a  minute  orifice  on  the  floor  of  the 
cavernous  portion  of  the  urethra  about  2.5  cm.  in  front  of  the  urogenital  diaphragm. 


Structure. — Each  gland  is  made  up  of  several  lobules,  held  together  by  a  fibrous  investment. 
Each  lobule  consists  of  a  number  of  acini,  lined  by  columnar  epithehal  cells,  opening  into  one 
duct,  which  joins  with  the  ducts  of  other  lobules  outside  the  gland  to  form  the  single  excretory 
duct. 


I 


1254 


SPLANCHNOLOGY 


THE  FEMALE  GENITAL  ORGANS  (ORGANA  GENITALIA  MULIEBRIA). 

The  female  genital  organs  consist  of  an  internal  and  an  external  group.  The 
internal  organs  are  situated  within  the  pelvis,  and  consist  of  the  ovaries,  the  uterine 
tubes,  the  uterus,  and  the  vagina.  The  external  organs  are  placed  below  the  urogenital 
diaphragm  and  below  and  in  front  of  the  pubic  arch.  They  comprise  the  mons 
pubis,  the  labia  majora  et  minora  pudendi,  the  clitoris,  the  bulbus  vestibuli,  and  the 
greater  vestibular  glands. 

The  Ovaries  (Ovaria). 

The  ovaries  are  homologous  with  the  testes  in  the  male.  They  are  two  nodular 
bodies,  situated  one  on  either  side  of  the  uterus  in  relation  to  the  lateral  wall  of 
the  pelvis,  and  attached  to  the  back  of  the  broad  ligament  of  the  uterus,  behind 
and  below  the  uterine  tubes  (Fig.  1161).  The  ovaries  are  of  a  grayish-pink  color, 
and  present  either  a  smooth  or  a  puckered  uneven  surface.  They  are  each  about 
4  cm.  in  length,  2  cm.  in  width,  and  about  8  mm.  in  thickness,  and  weigh  from  2 


Epoophoron 


Ligament  of  ovary 


External  uterine  orifice 


Fig.   1161. — Uterus  and  riglit  broad  ligament,  seen  from  behind.     The  broad  ligament  has  been  spread  out  and  the 

ovary  drawn  downward. 

to  3.5  gm.  Each  ovary  presents  a  lateral  and  a  medial  surface,  an  upper  or  tubal 
and  a  lower  or  uterine  extremity,  and  an  anterior  or  mesovarion  and  a  posterior 
free  border.  It  lies  in  a  shallow  depression,  named  the  ovarian  fossa,  on  the  lateral 
wall  of  the  pelvis;  this  fossa  is  bounded  above  by  the  external  iliac  vessels,  in  front 
by  the  obliterated  umbilical  artery,  and  behind  by  the  ureter.  The  exact  position 
of  the  ovary  has  been  the  subject  of  considerable  difference  of  opinion,  and  the 
description  here  given  applies  to  the  ovary  of  the  nulliparous  woman.  The  ovary 
becomes  displaced  during  the  first  pregnancy,  and  probably  never  again  returns 
to  its  original  position.  In  the  erect  posture  the  long  axis  of  the  ovary  is  vertical. 
The  tubal  extremity  is  near  the  external  iliac  vein ;  to  it  are  attached  the  ovarian 
fimbria  of  the  uterine  tube  and  a  fold  of  peritoneum,  the  suspensory  Ugament  of 
the  ovary,  which  is  directed  upward  over  the  iliac  vessels  and  contains  the  ovarian 
vessels.  The  uterine  end  is  directed  downward  toward  the  pelvic  floor,  it  is  usually 
narrower  than  the  tubal,  and  is  attached  to  the  lateral  angle  of  the  uterus,  immedi- 
ately behind  the  uterine  tube,  by  a  rounded  cord  termed  the  Ugament  of  the  ovary, 
which  lies  within  the  broad  ligament  and  contains  some  non-striped  muscular 


THE  OVARIES 


1255 


fibers.  The  lateral  surface  is  in  contact  with  the  parietal  peritoneum,  which  lines 
the  ovarian  fossa;  the  medial  surface  is  to  a  large  extent  covered  by  the  fimbriated 
extremity  of  the  uterine  tube.  The  mesovarian  border  is  straight  and  is  directed 
toward  the  obliterated  umbilical  artery,  and  is  attached  to  the  back  of  the  broad 
ligament  by  a  short  fold  named  the  mesovarium.  Between  the  two  layers  of  this 
fold  the  bloodvessels  and  nerves  pass  to  reach  the  hilum  of  the  ovary.  The  free 
border  is  convex,  and  is  directed  toward  the  ureter.  The  uterine  tube  arches  over 
the  ovary,  running  upward  in  relation  to  its  mesovarian  border,  then  curving  over 
its  tubal  pole,  and  finally  passing  downward  on  its  free  border  and  medial  surface. 


Fig.  1162. — Adult  ovary,  epoophoron,  and  uterine  tube.  (From  Farre,  after  Kobelt.)  a,  a.  Epoophoron  formed 
from  the  upper  part  of  the  Wolffian  body.  6.  Remains  of  the  uppermost  tubes  sometimes  forming  hydatids,  c.  Middle 
set  of  tubes,  d.  Some  lower  atrophied  tubes,  e.  Atrophied  remains  of  the  Wolffian  duct.  /.  The  terminal  bulb  or 
hydatid,     h.  The  uterine  tube.     i.  Hydatid  attached  to  the  extremity.     I.  The  ovary. 

Epoophoron  {parovarium;   organ  of    Rosenmuller)    (Figs.    1161,   1162). — The 
epoophoron  lies  in  the  mesosalpinx  between  the  ovary  and  the  uterine  tube,  and 
consists  of  a  few  short  tubules  (ductuli  transversi)  which  converge  toward  the  ovary 
while  their  opposite  ends  open  into  a 
rudimentary  duct,  the  ductus  longitu- 
dinalis  epoophori  {duct  of  Gartner) . 

Paroophoron.  —  The  paroophoron 
consists  of  a  few  scattered  rudimen- 
tary tubules,  best  seen  in  the  child, 
situated  in  the  broad  ligament  be- 
tween the  epoophoron  and  the  uterus. 

The  ductuli  transversi  of  the  epo- 
ophoron and  the  tubules  of  the  paro- 
ophoron are  remnants  of  the  tubules 
of  the  Wolffian  body  or  mesonephros; 
the  ductus  longitudinalis  epoophori  is  a 
persistent  portion  of  the  Wolffian  duct. 

In  the  fetus  the  ovaries  are  situ- 
ated, like  the  testes,  in  the  lumbar 
region,  near  the  kidneys,  but  they 
graduallv  descend  into  the  pelvis  (page 
1211). 

Structure  (Fig.  1163). — The  surface  of  the  ovary  is  covered  by  a  layer  of  columnar  cells  which 
constitutes  the  germinal  epithelium  of  Waldeyer.  This  epithelium  gives  to  the  ovary  a  dull 
gray  color  as  compared  with  the  shining  smoothness  of  the  peritoneum;  and  the  transition  be- 
tween the  squamous  epitheUum  of  the  peritoneum  and  the  columnar  cells  which  cover  the 
ovary  is  usually  marked  by  a  line  around  the  anterior  border  of  the  ovary.  The  ovary  consists 
of  a  number  of  vesicular  ovarian  follicles  imbedded  in  the  meshes  of  a  stroma  or  frame-work. 


Fig.  1163. — Section  of  the  ovary.  (After  Schron.)  1. 
Outer  covering.  1'.  Attached  border.  2.  Central  stroma. 
3.  Peripheral  stroma.  4.  Bloodvessels.  5.  Vesicular  follicles 
in  their  earliest  stage.  _  6,  7,  8.  More  advanced  follicles.  9. 
An  almost  mature  follicle.  9'.  Follicle  from  which  the  ovum 
has  escaped.    10.  Corpus  luteum. 


1^ 


1256 


SPLANCHNOLOGY 


Fibro-vascular  coat 


Membrana  gramdos 


'^^^-. 


The  stroma  is  a  peculiar  soft  tissue,  abundantly  supplied  with  bloodvessels,  consisting  for  the 
most  part  of  spindle-shaped  cells  with  a  small  amount  of  ordinary  connective  tissue.  These 
cells  have  been  regarded  by  some  anatomists  as  unstriped  muscle  cells,  which,  indeed,  they 
most  resemble;  by  others  as  connective-tissue  cells.  On  the  surface  of  the  organ  this  tissue  's 
much  condensed,  and  forms  a  layer  (tunica  albuginea)  composed  of  short  connective-tissue 
fibers,  with  fusiform  cells  between  them.  The  stroma  of  the  ovary  may  contain  interstitial  cells 
resembling  those  of  the  testis. 

Vesicular  Ovarian  Follicles  {Graafian  follicles). — Upon  making  a  section  of  an  ovarj-,  numerous 
round  ti'ansparent  vesicles  of  various  sizes  are  to  be  seen;  they  are  the  folhcles,  or  ovisacs  con- 
taining the  ova.  Immediately  beneath  the  superficial  covering  is  a  layer  of  stroma,  in  which  are 
a  large  number  of  minute  vesicles,  of  uniform  size,  about  0.25  mm.  in  diameter.  These  are  the 
follicles  in  their  earliest  condition,  and  the  layer  where  they  are  found  has  been  termed  the 
cortical  layer.  They  are  especially  numerous  in  the  ovary  of  the  young  child.  After  puberty, 
and  during  the  whole  of  the  child-bearing  period,  large  and  mature,  or  almost  mature  follicles 
are  also  found  in  the  cortical  layer  in  small  numbers,  and  also  "corpora  lutea,"  the  remains  of 
follicles  which  have  burst  and  are  undergoing  atrophy  .and  absorption.  Beneath  this  superficial 
stratum,  other  large  and  more  or  less  mature  follicles  are  found  imbedded  in  the  ovarian  stroma. 
These  increase  in  size  as  they  recede  from  the  surface  toward  a  highly  vascular  stroma  in  the 
center  of  the  organ,  termed  the  medullary  substance  {zona  vasculosa  of  Waldeyer).  This  stroma 
forms  the  tissue  of  the  hilum  by  which  the  ovary  is  attached,  and  through  which  the  bloodvessels 
enter:    it  does  not  contain  any  follicles. 

The  larger  follicles  (Fig.  1164)  consist  of  an  external  fibrovascular  coat,  connected  with  the 
surrounding  stroma  of  the  ovary  by  a  net -work  of  bloodvessels;  and  an  internal  coat,  which  con- 
sists of  several  layers  of  nucleated 
cells,  called  the  membrana  granulosa. 
At  one  part  of  the  mature  follicle  the 
cells  of  the  membrana  granulosa  are 
collected  into  a  mass  which  projects 
into  the  cavity  of  the  follicle.  This 
is  termed  the  discus  proligerus,  and 
in  it  the  ovum  is  imbedded.^  The 
follicle  contains  a  transparent  albumin- 
ous fluid. 

The  development  and  maturation 
of  the  follicles  and  ova  continue  un- 
interruptedly from  puberty  to  the  end 
of  the  fruitful  period  of  woman's  life, 
while  their  formation  commences  be- 
fore birth.  Before  puberty  the  ovaries 
are  small  and  the  follicles  contained 
in  them  are  disposed  in  a  compara- 
tively thick  layer  in  the  cortical  sub- 
stance; here  they  present  the  appear- 
ance of  a  large  number  of  minute 
closed  vesicles,  constituting  the  early 
condition  of  the  follicles;  many, 
however,  never  attain  full  develop- 
ment, but  shrink  and  disappear.  At  puberty  the  ovaries  enlarge  and  become  more  vascular, 
the  follicles  are  developed  in  greater  abundance,  and  their  ova  are  capable  of  fecundation. 

Discharge  of  the  Ovmn. — The  folhcles,  after  attaining  a  certain  stage  of  development,  gradu- 
ally approach  the  surface  of  the  ovary  and  burst;  the  ovum  and  fluid  contents  of  the  follicle 
are  liberated  on  the  exterior  of  the  ovary,  and  carried  into  the  uterine  tube  by  currents  set  up 
by  the  movements  of  the  cilia  covering  the  mucous  membrane  of  the  fimbriae. 

Corpus  Luteum. — After  the  discharge  of  the  ovum  the  lining  of  the  folhcle  is  thrown  into 
folds,  and  vascular  processes  grow  inward  from  the  surrounding  tissue.  In  this  way  the  space 
is  filled  up  and  the  corpus  luteum  formed.  It  consists  at  first  of  a  radial  arrangement  of  j-ellow 
cells  with  bloodvessels  and  lymphatic  spaces,  and  later  it  merges  with  the  surrounding  stroma. 
Vessels  and  Nerves. — ^The  arteries  of  the  ovaries  and  uterine  tubes  are  the  ovarian  from 
the  aorta.  Each  anastomoses  freely  in  the  mesosalpinx,  with  the  uterine  artery,  givinji  some 
branches  to  the  uterine  tube,  and  others  which  traverse  the  mesovarium  and  enter  the  hilum  of 
the  ovary.  The  veins  emerge  from  the  hilum  in  the  form  of  a  plexus,  the  pampiniform  plexus ; 
the  ovarian  vein  is  formed  from  this  plexus,  and  leaves  the  pelvis  in  company  with  the  artery. 
The  nerves  are  derived  from  the  hypogastric  or  pelvic  plexus,  and  from  the  ovarian  plexus,  the 
uterine  tube  receiving  a  branch  from  one  of  the  uterine  nerves. 


Zona  striata 
Germinal  vcsid 


Discus  proligerufi 


Fig.    1164. — Section  of  vesicu  I 


W4K 


)f  rat.     X  50. 


'  For  a  description  of  the  ovum,  see  page  38. 


THE  UTERINE  TUBE 


1257 


The  Uterine  Tube  (Tuba  Uterina  [Fallopii];  Fallopian  Tube;  Oviduct). 

(Figs.  1161,  1165). 

The  uterine  tubes  convey  the  ova  from  the  ovaries  to  the  cavity  of  the  uterus. 
They  are  two  in  number,  one  on  either  side,  situated  in  the  upper  margin  of  the 
broad  ligament,  and  extending  from  the  superior  angle  of  the  uterus  to  the  side  of 
the  pelvis.  Each  tube  is  about  10  cm.  long,  and  is  described  as  consisting  of  three 
portions:  (1)  the  isthmus,  or  medial  constricted  third;  (2)  the  ampulla,  or  inter- 
mediate dilated  portion,  which  curves  over  the  ovary;  and  (3)  the  infundibulum 
with  its  abdominal  ostium,  surrounded  by  fimbriae,  one  of  which,  the  ovarian  fimbria 


/ 
Ureter 
Sacrogenital  fold 


Ligament  of  ovary 
Uterine  tube 
Bound  ligament  of  vierua 


Pararectal  fossa 

Fio.   1165. — Female  pelvis  and  its  contents,  seen  from  above  and  in  front. 

is  attached  to  the  ovary.  The  uterine  tube  is  directed  lateralward  as  far  as  the 
uterine  pole  of  the  ovary,  and  then  ascends  along  the  mesovarian  border  of  the 
ovary  to  the  tubal  pole,  over  which  it  arches;  finally  it  turns  downward  and  ends 
in  relation  to  the  free  border  and  medial  surface  of  the  ovary.  The  uterine  opening 
is  minute,  and  will  only  admit  a  fine  bristle;  the  abdominal  opening  is  somewhat 
larger.  In  connection  with  the  fimbriae  of  the  uterine  tube,  or  with  the  broad  liga- 
ment close  to  them,  there  are  frequently  one  or  more  small  pedunculated  vesicles. 
These  are  termed  the  appendices  vesiculosse  (hydatids  of  Morgagni). 

Structure. — The  uterine  tube  consists  of  three  coats:  serous,  muscular,  and  mucous.  The 
external  or  serous  coat  is  peritoneal.  The  middle  or  muscular  coat  consists  of  an  external  longi- 
tudinal and  an  internal  circular  layer  of  non-striped  muscular  fibers  continuous  with  those  of 
the  uterus.  The  internal  or  mucous  coat  is  continuous  with  the  mucous  lining  of  the  uterus,  and, 
at  the  abdominal  ostium  of  the  tube,  with  the  peritoneum.  It  is  thrown  into  longitudinal  folds, 
which  in  the  ampulla  are  much  more  extensive  than  in  the  isthmus.  The  lining  epithelium  is 
columnar  and  ciliated.  This  form  of  epithelium  is  also  found  on  the  inner  surface  of  the  fimbriae, 
while  on  the  outer  or  serous  surfaces  of  these  processes  the  epithelium  gradually  merges  into 
the  endothelium  of  the  peritoneum. 

Fertilization  of  the  ovum  is  believed  (page  44)  to  occur  in  the  tube,  and  the  fertilized  ovum 
is  then  normally  passed  on  into  the  uterus ;  the  ovum,  however,  may  adhere  to  and  undergo  develop- 
ment in  the  uterine  tube,  giving  rise  to  the  commonest  variety  of  ectopic  gestation.  In  such  cases 
the  amnion  and  chorion  are  formed,  but  a  true  decidua  is  never  present;  and  the  gestation  usually 


1258 


SPLANCHNOLOGY 


ends  by  extrusion  of  the  ovum  through  the  abdominal  ostium,  although  it  is  not  uncommon  for 
the  tube  to  rupture  into  the  peritoneal  cavity,  this  being  accompanied  by  severe  hemorrhage, 
and  needing  surgical  interference. 


The  Uterus  (Womb)  (Figs.  1161,  1165,  1166). 


The  uterus  is  a  hollow,  thick-walled,  muscular  organ  situated  deeply  in  the 
pelvic  cavity  between  the  bladder  and  rectum.  Into  its  upper  part  the  uterine 
tubes  open,  one  on  either  side,  while  below,  its  cavity  communicates  with  that  of 


J 


posTcniOR 

FORNIX 


ANTERIOR 
FORNIK 


Fig.  1166. — Sagittal  section  of  the  lower  part  of  a  female  trunk,  right  segment.  SAf.  INT.  Small  intestine.  (Testut.) 

the  vagina.  When  the  ova  are  discharged  from  the  ovaries  they  are  carried  to  the 
uterine  cavity  through  the  uterine  tubes.  If  an  ovum  be  fertilized  it  imbeds  itself 
in  the  uterine  wall  and  is  normally  retained  in  the  uterus  until  prenatal  develop- 
ment is  completed,  the  uterus  undergoing  changes  in  size  and  structure  to  accom- 
modate itself  to  the  needs  of  the  growing  embryo  (see  page  59) .  After  parturition 
the  uterus  returns  almost  to  its  former  condition,  but  certain  traces  of  its  enlarge- 
ment remains.  It  is  necessary,  therefore,  to  describe  as  the  type-form  the  adult 
virgin  uterus,  and  then  to  consider  the  modifications  which  are  effected  as  a  resul* 
of  pregnancy. 


THE  UTERUS  ^^^^^  1259 

Tn  the  virgin  state  the  uterus  is  flattened  antero-posteriorly  and  is  pyriform 
in  shape,  with  the  apex  directed  downward  and  backward.  It  lies  between  the 
bladder  in  front  and  the  pelvic  or  sigmoid  colon  and  rectum  behind,  and  is  com- 
pletely within  the  pelvis,  so  that  its  base  is  below  the  level  of  the  superior  pelvic 
aperture.  Its  upper  part  is  suspended  by  the  broad  and  the  round  ligaments, 
while  its  lower  portion  is  imbedded  in  the  fibrous  tissue  of  the  pelvis. 

The  long  axis  of  the  uterus  usually  lies  approximately  in  the  axis  of  the  superior 
pelvic  aperture,  but  as  the  organ  is  freely  movable  its  position  varies  with  the 
state  of  distension  of  the  bladder  and  rectum.  Except  when  much  displaced  by  a 
fully  distended  bladder,  it  forms  a  forward  angle  with  the  vagina,  since  the  axis 
of  the  vagina  corresponds  to  the  axes  of  the  cavity  and  inferior  aperture  of  the 
pelvis. 

The  uterus  measures  about  7.5  cm,  in  length,  5  cm,  in  breadth,  at  its  upper 
part,  and  nearly  2.5  cm.  in  thickness;  it  weighs  from  30  to  40  gm.  It  is  divisible 
into  two  portions.  On  the  surface,  about  midway  between  the  apex  and  base, 
is  a  slight  constriction,  known  as  the  isthmus,  and  corresponding  to  this  in  the 
interior  is  a  narrowing  of  the  uterine  cavity,  the  internal  orifice  of  the  uterus.  The 
portion  above  the  isthmus  is  termed  the  body,  and  that  below,  the  cervix.  The 
part  of  the  body  which  lies  above  a  plane  passing  through  the  points  of  entrance 
of  the  uterine  tubes  is  known  as  the  fundus. 

Body  (corpus  uteri) .  —  The  body  gradually  narrows  from  the  fundus  to  the 
isthmus. 

The  vesical  or  anterior  surface  (fades  vesicalis)  is  flattened  and  covered  by 
peritoneum,  which  is  reflected  on  to  the  bladder  to  form  the  vesicouterine 
excavation.     The  surface  lies  in  apposition  with  the  bladder. 

The  intestinal  or  posterior  surface  (fades  intestinalis)  is  convex  transversely  and 
is  covered  by  peritoneum,  which  is  continued  down  on  to  the  cervix  and  vagina. 
It  is  in  relation  with  the  sigmoid  colon,  from  which  it  is  usually  separated  by  some 
coils  of  small  intestine. 

The  fundus  (fundus  uteri)  is  convex  in  all  directions,  and  covered  by  peritoneum 
continuous  with  that  on  the  vesical  and  intestinal  surfaces.  On  it  rest  some  coils 
of  small  intestine,  and  occasionally  the  distended  sigmoid  colon. 

The  lateral  margins  (margo  lateralis)  are  slightly  convex.  At  the  upper  end  of 
each  the  uterine  tube  pierces  the  uterine  wall.  Below  and  in  front  of  this  point 
the  round  ligament  of  the  uterus  is  fixed,  while  behind  it  is  the  attachment  of  the 
ligament  of  the  ovary.  These  three  structures  lie  within  a  fold  of  peritoneum 
which  is  reflected  from  the  margin  of  the  uterus  to  the  wall  of  the  pelvis,  and  is 
named  the  broad  ligament. 

Cervix  (cervix  uteri;  neck). — The  cervix  is  the  lower  constricted  segment  of 
the  uterus.  It  is  somewhat  conical  in  shape,  with  its  truncated  apex  directed 
downward  and  backward,  but  is  slightly  wider  in  the  middle  than  either  above  or 
below.  Owing  to  its  relationships,  it  is  less  freely  movable  than  the  body,  so  that 
the  latter  may  bend  on  it.  The  long  axis  of  the  cervix  is  therefore  seldom  in  the 
same  straight  line  as  the  long  axis  of  the  body.  The  long  axis  of  the  uterus  as  a 
whole  presents  the  form  of  a  curved  line  with  its  concavity  forward,  or  in  extreme 
cases  may  present  an  angular  bend  at  the  region  of  the  isthmus. 

The  cervix  projects  through  the  anterior  wall  of  the  vagina,  which  divides  it 
into  an  upper,  supravaginal  portion,  and  a  lower,  vaginal  portion. 

The  supravaginal  portion  (portio  supravaginalis  [cervicis])  is  separated  in  front 
from  the  bladder  by  fibrous  tissue  (parametrium),  which  extends  also  on  to  its  sides 
and  lateralward  between  the  layers  of  the  broad  ligaments.  The  uterine  arteries 
reach  the  margins  of  the  cervix  in  this  fibrous  tissue,  while  on  either  side  the  ureter 
runs  downward  and  forward  in  it  at  a  distance  of  about  2  cm.  from  the  cervix. 
Posteriorly,  the  supravaginal  cervix  is  covered  by  peritoneum,  which  is  prolonged 


[260 


SPLANCHNOLOGY 


below  on  to  the  posterior  vaginal  wall,  when  it  is  reflected  on  to  the  rectum, 
forming  the  rectouterine  excavation.  It  is  in  relation  with  the  rectum,  from 
which  it  may  be  separated  by  coils  of  small  intestine. 

The  vaginal  portion  (portio  vaginalis  [cervicis])  of  the  cervix  projects  free  into  the 
anterior  wall  of  the  vagina  between  the  anterior  and  posterior  fornices.  On  its 
rounded  extremity  is  a  small,  depressed,  somewhat  circular  aperture,  the  external 
orifice  of  the  uterus,  through  which  the  cavity  of  the  cervix  communicates  with 
that  of  the  vagina.  The  external  orifice  is  bounded  by  two  lips,  an  anterior  and  a 
posterior,  of  which  the  anterior  is  the  shorter  and  thicker,  although,  on  account 
of  the  slope  of  the  cervix,  it  projects  lower  than  the  posterior.  Normally,  both  lips 
are  in  contact  with  the  posterior  vaginal  wall. 

Interior  of  the  Uterus  (Fig.  1167). — The  cavity  of  the  uterus  is  small  in 
comparison  with  the  size  of  the  organ. 

The  Cavity  of  the  Body  (cavum  uteri)  is  a  mere  slit,  flattened  antero-posteriorly. 
It  is  triangular  in  shape,  the  base  being  formed  by  the  internal  surface  of  the 

fundus  between  the  orifices  of  the  uterine 
tubes,  the  apex  by  the  internal  orifice  of  the 
uterus  through  which  the  cavity  of  the  body 
communicates  with  the  canal  of  the  cervix. 

The  Canal  of  the  Cervix  {canalis  cervicis 
uteri)  is  somewhat  fusiform,  flattened  from 
before  backward,  and  broader  at  the  middle 
than  at  either  extremity.  It  communicates 
above  through  the  internal  orifice  with  the 
cavity  of  the  body,  and  below  through  the 
external  orifice  with  the  vaginal  cavity.  The 
wall  of  the  canal  presents  an  anterior  and  a 
posterior  longitudinal  ridge,  from  each  of 
which  proceed  a  number  of  small  oblique 
columns,  the  palmate  folds,  giving  the  appear- 
ance of  branches  from  the  stem  of  a  tree; 
to  this  arrangement  the  name  arbor  vitae 
uterina  is  applied.  The  folds  on  the  two 
fit  between  one  another  so  as  to  close  the 


I 


Uterine 
tube 


Internal 
orifice 


External 
orifice 


Fig.   1167. — Posterior  half  of  uterus  and  upper 
part  of  vagina. 


walls  are  not  exactly  opposed,  but 
cervical  canal. 

The  total  length  of  the  uterine  cavity  from  the  external  orifice  to  the  fundus 
is  about  6.25  cm. 

Ligaments. — The  ligaments  of  the  uterus  are  eight  in  number:  one  anterior; 
one  posterior;  two  lateral  or  broad;  two.uterosacral;  and  two  roimd  ligaments. 

The  anterior  ligament  consists  of  the  vesicouterine  fold  of  peritoneum,  which 
is  reflected  on  to  the  bladder  from  the  front  of  the  uterus,  at  the  junction  of  the 
cervix  and  body. 

The  posterior  ligament  consists  of  the  rectovaginal  fold  of  peritoneum,  which  is 
reflected  from  the  back  of  the  posterior  fornix  of  the  vagina  on  to  the  front  of  the 
rectum.  It  forms  the  bottom  of  a  deep  pouch  called  the  rectouterine  excavation, 
which  is  bounded  in  front  by  the  posterior  wall  of  the  uterus,  the  supravaginal 
cervix,  and  the  posterior  fornix  of  the  vagina;  behind,  by  the  rectum;  and  laterally 
by  two  crescentic  folds  of  peritoneum  which  pass  backward  from  the  cervix  uteri 
on  either  side  of  the  rectum  to  the  posterior  wall  of  the  pelvis.  These  folds  are 
named  the  sacrogenital  or  rectouterine  folds.  They  contain  a  considerable  amount 
of  fibrous  tissue  and  non-striped  muscular  fibers  which  are  attached  to  the  front 
of  the  sacrum  and  constitute  the  uterosacral  ligaments. 

The  two  lateral  or  broad  ligaments  (iigamentum  latum  uteri)  pass  from  the  sides  of 
the  uterus  to  the  lateral  walls  of  the  pelvis.    Together  with  the  uterus  they  form 


THE  UTERUS 

a  septum  across  the  female  pelvis,  dividing  that  cavity  into  two  portions.  In  the 
anterior  part  is  contained  the  bladder;  in  the  posterior  part  the  rectum,  and  in 
certain  conditions  some  coils  of  the  small  intestine  and  a  part  of  the  sigmoid  colon. 
Between  the  two  layers  of  each  broad  ligament  are  contained:  (1)  the  uterine 
tube  superiorly;  (2)  the  round  ligament  of  the  uterus;  (3)  the  ovary  and  its  ligament; 
(4)  the  epoophoron  and  paroophoron;  (5)  connective  tissue;  (6)  unstriped  muscular 
fibers;  and  (7)  bloodvessels  and  nerves.  The  portion  of  the  broad  ligament  which 
stretches  from  the  uterine  tube  to  the  level  of  the  ovary  is  known  by  the  name 
of  the  mesosalpinx.  Between  the  fimbriated  extremity  of  the  tube  and  the  lower 
attachment  of  the  broad  ligament  is  a  concave  rounded  margin,  called  the  infun- 
dibulopelvic  ligament. 

The  round  ligaments  {ligamentum  teres  uteri)  are  two  flattened  bands  between 
10  and  12  cm.  in  length,  situated  between  the  layers  of  the  broad  ligament  in  front 
of  and  below  the  uterine  tubes.  Commencing  on  either  side  at  the  lateral  angle 
of  the  uterus,  this  ligament  is  directed  forward,  upward,  and  lateralward  over  the 
external  iliac  vessels.  It  then  passes  through  the  abdominal  inguinal  ring  and  along 
the  inguinal  canal  to  the  labium  majus,  in  which  it  becomes  lost.  The  round 
ligaments  consists  principally  of  muscular  tissue,  prolonged  from  the  uterus;  also 
of  some  fibrous  and  areolar  tissue,  besides  bloodvessels,  lymphatics;  and  nerves, 
enclosed  in  a  duplicature  of  peritoneum,  which,  in  the  fetus,  is  prolonged  in  the 
form  of  a  tubular  process  for  a  short  distance  into  the  inguinal  canal.  This  process 
is  called  the  canal  of  Nuck.  It  is  generally  obliterated  in  the  adult,  but  sometimes 
remains  per^■ious  even  in  advanced  life.  It  is  analogous  to  the  saccus  vaginalis, 
which  precedes  the  descent  of  the  testis. 

In  addition  to  the  ligaments  just  described,  there  is  a  band  named  the  ligamentum  trans- 
versalis  colli  (Mackenrodt)  on  either  side  of  the  cervix  uteri.  It  is  attached  to  the  side  of  the 
cervix  uteri  and  to  the  vault  and  lateral  fornix  of  the  vagina,  and  is  continuous  externally  with 
the  fibrous  tissue  which  surrounds  the  pelvic  bloodvessels. 

The  form,  size,  and  situation  of  the  uterus  vary  at  different  periods  of  life  and  under  different 
circumstances. 


Uterine  tube. 


Cavity  of  vitrus 
Sigmoid  colon 


Hound  ligament  of 
uterus 

Bladder 

Symphysis  pubis 

Urethra. 
Vagina, 


Fig.   1168. — ^Sagittal  section  through  the  pelvis  of  a  newly  born  female,  child. 


I 


In  the  fetus  the  uterus  is  contained  in  the  abdominal  cavity,  projecting  beyond  the  superior 
aperture  of  the  pelvis  (Fig.  1168).    The  cervix  is  considerably  larger  than  the  body. 

At  -puberty  the  uterus  is  pyriform  in  shape,  and  weighs  from  14  to  17  gm.  It  has  descended 
into  the  pelvis,  the  fundus  being  just  below  the  level  of  the  superior  aperture  of  this  cavity.  The 
palmate  folds  are  distinct,  and  extend  to  the  upper  part  of  the  cavity  of  the  organ. 


1262  SPLANCHNOLOGY 

The  position  of  the  uterus  in  the  adult  is  liable  to  considerable  variation,  depending  chiefly 
on  the  condition  of  the  bladder  and  rectum.  When  the  bladder  is  empty  the  entire  uterus  is 
directed  forward,  and  is  at  the  same  time  bent  on  itself  at  the  junction  of  the  body  and  cervix, 
so  that  the  body  lies  upon  the  bladder.  As  the  latter  fills,  the  uterus  gradually  becomes  more 
and  more  erect,  until  with  a  fully  distended  bladder  the  fundus  may  be  directed  backward  toward 
the  sacrum. 

During  menstruation  the  organ  is  enlarged,  more  vascular,  and  its  surfaces  rounder;  the  external 
orifice  is  rounded,  its  labia  swollen,  and  the  lining  membrane  of  the  body  thickened,  softer,  and 
of  a  darker  color.  According  to  Sir  J.  Williams,  at  each  recurrence  of  menstruation,  a  mole- 
cular disintegration  of  the  mucous  membrane  takes  place,  which  leads  to  its  complete  removal, 
only  the  bases  of  the  glands  imbedded  in  the  muscle  being  left.  At  the  cessation  of  menstru- 
ation, a  fresh  mucous  membrane  is  formed  by  a  proliferation  of  the  remaining  structures. 

During  pregnancy  the  uterus  becomes  enormously  enlarged,  and  in  the  eighth  month  reaches 
the  epigastric  region.  The  increase  in  size  is  partly  due  to  growth  of  preexisting  muscle,  and 
partly  to  development  of  new  fibers. 

After  parturition  the  uterus  nearly  regains  its  usual  size,  weighing  about  42  gm.;  but  its  cavity 
is  larger  than  in  the  virgin  state,  its  vessels  are  tortuous,  and  its  muscular  layers  are  more  defined; 
the  external  orifice  is  more  marked,  and  its  edges  present  one  or  more  fissures. 

In  old  age  the  uterus  becomes  atrophied,  and  paler  and  denser  in  texture;  a  more  distinct 
constriction  separates  the  body  and  cervix.  The  internal  orifice  is  frequently,  and  the  external 
orifice  occasionally,  obliterated,  while  the  lips  almost  entirely  disappear. 

Structure. — The  uterus  is  composed  of  three  coats:  an  external  or  serous,  a  middle  or 
muscular,  and  an  internal  or  mucous. 

The  serous  coat  {tunica  serosa)  is  derived  from  the  peritoneum;  it  invests  the  fundus  and 
the  whole  of  the  intestinal  surface  of  the  uterus;  but  covers  the  vesical  surface  only  as  far  as 
the  junction  of  the  body  and  cervix.  In  the  lower  foiurth  of  the  intestinal  surface  the  peritoneum, 
though  covering  the  uterus,  is  not  closely  connected  with  it,  being  separated  from  it  by  a  layer 
of  loose  cellular  tissue  and  some  large  veins. 

The  muscular  coat  (tunica  muscularis)  forms  the  chief  bulk  of  the  substance  of  the  uterus. 
In  the  virgin  it  is  dense,  firm,  of  a  grayish  color,  and  cuts  almost  like  cartilage.  It  is  thick  opposite 
the  middle  of  the  body  and  fundus,  and  thin  at  the  orifices  of  the  uterine  tubes.  It  consists  of 
bundles  of  unstriped  muscular  fibers,  disposed  in  layers,  intermixed  with  areolar  tissue,  blood- 
vessels, lymphatic  vessels,  and  nerves.  The  layers  are  three  in  number:  external,  middle,  and 
internal.  The  external  and  middle  layers  constitute  the  muscular  coat  proper,  while  the  inner 
layer  is  a  greatly  hypertrophied  muscularis  mucosa;.  During  pregnancy  the  muscular  tissue 
becomes  more  prominently  developed,  the  fibers  being  greatly  enlarged. 

The  external  layer,  placed  beneath  the  peritoneum,  is  disposed  as  a  thin  plane  on  the  vesical 
and  intestinal  surfaces.  It  consists  of  fibers  which  pass  transversely  across  the  fundus,  and, 
converging  at  each  lateral  angle  of  the  uterus,  are  continued  on  to  the  uterine  tube,  the  round 
ligament,  and  the  ligament  of  the  ovary:  some  passing  at  each  side  into  the  broad  ligament, 
and  others  running  backward  from  the  cervix  into  the  sacrouterine  ligaments.  The  middle 
layer  of  fibers  presents  no  regularity  in  its  arrangement,  being  disposed  longitudinally,  obliquely, 
and  transversely.  It  contains  more  bloodvessels  than  either  of  the  other  two  layers.  The  internal 
or  deep  layer  consists  of  circular  fibers  arranged  in  the  form  of  two  hollow  cones,  the  apices  of 
which  surround  the  orifices  of  the  uterine  tubes,  their  bases  intermingling  with  one  another  on 
the  middle  of  the  body  of  the  uterus.  At  the  internal  orifice  these  circular  fibers  form  a  distinct 
sphincter. 

The  mucous  membrane  (tunica  mucosa)  (Fig.  1169)  is  smooth,  and  closely  adherent  to  the 
subjacent  tissue.  It  is  continuous  through  the  fimbriated  extremity  of  the  uterine  tubes,  with 
the  peritoneum;  and,  through  the  external  uterine  orifice,  with  the  lining  of  the  vagina. 

In  the  body  of  the  uterus  the  mucous  membrane  is  smooth,  soft,  of  a  pale  red  color,  lined  by 
columnar  ciUated  epithelium,  and  presents,  when  viewed  with  a  lens,  the  orifices  of  numerous 
tubular  follicles,  arranged  perpendicularly  to  the  surface.  The  structure  of  the  corium  differs 
from  that  of  ordinary  mucous  membranes,  and  consists  of  an  embryonic  nucleated  and  highly 
cellular  form  of  connective  tissue  in  which  run  numerous  large  lymphatics.  In  it  are  the  tube- 
like uterine  glands,  fined  by  ciliated  columnar  epithelium.  They  are  of  small  size  in  the  unim- 
pregnated  uterus,  but  shortly  after  impregnation  become  enlarged  and  elongated,  presenting 
a  contorted  or  waved  appearance  (see  page  60). 

In  the  cervix  the  mucous  membrane  is  sharply  differentiated  from  that  of  the  uterine  cavity. 
It  is  thrown  into  numerous  oblique  ridges,  which  diverge  from  an  anterior  and  posterior  longi- 
tudinal raph6.  In  the  upper  two-thirds  of  the  canal,  the  mucous  membrane  is  provided  with 
numerous  deep  glandular  follicles,  which  secrete  a  clear  viscid  alkahne  mucus;  and,  in  addition, 
extending  through  the  whole  length  of  the  canal  is  a  variable  number  of  Uttle  cysts,  presumably 
follicles  which  have  become  occluded  and  distended  with  retained  secretion.  They  are  called 
the  ovula  Nabothi.  The  mucous  membrane  covering  the  lower  half  of  the  cervical  canal  presents 
numerous  papillae.    The  epithelium  of  the  upper  two-thirds  is  cylindrical  and  ciliated,  but  below 


THE  UTERUS 


1263 


this  it  loses  its  cilia,  and  gradually  changes  to  stratified  squamous  epithelium  close  to  the  external 
orifice.  On  the  vaginal  surface  of  the  cervix  the  epithelium  is  similar  to  that  lining  the  vagina, 
fviz.,  stratified  squamous. 

Ciliated  epithelium 


Glands 


Circular 

muscular 

fibers 

Gland       Stroma. 
Fig.   1169. — Vertical  section  of  mucous  membrane  of  human  uterus.     (Sobotta.) 

ressels  and  Nerves. — The  arteries  of  the  uterus  are  the  uterine,  from  the  hypogastric;  and 
the  ovarian,  from  the  abdominal  aorta  (Fig.  1170).     They  are  remarkable  for  their  tortuou» 

Branches  to  tube 


Fig.  1170. — The  arteries  of  the  internal  organs  of  generation  of  the  female,  seen  from  behind.    (After  Hyrtl.) 


jurse  in  the  substance  of  the  organ,  and  for  their  frequent  anastomoses.    The  termination  of 

'  the  ovarian  artery  meets  that  of  the  uterine  artery,  and  forms  an  anastomotic  trunk  from  which 

branches  are  given  off  to  supply  the  uterus,  their  disposition  being  circular.     The  veins  are  of 


I 


SPLANCHNOLOGY 

large  size,  and  correspond  with  the  arteries.  They  end  in  the  uterine  plexuses.  In  the  impreg- 
nated uterus  the  arteries  carry  the  blood  to,  and  the  veins  convey  it  away  from,  the  intervillous 
space  of  the  placenta  (see  page  63).  The  lymphatics  are  described  on  page  714.  The  nerves 
are  derived  from  the  hypogastric  and  ovarian  plexuses,  and  from  the  third  and  fourth  sacral 
nerves.  l 

The  Vagina  (Fig.  1166).  I 

The  vagina  extends  from  the  vestibule  to  the  uterus,  and  is  situated  behind  the 
bladder  and  in  front  of  the  rectum;  it  is  directed  upward  and  backward,  its  axis 
forming  with  that  of  the  uterus  an  angle  of  over  90°,  opening  forward.  Its  walls 
are  ordinarily  in  contact,  and  the  usual  shape  of  its  lower  part  on  transverse  section 
is  that  of  an  H,  the  transverse  limb  being  slightly  curved  forward  or  backward, 
while  the  lateral  limbs  are  somewhat  convex  toward  the  median  line;  its  middle 
part  has  the  appearance  of  a  transverse  slit.  Its  length  is  6  to  7.5  cm.  along  its 
anterior  wall,  and  9  cm.  along  its  posterior  wall.  It  is  constricted  at  its  commence- 
ment, dilated  in  the  middle,  and  narrowed  near  its  uterine  extremity ;  it  surrounds 
the  vaginal  portion  of  the  cervix  uteri,  a  short  distance  from  the  external  orifice 
of  the  uterus,  its  attachment  extending  higher  up  on  the  posterior  than  on  the 
anterior  wall  of  the  uterus.  To  the  recess  behind  the  cervix  the  term  posterior 
fornix  is  applied,  while  the  smaller  recesses  in  front  and  at  the  sides  are  called  the 
anterior  and  lateral  fornices. 

Relations. — The  anterior  surface  of  the  vagina  is  in  relation  with  the  fundus  of  the  bladder, 
and  with  the  urethra.  Its  posterior  surface  is  separated  from  the  rectum  by  the  rectouterine 
excavation  in  its  upper  fourth,  and  by  the  rectovesical  fascia  in  its  middle  two-fourths;  the  lower 
fourth  is  separated  from  the  anal  canal  by  the  perineal  body.  Its  sides  are  enclosed  between 
the  Levatores  ani  muscles.  As  the  terminal  portions  of  the  ureters  pass  forward  and  medial- 
ward  to  reach  the  fundus  of  the  bladder,  they  run  close  to  the  lateral  fornices  of  the  vagina,  and 
as  they  enter  the  bladder  are  slightly  in  front  of  the  anterior  fornix. 

Structure. — The  vagina  consists  of  an  internal  mucous  lining  and  a  muscular  coat  separated 
by  a  layer  of  erectile  tissue. 

The  mucous  membrane  (tunica  mucosa)  is  continuous  above  with  that  lining  the  uterus.  Its 
inner  surface  presents  two  longitudinal  ridges,  one  on  its  anterior  and  one  on  its  posterior  wall. 
These  ridges  are  called  the  columns  of  the  vagina  and  from  them  numerous  transverse  ridges 
or  rugse  extend  outward  on  either  side.  These  ruga;  are  divided  by  furrows  of  variable  depth, 
giving  to  the  mucous  membrane  the  appearance  of  being  studded  over  with  conical  projections 
or  papillae;  they  are  most  numerous  near  the  orifice  of  the  vagina,  especially  before  parturition. 
The  epithelium  covering  the  mucous  membrane  is  of  the  stratified  squamous  variety.  The  sub- 
mucous tissue  is  very  loose,  and  contains  numerous  large  veins  which  by  their  anastomoses  form 
a  plexus,  together  with  smooth  muscular  fibers  derived  from  the  muscular  coat;  it  is  regarded 
by  Gussenbauer  as  an  erectile  tissue.    It  contains  a  number  of  mucous  crypts,  but  no  true  glands. 

The  muscular  coat  (tunica  muscularis)  consists  of  two  layers :  an  external  longitudinal,  which 
is  by  far  the  stronger,  and  an  internal  circular  layer.  The  longitudinal  fibers  are  continuous 
with  the  superficial  muscular  fibers  of  the  uterus.  The  strongest  fasciculi  are  those  attached 
to  the  rectovesical  fascia  on  either  side.  The  two  layers  are  not  distinctly  separable  from  each 
other,  but  are  connected  by  oblique  decussating  fasciculi,  which  pass  from  the  one  layer  to  the 
other.  In  addition  to  this,  the  vagina  at  its  lower  end  is  surrounded  by  a  band  of  striped  muscular 
fibers,-  the  Bulbocavemosus  (see  page  430). 

External  to  the  muscular  coat  is  a  layer  of  connective  tissue,  containing  a  large  plexus  of 
bloodvessels. 

The  erectile  tissue  consists  of  a  layer  of  loose  connective  tissue,  situated  between  the  mucous 
membrane  and  the  muscular  coat;  imbedded  in  it  is  a  plexus  of  large  veins,  and  numerous  bundles 
of  unstriped  muscular  fibers,  derived  from  the  circular  muscular  layer.  The  arrangement  of  the 
veins  is  similar  to  that  found  in  other  erectile  tissues. 

The  External  Genital  Organs  (Partes  Genitales  Externae  Muliebres) 

(Fig.  1171). 

The  external  genital  organs  of  the  female  are:  the  mons  pubis,  the  labia  majora 
et  minora  pudendi,  the  clitoris,  the  vestibule  of  the  vagina,  the  bulb  of  the  vestibule, 
and  the  greater  vestibular  glands.  The  term  pudendum  or  vulva,  as  generally  applied, 
includes  all  these  parts. 


I 
I 


1267 


The  Mammae  (Mammary  Gland;  Breasts). 


I 


The  mammae  secrete  the  milk,  and  are  accessory  glands  of  the  generative  system. 
.  They  exist  in  the  male  as  well  as  in  the  female;  but  in  the  former  only  in  the  rudi- 
mentary state,  unless  their  growth  is  excited  by  peculiar  circumstances.  In  the 
female  they  are  two  large  hemispherical  eminences  lying  within  the  superficial 
fascia  and  situated  on  the  front  and  sides  of  the  chest ;  each  extends  from  the  second 
rib  above  to  the  sixth  rib  below,  and  from  the  side  of  the  sternum  to  near  the  mid- 
axillary  line.  Their  weight  and  dimensions  differ  at  different  periods  of  life,  and 
in  different  individuals.  Before  puberty  they  are  of  small  size,  but  enlarge  as  the 
generative  organs  become  more  completely  developed.  They  increase  during  preg- 
nancy and  especially  after  delivery,  and  become  atrophied  in  old  age.  The  left 
mamma  is  generally  a  little  larger  than  the  right.  The  deep  surface  of  each  is 
nearly  circular,  flattened,  or  slightly  concave,  and  has  its  long  diameter  directed 
upward  and  lateralward  tow^ard  the  axilla;  it  is  separated  from  the  fascia  covering 
the  Pectoralis  major,  Serratus  anterior,  and  Obliquus  externus  abdominis  by  loose 
connective  tissue.  The  subcutaneous  surface  of  the  mamma  is  convex,  and  presents, 
just  below  the  center,  a  small  conical  prominence,  the  papilla. 

The  Mammary  Papilla  or  Nipple  (papilla  mammce)  is  a  cylindrical  or  conical 
eminence  situated  about  the  level  of  the  fourth  intercostal  space.  It  is  capable 
of  undergoing  a  sort  of  erection  from  mechanical  excitement,  a  change  mainly 
due  to  the  contraction  of  its  muscular  fibers.  It  is  of  a  pink  or  brownish  hue,  its 
surface  wrinkled  and  provided  with  secondary  papillae ;  and  it  is  perforated  by  from 
fifteen  to  twenty  orifices,  the  apertures  of  the  lactiferous  ducts.  The  base  of  the 
mammary  papilla  is  surrounded  by  an  areola.  In  the  virgin  the  areola  is  of  a  delicate 
rosy  hue;  about  the  second  month  after  impregnation  it  enlarges  and  acquires  a 
darker  tinge,  and  as  pregnancy  advances  it  may  assume  a  dark  brown  or  even  black 
color.  This  color  diminishes  as  soon  as  lactation  is  over,  but  is  never  entirely 
lost  throughout  life.  These  changes  in  the  color  of  the  areola  are  of  importance 
in  forming  a  conclusion  in  a  case  of  suspected  first  pregnancy.  Near  the  base  of 
the  papilla,  and  upon  the  surface  of  the  areola,  are  numerous  large  sebaceous  glands, 
the  areolar  glands,  which  become  much  enlarged  during  lactation,  and  present 
the  appearance  of  small  tubercles  beneath  the  skin.  These  glands  secrete  a  pecu- 
liar fatty  substance,  which  serves  as  a  protection  to  the  integument  of  the  papilla 
during  the  act  of  sucking.  The  mammary  papilla  consists  of  numerous  vessels, 
intermixed  with  plain  muscular  fibers,  which  are  principally  arranged  in  a  circular 
manner  around  the  base:  some  few  fibers  radiating  from  base  to  apex. 

Development. — ^The  mamma  is  developed  partly  from  mesoderm  and  partly  from 
ectoderm — its  bloodvessels  and  connective  tissue  being  derived  from  the  former,  its 
cellular  elements  from  the  latter.  Its  first  rudiment  is  seen  about  the  third  month, 
in  the  form  of  a  number  of  small  inward  projections  of  the  ectoderm,  which  invade 
the  mesoderm;  from  these,  secondary  tracts  of  cellular  elements  radiate  and  sub- 
.^-v-  -a  to  r--.  -.-ne  to  fy>^  '"-:+v>Ai;ti^  of  fl-^fo-i  ---diilar  *-i"-&oiCoo  :o,  and  nearly 
parallel  with,  each  other.  Together  with  the  connecting  skin  between  them, 
they  form  the  posterior  labial  commissure  or  posterior  boundary  of  the  pudendum. 
The  interval  between  the  posterior  commissure  and  the  anus,  from  2.5  to  3  cm. 
in  length,  constitutes  the  perineum.  The  labia  majora  correspond  to  the  scrotum 
in  the  male. 

The  Labia  Minora  {labia  minora  pudendi;  nymphoe)  are  two  small  cutaneous 
folds,  situated  between  the  labia  majora,  and  extending  from  the  clitoris  obliquely 
downward,  lateralward,  and  backward  for  about  4  cm.  on  either  side  of  the  orifice 
of  the  vagina,  between  which  and  the  labia  majora  they  end;  in  the  virgin  the  pos- 
terior ends  of  the  labia  minora  are  usually  joined  across  the  middle  line  by  a  fold 
of  skin,  named  the  frenulum  of  the  labia  or  fourchette.  Anteriorly,  each  labium 
80 


1264  "^^^^^  SPLANCHNOLOGY 

large  size,  and  correspond  with  the  arteries.  They  end  in  the  uterine  plexuses.  In  the  impreg 
nated  uterus  the  arteries  carry  the  blood  to,  and  the  veins  convey  it  away  from,  the  intervillous 
space  of  the  placenta  (see  page  63).  The  Isnoaphatics  are  described  on  page  714.  The  nerves 
are  derived  from  the  hypogastric  and  ovarian  plexuses,  and  from  the  third  and  fourth  sacral 
nerves.  ■ 

The  Vagina  (Fig.  1166).  ^ 

The  vagina  extends  from  the  vestibule  to  the  uterus,  and  is  situated  behind  the 
bladder  and  in  front  of  the  rectum;  it  is  directed  upward  and  backward,  its  axis 
forming  with  that  of  the  uterus  an  angle  of  over  90°,  opening  forward.  Its  walls 
are  ordinarily  in  contact,  and  the  usual  shape  of  its  lower  part  on  transverse  section 
is  that  of  an  H,  the  transverse  limb  being  slightly  curved  forward  or  backward, 
while  the  lateral  limbs  are  somewhat  convex  toward  the  median  line;  its  middle 
part  has  the  appearance  of  a  transverse  slit.  Its  length  is  6  to  7.5  cm.  along  its 
anterior  wall,  and  9  cm.  along  its  posterior  wall.  It  is  constricted  at  its  commence- 
ment, dilated  in  the  middle,  and  narrowed  near  its  uterine  extremity ;  it  surrounds 
the  vaginal  portion  of  the  cervix  uteri,  a  short  distance  from  the  external  orifice 
of  the  uterus,  its  attachment  extending  higher  up  on  the  posterior  than  on  the 
anterior  wall  of  the  uterus.  To  the  recess  behind  the  cervix  the  term  posterior 
fornix  is  applied,  while  the  smaller  recesses  in  front  and  at  the  sides  are  called  the 
anterior  and  lateral  fornices. 

Relations. — The  anterior  surface  of  the  vagina  is  in  relation  with  the  fundus  of  the  bladder, 
and  with  the  urethra.  Its  posterior  surface  is  separated  from  the  rectum  by  the  rectouterine 
excavation  in  its  upper  fourth,  and  by  the  rectovesical  fascia  in  its  middle  two-fourths;  the  lower 
fourth  is  separated  from  the  anal  canal  by  the  perineal  body.  Its  sides  are  enclosed  between 
the  Levatores  ani  muscles.  As  the  terminal  portions  of  the  ureters  pass  forward  and  medial- 
ward  to  reach  the  fundus  of  the  bladder,  they  run  close  to  the  lateral  fornices  of  the  vagina,  and 
as  they  enter  the  bladder  are  slightly  in  front  of  the  anterior  fornix. 

Structure. — The  vagina  consists  of  an  internal  mucous  lining  and  a  muscular  coat  separated 
by  a  layer  of  erectile  tissue. 

The  mucous  membrane  {tunica  mucosa)  is  continuous  above  with  that  lining  the  uterus.  Its 
inner  surface  presents  two  longitudinal  ridges,  one  on  its  anterior  and  one  on  its  posterior  wall. 
These  ridges  are  called  the  columns  of  the  vagina  and  from  them  numerous  transverse  ridges 
or  rugae  extend  outward  on  either  side.  These  ruga?  are  divided  by  furrows  of  variable  depth, 
giving  to  the  mucous  membrane  the  appearance  of  being  studded  over  with  conical  projections 
or  papillae;  they  are  most  numerous  near  the  orifice  of  the  vagina,  especially  before  parturition. 
The  epithelium  covering  the  mucous  membrane  is  of  the  stratified  squamous  variety.  The  sub- 
mucous tissue  is  very  loose,  and  contains  numerous  large  veins  which  by  their  anastomoses  form 
a  plexus,  together  with  smooth  muscular  fibers  derived  from  the  muscular  coat;  it  is  regarded 
by  Gussenbauer  as  an  erectile  tissue.  It  contains  a  number  of  mucous  crypts,  but  no  true  glands. 
The  muscular  coat  {tunica  muscularis)  consists  of  two  layers:  an  external  longitudinal,  which 
is  by  far  the  stronger,  and  an  internal  circular  layer.  The  longitudinal  fibers  are  continuous 
with  the  superficial  muscular  fibers  of  the  uterus.  The  strongest  fasciculi  are  those  attached 
to  the  rectovesical  fascia  on  either  side.  The  two  layers  are  not  distinctly  separable  from  each 
other,  but  are  connected  by  oblique  decussating  fasciculi,  which  pass  from  the  one  layer  to  the 
other.  In  addition  to  this,  the  vagina  at  its  lower  end  is  surrounded  by  a  band  of  striped  muscular 
fibers,-  the  Bulbocavemosus  (see  page  430). 

i^ne^pafs  ml§xM^^afa"^'^'li?''^  ^°^^  ^^  ^  l^^yer  of  connective  tissue,  containing  a  laree  olexus  of 
Their  posterior  ends  are  expanded  and  are  in  contact  with  the  greater  vestibular 
glands;  their  anterior  ends  are  tapered  and  joined  to  one  another  by  the  pars 
intermedia;  their  deep  surfaces  are  in  contact  with  the  inferior  fascia  of  the  uro- 
genital diaphragm;  superficially  they  are  covered  by  the  Bulbocavemosus. 

The  Greater  Vestibular  Glands  {glandulw  vestibularis  major  [BartJiolini];  Bar- 
tholin's glands)  are  the  homologues  of  the  bulbo-urethral  glands  in  the  male.  They 
consist  of  two  small,  roundish  bodies  of  a  reddish-yellow  color,  situated  one  on  either 
side  of  the  vaginal  orifice  in  contact  with  the  posterior  end  of  each  lateral  mass  of 
the  bulb  of  the  vestibule.  Each  gland  opens  b}^  means  of  a  duct,  about  2  cm.  long, 
immediately  lateral  to  the  hymen,  in  the  groove  between  it  and  the  labium  minus. 


I 
I 


riTj 


II 


THE  MAM  MM  ^^^^K         1267 

The  Mammae  (Mammary  Gland;  Breasts). 

The  mammae  secrete  the  milk,  and  are  accessor}^  glands  of  the  generative  system. 
They  exist  in  the  male  as  well  as  in  the  female;  but  in  the  former  only  in  the  rudi- 
mentary state,  unless  their  growth  is  excited  by  peculiar  circumstances.  In  the 
female  they  are  two  large  hemispherical  eminences  lying  within  the  superficial 
fascia  and  situated  on  the  front  and  sides  of  the  chest ;  each  extends  from  the  second 
rib  above  to  the  sixth  rib  below,  and  from  the  side  of  the  sternum  to  near  the  mid- 
axillary  line.  Their  weight  and  dimensions  differ  at  different  periods  of  life,  and 
in  different  individuals.  Before  puberty  they  are  of  small  size,  but  enlarge  as  the 
generative  organs  become  more  completely  developed.  They  increase  during  preg- 
nancy and  especially  after  delivery,  and  become  atrophied  in  old  age.  The  left 
mamma  is  generally  a  little  larger  than  the  right.  The  deep  surface  of  each  is 
nearly  circular,  flattened,  or  slightly  concave,  and  has  its  long  diameter  directed 
upward  and  lateralward  toward  the  axilla;  it  is  separated  from  the  fascia  covering 
the  Pectoralis  major,  Serratus  anterior,  and  Obliquus  externus  abdominis  by  loose 
connective  tissue.  The  subcutaneous  surface  of  the  mamma  is  convex,  and  presents, 
just  below  the  center,  a  small  conical  prominence,  the  papilla. 

The  Mammary  Papilla  or  Nipple  {'papilla  mammcE)  is  a  cylindrical  or  conical 
eminence  situated  about  the  level  of  the  fourth  intercostal  space.  It  is  capable 
of  undergoing  a  sort  of  erection  from  mechanical  excitement,  a  change  mainly 
due  to  the  contraction  of  its  muscular  fibers.  It  is  of  a  pink  or  brownish  hue,  its 
surface  wrinkled  and  provided  with  secondary  papillae ;  and  it  is  perforated  by  from 
fifteen  to  twenty  orifices,  the  apertures  of  the  lactiferous  ducts.  The  base  of  the 
mammary  papilla  is  surrounded  by  an  areola.  In  the  virgin  the  areola  is  of  a  delicate 
osy  hue;  about  the  second  month  after  impregnation  it  enlarges  and  acquires  a 
darker  tinge,  and  as  pregnancy  advances  it  may  assume  a  dark  brown  or  even  black 
color.  This  color  diminishes  as  soon  as  lactation  is  over,  but  is  never  entirely 
lost  throughout  life.  These  changes  in  the  color  of  the  areola  are  of  importance 
in  forming  a  conclusion  in  a  case  of  suspected  first  pregnancy.  Near  the  base  of 
the  papilla,  and  upon  the  surface  of  the  areola,  are  numerous  large  sebaceous  glands, 
the  areolar  glands,  which  become  much  enlarged  during  lactation,  and  present 
the  appearance  of  small  tubercles  beneath  the  skin.  These  glands  secrete  a  pecu- 
liar fatty  substance,  which  serves  as  a  protection  to  the  integument  of  the  papilla 
during  the  act  of  sucking.  The  mammary  papilla  consists  of  numerous  vessels, 
intermixed  with  plain  muscular  fibers,  which  are  principally  arranged  in  a  circular 
manner  around  the  base:  some  few  fibers  radiating  from  base  to  apex. 

Development. — The  mamma  is  developed  partly  from  mesoderm  and  partly  from 
ectoderm — its  bloodvessels  and  connective  tissue  being  derived  from  the  former,  its 
cSllular  elements  from  the  latter.  Its  first  rudiment  is  seen  about  the  third  month, 
in  the  form  of  a  number  of  small  inward  projections  of  the  ectoderm,  which  invade 
the  mesoderm;  from  these,  secondary  tracts  of  cellular  elements  radiate  and  sub- 
sequently give  rise  to  the  epithelium  of  the  glandular  follicles  and  ducts.  The 
development  of  the  follicles,  however,  remains  imperfect,  except  in  the  parous 
female. 

Structure  (Figs.  1172,  1173). — The  mamma  consists  of  gland  tissue;  of  fibrous  tissue,  con- 
necting its  lobes;  and  of  fatty  tissue  in  the  intervals  between  the  lobes.  The  gland  tissue,  when 
freed  from  fibrous  tissue  and  fat,  is  of  a  pale  reddish  color,  firm  in  texture,  flattened  from  before 
backward  and  thicker  in  the  center  than  at  the  circumference.  The  subcutaneous  surface  of 
the  mamma  presents  numerous  irregular  processes  which  project  toward  the  skin  and  are  joined 
to  it  by  bands  of  connective  tissue.  It  consists  of  numerous  lobes,  and  these  are  composed  of 
lobules,  connected  together  by  areolar  tissue,  bloodvessels,  and  ducts.  The  smallest  lobules 
consist  of  a  cluster  of  rounded  alveoli,  which  open  into  the  smallest  branches  of  the  lactiferous 
ducts;  these  ducts  unite  to  form  larger  ducts,  and  these  end  in  a  single  canal,  corresponding  with 
one  of  the  chief  subdivisions  of  the  gland.    The  number  of  excretory  ducts  varies  from  fifteen 


1268 


SPLANCHNOLOGY 


I 


to  twenty;  they  are  termed  the  tubuli  lactiferi.     They  converge  toward  the  areola,  beneath 
which  they  form  dilatations  or  ampullae,  which  serve  as  reservoirs  for  the  milk,  and,  at  the  base 


Lobule  un 
ravelled 


Lactiferous 
tvhvle 


Alveoli 


Fat 


Duct 


Ampulla 

Lobules.  

Loculi  in  connective 
tissue 

Fig.  1172. — Dissection  of  the  lower  half  of  the  mamma  during  the  period  of  lactation.     (Luschka.) 

of  the  papillae,  become  contracted,  and  pursue  a  straight  course  to  its  summit,  perforating  it 
by  separate  orifices  considerably  narrower  than  the  ducts  themselves.  The  ducts  are  composed 
of  areolar  tissue  containing  longitudinal  and  transverse  elastic  fibers;  muscular  fibers  are  entirely 

absent;  they  are  lined  by  columnar  epithe- 
lium resting  on  a  basement  membrane. . 
The  epithelium  of  the  mamma  differs  ac- 
cording to  the  state  of  activity  of  the 
organ.  In  the  gland  of  a  woman  who  is 
not  pregnant  or  suckling,  the  alveoli  are 
very  small  and  solid,  being  filled  with  a 
mass  of  granular  polyhedral  cells.  During 
pregnancy  the  alveoli  enlarge,  and  the  cells 
undergo  rapid  multiplication.  At  the  com- 
mencement of  lactation,  the  cells  in  the 
center  of  the  alveolus  undergo  fatty  degen- 
eration, and  are  eliminated  in  the  first  milk, 
as  colostrum  corpuscles.  The  peripheral 
cells  of  the  alveolus  remain,  and  form  a 
single  layer  of  granular,  short  columnar 
cells,  with  spherical  nuclei,  lining  the  base- 
ment membrane.  The  cells,  during  the 
state  of  activity  of  the  gland,  are  capable  of  forming,  in  their  interior,  oil  globules,  which  are 
then  ejected  into  the  lumen  of  the  alveolus,  and  constitute  the  milk  globules.  When  the  acini 
are  distended  by  the  accumulation  of  the  secretion  the  lining  epithelium  becomes  flattened. 

The  fibrous  tissue  invests  the  entire  surface  of  the  mamma,  and  sends  down  septa  between 
its  lobes,  connecting  them  together. 

The  fatty  tissue  covers  the  surface  of  the  gland,  and  occupies  the  interval  between  its  lobes. 
It  usually  exists  in  considerable  abundance,  and  determines  the  form  and  size  of  the  gland.  There 
is  no  fat  immediately  beneath  the  areola  and  papilla. 

Vessels  and  Nerves. — The  arteries  supplying  the  mammaj  are  derived  from  the  thoracic 
branches  of  the  axillary,  the  intercostals,  and  the  internal  mammary.  The  veins  describe  an 
anastomotic  circle  around  the  base  of  the  papilla,  called  by  Haller  the  circulus  venosus.  From 
this,  large  branches  transmit  the  blood  to  the  circumference  of  the  gland,  and  end  in  the  axillary 
and  internal  mammary  veins.  The  lymphatics  are  described  on  page  715.  The  nerves  are 
derived  from  the  anterior  and  lateral  cutaneous  branches  of  the  fourth,  fifth,  and  sixth  thoracic 


Fig.  1173. — Section  of  portion  of  mamma. 


THE  THYROID  GLAND 


1269 


THE   DUCTLESS   GLANDS. 

There  are  certain  organs  which  are  very  similar  to  secreting  glands,  but  differ 
from  them  in  one  essential  particular,  viz.,  they  do  not  possess  any  ducts  by  which 
their  secretion  is  discharged.  These  organs  are  known  as  ductless  glands.  They 
are  capable  of  internal  secretion — that  is  to  say,  of  forming,  from  materials  brought 
to  them  in  the  blood,  substances  which  have  a  certain  influence  upon  the  nutritive 
and  other  changes  going  on  in  the  body.  This  secretion  is  carried  into  the  blood 
stream,  either  directly  by  the  veins  or  indirectly  through  the  medium  of  the 
lymphatics. 

These  glands  include  the  thyroid,  the  parathyroids  and  the  thymus ;  the  pituitary 
body  and  the  pineal  body;  the  chromaphil  and  cortical  systems  to  which  belong  the 
suprarenals,  the  paraganglia  and  aortic  glands,  the  glomus  caroticum  and  perhaps 
the  glomus  coccygeum.  The  spleen  is  usually  included  in  this  list  and  sometimes  the 
lymph  and  hemolymph  nodes  described  with  the  lymphatic  system.  Other  glands 
s  the  liver,  pancreas  and  sexual  glands  give  off  internal  secretions,  as  do  the 
gastric  and  intestinal  mucous  membranes. 


External  carotid  artery 

Superior  thyroid  artery 
Superior  thyroid  vein 


Middle  thyroid  vein 


FiQ.   1174. — The  thyroid  gland  and  its  relations. 


THE  THYROID   GLAND   (GLANDULA  THYREIODEA;   THYROID  BODY) 

(Fig.  1174). 

The  thyroid  gland  is  a  highly  vascular  organ,  situated  at  the  front  and  sides  of 
the  neck;  it  consists  of  right  and  left  lobes  connected  across  the  middle  line  by  a 
narrow  portion,  the  isthmus.  Its  weight  is  somewhat  variable,  but  is  usually  about 
30  grams.  It  is  slightly  heavier  in  the  female,  in  whom  it  becomes  enlarged  during 
menstruation  and  pregnancy. 

The  lobes  {lobuli  gl.  thyreoideoe)  are  conical  in  shape,  the  apex  of  each  being 
directed  upward  and  lateralward  as  far  as  the  junction  of  the  middle  with  the  lower 


SPLANCHNOLOGY 


I 


third  of  the  thyroid  cartilage;  the  base  looks  downward,  and  is  on  a  level  with  the 
fifth  or  sixth  tracheal  ring.  Each  lobe  is  about  5  cm.  long;  its  greatest  width  is 
about  3  cm.,  and  its  thickness  about  2  cm.  The  lateral  or  superficial  surface  is  con- 
vex, and  covered  by  the  skin,  the  superficial  and  deep  fasciae,  the  Sternocleido- 
mastoideus,  the  superior  belly  of  the  Omohyoideus,  the  Sternohyoideus  and  Sterno- 
thyreoideus,  and  beneath  the  last  muscle  by  the  pretracheal  layer  of  the  deep 
fascia,  which  forms  a  capsule  for  the  gland.  The  deep  or  medial  surface  is  moulded 
over  the  underlying  structures,  viz.,  the  thyroid  and  cricoid  cartilages,  the  trachea, 
the  Constrictor  pharyngis  inferior  and  posterior  part  of  the  Cricothyreoideus, 
the  esophagus  (particularly  on  the  left  side  of  the  neck),  the  superior  and  inferior 
thyroid  arteries,  and  the  recurrent  nerves.  The  anterior  border  is  thin,  and  inclines 
obliquely  from  above  downward  toward  the  middle  line  of  the  neck,  while  the 
posterior  border  is  thick  and  overlaps  the  common  carotid  artery,  and,  as  a  rule, 
the  parathyroids. 

The  isthmus  {isthmus  gl.  thyreoidea)  connects  together  the  lower  thirds  of  the 
lobes;  it  measures  about  1.25  cm.  in  breadth,  and  the  same  in  depth,  and  usually 
covers  the  second  and  third  rings  of  the  trachea.  Its  situation  and  size  present, 
however,  many  variations.  In  the  middle  line  of  the  neck  it  is  covered  by  the  skin . 
and  fascia,  and  close  to  the  middle  line,  on  either  side,  by  the  Sternothyreoideus. 
Across  its  upper  border  runs  an  anastomotic  branch  uniting  the  two  superior 
thyroid  arteries;  at  its  lower  border  are  the  inferior  thyroid  veins.  Sometimes  the 
isthmus  is  altogether  w^anting. 

A  third  lobe,  of  conical  shape,  called  the  pyramidal  lobe,  frequently  arises  from 
the  upper  part  of  the  isthmus,  or  from  the  adjacent  portion  of  either  lobe,  but 
most  commonly  the  left,  and  ascends  as  far  as  the  hyoid  bone.  It  is  occasionally 
quite  detached,  or  may  be  divided  into  two  or  more  parts. 

A  fibrous  or  muscular  band  is  sometimes  found  attached,  above,  to  the  body 
of  the  hyoid  bone,  and  below  to  the  isthmus  of  the  gland,  or  its  pyramidal  lobe. 
When  muscular,  it  is  termed  the  Levator  glandulse  thyreoidese. 

Small  detached  portions  of  thyroid 
tissue  are  sometimes  found  in  the  vicin- 
ity of  the  lateral  lobes  or  above  the 
isthmus;  they  are  called  accessory  thy- 
roid glands  (gla7idulcB  thyreoideoe  acces- 
sorice) . 

Development. — The  thyroid  gland  is 
developed  from  a  median  diverticulum 
(Fig.  1175),  which  appears  about  the 
fourth  week  on  the  summit  of  the  tuber- 
culum  impar,  but  later  is  found  in  the 
furrow  immediately  behind  the  tuber- 
culum  (Fig.  979).  It  grows  downward 
and  backward  as  a  tubular  duct,  which 
bifurcates  and  subsequently  subdivides 
into  a  series  of  cellular  cords,  from 
which  the  isthmus  and  lateral  lobes  of 
the  thyroid  gland  are  developed.  The 
ultimo-branchial  bodies  from  the  fifth 
pharyngeal  pouches  are  enveloped  by 
the  lateral  lobes  of  the  thyroid  gland;  they  undergo  atrophy  and  do  not  form  true 
thyroid  tissue.  The  connection  of  the  diverticulum  with  the  pharynx  is  termed 
the  thyroglossal  duct;  its  continuity  is  subsequently  interrupted,  and  it  undergoes 
degeneration,  its  upper  end  being  represented  by  the  foramen  cecum  of  the  tongue, 
and  its  lower  by  the  pyramidal  lobe  of  the  thyroid  gland. 


Thyroid  gland 


Parathyroids 


Thymua 


Thymus 


Ultimo-branchial  body 


Fig.  1175. — Scheme  showing  development  of  bran- 
chial epithelial  bodies.  (Modified  from  Kohn.)  I, 
II,  III,  IV.     Branchial  pouches. 


THE  PARATHYROID  GLANDS 


1271 


Structure. — The  thyroid  gland  is  invested  by  a  thin  capsule  of  connective  tissue,  which  pro- 
jects into  its  substance  and  imperfectly  divides  it  into  masses  of  irregular  form  and  size.  When 
the  organ  is  cut  into,  it  is  of  a  brownish-red  color,  and  is  seen  to  be  made  up  of  a  number  of 
closed  vesicles,  containing  a  yellow  glairy  fluid,  and  separated  from  each  other  by  intermediate 
connective  tissue  (Fig.  1176). 


Colloid  material 

Colloid  in 
lymphatic  vessel 

Cubical 
epithelium 


Fig.   1176. — Section  of  thyroid  gland  of  sheep.     X  160. 

le  vesicles  of  the  thyroid  of  the  adult  animal  are  generally  closed  spherical  sacs;  but  in  some 
young  animals,  e.  g.,  young  dogs,  the  vesicles  are  more  or  less  tubular  and  branched.  This 
appearance  is  supposed  to  be  due  to  the  mode  of  growth  of  the  gland,  and  merely  indicates  that 
an  increase  in  the  number  of  vesicles  is  taking  place.  Each  vesicle  is  lined  by  a  single  layer  of 
cubical  epithelium.  There  does  not  appear  to  be  a  basement  membrane,  so  that  the  epithelial 
cells  are  in  direct  contact  with  the  connective-tissue  reticulum  which  supports  the  acini.  The 
vesicles  are  of  various  sizes  and  shapes,  and  contain  as  a  normal  product  a  viscid,  homogeneous, 
semifluid,  slightly  yellowish,  colloid  material;  red  corpuscles  are  found  in  it  in  various  stages 
of  disintegration  and  decolorization,  the  yellow  tinge  being  probably  due  to  the  hemoglobin, 
which  is  thus  set  free  from  the  colored  corpuscles.  The  colloid  material  contains  an  iodine  com- 
pound, iodothyrin,  and  is  readily  stained  by  eosin.  According  to  Bensley^  the  thyroid  gland 
prepares  and  secretes  into  the  vascular  channels  a  substance,  formed  under  normal  conditions  in 
the  outer  pole  of  the  cell  and  excreted  from  it  directly  without  passing  by  the  indirect  route 
through  the  follicular  cavity.  In  addition  to  this  direct  mode  of  secretion  there  is  an  indirect 
mode  which  consists  in  the  condensation  of  the  secretion  into  the  form  of  droplets,  having  high 
content  of  solids,  and  the  extension  of  these  droplets  into  the  follicular  cavity.  These  droplets 
are  formed  in  the  same  zone  of  the  cell  as  that  in  which  the  primary  or  direct  secretion  is  formed. 

This  internal  secretion  of  the  thyroid  is  supposed  to  contain  a  specific  hormone  which  acts  as  a 
chemical  stimulus  to  other  tissues,  increasing  their  metabolism. 

Vessels  and  Nerves. — The  arteries  supplying  the  thyroid  gland  are  the  superior  and  inferior 
th5a"oids  and  sometimes  an  additional  branch  (thyroidea  ima)  from  the  innominate  artery  or  the 
arch  of  the  aorta,  which  ascends  upon  the  front  of  the  trachea.  The  arteries  are  remarkable 
for  their  large  size  and  frequent  anastomoses.  The  veins  form  a  plexus  on  the  surface  of  the 
gland  and  on  the  front  of  the  trachea;  from  this  plexus  the  superior,  middle,  and  inferior  thyroid 
veins  arise;  the  superior  and  middle  end  in  the  internal  jugular,  the  inferior  in  the  innominate 
vein.  The  capillary  bloodvessels  form  a  dense  plexus  in  the  connective  tissue  around  the  vesicles, 
between  the  epithelium  of  the  vesicles  and  the  endothelium  of  the  lymphatics,  which  surround 
a  greater  or  smaller  part  of  the  circumference  of  the  vesicle.  The  lymphatic  vessels  run  in  the 
interlobular  connective  tissue,  not  uncommonly  surrounding  the  arteries  which  they  accompany, 
and  communicate  with  a  net-work  in  the  capsule  of  the  gland;  they  may  contain  colloid  material. 
They  end  in  the  thoracic  and  right  lymphatic  trunks.  The  nerves  are  derived  from  the  middle 
and  inferior  cervical  ganglia  of  the  sympathetic. 


II 


THE  PARATHYROID  GLANDS  (Fig.  1177). 


The  parathyroid  glands  are  small  brownish-red  bodies,  situated  as  a  rule  between 
the  posterior  borders  of  the  lateral  lobes  of  the  thyroid  gland  and  its  capsule. 
They  differ  from  it  in  structure,  being  composed  of  masses  of  cells  arranged  in  a 
more  or  less  columnar  fashion  with  numerous  intervening  capillaries.    They  meas- 


1  .\merioan  Journal  of  .\natomy,  1916.  xix. 


1272 


SPLANCHNOLOGY 


ure  on  an  average  about  6  mm.  in  length,  and  from  3  to  4  mm,  in  breadth,  and 
usually  present  the  appearance  of  flattened  oval  disks.  They  are  divided,  accord- 
ing to  their  situation,  into  superior  and  inferior.  The  superior,  usually  two  in  number, 
are  the  more  constant  in  position,  and  are  situated,  one  on  either  side,  at  the  level 
of  the  lower  border  of  the  cricoid  cartilage,  behind  the  junction  of  the  pharynx 
and  esophagus.  The  inferior,  also  usually  two  in  number,  may  be  applied  to  the 
lower  edge  of  the  lateral  lobes,  or  placed  at  some  little  distance  below  the  thyroid 
gland,  or  found  in  relation  to  one  of  the  inferior  thyroid  veins. ^ 


I 


Common  carotid 
artery 

Right  parathy- 
roids 


Inferior  thyroid 
artery 

Remnant  of  laryn- 
geal nerve 


Fig.   1177. — Parathyroid  glands.     (Halsted  and  Evans.) 

In  man,  they  number  four  as  a  rule;  fewer  than  four  were  found  in  less  than  1 
per  cent,  of  over  a  thousand  persons  (Pepere^),  but  more  than  four  in  over  33  per 
cent,  of  122  bodies  examined  by  Civalleri.  In  addition,  numerous  minute  islands 
of  parathyroid  tissue  may  be  found  scattered  in  the  connective  tissue  and  fat  of 
the  neck  around  the  parathyroid  glands  proper,  and  quite  distinct  from  them. 

Development. — The  parathyroid  bodies  are  developed  as  outgrowths  from  the 
third  and  fourth  branchial  pouches  (Fig.  1175). 

A  pair  of  diverticula  arise  from  the  fifth  branchial  pouch  and  form  what  are 
termed  the  ultimo-branchial  bodies  (Fig.  1175):  these  fuse  with  the  thyroid  gland, 
but  probably  contribute  no  true  thyroid  tissue. 

1  Consult  an  article  "Concerning  the  Parathyroid  Glands,"  by  D.  A.  Welsh,  Journal  of  Anatomy  and  Physiology, 
vol.  xxxii. 

2  Consult  Le  Ghiandole  paratiroidee,  by  A.  Pepere,  Turin,  1906. 


THE  THYMUS  GLAND 


1273 


Structure. — Microscopically  the  parathyroids  consist  of  intercommunicating  columns  of 
cells  supported  by  connective  tissue  containing  a  rich  supply  of  blood  capillaries.  Most  of  the 
cells  are  clear,  but  some,  larger  in  size,  contain  oxyphil  granules.  Vesicles  containing  colloid 
have  been  described  as  occurring  in  the  parathyroid,  but  the  observation  has  not  been  confirmed. 

No  doubt  the  parathyroid  glands  produce  an  internal  secretion  essential  to  the  well-being 
of  the  human  economy;  but  it  is  still  a  matter  of  dispute  what  symptoms  of  disease  are  pro- 
duced by  their  removal  and  suppression  of  their  secretion.  Pepere  believes  that  they  show 
signs  of  exceptional  activity  during  pregnancy,  and  that  parathyroid  insufficiency  is  a  main 
factor  in  the  production  of  tetany  in  infants  and  adults,  of  eclampsia,  and  of  certain  sorts  of 
fits.  It  is  probable  that  the  tetany  following  parathyroidectomy  is  due  to  the  accumulation  of 
ammonium  carbonate  and  Kendall  has  suggested  that  the  function  of  the  parathyroid  is  to  con- 
vert ammonium  carbonate  into  urea. 

THE  THYMUS  GLAND  (Fig.  1178). 

The  thymus  is  a  temporary  organ,  attaining  its  largest  size  at  the  time  of 
puberty  (Hammar),  when  it  ceases  to  grow,  gradually  dwindles,  and  almost 
disappears.  If  examined  when  its  growth  is  most  active,  it  will  be  found  to  con- 
sist of  two  lateral  lobes  placed  in  close  contact  along  the  middle  line,  situated 
partly  in  the  thorax,  partly  in  the  neck,  .and  extending  from  the  fourth  costal 
cartilage  upward,  as  high  as  the  lower  border  of  the  thyroid  gland.  It  is  covered 
y  the  sternum,  and  by  the  origins  of  the  Sternohyoidei  and  Sternothyreoidei. 


Trachea 
Thyroid  veins 

Right  vagvs 

Superior  vena  iii|ii(        lW" 


Thyroid  gland 

Left  common 
carotid  artery 
Left  internal 
jugular  vein 

Left  subclavian 


Fig.  117: 


mus  of  a  full-time  fetus,  exposed  in  situ. 


\^ 


Below,  it  rests  upon  the  pericardium,  being  separated  from  the  aortic  arch  and 
great  vessels  by  a  layer  of  fascia.  In  the  neck  it  lies  o^n  the  front  and  sides  of  the 
trachea,  behind  the  Sternohj-oidei  and  Sternothyreoidei.  The  two  lobes  generally 
differ  in  size;  they  are  occasionally  united,  so  as  to  form  a  single  mass;  and  some- 
times separated  by  an  intermediate  lobe.  The  thymus  is  of  a  pinkish-gray  color, 
soft,  and  lobulated  on  its  surfaces.  It  is  about  5  cm.  in  length,  4  cm.  in  breadth 
below,  and  about  G  mm.  in  thickness.  At  birth  it  weighs  about  15  grams,  at  puberty 
it  weighs  about  35  grams;  after  this  it  gradually  decreases  to  25  grams  at  twenty- 
ve  years,  less  than  15  grams  at  sixty,  and  about  6  grams  at  seventy  years. 
Development. — The  thymus  appears  in  the  form  of  two  flask-shaped  entodermal 
diverticula,  which  arise,  one  on  either  side,  from  the  third  branchial  pouch  (Fig. 
1175),  and  extend  lateralward  and  backward  into  the  surrounding  mesoderm  in 
front  of  the  ventral  aortae.  Here  they  meet  and  become  joined  to  one  another  by 
connective  tissue,  but  there  is  never  any  fusion  of  the  thymus  tissue  proper.  The 
pharyngeal  opening  of  each  diverticulum  is  soon  obliterated,  but  the  neck  of  the 
flask  persists  for  some  time  as  a  cellular  cord.  By  further  proliferation  of  the  cells 
lining  the  flask,  buds  of  cells  are  formed,  which  become  surrounded  and  isolated 
by  the  invading  mesoderm.    In  the  latter,  numerous  lymphoid  cells  make  their 


1274 


SPLANCHNOLOGY 


appearance,  and  are  aggregated  to  form  lymphoid  follicles.  These  lymphoid 
cells  are  probably  derivatives  of  the  entodermal  cells  which  lined  the  original 
diverticula  and  their  subdivisions.  Additional  portions  of  thymus  tissue  arci 
sometimes  developed  from  the  fourth  branchial  pouches.  Thymus  continues 
to  grow  until  the  time  of  puberty  and  then  begins  to  atrophy. 


I 


Artery 


Vein 


Fig.  1179. — Minute  structure  of  thymus.  Follicle  of  injected  thymus  from  calf,  four  days  old,  slightly  diagram- 
matic, magnified  about  50  diameters.  The  large  vessels  are  disposed  in  two  rings,  one  of  which  surrounds  the  follicle, 
the  other  lies  j  ust  within  the  margin  of  the  medulla.  (Watney.)  A  and  B.  From  thymus  of  camel,  examined  without 
addition  of  any  reagent.  Magnified  about  400  diameters.  A.  Large  colorless  cell,  containing  small  oval  masses  of 
hemoglobin.    Similar  cells  are  found  in  the  lymph  glands,  spleen,  and  medulla  of  bone.    B.  Colored  blood  corpuscles. 

Structure. — Each  lateral  lobe  is  composed  of  numerous  lobules  held  together  by  delicate 
areolar  tissue;  the  entire  gland  being  enclosed  in  an  investing  capsule  of  a  similar  but  denser 
structure.  The  primary  lobules  vary  in  size  from  that  of  a  pin's  head  to  that  of  a  small  pea,  and 
are  made  up  of  a  number  of  small  nodules  or  follicles,  which  are  irregular  in  shape  and  are  more 
or  less  fused  together,  especially  toward  the  interior  of  the  gland.  Each  follicle  is  from  1  to  2  mm. 
in  diameter  and  consists  of  a  medullary  and  a  cortical  portion,  and  these  differ  in  many  essential 
particulars  from  each  other.  The  cortical  portion  is  mainly  composed  of  lymphoid  cells,  supported 
by  a  network  of  finely  branched  cells,  which  is  continuous  with  a  similar  network  in  the  medullary 
portion.  This  network  forms  an  adventitia  to  the  bloodvessels.  In  thQ  medullary  portion  the 
reticulum  is  coarser  than  in  the  cortex,  the  lymphoid  cells  are  relatively  fewer  in  number,  and 
there  are  found  peculiar  nest-like  bodies,  the  concentric  corpuscles  of  HassaU,  These  concentric 
corpuscles  are  composed  of  a  central  mass,  consisting  of  one  or  more  granular  cells,  and  of  a 
capsule  which  is  formed  of  epithehoid  cells  (Fig.  117J9).  They  are  the  remains  of  the  epithelial 
tubes  which  grow  out  from  the  third  branchial  pouches  of  the  embryo  to  form  the  thymus. 

Each  follicle  is  surrounded  by  a  vascular  plexus,  from  which  vessels  pass  into  the  interior, 
and  radiate  from  the  periphery  toward  the  center,  forming  a  second  zone  just  within  the  margin 
of  the  medullary  portion.  In  the  center  of  the  medullary  portion  there  are  very  few  vessels,  and 
they  are  of  minute  size. 

Watney  has  made  the  important  observation  that  hemoglobin  is  found  in  the  thymus,  either 
in  cysts  or  in  cells  situated  near  to,  or  forming  part  of,  the  concentric  corpuscles.  This  hemo- 
globin occurs  as  granules  or  as  circular  masses  exactly  resembling  colored  blood  corpuscles.    He 


THE  HYPOPHYSIS  CEREBRI 


1275 


as  also  discovered,  in  the  lymph  issuing  from  the  thymus,  similar  cells  to  those  found  in  the 
gland,  and,  like  them,  containing  hemoglobin  in  the  form  of  either  granules  or  masses.  From 
these  facts  he  arrives  at  the  conclusion  that  the  gland  is  one  source  of  the  colored  blood  corpuscles. 
More  recently  Schaffer  has  observed  actual  nucleated  red-blood  corpuscles  in  the  thymus.  The 
function  of  the  thymus  is  obscure.  It  seems  to  furnish  during  the  period  of  growth  an  internal 
secretion  concerned  with  some  phases  of  body  metabolism,  especially  that  of  the  sexual  glands. 

Vessels  and  Nerves. — The  arteries  supplying  the  thymus  are  derived  from  the  internal 
mammary,  and  from  the  superior  and  inferior  thyroids.  The  veins  end  in  the  left  innominate 
vein,  and  in  the  thyroid  veins.  The  lymphatics  are  described  on  page  698.  The  nerves  are 
exceedingly  minute;  they  are  derived  from  the  vagi  and  sympathetic.    Branches  from  the  descen- 

Idens  hypoglossi  and  phrenic  reach  the  investing  capsule,  but  do  not  penetrate  into  the  substance 
of  the  gland. 
I 


THE  HYPOPHYSIS  CEREBRI. 


The  hypophysis  (pituitary  body)  (Fig.  1180)  is  a  small  reddish-gray  body,  about 
'^1  em.  in  diameter,  attached  to  the  end  of  the  infundibiilum  of  the  brain  and  resting 
in  the  hypophyseal  fossa. 


Anterior     Optic 


Ant.  cerebral  artery. 


Optic  chiasma,' 


Anterior  lobe 
of  hypophysis 


^Jnfundibulum 
Circular  sinus 


Cerebral  peduncle 


Corpus  mammiUare 
Post,  cerebral  artery 
Basilar  artery 

Pons 


Posterior  lobe 
Fig.  1180. — The  hypophysis  cerebri  in  position.     Shown  in  sagittal  section. 


Optic  ehiamrna 

3rd  ventricle 
Extension  of  pars  intennedia 
into  brain  stibstance 

Process  of  pars  intermedia 
Anterior  lobe 
Jntraglandular  cleft 

Pars  intennedia 
1  Fig.   1181. — Median  sagittal  section  through  the  hypophysis  of  an  adult  monkey.     Semidiagrammatic.      (Herring.) 


Posterior  lobe 


The  hypophysis  consists  of  an  anterior  and  a  posterior  lobe,  which  differ  from 
one  another  in  their  mode  of  development  and  in  their  structure  (Fig.  1181).    The 
anterior  lobe  is  the  larger  and  is  somewhat  kidney-shaped,  the  concavity  being 
jBfiirected  backward  and  embracing  the  posterior  lobe.    It  consists  of  a  pars  anterior 


1276 


SPLANCHNOLOGY 


and  a  pars  intermedia,  separated  from  each  other  by  a  narrow  cleft,  the  remnant 
of  the  pouch  or  diverticulmn.  The  pars  anterior  is  extremely  vascular  and  consists 
of  epithelial  cells  of  varying  size  and  shape,  arranged  in  cord-like  trabeculse  or 
alveoli  and  separated  by  large,  thin-walled  bloodvessels.  The  pars  intermedia  is  a 
thin  lamina  closely  applied  to  the  body  and  neck  of  the  posterior  lobe  and  extend- 
ing onto  the  neighboring  parts  of  the  brain;  it  contains  few  bloodvessels  and 
consists  of  finely  granular  cells  between  which  are  small  masses  of  colloid  material. 
The  pars  intermedia  in  spite  of  the  fact  that  it  arises  in  common  with  the  pars 
anterior  from  the  ectoderm  of  the  primitive  buccal  cavity  is  often  considered  as 
A  B  a  part  of  the  posterior  lobe; 

which  arises  from  the  floor  of 
the  third  ventricle  of  the 
brain.  Although  of  nervous 
origin  the  posterior  lobe  con- 
tains no  nerve  cells  or  fibers. 
It  consists  of  neuroglia  cells 
and  fibers  and  is  invaded  by 
columns  which  grow  into  it 
from  the  pars  intermedia; 
imbedded  in  it  are  large 
quantities  of  a  colloid  sub- 
stance histologically  similar 
to  that  found  in  the  thyroid 
gland.  In  certain  of  the 
lower  vertebrates,  e.  g.,  fishes, 
nervous  structures  are  pres- 
ent, and  the  lobe  is  of  large 
size. 

From  the  pars  intermedia 
a  substance,  no  doubt  an  in- 
ternal secretion,  causes  con- 
striction of  the  bloodvessels 
with  rise  of  arterial  blood- 
pressure.  This  substance 
seems  to  have  a  stimulating 
effect  on  most  of  the  smooth 
muscles,  acting  directly  upon 
the  muscle  causing  contrac- 
tion. It  also  increases  the  se- 
cretion of  the  urine;  of  the 
mammary  glands  when  in 
functional  activity;  and  of 
the  cerebrospinal  fluid.  Ex- 
tracts of  this  lobe  also  influ- 
ence the  general  metabolism  of  the  carbohydrates  by  accelerating  the  process  of 
glycogenolysis  in  the  liver. 

The  pars  anterior  exercises  a  stimulating  effect  on  the  growth  of  the  skeleton  and 
probably  on  connective  tissues  in  general. 

Enlargement  of  the  hypophysis  and  of  the  cavity  of  the  sella  turcica  are  found  in  the  rare 
disease  acromegaly,  which  is  characterized  by  gradual  enlargement  of  the  face,  hands,  and  feet, 
with  headache  and  often  a  pecuhar  type  of  bhndness.  This  blindness  is  due  to  the  pressure  of 
the  enlarging  hypophysis  on  the  optic  chiasma  (Fig.  1180). 

Development  of  the  Hypophysis  Cerebri. — This  in  the  adult  consists  of  a  large 
anterior,  consisting  of  the  pars  anterior  and  the  pars  intermedia,  and  a  small  pos- 


I 


Fig.  1182. — Vertical  sections  of  the  heads  of  early  embryos  of  the  rab- 
bit. Magnified.  (From  Mihalkovics.)  A.  From  an  embryo  5  mm. 
long.  B.  From  an  embryo  6  mm.  long.  C.  Vertical  section  of  the 
anterior  end  of  the  notochord  and  hypophysis,  etc.,  from  an  embryo  16 
mm.  long.  In  A  the  buccopharyngeal  membrane  is  still  present.  In  B 
it  is  in  the  process  of  disappearing,  and  the  stomodeum  now  communi- 
cates with  the  primitive  pharynx,  am.  Amnion,  c.  Fore-brain,  ch. 
Notochord.  /.  Anterior  extremity  of  fore-gut,  i.  h.  Heart,  if.  Infun- 
dibulum.  m.  Wall  of  brain  cavity,  mc.  Mid-brain.  mo.  Hind-brain. 
p.  Original  position  of  hypophyseal  diverticulum,  pj/.  ph.  Pharynx. 
«p.e.  Sphenoethmoidal,  be.  Central,  sp.o.  Sphenooccipital  parts  of  basis 
cranii.    iha.  Thalamus. 


THE  CHROMAPHIL  AND  CORTICAL  SYSTEMS  .         1277 

terior  lobe :  the  former  is  derived  from  the  ectoderm  of  the  stomodeum,  the  latter 
from  the  floor  of  the  fore-brain.  About  the  fourth  week  there  appears  a  pouch- 
like diverticulum  of  the  ectodermal  lining  of  the  roof  of  the  stomodeum.  This 
diverticulum,  pouch  of  Rathke  (Fig.  1182),  is  the  rudiment  of  the  anterior  lobe  of 
the  hypophysis;  it  extends  upward  in  front  of  the  cephalic  end  of  the  notochord 
and  the  remnant  of  the  buccopharyngeal  membrane,  and  comes  into  contact  wiih 
the  under  surface  of  the  fore-brain.  It  is  then  constricted  off  to  form  a  closed 
vesicle,  but  remains  for  a  time  connected  to  the  ectoderm  of  the  stomodeum  by  a 
solid  cord  of  cells.  Masses  of  epithelial  cells  form  on  either  side  and  in  the  front 
wall  of  the  vesicle,  and  by  the  growth  between  these  of  a  stroma  from  the  mesoderm 
the  development  of  the  anterior  lobe  is  completed.  The  upwardly  directed  hypo- 
physeal involution  becomes  applied  to  the  antero-lateral  aspect  of  a  downwardly 
directed  diverticulum  from  the  base  of  the  fore-brain  (page  744).  This  divertic- 
ulum constitutes  the  future  infundibulum  in  the  floor  of  the  third  ventricle 
while  its  inferior  extremity  becomes  modified  to  form  the  posterior  lobe  of  the 
hypophysis.  In  some  of  the  lower  animals  the  posterior  lobe  contains  nerve  cells 
and  nerve  fibers,  but  in  man  and  the  higher  vertebrates  these  are  replaced  by 
connective  tissue.  A  canal,  craniopharjmgeal  canal,  is  sometimes  found  extending 
from  the  anterior  part  of  the  fossa  hypophj'seos  of  the  sphenoid  bone  to  the  under 
surface  of  the  skull,  and  marks  the  original  position  of  Rathke's  pouch;  while  at 
the  junction  of  the  septum  of  the  nose  with  the  palate  traces  of  the  stomodeal 
end  are  occasionally  present  (Frazer). 


II 


THE  PINEAL  BODY. 


II 


II 


[^  The  pineal  body  (epiphysis)  is  a  small  reddish-gray  body,  about  8  mm.  in  length 
which  lies  in  the  depression  between  the  superior  colliculi.  It  is  attached  to  the 
roof  of  the  third  ventricle  near  its  junction  with  the  mid-brain.  It  develops  as  an 
outgrowth  from  the  third  ventricle  of  the  brain. 

In  early  life  it  has  a  glandular  structure  which  Peaches  its  greatest  development 
at  about  the  seventh  year.  Later,  especially  after  puberty,  the  glandular  tissue 
gradually  disappears  and  is  replaced  by  connective  tissue. 

Structure. — The  pineal  body  is  destitute  of  nervous  substance,  and  consists  of  follicles  lined 
by  epithelium  and  enveloped  by  connective  tissue.  These  follicles  contain  a  variable  quantity 
of  gritty  material,  composed  of  phosphate  and  carbonate  of  calcium,  phosphate  of  magnesium 
and  ammonia,  and  a  httle  animal  matter. 

It  contains  a  substance  which  if  injected  intravenously  causes  fall  of  blood-pressure.  It  seems 
probable  that  the  gland  furnishes  an  internal  secretion  in  children  that  inhibits  the  development 
of  the  reproductive  glands  since  the  invasion  of  the  gland  in  children,  by  pathological  growths 
which  practically  destroy  the  glandular  tissue,  results  in  accelerated  development  of  the  sexual 
organs,  increased  growth  of  the  skeleton  and  precocious  mentality. 


I 


THE  CHROMAPHIL  AND  CORTICAL  SYSTEMS. 

Chromaphil  or  chromaffin  cells,  so-called  because  they  stain  yellow  or  brownish  with 
chromium  salts,  are  associated  with  the  ganglia  of  the  sympathetic  nervous  system. 

Development. — They  arise  in  common  with  the  sympathetic  cells  from  the  neural 
crest,  and  are  therefore  ectodermal  in  origin.  The  chromaphil  and  sympathetic 
cells  are  indistinguishable  from  one  another  at  the  time  of  their  migration  from  the 
spinal  ganglia  to  the  regions  occupied  in  the  adult.  Differentiation  of  chromaphil 
cells  begins  in  embryos  about  18  mm.  in  length  but  is  not  complete  until  about 
birth.  The  chromaphiloblasts  increase  in  size  more  than  the  sympathoblasts  and 
stain  less  intensely  with  ordinary  dyes.  Later  the  chrome  reajction  develops.  The 
aortic  bodies  differentiate  first  and  are  prominent  in  20  mm.  embryos.  The  para- 
ganglia of  the  sympathetic  plexuses  differentiate  next  and  last  of  all  the  para- 
ganglia of  the  sympathetic  trunk.    The  carotid  body  is  completely  differentiated 


1278         .  SPLANCHNOLOGY 

in  30  mm.  embryos.    After  birth  the  chromaphil  organs  degenerate  but  the  para- 
ganglia can  be  recognized  with  the  microscope  in  sites  originally  occupied  by  them,  i 

The  paraganglia  are  small  groups  of  chromaphil  cells  connected  with  the  ganglia  j 
of  the  sympathetic  trunk  and  the  ganglia  of  the  celiac,  renal,  suprarenal,  aortic  and 
hypogastric  plexuses.    They  are  sometimes  found  in  connection  with  the  ganglia  of 
other  sympathetic  plexuses.    None  have  been  found  with  the  sympathetic  ganglia 
associated  with  the  branches  of  the  trigeminal  nerve. 

The  aortic  glands  or  bodies  are  the  largest  of  these  groups  of  chromaphil  cells 
and  measure  in  the  newborn  about  1  cm.  in  length.  They  lie  one  on  either  side  of 
the  aorta  in  the  region  of  the  inferior  mesenteric  artery.  They  decrease  in  size  with 
age  and  after  puberty  are  only  visible  with  the  microscope.  About  forty  they  dis- 
appear entirely.  Other  groups  of  chromaphil  cells  have  been  found  associated  with 
the  sympathetic  plexuses  of  the  abdomen  independently  of  the  ganglia. 

The  medullary  portions  of  the  suprarenal  glands  and  the  glomus  caroticum 
belong  to  the  chromaphil  system. 


The  Suprarenal  Glands  (Glandulae  Suprarenalis ;  Adrenal  Capsule) 

(Figs.  1183,  1184). 

The  suprarenal  glands  are  two  small  flattened  bodies  of  a  yellowish  color,  situated 
at  the  back  part  of  the  abdomen,  behind  the  peritoneum,  and  immediately  above 
and  in  front  of  the  upper  end  of  each  kidney ;  hence  their  name.  The  right  one  is 
somewhat  triangular  in  shape,  bearing  a  resemblance  to  a  cocked  hat;  the  left  is 
more  semilunar,  usually  larger,  and  placed  at  a  higher  level  than  the  right.  They 
vary  in  size  in  different  individuals,  being  sometimes  so  small  as  to  be  scarcely 
detected :  their  usual  size  is  from  3  to  5  cm.  in  length,  rather  less  in  width,  and  from 
4  to  6  mm.  in  thickness.    Their  average  w^eight  is  from  1.5  to  2.5  gm.  each. 

Development. — Each  suprarenal  gland  consists  of  a  cortical  portion  derived 
from  the  celomic  epithelium  and  a  medullary  portion  originally  composed  of 
sympatho-chromaffin  tissue.  The  cortical  portion  is  first  recognizable  about  the 
beginning  of  the  fourth  week  as  a  series  of  buds  from  the  celomic  cells  at  the  root 
of  the  mesentery.  Later  it  becomes  completely  separated  from  the  celomic 
epithelium  and  forms  a  suprarenal  ridge  projecting  into  the  celom  between  the 
mesonephros  and  the  root  of  the  mesentery.  Into  this  cortical  portion  cells  from 
the  neighboring  masses  of  sympatho-chromaffin  tissue  migrate  along  the  line  of 
its  central  vein  to  reach  and  form  the  medullary  portion  of  the  gland. 

Relations. — The  relations  of  the  suprarenal  glands  differ  on  the  two  sides  of 
the  body. 

The  right  suprarenal  is  situated  behind  the  inferior  vena  cava  and  right  lobe  of  the 
liver,  and  in  front  of  the  diaphragm  and  upper  end  of  the  right  kidney.  It  is  roughly 
triangular  in  shape;  its  base,  directed  downward,  is  in  contact  with  the  medial  and 
anterior  aspects  of  the  lipper  end  of  the  right  kidney.  It  presents  two  surfaces  for 
examination,  an  anterior  and  a  posterior.  The  anterior  surface  looks  forward  and 
lateralward,  and  has  two  areas:  a  medial,  narrow,  and  non-peritoneal,  which  lies 
behind  the  inferior  vena  cava;  and  a  lateral,  somewhat  triangular,  in  contact  with 
the  liver.  The  upper  part  of  the  latter  surface  is  devoid  of  peritoneum,  and  is  in 
relation  with  the  bare  area  of  the  liver  near  its  lower  and  medial  angle,  while  its 
inferior  portion  is  covered  by  peritoneum,  reflected  onto  it  from  the  inferior  layer 
of  the  coronary  ligament;  occasionally  the  duodenum  overlaps  the  inferior  portion. 
A  little  below  the  apex,  and  near  the  anterior  border  of  the  gland,  is  a  short  furrow 
termed  the  hilum,  from  which  the  suprarenal  vein  emerges  to  join  the  inferior  vena 
cava.  The  posterior  surface  is  divided  into  upper  and  lower  parts  by  a  curved  ridge: 
the  upper,  slightly  convex,  rests  upon  the  diaphragm;  the  lower,  concave,  is  in 


THE  SUPRARENAL  GLANDS 


1279 


contact  with  the  upper  end  and  the  adjacent  part  of  the  anterior  surface  of  the 
kidney. 

The  left  suprarenal,  slightly  larger  than  the  right,  is  crescentic  in  shape,  its  con- 
cavity being  adapted  to  the  medial  border  of  the  upper  part  of  the  left  kidney. 
It  presents  a  medial  border,  which  is  convex,  and  a  lateral,  which  is  concave;  its 
upper  end  is  narrow,  and  its  lower  rounded.    Its  anterior  surface  has  two  areas:  an 


Suprarenal  vein 


Hepatic  area 


Area  in  con- 
tact with  in- 
ferior   vena 


Gastric  area 


Pancreatic  area 


Suprarenal  vein 
Right.  Left. 

Fig.   1183. — Suprareaal  glands  viewed  from  the  front. 

upper  one,  covered  by  the  peritoneum  of  the  omental  bursa,  which  separates  it 
from  the  cardiac  end  of  the  stomach,  and  sometimes  from  the  superior  extremity 
of  the  spleen;  and  a  lower  one,  which  is  in  contact  with  the  pancreas  and  lienal 
artery,  and  is  therefore  not  covered  by  the  peritoneum.  On  the  anterior  surface, 
near  its  lower  end,  is  a  furrow  or  hilum,  directed  downward  and  forward,  from  which 
the  suprarenal  vein  emerges.  Its  posterior  surface  presents  a  vertical  ridge,  which 
divides  it  into  two  areas;  the  lateral  area  rests  on  the  kidney,  the  medial  and  smalles*' 
ron  the  left  crus  of  the  diaphragm. 


Diaphrag- 
matic area 


Jtenal  area 


Diaphragmatic 
area 


Renal  area 


Suprarenal 
vein 


Right.  Left. 

.  Fia.   1184. — Suprarenal  glands  viewed  from  behind. 

The  surface  of  the  suprarenal  gland  is  surrounded  by  areolar  tissue  containing^ 
much  fat,  and  closely  invested  by  a  thin  fibrous  capsule,  which  is  difficult  to  remove 
on  account  of  the  numerous  fibrous  processes  and  vessels  entering  the  organ  through 
the  furrows  on  its  anterior  surface  and  base. 

Small  accessory  suprarenals  {glandulce  suyrarenales  accessoriae)  are  often  to  be 
found  in  the  connective  tissue  around  the  suprarenals.  The  smaller  of  these,  on 
section,  show  a  uniform  surface,  but  in  some  of  the  larger  a  distinct  medulla  can  be 
made  out. 

Structure.- — On  section,  the  suprarenal  gland  is  seen  to  consist  of  two  portions  (Fig.  1185): 
an  external  or  cortical  and  an  internal  or  medullary.  The  former  constitutes  the  chief  part  of 
the  organ,  and  is  of  a  deep  yellow  color;  the  medullary  substance  is  soft,  pulpy,  and  of  a  dark  red 

I 


1280 


SPLANCHNOLOGY 


The  cortical  portion  {substantia  corticalis)  consists  of  a  fine  connective-tissue  net-work,  in 
which  is  imbedded  the  glandular  epithelium.  The  epithelial  cells  are  polj^hedral  in  shape  and 
possess  rounded  nuclei;  many  of  the  cells  contain  coarse  granules,  others  lipoid  globules.  Owirg 
to  differences  in  the  arrangement  of  the  cells,  three  distinct  zones  can  be  made  out:  (1)  the  zora 
glomerulosa,  situated  beneath  the  capsule,  consists  of  cells  arranged  in  rounded  groups,  with 
here  and  there  indications  of  an  alveolar  structure;  the  cells  of  this  zone  are  very  granular,  and 
stain  deeply.  (2)  The  zona  fasciculata,  continuous  with  the  zona  glomerulosa,  is  composed  of 
columns  of  cells  arranged  in  a  radial  manner;  these  cells  contain  finer  granules  and  in  many 
instances  globules  of  lipoid  material.  (3)  The  zona  reticularis,  in  contact  with  the  medulla, 
consists  of  cylindrical  masses  of  cells  irregularly  arranged;  these  cells  often  contain  pigmerit 
granules  which  give  this  zone  a  darker  appearance  than  the  rest  of  the  cortex. 

The  medullary  portion  {substantia  meduUari>>)  is  extremely  vascular,  and  consists  of  large 
cliromapliil  cells  arranged  in  a  network.  The  irregular  polyhedral  cells  have  a  finely  granular 
cystoplasm  that  are  probably  concerned  with  the  secretion  of  adrenalin.  '  In  the  meshes  of  the 
cellular  network  are  large  anastomosing  venous  sinuses  (sinusoids)  which  are  in  close  relationship 
with  the  chromaphil  or  medullary  cells.  In  many  places  the  endothelial  lining  of  the  blood  sinuses 
is  in  direct  contact  with  the  medullary  cells.  Some  authors  consider  the  endothelium  absent  in 
places  and  here  the  medullary  cells  are  directly  bathed  by  the  blood.  This  intimate  relationship 
between  the  chromaplul  cells  and  the  blood  stream  undoubtedly  facilitates  the  discharge  of  the 
internal  secretion  into  the  blood.  There  is  a  loose  meshwork  of  supporting  connective  tissue  con- 
taining non-striped  muscle  fibers.  This  portion  of  the  gland  is  richly  supplied  with  non-medullated 
nerve  fibers,  and  here  and  there  sympathetic  ganglia  are  found. 


Capsule 

Zona  glomervlosa 


I 


Zona  fascicvlata 


Zotia  reticularis 

Mvltinvcleated  mass 
of  protoplasm 


Medvlla 


Ganglion 

Pig.   1185. — Section  of  a  part  of  a  suprarenal  gland.     (Magnified.) 

Vessels  and  Nerves. — ^The  arteries  supplying  the  suprarenal  glands  are  numerous  and  of 
comparatively  large  size;  they  are  derived  from  the  aorta,  the  inferior  phrenic,  and  the  renal. 
They  subdivide  into  minute  branches  previous  to  entering  the  cortical  part  of  the  gland,  where 
they  break  up  into  capillaries  which  end  in  the  venous  plexus  of  the  medullary  portion. 

The  suprarenal  vein  returns  the  blood  from  the  medullary  venous  plexus  and  receives  several 
branches  from  the.  cortical  substance;  it  emerges  from  the  hilum  of  the  gland  and  on  the  right 
side  opens  into  the  inferior  vena  cava,  on  the  left  into  the  renal  vein. 

The  lymphatics  end  in  the  lumbar  glands. 

The  nerves  are  exceedingly  numerous,  and  are  derived  from  the  celiac  and  renal  plexuses, 
and,  according  to  Bergmann,  from  the  phrenic  and  vagus  nerves.  They  enter  the  lower  and 
medial  part  of  the  capsule,  traverse  the  cortex,  and  end  around  the  cells  of  the  medulla.  They 
have  numerous  small  ganglia  developed  upon  them  in  the  medullary  portion  of  the  gland. 

In  connection  with  the  development  of  the  medulla  from  the  sympathochromaffin  tissue,  it  is 
to  be  noted  that  this  portion  of  the  gland  secretes  a  substance,  adrenalin,  which  has  a  powerful 
influence  on  those  muscular  tissues  which  are  supplied  by  sympathetic  fibers. 


GLOMUS  COCCYGEUM 


1281 


Glomus  Caroticum  (Carotid  Glands;  Carotid  Bodies). 

The  carotid  bodies,  two  in  number,  are  situated  one  on  either  side  of  the  neck, 
behind  the  common  carotid  artery  at  its  point  of  bifurcation  into  the  external 
and  internal  carotid  trunks.  They  are  reddish  brown  in  color  and  oval  in  shape, 
the  long  diameter  measuring  about  5  mm. 


yx- 


-ic^ 


-Section  of  part  of  human  glomus  caroticum.     (Sohaper.)     Highly  magnified.    Numerous  bloodvessels   are 
seen  in  section  among  the  gland  cells. 

Each  is  invested  by  a  fibrous  capsule  and  consists  largely  of  spherical  or  irregular 
masses  of  cells  (Fig.  1186),  the  masses  being  more  or  less  isolated  from  one  another 
by  septa  which  extend  inward  from  the  deep  surface  of  the  capsule.  The  cells 
are  polyhedral  in  shape,  and  each  contains  a  large  nucleus  imbedded  in  finely 
granular  protoplasm,  which  is  stained  yellow  by  chromic  salts.  Numerous  nerve 
fibers,  derived  from  the  sympathetic  plexus  on  the  carotid  artery,  are  distributed 
throughout  the  organ,  and  a  net-work  of  large  sinusoidal  capillaries  ramifies  among 
the  cells. 


,9. 


iFiG.   1187. — Section  of  an  irregular  nodule  of  the  glomus  coccygeum.     (Sertoli.)      X  85.     The  section  shows  the 
fibrous  covering  of  the  nodule,  the  bloodvessels  within  it,  and  the  epithelial  cells  of  which  it  is  constituted. 


Glomus  Coccygeum  (Coccygeal  Gland  or  Body;  Luschka's  Gland). 

The  glomus  coccygeum  is  placed  in  front  of,  or  immediately  below,  the  tip  of  the 
coccyx.  It  is  about  2.5  mm.  in  diameter  and  is  irregularly  oval  in  shape;  several 
smaller  nodules  are  found  around  or  near  the  main  mass. 

1^    It  consists  of  irregular  masses  of  round  or  polvhedral  cells  (Fig.  1187),  the  cells 
L 


1282 


SPLANCHNOLOGY 


of  each  mass  being  grouped  around  a  dilated  sinusoidal  capillary  vessel.  Each  ce! 
contains  a  large  round  or  oval  nucleus,  the  protoplasm  surrounding  which  is  clear, 
and  is  not  stained  by  chromic  salts. ^ 


THE    SPLEEN    (LIEN). 


dl 


The  spleen  is  situated  principally  in  the  left  hypochondriac  region,  but  its  supe- 
rior extremity  extends  into  the  epigastric  region;  it  lies  between  the  fundus  of  the 
stomach  and  the  diaphragm.  It  is  the  largest  of  the  ductless  glands,  and  is  of 
an  oblong,  flattened  form,  soft,  of  very  friable  consistence,  highly  vascular,  and 
of  a  dark  purplish  color. 

Development. — The  spleen  appears  about  the  fifth  week  as  a  localized  thickening 
of  the  mesoderm  in  the  dorsal  mesogastrium  above  the  tail  of  the  pancreas.  With 
the  change  in  position  of  the  stomach  the  spleen  is  carried  to  the  left,  and  comes 
to  lie  behind  the  stomach  and  in  contact  with  the  left  kidney.  The  part  of  the 
dorsal  mesogastrium  which  intervened  between  the  spleen  and  the  greater  curva- 
ture of  the  stomach  forms  the  gastrosplenic  ligament. 

Relations. — The  diaphragmatic  surface  (fades  diaphragmatica;  external  or  yhrenic 
surface)  is  convex,  smooth,  and  is  directed  upward,  backward,  and  to  the  left, 
except  at  its  upper  end,  where  it  is  directed  slightly  medialward.  It  is  in  relation 
with  the  under  surface  of  the  diaphragm,  which  separates  it  from  the  ninth,  tenth, 
and  eleventh  ribs  of  the  left  side,  and  the  intervening  lower  border  of  the  left  lung 
and  pleura. 


Fern 

leaving 

hUvs 


Fig.  11S8. — The  visceral  surface  of  the  spleen. 

The  visceral  surface  (Fig.  1188)  is  divided  by  a  ridge  into  an  anterior  or  gastric 
and  a  posterior  or  renal  portion. 

The  gastric  surface  (/ac^e^g'as^n'ca),  which  is  directed  forward,  upward,  and  medial- 
ward,  is  broad  and  concave,  and  is  in  contact  with  the  posterior  wall  of  the  stomach; 

'  Consult  the  following  article:  "  Uber  die  menschliche  Steissdriise,"  von  J.  W.  Thomson  Walker,  Archiv  fur  mikro- 
skopische  Anatomie  und  Entwickelungageschichte,  Band  64,  1904. 


THE  SPLEEN  ^^^^^  1283 

and  below  this  with  the  tail  of  the  pancreas.  It  presents  near  its  medial  border  a 
long  fissure,  termed  the  hilum.  This  is  pierced  by  several  irregular  apertures,  for 
the  entrance  and  exit  of  vessels  and  nerves. 

The  renal  surface  (facies  renalis)  is  directed  medialward  and  downward.  It  is 
somewhat  flattened,  is  considerably  narrower  than  the  gastric  surface,  and  is  in 
relation  with  the  upper  part  of  the  anterior  srurface  of  the  left  kidney  and  occasion- 
ally with  the  left  suprarenal  gland. 

The  superior  extremity  (extremitas  superior)  is  directed  toward  the  vertebral 
column,  where  it  lies  on  a  level  with  the  eleventh  thoracic  vertebra.  The  lower 
extremity  or  colic  surface  (extrem  itas  inferior)  is  flat,  triangular  in  shape,  and  rests 
upon  the  left  flexure  of  the  colon  and  the  phrenicocolic  ligament,  and  is  generally 
in  contact  with  the  tail  of  the  pancreas.  The  anterior  border  {margo  anterior)  is  free, 
sharp,  and  thin,  and  is  often  notched,  especially  below;  it  separates  the  diaphragmatic 
from  the  gastric  surface.  The  posterior  border  {margo  posterior),  more  rounded  and 
blunter  than  the  anterior,  separates  the  renal  from  the  diaphragmatic  surface; 
it  corresponds  to  the  lower  border  of  the  eleventh  rib  and  lies  between  the  diaphragm 
and  left  kidney.  The  intermediate  margin  is  the  ridge  which  separates  the  renal 
and  gastric  surfaces.  The  inferior  border  (internal  border)  separates  the  diaphrag- 
matic from  the  colic  surface. 

The  spleen  is  almost  entirely  surrounded  by  peritoneum,  which  is  firmly  adherent 
to  its  capsule.  It  is  held  in  position  by  two  folds  of  this  membrane.  One,  the 
phrenicolienal  ligament,  is  derived  from  the  peritoneum,  where  the  wall  of  the  general 
peritoneal  cavity  comes  into  contact  with  the  omental  bursa  between  the  left  kidney 
and  the  spleen;  the  lienal  vessels  pass  between  its  two  layers  (Fig.  1039) .  The  other 
fold,  the  gastrolienal  ligament,  is  also  formed  of  two  layers,  derived  from  the 
general  cavity  and  the  omental  respectively,  where  they  meet  between  the  spleen 
and  stomach  (Fig.  1039);  the  short  gastric  and  left  gastroepiploic  branches  of  the 
lienal  artery  run  between  its  two  layers.  The  lower  end  of  the  spleen  is  supported 
by  the  phrenicocolic  ligament  (see  page  1155). 

The  size  and  weight  of  the  spleen  are  liable  to  very  extreme  variations  at  different 
periods  of  life,  in  different  individuals,  and  in  the  same  individual  under  different 
conditions.  In  the  adult  it  is  usually  about  12  cm.  in  length,  7  cm.  in  breadth,  and 
3  or  4  cm.  in  thickness,  and  weighs  about  200  grams.  At  birth  its  weight,  in  pro- 
portion to  the  entire  body,  is  almost  equal  to  what  is  observed  in  the  adult,  being 
as  1  to  350;  while  in  the  adult  it  varies  from  1  to  320  and  400.  hi  old  age  the  organ 
not  only  diminishes  in  weight,  but  decreases  considerably  in  proportion  to  the  entire 
body,  being  as  1  to  700.  The  size  of  the  spleen  is  increased  during  and  after  diges- 
tion, and  varies  according  to  the  state  of  nutrition  of  the  body,  being  large  in 
highly  fed,  and  small  in  starved  animals.  In  malarial  fever  it  becomes  much 
enlarged,  weighing  occasionally  as  much  as  9  kilos. 

Frequently  in  the  neighborhood  of  the  spleen,  and  especially  in  the  gastrolienal 
ligament  and  greater  omentum,  small  nodules  of  splenic  tissue  may  be  found,  either 
isolated  or  connected  to  the  spleen  by  thin  bands  of  splenic  tissue.  They  are  known 
as  accessory  spleens  (lien  accessorius;  supernumerary  spleen) .  They  vary  in  size 
from  that  of  a  pea  to  that  of  a  plum. 

Structure. — The  spleen  is  invested  by  two  coats:  an  external  serous  and  an  internal  fibro- 
elastic  coat. 

The  external  or  serous  coat  {tunica  serosa)  is  derived  from  the  peritoneum;  it  is  thin,  smooth, 
and  in  the  human  subject  intimately  adherent  to  the  fibroelastic  coat.  It  invests  the  entire 
organ,  except  at  the  hilum  and  along  the  lines  of  reflection  of  the  phrenicolienal  and  gastrolienal 
ligaments. 

The  fibroelastic  coat  {tunica  alhuginea)  invests  the  organ,  and  at  the  hilum  is  reflected  inward 
upon  the  vessels  in  the  form  of  sheaths.  From  these  sheaths,  as  well  as  from  the  inner  surface 
of  the  fibroelastic  coat,  numerous  small  fibrous  bands,  trabeculae  (Fig.  1189),  are  given  off  in  all 
directions;  these  uniting,  constitute  the  frame-work  of  the  spleen.    The  spleen  therefore  consists 


I 


1284 


SPLANCHNOLOGY 


of  a  number  of  small  spaces  or  areolae,  formed  by  the  trabecule;  in  these  areolae  is  contained 
the  splenic  pulp. 

The  fibroelastic  coat,  the  sheaths  of  the  vessels,  and  the  trabecula?,  are  composed  of  white  and 
yellow  elastic  fibrous  tissues,  the  latter  predominating.  It  is  owing  to  the  presence  of  the  elastic 
tissue  that  the  spleen  possesses  a  considerable  amount  of  elasticity,  which  allows  of  the  very 
great  variations  in  size  that  it  presents  under  certain  circumstances.     In  addition  to  tt 


Fig.  1189. — Transverse  section  of  the  spleen,  showing  the  trabecular  tissue  and  the  splenic  vein  and  its  tributaries. 

constituents  of  this  tunic,  there  is  found  in  man  a  small  amount  of  non-striped  muscular  fiber; 
and  in  sonie  mammalia,  e.  g.,  dog,  pig,  and  cat,  a  large  amount,  so  that  the  trabeculse  appear 
to  consist  chiefly  of  muscular  tissue. 

The  splenic  pulp  (pulpa  lienis)  is  a  soft  mass  of  a  dark  reddish-brown  color,  resembling  grumous 
blood;  it  consists  of  a  fine  reticulum  of  fibers,  continuous  with  those  of  the  trabeculae,  to  which 
are  applied  flat,  branching  cells.     The  meshes  of  the  reticulum  are  filled  with  blood,  in  which, 


Fia.  1190. — Transverse  section  of  the  human  spleen,  showing  the  distribution  of  the  splenic  artery  and  its  branches. 


however,  the  white  corpuscles  are  found  to  be  in  larger  proportion  than  they  are  in  ordinary 
blood.  Large  rounded  cells,  termed  splenic  cells,  are  also  seen;  these  are  capable  of  ameboid 
movement,  and  often  contain  pigment  and  red-blood  corpuscles  in  their  interior.  The  cells  of 
the  reticulum  each  possess  a  round  or  oval  nucleus,  and  like  the  splenic  cells,  they  may  contain 
pigment  granules  in  their  cytoplasm;  they  do  not  stain  deeply  with  carmine,  and  in  this  respect 
differ  from  the  cells  of  the  Malpighian  bodies.    In  the  young  spleen,  giant  cells  may  also  be  found. 


THE  SPLEEN 


1285 


each  containing  numerous  nuclei  or  one  compound  nucleus.  Nucleated  red-blood  corpuscles 
have  also  been  found  in  the  spleen  of  young  animals. 

Bloodvessels  of  the  Spleen. — The  lienal  artery  is  remarkable  for  its  large  size  in  proportion 
to  the  size  of  the  organ,  and  also  for  its  tortuous  course.  It  divides  into  six  or  more  branches, 
which  enter  the  hilum  of  the  spleen  and  ramify  throughout  its  substance  (Fig.  1190),  receiving 
sheaths  from  an  involution  of  the  external  fibrous  tissue.  Similar  sheaths  also  invest  the  nerves 
and  veins. 

Each  branch  runs  m  the  transverse  axis  of  the  organ,  from  within  outward,  diminishing  in 
size  during  its  transit,  and  giving  off  in  its  passage  smaller  branches,  some  of  which  pass  to  the 
anterior,  others  to  the  posterior  part.  These  ultimately  leave  the  trabecular  sheaths,  and  ter- 
minate in  the  proper  substance  of  the  spleen  in  small  tufts  or  pencils  of  minute  arterioles,  which 
open  into  the  interstices  of  the  reticulum  formed  by  the  branched  sustentacular  cells.  Each  of 
the  larger  branches  of  the  artery  supplies  chiefly  that  region  of  the  organ  in  which  the  branch 
ramifies,  having  no  anastomosis  with  the  majority  of  the  other  branches. 

The  arterioles,  supported  by  the  minute  trabeculse,  traverse  the  pulp  in  all  directions  in  bundles 
{jpencilli)  of  straight  vessels.  Their  trabecular  sheaths  gradually  undergo  a  transformation, 
become  much  thickened,  and  converted  into  adenoid  tissue;  the  bundles  of  connective  tissue 
becoming  looser  and  their  fibrils  more  deUcate,  and  containing  in  their  interstices  an  abundance 
of  lymph  corpuscles  (W.  Miiller). 


Trabecvla 


Lymphatic 
nodvle 


Spleen  pulp 


Fia.  1191. — Transverse  section  of  a  portion  of  the  spleen. 


The  altered  coat  of  the  arterioles,  consisting  of  adenoid  tissue,  presents  here  and  there  thick- 
enings of  a  spheroidal  shape,  the  Isrmphatic  nodules  {Malpighian  bodies  of  the  spleen).  These 
bodies  vary  in  size  from  about  0.25  mm.  to  1  mm.  in  diameter.  They  are  merely  local  expansions 
or  hyperplasise  of  the  adenoid  tissue,  of  which  the  external  coat  of  the  smaller  arteries  of  the  spleen 
is  formed.  They  are  most  frequently  found  surrounding  the  arteriole,  which  thus  seems  to 
tunnel  them,  but  occasionally  they  grow  from  one  side  of  the  vessel  only,  and  present  the  appear- 
ance of  a  sessile  bud  growing  from  the  arterial  wall.  In  transverse  sections,  the  artery,  in  the 
majority  of  cases,  is  found  in  an  eccentric  position.  These  bodies  are  visible  to  the  naked  eye 
on  the  surface  of  a  fresh  section  of  the  organ,  appearing  as  minute  dots  of  a  semiopaque  whitish 
color  in  the  dark  substance  of  the  pulp.  In  minute  structure  they  resemble  the  adenoid  tissue 
of  lymph  glands,  consisting  of  a  delicate  reticulum,  in  the  meshes  of  which  lie  ordinary  lymphoid 
cells  (Fig.  1191).  The  reticulum  is  made  up  of  extremely  fine  fibrils,  and  is  comparatively  open 
in  the  center  of  the  corpuscle,  becoming  closer  at  its  periphery.  The  cells  which  it  encloses 
are  possessed  of  ameboid  movement.  When  treated  with  carmine  they  become  deeply  stained, 
and  can  be  easily  distinguished  from  those  of  the  pulp. 

The  arterioles  end  by  opening  freely  into  the  splenic  pulp;  their  walls  become  much  attenuated, 
they  lose  their  tubular  character,  and  the  endothelial  cells  become  altered,  presenting  a  branched 
appearance,  and  acquiring  processes  which  are  directly  connected  with  the  processes  of  the 
reticular  cells  of  the  pulp  (Fig.  1192).  In  this  manner  the  vessels  end,  and  the  blood  flowing 
through  them  finds  its  way  into  the  interstices  of  the  reticulated  tissue  of  the  splenic  pulp.    Thus 


L 


TCHNOLOGY 


the  blood  passing  through  the  spleen  is  brought  into  intimate  relation  with  the  elements  of  thti 
pulp,  and  no  doubt  undergoes  important  changes. 

After  these  changes  have  taken  place  the  blood  is  collected  from  the  interstices  of  the  tissue 
by  the  rootlets  of  the  veins,  which  begin  much  in  the  same  way  as  the  arteries  end.  The  con- 
nective-tissue corpuscles  of  the  pulp  arrange  themselves  in  rows,  in  such  a  way  as  to  form  ar 
elongated  space  or  sinus.  They  become  elongated  and  spindle-shaped,  and  overlap  each  other 
at  their  extremities,  and  thus  form  a  sort  of  endothelial  lining  of  the  path  or  sinus,  which  is  the 
radicle  of  a  vein.  On  the  outer  surfaces  of  these  cells  are  seen  delicate  transverse  lines  or  markings, 
which  are  due  to  minute  elastic  fibrillse  arranged  in  a  circular  manner  around  the  sinus.  Thus 
the  channel  obtains  an  external  investment,  and  gradually  becomes  converted  into  a  small 


Branching  cell 


V   \ 


Small 
artery 


Vessel  continuoiLs 
with  processes  of 
network  cells 


Branching  cell 


I 


Fig.   1192. — Section  of  the  spleen,  showing  the  termination  of  the  small  bloodvessels. 


vein,  which  after  a  short  course  acquires  a  coat  of  ordinary  connective  tissue,  lined  by  a  layer  of 
flattened  epithelial  cells  which  are  continuous  with  the  supporting  cells  of  the  pulp.  The  smaller 
veins  unite  to  form  larger  ones;  these  do  not  accompany  the  arteries,  but  soon  enter  the  tra- 
becular sheaths  of  the  capsule,  and  by  their  junction  form  six  or  more  branches,  which  emerge 
from  the  hilum,  and,  uniting,  constitute  the  lienal  vein,  the  largest  radicle  of  the  portal  vein. 

The  veins  are  remarkable  for  their  numerous  anastomoses,  while  the  arteries  hardly  anastomose 
at  all. 

The  lymphatics  are  described  on  page  711. 

The  nerves  are  derived  from  the  celiac  plexus  and  are  chiefly  non-medullated.  They  are 
distributed  to  the  bloodvessels  and  to  the  smooth  muscle  of  the  capsule  and  trabeculae. 


SURFACE  ANATOMY  OF  THE  HEAD  AND  NECK. 


fFACE  ANATOMY  AND  SURFACE 
MARKINGS. 

Bones  (Fig.  1193). — Various  bony  surfaces  and  prominences  on  the  skull  can  be 
easily  identified  by  palpation.  The  external  occipital  protuberance  is  situated 
behind,  in  the  middle  line,  at  the  junction  of  the  skin  of  the  neck  with  that  of  the 
head.  The  superior  nuchal  line  runs  lateralward  from  it  on  either  side,  while  extend- 
ing downward  from  it  is  the  median  nuchal  crest,  situated  deeply  at  the  bottom 
of  the  nuchal  furrow.     Above  the  superior  nuchal  lines  the  vault  of  the  cranium 

I B        Zygomatic  tubercle  n^ 

■  H         Zygomaticofrontal 

m  suture  *"AV^ 

Supraorbital  foramen  -  -/^^^t^(s>y  i 

Nasion  _. 

AsteTion 

L.-j—Inion 
^/     I     Beid's  base 


Median  nuchal  crest 


H 


Auricular  point 
Pre-auricular  point 


Fig.   1193. — Side  view  of  head,  showing  surface  relations  of  bones. 

is  thinly  covered  with  soft  structures,  so  that  the  form  of  this  part  of  the  head  is 
almost  that  of  the  upper  portion  of  the  occipital,  the  parietal,  and  the  frontal 
bones.  The  superior  nuchal  line  can  be  followed  lateralward  to  the  mastoid  por- 
tion of  the  temporal  bone,  from  which  the  mastoid  process  projects  downward 
and  forward  behind  the  ear.  The  anterior  and  posterior  borders,  the  apex,  and 
the  external  surface  of  this  process  are  all  available  for  superficial  examination.  The 
anterior  border  lies  immediately  behind  the  concha,  and  the  apex  is  on  a  level 

( 1287 ) 


1288  SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


I 


with  the  lobule  of  the  auricula.  About  1  cm.  below  and  in  front  of  the  apex  of 
the  mastoid  process,  the  transverse  process  of  the  atlas  can  be  distinguished.  In 
front  of  the  ear  the  zygomatic  arch  can  be  felt  throughout  its  entire  length;  its 
posterior  end  is  narrow  and  is  situated  a  little  above  the  level  of  the  tragus;  its 
anterior  end  is  broad  and  is  continued  into  the  zygomatic  bone.  The  lower  border 
of  the  arch  is  more  distinct  than  the  upper,  which  is  obscured  by  the  attachment 
of  the  temporal  fascia.  In  front,  and  behind,  the  upper  border  of  the  arch  can  be 
followed  into  the  superior  temporal  line.  In  front,  this  line  begins  at  the  zygomatic 
process  of  the  frontal  bone  as  a  curved  ridge  which  runs  at  first  forward  and 
upward, on  the  frontal  bone,  and  then  curving  backward  separates  the  forehead 
from  the  temporal  fossa.  It  can  then  be  traced  across  the  parietal  bone,  where, 
though  less  marked,  it  can  generally  be  recognized.  Finally,  it  curves  downward, 
and  forward,  and  passing  above  the  external  acoustic  meatus,  ends  in  the  posterior 
root  of  the  zygomatic  arch.  Near  the  line  of  the  greatest  transverse  diameter  of 
the  head  are  the  parietal  eminences,  one  on  either  side  of  the  middle  line;  further 
forward,  on  the  forehead,  are  the  frontal  eminences,  which  vary  in  prominence  in 
different  individuals  and  are  frequently  unsymmetrical.  Below  the  frontal  emi- 
nences the  superciliary  arches,  which  indicate  the  position  of  the  frontal  sinuses, 
can  be  recognized;  as  a  rule  they  are  small  in  the  female  and  absent  in  children. 
In  some  cases  the  prominence  of  the  superciliary  arches  is  related  to  the  size  of 
the  frontal  sinuses,  but  frequently  there  is  no  such  relationship.  Situated  between, 
and  connecting  the  superciliary  ridges,  is  a  smooth,  somewhat  triangular  area,  the 
glabella,  below  which  the  nasion  (frontonasal  suture)  can  be  felt  as  a  slight  depres- 
sion at  the  root  of  the  nose. 

Below  the  nasion  the  nasal  bones,  scantily  covered  by  soft  tissues,  can  be  traced 
to  their  junction  with  the  nasal  cartilages,  and  on  either  side  of  the  nasal  bone 
the  complete  outline  of  the  orbital  margin  can  be  made  out.  At  the  junction  of 
the  medial  and  intermediate  thirds  of  the  supraorbital  margin  the  supraorbital 
notch,  when  present,  can  be  felt;  close  to  the  medial  end  of  the  infraorbital  margin 
is  a  little  tubercle  which  serves  as  a  guide  to  the  position  of  the  lacrimal  sac.  Below 
and  lateral  to  the  orbit,  on  either  side,  is  the  zygomatic  bone  forming  the  prominence 
of  the  cheek;  its  posterior  margin  is  easily  palpable,  and  on  it  just  above  the  level 
of  the  lateral  palpebral  commissure  is  the  zygomatic  tubercle.  A  slight  depression, 
about  1  dm.  above  this  tubercle,  indicates  the  position  of  the  zygomaticofrontal 
suture.  Directly  below  the  orbit  a  considerable  part  of  the  anterior  surface  of  the 
maxilla  and  the  whole  of  its  alveolar  process  can  be  palpated.  The  outline  of  the 
mandible  can  be  recognized  throughout  practically  its  entire  extent;  in  front  of 
the  tragus  and  below  the  zygomatic  arch  is  the  condyle,  and  from  this  the  posterior 
border  of  the  ramus  can  be  followed  to  the  angle;  from  the  angle  to  the  symphysis 
the  lower  rounded  border  of  the  mandible  can  be  easily  traced;  the  lower  part  of 
the  anterior  border  of  the  ramus  and  the  alveolar  process  can  be  made  out  without 
difficulty.  In  the  receding  angle  below  the  chin  is  the  hyoid  bone,  and  the  finger 
can  be  carried  along  the  bone  to  the  tip  of  the  greater  cornu,  which  is  on  a  level 
with  the  angle  of  the  mandible:  the  greater  cornu  is  most  readily  appreciated 
by  making  pressure  on  one  side,  when  the  cornu  of  the  opposite  side  will  be  rendered 
prominent  and  can  be  felt  distinctly  beneath  the  skin. 

Joints  and  Muscles. — The  temporomandibular  articulation  is  quite  superficial,  and 
is  situated  below  the  posterior  end  of  the  zygomatic  arch,  in  front  of  the  external 
acoustic  meatus.  Its  position  can  be  ascertained  by  defining  the  condyle  of  the 
mandible;  when  the  mouth  opens,  the  condyle  advances  out  of  the  mandibular 
fossa  on  to  the  articular  tubercle,  and  a  depression  is  felt  in  the  situation  of  the 
joint. 

The  outlines  of  the  muscles  of  the  head  and  face  cannot  be  traced  on  the  surface 
except  in  the  case  of  the  Masseter  and  Temporalis.     The  muscles  of  the  scalp 


SURFACE  ANATOMY  OF  THE  HEAD  AND  NECK 


1289 


are  so  thin  that  the  outHne  of  the  bone  is  perceptible  beneath  them.  Those  of 
the  face  are  small,  covered  by  soft  skin,  and  often  by  a  considerable  layer  of  fat, 
and  their  outlines  are  therefore  concealed ;  they  serve,  however,  to  round  off  and 
smooth  prominent  borders,  and  to  fill  up  what  would  otherwise  be  unsightly 
angular  depressions.  Thus  the  Orbicularis  oculi  rounds  off  the  prominent  margin 
of  the  orbit,  and  the  Procerus  fills  in  the  sharp  depression  below  the  glabella.  In 
like  manner  the  labial  muscles  converging  to  the  lips,  and  assisted  by  the  super- 
imposed fat,  fill  up  the  sunken  hollow  of  the  lower  part  of  the  face.  When  in 
action  the  facial  muscles  produce  the  various  expressions,  and  in  addition  throw 
the  skin  into  numerous  folds  and  wrinkles.  The  Masseter  imparts  fulness  to  the 
hinder  part  of  the  cheek;  if  firmly  contracted,  as  when  the  teeth  are  clenched,  its 
quadrilateral  outline  is  plainly  visible;  the  anterior  border  forms  a  prominent 
vertical  ridge,  behind  which  is  a  considerable  fulness  especially  marked  at  the 


Submaxillary  triangle 
Hyoid  hone 

Thyroid  cartilage 
Cricoid  cartilage 


Sternocle  idomastoideus 
Trapezius 

Supraclavicular  fossa 


» 


Clavicle 

^' 

Infraclavicular  fossa 

,       ,  ,  ^77,  ^      >  of  Slernocleidomastoideus 

Jugular  notch  bternal  head  ) 

Fig.   1194. — Anterolateral  view  of  head  and  neck.  * 

lower  part  of  the  muscle.  The  Temporalis  is  fan-shaped  and  fills  the  temporal 
fossa,  substituting  for  the  concavity  a  somewhat  convex  swelling,  the  anterior 
part  of  which,  on  account  of  the  absence  of  hair  on  the  overlying  skin,  is  more 
marked  than  the  posterior,  and  stands  out  in  strong  relief  when  the  muscle  is  in 
action. 

In  the  neck,  the  Platysma  when  contracted  throws  the  skin  into  oblique  ridges 
parallel  with  the  fasciculi  of  the  muscle.  The  Stemocleidomastoideus  has  the  most 
important  influence  on  the  surface  form  of  the  neck  (Figs.  1194,  1195).  When  the 
muscle  is  at  rest  its  anterior  border  forms  an  oblique  rounded  edge  ending  below  in 
the  sharp  outline  of  the  sternal  head;  the  posterior  border  is  only  distinct  for  about 
2  or  3  cm.  above  the  middle  of  the  clavicle.  During  contraction,  the  sternal  head 
stands  out  as  a  sharply  defined  ridge,  while  the  clavicular  head  is  flatter  and  less 
prominent;  between  the  two  heads  is  a  slight  depression:  the  fleshy  middle  portion 


1290 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


of  the  muscle  appears  as  an  oblique  elevation  with  a  thick,  rounded,  anterior  border, 
best  marked  in  its  lower  part.  The  sternal  heads  of  the  two  muscles  are  separated 
by  a  V-shaped  depression,  in  which  are  the  Stemohyoideus  and  Sternothyreoideus. 

Above  the  hyoid  bone,  near  the  middle  line,  the  anterior  belly  of  the  Digastricus 
produces  a  slight  convexity. 

The  anterior  border  of  the  Trapezius  presents  as  a  faint  ridge  running  from  the 
superior  nuchal  line,  downward  and  forward  to  the  junction  of  the  intermediate 
and  lateral  thirds  of  the  clavicle.  Between  the  Sternocleidomastoideus  and  the 
Trapezius  is  the  posterior  triangle  of  the  neck,  the  lower  part  of  which  appears  as 
a  shallow  concavity — the  supraclavicular  fossa.  In  this  fossa,  the  inferior  belly  of 
the  Omohyoideus,  when  in  action,  presents  as  a  rounded  cord-like  elevation  a  little 
above,  and  almost  parallel  to,  the  clavicle. 


I 


a 


Anterior  belly  of  Digastricus 
Mylohyoideus 

,  Hyoid  hone 

Thyroid  cartilage 
Cricoid  cartilage 
Sternccleidomasfoideus 
Supra  da  vicular  fossa 
Trapezius 


Clavicle 
Clavicular  head  )  of  Sternocleido- 
Sternal  head  J      vmstoideus 


FiQ.   1195. — Front  view  of  neck. 


Arteries. — The  positions  of  several  of  the  larger  arteries  can  be  ascertained 
from  their  pulsations. 

The  subclavian  artery  can  be  felt  by  making  pressure  downward,  backward,  and 
medialward  behind  the  clavicular  head  of  the  Sternocleidomastoideus ;  its  transverse 
cervical  branch  may  be  detected  parallel  to,  and  about  a  finger's  breadth  above, 
the  clavicle.  The  common  and  external  carotid  arteries  can  be  recognized  immediately 
beneath  the  anterior  edge  of  the  Sternocleidomastoideus.  The  external  maxillary 
artery  can  be  traced  over  the  border  of  the  mandible  just  in  front  of  the  anterior 
border  of  the  Masseter,  then  about  1  cm.  lateral  to  the  angle  of  the  mouth,  and 
finally  as  it  runs  up  the  side  of  the  nose.  The  pulsation  of  the  occipital  artery 
can  be  distinguished  about  3  or  4  cm.  lateral  to  the  external  occipital  protuberance; 
that  of  the  posterior  auricular  in  the  groove  between  the  mastoid  process  and  the 
auricula.  The  course  of  the  superficial  temporal  artery  can  be  readily  followed 
across  the  posterior  end  of  the  zygomatic  arch  to  a  point  about  3  to  5  cm.  above 
this,  where  it  divides  into  its  frontal  and  parietal  branches;  the  pulsation  of  the 
frontal  branch  is  frequently  visible  on  the  side  of  the  forehead.  The  supraorbital 
artery  can  usually  be  detected  immediately  above  the  supraorbital  notch  or  foramen. 


SURFACE  MARKINGS  OF  SPECIAL  REGIONS  OF  HEAD  AND  NECK     1291 


SURFACE  MARKINGS  OF  SPECIAL  REGIONS  OF  HEAD  AND  NECK. 

The  Cranium. — Scalp. — ^The  soft  parts  covering  the  upper  surface  of  the  skull 
form  the  scalp  and  comprise  the  following  layers  (Fig.  1196) :  (1)  skin,  (2)  subcuta- 
neous tissue,  (3)  Occipitalis  frontalis  and  galea  aponeurotica,  (4)  subaponeurotic  tissue, 
(5)  pericranium.  The  subcutaneous  tissue  consists  of  a  close  mesh-work  of  fibers, 
the  meshes  of  which  contain  fatty  tissue;  the  fibers  bind  the  skin  and  galea  aponeu- 
rotica firmly  together,  so  that  when  the  Occipitalis  or  the  Frontalis  is  in  action 
the  skin  moves  with  the  aponeurosis.  The  subaponeurotic  tissue,  which  intervenes 
between  the  galea  aponeurotica  and  the  pericranium,  is  much  looser  in  texture, 
I  and  permits  the  movement  of  the  aponeurosis  over  the  underlying  bones. 


Subcutaneous  tissue 

Galea  aponetirotica 
Pericranium 


Superior  sagittal  sinus 


Fig.   1 196. — Diagrammatic  section  of  scalp. 


\% 


Bony  Landmarks  (Fig.  1193). — In  addition  to  the  bony  points  already  described 
which  can  be  determined  by  palpation,  the  following  are  utilized  for  surface 
markings: 

Auricular  Point. — The  center  of  the  orifice  of  the  external  acoustic  meatus. 

Preauricular  Point. — A  point  on  the  posterior  root  of  the  zygotnatic  arch  imme- 
diately in  front  of  the  external  acoustic  meatus. 

Asterion. — The  point  of  meeting  of  the  lambdoidal,  mastooccipital,  and  masto- 
parietal  sutures;  it  lies  4  cm.  behind  and  12  mm.  above  the  level  of  the  auricular 
point. 

Pterion. — The  point  where  the  great  wing  of  the  sphenoid  joins  the  sphenoidal 
angle  of  the  parietal;  it  is  situated  35  mm.  behind,  and  12  mm.  above,  the  level 
of  the  frontozygomatic  suture. 

Inio7i. — The  "external  occipital  protuberance. 

Lambda. — The  point  of  meeting  of  the  lambdoidal  and  sagittal  sutures;  it  is 
in  the  middle  line  about  6.5  cm.  above  the  inion. 

Bregma. — The  meeting-point  of  the  coronal  and  sagittal  sutures;  it  lies  at  the 
point  of  intersection  of  the  middle  line  of  the  scalp  with  a  line  drawn  vertically 
upward  through  the  preauricular  point. 

A  line  passing  through  the  inferior  margin  of  the  orbit  and  the  auricular  point 

known  as  Reid's  base  line.    The  lambdoidal  suture  can  be  indicated  on  either 


1292 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


side  by  the  upper  two-thirds  of  a  line  from  the  lambda  to  the  tip  of  the  mastoid 
process.  The  sagittal  suture  is  in  the  line  joining  the  lambda  to  the  bregma.  The 
position  of  the  coronal  suture  on  either  side  is  sufficiently  represented  by  a  line 
joining  the  bregma  to  the  center  of  the  zygomatic  arch. 

The  floor  of  the  middle  fossa  of  the  skull  is  at  the  level  of  the  posterior  three- 
fourths  of  the  upper  border  of  the  zygomatic  arch;  the  articular  eminence  of  the 
temporal  bone  is  opposite  the  foramen  spinosum  and  the  semilunar  ganglion. 


Fig.   1197. — Drawing  of  a  cast  by  Cunningham  to  illustrate  the  relations  of  the  brain  to  the  skull. 

Brain  (Figs.  1197,  1198).— The  general  outline  of  the  cerebral  hemisphere,  on 
either  side,  may  be  mapped  out  on  the  surface  in  the  following  manner.  Starting 
from  the  nasion,  a  line  drawn  along  the  middle  of  the  scalp  to  the  inion  represents 
the  superior  border.  The  line  of  the  lower  margin  behind  is  that  of  the  transverse 
sinus  (see  page  1294),  or  more  roughly  a  line  convex  upward  from  the  inion  to  the 
posterior  root  of  the  zygomatic  process  of  the  temporal  bone;  thence  along  the 
posterior  two-thirds  of  the  upper  border  of  the  zygomatic  arch  where  the  line  turns 
up  to  the  pterion;  the  front  part  of  the  lower  margin  extends  from  the  pterion  to 
the  glabella  about  1  cm.  above  the  supraorbital  margin.  The  cerebellum  is  so  deeply 
situated  that  there  is  no  reliable  surface  marking  for  it;  a  point  4  cm.  behind  and 
1.5  cm.  below  the  level  of  the  auricular  point  is  situated  directly  over  it. 

The  relations  of  the  principal  fissures  and  gyri  of  the  cerebral  hemispheres  to 
the  surface  of  the  scalp  are  of  considerable  practical  importance,  and  several 
methods  of  indicating  them  have  been  devised.    Necessarily  these  methods  can 


SURFACE  MARKINGS  OF  SPECIAL  REGIONS  OF  HEAD  AND  NECK     1293 

only  be  regarded  as  approximately  correct,  yet  they  are  all  sufficiently  accurate 
for  surgical  purposes.  The  longitudinal  fissure  corresponds  to  the  medial  line  of 
the  scalp  between  the  nasion  and  inion.  In  order  to  mark  out  the  lateral  cerebral 
(Sylvian)  fissure  a  point,  termed  the  Sylvian  point,  which  practically  corresponds 
to  the  pterion,  is  defined  35  mm.  behind  and  12  mm.  above  the  level  of  the  fronto- 
zygomatic  suture;  this  point  marks  the  spot  where  the  lateral  fissure  divides. 
Another  method  of  defining  the  Sylvian  point  is  to  divide  the  distance  between 
the  nasion  and  inion  into  four  equal  parts;  from  the  junction  of  the  third  and 
fourth  parts  (reckoning  from  the  front)  draw  a  line  to  the  frontozygomatic  suture; 
from  the  junction  of  the  first  and  second  parts  a  line  to  the  auricular  point.  These 
two  lines  intersect  at  the  Sylvian  point  and  the  portion  of  the  first  line  behind 
this  point  overlies  the  posterior  ramus  of  the  lateral  cerebral  fissure.    The  position 


1^ 


Fig.  1198. — Relations  of  the  brain  and  middle  meningeal  artery  to  the  surface  of  the  skull.  1.  Nasion.  2.  Inion. 
3.  Lambda.  4.  Lateral  cerebral  fissure.  5.  Central  sulcus.  A.4..  Reid's  base  line.  5.  Point  for  trephining  the  anterior 
branch  of  the  middle  meningeal  artery.  C.  Suprameatal  triangle.  D.  Sigmoid  bend  of  the  transverse  sinus.  E. 
Point  for  trephining  over  the  straight  portion  of  the  transverse  sinus,  exposing  dura  mater  of  both  cerebrum  and 
cerebellum.     Outline  of  cerebral  hemisphe're  indicated  in  blue;  course  of  middle  meningeal  artery  in  red. 


of  the  posterior  ramus  can  otherwise  be  obtained  by  joining  the  Sylvian  point  to  a 
point  2  cm.  below  the  summit  of  the  parietal  eminence.  The  anterior  ascending 
ramus  can  be  marked  out  by  drawing  a  line  upward  at  right  angles  to  the  line 
of  the  posterior  ramus  for  2  cm.  and  the  anterior  horizontal  ramus  by  a  line  of  the 
same  length  drawn  horizontally  forward — both  from  the  Sylvian  point.  To  define 
the  central  sulcus  {fissure  of  Rolando)  two  points  are  taken;  one  is  situated  1.25 
cm.  behind  the  center  of  the  line  joining  the  nasion  and  inion;  the  second  is  at 
the  intersection  of  the  line  of  the  posterior  ramus  of  the  lateral  cerebral  fissure 
with  a  line  through  the  preauricular  point  at  right  angles  to  Reid's  base  line.  The 
upper  9  cm.  of  the  line  joining  these  two  points  overlies  the  central  sulcus  and  forms 
an  angle,  opening  forward,  of  about  70°  with  the  middle  line  of  the  scalp.  An 
alternative  method  is  to  draw  two  perpendicular  lines  from  Reid's  base  line  to  the 
op  of  the  head ;  one  from  the  preauricular  point  and  the  other  from  the  posterior 


1294  SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


border  of  the  mastoid  process  at  its  root.  A  line  from  the  upper  end  of  the  posterior 
line  to  the  point  where  the  anterior  intersects  the  line  of  the  posterior  ramus  of  th(; 
lateral  fissure  indicates  the  position  of  the  central  sulcus.  The  precentral  and 
postcentral  sulci  are  practically  parallel  to  the  central  sulcus;  they  are  situated 
respectively  about  15  mm.  in  front  of,  and  behind,  it.  The  superior  frontal  sulcus 
can  be  mapped  out  by  a  line  drawn  from  the  junction  of  the  upper  and  middle 
thirds  of  the  precentral  sulcus,  in  a  direction  parallel  with  the  longitudinal  sulcus, 
to  a  point  midway  between  the  middle  line  of  the  forehead  and  the  temporal  line, 

4  cm.  above  the  supraorbital  notch.  The  inferior  frontal  sulcus  begins  at  the  junc- 
tion of  the  middle  and  lower  thirds  of  the  precentral  sulcus,  and  follows  the  course 
of  the  superior  temporal  line.  I 

The  horizontal  limb  of  the  intraparietal  sulcus  begins  from  the  junction  of  the* 
lower  with  the  middle  third  of  the  postcentral  sulcus  and  curves  backward  parallel 
to  the  longitudinal  fissure,  midway  between  it  and  the  parietal  eminence;  it  then 
curves  downward  to  end  midway  between  the  lambda  and  the  parietal  eminence. 
The  external  part  of  the  parietooccipital  fissure  runs  lateralward  at  right  angles 
to  the  longitudinal  fissure  for  about  2.5  cm.  from  a  point  5  mm.  in  front  of  the 
lambda.  If  the  line  of  the  posterior  ramus  of  the  lateral  cerebral  fissure  be 
continued  back  to  the  longitudinal  fissure,  the  last  2.5  cm.  of  it  will  indicate  the 
position  of  the  parietooccipital  fissure. 

The  lateral  ventricle  may  be  circumscribed  by  a  quadrilateral  figure.  The  upper 
limit  is  a  horizontal  line  5  cm.  above  the  zygomatic  arch;  this  defines  the  roof  of 
the  ventricle.  The  lower  limit  is  a  horizontal  line  1  cm.  above  the  zygomatic  arch ; 
it  indicates  the  level  of  the  end  of  the  inferior  horn.  Two  vertical  lines,  one  through 
the  junction  of  the  anterior  and  middle  thirds  of  the  zygomatic  arch,  and  the  other 

5  cm.  behind  the  tip  of  the  mastoid  process,  indicate  the  extent  of  the  anterior 
horn  in  front  and  the  posterior  horn  behind. 

Vessels. — The  line  of  the  anterior  division  of  the  middle  meningeal  artery  is 
equidistant  from  the  frontozj-gomatic  suture  and  the  zygomatic  arch;  it  is  obtained 
by  joining  up  the  following  points:  (1)  2.5  cm.,  (2)  4  cm.,  and  (3)  5  cm.  from 
these  two  landmarks.  The  posterior  division  can  be  reached  2.5  cm,  above  the 
auricular  point. 

The  position  of  the  transverse  sinus  is  obtained  by  taking  two  lines:  the  first 
from  the  inion  to  a  point  2.5  cm.  behind  the  auricular  point;  the  second  from  the 
anterior  end  of  the  first  to  the  tip  of  the  mastoid  process.  The  second  line  corre- 
sponds roughly  to  the  line  of  reflection  of  the  skin  of  the  auricula  behind,  and  its 
upper  two-thirds  represents  the  sigmoid  part  of  the  sinus.  The  first  part  of  the 
sinus  has  a  slight  upward  convexity,  and  its  highest  point  is  about  4  cm.  behind 
and  1  cm.  above  the  level  of  the  auricular  point.  The  width  of  the  sinus  is 
about  1  cm. 

The  Face. — Air  Sinuses  (Fig.  1199). — The  frontal  and  maxillary  sinuses  vary 
so  greatly  in  form  and  size  that  their  surface  markings  must  be  regarded  as  only 
roughly  approximate.  To  mark  out  the  position  of  the  frontal  sinus  three  points 
are  taken:  (1)  the  nasion,  (2)  a  point  in  the  middle  line  3  cm.  above  the  nasion, 
(3)  a  point  at  the  junction  of  the  lateral  and  intermediate  thirds  of  the  supraorbital 
margin.  By  joining  these  a  triangular  field  is  described  which  overlies  the  greater 
part  of  the  sinus.  The  outline  of  the  maxillary  sinus  is  irregularly  quadrilateral 
and  is  obtained  by  joining  up  the  following  points:  (1)  the  lacrimal  tubercle,  (2) 
a  point  on  the  zygomatic  bone  at  the  level  of  the  inferior  and  lateral  margins  of  the 
orbit,  (3)  and  (4)  points  on  the  alveolar  process  above  the  last  molar  and  the  second 
premolar  teeth  respectively. 

External  Maxillary  Artery. — The  course  of  this  artery  on  the  face  may  be  indicated 
by  a  line  starting  from  the  lower  border  of  the  mandible  at  the  anterior  margin 
of  the  Masseter,  and  running  at  first  forward  and  upward  to  a  point  1  cm.  lateral 


I 


SURFACE  MARKINGS  OF  SPECIAL  REGIONS  OF  HEAD  AND  NECK     1295 

to  the  angle  of  the  mouth,  thence  to  the  ala  of  the  nose  and  upward  to  the  medial 
commissure  of  the  eye  (Fig,  1200). 

Trigeminal  Nerve. — ^Terminal  branches  of  this  nerve,  viz.,  the  supraorbital  branch 
of  the  ophthalmic,  the  infraorbital  of  the  maxillary,  and  the  mental  of  the  mandibular 
emerge  from  corresponding  foramina  on  the  face  (Fig.  1200).  The  supraorbital 
foramen  is  situated  at  the  junction  of  the  medial  and  intermediate  thirds  of  the 
supraorbital  margin.  A  line  drawn  from  this  foramen  to  the  lower  border  of  the 
mandible,  through  the  interval  between  the  two  lower  premolar  teeth,  passes  over 
the  infraorbital  and  mental  foramina;  the  former  lies  about  1  cm.  below  the  margin 
of  the  orbit,  while  the  latter  varies  in  position  according  to  the  age  of  the  individual; 
in  the  adult  it  is  midway  between  the  upper  and  lower  borders  of  the  mandible, 
in  the  child  it  is  nearer  the  lower  border,  while  in  the  edentulous  jaw  of  old  age 
it  is  close  to  the  upper  margin. 


Frontal  sinus 


Line  of  nasolacrinud 
duct 


Maxillary  sinus 


Fig 


1199. — Outline  of  bones  of  face,  showing  position  of 
air  sinuses. 


Fia. 


1200. — Outline    of    side  of    face,    showing    chief 
surface  markings. 


The  position  of  the  sphenopalatine  ganglion  is  indicated  from  the  side  by  a 
point  on  the  upper  border  of  the  zygomatic  arch,  G  mm.  from  the  margin  of  the 
zygomatic  bone. 

Parotid  Gland  (Fig.  1200). — The  upper  border  of  the  parotid  gland  corresponds  to 
the  posterior  two-thirds  of  the  lower  border  of  the  zygomatic  arch;  the  posterior 
border  to  the  front  of  the  external  acoustic  meatus,  the  mastoid  process,  and- the 
anterior  border  of  Sternocleidomastoideus.  The  inferior  border  is  indicated  by  a 
line  from  the  tip  of  the  mastoid  process  to  the  junction  of  the  body  and  greater 
cornu  of  the  hyoid  bone.  In  front,  the  anterior  border  extends  for  a  variable  dis- 
tance on  the  superficial  surface  of  the  Masseter.  The  surface  marking  for  the  parotid 
duct  is  a  line  drawn  across  the  face  about  a  finger's  breadth  below  the  zygomatic 
arch,  i.  e.,  from  the  lower  margin  of  the  concha  to  midway  between  the  red  margin 


1296 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


of  the  lip  and  the  ala  of  the  nose;  the  duct  ends  opposite  the  second  upper  mola 
tooth  and  measures  about  5  cm.  in  length. 

The  Nose. — The  outlines  of  the  nasal  bones  and  the  cartilages  forming  the  exter- 
nal nose  can  be  easily  felt.  The  mobile  portion  of  the  nasal  septum,  formed  by 
the  medial  crura  of  the  greater  alar  cartilages  and  the  skin,  is  easily  distinguished 
between  the  nares.  When  the  head  is  tilted  back  and  a  speculum  introduced 
through  the  naris,  the  floor  of  the  nasal  cavity,  the  lower  part  of  the  nasal  septum, 
and  the  anterior  ends  of  the  middle  and  inferior  nasal  conchae  can  be  examined. 
The  opening  of  the  nasolacrimal  duct,  which  lies  under  cover  of  the  front  of  the 
inferior  nasal  concha,  is  situated  about  2.5  cm.  behind  the  naris  and  2  cm.  above 
the  level  of  the  floor  of  the  nasal  cavitv. 


Pharyngopalatine  arch 


Palatine  tonsil 


Glossopdatine  arch 
Buccinator 


Yallate  papillce 


4 


•Isthmus 

faucium 


Fungiform  papillca 


Fia.   1201. — The  mouth  cavity.     The  cheeks  have  been  slit  transversely  and  the  tongue  pulled  forward. 

The  Mouth. — The  orifice  of  the  mouth  is  bounded  by  the  lips,  which  are  covered 
externally  by  the  whitish  skin  and  internally  by  the  red  mucous  membrane.  The 
size  of  the  orifice  varies  considerably  in  different  individuals,  but  seems  to  bear  a 
close  relationship  to  the  size  and  prominence  of  the  teeth ;  its  angles  usually  corre- 
spond to  the  lateral  borders  of  the  canine  teeth.  Running  down  the  center  of  the 
outer  surface  of  the  upper  lip  is  a  shallow  groove — ^the  philtrum.  If  the  lips  be 
everted  there  can  be  seen,  in  the  middle  line  of  each,  a  small  fold  of  mucous  mem- 
brane— the  frenulum — passing  from  the  lip  to  the  gum.    By  pulling  the  angle  of  the 


SURFACE  MARKINGS  OF  SPECIAL  REGIONS  OF  HEAD  ANu  NECK     1297 

mouth  outward  the  mucous  membrane  of  the  cheek  can  be  inspected,  and  on  this, 
opposite  the  second  molar  tooth  of  the  maxilla,  is  the  little  papilla  which  marks 
the  orifice  of  the  parotid  duct. 

In  the  floor  of  the  mouth  is  the  tongue  (Fig.  1201).  Its  upper  surface  is  convex 
and  is  marked  along  the  middle  line  by  a  shallow  sulcus;  the  anterior  two-thirds 
are  rough  and  studded  with  papillae;  the  posterior  third  is  smooth  and  tuberculated. 
The  division  between  the  anterior  two-thirds  and  the  posterior  third  is  marked 
by  a  V-shaped  furrow,  the  sulcus  terminalis,  which  is  situated  immediately  behind 
the  line  of  the  vallate  papillae. 


Anterior  lingual  gland 
Lingual  nerve 
Art.  frofuivda  linguce^     ,   ,, 

Vena  com,  n.  hypoglossi 
Longitudirudis  inferior 


Plica  fimbriata 


Vena  com.  n.  hypoglossi 


'^Frenulum 


Orifice  of  aitbmax,  dvxi 
Plica  svhlingtuilis 
I 


Fig.   1202. — The  mouth  cavity.     The  apex  of  the  tongue  is  turned  upward,  and  on  the  right  side  a  superficial 
dissection  of  its  under  surface  has  been  made. 


On  the  under  surface  of  the  tongue  (Fig.  1202)  the  mucous  membrane  is  smooth 
and  devoid  of  papillae.  In  the  middle  line,  the  mucous  membrane  extends  to  the 
floor  of  the  mouth  as  a  distinct  fold — the  frenulum — the  free  edge  of  which  runs 
forward  to  the  symphysis  menti.  Sometimes  the  ranine  vein  can  be  seen  immedi- 
ately beneath  the  mucous  membrane,  a  little  lateral  to  the  frenulum.  Close  to  the 
attachment  of  the  frenulum  to  the  floor  of  the  mouth,  the  slit-like  orifice  of  the 
submaxillary  duct  is  visible  on  either  side.  Running  backward  and  lateralward 
j^  from  the  orifice  of  the  submaxillary  duct  is  the  plica  sublingualis,  produced  by 
H|  the  projection  of  the  sublingual  gland  which  lies  immediately  beneath  the  mucous 
membrane.  The  plica  serves  also  to  indicate  the  line  of  the  submaxillary  duct 
and  of  the  lingual  nerve.  At  the  back  of  the  mouth  is  the  isthmus  faucium,  bounded 
above  by  the  palatine  velum,  from  the  free  margin  of  which  the  uvula  projects 
downward  in  the  middle  line.  On  either  side  of  the  isthmus  are  the  two  palatine 
arches,  the  anterior  formed  by  the  Glossopalatinus  and  the  posterior  by  the  Pharyn- 
82  " 


^ 


1298 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


gopalatinus.  Between  the  two  arches  of  either  side  is  the  palatine  tonsil,  abov(i 
which  is  the  small  supratonsillar  recess;  the  position  of  the  tonsil  corresponds  to 
the  angle  of  the  mandible.  When  the  mouth  is  opened  widely,  a  tense  band — 
the  pterygomandibular  raphe — can  be  seen  and  felt  lateral  to  the  glossopalatino 
arch.  Its  lower  end  is  attached  to  the  mandible  behind  the  last  molar  tooth, 
and  immediately  below  and  in  front  of  this  the  lingual  nerve  can  be  felt;  the  uppei' 

Kasal  septum 
/ 

/  Sasal  conchce 

Pharyngeal  recess 


I 


l=-   '■: 


Torus  of  auditory 
tvbe 


Pharyngeal  ostium  oj 
auditory  tube 

Fig.    1203. — Front  of  nasal  part  of  pharynx,  as  seen  with  the  laryngoscope. 

end  of  the  ligament  can  be  traced  to  the  pterygoid  hamulus.  About  1  cm.  in  front 
of  the  hamulus  and  1  cm.  medial  to  the  last  molar  tooth  of  the  maxilla  is  the  greater 
palatine  foramen  through  which  the  descending  palatine  vessels  and  the  anterior 
palatine  nerve  emerge.  Behind  the  last  molar  tooth  of  the  maxilla  the  coronoid 
process  of  the  mandible  is  palpable. 


VcUlecuda 


Median  glossoepiglottic  fold 


Epiglottis, 


/      yTuhc) clc  of  epiglotth 
Vocal  fold 

Ventricular  fold 


Aryepiglottic  fold 


Cuneiform  cartilage 


Comicvlate  cartilage 


Trachea 
KiQ.   1204. — Laryngoscopic  view  of  interior  of  larynx 

By  tilting  the  head  well  back  a  portion  of  the  posterior  pharyngeal  wall,  corre- 
sponding to  the  site  of  the  second  and  third  cervical  vertebrae,  can  be  seen  through 
the  isthmus  faucium.  On  introducing  the  finger  the  anterior  surfaces  of  the  upper 
cervical  vertebrae  can  be  felt  through  the  thin  muscular  wall  of  the  pharynx; 
if  the  finger  be  hooked  round  the  palatine  velum,  the  choanse  can  be  distinguished  in 
front,  and  the  pharyngeal  ostium  of  the  auditory  tube  on  either  side.  The  level 
of  the  choanse  is  that  of  the  atlas,  while  the  palatine  velum  is  opposite  the  body 
of  the  axis. 


SURFACE  MARKINGS  OF  SPECIAL  REGIONS  OF  HEAD  AND  NECK     1299 


With  the  laryngoscope  many  other  structures  can  be  seen.  In  the  nasal  part 
of  the  pharynx  (Fig.  1203),  the  choanse,  the  nasal  septum,  the  nasal  conchae,  and 
the  pharyngeal  ostia  of  the  auditory  tubes  can  all  be  examined.  Further  down,  the 
base  of  the  tongue,  the  anterior  surface  of  the  epiglottis  with  the  glossoepiglottic 
and  pharyngoepiglottic  folds  bounding  the  valleculae,  and  the  piriform  sinuses,  are 
readily  distinguished.  Beyond  these  is  the  entrance  to  the  larynx,  bounded  on 
either  side  by  the  aryepiglottic  folds,  in  each  of  which  are  two  rounded  eminences 
corresponding  to  the  corniculate  and  cuneiform  cartilages. 

Within  the  larynx  (Fig.  1204)  on  either  side  are  the  ventricular  and  vocal  folds 
(false  and  true  vocal  cords)  with  the  ventricle  between  them.  Still  deeper  are 
seen  the  cricoid  cartilage  and  the  anterior  parts  of  some  of  the  cartilaginous  rings 
of  the  trachea,  and  sometimes,  during  deep  inspiration,  the  bifurcation  of  the 
trachea. 

The  Eye. — The  palpebral  fissure  is  elliptical  in  shape,  and  varies  in  form  in  dif- 
ferent individuals  and  in  different  races  of  mankind;  normally  it  is  oblique,  in  a 
direction  upward  and  lateralward,  so  that  the  lateral  commissure  is  on  a  slightly 
higher  level  than  the  medial.  When  the  eyes  are  directed  forward  as  in  ordinary 
vision  the  upper  part  of  the  cornea  is  covered  by  the  upper  eyelid  and  its  lower 
margin  corresponds  to  the  level  of  the  free  margin  of  the  lower  eyelid,  so  that 
usually  the  lower  three-fourths  are  exposed. 
Hi  At  the  medial  commissure  (Fig.  1205)  are  the  caruncula  lacrimalis  and  the  plica 
semilunaris.  When  the  lids  are  everted,  the  tarsal  glands  appear  as  a  series  of 
nearly  straight  parallel  rows  of 
light  yellow  granules.  On  the 
margins  of  the  lids  about  5  mm. 
from  the  medial  commissure  are 
two  small  openings — the  lacrimal 
puncta;  in  the  natural  condition 
they  are  in  contact  with  the  con- 
junctiva of  the  bulb  of  the  eye, 
so  that  it  is  necessary  to  evert 
the  eyelids  to  expose  them.  The 
position  of  the  lacrimal  sac  is  indi- 
cated by  a  little  tubercle  which 
be  plainly  felt  on  the  lower 


l» 


Punctum  tacrimale  • — 

Plica  semilunaris  ■ — 

Caruncula  — 


Punctum  lacrimale 

Openings  of  tarsal 

glands 


can 


Fig.  1205. — Front  of  left  eye  with  eyelids  separated  to  show 
medial  canthus. 


margin  of  the  orbit;  the  sac  lies 
immediately  above  and  medial  to 
the  tubercle.  If  the  eyelids  be 
drawn  lateralward  so  as  to  tighten 
the  skin  at  the  medial  commissure 
a  prominent  core  can  be  felt  be- 
neath the  tightened  skin;  this  is  the  medial  palpebral  ligament,  which  lies  over 
the  junction  of  the  upper  with  the  lower  two-thirds  of  the  sdx;,  thus  forming  a 
useful  guide  to  its  situation.  The  direction  of  the  nasolacrimal  duct  is  indicated 
by  a  line  from  the  lacrimal  sac  to  the  first  molar  tooth  of  the  maxilla;  the  length 
of  the  duct  is  about  12  or  13  mm. 

On  looking  into  the  eye,  the  iris  with  its  opening,  the  pupil,  and  the  front  of  the 
lens  can  be  examined,  but  for  investigation  of  the  retina  an  ophthalmoscope  is  neces- 
sary. With  this  the  lens,  the  vessels  of  the  retina,  the  optic  disk,  and  the  macula 
lutea  can  all  be  inspected  (Fig.  1206). 

On  the  lateral  surface  of  the  nasal  part  of  the  frontal  bone  the  pulley  of  the 
Obliquus  superior  can  be  easily  reached  by  pushing  the  finger  backward  along  the 

^,  roof  of  the  orbit;  the  tendon  of  the  muscle  can  be  traced  for  a  short  distance  back- 

Hiward  and  lateralward  from  the  pulley. 


1300 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


Optic  disc 


Macula  lutea 


Sclera 
Choroid 

Retina 

Fig.   1206. — The  interiop-.of  the  posterior  half  of  the  left  eyeball. 

The  Ear. — The  various  prominences  and  fossse  of  the  auricula  (see  page  1034) 
are  visible  (Fig.  1207).    The  opening  of  the  external  acoustic  meatus  is  exposed  by 

drawing  the  tragus  forward;  at  the  orifice  are  a  few 
short  crisp  hairs  which  serve  to  prevent  the  entrance 
of  dust  or  of  small  insects;  beyond  this  the  secretion 
of  the  ceruminous  glands  serves  to  catch  any  small 
particles  which  may  find  their  way  into  the  meatus. 
The  interior  of  the  meatus  can  be  examined  through 
a  speculum.  At  the  line  of  junction  of  its  bony 
and  cartilaginous  portions  an  obtuse  angle  is  formed 
which  projects  into  the  antero-inferior  wall  and 
produces  a  narrowing  of  the  lumen  in  this  situation. 
The  cartilaginous  part,  however,  is  connected  to  the 
bony  part  by  fibrous  tissue  which  renders  the  outer 
part  of  the  meatus  very  movable,  and  therefore  by 
drawing  the  auricula  upward,  backward,  and  slightly 
outward,  the  canal  is  rendered  almost  straight.  In 
children  the  meatus  is  very  short,  and  this  should 
be  remembered  in  introducing  the  speculum. 

Through  the  speculum  the  greater  part  of  the  t3rm- 
panic  membrane  (Fig.  1208)  is  visible.  It  is  a  pearly- 
gray  membrane  slightly  glistening  in  the  adult,  placed 
obliquely  so  as  to  form  with  the  floor  of  the  meatus  an  angle  of  about  55°.  At 
birth  it  is  more  horizontal  and  situated  in  almost  the  same  plane  as  the  base  of  the 
skull.  The  membrane  is  concave  outward,  and  the  point  of  deepest  concavity — 
the  umbo — is  slightly  below  the  center.  Running  upward  and  slightly  forward 
from  the  umbo  is  a  reddish-yellow  streak  produced  by  the  manubrium  of  the 
malleus.  This  streak  ends  above  just  below  the  roof  of  the  meatus  at  a  small 
white  rounded  prominence  which  is  caused  by  the  lateral  process  of  the  malleus 
projecting  against  the  membrane.  The  anterior  and  posterior  malleolar  folds 
extend  from  the  prominence  to  the  circumference  of  the  membrane  and  enclose 
the  pars  flaccida.  Behind  the  streak  caused  by  the  manubrium  of  the  malleus  a 
second  streak,  shorter  and  very  faint,  can  be  distinguished;  this  is  the  long  crus 


Fig.   1207. — The  auricula  or  pinna. 
Lateral  surface. 


SURFACE  MARKINGS  OF  SPECIAL  REGIONS  OF  HEAD  AND  NECK     1301 


of  the  incus.  A  narrow  triangular  patch  extending  downward  and  forward  from  the 
umbo  reflects  the  hght  more  brightly  than  any  other  part,  and  is  usually  described 
as  the  cone  of  light. 

Post,  malleolar  fold 
Long  cms  of  incus  f 


Manubrium 
of  malleus 
Postero-superior 
qiiadrant 

Postero-inferior 
quadrant 


Pars  flacci'da 
I  Lat.  proc.  of  malleus 
/  Ant.  malleolar  fold 

i.  / 


Antero-superior 
f  quadrant 

Uttibo 


Fia.  1208.- 


Cone  of  light 


Antero-inferior  quadrant 
-The  right  tympanic  membrane  as  seen  through  a  speculum. 


Groove,  for  middle 
temporal  artery 


Parietal  notch 

Suprameatal 
triangle 

OOCIPITALia 


Articular  tubercle 
Postglenoid  process 

Mandibular  fossa 


Petrotympanic  fissure 
Vaginal  process 

Styloglossus 


Occipital  groove 


STYLOHYOIDECg 


Styloid  process 


FiQ.   1209. — Left  temporal  bone  showing  surface  markings  for  the  tympanic  antrum  (red),  transverse  sinus  (blue)t 

and  facial  nerve  (yellow). 

Tympanic  Antrum, — ^The  site  of  the  tympanic  antrum  is  indicated  by  the  supra- 
meatal triangle  (Fig.  1209).  This  triangle  is  bounded  above  by  the  posterior  root 
of  the  zygomatic  arch;  behind  by  a  vertical  line  from  the  posterior  border  of  the 
external  acoustic  meatus;  in  front  and  below  by  the  upper  margin  of  the  meatus. 
11  The  Neck  (Fig.  1210). — ^Larynx  and  Trachea. — In  the  receding  angle  below  the 
chin,  the  hyoid  bone  (page  1288),  situated  opposite  the  fourth  cervical  vertebra,  can 
easily  be  made  out.    A  finger's  breadth  below  it  is  the  laryngeal  prominence  of  the 


1302 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


th3rroid  cartilage;  the  space  intervening  between  the  hyoid  bone  and  the  thyroi(l 
cartilage  is  occupied  by  the  hyothyroid  membrane.  The  outHnes  of  the  thyroid 
cartilage  are  readily  palpated ;  below  its  lower  border  is  a  depression  corresponding 
to  the  middle  cricothyroid  ligament.  The  level  of  the  vocal  folds  corresponds  to 
the  middle  of  the  anterior  margin  of  the  thyroid  cartilage.  The  anterior  part  of 
the  cricoid  cartilage  forms  an  important  landmark  on  the  front  of  the  neck;  it 
lies  opposite  the  sixth  cervical  vertebra,  and  indicates  the  junctions  of  pharynx 
with  esophagus,  and  larynx  with  trachea.  Below  the  cricoid  cartilage  the  trachea 
can  be  felt,  though  it  is  only  in  thin  subjects  that  the  separate  rings  can  be  distin- 
guished; as  a  rule  there  are  seven  or  eight  rings  above  the  jugular  notch  of  the 
sternum,  and  of  these  the  second,  third,  and  fourth  are  covered  by  the  isthmus 
of  the  thyroid  gland. 


I 


Ext.  max.  art.  - 


-  '  Facial  nerve 


Ext.  carotid  art. 

Occipital  ai^. 
Lesser  ocdp.  nerve> 


I 


Lingual  art.  "\..- 
Sap.  thyroid  art.'     \j^^y 
Point  of  bifurcation  -  -'  \t^^\ V 
of  corn,  carotid  art. 


Com.  carotid  art _ 

Subclavian  art.  - 


Great  auric,  nerve 
Cervical  cutan.,nerve 
"j  Accessory  nerve 

Supraclavic.  nerves 

Line  of  upper  margin 
of  brachial  plexus 


Fig.   1210. — Side  of  neck,  showing  chief  surface  markings. 

Muscles. — ^The  posterior  belly  of  Digastricus  is  marked  out  by  a  line  from  the  tip 
of  the  mastoid  process  to  the  junction  of  the  greater  cornu  and  body  of  the  hyoid 
bone;  a  line  from  this  latter  point  to  a  point  just  lateral  to  the  symphysis  menti 
indicates  the  position  of  the  anterior  belly.  The  line  of  Omohyoideus  begins  at 
the  lower  border  of  the  hyoid  bone,  curves  downward  and  lateralward  to  cross 
Sternocleidom.astoideus  at  the  junction  of  its  middle  and  lower  thirds,  i.  e.,  opposite 
the  cricoid  cartilage,  and  then  runs  more  horizontally  to  the  acromial  end  of  the 
clavicle. 

Arteries. — ^The  position  of  the  common  carotid  artery  in  the  neck  is  indicated 
by  a  line  draw^n  from  the  upper  part  of  the  sternal  end  of  the  clavicle  to  a  point 
midway  between  the  tip  of  the  mastoid  process  and  the  angle  of  the  mandible. 
From  the  clavicle  to  the  upper  border  of  the  thyroid  cartilage  this  line  overlies 
the  common  carotid  artery,  beyond  this  it  is  over  the  external  carotid.  The 
external  carotid  artery  may  otherwise  be  marked  out  by  the  upper  part  of  a  line 
from  the  side  of  the  cricoid  cartilage  to  the  front  of  the  external  acoustic  meatus, 
arching  the  line  slightly  forward. 

The  points  of  origin  of  the  main  branches  of  the  external  carotid  in  the  neck 
are  all  related  to  the  tip  of  the  greater  cornu  of  the  hyoid  bone  as  follows:  (1)  the 
superior  thyroid,  immediately  below  it;  (2)  the  lingual,  on  a  level  with  it;  (3)  the 
facial,  and  (4)  the  occipital  a  little  above  and  behind  it. 


SURFACE  ANATOMY  OF  THE  BACK  1303 


I 


H 


II 


The  subclavian  artery  is  indicated  on  the  surface  by  a  curved  Hne,  convex  upward, 

from  the  sternoclavicular  articulation  to  the  middle  of  the  clavicle.    The  highest 

point  of  the  convexity  is  from  1  to  3  cm.  above  the  clavicle. 

j^      Veins. — ^The  surface  marking  for  the  internal  jugular  vein  is  slightly  lateral 

t  and  parallel  to  that  for  the  common  carotid  artery.    The  position  of  the  external 

jugular  vein  is  marked  out  by  a  line  from  the  angle  of  the  mandible  to  the  middle 

of  the  clavicle.    A  point  on  this  line  about  4  cm.  above  the  clavicle  indicates  the 

spot  where  the  vein  pierces  the  deep  fascia.    The  line  of  the  anterior  jugular  vein 

j    begins  close  to  the  symphysis  menti,  runs  downward  parallel  with  and  a  little 

l»  to  one  side  of  the  middle  line  and,  at  a  variable  distance  above  the  jugular  notch, 

turns  lateralward  to  the  external  jugular. 

Nerves. — ^The  facial  nerve  at  its  exit  from  the  stylomastoid  foramen  is  situated 

I  about  2.5  cm.  from  the  surface,  opposite  the  middle  of  the  anterior  border  of  the 

^  mastoid  process;  a  horizontal  line  from  this  point  to  the  ramus  of  the  mandi})le 

overlies  the  stem  of  the  nerve.    To  mark  the  site  of  the  accessory  nerve  a  line  is 

drawn  from  the  angle  of  the  mandible  to  a  point  on  the  anterior  border  of  Sterno- 

cleidomastoideus  about  3  to  4  cm.  below  the  apex  of  the  mastoid  process,  or  to  the 

midpoint  of  the  posterior  border  of  the  muscle;  the  line  is  continued  across  the 

posterior  triangle  to  Trapezius. 

The  cutaneous  branches  of  the  cervical  plexus  as  they  emerge  from  the  posterior 
border  of  Sternocleidomastoideus  may  be  indicated  as  follows:  the  lesser  occipital 
begins  immediately  above  the  midpoint  of  the  border  and  runs  along  the  border  to 
the  scalp;  the  great  auricular  and  cervical  cutaneous  both  start  from  the  middle 
of  the  border,  the  former  running  upward  toward  the  lobule  of  the  auricula,  the 
latter  crossing  Sternocleidomastoideus  at  right  angles  to  its  long  axis;  the  supra- 
clavicular nerves  emerge  from  immediately  below  the  middle  of  the  posterior  border 
and  run  down  over  the  clavicle.  The  phrenic  nerve  begins  at  the  level  of  the  middle 
of  the  thyroid  cartilage  and  runs  behind  the  clavicle  about  midway  between  the 
anterior  and  posterior  borders  of  Sternocleidomastoideus. 

The  upper  border  of  the  brachial  plexus  is  indicated  by  a  line  from  the  side  of 
the  cricoid  cartilage  to  the  middle  of  the  clavicle. 

Submaxillary  Gland. — On  either  side  of  the  neck  the  superficial  portion  of  the 
submaxillary  gland,  as  it  lies  partly  under  cover  of  the  mandible,  can  be  palpated. 


II 


SURFACE  ANATOMY  OF  THE  BACK. 

Bones. — ^The  only  subcutaneous  parts  of  the  vertebral  column  are  the  apices 
of  the  spinous  processes.  These  are  distinguishable  at  the  bottom  of  a  furrow 
which  runs  down  the  middle  line  of  the  back  from  the  external  occipital  protuber- 
ance to  the  middle  of  the  sacrum.  In  the  cervical  region  the  furrow  is  broad  and 
ends  below  in  a  conspicuous  projection  caused  by  the  spinous  processes  of  the 
seventh  cervical  and  first  thoracic  vertebrse.  Above  this,  the  spinous  process  of  the 
sixth  cervical  vertebra  sometimes  forms  a  projection;  the  other  cervical  spinous 
processes  are  sunken,  but  that  of  the  axis  can  be  felt.  In  the  thoracic  region  the 
furrow  is  shallow  and  during  stooping  disappears,  and  then  the  spinous  processes 
become  more  or  less  visible;  the  markings  produced  by  them  are  small  and  close 
together.  In  the  lumbar  region  the  furrow  is  deep  and  the  situations  of  the  spinous 
processes  are  frequently  indicated  by  little  pits  or  depressions,  especially  when  the 
muscles  in  the  loins  are  well-developed.  In  the  sacral  region  the  furrow  is  shallower, 
presenting  a  flattened  area  which  ends  below  at  the  most  prominent  part  of  the 
dorsal  surface  of  the  sacrum,  i.  e.,  the  spinous  process  of  the  third  sacral  vertebra. 
At  the  bottom  of  the  sacral  furrow  the  irregular  dorsal  surface  of  the  bone  may  be 
felt,  and  below  this,  in  the  deep  groove  running  to  the  anus,  the  coccsrx. 

The  only  other  portions  of  the  vertebral  column  which  can  be  felt  from  the 
surface  are  the  transverse  processes  of  the  first,  sixth,  and  seventh  cervical  vertebrae. 


1^ 


1304 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


Muscles. — ^The  muscles  proper  of  the  back  are  so  obscured  by  those  of  the^iipper 
extremity  (Fig.  1211)  that  they  have  very  Httle  influence  on  surface  form.  The 
Splenii  by  their  divergence  serve  to  broaden  out  the  upper  part  of  the  back  of  the 
neck  and  produce  a  fulness  in  this  situation.    In  the  loin  the  Sacrospinales,  bound 


Trajyeztus 

Spine  of  scapula 

Rhomhoideus  major 

Teres  major  j 

Deltoideua 


I 


Inf,  angle  of  scaptda 


Glutaeus  medius 


Glutceus  maximv^ 


Fig.   1211. — Surface  anatomy  of  the  back. 

down  by  the  lumbodorsal  fascia,  form  rounded  vertical  eminences  which  determine 
the  depth  of  the  spinal  furrow  and  taper  below  to  a  point  on  the  dorsal  surface  of 
the  sacrum.  The  continuations  of  the  Sacrospinales  in  the  lower  thoracic  region 
form  flattened  planes  which  are  gradually  lost  on  passing  upward. 


SURFACE  MARKINGS  OF  THE  BACK 


1305 


SURFACE  MARKINGS  OF  THE  BACK. 

^ony  Landmarks. — In  order  to  identify  any  particular  spinous  process  it  is 
customary  to  count  from  the  prominence  caused  by  the  seventh  cervical  and  first 


[Fig.  1212. — Diagram  showing  the  relation  of  the  medulla  spinalis  to  the  dorsal  surface  of  the  trunk. 

are  outlined  in  red. 


The  bones 


Level  of 

No.  of 

Level  of 

tip 

Level  of 

No.  of           Level  of  tip 

body  of 

nerve. 

of  spine 

of 

body  of 

nerve.             of  spine  of 

C.  1 

C.  1 

T.  8 

T.  9 

7  T. 

2 

{I 

9 

10 

8 

I'c. 

10 

11 

9 

3 

4 

2 

12 

10 

4 

5 

3 

11 

L.  1 

11 

5 

6 

4 

2 

6 

7 

5 

12 

■3 

8 

6 

,  , 

14J 

12 

'7 

T.  1 

7 

S.  ll 

T.  1 

2 

1  T. 

^         0 

3 

. . 

L.  1 

21 

3 

4 

2 

3 

4 

5 

3 

4 

1  L. 

5 

6 

4 

5 

6 

7 

5 

C.  ij 

7 

8 

6 

L.  2 

I 


1306 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


thoracic;  of  these  the  latter  is  the  more  prominent.  The  root  of  the  spine  of  the 
scapula  is  on  a  level  with  the  tip  of  the  spinous  process  of  the  third  thoracic  vertebra, 
and  the  inferior  angle  with  that  of  the  seventh.  The  highest  point  of  the  iliac 
crest  is  on  a  level  with  the  spinous 


I 


process  of  the  fourth  lumbar,  and  the 
posterior  superior  iliac  spine  with  that 
of  the  second  sacral. 

The  transverse  process  of  the  atlas 
is  about  1  cm.  below  and  in  front  of 
the  apex  of  the  mastoid  process.  The 
transverse  process  of  the  sixth  cervical 
vertebra  is  opposite  the  cricoid  cartil- 
age; below  it  is  the  transverse  pro- 
cess of  the  seventh  and  occasionally 
a  cervical  rib. 


Fig.  1213. — Sagittal  section  of  vertebral  canal  to 
show  the  lower  end  of  the  medulla  spinalis  and  the 
filum  terminale.  (Testut.)  Li,  Lv.  First  and  fifth 
lumbar  vertebrae.  Sii.  Second  sacral  vertebra.  1. 
Dura  mater.  2.  Lower  part  of  subarachnoid  cavity. 
3.  Lower  extremity  of  medulla  spinalis.  4.  Filum  ter- 
minale internum,  and  5,  Filum  terminale  externum. 
6.  Attachment  of  filum  terminale  to  first  segment  of 
coccyx^ 


z  "dCervicall  ®, 


3''!^  Cervical. 


^V-Cervicall      \ 

r 

ePhCervvcal  \  ®^ 

k©  y  r'^CervicaL 
6^hCeTvical\  /g\ 

Z^Thoracic  -I 


-piCervicah 


j^-t  Thoracic 


^^h- Thoracic 


6''^Thoracic< 


>3^Thoracic 


■S^hThoracic 


-y>^-^Thc 


e'^Thc 


ithThc 


Yd'^^Thoracic 


\®\ 


tz^Mlvoracic 


Z^Lwmhar  < 


t'i^LuwhaT    s(ll)^ 


>u^hThoracic 


i^PLwnhar 


>  a'^!^Lu7nbar 


S^'^Lumbar 


Coccygeal 


Fig.  1214. — Scheme  showing  the  relations  of  the 
regions  of  attachment  of  the  spinal  nerves  to  the  verte- 
bral spinous  processes.     (After  Reid.) 


Medulla  Spinalis.— The  position  of  the  lower  end  of  the  medulla  spinalis  varies 
slightly  with  the  movements  of  the  vertebral  column,  but,  in  the  adult,  in  the 
upright  posture  it  is  usually  at  the  level  of  the  spinous  process  of  the  second  lumbar 
vertebra  (Fig.  1212) ;  at  birth  it  lies  at  the  level  of  the  fourth  lumbar. 

The  subdural  and  subarachnoid  cavities  end  below  opposite  the  spinous  process 
of  the  third  sacral  vertebra  (Fig.  1213). 


SURFACE  ANATOMY  OF  THE  THORAX  1307 

Spinal  Nerves  (Fig.  1214). — The  table  on  page  1305,  after  Macalister,  shows  the 
relations  which  the  places  of  attachment  of  the  nerves  to  the  medulla  spinalis 
present  to  the  bodies  and  spinous  processes  of  the  vertebrse. 


1^ 


SURFACE  ANATOMY  OF  THE  THORAX. 


n 


II 


i» 


IP 

I 


Bones. — ^The  skeleton  of  the  thorax  is  to  a  very  considerable  extent  covered  by 
muscles,  so  that  in  the  strongly  developed  muscular  subject  it  is  for  the  most  part 
concealed.  In  the  emaciated  subject,  however,  the  ribs,  especially  in  the  lower  and 
lateral  regions,  stand  out  as  prominent  ridges  with  the  sunken  intercostal  spaces 
between  them. 

In  the  middle  line,  in  front,  the  superficial  surface  of  the  sternum  can  be  felt 
throughout  its  entire  length  at  the  bottom  of  a  furrow,  the  sternal  furrow^  situated 
between  the  Pectorales  majores.  These  muscles  overlap  the  anterior  surface 
somewhat,  so  that  the  whole  width  of  the  sternum  is  not  subcutaneous,  and  this 
overlapping  is  greatest  opposite  the  middle  of  the  bone;  the  furrow^  therefore,  is 
wdde  at  its  upper  and  lower  parts  but  narrow  in  the  middle.  At  the  upper  border 
of  the  manubrium  sterni  is  the  jugular  notch:  the  lateral  parts  of  this  notch  are 
obscured  by  the  tendinous  origins  of  the  Sternocleidomastoidei,  which  appear  as 
oblique  cords  narrowing  and  deepening  the  notch.  Lower  down  on  the  subcu- 
taneous surface  is  a  w^ell-defined  transverse  ridge,  the  sternal  angle;  it  denotes  the 
junction  of  the  manubrium  and  body.  From  the  middle  of  the  sternum  the  sternal 
furrow  spreads  out  and  ends  at  the  junction  of  the  body  with  the  xiphoid  process. 
Immediately  below  this  is  the  infrastemal  notch;  between  the  sternal  ends  of  the 
seventh  costal  cartilages,  and  below^  the  notch,  is  a  triangular  depression,  the 
epigastric  fossa,  in  which  the  xiphoid  process  can  be  felt. 

On  either  side  of  the  sternum  the  costal  cartilages  and  ribs  on  the  front  of  the 
thorax  are  partly  obscured  by  the  Pectoralis  major,  through  which,  however,  they 
can  be  felt  as  ridges  with  yielding  intervals  between  them  corresponding  to  the 
intercostal  spaces.  Of  these  spaces,  that  between  the  second  and  third  ribs  is  the 
widest,  the  next  two  are  somewhat  narrower,  and  the  remainder,  with  the  exception 
of  the  last  two,  are  comparatively  narrow. 

Below  the  lower  border  of  the  Pectoralis  major  on  the  front  of  the  chest,  the 
broad  flat  outlines  of  the  ribs  as  they  descend,  and  the  more  rounded  outlines  of  the 
costal  cartilages,  are  often  visible.  The  low^er  boundary  of  the  front  of  the  thorax, 
which  is  most  plainly  seen  by  bending  the  body  backward,  is  formed  by  the  xiphjid 
process,  the  cartilages  of  the  seventh,  eighth,  ninth,  and  tenth  ribs,  and  the  ends  of 
the  cartilages  of  the  eleventh  and  twelfth  ribs. 

On  either  side  of  the  thorax,  from  the  axilla  downw^ard,  the  flattened  external 
surfaces  of  the  ribs  may  be  defined.  Although  covered  by  muscles,  all  the  ribs, 
with  the  exception  of  the  first,  can  generally  be  followed  wdthout  difficulty  over  the 
front  and  sides  of  the  thorax.  The  first  rib  being  almost  completely  covered  by 
the  clavicle  can  only  be  distinguished  in  a  small  portion  of  its  extent. 

At  the  back,  the  angles  of  the  ribs  lie  on  a  slightly  marked  oblique  line  on  either 
side  of,  and  some  distance  from,  the  spinous  processes  of  the  vertebrae.  The  line 
diverges  somewhat  as  it  descends,  and  lateral  to  it  is  a  broad  convex  surface  caused 
by  the  projection  of  the  ribs  beyond  their  angles.  Over  this  surface,  except  where 
covered  by  the  scapula,  the  individual  ribs  can  be  distinguished. 

Muscles. — ^The  surface  muscles  covering  the  thorax  belong  to  the  musculature 
of  the  upper  extremity  (Figs.  1215,  1219),  and  will  be  described  in  that  section 
(page  1325).  There  is,  however,  an  area  of  practical  importance  bounded  by  these 
muscles.  It  is  limited  above  by  the  lower  border  of  Trapezius,  below  by  the  upper 
border  of  Latissimus  dorsi,  and  laterally  by  the  vertebral  border  of  the  scapula;  the 


1308 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


floor  is  partly  formed  by  Rhomboideus  major.  If  the  scapula  be  drawn  forward  by 
folding  the  arms  across  the  chest,  and  the  trunk  bent  forward,  parts  of  the  sixth 
and  seventh  ribs  and  the  interspace  between  them  become  subcutaneous  and  avail- 
able for  ausculation.    The  space  is  therefore  known  as  the  triangle  of  ausculation. 


I 


Trapezius 


—  Latissimus  dor  si 


Pectoralis  major 


Serraius  anterior 


Obliquus  exlernus 
Rectus  abdominis 


Fia.  1215.— The  left  side  of  the  thorax. 

Mamma. — The  size  of  the  mamma  is  subject  to  great  variations.  In  the  adult 
nulliparous  female,  it  extends  vertically  from  the  second  to  the  sixth  rib,  and 
transversely  from  the  side  of  the  sternum  to  the  midaxillary  line.  In  the  male  and 
in  the  nulliparous  female  the  mammary  papilla  is  situated  in  the  fourth  interspace 
about  9  or  10  cm.  from  the  middle  line,  or  2  cm.  from  the  costochondral  junction. 


SURFACE  MARKINGS  OF  THE  THORAX. 

Bony  Landmarks. — ^The  second  costal  cartilage  corresponding  to  the  sternal 
angle  is  so  readily  found  that  it  is  used  as  a  starting-point  from  which  to  count  the 
ribs.  The  lower  border  of  the  Pectoralis  major  at  its  attachment  corresponds  to 
the  fifth  rib;  the  uppermost  visible  digitation  of  Serratus  anterior  indicates  the 
sixth  rib. 

The  jugular  notch  is  in  the  same  horizontal  plane  as  the  lower  border -of  the  body 
of  the  second  thoracic  vertebra;  the  sternal  angle  is  at  the  level  of  the  fifth  thoracic 
vertebra,  while  the  junction  between  the  body  and  xiphoid  process  of  the  sternum 
corresponds  to  the  fibrocartilage  between  the  ninth  and  tenth  thoracic  vertebrae. 

The  influence  of  the  obliquity  of  the  ribs  on  horizontal  levels  in  the  thorax  is 
well  shown  by  the  following  line.  "  If  a  horizontal  line  be  drawn  around  the  body 
at  the  level  of  the  inferior  angle  of  the  scapula,  while  the  arms  are  at  the  sides,  the 


SURFACE  MARKINGS  OF  THE  THORAX 


1309 


line  would  cut  the  sternum  in  front  between  the  fourth  and  fifth  ribs,  the  fifth  rib 
in  the  nipple  line,  and  the  ninth  rib  at  the  vertebral  column."    (Treves). 

Diaphragm. — -The  shape  and  variation^  of  the  diaphragm  as  seen  by  skiag- 
raphy have  already  been  described  (page  407) . 

Surface  Lines. — For  clinical  purposes,  and  for  convenience  of  description,  the 
surface  of  the  thorax  has  been  mapped  out  by  arbitrary  lines  (Fig.  1220).  On  the 
front  of  the  thorax  the  most  important  vertical  lines  are  the  midstemal,  the  middle 
line  of  the  sternum ;  and  the  mammary,  or,  better  midclavicular,  which  runs  verti- 
cally downward  from  a  point  midway  between  the  center  of  the  jugular  notch  and 
the  tip  of  the  acromion.  This  latter  line,  if  prolonged,  is  practically  continuous 
with  the  lateral  line  on  the  front  of  the  abdomen.  Other  vertical  lines  on  the  front 
of  the  thorax  are  the  lateral  sternal  along  the  ternal  margin,  and  the  parasternal 
midway  between  the  lateral  sternal  and  the  mammary. 

On  either  side  of  the  thorax  the  anterior  and  posterior  axillary  lines  are  drawn 
vertically  from  the  corresponding  axillary  folds;  the  midaxillary  line  runs  down- 
ward from  the  apex  of  the  axilla. 

On  the  posterior  surface  of  the  thorax  the  scapular  line  is  drawn  vertically 
through  the  inferior  angle  of  the  scapula. 


I 


Fio.  1216. — Front  of  thorax,  showing  surface  relations  of  bones,  lungs  (purple),  pleura  (blue),  and  heart  (red 
outline).     P.  Pulmonary  valve.     A.  Aortic  valve,     p.  Bicuspid  valve.     T.  Tricuspid  valve. 

Pleurae  (Figs.  1216,  1217). — The  lines  of  reflection  of  the  pleurae  can  be  indicated 
on  the  surface.  On  the  right  side  the  line  begins  at  the  sternoclavicular  articulation 
and  runs  downward  and  medialward  to  the  midpoint  of  the  junction  between  the 
manubrium  and  body  of  the  sternum.  It  then  follows  the  midstemal  line  to  the 
lower  end  of  the  body  of  the  sternum  or  on  to  the  xiphoid  process,  where  it  turns 
lateral  ward  and  downward  across  the  seventh  sternocostal  articulation.  It  crosses 
the  eighth  costochondral  junction  in  the  mammary  line,  the  tenth  rib  in  the  mid- 
axillary  line,  and  is  prolonged  thence  to  the  spinous  process  "of  the  twelfth  thoracic 
vertebra. 


SURF  J 

On  the  left  side,  beginning  at  the  sternoclavicular  articulation,  it  reaches  tht 
midpoint  of  the  junction  between  the  manubrium  and  body  of  the  sternum,  and 
extends  down  the  midsternal  line  in  contact  with  that  of  the  opposite  side  to  the 
level  of  the  fourth  costal  cartilage.  It  then  diverges  lateralward  and  is  continued 
downward  slightly  lateral  to  the  sternal  border,  as  far  as  the  sixth  costal  cartilage 
Running  downward  and  lateralward  from  this  point  it  crosses  the  seventh  costsj 
cartilage,  and  from  this  onward  it  is  similar  to  the  line  on  the  right  side,  but  at 
slightly  lower  level. 

Lungs  (Figs.  1216,  1217). — ^The  apex  of  the  lung  is  situated  in  the  neck  above  the 
medial  third  of  the  clavicle.  The  height  to  which  it  rises  above  the  clavicle  varies 
very  considerably,  but  is  generally  about  2.5  cm.  It  may,  however,  extend  as 
high  as  4  or  5  cm.,  or,  on  the  other  hand,  may  scarcely  project  above  the  level 
of  this  bone. 


I 


Fig.   1217. — Side  of  thorax,  showing  surface  markings  for  bones,  lungs  (purple),  pleura    (blue),   and  spleen  (green). 


In  order  to  mark  out  the  anterior  borders  of  the  lungs  a  line  is  drawn  from  each 
apex  point — 2.5  cm.  above  the  clavicle  and  rather  nearer  the  anterior  than  the 
posterior  border  of  Sternocleidomastoideus — downward  and  medialward  across  the 
sternoclavicular  articulation  and  manubrium  sterni  until  it  meets,  or  almost  meets, 
its  fellow  of  the  other  side  at  the  midpoint  of  the  junction  between  the  manubrium 
and  body  of  the  sternum.  From  this  point  the  two  lines  run  downward,  prac- 
tically along  the  midsternal  line,  as  far  as  the  level  of  the  fourth  costal  cartilages. 
The  continuation  of  the  anterior  border  of  the  right  lung  is  marked  by  a  prolonga- 
tion of  its  line  vertically  downward  to  the  level  of  the  sixth  costal  cartilage,  and 
then  it  turns  lateralward  and  downward.  The  line  on  the  left  side  curves  lateralward 
and  downward  across  the  fourth  sternocostal  articulation  to  reach  the  parasternal 
line  at  the  fifth  costal  cartilage,  and  then  turns  medialward  and  downward  to  the 
sixth  sternocostal  articulation. 


SURFACE  MARKINGS  OF  THE  THORAX  1311 


In  the  position  of  expiration  the  lower  border  of  the  lung  may  be  marked  by  a 
slightly  curved  line  with  its  convexity  downward,  from  the  sixth  sternocostal 
junction  to  the  tenth  thoracic  spinous  process.  This  line  crosses  the  mid-clavic- 
ular line  at  the  sixth,  and  the  midaxillary  line  at  the  eighth  rib. 

The  posterior  borders  of  the  lungs  are  indicated  by  lines  drawn  from  the  level 
of  the  spinous  process  of  the  seventh  cervical  vertebra,  down  either  side  of  the 
vertebral  column,  across  the  costovertebral  joints,  as  low  as  the  spinous  process 
o'f  the  tenth  thoracic  vertebra. 

The  position  of  the  oblique  fissure  in  either  lung  can  be  shown  by  a  line  drawn 
from  the  spinous  process  of  the  second  thoracic  vertebra  around  the  side  of  the 
thorax  to  the  sixth  rib  in  the  mid-clavicular  line;  this  line  corresponds  roughly  to 
the  line  of  the  vertebral  border  of  the  scapula  when  the  hand  is  placed  on  the  top  of 
the  head.  The  horizontal  fissure  in  the  right  lung  is  indicated  by  a  line  drawn  from 
the  midpoint  of  the  preceding,  or  from  the  point  where  it  cuts  the  midaxillary  line, 
to  the  midsternal  line  at  the  level  of  the  fourth  costal  cartilage. 
Hk  Trachea. — This  may  be  marked  out  on  the  back  by  a  line  from  the  spinous 
process  of  the  sixth  cervical  to  that  of  the  fourth  thoracic  vertebra  where  it  bifur- 
cates; from  its  bifurcation  the  two  bronchi  are  directed  downward  and  lateralward. 
In  front,  the  point  of  bifurcation  corresponds  to  the  sternal  angle. 

Esophagus. — The  extent  of  the  esophagus  may  be  indicated  on  the  back  by  a 
line  from  the  sixth  cervical  to  the  level  of  the  ninth  thoracic  spinous  process, 
2.5  cm.  to  the  left  of  the  middle  line. 

Heart. — ^The  outline  of  the  heart  in  relation  to  the  front  of  the  thorax  (Figs 
1216,  1218)  can  be  represented  by  a  quadrangular  figure.  The  apex  of  the  heart 
is  first  determined,  either  by  its  pulsation  or  as  a  point  in  the  fifth  interspace, 
9  cm.  to  the  left  of  the  midsternal  line.  The  other  three  points  are:  (a)  the  seventh 
right  sternocostal  articulation;  (6)  a  point  on  the  upper  border  of  the  third  right 
costal  cartilage  1  cm.  from  the  right  lateral  sternal  line;  (c)  a  point  on  the  lower 
border  of  the  second  left  costal  cartilage  2.5  cm.  from  the  left  lateral  sternal  line. 
A  line  joining  the  apex  to  point  (a)  and  traversing  the  junction  of  the  body  of  the 
sternum  with  the  xiphoid  process  represents  the  lowest  limit  of  the  heart — its 
acute  margin.  The  right  and  left  borders  are  represented  respectively  by  lines 
joining  (a)  to  (b)  and  the  apex  to  (c);  both  lines  are  convex  lateralward,  but  the 
convexity  is  more  marked  on  the  right  where  its  summit  is  4  gm.  distant  from  the 

■  ■^midsternal  line  opposite  the  fourth  costal  cartilage. 
I  A  portion  of  the  area  of  the  heart  thus  mapped  out  is  uncovered  by  lung,  and 
therefore  gives  a  dull  note  on  percussion;  the  remainder  being  overlapped  by  lung 
gives  a  more  or  less  resonant  note.  The  former  is  known  as  the  area  of  superficial 
cardiac  dulness,  the  latter  as  the  area  of  deep  cardiac  dulness.  The  area  of  super- 
ficial cardiac  dulness  is  somewhat  triangular;  from  the  apex  of  the  heart  two  lines 
are  drawn  to  the  midsternal  line,  one  to  the  level  of  the  fourth  costal  cartilage, 
the  other  to  the  junction  between  the  body  and  xiphoid  process;  the  portion  of  the 
midsternal  line  between  these  points  is  the  base  of  the  triangle.  Latham  lays 
down  the  following  rule  as  a  sufficient  practical  guide  for  the  definition  of  the  area 
of  superficial  dulness.  "Make  a  circle  of  two  inches  in  diameter  around  a  point 
midway  between  the  nipple  and  the  end  of  the  sternum." 

The  coronary  sulcus  can  be  indicated  by  a  line  from  the  third  left,  to  the  sixth 
right,  sternocostal  joint.  The  anterior  longitudinal  sulcus  is  a  finger's  breadth  to 
the  right  of  the  left  margin  of  the  heart. 

The  position  of  the  various  orifices  is  as  follows:  The  pulmonary  orifice  is  sit- 
uated in  the  upper  angle  of  the  third  left  sternocostal  articulation;  the  aortic 
orifice  is  a  little  below  and  medial  to  this,  close  to  the  articulation.  The  left  atrio- 
ventricular opening  is  opposite  the  fourth  costal  cartilage,  and  rather  to  the  left 
of  the  midsternal  line;  the  right  atrioventricular  opening  is  a  little  lower,  opposite 


I 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


I 


the  fourth  interspace  of  the  right  side.    The  Hnes  indicating  the  atrioventricular 
openings  are  sHghtly  below  and  parallel  to  the  line  of  the  coronary  sulcus. 

Arteries. — The  line  of  the  ascending  aorta  begins  slightly  to  the  left  of  the  mid- 
sternal  line  opposite  the  third  costal  cartilage  and  extends  upward  and  to  the 
right  to  the  upper  border  of  the  second  right  costal  cartilage.  The  beginning  of 
the  aortic  arch  is  indicated  by  a  line  from  this  latter  point  to  the  midsternal  line 
about  2.5  cm.  below  the  jugular  notch.  The  point  on  the  midsternal  line  is  oppo- 
site the  summit  of  the  arch,  and  a  line  from  it  to  the  right  sternoclavicular  articu- 
lation represents  the  site  of  the  innominate  artery,  while  another  line  from  a  point 
slightly  to  the  left  of  it  and  passing  through  the  left  sternoclavicular  articulation 
indicates  the  position  of  the  left  common  carotid  artery  in  the  thorax. 


n 


Fig.  1218. — Diagram  showing  relations  of  opened  heart  to  front  of  thoracic  wall.  Ant.  Anterior  segment  of  tri- 
cuspid valve.  A  O.  Aorta.  A.P.  Anterior  papillary  muscle.  In.  Innominate  artery.  L.C.C.  Left  common  carotid 
artery.  L.S.  Left  subclavian  artery.  L.V.  Left  ventricle.  P. A.  Pulmonary  artery.  R.A.  Right  atrium.  R.V. 
Right  ventricle.     V.S.  Ventricular  septum. 

The  internal  mammary  artery  descends  behind  the  first  six  costal  cartilages 
about  1  cm.  from  the  lateral  sternal  line. 

Veins. — The  line  of  the  right  innominate  vein  crosses  the  right  sternoclavicular 
joint  and  the  upper  border  of  the  first  right  costal  cartilage  about  1  cm.  from  the 
lateral  sternal  line;  that  of  the  left  innominate  vein  extends  from  the  left  sterno- 
clavicular articulation  to  meet  the  right  at  the  upper  border  of  the  first  right 
costal  cartilage.  The  junction  of  the  two  lines  indicates  the  origin  of  the  superior 
vena  cava,  the  line  of  which  is  continued  vertically  down  to  the  level  of  the  third 
right  costal  cartilage.  The  end  of  the  inferior  vena  cava  is  situated  opposite  the 
upper  margin  of  the  sixth  right  costal  cartilage  about  2  cm.  from  the  mid- 
sternal line. 


SURFACE  ANATOMY  OF  THE  ABDOMEN  1313 


SURFACE   ANATOMY  OF  THE   ABDOMEN. 

kin. — The  skin  of  the  front  of  the  abdomen  is  thin.  In  the  male  it  is  often 
thickly  hair-clad,  especially  toward  the  lower  part  of  the  middle  line;  in  the  female 
the  hairs  are  confined  to  the  pubes.  Just  below  the  line  of  the  iliac  crest,  especially 
marked  in  fat  subjects,  is  a  shallow  groove  termed  the  iliac  furrow,  while  in  the 
site  of  the  inguinal  ligament  a  sharper  fold  known  as  the  fold  of  the  groin  is  easily 
distinguishable. 

After  distension  of  the  abdomen  from  pregnancy  or  other  causes  the  skin  com- 

■I  monly  presents  transverse  white  lines  which  are  quite  smooth,  being  destitute 
^  of  papillae;  these  are  known  as  striae  gravidarum  or  striae  albicantes.  The  linea 
nigra  of  pregnancy  is  often  seen  as  a  pigmented  brown  streak  in  the  middle  line 
between  the  umbilicus  and  symphysis  pubis. 

In  the  middle  line  of  the  front  of  the  abdomen  is  a  shallow  furrow  which  extends 
Hi  from  ,the  junction  between  the  body  of  the  sternum  with  the  xiphoid  process  to  a 
^"  short  distance  below  the  umbilicus;  it  corresponds  to  the  linea  alba.  The  umbilicus 
is  situated  in  the  middle  line,  but  it  varies  in  position  as  regards  its  height;  in  an 
adult  subject  it  is  always  placed  above  the  middle  point  of  the  body,  and  in  a  nor- 
mal well-nourished  subject  is  from  2  to  2.5  cm.  above  the  level  of  the  tubercles 
Bof  the  iliac  crests. 
Bones. — The  bones  in  relation  with  the  surface  of  the  abdomen  are  (1)  the  lower 
part  of  the  vertebral  column  and  the  lower  ribs  and  (2)  the  pelvis;  the  former 
have  already  been  described  (page  1303),  the  latter  will  be  considered  with  the 
lower  limb. 

Muscles  (Fig,  1219). — The  only  muscles  of  the  abdomen  which  have  any  consider- 
able influence  on  surface  form  are  the  Obliquus  externus  and  the  Rectus.  The 
upper  digitations  of  origin  of  Obliquus  externus  are  well-marked  in  a  muscular  sub- 
ject, interdigitating  with  those  of  Serratus  anterior;  the  lower  digitations  are  cov- 
ered by  the  border  of  Latissimus  dorsi  and  are  not  visible.  The  attachment  of  the 
Obliqui  externus  and  internus  to  the  crest  of  the  ilium  forms  a  thick  oblique  roll 
which  determines  the  iliac  furrow.  Sometimes  on  the  front  of  the  lateral  region  of 
the  abdomen  an  undulating  line  marks  the  passing  of  the  muscular  fibers  of  the 
Obliquus  externus  into  its  aponeurosis.  The  lateral  margin  of  the  Obliquus  externus 
is  separated  from  that  of  the  Latissimus  dorsi  by  a  small  triangular  interval — the 
lumbar  triangle — ^the  base  of  which  is  formed  by  the  iliac  crest,  and  its  floor  by 

■  L  Obliquus  internus. 

■  I      The  lateral  margin  of  Rectus  abdominis  is  indicated  by  the  linea  semilunaris, 

which  may  be  exactly  defined  by  putting  the  muscle  into  action.  The  surface  of 
B  ■  the  Rectus  presents  three  transverse  furrows,  the  tendinous  inscriptions :  the  upper 
B  m  two  of  these,  viz.,  one  opposite,  or  a  little  below^,  the  tip  of  the  xiphoid  process, 

and  the  other  midway  between  this  point  and  the  umbilicus,  are  usually  well- 
i  marked;  the  third,  opposite  the  umbilicus,  is  not  so  distinct.  Between  the  two 
Bp  Recti  the  linea  alba  can  be  palpated  from  the  xiphoid  process  to  a  point  just  below 
"^  the  umbilicus;  it  is  represented  by  a  distinct  dip  between  the  muscles:  beyond 

this  the  muscles  are  in  apposition. 

Vessels.^ — In  thin  subjects  the  pulsation  of  the  abdominal  aorta  can  be  readily 

■  felt  by  making  deep  pressure  in  the  middle  line  above  the  umbilicus. 
I  Viscera. — Under  normal  conditions  the  various  portions  of  the  digestive  tube 
cannot  be  identified  by  simple  palpation.  Peristalsis  of  the  coils  of  small  intestine 
can  be  observed  in  some  persons  with  extremely  thin  abdominal  walls  when  some 
degree  of  constipation  exists.  In  cases  of  constipation  it  is  sometimes  possible  to 
trace  portions  of  the  great  intestine  by  feeling  the  fecal  masses  within  the  gut. 
In  thin  persons  with  relaxed  abdominal  walls  the  iliac  colon  can  be  felt  in  the  left 
83 


1314 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


iliac  region — rolling  under  the  fingers  when  empty  and  forming  a  distinct  ^oimoi 
when  distended. 

The  greater  part  of  the  liver  lies  under  cover  of  the  lower  ribs  and  their  cartilages, 
but  in  the  epigastric  fossa  it  comes  in  contact  with  the  abdominal  wall.     The 


I 


I- 


terrains 
antericr 
Hectus  abdominis 

Linea  alba 
Aponeurosis  of 
Obliquus  extemus 

Muscular  fibers  of 
Obliquus  extemus 


Anterior  superior 
iliac  spine 


Ingui'iutl  ligament 


Fig.   1219. — Surface  anatoniv  of  the  front  of  the  thorax  and  abdomen. 


position  of  the  liver  varies  according  to  the  posture  of  the  body.  In  the  erect 
posture  in  the  adult  male  the  edge  of  the  liver  projects  about  1  cm.  below  the 
lower  margin  of  the  right  costal  cartilages,  and  its  inferior  margin  can  often  be  felt 
in  this  situation  if  the  abdominal  wall  is  thin.    In  the  supine  position  the  liver 


SURFACE  MARKINGS  OF  THE  ABDOMEN  1315 

recedes  above  the  margin  of  the  ribs  and  cannot  then  be  detected  by  the  finger; 

'"  in  the  prone  position  it  falls  forward  and  is  then  generally  palpable  in  a  patient 
with  loose  and  lax  abdominal  walls.  Its  position  varies  with  the  respiratory 
movements;  during  a  deep  inspiration  it  descends  below  the  ribs;  in  expiration 
it  is  raised.  Pressure  from  without,  as  in  tight  lacing,  by  compressing  the  lower 
part  of  the  chest,  displaces  the  liver  considerably,  its  anterior  edge  frequently 
extending  as  low  as  the  crest  of  the  ilium.  Again  its  position  varies  greatly  with 
the  state  of  the  stomach  and  intestines;  when  these  are  empty  the  liver  descends, 
when  they  are  distended  it  is  pushed  upward. 
The  pancreas  can  sometimes  be  felt,  in  emaciated  subjects,  when  the  stomach 

It  and  colon  are  empty,  by  making  deep  pressure  in  the  middle  line  about  7  or  8  cm. 
above  the  umbilicus. 

The  kidneys  being  situated  at  the  back  of  the  abdominal  cavity  and  deeply 
placed  cannot  be  palpated  unless  enlarged  or  misplaced. 


k 


SURFACE  MARKINGS   OF  THE  ABDOMEN. 


1^ 


II 


Bony  Landmarks. — Above,  the  chief  bony  markings  are  the  xiphoid  process, 
the  lower  six  costal  cartilages,  and  the  anterior  ends  of  the  lower  six  ribs.  The 
junction  between  the  body  of  the  sternum  and  the  xiphoid  process  is  on  the  level 
of  the  tenth  thoracic  vertebra.  Below,  the  main  landmarks  are  the  symphysis 
pubis  and  the  pubic  crest  and  tubercle,  the  anterior  superior  iliac  spine,  and  the 
iliac  crest. 

Muscles  (Fig.  1227). — The  Rectus  lies  between  the  linea  alba  and  the  linea  semi- 
lunaris; the  former  is  indicated  by  the  middle  line,  the  latter  by  a  curved  line, 
convex  lateralward,  from  the  tip  of  the  cartilage  of  the  ninth  rib  to  the  pubic 
tubercle;  at  the  level  of  the  umbilicus  the  linea  semilunaris  is  about  7  cm.  from  the 
middle  line.  The  line  indicating  the  junction  of  the  muscular  fibers  of  Obliquus 
extemus  with  its  aponeurosis  extends  from  the  tip  of  the  ninth  costal  cartilage 
to  a  point  just  medial  to  the  anterior  superior  iliac  spine. 

The  umbilicus  is  at  the  level  of  the  fibrocartilage  between  the  third  and  fourth 
lumbar  vertebrae. 

The  subcutaneous  inguinal  ring  is  situated  1  cm.  above  and  lateral  to  the  pubic 
tubercle;  the  abdominal  inguinal  ring  lies  1  to  2  cm.  above  the  middle  of  the  inguinal 
ligament.  The  position  of  the  inguinal  canal  is  indicated  by  a  line  joining  these 
two  points. 

Surface  Lines. — For  convenience  of  description  of  the  viscera  and  of  reference 
to  morbid  conditions  of  the  contained  parts,  the  abdomen  is  divided  into  nine 
regions,  by  imaginary  planes,  two  horizontal  and  two  sagittal,  the  edges  of  the  planes 
being  indicated  by  lines  drawn  on  the  surface  of  the  body  (Fig.  1220).  In  the  older 
method  the  upper,  or  subcostal,  horizontal  line  encircles  the  body  at  the  level  of  the 
lowest  points  of  the  tenth  costal  cartilages;  the  lower,  or  intertubercular,  is  a  line 
carried  through  the  highest  points  of  the  iliac  crests  seen  from  the  front,  i.  e., 
through  the  tubercles  on  the  iliac  crests  about  5  cm.  behind  the  anterior  superior 
spines.   An  alternative  method  is  that  of  Addison,  who  adopts  the  following  lines: 

(1)  An  upper  transverse,  the  transpyloric,  halfway  between  the  jugular  notch 
and  the  upper  border  of  the  symphysis  pubis;  this  indicates  the  margin  of  the 
transpyloric  plane,  which  in  most  cases  cuts  through  the  pylorus,  the  tips  of  the 
ninth  costal  cartilages  and  the  lower  border  of  the  first  lumbar  vertebra;  (2)  a 
lower  transverse  line  midway  between  the  upper  transverse  and  the  upper  border 
of  the  symphysis  pubis;  this  is  termed  the  transtubercular,  since  it  practically  corre- 
sponds to  that  passing  through  the  iliac  tubercles;  behind,  its  plane  cuts  the  body 
of  the  fifth  lumbar  vertebra. 


1316 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


By  means  of  these  horizontal  planes  the  abdomen  is  divided  into  three  zones 
named  from  above,  the  subcostal,  umbilical,  and  hypogastric  zones.  Each  of  these- 
is  further  subdivided  into  three  regions  by  the  two  sagittal  planes,  which  are  indi- 
cated on  the  surface  by  a  right  and  a  left  lateral  line  drawn  vertically  through 
points  halfway  between  the  anterior  superior  iliac  spines  and  the  middle  line.  The 
middle  region  of  the  upper  zone  is  called  the  epigastric,  and  the  two  lateral  regions 


I 


Lateral  sternal  line 

/  Parasternal  line 
Mammary  line 


/  \  Ti'anspylo'ric 
\         plane 


\Ira7is  bu.be  rcu  lar 
plane 


•  -  Lbjt  lateral  line 


Fig.   1220. — Surface  lines  of  the  front  of  the  thorax  and  abdomen. 


the  right  and  left  hypochondriac.  The  central  region  of  the  middle  zone  is  the 
umbilical,  and  the  two  lateral  regions  the  right  and  left  lumbar.  The  middle  region 
of  the  lower  zone  is  the  hypogastric  or  pubic,  and  the  lateral  are  the  right  and  left 
iliac  or  inguinal.  The  middle  regions,  viz.,  epigastric,  umbilical,  and  pubic,  can  each 
be  divided  into  right  and  left  portions  by  the  middle  line.  In  the  following  descrip- 
tion of  the  viscera  the  regions  marked  out  by  Addison's  lines  are  those  referred  to. 


SURFACE  MARKINGS  OF  THE  ABDOMEN 


1317 


Stomach  (Fig.  1223). — ^The  shape  of  the  stomach  is  constantly  undergoing  altera- 
tion; it  is  affected  by  the  particular  phase  of  the  process  of  gastric  digestion,  by 


Fig.  1221. — -With  the  patient  in  the  erect  posture. 


Fia.  1222. — With  the  patient  lying  down. 


Figs.   1221  and  1222. — Radiographs  of  a  moderately  distended  stomach,  showing   the   influence  of   posture. 

(Modified  from  Hertz.) 

the  state  of  the  surrounding  viscera,  and  by  the  amount  and  character  of  its  con- 
tents.   Its  position  also  varies  with  that  of  the  body   (Figs.   1221,    1222),  so 


Orifice  nj 
vermiform  process 


TYaivspyloric 
plane 


■  V  Tr arts  tub ercvblav 
plane 


Fig.   1223. — Front  of  abdomen,  showing  surface  markings  for  liver,  stomach,  and  great  intestine. 

that  it  is  impossible  to  indicate  it  on  the  surface  with  any  degree  of  accuracy.  The 
measurements  given  refer  to  a  moderately  filled  stomach  with  the  body  in  the 
c supine  position. 


1318 


[ND  SURFACE  MARKINGS 


I 


The  cardiac  orifice  is  opposite  the  seventh  left  costal  cartilage  about  2.5  cm. 
from  the  side  of  the  sternum;  it  corresponds  to  the  level  of  the  tenth  thoracic  verte- 
bra. The  pyloric  orifice  is  on  the  transpyloric  line  about  1  cm.  to  the  right  of  the 
middle  line,  or  alternately  5  cm.  below  the  seventh  right  sternocostal  articulation; 
it  is  at  the  level  of  the  first  lumbar  vertebra.  A  curved  line,  convex  downward  and 
to  the  left,  joining  these  points  indicates  the  lesser  curvature.  In  the  left  lateral 
line  the  fundus  of  the  stomach  reaches  as 'high  as  the  fifth  interspace  or  the  sixth 


'  Heart  contour 


Stomach 


Small  intestine 


._  Sigmoid 
flexure 


Cecum 


Peritoneum 


J-  madder 


Fig.   1224. — Topography  of  thoracic  and  abdominal  viscera. 

costal  cartilage,  a  little  below  the  apex  of  the  heart.  To  indicate  the  greater  cur- 
vature a  curved  line  is  drawn  from  the  cardiac  orifice  to  the  summit  of  the  fundus, 
thence  downward  and  to  the  left,  finally  turning  medialward  to  the  pyloric  orifice, 
but  passing,  on  its  way,  through  the  intersection  of  the  left  lateral  with  the  trans- 
pyloric line.  The  portion  of  the  stomach  which  is  in  contact  with  the  abdominal 
wall  can  be  represented  roughly  by  a  triangular  area  the  base  of  which  is  formed  by 
a  line  drawn  from  the  tip  of  the  tenth  left  costal  cartilage  to  the  tip  of  the  ninth 


SURFACE  MARKINGS  OF  THE  ABDOMEN 


1319 


right  cartilage,  and  the  sides  by  two  lines  drawn  from  the  end  of  the  eighth  left 
costal  cartilage  to  the  ends  of  the  base  line. 

A  space  of  some  clinical  importance — the  space  of  Traube^ — overlies  the  stomach 
and  may  be  thus  indicated^  It  is  semilunar  in  outline  and  lies  within  the  following 
boundaries:  the  lower  edge  of  the  left  lung,  the  anterior  border  of  the  spleen,  the 
left  costal  margin  and  the  inferior  margin  of  the  left  lobe  of  the  liver. 

Duodenum  (Fig.  1225). — The  superior  part  is  horizontal  and  extends  from  the 
pylorus  to  the  right  lateral  line;  the  descending  part  is  situated  medial  to  the 
right  lateral  line,  from  the  transpyloric  line  to  a  point  midway  between  the  trans- 
pyloric  and  transtubercular  lines.  The  horizontal  part  runs  with  a  slight  upward 
slope  from  the  end  of  the  descending  part  to  the  left  of  the  middle  line ;  the  ascending 
part  is  vertical,  and  reaches  the  transpyloric  line,  where  it  ends  in  the  duodeno- 
jejunal flexure,  about  2.5  cm.  to  the  left  of  the  middle  line. 


Transpylorie 

plane 


TYans  tuber  cvUar 
plane 


Fig.  1225. — ^Front  of  abdomen,  showing  surface  markings  for  duodenum,  pancreas,  and  kidneys.  A  A'.  Plane 
through  joint  between  body  and  xiphoid  process  of  sternum.  B  B'.  Plane  midway  between  A  A'  and  transpyloric 
plane.     C  C .  Plane  midway  between  transpyloric  and  transtubercular  planes. 


Small  Intestine. — The  coils  of  small  intestine  occupy  the  front  of  the  abdomen. 
For  the  most  part  the  coils  of  the  jejunum  are  situated  on  the  left  side,  i.  e.,  in  the 
left  lumbar  and  iliac  regions,  and  in  the  left  half  of  the  umbilical  region.  The  coils 
of  the  ileum  lie  toward  the  right  in  the  right  lumbar  and  iliac  regions,  in  the  right 
half  of  the  umbilical  region,  and  in  the  hypogastric  region;  a  portion  of  the  ileum 
is  within  the  pelvis.  The  end  of  the  ileum,  i.  e.,  the  ileocolic  junction,  is  slightly 
below  and  medial  to  the  intersection  of  the  right  lateral  and  transtubercular  lines. 

Cecum  and  Vermiform  Process. — The  cecum  is  in  the  right  iliac  and  hypo- 
gastric regions;  its  position  varies  with  its  degree  of  distension,  but  the  midpoint 
of  a  line  drawn  from  the  right  anterior  superior  iliac  spine  to  the  upper  margin  of 
the  symphysis  pubis  will  mark  approximately  the  middle  of  its  lower  border. 

The  position  of  the  base  of  the  vermiform  process  is  indicated  by  a  point  on  the 
lateral  line  on  a  level  with  the  anterior  superior  iliac  spine. 

Ascending  Colon. — The  ascending  colon  passes  upward  through  the  right 
lumbar  region,  lateral  to  the  right  lateral  line.  The  right  colic  flexure  is  situated  in 
the  upper  and  right  angle  of  intersection  of  the  subcostal  and  right  lateral  lines. 

Transverse  Colon. — The  transverse  colon  crosses  the  abdomen  on  the  confines 
of  the  umbilical  and  epigastric  regions,  its  lower  border  being  on  a  level  slightly 


1320  SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


above  the  umbilicus,  its  upper  border  just  below  the  greater  curvature  of  th(j 
stomach. 

Descending  Colon. — The  left  colic  flexure  is  situated  in  the  upper  left  angle  of 
the  intersection  between  the  left  lateral  and  transpyloric  lines.  The  descending 
colon  courses  down  through  the  left  lumbar  region,  lateral  to  the  left  lateral  line, 
as  far  as  the  iliac  crest  (see  footnote  p.  1181). 

Hiac  Colon. — The  line  of  the  iliac  colon  is  from  the  end  of  the  descending  colon 
to  the  left  lateral  line  at  the  level  of  the  anterior  superior  iliac  spine. 

Liver  (Fig.  1223). — The  upper  limit  of  the  right  lobe  of  the  liver,  in  the  middle 
line,  is  at  the  level  of  the  junction  between  the  body  of  the  sternum  and  the  xiphoid 
process;  on  the  right  side  the  line  must  be  carried  upward  as  far  as  the  fifth  costal 
cartilage  in  the  mammary  line,  and  then  downward  to  reach  the  seventh  rib  at 
the  side  of  the  thorax.  The  upper  limit  of  the  left  lobe  can  be  defined  by  continuing 
this  line  downward  and  to  the  left  to  the  sixth  costal  cartilage,  5  cm.  from  the 
middle  line.  The  lower  limit  can  be  indicated  by  a  line  drawn  1  cm.  below  the 
lower  margin  of  the  thorax  on  the  right  side  as  far  as  the  ninth  costal  cartilage, 
thence  obliquely  upward  to  the  eighth  left  costal  cartilage,  crossing  the  middle 
line  just  above  the  transpyloric  plane  and  finally,  with  a  slight  left  convexity,  to 
the  end  of  the  line  indicating  the  upper  limit. 

According  to  Birmingham  the  limits  of  the  normal  liver  may  be  marked  out 
on  the  surface  of  the  body  in  the  following  manner.  Take  three  points:  (a)  1.25 
cm.  below  the  right  nipple;  (6)  1.25  cm.  below  the  tip  of  the  tenth  rib;  (c)  2.5  cm. 
below  the  left  nipple.  Join  (a)  and  (c)  by  a  line  slightly  convex  upward ;  (a)  and 
(6)  by  a  line  slightly  convex  lateralward ;  and  (b)  and  (c)  by  a  line  slightly  convex 
downward. 

The  fundus  of  the  gall-bladder  approaches  the  surface  behind  the  anterior 
end  of  the  ninth  right  costal  cartilage  close  to  the  lateral  margin  of  the  Rectus 
abdominis. 

Pancreas  (Fig.  1225). — The  pancreas  lies  in  front  of  the  second  lumbar  vertebra. 
Its  head  occupies  the  curve  of  the  duodenum  and  is  therefore  indicated  by  the  same 
lines  as  that  viscus;  its  neck  corresponds  to  the  pylorus.  Its  body  extends  along 
the  transpyloric  line,  the  bulk  of  it  lying  above  this  line  to  the  tail  which  is  in  the 
left  hypochondriac  region  slightly  to  the  left  of  the  lateral  line  and  above  the 
transpyloric. 

Spleen  (Figs.  1217,  1226). — To  map  out  the  spleen  the  tenth  rib  is  taken  as 
representing  its  long  axis;  vertically  it  is  situated  between  the  upper  border  of  the 
ninth  and  the  lower  border  of  the  eleventh  ribs.  The  highest  point  is  4  cm,  from 
the  middle  line  of  the  back  at  the  level  of  the  tip  of  the  ninth  thoracic  spinous 
process;  the  lowest  point  is  in  the  midaxillary  line  at  the  level  of  the  first  lumbar 
spinous  process. 

Kidneys  (Figs.  1225,  1226). — The  right  kidney  usually  lies  about  1  cm.  lower 
than  the  left,  but  for  practical  purposes  similar  surface  markings  are  taken  for 
each. 

On  the  front  of  the  abdomen  the  upper  pole  lies  midway  between  the  plane  of 
the  lower  end  of  the  body  of  the  sternum  and  the  transpyloric  plane,  5  cm.  from 
the  middle  line.  The  lower  pole  is  situated  midway  between  the  transpyloric 
and  intertubercular  planes,  7  cm.  from  the  middle  line.  The  hilum  is  on  the 
transpyloric  plane,  5  cm.  from  the  middle  line.  Round  these  three  points  a 
kidney-shaped  figure  4  cm.  to  5  cm.  broad  is  drawn,  two-thirds  of  which  lies  medial 
to  the  lateral  line.  To  indicate  the  position  of  the  kidney  from  the  back,  the 
parallellogram  of  Morris  is  used;  two  vertical  lines  are  drawn,  the  first  2.5  cm., 
the  second  9.5  cm.  from  the  middle  line;  the  parallelogram  is  completed  by  two 
horizontal  lines  drawn  respectively  at  the  levels  of  the  tips  of  the  spinous  process 
of  the  eleventh  thoracic  and  the  lower  border  of  the  spinous  process  of  the  third 


I 


SURFACE  MARKINGS  OF  THE  ABDOMEN 


1321 


lumbar  vertebra.     The  hilum  is  5  cm.  from  the  middle  line  at  the  level  of  the 

I    spinous  process  of  the  first  lumbar  vertebra. 
L      Ureters. — -On  the  front  of  the  abdomen,  the  line  of  the  ureter  runs  from  the 

hilum  of  the  kidney  to  the  pubic  tubercle;  on  the  back,  from  the  hilum  vertically 

downward,      passing      practically 

through  the  posterior  superior  iliac  '""       i'' '      - 

,.  spine  (Fig.  1226). 
|P      Vessels  (Fig.  1227)  .—The  inferior 

epigastric  artery  can  be  marked  out 

by  a  line  from  a  point  midway  be- 
I  tween  the  anterior  superior  iliac 
'^  spine  and  the  pubic  symphysis  to 

the  umbilicus.    This  line  also  indi- 
cates the  lateral  boundary  of  Hessel- 

bach's  triangle — an  area  of  impor- 
tance in  connection  with  inguinal 

hernia;  the  other  boundaries  are  the 

lateral  edge  of  Rectus  abdominis, 

and  the  medial  half  of  the  inguinal 

ligament.    The  line  of  the  abdominal 

aorta  begins  in  the  middle  line  about 

4  cm.  above  the  transpyloric  line 

and  extends  to  a  point  2  cm.  below 

and  to  the  left  of  the  umbilicus^ — 

or  more  accurately  to  a  point  2  cm. 


Fig.  1226. — Back  of  lumbar  region,  showing  surface  markings 
for  kidneys,  ureters,  and  spleen.  The  lower  portions  of  the  lung 
and  pleura  are  shown  on  the  right  side. 

to  the  left  of  the  middle  line  on  a  line  which 


passes  through  the  highest  points  of  the  iliac  crests  (A  A',  Fig.   1227).     The 


TYanspylorit 
plane. 


Abdominal  inguinal  ring 
Subcutaneous  inguinal  ring 

Femoral  ring 
Fig.  1227. — Front  of  abdomen,  showing  surface  markings  for  arteries  and  inguinal  canal. 

point  of  termination  of  the  abdominal  aorta  corresponds  to  the  level  of  the  fourth 
lumbar  vertebra;  a  line  drawn  from  it  to  a  point  midway  between  the  anterior 
superior  iliac  spine  and  the  symphysis  pubis  indicates  the  common  and  external 


1322  SURFACE  ANATOMY  AND  SURFACE  MARKINGS 

iliac  arteries.  The  common  iliac  is  represented  by  the  upper  third  of  this  line,  the 
external  iliac  by  the  remaining  two-thirds. 

Of  the  larger  branches  of  the  abdominal  aorta,  the  celiac  artery  is  4  cm.,  the 
superior  mesenteric  2  cm.  above  the  transpyloric  line;  the  renal  arteries  are  2  cm. 
below  the  same  line.  The  inferior  mesenteric  artery  is  4  cm.  above  the  bifurcation 
of  the  abdominal  aorta. 

Nerves. — The  thoracic  nerves  on  the  anterior  abdominal  wall  are  represented  by 
lines  continuing  those  of  the  bony  ribs.  The  termination  of  the  seventh  nerve  is 
at  the  level  of  the  xiphoid  process,  the  tenth  reaches  the  vicinity  of  the  umbilicus, 
the  twelfth  ends  about  midway  between  the  umbilicus  and  the  upper  border  of 
the  symphysis  pubis.  The  first  lumbar  is  parallel  to  the  thoracic  nerves;  its  ilio- 
hypogastric branch  becomes  cutaneous  above  the  subcutaneous  inguinal  ring;  its 
ilioinguinal  branch  at  the  ring. 

SURFACE  ANATOMY  OF  THE  PERINEUM. 

Skin. — In  the  middle  line  of  the  posterior  part  of  the  perineum  and  about  4  cm. 
in  front  of  the  tip  of  the  coccyx  is  the  anal  orifice.  The  junction  of  the  mucous 
membrane  of  the  anal  canal  w^ith  the  skin  of  the  perineum  is  marked  by  a  white 
line  which  indicates  also  the  line  of  contact  of  the  external  and  internal  Sphincters. 
In  the  anterior  part  of  the  perineum  the  external  genital  organs  are  situated. 
The  skin  covering  the  scrotum  is  rough  and  corrugated,  but  over  the  penis  it  is 
smooth;  extending  forward  from  the  anus  on  to  the  scrotum  and  penis  is  a  median 
ridge  which  indicates  the  scrotal  raphe.  In  the  female  are  seen  the  skin  reduplica- 
tions forming  the  labia  majora  and  minora  laterally,  the  frenulum  of  the  labia 
behind,  and  the  prepuce  of  the  clitoris  in  front;  still  more  anteriorly  is  the  mons 
pubis. 

Bones. — In  the  antero-lateral  boundaries  of  the  perineum,  the  whole  outline 
of  the  pubic  arch  can  be  readily  traced  ending  in  the  ischial  tuberosities.  Behind 
in  the  middle  line  is  the  tip  of  the  coccyx. 

Muscles  and  Ligaments. — ^The  margin  of  the  Glutaeus  maximus  forms  the  postero- 
lateral boundary,  and  in  thin  subjects,  by  pressing  deeply,  the  sacrotuberous 
ligament  can  be  felt  through  the  muscle.  The  only  other  muscles  influencing 
surface  form  are  the  Ischiocavernosus  covering  the  crus  penis,  which  lies  on  the  side 
of  the  pubic  arch,  and  the  Sphincter  ani  extemus,  which,  in  action,  closes  the  anal 
orifice  and  causes  a  puckering  of  the  skin  around  it. 

SURFACE  MARKINGS  OP  THE  PERINEUM. 

A  line  drawn  transversely  across  in  front  of  the  ischial  tuberosities  divides  the 
perineum  into  a  posterior  or  rectal,  and  an  anterior  or  urogenital,  triangle.  This 
line  passes  through  the  central  point  of  the  perineum,  which  is  situated  about 
2.5  cm.  in  front  of  the  center  of  the  anal  aperture  or,  in  the  male,  midway  between 
the  anus  and  the  reflection  of  the  skin  on  to  the  scrotum. 

Rectum  and  Anal  Canal. — A  finger  inserted  through  the  anal  orifice  is  grasped 
by  the  Sphincter  ani  externus,  passes  into  the  region  of  the  Sphincter  ani  internus, 
and  higher  up  encounters  the  resistance  of  the  Puborectalis;  beyond  this  it  may 
reach  the  lowest  of  the  transverse  rectal  folds.  In  front,  the  urethral  bulb  and 
membranous  part  of  the  urethra  are  first  identified,  and  then  about  4  cm.  above 
the  anal  orifice  the  prostate  is  felt;  beyond  this  the  vesiculse  seminales,  if  enlarged, 
and  the  fundus  of  the  bladder,  when  distended,  can  be  recognized.  On  either  side 
is  the  ischiorectal  fossa.  Behind  are  the  anococcygeal  body,  the  pelvic  surfaces 
of  the  coccyx  and  lower  end  of  the  sacrum,  and  the  sacrospinous  ligaments  (Fig. 
1228). 


I 


SURFACE  MARKINGS  OF  THE  PERINEUM 


1323 


In  the  female  the  posterior  wall  and  fornix  of  the  vagina,  and  the  cervix  and 
body  of  the  uterus  can  be  felt  in  front,  while  somewhat  laterally  the  ovaries  can 
just  be  reached. 


Ureter 


Dtictiis  deferens 


Urethra 


External  urethral 
orifice 


Sacrum 


Rectovesical 
excavation 


Coccyx 

Ejaculatory  duct 
Anal  canal 


Fig.   1228. — Median  sagittal  section  of  male  pelvis. 


Male  Urogenital  Organs. — ^The  corpora  cavernosa  penis  can  be  followed  backward 
to  the  crura  which  are  attached  to  the  sides  of  the  pubic  arch.  The  glans  penis, 
covered  by  the  prepuce,  and  the  external  urethral  orifice  can  be  examined,  and  the 
course  of  the  urethra  traced  along  the  under  surface  of  the  penis  to  the  bulb  which 
is  situated  immediately  in  front  of  the  central  point  of  the  perineum.  Through 
the  wall  of  the  scrotum  on  either  side  the  testis  can  be  palpated;  it  lies  toward 
the  back  of  the  scrotum,  and  along  its  posterior  border  the  epididymis  can  be  felt; 
passing  upward  along  the  medial  side  of  the  epididymis  is  the  spermatic  cord, 
which  can  be  traced  upward  to  the  subcutaneous  inguinal  ring. 

By  means  of  a  sound  the  general  topography  of  the  urethra  and  bladder  can 
be  investigated ;  with  the  urethroscope  the  interior  of  the  urethra  can  be  illuminated 
and  viewed  directly;  with  the  cystoscope  the  interior  of  the  bladder  is  in  a  similar 
manner  illuminated  for  visual  examination.  In  the  bladder  the  main  points  to 
which  attention  is  directed  are  the  trigone,  the  loras  uretericus,  the  plicae  uretericse, 
and  the  openings  of  the  ureters  and  urethra  (see  Fig.  1240). 

Female  Urogenital  Organs. — In  the  pudendal  cleft  (Fig.  1229)  between  the  labia 
minora  are  the  openings  of  the  vagina  and  urethra.  In  the  virgin  the  vaginal  open- 
ing is  partly  closed  by  the  hymen — after  coitus  the  remains  of  the  hymen  are  rep- 
resented by  the  carunculse  hymenales.  Between  the  hymen  and  the  frenulum  of 
the  labia  is  the  fossa  navicularis,  while  in  the  groove  between  the  hymen  and  the 
labium  minus,  on  either  side,  the  small  opening  of  the  greater  vestibular  (Bartholin's) 
gland  can  be  seen.     These  glands  when  enlarged  can  be  felt  on  either  side  of  the 


1324 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


Clitoris 


Vestibule 


External  urethral 
orifice 


Vaginal  orifice 
Hymen 


Fig.  1229. — External  genital  organs  of  female.    The  labia  minora  have  been  drawn  apart. 


Sacrum 


Coccyx 

Recto-uterine 
excavation 
External  uterine 
orifice 


Anal  catial 


Vesicouteririe 
excavation 


Urethra  -. 


Fig.   1230. — Median  sagittal  section  of  female  pelvis. 


SURFACE  ANATOMY  OF  THE  UPPER  EXTREMITY  1325 


posterior  part  of  the  vaginal  orifice.  By  inserting  a  finger  into  the  vagina  the  fol- 
lowing structures  can  be  examined  through  its  wall  (Fig.  1230).  Behind,  from 
below  upward,  are  the  anal  canal,  the  rectum,  and  the  rectouterine  excavation. 
Projecting  into  the  roof  of  the  vagina  is  the  vaginal  portion  of  the  cervix  uteri 
with  the  external  uterine  orifice;  in  front  of  and  behind  the  cervix  the  anterior 
and  posterior  vaginal  fomices  respectively  can  be  examined.  With  the  finger  in  the 
vagina  and  the  other  hand  on  the  abdominal  wall  the  whole  of  the  cervix  and 
body  of  the  uterus,  the  uterine  tubes,  and  the  ovaries  can  be  palpated.  If  a  speculum 
be  introduced  into  the  vagina,  the  walls  of  the  passage,  the  vaginal  portion  of  the 
cervix,  and  the  external  uterine  orifice  can  all  be  exposed  for  visual  examination. 
Ht  The  external  urethral  orifice  lies  in  front  of  the  vaginal  opening;  the  angular 
^  gap  in  which  it  is  situated  between  the  two  converging  labia  minora  is  termed  the 
vestibule.  The  urethral  canal  in  the  female  is  very  dilatable  and  can  be  explored 
with  the  finger.  About  2.5  cm.  in  front  of  the  external  orifice  of  the  urethra  are 
the  glans  and  prepuce  of  the  clitoris,  and  still  farther  forward  is  the  mons  pubis. 


k 


SURFACE  ANATOMY  OF  THE  UPPER  EXTREMITY. 


Skin. — The  skin  covering  the  shoulder  and  arm  is  smooth  and  very  movable 
on  the  underlying  structures.  In  the  axilla  there  are  numerous  hairs  and  many 
sudoriferous  and  sebaceous  glands.  Over  the  medial  side  and  front  of  the  forearm 
the  skin  is  thin  and  smooth,  and  contains  few  hairs  but  many  sudoriferous  glands; 
over  the  lateral  side  and  back  of  the  arm  and  forearm  it  is  thicker,  denser,  and 
contains  more  hairs  but  fewer  sudoriferous  glands.  In  the  region  of  the  olecranon 
it  is  thick  and  rough,  and  is  very  loosely  connected  to  the  underlying  tissue  so 
that  it  falls  into  transverse  wrinkles  when  the  forearm  is  extended.  At  the  front 
of  the  wrist  there  are  three  transverse  furrows  in  the  skin;  they  correspond  respec- 
tively from  above  downward  to  the  positions  of  the  styloid  process  of  the  ulna, 
the  wrist-joint,  and  the  midcarpal  joint. 

The  skin  of  the  palm  of  the  hand  differs  considerably  from  that  of  the  forearm. 
At  the  wrist  it  suddenly  becomes  hard  and  dense  and  covered  with  a  thick  layer  of 
epidermis;  on  the  thenar  eminence  these  characteristics  are  less  marked  than  else- 
where. In  spite  of  its  hardness  and  density  the  skin  of  the  palm  is  exceedingly 
sensitive  and  very  vascular,  but  it  is  destitute  of  hairs  and  sebaceous  glands.  It 
is  tied  down  by  fibrous  bands  along  the  lines  of  flexion  of  the  digits,  exhibiting 
certain  furrows  of  a  permanent  character.  One  of  these,  starting  in  front  of  the 
wrist  at  the  tuberosity  of  the  navicular  bone,  curves  around  the  thenar  eminence 
and  ends  on  the  radial  border  of  the  hand  a  little  above  the  metacarpophalangeal 
joint  of  the  index  finger.  A  second  line  begins  at  the  end  of  the  first  and  extends 
obliquely  across  the  palm  to  reach  the  ulnar  border  about  the  middle  of  the  fifth 
metacarpal  bone.  A  third  line  begins  at  the  ulnar  border  about  2.5  cm.  distal  to 
the  end  of  the  second  and  extends  across  the  heads  of  the  fifth,  fourth,  and  third 
metacarpal  bones.  The  proximal  segments  of  the  fingers  are  joined  to  one  another 
on  the  volar  aspect  by  folds  of  skin  constituting  the  "web"  of  the  fingers;  these 
folds  extend  across  about  the  level  of  the  centers  of  the  proximal  phalanges  and  their 
free  margins  are  continuous  with  the  transverse  furrows  at  the  roots  of  the  fingers. 
Since  the  web  is  confined  to  the  volar  aspect  the  fingers  appear  shorter  when  viewed 
^  from  in  front  than  from  behind. 

I-  Over  the  fingers  and  thumb  the  skin  again  becomes  thinner,  especially  at  the 
'  flexures  of  the  joints  (where  it  is  crossed  by  transverse  furrows)  and  over  the  ter- 
minal phalanges;  it  is  disposed  on  numerous  ridges  in  consequence  of  the  arrange- 
ment of  the  papillae  in  it.  These  ridges  form,  in  different  individuals,  distinctive 
and  permanent  patterns  which  can  be  used  for  purposes  of  identification.  The 
superficial  fascia  in  the  palm  of  the  hand  is  made  up  of  dense  fibro-fattj'  tissue  which 


i_ 


1326  SURFACE  ANATOMY  AND  SURFACE  MARKINGS 

binds  the  skin  so  firmly  to  the  palmar  aponeurosis  that  very  little  movement  is 
permitted  between  the  two. 

On  the  back  of  the  hand  and  fingers  the  subcutaneous  tissue  is  lax,  so  that  the 
skin  is  freely  movable  on  the  underlying  parts.  Over  the  interphalangeal  joints 
the  skin  is  very  loose  and  is  thrown  into  transverse  wrinkles  when  the  fingers 
are  extended. 

Bones. — The  clavicle  can  be  felt  throughout  its  entire  length.  The  enlarged 
sternal  extremity  projects  above  the  upper  margin  of  the  sternum  at  the  side  of 
the  jugular  notch,  and  from  this  the  body  of  the  bone  can  be  traced  lateralward 
immediately  under  the  skin.  The  medial  part  is  convex  forward,  but  the  surface 
is  partially  obscured  by  the  attachments  of  Sternocleidomastoideus  and  Pectoralis 
major;  the  lateral  third  is  concave  forward  and  ends  at  the  acromion  of  the  scapula 
in  a  slight  enlargement.  The  clavicle  is  almost  horizontal  when  the  arm  is  lying 
by  the  side,  although  in  muscular  subjects  it  may  incline  a  little  upward  at  its 
acromial  end,  which  is  on  a  plane  posterior  to  the  sternal  end. 

The  only  parts  of  the  scapula  that  are  truly  subcutaneous  are  the  spine  and 
acromion,  but  the  coracoid  process,  the  vertebral  border,  the  inferior  angle,  and  to 
a  lesser  extent  the  axillary  border  can  also  be  readily  defined.  The  acromion  and 
spine  are  easily  recognizable  throughout  their  entire  extent,  forming  with  the 
clavicle  the  arch  of  the  shoulder.  The  acromion  forms  the  point  of  the  shoulder; 
it  joins  the  clavicle  at  an  acute  angle — the  acromial  angle — slightly  medial  to,  and 
behind  the  tip  of  the  acromion.  The  spine  can  be  felt  as  a  distinct  ridge,  marked 
'  on  the  surface  as  an  oblique  depression  which  becomes  less  distinct  and  ends  in  a 
slight  dimple  a  little  lateral  to  the  spinous  processes  of  the  vertebrae.  Below  this 
point  the  vertebral  border  can  be  traced  downward  and  lateralward  to  the  inferior 
angle,  which  can  be  identified  although  covered  by  Latissimus  dorsi.  From  the 
inferior  angle  the  axillary  border  can  usually  be  traced  upward  through  its  thick 
muscular  covering,  forming  with  its  enveloping  muscles  the  posterior  fold  of  the 
axilla.  The  coracoid  process  is  situated  about  2  cm.  below  the  junction  of  the 
intermediate  and  lateral  thirds  of  the  clavicle;  it  is  covered  by  the  anterior  border 
of  Deltoideus,  and  thus  lies  a  little  lateral  to  the  infraclavicular  fossa  or  depression 
which  marks  the  interval  between  the  Pectoralis  major  and  Deltoideus. 

The  humerus  is  almost  entirely  surrounded  by  muscles,  and  the  only  parts 
which  are  strictly  subcutaneous  are  small  portions  of  the  medial  and  lateral  epi- 
condyles;  in  addition  to  these,  however,  the  tubercles  and  a  part  of  the  head  of  the 
bone  can  be  felt  under  the  skin  and  muscles  by  which  they  are.  covered.  Of  these, 
the  greater  tubercle  forms  the  most  prominent  bony  point  of  the  shoulder,  extending 
beyond  the  acromion;  it  is  best  recognized  when  the  arm  is  lying  passive  by  the 
side,  for  if  the  arm  be  raised  it  recedes  under  the  arch  of  the  shoulder.  The  lesser 
tubercle,  directed  forw^ard,  is  medial  to  the  greater  and  separated  from  it  by  the 
intertubercular  groove,  which  can  be  made  out  by  deep  pressure.  When  the  arm 
is  abducted  the  lower  part  of  the  head  of  the  humerus  can  be  examined  by  pressing 
deeply  in  the  axilla.  On  either  side  of  the  elbow-joint  and  just  above  it  are  the 
medial  and  lateral  epicondyles.  Of  these,  the  former  is  the  more  prominent,  but  the 
medial  supracondylar  ridge  passing  upward  from  it  is  much  less  marked  than  the 
lateral,  and  as  a  rule  is  not  palpable;  occasionally,  however,  the  hook-shaped  supra- 
condylar process  (page  211)  is  found  on  this  border.  The  position  of  the  lateral 
epicondyle  is  best  seen  during  semiflexion  of  the  forearm,  and  is  indicated  by 
a  depression;  from  it  the  strongly  marked  lateral  supracondylar  ridge  runs 
upward. 

The  most  prominent  part  of  the  ulna,  the  olecranon,  can  always  be  identified  at 
the  back  of  the  elbow-joint.  When  the  forearm  is  flexed  the  upper  quadrilateral 
surface  is  palpable,  but  during  extension  it  recedes  into  the  olecranon  fossa.  During 
extension  the  upper  border  of  the  olecranon  is  slightly  above  the  level  of  the  medial 


I 


1^ 


IK 


I 


SURFACE  ANATOMY  OF  THE  UPPER  EXTREMITY  TST, 

epicondyle  and  nearer  to  this  than  to  the  lateral;  when  the  forearm  is  fully  flexed 
the  olecranon  and  the  epicondyles  form  the  angles  of  an  equilateral  triangle.  On 
the  back  of  the  olecranon  is  a  smooth  triangular  subcutaneous  surface,  and  running 
down  the  back  of  the  forearm  from  the  apex  of  this  triangle  the  prominent  dorsal 
border  of  the  ulna  can  be  felt  in  its  Avhole  length:  it  has  a  sinuous  outline,  and  is 
situated  in  the  middle  of  the  back  of  the  limb  above;  but  below,  where  it  is  rounded 
off,  it  can  be  traced  to  the  small  subcutaneous  surface  of  the  styloid  process  on  the 
medial  side  of  the  wrist.  The  styloid  process  forms  a  prominent  tubercle  continuous 
above  with  the  dorsal  border  and  ending  below  in  a  blunt  apex  at  the  level  of  the 
wrist-joint;  it  is  most  evident  when  the  hand  is  in  a  position  midway  between 
supination  and  pronation.  When  the  forearm  is  pronated  another  prominence, 
the  head  of  the  ulna,  appears  behind  and  above  the  styloid  process. 

Below  the  lateral  epicondyle  of  the  humerus  a  portion  of  the  head  of  the  radius 
is  palpable;  its  position  is  indicated  on  the  surface  by  a  little  dimple,  which  is  best 
seen  when  the  arm  is  extended.  If  the  finger  be  placed  in  this  dimple  and  the 
semiflexed  forearm  be  alternately  pronated  and  supinated  the  head  of  the  radius 
will  be  felt  distinctly,  rotating  in  the  radial  notch.  The  upper  half  of  the  body  of 
the  bone  is  obscured  by  muscles;  the  lower  half,  though  not  subcutaneous,  can  be 
readily  examined,  and  if  traced  downward  is  found  to  end  in  a  lozenge-shaped  con- 
vex surface  on  the  lateral  side  of  the  base  of  the  styloid  process;  this  is  the  only 
subcutaneous  part  of  the  bone,  and  from  its  lower  end  the  apex  of  the  styloid  process 
bends  medialward  toward  the  wrist.  About  the  middle  of  the  dorsal  surface  of 
the  lower  end  of  the  radius  is  the  dorsal  radial  tubercle,  best  perceived  when  the 
wrist  is  slightly  flexed;  it  forms  the  lateral  boundary  of  the  oblique  groove  for  the 
tendon  of  Extensor  pollicis  longus. 

On  the  front  of  the  wrist  are  two  subcutaneous  eminences,  one,  on  the  radial 
side,  the  larger  and  flatter,  produced  by  the  tuberosity  of  the  navicular  and  the  ridge 
on  the  greater  multangular;  the  other,  on  the  ulnar  side,  by  the  pisiform.  The  tuber- 
osity of  the  navicular  is  distal  and  medial  to  the  styloid  process  of  the  radius,  and 
is  most  clearly  visible  when  the  wrist-joint  is  extended;  the  ridge  on  the  greater 
multangular  is  about  1  cm.  distal  to  it.  The  pisiform  is  about  1  cm.  distal  to  the 
lower  end  of  the  ulna  and  just  distal  to  the  level  of  the  styloid  process  of  the  radius; 
it  is  crossed  by  the  uppermost  crease  which  separates  the  front  of  the  forearm  from 
the  palm  of  the  hand.  The  rest  of  the  volar  surface  of  the  bony  carpus  is  covered 
by  tendons  and  the  transverse  carpal  ligament,  and  is  entirely  concealed,  with 
the  exception  of  the  hamulus  of  the  hamate  bone,  which,  however,  is  difficult  to 
define.  On  the  dorsal  surface  of  the  carpus  only  the  triangular  bone  can  be  clearly 
iinade  out. 

Distal  to  the  carpus  the  dorsal  surfaces  of  the  metacarpal  bones,  covered  by  the 
Extensor  tendons,  except  the  fifth,  are  visible  only  in  very  thin  hands;  the  dorsal 
surface  of  the  fifth  is,  however,  subcutaneous  throughout  almost  its  whole  length. 
Slightly  lateral  to  the  middle  line  of  the  hand  is  a  prominence,  frequently  well- 
marked,  but  occasionally  indistinct,  formed  by  the  styloid  process  of  the  third 
metacarpal  bone;  it  is  situated  about  4  cm.  distal  to  the  dorsal  radial  tubercle. 
The  heads  of  the  metacarpal  bones  can  be  plainly  seen  and  felt,  rounded  in  contour 
and  standing  out  in  bold  relief  under  the  skin  when  the  fist  is  clenched;  the  head 
of  the  third  is  the  most  prominent.  In  the  palm  of  the  hand  the  metacarpal  bones 
are  covered  by  muscles,  tendons,  and  aponeuroses,  so  that  only  their  heads  can  be 
distinguished.  The  base  of  the  metacarpal  bone  of  the  thumb,  however,  is  promi- 
nent dorsally,  distal  to  the  styloid  process  of  the  radius;  the  body  of  the  bone  is 
easily  palpable,  ending  at  the  head  in  a  flattened  prominence,  in  front  of  which 
are  the  sesamoid  bones. 

The  enlarged  ends  of  the  phalanges  can  be  easily  felt.  When  the  digits  are 
bent  the  proximal  phalanges  form  prominences,  which  in  the  joints  between  the 


[NDSURFACE  MARKINGS 


I 


first  and  second  phalanges  are  slightly  hollow,  but  flattened  and  square-shaped  in 
those  between  the  second  and  third. 

Articulations. — The  sternoclavicular  joint  is  subcutaneous,  and  its  position  is 
indicated  by  the  enlarged  sternal  extremity  of  the  clavicle,  lateral  to  the  long 
cord-like  sternal  head  of  Sternocleidomastoideus.  If  this  muscle  be  relaxed  a 
depression  between  the  end  of  the  clavicle  and  the  sternum  can  be  felt,  defining 
the  exact  position  of  the  joint. 

The  position  of  the  acromioclavicular  joint  can  generally  be  ascertained  by 
determining  the  slightly  enlarged  acromial  end  of  the  clavicle  which  projects  above 
the  level  of  the  acromion;  sometimes  this  enlargement  is  so  considerable  as  to 
form  a  rounded  eminence. 

The  shoulder-joint  is  deeply  seated  and  cannot  be  palpated.  If  the  forearm 
be  slightly  flexed  a  curved  crease  or  fold  with  its  convexity  downward  is  seen  in 
front  of  the  elbow,  extending  from  one  epicondyle  to  the  other;  the  elbow-joint 
is  slightly  distal  to  the  center  of  the  fold.  The  position  of  the  radiohumeral  joint 
can  be  ascertained  by  feeling  for  a  slight  groove  or  depression  between  the  head 
of  the  radius  and  the  capitulum  of  the  humerus,  at  the  back  of  the  elbow-joint. 

The  position  of  the  proximal  radioulnar  joint  is  marked  on  the  surface  at  the 
back  of  the  elbow  by  the  dimple  which  indicates  the  position  of  the  head  of  the 
radius.  The  site  of  the  distal  radioulnar  joint  can  be  defined  by  feeling  for  the 
slight  groove  at  the  back  of  the  wrist  between  the  prominent  head  of  the  ulna 
and  the  lower  end  of  the  radius,  when  the  forearm  is  in  a  state  of  almost  complete 
pronation. 

Of  the  three  transverse  skin  furrows  on  the  front  of  the  wrist,  the  middle  corre- 
sponds fairly  accurately  with  the  wrist-joint,  while  the  most  distal  indicates  the 
position  of  the  midcarpal  articulation. 

The  metacarpophalangeal  and  interphalangeal  joints  are  readily  available  for 
surface  examination;  the  former  are  situated  just  distal  to  the  prominences  of  the 
knuckles,  the  latter  are  sufficiently  indicated  by  the  furrows  on  the  volar,  and  the 
wrinkles  on  the  dorsal  surfaces. 

Muscles  (Figs.  1194, 1231, 1232). — ^The  anterior  border  of  the  Trapezius  presents  as 
a  slight  ridge  running  downward  and  forward  from  the  superior  nuchal  line  of  the 
occipital  bone  to  the  junction  of  the  intermediate  and  lateral  thirds  of  the  clavicle. 
The  inferior  border  of  the  muscle  forms  an  undulating  ridge  passing  downward 
and  medialward  from  the  root  of  the  spine  of  the  scapula  to  the  spinous  process 
of  the  twelfth  thoracic  vertebra. 

The  lateral  border  of  the  Latissimus  dorsi  (Fig.  1215)  may  be  traced,  when  the 
muscle  is  in  action,  as  a  rounded  edge  starting  from  the  iliac  crest  and  slanting 
obliquely  forward  and  upward  to  the  axilla,  where  it  takes  part  with  the  Teres 
major  in  forming  the  posterior  axillary  fold. 

The  Pector alls  major  (Fig.  1219)  conceals  a  considerable  part  of  the  thoracic  wall 
in  front.  Its  sternal  origin  presents  a  border  which  bounds,  and  determines  the 
width  of  the  sternal  furrow.  The  upper  margin  is  generally  well-marked  medially 
and  forms  the  medial  boundary  of  a  triangular  depression,  the  infraclavicular  fossa, 
which  separates  the  Pectoralis  major  from  the  Deltoideus;  it  gradually  beconaes 
less  marked  as  it  approaches  the  tendon  of  insertion  and  is  closely  blended  with 
the  Deltoideus.  The  lower  border  of  Pectoralis  major  forms  the  rounded  anterior 
axillary  fold.  Occasionally  a  gap  is  visible  between  the  clavicular  and  sternal  parts 
of  the  muscle. 

When  the  arm  is  raised  the  lowest  slip  of  origin  of  Pectoralis  minor  produces  a 
fulness  just  below  the  anterior  axillary  fold  and  serves  to  break  the  sharp  outline 
of  the  lower  border  of  Pectoralis  major. 

The  origin  of  the  Serratus  anterior  (Figs.  1215,  1219)  causes  a  very  characteristic 
surface  marking.    When  the  arm  is  abducted  the  lower  five  or  six  serrations  form 


SURFACE  ANATOMY  OF  THE  UPPER  EXTREMITY 


1329 


I 


a  zigzag  line  with  a  general  convexity  forward;  when  the  arm  is  by  the  side  the 
highest  visible  serration  is  that  attached  to  the  fifth  rib. 

The  Deltoideus  with  the  prominence  of  the  upper  end  of  the  humerus  produces 
the  rounded  contour  of  the  shoulder;  it  is  rounded  and  fuller  in  front  than  behind, 
where  it  presents  a  somewhat  flattened  form.  Above,  its  anterior  border  presents 
a  slightly  curved  eminence  which  forms  the  lateral  boundary  of  the  infraclavicular 
fossa;  below,  it  is  closely  united  with  the  Pectoralis  major.  Its  posterior  border 
is  thin,  flattened,  and  scarcely  marked  above,  but  is  thicker  and  more  prominent 
below.  The  insertion  of  Deltoideus  is  marked  by  a  depression  on  the  lateral  side 
of  the  middle  of  the  arm. 


Flex,  cai-p.  rad. 
I    Abd.  poll  long. 
I    Ext.  poll.  brev. 


Lateral  group  of 
antibrachial  muscles 

I         Brachialis 

I  j   Biceps  brachii 


Flex.  carp,  xdnaris 
Palmarin  longus 


Medfal  grotip  o. 
antibrachial  muscles 

A  nticubital  fossa 


r    *t> 


Fig.  1231. — Front  of  right  upper  extremity. 


Of  the  scapular  muscles  the  only  one  which  influences  surface  form  is  the  Teres 
major;  it  assists  the  Latissimus  dorsi  in  forming  the  thick,  rounded,  posterior 
axillary  fold. 

When  the  arm  is  raised  the  Coracobrachialis  reveals  itself  as  a  narrow  elevation 
emerging  from  under  cover  of  the  anterior  axillary  fold  and  running  medial  to  the 
body  of  the  humerus. 


Deltoideus 


Medial  eminence 


Biceps  brachii 


Lateral  eminence 


Abd.  poll.  long. 
Ext.  poll.  brev. 


Triceps  brachii  j      | 

Medial  epicondyle      I 

Olecranon 


Head  of  ulna 
[         Ext.  carp,  ulnaris 
Flex.  carp,  ulnaris 
Anconceus 


Fig.  1232. — Back  of  right  upper  extremity. 

On  the  front  and  medial  aspects  of  the  arm  is  the  prominence  of  the  Biceps 
brachii,  bounded  on  either  side  by  an  intermuscular  depression.  It  determines  the 
contour  of  the  front  of  the  arm  and  extends  from  the  anterior  axillarj-  fold  to  the 
bend  of  the  elbow;  its  upper  tendons  are  concealed  by  the  Pectoralis  major  and 
Deltoideus,  and  its  lower  tendon  sinks  into  the  anticubital  fossa.  When  the  muscle 
is  fully  contracted  it  presents  a  globular  form,  and  the  lacertus  fibrosus  attached 
84 


L 


1330  SURFACE  ANATOMY  AND  SURFACE  MARKINGS 

to  its  tendon  of  insertion  becomes  prominent  as  a  sharp  ridge  running  do'v 
and  medialward. 

On  either  side  of  the  Biceps  brachii  at  the  lower  part  of  the  arm  the  Brachiali:} 
is  discernible.  Laterally  it  forms  a  narrow  eminence  extending  some  distance  up 
the  arm;  medially  it  exhibits  only  a  little  fulness  above  the  elbow. 

On  the  back  of  the  arm  the  long  head  of  the  Triceps  brachii  may  be  seen  as  a 
longitudinal  eminence,  emerging  from  under  cover  of  Deltoideus  and  gradually' 
passing  into  the  flattened  plane  of  the  tendon  of  the  muscle  at  the  lower  part  of 
the  back  of  the  arm.  When  the  muscle  is  in  action  the  medial  and  lateral  heads 
become  prominent. 

On  the  front  of  the  elbow  are  two  muscular  elevations,  one  on  either  side,  sep- 
arate above  but  converging  below  so  as  to  form  the  medial  and  lateral  boundaries 
of  the  anticubital  fossa.  The  medial  elevation  consists  of  the  Pronator  teres  and 
the  Flexors,  and  forms  a  fusiform  mass,  p(^nted  above  at  the  medial  epicondyle 
and  gradually  tapering  off  below.  The  Pronator  teres  is  the  most  lateral  of  the 
group,  while  the  Flexor  carpi  radialis,  lying  to  its  medial  side,  is  the  most  prominent 
and  may  be  traced  downward  to  its  tendon,  which  is  situated  nearer  to  the  radial 
than  to  the  ulnar  border  of  the  front  of  the  wrist  and  medial  to  the  radial  artery. 
The  Palmaris  longus  presents  no  surface  marking  above,  but  below,  its  tendon 
stands  out  when  the  muscle  is  in  action  as  a  sharp,  tense  cord  in  front  of  the  middle 
of  the  wrist.  The  Flexor  digitorum  sublimis  does  not  directly  influence  surface 
form;  the  position  of  its  four  tendons  on  the  front  of  the  lower  part  of  the  forearm 
is  indicated  by  an  elongated  depression  between  the  tendons  of  Palmaris  longus 
and  Flexor  carpi  ulnaris.  The  Flexor  carpi  ulnaris  determines  the  contoui  of  the 
medial  border  of  the  forearm,  and  is  separated  from  the  Extensor  group  of  muscles 
by  the  ulnar  furrow  produced  by  the  subcutaneous  dorsal  border  of  the  ulna;  its 
tendon  is  evident  along  the  ulnar  border  of  the  lower  part  of  the  forearm,  and  is 
most  marked  when  the  hand  is  flexed  and  adducted. 

The  elevation  forming  the  lateral  side  of  the  anticubital  fossa  consists  of  the 
Brachioradialis,  the  Extensors  and  the  Supinator;  it  occupies  the  lateral  and  a 
considerable  part  of  the  dorsal  surface  of  the  forearm  in  the  region  of  the  elbow, 
and  forms  a  fusiform  mass  which  is  altogether  on  a  higher  level  than  that  produced 
by  the  medial  elevation..  Its  apex  is  between  the  Triceps  brachii  and  Brachialis 
some  distance  above  the  elbow-joint;  it  acquires  its  greatest  breadth  opposite  the 
lateral  epicondyle,  and  below  this  shades  off  into  a  flattened  surface.  About  the 
middle  of  the  forearm  it  divides  into  two  diverging  longitudinal  eminences.  The 
lateral  eminence  consists  of  the  Brachioradialis  and  the  Extensores  carpi  radiales 
longus  and  brevis,  and  descends  from  the  lateral  supracondylar  ridge  in  the  direction 
of  the  styloid  process  of  the  radius.  The  medial  eminence  comprises  the  Extensor 
digitorum  communis,  Extensor  digiti  quinti  proprius,  and  the  Extensor  carpi  ulnaris; 
it  begins  at  the  lateral  epicondyle  of  the  humerus  as  a  tapering  mass  which  is  sep- 
arated above  from  the  Anconseus  by  a  w^ell-marked  furrow,  and  below  from  the 
Pronator  teres  and  Flexor  group  by  the  ulnar  furrow.  The  medial  border  of  the 
Brachioradialis  starts  as  a  rounded  elevation  above  the  lateral  epicondyle;  lower 
down  the  muscle  forms  a  prominent  mass  on  the  radial  side  of  the  upper  part  of 
the  forearm;  below  it  tapers  to  its  tendon,  which  may  be  traced  to  the  styloid 
process  of  the  radius.  The  Anconseus  presents  as  a  triangular  slightly  elevated 
area,  immediately  lateral  to  the  subcutaneous  surface  of  the  olecranon  and  differ- 
entiated from  the  Extensor  group  by  an  oblique  depression;  the  upper  angle  of 
the  triangle  is  at  the  dimple  over  the  lateral  epicondyle. 

At  the  lower  part  of  the  back  of  the  forearm  in  the  interval  between  the  two 
diverging  eminences  is  an  oblique  elongated  swelling;  full  above  but  flattened 
and  partially  subdivided  below;  it  is  caused  by  the  Abductor  pollicis  longus 
and   the  Extensor  pollicis  brevis.    It  crosses  the  dorsal  and  lateral  surfaces  of 


If 


SURFACE  MARKINGS  OF  THE  UPPER  EXTREMITY  1331 

tne  radius  to  the  radial  side  of  the  wrist-joint,  whence  it  is  continued  on  to 
the  dorsal  surface  of  the  thumb  as  a  ridge  best  marked  when  the  thumb  is 
extended. 

The  tendons  of  most  of  the  Extensor  muscles  can  be  seen  and  felt  on  the  back 
of  the  wrist.  Laterally  is  the  oblique  ridge  produced  by  the  Extensor  pollicis 
longus.  The  Extensor  carpi  radialis  longus  is  scarcely  palpable,  but  the  Extensor 
carpi  radialis  brevis  can  be  identified  as  a  vertical  ridge  emerging  from  under  the 
ulnar  border  of  the  tendon  of  the  Extensor  pollicis  longus  when  the  wrist  is  extended. 
Medial  to  this  the  Extensor  tendons  of  the  fingers  can  be  felt,  the  Extensor  digiti 
quinti  proprius  being  separated  from  the  tendons  of  the  Extensor  digitorum 
communis  by  a  slight  furrow. 

The  muscles  of  the  hand  are  principally  concerned,  as  regards  surface  form,  in 
producing  the  thenar  and  hypothenar  eminences,  and  cannot  be  individually  dis- 
tinguished; the  thenar  eminence,  on  the  radial  side,  is  larger  and  rounder  than  the 
hypothenar,  which  is  a  long  narrow  elevation  along  the  ulnar  side  of  the  palm. 
When  the  Palmaris  brevis  is  in  action  it  produces  a  wrinkling  of  the  skin  over  the 
hypothenar  eminence  and  a  dimple  on  the  ulnar  border.  On  the  back  of  the  hand 
the  Interossei  dorsales  give  rise  to  elongated  swellings  between  the  metacarpal 
bones;  the  first  forms  a  prominent  fusiform  bulging  when  the  thumb  is  adducted, 
the  others  are  not  so  marked. 

Arteries. — Above  the  middle  of  the  clavicle  the  pulsation  of  the  subclavian  artery 
can  be  detected  by  pressing  downward,  backward,  and  medialward  against  the 
first  rib.  The  pulsation  of  the  axillary  artery  as  it  crosses  the  second  rib  can  be 
felt  below  the  middle  of  the  clavicle  just  medial  to  the  coracoid  process;  along  the 
lateral  wall  of  the  axilla  the  course  of  the  artery  can  be  easily  followed  close  to  the 
medial  border  of  Coracobrachialis.  The  brachial  artery  can  be  recognized  in  practi- 
cally the  whole  of  its  extent,  along  the  medial  margin  of  the  Biceps;  in  the  upper 
two-thirds  of  the  arm  it  lies  medial  to  the  humerus,  but  in  the  lower  third  is  more 
directly  on  the  front  of  the  bone.  Over  the  lower  end  of  the  radius,  between  the 
styloid  process  and  Flexor  carpi  radialis,  a  portion  of  the  radial  artery  is  superficial 
and  is  used  clinically  for  observations  on  the  pulse. 

Veins. — The  superficial  veins  of  the  upper  extremity  are  easily  rendered  visible 
by  compressing  the  proximal  trunks;  their  arrangement  is  described  on  pages  660 
to  662. 

Nerves. — The  uppermost  trunks  of  the  brachial  plexus  are  palpable  for  a  short 
distance  above  the  clavicle  as  they  emerge  from  under  the  lateral  border  of  Sterno- 
cleidomastoideus;  the  larger  nerves  derived  from  the  plexus  can  be  rolled  under  the 
finger  against  the  lateral  axillary  wall  but  cannot  be  identified.  The  ulnar  nerve 
can  be  detected  in  the  groove  behind  the  medial  epicondyle  of  the  humerus. 

SURFACE    MARKINGS    OF    THE    UPPER   EXTREMITY. 

Bony  Landmarks. — The  bony  landmarks  as  described  above  are  so  readily  avail- 
able for  surface  recognition  that  no  special  measurements  are  required  to  indicate 
them.  It  may  be  noted,  however,  that  the  medial  angle  of  the  scapula  is  applied 
to  the  second  rib,  while  the  inferior  angle  lies  against  the  seventh.  The  intertuber- 
cular  groove  of  the  humerus  is  vertically  below  the  acromioclavicular  joint  when 
the  arm  hangs  by  the  side  with  the  palm  of  the  hand  forward. 

Articulations. — The  acromioclavicular  joint  is  situated  in  a  plane  passing  sagit- 
tally  through  the  middle  line  of  the  front  of  the  arm.  The  line  of  the  elbow-joint 
is  not  straight;  the  radiohumeral  portion  is  practically  at  right  angles  to  the  long 
axis  of  the  humerus  and  is  situated  about  2  cm.  distal  to  the  lateral  epicondyle; 
the  ulnohumeral  portion  is  oblique,  and  its  medial  end  is  about  2.5  cm.  distal  to  the 
medial  epicondyle.    The  position  of  the  wrist-joint  can  be  indicated  by  drawing  a 


1332 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


curved  line,  with  its  convexity  upward,  between  the  styloid  processes  of  the  radius 
and  ulna;  the  summit  of  the  convexity  is  about  1  cm.  above  the  center  of  a  straight 
line  joining  the  two  processes. 


SheatTis  of  terminal 
parts  of  Flexorea 
digitarum 


Musdea  of  thenar 
eminerice 


Sheath  of  Flexor 
pollicis  longtis 


Sheath  of  Flexor  carpi 
radialis 


Muscles  of  hypo- 
thenar  eminence 


Common  sheath  of 
Flexores  digitorum, 
svblimis  and 
profundics 


Flexor  carpi  ulnaris 


Fio.   1233. — The  mucous  sheaths  of  the  tendons  on  the  front  of  the  wrist  and  digits. 

Muscles. — The  only  muscles  of  the  upper  extremity  which  occasionally  require 
definition  by  surface  lines  are  the  Trapezius,  the  Latissimus  dorsi,  and  the  Pectorales 
major  and  minor.  The  antero-superior  border  of  Trapezius  is  indicated  by  a  line 
from  the  superior  nuchal  line  about  3  cm.  lateral  to  the  external  occipital  protuber- 
ance to  the  junction  of  the  intermediate  and  lateral  thirds  of  the  clavicle;  the  line 
of  the  lower  border  extends  from  the  spinous  process  of  the  twelfth  thoracic  vertebra 
to  the  vertebral  border  of  the  scapula  at  the  root  of  the  spine.    The  upper  border 


SURFACE  MARKINGS  OF  THE  UPPER  EXTREMITY 


1333 


of  Latissimus  dorsi  is  almost  horizontal,  running  from  the  spinous  process  of  the 
seventh  thoracic  vertebra  to  the  inferior  angle  of  the  scapula  and  thence  somewhat 
obliquely  to  the  intertubercular  sulcus  of  the  humerus ;  the  lower  border  corresponds 
roughly  to  a  line  drawn  from  the  iliac  crest  about  2  cm.  from  the  lateral  margin  of 


Abd.  poll,  long. 


b 


Ext.  carp.  rod.  long. 
Ext.  carp.  rod.  brev. 


Fig.  1234. — The  mucous  sheatha  of  the  tendons  on  the  back  of  the  wrist. 

the  Sacrospinalis  to  the  intertubercular  sulcus.  The  upper  margin  of  Pectoralis 
major  extends  from  the  middle  of  the  clavicle  to  the  surgical  neck  of  the  humerus; 
its  lower  border  is  practically  in  the  line  of  the  fifth  rib  and  reaches  from  the  fifth 
costochondral  junction  to  the  middle  of  the  anterior  border  of  Deltoideus.  The 
two  lines  indicating  the  borders  of  Pectoralis  minor  begin  at  the  coracoid  process 


l_ 


1334 


SURFACE  ANATOMY  A\ 


mRFACE  MARKINGS 


of  the  scapula  and  extend  to  the  third  and  fifth  ribs  respectively,  just  lateral  to  the 
corresponding  costal  cartilages.  On  the  front  of  the  elbow-joint  a  triangular  space 
— the  anticubital  fossa — is  mapped  out  for  convenience  of  reference.  The  base  of 
the  triangle  is  a  line  joining  the  medial  and  lateral  epicondyles,  while  the  sides  are 
formed  respectively  by  the  salient  margins  of  the  Brachioradialis  and  Pronatof, 
teres. 


I 


Fia.  1235. — Front  of  right  upper  extremity,  showing  surface  markings  for  bones,  arteries,  and  nerves. 

Mucous  Sheaths. — On  the  volar  surfaces  of  the  wrist  and  hand  the  mucous 
sheaths  of  the  Flexor  tendons  (Fig.  1233)  can  be  indicated  as  follows.  The  sheath 
for  Flexor  pollicis  longus  extends  from  about  3  cm.  above  the  upper  edge  of  the 
transverse  carpal  ligament  to  the  terminal  phalanx  of  the  thumb.  The  common 
sheath  for  the  Flexores  digitorum  reaches  about  3.5  to  4  cm.  above  the  upper  edge 
of  the  transverse  carpal  ligament  and  extends  on  the  palm  of  the  hand  to  about 
the  level  of  the  centers  of  the  metacarpal  bones.  The  sheath  for  the  tendons  to  the 
little  finger  is  continued  from  the  common  sheath  to  the  base  of  the  terminal  phalanx 
of  this  finger;  the  sheaths  for  the  tendons  of  the  other  fingers  are  separated  from 
the  common  sheath  by  an  interval;  they  begin  opposite  the  necks  of  the  meta- 
carpal bones  and  extend  to  the  terminal  phalanges.  The  mucous  sheaths  of  the 
Extensor  tendons  are  shown  in  Fig.  1234  (see  also  page  459). 


Fig.   1236. — Back  of  right  upper  extremity,  showing  surface  markings  for  bones  and  nerves. 

Arteries  (Fig.  1235). — The  course  of  the  axillary  artery  can  be  marked  out  by 
abducting  the  arm  to  a  right  angle  and  drawing  a  line  from  the  middle  of  the 
clavicle  to  the  point  where  the  tendon  of  the  Pectoralis  major  crosses  the  promi- 
nence of  the  Coracobrachialis.  Of  the  branches  of  the  axillary  artery,  the  origin 
of  the  thoracoacromial  corresponds  to  the  point  where  the  artery  crosses  the 
upper  border  of  Pectoralis  minor;  the  lateral  thoracic  takes  practically  the  line  of 
the  lower  border  of  Pectoralis  minor;  the  subscapular  is  sufficiently  indicated  by 


SURFACE  MARKINGS  OF  THE  UPPER  EXTREMITY 


1335 


i 

m 


MY 


l» 


the  axillary  border  of  the  scapula;  the  scapular  circumflex  is  given  off  the  sub- 
scapular opposite  the  midpoint  of  a  line  joining  the  tip  of  the  acromion  to  the 
lower  edge  of  the  deltoid  tuberosity',  while  the  humeral  circumflex  arteries  arise 
from  the  axillary  about  2  cm.  above  this.  The  position  of  the  brachial  artery  is 
marked  by  a  line  drawn  from  the  junction  of  the  anterior  and  middle  thirds  of  the 
distance  between  the  anterior  and  posterior  axillary  folds  to  a  point  midway 
between  the  epicondyles  of  the  humerus  and  continued  distally  for  2.5  cm.,  at 
which  point  the  artery  bifurcates.  With  regard  to  the  branches  of  the  brachial 
artery — the  profunda  crosses  the  back  of  the  humerus  at  the  level  of  the  insertion 
of  Deltoideus;  the  nutrient  is  given  off  opposite  the  middle  of  the  body  of  the 
humerus;  a  line  from  this  point  to  the  back  of  the  medial  condyle  represents 
the  superior  ulnar  collateral ;  the  inferior  ulnar  collateral  is  given  off  about  5  cm. 
above  the  fold  of  the  elbow-joint  and  runs  directly  medial  ward. 

The  position  of  the  radial  artery  in  the  forearm  is  represented  by  a  line  from  the 
lateral  margin  of  the  Biceps  tendon  in  the  center  of  the  anticubital  fossa  to  the 
medial  side  of  the  front  of  the  styloid  process  of  the  radius  when  the  limb  is 
in  the  position  of  supination.  The  situation  of  the  distal  portion  of  the  artery 
is  indicated  by  continuing  this  line 
around  the  radial  side  of  the  wrist 
to  the  proximal  end  of  the  first  inter- 
metacarpal space. 

On  account  of  the  curved  direction 
of  the  ulnar  artery,  two  lines  are  re- 
quired to  indicate  its  course;  one  is 
drawn  from  the  front  of  the  medial 
epicondyle  to  the  radial  side  of  the 
pisiform  bone;  the  lower  two-thirds 
of  this  line  represents  two-thirds  of 
the  artery;  the  upper  third  is  repre- 
sented by  a  second  line  from  the  center 
of  the  hollow  in  front  of  the  elbow- 
joint  to  the  junction  of  the  upper  and 
middle  thirds  of  the  first  line. 

The  superficial  volar  arch  (Fig.  1237) 
•can  be  indicated  by  a  line  starting 
from  the  radial  side  of  the  pisiform 
bone  and  curving  distalward  and 
lateralward  as  far  as  the  base  of  the 
thumb,  with  its  convexity  toward  the 
fingers.  The  summit  of  the  arch  is 
usually  on  a  level  with  the  ulnar 
border  of  the  outstretched  thumb. 
The  deep  volar  arch  is  practically 
transverse,  and  is  situated  about  1 
cm.  nearer  to  the  carpus. 

Nerves  (Figs.  1235,  1236).— In  the 
arm  the  line  of  the  median  nerve  is 
practically  the  same  as  that  for  the 
brachial  artery;  at  the  bend  of  the 
elbow  the   nerve    is   medial  to    the 

artery.  The  course  of  the  nerve  in  the  forearm  is  marked  by  a  line  starting 
from  a  point  just  medial  to  the  center  of  one  joining  the  epicondyles,  and  ex- 
tending to  the  lateral  margin  of  the  tendon  of  Palmaris  longus  at  the  wrist. 

The  ulnar  nerve  follows  the  line  of  the  brachial  artery  in  the  upper  half  of  the 


Radial  artery  — 


Fig.  1237.— Palm  of  left  hand, 
creases  and  bones,  and  surface 
arches. 


Ulnar 
artery 


showing  position  of  skin 
markings    for    the   volar 


1336  SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


arm,  but  at  the  middle  of  the  arm  it  diverges  and  descends  to  the  back  of  the 
medial  epicondyle.  In  the  forearm  it  is  represented  by  a  line  from  the  front 
of  the  medial  epicondyle  to  the  radial  side  of  the  pisiform  bone. 

The  course  of  the  radial  nerve  can  be  indicated  by  a  line  from  just  below  the 
posterior  axillary  fold,  to  the  lateral  side  of  the  humerus  at  the  junction  of  its 
middle  and  lower  thirds;  thence  it  passes  vertically  downward  on  the  front  of 
the  arm  to  the  level  of  the  lateral  epicondyle.  The  course  of  the  superficial 
radial  nerve  is  represented  by  a  continuation  of  this  line  downward  to  the  junction 
of  the  middle  and  lower  thirds  of  the  radial  artery ;  it  then  crosses  the  radius  and 
runs  distalward  to  the  dorsum  of  the  base  of  the  first  metacarpal  bone. 

The  axillary  nerve  crosses  the  humerus  about  2  cm.  above  the  center  of  a  line 
joining  the  tip  of  the  acromion  to  the  lower  edge  of  the  deltoid  tuberosity. 

SURFACE    ANATOMY    OF    THE   LOWER   EXTREMITY. 

Skin. — The  skin  of  the  thigh,  especially  in  the  hollow  of  the  groin  and  on  the 
medial  side,  is  thin,  smooth  and  elastic,  and  contains  few  hairs  except  on  the  neigh- 
borhood of  the  pubis.  Laterally  it  is  thicker  and  the  hairs  are  more  numerous. 
The  junction  of  the  skin  of  the  thigh  with  that  on  the  front  of  the  abdomen  is 
marked  by  a  well-defined  furrow  which  indicates  the  site  of  the  inguinal  ligament; 
the  furrow  presents  a  general  convexity  downward,  but  its  medial  half,  which  is 
the  better  marked,  is  nearly  straight.  The  skin  over  the  buttock  is  fairly  thick 
and  is  characterized  by  its  low  sensibility  and  slight  vascularity;  as  a  rule  it  is 
destitute  of  conspicuous  hairs  except  toward  the  post-anal  furrow,  where  in  some 
males  they  are  abundantly  developed.  An  almost  transverse  fold — the  gluteal 
fold — crosses  the  lower  part  of  the  buttock;  it  practically  bisects  the  lower  margin 
of  the  Glutseus  maximus  and  is  most  evident  during  extension  of  the  hip-joint. 
The  skin  over  the  front  of  the  knee  is  covered  by  thickened  epidermis;  it  is  loose 
and  thrown  into  transverse  wrinkles  when  the  leg  is  extended.  The  skin  of  the  leg 
is  thin,  especially  on  the  medial  side,  and  is  covered  with  numerous  large  hairs. 
On  the  dorsum  of  the  foot  the  skin  is  thin,  loosely  connected  to  subjacent  parts, 
and  contains  few  hairs,  on  the  plantar  surface,  and  especially  over  the  heel,  the 
epidermis  is  of  great  thickness,  and  here,  as  in  the  palm  of  the  hand,  there  are 
neither  hairs  nor  sebaceous  glands. 

Bones. — The  hip  bones  are  largely  covered  with  muscles,  so  that  only  at  a  few 
points  do  they  approach  the  surface.  In  front  the  anterior  superior  iliac  spine  is 
easily  recognized,  and  in  thin  subjects  stands  out  as  a  prominence  at  the  lateral 
end  of  the  fold  of  the  groin;  in  fat  subjects  its  position  is  indicated  by  an  oblique 
depression,  at  the  bottom  of  which  the  bony  process  can  be  felt.  Proceeding 
upward  and  backward  from  this  process  the  sinuously  curved  iliac  crest  can  be 
traced  to  the  posterior  superior  iliac  spine,  the  site  of  which  is  indicated  by  a  slight 
depression;  on  the  outer  lip  of  the  crest,  about  5  cm.  behind  the  anterior  superior 
spine,  is  the  prominent  iliac  tubercle.  In  thin  subjects  the  pubic  tubercle  is  very 
apparent,  but  in  the  obese  it  is  obscured  by  the  pubic  fat;  it  can,  however,  be 
detected  by  following  up  the  tendon  of  origin  of  Adductor  longus.  Another  part 
of  the  bony  pelvis  which  is  accessible  to  touch  is  the  ischial  tuberosity,  situated 
beneath  the  Glutseus  maximus,  and,  when  the  hip  is  flexed,  easily  felt,  as  it  is  then 
uncovered  by  muscle. 

The  femur  is  enveloped  by  muscles,  so  that  in  fairly  muscular  subjects  the  only 
accessible  parts  are  the  lateral  surface  of  the  greater  trochanter  and  the  low^er 
expanded  end  of  the  bone.  The  site  of  the  greater  trochanter  is  generally  indicated 
by  a  depression,  owing  to  the  thickness  of  the  Glutsei  medius  and  minimus  which 
project  above  it;  when,  however,  the  thigh  is  flexed,  and  especially  if  it  be  crossed 
over  the  opposite  one,  the  trochanter  produces  a  blunt  eminence  on  the  surface. 


I 


SURFACE  ANATOMY  OF  THE  LOWER  EXTREMITY  1337 

The  lateral  condyle  is  more  easily  felt  than  the  medial;  both  epicondyles  can  be 
readily  identified,  and  at  the  upper  part  of  the  medial  condyle  the  sharp  adductor 
tubercle  can  be  recognized  without  difficulty.  When  the  knee  is  flexed  a  portion 
of  the  patellar  surface  is  uncovered  and  is  palpable. 

The  anterior  surface  of  the  patella  is  subcutaneous.  When  the  knee  is  extended 
the  medial  border  of  the  bone  is  a  little  more  prominent  than  the  lateral,  and  if 
the  Quadriceps  femoris  be  relaxed  the  bone  can  be  moved  from  side  to  side.  When 
the  joint  is  flexed  the  patella  recedes  into  the  hollow  between  the  condyles  of  the 
femur  and  the  upper  end  of  the  tibia,  and  becomes  firmly  applied  to  the  femur. 

A  considerable  portion  of  the  tibia  is  subcutaneous.  At  the  upper  end  the  con- 
dyles can  be  felt  just  below  the  knee;  the  medial  condyle  is  broad  and  smooth, 
and  merges  into  the  subcutaneous  surface  of  the  body  below;  the  lateral  is  narrower 
and  more  prominent,  and  on  it,  about  midway  between  the  apex  of  the  patella 
and  the  head  of  the  fibula,  is  the  tubercle  for  the  attachment  of  the  iliotibial  band. 
In  front  of  the  upper  end  of  the  bone,  between  the  condyles,  is  an  oval  eminence, 
the  tuberosity,  which  is  continuous  below  with  the  anterior  crest  of  the  bone.  This 
crest  can  be  identified  in  the  upper  two-thirds  of  its  extent  as  a  flexuous  ridge, 
but  in  the  lower  third  it  disappears  and  the  bone  is  concealed  by  the  tendons  of 
the  muscles  on  the  front  of  the  leg.  Medial  to  the  anterior  crest  is  the  broad 
surface,  slightly  encroached  on  by  muscles  in  front  and  behind.  The  medial 
malleolus  forms  a  broad  prominence,  situated  at  a  higher  level  and  somewhat 
farther  forward  than  the  lateral  malleolus;  it  overhangs  the  medial  border  of  the 
arch  of  the  foot;  its  anterior  border  is  nearly  straight,  its  posterior  presents  a  sharp 
edge  which  forms  the  medial  margin  of  the  groove  for  the  tendon  of  Tibialis 
posterior. 

The  only  subcutaneous  parts  of  the  fibula  are  the  head,  the  lower  part  of  the 
body,  and  the  lateral  malleolus.  The  head  lies  behind  and  lateral  to  the  lateral 
condyle  of  the  tibia,  and  presents  as  a  small  prominent  pyramidal  eminence  slightly 
above  the  level  of  the  tibial  tuberosity;  its  position  can  be  readily  located  by 
following  downward  the  tendon  of  Biceps  femoris.  The  lateral  malleolus  is  a 
narrow  elongated  prominence,  from  which  the  lower  third  or  half  of  the  lateral 
surface  of  the  body  of  the  bone  can  be  traced  upward. 

On  the  dorsum  of  the  tarsus  the  individual  bones  cannot  be  distinguished,  with 
the  exception  of  the  head  of  the  talus,  which  forms  a  rounded  projection  in  front 
of  the  ankle-joint  when  the  foot  is  forcibly  extended.  The  whole  dorsal  surface  of 
the  foot  has  a  smooth  convex  outline,  the  summit  of  which  is  the  ridge  formed  by 
the  head  of  the  talus,  the  navicular,  the  second  cuneiform,  and  the  second  meta- 
tarsal bone;  from  this  it  inclines  gradually  lateralward,  and  rapidly  medialward. 
On  the  medial  side  of  the  foot  the  medial  process  of  the  tuberosity  of  the  calcaneus 
and  the  ridge  separating  the  posterior  from  the  medial  surface  of  the  bone  are 
distinguishable;  in  front  of  this,  and  below  the  medial  malleolus,  is  the  susten- 
taculum tali.  The  tuberosity  of  the  navicular  is  palpable  about  2.5  to  3  cm.  in 
front  of  the  medial  malleolus. 

Farther  forward,  the  ridge  formed  by  the  base  of  the  first  metatarsal  bone  can 
be  obscurely  felt,  and  from  this  the  body  of  the  bone  can  be  traced  to  the  expanded 
head;  beneath  the  base  of  the  first  phalanx  is  the  medial  sesamoid  bone.  On  the 
lateral  side  of  the  foot  the  most  posterior  bony  point  is  the  lateral  process  of 
the  tuberosity  of  the  calcaneus,  with  the  ridge  separating  the  posterior  from  the 
lateral  surface  of  the  bone.  In  front  of  this  the  greater  part  of  the  lateral  sur- 
face of  the  calcaneus  is  subcutaneous;  on  it,  below  and  in  front  of  the  lateral 
malleolus,  the  trochlear  process,  when  present,  can  be  felt.  Farther  forward  the 
base  of  the  fifth  metatarsal  bone  is  prominent,  and  from  it  the  body  and  expanded 
head  can  be  traced. 

As  in  the  case  of  the  metacarpals,  the  dorsal  surfaces  of  the  metatarsal  bones 


1338 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


Tensor  fasciae  latce. 


Femoral  triangle 


Sartoriii3 


are  easily  defined,  although  their  heads  do  not  form  prominences;  the  plantar 
surfaces  are  obscured  by  muscles.  The  phalanges  in  their  whole  extent  are  readily 
palpable. 

Articulations. — The  hip-joint  is  deeply  seated  and  cannot  be  palpated. 
The  interval  between  the  tibia  and  femur  can  alwaj's  be  easily  felt;  if  the  knee- 
joint  be  extended  this  interval  is  on  a  higher  level  than  the  apex  of  the  patella, 
but  if  the  joint  be  slightly  flexed  it  is  directly  behind  the  apex.  When  the  knee 
is  semiflexed,  the  medial  borders  of  the  patella  and  of  the  medial  condyle  of 
the  femur,  and  the  upper  border  of  the  medial  condyle  of  the  tibia,  bound  a  tri- 
angular depressed  area  which  indicates  the  position  of  the  joint. 

The  ankle-joint  can  be  felt  on 
either  side  of  the  Extensor  tendons, 
and  during  extension  of  the  joint 
the  superior  articular  surface  of 
the  talus  presents  below  the  ante- 
rior border  of  the  lower  end  of  the 
tibia. 

Muscles. — Of  the  muscles  of  the 
thigh,  those  of  the  anterior  femoral 
region  (Fig.  1238)  contribute  largely 
to  surface  form.  The  Tensor  fasciae 
latse  produces  a  broad  elevation 
immediately  below  the  anterior 
part  of  the  iliac  crest  and  behind 
the  anterior  superior  iliac  spine; 
from  its  lower  border  a  groove 
caused  by  the  iliotibial  band  ex- 
tends downward  to  the  lateral  side 
of  the  knee-joint.  The  upper  por- 
tion of  Sartorius  constitutes  the 
lateral  boundary  of  the  femoral 
triangle,  and,  when  the  muscle  is 
in  action,  forms  a  prominent 
oblique  ridge  which  is  continued 
below  into  a  flattened  plane  and 
then  gradually  merges  into  a  gen- 
eral fulness  on  the  medial  side  of 
the  knee-joint.  When  the  Sarto- 
rius is  not  in  action,  a  depression 
exists  between  the  Quadriceps 
femoris  and  the  Adductors,  and 
extends  obliquely  downward  and 
medialward  from  the  apex  of  the 
femoral  triangle  to  the  side  of  the 
knee.  In  the  angle  formed  by  the  divergence  of  Sartorius  and  Tensor  fasciae 
latse,  just  below  the  anterior  superior  iliac  spine,  the  Rectus  femoris  appears,  and 
in  a  muscular  subject  its  borders  can  be  clearly  defined  when  the  muscle  is  in  action. 
The  Vastus  lateralis  forms  a  long  flattened  plane  traversed  by  the  groove  of  the 
iliotibial  band.  The  Vastus  medialis  gives  rise  to  a  considerable  prominence  on 
the  medial  side  of  the  lower  half  of  the  thigh;  this  prominence  increases  toward 
the  knee  and  ends  somewhat  abruptly  with  a  full  curved  outline.  The  Vastus 
intermedius  is  completely  hidden.  The  Adductores  cannot  be  differentiated  from 
one  another,  with  the  exception  of  the  upper  tendon  of  Adductor  longus  and 
the  lower  tendon  of  Adductor  magnus.    When  the  Adductor  longus  is  in  action  its 


Quadriceps  femoris 


Patella 


Tuberosity  of  tibia 


Fig.  1238. — Front  and  medial  aspect  of  right  thigh. 


SURFACE  ANATOMY  OF  THE  LOWER  EXTREMITY 


1339 


»» 


upper  tendon  stands  out  as 
a  prominent  ridge  running 
obliquely  downward  and 
lateralward  from  the  neigh- 
borhood of  the  pubic  tu- 
bercle, and  forming  the  me- 
dial border  of  the  femoral 
triangle.  The  lower  tendon 
of  Adductor  magnus  can  be 
distinctly  felt  as  a  short 
ridge  extending  downward 
between  the  Sartorius  and 
Vastus  medialis  to  the  ad- 
ductor tubercle.  The  ad- 
ductores  fill  in  the  triangular 
space  at  the  upper  part  of 
the  thigh,  between  the  femur 
and  the  pelvis,  and  to  them 
is  due  the  contour  of  the 
medial  border  of  the  thigh, 
;he  Gracilis  contributing 
rgely  to  the  smoothness 
if  the  outline. 

The  Glutaeus  maximus  (Fig. 
1239)  forms  the  full  rounded 
outline  of  the  buttock;  it  is 
more  prominent  behind, 
compressed  in  front,  and 
ends  at  its  tendinous  inser- 
tion in  a  depression  imme- 
diately behind  the  greater 
trochanter;  its  lower  border 
crosses  the  gluteal  fold 
obliquely  downward  and 
lateralward.  The  upper  is 
part  of  Gluta?us  medius 
visible,  but  its  lower  part 
with  Glutaeus  minimus  and 
the  external  rotators  are 
completely  hidden.  From 
beneath  the  lower  margin 
of  Glutfeus  maximus  the 
hamstrings  appear;  at  first 
they  are  narrow  and  not 
well-defined,  but  as  they 
descend  they  become  more 
prominent  and  eventually 
divide  into  two  well-marked 
ridges  formed  by  their  ten- 
dons; these  constitute  the 
upper  boundaries  of  the 
popliteal  fossa.  The  tendon 
of  Biceps  femoris  is  a  thick 
cord  running  to  the  head  of 


Tensor  fascice 
latCB 


Gluteal  fold 


Hamstrings 


Biceps  femoris  • 


-  Semimembranostis 
"  Semitendinosus 


^  Popliteal  fossa 


Gastrocnemiua 


Soletts 


Perona  longus  and  brevis 


Medial  malledlua 


Tendo  calcaneus 


Fia. 


Lateral  malleolus 
1239. — Back  of  left  lower  extremity. 


1^ 


1340 


JRFACE  ANATOMY  AND  SURFACE  MARKINGS 


I 


Biceps  femoris 
Popliteal  fossa  - 


Quadriceps 
femoris 


Patella 


Tuberosity 
of  tibia 


Oastrocnemius 

Peronceus 
longus 


Tibialis  anterior 


the  fibula;  the  tendons  of  the  Semimembranosus  and  Semitendinosus  as  they  run 
medialward  to  the  tibia  are  separated  by  a  slight  furrow;  the  Semitendinosus  is 
the  more  medial,  and  can  be  felt  in  certain  positions  of  the  limb  as  a  sharp  cord, 
while  the  Semimembranosus  is  thick  and  rounded.  The  Gracilis  is  situated  a  little 
in  front  of  them. 

The  Tibialis  anterior  (Fig.  1240)  presents  a  fusiform  enlargement  at  the  lateral 
side  of  the  tibia  and  projects  beyond  the  anterior  crest  of  the  bone;  its  tendon  can 
be  traced  on  the  front  of  the  tibia  and  ankle-joint  and  thence  along  the  medial  side 
of  the  foot  to  the  base  of  the  first  metatarsal  bone.  The  fleshy  fibers  of  Peronaeus 
longus  are  strongly  marked  at  the  upper  part  of  the  lateral  side  of  the  leg;  it  is 

separated  by  furrows  from  Extensor 
digitorum  longus  in  front  and  Soleus 
behind.  Below,  the  fleshy  fibers  end 
abruptly  in  a  tendon  which  overlaps 
the  more  flattened  elevation  of  Pero- 
naeus brevis;  below  the  lateral  mal- 
leolus the  tendon  of  Peronaeus  brevis 
is  the  more  marked. 

On  the  dorsum  of  the  foot  (Fig. 
1241)  the  tendons  emerging  from 
beneath  the  transverse  and  cruciate 
crural  ligaments  spread  out  and 
can  be  distinguished  as  follows: 
the  most  medial  and  largest  is 
Tibialis  anterior,  the  next  is  Ex- 
tensor hallucis  proprius,  then  Ex- 
tensor digitorum  longus  dividing 
into  four  tendons,  to  the  second, 
third,  fourth,  and  fifth  toes,  and 
lastly  Peronaeus  tertius.  The  Ex- 
tensor digitonun  brevis  produces  a 
rounded  outline  on  the  dorsum  of 
the  foot  and  a  fulness  in  front  of  the 
lateral  malleolus.  The  Interossei 
dorsales  bulge  between  the  metatar- 
sal bones. 

At  the  back  of  the  knee  is  the 
popliteal  fossa,  bounded  above  by 
the  tendons  of  the  hamstrings  and 
below  by  the  Gastrocnemius.  Below 
this  fossa  is  the  prominent  fleshy 
mass  of  the  calf  of  the  leg  produced 
by  Gastrocnemius  and  Soleus  (Fig. 
1 239) .  When  these  muscles  are  in  action  the  borders  of  Gastrocnemius  form  two  well- 
defined  curved  lines  which  converge  to  the  tendocalcaneus;  the  medial  border  is  the 
more  prominent.  At  the  same  time  the  edges  of  Soleus  can  be  seen  forming,  on 
either  side  of  Gastrocnemius,  curved  eminences,  of  which  the  lateral  is  the  longer. 
The  fleshy  mass  of  the  calf  ends  somewhat  abruptly  in  the  tendocalcaneus,  which 
tapers  in  the  upper  three-fourths  of  its  extent  but  widens  out  slightly  below. 
Behind  the  medial  border  of  the  lower  part  of  the  tibia  (Fig.  1242)  a  well-defined 
ridge  is  produced  by  the  tendon  of  Tibialis  posterior  during  contraction  of  the 
muscle. 

On  the  sole  of  the  foot  the  Abductor  digiti  quinti  forms  a  narrow  rounded  eleva- 
tion on  the  lateral  side,  and  the  Abductor  hallucis  a  lesser  elevation  on  the  medial 


Lateral 
malleolus 


Fig.  1240. — Lateral  aspect  of  right  leg. 


SURFACE  ANATOMY  OF  THE  LOWER  EXTREMITY 


1341 


side.    The  Flexor  digitorum  brevis,  bound  down  by  the  plantar  aponeurosis,  is  not 
very  apparent;  it  produces  a  flattened  form,  and  the  thickened  skin  underlying 
jit  is  thrown  into  numerous  wrinkles. 


Tibialis  anterior 
'^^^C^f^S,      I      Extensor  dig.  longus 


Ext.  Jiall.  long. 

Ext.  dig.  brevis 


Tendo  calcaneus 

Peronceus  longus 

Peronceus  brevis  Peronceus  tertius 

Fia.   1241. — The  mucous  sheaths  of  the  tendons  around  the  ankle.     Lateral  aspect. 

Arteries. — The  femoral  artery  as  it  crosses  the  brim  of  the  pelvis  is  readily  felt; 
in  its  course  down  the  thigh  its  pulsation  becomes  gradually  more  difficult  of  recog- 
nition. When  the  knee  is  flexed  the  pulsation  of  the  popliteal  artery  can  easily  be 
detected  in  the  popliteal  fossa. 


Tibialis  anterior 
Tibialis  posterior 


Flexor  dig.  longus 
Ext.  hall.  long.  ^ 


Plantaris 

Tendo  calcaneus 


Fig.   1242. — The  mucous  sheaths  of  the  tendons  around  the  ankle.     Medial  aspect. 

On  the  lower  part  of  the  front  of  the  tibia  the  anterior  tibial  artery  becomes 
superficial  and  can  be  traced  over  the  ankle  into  the  dorsalis  pedis ;  the  latter  can 
be  followed  to  the  proximal  end  of  the  first  intermetatarsal  space.    The  pulsation 


1342 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


of  the  posterior  tibial  artery  becomes  evident  near  the  lower  end  of  the  back  of  tlie 
tibia,  and  is  easily  detected  behind  the  medial  malleolus. 

Veins. — By  compressing  the  proximal  trunks,  the  venous  arch  on  the  dorsum 
of  the  foot,  together  with  the  great  and  small  saphenous  veins  leading  from  it  (s(3e 
page  669),  are  rendered  visible. 

Nerves. — The  only  nerve  of  the  lower  extremity  which  can  be  located  by  palpa- 
tion is  the  common  peroneal  as  it  winds  around  the  lateral  side  of  the  neck  of  the 
fibula. 

SURFACE   MARKINGS    OF   THE   LOWER  EXTREMITY. 

Bony  Landmarks. — The  anterior  superior  iliac  spine  is  at  the  level  of  the  sacral 
promontory — ^the  posterior  at  the  level  of  the  spinous  process  of  the  second  sacral 
vertebra.  A  horizontal  line  through  the  highest  points  of  the  iliac  crests  passes 
also  through  the  spinous  process  of  the  fourth  lumbar  vertebra,  while,  as  already 
pointed  out  (page  1315),  the  transtubercular  plane  through  the  tubercles  on  the 
iliac  crests  cuts  the  body  of  the  fifth  lumbar  vertebra.  The  upper  margin  of  the 
greater  sciatic  notch  is  opposite  the  spinous  process  of  the  third  sacral  vertebra, 
and  slightly  below  this  level  is  the  posterior  inferior  iliac  spine.  The  surface  mark- 
ings of  the  posterior  inferior  iliac  spine  and  the  ischial  spine  are  both  situated  in  a 
line  which  joins  the  posterior  superior  iliac  spine  to  the  outer  part  of  the  ischial 
tuberosity;  the  posterior  inferior  spine  is  5  cm.  and  the  ischial  spine  10  cm.  below 
the  posterior  superior  spine;  the  ischial  spine  is  opposite  the  first  piece  of  the 
coccyx. 

With  the  body  in  the  erect  posture  the  line  joining  the  pubic  tubercle  tc  the  top 
of  the  greater  trochanter  is  practically  horizontal;  the  middle  of  this  line  overlies 
the  acetabulum  and  the  head  of  the  femur. 


Sacrotuherous  ligament 
Sacrospinous  ligament 


Greater  trochanter 
"     of  femur 


Ischial  tvberosity 

Fig.  1243. — N61aton's  line  and  Bryant's  triangle. 


A  line  used  for  clinical  purposes  is  that  of  Nelaton  (Fig.  1243),  which  is  drawn 
from  the  anterior  superior  iliac  spine  to  the  most  prominent  part  of  the  ischial 


SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


1343 


Superior  gluteal 
artery 


Inferior  gluteal 

artery 
Internal  pudendal 

artery 


Fio.   1244. — Left  gluteal  region,  showing  surface  markings  for  arteries  and  sciatic  nerve. 


Femoral  nerve 
Femoral  artery 


Adductor  tubercle 


Anterior  tibial  artery 


Deep  peronceal  nerve 


Fig.   1245. —  Front  of  right  thigh,  showing  surface 
markings  for  bones,  femoral  artery  and  femoral  nerve. 


1^ 


Fig.  1246. — Lateral  aspect  of  right  leg,  showing 
surface  markings  for  bones,  anterior  tibial  and 
dorsalis  pedis  arteries,  and  deep  peroneal  nerve. 


1344 


SURFACE  MARKINGS  OF  THE  LOWER  EXTREMITY 


Common 
peroneal, 
nerve 

Anterior 
tibial^ 
artery 


■Sciatic  nerve 


-Popliteal  artery 


-Tibial  nerve 

Posterior  tibial 
artenj 


Fia.   1247. — Back  of  left  lower  extremity,  showing  surface  markings  for  bones,  vessels,  and  nervtta 


II 


l» 


SURFACE  MARKINGS  OF  THE  LOWER  EXTREMITY  1345 

tuberosity;  it  crosses  the  center  of  the  acetabuhim  and  the  upper  border  of  the 
greater  trochanter.  Another  surface  marking  of  chnical  importance  is  Bryant's 
triangle,  which  is  mapped  out  thus:  a  line  from  the  anterior  superior  iliac  spine 
to  the  top  of  the  greater  trochanter  forms  the  base  of  the  triangle;  its  sides  are 
formed  respectively  by  a  horizontal  line  from  the  anterior  superior  iliac  spine  and 
a  vertical  line  from  the  top  of  the  greater  trochanter. 

Articulations. — The  posterior  superior  iliac  spine  overlies  the  center  of  the  sacro- 
iliac articulations. 

The  hip-joint  may  be  indicated,  as  described  above,  by  the  center  of  a  horizontal 
line  from  the  pubic  tubercle  to  the  top  of  the  greater  trochanter;  or  more  generally, 
it  is  below  and  slightly  lateral  to  the  middle  of  the  inguinal  ligament.  The  knee-joint 
is  superficial  and  requires  no  surface  marking.  The  level  of  the  ankle-joint  is  that 
of  a  transverse  line  about  1  cm.  above  the  level  of  the  tip  of  the  medial  malleolus. 
If  the  foot  be  forcibly  extended,  the  head  of  the  talus  appears  as  a  rounded  promi- 
nence on  the  medial  side  of  the  dorsum;  just  in  front  of  this  prominence  and  behind 
the  tuberosity  of  the  navicular  is  the  talonavicular  joint.  The  calcaneocuboid  joint 
is  situated  midway  between  the  lateral  malleolus  and  the  prominent  base  of  the 
fifth  metatarsal  bone;  the  line  indicating  it  is  parallel  to  that  of  the  talonavicular 
joint.  The  line  of  the  fifth  tarsometatarsal  joint  is  very  oblique;  it  starts  from  the 
projection  of  the  base  of  the  fifth  metatarsal  bone,  and  if  continued  would  pass 
through  the  head  of  the  first  metatarsal.  The  lines  of  the  fourth  and  third  tarso- 
metatarsal joints  are  less  oblique.  The  first  tarsometatarsal  joint  corresponds  to  a 
groove  which  can  be  felt  by  making  firm  pressure  on  the  medial  border  of  the  foot 
2.5  cm.  in  front  of  the  tuberosity  of  the  navicular  bone;  the  position  of  the  second 
tarsometatarsal  joint  is  1.25  cm.  behind  this.  The  metatarsophalangeal  joints  are 
about  2.5  cm.  behind  the  webs  of  the  corresponding  toes. 

Muscles. — None  of  the  muscles  require  any  special  surface  lines  to  indicate 
them,  but  there  are  three  intermuscular  spaces  which  occasionally  require  defini- 
tion, viz.,  the  femoral  triangle,  the  adductor  canal,  and  the  popliteal  fossa. 

The  femoral  triangle  is  bounded  above  by  the  inguinal  ligament,  laterally  by  the 
medial  border  of  Sartorius,  and  medially  by  the  medial  border  of  Adductor  longus. 
In  the  triangle  is  the  fossa  ovalis,  through  Avhich  the  great  saphenous  vein  dips  to 
join  the  femoral;  the  center  of  this  fossa  is  about  4  cm.  below  and  lateral  to  the 
pubic  tubercle,  its  vertical  diameter  measures  about  4  cm.  and  its  transverse  about 
1,5  cm.    Tlie  femoral  ring  is  about  1.25  cm.  lateral  to  the  pubic  tubercle. 

The  adductor  canal  occupies  the  medial  part  of  the  middle  third  of  the  thigh;  it 
begins  at  the  apex  of  the  femoral  triangle  and  lies  deep  to  the  vertical  part  of 
Sartorius.  The  popliteal  fossa  is  bounded:  above  and  medially  by  the  tendons 
of  Semimembranosus  and  Semitendinosus;  above  and  laterally  by  the  tendon  of 
Biceps  femoris;  below  and  medially  by  the  medial  head  of  Gastrocnemius;  below 
and  laterally  by  the  lateral  head  of  Gastrocnemius  and  the  Plantaris. 

Mucous  Sheaths. — ^The  positions  of  the  mucous  sheaths  around  the  tendons 
about  the  ankle-joints  are  sufficientlv  indicated  in  Figs.  1241,  1242  (see  also  page 
489). 

Arteries. — The  points  of  emergence  of  the  three  main  arteries  on  the  buttock, 
viz.,  the  superior  and  inferior  gluteals  and  the  internal  pudendal,  may  be  indicated 
in  the  following  manner  (Fig.  1244).  With  the  femur  slightly  flexed  and  rotated 
inward,  a  line  is  drawn  from  the  posterior  superior  iliac  spine  to  the  posterior  supe- 
ior  angle  of  the  greater  trochanter;  the  point  of  emergence  of  the  superior  gluteal 
artery  from  the  upper  part  of  the  greater  sciatic  foramen  corresponds  to  the  junction 
of  the  upper  and  middle  thirds  of  this  line.  A  second  line  is  drawn  from  the  poste- 
rior superior  iliac  spine  to  the  outer  part  of  the  ischial  tuberosity;  the  junction 
of  its  lower  with  its  middle  third  marks  the  point  of  emergence  of  the  inferior 
gluteal  and  internal  pudendal  arteries  from  the  lower  part  of  the  greater  sciatic 
8.5 


1^ 


1346  SURFACE  ANATOMY  AND  SURFACE  MARKINGS 


I 


foramen.  The  course  of  the  femoral  artery  (Fig.  1245)  is  represented  by  the  iippi^r 
two-thirds  of  a  Hne  from  a  point  midway  between  the  anterior  superior  iliac  spine 
and  the  symphysis  pubis  to  the  adductor  tubercle,  with  the  thigh  abducted  ard 
rotated  outward;  the  profunda  femoris  arises  from  it  about  1  to  5  cm.  below  the 
inguinal  ligament.  The  course  of  the  upper  part  of  the  popliteal  artery  (Fig.  1247) 
is  indicated  by  a  line  from  the  lateral  margin  of  Semimembranosus  at  the  junction 
of  the  middle  and  lower  thirds  of  the  thigh,  obliquely  downward  to  the  middle  of 
the  popliteal  fossa;  from  this  point  it  runs  vertically  downward  for  about  2.5  cm. 
or  to  the  level  of  a  line  through  the  lower  part  of  the  tibial  tuberosity.  The  lire 
indicating  the  anterior  tibial  artery  (Fig.  1246)  is  drawn  from  the  medial  side  of 
the  head  of  the  fibula  to  a  point  midway  between  the  malleoli;  the  artery  begins 
about  3  cm.  below  the  head  of  the  fibula.  The  dorsalis  pedis  artery  is  represented 
on  the  dorsum  of  the  foot  by  a  line  from  the  center  of  the  interval  between  the 
malleoli  to  the  proximal  end  of  the  first  intermetatarsal  space. 

The  course  of  the  posterior  tibial  artery  (Fig.  1247)  can  be  shown  by  a  line  from 
the  end  of  the  popliteal  artery,  i.  e.,  2.5  cm.  below  the  center  of  the  popliteal  fossa, 
to  midway  between  the  tip  of  the  medial  malleolus  and  the  center  of  the  convexity 
of  the  heel;  its  main  branch,  the  peroneal  artery,  begins  about  7  or  8  cm.  below  the 
level  of  the  knee-joint  and  follows  the  line  of  the  fibula  to  the  back  of  the  lateral 
malleolus.  The  medial  and  lateral  plantar  arteries  begin  from  the  end  of  the  poste- 
rior tibial;  the  medial  extends  to  the  middle  of  the  plantar  surface  of  the  ball  of  the 
great  toe,  the  lateral  to  within  a  finger's  breadth  of  the  tuberosity  of  the  fifth 
metatarsal  bone;  from  this  latter  point  the  plantar  arch  crosses  the  foot  trans- 
versely to  the  proximal  end  of  the  first  intermetatarsal  space. 

Veins. — The  line  of  the  great  saphenous  vein  is  from  the  front  of  the  medial 
malleolus  to  the  center  of  the  fossa  ovalis;  the  small  saphenous  vein  runs  from  the 
back  of  the  lateral  malleolus  to  the  center  of  the  popliteal  fossa. 

Nerves. — The  course  of  the  sciatic  nerve  (Fig.  1247)  can  be  indicated  by  a  line 
from  a  point  midway  between  the  outer  border  of  the  ischial  tuberosity  and  the 
posterior  superior  angle  of  the  greater  trochanter  to  the  upper  angle  of  the  popliteal 
fossa.  The  continuation  of  this  line  vertically  through  the  center  of  the  popliteal 
fossa  represents  the  position  of  the  tibial  nerve,  while  the  common  peroneal  nerve 
follows  the  line  of  the  tendon  of  Biceps  femoris.  The  lines  for  the  deep  peroneal 
nerve  and  the  continuation  of  the  tibial  nerve  correspond  respectively  to  those  for 
the  anterior  and  posterior  tibial  arteries. 


INDEX. 


Abdomen,  1147 

apertures  in  walls  of,  1147 
boundaries  of,  1147 
fascia  of,  408 

triangular,  412 
lymph  glands  of,  703 
muscles  of,  408 
actions  of,  417 
nerves  of,  417 
regions  of,  1147 
surface  anatomy  of,  1313 
markings  of,  1315 
Abdominal  aorta,  603 
branches  of,  603 
surface  markings  of,  1321 
aortic  plexus,  987 
muscles,  408 
ring,  deep,  418 
external,  410 
inguinal,  418 
internal,  418 
wall,  lymphatic  vessels  of,  706 
Abducent  nerve,  899 

composition  and  central  con- 
nections of,  861 
Abductor    digiti    quinti     muscle 
(foot),  492 
actions  of,  496 
nerves  of,  495 
variations  of,  492 
(hand),  463 
actions  of,  464 
nerves  of,  464 
variations  of,  464 
hallucis  muscle,  491 
actions  of,  495 
nerves  of,  495 
variations  of,  491 
indicis  muscle,  464 
minimi  digiti  muscle,  463 
poUicis  brevis  muscle,  461 
actions  of,  462 
nerves  of,  462 
variations  of,  462 
longus  muscle,  455 
actions  of,  456 
nerves  of,  456 
variations  of,  455 
muscle,  461 
Aberrant  ducts  of  testis,  1246 
Abnormalities    of    vertebral  col- 
umn, 116 
Accelerator  urinse  muscle,  428 
Accessory  hemiazygos  vein,  667 
nerve,  913 

composition  and  central  con- 
nections of,  855 
cranial  part  of,  913 
spinal  part  of,  913 
obturator  nerve,  955 
olivary  nuclei,  781 
organs  of  digestive  tube,  1100 

of  eye,  1021 
pancreatic  duct,  1202 
part  of  parotid  gland,  1134 
processes,  106 
pudendal  artery,  618 
sinuses  of  nose,  998 


Accessory  spleens,  1283 
thyroid  glands,  1270 
Acetabular  fossa,  237 

notch,  237 
Acetabulum,  237 
Achromatic  spindle,  37 
Acoustic   meatus,    external,    145, 
183,  1036 
development  of,  1033 
internal,  143,  193 
nerve,  905,  1035 

composition  and  central  con- 
nections of,  857 
development  of,  1033 
nuclei  of,  788,  906 
Acromioclavicular  joint,  315 
movemehts  of,  316 
surface    anatomy   of,    1328, 
1331 
Acromion,  203 
Acromiothoracic  artery,  588 
Adamanto  blasts,  1123 
Adductor  brevis  muscle,  473 
actions  of,  474 
nerves  of,  474 
variations  of,  474 
canal,  627 
hallucis  muscle,  493 
actions  of,  496 
nerves  of,  495 
variations  of,  494 
longus  muscle,  472 
actions  of,  474 
nerves  of,  474 
variations  of,  474 
magnus  muscle,  473 
actions  of,  474 
nerves  of,  474 
variations  of,  474 
minimus  muscle,  474 
obliquus  hallucis  muscle,  493 

pollicis  muscle,  462 
pollicis  muscles,  actions  of,  462 
nerves  of,  462 
variations  of,  462 
obliquus  muscle,  462 
transversus  muscle,  462 
transversus  pollicis  muscle,  462 
tubercle,  246 
Adipose  capsule  of  kidney,  1220 
Adminiculuni  linece  albae.  All 
Adrenal  capsule,  1278 

gland,  lymphatic  capillaries  in, 
686 
Adrenalin,  1280 
Afferent  nerves,  729 

vessels  of  kidney,  1224 
After-birth,  64 
Agger  nasi,  161 
Aggregated    lymphatic    nodules, 

1176 
Agminated  follicles,  1176 
Air  cells,  ethmoidal,  154,  998 
mastoid,  142 
sinuses  of  nose,  998 
of  skull,  80 
Ala  cinerea,  800 
lobuli  centralis,  789 
nasi,  992 
OSS.  ilii,  232 


Alse  of  ethmoid,  153 

of  sacrum,  110 

of  vomer,  170 
Alar  cartilages  of  nose,  993 

lamina,  735 
Alcock,  canal  of,  421 
Alimentary  canal,  1100 

lymphatic  capiljaries  in,  684 
Allantoic  vessels,  54 
AUantois,  54 
Alveolar  arch,  161 

arteries,  561 

border  of  mandible,  173 

canals,  158 

index,  199 

nerves,  890,  891,  896 

point,  161,  198 

process  of  maxilla,  161 
Alveoli,  formation  of,  1124 
Alveus,  833,  840 
Amacrine  cells  of  retina,  1017 
Amnion,  56 

false,  56 
Amniotic  cavity,  56 

ectoderm,  56 

fold,  56 
Amphiarthroses,  284 
Ampulla  of  ductus  deferens,  1246 

rectal,  1183 

of  uterine  tube,  1257 

of  Vater,  1199 
Ampullae  of  semicircular  canals, 
1049 

of  tubuli  lactiferi,  1268 
Amygdala,  835 
Amygdaline  nucleus,  791 
Amygdaloid  nucleus,  869 
Anal  canal  or  anal  part  of  rectum, 
1184 
development  of,  1108 
lymphatic  vessels  of,  711 
membrane  of,  1110 
valves  of,  1184 

fascia,  421 
Anaphase  of  karyokinesis,  37 
Anastomoses  of  arteries,  543 
around  elbow-joint,  592 

knee-joint,  634 
crucial,  630 
Anastomotic    branch    of   inferior 

gluteal  artery,  020 
Anastomotica  magna  of  brachial 
artery,  592 
of  femoral  artery,  031 
Anatomical  neck  of  humerus,  209 
Anconseus  muscle,  454 
actions  of,  456 
nerves  of,  456 
Angiology,  497 
Angle  of  Louis,  121,  note 

iridial  or  filtration,  1007 

of  mandible,  174 

of  pubis,  236 

of  rib,  124 

sacro  vertebral,  106 

of  sternum,  121 

subscapular.  203 
Angular  artery,  556 

gyrus,  823 

movement,  286 

( 1347  ) 


1348 


INDEX 


Angular  vein,  645 
Angulus  Ludovici,  121 
Animal  cell,  35 
Ankle  bone,  266 
Ankle-joint,  349 
movements  of,  351 
relations  of  tendons  and  vessels 

to,  351 
surface  anatomy  of,  1338 
markings  of,  1343 
Annular  ligament,  456,  458 
of  ankle,  488,  489 
of  radius,  324 
of  wrist,  anterior,  456 
posterior,  458 
Annulus  fibrosus    fof   interverte- 
bral fibrocartilage],  289 
inguinalis  abdominis,  418 

subcxitaneus,  410 
oralis,  531 

tendineus  communis,  1022 
Anococcygeal  body,  1184 
nerves,  968 
raphe,  426 
Ansa  hypoglossi,  928 
lentiformis,  835,  837 
subclavia  [Vieusseni],  981 
Anterior   annular  ligament,  456, 
488 
basis  bundle,  760 
calcaneoastragaloid     ligament, 

352 
circumflex  artery,  589 
common  ligament,  287 
condyloid  foramen,  131 
cornu  of  medulla  spinalis,  753 
costovertebral  ligament,  299 
crural  ner-\'e,  955 
inferior  ligament,  348 
intercostal  arteries,  584 
interosseous  artery,  596 

nerve,  938 
ligament,  327 
perforated  substance,  869 
peroneal  artery,  638 
pillar  of  fauces,  1137 
pillars  of  fornix,  838 
pulmonary  nerves,  913 
radial  carpal  artery,  594 
radioulnar  ligament,  325 
superior  dental  nerve,  891 

ligament,  301,  348 
talotibial  ligament,  351 
temporal  artery,  559 
tibial  nerve,  965 
ulnar  carpal  artery,  598 
Antero-lateral  faeciculas,    super- 
ficial, 854 
ganglionic  arteries,  573 
muscles  of  abdomen,  408 
Antero-medial  ganglionic  arteries, 

571 
Antibrachial  fascia,  445 

cutaneous  nerve,  dorsal,  944 
lateral,  935 
medial,  937 
Anticubital  fossa,  589 
Antihelix,  1033 
Antitragicus  muscle,  1035 
Antitragus,  1034 
Antrum  cardiacum,  1161 
of  Highmore,  159,  999 
pyloric,  1162,  1163 
tympanic,  142,  1042 
entrance  to,  1042 
Anus,  1100,  1184 

lymphatic  vessels  of,  711 
Aorta,  545 

abdominal,  602 

branches  of,  603 
abdominalis,  602 
arch  of,  547 

branches  of,  548 
peculiarities  of,  548 
of  branches  of,  548 


Aorta  ascendens,  545 

ascending,  545 

bulb  of,  545 

coarctation  of,  547 

descending,  598 

ihoracalis,  598 

rami  mediastinales,  600 
pericardiaci,  600 

thoracic,  598 
branches  of,  600 

transverse,  547 
Aortse,  anterior  ventral,  516 

dorsal,  517 

primitive,  506 
Aortic  arches,  516 

bodies,  1278 

glands,  1269,  1278 

hiatus,  406 

isthmus,  517,  546 

lymph  glands,  705 

opening  of  heart,  534 

plexus,  987 

semilunar  valves,  534 

septum,  514 

sinuses,  534 

spindle,  547 

vestibule,  534 
Aorticorenal  ganglion,  985 
Apertura  pelvis  [minoris]  inferior, 
240 
superior,  239     - 

tympanies     canaliculi     chorda; 
1038 
Aperture,  anterior  nasal,  196 
Apertures  in  walls  of   abdomen, 

1147 
Apex  cordis,  527 

of  fibula,  260 

of  heart,  527 

linguce,  1125 

of  nose,  992 

OSS.  sacri,  110 

prostatce,  1252 

pulmonis,  1094 
Aponeurosis,  376 

epicranial,  380 

lumbar,  397 

of  obliquus  externus,  410 

palatine,  1139 

palmar,  460 

pabnaris,  460 

pharyngeal,  1143 

plantar,  490 

plantaris,  490 

suprahyoid,  392 
Apparatus  digestorius,  1100 

lacrimalis,  1028 

respiratorius,  1071 

urogenitalis,  1204 
Appendages  of  testis,  1242 
Appendices  epiploicce,  1158 

vesiculosa,  1257 
Appendicular  artery,  607 

skeleton,  79 
Appendix,  auricular,  left,  533 
right,  529 

ensiform,  121 

of  epididymis,  1242 

of  testis,  1242 

of  ventricle  of  larynx,  1080 

ventriculi  laryngis,  1080 

vermiform,  1178 

xiphoid,  121 
Aquceductus  cerebri,  806 

cochlece,  144,  181 

Fallopii,  143 

vestibuli,  143 
Aqueduct,  cerebral,  806 

of  cochlea,  144 

of  Sylvius,  766,  806 
Aqueous  humor,  1018 
Arachnoid,  876 

granulations,  878 

structtue  of,  876 

viUi,  878 


Arachnoidea  encephali,  876 

spinalis,  876 
Arantii,  corpus,  533,  535 
Arbor  vitce  fof  cerebellum],  791 

uterina,  1260 
Arch,  alveolar,  161 

of  aorta,  547 

branches  of,  548 
peculiarities  of,  548 

of  atlas,  99 

axillary,  434 

carotid,  516 

crural,  deep,  419 

glossopalatine,  1137 

lumbocostal,  405 

palmar,  deep,  595 
superficial,  598 

pharyngopalatine,  1137 

plantar,  639 

pubic,  240 

of  a  vertebra,  96 

volar,  deep,  595 
superficial,  598 

zygomatic,  183 
Arches,  aortic,  506,  516 

branchial  or  visceral,  65 

of  fauces,  1137 

of  foot,  360 

supercihary,  135,  178,  183 
Architecture  of  femur,  248 
Arcuate  arterv,  637 

fibers,  782,  783 

ligaments,  404 

line  of  ilium,  234 

nucleus,  782 
Arcus  aortcp,  547 

cartilaginis  cricoidece,  1074 

glossopalalinus,  1137 

lumbocostalis  lateralis  [Halleri], 
405 
medialis  [Halleri],  404 

parietooccipitalis,  823 

pharyngopalafinus,  1 137 

volaris  profundus,  595 
superficialis,  598 
Area  acustica,  800 

cribrosa  media,  143 
superior,  143 

facialis,  143 

olfactory,  67 

oval,  of  Flechsig,  764 

parolfactoria,  827 

pericardial,  47 

postrema,  800 

proamniotic,  47 
Areas  of  cerebral  cortex,  849 

of  Cohnheim,  374 

vascular,  505 
Areola  of  mamma,  1267 
Areola}  of  bone,  93,  94 
Areolar  glands,  1267 
Arm  bone,  209 

fascia  of,  442 

muscles  of,  442 

development  of,  371 
Arnold's  nerve,  911 
Arrectores  pilorum  muscle,  1069 
Arteria  alveolaris  inferior,  561 
superior  posterior,  562 

angularis,  556 

anonyma,  548 

arcuata,  637 

auditiva  interna,  580 

auricularis  posterior,  557 
ramus  auricularis,  556 
occipitalis,  557 
profundus,  560 

axillaris,  586 

basilaris,  580 

ra7ni  ad  pontem,  580 

brachialis,  589 

rami  muscidares,  592 

buccinatoria,  561 

bulbi  urethra;,  619 

canalis  pterygoidei,  562,  568 


V 


INDEX 


1349 


Arteria  carotis  communis,  549 

externa,  551 

interna,  566 

ramus    caroticotympanicus , 
568 
centralis  retince,  571,  1018 
cerebelli  inferior  anterior,  580 
posterior,  580 

superior,  580 
cerebri  anterior,  571 

media,  572 

posterior,  580 
cervicalis  ascendens,  581 

profunda,  585 
chorioiden,  574 

circumfiexa  femoris  lateralis,  630 
medialis,  630 

humeri  anterior,  589 
posterior,  589 

ilium  profunda,  623 
superficialis ,  629 

scapulas,  588 
coeliaca,  603 
colica  dextra,  609 

media,  609 

sinistra,  610 
collateralis  ulnaris  inferior,  592 

superior,  591 
comes  nervi  phrenici,  583 
comitans  nervi  ischiadici,  620 
communicans  anterior,  572 

posterior,  573 
coronaria  [cordis]  dextra,  54 G 

sinistra,  547 
cystica,  605 
dorsalis  hallucis,  637 

nasi,  571 

pedis,  636 

ramus  plantaris  profundus, 
'637 
epigastrica  inferior,  623 

superficialis,  629 

superior,  585 
femoralis,  623 

rami  musculares,  629 
frontalis,  blO 
gastrica  dextra,  604 

sinistra,  603 
gastroduodcnalis,  604 
gastroepiploica  dextra,  604 

sinistra,  606 
^enw  media,  633 

suprema,  631 
glutwa  inferior,  620 

ramus  iliacus,  621 
lumbalis,  621 

superior,  622 
hoBmorrhoidalis  inferior,  619 

media,  615 

superior,  610 
hepatica,  603 
hypogastrica,  614 
ileocolica,  607 
iliaca  externa,  622 
iliolumhalis,  621 
infraorbitalis,  562 
interossea  communis,  596 

dorsalis,  596 

volaris,  596 
labialis  inferior,  555 

superior,  555 
lacrimalis,  669 
laryngea  inferior,  581 

superior,  552 
lienalis,  605 

rami  pancreatici ,  606 
lingualis,  553 

rami  dorsales  lingua,  553 

ramus  hyoideus,  553 
malleolaris  anterior  lateralis,  635 
medialis,  635 

posterior  medialis,  639 
mammaria  interna,  583 

rami  inter costales,  584 
perforantes,  584 


^rfen'a  mammaria  interna,  rami 
sternales,  584 
masseterica,  561 
maxillaris  externa,  553 

rami  glandidares,  555 
ramus  tonsillaris,  555 
interna,  559 

rami  pterygoidei,  561 
ramus     meningeus     acces- 
sorius,  561 
mediana,  596 
meningea  anterior,  568 

media,  560 
mescnterica  inferior,  609 

superior,  606 
muscidophrenica,  584 
nutricia  fibula;,  638 
humeri,  591 
tibiae,  638 
obturatoria,  616 
occipitalis,  556 

romi  musculares,  556 
ramus  auricularis,  556 
descendens,  557 
meningeus,  5o7 
ophthnlmica,  568 
palatina  ascendens,  555 

descendens,  562 
pancreatica  magna,  606 
pancreaticoduodenalis  inferior, 
607 
superior,  605 
perforans  prima,  631 
secunda,  631 
<crtia,  631 
pericardiacophrenica,  583 
perinei,  619 
peronwa,  638 

ramus      calcaneus     lateralis, 
638 
communicans,  638 
perforans,  638 
pharyngea  ascendens,  557 
rami  pharyngei,  558 
plantaris  lateralis,  639 

medialis,  639 
poplitea,  632 
princeps  ceroids,  557 
hallucis,  640 
poinds,  595 
profunda  brachii,  591 
femoris,  629 
penis,  620 
pudenda  externa  profunda,  629 
superficialis,  629 
interna,  617 
pulmonalis,  543 
ramus  dexter,  545 
sinister,  545 
radialis,  592 

rami  musculares,  594 

perforantes,  595 
ramus  carpeus  dorsalis,  594 
volaris,  594 
volaris  superficialis,  594 
recurrens  radialis,  594 
tibialis  anterior,  635 
posterior,  635 
recurrentes  ulnaris  anterior,  596 

posterior,  596 
sacralis  lateralis,  621 

media,  613 
spheno palatina,  562 
spinalis  anterior,  579 

posterior,  579 
stemocleidomastoidea,  556 
stylomastoidea,  557 
subclavia,  575 
sublingualis,  553 
submentalis,  555 
subscapularis,  588 
supraorbitalis,  569 
tarsea  lateralis,  637 
temporalis  media,  558 
superficialis,  558 


Arteria     temporalis     superficialis, 
rami    auriculares     ante- 
riores.  559 
ramus  frontalis,  559 
parietalis.  559 
thoracalis  lateralis,  588 

suprema,  587 
ihoracoacromialis,  588 
thyreoidea  ima,  549 
inferior,  581 

rami  oesophagei,  581 
tracheales,  581 
superior,  552 

ramus  cricothyreoideus,  552 
hyoideus,  552 
sternocleidomastoideus, 
552 
tibialis  anterior,  634 

rami  musculares,  635 
posterior,  637 

rami  calcanei  mediales,  639 
ramus  communicans,  639 
transversa  colli,  582 

ramus  ascendens,  582 
descendens,  582 
faciei,  558 
scamdae,  582 
tympanica  anterior,  560 

inferior,  558 
ulnaris,  595 

rami  musculares,  598 
ramus  carpeus  dorsalis,  598 
volaris,  598 
volaris  profundus,  598 
urethralis,  619 
uterina,  615 
vaginalis,  616 
vertebralis,  578 

rami  spinales,  579 
ramus  meningeus,  579 
vesicalis  inferior,  615 
medialis,  615 
superior,  615 
volaris  indicis  radialis,  595 
ArtericE  bronchioles,  600 
ciliares,  571 
digitales  volares  communes,  598 

propricB,  598 
gaslriccB  breves,  606 
grenw  inferiores,  633 

superiores,  633 
iliaccB  communes,  613 
inter  costales,  600 
intestinales,  607 
lumbales,  612 
metacarpew  volares,  595 
metatarsecs  plantares,  640 
cesophagecE,  600 
ovaricae,  611 

palpebrales  mediales,  570 
phrenicce  inferiores,  612 
propria!  renales,  1223 
recto,  1224 
renames, '610 
sigmoidece,  610 
spermaticce  interna,  611 
suprarenales  media,  610 
surales,  633 
tarsecB  mediales,  637 
tunica  adventitia,  499 
intima,  498 
media,  498 
Arterial  mesocardium,  526 
Arterioles,  497 

Artery    or    Arteries,    abdominal 
aorta,  602 
accessory  pudendal,  618 

meningeal,  561 
acromiothoracic,  588 
alveolaF,  561 
anastomoses  of,  543 
anastomotic  branch  of  inferior 

gluteal,  620 
anastomotica   magna,    of   bra- 
chial. 592 


[350 


Artery  or  Arteries,  anastomotica 
magna  of  femoral,  631 
angular,  556 
anterior  cerebral,  571 
choroidal,  574 
ciliary,  571 
communicating,  571 
humeral  circumflex,  589 
inferior  cerebellar,  580 
meningeal,  568 
spinal,  579 
tibial,  634 
tympanic,  560 
antero-lateral  ganglionic,  573 
antero-medial  ganglionic,  561 
aorta,  545 

abdominal,  602 
arch  of,  547 
ascending,  545 
descending,  598 
thoracic,  598 
appendicular,  607 
arcuate,  637 
articular,  633 
ascending  cervical,  581 
palatine,  555 
pharyngeal,  557 
auditory,  580 

internal,  580 
auricular,  anterior,  559 
deep,  560 
of  occipital,  557 
posterior,  557 
axillary,  586 
azygos,  of  knee,  633 

of  vagina,  616 
basilar,  580 
brachial,  589 
brachiocephalic,  548 
of  brain,  574 
bronchial,  600,  1100 
buccal,  561 
buccinator,  561 
bulbar,  580 
calcaneal,  638,  639 
capsular,  middle,  610 
caroticotympanic,  568 
carotid,  common,  549 
external,  551 
internal,  566 
carpal,  dorsal,  594 
radial,  594 
ulnar,  598 
volar,  594,  598 
cavernous,  568 
cecal,  of  ileocolic,  607 
central,  of  retina,  571,  1018 
cerebellar,  580 
cerebral,  anterior,  571 
middle,  572 
posterior,  580 
of  cerebral  hemorrhage,  573 
cervical,  ascending,  581 
deep,  585 
superficial,  582 
transverse,  582 
choroid,  574 
choroidal,  574,  581 
ciliary,  571 
circle  of  Willis,  574 
circumflex,  femoral,  630 

humeral,  589 
coccygeal  of  inferior  gluteal,  620 
cochlear,  1059 
coeliac,  603 
colic,  609,  610 
comdtans  iiervi  ischiadici,  620 

phrenici,  583 
common  carotid,  549 
iliac,  613 
interosseous,  596 
communicating,  anterior,  571 
of  dorsalis  pedis,  637 
posterior,  573 
coronary,  of  heart,  546 


INDEX 

Artery  or  Arteries,  coronary,   of 
lips,  555 
of  stomach,  603 
of   corpus   cavernosum,    penis, 

620 
costocervical  trunk,  585 
cremasteric,  623 
cricothyroid,  552 
cystic,  605 
deep  auricular,  560 
epigastric,  623 
external  pudendal,  629 
iliac  circumflex,  623 
palmar  arch,  595 
of  penis,  617 
plantar,  637 
temporal,  561 
volar  branch  of  ulnar,  598 
dental,  inferior,  561 

posterior,  562 
descending  aorta,  598 

development  of,  505,  514 
branch  of  occipital,  557 
palatine,  562 
digital,  foot,  640 
hand,  598 
_  volar,  598 
distribution  of,  543 
dorsal  carpal  of  radial,  594 
of  ulnar,  598 
interosseous,  596 
metacarpal,  594 
nasal,  571 
of  penis,  620 
dorsales  linguse,  553 
dorsalis  hallucis,  637 
pedis,  636 
scapulae,  588 
of  ductus  deferens,  615 
epigastric,  deep  or  inferior,  623 
superficial,  629 
superior,  585 
esophageal,  of  aorta,  600 
of  inferior  thyroid,  581 
ethmoidal,  570 
external  carotid,  551 
iliac,  622 
maxillary,  553 
plantar,  639 
pudendal,  029 
facial,  553 

transverse,  558 
femoral,  623 

circumflex,  630 
fibular,  635 
frontal.  570 

ganglionic,  571,  573,  581 
gastric,  603,  604,  606 
gastroduodenal,  604 
gastroepiploic,  604,  606 
genicular,  631,  633,  634 
gluteal,  620 
of  head  and  neck,  549 
helicine,  1251 
hemorrhoidal,  inferior,  619 
middle,  615 
superior,  610 
hepatic,  603 
highest  genicular,  631 
intercostal,  585 
thoracic,  587 
humeral  circumfiex,  589 
hypogastric,  614 

obliterated,  615 
ileal,  of  ileocolic,  607 
ileocolic,  607 

iliac  circumflex,  deep,  623 
superficial,  629 
common,  613 
external,  622 
internal,  614 
iliolumbar,  621 
inferior  alveolar,  561 
articular,  of  knee,  633 
cerebellar,  580 


I 


Artery  or  Arteries,    inferior   epi 
gastric,  623 

genicular,  633 

gluteal,  620 

hemorrhoidal,  619 

labial,  555 

laryngeal,  581 

mesenteric,  609 

pancreaticoduodenal,  607 

phrenic,  612 

profunda,  591 

thyroid,  581 

tympanic,  558 

ulnar  collateral,  592 
infrahyoid,  552 
infraorbital,  562 
infrascapular,  588 
innominate,  548 
intercostal,  600,  601 

branches  of  internal    mam' 
mary,  583 

highest,  585 

superior,  585 
interlobular,  of  kidney,  1223 
internal  auditory,  580,  1059 

carotid,  566 

iliac,  614 

mammary,  583 

maxillary,  559 

palpebral,  570 

plantar,  639 

pudendal  or  pudic,  617 

spermatic,  611 
interosseous,  anterior,  596 

common,  596 

dorsal,  596 

palmar,  595 

posterior,  596 

volar,  596 
intestinal,  607 
labial,  555 
of  labyrinth,  1059 
lacrimal,  569 
laryngeal,  inferior,  581 

superior,  552 
lateral  calcaneal,  638 

femoral  circumflex,  030 

nasal,  556 

palpebral,  569 

sacral,  621 

tarsal,  637 
left  colic,  610 

gastric,  603 

gastroepiploic,  606 
lienal,  605 
lingual,  553 

deep,  553 
long  ciliary,  571 

thoracic,  588 
of  lower  extremity,  623 
lumbar,  612 
malleolar,  635 

internal,  639 
mammary,  internal,  583 
masseteric,  561 
maxillary,  external,  553 

internal,  559 
medial  palpebral,  570 
mediana,  696 
mediastinal,  from  aorta,  600 

from  internal  mammary,  583 
medidural,  560 
medullary,  580 
meningeal,  accessory,  561 

anterior,  568 

of  ascending  pharyngeal,  558 

middle,  560 

of  occipital,  557 

small,  561 

of  vertebral,  579 
mesenteric,  inferior,  609 

superior,  606 
metatarsal,  637 
middle  cerebral,  572 

genicular,  633 


INDEX 


1351 


trterv  or  Arteries,  middle  hemor- 
^  rhoida],  615 

meningeal,  560 

sacra],  612 
mode  of  division  of,  543 

of  origin  of  branches,  543 
musculophrenic,  583 
mylohyoid,  561 
nasal,  571 

dorsal,  571 

lateral,  556 
nasopalatine,  562 
nerves  of,  499 
obturator,  616 
occipital,  556 
ophthalmic,  568 
ovarian,  611 
palatine,  ascending,  555 

of  ascending  pharyngeal,  557 

descending,  562 
palmar  arch,  deep,  595 

superficial,  598 
palpebral,  569,  570 

internal,  570 
pancreatic,  of  lienal,  606 
pancreaticoduodenal,  605 
parvidural,  561 
perforating,  of  foot,  040 

of  hand,  595 

of  internal  mammary,  584 

of  thigh,  631 
pericardiacophrenic,'  584 
pericardial,  584,  600 
perineal,  619 

superficial,  619 
peroneal,  638 

anterior,  638 
pharyngeal,  ascending,  557 

of  internal  maxillary,  562 
phrenic,  inferior,  612 

superior,  601 
plantar,  deep,  637 

lateral  (external),  639 

medial  (internal),  639 

metatarsal,  640 
pontine,  580 
popliteal,  632 
posterior  auricular,  557 

cerebral,  580 

communicating,  573 

humeral  circumflex,  589 

inferior  cerebellar,  580 

meningeal,    from    vertebral, 
579 

scapular,  582 

scrotal,  619 

superior  alveolar,  562 

tibial,  637 
postero-medial  ganglionic,  574, 

581 
princeps  cervicis,  557 

pollicis,  595 
profunda,  591 

brachii,  591 

cervicalis,  585 

femoris,  629 

linguae,  553 

superior,  591 
of  pterygoid  canal,  562,  568 
pudendal,  external,  629 

internal,  617 
in  female,  620 
in  niale,  617 
pudic,  external,  629 

internal,  617 
pulmonai-y,  543 
pyloric,  604 
radial,  592 

recurrent,  594 
radialis  indicis,  595 
ranine,  553 
recurrent,  of  hand,  595 

interosseous,  597 

radial,  594 

tibial,  635 


Artery     or     Arteries,     recurrent 

tdnar,  596 
renal,  610 
right  colic,  609 

gastric,  604 

gastroepiploic,  606 
sacral,  lateral,  621 

middle,  613 
scapular  circumflex,  588 

posterior,  582 

transverse,  582 
sciatic,  620 
scrotal,  posterior,  619 
sheaths  of,  499 
short  ciliary,  571 

gastric,  606 
sigmoid,  610 
spermatic,  611 

external,  623 

internal,  611 
sphenopalatine,  562 
spinal,  579 
splenic,  605 

sternocleidomastoid,  552,  556 
sternomastoid,  552,  556 
striate,  573 
structure  of,  498 
stylomastoid,  557 
subclavian,  575 
subcostal,  601 
sublingual,  553 
submaxillarj^  555 
submental,  555 
subscapular,  588 
superficial  cer%TLcal,  582 

epigastric,  6^9 

external  pudendal,  629 

iliac  circumflex,  629 

palmar  arch,  598 

temporal,  558 

volar,  594 
arch,  598 
superior  articular,  of  knee,  633 

cerebellar,  580 

epigastric,  585 

gluteal,  622 

hemorrhoidal,  610 

intercostal,  585 

labial,  555 

lar>-ngeal,  552 

mesenteric,  606 

phrenic,  601 

profunda,  591 

thoracic,  587 

thyroid,  552 

tympanic,  561 

ulnar  collateral,  591 

vesical,  615 
superhyoid,  553 
supraorbital,  569 
suprarenal,  610,  612 
suprascapular,  582 
sural,  633 

systemic  distribution  of,  543 
tarsal,  637 
temporal,  558 

deep,  561 

middle,  558 

superficial,  558 
thoracic,  587,  588 

aorta,  598 

axis,  588 

highest,  587 

lateral,  588 

superior,  587 
thoracoacromial,  588 
thyreoidea  ima,  549 
thyrocervical  trunk,  581 
thyroid  axis,  581 

inferior,  581 

superior,  552 
tibial,  anterior,  634 

posterior,  637 

recurrent,  635 
tonsillar,  555 


Artery    or    Arteries,    transversa 

coUi,  582 
transverse  cervical,  582 

facial,  558 

perineal,  619 

scapular,  582 
transversalis  colli,  582 
of  trunk,  598 
tympanic,  558,  560 
iilnar,  595 

recurrent,  596 
umbilical,  in  fetus,  540 
of  upper  extremity,  575 
urethral,  619 
of  urethral  bulb,  619 
uterine,  615 
vaginal,  616 
vasa  aberrantia,  590 

brevia,  606 

intestini  tenuis,  607 
vertebral,  578 
vesical,  615 
vestibiilar,  1059 
Vidian,  562,  568 
volar  arch,  deep,  595 
superficial,  598 

carpal,  594 

digital,  common,  598 

interosseous,  596 

metacarpal,  595 

proper,  598 
volaris  indicis  radialis,  595 
Arthrodia,  286 
Articular  arteries,  633 
capsules,  279 
cartilage,  282 

disk  of  acromioclavicular  joint, 
315 

of  distal  radioulnar  joint,  325 

of  sternoclavicular  joint,  314 

of  temporomandibiilar  joint, 
258 
lamella  of  bone,  279 
meniscus,  298 
processes  of  vertebrae,  96 
tubercle  of  temporal  bone,  139, 

180 
Articulatio  acromioclavicularis, 315 
atlantoepistrophica,  292 
calcaneocuboidea,  354 
coxce,  333 
cubiti,  321 

cuneonavicular  is,  356 
ellipsoidea,  286 
genu,  339 
humeri,  317 
mandibularis,  297 
radiocarpea,  327 
radioulnar  is,  324 

distalis,  325 

proximalis,  324 
sacroiliaca,  306 
sellaris,  286 
sternoclavicularis,  313 
talocalcanea,  352 
talocalcaneonavicular  is,  353 
talocruralis,  349 
tibiofibularis,  348 
trochoidea,  285 
Articulation  or  Articulations,  279 
acromioclavicular,  315 
amphiarthroses,  285 
of  ankle,  349 
atlantooccipital,  295 
of  atlas  with   axis   or  epistro- 
pheus, 292 

with  occipital  bone,  295 
calcaneocuboid,  354 
of  calcaneus  and  astragalus,  352 

with  the  cuboid,  354 
carpometacarpal,  330 
of  carpus,  328 
of  cartilages  of  ribs  with  each 

other,  304 
classification  of,  284 


1352 


INDEX 


Articulation  or  Articulations,  con- 
dyloid, 285 
costocentral,  299 
costochondral,  304 
costosternal,  302 
costotransverse,  300 
costovertebral,  299 
coxal,  333 

cuboideonavicular,  356 
cuneocuboid,  357 
cuneonavicular,  356 
diarthroses,  285 
of  digits,  333 
of  elbow,  321 
gomphosis,  284 
of  hip,  333 
humeral,  317 
immovalole,  284 
inferior,  325 
intercarpal,  328 
interehondral,  304 
intercuneiform,  357 
intermetacarpal,  331 
intermetatarsal,  358 
intertarsal,  352 
of  knee,  339 
of  lower  extremity,  333 
of  mandible,  297 
metacarpophalangeal,  332 
metatarsophalangeal,  359 
movable,  285 
movements  of,  286 
of    navicular    with    cuneiform 

bones,  356 
of  pelvis,  306 

with  vertebral  column,  306 
of  phalanges  of  foot,  359 

of  hand,  333 
of  pubic  bones,  310 

symphysis,  310 
radiocarpal,  327 
radioulnar,  324,  325 
by  reciprocal  reception,  286 
sacrococcygeal  symphysis,  309 
sacroiliac,  306 
of  sacrum  and  coccyx,  309 
scapuloclavicular,  315 
schindylesis,  284 
of  shoulder,  317 
sternoclavicular,  313 
sternocostal,  302 
of  sternum,  304 
sutura,  284 
symphysis,  285 

pubis,  310 
synarthroses,  284 
synchondrosis,  284 
syndesmosis,  285 
talocalcaneal,  352 
talocalcaneonavicular,  353 
talocrural,  349 
tarsometatarsal,  358 
of  tarsus,  352 
temporomandibular,  297 
tibiofibular,  348 

syndesmosis,  348 
tibiotarsal,  349 
of  trunk,  287 
of  upper  extremity,  313 
of  vertebral  arches,  289 

bodies,  287 

column,  287 

with  cranium,  295 
with  pelvis,  306 
of  wrist,  327 
Articulationes  capilulorum,  299 
carpometacarpeoe,  330 

pollicis,  330 
costotransversarioe,  300 
costovertebrales,  299 
diyitorum  manus,  333 

pedis,  359 
intercarpece,  328 
inter chondr ales,  304 
intermetacarpecE,  331 


Articulationes  iniermetatarsew,  358 
intertarseoe,  352 
mctatarsophalangeoe,  359 
ossiculorum  audilus,  1045 
sternocostalcs,  302 
tarsometatarsece ,  358 
Aryepiglottic  fold,  1079 
Aryepiglotticus  muscle,  1083 
Arytsenoideus  muscle,  1082 
Arytenoid  cartilages,  1075 
glands,  1084 
swellings,  1071 
Ascending  aorta,  545 
cervical  artery,  582 
colon,  11  SO 

frontal  convolution,  821 
lumbar  vein,  667 
oblique  muscle,  412 
palatine  artery,  555 
parietal  convolution,  823 
pharyngeal  artery,  557 
ramus  of  ischium,  235 
of  OS  pubis,  235 
Association     fibers     of     cerebral 
hemispheres,  843 
neurons,  755 
Asterion,  183,  198 
Astragalus,  266 

ossification  of,  275 
Atavistic  epiphyses,  95 
Atlantooccipital  articulation,  295 
Atlas,  99 

development  of  anterior  arch 

of,  82 
ossification  of,  113 
Atresia,  congenital,  of  pupil,  1003 
Atria  of  bronchi,  1098 
Atrial  canal,  508 
Atrioventricular   bundle   of   His, 
537 
opening,  left,  533,  534 
right,  531 
Atrium  dextrum,  629 
of  heart,  left,  533 
primitive,  508 
right,  529 
of  nasal  fossa,  994 
sinistrum,  533 
Attic  or  epitympanic  recess,  142, 

1038 
Attolens  aurem  muscle,  1035 
Attrahens  aurem  muscle,  1035 
Auditory  artery,  580 
internal,  580 
canal,  external,  1036 
meatus,  external,  1036 
nerve,  905 
ossicles,  1044 

development  of,  1033 
pit,  1029 
plate,  1029 

teeth  of  Buschke,  1055 
tube,  1042 

cartilaginous  portion  of,  1043 
cushion  of,  1043,  1147 
isthmus  of,  1043 
osseous  portion  of,  1043 
pharyngeal  ostium  of,  1141 
tonsil  of,  1043 
torus  tubarius,  1043 
veins,  1059 
vesicle,  1030 
Auerbach's  plexus,  1177 
Auricle,  left,  533 

right,  523 
Auricula  dextra,  529 
of  ear,  1033 

cartilage  of,  1034 
development  of,  1033 
ligaments  of,  1035 
muscles  of,  1035 
vessels  and  nerves  of,  1036 
of  heart,  left,  533 

right,  529 
sinistra,  533 


Auricular  appendix,  left,  533 
right,  529 
artery,  anterior,  559 
deep,  560 
of  occipital,  557 
posterior,  557 
lymph  glands,  693 
nerve,  anterior,  895 
great,  926 
posterior,  905 
of  vagus,  911 
point,  198 
surface  of  ilium,  234 

of  sacrum,  108 
tubercle  of  Darwin,  1033 
vein,  posterior,  646 
Auricularis  muscles,  1035 
Auriculotemporal  nerve,  895 
Auriculoventricular  groove,  527 
Auris  interna,  1047 
Auscultation,  triangle  of,  434 
Axes  of  pelvis,  240 
Axial  filament  of  spermatozoon,  43 

skeleton,  79 
Axilla,  585 

fascia  of,  436 
Axillary  arch,  434 
artery,  586 

branches  of,  587 
surface  markings  of,  1331 
lymph  glands,  699 
nerve,  934 
sheath,  586 
vein,  663 
Axis,  celiac,  603 
of  lens,  1019 
optic,  1001 
thoracic,  588 
thyroid,  581 
of  vertebra,  100 
ossification  of,  113 
Axis-cylinder  process,  723 
Axon  of  nerve  cells,  723 
Azygos  arteries  of  vagina,  616 
artery,  articular,  633 
uvulae  muscle,  1139 
vein,  667 


B 


Back,  muscles  of,  396 
Baillarger,  band  of,  835,  845 
Ball-and-socket  joint,  285 
Band  of  Baillarger,  835,  845 

of  Bechterew,  846 

of  Gennari,  846 

of  Giacoinini,  827 

iliotibial,  468 

moderator,  532 
Bare  area  of  liver,  1150 
Bartholin,  duct  of,  1136 

glands  of,  1213,  1266 
Basal  column,  posterior,  75S 

lamina,  735 

optic  nucleus  of  Meynert,  S13 

plate  of  placenta,  63 

ridge,  or  cingulum  of  tooth,  1 1 16 

vein,  653 
Base  of  cerebral  peduncle,  802 

of  heart,  527 

of  sacrum,  109 

of  skull,  inferior  surface,  179 
upper  surface  of,  190 
Basichromatin,  37 
Basihyal  of  hyoid  bone,  177 
Basilar  arterj',  580 

crest,  1054 

membrane,  1056 

part  of  occipital  bone,  132 

plexus  of  veins,  660 

sinus,  660 
Basilic  vein,  662 
median,  661 
Basion,  181,  198 


INDEX 


II 


Basis  bundle,  anterior,  760 
lateral,  762 
cordis,  527 
OSS.  sacri.  109 
peduncuH,  802 
prostatce,  1252 
pulmonis,  1094 
Basivertebral  veins,  668 
Basket  ceLs  of  cerebellum,  794 
Bechterew,  band  of,  846 
nucleus  of,  788 
pontospinal  fasciculus  of,  872 
Bed  of  stomach,  1162 
Bell,  nerve  of,  928,  933 
Bellini,  duct  of,  1223 
Bertin,  ligament  of,  335 
Betz,  giant  cells  of,  845 
Biceps  brachii  muscle,  443 
actions  of,  444 
nerves  of,  444 
variations  of,  444 
femoris  muscle,  478 
actions  of,  480 
nerves  of,  480 
variations  of,  479 
flexor  cubiti  muscle,  443 
muscle,  443 
Bicipital  fascia,  444 
groove,  209 
ridges,  209 
Bicuspid  teeth,  1118 

valve,  534 
Bigelow,  Y-shaped    ligament  of, 

335 
Bile  capillaries,  1197 
ducts,  1197,  1198 

lymphatic  capillaries  in,  686 
structure  of,  1199 
Bipolar  cells  of  retina,  1016 
Bird's  nest  of  cerebellum,  791 
Biventer  cervicis  muscle,  400 
Bi ventral  lobes  of  cerebellum,  791 
Bladder,  1227 
gall,  1197 
urinary,  1227 
in  child,  1229 
development  of,  1212 
distended,  1228 
empty,  1227 
female,  1230 
interior  of,  1231 
ligaments  of,  1231 
lymphatic  vessels  of,  712 
structure  of,  1232 
trigone  of,  1231 
vessels  and  nerves  of,  1233 
Blandin,  glands  of,  1131 
Blastodermic  vesicle,  46 
Blastopore,  47 
Blood,  composition  of,  503 
corpuscles,  503 

development  of,  505 
origin  of,  505 
course  of,  in  an  adult,  497 

in  fetus,  540 
islands,  506 
liquor  sanguinis,  503 
plasma,  503 
platelets,  505 
Bochdalek,  cornucopia  of,  798 
Body    or    Bodies,    anococcygeal, 
1184 
aortic,  1278 
carotid,  1281 
ciliary,  1010 
coccygeal,  1281 
geniculate,  811 
Malpighian,  of  kidney,  1221 

of  spleen,  1285 
olivary,  769 
of  penis,  1249 
perineal,  1184 
pineal,  1277 
pituitary,  814,  1275 
poUu:,  40 


Body  or  Bodies,  restiform,  793 
of  stomach,  1163 
thyroid,  1269 
trapezoid,  787 
of  uterus,  1259 
of  a  vertebra,  96 
Body-stalk,  53,  57 
Bone  or  Bones,  86 
ankle,  266 
arm,  209 

articular  lamella  of,  279 
astragalus,  266 
atlas,  99 
axis,  100 
breast,  119 
calcaneus,  263 
calf,  260 
canaliculi  of,  91 
cancellou''  tissue  of,  86 
capitate,  226 
carpal.  221 
cells,  91 

chemical  composition  of,  91 
classes  of,  \-iz.,  long,  flat,  mixed 

or  irregular,  short,  79 
clavicle,  280 
coccyx, 111 
collar,  200 

compact  tissue  of,  86 
cranial,  129 
cuboid,  269 
cuneiform,  of  carpus,  224 

of  tarsus,  270 
development  of,  8G 
diploe  of,  80 
of  ear,  1044 
of  elbow,  214 
eminences  and  depressions  of, 

80 
epistropheus,  100 
ethmoid,  153 
facial,  156 
femur,  242 
fibula,  260 
flat,  79 
of  foot.  262 
frontal,  135 
hamate,  227 
of  hand,  221 
Haversian  canals  of,  89 

systems  of,  89 
hip,  231 
humerus,  209 
hyoid,  177 
ilium,  231 
incus,  1044 

inferior  nasal  conchae,  169 
innominate,  231 
interparietal,  132 
ischium,  234 
lacrimal,  163 

lesser,  164 
lacunze  of,  90 
lamellae  of,  90 
lingual,  177 
long,  79 
of  lower  extremity,  231 

jaw,  172 
lunate,  221 
lymphatics  of,  89 
malar,  164 
malleus,  1044 
mandible,  172 
marrow  of,  87 
maxillae,  157 
medullary  artery  of,  88 

membrane  of,  87 
metacarpal,  227 
metatarsal,  272 
minute  anatomy  of,  89 
multangular,  greater,  225 

lesser,  225 
nasal,  156 
na\acular,  of  carpus,  221 

of  tarsus,  270 


Bone  or  Bones,  nerves  of,  88 

number  of,  in  body,  79 

nutrient  arterj'  of,  88 

occipital,  129 

OS  calcis,  263 
coxa?,  231 
magnum,  226 

ossification  of,  91 

palate,  166 

palatine,  166 

parietal,  133 

patella,  255 

peh-ic,  238 

perforating  fibers  of,  90 

periosteum  of,  87 

lymphatic  capillaries  in,  684 

phalanges  of  foot,  275 
of  hand,  230 

pisiform,  225 

pubis,  236 

radius,  219 

ribs,  123 

sacrum,  106 

scaphoid,  221,  270 

scapula,  202 

semilunar,  224 

sesamoid,  277 

shin,  256 

short,  79 

sphenoid,  147 

sphenoidal  conchae,  152 

stapes,  1045 

sternum,  119 

strength    of,     compared    with 
other  materials,  87 

structure  and  physical  proper- 
ties of,  86 

surfaces  of,  80 

sutural,  156 

talus,  266 

tarsal,  263 

temporal,  138 

thigh,  242 

tibia,  256 

trap>ezium,  225 

trapezoid,  225 

triangular,  224 

turbinated,  169 

ulna,  214 

unciform,  227 

of  upper  extremity,  200 
jaw,  157 

vertebra  prominens,  101 

vertebrae,  cerx-ical,  97 
coccygeal,  106 
lumbar,  104 
thoracic,  102 
sacral,  106 

vessels  of,  88 

vomer,  170 

Wormian,  156 

zygomatic,  164 
Bowman,  capsule  of,  1222 

glands  of,  996 

membrane  of,  1008 

muscle  of,  1011 
Brachia     conjunctiva     of     cere- 
bellum, 792 

of  corpora  quadrigemina,  805 

pontis,  793 
Brachial  arterj-,  589 
branches  of,  590 
peculiarities  of,  590 
surface  marking  of,  1335 

cutaneous  nerve,  lateral,  934 
medial,  937 
posterior,  943 

fascia,  442 

plexus,  930 

veins,  663 
Brachialis  anticus  muscle,  444 

muscle,  444 

actions  of,  444 
nerves  of,  444 
variations  of,  444 


1354 


INDEX 


Brachiocephalic  artery,  548 

veins,  664 
Brachioradialis  muscle,  451 
actions  of.  456 
nerves  of,  456 
variations  of,  451 
Brain,  arteries  of,  574 

commissures  of,  809 

development  of,  736 

divisions  of,  766 

dura  of,  872 

meninges  of,  872 

pathways  from,  to  spinal  cord, 
870 

pia  of,  878 

sensory  pathways  from  spinal 
cord  to,  851 

surface  markings  of,  1292 

veins  of,  652 

weight  of,  848 
Branchial  arches,  65 

grooves,  65 
Breadth  index  of  skull,  198 
Breast  bone,  119 
Breasts  or  mammae,  1267 

development  of,  1267 
Bregma,  178,  198 
Bregmatic  fontanelle,  190 
Bridge  of  nose,  992 
Brim  of  pelvis,  238 
Broad  ligaments  of  uterus,  1154, 

1260 
Broca,  cap  of,  822 

diagonal  band  of,  869  . 

gyrus  of,  822 

limbic  lobe  of,  825 

parolfactory  area  of,   826 
Bronchi,  1084 

divisions  of,  1097 

eparterial,  1097 

hyparterial,  1097 

intrapulmonary,  1098 

left,  1085 

lymphatic  capillaries  in,  686 

right,  1085 
Bronchial  arteries,  600,  1100 

nerves,  913 

veins,  667,  1100 
Bronchomediastinal  trunks,  717, 

718 
Bronchus  dexter,  1085 

sinister,  1085 
Brunner's  glands,  1176 
Bryant's  triangle,  1343 
Buccce,  1112 
Buccal  artery,  561 

branches  of  facial  nerve,  905 

cavity,  1110 

glands,  1112 

nerve,  long,  895 
Buccinator  artery,  561 

muscle,  384 

relations  of,  384 

nerve,  895 
Bucconasal  membrane,  70 
Buccopharyngeal  fascia,  390 

membrane,  47 
Bulb  of  aorta,  545 

of  corpuscavernosum  penis,  1248 

of  eye,  1000 

olfactory,  826,  848 

of  posterior  cornu,  831 

spinal,  767 

vaginal,  1266 

of  vestibule,  1266 
Bulbar  arteries,  580 
Bulbocavernosus  muscle,  428,  430 

actions  of,  428.  430 
Bulbospinal  fasciculus,  854 
Bulbourethral  glands  of  Cowper, 

1215,  1253 
Bulbs  of  internal  jugular  vein,  648 
Bulbus  cordis,  508 

oculi,  1000 

olfactorius,  826 


Bidhiis  vestihuli,  1266 
Bulla  elhmoidalis,  195,  995 
Bundle  of  His,  537 
oval,  735 

of  Vicq  d'Azyr,  810,  813,  839, 
869 
Burdach,  tract  of,  752,  763 
Burns'  space,  389 
Bursa,  omental,  1152,  1155 
development  of,  1106 
omentalis,  1155 
pharyngeal,  1141 
prepatellar,  471 
Bursse     beneath     gluteus   maxi- 
mus,  474 
mucosa\  283 
near  knee-joint,  345 
shoulder-joint,  319 


Cacuminal  lobe,  790 
Calamus  scriptorius,  799 
Calcaneal  arteries,  638,  639 
lateral,  638 
medial,  639 

nerve,  internal,  963 
medial,  963 

sulcus,  263 

tuberosity,  266 
Calcaneoastragaloid  articulation , 
352 

ligaments,  352 
Calcaneocuboid  ligaments,  354 
Calcaneonavicular  ligaments,  355 
Calcaneotibial  ligament,  350 
Calcaneus,  263 

ossification  of,  275 
Calcar  avis,  831 
Calcarine  fissure,  820 
Calf  bone,  260 

Calices  of  kidney,  1221,  1225 
Callosal  convolution,  825 

fissure,  825,  828 
Callosomarginal  fissure,  820 
Camper,  fascia  of,  408 
Canaliculi  of  bone,  89 

dental,  1119 
Canaliculus,    inferior    tympanic, 
144,  181 

mastoid,  144,  181 
Canalis  centralis  cochleae,  143 

craniopharyngeus,  153 

rcuniens  [oillcnssn],  1052,  1054 
Canal  or  Canals,  adductor,  627 

Alcock's,  421 

alimentary,  1100 

alveolar,  158 

atrial,  608 

auditory,  external,  1036 

carotid,  143,  181 

central,  of  medulla  spinalis,  754 

of  cervix  of  uterus,  1260 

condyloid,  131 

craniopharyngeal,  153,  1277 

ethmoidal,  138,  154 

femoral,  625 

Haversian,  of  bone,  89 

of  Huguier,  141,  904,  1039 

Hunter's,  627 

hyaloid,  1018 

hypoglossal,  131 

incisive,  162,  180 

infraorbital,  159 

inguinal,  418 

lacrimal,  1028 

mandibular,  173 

neural,  50 

neurenteric,  50 

of  Nuck,  1211,  1261 

of  Petit,  1019 

pharyngeal,  180 

pterygoid,  181 

pterygopalatine,  1^9,  108 


Canal  or  Canals,  sacral,  110 
of  Schlemm,  1005 
semicircular,  1049 

membranous,  1052 
spermatic,  418 
spiral,  of  modiolus,  1051 
vertebral,  110 
Canales  semicirculares  asset,  1( 
Canaliculus  innominatus  of  Ar- 
nold, 150,  note 
Canalis  adductorius,  627 

centralis  [medulla  spinalis],  754 
cervicis  uteri,  1260 
inguinalis,  418,  1239 
sacralis,  110 

semicircularis  lateralis,  1041 
posterior,  1049 
superior,  1049 
Cancellous  tissue  of  bone,  86  \ 
Canine  eminence,  158 
fossa,  loS 
teeth,  1117 
Caninus  muscle,  383 
actions  of,  383 
nerves  of,  383 
Canthi  of  eyelids.  1025 
Cap  of  Broca,  822 
Capillaries,  499 
bile,  1179 
lymphatic,  684 
structure  of,  500 
Capitate  bone,  226 
Capituluni  fibulas,  260 
humeri,  212 
mallei,  1044 
stapedis,  1045 
Capsula    articularis.      See    Indi- 
vidual joints. 
cricoarytoenoidea,  1087 
externa,  837 
extrema,  835 
interna,  836 
lentis,  1019 
vasculosa  lentis,  1003 
Capsular  artery,  middle,  610 
Capsule,  adipose,  of  kidney,  1220 
adrenal,  1278 
of  Bowman,  1221 
of  brain,  835,  836,  837 
of  Glisson,  1157,  1194 
of  lens,  1019 
of  Tenon,  1024 
Caput  cwcum  coli,  1177 
femoris,  243 
humeri,  209 
pancreatis,  1200 
tali,  267 
Cardiac  cycle,  538. 

ganglion  of  Wrisberg,  984 
glands  of  stomach,  1166 
muscular  tissue,  536 
nerves,  cervical,  912 
from  sympathetic,  979 
from  vagus,  912 
great,  979 
inferior,  912 
middle,  979 
superior,  912 
thoracic,  912 
notch,  1096 

orifice  of  stomach,  1161 
plexus  of  nerves,  984 
veins,  042 
Cardinal  veins,  520 
Caroticoclinoid  foramen,  151,  191 

ligament,  153 
Caroticotympanic  artery,  568 

nerve,  1047 
Carotid  arch,  516 
artery,  common,  549 

branches    of    (occasional) , 

551 
peculiarities  of,  551 
surface  markings  of,  1302 
external.  551 


V. 


INDEX 


1355 


1 


arotid  arterv,  external,  branches 
of,  552 
surface  markings  of,  1302 
internal,  566 

branches  of,  568 
peculiarities  of,  567 

bodies,  1281 

canal,  143,  181 

ganglion,  977 

glands,  1281 

groove,  148,  191 

nerve,  internal,  977 

nerves  from  glossopharyngeal, 
909 

plexus,  977 
internal,  977 

sheath,  389 

triangles,  564 
Carpal  arteries  from  radial,  594 
from  ulnar,  598 

bones,  221 

net-work,  594 
Carpometacarpal    articulations, 

330 
Carpus,  221 

articulations  of,  328 

ossification  of,  230 

surface  form  of,  1327 
Cartilage  or  Cartilages,  articular, 
280 

arytenoid,  1075 

of  auricula,  1034 

cells,  279 

corniculate,  1075 

costal,  127,  281 

cricoid,  1074 

cuneiform,  1075 

of  epiglottis,  1075 

epiphysial,  93 

ethmovomerine,  171 

histology  of,  279 

hyaline,  279 

intrathyroid,  1074 

lacunae,  280 

of  larynx,  1073 
structure  of,  1076 

lateral,  993 

of  nose,  992,  993 

Meckel's,  66,  174 

parachordal,  84 

permanent,  279 

of  pinna,  1034 

of  Santorini,  1075 

of  septum  of  nose,  993 

sesamoid,  993 

temporary,  280 

thyroid,  1073 

trabecules  cranii,  84 

of  trachea,  1086 

vomeronasal,  996 

white  fibro-,  279,  281 

of  Wrisberg,  1075 
Cartilagines  alares  minores,  993 

arytcenoidecc,  1075 

comiculatT.  1075 

costalcs,  127 

cuneifortnes,  1075 

laryngis,  1073 

nasi,  992 
Cartilaginous  ear  capsules,  85 

vertebral  column,  82 
Cartilago  alaris  major,  993 
cms  laterale,  993 
mediale,  993 

auriculce,  1034 

cricoidea,  1074 

epiglottica,  1075 

nasi  lateralis,  993 

septi  nasi,  992 

thyreoidea,  1073 

triticea,  1077 
Carimcula  lacrimalis,  1028 
Carunculae  hymenales,  1266 
Cauda  equina,  750 

helicis,  1034 


b 


Cauda  pancreatis,  1201 
Caudal  fold  of  embryo,  53 
Caudate  lobe  of  liver,  1192 

nucleus,  833 

process  of  liver,  1192 
Caudatum,  833 
Cavernous  arteries,  568 

nerves  of  penis,  989 

plexus,  978 

portion  of  urethra,  1235 

sinuses,  658 
nerves  in,  900 

spaces  of  penis,  1250 
Cavity  or  Cavities,  amniotic,  56 

body  or  celom,  50 

buccal,  1110 

cotyloid,  237 

glenoid,  207 

of  lesser  pelvis,  239 

mediastinal,  1090,  1092 

of  mouth  proper,  1110 

nasal,  194,  994 

oral,  1110 

peritoneal,  1150 

of  septum  pellucidum,  840 

sigmoid,  of  radius,  220 
of  ulna,  215 

subarachnoid,  876 

subdural;  875 

of  thorax,  524 

tympanic,  1038 

of  uterus,  1260 
Cavuin  concha,  1034 

laryngis,  1078 

Meckelii,  886 

nasi,  194,  994 

oris,  1110 

proprium,  1110 

septi  pellucidi,  840 

subarachnoideale,  876 

tympani,  paries  carotica,  1042 
labyrinthica,  1040 
mastoidea,  1042 

tympanum,  1037 

paries  jugularis,  1038 
membranacea,  1038 
tegmcntalis,  1038 

uteri,  1260 
Cecal  arteries,  607 

fossjE,  1160 
Cecum,  1177 

lymphatic  vessels  of,  710 
Celiac  artery,  603 

axis,  603 

branches  of  vagus  nerve,  913 

ganglion,  985 

plexus,  985 
Cell  or  Cells,  animal,  35 

basket,  of  cerebellum,  796 

of  Betz,  845 

of  bone,  91 

centro-acinar,    of    Langerhans, 
1204 

chromaffin,  1277 

clasmatocytes,  377 

of  Claudius,  1058 

definition  of,  35 

of  Deiters,  1058 

divisions  of,  37 

of  Dogiel,  921 

enamel,  1123 

germinal,  of    medulla  spinalis, 
733 

giant,  88 
of  Betz,  845 

of  Golgi,  845 

of  fundus  glands,  1166 

granule,  377 

gustatory-,  991 

of  Hensen,  1058     • 

lamellar,  377 

of  Martinotti,  845 

mass,  inner,  46 
intermediate,  50 

Mastzellen,  377 


Cell  or  Cells,  membrane,  36 

nerve,  721 

nucleus  of,  36 

olfactory,  996 

pigment,  377 

plasma,  377 

of  Purkinje,  794 

reproduction  of,  37 

of  Sertoli,  1243 

of  spinal  ganglia,  730,  919 

splenic,  1284 

structure  of,  35 

wandering,  377 
Cella,  829 

Cellulce  ethmoidales,  998 
Cement  of  teeth,  1120 
formation  of,  1124 
Centers  of  ossification,  93 

visual,  814 
Central  artery  of  retina,  571 

canal  of  medulla  spinalis,  754 

cells  of  fundus  glands,  1166 

fissure,  819 

gray  stratum  of  cerebral  aque- 
duct, 806 

ligament   of   medulla    spinalis, 
879 

lobe,  825 

nervous  system,  721 

part  of  lateral  ventricle,  829 

sulcus,  819 

tendinouspoint  of  perineum, 427 

tendon  of  diaphragm,  406 

tract  of  cranial  nerves,  805 
of  trigeminal  nerves,  805 
Centrifugal  nerve  fibers,  729 
Centriole,  37 

bodies  of  ovum,  40 

of  spermatozoon,  42,  43 
Centripetal  nerve  fibers,  729 
Centroacinar  cells  ol  Langerhans, 

1204 
Centrosome,  37 
Centrosphere,  37 
Centrum  ovale  majus,  828 

minus,  827 
Cephalic    flexure    of    embryonic 
brain,  737 

fold  of  embryo,  53 

index,  198 

portion  of  sympathetic  system, 
977 

vein,  661 

accessory,  662 
Ceratohyal  of  hyoid  bone,  178 
Cerebellar  arteries,  580 

fasciculus,  direct,  758 

notches,  788 

peduncles,  793 

tract,  direct,  761,  778 
of  Flechsig,  761 

veins,  652 
Cerebellum,  788 

brachia  conjunctiva,  792 
pontis,  793 

development  of,  740 

fibrce  proprioe,  794 

gray  substance  of,  794 

lobes  of,  788 

nucleus  dentatus,  796 

peduncles  of,  793 

structure  of,  791 

surfaces  of,  789,  790 

vermis  of,  788 

white  substance  of,  791 
Cerebral  arteries,  anterior,  571 
middle,  572 
posterior,  580 

aqueduct,  806 

cortex,  nerve  cells  of,  845 
fibers  of,  846 
structure  of,  845 
types  of,  847 

fissure,  lateral,  819 

hemispheres,  817 


1356 


Cerebral  hemispheres,  borders  of, 
818 
development  of,  744 
fibers  of,  association,  843 
commissural,  843 
projection,  843 
transverse,  843 
fissures  of,  819 
gray  substance  of,  843 
gyri  of,  821 
interior  of,  827 
lobes  of,  821,  822 
localization  of,  849 
nerves,    881.       See    Cranial 

nerves. 
poles  of,  818 
structure  of,  842 
sulci  of,  819,  820,  821 
surfaces  of,  818 
white  substance  of,  842 
peduncles.  800 

structure  of,  800 
veins,  652 

ventricles,  797,  815,  829 
Cerebrospinal  fasciculus,  759,  760 
fibers  of  internal  capsule,  836 
fluid,  880 
Ceruminous  glands,  1037 
Cervical  artery,  ascending,  581 
deep,  585 
superficial,  582 
transverse,  582 
branch  of  facial  nerve,  905 
cardiac  nerves,  912 
enlargement   of   medulla  spin- 
alis, 732 
fascia,  3S8 

flexure  of  embryonic  brain,  131 
ganglion,  978,  979,  980 
lymph  glands,  697 
muscles,  lateral,  388 
nerve,  cutaneous  or  transverse, 
927 
of  facial,  903 
nerves,  921 

divisions  of,  anterior,  925 
posterior,  921 
pleura,  1088 
plexus,  925 

branches  of,  926,  927 
portion  of  sympathetic,  978 
rib,  102,  128 
veins,  651 
vertebrae,  97 
Cervicalis  ascendens  muscle,  399 
Cervix  uteri,  1239 

portio  supravaginalis,  1239 
vaginalis,  1260 
of  uterus,  1239 
Chambers  of  eye,  1012 
Check  ligaments,  296 

of  eye,  1024 
Cheeks,  1112 
Chest,  117 
Chiasma,  optic,  814,  883 

opticum,  814,  883 
Chiasmatic  groove,  147,  190 
Choana;,  180,  196,  994 
Chondrin,  282 
Chondrocranium,  84 
Chondro-epitrochlearis       muscle, 

437 
Chondroglossus  muscle,  1130 
Chondromucoid,  282 
Chondrosternal  ligament,  302 

intra-articular,  303 
Chondroxiphoid  ligaments,  304 
Chorda  obliqua,  325 

tympani  nerve,  904 
Chordx  tendinew   [left   ventricle], 
535 
[right  ventricle],  532 
Willisi,  653 
Chordal  furrow,  52 

portion  of  base  of  skull,  84 


INDEX 


Chorioidea,  1009 

lamina  choriocapillaris,  1010 
vasculosa,  1010 
Chorion,  60 

frondosum,  62 

la;ve.  61 
Chorionic  villi,  60 
Choroid  artery,  574 

coat  of  ej'eball,  1009 
structure  of,  1010 

plexuses  of  fourth  ventricle,  798 
of  lateral  ventricle,  840 
of  third  ventricle,  813 

vein,  653 
Choroidal  artery,  anterior,  374 
posterior,  581 

fissure,  841,  1002 
Chromaffin  cells,  1277 
Chromapliil  and  cortical  systems, 
1277 
development  of,  1277 
Chromatin,  36 
Chromatolysis,  724 
Chromosomes,  37 
Chyle,  683 

Chyliferous  vessels,  683 
Cilia,  1025 
Ciliaris  muscle,  1010 
Ciliary  arteries,  571 

body, 1010 

ganglion,  888 

glands,  1023 

muscle,  1011 

nerves,  888 

processes,  1010 
Cingulate  gyrus,  823 

sulcus,  820 
Cingulum  of  cerebral  hemisphere. 
843 

of  teeth,  1116 
Circle,  arterial,  of  Willis,  574 
Circular  folds  of  small  intestine, 
1173 

sinus,  659 

sulcus,  821,  825 
Circulating  fluids,  503 
Circulation  of  blood  in  adult,  497 

in  fetus,  540 
Circulus  arteriosus  major,  1014 
minor,  1014 

major  [iris],  571,  1014 

minor  [iris],  371,  1014 

venosus  [mamma],  1268 
Circumduction,  286 
Circumferential  fibrocartilage,  282 
Circumflex  arteries,  femoral,  630 
humeral,  589 

nerve,  934 
Circuminsular  fissure,  821 
Circumvallate  papillae,  1126 
Cistema  basalis,  876 

chyli,  691 

cerehellomedullaris,  876 

chiasmatis,  877 

fossce  cerebri  lateralis,  877 

inter  peduncular  is,  876 

magna,  876 

pontis,  876 

vencE  magnce  cerebri,  877 
Cisternae  subarachnoid,  876 

subarachnoidalcs ,  876 
Clarke's  column,  758 
Clasmatocytes,  377 
Claudius,  cells  of,  1058 
Claustrum,  835 
Clava,  774 
Clavicle,  200 

ossification  of,  202 

peculiarities  of,  in  sexes,  202 

structure  of,  202 

surface  anatomy  of,  1326 
Clavicula,  200 
Clavipectoral  fascia,  437 
Cleft  palate,  199 
CleJdohyoideus  muscle,  393 


I 


il 

,  121^ 

m 


Clinging  fibers  of  cerebellum,  796 
Clinoid  processes,  anterior,    131, 
190 
middle,  147,  190 
posterior,  147,  190 
Clitoris,  1266 

frenulum  of,  1266 

glans  of,  1266 

nerves  of,  968 

prepuce  of,  1266 
Clivus  of  sphenoid,  148 

monticuli  of  cerebellum,  790 
Cloaca,  ectodermal,  1109 

entodermal,  1109 

pelvic  portion  of,  1212 

phallic  portion  of,  1213 

vesicourethral  portion  of,  1212 
Cloacalduct,  1109 

membrane,  1109 

tubercle,  1213 
Cloquet,  lymph  gland  of,  703 
Closing  membranes,  65 
Coarctation  of  aorta,  547 
Coccygeal  arteries,  620 

body.  1281 

cornua.  111 

gland,  1281 

nerve,  division  of,  anterior,  957 
posterior,  925 

plexus,  968 
Coccygeus  muscle,  424 
actions  of,  424 
nerves  of,  424 
Coccyx,  111 

ossification  of,  114 
Cochlea,  1050 

aqueduct  of,  144,  181 

cupula  of,  1050,  1051 

hamulus  lamince  spiralis,  1051 

helicotrema  of,  1051 

modiolus  of,  1050 

scalae  of,  1031 

spiral  canal  of,  1051 
lamina  of,  1051 

vessels  of,  1059 
Cochlear  artery,  1059 

nerve,  906,  1059 

composition  and  central  con- 
nections of,  857 

nuclei,  788,  906 

root  of  acoustic  nerve,  906 
Cochleariform  process,  143,  1042 
Cog-tooth  of  malleus,  1044 
Cohnheim,  areas  of,  374 
Colic  arteries  of  ileocolic,  609 
left,  610 
middle,  609 
right,  609 

flexures,  right  and  left,  1180 

impression,  1189 

valve,  1179 
Collar  bone,  200 
Collateral  circulation,  343 

eminence,  833 

fissure.  820 

ganglia,  977 
Collecting  tubes  of  kidney,  1223 
CoUes,  fascia  of,  235,  409,  42a 
Colliculi,  inferior,  805,  806 

superior,  803,  806 
CoUiculus  of  arytenoid  cartilage, 
1073 

facialis,  799 

inferior,  806 

nervi  optici,  1015 

superior,  806 
Collum  anatom.icum,  209 

femoris,  243 

mallei,  1044 

tali,  269 
Coloboma,  1002 
Colon,  1180 

ascendens,  1180 

ascending,  1180 

descendens,  1181 


Iv 


INDEX 


1357 


^ 


II 

II 
II 

II 


'Colon,  descending,  1181 
iliac,  1182 
left  or  splenic  flexure  of,  1181 
pelvic,  1182 

right  or  hepatic  flexure  of,  1180 
sigmoid,  1182 
siqmoideum,  1182 
structure  of,  1184 
tela  submucosa,  1186 
transverse,  1180 
transversum,  1180 
"     tunica  mucosa,  1186 
muscularis,  1185 
serosa,  1184 
vessels  and  nerves  of,  1187 
Colored  lines  of  Retzius,  1120 

or  red  corpuscles,  503 
Colorless  corpuscles,  504 
Colostrum  corpuscles,  1208 
Columna  anterior  {medulla  spin- 
alis], 753 
fornicis,  838 

lateralis  [medulla  spinalis],  753 
nasi,  992 

posterior  [medulla  spinalis],  753 
vertebralis,  96 
■Columnce  carneee,  532 
Columns  of  Clarke,  758 
of  fornix,  838 
of  medulla  spinalis,  756,   757, 

758 
rectal,  of  Morgagni,  1185 
renal,  1221 
of  vagina,  1264 
vertebral,  96,  114 
Comes  nervi  phrenici,  584 
Comitans  nervi  ischiadici,  620 
Comma-shaped  fasciculus,  764 
■Commissura     laboriuni     anterior, 
1265 
palpebrarum  lateralis,  1025 
medialis,  1025 
Commissural    fibers    of    cerebral 

hemispheres,  843 
Commissure  of  brain,  809 
anterior,  747,  840 
middle  or  gray,  809 
posterior,  743,  812 
of  corpus  callosum,  747 
habenular,  812 
hippocampal,  838,  869 
of  Gudden,  814 
of  labia  majora,  1265 
of    medulla    spinalis,    anterior 
and  posterior  gray,  754 
anterior  white,  752 
optic,  814 
Commissures,  palpebral,  1025 
Common  bile  duct,  1198 
lymphatics  of,  711 
carotid  artery,    549 
dental  germ,  1122 
iliac  arteries,  613 
glands,  704 
veins,  677 
integument,  1062 
interosseous  artery.  596 
•peroneal  nerve,  694 
Communicans  fibularis  nerve,  694 

tibialis  nerve,  962 
Communicantescervicales  nerves, 

928 
Communicating  artery,  anterior, 
571 
from  dorsalis  pedis,  637 
posterior,  573 
Compact  tissue  of  bone,  86 
Comparison  of  bones  of  hand  and 

foot,  276 
Complexus  muscle,  400 
Composition  and  central  connec- 
tions of   cranial   nerves, 
855 
of  spinal  nerves,  849 
ompressor  naris  muscle,  382 


Concha  of  auricula,  1034 

nasal,  inferior,  169 

articulations  of,  170 
ossiffication  of,  170 
middle,  156 
superior,  156 

nasalis  inferior,  169 
Conchse,  sphenoidal,  152 

sphenoidales ,  152 
Conchal  crest,  160,  167 
Condyle  of  mandible,  174 
Condyles  of  femur,  247 

occipital,  131 

of  tibia,  256 
Condyloid  articulation,  286 

canal,  131 

foramen,  anterior,  131 

fossa,  131,  181 

process  of  mandible,  174 
Cone  of  attraction,  45 

bipolars  of  retina,  1017 

granules  of  retina,  1017 

of  origin  of  axon,  724 
Cones  of  retina,  1017 
Confluence  of  sinuses,  131,  658 
Conflucns  sinuum,  658 
Coni  vasculosi,  1244 
Conical  papillae,  1127 
Conjoined     tendon     of     internal 

oblique        and        transversalis 

muscles,  414 
Conjugate  diameter  of  pelvis,  239 
Conjunctiva,  1026 
Connecting  fibrocartilages,  282 
Connective  tissue.extraperitoneal. 

418 
Conoid  ligament,  315 

tubercle,  200 
Constriction,duodenopyloric,1162 
Constrictor  muscles,  1142 

pharyngis  inferior  muscle,  1142 
medius  muscle,  1143 
superior  muscle,  1143 

urethne  muscle,  429,  431 
Conus  arteriosus,  531 

elasticus  [larynx],  1078 

medullaris,  749 
Convoluted  tubes  of  kidney,  1223 
Convolution,  callosal,  825 

frontal,  ascending,  821 

occipitotemporal,  823 

parietal,  ascending,  823 
Cooper,  ligament  of,  412 
Copula,  1103 
Cor,  526 

Coracoacromial  ligament,  316 
Coracobrachialis  muscle,  443 
actions  of,  444 
nerves  of,  444 
variations  of,  443 
Coracoclavicular  fascia,  437 
Coracohumeral  ligament,  317 
Coracoid  process,  207 

tuberosity,  200 
Cord,  gangliated,  976 

spermatic,  1239 

spinal,  749 

umbilical,  57 

vocal,  false,  1079 
inferior,  1080 
superior,  1079 
true,  1080 
Corium  or  cutis  vera,  1065 

layers  of,  1065 

stratum  papillare,  1065 
reticular  e,  1065 
Cornea.  1006 

structure  of,  1007 
Corneal  corpuscles,  1008 

endothelium,  1009 

epithelium,  1007 

spaces,  1008 
Corniculate  cartilages,  1075 
Cornu  anterius,  830 

inferior,  831 


Cornu  of  medulla  spinalis,  753 

posterius,  831 
Cornua  of  coccyx,  111 
of  hyoid  bone,  178 
of  lateral  ventricles,  830,  831 
majora  [os  hyoidei],  178 
minora  [os  hyoidei],  178 
of  sacrum,  108 

of  thyroid  cartilage,  1073,  1074 
Cornucopia  of  Bochdalek,  798 
Corona  glandis,  1249 
radiata  [brain],  837 

[ovum],  40 
Coronal  suture,  178,  183 
Coronary  artery  of  heart,  546 
peculiarities  of,  547 

of  lips,  555 

of  stomach,  603 
ligament  of  liver,  1150 
ligaments  of  knee,  343 
plexuses,  985,  987 
sinus,  642 

opening  of,  530 
sulcus  of  heart,  526 
veins,  642 

of  stomach,  682 
Coronoid  fossa,  212 

process  of  mandible,  174 

of  ulna,  214 
Corpora  cavernosa  clitoridis,  1266 

penis,  1248 
bulbs  of,  1248 
crura  of,  1248 
mammillaria,  813 
quadrigemina,  805 

brachia  of,  805,  806 

structure  of,  806  , 

Corpus  albicantia,  813 
Arantii,  533 
callosum,  818,  828 

developrrient  of,  747 

genu  of,  828 

peduncle  of,  827 

rostrum  of,  828 

splenium  of,  828 
cavernosum,  artery  to,  620 

urethra,  1247 
ciliare,  1010 
femoris,  246 
fibulm,  260 

fornicis,  838  ,    . 

geniculatum  laierale,  811 

mediate,  811 
Highmori,  1243 
humeri,  209 
incudis,  1044 
luteum,  1256 
maxilla;,  158 
OSS.  hyoidei,  111 

ilii,  231 

ischii,  234 

pubis,  235 
pancreatis,  1201 
papillare  [corium],  1065 
penis,  1249 
pineale,  812 
radii,  219 
sphenoidale,  147 
spongiosum,  1248 
sterni,  120 
striatum,  833 

vein  of,  838 
subthalamicum,  812 
tali,  267 
tibia:,  257 
ulncE,  215 
uteri,  1259 
vertebrcp,  96 
vitreum.,  1018 
Corpuscles,  colored,  503 

development  of,  505 
colorless,  504 
genital,  1060 

of  Golgi  and  Mazzoni,  1061 
of  Grandry,  1060 


1358 


Corpuscles  of  Hassall,  1274 
of  Herbst,  1061 
Pacinian,  1060 
of  Ruffini,  1061 

of      Wagner     and       Meissner, 
1061 
Corrugator  cutis  ani  muscle,  425 
muscle,  381 
actions  of,  381 
nerves  of,  381 
supercilii  muscle,  381 
Cortex  of  cerebellum,  794 

of  cerebrum    845 
Corti,  ganglion  of,  1051,  1059 
organs  of,  1056 
pillars  or  rods  of,  1056 
spiral  organ  of,  1050 
tunnel  of,  1057 
Cortical  arches  of  kidney,  1221 
arterial  system  of  Ijrain,  574 
portion    of    suprarenal    gland, 

1280 
substance  of  kidney,  1221 

of  lens,  1020 
visual  center,  882 
Corticostriate  fibers,  835 
Costoi,  123 

Costal  cartilages,  127,  280 
element  or  process,  98 
groove,  124 
pleura,  1088 
tuberosity,  202 
Costocentral  articulation,  299 
Costocervical  trunk,  585 
Costochondral  articulations,  304 
Costocoracoid  ligament,  437 

membrane,  628 
Cortocoracoideus  muscle,  437 
Costomediastinal  sinus,  1090 
Costosternal  articulations,  302 
Costotransverse  articulations,  300 

ligaments,  302 
Costovertebral  articulations,  299 

ligament,  anterior,  299 
Cotyloid  cavity,  237 
ligament,  237,  436 
Covering  bones,  85 
Coverings  of  ovum,  40 

of  testes,  1236 
Cowper's  glands,  1213,  1253 
Coxal. articulation,  333 
movements  of,  338 
muscles  in  relation  to,  338 
Cranial  arachnoid,  876 
bones,  129 
dura  mater,  872 
fossa,  anterior,  190 
middle,  190 
posterior,  190,  192 
nerves,  881 
abducent,  899 
accessory,  913 
acoustic,  905 

composition  and  central  con- 
nections of,  855 
development  of,  748 
facial,  901 

glossopharyngeal,  906 
hypoglossal,  914 
oculomotor,  884 
olfactory,  881 
optic.  882 
tracts  of,  804,  805 
trigeminal,  886 
trochlear,  885 
vagus,  910 
pia  mater,  879 
sympathetics,  970 
Craniology,  197 
Craniopharyngeal  canal,  1277 
Cranium,  128 

bones  of,  128,  129       . 
breadth  of,  198 
development  of,  83 
height  of,  198 


INDEX 

Cranium,    horizontal    circumfer- 
ence of,  198 

length  of,  198 

longitudinal  arc  of,  198 
Cfemaster  muscle,  414 
Cremasteric  artery,  623 

fascia,  414 
Crescents  of  Gianuzzi,  1136 
Crest  or  Crests,  basilar,  1054 

conchal,  159,  167 

ethmoidal,  161,  167 

frontal,  136 

of  ilium,  234 

incisor,  163 

infratemporal,  150,  183 

internal  occipital,  131,  193 

intertrochanteric,  246 

lacrimal,  161,  164 

nasal,  163,  167 

neural,  51,  736 

obturator,  236 

of  pubis,  236 

of  right  atrium,  529 

sphenoidal,  149 

supramastoid,  139 

of  tibia,  257 

of  tubercles  of  humerus,  209 

urethral,  in  female,  1236 
in  male,  1234 
Cribriform  plate  of  ethmoid,  153 
CricoarytiBnoideus  lateralis  mus- 
cle, 1082 

posterior  muscle,  1082 
Cricoarytenoid  ligament,  1078 

muscles,  1082 
Cricoid  cartilage,  1074 
Cricothyreoideus  muscle,  1081 
Cricothyroid  artery,  552 

ligament,  middle,  1078 

membrane,  1078 

muscle,  1081 
Cricotracheal  ligament,  1077 
Crista    arcuata     [arytenoid    car- 
tilage], 1075 

colli  costcc,  123 

falciformis,  143 

gain,  153 

terminalis  [of  His],  509 

vestibuli,  1047 
Crossed  commissural  fibers,  755 

pyramidal  tract,  760 
Crosses  of  Ranvier,  727 
Crown  of  a  tooth,  1117 
Crucial  anastomosis,  630 

ligaments,  342 
Cruciate  crural  ligament,  488 

eminence  of  occipital  bone,  130 

ligament  of  atlas,  295 

ligaments  of  knee,  342 
Crura  cerebri,  800 

of  diaphragm,  405 

of  fornix,  840 

of  penis,  1248 

of  stapes,  1045 

of  subcutaneous  inguinal  ling, 
410 
Crural  arch,  deep,  419 

nerve,  anterior,  955 

septum,  626 

sheath,  625 
Crureus  muscle,  471 
Crus  cerebri,  800 

commune  [semicircular  canals], 
1049 

fomicis,  840 

helicis,  1034 

penis,  1248 
Crusta  or  pes  of  cerebral  peduncle, 
802 

petrosa  of  teeth,  1120 
formation  of,  1120 
Cruveilhier,  glenoid  ligaments  of, 

332,  359 
Crypts  of  Lieberkiihn,  1174 
Crystalline  lens,  1019 


I 


Crystalline    lens,     cortical     sub- 
stance of,  1020 
development  of,  1002 
nucleus  of,  1020 
Cuboid  bone,  269 
Cuboideonavicular  articulation. 

356 
Culmen  monticuli  [cerebellum],78& 
Cuneate  nucleus,  774 

tubercle,  774 
Cuneiform  bone  of  carpus,  225 
of  tarsus,  first,  270 

second,  271  ■ 

third,  271  M 

cartilages,  1075  i 

tubercle,  1079 
Cuneocuboid  articulation,  357 
Cuneonavicular  articulation,  356' 
Cuneus,  823 
Cup,  optic,  1001 
Cupula  of  cochlea,  1051 

of  pleura,  1088 
Curoatura  ventriculi  major,  1162 

minor,  1162 
Curvatures  of  stomach,  1162 
Curved  lines  of  ilium,  232,  233 
Curves  of  vertebral  column,  114 
Cushion  of  auditory  tube,  1141 

of  epiglottis,  1076 
Cushions,  endocardial,  512 
Cusps  of  bicuspid  valve,  534 

of  tricuspid  valve,  531 
Cutaneous  cervical  nerve,  927 

nerve,  external,  953 
internal,  937,  955 

lesser,  937 
middle,  955 
Cuticle,  1062 
Cuticula  dentis,  1123 
Cutis  plate,  80 

vera  or  corium,  1065 
Cutting  teeth,  1115 
Cuvier,  ducts  of,  520 
Cycle,  cardiac,  538 
Cymba  conchas,  1034 
Cystic  artery,  605 

duct,  1198 

vein,  682 
Cyton,  723 
Cytoplasm,  35 
Cytotrophoblast,  47 


Dacryon,  189,  1198 

Dartos  tunic,  1238 

Darwin,    auricular    tubercle    of, 

1033 
Daughter  chromosomes,  37 
Decidua,  59 

basalis,  60 

capsularis,  60 

parietalis,  60 

placentalis,  60 

stratum  compactum  of,  59 
spongiosum  of,  60 

unaltered  or  boundary  layer  of, 
00 
Decidual  cells,  59 
Decussation  of  lemniscus,  777 

of  optic  nerves,  883 

pyramidal,  767 

sensory,  777 
Deep  abdominal  ring,  418 

artery  of  penig,  617 

auricular  artery,  560 

cerebral  veins,  653 

cervical  artery,  585 
fascia,  388 
lymph  glands,  697 
vein,  651 

crural  arch,  419 

epigastric  artery,  623 
vein,  672 


C 


INDEX 


1359 


• 


>eep  external  pudic  artery, 

fascia  of  arm,  442 
of  forearm,  445 

femoral  artery,  629 

iliac  circumflex  vein,  673 

lingual  artery,  553 

muscles  of  back,  396 

palmar  arch,  595 

peroneal  nerve,  965 

petrosal  nerve,  892 

plantar  artery,  637 

Sylvian  vein,  653 

temporal  arteries,  561 
nerves,  895 

transverse  fascia  of  leg,  483 
Degeneration,  Wallerian,  759 
Deglutition,  1140 
Deiters,  cells  of,  1058 

nucleus  of,  788,  803 
Deltoid  ligament,  350 

muscle,  439 

tuberosity,  211 
Deltoideus  muscle,  439 
actions  of,  440 
nerves  of,  440 
variations  of,  440 
Demilunes  of  Heidenhain,  1136 
Demours,  membrane  of,  1008 
Dendrons  of  nerve  cells,  723 
Dens,  or  odontoid  process  of  axis, 
99 

serotinus,  1118 
Dental  arterj-,  inferior,  561 
posterior,  562 

canaliculi,  1119 

formulse,  1114 

furrow,  1122 

germs,  1122 

lamina,  1122 

nerve,  inferior,  896 

pulp,  1118 

sac,  1123 
Dentate  fissure,  826 

gyrus,  827,  868 

ligament,  880 
Denies,  1112 

canini,  1116 

decidui,  1118 

incisivi,  1115 

molar  es,  1118 

pemianentes,  1115 

prcemolares,  1118 
Dentin,  1119 

formation  of,  1123 

intertubular,  1120 

secondary,  1120 
Dentinal  canaliculi,  1119 

fibers,  1119 

matrix,  1119 

sheath  of  Neumann,  1119 

tubules,  1109 
Depressions  for  arachnoid  granu- 
lations. 134 
Depressor  alse  nasi  muscle,  382 

anguli  oris  muscle,  381 

labii  inferioris  muscle,  383 

septi  muscle,  382 
actions  ot,  382 
nerves  of,  382 
Dermal  bones,  85 
Dermic  coat  of  hair  follicle,  1076 
Dermis,  1065 

Descemet,  membrane  of,  1008 
Descendens  cervicalis  nerve,  928 
Descending  aorta,  598 

colon,  1181 

comma-shaped  fasciculus,  764 

oblique  muscle,  409 

palatine  artery,  562 

process  of  lacrimal  bone,  164 

ramus  of  hypoglossal  nerve,  918 
of  ischium,  235 
of  OS  pubis,  237 
Descent  of  testis,  1210 
Detrusor  urinse  muscle,  1233 


Deutoplasm,  39 
Development  of  allantois,  54 

of  amnion,  56 

of  anal  canal,  1108 

of  arteries,  515 

of  body  cavities,  72 

of  bone,  86 

of  brain,  736 

of  branchial  or  visceral  arches, 
65 

of  chorion,  60 

of  chromaphil  and  cortical  sys- 
tems, 1277 

of  cranial  nerves,  748 

of  deciduous  teeth,  1122 

of  diencephalon,  742 

of  digestive  tube,  1101 

of  ear,  1029 

of  external   organs  of  genera- 
tion, 1213 

of  eye,  1001 

of  face,  67 

of  fetal  membranes,  54 

of  heart,  506 

of  hypophysis  cerebri,  1276 

of  joints,  283 

of  kidney,  1211 

of  limbs,  71 

of  liver,  1193 

of  lymphatic  system,  768 

of  mammae,  1101 

of  medulla  spinalis,  749 

of  mouth,  1101 

of  muscles,  371 

of  nervous  system,  733 

of  neural  groove  and  tube,  50 

of  nose,  67 

of  noijochord,  52 

of  ovaries,  1207 

of  palate,  70 

of  palatine  tonsils,  1103 

of  pancreas,  1202 

of  parathyroid  glands,  1272 

of  permanent  teeth,  1124 

of  pharyngeal  pouches,  65 

of  placenta,  62 

of  primitive  segments,  52 
streak,  47 

of  prostate,  1213 

of  rectum,  1108 

of  respiratory  organs,  1071 

of  ribs,  82 

of  salivary  glands,  1102 

of  skeleton,  80 

of  skin,  1066 

of  skull,  83 

of  spinal  nerves,  735 

of  spleen,  1282 

of  sternum,  83 

of  suprarenal  glands,  1278 

of  teeth,  1121 

of  testis,  1210 

of  thymus,  1273 

of  thjToid  gland,  1270 

of  tongue,  1102 

of  umbilical  cord,  57 

of  urethra,  1215 

of  urinary  bladder,  1212 

and  generative  organs,  1205 

of  vascular  system,  505 

of  veins,  518 

of  venous  sinuses  of  dura  mater, 
522 

of  vertebral  column,  80 

of  visceral  arches,  65 

of  yolk-sac,  54 
Diagonal  band  of  Broca,  869 
Diameters  of  peK-is,  239,  240 
Diaphragm,  Ij'mphatic  vessels  of, 
717 

muscles  of,  404 
actions  of,  406 
nerves  of,  406 
variations  of,  406 

pelvic,  420,  1147 


Diaphragm,  urogenital,  42S 
Diaphragma  t^ellw,  874 
Diaphragmatic  lymph  glands,  715 
part  of  pelvic  fascia,  421 
pleura,  1088 
surface  of  heart,  529 
Diarthroses,  285 
Diaster,  37 
Diencephalon,  807 

development  of,  742 
Digastric  fossa,  141 
muscle,  391 
nerve  from  facial,  905 
triangle,  564 
Digastricus  muscle,  391 
actions  of,  393 
nerves  of,  393 
variations  of,  392 
Digestion,  organs  of,  1100 
Digestive  apparatus,  1100 
development  of,  1101 
tube,  1100 
Digital  arteries  of  foot,  640 

from   superficial   volar   arch, 

598 
of  hand, 598 
fossa  of  epididymis,  1242 

of  femur,  244 
nerves  of  lateral  plantar,  963 
of  medial  plantar,  963 
of  median,  938 
of  musculocutaneous.  937 
of  radial,  943 
of  ulnar,  939 
vaginal  ligaments,  449 
veins  of  foot,  669 
of  hand,  660 
Digits,  articulations  of,  333 
Dilatator  naris  anterior  muscle, 
382 
action  of,  382 
nerves  of,  382 
posterior  muscle,  382 
action  of,  382 
nerves  of,  382 
pupillse  muscle,  1013 
tubse  muscle,  1044 
Diploe,  80 

Diploic  veins,  651,  652 
Direct  cerebellar  fasciculus,  758 
tract,  778 

of  Flechsig,  761 
pyramidal  tract,  759 
Discharge  of  ovum,  1256 
Discus  articularis,  298 

proligerus,  1256 
Disk,  interpubic,  311 

optic,  1015 
Disks,  tactile,  of  Merkel,  1059 
Diverticulum  ilei,  1172 

Meckel's,  54,  1172 
Divisions  of  bronchi,  1197 

of  cells,  37 
Dobie's  line,  375 
Dogiel,  cells  of,  921 
Dorsal  aorta;,  517 
artery  of  penis,  620 
carpal  artery,  of  radial,  594 
of  ulnar,  598 
ligament,  458 
cutaneous  nerves,  963,  966 
fissure  of  medulla  oblongata, 767 
interossei  muscles,  464,  495 
interosseous  artery,  596 

nerve,  944 
lamina,  735 
mesogastrium,  1103 
metacarpal  arteries,  594 

veins,  663 
nasal  artery,^  571 
nerve  of  penis,  968 
peripheral  band,  764 
pulmonary  nerves,  913 
scapular  nerve,  932 
spinal  artery,  579 


Dorsal  veins  of  penis,  676 
venous  arch  of  foot,  669 
net-work  of  hand,  660 
vestibular  nucleus,  788 
Dorsalis  haUucis  artery,  637 
lingure  artery,  555 
pedis  artery,  636 

branches  of,  637 
peculiarities  of,  636 
relations,  636 
surface  markings  of,  1346 
scapulw  artery,  588 
Dorsoepitrochlearis  brachii  mus- 
cle, 434 
Dorsomedian  fissure  of  medulla 

oblongata,  767 
Dorsum  ilii,  232 
lingua;,  1125 
nasi,  992 
sellw,  147,  190 
of  tongue,  1125 
Douglas,  pouch  of,  1152 
Drum,  1037 

Duct    or    Ducts,  accessory    pan- 
creatic, 1202 
of  Bartholin,  1136 
of  Bellini,  1223 
of  bulbourethral  glands,  1253 
cloacal,  1109 
common  bile,  1198 
of  Cuvier,  520 
cystic,  1198 
ejaculatory,  1247 
frontonasal,  138 
of  Gartner,  1255 
hepatic,  1197 
lacrimal,  1028 
lactiferous,  1268 
of  liver,  1197 
lymphatic,  right,  691 
MuUerian,  1206 
nasolacrimal  or  nasal,  1029 
pancreatic,  1202 
parotid,  1134 
pronephric,  1205 
prostatic,  1253 

orifices  of,  1234 
of  Rivinus,  1136 
of  Santorini,  1202 
semicircular,  1052 
seminal,  1245 
Skene's,  1213 
Stensen's,  1134 
sublingual,  1136 
submaxillary,  1135 
thoracic,  690 
thyroglossal,  1126,  1270 
vitelline,  54 
Wharton's,  1135 
of  Wirsung,  1202 
Wolffian,  1205 
Ductless  glands,  1269 
parathyroids,  1271 
spleen,  1282 
suprarenals,  1278 
thymus,  1273 
thyroid,  1269 
Ductuli  aberrantes  [testis],  1246 
efferentes  [testis],  1244 
tr ansver si  [epoophoTon],  1255 
Ductus  arteriosus,  540 
choledochus,  1198 
cochlearis,  1054 
cysticus.  1198 
deferens,  1245 
ampulla  of,  1246 
structure  of,  1246 
ejaculatorii,  1247 
endolymphaticus,  1048,  1052 
hepaticus,  1197 
lacrimalis,  1028 
longitudinalis  epoophori,  1255 
lymphaticus  dexter,  691 
nasolacrimalis,  1029 
pancreaticus  [Wirsungi],  1202 


INDEX 

Ductus  parotideus,  1134 
Santorini,  1202 
semicircular  es,  1052 
submaxillaris,  1135 
ihoracicus,  690 
utriculosaccularis,  1052 
venosus,  519,  542 
development  of,  519 
fossa  for,  1191 
obliterated,  681 
Duodenal  fossa?,  1159 
glands,  1176 
impression,  1190 
Duodenojejunal  flexure,  1169 
fold,  1159 
fossa,  1159 
Duodenomesocolic  fold,  1159 
Duodenopyloric     constriction, 

1162 
Duodenum,  1168 

ascending  portion,  1169 
descending  portion,  1169 
horizontal  portion,  1169 
lymphatic  vessels  of,  710 
superior  portion,  1169 
suspensory  muscle  of,  1170 
vessels  and  nerves  of,  1170 
Dura  mater,  cranial,  872 
arteries  of,  872 
endosteal  layer  of,  875 
meningeal  layer  of,  875 
nerves  of,*  875 
processes  of,  873 
veins  of,  875 
encephali,  872 
spinal,  875 

structure  of,  876 
spinalis,  875 

venous    sinuses    of,  develop- 
ment of,  522 
Dural  nerve,  911 


E 


Ear,  1029 

auricula  of,  1033 
muscles  of,  1035 

cartilaginous  capsules  of,  85 

cochlea,  1050 

development  of,  1029 

external,  1033 

internal,  or  labyrinth,  1047 

meatus   acusticus   externus, 
1036 

membranous  labyrinth,  1051 

middle,  1037 

osseous  labyrinth,  1047 

pinna  of,  1033 

semicircular  canals  of,  1049 

tympanic  cavity  of,  1037 
muscles  of,  1046 
ossicles  of,  1044 
vessels     and     nerves     of, 
1046 

vestibule  of,  1047 
Eberstaller,  medial  frontal  sulcus 

of,  822 
Ectoderm,  47 
Ectodermal  cloaca,  1109 
Efferent  nerves,  729 
Eighth  nerve,  905 
Ejaculator  urinse  muscle,  428 
Ejaculatory  ducts,  1247 
Elastic  fibrocartilage,  282 

lamina?  of  cornea,  1008 

membrane  of  larynx,  1077 
Elbow  bone,  214 
Elbow-joint,  321 

anastomoses  around,  592 

movements  of,  322 

surface  anatomy  of,  1328 
markings  of,  1331 

vessels  and  nerves  of,  322 
Eleventh  nerve,  313 


I 


Embryo,   form    of,    at    differeni 
stages,  74 

separation  of,  53 
Embryology,  38 
Embryonic  disk,  47 

pole,  46 
Eminence,  canine,  158 

collateral,  833 

cruciate,  130 

frontal,  135,  178,  183 

hypothenar,  456 

iliopectineal,  234 

inter  condyloid,  of  tibia,  25l 

medial,  of  rhomboid  fossa,  799 

parietal,  133,  178,  183 

pyramidal,  of  pons,  785 
of  tympanic  cavity,  104! 

thenar,  456 
Eminences    and    depressions    of 

bones,  80 
Eminentia  arcuata,  142 

articularis,  139 

collateralis,  833 

pyramidalis,  1042 

saccularis,  813 
Emissary  veins,  660 
Enamel  cells,  1123 

droplet,  1123 

epithelium,  1123 

fibers  or  prisms,  1120 

organ, 1123 

of  teeth,  1120 

formation  of,  1123 
Enarthrosis,  286 
Encephalon,  766 
End-arteries,  1223 
End-bulbs  of  Krause,  1060 
End-plates,  motor,  of  Kuhne,  730 
Endocardial  cushions,  512 
Endocardium,  535 
Endognathion,  199 
Endolymph,  1051 
Endomysium,  373 
Endoneurium,  728 
Endosteal  layer  of  dura  mater, 

875 
Endothelium,  corneal,  1009 
Enlargements  of  medulla  spinalis, 

751 
Ensiform  appendix,  121 
Entoderm,  47 
Entodermal  cloaca,  1109 
Entrance  of  larynx,  1079 
Eosinophil  corpuscles,  504 
Eparterial  branch  of  right  bron- 
chus, 1085,  1097 
Ependymal  layer,  733 
Epicardium,  535 
Epicondyles  of  humerus,  212 
Epicranial  aponeurosis,  380 
Epidermic   coat   of   hair   follicle, 

1068 
Epidermis,  development  of,  1066 

structure  of,  1062 
Epididymis,  1242 
Epidural  space,  875 
Epigastric    artery,    deep    or    in- 
ferior, 623 
peculiarities  of,  623 
surface  markings  of,  1321 
superficial,  629 
superior,  585 

lyniph  glands,  704 

region,  1149 

vein,  deep,  762 
inferior,  672 
Epiglottis,  1075 

tubercle  or  cushion  of,  1076 
Epimysium,  373 
Epineurium,  728 
Epiotic  center  of  temporal  bone, 

146 
Epiphyses,  atavistic,  95 

pressure,  95 

traction,  95 


V. 


F 

^^M        Kninhvsifi 

I 
I 


Epiphysial  cartilage,  03 
Epiphysis,  35,  812,  1277 
Epiploic  foramen,  1156 
Epitrochleo-anconaeus  muscle,  448 
Epistropheus,  100 
Epithalamus,  743,  812 
fasciculus  retrofiexus   [of   Mev- 

nert],  812 
ganglion  habenulcE,  812 
pineal  body,  812 

structure  of,  812 
posterior  commissure,  812 

nucleus  of,   812 
trioonum  hahenuUv,  812 
Epithelium,  enamel,  1123 

germinal,  of    Waldever,    1209, 

1255 
stratified,  of  cornea,  1007 
transitional,  1223 
Epi tympanic  recess,  142,  1038 
Eponychium,  1067 
Epoophoron,  1206,  1255 
Equator  of  lens,  1019 
Erector  clitoridis  muscle,  430 
penis  muscle,  428 
spina;  or  sacrospinalis  muscle, 
397 
Eruption  of  teeth,  1124 
Erythroblasts,  88 
Esophageal  arteries,  581,  600 
glands,  1146 

hiatus  in  diaphragm,  406 
nerves,  913 
plexus,  913 
Esophagus,  1144 

abdominal  portion  of,  1146 
cervical  portion  of,  1145 
lymphatic  vessels  of,  719 
nerves  of,  1146 
structure  of,  1146 
tela  submucosa,  1146 
thoracic  portion  of,  1145 
tunica  mucosa,  1146 
muscularis,  1146 
vessels  of,  1146 
Ethmoid  bone.  153 

articulations  of,  156 
cribriform  plate  of,  153 
crest,  161,  167 
foramina,  189 
horizontal  lamina  of,  153 
labyrinth  or  lateral  mass  of, 

154 
lamina  papyracea  of,  155 
OS  planum  of,  155 
ossification  of,  155 
perpendicular  plate  of,  153 
uncinate  process  of,  155 
vertical  plate,  154 
Ethmoidal  arteries,  570 
canals,  138,  154 
cells,  154,  998 
notch,  137 
plate,  85 
process  of  inferior  nasal  concha, 

169 
spine,  147,  190 
Ethmovomerine  cartilage,  171 
Eustachian  tube,  1042 

valve,  530 
Excavation,  rectouterine,  1152 
retrovesical,  1152 
vesicouterine,  1152 
Exner,  plexus  of.  846 
Exognathion,  200 
^m     Extensor,    carpi    radialis    acces- 
^B  sorius  muscle,  452 

^B  bre\-is  muscle,  452 

^1  actions  of,  456 

^B  nerves  of,  456 

^V  variations  oi,  452 

^1  intermedius  muscle,  452 

^B  longus  muscle,  452 

^B  actions  of,  456 

^1  nerves  of,  456 

■  S6 


INDEX 


Extensor    carpi    radialis    longus 
muscle,  variations  of,  452 
ulnaris  muscle,  454 
actions  of,  456 
nerves  of,  456 
variations  of,  454 
coccygis  muscle,  401 
digiti   quinti  proprius  muscle, 
454 
actions  of,  456 
nerves  of,  456 
'variations  of,  454 
digitorum  brevis  muscle,  488 
actions  of,  488 
nerves  of,  488 
variations  pf ,  488 
communis  muscle,  452 
actions  of,  456 
•nerves  of,  456 
variations  of,  454 
longus  muscle,  481 
actions  of,  482 
nerves  of,  482 
variations  of,  482 
hallucis  longus  muscle,  481 
actions  of,  482 
nerves  of,  482 
variations  of,  481 
indicis  proprius  muscle,  456 
actions  of,  456 
ner\^es  of,  456 
variations  of,  456 
minimi  digiti  muscle,  454 
ossis  metacarpi  pollicis  muscle, 
455 
metatarsis    hallucis    muscle, 
481 
pollicis  brevis  muscle,  455 
actions  of,  456 
nerves  of,  456 
variations  of,  455 
longus  muscle,  455 
actions  of,  456 
nerves  of,  456    . 
primi  internodii  pollicis  muscle, 

456 
proprius  hallucis  muscle,  481 
secundi    internodii    pollicis 
muscle,  455 
Exterior  of  skull,  178 
External  abdominal  ring,  410 
arcuate  ligament,  405 
i      auditory  canal,  1036 
meatus,  1036 
calcaneal  arterj',  638 
calcaneoastragaloid     ligament, 

352 
canthus  of  ej^elids,  1025 
circumflex  arterj-,  630 
cutaneous  nerve,  953 
geniculate  body,   811 
intercostal  muscles,  403 
lateral  ligament.  297,  322,  328 
ligament  of  malleus,  1045 
malleolar  artery,  635 
oblique  muscle,  409 
plantar  artery,  039 

nerve,  963 
popliteal  nerve,  964 
pterygoid  muscle,  386 
pudic  arteries,  629 
respiratory  nerve  of  Bell,  933 
saphenous  vein,  670 
semilunar  fibrocartilage,  343 
spermatic  fascia,  1238 
sphincter  ani  muscle,  425 
Extraspinal  veins,  668 
Extremitas  acromialis   [claTiculd\, 
202 
stemalis  [clavicrila],  202  . 
Extremity  of  penis,  1250 
Extrinsic      muscles    of     tongue, 

1129 
Eye.  1000 
Eyeball  or  bulb  of  eye,  1000 


1361 


Eyeball,  accessory  organs  of,  1021 
aqueous  humor,  1018 
capsule  of  Tenon,  1024 
chambers  of,  1012 
choroid,  1009 
ciliary  body,  1010 

muscle,  1011  ' 

processes,  1010 
conjunctiva,  1026 
cornea,  1006 
crystalline  lens,  1019 
development  of,  1001 
fascia  bulbi,  1024 
fibrous  tunic,  1005 
hyaloid  membrane,  1018 
iris,  1012 

orbiculus  ciliaris,  1010 
pupil,  1012 

pupillary  membrane,  1003 
refracting  media,  1018 
retina,  1014 

pigmented  layer  of,  1015 

proper,  1015 

supporting    frame-work     of, 
1017 
sclera,  1005 
tunics  of,  1005 

vascular,  1009 
uvea,  1013 

vessels  and  ner%'^es  of,  1021 
vitreous  body,  1018 
Eyebrows,  1025 
Eyelashes,  1025 
Eyelids,  102f5 
canthus  of,  1025 
development  of,  1005 
structure  of,  1025 
surface  anatomy  of,  1299 
tarsi  of,  1025 
Eye-teeth,  1117 


Face,  bones  of,  156 
development  of,  67 
lymphatics  of,  692 
surface  anatomy  of,  1294 
Facial  artery,  553 
transverse,  558 
bones,  156 
canal,  142 
hiatus  of,  142 
prominence  of,  1042 
lymph  glands,  694 
nerve,  901 

composition  and  central  con- 
nections of,  861    ■ 
sympathetic  efferent  fibers  of, 
970 
vein,  anterior,  645 
common,  645 
deep,  645 
posterior,  645 
transverse,  645 
Falciform  ligament  of  liver,  1150 
1192 
margin  of  fossa  ovalis,  469 
process  of  sacrotuberous  liga- 
ment, 309 
Fallopian  tubes,  1257 
Fallopius,    aqueduct    of,    promi- 
nence of,  1042 
False  ligaments  of  bladder,  1231 
pelvis,  239 
ribs,  123    ' 
vocal  cords,  1079 
Falx  aponeurotica  inguinalis,  414 
cerebelli,  873 
cerebri,  873 
Fascia  or  Fascise,  376 
of  abdomen,  408 
triangular,  412 
anal,  421 
of  ankle,  488 


1362 


Fascia    or    Fascise,    antibrachial, 

445 
antibrachii,  445 
of  arm,  442 
axillary-,  436 
bicipital,  444 
brachial,  442 
brachii,  4'42 
buccopharyngeal,  390 
bulb.  1204 
of  Camper,  408 
cervical,  387,  388 
clavipectoral,  437 
of  Colles,  235,  409,  426 
colli,  388 

coracoclavicular,  437 
coracoclavicularis,  437 
cremasteric,  414 
cribrosa,  468 
cruris,  480 
deep,  378 
of  deltoideus,  439 
dentata  hippocampi,  827 
diaphragmatic  part  of  pelvic, 

421 
dorsal,  of  foot,  490 
endopelvic,  422 
of  forearm,  445 
general  description  of,  376 
of  hand,  456 
iliaca,  466 
iliopectineal,  466 
infraspinala,  441 
infraspinatous,  441 
infundibuliform,  418 
intercolumnar,  1238 
intercostal,  402 
intercrural,  411 
lata.  468 

falciform  margin  of,  469 

fossa  ovalis  of,  469 

iliotibial  tract  or  band  of,  468 
of  leg,  480 

deep  transverse,  483 
lumbar,  397 
masseteric,  385 
of  obturator  internus,  420 
orbital,  1025 
palmar,  460 

parotideomasseteric,  385 
pectoral,  435 
pelvic,  420 
plantar,  490 
pretracheal,  390 
prevertebral,  390 
of  piriformis,  421 
of  psoas  and  iliacus,  466 
of  quadratus  lumborum,  419 
rectal,  422 
rectovesical,  422 
renal,  1220 
of  Scarpa,  408 
Sibson's,  1089 

spermatic,  external,  411,  1238 
subscapular,  440 
subscapularis,  440 
superficial,  377 
supraspinata,  440 
supraspinatous,  440 
temporal,  386 
of  thigh,  467 
of  thoracic  region,  435 
transversalis,  418 
triangular,  of  abdomen,  412     • 
of  upper  extremity,  431 
of  urogenital  diaphpagm,  428, 
429,  430 

region,  426 
vesical,  422 
Fasciculi,  intrafusal,  1061 

longitudinales,  785 
Fasciculus,  buUjospinal,  854 
cerebelloolivary,  781 
cerebrospinal,  759,  760 
cerebrospinalis  anterior,  759 


INDEX 

Fasciculus,    cerebrospinalis    later- 
alis, 760 
comma-shaped,  704 
cuneatus,  762 
gracilis,  762 
lateral  proper,  762 

spinothalamic,  762 
lateralis  proprius,  762 
of  Lissauer,  762 
longitudinal,  inferior,  844 
medial,  762,  784,  803 
posterior,  803 
superior,  844 
mam m illotegjnentalix,  867 
mammiilo-thalamic,  869 
occipitofrontal,  844 
olfactory,  840 
olivospinal,  761,  854 
perpendicular,  844 
pontospiual,  872 
posterior  proper,  764 
retroflexus  of  Meynert,  812 
rubrospinal,  761,  870 
secondary  sensory,  762 
solitarius,  785 
spinocerebellar,  dorsal,  761,  778 

ventral,  761 
spinoolivary,  854 
spinotectal,  762 
spinothalamic,  762 
superficial  antero-lateral,  854 
tectospinal,  760,  871 
thalamomammillary,  839 
uncinate,  843 
ventral  spinothalamio,  854 
vestibulospinal,  760,  803,  872 
Fasciola  cinerea,  827 
Fauces,  arches  or  pillars  of,  1137 
isthmus  of,  1137 
muscles  of,  actions  of,  1140 
Female  genital  organs,  1254 
bulb  of  vestibule,  1264 
carunculffi  hj'menales,  1266 
clitoris,  1266 
development  of,  1205 
epoophoron,  1255 
fourchette,  1265 
glands  of  Bartholin,  1266 
greater  vestibular,  1266 
hymen,  1266 
labia  majora,  1265 

minora,  1265 
mons  pubis,  1265 
navicular  fossa,  1266 
ovaries,  1254 
uterine  tubes,  1257 
uterus  or  womb,  1258 
vagina,  1264 
vestibule,  1266 
pronucleus,  42 
urethra,  1236 
Femoral  artery,  623 
branches  of,  629 
peculiarities  of,  629 
surface  marking  of,  1346 
canal,  625 

circumflex  arteries,  630 
cutaneous  nerve,  anterior,  955 
lateral,  951 
posterior,  959 
fossa,  626 
nerve,  955 
ring,  625 
septum,  626 
sheath,  625 
triangle,  626 
vein,  672 
Femur,  242 

architecture  of,  248 
inner,  of  upper,  249 
of  distal  portion,  253 
condyles  of,  247 
head  of,  243 
neck  of,  243 
ossification  of,  255 


Femur,  spiral  line  of,  245 

surface  anatomv  of,  1336 

trochanters  of,  243,  244 
Fenestra  cochlece,  1040 

ovalis,  1040 

rotunda,  1040 

vestibuli,  1040 
Fertilization  of  ovum,  44 
Fetal  membranes,  54 
Fetus,  circulation  in,  540 

foramen  ovale  in,  512,  539 

valve  of  inferior  vena  cava  in, 
540 

vascular     system     in,     peculi- 
arities of,  539 
Fibers,  arcuate,  782 

dentinal,  1119 

intercolumnar,  410 

intercrural,  410 

intrafusal,  1061 

of  muscles,  373 

nerve,  721" 

non-medullated,  728 

olfactorv  projections,  869 

of  Purkinje,  536' 

of  Remak,  728 

sustentacular,  of  MiiUer,  1017 

of  tactile  discrimination,  854 

taste,  861 

of  Tomes,  1119 

touch,  854 
Fibrce  intercrurales,  410 

pontis  profunda',  785 
superficiales,  785 

propria:  [cerebellum],  794 
Fibrocartilage,  281 

circumferential,  282 

connecting,  282 

interarticular,  281 

intervertebral,  289 

semilunar,  of  knee,  342,  343 

stratiform,  282 

yellow  or  elastic,  282 
Fibrocartilaginous  lamina,  inter- 
pubic,  311 
Fibrous  capsule  of  Glisson,  1194 

pericardium,  525 

rings  of  heart,  536 

eheatha    of    flexor    tendons    of 
fingers,  449 
of  toes,  492 

tunic  of  kidney,  1220 
Fibula,  260 

ossification  of,  262 

surface  form  of,  1337 
Fibular  artery,  635 

collateral    ligament    of    knee- 
joint,  341 
Fifth  metacarpal  bone,  228 

metatarsal  bone,  274 

nerve,  880 

ventricle,  840 
Filiform  papilla;  of  tongue,  1127 
Fillet,  medial,  803 
Filtration  angle  of  eye,  1007 
Filum  termi7iale,  750 
Fimbria  hippocampi,  840 

ovarian,  1257 
Fimbriie  of  uterine  tube,  1 257 
Fimbriodentate  fissure,  827,  840 
First  cuneiform  bone,  270 

dorsal  metacarpal  artery,  595 
metatarsal  artery,  636 

metacarpal  bone,  228 

metatarsal  bone,  272 

nerve,  881 
Fissura  antitragohelicina,  1034 

calcarina,  820 

cerebri  lateralis  [Sylvii],  819 
longitudinalis,  81S 

collateralis,  820 

hippocampi,  826 

mediana  anterior  [medulla?  ob- 
longatae],  767 
spinalis],  752 


I 
I 


INDEX 


1363 


Fissura  mediana  posterior  [medul- 
lae  oblongatse],  767 
parietooccipiialis,  820 
petrotympanica,  1038 
prima  [cerebsUum],  740 
[rhinencephalon],  827 
secunda  [cerebellum],  740 
Fissure  or  Fissures,  anterior  me- 
dian of  medulla  spinalis,  752 
callosomarginal,  820 
of  cerebellum,  738,  789 
development  of,  741 
floccular,  741 
horizontal,  789 
Ijostcentral,  789 
postnodular,  741,  790 
postpyramidal,  790 
precentral,  789 
preclival,    789 
prepyramidal,  790 
of  cerebrum,  819 
calcarine,  820 
callosal,  825,  828 
central,  819 
collateral,  820 
development  of,  747 
external  rhinal,  744 
fimbriodentate,  827,  840 
hippocampal,  74G,  826 
interlobular,  819 
lateral,  746,  819 
longitudinal,  818 
parietooccipital,  820 
of  Rolando,  819 
of  Sylvius,  819 
transverse,  842 
choroidal,  841,  1002 
,  circuminsular,  821 
dentate,  826 
Glaserian.  140,  1038 
of  liver,  1191 
longitudinal.  818 
of  lungs,  1096 
of  medulla  oblongata,  767 
orbital,  inferior,  184,  189 
superior,  151,  189,  l92 
petrooccipital,  181,  193 
petrosphenoidal,  181 
petrotympanic,  140,  180,  1038 
pterygoid,  151 
pterygomaxillary,  185 
of  Rolando,  819 
sphenomaxillary,  184 
of  Sylvius,  747,  819 
tympanomastoid,  181 
vestibular,  1051 
Fixation  of  kidney,  1220 

of  muscles,  362 
Flat  bones,  79 
Flechsig,  cerebellar  tract  of,  761 

oval  area  of,  764 
Flexor    accessorius    longus    digi- 
torum  muscle,  485 
muscle,  493 
brevis    minimi    digiti    muscle, 

464,  494 
carpi  radialis  muscle,  446 
actions  of,  450 
nerves  of,  450 
variations  of,  446 
ulnaris  muscle,  447 
actions  of,  450 
nerves  of,  450 
variations  of,  448 
digiti  quinti  brevis  muscle   of 
foot,  494 
actions  of,  496 
nerves  of,  495 
of  hand,  464 
actions  of,  464 
nerves  of,  464 
digitorum  brevis  muscle,  491 
actions  of,  496 
nerves  of,  495 
variations  of,  492 


Flexor  digitorium  longus  muscle, 
485 
actions  of,  486 
nerves  of,  486 
variations  of,  485 
profundus  muscle,  448 
actions  of,  450 
nerves  of,  450 
variations  of,  449 
sublimis  muscle,  448 
actions  of,  450 
nerves  of,  450 
variations  of,  448 
hallucis  brevis  muscle,  493 
actions  of,  496 
nerves  of,  495 
variations  of,  493 
longus  muscle,  485 
actions  of,  486 
nerves  of,  486 
variations  of,  485 
pollicis  brevis  muscle,  461 
actions  of,  462 
nerves  of,  462 
variations  of,  462 
longus  muscle,  449 
actions  of,  450 
nerves  of,  450 
variations  of,  449 
Flexure,  cervical,  737 
colic,  left,  1181 

right,  1180 
hepatic,  1180 
pontine,  737 
splenic,  1181 
ventral  cephalic,  737 
Floating  ribs,  123 
Floccular  fissure,  741 
Flocculus,  791 

Floor  of  fourth  ventricle,  798 
Floor-plate   of    medulla   spinalis, 

733 
Fluid,  cerebrospinal,  877 
Fluids,  circulating,  503 
Fold  or  Folds,  amniotic,  56 
aryepiglottic,  1079 
caudal,  53 
cephalic,  53 
duodenojejunal,  1159 
gastropancreatic,  1156 
glossoepiglottic,  1075 
ileocecal,  1160 
malleolar,  1039 
rectouterine,  1260 
sacrogenital,  1154,  1260 
salpingopalatine,  1142 
salpingopharyngeal,  1142 
transverse,  of  rectum,  1183 
of  Treves,  1160 
umbilical,  1231 
ventricular,  of  larynx,  1079 
vestigial,  of  Marshall,  522,  526 
vocal,  of  larynx,  1080 
Folium  cacuminis,  790 

vermis,  790 
Follicle  of  hair,  1067 
Follicles,  agminated,  1176 

Graafian,  or  vesicular  ovarian, 
1256 
Fontana,  spaces  of,  1009 
Fontanelles,  196 
Foot,  arches  of,  360 
fascia  of,  490 
muscles  of,  490 
ossification  of  bones  of,  275 
phalanges  of,   articulations  of, 

359 
skeleton  of,  262 

surface  anatomy  of,  1337 
Foramen,  caroticoclinoid,  151, 191 
cecum  of  frontal  bone,   137 
of  medulla  oblongata,  767 
of  tongue,  1103,  1125 
condyloid,  anterior,  131 
epiploieum,  HOC,  1156 


Foramen  of  Huschke,  145,  147 

incisive,  162,  180 

infraorbital,  158,  187 

interventricular,  816,  840 

intervertebral,  96 

jugular,  181,  193 

lacerum,  181,  192 

magnum,  129,  132,  192 

Majendii,  798 

mandibular,  173 

mastoid,  141,  183 

mental,  172,  188 

of  Monro,  816,  840 

obturator,  237 

optic,  147,  151,  190 

ovale  of  heart,  512,  539 
of  sphenoid,  150,  180,  192 

palatine,  180 

parietal,  178 

rotundum,  150,  192 

sciatic,  309 

singulare,  143 

sphenopalatine,  168 

spinosum,  150,  180,  192 

sternal,  121 

stylomastoid,  144,  181 

supraorbital,  136,  186,  189 

supratrochlear,  '212 

thyroid,  237 

transversarium,  98 

vena-caval,  406 

vertebral,  96 

Vesalii,  150,  192 

of  Winslow,  603,  1156 

zygomaticofacial,  164,   187 

zygomaticoorbital,  165 

zygomaticotemporal,  164,  183 
Foramina,  ethmoidal,  189 

intervertebral,  96 

of  Luschka,  798,  877 

for  olfactory  nerves,  153 

in  roof  of  fourth  ventricle,  799 

sacral,  106,  108 

of  Scarpa,  162,  180 

of  Stensen,  162,  180 

Thebesii,  530 

venarum  minimarum,  530 
Forceps,  anterior,  829 

posterior,  829 
Forearm,  fascia  of,  445 

muscles  of,  445 
Fore-brain,  51,  741,  807. 
Foregut,  53,  1101 
Foreskin,  1250 
Form    of    embryo    at    different 

stages,  74 
Formaiio  reclicularis  alba,  784 
grisea,  784 

of  medulla  spinalis,  754 
FornicolumnS,  838 
Fornix  of  brain,  838 
body  of,  838 
columns  of,  838 
crura  of,  840 
development  of,  747 
pillars  of,  838,  840 

of  conjunctiva,  1027 
Fossa  or  Fossse,  acetabular,  237 

anticubital,  589 

canine,  158 

cecal,  1160 

cochlearis,  1048 

condyloid,  131,  181 

coronoid,  212 

cranii  anterior,  190 
media,  190 
posterior,  192 

digastric,  141 

digital,  of  epididymis,  1242 
of  femur,  244 

for  ductus  venosus,  1191 

duodenal,  1159 

duodenojejunal,  1159 

femoral,  626 

for  gall-bladder,  1191 


1364 


Fossa  or  Fossae,  glenoid,  140 

hyaloid,  1018 

hypophyseos,  147,  190 

ileocecal,  IIGO 

iliac,  234 

incisive,  158,  172,  188 

incudis,  1042 

for  inferior  vena  cava,  1191 

infraspinatous,  203 

infratemporal,  184 

infratemporalis,  184 

intercondyloid,  of  femur,  247 
of  tibia,  25G 

interpeduncular,  800,  816 

intersigmoid,  1161 

ischiorectal,  425 

ischioreclalis,  425 

jugular,  144 

lacrimal,  137,  188 

of  liver,  1191 

mandibular,  140,  180,  183 

mastoid,  140     ■ 

nasal,  994 

navicular  is  [urethra],  1235 
[vulva],  1266 

occipital,  inferior,  193 

olecranon,  212 

ovalis  of  fascia  lata,  469 
of  heart,  531 

ovarian,  1154,  1254 

pararectal,  1154 

paravesical,  1154 

pericecal,  1160 

peritoneal,  1158 

popliteal,  631 

pterygoid,  151 

pterygopalalina,  185 

ptervgopalatine,  185 

radial,  212 

retrocecal,  1161 

retroperitoneal,  1158 

rhomboid,  798 

rhomboidea,  798 

of  RosenmilUer,  1141,  1142 

sagittalis  sinistra  [liver],  1141 

scaphoid,  151,  180 

of  skull,  anterior,  190 
middle,  190 
posterior,  192 

sphenomaxillary,  185 

subarcuate,  143 

subscapular,  202 

supraspinatous,  203 

supratonsillar,  1138 

Sylvian,  747 

temporal,  183 

temporalis,  183 

triangularis,  1034 

trochanteric,  244 

for  umbilical  vein,'  1191 

vencB  cavcB,  1191 

vermian,  131 

vesicce  fcllew;  1191 
Fountain  decussation  of  Meynert, 

806 
Fourchette,  1265 
Fourth  metacarpal  bone,  228 

metatarsal  bone,  274 

nerve,  885 

ventricle,  797 
floor  of,  798 
F ovea' capitis  femor is,  243 

centralis  retina,  1015,  1017 
structure  of,  1017 

dentis,  99 

of  rhomboid  fossa,  800 

trochlear,  137,  188 
Foveolffi,  Howship's,  88 
Free  nerve-endin2;s,  1059 
Freely  movable  joints,  285 
Frenula  of  colic  valve,  1179 

of  lips,  1111 
Frenulum  of  clitoris,  1266 

of  labia  minora,  1265 

linguae,  1125 


INDEX 


Frenulum  of  prepuce,  1250 

veli,  805 
Frommann's  lines,  727 
Frontal  air  sinuses,  138,  998 

artery,  750 

bone,  135 

articulations  of,  138 
■  orbital  or  horizontal  part  of, 

137 
ossification  of,  138 
squama  of,  135 
structure  of,  138 

convolution,  ascending,  821 

crest,  136 

eminences,  135,  178,  183 

gyri,  821,  822 

lobe,  821 

nerve,  887 

operculum,  825 

process  of  maxilla,  161 

sulci,  821 

suture, 135,  178 

vein,  644 
Frontalis  muscle,  actions  of,  380 
nerves  of,  380 
variations  of,  380 
Frontoethmoidal  suture,  190 
Frontomaxillary  suture,  189 
Frontonasal  duct,  138 

process,  97 
Frontopontine  fibers,  802 
Frontosphenoidal  process  of  zygo- 
matic bone,  164 
Fundiform  ligament  of  penis,  1249 
Fundus  glands  of  stomach,  1166 

tympani,  1038 

of  uterus,  1259 
Fungiform     papilla?    of    tongue, 

1126 
Funiculi  of  medulla  spinalis,  758, 

759 
Funiculus  separans,  800  ' 

spermaticus,  1239 
Furcal  nerve,  949 
Furcula,  1071,1103 
Furrow,  chorda! ,  52 

dental,  1122 

nasooptic,  69,  1005 
Furrowed  band  of  cerebellum,  971 
Fusiform  gyrus,  823,  824 


Galea  aponeurotica,  380 
Galen,  veins  of,  653 
Gall-bladder,  1197 

fossa  for,  1191 

lymphatic  capillaries  in,  686 
vessels  of,  711 

structure  of,  1198 
Gangliated  cord,  976 
Ganglion  or  Ganglia,  730 

aorticorenal,  985 

cardiac,  of  Wrisberg,  984 

carotid,  977     - 

celiac,  985 

cervical,  978,  980 

cervicale  inferius,  980 
medium,  979 
superius,  978 
.    ciliary,  888 

cceliaca,  985 

collateral,  976 

of  Corti,  1051,  1059 

Gasserian,  886 

genicular,  902 

geniculi,  902 

of  glossopharyngeal,  906 

habenulce,  812 

impar,  984 

inferior,  90S 

interpeduncular,  800,  802,  868 

jugular,  908,  911 

jugular c,  911 


I 


Ganglion  or   Ganglia,    Langle/'s, 
1137 
lenticular,  888 
Meckel's,  891 
nodosum,  911 
ophthalmic,  888 
otic,  897 
oticum,  897 
petrosum,  90S 
petrous,  908 
phrenicum,  986 
ridge  or  neural  crest,  51,  736 
of  Scarpa,  1058 
semilunar,  of  abdomen,  985 

of  trigeminal  nerve,  886 
semilunare  [Gasseri],  886 
sphenopalatine,  891 

raini  /nasales   posteriores  in- 
feriores,  893 
superiores,  893 
orbitales,  893 
spinal,  918 
spinale,  918 
spiral,  of  coclilea,  1059 
splanchnicum,  981 
submaxillare,  898 
submaxillary,  898 
superior,  of    glossopharyngeal, 
908 
mesenteric,  987 
superius,  908 
of  vagus,  910 
vestibular,  1058 
of  Wrisberg,  984 
Ganglionic     arterial     system    of 
brain,  574 
arteries,  anterolateral,  573 
antero-medial,  571 
postero-lateral,  581 
postero-medial,  574,  581 
layer  of  retina,  1016 
Gartner,  duct  of,  1206,  1255 
Gasserian  ganglion,  886 
Gaster,  1161 

Gastric  arteries,  short,  606 
artery,  left,  603 

right,  604 
glands,  1166 
impression,  1189 
lymph  glands,  706 
nerves  from  vagus,  913 
plexuses     from     sympathetic, 
986,  987 
from  vagus,  913 
veins,  short,  681 
Gastrocnemius  muscle,  482 
.     actions  of,  483 
nerves  of,  483 
variations  of,  483 
Gastrocolic  ligament,  1153 

omentum,  1157 
Gastroduodenal  artery,  604 
Gastroepiploic  arteries,  604,  606 
gland,  right,  706 
veins,  681,  682 
Gastrohepatic  omentum,  1156 
Gastrolienal  ligament,  1155 
GastropanfTcatic  fold,  1156 
Gastrophrenic  ligament,  1162 
Gemelli  muscles,  actions  of,  478 

nerves  of,  478 
Gemellus  inferior  muscle,  477 

superior  muscle,  477 
General     sensations,     peripheral 
terminations  of  nerve  of,  1059 
Generation,  development  of  ex- 
ternal organs  of,  1213 
Genicular  arteries,  631,  633 

ganglion  of  facial  nerve,  902 
Geniculate  bodies,  811 
Geniculum  of  facial  nerve,  902 

of  internal  capsule,  836 
Genioglossus  muscle,  1129 
Geniohyoglossus  muscle,  1129 
Geniohyoid  muscle,  393 


E 


eniohyoideus  muscle,  393 
action  of,  393 
nerves  of,  393 
variations  of,  393 
Genital  cord,  1207 

corpuscles,  1060 

organs  of  female,  1254 
external,  1264 
of  male,  1236 

glands,  1207 

ridge,  1207 

swellings,  1214 

tubercle,  1213 
Genitocrural  nerve,  953 
Genitofemoral  nerve,  953 
Gennari,  band  of,  845,  847 
Genu  of  corpus  callosum,  828 

of  internal  capsule,  836 
Gerlach,  tube  tonsil  of,  1043 
(Germ  centers,  689 

dental,  1122 

erminal  cells,  35 

epithelium,  1207,  1255 

path,  1210 

spot,  39 

vesicle,  39 
Giacomini,  band  of,  827 
Giant  cells,  88 

of  Betz,  845 
Gianuzzi,  crescents  of,  1136 
Gimbernat's  ligament,  412 
Gingivw,  1112 
Ginglymus,  285 
Girald^s,  organ  of,  1246 
Girdle  of  inferior  extremity,  200 

pelvic,  200 

shoulder,  200 

of  superior  extremity,  200 
Glabella,  135,  178,  198 
Gladiolus,  120 

Gland    or   Glands,   accessory,  of 
mouth,  1137 
part  of  parotid,  1134 

anterior  lingual,  1131 

aortic,  1269 

areolar,  1267 

arytenoid,  1084 

of  Bartholin,  1266 

of  Blandin,  1131 

of  Bowman,  996 

Brunner's,  1176 

buccal,  1112 

bulbourethral,  1253 

cardiac,  1166 

carotid,  1281 

ceruminous,  1037 

ciliary,  1025 

coccygeal,  1281 

Cowpcr's,  125? 

ductless,  1269 

duodenal,  1176 

esophageal,  1146 
^fundus,  1166 

gastric,  1166 

gastro-epiploic,  right,  706 

genital,  1207 

intestinal,  1174 

labial,  1111 

lacrimal,  1028 

of  larynx,  1084 

lenticular,  of  stomach,  1167 

of  Littre,  1235 

Luschka's,  1281 

mammae,  1267 

mammary,  1267 

Meibomian,  1026 

molar,  1112 

mucous,  of  tongue,  1131 

of  Nuhn,  1131 

oxyntic,  1166 

parathyroid,  1271 

parotid,  1132 

Payer's,  1176 

preputial,  1250 

prostate,  1251 


INDEX 


Gland  or  Glands,  pyloric,  1166 
salivary,  1132 
sebaceous,  1069 
serous,  of  tongue,  1137 
solitary,  1176 
sublingual,  1136 
submaxillary,  1135 
sudoriferous,  1070 
suprarenal,  1278 
sweat,  1070 
tarsal,  1026 
thymus,  1273 
thyroid,  1269 
of  tongue,  1131 
trachoma,  1028 
urethral,  1235 
uterine,  1262 
vestibular,  greater,  1266 
Glandula  lacrimalis,  1028 
parotis,  1132 
sublingualis,  1136 
submaxillaris,  1135 
suprarenalis,  1278 
thyreoidea,  1269 
vestibularis  major   [Barlholini], 
1266 
Glandulw  bulbourethrales,  1253 
duodenales  [Brunneri],  1176 
intestinales  [Lieberkuhni],  1174 
labiates,  1111 
aesophagece,  1146 
Pacchioni,  878 
sebacew,  1069 
sudorifera,  1070 
suprarenales  accessories,  1279 
tar  sales  [Meibomi],  1026 
thyreoidece  accessorioe,  1270 
Glans  clitoridis,  1266 

penis,  1248 
Glaserian  fissure,  140,  1038 
Glenohumeral  ligaments,  318 
Glenoid  cavity,  207 
fossa,  104 

ligament   of   Cruveilhier,    332, 
359 
of  shoulder,  319 
Glenoidal    labrum    of    hip-joint, 
336 
of  shoulder-joint,  319 
Gliding  joints,  285 
movement,  286 
Glisson's  capsule,  1157,  1194 
Globular  processes  of  His,  68 
Globus  major  [epididymis],  1242 
minor  [epididymis],  1242 
pallidus,  834 
Glomera  carotica,  1281 
Glomus  caroticum,  1281 

coccygeum,  1281 
Glossoepiglottic  folds,  1075,  1125 
Glossopalatine  arch,  1137 
'Glossopalatinus     muscle,      1129, 

1139  note 
Glossopharyngeal  nerve,  906 

composition  and  central  con- 
nections of,  856 
sympathetic    afferent    fibers 
of,  972 
Glottis  respiratoria,  1080 
vocalis,  1080 
rima  of,  1080 
GlutiEus  maximus  muscle,  474 
actions  of,  478 
nerves  of,  478 
raedius  muscle,  474 
actions  of,  478 
nerves  of,  478 
variations  of,  475 
minimus  muscle,  475 
actions  of,  478 
nerves  of,  478 
variations  of,  475 
Gluteal  artery,  inferior,  620 
superior,  622 
lines  of  ilium,  232 


1365 


Gluteal  muscles,  474 

nerves,  959 

tuberosity,  246 

veins,  674 
Gnathic  index,  246 
Golgi,  cells  of,  845 

organs  of,  1061 
Golgi  and  Mazzoni,  corpuscles  of, 

1061 
Goll,  tract  of,  752,  762 
Gomphosis,  284 
Gonion,  198 

Gower's,  tract  of,  761,  854 
Graafian  follicles,  1256 
structure  of,  1256 
Gracile  nucleus,  774 
Gracilis  muscle,  471 
actions  of,  474 
nerves  of,  474 
Grandry,    tactile    corpuscles    of, 

1060 
Granular  layer  of  dentin,  1119 
Granulationes  arachnoideales,   878 
Granulations,  arachnoid,  878 
Granule  cells,  377         ^ 
Gray  commissure  of  brain,  809 

commissures  of  meduUaspinalis, 
754 

or  gelatinous  nerve  fibers,  728 

substance  of  cerebellum,  794 
of  cerebral  hemispheres,  845 
of  cortex,  794 
of  medulla  oblongata,  779 
spinalis,  753 
Great  auricular  nerve,  926 

cardiac  nerve,  979 
vein,  642 

cerebral  vein,  653 

longitudinal  fissure,  818 

omentum,  1157 

sacrosciatic  ligament,  309 

saphenous  vein,  669 

splanchnic  nerve,  981 

transverse  fissure  of  brain,  842 

wings  of  sphenoid,  149 
Greater  cavernous  nerve,  989 

curvature  of  stomach,  1162 

multangular  bone,  225 

occipital  nerve,  923 

omentum,  1157 

palatine  foramen,  180 

pelvis,  238 

peritoneal  sac,  1150 

sciatic  foramen,  309 
notch,  235 

sigmoid  cavity,  215 

splanchnic  nerve,  981 

superficial  petrosal  nerve,  892, 
903 

trochanter,  244 

vestibular  glands,  1213,  1266 
Groove,  auriculoventricular,  526 

bicipital,  209 

carotid,  148,  191 

chiasmatic,  147,  190 

costal,  124 

infraorbital,  159 

interatrial,  527 

intertubercular,  of  humerus, 209' 

lacrimal,  159,  189 

musculospiral,  211 

mylohyoid,  173 

neural,  50 

obturator,  237 

occipital,  141 

optic,  147 

primitive,  47 

pterygopalatine,  151 

for  radial  nerve,  211 

vertebral,  115 
Gubernaculum  dentis,  1124 

testis,  1211 
Gudden,  commissure  of,  883 

mammillo-tegmental  bundle  of, 
867 


1366 


INDEX 


Gullet,  1144 
Gums,  1112 
Gustatory  calyculi,  991 
cells,  991 
hair,  992 
pore,  991 
Gyre,  medifrontal,  822 
precentral,  821 
subfrontal,  822 
superfrontal,  821 
Gyri  of  brain,  821 

angular,  823 

of  Broca,  822 

central,  anterior,  821 
posterior,  823 

cingulate,  826 

cuneus,  823 

dentate,  827,  868 

frontal,  821,  822 

fusiform,  823 

hippocampal,  826 

of  insula,  825 

of  limbic  lobe,  825 

lingual,  823 

occipital,  823 

orbital,  822 

precuneus,  823 

quadrate,  823 

straight,  822 

subcallosal,  827,  869 

superior  parietal  lobule,  823 

supracallosal,  827 

supramarginal,  823 

temporal,  824 

transverse,  of  Heschl,  824 

uncus,  826 
Gyrus  of  Broca,  822 
centralis  anterior,  821 

posterior,  823 
cinguli,  825 
dentatus,  827 
epicallosus,  827 
frontalis  inferior,  822 

medius,  822 

superior,  821 
hippocampi,  826 
marginal,  822 
subcallosus,  827,  869 


H 

Habenular  commissure,  812 
Hair  cells  of  spiral  organ  of  Corti, 

1057 
Hairs,  1067 

cuticle  of,  1069 

follicle  of,  1067 

gustatory,  992 

olfactory,  996 

roots  of,  1067 

scapus  or  shaft  of,  1069 

structure  of,  1068 
Haller,  vas  aberrans  of,  1246 
Hamate  bone,  227 
Hamstring  muscles,  478 
Hamulus  of  hamate  bone,  227 

lacrimal,  164 

lamince  spiralis,  1051 

pterygoid,  150,  180 
Hand,  muscles  of,  456 

phalanges  of,  articulations  of, 
333 

skeleton  of,  221 

surface  anatomy  of,  1327 
markings  of,  1330 
Hard  palate,  1112 
Harrison's  sulcus,  128 
Hasner,  plica  lacrimalis  of,  1029 
Hassal,  corpuscles  of,  1274 
Haversian  canals  of  bone,  89 

systems  of  bone,  89 
Head,  arteries  of,  549 

lymphatics  of,  692 

muscles  of,  378 


lead,    muscles    of,    development 
of,  372 

veins  of,  644 
Head-cap  of  spermatozoon,  42 
Hearing,  organ  of,  1029 
Heart,  526 

arteries  of,  538 

atrioventricular  bundle  of  His, 
537 
node,  537 

atrium,  left,  533 
right,  529 

component  parts  of,  526 

development  of,  506 

endocardium,  535 

fibers  of  atria,  537 
of  ventricles,  537 

fibrous  rings  of,  536 

lymphatic  capillaries  of,  687     - 
vessels  of,  718 

nerves  of,  538 

sinoatrial  node  of,  537 

size  and  weight  of,  526 

structure  of,  535 

surface  marking  of,  1311 

trigonum  fibrosum,  536 

veins  of,  642 

ventricle,  left,  534 
right,  531 
Heidenhain,  demilunes  of,  1136 
Height  index  of  skull,  198 
Helicine  arteries,  1251 
Helicis  major  muscle,  1035 

minor  muscle,  1035 
Helicotrema,  1050 
Helix,  1033 
Helwig's  bundle,  854 
Hemiazygos  vein,  667 

accessory,  667 
Hemispheres,  cerebellar,  788 

cerebral,  817 
Hemorrhoidal  artery,  inferior,  619 
middle,  615 
superior,  010 

nerve,  inferior,  968 

plexuses  of  nerves,  987,  988 

vein,  middle,  676 
superior,  681 

venous  plexus,  676 
Henle,  loop  of,  1223 
Henle's  layer  of  hair  follicle,  1068 
Hensen,  canalis  reuniens  of,  1054 

kn9t  of,  47 

stripe  of,  1058 

supporting  cells  of,  1058 
Hepar,  1188 

capsula  fibrosa  [Glissoni],  1195 

fades  inferior,  1189 
posterior,  1190 
superior,  1189 

margo  anterior,  1191 

tunica  serosa,  1195 
Hepatic  artery,  603 

branches  of  vagus  nerve,  913 

cells,  1196 

cylinders,  1193 

duct,  1197 

flexure  of  colon,  1180 

lymph  glands,  706 

plexus,  986 

veins,  680 
Hepatoduodenal  ligament,   1151, 

1157 
Hepatogastric     ligament,     1151, 

1157 
Hepatorenal  ligament,  1150 
Herbst,  corpuscles  of,  1061 
Hernia,  congenital,  complete,  1187 
incomplete,  1188 

into  funicular  process,  1189 
Herophilus,  torcular  of,  658 
Heschl,  gyri  of,  824 
Hesselbach,     interfoveolar     liga- 
ment of,  415 

triangle  of,  1221 


Hiatus,  aortic,  406 

esophageal,  406 

of  facial  canal,  142 

semilunaris,  195,  995 
Higher  or  cortical  visual  centers, 

814 
Highest  intercostal  artei-y,  585 
veins,  666 

nuchal  line,  129 

thoracic  artery,  587 
Highmore,  antrum  of,  159,' 
Hilum  of  kidney,  1219 
Hi] us  of  lung,  1095 

of  spleen,  1283 
Hind-brain,  738,  767 
Hind-gut,  53,  1101 
Hinge-joint,  285 
Hip  bone,  231 

articulations  of,  238 
ossification  of,  237 
structure  of,  237 
surface  anatomy  of,  1336 
Hip-joint,  333 

movements  of,  338 

muscles  in  relation  with,  338 

surface  marking  of,  1343 
Hippocampal    commissure,    838, 
869 

fissure,  746,  826 

gyrus,  826 
Hippocampus,  746,  832 

major,  832 
His,   atrioventricular   bundle   of, 
537 

globular  processes  of,  68 
Holoblastic  ova,  45 
Horizontal  cells  of  retina,  1017 

part  of  palatine  bone,  167 

semicircular  canal,  1049 

sulcus  of  cerebellum,  789 
Houston's  valves  of  rectiun,  1183 
Howship's  foveolse,  88 
Huguier,  carial  of,  141,  904,  1039 
Humeral  articulation,  317 
bursie  in  relation  to,  319 
movements  of,  319 
_  vessels  and  nerves  of,  319 

circumflex  arteries,  589 
Humerus,  209 

ossification  of,  213 

structure  of,  212 

surface  anatomy  of,  1326 
Humor,  aqueous,   1018 
Hunter's  canal,  627 
Huschke,  auditory  teeth  of,  1055 

foramen  of,  145,  147 
Huxley's    layer   of    hair   follicle, 

1068 
Hyaline  cartilage,  279 

cell,  504 
Hyaloid  canal,  1018 

fossa,  1018 

membrane  of  eye,  1018 
Hyaloplasm,  36 

Hydatid  of  Morgagni,  1207, 1242, 
1257 

pedunculated,    of    epididymis, 
1242 
Hymen,  1266 

Hyoepiglottic  ligament,  1077 
Hyoglossal  membrane,  1132 
Hyoglossus  muscle,  1129 
Hyoid  arteries,  552,  553 

bone,  177 
body  of,  177 
cornua  of,  177 
ossification  of,  178 
Hyothyroid  ligaments,  1077 

membrane,  1076 
Hyparterial  bronchi,  1085,  1097 
Hypochondriac  regions,  1149 
Hypochordal  bar  or  brace,  82 
Hypogastric  artery,  614 
branches  of,  615 
in  fetus,  540 


INDEX 


Hypogastric    arterj-,    obliterated, 
615 
peculiarities  of,  615 
lymph  glands,  704 
plexus,  9S;7 
region,  1149 
vein,  673 
zone,  1148 
Hypoglossal  nerve,  914 

composition  and  central  con- 
nections of,  855 
nucleus  of,  779 
Hypophysis  cerebri,  814,  1275 

development  of,  1276 
Hypothalami,    pars  mammillaria, 
743 
optica,  744 
Hypothalamus,  812 

corpora  mammillaria,  813 
hvpophysis  or  pituitary  body, 

814,  1275 
infundibulum,  813 
optic  chiasma,  814 
subthalamic  tegmental  region, 
812 
corpus     subthalamicum,     or 

nucleus  of  Luvs,   812 
stratum  dorsale,  812 
zona  iucerta,  812 
tuber  cincrum,  813 
Hypothenar  eminence,  456 


Ileocecal  fold,  1160 
fossae,  1160 
valve,  1179 
Ileocolic  arterj-,  607 
lymph  glands,  709 
Ileum,  1170 

lymphatic  vessels  of,  710 
Iliac  arteries,  common,  613 
peculiarities  of,  614 
surface  markings  of,  1322 
external,  622 

surface  markings  of,  1322 
internal,  614 

peculiarities  of,  614 
circumflex  artery,  deep,  623 
superficial,  629 
vein,  deep,  673 
superficial,  669 
colon,  1182 
fascia,  466 
fossa,  234 
furrow,  1313 
lymph  glands,  703,  704 
region,  1149 
spines,  234 
tuberosity,  234 
vein,  common,  677 

peculiarities  of,  677 
external,  672 
internal,  673 
Iliacus  muscle,  467 
actions  of,  467 
fascia  of,  466 
nerves  of,  467 
variations  of,  467 
Iliocapsularis  muscle,  467 
Iliococcygeus  muscle,  424 
Iliocostalis  cervicis  muscle,  399 
dorsi  muscle,  399 
lumborum  muscle,  399 
Iliofemoral  ligament,  334 
Iliohypogastric  nerve,  950 
Ilioinguinal  nerve,  952 
Iliolumbar  artery,  621 
ligament,  306 
vein,  678 
Iliopectineal  eminence,  234 

fascia,  466 
Iliosacralis  muscle,  424 
Iliotibial  band  or  tract,  468 


Iliotrochanteric  ligament,  335 
Ilium,  231 

ala  of,  232 

body  of,  231 

crest  of,  234 

dorsum  of,  232 

gluteal  lines  of,  233 

spines  of,  234 
Imbedding    or    implantation    of 

ovum,  58 
Immovable  articulations,  284 
Impression,  colic,  1189 

duodenal,  1190 

gastric,  1189 

renal,  1189 

rhomboid,  202 

suprarenal,  1191 

trigeminal,  143 
Incisive  bone,  162 

canals,  162,  180 

foramen,  162,  180 

fossa,  158,  172,  188 

teeth,  1115 
Incisor  crest,  163 

teeth,  1115 
I ncisur a  annularis,  1162 

apicis  cordis,  527 

cardiaca,  1162 

fastigii,  741 

radialis,  215 

semilunaris,  215 

temporalis,  826 

tentorii,  874 
Incremental  lines  of  Salter,  1120 
Incus,  1044 

crus  breve,  1044 
longum,  1045 

development  of,  1033 

ligaments  of,  1045,  1046 

process  of,  long,  1045 
short,  1044 
Index,  cephalic  or  breadth,  198 

gnathic  or  alveolar,  199 

nasal,  198 

orbital,  198 

vertical  or  height,  198 
Indusium  griseum,  827,  868 
Inferior  articular  arteries,  633 

articulation,  325 

calcaneonavicular    ligament, 
355 

cereVjellar  peduncles,  793 

constrictor  muscle,  1142 

dental  artery,  561 
nerve,  896_ 

epigastric  vein,  672 

ganglion.  908,  911 

laryngeal  nerve,  912 

longitudinal  sinus,  655 

maxillary  nerve,  893 

medullary  velum,  794 

oblique  muscle,  1023 

profunda  artery,  591 

pubic  ligament,  310 

quadrigeminal  body,  806 

semilunar  lobule,  791 

tarsal  plate,  1025 

thyroarytenoid  ligaments,  1080 

vocal  cords,  1080 
Infraclavicular  branches  of  bra- 
chial plexus,  933 
Infracostales  muscle,  403 
Infraglenoid  tuberosity,  205 
Infrahyoid  artery,  552 

muscles,  391 
Infraorbital  artery,  562 

canal,  159 

foramen,  158,  187 

groove,  159 

nerve,  889  note 

plexus  of  nerves,  891 
Infrapatellar  pad  of  fat,  344 
Infrascapular  artery,  588 
Infraspinatous  fascia,  441 

fossa,  203 


Infraspinatus  muscle,  441 
actions  of,  442 
nerves  of,  442 
Infrasternal  notch,  1307 
Infratemporal  crest,  150,  183 

fossa,  184 

surface  of  maxilla,  158 
Infratrochlear  nerve,  888 
Infundibuliform  fascia,  418 
Infundibulopelvic  ligament,  1261 
infundibulum  of  brain,  813 

of  ethmoid  bone,  156, 195, 995 
Inguinal  aponeurotic  falx,  414 

canal,  418 

glands,  702 

ligament,  411 
reflected,  412 

regions,  1149 

ring,  abdominal,  418 
subcutaneous,  '410 
Inion,  185, 198 
Inlet  of  pelvis,  239 
Inner  cell-mass,  46 
Innominate  artery,  548 

bone,  231 

articulations  of,  238 
ossification  of,  237 

veins,  664 

peculiarities  of,  666 
Inscriptions,  tendinous,  of  rectus 

abdominis,  416 
Insertion  of  muscles,  362 
Insula,  825 

circular  sulcus  of,  825 

development  of,  825 

gyri  of,  825 

opercula  of,  825 
Integument,  common,  1062 
Interalveolar  cell-islets,  1204 
Interarticular  chondrosternal  lig- 
ament, 303 

costocentral  ligaments,  300 

fibrocartilages,  281 

sternocostal  ligaments,  303 
Interatrial  groove,  527 
Intercalatum,  802 
Intercapitular  veins,  661,  669 
Intercarpal  articulations,  328 

movements  of,  330 
Intercavernous  sinuses,  659 
Intercellular  biliary  passages, 

1197 
Intercentral  ligaments,  287 
Interchondral  ligaments,  304 
Interclavicular  ligament,  314 
Interclinoid  ligament,  153 
Intercolumnar  fascia,  1238 

fibers,  410 
Intercondyloid  eminence  of  tibia, 
256 

fossa  of  femur,  247 
of  tibia,  posterior,  256 
Intercostal   arteries   from    aorta, 
600 
highest,  585 

from  internal  mammary,  583 
superior,  585 

fasciae,  402 

lymph  glands,  715 

membranes,  403 

muscles,  403 

nerves,  945 

spaces,  123 

veins,  666 
Intercostales  externi  muscles,  403 
variations  of,  403 

interni  muscles,  403 
variations  of,  403 
Intercostobrachial  nerve,  946,  947 
Intercrural  fascia,  411 

fibers,  410 
Intercuneiform  articulations,  357 
Interfoveolar  ligament  of  Hessel- 

bach,  415 
Interglobular  spaces,  1120 


INDEX 


Interior  of  bladder,  1231 
of  larynx,  1078 
of  skull,  189 
of  uterus,  1260 
Interlobular   arteries   of    kidney, 

1223 
Intermediate  cell-mass,  50 
Intermetacarpal  articulations,  331 
Intermetatarsal  articulations,  358 
Internal  abdominal  ring,  418 
acoustic  meatus,  143 
arcuate  ligament,  404 
calcaneal  arteries,  639 

nerves,  963 
calcaneoastragaloid     ligament, 

352 
calcaneonavicular  ligament,  355 
canthus  of  eyelids,  1025 
capsule  of  brain,  836 
circumflex  artery,  630 
cutaneous  nerve,  937,  955 

lesser,  937 
geniculate  body,  811 
iliac  artery,  614 
glands,  704 
vein,  673 
intercostals  muscle,  403 
lateral  ligament.  297,  322,  328 
malleolar  artery,  635,  639 
mammary  artery,  583 

gland,  715 
maxillary  glands,  694 
oblique  muscle,  412 
palpebral  arteries,  570 
plantar  artery,  639 

nerve,  963 
popliteal  nerve,  960 
pterygoid  muscle,  387 
pudendal  artery,  617 

veins,  674 
pudic  artery,  617 
nerve,  967 
veins,  674 
respiratory  nerve  of  Bell,  928 
saphenous  nerve,  956 

vein,  669 
semilunar  fibrocartilage,  343 
sphincter  ani  muscle,  426 
Internodal  segments  of  nerve3,727 
Interossei  niuscles  of  foot,  495 
actions  of,  495 
nerves  of,  495 
of  hand,  464 
actions  of,  465 
nerves  of.  465 
Interosseous  arteries, 595,  596,  597 
ligament,  302 
membrane  of  foreai-m,  325 

of  leg,  348 
nerve,  dorsal  or  posterior,  944 
volar  or  anterior,  Q38 
Interparietal  bone,  132 
Interpeduncular  fossa,  816 

ganglion,  800,  802,  868 
Interphalangeal       articulations, 

333,  359 
Interpleural  space,  1090 
Interpubic  disk,  311 

fibrocartilaginous  lamina,  311 
Intersegmental  neurons,  755 

septa,  80 
Intersigmoid  fossa,  1167 
Interspinal  ligaments,  291 
Interspinales  muscles,  400 
actions  of,  402 
nerves  of,  402 
Interspinou:s  ligament,  291 
Intersternal  ligaments,  304 
Intertarsal  articulations,  352 
Intertragic  notch,  1034 
Intertransversales  muscle,  401 
■  Intertransversarii  muscles,  401 
actions  of,  402 
nerves  of,  402 
Intertransverse  ligaments,  291 


Intertrochanteric  crest,  246 

line,  245 
Intertubercular  plane,  1147 
Intertubular  dentin,  1120 
Intervenous  tubercle,  531 
Interventricular     foramen,     816, 
840 

septum,  534 
Intervertebral  fibrocartilages,  289 

foramina,  96 

veins,  669 
Intervillous  space,  59 
Intestinal  arteries,  607 

glands,  1174 

villi,  1174 
Intestine,  development  of,  1101 

large,  1177 

lymphatic  nodules  of,  1176 

lymphatics  of,  710 

small,  1168 

structure  of,  1172 

vessels  and   nerves  of,   1176 

surface  markings  of,  1319 
Intestinum  ccecum,  1177 

crassum,  1177 

ileum,  1171 

jejunum,  1170 

rectum,,  1183 

tenue,  1168 

tela  submucosa,  1172 
tunica  mucosa,  1173 
muscularis,  1172 
serosa,  1172 
Intra-articular  ligament,  300 
Intracartilaginous  ossification,  93 
Intra-epithelial  plexus  of  cornea, 

1009 
Intrafusal  fasciculi,  1061 

fibers,  1061 
Intrajugular  process,  131 
Intralobular  veins,  1196 
Intramembranous  ossification,  91 
Intraparietal  sulcus,  822 
Intrapulmonary  bronchi,  1098 
Intraspinal  veins,  668 
Intrathyroid  cartilage,  1074 
Intrinsic  muscles  of  tongue,  1130 

spinal  reflex  paths,  850 
lodothyrin,  1271 
Iridial  angle,  1007 
Iris,  1012 

structure  of,  1013 

vessels  and  nerves  of,  1014 
Irregular  bones,  80 
Ischiocapsular  ligament,  334 
Ischiocavernosus  muscle,  428,  430 

action  of,  428,  430 
Ischiortcial  fossa,  425 
Ischium,  234 

body  of,  234 

rami  of,  235 

spine  of,  235 

tuberosity  of,  235 
Island  of  Reil,  825 
Islands,  blood,  506 

of  Langerhans,  1204 
Isthmus,  aortic,  517,  .547 

of    external    acoustic    meatus 
1043 

faucium,  1137 

glandula  thyreoidea,  1270 

of  limbic  lobe,  825 

rhombencephali,  738 

of  thyroid  gland,  1269 

of  uterine  tube,  1257 
Iter  chorda  anterius,  1039 

posterius,  1038 
Ivory  of  teeth,  1119 


Jacob's  membrane,  1017 
Jacobson,  nerve  of,  909, 1047 

vomeronasal  organs  of,  71,  996 


capil- 


ngeiu 


il 

144 

41 


Jejunum,  1170 

lymphatic  vessels  of,  710 
Jelly  of  Wharton,  58 
Joint  capsules,    lymphatic 

laries  in,  684 
Joints.    See  Articulations. 

development  of,  283 
Jugular  foramen,  181,  193 
fossa,  144 

ganglion    of    glossophary 
nerve,  908 
of  vagus  nerve,  911 
nerve,  978 
notch,  120,  131 
process,  131,  181 
surface  of  temporal  bone, 
tubercle,  131 
vein,  anterior,  647 
external,  646 
internal,  648 

bulbs  of,  648 
posterior  external,  647 
Jugum  sphenoidale,  153 
Junctional  tube,  1223 


Karygkinesis,  37 
Karyomitome,  36 
Karyomitosis,  37 
Karyoplasm,  36 
Kerckring,  ossific  center  of,  133 
Kerkring,  valves  of,  1173 
Kidnevs,  1215 

calyces  of,  1221,  1225 

cortical  substance  of,  1221 

development  of,  1211 

fixation  of,  1220 

hilum  of,  1219 

lymphatic  capillaries  in,  687 
vessels  of,  712 

Malpighian  bodies  of,  1221 
capsule,  1221 

medullary  substance  of,  1221 

minute  anatomy  of,  1221 

nerves  of,  1225 

paranephric  body,  1220 

renal  artery,  610 
fascia,  1220 
pelvis,  1221 
sinus,  1221 
tubules,  1221 

structure  of,  1220 

surface  marking  of,  1320 

veins  of,  679,  1224 

weight  and  dimensions  of,  1215 
Knee  cap,  255 
Knee-joint,  339 

bursas  of,  345 

movements  of,  346 

surface  anatomy  of,  133S 
Krause,  end-bulbs  of,  1060 

membrane  of,  375 
Kiihne,  motor  end-plates  of,  730 


Labbe,-    posterior     anastomotic 

vein  of,  652 
Labia  cerebri,  827 

Tnajora,  1265 

minora,  1265 

oris,  1111 
Labial  arteries,  555 

commissures,  1265 

glands,  1111 

grooves,  1102 
Labiodental  lamina,  1122 
Labrum  (jlenoidalc,  319,  336 
Labyrinth,  membranous,  1051 
development  of,  1032 
vessels  of,  1059 

osseous,  1047 


INDEX 


1369 


II 


L; 

I 


Labyrinlhus  ethmoidalis ,  154 
membranaceus,  1051 
osseus,  1047 
Lacertus  fibrosus,  444 
Laciniate  ligament,  489 
Lacrimal  apparatus,  1028 
artery,  569 
bone,  163 

articulations  of,  164 
lesser,  164 
ossification  of,  164 
canals,  1028 
caruncula,  1028 
crest,  posterior,  164 
ducts  or  canals,  1028 

ampullae  of,  1028 
fossa,  137,  188 
glands,  1028 
groove,  159,  189 
hamulus,  164 
nerve,  887 
notch, 159 
papilla,  1025 
process  of  inferior  nasal  concha, 

169 
punctum,  1025 
sac,  1028 
tubercle,  161 
Lacteals,  683 
Lactiferous  ducts,  1268 
Lacuna  magna  [of  urethra],  1235 
Lacunae  of  bone,  89,  90 
of  cartilage,  280 
of  urethra,  1235 
venous,  655 
Lacunar  ligament,  412 
Lacus  lacrimalis,  1025,  1028 
Lagena,  1054 
Lambda,  178,  198 
Lambdoidal  suture,  132,  135,  183 
Lamellae  of  bone,  89 
articular,  279 
circumferential,  89 
interstitial,  89 
primary  or  fundamental,  90 
secondary  or  special,  90 
lamellar  cells,  377 
Lamina  affixia,  838 
basalis,  1010 

cartilaginis  cricoidece,  1047 
choriocapillaris,  1010 
cribrosa  sclera,  1005 
dorsal  or  alar,  735 
elastic,  of  cornea,  1008 
elastica  anterior,  1008 

posterior,  1008 
fibrocartilaginca  interpubica,  311 
labiodental,  1122 
lingual,  1122 
medullary,  810 
nasal,  68 
reticular,  1058 
spiral,  of  cochlea,  1051 
spiralis  ossea,  1051 
supruchorioidea,  1005,  1010 
terminalis,  742,  816 
vasculosa,  1010 
ventral  or  basal,  735 
of  vertebrae,  96 
Lancisi,  nerves  of,  868 
Langerhans,    centro-acinar    cells 
of,  1204 
islands  of,  1204 
Langhans,  layer  of,  47 
Langley's  ganglion,  1137 
Lantermann,  segments  of,  727 
Large  deep  petrosal  nerve,  892 
intestine,  1177 
cecum,  1177 
colic  valve,  1179    - 
colon,  1180 

ascending,  1180 
descending,  1181 
iliac,  1182 
sigmoid  or  pelvic,  1182 


Large  intestine,  colon,  transverse, 
1180 
rectum,  1183 

superficial  petrosal  nerve,  892, 
903 
Laryngeal  artery,  inferior,  581 
superior,  552 

nerves,  912 

part  of  pharynx,  1142 

prominence,  1073 

saccule,  1080 

sinus,  1080 
Larynx,  1072 

cartilages  of,  1073 

conus  elasticus  of,  1078 

elastic  membrane  of,  1077 

glands  of,  1084 

interior  of,  1078 

ligaments  of,  1076 

lymphatic  vessels  of,  698,  1084 

mucous  membrane  of,  1083 

muscles  of,  1081 
actions  of,  1083 

nerves  of,  1084 

rima  glottidis  of,  1080 

surface  marking  of,  1301 

ventricle  of,  1080 

ventricular  folds  of ,  1079 

vessels  of,  1084 

vestibule  of,  1078 

vocal  folds  of,  1080 
Lateral  cartilages,  993 

cricoarytenoid  muscle,  1081 

sinuses,  657 

spinothalamic  fasciculus,  762 

thyrohyoid  ligament,  1077 
Latissimus  dorsi  muscle,  432 
actions  of,  435 
nerves  of,  434 
variations  of,  434 
Layer  of  Langhans,  47 

of  rods  and  cones,  1017 
Layers  of  cerebral  cortex,  845 
Least  splanchnic  nerve,  981 
Left  atrium,  533 

auricle,  533 

auricular  appendix,  533 

coronary  plexus,  985 
vein,  642 

lobe  of  liver,  1192 

ventricle,  534 
Leg,  fascia  of,  480 

deep  transverse,  483 

muscles  of,  480 

development  of,  372 
Lemniscus,  lateral,  805 

lateralis,  805 

medial,  804 

medialis,  804 

spinal,  762 
Lens,  capsule  of,  1019 
vascular,  1003 

changes  produced  in,  by  age, 
1021 

crystallina,  1019 

crystalline,  1019 

development  of,  1002 

equator  of,  1019 

poles  of,  1019 

structure  of.  1020 

suspensory  ligament  of,  1018 

vesicle,  1001 
Lenticula,  834 
Lenticular  ganglion,  888 

glands  of  stomach,  1167 

nucleus,  834 

process  of  incus,  1045 
Lentiform  nucleus,  834 
Lesser  cavernous  nerve,  989 

curvature  of  stomach,  1162 

internal  cutaneous  nerve,  937 

lacrimal  bone,  164 

multangular  bone,  225 

omentum,  1156 

pelvis,  239 


Lesser  peritoneal  sac,  1152,  1155 
sac  or  omental  bursa  of  peri- 
toneum, 1155 

boundaries  of ,  1156 
sciatic  foramen,  309 

notch,  235 
sigmoid  cavity,  215 
splanchnic  nerve,  981 
trochanter,  245 
Leucocytes,  504 
Levator  anguli  oris  muscle,  383 

scapulas  muscle,  435 
ani  muscle,  422 

actions  of,  424 
nerves  of,  424 
clavdculse  muscle,  435 
glandulae    thyreoideise    muscle, 

1270 
menti  muscle,  383 
palati  muscle,  1139 
palpebrae      superioris     muscle, 
1021 
actions  of,  1023 
nerves  of,  1023 
prostatae  muscle,  424 
scapulae  muscle,  435 
actions  of,  435 
nerves  of,  435 
variations  of,  435 
veli  palatini  muscle,  1139 
Levatores  costarum  muscle,  403 
Lieberkiihn,  crypts  of ,  1174 
Lien,  1228 

accessorius,  1283 
extremitas  inferior,  1283 

superior,  1283 
fades  gastrica,  1282 

renalis,  1283 
margo  anterior,  1283 

posterior,  1283 
Lienal  artery,  605 
plexus  of  nerves,  986 
vein,  681 
Ligament  or  Ligaments,  acromio- 
clavicular, 315 
alar  296 

of  ankle,  349,  350,  351 
annular,  of  ankle,  488,  489 

of  radius,  324 

of  stapes,  1046 

of  wrist,  456,  458 
anterior,  327 

inferior,  348 

longitudinal,  287 

superior,  301,  348 
apical  odontoid,  296 
arcuate,  405 
atlantoaxial,  293 
atlantooccipital,  296 

membrane,  posterior,  296 
of  auricula  or  pinna,  1035 
of  Bertin,  335 
bifurcated,  354,  355 
of  Bigelow,  335 
of  bladder,  1231 
broad,  of  uterus,  1260 
calcaneoastragaloid,  352 
calcaneocuboid,  354 
calcaneofibular,  351 
calcaneona\ncular,  plantar,  355 
calcaneotibial,  350 
capsular.  See  Individual  Joints, 
caroticoclinoid,  153 
carpometacarpal,  331 
of  carpus,  328,  329 
central,  of  medulla  spinalis,  879 
check,  296 

of  eye,  1024 
chondrosternal,  302 

intra-articular,  303 
chondroxiphoid,  304 
common,  anterior,  287 

posterior,  288 
conoid,  315 
of  Cooper,  412 


1370 


INDEX 


Ligament  or  Ligaments,   coraco- 

acromial,  316 
coracoclavicular,  315 
coracohumeral,  318 
coronary,  of  knee,  343 

of  liver,  1150,  1192 
costoclavicular,  310 
coetocoracoid,  437 
costotransverse,  301 

middle,  302 

posterior,  301,  302 
costovertebral,  anterior,  299 
costoxiphoid,  304 
cotyloid,  237,  436 
cricoarytenoid,  posterior,  1078 
cricotracheal,  1077 
crucial,  342 
cruciate,  of  atlas,  295 

crural,  488 

of  knee,  342 
cuboideonavicular,  357 
deltoid,  of  ankle-joint,  350 
dentate,  880 
digital  vaginal,  449 
dorsal  carpal,  458 

radiocarpal,  327 

radioulnar,  325 
ofelbow,321,322 
falciform,  of  liver,  1150,  1192 
fibular  collateral,  of  knee-joint, 

341 
fundiform,  of  penis,  1249 
gastrocolic,  1151,  1153 
gastrolienal,  1155 
gastrophrenic,  1162 
Gimbernat's,  412 
glenohumeral,  318 
glenoid,  319 

of  Cruvcilhier,  332,  359 

of  shoulder-joint,  318 
glenoidal  labrum  of  hip-joint, 
336 
of  shoulder-joint,  319 
hepatoduodenal,  1151,  1157 
^  hepatogastric,  1151,  1157 
hepatorenal,  1150,  1192 
of  Hesselbach,  415 
of  hip-joint,  334 
hyoepiglottic,  1077 
iliofemoral,  334 
iliolumbar,  306 
iliotrochanteric,  335 
of  incus,  1046 
inferior  transverse  of  scapula, 

317 
infundibulopelvic,  1261 
inguinal,  411 

reflected,  412 
interarticular,  of  ribs,  300 

sternocostal,  303 
intercarpal,  328,  329 
intercentral,  287 
interchondral,  304 
interclavicular,  314 
interclinoid,  153 
intercuneiform,  357 
interfoveolar,  415 
intermetacarpal,  331 
intermetatarsal,  358 
interosseous,  302 
interphalangeal,  333,  369 
interpubic       fibrocartilaginous 

lamina,  311 
interspinal,  291 
interspinous,  291 
intersternal,  304 
intertarsal,  352 
intertransverse,  29l,  310 
intra-articular,  300 
ischiocapsular,  325 
of  knee-joint,  340 
laciniate,  489 
lacunar,  412 
of  larynx,  1076 
lateral  atlantooccipital,  296 


Ligament   or    Ligaments,    lateral 
external,  297,  322,  328 

internal,  297,  322,  328 

of  uterus,  1260 
left  triangular,  of  liver,  1151 
of  left  vena  cava,  526 
long  plantar,  354 
of  Mackenrodt,  1261 
of  malleus,  1045 
medial  palpebral,  380 
metacarpophalangeal,  332 
metatarsophalangeal,  369 
middle  cricothyroid,  1078 
mucosum,  of  knee,  344 
of  neck  of  rib,  302 
nuchaj,  290 
oblique  cord,  325 

popliteal,  340 
occipitoaxial,  296 
odontoid,  296 
orbicular,  324 
of  ovary,  1254 
palmar,  328,  331 
palpebral,  1026 
pectinate,  of  iris,  1009 
of  pelvis,  403 
phrenicocolic,  1158 
phrenicolienal,  1155 
ohrenicopericardiac,  right,  678 
of  pinna  or  auricula,  1035 
plantar,  long,  354 
posterior,  328 

cricoarytenoid,  1078 

inferior,  348 

of  knee,  340 

longitudinal,  288 

sacroiliac,  307 

superior,  348 
Poupart's,  411 
pterygomandibular,  384 
pterygospinous,  153,  388 
pubic,  310 
pubocapsular,  334 
pubofemoral,  335 
pulmonary,  1088,  1090 
quadrate,  324 

radial  collateral,  of  elbow-joint, 
322 
of  wrist-joint,  327 
radiate,  299 

sternocostal,  302 
of  radiocarpal  joint,  327 
radioulnar,  325 
reflected  inguinal,  412 
rhomboid,  314 

right  triangular  of  liver,  1151 
round,  of  liver,  1192 

of  uterus,  1261 
sacrococcygeal,  309 
sacroiliac,  307 
sacrosciatic,  309 
sacrospinous,  309 
sacro tuberous,  309 
of  scapula,  316 
of  shoulder-joint,  317 
sphenomandibular,  297,  388 
spinoglenoid,  317 
spiral,    of    ductus    coehlearis, 

1054 
stellate,  299 
sternoclavicular,  313 
sternocostal,  302 
sternopericardiac,  526 
of  sternum,   302 
structure  of,  282 
stylohyoid,  392 
stylomandibular,  298,  388 
subpubic,  310 
superficial     transverse     of 

fingers,  461 
superior  transverse  of  scapula, 

317 
suprascapular,  317 
supraspinal,  290 
supraspinous,  290 


spei 


Ligament  or  Ligament 
sory,  of  axilla,  436 

of  eye,  1025 

of  lens,  1018 

of  mamma,  435 

of  ovary,  1254 

of  penis,  1249 
talocalcaneal,  352,  353 
talonavicular,  dorsal,  354 
talotibial,  350 
tarsometatarsal,  358 
of  tarsus,  352 
temporomandibular,  297 
tendo  oculi,  381 
teres,  of  hip,  336 
thyroarytenoid,  inferior,  IQJ 
thyroepiglottic,  1078 
thyrohyoid,  1077 
tibial  collateral,  of  knee-j 

341 

tibiofibular,  348 
tibionavicular,  350 
transversalis  colli  uteri,  1261 
transverse  acetabular,  336 

of  atlas,  293 

carpal,  456 

crural,  488 

humeral,  319 

inferior,  349 

of  knee,  343 

metacarpal,  331 

metatarsal,  359 

of  pelvis,  429 

of  scapula,  317 
trapezoid,  315 
triangular,  of  liver,  1192 

of  urethra,  428 
of  tubercle  of  rib,  302 
ulnar  collateral,  of  elbow-joint, 
321 
of  wrist-joint,  327 
uterosacral,  1260 
of  uterus,  1260 
ventricular,  of  larynx,  1080 
of  vertebrae,  287 
volar  carpal,  456 

metacarpophalangeal,  332 

radiocarpal,  327 

radioulnar,  325 
of  Wrisberg,  343 
of  wrist-joint,  327 
Y-shaped,  of  Bigelow,  335 
of  Zinn, 1022 
I/igamenta  accessoria  plantaria,3o9 
alaria,  296 

auricularia  [Valsalva],  1036 
basium  [oss.  metacarp.]  dorsalia, 
331 
interossea,  331 
volaria,  331 

[oss.  metatars.]  dorsalia,  358 
interossea,  358 
plantaria,  358 
carpometacarpece  dorsalia,  33 1 

volaria,  331 
collateralia,  359 
costoxiphoidea,  304 
cruciata  genu,  342 
cuneoinetatarsea  interossea,  359 
intercarpea  dorsalia,  328 

interossea,  328 

volaria,  328 
inter cuneif or mia  interossea,  357 

plantaria,  357 
inter spinalia,   291 
intertransversaria,  291 
navicularicuneiformia   dorsalia, 
356 

plantaria,  356 
ossiculorum  auditus,  1045 
sternocostalia  radiata,  302 
suspensoria  [of  mamma],  435 
tarsometatarsea  dorsalia,  358 

plantaria,  358 
vocales,  1080 


INDEX 


1371 


jigamentous  action  of  muscles, 

287 
Ligamentum  acromioclaviculare, 
L       315 

■  annulare  baseos  stapedis,  1046 
'        radii,  324 

arcuat'um  pubis,  310 
bifurcatuin,  354 
calcaneocuboideum  dorsale,  354 

plantare,  354 
calcaneo fibular  a,  351 
calcaneonavicular e  plantare,  355 
capituli  costce  interarticulare,300 

radiatum,  299 
capituloTum[oss.  metacarpalium] 

transversum,  331 
carpi  dorsale,  458 

transversum,  456 

volare,  456 
collaterale  fibulare,  341 

radiale,  3^2,  32S 

tibiale,  341 

Miware,  322,  328 
coZh"  costce,  302 
conoideum,  315 
coracoacromiale,  316 
coracoclaviculare,  315 
coracohumerale,  317 
coronarium  hepatis,  1192 
costoclavicular e,  314 
costotransversarium  anterius, 
301 

posterius,  301 
cricoarytcenoideum  posterius, 

1078 
cricolhyreoideum  medium,  1078 
cricotracheale,  1077 
cruciatum  anterius,  342 

posterius,  342 
cuboideonaviculare  dorsale,  357 

plantare,  357 
deltoideum,  350 
denticulatutn,  879 
Jalciforme  hepatis,  1192 
hyoepiglotticum,  1077 
hyothyreoideum  laterale,  1077 

medium,  1077 
iliofemorale,  335 
iliolumbale,  306 
incudis  posterius,  1045 

superius,  1046 
inguinale  [Pourparti],  411 

reflexum  [Colleri],  412 
inter claviculare,  314 
ischiocapsulare,  335 
lacunare  [Gimbei-nati],  412 
latum  pulmonis,  1090 

w/eri,  1260 
longitudinale  anterius,  287 

posterius,  288 
mallei  anterius,  1045 

laterale,  1045 

superius,  1045 
malleoli  lateralis  anterius,  348 

posterius,  348 
mucosum,  344 
nuchce,  290 
patella',  340 
plantare  longum,  354 
popliteum  obliquum,  340 
pubicum  superius,  310 
pubocapsulare,  335 
pulmonale,  1090 
radiocarpeum  dorsale,  328 

t'oZare,  327 
sacrococcygeum  anterius,  309 

laterale,  310 

posterius,  309 
sacroiliacum  anterius,  307 

interosseum,  308 

posterius,  307 
sacrospinosum,  309 
sacrotuberosum,  309 
sphenotnandibulare,  297 
sternoclavicular e,  313 


Ligamentum     sternocostale     inier- 
articulare,  303 
stylomandibular e,  298 
supraspinale,  290 
talocalcaneum  anterius,  352 
interosseum,  353 
laterale,  352 
mediale,  353 
posterius,  352 
talofibulare  anterius,  351 

posterius,  352 
talonaviculare  dorsale,  354 
temporomandibulare,  297 
/eres  femoris,  336 
hepatis,  1193 
uteri,  1261 
thyroepiglotticum,  1078 
transversalis  colli  uteri,  1261 
transversum  acetabuli,  336 
atlantis,  293 

crws  infer ius,  295 
superius,  295 
cruris,  488 
genu,  343 

scapuke  inferius;  317 
superius,  317 
trapezoideum ,  315 
triangulare  dextrum,  1192 

sinistT~um,  1193 
tuberculi  costce,  302 
venosum,  1193 
Ligature  of    arteries.     <See   each 

Artery. 
Ligula,  797 
Limbic  lobe,  825 
Limbs,  development  of,  71 
Limbus  fossae  ovalis,  513 
lamince  spiralis,  1055 
Limiting   membranes   of    retina 

1017 
Line  or  Lines,  arcuate,  of  ilium, 
234 
colored,  of  Retzius,  1120 
curved,  of  ilium,  232 
gluteal,  of  ilium,  232 
incremental,  of  Salter,  1120 
intercondyloid,  247 
intertrochanteric,  245 
mylohyoid,  173 
nuchal,  129,  182 
oblique,  of  fibula,  261- 
of  mandible.  172 
of  radius,  219 
pectineal,  246 
popliteal,  of  tibia,  258 
of  Schreger,  1120 
spiral,  of  femur,  245 
temporal,  134,  136,  178,  183 
Linea  alba,  416 
aspera,  246 
quadrata,  246 
semicircularis,  416 
splendens,  879 
Linece  semilunares,  417 
Lingua,  1125 

fades  inferior,  1125 
tunica  mucosa,  1131 
Lingual  artery,  553 
deep,  553 
bone,  177 
branches   of   glossopharyngeal 

nerve,  909 
gyrus,  823 
lamina,  1122 
lymph  glands,  694 
nerve,  895 
tonsil,  1131 
veins,  648 
Lingula  cerebelli,  789 
of  cerebellum,  789 
of  mandibulse,  173 
of  sphenoid,  148,  192 
Linin,  36 

Lip,  tympanic,  1055 
vestibular,  1055 


Lips,  1111 
Liquor  amnii,  56 
sangumis,  503 
Lissauer,  fasciculus  of,  762 

tract  of,  762 
Littre,  urethral  glands  of,  1235 
Liver,  1188 

bare  area  of,  1150 
bile  ducts  of,  1197 
common,  1198 
cystic  duct,  1198 
development  of,  1193 
excretory  apparatus  of,  1197 
fixation  of,  1193 
fossae  of,  1191 
gall-bladder,  1197 
hepatic  artery,  603,  1196 
cells,  1196 
duct,  1197 
veins,  680 
ligaments  of,  1192 
lobes  of,  1191,  1192 
lobules  of,  1195 
longitudinal  fissures  of,  1191 
lymphatic  capillaries  in,  685 
vessels  of,  711 
^    nerves  of,  1194 

portal  vein,  681,  1196 
structure  of,  1195 
surface  markings  of,  1320 
surfaces  of,  1188 
vessels  of,  1194 
Lobe  or  Lobes,  cacuminal,  790 
of  cerebellum,  788 
of  cerebral  hemisphere,  821 
frontal,  821 
insula,  825 
limbic,  825 
occipital,  823 
olfactory,  826 
parifetal,  822 
precuneus,  823 
quadrate,  823 
temporal,  823 
of  liver,  1191,1192 
of  lung,  1097 
nodular,  791 
Spigelian,  1192 
of  thymus,  1273 
of  thyroid  gland,  1269 
tuber al,  791 
uvular,  791 
Lobule  of  auricula,  1034 
biventral,  791 
inferior  semilunar,  791 
paracentral,  822 
parietal,  823 
postero-inferior,  790 
postero-superior,  791 
Lobules  of  liver,  1195 

of  testes,  1243 
Lobuli  glandiilce  thyreoidece,  1269 

hepatis,  1195 
Lobulus  centralis,  790 
parietalis  inferior,  823 

superior,  823 
semilunaris  inferior,  791 
superior,  790 
Lobus  caudatus,  1192 
clivi,  790 
culminis,  790 
frontalis,  821 
hepatis  dexter ,  1191 

sinister,  1192 
noduli,  791 
occipitalis,  823 
olfactorius,  826 
parietalis,  822 
pyramidis,  791 
quadratus,  1192 
semilunaris,  790 
temporalis,  823 
tuberus,  791 
uvulae,  791 
Localization,  cerebral,  849 


1372 


Lock  wood,  tendon  of,  1022 
Locus  cwruleus,  800 
Loewenthal's  tract,  872 
Long  bones,  79 
buccal  nerve,  895 
calcaneocuboid  ligament,  354 
ciliary  nerves,  888 
external  lateral  ligament,  341 
or  internal  saphenous  nerve, 956 
root  of  ciliary  ganglion,  888 
saphenous  nerve,  956 

vein,  669 
subscapular  nerve,  934 
thoracic  artery,  588 
nerve,  933 
Longissimus  capitis  muscle,  399 
cervicis  muscle,  399 
dorsi  muscle,  399 
Longitudinal  fasciculus,  inferior, 
844 
posterior,  803 
superior,  844 
fissure,  cerebral,  818 
great,  818 
of  liver,  1191 
sinuses,  654,  655 
stride,  lateral  and  medial,  827 
sulci  of  heart,  527 
Longitudinalis     linguse     inferior 
muscle,  1130 
superior  muscW,  1130 
Longua  capitis  muscle,  349 
actions  of,  396 
nerves  of,  395 
colli  muscle,  394 
action  of,  396 
nerves  of,  396 
Loop  of  Henle,  1223 
Lower  extremity,  arteries  of,  623 
articulations  of,  333 
bones  of,  231         * 
lymphatic  glands  of,  701 

vessels  of,  701 
muscles  of,  465 
surf  ace  anatomy  of ,  1336 

markings  of,  1342 
veins  of,  669 
jaw,  bones  of,  172 
lateral  cartilage,  993 
visual  centers,  814 
Lower,  tubercle  of,  531 
Lumbar  aponeurosis,  397 
arteries,  612 

enlargement  of  medulla  spina- 
lis, 752 
fascia,  397 
lymph  glands,  705 
nerves,  anterior,  948 

posterior,  924 
plexus  of  nerves,  949 
regions  of  abdomen,  1149 
triangle,  434 
vein,  ascending,  667,  678 
veins,  678 
"vertebrae,  104 
Lumbocostal  arch,  404 
Lumbodorsal  fascia,  397 
Lumbosacral  plexus,  948 

trunk,  948 
Lumbricales  muscles  of  foot,  493 
actions  of,  496 
nerves  of,  495 
variations  of,  493 
of  hand, 464 
actions  of,  465 
nerves  of,  465 
variations  of,  464 
Lunate  bone,  224 

surface  of  acetabulum,  237 
Lung-buds,  1071 
Lungs,  1093 

development  of,  1071 
fissures  and  lobes  of,  1090 
nerves  of,  1100 
root  of,  .1 097 


INDEX 


Lungs,  structure  of,  1098 
surface  markings  of,  1310 
vessels  of,  1100 
Lunulas  of  nails,  1066 

of  semilunar  valves,  533 
Luschka,  foramina  of,  877 

gland  of,  1281 
Luys,  nucleus  of,  812 
Lymph  Gland  or  Glands  of  abdo- 
men, 703 

aortic,  705 

auricular,  693 

axillary,  699 

buccinator,  694 

cervical,  697 

of  Cloquet,  703 

deltoideopectoral,  699 

diaphragmatic,  715 

epigastric,  704 

of  face,  692 

facial,  694 

gastric,  706 

gastroepiploic,  right,  700 

of  head,  692 

hepatic,  706 

hypogastric,  704 

iliac,  703,  704 

ileocolic,  709 

infraorbital,  694 

inguinal,  702 

intercostal,  715 

internal  mammary,  715 

lingual,  694 

of  lower  extremity,  701 

lumbar,  705 

mastoid,  693 

maxillary,  694 

mediastinal,  717 

mesenteric,  709,  710 

mesocolic,  709 

of  neck,  697 

obturator,  704 

occipital,  692 

pancreaticoduodenal,  710 

pancreaticolienal,  706 

pararectal,  710 

para  tracheal,  697 

parietal,  703 

parotid,  693 

of  pelvis,  703 

popliteal,  701 

preauricular,  693 

retropharyngeal,  694 

of  Roscnmiiller,  703 

sacral,  704 

splenic,  706 

Stahr,  middle  gland  of,  697 

sternal,  715 

structure  of,  688 

subinguinal,  702 

submaxillary,  697 

submental,  697 

suprahyoid,  697 

supramandibular,  694 

supratrochlear,  699 

of  thorax,  715 

tibial,  anterior,  701 

of  tongue,  696 

tracheobronchial,  717 

of  upper  extremity,  699 

visceral,  of     abdomen     and 
pelvis,  706 
path,  688 
sinus,  689 
Lymphatic  capillaries,  684 

distribution  of,  684 
duct,  right,  691 
nodules,  aggregated,  1176 

solitary,  1176 

of  spleen,  1285 
system,  683 

trunks,      bronchomediastinal, 
691,  692,  717 

intestinal,  691 

jugular,  691.  692 


II 


Lymphatic  trunks,  lumbar,  691 

subclavian,  691,  692 
vessels,  687 

of  abdominal  viscera,  710 
wall,  706 

of  anal  canal  and  aijus,  711 

of     auricula     and     externat 
acoustic  meatus,  694 

of  bladder,  712 

of  cecum,  710 

of  colon,  711 

of  common  bile-duct,  711 

development  of,  768 

of  diaphragm,  717 

of  ductus  deferens,  713 

of  duodenum,  710 

of  esophagus,  719 

of  external  genitals,  706 

of  face,  695 

of  gall-bladder,  711 

of  gluteal  region,  703 

of  heart,  718 

of  ileum,  710 

of  jejunum,  710 

of  kidney, 712 

lacteals,  683 

of  larynx,  698 

of  liver,  711 

of  lower  extremity,  703 

of  lungs,  718 

of  mamma,  715 

of  mouth,  695 

of  nasal  cavities,  695 

of  neck,  698 

of  ovary,  714 

of  palatine  tonsil,  695 

of  pancreas,  711 

of  pelvic  viscera,  710 

of  pelvis,  706 

of  perineum,  706 

of  pharynx,  698 

of  pleura,  719 

of  prostate,  713 

of  rectum,  711 

of  reproductive  organs,  7  IS 

of  scalp,  694 

of  spleen,  711 

of  stomach,  710 

structure  of,  687 

of  suprarenal  glands,  711 

of  testes,  713 

of  thoracic  viscera,  718 
wall,  715 

of  thymus,  719 

of  thyroid  gland,  698 

of  tongue,  696 

of  upper  extremity,  700 

of  ureter,  712 

of  urethra,  713 

of  urinary  organs,  712 

of  uterine  tube,  714 

of  uterus,  714 

of  vagina,  714 

of  vermiform  process,  710- 

of  vesicuhr  seminales,  713- 
Lymphocyte,  504 
LymphoglanduUv ,  688 
auriculares,  693 
axillares,  699 
cervicales,  697 
epigastriac,  704 
faciales  profunda,  694 
gastricw,  706 
hepaticcp,  706 
hypogasiricce,  704 
inguinale fi,  702 
inter costales,  715 
linguales,  694 
lumbales,  705 
mediastinales,  717 
tnesentericce,  709 
mesocolicd!,  709 
occipilales,  692 
pancreaticolicnales,  706 
popliteoe,  701 


I 


I 


INDEX 


1373 


Lymphoulandula',  sternales,  715 

subinguinales ,  702 

submaxiilares,  697 

tibialis  anterior,  701 
Lyra  of  fornix,  838.  869 


Mace' 


M 


ACEWEN,  suDramcatal  triangle 

of.  140 
Mdckenrodt,  ligament,  of,  1261 
Macula  acuslica  sacculi,  1052 
utriculi,  1051 

cribrosa  media,  1047 
superior,  1048 

li4ea,  1015,  1017 
structure  of,  1017 
Majendie,  foramen  of,  798,  877 
Malar  bone,  164 

process  of  maxilla,  161 
Male  genital  organs,  1236 

bulbourethral  glands, 1213, 

1253 
ductus  deferens,  1245 
ejaculatory  duct,  1247 
penis,  1247 
prostate,  1251 
testes  and  their  coverings, 

1236 
vesiculcE  seminales,  1246 

pronucleus,  45 

urethra,  1234 
Malleolar  arteries,  635 

folds,  1039 

sulcus,  260 
Malleolus,  lateral,  260 

medial,  259 
Malleus,  1044 

development  of,  1033 

ligaments  of,  1045 
Malpighian  bodies,  kidney,  1221 
of  spleen,  1285 

capsules  of  kidney,  1221 
Mamma;,  1267 

development  of,  1267 

lymphatic  vessels  of,  715 

nerves  of,  1268 

papilla  or  nipple  of,  1267 

structure  of,  1267 

vessels  of,  1268 
Mammary  arteries,  583,  588 

gland,  1267 
internal,  715 

veins,  internal,  666 
Mammillary  process,  106 
Mammillo-thalamic    fasciculus, 

869 
Mandible,  172 

angle  of.  174 

articulations  of,  175 

body  ( f,  172 

changes  in,  due  to  age,  175 

condyloid  process  of,  174 

coronoid  process  of,  174 

ossification  of,  174 

ramus  of,  173 
Mandibula,  172 
Mandibular  arch,  66 

branches  of  facial  nerve,  905 

canal,  173 

foramen,  173 

fossa,  140,  ISO,  183 

nerve,  893 

notch,  174 
Mantle  layer,  733 
Manubrium  of  malleus,  1044 

of  sternum,  119 
Margin,  supraorbital,  135 
Marginal  gyrus,  822 

layer,  733 

veins  of  foot,  669 
Margins  of  heart,  529 
Marrow  of  bone,  87 


Marshall,   oblique  vein  of,   522, 
526,  643 
vestigial  fold  of,  522,  526,  643 
Martinotti,  cells  of,  845, 
Massa  intermedia,  809,  816 
Masses,  lateral,  of  atlas,  99 
Masseter  muscle,  385 
action  of,  387 
nerves  of,  387 
Masseteric  artery,  561 
fascia,  385 
nerve,  894 
Mastoid  canaliculus,  144,  181 
cells,  142 
foramen,  141,  183 
fossa,  140 
glands,  693 
notch,  141,  181 
portion  of  temporal  bone,  141 
process,  141 
Mastzellcn,  377 
Matrix  of  nail,  1066 
Maturation  of  ovum,  40 
Maxilla,  157 

articulations  of,  163 
changes  in,  due  to  age,  163 
ossification  of,  163 
Maxillary  artery,  external,  553 
peculiarities  of,  556 
internal,  559 
glands,  internal,  694 
nerve,  889 

inferior.  893 
process  of  inferior  nasal  concha, 
169 
of  palatine  bone,  168 
of  zygomatic  bone,  166 
processes  of  fetus,  66 
sinus,  159,  999 
tuberosity,  159 
vein,  internal,  646 
Meatus  acusticus  exlemus,  1036 
cartilagineus ,  1036 
osseus,  1036 
auditory,  external,  1036 
external  acoustic,  145, 183, 1036 
internal,  146,  193 
urinarius,  1235 
urinary,  1266 
Meatuses  of  nose,  195,  994,  995 
Mechanics  of  muscle,  362 
Mechanism  of  pelvis,  311 
of  respiration,  407 
of  thorax,  304 
Meckel's  cartilages,  66.  174 
diverticulum,  54,  1172 
ganglion,  891 
Media,  refracting,  of  bulb  of  eye, 

1018 
Medial  geniculate  body,  811 
lemniscus,  804 
longitudinal  fasciculus,  803 
wall  of  nasal  cavity,  995 
Median  antibrachial  vein,  662 
basilic  vein,  661 
nerve,  938 
Mediastinal  arteries  from  aorta, 
600 
from  internal  mammary,  583 
lymph  glands,  717 
pleura,  1088 
Mediastinum,  1090 

testis,  1243 
Medicornu,  831 
Medidural  artery,  560 
Medifrontal  gvre,  822 
Medulla  of  hair,  1069 
oblongata,  767 

anterior  district  of,  768 
arcuate  fibers  of,  782 
development  of,  739 
fasciculus  cuneatus,  776 

gracilis,  776 
fissures  and  sulci  of,  767,  768 
gray  substance  of,  779 


Medulla  oblongata,  formatio  reti- 
cularis, 784 

lateral  district  of,  769 

olive  of,  769 

posterior  district  of,  774 

pyramid  of,  768 

restiform  bodies  of,  782 

structure  of,  775 
spinalis,  749 

central  canal  of,  754 

columns  of,  753 

development  of,  749 

distribution  of  nerve  cells  in, 
755 
"  enlargements  of,  751 

fissures  of,  752 

gray  commissures  of,  754 
substance  of,  753 

ligamentum  denticulaturn,  877 

meninges  of,  872' 

neuroglia  of,  753 

sulci  of,  752 

veins  of,  669 

white  commissure  of,  752 
substance  of,  758 
Medullary  artery  of  bone,  88 
lamina,  810 
laminae   of   lentiform   nucleus, 

834 
membrane  of  bone,  87 
portion    of    suprarenal    gland, 

1280 
segments  of  nerves,  727 
sheath  of  nerve-fibers,  725,  726 
spaces  of  bone,  94^ 
substance  of  kidney,  1221 
velum,  793,  797 
Medullated  nerve-fibers,  724 
Meibomian  glands,  1026 
Meissner's  plexus,  1177 

tactile  corpuscles,  1061 
Membrana  atlantooccipitalis.  An- 
terior, 295 

posterior,  296 
granulosa  [of  Graafian  follicle], 

1256 
hyothyreoidea,  1076 
interossea  antebrachii,  325 

cruris,  348 
pupillaris,  1014 
tectoria  [of  atlas  and  occipital 

bone],  296 
Membrane,  anal,  1110 
arachnoid,  876 
atlantooccipital,  295,  296 
basilar,  1054,  1056 
of  Bowman,  1008 
costocoracoid,  437 
cricothyroid,  1078 
of  Demours,  1008 
of  Descemet,  1008 
elastic,  of  larynx,  1077 
fenestrated,  498 
hyaloid,  1018 
hyoglossal,  1132 
hyothyroid,  1076 
intercostal,  403 
interosseous,  of  forearm,  325 

of  leg,  348 
Jacob's,  1017 
of  Krausc,  375 
limiting,  1017 
medullary,  of  bone,  87 
of  Nasmyth,  1123 
nuclear,  36 
obturator,  476 
pharyngeal,  1101 
pupillary,  1003,  1014 
of  Reissner,  1054 
tectorial,  of  ductus  cochlearis, 

1058 
thyrohyoid,  1076 
tympanic,  1039 
vestibular,  1054 
vitelline,  45 


1374 


Membranes  of  brain  and  medulla 
spinalis,  872 
fetal,  54 
synovial,  279 

Membranous  cochlea,  1054 
cranium,  84 
labyrinth,  1015 
portion  of  urethra,  1235 
semicircular  canals,  1052 
vertebral  column,  81 

Meningeal  artery,  accessory,  5G1 
anterior,  568 
from  ascending  pharyngeal, 

558 
middle,  560 

surface  marking  of,  1294 
from  occipital,  557 
from  vertebral,  579 
branch  of  spinal  nerve,  921 
layer  of  cKira  mater,  875 
nerve  from  hypoglossal,  918 
from  maxillary,  889 

Meninges  of  brain  and  medulla 
spinalis,  872 

Menisci,  281 

of  knee-joint,  342 

Meniscus,  articular,  298 

Mental  foramen,  172,  188 
nerve,  897 
point,  198 
protuberance,  172 
spines,  172 
tubercle,  172 

Mentalis  muscle,  383 

Mentohyoideus  muscle,  392 

Merkel,  tactile  disks  of,  1059 

Meroblastic  ova,  45 

Mesencephalon,  51,  741,  800 

Mesenteric  arteries,  606,  609 
lymph  glands,  709 
plexuses  of  nerves,  987 
veins,  681,  682 

Mesenteries,  1157 

mesentery  proper,  1157 
sigmoid  mesocolon,  1153,  1157 
transverse  mesocolon,  1157 

Mesenteriole  of  vermiform  pro- 
cess, 1178 

Mesenterium,  1157 

Mesocardium,  arterial,  526 
venous,  526 

Mesocolic  lymph  glands,  709 

Mesocolon,  sigmoid,  1153,  1157 
transverse,  1157 

Mesoderm,  49 
formation  of,  47 

Mesogastrium,  1103 

Mesognathion,  199 

Mesonephros,  1205 

Mesorchium,  1207 

Mesosalpinx,  1261 

Mesovarium,  1207,  1255 

Metacarpal  bones,  227 
articulations  of,  230 
characteristics  of,  228 
ossification  of,  230 

Metacarpophalangeal    articula- 
tions, 332 

Metacarpus,  227 

Metanephros,  1205 

Metaphase  of  karyokinesis,  37 

Metatarsal  arteries,  637 
bones,  272 

characteristics  of,  272 
veins,  672 

Metatarsophalangeal      articula- 
tions, 359 

Metatarsus,  272 
ossification  of,  275 

Metathalamus,  743,  811 

Metencephalon,  738 

Metopic  suture,  135 

Meynert,  basal  optic  nucleus  of, 
813 
fasciculus  retroflexus  of,  812 


INDEX 


eynert,    fountain     decussation 

of,  806 
substantia  innominata  of,  837 
Microcytes,  503 
Mid-brain,  54,  741,  800 
Mid-carpal  joint,  329 
Middle  capsular  artery,  610 
cerebellar  peduncles,  793 
commissure  of  brain,  809 
constrictor  muscle,  1143 
costotransverse  ligament,  302 
cutaneous  nerve,  955 
dental  nerve,  891 
subscapular  nerve,  934 
thyrohyoid  ligament,  1077 
tibiofibular  ligament,  348 
Milk  teeth,  1118 
Mitochondria  sheath,  43 
Mitral  cells,  848,  997 
orifice,  534 
valve,  534 
Moderator  band,  532 
Modiolus  of  cochlea,  1050 
Molar  glands,  1112 

teeth,  1118 
Molecular    layer    of    cortex    of 
cerebellum,  794 
of  cerebrum,  845 
Monakow,  rubrospinal  fasciculus 

of,  761 
Monaster  or  mother  star,  37 
Monro,  foramen  of,  816,  840 

sulcus  of,  741,  816 
Mons  pubis,  1265 

Veneris,  1265 
Morgagni,  hydatid  of,  1207, 1242, 
1257 
rectal  columns  of,  1184 
sinus  of,  1143 
Morula,  46 
Moss  fibers,  796 
Mother  star  or  monaster,  37 
Motor  areas  of  cerebral  cortex, 
847 
end-plates,  730 
nerves,  730 

neurons,  lower  and  upper,  870 
tract,  870 
Mott,    spino-quadrigeminal    sys- 
tem of,  762 
Mouth,  1110 

development  of,  1101 
lymphatics  of,  695 
mucous  membrane  of,  1110 
muscles  of,  382 
variations  of,  385 
Movable  articulations,  285 
Movements  admitted  in  joints, 

286 
Mucous  glands  of  tongue,  1131 
sheaths,  283 

of  tendons  around  ankle,  489 
on  back  of  wrist,  459 
on  front  of  wrist,  457 
Miiller,     orbitalis     muscle     of, 
1024 
sustentacular  fibers  of,  1017 
Mlillerian  duct,  1206 

eminence,  1207 
Multangular  bones,  225 
Multicuspid  teeth,  1118 
Multifidus  muscle,  400 
action  of,  402 
nerves  of,  402 
spinse  muscle,  400 
Muscle  or  Muscles  of  abdomen, 
408 
abductor  hallucis,  491 
digili  quinti  (foot),  492 

(hand),  463 
indicis,  464 
minimi  digiti,  463 
poinds,  461 
brevis,  461 
longus,  455 


Muscle   or    Muscles,    accelerator 

urinaj,  428 
accessorius,  399 

of  foot,  493 
action  of,  on  joints,  36S 
adductor  brevis,  473 

hallucis,  493 

longus,  472 

Tnagnus,  473 

minimus.  474 

obliquus  hallucis,  493 
pollicis,  462 

poinds  obliquus,  462 
transversus,  462 
of  anal  region,  424 
anconceus,  454 
anterior  crural,  480 

femoral,  467 

vertebral,  394 
anterolateral,  of  abdomen,  408 
antitragicus,  1035 
of  arm,  442 

development  of,  371 
arrectores  pilorum,  1069 
articularis  genu  or  subcrureus. 

All 
aryepiglotticus,  1083 
arytanoideus,  1082 
attollens  aurem,  1035 
attrahens  aurem,  1035 
of  auricula  or  pinna,  1035 
auricularis,  1035 
axillary  arch,  434 
azygos  uvulve ,  1139 
of  back,  396 
biceps,  433 

brachii,  433 

femoris,  478 

flexor  cubiti,  443 
biventer  cervicis,  400 
Bowman's,  1011 
brachialis,  444 

anticus,  444 
brachioradialis,  451 
buccinator,  384 
bulbocavernosus,  428,  430 
caninus,  383 
cardiac,  536 
cervical,  387,  388 
cervicalis  ascendens,  399 
chondro-epitrochlearis,  437 
chondroglossus,  1130 
dliaris,  1010 
cleidohyoideus,  393 
coccygeus,  424 
columns,  374 
complexus,  400 
compressor  naris,  382 

urethra,  429,  431 
constrictors  of  pharvnx,  1142 

urethrse,  429.  431 
coracobrachialis,  443 
corrugator,  381 

cutis  ani,  425 

supercilii,  381 
costocoroideus,  437 
cremaster,  414 
cricoarytaeiioideus ,  1082 
cricoarytenoid,  1082 
cricothyreoideus,  1081 
cricothyroid,  1081 
crureus,  471 
deltoid,  439 
deltoideus,  439 
depressor  alse  nasi,  382 

anguli  oris,  383 

labii  inferioris,  383 

septi,  382 
detrusor  urina:,  1233 
development  of,  371 
diaphragm,  404. 
digastric,  391 
digastricus,  391 
dilatator  naris,  382 
pupillcc,  1013 


I 


INDEX 


1375 


iSscle  or  Muscles,  dilalator  tuba, 

1044 
dorsal  antibrachial,  451 
dorsoepitrochlearis  brachii,  434 
ejaculator  urinw,  428 
epicranius,  378 
epitrochleo-arifonseus,  448 
erector  cliforidis,  430 

penis,  428 

spinae,  397 

I  extensor    carpi    radialis    acces- 
sorius,  452 
brevior,  452 
hrevis,  452 
intermedius,  452 
longior,  452 
longus,  452 
ulnaris,  454 
coccygis,  401 

digiti  quinti  propritis,  454 
digitorum  brevis,  490 

I  communis,  452 

longus,  481 
hallucis  longus,  481 
indicis,  456 
proprius,  456 
minimi  digiti,  454 
ossis  metacarpi  hallucis,  481 

pollicis,  455 
poinds  brevis,  455 

longus,  455 
primi  internodii  pollicis,  455 
proprius  hallucis,  481 
secundi  internodii  pollicis, 455 
external  sphincter  ani,  425 
of  eyelids,  380 
fasciculi  of,  373 
fibers  of,  373 
fixation,  362 
flexor  accessorius,  493 

longus  digitorum,  485 
brevis  minimi  digiti,  464,  494 
carpi  radialis,  446 

ulnaris,  447 
digiti  quinti  brevis  [foot],  494 

[of  hand),  464 
digitorum  brevis,  491 
longus,  485 
profundus,  448 
sublimis,  448 
hallucis  brevis,  493 

longus,  485 
pollicis  brevis,  461 
longus,  449 
of  foot,  490 
of  forearm,  445 
form  of,  361 
frontalis,  379 
gastrocnemius,  482 
gemellus,  477 
genioglossus,  1129 
geniohjoglossus,  1129 
geniohyoid,  393 
geniohyoideus,  393 
glossopalatinus,  1129,  1139  noie 
glutcEus  maximus,  474 
medius,  474 
minimus,  475 
of  gluteal  region,  474 
gracilis,  471 
hamstring,  478 
of  hand, 456 
of  head,  378 

development  of,  372 
helicis  major,  1035 

minor,  1035 
hyoglossus,  1129 
of  iliac  region,  466 
iliacus,  467 

minor,  467 
iliocapsularis,  467 
iliococcygeus,  424 
iliocostalis,  399 
cervicis,  399 
dor  si,  399 


luscle    or    Muscles,     iliocostalis 

lumborum,  399 
iliosacralis,  424 
incisivus  labii,  385 
infracostal,  403 
infrahyoid,  391 
infraspinatus,  441 
insertion  of,  362 
intercostal,  402,  403 
inter  CO  stales,  402,  403 
intermediate  volar,  465 
internal  sphincter  ani,  426 
interossei,  dorsal,  495 

of  foot,  495 

of  hand, 464 

plantar,  495 
inter spinales,  400 
intertransversales,  401 
intertransversarii,  401 
ischiocavemosus,  428,  430 
of  larynx,  1081 
lateral  cervical,  388 

crural,  486 

vertebral,  396 

volar,  461 
latissimus  dorsi,  432 
of  leg,  480 

development  of,  372 
levator  anguli  oris,  383 
scapulae,  435 

ani,  422 

cla\'icul£e,  435 

glandula-  thyreoideo',  1270 

menti,  383 

palati,  1139 

palpebrcB  superioris,  1021 

prostaloe,  424 

scapulas,  435 

veli  palatini,  1139 
levator es  costarum,  403 
lingualis,  1130 
longissimus  capitis,  399 

cervicis,  399 

dorsi,  399 
longitudinalis  Ungues,  1130 
longus  capitis,  395 

coiZi,  394 
of  lower  extremity,  465 
lumbricales  [of  foot],  493 

[of  hand],  464 
lymphatics  of,  376 
masseter,  385 
of  mastication,  385 
mechanics  of,  362 
medial  femoral,  471 

roZar,  462 
mentalis,  383 
mentohyoideus,  392 
of  mouth,  382 
multifidus,  400 

spinte,  400 
mylohyoid,  393 
mylohyoideus,  393 
nasalis,  382 
nasolabialis,  385 
nerves       and       vessels        of, 

376 
of  nose,  382 
oblique,  409,  412 

inferior,  1023 

superior,  1022 
obliquus  auricula,  1035 

capitis,  402 

externus  abdominis,  410 

inferior,  402 

internus  abdominis,  412 

oculi,  1022,  1023 

superior,  402 
obturator  externus,  477 

internus,  477 
occipitalis,  379 
occipitofrontalis,  378 
ocular,  1021 
omohyoid,  394 
omohyoideus,  394 


Muscle  or  Muscles,  opponens  digiti 
quinti  [of  foot],  494 
[of  hand],  464 

minimi  digiti,  464 

pollicis,  461 
orbicularis  oculi,  380 

oris,  384 

palpebrarum,  380 
orbitalis  of  H.  Midler,  1024 
origin  of,  362 
of  palate,  1139 
palatoglossus,  1129,  1139  note 
palatopharyngeus,  1139 
palmaris  brevis,  463 

longus,  446 
pectineus,  472 
pectoralis  major,  436 

minimus,  438 

minor,  438 
of  pelvis,  420 
perineal,  superficial  transverse, 

427,  430 
of  perineum,  424 
peronseus  accessorius,  487 

brevis,  487 

longus,  486 

quart  us,  487 

quinti  digiti,  487 

tertius,  482 
peroneo calcaneus    externum, 
4§7 

internus,  485 
peroneocuboideus,  487 
peroneotibialis,  485 
pharyngopalatinus,  1 139 
of  pharynx,  1142 
of  pinna  or  auricula,  1035 
piriformis,  47 Q 
pisiannularis,  464 
pisimetacarpus,  464 
pisiuncinatus,  464 
plantar,  first  layer,  491 

fourth  layer,  495 

second  layer,  493 

third  layer,  493 
plantaris,  483 
plate,  80 
platysma,  388 
popliteus,  484 

minor,  485 
posterior  crural,  482 

femoral,  478 
procerus,  382 
pronator  quadratus,  449 

teres,  446 
psoas  magnus,  467 

major,  467 

minor,  467 

parvus,  467 
pterygoid,  386 
pterygoideus  externus,  388 

internus,  387 
pubococcygeus,  424 
puborectalis,  424 
pubovesicales,  1231 
pull,  action  of,  on  tendon,  364 

direction  of,  363 
pyramidalis  abdominis,  416 

nasi,  382 
quadratus  femoris,  477 

labii,  383 

lumborum,  420 

menti,  383 

planta-,  493 
quadriceps  extensor,  470 

femoris,  470 
recti  [of  eyeball],  1022 
rectococcygeal,  1186 
rectovesicales,  1231 
rectus  abdominis,  415 

capitis  anterior,  395 
lateralis,  395 
posterior,  401 
anticus,  395 
posticus,  401 


1376 


INDEX 


MuspIo  or  Muscles,  rectus  femoris, 

470 
retrahens  aurem,  1035 
rhomhoideus  major,  434 

minor,  434 

occipitalis,  435 
risorius,  385 
rotatores,  400 

spina*,  400 
sacrospinalis,  397 
salpingopharyngeus,  1143 
sarcous  elements  of,  375 
sarlorius,  470 
scalenus  anterior,  396 

anticus,  396 

fnedius,  396 

pleuralis,  396 

posterior,  396 

posticus,  396 
of  scalp,  378 
semimembranosus,  479 
semispinalis  capitis,  400 

cervicis,  400 

colli,  400 

dorsi,  400 
semitendinosus,  479 
sense,  impulses  of,  851 
serratus  anterior,  438 

magnus,  529 

posterior,  404 

posticus,  404 
soleus,  493 
sheaths,    lymphatic    capillaries 

in,  684 
of  shoulder-girdle,  development 

of,  371 
sphincter  ani,  425 
exlernus,  425 
internus,  426 

pupillo',  1013 

recti,  424 

urethral  membranacea;, 4:29, 'iSl 

vagina,  430 

vesicae,  1233 
spinalis  capitis,  400 

cervicis,  400 

colli,  400 

dorsi,  399 
splenius  capitis,  397 

cervicis,  397 

colli,  397 
stapedius,  1046 
sternalis,  437 
stern6cla\'icularis,  438 
sternocleidomastoid&us,  390 
sternohyoid,  393 
sternohyoideus,  393 
sternomastoid,  390 
sternothyreoideus ,  393 
sternothyroid,  393 
strength  of,  364 
striped,  373 
styloglossus,  1130 
stylohyoid,  392 
stylohyoideus,  392 
stylopharyngeus ,  1143 
subanconwus,  445 
subclavius,  438 
subcostales,  403 
subcrureus,  All 
suboccipital,  401 
subscapularis ,  440 
superficial  cervical,  387 
supinator ,  454 

brevis,  454 

longus,  451 
suprahyoid,  391 
supraclavicularis,  390 
supracostalis,  403 
supraspinatus,  440 
suspensory,  of  duodenum,  1170 
synergic,  362 
temporal,  386 
temporalis,  386 
tendons  of,  376 


Muscle  or  Muscles,  tensor  palati, 
1139 

tarsi,  380 

tympani,  1046 

t)eh'  palatini,  1139 
<eres  m,ajor,  442 

minor,  441 
of  thigh,  467 
of  thorax,  402 
tibiofacialis  anterior,  480 
thyi-eoarytfenoideus,  1083 
thyreoepiglotticus,  1083 
thyrohyoidcus,  394 
thyroarytenoid,  1083 
thyrohyoid,  394 
tibialis  anterior,  480 

anticus,  480 

posterior,  485 
of  tongue,  1128 
trachealis,  1087 
trachelomastoid,  399 
tragicusj  1035 
transversalis,  414 

cervicis,  399 
transversus  abdominis,  414 

auriculw,  1035 

linguw,  1130 

menti,  383 

nuchcB,  380 

pedis,  493 

perinsei,  427,  429 
profundus,  429,  431 

superficialis  [in  female], '430 
I  [in  male],  427 

thoracis,  403 
trapezius,  432 
,    triangularis,  383 

sterni,  403 
triceps,  444 

brackii,  444 

extensor  cubiti,  444 

swro',  483 
of  trunk,  396 
of  tympanic  cavity,  1046 
of  upper  extremity,  432 
of  ureters,  1232 
urogenital  region  [female],  430 

[male],  426 
of  uvula,  1139 
vastus  externus,  470 

intermedius,  471 

internus,  471 

lateralis,  470 

medialis,  471 
ventricularis,  1083 
ventrolateral,  of  neck,  develop- 
ment of,  371 
vertebral,  394,  396 
verticalis  linguce,  1131 
vocalis,  1083 
volar  antibrachial,  445 
voluntary,  373 
work  accomplished  by,  305 
zygomaticus,  383 

ma,jor,  383 
Muscular  fibers  of  heart,  535 
process  of  arytenoid  cartilage, 

1075 
triangle,  394,  563 
Muscularis  mucosce,  1173 
Musculi  oculi,  1021 

ossiculorum  auditus,  1046 
papillares  [of  left  ventricle],  534 

[of  right  ventricle],  532 
pectinati  [of  left  auricle],  534 

[of  right  auricle],  529 
pubovesicales,  1232 
Musculocutaneous  nerve  of  arm, 
935 

of  leg,  966 
Musculophrenic  artery,  583 
Musculospiral  groove,  211 

nerve,  943 
Myelencephalon,  738 
Myelocytes,  88 


Myeloplaxes,  88 
Mylohyoid  artery,  561 
groove,  173 
line,  173 
muscle,  393 
nerve,  896 
Mylohyoideus  muscle,  393 
action  of,  393 
nerves  of,  393 
variations  of,  393 
Myocardium,  535 
Myocel,  52 
Myology,  361 


N 


Nails,  1066 
Nares,  992,  994 
Nasal  aperture,  anterior,  196 
artery,  571 

lateral,  556 
bones,  156 

articulations  of,  157 
ossification  of,  157 
cartilages,  992.  993 
cavities,  194,  994 
arteries  of,  996 
lymphatic  capillaries  in,  686 

vessels  of,  695 
mucous  membrane  of,  996 
nerves  of,  996,  997 
veins  of,  997 
vestibule  of,  994 
concha,  inferior,  169 
middle,  156 
superior,  156 
crest,  163,  167 
duct,  1029 
fossa,  994 
index,  198 
laminee,  68 

mucous  membrane,  996 
nerve  from  ophthalmic,  888 
nerves  from  nasopalatine  gan- 
glion, 893 
notch  of  frontal  bone,  136 

of  maxilla,  158 
part  of  frontal  bone,  136 

of  pharynx,  1141 
process  of  frontal  bone,  136 

of  maxilla,  161 
processes  of  fetus,  67 
septum,  194,  995 
spine,  anterior,  158,  163 
of  frontal  bone.  136 
posterior,  167,  180^ 
Nasalis  muscle,  382 
action  of,  382 
nerves  of,  382 
Nasion,  136,  186,  198 
Nasmyth's  membrane,  1123 
Nasociliary  nerve,  888 
Nasofrontal  vein,  659 
Nasolabialis  muscle,  385 
Nasolacrimal  duct,  1029 
Nasooptic  furrow,  69,  1005 
Nasopalatine  nerve,  893 

recess,  996 
Nasopharynx,  1141 
Nasus  exlernus,  992 
Navicular  bone  of  carpus,  221 
of  tarsus,  270 
fossa,  1266 
Neck,  lymphatic  glands  of,  697 
vessels  of,  698 
muscles  of,  387 

development  of,  371 
triangles  of,  562 
veins  of,  646 
N6laton's  line,  1342 
Neopallium,  744 
Nerve  cells,  721 

of  cerebellar  cortex,  794 
of  cerebral  cortex,  845 


INDEX 


1377 


■  cells  of  medulla  spinalis, 

755, 757 
endings,  free,  1059 
fasciculi  of  medulla  spinalis, 759 
fibers  of  cerebral  cortex,  846 

medullated,  724 

non-medullated,  728 
roots,  916,  948 
Nerve  or  Nerves,  abducent,  899 
accessory,  913 
acoustic,  905,  1058 
alveolar,  S90,  891 

inferior,  895 
anococcygeal,  968 
anterior  crural,  953 

interosseous,  938 

superior  alveolar,  891 

thoracic,  933 

tibial,  965 
antibrachial     cutaneous,     936, 

937 
Arnold's,  911 
auditory,  905 

auricular  of  auriculotemporal, 
895 

great,  926 

posterior,  905 

of  vagus,  911 
auriculotemporal,  895 
axillary,  934 

brachial  cutaneous,  lateral,  934 
medial,  937 
posterior,  943 
bronchial,  913 
buccal,  of  facial,  905 

long,  895 
buccinator,  895 
calcaneal,  medial,  963 
cardiac,  cervical,  912 

great,  979 
•  of  sympathetic,  979 

thoracic,  912 

of  vagus,  912 
caroticotympanic,  978,  1047 
carotid     of     glossopharyngeal, 

909 
cavernous,  of  penis,  989 
celiac,  of  vagus,  913 
cerebral,  881.     See  Cranial, 
cerebrospinal,  structure  of,  728 
cervical,  928 

cutaneous,  927 

divisions  of,  921,  925 

of  facial,  905 

transverse,  927 
chorda  tympani,  904,  1047 
ciliary,  888,  889 
circumflex,  934 
of  clitoris,  968 

coccygeal,  division  of,  925,  957 
cochlear,  906,  1059 
cranial,  881 

abducent,  899 

accessory,  913     ^ 

acoustic,  905 

central  tract  of,  804 

composition  and  central  con- 
nections of,  855 

facial,  901 

glossopharyngeal,  906 

hypoglossal,  914 

oculomotor,  884 

olfactory,  881 

optic,  882 

thalamic  tract  of,  805 

trigeminal,  886 

trochlear,  885 

vagus,  910 
crural,  anterior,  955 
cutaneous  cervical,  927 

external,  953 

internal,  937,  955 
lesser,  937 

middle,  955 
deep  branch  of  radial,  944 


Nerve  or  Nerves,  deep  branch  of 
ulnar,  943 

peroneal,  965 

petrosal,  892 

temporal,  894 
descending    ramus    of    hypo- 
glossal, 918 
development  of,  735,  747 
digastric,  from  facial,  905 
digital,  of  lateral  plantar,  963 

of  medial  plantar,  963 

of  median,  938 

of  radial,  944 

of  superficial  peroneal,  966 

of  ulnar,  943 
dorsal  antibrachial  cutaneous, 
944 

branch  of  ulnar,  942 

cutaneous,  963,  966 

digital,  965 

of  penis,  968 

scapular,  932 
of  dura  mater,  875 
dural,  911 
eighth,  905 
eleventh,  913 
end-organs  of,  1059 
endoneurium  of,  728 
epineurium  of,  728 
esophageal,  913 
external  nasal,  891 

plantar,  963 

popliteal,  964 

saphenous,  963 

spermatic,  953 
facial,  901 
femoral,  955 

cutaneous,  anterior,  955 
lateral,  953 
posterior,  959 
fifth,  886 
first,  881 
fourth,  885 
frontal,  887 
ganglia  of,  730 
gastric     branches     of     vagus, 

913 
genitocrural,  953 
genitofemoral,  953 
glossopharvngeal,  906 
gluteal,  959,  960 
great  auricular,  926 
greater  occipital,  923 

splanchnic,  981 

superficial  petrosal,  892 
hemorrhoidal,  inferior,  968 
hepatic  branches  of  vagus,  913 
hypoglossal,  914 
iliohypogastric,  950 
ilioinguinal,  952 
incisive,  897 
inferior  dental,  897 
infraorbital,  889  note 
infrapatellar,  956 
infratrochlear,  888 
intercostal,  945 
intercostobrachial,  946 
intermedins  of  Wrisberg,  901 
internal  calcaneal,  963 

cutaneous  of  arm,  937 

carotid,  977 

plantar,  963 

popliteal,  960 

saphenous,  956 
interosseous,  dorsal,  944 

volar,  938 
Jacobson's,  909,  1047 
jugular,  978 
labial  posterior,  968 

superior,  891 
lacrimal,  887 
of  Lancisi,  868 
laryngeal,  912 

larvngopharyngeal    of   sympa- 
thetic, 978 


Nerve  or  Nerves,  lateral  anti- 
brachial cutaneous,  935, 
936 

brachial  cutaneous,  934 

femoral  cutaneous,  953 

plantar,  963 

sural  cutaneous,  964 
lesser  splanchnic,  891 
lingual,  895 

of  glossopharyngeal,  909 
long  ciliary,  888 

saphenous,  956 

subscapular,  934 

thoracic,  933 
lowest  splanchnic,  981 
lumbar,  divisions  of,  924,  948 
lumboinguinal,  953 
lumbosacral  trunk,  948 
mandibular,  893 

of  facial,  905 
masseteric,  894 
maxillary,  889 

inferior,  893 
medial  antibrachial  cutaneous, 
937 

brachial  cutaneous,  937 

sural  cutaneous,  962 

plantar,  963 
median,  938 
meningeal,  of  hypoglossal,  918 

of  maxillary,  889 

middle,  889 

of  spinal,  916 

of  vagus,  911 
mental,  897 
motor,  730 
musculocutaneous,  of  arm,  935 

of  leg,  966 
musculospiral,  943 
mylohyoid,  896 
nasal,  of  ophthalmic,  888 

from     sphenopalatine     gan- 
glion, 893 
nasociliary,  888 
nasopalatine,  893 
ninth,  906 
obturator,  953 

accessory,  955 
occipital,  greater,  923 

smaller,  926 

third,  923 
oculomotor,  884 
olfactory,  881 
ophthalmic,  887 
optic,  882 
orbital,  893 
origins  of,  729 
palatine,  893 

palmar  cutaneous,  of  median, 
938 
of  ulnar,  942 
palpebral,  inferior,  891 
perforating  cutaneous,  967 
perineal,  968 
perineurium  of,  728 
plexus  of,  728 

annular,  1009 

aortic  abdominal,  987 

Auerbach's,  1177 

brachial,  930 

cardiac,  984 

carotid,  977 

cavernous,  978 

celiac,  985 

cervical,  925 

posterior,  921,  922,  923 

choroid,  of  fourth  ventricle, 
798 
of  lateral  ventricle,  840 
of  third  ventricle,  815 

coccygeal,  968 

of  cornea,  1009 

coronary,  985,  987 

esophageal,  910,  913 

of  Exner,  846 


1378 


iServe  or  Nerves,  plexus  of,  gas- 
tric, 913,  987 

hemorrhoidal,  987 

hepatic,  986 

hypogastric,  987 

infraorbital,  891 

lienal,  986 

lumbar,  948 

lumbosacral,  948 

Meissner's,  1177 

mesenteric,  987 

myenteric,  1177 

ovarian,  987 

parotid,  902 

patellar,  953,  956 

pelvic,  987 

pharyngeal,  909,  912,  979 

phrenic,  985 

prostatic,  988 

pudendal,  960 

pulmonary,  910,  913 

renal,  987 

sacral,  957 

solar,  985 

spermatic,  987 

splenic,  986 

of  submucosa,  1177 

subsartorial,  956 

suprarenal,  987 

tonsillar,  909 

tympanic,  1047 

uterine,  989 

vaginal,  989 

vesical,  988 
peroneal,  964,  965,  968 
petrosal,  deep,  892,  977 

external,  978 

greater  superficial,  892 
smaller  superficial,  1047 

large,  deep,  892 

superficial,  892,  903 
pharyngeal,    oi    glossopharyn- 
geal, 909 

of  sphenopalatine  ganglion, 
893 

of  vagus,  911 
phrenic,  928 
plantar,  963 
pneumogastric,  910 
popliteal,  960,  694 
of  pterygoid  canal,  892,  977 
to  pterygoideus  externus,  895 

internus,  894 
pterygopalatine,  893 
pudendal,  967 

inferior,  960 
pudic,  internal,  967 
pulmonary,  913 
radial,  943 
rami  communicantes,  gray  and 

white,  902,  976 
recurrent,  912 
reflexes,  trigeminal,  899 
respiratory,  of  Bell,  928,  933 
to  rhomboids,  932 
roots,  764,  918 
sacral,  957 
saphenous,  956,  963 
sciatic,  960 
scrotal,  posterior,  968 
second,  882 
seventh,  901 
short  ciliary,  889 
sixth,  899 

smaller  occipital,  926 
spermatic,  external,  953 
sphenopalatine     branches     of 

maxillary,  890 
spinal,  916 

accessory,  913 

composition  and  central  con- 
nections of,  849 

development  of,  735 

divisions  of,  921,  925 

roots  of,  764,  916 


INDEX 

Nerve  or  Nerves,  splanchnic,  981 
to  stapedius,  904 
stylohyoid,  905 
to  subclavius,  933 
subscapular,  933,  934 
superior  labial,  891 
superficial  branch  of  radial,  944 

of  ulnar,  942 
supra-acromial,  928 
supraclavicular,  928 
supraorbital,  888 
suprascapular,  932 
suprasternal,  928 
supratrochlear,  888 
sural,  963 

lateral  cutaneous,  964 
sympathetic,  968 

cranial,  970 

sacral,  973 

structure  of,  729 

thoracolumbar,  974 
of  taste,  992 
temporal,  deep,  895 

of  facial,  905 
temporomalar,  889 
tenth,  910 
terminations  of,  729 
third,  884 

thoracic,  divisions  of,  923,  933 
thoracodorsal,  934 
thyrohyoid,  918 
tibial,  960 

anterior,  965 
ot  tongue,  1132 
tonsillar,  909 
transverse  cervical,  927 
trifacial,  886 
trigeminal,  886 

central  tract  of,  805 
trochlear,  885 
twelfth,  914 
tympanic,  of  glossopharyngeal, 

909,  1047 
ulnar,  939 

collateral,  943 
ol  urethral  bulb,  968 
vagus,  910 
vestibular,  906,  1058 
Vidian,  892 
volar  digital,  938 

interosseous,  938 
of  Wrisberg,  937 
zygomatic,  889 

of  facial,  905 
zygomaticofacial,  890 
zygomaticotemporal,  890 
Nervi  anococcygei,  968 
auriculares  anteriores,  895 
carotid  exlerni,  979 
cavernosi  penis  minor es,  989 
cerebrates,  881 
cervicales,  921,  925 
ciliares  longi,  888 
clunium  inferiores,  960 
coccygeus,  925,  957 
communicantes  cervicales,  928 

hypoglossi,  928 
digitales  dorsales  hallucis,  965 

plantar  es  communes,  963 
proprii,  963 
ethmoidales,  888 
inter costales,  945 
lumbales,  924 

anteriores,  948 

posleriores,  924 
nervorum,  728 
olfactorii,  881 
palatini,  893 
sacrales,  924,  957,  968 
sphenopalatini,  890 
spinales,  916 

rami  anteriores,  925 
posleriores,  928 
subscapular  es,  933 
supraclaviculares,  928 


Nervi  temporales  profundi, 
thoracales,  923 

anteriores,  933,  944  

Nervous  system,  description  of, 
721 
development  of,  733 
Nervus  abducens,  899 
accessorius,  913 

ramus  externus,  913 
internus,  913 
acusticus,  1058 
alveolaris  inferior,  896 
auricularis  magnus,  926 

posterior,  905 
auriculotemporalis ,  895 
axillaris,  934 
buccinatorius,  905 
canalis  pterygoidei,  892 
cardiacus  inferior,  981 
medius,  979 

superior,  979  

caroticotympanicus  inferior,  909 

superior,  909 
cavernous  penis  major,  989 
cochlearis,  1059 
clunium  inferior  medialis,  967 

inferiores,  960 
communicans  fibularis,  964 

tibialis,  962 
cutaneus    antebrachii    dorsalis, 
944 
lateralis,  936 
medialis,  937 
brachii  medialis,  937 

posterior,  943 
colli,  927 
dorsalis  intermedius,  966 

medialis,  966 
femoralis  lateralis,  953 

posterior,  959 
surcB  lateralis,  964 
medialis,  962 
descendens  cervicales,  928 
dorsalis  clitoridis,  968 
penis,  968 
scapulce,  932 
facialis,  901 

rami  buccales,  905 
temporales,  905 
zygomatici,  905 
ramus  colli,  905 
digastricus.  905 
marginalis  mandibulcc,  905 
stylohyoideus,  905 
femoralis,  955 
frontalis,  887 
furcalis,  949 
genito femoralis,  953 
glossopharyngeus,  906 
ganglion  petrosum,  908 

superius,  908 

rami  linguales,  909 

pharyngei,  909 

tonsillcves,  909 

ramus  stylopharyngeus,  909 

glutaeus  inferior,  959 

superior,  959 
hwmorrhoidalis  inferior,  968 
hypoglossus,  914 

ramus  descendens,  916 
thyreohyoideus,  916 
iliohypogastricus,  950 
ilioinguinalis ,  952 
infralrochlearis,  888 
intermedius  [of  Wrisberg],  901 
interosse^is  dorsalis,  944 

volaris,  938 
ischiadicus,  960 
lacrimalis,  887 
laryngeus  superior,  912 
lingualis,  895 
lumboinguinalis ,  953 
mandibular  is,  893 
massetericus,  894 
maxillaris,  889 


INDEX 


1379 


I 


emis  maxillaris,  rami  alveolares 
superiores       posteriores, 
890 
labialis  superiores,  891 
nasales  externi,  891 
palpebrales  inferiores,  819 
ramus  alveolaris  superior  an- 
teriores,  891 
medius,  891 
meatus  auditorii  externi,  895 
medianus,  938 
meningeus  medius,  889 
musculocutaneus,  935 
mylohyoideus,  896 
nasociliaris,  888 
obturatorius,  953 

accessorius,  955 
occipitalis  major,  923 

minor,  926 
oculojnotorius,  884 
ophthalmicus,  887 
opticus,  882 
palatinus,  893 
perinei,  968 
peronceus  coynmunis,  964 

profundus,  965 
petrosus  profundus,  892 

superficialis  major,  892 
phrenicus,  928 
plantaris  lateralis,  963 

medialis,  963 
pterygoideus  extemus,  895 

internus,  894 
pudendus,  967 
radialis,  943 
recurrens,  912 
saphenus,  956 
spermaticus  extemus,  953 
spinosus,  894 
splanchnicus,  981 
stapedius,  904 
subclavius,  933 
subscapularis,  932 
supraorbitalis ,  888 
supratrochlearis,  888 
suralis,  963 
thoracalis  longus,  933 
thoracodorsalis,  934 
tibialis,  960,  962,  963 
trigeminus,  886 
trochlearis,  885 
tympanicus,  909 
ulnaris,  938 

rami  muscular es,  942 
ramus  cutaneus  palmaris,  942 
dorsalis  manus,  942 
profundus,  943 
superficialis,  942 
volaris  inanus,  942 
vagus,  910 

rami  bronchiales,  913 
cardiaci,  912 
coeliaci,  913 
gastrici,  913 
hepatica,  913 
OEsophagei,  913 
ramus  auricularis,  911 
meningeus,  911 
pharyngeus,  911 
vestibularis,  1058 
zygomaticus,  889 
Net-work,  carpal,  594 

malleolar,  636 
Neumann,    dentinal    sheath    of, 

1119 
Neural  arch,  96 
canal,  50 
crest,  51,  736 
folds,  50 
groove,  50 
tube,  50 
Neurenteric  canal,  50 
Neuroblasts,  733 
Neurocentral  synchondrosis,  112 
Neuroglia,  722 


Neuroglia  of  cord,  754,  755 
Neurokeratin,  725 
Neurolemma,  725 
Neurology,  721 
Neuromieres,  750 
Neuromuscular  spindles,  1061 
Neuron  theory,  732 
Neurons,  motor,  870 
Neurotendinous  spindles,  1061 
Neutrophil    colorless    corpuscles, 

504 
Nidus  avis  of  cerebellum,  791 
Ninth  nerve,  906 
Nipple  or  papilla  of  mamma,  1267 
Nissl's  granules,  723 
Node,  atrioventricular,  537 

sinoatrial,  537 
Nodes  of  Ranvier,  727 
Nodular  lobe,  790 
Nodule  of  cerebellum,  790 
Moduli  lymphatici  aggregati,  1176 

solitarii,  1176,  1187 
Modulus  vermis,  790 
Non-medullated  nerve  fibers,  728 
Normse  of  skull,  basalis,  179 
frontalis,  185 
lateralis,  182 
occipitalis,  185 
verticalis,  178 
Normoblasts,  88 
Nose,  992 

accessory  sinuses  of,  998 

alar  cartilages  of,  993 

arteries  of,  993,  996 

cartilage  of  septum  of,  992 

cartilaginous    frame-work    of, 
992 

cavities  of,"  994 

development  of,  67 

external,  992 

lateral  cartilage  of,  993 

lymphatics  of,  695 

mucous  membrane  of,  996 

muscles  of,  382 
variations  of,  382 

nerves  of,  997 

veins  of,  997 
Notch,  acetabular,  237 

cardiac,  1096 

cerebellar,  788 

ethmoidal,  137 

intertragic,  1034 

jugular,  131 

lacrimal,  159 

mandibular,  174 

mastoid,  141,  181 

nasal,  of  frontal,  136 
of  maxilla,  158 

parietal,  141 

preoccipital,  818 

presternal,  120 

of  Rivinus,  1038 

scapular,  204 

sciatic,  234 

sphenopalatine,  169 

superior  thyroid,  1073 

supraorbital,  136,  186,  189 

ulnar,  of  radius,  220 

umbilical,  of  iiver,  1191 

vertebral,  97 
Notochord,  52 
Nuchal  line,  129,  182 
Nuck,  canal  of,  1211,  1261 
Nuclear  layer  of  cerebellar  cortex, 
795 

layers  of  retina,  1016 

matrix,  36 

membrane,  36 

substance,  36 
Nucleated    sheath    of    Schwann, 

725 
Nuclei  of  cochlear  nerve,  788, 906 

of  glossopharyngeal  and  vagus 
nerves,  779,  780 

of  oculomotor  nerve,  884 


Nuclei,  olivary,  781 

of  origin  of  motor  nerves,  881 

poniis,  786 

of      termination     of     sensory 
nerves,  908 

of  trigeminal  nerve,  787,  807 

of  vestibular  nerve,  788,  881 
Nucleoli,  37 
Nucleus  of  abducent  nerve,  787 

of  accessory  nerve,  913 

ambiguus,  779 

amygdalrc,  835 

amygdaline,  791 

amygdaloid,  869 

arcuatus,  782 

of  Bechterew,  788 

caudate,  833 

caudatus,  833 

of  a  celt,  36 

of  Darkschewitsch,  812 

of  Deiters,  788,  803 

dentatus  [of  cerebellum],  796 

dorsalis,  758 

emboliformis,  796 

of  facial  nerve,  787,  902      • 

fastigii,  796 

globosus,  796 

of  hypoglossal  nerve,  779 

inferior  central,  784 

inter calatus,  799 

of  lateral  lemniscus,  906 

lateralis,  784 

of  lens,  1020 

lenticular,  834 

lentiform,  834 

lentiformis,  834 

ofLuys,  812 

of  medial  longitudinal  fascicu- 
lus. 803 

nervus  abduceniis,  787 
facialis,  787 
trigemini,  787 

of  oculomotor  nerve,  807,  884 

olivaris  superior,  787 

olivary,  781,  787 

of  posterior  commissure,  812 

pulposus,  82 

red,  802 

of  Roller,  784 

segmentation,  45 

sensory,  902 

trapezoid,  787 

of  trochlear  nerve,  807,  885 
of  vagus  nerve,  780 
Nuel,  space  of,  1058 
Nuhn,  glands  of,  1131 
Nutrient  artery  of  bone,  88 
Nutritive  yolk,  39 
Nymphae,  1265 


Obelion,  178,  198 
Obex,  798 
Oblique  cord,  325 
ligament,  325 
line  of  fibula,  261 
of  mandible,  172 
of  radius,  219 
muscles,  409,  412 
inferior,  1023 
superior,  1022 
popliteal  ligament,  340 
ridge  of  clavicle,  200 
sinus  of  pericardium,  526 
vein  of  left  atrium,  526,  643 
of  Marshall,  526,  643 
Obliquis  oculi  muscles,  actions  of, 
1023 
nerves  of,  1023 
Obliquus  auriculae  muscle,  1035 
capitis  inferior  muscle,  402 
action  of,  402 
nerves  of,  402 


1380 


INDEX 


Obliquus  capitis  superior  muscle, 
402 
action  of,  402 
nerves  of,  402 
externus  abdominis  muscle,  409 

variations  of,  412 
inferior  muscle,  402 
internus  abdominis  muscle,  412 

variations  of,  414 
oculi  inferior  muscle,  1023 

superior  muscle,  1022 
superior  muscle,  402 
Obliterated  ductus  venosus,  681 
hypogastric  artery,  615 
umbilical  vein,  681,  1150 
Obturator  artery,  616 
crest,  236 

externus  muscle,  477 
actions  of,  478 
nerves  of,  478 
foramen,  237 
groove,  237 
internus  muscle.  477 
actions  of,  478 
fascia  of,  420 
nerves  of,  478 
lymph  gland,  704 
membrane,  476 
nerve,  953 

accessory,  955 
tubercle,  237 
vein,  676 
Occipital  artery,  556 
bone,  129 

articulations  of,  133 
basilar  part  of,  132 
lateral  parts  of,  131 
ossification  of,  132 
squama  of,  129 
structure  of,  123 
condyles,  131 
crest,  internal,  131,  193 
fossa;,  131 
groove,  141,  181 
lobe,  823 

lymph  glands,  692 
nerve,  923,  926 
point,  198 

protuberance,  129,  130, 182,  183 
sinus,  658 
sulcus,  823 
triangle,  394,  565 
vein,  646 
Occipitalis  muscle,  actions  of,  380 
nerves  of,  380 
variations  of,  380 
Occipitoaxial  ligaments,  296 
Occipitofrontal  fasciculus,  844 
Occipitofrontalis  muscle,  378 
Occipitomastoid  suture,  183 
Occipitotemporal       convolution, 

823 
Ocular  muscles,  1021 
Oculomotor  sulcus,  801 
nerve,  884  _ 

composition  and  central  con- 
nections of,  863 
sympathetic    efferent    fibers 
of,  970 
Odontoblasts,  1118,  1123 
Odontoid  ligaments,  296 

process  of  axis,  100 
Olecranon,  214 

fossa,  212 
Olfactory  areas,  67 
bulb,  826,  848 

structure  of,  848 
cells,  996 
fasciculus,  840 
hair,  996 
lobe,  826 
nerves,  881 

composition  and  central  con- 
nections of,  866 
development  of,  1001 


Olfactory  pits,  68 
projection  fibers,  869 
sulcus,  822 
tract,  826 
trigone,  827 
Oliva,  769 
Olive,  769 

peduncle  of,  781 
Olivary  body,  769 

nucleus,  781,  787 
Olivospinal  fasciculus,  854 
Omental  bursa,  1152,  1155 

recess,  1156 
Omentum,  gastrocolic,  1157 
gastrohepatic,  1156 
greater,  1157 
lesser,  1156 
small,  1156 
Omohyoid  muscle,  394 
Omohyoideus  muscle,  394 
action  of,  394 
nerves  of,  394 
variations  of,  394 
Ontogeny,  35 
Oocytes,  38,  41 
Oogonia,  34 
Ooplasm,  39 

Opening  of  aorta  in  left  ventricle, 
534 
aortic,  in  diaphragm,  406 
caval,  in  diaphragm,  406 
of  coronary  sinus,  530 
esophageal,  in  diaphragm,  406 
of  inferior  vena  cava,  530 
of  pulmonary  artery,  531 

veins,  533 
saphenous,  468 
of  superior  cava,  529 
of  thorax,  524 
Openings,    atrioventricular,   531, 
534 
in  roof  of  fourth  ventricle,  798 
Opercula  of  insula,  825 
Ophryon,  198 
Ophthalmic  artery,  568 
ganglion,  888 
nerve,  887 
veins,  658 
Opisthion,  181,  198 
Opisthotic    center    of    temporal 

bone,  164 
Opponens   digiti   quinti   muscle, 
464 
actions  of,  464 
nerves  of,  464 
minirni  digiti  muscle,  464 
poUicis  muscle,  461 
actions  of,  462 
nerves  of,  462 
variations  of,  462 
Optic  axis,  1001 
chiasma,  814,  883 
commissure,  814 
cup, 1001 
disk,  1015 

foramen,  147,  151,  190 
groove,  147 
nerve,  882 

composition  and  central  con- 
nections of,  864 
radiations,  814 
recess,  816 
stalk,  742,  1001 
thalamus,  808 
tracts,  814,  884 
vesicle,  742,  1001 
Ora  serrata,  1014,  1018 
Oral  cavity,  1110 

part  of  pharynx,  1142 
Orbicular  ligament,  342 
Orbicularis  oculi  muscle,  380 
actions  of,  381,  385 
lacrimal  part,  380 
nerves  of,  381,  385 
orbital  part,  380 


Orbicularis  oculi  muscle,   palpe- 
bral part,  380 
oris  muscle,  384 
palpebrarum  muscle,  380 
Orbiculus  ciliaris  nmscle,  1010 
Orbitw,  188 
Orbits,  188 

relation  of  nerves  in,  900 
Orbital  fascia,  1025 

fissures,  151,  184,  189,  192 

gyri,  822 

index,  198 

nerve,  889 

operculum,  825 

plates,  137 

process  of  palatine  bone,  168 

of  zygomatic  bone,  165 
septum,  1026 
sulcus,  822 
vein,  645 
Orbitalis  muscle  of  H.    Mullt 

1024 
Orbitosphenoids,  151 
Organ,  enamel,  1123 
of  Girald^s,  1246 
of  hearing,  1029 
of  liosenmullcr,  1206,  1255 
of  sight,  1000 
of  smell,  992 
spiral,  of  Corti,  1056 
Organa  genitalia  muliebria,  1254 
virilia,  1236 
oculi  accessoria,  1021 
Organon  auditus,  1029 
gustus,  991 
olfactorius,  992 
spirals  ICorti],  1056 
visus,  1000 
Organs  of  digestion,  1100 
genital,  of  female,  1254 

of  male,  1236 
of  Golgi,  376 
of  the  senses,  991 
of  taste,  991 
urogenital,  1204 
vomeronasal,  of  Jacobson,  71, 
996 
Orifice,  atrioventricular,  531,  533 
cardiac,  of  stomach,  1161 
mitral,  534 
of  mouth,  1110 
pyloric,  of  stomach,  1162 
urethral,  1232,  1235,  1266 
of  uterus,  1259,  1260 
vaginal,  1266 
Orifices  of  ureters,  1232 
Origin  of  muscles,  362 
Os  acetabuli,  238 
calcis,  263 
capitatum,  226 
coccygis,  11' 
cordis,  536 
coxae,  231 

articulations  of,  238 
ossification  of,  237 
structure  of,  237 
cuboideum,  269 
cuneiforme  primum 
secundum,  271 
tertium,  271 
ethmoidale,  153 
frontale,  135 
hamatum.  111 
hyoideum,  177 
ilii,  231 
incisivum,  162 
innominatum,  231 
ischii,  234 
lacrimale,  163 
lunatum,  224 
magnum,  227 
muUangulum,  225 
naviculare  manus,  221 

pedis,  270 
occipitale,  129 


270 


INDEX 


1381 


Os  palaiinum,  166 

parietale,  133 

pisi/orme,  225 

planum,  155 

pubis,  236 

sacrum,  106 

sphenoidale,  147 
ate  magna,  149 
parea,  151 

temporale,  138 

trigonum,  269 

triquetum,  225 

zygomaticum ,  164 
Ossa  carpi,  221 

cranii,  129 

extremitatis  inferioris,  231 
superioris,  200 

faciei,  156 

metacarpalia,  228 

metatarsalia,  272 

nasalia,  156 

sesamoidea,  277 

<arsi,  263 
Ossein,  91 

Ossicles,  auditory,  1044 
development  of,  1033 
ligaments  of,  1045 
Ossicula  auditus,  1044 
Ossification  of  atlas,  113 

of  axis,  113 

of  clavicle,  202 

of  coccyx,  114 

of  ethmoid,  156 

of  femur,  255 

of  fibula,  262 

of  foot,  275 

of  frontal,  138 

of  hand, 230 

of  hip  bone,  237 

of  humerus,  213 

of  hyoid,  178 

of  inferior  nasal  concha,  170 

intracartilaginous,  93 

intramembranous,  91 

of  lacrimal,  164 

of  lumbar  vertebrae,  113 

of  mandible,  174 

of  maxilla,  163 

of  nasal,  157 

of  occipital,  132 

of  OS  coxae  or  innominatum,  237 

of  palatine,  169 

of  parietal,  135 

of  patella,  256 

of  radius,  220 

of  ribs,  127 

of  sacrum,  113 

of  scapula,  208 

of  seventh   cervical    vertebra, 
113 

of  sphenoid,  152 

of  sternum,  121 

of  temporal,  145 

of  tibia,  260 

of  ulna,  219 

of  vertebral  column,  111 

of  vomer,  171 

of  zygomatic,  166 
Osteoblasts,  87 
Osteoclasts,  88,  1124 
Osteodentin,  1120 
Osteogenetic  filjers,  92 
Osteology,  79 

Ostium,    abdominal,    of    uterine 
tube,  1257 

maxillare,  995 

pharyngeal,  of  auditory  tube, 
1141 

primitive  urogenital,  1215 

primum  [heart],  512 

secundum  [heart],  512 
Otic  ganglion,  897 
Otoconia,  1054 
Outlet  of  pelvis,  240 
Ova,  primitive,  1207 


Oval  area  of  Flechsig,  764 

bundle,  735 
Ovaria,  1254 
Ovarian  arteries,  611 

fossa,  1154,  1254 

plexus  of  nerves,  987 

veins,  679 
Ovaries,  1254 

descent  of,  1207 

development  of,  1207 

ligaments  of,  1254 

lymphatic  capillaries  of,  687 
vessels  of,  714 

nerves  of,  1256 

structure  of,  1255 

vesicular  or  Graafian  follicles 
of,  1256 

vessels  of,  1256 
Oviduct,  1257 
Ovula  Nabothi,  1262 
Ovum,  35,  38 

corona  radiata  of,  39 

coverings  of,  40 

discharge  of,  1256 

fertilization  of,  44 

germinal  spot  of,  39 
vesicle  of,  39,  40 

implantation  or  imbedding  of, 
58 

maturation  of,  40 

mature,  40 

segmentation  of,  45 

structure  of,  38 

yolk  of,  39 

zona  pellucida  or  radiata  of, 
40 
Oxvntic  cells,  1167 

glands,  1167 
Oxyphil  colorless  corpuscles,  504 


Pacchionian  glands,  878 
Pacinian  corpuscles,  1060 
Pad,  retropubic,  1228 
Pain,  impulses  of,  853 
Palatal  process  of  maxilla,  162 
Palate,  1112 
arches  of,  1112 
bone,  166 

development  of,  70 
hard,  1112 
soft,  1112 
Palatine  aponeurosis,  1139 
artery,  ascending,  555 

of  ascending  pharyngeal,  557 
descending,  562 
bone,  166 

articulations  of,  169 
horizontal  part  of,  167 
orbital  process  of,  168 
ossification  of,  169 
pyramidal  process  or  tuber- 
osity of,  168 
sphenoidal  process  of,  169 
vertical  part  of,  167 
foramen,  180 
nerves,  893 
process  of  maxilla,  162 
processes  of  fetus,  70 
tonsils,  1137 
uvula,  1112 
velum,  1112 
Palatoglossus  muscle,  1129,  note, 

1139 
Palatopharyngeus  muscle,  1139 
Palatum,  1112 
durum,  1112 
molle,  1112 
Palmar  aponeurosis,  460 
arch,  deep,  595 

superficial,  598 
cutaneous    branch    of    median 
nerve,  938 


Palmar     cutaneous     branch     of 
ulnar  nerve,  942 

fascia,  460 

interossei  muscles,  465 

interosseous  arteries,  596 

ligaments,  328,  331 

nerves  of  ulnar,  942,  943 
Palmaris  brevis  muscle,  463 
actions  of,  464 
nerves  of,  464 
variations  of,  464 

longus  muscle,  446 
actions  of,  450 
nerves  of,  450 
variations  of,  446 
Palpebral,  1025 
Palpebral  arteries,  569,  570 

commissures  or  canthi,  1025 

fissure,  1025 

ligament,  1026 
medial,  381 

nerves  from  maxillary,  891 

raphe,  lateral,  381 
Pampiniform     plexus     of     sper- 
matic cord,  678 
Pancreas,  1199 

accessory  duct  of,  1202,  1203 

body  of,  1201 

development  of,  1203 

duct  of,  1022,  1203 

head  of,  1200 

lymphatic  vessels  of,  711 

neck  of,  1201 

nerves  of,  1204 

structure  of,  1203 

surface  marking  of,  1320 

tail  of,  1201 

uncinate  process  of,  1200 

vessels  of,  1204 
Pancreatic  arteries,  606 

duct,  1202 

accessory,  1202,  1203 

veins,  681 
Pancreatica  magna  artery,  606 
Pancreaticoduodenal  arteries,  604, 
607 

lymph  glands,  710 

veins,  682 
Pancreaticolienal  lymph   glands, 

706 
Papilla,  lacrimal,  1025 

foliata,  1132 

mammoe,  1267 
Papillae,  circum vallate,  1126 

conical,  1127 

filiform,  1127 

fungiform,  1126 

of  skin,  1065 

of  tongue,  1126 
Papillary  layer  of  skin,  1065 

process,  1191 
Paracentral  lobule,  822 
Parachordal  cartilages,  84 
Paradidymis,  1246 
Paraganglia,  1269.  1278 
Parallel  striae  of  Retzius,  1120 
Paramastoid  process,  131 
Paramedial  sulcus,  822 
Parametrium,  1259 
Paranephric  body,  1220 
Paranucleus,  1204 
Paraplasm,  36 
Paraplexus,  840 
Pararectal  fossa,  1154 

lymph  glands,  710 
Parathyroid  glands,  1271 
development  of,  1272 
structure  of,  1273 
Paravesical  fossa,  1154 
Paraxial  mesoderm,  50 
Parietal  bone,  133 

articulations  of,  135 
ossification  of,  233 

cells  of  fundus  glands,  1167 

convolution,  ascending,  823 


1382 


INDEX 


Parietal  eminence,  133,  178,  183 
foramen,  134,  178 
lobe,  822 

gyri  of,  823 
notch,  141 
operculum,  825 
pleura,   1087 
veins,  520 
Parietomastoid  suture,  183 
Parietooccipital  fissure,  820 
Parietotemporal  artery,  573 
Parolfactory  area  of  Broca,  827 
Paroophoron,  1206,  1255 
Parotid  duct,  1134 
gland,  1132 

accessory  part  of,  1134 
nerves  of,  1134 
structure  of,  1134 
surface  marking  of,  1295 
vessels  of,  1134 
lymph  glands,  693 
plexus,  902 
Parotideomasseteric  fascia,  385 
Parovarium,  1255 
Partes   genitales     exlernm   mulie- 

bres,  1264 
Parumbilical  veins,  682 
Patella,  255 

articulation  of,  256 
movements  of,  346 
ossification  of,  256 
structure  of,  256 
surface  anatomy  of,  1337 
Patellar  plexus,  953.  956 
retinacula,  340 
surface  of  femur,  248 
Pathways    from    brain   to   spinal 

cord,  870 
Pectinate  ligament  of  iris,  1009 
Pectineal  line,  246 
Pectineus  muscle,  472 
actions  of,  474 
nerves  of,  474 
variations  of,  474 
Pectiniforme  septum,  1248 
Pectoralis  major  muscle,  436 
actions  of,  439 
nerves  of,  439 
variations  of,  438 
minimus  muscle,  438 
minor  muscle,  438 
actions  of,  439 
nerves  of,  439 
variations  of,  438 
Peculiar  thoracic  vertebrae,  104 
Pedicles  of  a  vertebra,  96 
Peduncle  of  corpus  callosum,  827 

of  olive,  781 
Peduncles  of  cerebellum,  792 

cerebral,  800 
Pedunculus  cerebri,  800 
Pelvic  colon,  1182 
diaphragm,  420 
fascia  of,  420 
fascia,  420 

endopelvic  part  of,  422 
girdle,  200 
plexuses,  987 

portion  of  sympathetic  system, 
984 
Pelvis,  238,  1149 
articulations  of,  306 
axes  of,  240 
boundaries  of,  238 
brim  of,  238 
cavity  of  lesser,  239 
diameters,  239,  240 
in  fetus,  242 
greater  or  false,  238 
inferior   aperture  or  outlet  of, 

240 
lesser  or  true,  239 
ligaments  of,  307,  308 
linea  terminalis  of,  238 
lymph  glands  of,  703 


Pelvis,  major,  238 

male    and    female,    differences 
between,  241 

mechanism  of,  311 

minor,  239 

position  of,  241 

renal,  1221 

superior  aperture  or  inlet  of, 
239 

surface  anatomy  of,  1336 
Penis,  1247 

body  of,  1249 

corona  glandis,  1249 

corpora  cavernosa,  1248 

corpus    cavemosum  urelhrcB,  or 
corpus  spongiosum,  1248 

crura  of,  1248 

deep  artery  of,  620 

dorsal  artery  of,  620 
veins  of,  676 

extremity  of,  1250 

fundiform  ligament  of,  1249 

glands,  1248 

nerves  of,  1250 

prepuce  or  foreskin  of,  1250 

root  of,  1249 

septum  pectiniforme,  1248 

structure  of,  1250 

suspensory  ligament  of,  1249 
Perforated  substance,  800,  827 
Perforating  arteries,  of  hand,  595 
from  internal  mammary,  584 
from  plantar,  640 
fi'om  profunda  femoris,  631 

cutaneous  nerve,  967 

fibers  of  Sharpey,  90 
Perforator  of  spermatozoon,  42 
Pericardiacophrenic  artery,  584 
Pericardial  area,  46 

lymphatic  capillaries  in,  684 

arteries,  584,  600 

pleura,   1089 
Pericardium,  524 

fibrous,  526,  526 

nerves  of,  526 

oblique  sinus  of,  52Q 

relations  of,  525 

serous,  525 

structure  of,  525 

transverse  sinus  of,  526 

vessels  of,  526 

vestigial  fold  of,  526 
Pericecal  folds,  1160 

fossaj,  1160 
Perichondrium,  279 
Perilymph,  1051 
Perimysium,  373 
Perineal  arterj',  619 

body, 1185 

branch  of  fourth  sacral  nerve, 
968 

muscle,  superficial  transverse, 
427,  430 

nerve,  968 
Perineum,  boundaries  of,  424 

central  tendinous  point  of,  427 

lymphatic  vessels  of,  706 

muscles  of,  424 
Perineurium,  728 
Periosteum,  87 

of  bone,  lymphatic    capillaries 
in.  684 
Peripheral  end-organs,  1059 

nervous  system,  728 

organs  of  special  senses,  991 

terminations  of  nerves  of 
general  sensations,  1059 
Periscleral  lymph  space,  1024 
Peritoneal  cavity,  1150 

lymphatic  capillaries  in,  684 

fossae  or  recesses,  1158 

sacs,  1150,  1152,  1155 
Peritoneum,  1149 

epiploic  foramen  of,  1156 

lesser  sac  of,  1155 


Peritoneum,  ligaments  of,  1156 
main  cavity  or  greater  sac  of, 
1150 
horizontal   disposition   of, 

1153,   1154,    1155 
vertical  disposition  of,  11 50 
mesenteries,  1157 
omenta,   1156 
omental  bursa  of,  1155 

vertical  disposition  of,  1152 
parietal  portion  of,  1150 
visceral  portion  of,  1150 
Permanent  cartilage,  279 
choanae,  70 
kidney,  1211 
teeth,    1115 

development  of,  1124 
Peronsei  muscles,  actions  of,  488 
nerves  of,  487 
variations  of,  487 
Peronaeus  accessorius  muscle,  487 
brevis  muscle,  487 
longus  muscle,  486 
quartus  muscle,  487 
quinti  digiti  muscle,  487 
tertius  muscle,  482 
actions  of,  482 
nerv^es  of,  482 
Peroneal  arteries,  638 
nerves,  964,  965 
retinacula,  489 
septa,  480 
Peroneocalcaneus  externus  mus- 
cle, 487 
internus  muscle,  485 
Peroncocuboideus  muscle,  487 
Peroneotiljialis  muscle,  485 
Perpendicular  fasciculus,  844 
line  of  ulna,  218 
plate  of  ethmoid,  154 
Pes  or  base  of  cereljral  peduncle, 
802 
hippocampi,  833 
Petit,  canal  of,  1019 

triangle  of,  434 
Petrooccipital  fissure,  181 
Petrosal  nerve,  deep,  892 
external,  979 
large  deep,  892 

superficial,  892,  903 
superficial,  greater,  892,  903 

smaller,  1047 
process,  147 
sinuses,  648,  659 
Petrosphenoidal  fissure,  181 
Petrosquamous  sinus,  658 

suture,  142,  145 
Petrotympanic  fissure,  140,  180 
Petrous  ganglion,  908 

portion  of  temporal  bone,  142 
Peyer's  glands,  1176 

patches,  1176 
Phalangeal   processes   of   Corti's 

rods,  1058 
PJialanges  digitorum  manus,  230 
pedis,  275 
of  foot,  275 

articulations  of,  359 
ossification  of,  275 
of  hand,  230 

articulations  of,  333 
ossification  of,  231 
ungual,  275 
Pharyngeal  aponeurosis,  1143 
artery,  ascending,  557 
bursa,  1142 
grooves,  65 
membrane,  1101 
nerve    from    glossopharyngeal, 
909 
from     sphenopalatine     gan- 
glion, 893 
from  vagus,  911 
ostium  of  auditory  tube,  1141 
plexus  of  nerves,  909,  912,  979 


INDEX 


1383 


II 


Pharyngeal  pouches,  65 

recess,  1142 

tonsil,  1142 

tubercle,  132,  180 

veins,  649 
Pharyngopalatine  arch,  1137 
Pharvngopalatinus  muscle,  1139 
Pharynx.  1141 

aponeurosis  of,  1143 

development  of,  1103 

laryngeal  part  of,  1142 

lymphatic  vessels  of,  698 

mucous  coat  of,  1144 

muscles  of,  1142 
actions  of,  1143 
nerves  of,_  1 143 

nasal  part  o'f,  1141 

oral  part  of,  1 142 

structure  of,  1143 
Philtrum,  385 
Phrenic  arteries,  601,  612 

nerve,  92S 

plexus  of  nerves,  985 

veins,  666,  679 
Phrenieocolic  ligament,  1158 
Phrenicocostal  sinus,  1089 
Phrenicolienal  ligament,  1155 
Phrenicopericardiac  ligament,  678 
Phylogenv,  35 
Pia  of  brain,  879 

of  cord,  879 

mater,  cranial,  879 
encephali,  879 
spinal,  879 
spinaHs,  879 
Pigment  of  iris,  1013 

of  skin,  1064 
Pigmented  layer  of  retina,  1015 
Pili,   1067 
Pillars  of  Corti,  1056 

of  external  abdominal  ring,  410 

of  fauces,  1112 

of  fornix,  838,  840 
Pineal  body,  812,  1277 
structure  of,  1277 

recess,  743,  816 
Pinna, 1033 

cartilage  of,  1034 

ligaments  of,  1035 
Piriformis  muscle,  476 
actions  of,  478 
fascia  of,  421 
nerves  of,  478 
variations  of,  476 
Pisiannularis  muscle,  464 
Pisiform  lx>ne,  225 
Pisimetacarpus  muscle,  464 
Pisiuncinatus  muscle,  464 
Pisohamate  ligament,  329 
Pisometacarpal  ligament,  329 
Pits,  olfactorv,  68 
Pituitary  body,  814,  1257 
Pivot-joint,  285 
Placenta,  62 

circulation  through,  63,  540 

cotyledons  of,  63 

fetal  portion  of,  62 

maternal  portion  of,  62 

previa,  64 

separation  of,  64 
Plane,  intertubcrcular,  1147 

subcostal,  1148 

transpyloric,  1147 
Plantar  aponeurosis,  490 

arch,  639 

arteries,  639 

cutaneous  venous  arch,  669 

digital  veins,  671 

fascia,  490 

interossei  muscles,  495 

ligament,  long,  354 

metatarsal  arteries,  640 

nerves,  963 
Plantaris  muscle,  483 
actions  of,  483 


Plantaris  muscle,  nerves  of,  483 
Planum  nuchale,  120 

occipitale,  130 
Plasma  cells,  377 
Plate  or  Plates,  cribriform,  of  eth- 
moid, 153 
ethmoidal,  85 
orbital,  of  frontal,  137 
perpendicular,  of  ethmoid,  154 
pterygoid,  of  sphenoid,  151 
tarsal,  1025 
Platelets  of  blood,  505 
Platysma  muscle,  388 

action  of,  388 

nerves  of,  388 
Pleura,  1087 
cavity  of,  1088 
cervical,  1088 
costal,  1088 
cupula  of,  1088 
diaphragmatic,  1088 
lymphatic  vessels  of,  719 
mediastinal,  1088 
nerves  of,  1090 
parietal,  1087 
pericardial,  1088 
pulmonary,  1087 
reflections  of,  1088 
structure  of,  1090 
surface  markings  of,  1309 
vessels  of,  1090 
Pleural  cavity,  lymphatic  capil- 
laries in,  684 
Plexiform  layers  of  retina,  1016 
Plexus  of  nerves,  annular,  1009 

aortic  abdominal,  987 

Auerbach's,  1177 

brachial,  930 

cardiac,  984 

cavernous,  978 

celiac,  985 

cervical,  925 

posterior,  912,  922,  923 

choroid,  of  fourth  ventricle, 
798 
of  lateral  ventricle,  840 
of  third  ventricle,  815 

coccygeal,  968 

of  cornea,  1009 

coronary,  985,  987 

esophageal,  913 

of  Exner,  846 

gastric,  987 

hemorrhoidal,  987 

hepatic,  986 

hypogastric,  987 

infraorbital,  891 

internal  carotid,  977 

lienal,  986 

lumbar,  948 

lumbosacral,  948 

Meissner's,  1177 

mesenteric,  987 

myenteric,  1177 

ovarian,  987 

parotid,  902 

patellar,  953,  956 

pelvic,  987 

pharyngeal,  909,  912,  979 

phrenic,  985 

prostatic,  988 

pudendal,  966 

pulmonary,  910,  913 

renal,  987 

sacral,  957 

solar,  985 

spermatic,  987 

splenic,  986 

subsartorial,  956 

suprarenal,  987 

tonsillar,  909 

tympanic,  1047 

uterine,  989 

vaginal,  989 

vesical,  988 


Plexus  of  veins,  basilar,  660 
hemorrhoidal,  670 
pterygoid,  645 
pudendal,  676 
uterine,  676 
vertebral,  668 
vesical,  676 
vesicoprostatic,  676 
Plexus  aorticus  ahdominalis,  987 
arterice  ovaricoE,  987 
brachialis,  930 
cardiacus,  984 
caroticus  internus,  977 
cavernosus,  978 
cervicalis,  925 

chorioideus  ventriculi,  840,  841 
cceliacus,  985 
coronarius,  985 
gastricus  superior,  987 
hepaticus,  986 
hypogastricus,  987 
lienalis,  986 
lumbalis,  949 
lumbosacralis,  948 
niesentericus  inferior,  987 
phrenicus,  985 
prostaticus,  988 
pudendus,  966 
Tcnalis,  987 
sacralis,  957 
spermaticus,  987 
suprarenalis,  987 
venosi  basilaris  660 
hwmorrhoidalis,  676 
pterygoideus,  645 
pudendalis,  676 
vertebrales,  668 
vesicalis,  676 
Plica  circulares  [Kerkringi],  1173 
fiinbriata  [tongue],  1125 
gubernatrix,    1211 
lacrimalis  of  Hasner,  1029 
semilunaris  [conjunctiva],  1028 

[tonsil],  1138 
sublingualis,  1136 
triangularis  [tonsil],  1138 
vascularis,  1211 
vesicalis  transversa,  1154 
Plicae  uretericoe,  1232 

ventriculares  [laryngis],  1079 
vocales,  1080 
Pneumogastric  nerve,  910 
Polar  bodies  or  polocytes,  40 
Poles    of    cerebral    hemispheres, 
818 
of  eyeball,  1001 
of  lens,  1019 
Polymorphonuclear  leucocytes, 

504 
Polyspermy,  45 
Pomum  Adami,  1073 
Pons,  785 

development  of,  740 
hepatis,  1191 
structure  of,  785 
Varoli,  785 
Ponticulus  [auricula],  1034 
Pontine  arteries,  580 
Pontospinal  fasciculus,  872 
Popliteal  artery,  632 
branches  of,  633 
peculiarities  of,  633 
surface  marking  of,  1346 
fossa  or  space,  631 
line  of  tibia^  258 
lymph  glands,  701 
nerves,  960,  964 
surface  of  femur,  246 
vein,  672 
Popliteus  muscle,  484 
actions  of,  486 
minor,  485 
nerves  of,  486 
variations  of.  485 
Pore,  gustatory,  991 


1384 


Porta  of  liver,  1191 
Portal  vein,  681 

development  of,  681 
Postanal  gut,  1110 
Postaxial  borders  of  limbs,  71 
Postcentral  sulcus,  822 
Postcornu,  831 

Posterior  annular  ligament,  458 
basis  bundle,  764 
calcaneoastragaloid     ligament, 

352 
circumflex  artery,  589 
common  ligament,  288 
cornu  of  medulla  spinalis,  753 
costotransverse  ligament,  302 
cricoarytenoid  muscle,  1082 
deep  cervical  vein,  651 
dental  artery,  562 
ground  bundle,  764 
inferior  ligament,  348 
interosseous  artery,  596 

nerve,  944 
ligament,  327 
pillar  of  fauces,  1137 
proper  fasciculus,  764 
pulmonary  nerves,  913 
radial  carpal  artery,  594 
radioulnar  ligament,  325 
sacrosciatic  ligament,  309 
scapular  artery,  582 

nerve,  932 
superior  ligament,  348 
talotibial  ligament,  350 
temporal  artery,  559 
ulnar  carpal  artery,  598 
vertebral  vein,  651 

Postero-lateral  ganglionic  arteries, 
581 

Postero-medial    ganglionic    arte- 
ries, 547, 581 

Postgemina,  806 

Postnodular  fissure,  790 

Postpartum  hemorrhage,  64 

Postpyramidal  fissure,  790 

Postsphenoid  part  of  sphenoid, 
152 

Pouch  of  Douglas,  1152 
of  Prussak,  1046 
of  Rathke,  1277 

Pouches,  pharyngeal,  65 

Poupart's  ligament,  411 

Prceputium  clitoridis,  1266 

Preauricular  lymph  glands,  693 
point,  1291 
sulcus  of  ilium,  234 

Preaxial  borders  of  limbs,  71 

Precentral  gyre,  821 
sulcus,  821 

Prechordal    portion    of    base    of 
fetal  skull,  84 

Precommissure,  840 

Precornu,  830 

Precuneus,  823 

Pregemina,  806 

Premaxilla,  126 

Premolar  teeth,  1118 

Preoccipital  notch,  818 

Prepatellar  bursa,  471 

Prepuce  of  clitoris,  1266 
of  penis,  1250 

development  of,  1215 

Preputial  glands,  1250 
sac,  1250 

Prepyramidal  fissure,  790 
tract,  761 

Presphenoid,  152 

Pressure  epiphyses,  95 

Presternal  notch,  120 

Pretracheal  fascia,  390 

Prevertebral  fascia,  389 
part  of  base  of  skull,  84 

Primary  areolae  of  bone,  93 
oocytes,  38 
spermatocytes,  43 

Primitive  aortae,  506 


Primitive  atrium,  508,  512 
costal  arches,  82 
digestive  tube,  53 
fibrillse  of  Schultze,  725 
groove,  47 
jugular  veins,  520 
ova, 1209 
palate,  70 
segments,  52 

sheath  of  nerve  fiber,  727 
streak,  47 

urogenital  ostium,  1215 
ventricle  of  heart,  508 
Princeps  cervicis  artery,  557 

pollicis  artery,  595 
Prismata  adamantina,  1120 
Proamnion,  47 
Procerus  muscle,  382 

action  of,  382 

nerves  of,  382 
Process  or  Processes,  alveolar,  161 
articular,  of  vertebra;,  96 
ciliary,  1010 
clinoid,  147,  151,  190 
condyloid,  of  mandible,  174 
coracoid,  207 
coronoid,  of  mandible,  174 

of  ulna,  214 
costal,  98 

descending,  of  lacrimal,  164 
of  dura  mater,  873 
frontal,  of  maxilla,  161 
frontonasal,  67 
frontosphenoidal,  of  zygomatic, 

164 
globular,  of  His,  68 
of  inferior  nasal  concha,  169 
intrajugular,  131 
jugular,  131,  181 
lateral  nasal,  68 
lenticular,  of  incus,  1045 
malar,  of  maxilla,  161 
mastoid,  141 
maxillary,  of  fetus,  69 

of  inferior  nasal  concha,  169 

of  palatine  bone,  168 

of  zygomatic  bone,  166 
muscular,  of  arytenoid,  1075 
nasal,  of  frontal  bone,  136 

of  maxilla,  161 
odontoid,  of    axis   or   epistro- 
pheus, 100 
orbital,  of  palatine  bone,  168 

of  zygomatic  bone,  165 
palatal,  of  maxilla,  162 
palatine,  of  fetus,  70 

of  maxilln,  162 
papillary,  of  liver,  1191 
paramastoid,  131 
petrosal,  147 

phalangeal,  of  Corti'srods,  1057 
pterygoid,  of  sphenoidal  bone, 

151 
pyramidal,    of   palatine    bone, 

168,180 
sphenoidal,   of  palatine    bone, 
169 

of  septal  cartilage  of  nose, 
993 

turbinated,    152 
spinous,  of  ilium.  234 

of  vertebrae,  96 
styloid,  of  fibula,  260 

of  radius,  220 

of  temporal  bone,  145,  181 

of  ulna,  218 
temporal,  of  zygomatic,  166 
transverse,  of  vertebra?,  96 
trochlear,  of  calcaneus,  266 
uncinate,  of  ethmoid,  155 
vaginal,  of  sphenoid,  151 

of  temporal,  144,  145 
vermiform,  1178 
of  vertebrae,  106 
vocal,  of  arytenoid,  1075 


Process  or  Processes,  xiphoid,  121 

zygomatic,  of  frontal,  136 
of  maxilla,  161 
of  temporal  bone,  139 
Processus  alveolaris  [maxillce],  161 

brevis  [malleus],  1044 

ciliares,  1010 

cochleariformis,  145,  1042 

condyloideufi  [mandibula],  174 

coracoideus  [scapulw],  207 

coronoideus  [mandibulce],  174 
[ulnare],  214 

frontalis  [maxilla],  161 

gracilis  [malleus],  1044 

orbitalis  [os  palatinum],  168 

palatinus  \maxillw],  162 

pterygoidei,   151' 

pyraniidalis  [os  palatinum],  168 

spinosus,  97 

splenoidalis  [os  palatinum],  169 

transversi,  97 

tubarius,  152 

vermiformis,  1178 

xiphoideus,  121 

zygomaticus,  161 
Proctodeum,  1110 
Prodentin,1123 
Profunda  arteries,  591 

brachii  artery,  591 

cervicaiis  artery,  585 

femoris  artery,  629 
vein,  672 

linguae  artery,  553 
Projection  fibers  of  cerebral  hemi- 

sheres,  842 
Prominence  of  aqueduct  of  Fal- 
lopius,  1042 

of  facial  canal,  1042 

laryngeal,  1073 
Prominentia  canalis  facialis,  1042 
Promontorium,  1042 
Promontory  of  tympanic  cavity, 

1042 
Pronator  quadratus  muscle,  449 
actions  of,  450 
nerves  of,  450 
variations  of,  450 

teres  muscle,  446 
actions  of,  450 
nerves  of,  450 
variations  of.  446 
Pronephric  duct,  1205 
Pronephros,  1205 
Pronucleus,  female,  42 

male,  45 
Prootic  center  of  temporal  bone, 

146 
Prophase  of  karyokinesis,  37 
Prosencephalon,  51,  807 
Prostata,  1251 
Prostate,   1251 

development  of,  1213 

gland,  1251 

lobes  of,  1252 

lymphatic  capillaries  of,  687 
vessels  of,  713 

nerves  of,  1253 

structure  of,  1253 

vessels  of,  1253 
Prostatic  ducts,  orifices  of,  1234 

plexus  of  nerves,  988 

portion  of  urethra,  1234 

sinus,   1234 

utricle,  1234 
Prosthion,  198 
Prothrombin,   505 
Protoplasm,  35 
Protoplasmic     process   of   nerve 

cells,  723 
Protuberance,  mental,  172 

occipital,  129,  130.  183 
Prussak,  pouch  of,  1046 
Psalterium,  838 
Pseudocele,  840 
PseudonucleoU,  37 


INDEX 


1385 


Pseudopodium,  505 
Psoas  magnus  muscle,  467 
major  muscle,  467 
actions  of,  467 
fascia  covering,  466 
nerves  of,  467 
minor  muscle,  467 
actions  of,  467 
nerves  of,  467 
par\'us  muscle,  467 
Pterion,  151,  182,  198 

ossicle,  156 
Pterotic  center  of  temporal  bone, 

146 
Pterygoid  canal,  151,  180 
fissure,   151 
fossa  of  sphenoid,  151 
hamulus,  151,  180 
muscles.  386 
plates,  151 
plexus  of  veins,  645 
processes  of  sphenoid,  151 
tubercle,  152 
Pterygoideus    externus    muscle, 
386 
action  of,  387 
nerves  of,  387 
internus  muscle,  387 
action  of,  3s7 
nerves  of,  387 
Pterygomandibular  ligament,  384 

raphe,  384 
Pterygomaxillary  fissure,  185 
Pterygopalatine  canal,  159,  168 
fossa,  185 
groove,  151 
nerve,  893 
Pterygospinous  ligament,  153,388 
Pubic  arch,  240 

bones,  articulation  of,  309 
ligaments,  310 
region,   1149 
tubercle  or  spine,  236 
vein,  673 
Pubis,  236 
angle  of,  236 
body  of,  236 
crest  of,  236 

iliopectineal  eminence  of,  236 
obturator  crest  of,  236 
rami  of,  236 
symphysis  of,  310 
tubercle  or  spine  of,  236 
Pubocapsular  ligament,  334 
Pubococcygeus  muscle,  424 
Pubofemoral  ligament,  335 
Puborectalis  muscle,  424 
Pubovesicales  muscles,  1231 
Pudendal  artery,  accessory,  618 
internal,  in  female,  620 
in  male,  617 
cleft  or  rima,  1256 
nerve,  967 

inferior,  960 
plexus,  nervous,  966 

venous,  676 

veins,  internal,  673 

Pudendum,  1264 

Pudic  arteries,  617,  629 

nerve,  internal,  967 

veins,  internal,  674 

Pulmonary  artery,  543 

opening  of,  in  right  ventricle, 
531 
ligaments,  1088,  1090 
nerves,  913 
pleura,  1087 
semilunar  valves,  532 
veins,  642 

openings  of,  in  left  atrium 
533 
Pulmones,  1093 
fades  costalis,  1094 

mediastinalis,  1095 
inargo  anterior,  1096 


Pulmones  margo  inferior,  1096 

posterior,  1096 
Pulp  cavity  of  teeth,  1118 

dental,  1118 

of  spleen,  1284 
Pulvinar,  808 
Puncta  lacrimalia,  1028 

vasculosa,  827 
Pupil,  1012 

congenital  atresia  of,  1003 
Pupillary  membrane,  1003,  1014 
Purkinje,  cells  of,  794 

fibers  of,  536, 
Putamen,  834 
Pyloric  antrum,  1162,  1163 

artery,  604 

glands,  1166 

orifice  of  stomach,  1162 

part  of  stomach,  1162,  1163 

valve,  1164 

vein,  682 
Pyramid,  1042 

of  cerebellum,  791 

of  medulla  oblongata,  768 

of  temporal  bone,  142 

of  vestibule,  1048 
Pyramidal  cells  of  cerebral  cortex, 
845 

decussation,  768 

eminence  of  tympanic  cavity, 
1042 

lobe  of  thyroid  gland,  1270 

process  of  palatine  bone,  168, 
180 

tracts,  759,  760 
Pyramidalis  muscle,  416 
variations  of,  417 

nasi  muscle,  382 
Pyramids,  renal,  1221 
Pyramis  meduUce  oblongata,  768 


Quadrate  lobe  of  liver,  1192 
Quadratus  femoris  muscle,  477 
actions  of,  478 
nerves  of,  478 
labii  inferioris  muscle,  383 
action  of,  383 
nerves  of,  383 
superioris  muscle,  383 
action  of,  383 
nerves  of,  383 
lumborum  muscle,  420 
actions  of,  420 
fascia  covering,  419 
nerves  of,  420 
variations  of,  420 
menti  muscle,  383 
plantse  niuscle,  493 
actions  of,  496 
nerves  of,  496 
variations  of,  496 
Quadriceps  extensor  muscle,  470 
femoris  muscle,  470 
actions  of,  471 
nerves  of,  471 
Quadrigeminal  bodies,  805 


Radial  artery,  592 

branches  of,  594 

carpal,  594 

peculiarities  of,  594 

recurrent,  594 

surface  marking  of,  1335 
fibers  of  cerebral  cortex,  846 
fossa,  212 
nerve,  943 
sulcus,  211 
tuberosity,  219 
Radialis  indicis  artery,  595 


Radiate  ligament,  299 

sternocostal  ligaments,  302 
Radiocarpal  articulation,  327 

movements  of,  328 
Radioulnar  articulations,  324, 325 

ligaments,  325 

union,  middle,  325 
Radius,  219 

grooves  on  lower  end  of,  220 

oblique  line  of,  219 

ossification  of,  220 

sigmoid  cavity  of,  220 

structure  of,  220 

surface  anatomy  of,  1327 

tuberosity  of,  219 

ulnar  notch  of,  220 
Radix  arcus  vertebrae,  97 

lingua;,  1125 

penis,  1249 

pili,  1067 

pulmonis,  1097 
Rami  of  ischium,  236 

of  pubis,  236 
Ramus  of  mandible,  173 
Ranine  artery,  553 

vein,  648,  649 
Ranvier,  crosses  of,  727 

nodes  of,  727 
Raph6,  anococcygeal,  426 

lateral  palpebral,  381 

of  palate,  1112 

pterygomandibular,  384 

of  scrotum,  1237 
Rathke,  pouch  of,  1277 
Receptaculum  chyli,  691 
Recess,  epitympanic,  142,  1038 

nasopalatine,  996 

omental,  1156 

optic,  816 

pharyngeal.  1141,  1142 

pineal,  743,  816 

sphenoethmoidal,  195,  994 
Recesses,  lateral,  of  fourth  ven- 
tricle, 797 

peritoneal,  1158 

of  Troltsch,  1046 
Recessus  ellipticus,  1048 

infundibuli,  816 

inter  sigmoideus,  1161 

pinealis,  743,  816 

sacciformis,  326 

spkcericus,  1047 

suprapinealis,  816 
Reciprocal  reception,  articulation 

by, 286 
Rectal  ampulla,  1183 

columns  of  Morgagni,  1185 

layer  of  pelvic  fascia,  422 
Recti  muscles,  actions  of,  1023 

nerves  of,  1023 
Rectococcygeal  muscles,  1186 
Rectouterine  folds,  1260 
Rectovesical  excavation,  1152 

folds,  1154 

layer  of  pelvic  fascia,  422 
Rectovesicales  muscles,  1231 
Rectum,  1183 

ampulla  of,  1183 

anal  part  of,  1184 

development"  of,  1108 

Houston's  valves  of,  1183 

lymphatic  vessels  of,  711 

relations  of,  1 1 84 
Rectus  abdominis  muscle,  415 
sheath  of,  416 

capitis  anterior  muscle,  395 
action  of,  396 
nerves  of,  395 
anticus  major  muscle,  395 

minor  muscle,  395 
lateralis  muscle,  395 
action  of,  396 
nerves  of,  395 
posterior  major  muscle,  401 
action  of,  402 


1386 


INDEX 


Rectus    capitis    posterior   major 

muscle,  nerves  of,  402 

minor  muscle,  401 

action  of,  402 

nerves  of,  402 

femoris  muscle,  470 
actions  of,  471 
nerves  of,  471 

muscles  of  eyeball,  1022 
Recurrent    artery,    interosseous, 
597 
radial,  594 
tibial,  635 
ulnar,  596 

branches  from  deep  volar  arch, 
595 

laryngeal  nerve,  912 

nerve,  912 
Red  corpuscles,  503 

nucleus,  802 
Reflected  inguinal  ligament,  412 
Reflections  of  pleurae,  1088 
Reflex  paths,  spinal  intrinsic,  850 
Refracting  media  of  eye,  1018 
Regions  of  abdomen,  1147 
Reil,  island  of,  825 
Reissner,    vestibular    membrane 

of,  1054 
Renal  arteries,  610 

columns,  1221 

fascia,  1220 

impression,  1189 

pelvis,  1221,  1225 

plexus,  987 

pyramids,  1221 

sinus,   1221 

tubules,   1221 

veins,  679 

vessels,   afferent   and  efferent, 
1221,  1224 
Renes,  1215 

Reproduction  of  cells,  37 
Respiration,  mechanism  of,  407 
Respiratory  apparatus,  1071 
development  of,  1071 

nerve  of  Bell,  928,  933 

system,  1071 
Restiform  bodies  of  medulla,  973 
Rete  canalis  hypoglossi,  660 

foraminis  ovalis,  660 

testis,  1244 
Retia  venosa  vertebrarum,  668 
Reticular  lamina,  1058 

layer  of  skin,  1065 
Reticularis  alba,  784 

grisea,  784 
Retina,  1014 

central  artery  of,  571 

development  of,  1002 

fovea  centralis,  1015 

layers  of,  1015 

macula  lutea,  1015 

membrana  limitans  1017 

or  a  serrata,  1014 

structure  of,  1015 

supporting  frame-work  of ,  1017 
Retinacula  of  hip-joint,  334 

patellar.  340 

peroneal,  489 
Retrahens  aurem"  muscle,  1035 
Retrocecal  fossa,  1161 
Retroglandular  sulcus  of   penis, 

1249 
Retroperitoneal  fossae,  1158 
Retropharyngeal   lymph   glands, 
694 

space,  390 
Retropubic  pad,  1228 
Retrovesical  excavation,  1152 
Retzius,  colored  lines  of,  1120 
Rhinal  fissure,  external,  744 
Rhinencephalon,  744,  826 
Rhombencephalon,  51,  738,  767 
Rhombic  grooves,  740 

lip,  739 


Rhomboid  fossa,  798 

impression,  202 

ligament,  314 
Rhomboidei  muscles,actionsof  ,435 
nerves  of,  435 
variations  of,  435 
Rhomboideus  major  muscle,  434 

minor  muscle,  434 

occipitalis  muscle,  435 
Rhomboids,  nerve  to,  932 
Ribs,  123 

common  characteristics  of,  123 

development  of,  82 

false,  123 

floating  or  vertebral,  123 

ossification  of,  127 

peculiar,  125 

structure  of,  125 

true,  123 

vertebrochondral,  123 

vertebrosternal,  123 
Ridge,  ganglion,  51,  736 

supracondylar,  211 

trapezoid  or  oblique,  200 
Ridges,  bicipital,  209 
Right  atrium,  529 

auricle,  529 

auricular  appendix,  529 

coronary  plexus,  985 
veins,  642 

gastroepiploic  glands,  706 

ventricle,  531 
Rima  glotiidis,  1080 

of  mouth,  1110 

palpebrarum,  1025 

pudendal,   1265 
Ring,  femoral,  625 

subcutaneous,  410 

tympanic,  146 
Rings,  abdominal,  410,  418 

fibrous,  of  heart,  536 
Risorius  muscle,  385 
action  of,  385 
nerves  of,  385 
Rivinus,  ducts  of,  1136 

notch  of,  1038 
Rod-bipolars  of  retina,  1017 
Rod-granules  of  retina,  1017 
Rods  and  cones,  layer  of,  1017 

of  Corti,  1056 

of  retina,  1017 
Rolando,  fissure  of,  819 

substantia  gelatinosa  of,  753 

tubercle  of,  775 
Roller,  nucleus  of,  784 
Roof   plate   of   medulla   spinalis, 

133 
Root  of  lung,  1097 

of  penis,  1249 
Root-sheaths  of  hair,  1068 
Roots  of  spinal  nerves,  764,  916 

of  teeth,   1114 

of  zygomatic  process,  139 
Rosenmiiller,  fossa  of,  1141,  1142 

lymph  gland  of,  703 

organ  of,  1206,  1255 
Rostrum  of  corpus  callosum,  828 

sphenoidal,  149 

Rotary  joint,  285 

Rotation,  movement  of,  286 

Rotatores  muscles,  400 

action  of,  402 

nerves  of,  402 

spinEB  muscle,  400 
Round  ligament  of  liver,  1192 

of  uterus,  1261 
Rubrospinal  fasciculus,  870 
Ruffini,  corpuscles  of,  1061 
Rust-colored  layer  of  cerebellar 

cortex,  795 


Sac,  dental,  1123 
lacrimal,  1028 


Sac,  preputial,  1250 

Sacs  of  peritoneum,  1150,  1152 

Saccule,  laryngeal,  1080 

of  vestibule,  1051,  1052 
Sacculus,  1052 
Saccus  lacrimalis,  1028 

vaginalis,  1211 
Sacral  arteries,  lateral,  621 

artery,  middle,  613 

canal,  110 

cornua, 108 

crests,  107,  108 

foramina,  106,  108 

groove,  107 

hiatus,   107 

lymph  glands,  704 

nerves,  divisions  of,  924,  957 

nucleus  of  medulla  spinalis,  758 

plexus,  957 

sympathetics,  973 

tuberosity,  108 

veins,  673,  677 
Sacrococcvgeal  ligaments,  309 
Sacrogenital  folds,  1154,  1260 
Sacroiliac  articulation,  306 

ligaments,  307,  308 
Sacrosciatic  ligaments,  309 
Sacrospinalis  muscle,  397 
Sacro vertebral  angle,  106  '• 

Sacrum,  106 

alaof,  110 

apex  of,  110 

articulations  of.  111 

auricular  surface  of,  108 

base  of,  109 

ossification  of,  113 

structure  of ,  1 1 1 

variations  of ,  1 1 1 
Saddle-joint,  286 
Sagittal  fossa  of  liver,  1191 

sinuses,  654,  655 

sulcus,  131,  134,  136 

suture,  134,  178 
Salivary  glands,  1132 

development  of,  1102 
parotid,   1132 
structure  of,  1136 
sublingual,  1130 
submaxillary,  1135 
Salpingopalatine  fold,  1142 
Salpingopharyngeal  fold,  1142 
Salpingopharyngeus  muscle,  1143 
Salter,  incremental  lines  of,  1120 
Santorini,  cartilages  of,  1075 

duct  of,  1202 
Saphenous  nerves,  956,  963 

opening;  469 

veins,  669,  670 
Sarcolemma,  373 
Sarcomere,  375 
Sarcoplasm,  374 
Sarcostyles,  374 

Sarcous  elements  of  muscles,  375 
Sartorius  muscle,  470 
Scala  media  [cochlea],  1054 

tympani,  1051 

vestibuli,  1051 . 
Scalene  tubercle,  125 
Scaleni  muscles,  actions  of,  396 
nerves  of,  396 
variations  of,  396 
Scalenus  anterior  muscle,  396 

anticus  muscle,  396 

medius  muscle,  396 

pleuralis  muscle,  396 

posterior  muscle,  396 

posticus  muscle,  396 
Scalp,  lymphatic  vessels  of,  694 

skin  of,  378 
Scapha, 1034 
Scaphoid  bone,  221,  270 

fossa  of  sphenoid,  151,  180 
Scapula,  202 

acromion  of,  203 

coracoid  process  of,  207 


INDEX 


1387 


^Scapula,  glenoid  cavity  of,  207 

ligaments  of,  316 

ossification  of,  208 

spine  of,  203 

structure  of,  207 

surface  anatomy  of,  1326 
Scapular  arteries,  582 

circumflex  artery,  588 

nerve,  posterior,  932 

notch, 204 
Scapuloclavicular       articulation, 

315 
Scapus  or  shaft  of  hair,  1069 

pili,  1069 
Scarpa,  fascia  of,  408 

foramina  of,  162,  180 

ganglion  of,  1058 

triangle  of,  626 
Schindj'lesis,  284 
Schlemm,  canal  of,  1005 
Schreger,  lines  of,  1120 
Schultze,  primitive  fibrilla;  of,  725 
Schwann,  white  matter  of,  726 
Sciatic  artery,  620 

foramen,  309 

nerves,  959,  960 

notch,  235 

veins,   674 
Sclera,  1005 

structure  of,  1006 
Scleral  spur,  1007 
Sclerocorneal  junction,  1005 
Sclerotogcnoiis  layer,  80 
Sclerotome,  80 
Scrotal  arteries,  posterior,  619 

nerves,  posterior,  968 
Scrotum,  1237 

dartos  tunic  of,  1238 

integument  of,  1237 

nerves  of,  1239 

raphe  of,  1237 

vessels  of,  1239 
Sebaceous  glands,  1069 
Second  cuneiform  lione,  271 

metacarpal  bone,  228 

metatarsal  bone,  271 

nerve,  882 
Secondary  areolae  of  bone,  94 

dentin,   1120 

oocytes,  41 

sensory  fasciculus,  762 

spermatocytes,  43 

tympanic  membrane,  1040 
Secretion,  internal,  1269 
Segment,  internodal,  727 

of  Lantermann,  727 

medullary,  727 
Segmentation  of  cells,  37 

of  fertilized  ovum,  45 

nucleus,  45 
Segments,  primitive,  52 

spinal,  750 
Sella  turcica,  147,  190 
Semicanalis  m.  tensoris  tympani, 
145,  1042 

tuba^  audil)Vfr,  145,  1042 
Semicircular  canals,  1047,  1052 

ducts,  1052 
Semilunar  bone,  224 

fibrocartilages  of  knee,  342,  343 

ganglion  of  alidomen,  985 
of  trigeminal  nerve,  886 

lobules  of  cerebellum,  790 
Semimembranosus  muscle,  479 
actions  of,  4!S0 
nerves  of,  480 
variations  of,  479 
Seminal  duct,  1245 

vesicles,   1246 
Semispinalis  capitis  muscle,  400 

cervicis  muscle,  400 

colli  muscle,  400 

dorsi  muscle,  400 

muscles,  actions  of,  402 
nerves  of,  402 


Semitendinosus  muscle,  479 
actions  of,  480 
nerves  of,  480 
Sensations,    peripheral    termina- 
tions of  nerves  of,  1059 
Senses,  organs  of,  991 

special,   peripheral   organs   of, 
991 
Sensory  areas  of  cerebral  cortex, 
849 
decussation,  777 
pathways   from  spinal  cord  to 
brain,  851 
Septum,  aortic,  514 

canalis     musculoluharii,      145, 

1042 
crural,  626 
feniorale,  626 
inferius  of  heart,  512 
intermedium,  512 
interventricular,  534 
lucidum,  840 
mobile  nasi,  993 
nasi,  194 
of  nose,  194,  995 
orbital,  1026 
pectinifonne  penis,  1248 
pellucidum,  840 
primum,  512 
secundum,  512 
spuriu7n,b\Q 
subarachnoid,  877 
of  tongue,  1132 
transversum,  72 

of  semicircular  ducts,  1052 
urorectal,  1109 
ventricular,  512,  535 
ventriculorurn,  535 
Serosa,  or  false  amnion,  56 
Serous  glands  of  tongue,  1131 

pericardium,  526 
Serratus  anterior  muscle,  438 
actions  of,  439 
nerves  of,  439 
variations  of,  439 
magnus  muscle,  438 
posterior  inferior  muscle,  404 
variations  of,  404 
superior  muscle,  404 
variations  of,  404 
posticus  muscles,  404 
Sertoli,  cells  of,  1243 
Sesamoid  bones,  277 

cartilages,  993 
Seventh  nerve,  901 
Shaft  of  hair,  1069 
Sheath  or  Sheaths  of  arteries,  499 
carotid,  389 
crural,  625 

dentinal,  of  Neumann,  1119 
femoral,  625 
of  flexor  tendons  of  fingers,  449 

of  toes,  492 
mucous,  283 

of  tendons  around  ankle,  489 
on  back  of  wrist,  459 
in  front  of  wrist,  457 
of  rectus  abdominis  muscle,  416 
Shin  bone,  256 
Short  bones,  79 

calcaneocuboid  ligament,  354 
gastric  veins,  681  . 
plantar  ligament,  354 
saphenous  nerve,  963 
vein,  670 
Shoulder  blade,  202 
girdle,  200 
muscles  of,  439 

development  of,  371 
Shoulder-joint,  317 
bursse  near,  319 
movements  of,  319 
vessels  and  nerves  of,  319 
Sibson's  fascia,  1089 
Sight,  organ  of,  1000 


Sigmoid  arteries,  610 

cavity  of  radius,  220 
of  ulna,  215 

colon,  1182 

flexure,  1182 

mesocolon,  1153 

sinus,  657 

sulcus,  142 
Sinus  or  Sinuses,  aortic,  534 

basilar,  660 

cavernous,  658 

cervicalis,  67 

circular,  659 

confluence  of,  658 

coronary,  642 

costomediastinal,   1090 

cranial,  135  note 

of  dura  mater,  654 

of  epididymis,  1242 

of  external  jugular  vein,  647 

frontal,  138,  998 

intercavernous,  659 

laryngeal,  1080 

lateral,  657 

longitudinal,  654,  655 

maxillary,  159,  999 

of  Morgagni,  1143 

of  nose,  998 

occipital,  658 

of  pericardium,  526 

petrosal,  659 

petrosquamous,  658 

phrenicocostal,  1089 

pocularis,  1234 

prostatic,  1234 

pyriformis,  1142 

renal,  1221 

rhomboidalia,  51 

sagittal,  654,  655 

septum,  511 

sigmoid,  657    . 

sphenoidal,  149,  998 

sphenoparietal,  658 

straight,  655 

tentorial,  655 

tonsillaris,  67 

transverse,  657,  660 

urogenital,  1213 

of  Valsalva,  533,  534 

venarum,  528 

venosus,  508 
Sinus  or  Sinuses,  cavernosus,  658 

coronarius,  642 

durcE  matris,  654 

frontales,  998 

inter cavernosi,  659 

maxillaris,  159,  999 

occipitalis,  658 

paranasales,  998 

petrosus,  648,  659 

rectus,  655 

sagittalis,  654,  655 

sphenoidales,  998 

tarsi,  267 

transversus,  657 

venosus,  529 
sclera,  1005 
Sinusoids  of  Minot,  501 
Sixth  nerve,  899 
Skein,  or  spirem,  37 
Skeleton,  79 

development  of,  80 
Skene's  duct,  1213 
Skin,  1062 

appendages  of,  1066 
hairs,  1067 
nails,  1066 

sebaceous  glands,  1069 
sudoriferous  or  sweat  glands, 
1070 

arteries  of,  1066 

corium  or  cutis  vera,  1065 

development  of,  1066 

epidermis  or  cuticle,  1062 

furrows  of,  1062 


]388 


INDEX 


Skin,  lymphatic  capillaries  in,  684 
nerves  of,  1066 
papillary  layer  of,  1065 
reticular  layer  of,  1065 
stratum  corneum,  1062 

mucosum,  1062 
true  1065 
Skull,   128 

development  of,  83 
differences  in,  due  to  age,  196 
exterior  of,  178 
fossa  of,  190,  192 
interior  of,  189 
norma  basalis,  178,  179 
frontalis,  185 
lateralis,  182 
occipitalis,  185 
verticalis,  178 
sexual  differences  in,  197 
surface  anatomy  of,  1278 
tables  of,  195 

upper  surface  of  base  of,  190 
Skull-cap,  inner  surface  of,  189 
Slightly  movable  joints,  285 
Small  cardiac  vein,  642 
cavernous  nerves,  989 
intestine,  1168 

areolar  or  submucous   coat 

of,  1172 
circular  folds  of,  1173 
duodenum,  1168 
glands  of,  1176 
ileum,  1170 
jejunum,  1170 
lymphatic  nodules  of,  1 176 

vessels  of,  710 
Meckel's     diverticulum     of, 

1172 
mucous  membrane  of,  1173 
muscular  coat  of,  1172 
nerves  of,  1176 
Peyer's  glands  of,  1176 
serous  coat  of,  1172 
valvulce  conniventes  of,  1173 
vessels  of,  1176 
villi  of,  1174 
saphenous  vein,  670 
sciatic  nerve,  959 
wings  of  sphenoid,  151 
Smaller  occipital  nerve,  926 
Smallest  cardiac  veins,  643 
Smell,  organ  of,  992 
Soft  palate,  1112 

aponeurosis  of ,  1139 
arches  or  pillars  of,  1112 
muscles  of,  1 139 
Solar  plexus,  985 
Sole    of    foot,    muscles    of,    first 
layer,  491 
fourth  layer,  495 
second  layer,  493 
third  layer,  493 
Soleus  muscle,  483 
actions  of,  483 
nerves  of,  483 
variations  of,  483 
Solitary  cells  of  medulla  spinalis, 
758 
glands,  1176 
Somatic  cells,  35 

fibers  of  spinal  nerves,  920 
layer  of  tnesoderm,  50 
Somatopleure,  50 
Space  or  Spaces,  of  angle  of  iris, 
1009 
of  Burns,  389 
corneal,  1008 
interpleural,  1090 
of  Fontana,  1009 
intercostal,  123 
interglobular,  1120 
of  Nuel,  1058 
popliteal,  631 
retropharyngeal,  390 
subarachnoid,  876 


Space  or  Spaces,  suprasternal,  389 
Spatia  zonular  is,  1019 
Spatium  perichorioideale,  1005 
Spermatic  artery,  internal,  611 
canal,  418 
cord,  1239 

structure  of,  1239 
fascia,  external,  411,  1238 
plexus  of  nerves,  987 
veins,  678 
Spermatids,  43,  1243 
Spermatoblasts,  1243 
Spermatocjtes,  43,  1243 
Spermatogonia,  43,  1243 
Spermatozoon  42,  1243 

body  or  connecting  piece  of,  42 
formation  of,  1243 
head  of,  42 
neck  of,  42 
perforator  of,  42 
tail  of,  43 
Sphenoethmoidal  recess,  195,  994 

suture,  190 
Sphenofrontal  suture,  182,  190 
Sphenoid  bone,  147 

articulations  of,  153 
body  of,  147 
ossification  of,  152 
pterygoid  processes  of,  151 
wings  of,  149,  151 
Sphenoidal  air  sinuses,  149,  998 
conchse,  152 
crest,  149 

process  of  palatine  bone,  169 
of  septal  cartilage  of  nose, 
993 
rostrum,  149 
spine,  150,  180 
turbinated  processes,  152 
Sphenomandibular  ligament,  297, 

388 
Sphenomaxillary  fissure,  184 

fossa,  185 
Sphenopalatine  artery,  562 
foramen,  168 
ganglion,  891 
nerves,  890 
notch,  169 
Sphenoparietal  sinus,  658 

suture,   182 
Sphenosquamosal  suture,  182 
Sphenozygomatic  suture,  182 
Sphincter   ani   externus   muscle, 
425 
internus  muscle,  426 
pupillae  muscle,  1013 
recti  muscle,  424 
urethriB  membranaceaj  muscle, 

429, 431 
vaginse  muscle,  430 
Spigelian  lobe  of  liver,  1192 
Spina  helicis,  1034 
scapulw,  203 
vestibuli,  510 
Spinal  accessory  nerve,  913 
arteries,  579 
bulb,  767 
column,  96 
cord,  749 
dura  of,  875 

pathways  from  brain  to,    870 
pia  of,  879 

sensory   pathways   from,     to 
brain,  851 
ganglia,  917 
lemniscus,  762 
nerves,  916 

composition  and  central  con- 
nections of,  849 
connections  with  sympa- 
thetic, 920 
development  of,  1 19 
divisions  of,  921,  925 
fibers  of,  920 
points  of  emergence  of,  916 


Spinal  nerves,  roots  of,  764,  9161 
size  and  direction  of,  917 
structure  of,  920 

reflex  paths,  intrinsic,  850 

segments,  750 
Spinalis  capitis  muscle,  400 

cervicis  muscle,  400 

colli  muscle,  400 

dorsi  muscle,  399 
Spindle,  achromatic,  37 

aortic,  547 

neuromuscular,  1061 

neurotendinous,  1061 
Spine  or  Spines,  ethmoidal,  1471 
190 

of  frontal  bone,  136 

iliac,  234 

ischial,  235 

mental,  172 

nasal,  158,  163,  167,  180,  187 

pubic,  236 

of  scapula,  203 

sphenoidal,  150,  180 

suprameatal,  145,  183 

of  tibia,  256 

trochlear,  137 
Spinoglenoid  ligament,  317 
Spinoolivary  fasciculus,  854 
Spinoquadrigeminal      system     of 

Mott,  762 
Spinotectal  fasciculus,  762,  S54 
Spinothalamic  fasciculus,  762 
Spinous  process  of  a  vertebra,  96 
Spiral  canal  of  modiolus,  1051 

ligament,  1054 

line  of  femur,  245 

organ  of  Corti,  1056 

thread  of  spermatozoon,  43 

tube  of  kidney,  1223 
Spirem  or  skein,  37 
Splanchnic   fibers   of   spinal 
nerves,  920 

layer  of  mesoderm,  50 

nerves,  981 
Splanchnology,  1071 
Splanchnoj'leure,  50 
Spleen  or  lien,  1282 

accessory,  1283 

bloodvessels  of,  1285 

development  of,  1282 

lymphatic  cainilarics  in,  686 
nodulus  of,  1285 
vessels  of,  711 

Malpighian  bodies  of,  1285 

relations  of,  1282 

size  and  weight  of,  1283 

structure  of,  1283 

supernumerary,  1283 

surface  marking  of,  1 320 
Spienial  center  of  ossification,  175 
Splenic  artery,  605 

distribution  of,  1285 

cells,  1284 

glands,  706 

flexure  of  colon,  11  SO 

plexus,  986 

pulp, 1284 

vein,  681 
Splenii  muscles,  actions  of,  397 

nerves  of,  397 
Splenium  of  corpus  callosum,  828 
Splenius  capitis  muscle,  397 

cervicis  muscle,  397 
variations  of,  397 

colli  muscle,  397 
Spongioblasts,  733 
Spongioplasm,  36 
Spring  ligament,  356 
Spur  of  malleus,  1044 

scleral,  1007 
Squama,  frontal,  135 
occipital,  129 
temporal,  139 
Squamosal  suture,  183 
Stahr,  middle  gland  of,  697 


INDEX 


1389 


ialks,  optic,  742,  1001 

of  thalamus,  811 
Stapedius  muscle,  1046 
Stapes,  1045 

annular  ligament  of,  1045 

development  of,  1033 
Stellate  ligament,  299 

veins  of  kidnej-,  1224 
Stensen,  duct  of,  1134 

foramina  of,  126,  180 
Stephanion,  183,  198 
Sternal  angle,  121 

end  of  clavicle,  202 

foramen,  121 

furrow,  1307 

glands,  715 

plate,  83 
Sternalis  muscle,  437 
SternebrjB,  120 
Sternoclavicular  articulation,  313 

surface  anatomy  of,  1328 
Sternoclavicularis  muscle,  438 
Sternocleidomastoid  artery,  552, 

556 
Sternocleidomastoideus     muscle, 
390 
variations  of,  390 
Sternocostal  ligaments,  302 

surface  of  heart,  528 
Sternohyoid  muscle,  393 
Sternohyoideus  muscle,  393 
variations  of,  393 
ternomastoid  artery,  552,  556 

muscle,  390 
Sternopericardiac  ligaments,  526 
Sternothyreoideus  muscle,  393 

variations  of,  394 
Sternothvroid  muscle,  393 
Sternum,  119 

articulations  of,  123 

development  of,  83 

ossification  of,  121 

structure  of,  121 
Stomach,  1161 

bed,  1162 

body  of,  1163 

cardiac  glands  of,  1166 
orifice  of,  1161 

component  parts  of,  1163 

curvatures  of,  1162 

development  of,  1103 

fundus  of,  1163 
glands  of,  1166 

incisura  angularis,  1162 

interior  of,  1162 

lymphatic  vessels  of,  710 

mucous  membrane  of,  1166 

muscular  coat  of,  1164 

nerves  of,  1167 

openings  of,  1161 

position  of,  1163 

pyloric  antrum,  1162,  1163 
glands,  1166 
orifice,  1162 
valve,  1164 

serous  coat  of,  1164 

shape  and  position  of,  1161 

structure  of,  1164 

subdivisions  of,  1163 

sulcus  inlermedius,  1162 

surface  marking  of,  1317 

surfaces  of,  1162 

teeth,  1117 

vessels  of,  1167 
Stomodeum,  1101 
Stratiform  fibrocartilage,  282 
Stratum  cinereum,  806 

compacium  [decidua],  59 

corneum,  1062 

dorsale,  812 

germinativum,  1063 

granulosum,  1063 

intermedium  [choroid],  1010 

lemnisci,  806 

lucidum,  1063 


'Iratum.  opticum  [retina],  1015 
[superior  colliculus],  806 

spongiosum  [decidua],  60 

zonale,  806 
Streak,  primitive,  47 
Stria,  longitudinal,  827 
Striate  arteries,  573 

veins,  inferior,  653 
Striated  muscle,  lymphatic   capil- 
laries in,  684 
Stripe  of  Hensen,  1058 
Striped  muscle,  373 
Stroma  of  iris,  1013 

of  kidney,  1225 

of  ovary,  1256 
Styloglossus  muscle,  1130 
Stylohyal  part  of  styloid  process^ 

145 
Stylohyoid  ligament,  392 

muscle,  392 

nerve,  from  facial,  905 
Stylohyoideus  muscle,  392 

variations  of,  392 
Styloid  process  of  fibula,  260 
of  radius,  220 
of  temporal  bone,  145,  181 
of  ulna,  218 
Stylomandibular  ligament,  388 
Stylomastoid  artery,  557 

foramen,  144,  181 
Stylopharyngeus  muscle,  1143 
Subanconeus  muscle,  445 
Subarachnoid  cavity,  876 

cisterns!,  876 

septum,  877 

space,  876 
Subarcuate  fossa,  143 
Subcallosal  gyrus,  827,  869 
Subcardinal  veins,  520 
Subclavian  arteries,  575 
first  part  of  left,  577 

of  right,  576 
second  portion  of,  577 
surface  anatomy  of,  1290 

marking  of,  1303 
third  portion  of,  577 

triangle,  394,  565 

vein,  664 
Subclavius  muscle,  438 

variations,  438 
Subcostal  arteries,  601 

zone,  1148 
Subcostales  muscles,  403 
Subcrureus    or    articularis    genu 

muscle,  471 
Subcutaneous  inguinal  ring,  410 
Subdural  cavity,  875 
Subepithelial    plexus    of    cornea, 

1009 
Subfrontal  gyre,  822 
Subinguinal  lymph  glands,  702 
Sublingual  artery,  553 

gland,  1136 
Sublobular  veins,  1196 
Submaxillary  artery,  555 

duct,  1135 

ganglion,  898 

gland,  1135 

lymph  glands,  697 

triangle,  392,  564 
Submental  artery,  555 

lymph  glands,  697 

triangle,  392 
Subnasal  point,  198 
Suboccipital  muscled,  401 

triangle,  402,  578 
Subparietal  sulcus,  823 
Subperitoneal  connective  tissue, 

418 
Subpleural    mediastinal    plexus, 

584 
Subpubic  ligament,  310 
Subsartorial  plexus,  956 
Subscapular  angle,  203 

artery,  588 


Subscapular  fascia,  440 

fossa,  202 

nerves,  933 
Subscapularis  muscle,  440 
Subserous  areolar  tissue,  1150 
Substantia  adamantina,  1120 

alba,  758 

eburnea,  1119 

ferruginea,  800 

gelatinosa  centralis,  754 
of  Rolando,  753 
nerve  cells  in,  758 

grisea  centralis,  753 

innominata  of  Meynert,  837 

nigra,  802 

ossea,   1120 

perforata  anterior,  827 

propria  [cornea],  1007 
Subthalamic    tegmental    region, 

812 
Suctorial  pad,  384 
Sudoriferous  glands,  1070 
Sulci    and    fissures    of    cerebral 
hemisphere,  819 
development  of,  747 

of  medulla  oblongata,  767 
spinalis,  752 
Sulcus,  anterior  longitudinal,  of 
heart,  527 

antihelicis  transversus,  1034 

arterice  vertebralis,  99 

basilaris,  785 

calcaneal,  263 

central,  819 

centralis  [Rolandi],  819 

cingulate,  820 

cinguli,  820 

circular,  821,  825 

circularis,  821 
comece,  1007 

coronary,  of  heart,  526 

frontal,  821 

horizontal,  of  cerebellum,  789 

inlermedius  [stomach],  1162 

intraparieta),  822 

lateral  cerebral,  801 

limitans  [rhomboid  fossa],  799 

lunatus,  823  note 

malleolar,  262 

medial  frontal,  of  Eberstaller, 
822 

median,  of  rhomboid  fossa,  799 
of  tongue,  1125 

medianus  posterior,  752 

of  Monro,  741,  742,  816 

occipital,  823 

oculomotor,  801 

olfactory,  822 

orbital,  822 

paramedial,  822 

postcentral,  822 

posterior    longitudinal,    of 
heart,  527 

preauricular,  of  ilium,  234 

precentral,  821 

radial,  211 

retroglandular,  1249 

sagittalis,  131,  134,  136 

sigmoid,  142 

spirales,  1055 

subparietal,  823 

tali,  267 

temporal,  824 

terminal,  of  right  atrium,  529 
of  tongue,  1125 

tubw  audit ivw,  150,  181 

tympanic,  145,  1037,  1039 

vallecula,  790 
Supercilia,  1025 

Superciliary  arches,  135,  178,  183 
Superficial    antero-lateral    fasci- 
culus, 854 

cervical  artery,  582 
lymph  glands  697 
muscle,  387 


1390 


INDEX 


Superficial  cervical  nerve,  927 

epigastric  artery,  629 

external  pudendal  artery,  629 
pudic  artery,  623 

iliac  circumflex  artery,  629 

long  plantar  ligament,  354 

palmar  arch,  598 

perineal  artery,  619 

peroneal  nerve,  966,  968 

Sylvian  vein,  652 

temporal  artery,  558 
vein,  645 

transverse  ligament  of  fingers, 
461 
perineal  muscle,  427,  430 

volar  artery,  594 
Superficialis  volae  artery,  594 
Superfrontal  gyre,  821 
Superior  articular  arteries,  633 

calcaneocuboid  ligament,  354 

cerebellar  peduncles,  792 

constrictor  muscle,  1143 

dental  nerve,  890 

intercostal  artery,  585 

lingualis  muscle,  1130 

longitudinal  sinus,  654 

maxillary  nerve,  889 

medullary  velum,  793 

nasal  concha,  156 

nuchal  line,  130 

oblique  muscle,  1022 

orbital  fissure,  151,  189 

petrosal  sinus,  659 

profunda  artery,  59 1 

sagittal  sinus,  654 

semicircular  canal,  1049 

tarsal  plate,  1025 

thoracic  artery,  587 

tibiofibular  articulation,  348 

tympanic  artery,  561 

vesical  artery,  615 

vocal  cords,  1079 
Supernumerary  spleen,  1283 
Supinator  brevis  muscle,  454 

longus  muscle,  451 

muscle,  454 
Supra-acromial  nerves,  928 
Supporting  cells  of  Hensen,  1058 
of  Sertoli,  1243 

frame-work  of  retina,  1017 
Supracallosal  gyrus,  827 
Supraclavicular    branches    of 
brachial  plexus,  932 

nerves,  928 
Supraclavicularis  muscle,  390 
Supracondylar  process,  212  note 

ridges,  211 
Supracostalis  muscle,  403 
Supraglenoid  tuberosity,  207 
Suprahyoid  aponeurosis,  392 

artery,  553 

lymph  glands,  697 

muscles,  391 

triangle,  392,  565 
Supramarginal  gyrus,  823 
Supramastoid  crest,  139 
Suprameatal  spine,  145,  183 

triangle,  140,  183 
Supraorbital  artery,  569 

foramen,  136,  186,  189 

margin,  135 

nerve,  887 

notch, 136, 186, 189 

vein,  644 
Suprarenal  arteries,  610,  612 

glands,  1278 

,   development  of,  1278 
lymphatic  vessels  of,  711- 
nerves  of,  1280 
vessels  of,  1280 

impression,  1191 

plexus,  987 

veins,  679 
Suprascapular  artery,  582 

ligament,  317 


Suprascapular  nerve,  932 
Supraspinal  ligament,  290 
Supraspinatous  fascia,  440 

fossa,  203 
Supraspinatus  muscle,  440 
Supraspinous  ligament,  290 
Suprasternal  nerves,  298 

space,  389 
Supratonsillar  fossa,  1138 
Supratrochlear  foramen,  212 

nerve,  888 
Sural  arteries,  633 

cutaneous  nerve,  medial,  962 
nerve,  903 
Surface    anatomy     and     surface 

markings  of  abdomen,  1315 
accessory  nerve,  1303 
acromioclavicular  joint, 1328, 

1331 
adductor  canal,  1343 
ankle-joint,  1338,  1343 
anterior  tibial  artery,   1341, 

1346 
aorta,  abdominal  1313,  1321 

ascending,  1312 
aortic  arch,  1312 
axillary  artery,  1331,  1334 

nerve,  1336 
back,  1303 
bones  of  cranium,  1291 

of  lower  extremity,  1336 

of  thorax,  1308 

of  upper  extremity,  1325 
brachial  artery,  1331,  1335 

plexus,  1303,  1331 
brain,  1292 

Bryant's  triangle,  1343 
calcaneus,  1337 
carpal  bones,  1327 
caruneula  lacrimalis,  1299 
cecum,   1319 
celiac  artery,  1322 
cerebellum,' 1292 
cerebral  hemisphere,  1292 
cervical     cutaneous     nerve, 

1303 
clavicle,  1326 
colon,  ascending,  1319 

descending,  1320 

iliac,  1320 

transverse,  1319 
common  carotid  artery,  1302 

iliac  artery,  1322 

peroneal  nerve,  1342,  1346 
deep  peroneal  nerve,  1346 
deltoideus  muscle,  1329 
diaphragm,  1309 
dorsalis  .pedis  artery,   1341, 

1346 
duodenum,  1319 
ear,  1300 
elbow-joint,  1331 
esophagus,  1311 
external  carotid  artery,  1302 

iliac  artery,  1322 
■  maxillary  arterv,  1294 
eye,  1299 
facial  nerve,  1303 
femoral  arterv,  1341,  1346 

triangle  1343 
femur,  1336 
fibula,  1337 
fissures  of  brain,  1293 
fold  of  groin,  1313 
frontal  sinus,  1294 
gall-bladder,  1320 
gluteal  arteries,  1343 

fold,  1336 
great  auricular  nerve,  1303 
head  and  neck,  1287 
heart,  1311 

coronary  sulcus,  1311 

longitudinal  sulcus,  1311 

orifices  of,  1311 
Hesselbach's  triangle,  1321 


Surface     anatomy    and    surface- 
markings    of    hip    bones^ 

1336 
hip-joint,  1338,  1343 
humeral    circumflex    artery^ 

1335 
humerus,   1326 
hyoid  bone,  1301 
ileocolic  junction,  1319 
iliac  arteries,  1322 

furrow,  1313 
inferior,     epigastric     artery„ 
1321 

vena  cava,  1312 
infrasternal  notch,  1307 
inguinal    rings    and     cane 

1315 
innominate  artery,  1312 

veins,   1312 
internal    mammary    artery, 

1312 

pudendal  artery,  1343 
intestines,  1319,  1320 
joints  of  fingers,  1328 

of  foot,  1343 
jugular  notch,  1307 

veins,  1303 
kidneys,  1320 
knee-joint,  1338 
lacrimal  puncta,  1299 

sac,  1299 
larynx,  1299,  1301 
lateral  plantar  artery,  1346 

thoracic  artery,  1334 

ventricle  of  brain,  1294 
latissimus  dorsi,  1328,  1333 
left  common  carotid  artery 

in  thorax,  1312 
lesser  occipital  nerve,  1303 
linea  semilunaris,  1313 
liver,  1314,  1320 
lower  extremity,  1336 
lumbar  triangle,  1313 
lungs,  1310 
mamma,  1308 
maxillary  sinus,  1294 
medial  plantar  artery,  1346 
median  nerve,  1335 
medulla  spinalis,  1306 
mesenteric  arteries,  1322 
metacarpal  bones,  1327 
middle     meningeal     artery^ 

1294 
mouth,  1296 

mucous       sheaths       around 
ankle,  1343 
of  wrist  and  hand,  1334 
muscles  of  abdomen,  1315 

of  arm,  1328 

of  buttock,  1338 

of  foot,  1340 

of  forearm,  1329 

of  head   and   neck,    1288^ 
1289,  1301 

of  hand,  1331 

of  leg,  1340 

of  thigh,  1338 
nasal  part  of  pharynx,  1299 
nasolacrimal  duct,  1299 
neck,  1301 
Nelaton's  line,  1342 
nose,  1296 
palatine  arches,  1297 
palmar  or  volar  arches,  1335- 
palpebral  fissure,  1299 
pancreas,  1315,  1320 
parotid  duct,  1295 

gland,  1295 
patella,  1337 

pectorales  muscles,  1328,1333 
pelvis,  1336 
perineum,  1322 
peroneal  artery,  1346 

nerves,  1346 
phalanges  of  foot,  1338 


INDEX 


1391 


^Surface    anatomy     and     surface 

markings  of    phalanges   of 

hand, 1327 
phrenic  nerve,  1303 
plantar  arch,  1346 

arteries,  1346 
pleurae,  1309 
plica  semilunaris,  1299 
popliteal  artery,  1341 

fossa,  1343 
posterior  tibial  artery,  1342, 

1346 
profunda  brachii  artery,  1335 

femoris  artery,  1346 
pupU, 1299 
radial  artery,  1331,  1335 

nerve,  1336 
radioulnar  joints,  1328 
radius,  1327 

rectum  and  anal  canal,  1322 
Reid's  base  line,  1291 
renal  arteries,  1322 
sacroiliac  joint,  1343 
saphenous  veins,  1346 
scapula,  1326 
scapular    circumflex    aitery, 

1335 
sciatic  nerve,  1346 
serratus  anterior  muscle,  1328 
shoulder-joint,  1328 
spinal  nerves,  1307 
spleen,  1320 

sternal  angle,  1307,  1309 
sternoclavicular  joint,  1328 
sternocleidomastoideus 

muscle,  1289 
stomach,  1317 
striae    gravidarum    or    albi- 

cantes,  1313 
subclavian  artery,  1303, 1331 
subdural   and   subarachnoid 

cavities,  1306 
submaxillarj'  gland,  1303 
subscapular  artery,  1334 
supraclavicular  nerves,  1303 
superior  vena  cava,  1312 
talus,  1337 
tarsus  and  foot,  1337 
temporomandibular       joint, 

1288 
tendinous  inscriptions  of  rec- 
tus abdominis,  1313 
thoracoacromial  artery,  1334 
thorax,  1307 
tibia,  1337 
tibial  nerve,  1346 
tongue,  1297 
tonsil,  1298 
trachea,  1301, 1311 
transverse  sinus,  1294 
trapezius,  1332 
trigeminal  nerve,  1295 
tympanic  antrum,  1301 

membrane,  1300 
ulna,  1326 
ulnar  artery,  1335 

collateral  arteries,  1335 

nerve,  1331,  1335 
umbilicus,  1313,  1315 
upper  extremity,  1325 
urogenital    organs,     female, 
1323 
male,  1323 
vermiform  process,  1319 
vertebral  column,  1303 
volar  or  palmar  arches,  1335 
wrist  and  hand,  1327 
wrist-joint,  1327,  1331 
Suspensory  ligament  of  axilla,  436 
of  eye,  1025 
of  lens,  1018 
of  ovary,  1254 
of  penis,  1249 
Sustentacular   fibers    of    MliUer, 
1017 


Sustentaculum  lienis,  1158 

tali,  266 
Sutura  dentala,  284 

harmonia,  284 

limbosa,  284 

notha,  284 

serrata,  284 

squamosa,  284 

vera,  284 
Sutural  bones,  156 
Suture,  coronal,  178,  183 

frontal,  178  ^ 

frontoethmoidal,  190 

frontomaxillary,  189 

lambdoidal,  132,  135,  178,  183 

metopic,  135 

occipitomastoid,  183 

parietomastoid,  183 

petrooccipital,  193 

petrosquamous,  142,  145 

sagittal,  178 

sphenoethmoidal,  190 

sphenofrontal,  182,  190 

sphenoparietal,  182 

sphenopetrosal,  190 

sphenosquamosal,  182 

sphenozygomatic,  182 

squamosal,  183 

zygomaticofrontal,  182 

zygomaticomaxillary,  189 

zygomaticotemporal,  182 
Sweat  glands,  1070 
Syh-ian  fissure,  747 

fossa,  747 

veins,  652,  653 
Sylvius,  aqueduct  of,  766, 767, 806 

fissure  of,  819 
Sympathetic     fibers     of     spinal 
nerves,  920 

nerves,  968 

connections      with       spinal 
nerves,  976 

plexuses,  984,  985,  987 

system,  cephalic  portion  of,  977 
cephalic  portion  of,  977 
cervical  portion  of,  978 
pelvic  portion  of,  984 
thoracic  portion  of,  981 

trunks,  976 
Symphysis  of  mandible,  127 

ossium  pubis,  310 

pubis,  310 

sacrococctjoea,  309 
Synarthroses,  286 
Synchondrosis,  284 

neurocentral,  112 
Syncytiotrophoblast,  47 
Syncytium,  47 
Syndesmology,  279 
Syndesmosis,  285 

tibiofibular  is,  348 
Synergic  muscles,  362 
Synovia,  283 
Synovial    membrane,    282.      See 

also  Individual  Joints. 
Systemic  circulation,  497 

veins,  641 


Tables  of  the  skull,  79 
Tactile  corpuscles  of  Golgi  and 
Mazzoni,  1061 
of  Grandrv,  1060 
of  Pacini,  1060 
of  Ruffini,  1061 
of    Wagner    and    Meissner, 
1061 
discrimination,  fibers  of,  854 
Tcenia  pontis,  785 

semicircularis,  837,  869 
thalami,  809 
ventriculi  guarti,  797 
TcenioB  coli,  1185 


Taeniae  of  fourth  ventricle,  797 
of  muscular  coat  of  large  intes- 
tine, 1177 
Talocalcaneal  articulation,  352 
Talocalcaneonavicular     articula- 
tion, 353 
Talotibial  ligaments,  351 
Talus,  266 

ossification  of,  275 
Tangential     fibers     of     cerebral 

cortex,  846 
Tapetum  of  choroid,  1010 
of  corpus  callosum,  829 
Tarsal  arteries,  637 
bones,  263 
glands,  1026 
plates,  1025 
Tarsi  of  eyelids,  1025 
Tarsometatarsal      articulations, 

358 
Tarsus,  263 

articulations  of,  352 
inferior,  1025 
ossification  of,  275 
superior,  1025 
surface  markings  of,  1343 
synovial  membranes  of,  358 
Taste  fibers,  867 
nerves  of,  992 
organ  of,  991 
Taste-buds,  991 
Tectorial    membrane    of    ductus 

cochlearis,  1058 
Tectospinal  itasciculus,  871 
Teeth,  1112 
bicuspid,  1118 
canine,  1117 
cement  or  cnista  petrosa  of, 

1120 
crown  of,  1116,  1117 
cutting,  1115 
deciduous,  1118 
dental  canaliculi  of,  1119 
dentin  of,  1119 
development  of,  1121 
enamel  of,  1120 
eruption  of,  1124 
eye,  1117 

general  characters  of,  1114 
incisive,  1115 
incisors,  1115 
ivory  of,  1119 
milk,  1118 
molar,  1118 
multicuspid,  1118 
necks  of,  1114 
permanent,  1115 
successional,  1124 
superadded,  1124 
premolar,  1118 
pulp  cavity  of,  1118 
roots  of,  1114 
stomach,  1117 
structure  of,  1118 
substantia  adamantina  of,  1120 
eburnea  of,  1119 
ossea  of,  1120 
temporary,  1118 
wisdom,  1118 
Tegmen  tympani,  124,  1038 
Tegmental  part  of  pons,  786 
Tegmentum,  802 
Tela  chorioidea  [fourth  ventricle], 
798 
[third  ventricle],  841 
Telencephalon,  743,  817 
Telophase  of  karyokinesis,  38 
Temperature,  impulses  of,  853 
Temporal  arteries,  558,  561 
bone,  138 

articulations  of,  147 
mastoid  portion  of,  141 
ossification  of,  145 
petrous  portion  of,  142 
pyramid  of,  142 


1392 


Temporal  bone,  squama  of,  139 
structure  of,  145 
tympanic  part  of,  145 
fascia,  386 
fossa,  183 
gyri,  824 

lines,  134,  136,  178,  183 
lobe,  823 
muscle,  386 

nerves  of  auriculotemporal,  895 
deep,  895 
of  facial,  905 
operculum,  825 

process  of  zygomatic  bone,  166 
veins,  645 
Temporalis  muscle,  386 
Temporary  teeth,  1118 
Temporomalar  nerve,  889 
Temporomandibular  articulation, 
297 
surface  anatomy  of,  1288 
Temporomaxillary  vein,  646 
Tendinous  arch  of  pelvic  faseia, 
422 
inscriptions  of  rectus  abdomi- 
nis muscle,  416 
Tendo  Achillis,  483 
calcaneus,  483 
oculi,  468 
Tendon,  action  of  muscle  pull  on, 
364 
central,  of  diaphragm,  406 
conjoined,  of  internal  oblique 
and  transversalismuscles,414 
of  conus  arteriosus,  531 
superior,  of  Lockwood,  1022 
of  Zinn,  1022 
Tendons,  376 

on  back  of  wrist,  relations  of, 
458 
Tendril  fibers  of  cerebellum,  796 
Tenon,  capsule  of,  1037 
Tensor  fasciae   latse  muscles,  ac- 
tions of,  478 
nerves  of,  478 
palati  muscle,  1139 
tarsi  muscle,  380 
tympani  muscle,  1046 

semicanal  for,  145,  1042 
veli  palatini  muscle,  1139 
Tenth  nerve,  910 
Tentorial  sinus,  655 
Tentorium  cerebelli,  874 
Teres  major  muscle,  442 
minor  muscle,  441 

variations  of,  442 
Terminal  crest  of  right  atrium, 
529 
sulcus  of  right  atrium,  529 
vein,  653 

ventricle,  735,  754 
Testes,  1236,  1240 
•    appendages  of,  1242 
coni  vasculosi  of,  1244 
coverings  of,  1236 
descent  of,  1210 
development  of,  1210 
ductuli  efferentes,  1244 
ductus  deferens,  1245 
guhernaculum  testis,  1211 
lobules  of,  1243 
lymphatic  capillaries  of,  687 

vessels  of,  713 
mediastinum  testis,  1243 
rete  testis,  1244 
structure  of,  1243 
tubuli  recti,  1244 

seminiferi,  1243 

tunica  alhuginea,  1242 

vaginalis,  1242 

vasculosa,  1242 

Thalamencephalon,  808 

Thalami,  742,  808 

connections  of,  810 

development  of,  742 


INDEX 

Thalami,    intermediate    mass  of, 
742, 743,  809 

stalks  of,  811 

structure  of,  810 

surfaces  of,  808,  809 
Thalamic  tract  of   cranial  nerves, 

805 
Thalamomammillary     fasciculus, 

839 
Thebesius,  foramina  of,  530 

valve  of,  530,  642 

veins  of,  643 
Thenar  eminence,  456 
Thigh  bone,  242 

fascia  lata  of,  468 
superficial,  468 

muscles  of,  467 
Third  cuneiform  bone,  271 

metacarpal  bone,  228 

metatarsal  bone,  274 

nerve,  884 

trochanter,  246 

ventricle  of  brain,  815 
Thoracic  aorta,  598 

peculiarities  of,  599 

arteries,  587,  588 

axis,  588 

cardiac  nerves,  912 

duct,  690 

nerves,  divisions  of,  923,  944 

portion  of  gangliated  cord,  981 

vertebrae,  102 
Thoracoacromial  artery,  588 
Thoracodorsal  nerve,  934 
Thoracoepigastric  vein,  670 
Thoracolumbar  sympathetics,  974 
Thorax,  117 

boundaries  of,  117 

cavity  of,  524 

lymph  glands  of,  715 

lymphatic  vessels  of,  715,  716 

mechanism  of,  304 

muscles  of,  402 

openings  of,  117,  118,  524 
parts  passing  through,  524 

skeleton  of,  117 

surface  anatomy  of,  1307 
markings  of,  1308 
Thromboplastin,  505 
Thumb,  carpometacarpal  articu- 
lation of,  330 
Thymus,  1273 

development  of,  1273 

glands,  1273 

lymphatic  capillaries  in,  686 
vessels  of,  719 

nerves  of,  1275 

structure  of,  1274 

vessels  of,  1275 
Thyreoarytaenoideus       muscle, 

1083 
Thyreohyoideus  muscle,  394 
action  of,  394 
nerves  of,  394,  916 
Thyreoidea  ima  artery,  549 
Thyroarytenoid  ligaments,  1080 

muscle,  1083 
Thyrocervical  trunk,  581 
Thyroepiglottic  ligament,  1078 

muscle,  1083 
Thyroglossal  duct,  1126 
Thyrohyals  of  hyoid  bone,  178 
Thyrohyoid  ligaments,  1077 

membrane,  1076 

muscle,  394 
Thyroid  arteries,  552,  581 

axis,  581 

body, 1269 

cartilage,  1073 

foramen,  237 

gland,  1269 

development  of,  1270 

isthmus  of,  1270 

lobes  of,  1269 

lymphatic  capillaries  in,  686 


I 


1270 


Thyroid    gland,    lymphatic 
sels  of,  697 
nerves  of,  1271 
pyramidal  lobe  of 
structure  of,  1271 
vessels  of,  1271 
notch,  superior,  1073 
veins,  649,  666 
Thyroids,  accessory,  1270 
Tibia,  256 

condyles  of,  256 
ossification  of,  260 
spine  of,  256 
surface  anatomy  of,  133' 
tuberosity  of,  256 
Tibial  artery,  anterior,  634 
branches  of,  635 
peculiarities  of,  635 
surface  marking  of,  1337 
posterior,  637 
branches  of,  038 
peculiarities  of,  638 
surface  marking  of,  1346 
recurrent,  635 
collateral    ligament    of    knee 

joint,  341 
nerve,  960 

anterior,  965 
surfaces  of  femur,  248 
veins,  672 
Tibialis  anterior  muscle,  480 
anticus  muscle,  480 
posterior  muscle,  485 
Tibiofacialis  muscle,  480 
Tibiofibular  articulation,  348 
ligament,  middle,  348 
syndesmosis,  348 
Tibionavicular  ligament,  350 
Tibio tarsal  articulation,  349 
Tomes'  fibers,  1119 
Tongue,  1125 

development  of,  1102 
dorsum  of,  1125 
frenulum  of,  1125 
glands  of,  1131 
lymph  gland  of,  696 
lymphatic  vessels  of,  696 
mucous  membrane  of,  1131 
muscles  of,  1128 

actions  of,  1131 
nerves  of,  1132 
papillae  of,  1126 
septum  of,  1132 
structure  of,  1131 
vessels  of,  1132 
Tonsilla  cerebelli,  791 
Tonsillce  intestinales,  1176 

palatinw,  1137 
Tonsillar  artery,  555 

nerves  from  glossopharvngeal, 

909 
sinus,  1138 
Tonsils,  1137 
lingual,  1131 
palatine,  1137 

development  of,  1103 
lymphatic  vessels  of,  695 
nerves  of,  1139 
structure  of,  1139 
vessels  of,  1139 
pharyngeal,  1142 
Torcular  Herophiii,  131,  658 
Torus  of  auditory  tube,  1141 
uretericus,  1232 
uterinus,  1154 
Touch  fibers,  854 
Trabeculce  carnece,  532,  535 
cranii,  84 
of  penis,  1250 
of  spleen,  1283 
of  testis,  1243 
Trachea,  1084 

lymphatic  capillaries  in,  686 
nerves  of,  1087 
relations  of,  1084 


I 

1. 

I 


INDEX 


I 


I 


Trachea,  structure  of,  1086 

vessels  of,  1087 
Trachealis  muscle,  1087 
Trachelomastoid  muscle,  399 
Tracheobronchial  glands,  717 
Trachoma  glands,  1028 
Tract  or  Tracts,  anterior    basis 
bundle,  760 
of  Burdach,  752,  763 
central,  of  cranial  nerves,  804 

of  trigeminal  nerve,  805 
cerebellar,  of  Flechsig,  761 
comma,  764 

dorsal  peripheral  band,  764 
of  Goll,  752,  762 
of  Gowers,  761,  754 
lateral  basis  bundle,  762 
of  Lissaucr,  762 
olfactory,  826 
optic,  814,  884 
prepyramidal,  761 
pyramidal,  759,  760 
thalamic,  of  cranial  nerves,  805 
Traction  epiphyses,  95 
Tractus  iliotibialis,  468 

olfactomcsencephalicus,  867 

olfactorius,  826 

peduncularis    transversus,    802 

note 
spiralis  foraminosus,  143, 1050 
Tra^cus  muscle,  1035 
Tragus,  1034 
Transpyloric  plane,  1147 
Transversa  colli  artery,  582 
Transversalis  cer\'icis  muscle,  399 
colli  artery,  582 
fascia,  418 
muscle,  414 
Transverse  acetabular   ligament 
of  hip-joint,  336 
aorta,  547 

carpal  ligament,  456 
cervical  arteries,  582 

nerve,  927 
colon,  1180 
crural  ligament,  488 
facial  artery,  558 

vein,  645 
fibers  of  cerebral  hemispheres, 

841,  842 
fissure  of  brain,  842 

of  liver,  1191 
folds  of  rectum,  1183 
ligament  of  atlas,  293 
of  fingers,  461 
humeral,  319 
of  knee,  343 
metacarpal,  331 
metatarsal,  359 
of  pelvis,  429 
ligaments  of  scapula,  317 
lingualis  muscle,  1130 
mesocolon,  1157 
occipital  sulcus,  823 
process  of  a  vertebra,  96 
scapular  artery,  582 
sinus,  660 

of  pericardium,  526 
temporal  gj^ri,  824 
Transversus    abdominis    muscle, 
414 
variations  of,  414 
auriculae  muscle,  1035 
linguae  muscle,  1130 
menti  muscle,  383 
nuchae  muscle,  380 
pedis  muscle,  493 
perina-i  muscle,   427 

profundus  muscle  in  female, 
431 
in  male,  429 
superficialis  muscle,    actions 
of,  428,  430 
in  female,  430 
in  male,  427 
88 


Transversus  thoracis  muscle,  403 
Trapezium,  225 
Trapezius  muscle,  432 
actions  of,  435 
nerves  of,  434 
variations  of,  432  * 
Trapezoid,  225 

body, 787 

ligament,  315 

nucleus,  787 

ridge,  200 
Treves,  bloodless  fold  of,  1160 
Triangle  of  auscultation,  434 

Brvant's,  1343 

carotid,  392,  394,  564 

digastric,  564 

femoral,  626 

of  Hesselbach,  1321 

lumbar,  434 

muscular,  394,  563 

of  neck,  562 

occipital,  394,  565 

of  Petit,  434 

Scarpa's,  626 

subclavian,  394,  565 

submaxillary,  392,  564 

submental,  392 

suboccipital,  402,  578 

suprahj^oid,  392,  565 

suprameatal,  140,  183 
Triangular  articular  disk,  325 

bone,  224 

fascia  of  abdomen,  412 

ligament,  428 

of  liver,  1150,  1151 
Triangularis  muscle,    383 

sterni  muscle,  403 
Triceps  brachii  muscle,  444 

extensor  cubiti  muscle,  444 

muscle,  444 

surse  muscle,  483 
Tricuspid  valve,  531 
Trifacial  nerve,  886 
Trigeminal  impression,  143 

nerve,  886 

central  tract  of,  805 
composition  and  central  con- 
nections of,  862 
reflexes,  899 

surface  marking  of,  1295 
Trigone,  olfactory,  827 
Trigonutn  collaterale,  833 

femorale,  626 

habenvlce,  812 

hypoglossi,  799 

olfactoriujn,  827 

vagi,  781 

vesicce,  1231 
Trochanter,  greater,  244 

lesser,  245 

third,  246 
Trochanteric  fossa,  244 
Trochlea  of  humerus,  212 
Trochlear  fovea,  137,  188 

nerve,  885 

composition  and  central  con- 
nections of,  863 

process  of  calcaneus,  266 

spine,  137 
Trochoid  joint,  285 
Trolard,  anastomotic  vein  of,  652 
Troltsch,  recess  of,  1046 
Trophoblast,  46 
True  nucleoli,  37 

pelvis,  239 

skin,  1065 

vocal  cords,  lOSO 
Truncus  arteriosus,  508,  514 

costocervicalis,  585 

sympathicus,  976 

th;jreocervicalis,  581 
Trunk,  arteries  of,  598 

articulations  of,  287 

costocervical,  585 

thyrocervical,  581 


Tuba  auditiva,  1042 

uterina  [Fallopii],  1257 
Tube,  auditory,  1042 

digestive,  1100 

Eustachian,  1042 

Fallopian,  1257 

neural,  50 

uterine,  1257 
Tuber  cinereum,  775 

frontale,  135 

omentale  [liver],  1189 
[pancreas],  1201 

parietale,  133 

valvulce,  791 

vermis  [cerebellum],  791 
Tubera;  lobe,  791 
Tubercle,  adductor,  246 

anterior,  99 

articular,    of    temporal    bone, 
139,  180 

auricular,  of  Darwin,  1033 

conoid,  200 

cuneate,  774 

cuneiform,  1079 

of  epiglottis,  1076 

of  femur,  245 

of  humerus,  209 

intervenous,  531 

jugular,  131 

lacrimal,  161 

of  Lower,  531 

mental,  172 

obturator,  273 

peroneal,  266 

pharyngeal,  132,  180 

posterior,  99 

pterygoid,  152 

pubic,  236 

of  rib,  124 

of  Rolando,  775 

scalene,  125 
Tuberculum  acuslicum,  800,  906 

impar,  1102 

intervenosum,  531 

majus  [humeri],  209 

minus  [humeri],  209 

sella;,  147,  190 
Tuberosity,  calcaneal,  266 

coracoid,  200 

costal,  202 

of  cuboid,  269 

deltoid,  211 

of  fifth  metatarsal  bone,  274 

gluteal,  246 

iliac,  234 

infraglenoid,  205 

of  ischium,  235 

maxillar5%  159 

of  navicular  bone,  270 

of  palatine  bone,  168 

radial,  219 

supraglenoid,  207 

of  tibia,  256 

of  ulna,  214 
Tubules,  renal,  1223 
Tubidi  lactiferi,  1268 

recti  [testis],  1244 

seminiferi,  1243 
Tunic,  dartos,  1238 

fibrous,  of  kidney,  1220 
Tunica  adventitia,  499 

albuginea  [ovary],  1256 
[testis],  1242 

conjunctiva  bulbi,  1027 

dartos,  1238 

elastica  externa,  499 

fibrosa  oculi,  1005 

intima,  498 

media,  498 

serosa,  1149 

vaginalis,  1242 

communis  [testis   et   funiculi 

spermatid],  1239 
propria  testis,  1242 

vasculosa  [testis],  1243 


1394 


INDEX 


Tunica  vasculosa  oculi,  1009 
Tunics  of  eveball,  1005 
Tunnel  of  Corti.  1057 
Turbinated  bone,  169 

processes,  sphenoidal,  152 
Turner,   intraparietal   sulcus  of, 

822 
Twelfth  nerve,  914 
Tympanic  antrum,  142 
artery,  560 

from  ascending  pharyngeal, 

558 
from      internal      maxillary 
560 
canaliculus,  inferior,  144,  181 
cavity,  1037 

arteries  of,  1046 

attic  or  epitympduic  recess 

of,  1038 
carotid  or  anterior  wall  of, 

1042 
jugular  wall  or  floor  of,  1038 
labyrinthic   or   median  wall 

of,  1040 
mastoid  or  posterior  wall  of, 

1042 
membranous  or  lateral  wall 

of,  1038 
mucous  membrane  of,  1046 
muscles  of,  1046 
nerves  of,  1046 
ossicles  of,  1044 
tegmental   wall   or   roof   of, 

1038 
vessels  of,  1046 
lip,  1055 
membrane,  1039 
nerve  (Jacobson's),  909,  1047 
plexus,  909,  1047 
ring,  146 

sulcus,  145,  1037,  1039 
Tympanohyal    part    of    styloid 

process,  145 
Tympanomastoid  fissure,  144, 181 
Tympanum,  1037 


U 


Ulna,  214 

articulations  of,  219 

coronoid  process  of,  214 

radial  notch  of,  215 

semilunar  notch  of,  215 

sigmoid  cavities  of,  215 

styloid  process  of,  218 

surface  anatomy  of,  1326 
Ulnar  artery,  595 

surface  marking  of,  1335 

notch  of  radius,  220 
Ultimobranchial  bodies,  1273 
Umbilical   arteries  in   fetus,   61, 
540 

cord,  57 

folds,  1231 

fossa  of  liver,  1191 

notch  of  liver,  1191 

veins,  61,  507,  519 
obliterated,  681,  1150 

zone,  1148,  1149 
Umbilicus,  417 
Umbo    of    membrana    tympani, 

1039 
Unciform  bone,  227 
Uncinate  fasciculus,  843 
Unconscious    muscle     sense,    im- 
pulses of,  851 
Uncus,  826 

Ungual  phalanges,  230,  275 
Ungues,  1066 
Urachus,  1213 
Ureter,  1225 

arteries  of,  1227 

lymphatic  vessels  of,  712 

muscles  of,  1233 


Ureter,  nerves  of,  1227 

orifices  of,  1232 
Urethra,  development  of,  1215 

female,  1236 

male,  1234 

crest  or  verumontanum   of, 

1234 
lymphatic  vessels  of,  713 

muliebris,  1236 

virilis,  1234 
Urethral  artery,  619 

bulb,  1235 

crest,  in  female,  1236 
in  male,  1234 

glands,  1235 

orifices,  1232,  1235,  1266 

plate,  1215 
Urinary  bladder,  female,  1230 
lymphatic  capillaries  in,  687 
male,  1227 

meatus,  1266 

organs,  1215 
Urogenital  apparatus,  1204 

diaphragm,  428 

fold,  1206 

organs,  1204 

ostium,  primitive,  1215 
Urorectal  septum,  1109 
Uterine  artery,  615 

glands,  1262 

plexus  of  nerves,  989 

plexuses  of  veins,  676 

tube,  1257 
Uterosacral  ligaments,  1260 
Uterus,  1258 

in  adult,  1262 

after  parturition,  1262 

cervix  of,  1259 

development  of,  1207 

during  menstruation,  1262 
pregnancy,  1262 

in  fetus,  1261 

form,  size,  and  situation  of,  1261 

fundus  of,  1259 

interior  of,  1260 

isthmus  of,  1259 

ligaments  of,  1260 

lymphatic  capillaries  of,  687 
vessels  of,  714 

masculinus.  or  prostatic  utricle, 
1234,  1235 

nerves  of,  1263 

in  old  age,  1262 

at  puberty,  1261 

virgin  state  of,  1259 
Utricle,  prostatic,  1234 

of  vestibule,  1051 
Utriculus,  1051 
Uvea,  1013 
Uvula  of  cerebellum,  791 

palatine,  1112 

vermis,  791 

vesicas,  1232 
Uvular  lobe,  791 


Vagina,  1264 

lymphatic  vessels  of,  714 
VagincB  mucosae,  283 
Vaginal  artery,  616 
bulb,  1266 
orifice,  1266 
plexus  of  nerves,  989 
plexuses  of  veins,  677 
process  of  temporal  bone,  144, 

145 
processes  of  sphenoid  bone,  151 
Vagus  nerve,  910 

composition  and  central  con- 
nections of,  855 
sympathetic    afferent    fibers, 
973 
efferent  fibers  of,  972 


Vallecula  cerebelli,  788 
Vallecula;  of  tongue,  1075 
Vallum,  1126 

Valsalva,  sinuses  of,  533,  534 
Valve,  bicuspid,  534 

colic,  1179 

of  coronary  sinus,  530,  642 

Eustachian,  530 

ileocecal,  1179 

of  inferior  vena  cava,  530,  678 

mitral,  534  i 

pyloric,  1164 

Thebesian,  530,  642 

tricuspid,  531 

of  Vieussens,  793 
Valves,  anal,  1184 

of  heart,  development  of,  514 

of  Houston,  1183 

of  Kerkring,  1173 

of  lymphatics,  687 

right  and  left  venous,  510 

semilunar  aortic,  534 
pulmonarj-,  532 

of  veins,  501 
Valvulabicuspidalis  [lyietralis],  534 

coli,  1179 

sinus  coronarii  [Thebesii],  531 

tricuspidalis,  531 

vence  cavce  inferioris,  530 
Valvulae  conniventes,  1173 
Vas  aberrans  of  Haller,  124^ 

deferens,  1245 

spirale,  1056 
Vasa   aberrantia    [from    brachial 
artery],  590 

brevia  arteries,  606 

intestini  tenuis  arteries,  607 

vasorum  [arteries],  499 
[veins],  502 
Vascular  areas  of  yolk-sac,  505 

capsule  of  lens,  1003 

system,  changes  in,   at   birth, 
542 
development  of.  505 
peculiarities  in  fetus,  539 
Vasomotor  nerve  fibers,  728 
Vastus  externus  muscle,  470 

intermedius  muscle,  471 

internus  muscle,  471 

lateralis  muscle,  470 

medialis  muscle,  471 
Vater,  ampulla  of,  1199 
Vein  or  Veins,  of  abdomen,  672 

anastomotic,  of  Labbe,  652 

angular,  645 

auditory,  1059 

auricular,  646 

axillary,  663 

azygos,  667 

basal,  653 

basilic,  662 
median,  661 

basivertebral,  668 

brachial,  663 

brachiocephalic,  664 

of  brain,  652 

bronchial,  697,  1100  ,^^ 

cardiac,  642,  643  ^M 

cardinal,  520  ^^" 

cephalic,  661 
accessory,  662 

cerebellar,  653 

cerebral,  652,  653 

choroid.  653 

coats  of,  501 

common  facial,  645 
iliac,  677 

coronary,  642 
of  stomach,  682 

of  corpus  striatum,  838 

cystic,  682 

deep  cerebral,  653 
cervical,  651 
epigastric,  672 
facial,  645 


INDEX 


1395 


Vein  or  Veins,  deep.of  forearm, 663 

of  hand,  663 

of  lower  extremity,  671 

of  upper  extremity,  663 
development  of,  518 
digital,  of  foot,  669 

of  hand,  660 
diploic,  651 
dorsal  digital,  660 

metacarpal,  660,  663 

of  penis,  676 
emissary,  660 
epigastric,  672 
extraspinal,  668 
facial,  645 
femoral,  672 
frontal,  644 
of  Galen,  653 
gastroepiploic,  681 
gluteal,  673 
of  hand, 660,  663 
of  head  and  neck,  643 
of  heart,  642 
hemiazj'gos,  667 
hemorrhoidal,  676,  681 
hepatic,  680 
histology  of,  501 
hypogastric,  673 
iliac,  672,  673,  677,  678 
iliolumbar,  678 
inferior  vena  cava,  677 
innominate,  066 
intercapitular,  661,  669 
intercostal,  highest,  666 
interlobular,  of  kidney,  1224 

of  liver,  1196 
intervertebral,  669 
intralobular,  of  liver,  1197 
intraspinal,  668 
jugular,  646,  647,  648 

primitive,  520 
of    Labbe,    posterior    anasto- 
motic, 652 
labial,  645 
lateral  sacral,  673 
of  left  atrium,  526 
lienal  or  splenic,  681 
lingual,  648 
of  lower  extremity,  669 
lumbar,  678 

ascending,  667 
mammary,  internal,  666 
marginal,  of  foot,  669 
masseteric,  645 
maxillary,  internal,  646 
median  antibrachial,  662 

basilic,  661 
of  medulla  spinalis,  669 
mesenteric,  682 
metatarsal,  672 
nasofrontal,  659 
of  neck,  646 
oblique,  of  left    atrium  [Mar- 

shalli],  522,  526,  643 
obturator,  673 
occipital,  646 
ophthalmic,  658 
orbital,  645 
ovarian,  679 
palpebral,  645 
pancreatic,  681 
pancreaticoduodenal,  682 
parumbilical,  682 
of  pelvis,  672 
penis,  dorsal  of,  676 
peroneal,  672 
pharyngeal,  649 
phrenic,  inferior,  679 

superior,  666 
plantar,  671 
plexus  of,  basilar,  660 

hemorrhoidal,  676 

prostatic  676 

pterygoid  645 

pudendal,  676 


Vein  or  Veins,  plexus  of,  uterine, 
676 

vaginal,  677 

vertebral,  668 

vesical,  676 

vesicoprostatic,  676 
popliteal,  672 
portal,  680 

posterior  of  left  ventricle,  643 
primitive  jugular,  520 
profunda  femoris,  672 
pubic,  673 

pudendal,  internal,  674 
pudic,  674 
pulmonary,  642 
pyloric,  682 
ranine,  648 
renal,  679,  1224 
sacral,  673,  677 
saphenous,  670 
sciatic,  674 
short  gastric,  681 
spermatic,  678 
of  spinal  cord,  669 
splenic  or  lienal,  681 
striate,  inferior,  653 
structure  of,  501 
subcardinal,  520 
subclavian,  664 
sublobular,  of  liver,  1197 
superficial,  641 

of  lower  extremity,  669 

of  upper  extremity,  660 
superior  cerebral,  652 

mesenteric,  682 

phrenic,  666 

vena  cava,  666 
supraorbital,  645 
suprarenal,  679 
Sylvian,  652,  653 
systemic,  642 
temporal,  645 
temporomaxillary,  646 
terminal,  653 
of  Thebesius,  643 
thoracoepigastric,  670 
of  thorax,  664 
thyroid,  inferior,  666 

middle,  649 

superior,  649 
tibial,  672 

transverse  facial,  645 
Trolard,  great  anastomotic  of, 

652 
umbilical,  62,  507 

obliterated,  681,  1150 
of  upper  extremity,  660 
valves  of,  501 
vena  azygos  major,  667 
minor,  667 

cava,  inferior,  667 
superior,  666 
vertebral,  651 
of  vertebral  column,  667 
visceral,  518 
vitelline,  506,  518 
volar,  661,663 
Velamentous    insertion    of    um- 
bilical cord,  65 
Velum  inter positum,  841 
medullar ce,  793,  794 
medullary,  793,  794,  797 
palatine,  1112 
Vena  angular  is,  645 
anonyma  dextra,  664 

sinistra,  666 
auricularis  posterior,  646 
axillaris,  663 
azygos,  667 
basilica,  662 
cava  inferior,  677 

superior,  666 

surface  marking  of,  1312 
caval  foramen  in  diaphragm,406 
cephalica  accessoria,  662 


Vena  cerebri  mo/gna,  653 

tnedia,  652 
cervicalis  profunda,  651 
circumflexa  {Hum  profunda,  673 
cordis,  642,  643 
coronaria  ventriculi,  682 
corporis  striata,  653 
cystica,  682 
epigastrica  inferior,  672 
facialis  anterior,  645 

posterior,  646 
femoralis,  672 
frontalis,  644 
gastroepiploica,  681,  682 
hcemorrhoidalis  media,  676 
hemiazygos,  677 

accessoria,  677 
hypogastrica,  673 
iliaca  externa,  672 
jugularis  anterior,  647 

externa,  646 

interna,  648 

posterior,  647 
linealis,  681 

magna  [Galeni],  653,  842 
maxillaris  interna,  646 
mediana  antibrachii,  662 

cubiti,  661 
mesenterica  inferior,  681 

superior,  682 
obliqua  atrii  sinistri  [Marshalli\,, 

643 
obturatoria,  676 
occipitalis,  646 
ophihaltnica,  659 
poplitea,  672 
portoB,  681 

posterior  ventriculi  sinistri,  643 
profunda  femoris,  672 
saphena  magna,  669 

parva,  670 
subclavia,  664 
supraorbitalis,  645 
temporalis  superficialis,  645 
terminalis,  653 
thyreoidea  superioris,  649 
vertebralis,  649 
Vence  advehentes,  519 
anonymce,  664 
basivertebrales,  668 
brachiales,  663' 
bronchiales,  667 
cerebelli,  653 
cerebri,  652,  653 
comitantes,  641 
cordis,  642 

minimce,  530 
digitales  plantares,  671 
diploicoe,  651 
dorsales  penis,  676 
Galeni,  842 
gastricce  breves,  681 
glutaece,  674 
hepaticw,  680 
iliacce  communes,  677 
intercostales  suprema,  666 
intervertebrales,  669 
linguales,  648 
lumbales,  678 
mammarice  interna,  666 
ovariacce,  679 
pancreaticce,  681 
pancreaticoduodenales ,  682 
parumbilicales,  682 
pliaryngece,  649 
phrenicoe  inferiores,  679 
proprice  renales.  1225 
pulmonales,  642 
rectw  [kidney],  1224 
renales,  679 
revehentes,  519 
sacrales,  676,  677 
spermaticcB,  678 
spinales,  669 
stellatoB  [kidney],  1224 


1396 


INDEX 


Vence  suprarenales,  669 
thyreoidece  inferiores,  666 
tibiales,,  672 
rorlicosce,  1010,  1021 
Venous  arches,  669 
lacunse  of  dura  mater,  655 
mesocardium,  526 
plexus,  hemorrhoidal,  676 
ovarian,  679,  1256 
pampiniform,  678, 1240,  1256 
pharyngeal,  649 
pterygoid,  645 
pudendal,  676 
spermatic,  678,  1240 
uterine,  676 
vaginal,  677 
vesical,  676 
sinuses,  641 

of  dura  mater,  654 

development  of,  522 
valves,  right  and  left,  510 
Ventral  cochlear  nucleus,  788 
fissure   of  medulla  oblongata, 

767 
lamina,  735 

longitudinal  bundle,  803 
mesogastrium,  1103 
psalterium,  869 
pulmonary  nerves,  193 
spinal  artery,  579 
spinothalamic  fasciculus,  854 
Ventricle  of  fornix,  838 
of  mid-brain,  806 
terminal,  of   medulla  spinalis, 

754 
of  Verga,  838 
Ventricles  of  brain,  797, 798,  815, 
829 
of  heart,  508,  531,  534 
of  larynx,  1080 
Ventricular  folds  of  larynx,  1079 
ligament  of  larynx,  1080 
septum,  512,  534 
Ventricularis  muscle,  1083 
Ventriculus,  1161 
dexter,  531 

laryngis  [Morgagni\,  1080 
lateralis,  829 
quartus,  797 
tertius,  815 
Ventromedian  fissure  of  medulla 

oblongata,  767 
Verga,  ventricle  of,  838 
Vermian  fossa,  131 
Vermiform  process  or  appendix, 

1178 
Vermis  of  cerebellum,  788,  790 
Vertebra  prominens,  101 
Vertebrae,  96 
cervical,  97 
coccygeal,  106 
ligaments  of,  287-291 
lumbar,  104 
sacral,  106 
thoracic,  102 
Vertebral  arch,  96 

arches,  articulations  of,  289 
artery,  578 
canal,  116 
column,  96,  114 

articulations  of,  287 
surface  form  of,  1305 
veins  of.  667 
foramen,  96 
groove,  115 
notches,  97 

part  of  base  of  skull,  84 
ribs,  123 
veins,  651 

venous  plexuses,  668 
Vertical  index  of  skull,  198 
lingualis  muscle,  1131 
part  of  palatine  bone,  167 
Vertical  is  lingusB  muscle,  1131 
V^erumontanum,  1234 


Vesica  fellea,  1197 

urinaria,  1227 
Vesical  artery,  015 

layer  of  pelvic  fascia,  422 

plexus  of  nerves,  988 
of  veins,  676 
Vesicle,  auditory,  1030 

blastodermic,  46 

germinal,  39 

lens,  1001 

optic,  742,  1001 
Vcsicoprostatic  plexus  of  veins, 

676 
Vesicouterine  excavation,  1152 
Vesiculce  seminales,  1246 
Vesicular  ovarian  follicles,  1256 
Vestibular  arteries,  1059 

bulb,  1266 

fissure,  1051 

ganglion,  1058 

glands,  greater,  1266 

lip,  1055 

membrane,  1064 

nerve,  906,  1058 

composition  and  central  con- 
nections of,  860 
nuclei  of,  788 
Vestibule,  aortic,  534 

of  internal  ear,  1047 

of  lar>-nx,  1078 

of  mouth,  1110 

of  nasal  cavity,  994 

of  omental  bursa,  1156 

of  vagina,  1266 
Vestibulospinal     fasciculus,    803, 
872 

tract,  760 
Veslibulum,  1047 

oris,  1110 

vagince,  1266 
Vestigial  fold  of  Marshall,  643 

of  pericardium,  526 
Vicq  d'Azyr,  bundle  of,  810,  813, 

839. 869 
Vidian  artery,  562,  568 

nerve,  892 
Vieussens,  valve  of,  793 
Villi,  arachnoid,  878 

of  chorion,  60 

of  intestine,  1174 
Visceral  arches,  65 

veins,  518 
Visual  area  of  cortex,  847 

centres,  814 

purple,  1015 
Visuopsychic,  area,  847 
Visuosensory  area,  847 
Vitelline  circulation,  54,  507 

duct,  1103 

fluid,  54 

membrane,  45 

veins,  506,  518 
Vitreous  body  of  eye,  1018 

table  of  skull,  79 
Vocal  cords,  1079,  1080 

folds,  1080 

process  of  arytenoid  cartilage, 
1075 
Vocalis  muscle,  1083 
Voice,  organs  of,  1072 
Volar  arches,  595,  598 

surface  markings  of,  1335 

branch  of  ulnar  nerve,  942 

carpal  artery,  594 
ligament,  456 
net- work,  594 

digital  arteries,  598 
nerves,  938 

interosseous  artery,  596 
nerve,  938 

metacarpal  arteries,  595 
veins,  663 

venous  arches,  663 
Volaris    indicis    radialis     artery, 

595 


cor- 


Vomer,  170 

Vomeronasal  cartilage,  996 

organs,  71,  996 
Vulva,  1264 


W 

Wagner     and     Meissner, 

pusclesof,  1061 
Waldeyer,    germinal    epithelium 
of,  1029 

odontoblasts  of,  1118 

zona  vasculosa  of,  1256  . 

Wallenburg,  basal  olfactory  bun-'J 

die  of,  867 
Wallerian  degeneration,  759 
Wandering  cells,  377 
Wharton,  duct  of,  1135 

jelly  of,  58 
Willis,  circle  of,  574 
Windpipe,   1084 
Winslow,  foramen  of,  603,  1106. 

1156 
Wirsung,  duct  of,  1202 
Wisdom  teeth  ,1118 
Wolffian  body,  1205 

duct,  1205 

tubules,  1205 
Womb,  1258 
Wormian  bones,  156 
Wrisberg,    cardiac    ganglion    of, 
984 

cartilages  of,  1075 

ligament  of,  343 

nerve  of,  937 

nervus  intermedins  of,  901 
Wrist-joint,  327 

surface  anatomy  of,  1331 


V  bun-' I 

•J 


Xiphoid  appendix,  121 
process,  121 


Y-SHAPED     cartilage  of    acetab- 
ulum, 237 

ligament  of  Bigelow,  335 
Yolk,  formative,  39 

nutritive,  39 
Yolk-sac,  54 
Yolk-stalk,  1103 


Zigzag  tubule,  1223 

Zinn,  ligament  or  tendon  of,  1022 
zonule  of,  1018 

Zones  of  abdomen,  1148,  1149 

Zonula  ciliaris,  1018 

Zonule  of  Zinn,  1018 

Zygomatic  arch,  183 

bone,  164  ^^_ 

branch  of  facial  nerve,  905  alB 
nerve,  889  ^" 

process  of  frontal  bone,  136 
of  maxilla,  161 
of  temporal  bone,  139 

Zygomaticofacial    foramen,    164, 
187 
nerve,  889 

Zygomaticofrontal  suture,  182 

Zygomaticoorbital  foramina,  165 

Zygomaticotemporal    foramen, 
164,  183 
nerve,  989,  890 
suture,  182 

Zygomaticus  muscle,  383 


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'^^^y 


FEB  2  -  193a 
MAR  2  8  1939 

OCT  6   133a 

NOV  1419^ 


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il^ 


^.t^ 


■jL^ 


1  ^  \bA'l 


OEC  2 1 1942 
14  DAY 

APR  ^5'M 
APR    i  1961 


U  DAY 

OCT  25  1967 


2W-10, '36(a) 


